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Glacier Status and Contribution to Streamflow in the OlympicMountains USAJon L RiedelNational Park Service

Steve WilsonPortland State Universtiy

William BaccusNational Park Service

Michael LarrabeeNational Park Service

TJ FudgeUniversity of Washington - Seattle Campus

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Citation DetailsRIEDEL J WILSON S BACCUS W LARRABEE M FUDGE T amp FOUNTAIN A (2015) Glacier status and contribution tostreamflow in the Olympic Mountains Washington USA Journal of Glaciology 61(225)

AuthorsJon L Riedel Steve Wilson William Baccus Michael Larrabee TJ Fudge and Andrew G Fountain

This article is available at PDXScholar httppdxscholarlibrarypdxedugeology_fac82

Glacier status and contribution to streamflow in theOlympic Mountains Washington USA

JL RIEDEL1 Steve WILSON2 William BACCUS3 Michael LARRABEE1 TJ FUDGE4

Andrew FOUNTAIN2

1North Cascades National Park Sedro-Woolley WA USA2Department of Geology Portland State University Portland OR USA

3Olympic National Park Port Angeles WA USA4Department of Earth and Space Sciences University of Washington Seattle WA USA

Correspondence JL Riedel ltjon_riedelnpsgovgt

ABSTRACT The Olympic Peninsula Washington USA currently holds 184 alpine glaciers larger than001 km2 and their combined area is 302 095 km2 Only four glaciers are gt1 km2 and 120 of theothers are lt01 km2 This represents a loss of 82 glaciers and a 34 decrease in combined area since1980 with the most pronounced losses occurring on south-facing aspects and in the more aridnortheastern part of the range Annual rate of loss in glacier area for seven of the largest glaciersaccelerated from 026 km2 andash1 (1900ndash80) to 054 km2 andash1 (1980ndash2009) Thinning rates on four of thelargest glaciers averaged nearly 1mandash1 from 1987 to 2010 resulting in estimated volume losses of17ndash24 Combined glacial snow firn and ice melt in the Hoh watershed is in the range63ndash797106m3 or 9ndash15 of total MayndashSeptember streamflow In the critical AugustndashSeptemberperiod the glacial fraction of total basin runoff increases to 18ndash30 with one-third of the water directlyfrom glacial ice (ie not snow and firn) Glaciers in the Elwha basin produce 12ndash15 13106m3

(25ndash40) while those in the Dungeness basin contribute 25ndash31028106m3 (30ndash38)

KEYWORDS climate change glacier hydrology ice and climate mountain glaciers

INTRODUCTIONMountain glaciers throughout the world are vital hydrologicresources and sensitive indicators of climate change In thePacific Northwest glaciers provide stability to aquaticecosystems hydroelectric industries and municipal andagricultural water supplies by providing runoff during theannual summer drought Several rare threatened or en-dangered species of fish including bull trout (Salvelinusconfluentus) and summer-run Chinook salmon (Onco-rhynchus tshawytscha) (Mantua and others 2010) dependon the cold water released by glaciers during the summerAlpine glaciers host unique ecosystems and are the solehabitat for species such as the ice worm (Mesenchytraeussolifugus) (Hodson and others 2008) Predation of ice wormsby rosy finches (Leucostitche arctoa) and other alpine specieslinks the glacier ecosystem to adjacent alpine food websThese ecosystems industries and water resources are all

directly affected by the sensitive response of glaciers toclimate change Increasing air temperature increases the rateof glacial melt and lengthens the melt season In winterincreasing temperatures can change the phase of theprecipitation from snow to rain resulting in less snowaccumulation particularly in the warm snowpacks commonin this region (Nolin and Daly 2006) Glaciers in thesemountains are also relatively small and thin with highbalance gradients allowing them to rapidly adjust their sizeto a changing climate Combined these factors lead to rapidadjustment in the extent of small alpine glaciers makingthem unstable components of alpine hydrologic systems atmulti-decadal timescalesThe climate of this region has changed significantly in the

past 50 years Rasmussen and Conway (2001) reported thatmean summer temperature in western Washington State

USA increased by 1degC from 1948 to 1996 while averageJanuaryndashMarch temperature at Blue Glacier has increasedby 3degC (Rasmussen and Conway 2001) The last inventoryof glaciers in the Olympic Mountains Washington in 1980identified 266 glaciers (Spicer 1986 Fig 1) Quantifyingchanges in the area and volume of these glaciers in the past30 years is an important step towards understanding theimpacts of a warming climate on the hydrology regionalaquatic ecosystems and water supplies on the OlympicPeninsula In this paper we present a new geospatialdatabase of the area and hypsometry of all glaciers largerthan 001 km2 These data are used to assess changes inglacier size distribution and volume since 1980 and arecombined with a positive degree-day model to estimatemodern summer runoff produced by glaciers for three largewatersheds

STUDY AREAThe Olympic Peninsula is located on the western edge ofNorth America it is incised by the Pacific Ocean to the westand Puget Sound to the east (Fig 1) The center of thepeninsula is marked by rugged mountains isolated by deepvalleys The bedrock geology of the Olympic Mountains iscomposed largely of uplifted basalt and sedimentary rocksthat accumulated on the floor of the Pacific Ocean fromabout 18 to 57Ma ago (Tabor and Cady 1978) The climateof the peninsula varies dramatically with aspect elevationand distance from the Pacific Ocean The western slopes ofthe highest Olympic peaks are estimated to receive as muchas 66mandash1 precipitation (PRISM Group 2006) Easternpeaks by contrast receive lt2mandash1 Most precipitation fallsbetween November and April and glaciers receive 10m

Journal of Glaciology Vol 61 No 225 2015 doi 1031892015JoG14J1388

of snowfall each winter (Davey and others 2006) Meanannual temperature and temperature range also vary fromwest to east with higher elevations on east side peakstypically 15ndash20degC warmer than west side locations (Daveyand others 2006) The climate has pronounced interannualand decadal variations in temperature and precipitationassociated with the Southern Oscillation (El NintildeoLa Nintildea)and the Pacific Decadal Oscillation (Mantua and others1997) Erosion by glaciers streams hillslope processes and

active tectonic uplift has created 2400m of local relief fromthe summit of Mount Olympus (2429m) to sea levelRepeated ice ages and development of long alpine valleyglaciers carved deep U-shaped troughs that radiate from thecenter of the peninsula (Tabor and Cady 1978) Glaciers arecurrently distributed across the mountains with the largeston Mount Olympus on the wetter windward side of therange (Fig 2)

METHODSThe glacier geospatial database was developed using 1mpixel size orthorectified vertical air photographs taken in2009 by the US National Agriculture Imagery Program(NAIP) Each glacier was digitized directly from thephotographs at a scale of 1 2000 with vertices spacedevery 5m All perennial accumulations of ice gt001 km2 inarea were included in the inventoryUp to three polygons were digitized for each glacier The

first area mapped represents the minimum extent of what isclearly glacier ice as determined by the presence ofcrevasses surface ponds or blue glacial ice This outlineincludes only that part of the glacier that is free of debris butmay include minor areas of debris cover if the debris isdiscontinuous or thin The second polygon mapped hadsignificant debris cover seasonal snow or shadows overglacial ice as confirmed by the presence of crevasses glacialice exposed on crevasse walls or steep glacier margins andice-marginal channels The third area delineated included afew sites where we could not positively determine from theNAIP imagery if there was ice beneath thick hummockydebris near a glacierrsquos terminusThe use of up to three polygons per glacier has two

purposes Firstly quantifying debris-covered area on the

Fig 1 Location of the Olympic Peninsula and Washington Stateand boundary of Olympic National Park

Fig 2 Modern glacier distribution in the central Olympic Peninsula

Riedel and others Glaciers in the Olympic Mountains 9

glacier allows for observations of how debris cover may beinfluencing the rate of change of glaciers Secondly havinga maximum outline for areas of possible ice allows for aquantification of overall glacier area uncertainty providinga level of significance and statistical credibility to thegeospatial dataGlacier change during the past several decades was

quantified by comparing our new inventory with those ofMatthes (1946) Meier (1961) and Spicer (1986) The Spicerdata were obtained from aerial photographs taken between1976 and 1982 and this inventory is particularly usefulbecause it was based on higher-resolution images than thoseavailable to Meier or MatthesHigh-precision elevation transects were measured in

autumn 2010 along longitudinal profiles on four glaciersusing GPS GPS positions were collected at 1 s intervals andwere processed using the kinematic Precise Point Pos-itioning (PPP) service from the Canadian Natural ResourcesDepartment (Heroux and Kouba 2001) PPP processing usescorrected satellite orbits and does not require a fixedreference station The measurement uncertainty was 1mdetermined by reference measurements taken over solidground near the glacier margins The glaciers chosenrepresent a west-to-east precipitation gradient and despitethe limited number the sample represents about two-thirdsof the glacier area Glacier thickness changes were made bycomparing elevation profiles with elevations from the 1987US Geological Survey digital elevation models (DEMs)based on photography from the same year To calculatevolume loss the thinning amount within each 20melevation bin was averaged and then multiplied by the areaof the glacier in that bin The upper parts of the glaciers wellabove the equilibrium-line altitude were not profiled butwe observed little thinning in these areas For Blue Glacierthe icefall and steep terminus could not be profiled For theicefall we fit a quadratic equation to the thinningelevationrelationship but the choice is not critical because of thesmall glacier areas We extrapolated the rate of thinning toestimate loss for the lowest elevation band at the terminusand assumed that it had a wedge shapeAnnual glacial meltwater discharge in the Hoh (51

glaciated) Elwha (05) and Dungeness (03) basins wasestimated using a model based on glacier hypsometry and

summer melt (Figs 2 and 3 Riedel and others 2008)Summer (1 Mayndash30 September) melt was estimated with apositive degree-day (PDD) model (Rasmussen and Wenger2009) Glacier hypsometry across a watershed was calcu-lated in 50m elevation bands using a 1987 10m DEM as abase map and glacier area from our inventoryThe PDD model is based on air temperature at the

elevations of glaciers and was calibrated with summerbalance measurements taken from 1963 to 1994 at altitudesof 1500 and 2050masl on Blue Glacier (Conway andothers 1999) Upper-air temperatures were acquired fromthe US National Centers for Environmental PredictionUSNational Center for Atmospheric Research (NCEPNCAR)reanalysis database for the nearest gridpoint (475degN125degW) 150 km west-southwest of Blue Glacier Upper-air temperatures were used because they more accuratelyrepresent air temperatures at the glacier surface than donearby terrestrial-based temperature measurements (Ras-mussen and Wenger 2009)Following methods outlined by DeWoul and Hock (2005)

and Rasmussen and Wenger (2009) summer melt at a givenaltitude bs ethzTHORN is

bs ethzTHORN frac14 Xtn

tfrac14t1

Tthornetht zTHORN thorn

wherePTthorn represents summation of average daily air

temperature accounting only values gt0degC for a selectedperiod The coefficients and are determined by linearregression minimizing model error Air temperature at 1500and 2050m is determined by linear interpolation of1200UTC air temperatures at 850 and 700mbar levels(approximate altitudes of 1450 and 3000m respectively)Melt above between and below these elevations was basedon a linear regressionThe model did not partition ice firn and snow contribu-

tions to total glacier melt and used a single melt coefficientWe did not attempt to separately quantify these phases fortwo reasons First the melt season starts weeks earlier at theterminus of these glaciers than in their accumulation zonesThus even late in the melt season glacial runoff includessnow (and firn) making it difficult to pick a date when thereis mostly ice melt particularly when the mass balance waspositive the previous year and a lot of firn is exposed tosurface melting Second the glacier microclimate delayssnowmelt on the glacier interannually as well as seasonallycompared with the surrounding landscape These consid-erations make glacial snow and firn melt important factorswhen considering the hydrologic importance of glaciers

RESULTS AND DISCUSSIONThere are currently 184 glaciers larger than 001 km2 on theOlympic Peninsula but 120 are lt01 km2 and only four aregt1 km2 (Fig 4) The higher-resolution NAIP photographsand field checks allowed us to identify another 117 smallsnowndashfirnndashice patches smaller than 001 km2 covering05 km2 Some of these were gt001 km2 in 1980 andnow fall into this smaller size category Previous estimatesalso missed some glaciers greater than 001 km2 because ofthe lower resolution of the photographs available at the time(Table 1 Meier 1961 Spicer 1986) Changes in thenumber of glaciers also reflect substantial glacier thinningwhich can cause one large glacier to divide into two (or

Fig 3 Modern areandashaltitude distribution of glaciers in three largewatersheds

Riedel and others Glaciers in the Olympic Mountains10

more) smaller glaciers For example continued climatewarming will eventually lead Blue Glacier to divideWe identified 083 km2 of debris-covered ice half of

which is on Blue and Black Glaciers on Mount OlympusSpicer (1986) identified 12 lsquorock glaciersrsquo in a previousinventory but we did not track changes in them indi-vidually The presence of debris-covered ice is expected toincrease as the climate warms glaciers thin and in somecases glacier flow velocities decline Debris cover of morethan a few centimeters can dramatically slow melting andin the future many of the Peninsularsquos glaciers may becomerock glaciers Heusser (1957) noted that debris cover onlower White and Hoh Glaciers slowed recession in the early20th century Ferry Glacier was one of the 50 largest glaciersin the Olympics Mountains in 1980 with an area of

017 km2 but by 2009 what remained of the glacier wascovered by a rockfall making it difficult to determine howmuch if any ice remainsAll the glaciers counted in a previous inventory have

decreased in size in the past 30 years and our countrepresents a decrease of 82 glaciers from the 266 noted in1980 (Fig 2 Spicer 1986) Total glacier cover now standsat 3020 095 km2 not including features smaller than001 km2 Uncertainty associated with the 1m resolution ofthe NAIP imagery is compounded by shadows and debriscover and varies substantially between glaciers largerglaciers have ten times the uncertainty of smaller glaciers(Table 1) Total uncertainty represents only 6 of the totalestimated change in glacier area not enough to affect theconclusion that glaciers are in rapid decline

Fig 4 Histogram of the number of glaciers by size category note size of categories changes Perennial snow and ice features lt001 km2 notshown

Table 1 Area (km2) of select glaciers at various times in the past century Data for 1980 and early 20th century from Spicer (1986) SeeFigure 2 for locations

Glacier (mountainndashaspect) Little Ice Age maximum Early 20th century 1980 2009 Change 1980ndash2009

(photograph date) ( error)

West of the Elwha valleyBlue (OlympusndashNE) 717 561(1899) 61 535 (0079) ndash12

Humes (OlympusndashE) 263 202 (1907) 185 148 (0088) ndash20

Hoh (OlympusndashNE) 807 54 (1933) 489 403 (0055) ndash18

White (TomndashN) 779 512 (1924) 469 390 (0055) ndash17

Jeffers (OlympusndashSE) 281 na 08 031 (0127) ndash61

Hubert (OlympusndashSW) 239 na 110 071 (0058) ndash35

Carrie (BaileysndashNE) na na 098 062 (0011) ndash37

East of the Elwha valleyChristie (ChristiendashN) na na 02 0099 (0003) ndash51

Lillian (McCartneyndashN) na na 014 0029 (0001) ndash21

Cameron (Cameron) na na 016 0103 (0003) ndash36

Anderson (AndersonndashS) 158 122 (1927) 061 014 (0003) ndash77

Eel (AndersonndashN) 230 177 (1920) 111 085 (0008) ndash23

Total eight named glaciers 3474 na 2115 1677 21

OLYM total na 6657 4594 3020 (0945) ndash34

Based on aerial photographs taken between 1976 and 1982

Riedel and others Glaciers in the Olympic Mountains 11

Combined glacier area decreased by 157 km2 from 1980(459 km2) to 2009 (302 km2) a loss of 34 (Table 1 Spicer1986) Mean glacier area decreased from 017 km2 in 1980 to011 km2 in 2009 In 1980 eight of 266 glaciers were gt1 km2

(Spicer 1986) there are now only four that exceed that size(Blue Hoh White and Humes glaciers) All of these glaciersare on Mount Olympus the highest mountain on thePeninsula located on the windward (wet) west side of the

Olympic Mountains (Figs 2 and 5) Other clusters of glaciersin the 005ndash02 km2 size range occur in the Bailey Range andon Mount Christie and Mount Anderson (Fig 2) Thesesummits are all either on the wetter windward side of therange (Baileys) or benefit from storms that penetrate deep intothe mountains along the Quinnault RiverAspect and distance inland from the Pacific moisture

source have had a strong influence on glacier response to the

Fig 5 Change in glacier extent on Mount Olympus (a) and Mount Anderson (b) from AD1980 to present

Riedel and others Glaciers in the Olympic Mountains12

warming climate Glaciers in the eastern part of the Peninsulaand those that face south lost more area than those facingnorth and on the wetter windward slope (Table 1) Glacierlosses were most pronounced in the drier northeastern part ofthe Peninsula where for example little remains of LillianGlacier on McCartney Peak (Fig 6) For the most partglaciers east of the Elwha River now exist almost exclusivelyon shaded northern aspects where melting is slower and theymay benefit from secondary sources of accumulation (egwind redeposition and snow avalanche)The influence of aspect is well illustrated on Mount

Anderson Since 1980 Anderson Glacier has lost 77 of itsarea compared with a 23 loss for adjacent north-facing EelGlacier (Table 1 Figs 5 and 7) Aspect is also a critical factorto glacier status on Mount Olympus where southeast-facingJeffers Glacier shrank by 61 in 30 years while north-facing Hoh and White Glaciers declined by 17ndash18 (Fig 5)North-facing glaciers east of the Elwha lost 21ndash51 of theirarea in 30 years whereas the north-facing glaciers on MountOlympus lost 12ndash20 over the same period Glaciers in theBailey Range with north aspects had area losses comparablewith glaciers on the south side of Olympus and with north-facing glaciers east of the Elwha (eg Carrie GlacierTable 1)The rate of ice loss for six glaciers from AD1900 to 1980

was 026 km2 andash1 although this included a period of positivebalance at Blue Glacier from 1959 to 1975 (Hubley 1956Spicer 1986 Rasmussen and Conway 2001) Since 1980the rate of decline in combined ice extent across theOlympic Mountains doubled to 054 km2 andash1 Acceleratingdecline of glacier area is also reflected in strongly negative

cumulative balance on Blue Glacier since the mid-1980s(Rasmussen and Conway 2001)Decline in glacier area in recent decades on the Olympic

Peninsula exceeds losses east of the FraserndashPuget lowlandsIn the southern Coast Mountains of British Columbia glacierarea declined 10 from 1985 to 2005 (Bolch and others2010) while Granshaw and Fountain (2006) estimated lossof glaciers in the North Cascades National Park over a40 year period ending in 1998 at 7 The more rapid lossof glaciers in the Olympics is more comparable with theobserved loss of 20 over a similar period on VancouverIsland (Bolch and others 2010) Rapid loss of glaciers incoastal ranges is likely due to their sensitivity to changes intemperature that strongly influence spring ablation andearly-fall accumulation (LaChapelle 1965) Accumulatingevidence indicates that the recent loss of glacier area andvolume through multiple decades for all glaciers in thePacific Northwest has not occurred since at least AD 1694(Malcomb and Wiles 2013)Glacier area measurements were combined with surface

elevation profiles to assess thickness changes from 1987 to2010 for four of the largest glaciers in the OlympicMountains (Table 2) Only Blue Glacier has ice thicknessdata and a known glacier volume (Allen and others 1960)the other glacier volumes were estimated assuming anaverage ice thickness and by the ratio of the glacierrsquos area to

Fig 6 Changes in Lillian Glacier on McCartney Peak from 1905 (aNPS photograph) to the present (b photograph by J McLean)

Fig 7 Changes in Anderson Glacier from 1936 (a photograph byA Curtis) to the present (b photograph by R Hoffman)

Riedel and others Glaciers in the Olympic Mountains 13

Blue Glacierrsquos area Blue Glacier on Mount Olympus hadthe largest volume loss since 1987 because it has the largestarea The largest percent change however was for south-facing Humes Glacier at ndash22 while north-facing Blue andHoh Glaciers lost 15 and 16 respectively (Table 2) Inaddition to its aspect Humes Glacier had the mostsignificant volume reduction because it is at a lowerelevation than its neighbors Hoh Blue and White glaciersFurther to the east north-facing Eel Glacier has lost 14 ofits volume (0013 km3) since 1987Even with a 34 decline in area and 20 decline in

volume in the last 30 years glaciers continue to providesignificant amounts of water to streams on the OlympicPeninsula We used the hypsometry of glaciers and summer-melt versus elevation curves from the PDD model toestimate glacial contribution to summer streamflow forthree large basins that represent a range in climate andglacial cover (Table 3 Figs 8 and 9) As shown in Figure 8the model accurately reproduced the amount of summermelt as measured by melt stakes at two locations The modeland melt data also show that summer melt at 1500m variesby 20ndash25 (1m) between extreme years with lessvariability at higher elevations Model error at 1500m is050mwe andash1 (r2 = 068) based on the residual mean sumof errors at 2050m it is 028mwe andash1 (r2 = 076) Thesevalues represent an error of 10 in the total summermelt estimateAbout 66 of the glacier-covered landscape in the

Olympic Mountains is found in the Hoh River watershed

(20 km2) more than half of the remaining glacial cover is inthe Queets and Elwha watersheds (Fig 2) Based on thePDD model and basin-wide glacier hypsometry glacierscurrently provide 63ndash797106m3 of water to the HohRiver annually from 1 May to 30 September In the Elwhawatershed glaciers provide 12ndash1513 106m3 of sum-mer runoff while in the Dungeness basin they provide 25ndash31028106m3 The other large watersheds on theOlympic Peninsula have lt5 glacial contribution tosummer streamflow Given a 20 loss in glacier volumeglacial runoff on the Peninsula has decreased a similaramount in the past 30 yearsOur PDD model estimates of glacial runoff combine

snow firn and ice contributions but we recognize that theyare likely dominated by snowmelt LaChapelle (1965)suggested snowmelt was 16 and 42 times firn and icemelt on Blue Glacier in 1958 and 1962 respectively andthat ice melt occurred primarily in September and OctoberGiven reduced winter accumulation in the last 50 years anda longer melt season (Rasmussen and Conway 2001) thesnow to firnice melt ratios are now probably smallerThe volume loss calculations allowed us to assess the

glacier ice (not snow or firn) contribution to summerstreamflow in the Hoh basin (Tables 2 and 3) Volumeof ice loss for Hoh and Blue Glaciers averaged 63106m3we andash1 from 1987 to 2010 assuming a similarcontribution from the other 1065 km2 of glaciers in the Hohvalley the 23 year average annual glacial ice ablation is117 106m3we Using the PDD model estimate of an

Table 3 Range of modern glacial ice snow and firn contribution tosummer (1 Mayndash30 September) streamflow for three rivers

Watershed Basin

area

Glacier

area

Glacial runoff Total summer

runoff

2010 low 2009 high

km2 km2 106 m3 106 m3

Hoh 655 2003 63 79 89ndash154

Elwha 697 372 12 15 25ndash40

Dungeness 404 113 245 308 30ndash38

Includes snow firn and ice

Fig 8 Degree-day model of Blue Glacier summer balance (dashedline) used to estimate range in glacier runoff Measured values(square and diamond) from Conway and others (1999)

Fig 9 Modern range in summer (1 Mayndash30 September) glacialrunoff for three Olympic Peninsula watersheds determined by aPDD model for negative (2009) and positive (2010) net mass-balance years Runoff includes snow firn and ice from glaciers ineach basin Percentage of basin above gage site covered by glaciersshown in parentheses

Table 2 Volume change estimates for four glaciers 1987ndash2010Volume changes are not adjusted to water equivalence

Glacier Area 2009 Volume 2010 Volume loss

1987ndash2009

Change

1987ndash2010

km2 km3 km3

Hoh 403 049 0078 ndash16

Blue 535 057 0084 ndash15

Humes 148 017 0038 ndash22

Eel 085 009 0013 ndash14

Volume and change estimates less certain due to lack of ice radarmeasurements

Riedel and others Glaciers in the Olympic Mountains14

average annual total glacier summer contribution of71106m3we for the Hoh River the ice fractioncontributed 16 of total glacier runoff for MayndashSeptem-ber mostly late in the melt seasonEstimates of glacier volume loss and results from the

glacial runoff model highlight the importance of glaciers tolate-summer streamflow at the Hoh River gaging station nearForks (Fig 1) Comparing the streamflow data with the PDDmodel results glacial snow firn and ice contribute 359ndash397106m3we or 18ndash30 of total streamflow forAugustndashSeptember compared with 9ndash15 for the entiremelt seasonVolume change estimates also provide a means to assess

the glacial ice (not snow and firn) contribution to late-summer streamflow assuming that all the volume loss wasice that melted in August and September The averageAugustndashSeptember discharge in the lower Hoh River for thepast 23 years is 160 106m3 Based on the 23 year volumeloss estimate of average annual icemelt of 117 106m3wefor the Hoh basin glacier ice provided 7 of the dischargeon the lower Hoh River and 31 of the total glaciercontribution (including snow and firn) Although a smallfraction of total streamflow the glacier ice contributionoccurs when the contribution from snow and firn melt hasdeclined and summer rainfall is minimal and represents theaverage minimum reduction of AugustndashSeptember stream-flow that would occur in the lower Hoh River in the future ifglaciers disappeared The importance of this lsquofossilrsquo water ismagnified during summers when the previous winterrsquossnowfall is low and will become more critical in the futureas the snowpack declinesThe marked loss of glaciers on the Olympic Peninsula in

the past 30 years is largely a result of a 1degC rise in meanannual temperature (Rasmussen and Conway 2001) andillustrates how sensitive these relatively small thin low-elevation temperate glaciers are to climate change Thistemperature increase has directly increased the summermelt rate lengthened the melt season and decreased theduration of the accumulation season resulting in less wintersnow accumulation LaChapelle (1965) notes that theelevation of the freezing level is particularly important inearly fall as it controls how much precipitation falls as snowwhile Rasmussen and others (2000) suggest that springweather is a more important influence on ablation Coolcloudy conditions that often prevail in spring in thismaritime climate lead to lower melt rates at the time ofthe summer solstice particularly during the wet and coldphases of the Southern Oscillation and Pacific DecadalOscillation Recent climate warming appears stronger inwinter at Blue Glacier where average winter temperaturehas risen 3degC in the past half-century (Rasmussen andothers 2000) As a result average winter snow accumu-lation has decreased 500mm near 1500m at the glacierterminus since 1948 (Rasmussen and others 2000)Most of the glaciers on the Peninsula are currently not in

equilibrium with the present climate and are expected tocontinue to shrink in the near future even if accumulationincreases and temperature stops rising In the next severaldecades glaciers are likely to continue to disappear rapidlybased on projected future temperature increases of severaldegrees in the next 70 years Mote and Salatheacute (2010)estimate that mean annual temperature in Washington Statewill increase by at least 12degC by 2040 and at least 28degC by2080 Future temperature increases may be even higher near

the elevation of glaciers given positive feedback mechan-isms Further it is possible that the periodic increases inprecipitation associatedwith the cool wet phase of the PacificDecadal Oscillationmay havewaned in the past few decadeswith a warming climate (Josberger and others 2007)The preponderance of small glaciers remaining on the

Peninsula (145 of 184 are lt01 km2) means that most arevulnerable to melting away completely in the near future(Fig 2) The glaciers most threatened by future climatewarming are generally those that face south in the drier andwarmer climate prevalent on the eastern side of thePeninsula Glaciers on the northeast part of the mountainson Mount Deception McCartney Peak and Cameron Peakmay be the most threatened due to their isolation fromPacific moisture and climate model projections of highersummer potential evapotranspiration that could translate tohigher summer melt rates (Elsner and others 2010) Glacierson the northern side of the Bailey Range and in theheadwaters of the Queets and Elwha Rivers should fareslightly better because of their proximity to large valleys thatfunnel moisture from the Pacific Ocean However theiraccumulation zones are several hundred meters lower thanthose on the large glaciers of Mount Olympus If the climatewarms at the projected rates it is likely that within a centuryglaciers in the Olympic Mountains will be confined to theMount Olympus massifLoss of glaciers due to warming climate has several

significant implications for the Olympic Peninsula includ-ing loss of glacial habitat exposure of vast areas of looseglacial sand and gravel higher summer stream temperaturesand lower late-summer flows in most watersheds Decline inglacier meltwater production will exacerbate changes inaquatic habitat associated with a warming climate Mantuaand others (2010) identified summer temperature andstreamflow as critical physical habitat features for salmonLoss of glaciers will reduce summer streamflow andcontribute to higher summer stream temperatures to thedetriment of species such as the bull trout (Salvelinusconfluentus) (Halofsky and others 2011) Other ecosystemswill also be affected by the loss of glaciers For examplealpine food webs will be diminished by the loss of speciessuch as the ice worm which is preyed upon by rosy finchesand other alpine species

CONCLUSIONSThe glacier geospatial database we developed provides animportant benchmark for assessing glacier extent and glacialrunoff changes in the Olympic Mountains for the past30 years and into the future The combined area of allglaciers has decreased 34 in the past 30 years with ice lossaccelerating to a rate more than twice as fast as that from1900 to 1980 Only four of the 184 remaining glaciers aregt1 km2 in area Glaciers on the southern side of themountains at lower elevations and in the northeastern partof the Peninsula exhibited the greatest area and volume lossesand are the most likely to disappear in the next centuryGlacier decline in the past 30 years in the Olympics is greaterthan in the Cascades and southern Coast Mountains but iscomparable with Vancouver Island Based on ice volumelosses glacial contribution to summer streamflow hasdeclined 20 in the past 30 years but remains significantfor the Hoh River at 63ndash797106m3 andash1 Glaciers con-tribute lt5 to summer streamflow in all other large

Riedel and others Glaciers in the Olympic Mountains 15

watersheds in the Olympic Mountains Delivery of this coldfresh water to streams becomes more critical in the latesummer when rainfall is minimal and snowmelt hasdeclined On the lower Hoh River glacial ice contributes7 of the AugustndashSeptember streamflow which representsthe minimum reduction in flow that would occur if all theglaciers melted away Continued loss of glaciers will directlyimpact aquatic ecosystems through higher stream tempera-tures and lower summer base flows

ACKNOWLEDGEMENTSWe thank the US National Park Service Climate ChangeProgram for funding this research and Olympic and NorthCascades national parks and Portland State University for in-kind support Sharon Brady Roger Hoffman and SteveDorsch contributed GIS and cartographic expertise Finallywe want to acknowledge Richard Spicer for the valuablebaseline he created on the status of Olympic glaciers in theearly 1980s

REFERENCESAllen CR Kamb WB Meier MF and Sharp RP (1960) Structure ofthe lower Blue Glacier Washington J Geol 68(6) 601ndash625

Bolch T Menounos B andWheate R (2010) Landsat-based inventoryof glaciers in western Canada 1985ndash2005 Remote SensEnviron 114(1) 127ndash137 (doi 101016jrse200908015)

Conway H Rasmussen LA and Marshall HP (1999) Annual massbalance of Blue Glacier USA 1955ndash97 Geogr Ann A 81(4)509ndash520

Davey CA Redmond KT and Simeral DB (2006) Weather andclimate inventory National Park Service North Coast andCascades Network (National Resource Technical Report NPSNCCNNRTR-2006010) National Resource Program CenterFort Collins CO

De Woul M and Hock R (2005) Static mass-balance sensitivity ofArctic glaciers and ice caps using a degree-day approach AnnGlaciol 42 217ndash224 (doi 103189172756405781813096)

Elsner MM and 8 others (2010) Implications of 21st-century climatechange for the hydrology of Washington State Climatic Change102(1ndash2) 225ndash260 (doi 101007s10584-010-9855-0)

Granshaw FD and Fountain AG (2006) Glacier change (1958ndash1998) in the North Cascades National Park ComplexWashington USA J Glaciol 52(177) 251ndash256 (doi 103189172756506781828782)

Halofsky JE Peterson DL OrsquoHalloran KA and Hoffman CH eds(2011) Adapting to climate change at Olympic National Forestand Olympic National Park (Gen Tech Rep PNW-GTR-844)Pacific Northwest Research Station US Department of Agricul-ture Portland OR httpwwwtreesearchfsfeduspubs38702

Heroux P and Kouba J (2001) GPS precise point positioning usingIGS orbit products Phys Chem Earth 26(6ndash8) 573ndash578

Heusser CJ (1957) Variations of Blue Hoh and White Glaciersduring recent centuries Arctic 10(3) 139ndash150 (doi 1014430arctic3761)

Hodge SM (1974) Variations in the sliding of a temperate glacierJ Glaciol 13(69) 349ndash369

Hodson A and 7 others (2008) Glacial ecosystems Ecol Monogr78(1) 41ndash67 (doi 10189007-01871)

Hubley RC (1956) Glaciers of the Washington Cascade andOlympic Mountains their present activity and its relation tolocal climatic trends J Glaciol 2(19) 669ndash674 (doi 103189002214356793701938)

Josberger EG Bidlake WR March RS and Kennedy BW (2007)Glacier mass-balance fluctuations in the Pacific Northwest andAlaska USA Ann Glaciol 46 291ndash296 (doi 103189172756407782871314)

LaChapelle ER (1965) The mass budget of Blue Glacier Washing-ton J Glaciol 5(41) 609ndash623

Malcomb NL and Wiles GC (2013) Tree-ring-based reconstructionsof North American glacier mass balance through the Little IceAge contemporary warming transition Quat Res 79(2)123ndash137 (doi 101016jyqres201211005)

Mantua NJ Hare SR Zhang Y Wallace JM and Francis RC (1997) APacific interdecadal climate oscillation with impacts on salmonproduction Bull Am Meteorol Soc 78(6) 1069ndash1079 (doi1011751520-0477(1997)078lt1069APICOWgt20CO2)

Mantua N Tohver I and Hamlet A (2010) Climate change impactson streamflow extremes and summertime stream temperatureand their possible consequences for freshwater salmon habitatin Washington State Climatic Change 102(1ndash2) 187ndash223 (doi101007s10584-010-9845-2)

Matthes FE (1946) Report of Committee on Glaciers 1945 Eos27(2) 219ndash233

Meier MF (1961) Distribution and variations of glaciers in theUnited States exclusive of Alaska IASH Publ 54 (GeneralAssembly of Helsinki 1960 ndash Snow and Ice) 420ndash429

Mote PW and Salatheacute EP Jr (2010) Future climate in the PacificNorthwest Climatic Change 102(1ndash2) 29ndash50 (doi 101007s10584-010-9848-z)

Nolin AW and Daly C (2006) Mapping lsquoat riskrsquo snow in thePacific Northwest J Hydromet 7(5) 1164ndash1171 (doi 101175JHM5431)

PRISM Group (2006) United States average monthly and annualprecipitation 1971ndash2000 Oregon State University CorvallisOR httpprismoregonstateedu

Rasmussen LA and Conway H (2001) Estimating South CascadeGlacier (Washington USA) mass balance from a distant radio-sonde and comparison with Blue Glacier J Glaciol 47(159)579ndash588 (doi 103189172756501781831873)

Rasmussen LA and Wenger JM (2009) Upper-air model of summerbalance on Mount Rainier USA J Glaciol 55(192) 619ndash624(doi 103189002214309789471012)

Rasmussen LA Conway H and Hayes PS (2000) The accumulationregime of Blue Glacier USA 1914ndash96 J Glaciol 46(153)326ndash334 (doi 103189172756500781832846)

Riedel JR Burrows RA and Wenger JM (2008) Long-term monitoringof small glaciers at North Cascades National Park a prototypepark model for the North Coast and Cascades Network (NaturResour Rep NPSNCCNNRR-2008066) National Park ServiceFort Collins CO

Spicer RC (1986) Glaciers in the Olympic Mountains Washingtonpresent distribution and recent variations (PhD thesis Uni-versity of Washington)

Tabor RW and Cady WM (1978) Geologic map of the OlympicPeninsula Washington (Misc Inv Map 994) US GeologicalSurvey Reston VA

MS received 19 July 2014 and accepted in revised form 11 September 2014

Riedel and others Glaciers in the Olympic Mountains16

of snowfall each winter (Davey and others 2006) Meanannual temperature and temperature range also vary fromwest to east with higher elevations on east side peakstypically 15ndash20degC warmer than west side locations (Daveyand others 2006) The climate has pronounced interannualand decadal variations in temperature and precipitationassociated with the Southern Oscillation (El NintildeoLa Nintildea)and the Pacific Decadal Oscillation (Mantua and others1997) Erosion by glaciers streams hillslope processes and

active tectonic uplift has created 2400m of local relief fromthe summit of Mount Olympus (2429m) to sea levelRepeated ice ages and development of long alpine valleyglaciers carved deep U-shaped troughs that radiate from thecenter of the peninsula (Tabor and Cady 1978) Glaciers arecurrently distributed across the mountains with the largeston Mount Olympus on the wetter windward side of therange (Fig 2)

METHODSThe glacier geospatial database was developed using 1mpixel size orthorectified vertical air photographs taken in2009 by the US National Agriculture Imagery Program(NAIP) Each glacier was digitized directly from thephotographs at a scale of 1 2000 with vertices spacedevery 5m All perennial accumulations of ice gt001 km2 inarea were included in the inventoryUp to three polygons were digitized for each glacier The

first area mapped represents the minimum extent of what isclearly glacier ice as determined by the presence ofcrevasses surface ponds or blue glacial ice This outlineincludes only that part of the glacier that is free of debris butmay include minor areas of debris cover if the debris isdiscontinuous or thin The second polygon mapped hadsignificant debris cover seasonal snow or shadows overglacial ice as confirmed by the presence of crevasses glacialice exposed on crevasse walls or steep glacier margins andice-marginal channels The third area delineated included afew sites where we could not positively determine from theNAIP imagery if there was ice beneath thick hummockydebris near a glacierrsquos terminusThe use of up to three polygons per glacier has two

purposes Firstly quantifying debris-covered area on the

Fig 1 Location of the Olympic Peninsula and Washington Stateand boundary of Olympic National Park

Fig 2 Modern glacier distribution in the central Olympic Peninsula

Riedel and others Glaciers in the Olympic Mountains 9

glacier allows for observations of how debris cover may beinfluencing the rate of change of glaciers Secondly havinga maximum outline for areas of possible ice allows for aquantification of overall glacier area uncertainty providinga level of significance and statistical credibility to thegeospatial dataGlacier change during the past several decades was

quantified by comparing our new inventory with those ofMatthes (1946) Meier (1961) and Spicer (1986) The Spicerdata were obtained from aerial photographs taken between1976 and 1982 and this inventory is particularly usefulbecause it was based on higher-resolution images than thoseavailable to Meier or MatthesHigh-precision elevation transects were measured in

autumn 2010 along longitudinal profiles on four glaciersusing GPS GPS positions were collected at 1 s intervals andwere processed using the kinematic Precise Point Pos-itioning (PPP) service from the Canadian Natural ResourcesDepartment (Heroux and Kouba 2001) PPP processing usescorrected satellite orbits and does not require a fixedreference station The measurement uncertainty was 1mdetermined by reference measurements taken over solidground near the glacier margins The glaciers chosenrepresent a west-to-east precipitation gradient and despitethe limited number the sample represents about two-thirdsof the glacier area Glacier thickness changes were made bycomparing elevation profiles with elevations from the 1987US Geological Survey digital elevation models (DEMs)based on photography from the same year To calculatevolume loss the thinning amount within each 20melevation bin was averaged and then multiplied by the areaof the glacier in that bin The upper parts of the glaciers wellabove the equilibrium-line altitude were not profiled butwe observed little thinning in these areas For Blue Glacierthe icefall and steep terminus could not be profiled For theicefall we fit a quadratic equation to the thinningelevationrelationship but the choice is not critical because of thesmall glacier areas We extrapolated the rate of thinning toestimate loss for the lowest elevation band at the terminusand assumed that it had a wedge shapeAnnual glacial meltwater discharge in the Hoh (51

glaciated) Elwha (05) and Dungeness (03) basins wasestimated using a model based on glacier hypsometry and

summer melt (Figs 2 and 3 Riedel and others 2008)Summer (1 Mayndash30 September) melt was estimated with apositive degree-day (PDD) model (Rasmussen and Wenger2009) Glacier hypsometry across a watershed was calcu-lated in 50m elevation bands using a 1987 10m DEM as abase map and glacier area from our inventoryThe PDD model is based on air temperature at the

elevations of glaciers and was calibrated with summerbalance measurements taken from 1963 to 1994 at altitudesof 1500 and 2050masl on Blue Glacier (Conway andothers 1999) Upper-air temperatures were acquired fromthe US National Centers for Environmental PredictionUSNational Center for Atmospheric Research (NCEPNCAR)reanalysis database for the nearest gridpoint (475degN125degW) 150 km west-southwest of Blue Glacier Upper-air temperatures were used because they more accuratelyrepresent air temperatures at the glacier surface than donearby terrestrial-based temperature measurements (Ras-mussen and Wenger 2009)Following methods outlined by DeWoul and Hock (2005)

and Rasmussen and Wenger (2009) summer melt at a givenaltitude bs ethzTHORN is

bs ethzTHORN frac14 Xtn

tfrac14t1

Tthornetht zTHORN thorn

wherePTthorn represents summation of average daily air

temperature accounting only values gt0degC for a selectedperiod The coefficients and are determined by linearregression minimizing model error Air temperature at 1500and 2050m is determined by linear interpolation of1200UTC air temperatures at 850 and 700mbar levels(approximate altitudes of 1450 and 3000m respectively)Melt above between and below these elevations was basedon a linear regressionThe model did not partition ice firn and snow contribu-

tions to total glacier melt and used a single melt coefficientWe did not attempt to separately quantify these phases fortwo reasons First the melt season starts weeks earlier at theterminus of these glaciers than in their accumulation zonesThus even late in the melt season glacial runoff includessnow (and firn) making it difficult to pick a date when thereis mostly ice melt particularly when the mass balance waspositive the previous year and a lot of firn is exposed tosurface melting Second the glacier microclimate delayssnowmelt on the glacier interannually as well as seasonallycompared with the surrounding landscape These consid-erations make glacial snow and firn melt important factorswhen considering the hydrologic importance of glaciers

RESULTS AND DISCUSSIONThere are currently 184 glaciers larger than 001 km2 on theOlympic Peninsula but 120 are lt01 km2 and only four aregt1 km2 (Fig 4) The higher-resolution NAIP photographsand field checks allowed us to identify another 117 smallsnowndashfirnndashice patches smaller than 001 km2 covering05 km2 Some of these were gt001 km2 in 1980 andnow fall into this smaller size category Previous estimatesalso missed some glaciers greater than 001 km2 because ofthe lower resolution of the photographs available at the time(Table 1 Meier 1961 Spicer 1986) Changes in thenumber of glaciers also reflect substantial glacier thinningwhich can cause one large glacier to divide into two (or

Fig 3 Modern areandashaltitude distribution of glaciers in three largewatersheds

Riedel and others Glaciers in the Olympic Mountains10

more) smaller glaciers For example continued climatewarming will eventually lead Blue Glacier to divideWe identified 083 km2 of debris-covered ice half of

which is on Blue and Black Glaciers on Mount OlympusSpicer (1986) identified 12 lsquorock glaciersrsquo in a previousinventory but we did not track changes in them indi-vidually The presence of debris-covered ice is expected toincrease as the climate warms glaciers thin and in somecases glacier flow velocities decline Debris cover of morethan a few centimeters can dramatically slow melting andin the future many of the Peninsularsquos glaciers may becomerock glaciers Heusser (1957) noted that debris cover onlower White and Hoh Glaciers slowed recession in the early20th century Ferry Glacier was one of the 50 largest glaciersin the Olympics Mountains in 1980 with an area of

017 km2 but by 2009 what remained of the glacier wascovered by a rockfall making it difficult to determine howmuch if any ice remainsAll the glaciers counted in a previous inventory have

decreased in size in the past 30 years and our countrepresents a decrease of 82 glaciers from the 266 noted in1980 (Fig 2 Spicer 1986) Total glacier cover now standsat 3020 095 km2 not including features smaller than001 km2 Uncertainty associated with the 1m resolution ofthe NAIP imagery is compounded by shadows and debriscover and varies substantially between glaciers largerglaciers have ten times the uncertainty of smaller glaciers(Table 1) Total uncertainty represents only 6 of the totalestimated change in glacier area not enough to affect theconclusion that glaciers are in rapid decline

Fig 4 Histogram of the number of glaciers by size category note size of categories changes Perennial snow and ice features lt001 km2 notshown

Table 1 Area (km2) of select glaciers at various times in the past century Data for 1980 and early 20th century from Spicer (1986) SeeFigure 2 for locations

Glacier (mountainndashaspect) Little Ice Age maximum Early 20th century 1980 2009 Change 1980ndash2009

(photograph date) ( error)

West of the Elwha valleyBlue (OlympusndashNE) 717 561(1899) 61 535 (0079) ndash12

Humes (OlympusndashE) 263 202 (1907) 185 148 (0088) ndash20

Hoh (OlympusndashNE) 807 54 (1933) 489 403 (0055) ndash18

White (TomndashN) 779 512 (1924) 469 390 (0055) ndash17

Jeffers (OlympusndashSE) 281 na 08 031 (0127) ndash61

Hubert (OlympusndashSW) 239 na 110 071 (0058) ndash35

Carrie (BaileysndashNE) na na 098 062 (0011) ndash37

East of the Elwha valleyChristie (ChristiendashN) na na 02 0099 (0003) ndash51

Lillian (McCartneyndashN) na na 014 0029 (0001) ndash21

Cameron (Cameron) na na 016 0103 (0003) ndash36

Anderson (AndersonndashS) 158 122 (1927) 061 014 (0003) ndash77

Eel (AndersonndashN) 230 177 (1920) 111 085 (0008) ndash23

Total eight named glaciers 3474 na 2115 1677 21

OLYM total na 6657 4594 3020 (0945) ndash34

Based on aerial photographs taken between 1976 and 1982

Riedel and others Glaciers in the Olympic Mountains 11

Combined glacier area decreased by 157 km2 from 1980(459 km2) to 2009 (302 km2) a loss of 34 (Table 1 Spicer1986) Mean glacier area decreased from 017 km2 in 1980 to011 km2 in 2009 In 1980 eight of 266 glaciers were gt1 km2

(Spicer 1986) there are now only four that exceed that size(Blue Hoh White and Humes glaciers) All of these glaciersare on Mount Olympus the highest mountain on thePeninsula located on the windward (wet) west side of the

Olympic Mountains (Figs 2 and 5) Other clusters of glaciersin the 005ndash02 km2 size range occur in the Bailey Range andon Mount Christie and Mount Anderson (Fig 2) Thesesummits are all either on the wetter windward side of therange (Baileys) or benefit from storms that penetrate deep intothe mountains along the Quinnault RiverAspect and distance inland from the Pacific moisture

source have had a strong influence on glacier response to the

Fig 5 Change in glacier extent on Mount Olympus (a) and Mount Anderson (b) from AD1980 to present

Riedel and others Glaciers in the Olympic Mountains12

warming climate Glaciers in the eastern part of the Peninsulaand those that face south lost more area than those facingnorth and on the wetter windward slope (Table 1) Glacierlosses were most pronounced in the drier northeastern part ofthe Peninsula where for example little remains of LillianGlacier on McCartney Peak (Fig 6) For the most partglaciers east of the Elwha River now exist almost exclusivelyon shaded northern aspects where melting is slower and theymay benefit from secondary sources of accumulation (egwind redeposition and snow avalanche)The influence of aspect is well illustrated on Mount

Anderson Since 1980 Anderson Glacier has lost 77 of itsarea compared with a 23 loss for adjacent north-facing EelGlacier (Table 1 Figs 5 and 7) Aspect is also a critical factorto glacier status on Mount Olympus where southeast-facingJeffers Glacier shrank by 61 in 30 years while north-facing Hoh and White Glaciers declined by 17ndash18 (Fig 5)North-facing glaciers east of the Elwha lost 21ndash51 of theirarea in 30 years whereas the north-facing glaciers on MountOlympus lost 12ndash20 over the same period Glaciers in theBailey Range with north aspects had area losses comparablewith glaciers on the south side of Olympus and with north-facing glaciers east of the Elwha (eg Carrie GlacierTable 1)The rate of ice loss for six glaciers from AD1900 to 1980

was 026 km2 andash1 although this included a period of positivebalance at Blue Glacier from 1959 to 1975 (Hubley 1956Spicer 1986 Rasmussen and Conway 2001) Since 1980the rate of decline in combined ice extent across theOlympic Mountains doubled to 054 km2 andash1 Acceleratingdecline of glacier area is also reflected in strongly negative

cumulative balance on Blue Glacier since the mid-1980s(Rasmussen and Conway 2001)Decline in glacier area in recent decades on the Olympic

Peninsula exceeds losses east of the FraserndashPuget lowlandsIn the southern Coast Mountains of British Columbia glacierarea declined 10 from 1985 to 2005 (Bolch and others2010) while Granshaw and Fountain (2006) estimated lossof glaciers in the North Cascades National Park over a40 year period ending in 1998 at 7 The more rapid lossof glaciers in the Olympics is more comparable with theobserved loss of 20 over a similar period on VancouverIsland (Bolch and others 2010) Rapid loss of glaciers incoastal ranges is likely due to their sensitivity to changes intemperature that strongly influence spring ablation andearly-fall accumulation (LaChapelle 1965) Accumulatingevidence indicates that the recent loss of glacier area andvolume through multiple decades for all glaciers in thePacific Northwest has not occurred since at least AD 1694(Malcomb and Wiles 2013)Glacier area measurements were combined with surface

elevation profiles to assess thickness changes from 1987 to2010 for four of the largest glaciers in the OlympicMountains (Table 2) Only Blue Glacier has ice thicknessdata and a known glacier volume (Allen and others 1960)the other glacier volumes were estimated assuming anaverage ice thickness and by the ratio of the glacierrsquos area to

Fig 6 Changes in Lillian Glacier on McCartney Peak from 1905 (aNPS photograph) to the present (b photograph by J McLean)

Fig 7 Changes in Anderson Glacier from 1936 (a photograph byA Curtis) to the present (b photograph by R Hoffman)

Riedel and others Glaciers in the Olympic Mountains 13

Blue Glacierrsquos area Blue Glacier on Mount Olympus hadthe largest volume loss since 1987 because it has the largestarea The largest percent change however was for south-facing Humes Glacier at ndash22 while north-facing Blue andHoh Glaciers lost 15 and 16 respectively (Table 2) Inaddition to its aspect Humes Glacier had the mostsignificant volume reduction because it is at a lowerelevation than its neighbors Hoh Blue and White glaciersFurther to the east north-facing Eel Glacier has lost 14 ofits volume (0013 km3) since 1987Even with a 34 decline in area and 20 decline in

volume in the last 30 years glaciers continue to providesignificant amounts of water to streams on the OlympicPeninsula We used the hypsometry of glaciers and summer-melt versus elevation curves from the PDD model toestimate glacial contribution to summer streamflow forthree large basins that represent a range in climate andglacial cover (Table 3 Figs 8 and 9) As shown in Figure 8the model accurately reproduced the amount of summermelt as measured by melt stakes at two locations The modeland melt data also show that summer melt at 1500m variesby 20ndash25 (1m) between extreme years with lessvariability at higher elevations Model error at 1500m is050mwe andash1 (r2 = 068) based on the residual mean sumof errors at 2050m it is 028mwe andash1 (r2 = 076) Thesevalues represent an error of 10 in the total summermelt estimateAbout 66 of the glacier-covered landscape in the

Olympic Mountains is found in the Hoh River watershed

(20 km2) more than half of the remaining glacial cover is inthe Queets and Elwha watersheds (Fig 2) Based on thePDD model and basin-wide glacier hypsometry glacierscurrently provide 63ndash797106m3 of water to the HohRiver annually from 1 May to 30 September In the Elwhawatershed glaciers provide 12ndash1513 106m3 of sum-mer runoff while in the Dungeness basin they provide 25ndash31028106m3 The other large watersheds on theOlympic Peninsula have lt5 glacial contribution tosummer streamflow Given a 20 loss in glacier volumeglacial runoff on the Peninsula has decreased a similaramount in the past 30 yearsOur PDD model estimates of glacial runoff combine

snow firn and ice contributions but we recognize that theyare likely dominated by snowmelt LaChapelle (1965)suggested snowmelt was 16 and 42 times firn and icemelt on Blue Glacier in 1958 and 1962 respectively andthat ice melt occurred primarily in September and OctoberGiven reduced winter accumulation in the last 50 years anda longer melt season (Rasmussen and Conway 2001) thesnow to firnice melt ratios are now probably smallerThe volume loss calculations allowed us to assess the

glacier ice (not snow or firn) contribution to summerstreamflow in the Hoh basin (Tables 2 and 3) Volumeof ice loss for Hoh and Blue Glaciers averaged 63106m3we andash1 from 1987 to 2010 assuming a similarcontribution from the other 1065 km2 of glaciers in the Hohvalley the 23 year average annual glacial ice ablation is117 106m3we Using the PDD model estimate of an

Table 3 Range of modern glacial ice snow and firn contribution tosummer (1 Mayndash30 September) streamflow for three rivers

Watershed Basin

area

Glacier

area

Glacial runoff Total summer

runoff

2010 low 2009 high

km2 km2 106 m3 106 m3

Hoh 655 2003 63 79 89ndash154

Elwha 697 372 12 15 25ndash40

Dungeness 404 113 245 308 30ndash38

Includes snow firn and ice

Fig 8 Degree-day model of Blue Glacier summer balance (dashedline) used to estimate range in glacier runoff Measured values(square and diamond) from Conway and others (1999)

Fig 9 Modern range in summer (1 Mayndash30 September) glacialrunoff for three Olympic Peninsula watersheds determined by aPDD model for negative (2009) and positive (2010) net mass-balance years Runoff includes snow firn and ice from glaciers ineach basin Percentage of basin above gage site covered by glaciersshown in parentheses

Table 2 Volume change estimates for four glaciers 1987ndash2010Volume changes are not adjusted to water equivalence

Glacier Area 2009 Volume 2010 Volume loss

1987ndash2009

Change

1987ndash2010

km2 km3 km3

Hoh 403 049 0078 ndash16

Blue 535 057 0084 ndash15

Humes 148 017 0038 ndash22

Eel 085 009 0013 ndash14

Volume and change estimates less certain due to lack of ice radarmeasurements

Riedel and others Glaciers in the Olympic Mountains14

average annual total glacier summer contribution of71106m3we for the Hoh River the ice fractioncontributed 16 of total glacier runoff for MayndashSeptem-ber mostly late in the melt seasonEstimates of glacier volume loss and results from the

glacial runoff model highlight the importance of glaciers tolate-summer streamflow at the Hoh River gaging station nearForks (Fig 1) Comparing the streamflow data with the PDDmodel results glacial snow firn and ice contribute 359ndash397106m3we or 18ndash30 of total streamflow forAugustndashSeptember compared with 9ndash15 for the entiremelt seasonVolume change estimates also provide a means to assess

the glacial ice (not snow and firn) contribution to late-summer streamflow assuming that all the volume loss wasice that melted in August and September The averageAugustndashSeptember discharge in the lower Hoh River for thepast 23 years is 160 106m3 Based on the 23 year volumeloss estimate of average annual icemelt of 117 106m3wefor the Hoh basin glacier ice provided 7 of the dischargeon the lower Hoh River and 31 of the total glaciercontribution (including snow and firn) Although a smallfraction of total streamflow the glacier ice contributionoccurs when the contribution from snow and firn melt hasdeclined and summer rainfall is minimal and represents theaverage minimum reduction of AugustndashSeptember stream-flow that would occur in the lower Hoh River in the future ifglaciers disappeared The importance of this lsquofossilrsquo water ismagnified during summers when the previous winterrsquossnowfall is low and will become more critical in the futureas the snowpack declinesThe marked loss of glaciers on the Olympic Peninsula in

the past 30 years is largely a result of a 1degC rise in meanannual temperature (Rasmussen and Conway 2001) andillustrates how sensitive these relatively small thin low-elevation temperate glaciers are to climate change Thistemperature increase has directly increased the summermelt rate lengthened the melt season and decreased theduration of the accumulation season resulting in less wintersnow accumulation LaChapelle (1965) notes that theelevation of the freezing level is particularly important inearly fall as it controls how much precipitation falls as snowwhile Rasmussen and others (2000) suggest that springweather is a more important influence on ablation Coolcloudy conditions that often prevail in spring in thismaritime climate lead to lower melt rates at the time ofthe summer solstice particularly during the wet and coldphases of the Southern Oscillation and Pacific DecadalOscillation Recent climate warming appears stronger inwinter at Blue Glacier where average winter temperaturehas risen 3degC in the past half-century (Rasmussen andothers 2000) As a result average winter snow accumu-lation has decreased 500mm near 1500m at the glacierterminus since 1948 (Rasmussen and others 2000)Most of the glaciers on the Peninsula are currently not in

equilibrium with the present climate and are expected tocontinue to shrink in the near future even if accumulationincreases and temperature stops rising In the next severaldecades glaciers are likely to continue to disappear rapidlybased on projected future temperature increases of severaldegrees in the next 70 years Mote and Salatheacute (2010)estimate that mean annual temperature in Washington Statewill increase by at least 12degC by 2040 and at least 28degC by2080 Future temperature increases may be even higher near

the elevation of glaciers given positive feedback mechan-isms Further it is possible that the periodic increases inprecipitation associatedwith the cool wet phase of the PacificDecadal Oscillationmay havewaned in the past few decadeswith a warming climate (Josberger and others 2007)The preponderance of small glaciers remaining on the

Peninsula (145 of 184 are lt01 km2) means that most arevulnerable to melting away completely in the near future(Fig 2) The glaciers most threatened by future climatewarming are generally those that face south in the drier andwarmer climate prevalent on the eastern side of thePeninsula Glaciers on the northeast part of the mountainson Mount Deception McCartney Peak and Cameron Peakmay be the most threatened due to their isolation fromPacific moisture and climate model projections of highersummer potential evapotranspiration that could translate tohigher summer melt rates (Elsner and others 2010) Glacierson the northern side of the Bailey Range and in theheadwaters of the Queets and Elwha Rivers should fareslightly better because of their proximity to large valleys thatfunnel moisture from the Pacific Ocean However theiraccumulation zones are several hundred meters lower thanthose on the large glaciers of Mount Olympus If the climatewarms at the projected rates it is likely that within a centuryglaciers in the Olympic Mountains will be confined to theMount Olympus massifLoss of glaciers due to warming climate has several

significant implications for the Olympic Peninsula includ-ing loss of glacial habitat exposure of vast areas of looseglacial sand and gravel higher summer stream temperaturesand lower late-summer flows in most watersheds Decline inglacier meltwater production will exacerbate changes inaquatic habitat associated with a warming climate Mantuaand others (2010) identified summer temperature andstreamflow as critical physical habitat features for salmonLoss of glaciers will reduce summer streamflow andcontribute to higher summer stream temperatures to thedetriment of species such as the bull trout (Salvelinusconfluentus) (Halofsky and others 2011) Other ecosystemswill also be affected by the loss of glaciers For examplealpine food webs will be diminished by the loss of speciessuch as the ice worm which is preyed upon by rosy finchesand other alpine species

CONCLUSIONSThe glacier geospatial database we developed provides animportant benchmark for assessing glacier extent and glacialrunoff changes in the Olympic Mountains for the past30 years and into the future The combined area of allglaciers has decreased 34 in the past 30 years with ice lossaccelerating to a rate more than twice as fast as that from1900 to 1980 Only four of the 184 remaining glaciers aregt1 km2 in area Glaciers on the southern side of themountains at lower elevations and in the northeastern partof the Peninsula exhibited the greatest area and volume lossesand are the most likely to disappear in the next centuryGlacier decline in the past 30 years in the Olympics is greaterthan in the Cascades and southern Coast Mountains but iscomparable with Vancouver Island Based on ice volumelosses glacial contribution to summer streamflow hasdeclined 20 in the past 30 years but remains significantfor the Hoh River at 63ndash797106m3 andash1 Glaciers con-tribute lt5 to summer streamflow in all other large

Riedel and others Glaciers in the Olympic Mountains 15

watersheds in the Olympic Mountains Delivery of this coldfresh water to streams becomes more critical in the latesummer when rainfall is minimal and snowmelt hasdeclined On the lower Hoh River glacial ice contributes7 of the AugustndashSeptember streamflow which representsthe minimum reduction in flow that would occur if all theglaciers melted away Continued loss of glaciers will directlyimpact aquatic ecosystems through higher stream tempera-tures and lower summer base flows

ACKNOWLEDGEMENTSWe thank the US National Park Service Climate ChangeProgram for funding this research and Olympic and NorthCascades national parks and Portland State University for in-kind support Sharon Brady Roger Hoffman and SteveDorsch contributed GIS and cartographic expertise Finallywe want to acknowledge Richard Spicer for the valuablebaseline he created on the status of Olympic glaciers in theearly 1980s

REFERENCESAllen CR Kamb WB Meier MF and Sharp RP (1960) Structure ofthe lower Blue Glacier Washington J Geol 68(6) 601ndash625

Bolch T Menounos B andWheate R (2010) Landsat-based inventoryof glaciers in western Canada 1985ndash2005 Remote SensEnviron 114(1) 127ndash137 (doi 101016jrse200908015)

Conway H Rasmussen LA and Marshall HP (1999) Annual massbalance of Blue Glacier USA 1955ndash97 Geogr Ann A 81(4)509ndash520

Davey CA Redmond KT and Simeral DB (2006) Weather andclimate inventory National Park Service North Coast andCascades Network (National Resource Technical Report NPSNCCNNRTR-2006010) National Resource Program CenterFort Collins CO

De Woul M and Hock R (2005) Static mass-balance sensitivity ofArctic glaciers and ice caps using a degree-day approach AnnGlaciol 42 217ndash224 (doi 103189172756405781813096)

Elsner MM and 8 others (2010) Implications of 21st-century climatechange for the hydrology of Washington State Climatic Change102(1ndash2) 225ndash260 (doi 101007s10584-010-9855-0)

Granshaw FD and Fountain AG (2006) Glacier change (1958ndash1998) in the North Cascades National Park ComplexWashington USA J Glaciol 52(177) 251ndash256 (doi 103189172756506781828782)

Halofsky JE Peterson DL OrsquoHalloran KA and Hoffman CH eds(2011) Adapting to climate change at Olympic National Forestand Olympic National Park (Gen Tech Rep PNW-GTR-844)Pacific Northwest Research Station US Department of Agricul-ture Portland OR httpwwwtreesearchfsfeduspubs38702

Heroux P and Kouba J (2001) GPS precise point positioning usingIGS orbit products Phys Chem Earth 26(6ndash8) 573ndash578

Heusser CJ (1957) Variations of Blue Hoh and White Glaciersduring recent centuries Arctic 10(3) 139ndash150 (doi 1014430arctic3761)

Hodge SM (1974) Variations in the sliding of a temperate glacierJ Glaciol 13(69) 349ndash369

Hodson A and 7 others (2008) Glacial ecosystems Ecol Monogr78(1) 41ndash67 (doi 10189007-01871)

Hubley RC (1956) Glaciers of the Washington Cascade andOlympic Mountains their present activity and its relation tolocal climatic trends J Glaciol 2(19) 669ndash674 (doi 103189002214356793701938)

Josberger EG Bidlake WR March RS and Kennedy BW (2007)Glacier mass-balance fluctuations in the Pacific Northwest andAlaska USA Ann Glaciol 46 291ndash296 (doi 103189172756407782871314)

LaChapelle ER (1965) The mass budget of Blue Glacier Washing-ton J Glaciol 5(41) 609ndash623

Malcomb NL and Wiles GC (2013) Tree-ring-based reconstructionsof North American glacier mass balance through the Little IceAge contemporary warming transition Quat Res 79(2)123ndash137 (doi 101016jyqres201211005)

Mantua NJ Hare SR Zhang Y Wallace JM and Francis RC (1997) APacific interdecadal climate oscillation with impacts on salmonproduction Bull Am Meteorol Soc 78(6) 1069ndash1079 (doi1011751520-0477(1997)078lt1069APICOWgt20CO2)

Mantua N Tohver I and Hamlet A (2010) Climate change impactson streamflow extremes and summertime stream temperatureand their possible consequences for freshwater salmon habitatin Washington State Climatic Change 102(1ndash2) 187ndash223 (doi101007s10584-010-9845-2)

Matthes FE (1946) Report of Committee on Glaciers 1945 Eos27(2) 219ndash233

Meier MF (1961) Distribution and variations of glaciers in theUnited States exclusive of Alaska IASH Publ 54 (GeneralAssembly of Helsinki 1960 ndash Snow and Ice) 420ndash429

Mote PW and Salatheacute EP Jr (2010) Future climate in the PacificNorthwest Climatic Change 102(1ndash2) 29ndash50 (doi 101007s10584-010-9848-z)

Nolin AW and Daly C (2006) Mapping lsquoat riskrsquo snow in thePacific Northwest J Hydromet 7(5) 1164ndash1171 (doi 101175JHM5431)

PRISM Group (2006) United States average monthly and annualprecipitation 1971ndash2000 Oregon State University CorvallisOR httpprismoregonstateedu

Rasmussen LA and Conway H (2001) Estimating South CascadeGlacier (Washington USA) mass balance from a distant radio-sonde and comparison with Blue Glacier J Glaciol 47(159)579ndash588 (doi 103189172756501781831873)

Rasmussen LA and Wenger JM (2009) Upper-air model of summerbalance on Mount Rainier USA J Glaciol 55(192) 619ndash624(doi 103189002214309789471012)

Rasmussen LA Conway H and Hayes PS (2000) The accumulationregime of Blue Glacier USA 1914ndash96 J Glaciol 46(153)326ndash334 (doi 103189172756500781832846)

Riedel JR Burrows RA and Wenger JM (2008) Long-term monitoringof small glaciers at North Cascades National Park a prototypepark model for the North Coast and Cascades Network (NaturResour Rep NPSNCCNNRR-2008066) National Park ServiceFort Collins CO

Spicer RC (1986) Glaciers in the Olympic Mountains Washingtonpresent distribution and recent variations (PhD thesis Uni-versity of Washington)

Tabor RW and Cady WM (1978) Geologic map of the OlympicPeninsula Washington (Misc Inv Map 994) US GeologicalSurvey Reston VA

MS received 19 July 2014 and accepted in revised form 11 September 2014

Riedel and others Glaciers in the Olympic Mountains16

glacier allows for observations of how debris cover may beinfluencing the rate of change of glaciers Secondly havinga maximum outline for areas of possible ice allows for aquantification of overall glacier area uncertainty providinga level of significance and statistical credibility to thegeospatial dataGlacier change during the past several decades was

quantified by comparing our new inventory with those ofMatthes (1946) Meier (1961) and Spicer (1986) The Spicerdata were obtained from aerial photographs taken between1976 and 1982 and this inventory is particularly usefulbecause it was based on higher-resolution images than thoseavailable to Meier or MatthesHigh-precision elevation transects were measured in

autumn 2010 along longitudinal profiles on four glaciersusing GPS GPS positions were collected at 1 s intervals andwere processed using the kinematic Precise Point Pos-itioning (PPP) service from the Canadian Natural ResourcesDepartment (Heroux and Kouba 2001) PPP processing usescorrected satellite orbits and does not require a fixedreference station The measurement uncertainty was 1mdetermined by reference measurements taken over solidground near the glacier margins The glaciers chosenrepresent a west-to-east precipitation gradient and despitethe limited number the sample represents about two-thirdsof the glacier area Glacier thickness changes were made bycomparing elevation profiles with elevations from the 1987US Geological Survey digital elevation models (DEMs)based on photography from the same year To calculatevolume loss the thinning amount within each 20melevation bin was averaged and then multiplied by the areaof the glacier in that bin The upper parts of the glaciers wellabove the equilibrium-line altitude were not profiled butwe observed little thinning in these areas For Blue Glacierthe icefall and steep terminus could not be profiled For theicefall we fit a quadratic equation to the thinningelevationrelationship but the choice is not critical because of thesmall glacier areas We extrapolated the rate of thinning toestimate loss for the lowest elevation band at the terminusand assumed that it had a wedge shapeAnnual glacial meltwater discharge in the Hoh (51

glaciated) Elwha (05) and Dungeness (03) basins wasestimated using a model based on glacier hypsometry and

summer melt (Figs 2 and 3 Riedel and others 2008)Summer (1 Mayndash30 September) melt was estimated with apositive degree-day (PDD) model (Rasmussen and Wenger2009) Glacier hypsometry across a watershed was calcu-lated in 50m elevation bands using a 1987 10m DEM as abase map and glacier area from our inventoryThe PDD model is based on air temperature at the

elevations of glaciers and was calibrated with summerbalance measurements taken from 1963 to 1994 at altitudesof 1500 and 2050masl on Blue Glacier (Conway andothers 1999) Upper-air temperatures were acquired fromthe US National Centers for Environmental PredictionUSNational Center for Atmospheric Research (NCEPNCAR)reanalysis database for the nearest gridpoint (475degN125degW) 150 km west-southwest of Blue Glacier Upper-air temperatures were used because they more accuratelyrepresent air temperatures at the glacier surface than donearby terrestrial-based temperature measurements (Ras-mussen and Wenger 2009)Following methods outlined by DeWoul and Hock (2005)

and Rasmussen and Wenger (2009) summer melt at a givenaltitude bs ethzTHORN is

bs ethzTHORN frac14 Xtn

tfrac14t1

Tthornetht zTHORN thorn

wherePTthorn represents summation of average daily air

temperature accounting only values gt0degC for a selectedperiod The coefficients and are determined by linearregression minimizing model error Air temperature at 1500and 2050m is determined by linear interpolation of1200UTC air temperatures at 850 and 700mbar levels(approximate altitudes of 1450 and 3000m respectively)Melt above between and below these elevations was basedon a linear regressionThe model did not partition ice firn and snow contribu-

tions to total glacier melt and used a single melt coefficientWe did not attempt to separately quantify these phases fortwo reasons First the melt season starts weeks earlier at theterminus of these glaciers than in their accumulation zonesThus even late in the melt season glacial runoff includessnow (and firn) making it difficult to pick a date when thereis mostly ice melt particularly when the mass balance waspositive the previous year and a lot of firn is exposed tosurface melting Second the glacier microclimate delayssnowmelt on the glacier interannually as well as seasonallycompared with the surrounding landscape These consid-erations make glacial snow and firn melt important factorswhen considering the hydrologic importance of glaciers

RESULTS AND DISCUSSIONThere are currently 184 glaciers larger than 001 km2 on theOlympic Peninsula but 120 are lt01 km2 and only four aregt1 km2 (Fig 4) The higher-resolution NAIP photographsand field checks allowed us to identify another 117 smallsnowndashfirnndashice patches smaller than 001 km2 covering05 km2 Some of these were gt001 km2 in 1980 andnow fall into this smaller size category Previous estimatesalso missed some glaciers greater than 001 km2 because ofthe lower resolution of the photographs available at the time(Table 1 Meier 1961 Spicer 1986) Changes in thenumber of glaciers also reflect substantial glacier thinningwhich can cause one large glacier to divide into two (or

Fig 3 Modern areandashaltitude distribution of glaciers in three largewatersheds

Riedel and others Glaciers in the Olympic Mountains10

more) smaller glaciers For example continued climatewarming will eventually lead Blue Glacier to divideWe identified 083 km2 of debris-covered ice half of

which is on Blue and Black Glaciers on Mount OlympusSpicer (1986) identified 12 lsquorock glaciersrsquo in a previousinventory but we did not track changes in them indi-vidually The presence of debris-covered ice is expected toincrease as the climate warms glaciers thin and in somecases glacier flow velocities decline Debris cover of morethan a few centimeters can dramatically slow melting andin the future many of the Peninsularsquos glaciers may becomerock glaciers Heusser (1957) noted that debris cover onlower White and Hoh Glaciers slowed recession in the early20th century Ferry Glacier was one of the 50 largest glaciersin the Olympics Mountains in 1980 with an area of

017 km2 but by 2009 what remained of the glacier wascovered by a rockfall making it difficult to determine howmuch if any ice remainsAll the glaciers counted in a previous inventory have

decreased in size in the past 30 years and our countrepresents a decrease of 82 glaciers from the 266 noted in1980 (Fig 2 Spicer 1986) Total glacier cover now standsat 3020 095 km2 not including features smaller than001 km2 Uncertainty associated with the 1m resolution ofthe NAIP imagery is compounded by shadows and debriscover and varies substantially between glaciers largerglaciers have ten times the uncertainty of smaller glaciers(Table 1) Total uncertainty represents only 6 of the totalestimated change in glacier area not enough to affect theconclusion that glaciers are in rapid decline

Fig 4 Histogram of the number of glaciers by size category note size of categories changes Perennial snow and ice features lt001 km2 notshown

Table 1 Area (km2) of select glaciers at various times in the past century Data for 1980 and early 20th century from Spicer (1986) SeeFigure 2 for locations

Glacier (mountainndashaspect) Little Ice Age maximum Early 20th century 1980 2009 Change 1980ndash2009

(photograph date) ( error)

West of the Elwha valleyBlue (OlympusndashNE) 717 561(1899) 61 535 (0079) ndash12

Humes (OlympusndashE) 263 202 (1907) 185 148 (0088) ndash20

Hoh (OlympusndashNE) 807 54 (1933) 489 403 (0055) ndash18

White (TomndashN) 779 512 (1924) 469 390 (0055) ndash17

Jeffers (OlympusndashSE) 281 na 08 031 (0127) ndash61

Hubert (OlympusndashSW) 239 na 110 071 (0058) ndash35

Carrie (BaileysndashNE) na na 098 062 (0011) ndash37

East of the Elwha valleyChristie (ChristiendashN) na na 02 0099 (0003) ndash51

Lillian (McCartneyndashN) na na 014 0029 (0001) ndash21

Cameron (Cameron) na na 016 0103 (0003) ndash36

Anderson (AndersonndashS) 158 122 (1927) 061 014 (0003) ndash77

Eel (AndersonndashN) 230 177 (1920) 111 085 (0008) ndash23

Total eight named glaciers 3474 na 2115 1677 21

OLYM total na 6657 4594 3020 (0945) ndash34

Based on aerial photographs taken between 1976 and 1982

Riedel and others Glaciers in the Olympic Mountains 11

Combined glacier area decreased by 157 km2 from 1980(459 km2) to 2009 (302 km2) a loss of 34 (Table 1 Spicer1986) Mean glacier area decreased from 017 km2 in 1980 to011 km2 in 2009 In 1980 eight of 266 glaciers were gt1 km2

(Spicer 1986) there are now only four that exceed that size(Blue Hoh White and Humes glaciers) All of these glaciersare on Mount Olympus the highest mountain on thePeninsula located on the windward (wet) west side of the

Olympic Mountains (Figs 2 and 5) Other clusters of glaciersin the 005ndash02 km2 size range occur in the Bailey Range andon Mount Christie and Mount Anderson (Fig 2) Thesesummits are all either on the wetter windward side of therange (Baileys) or benefit from storms that penetrate deep intothe mountains along the Quinnault RiverAspect and distance inland from the Pacific moisture

source have had a strong influence on glacier response to the

Fig 5 Change in glacier extent on Mount Olympus (a) and Mount Anderson (b) from AD1980 to present

Riedel and others Glaciers in the Olympic Mountains12

warming climate Glaciers in the eastern part of the Peninsulaand those that face south lost more area than those facingnorth and on the wetter windward slope (Table 1) Glacierlosses were most pronounced in the drier northeastern part ofthe Peninsula where for example little remains of LillianGlacier on McCartney Peak (Fig 6) For the most partglaciers east of the Elwha River now exist almost exclusivelyon shaded northern aspects where melting is slower and theymay benefit from secondary sources of accumulation (egwind redeposition and snow avalanche)The influence of aspect is well illustrated on Mount

Anderson Since 1980 Anderson Glacier has lost 77 of itsarea compared with a 23 loss for adjacent north-facing EelGlacier (Table 1 Figs 5 and 7) Aspect is also a critical factorto glacier status on Mount Olympus where southeast-facingJeffers Glacier shrank by 61 in 30 years while north-facing Hoh and White Glaciers declined by 17ndash18 (Fig 5)North-facing glaciers east of the Elwha lost 21ndash51 of theirarea in 30 years whereas the north-facing glaciers on MountOlympus lost 12ndash20 over the same period Glaciers in theBailey Range with north aspects had area losses comparablewith glaciers on the south side of Olympus and with north-facing glaciers east of the Elwha (eg Carrie GlacierTable 1)The rate of ice loss for six glaciers from AD1900 to 1980

was 026 km2 andash1 although this included a period of positivebalance at Blue Glacier from 1959 to 1975 (Hubley 1956Spicer 1986 Rasmussen and Conway 2001) Since 1980the rate of decline in combined ice extent across theOlympic Mountains doubled to 054 km2 andash1 Acceleratingdecline of glacier area is also reflected in strongly negative

cumulative balance on Blue Glacier since the mid-1980s(Rasmussen and Conway 2001)Decline in glacier area in recent decades on the Olympic

Peninsula exceeds losses east of the FraserndashPuget lowlandsIn the southern Coast Mountains of British Columbia glacierarea declined 10 from 1985 to 2005 (Bolch and others2010) while Granshaw and Fountain (2006) estimated lossof glaciers in the North Cascades National Park over a40 year period ending in 1998 at 7 The more rapid lossof glaciers in the Olympics is more comparable with theobserved loss of 20 over a similar period on VancouverIsland (Bolch and others 2010) Rapid loss of glaciers incoastal ranges is likely due to their sensitivity to changes intemperature that strongly influence spring ablation andearly-fall accumulation (LaChapelle 1965) Accumulatingevidence indicates that the recent loss of glacier area andvolume through multiple decades for all glaciers in thePacific Northwest has not occurred since at least AD 1694(Malcomb and Wiles 2013)Glacier area measurements were combined with surface

elevation profiles to assess thickness changes from 1987 to2010 for four of the largest glaciers in the OlympicMountains (Table 2) Only Blue Glacier has ice thicknessdata and a known glacier volume (Allen and others 1960)the other glacier volumes were estimated assuming anaverage ice thickness and by the ratio of the glacierrsquos area to

Fig 6 Changes in Lillian Glacier on McCartney Peak from 1905 (aNPS photograph) to the present (b photograph by J McLean)

Fig 7 Changes in Anderson Glacier from 1936 (a photograph byA Curtis) to the present (b photograph by R Hoffman)

Riedel and others Glaciers in the Olympic Mountains 13

Blue Glacierrsquos area Blue Glacier on Mount Olympus hadthe largest volume loss since 1987 because it has the largestarea The largest percent change however was for south-facing Humes Glacier at ndash22 while north-facing Blue andHoh Glaciers lost 15 and 16 respectively (Table 2) Inaddition to its aspect Humes Glacier had the mostsignificant volume reduction because it is at a lowerelevation than its neighbors Hoh Blue and White glaciersFurther to the east north-facing Eel Glacier has lost 14 ofits volume (0013 km3) since 1987Even with a 34 decline in area and 20 decline in

volume in the last 30 years glaciers continue to providesignificant amounts of water to streams on the OlympicPeninsula We used the hypsometry of glaciers and summer-melt versus elevation curves from the PDD model toestimate glacial contribution to summer streamflow forthree large basins that represent a range in climate andglacial cover (Table 3 Figs 8 and 9) As shown in Figure 8the model accurately reproduced the amount of summermelt as measured by melt stakes at two locations The modeland melt data also show that summer melt at 1500m variesby 20ndash25 (1m) between extreme years with lessvariability at higher elevations Model error at 1500m is050mwe andash1 (r2 = 068) based on the residual mean sumof errors at 2050m it is 028mwe andash1 (r2 = 076) Thesevalues represent an error of 10 in the total summermelt estimateAbout 66 of the glacier-covered landscape in the

Olympic Mountains is found in the Hoh River watershed

(20 km2) more than half of the remaining glacial cover is inthe Queets and Elwha watersheds (Fig 2) Based on thePDD model and basin-wide glacier hypsometry glacierscurrently provide 63ndash797106m3 of water to the HohRiver annually from 1 May to 30 September In the Elwhawatershed glaciers provide 12ndash1513 106m3 of sum-mer runoff while in the Dungeness basin they provide 25ndash31028106m3 The other large watersheds on theOlympic Peninsula have lt5 glacial contribution tosummer streamflow Given a 20 loss in glacier volumeglacial runoff on the Peninsula has decreased a similaramount in the past 30 yearsOur PDD model estimates of glacial runoff combine

snow firn and ice contributions but we recognize that theyare likely dominated by snowmelt LaChapelle (1965)suggested snowmelt was 16 and 42 times firn and icemelt on Blue Glacier in 1958 and 1962 respectively andthat ice melt occurred primarily in September and OctoberGiven reduced winter accumulation in the last 50 years anda longer melt season (Rasmussen and Conway 2001) thesnow to firnice melt ratios are now probably smallerThe volume loss calculations allowed us to assess the

glacier ice (not snow or firn) contribution to summerstreamflow in the Hoh basin (Tables 2 and 3) Volumeof ice loss for Hoh and Blue Glaciers averaged 63106m3we andash1 from 1987 to 2010 assuming a similarcontribution from the other 1065 km2 of glaciers in the Hohvalley the 23 year average annual glacial ice ablation is117 106m3we Using the PDD model estimate of an

Table 3 Range of modern glacial ice snow and firn contribution tosummer (1 Mayndash30 September) streamflow for three rivers

Watershed Basin

area

Glacier

area

Glacial runoff Total summer

runoff

2010 low 2009 high

km2 km2 106 m3 106 m3

Hoh 655 2003 63 79 89ndash154

Elwha 697 372 12 15 25ndash40

Dungeness 404 113 245 308 30ndash38

Includes snow firn and ice

Fig 8 Degree-day model of Blue Glacier summer balance (dashedline) used to estimate range in glacier runoff Measured values(square and diamond) from Conway and others (1999)

Fig 9 Modern range in summer (1 Mayndash30 September) glacialrunoff for three Olympic Peninsula watersheds determined by aPDD model for negative (2009) and positive (2010) net mass-balance years Runoff includes snow firn and ice from glaciers ineach basin Percentage of basin above gage site covered by glaciersshown in parentheses

Table 2 Volume change estimates for four glaciers 1987ndash2010Volume changes are not adjusted to water equivalence

Glacier Area 2009 Volume 2010 Volume loss

1987ndash2009

Change

1987ndash2010

km2 km3 km3

Hoh 403 049 0078 ndash16

Blue 535 057 0084 ndash15

Humes 148 017 0038 ndash22

Eel 085 009 0013 ndash14

Volume and change estimates less certain due to lack of ice radarmeasurements

Riedel and others Glaciers in the Olympic Mountains14

average annual total glacier summer contribution of71106m3we for the Hoh River the ice fractioncontributed 16 of total glacier runoff for MayndashSeptem-ber mostly late in the melt seasonEstimates of glacier volume loss and results from the

glacial runoff model highlight the importance of glaciers tolate-summer streamflow at the Hoh River gaging station nearForks (Fig 1) Comparing the streamflow data with the PDDmodel results glacial snow firn and ice contribute 359ndash397106m3we or 18ndash30 of total streamflow forAugustndashSeptember compared with 9ndash15 for the entiremelt seasonVolume change estimates also provide a means to assess

the glacial ice (not snow and firn) contribution to late-summer streamflow assuming that all the volume loss wasice that melted in August and September The averageAugustndashSeptember discharge in the lower Hoh River for thepast 23 years is 160 106m3 Based on the 23 year volumeloss estimate of average annual icemelt of 117 106m3wefor the Hoh basin glacier ice provided 7 of the dischargeon the lower Hoh River and 31 of the total glaciercontribution (including snow and firn) Although a smallfraction of total streamflow the glacier ice contributionoccurs when the contribution from snow and firn melt hasdeclined and summer rainfall is minimal and represents theaverage minimum reduction of AugustndashSeptember stream-flow that would occur in the lower Hoh River in the future ifglaciers disappeared The importance of this lsquofossilrsquo water ismagnified during summers when the previous winterrsquossnowfall is low and will become more critical in the futureas the snowpack declinesThe marked loss of glaciers on the Olympic Peninsula in

the past 30 years is largely a result of a 1degC rise in meanannual temperature (Rasmussen and Conway 2001) andillustrates how sensitive these relatively small thin low-elevation temperate glaciers are to climate change Thistemperature increase has directly increased the summermelt rate lengthened the melt season and decreased theduration of the accumulation season resulting in less wintersnow accumulation LaChapelle (1965) notes that theelevation of the freezing level is particularly important inearly fall as it controls how much precipitation falls as snowwhile Rasmussen and others (2000) suggest that springweather is a more important influence on ablation Coolcloudy conditions that often prevail in spring in thismaritime climate lead to lower melt rates at the time ofthe summer solstice particularly during the wet and coldphases of the Southern Oscillation and Pacific DecadalOscillation Recent climate warming appears stronger inwinter at Blue Glacier where average winter temperaturehas risen 3degC in the past half-century (Rasmussen andothers 2000) As a result average winter snow accumu-lation has decreased 500mm near 1500m at the glacierterminus since 1948 (Rasmussen and others 2000)Most of the glaciers on the Peninsula are currently not in

equilibrium with the present climate and are expected tocontinue to shrink in the near future even if accumulationincreases and temperature stops rising In the next severaldecades glaciers are likely to continue to disappear rapidlybased on projected future temperature increases of severaldegrees in the next 70 years Mote and Salatheacute (2010)estimate that mean annual temperature in Washington Statewill increase by at least 12degC by 2040 and at least 28degC by2080 Future temperature increases may be even higher near

the elevation of glaciers given positive feedback mechan-isms Further it is possible that the periodic increases inprecipitation associatedwith the cool wet phase of the PacificDecadal Oscillationmay havewaned in the past few decadeswith a warming climate (Josberger and others 2007)The preponderance of small glaciers remaining on the

Peninsula (145 of 184 are lt01 km2) means that most arevulnerable to melting away completely in the near future(Fig 2) The glaciers most threatened by future climatewarming are generally those that face south in the drier andwarmer climate prevalent on the eastern side of thePeninsula Glaciers on the northeast part of the mountainson Mount Deception McCartney Peak and Cameron Peakmay be the most threatened due to their isolation fromPacific moisture and climate model projections of highersummer potential evapotranspiration that could translate tohigher summer melt rates (Elsner and others 2010) Glacierson the northern side of the Bailey Range and in theheadwaters of the Queets and Elwha Rivers should fareslightly better because of their proximity to large valleys thatfunnel moisture from the Pacific Ocean However theiraccumulation zones are several hundred meters lower thanthose on the large glaciers of Mount Olympus If the climatewarms at the projected rates it is likely that within a centuryglaciers in the Olympic Mountains will be confined to theMount Olympus massifLoss of glaciers due to warming climate has several

significant implications for the Olympic Peninsula includ-ing loss of glacial habitat exposure of vast areas of looseglacial sand and gravel higher summer stream temperaturesand lower late-summer flows in most watersheds Decline inglacier meltwater production will exacerbate changes inaquatic habitat associated with a warming climate Mantuaand others (2010) identified summer temperature andstreamflow as critical physical habitat features for salmonLoss of glaciers will reduce summer streamflow andcontribute to higher summer stream temperatures to thedetriment of species such as the bull trout (Salvelinusconfluentus) (Halofsky and others 2011) Other ecosystemswill also be affected by the loss of glaciers For examplealpine food webs will be diminished by the loss of speciessuch as the ice worm which is preyed upon by rosy finchesand other alpine species

CONCLUSIONSThe glacier geospatial database we developed provides animportant benchmark for assessing glacier extent and glacialrunoff changes in the Olympic Mountains for the past30 years and into the future The combined area of allglaciers has decreased 34 in the past 30 years with ice lossaccelerating to a rate more than twice as fast as that from1900 to 1980 Only four of the 184 remaining glaciers aregt1 km2 in area Glaciers on the southern side of themountains at lower elevations and in the northeastern partof the Peninsula exhibited the greatest area and volume lossesand are the most likely to disappear in the next centuryGlacier decline in the past 30 years in the Olympics is greaterthan in the Cascades and southern Coast Mountains but iscomparable with Vancouver Island Based on ice volumelosses glacial contribution to summer streamflow hasdeclined 20 in the past 30 years but remains significantfor the Hoh River at 63ndash797106m3 andash1 Glaciers con-tribute lt5 to summer streamflow in all other large

Riedel and others Glaciers in the Olympic Mountains 15

watersheds in the Olympic Mountains Delivery of this coldfresh water to streams becomes more critical in the latesummer when rainfall is minimal and snowmelt hasdeclined On the lower Hoh River glacial ice contributes7 of the AugustndashSeptember streamflow which representsthe minimum reduction in flow that would occur if all theglaciers melted away Continued loss of glaciers will directlyimpact aquatic ecosystems through higher stream tempera-tures and lower summer base flows

ACKNOWLEDGEMENTSWe thank the US National Park Service Climate ChangeProgram for funding this research and Olympic and NorthCascades national parks and Portland State University for in-kind support Sharon Brady Roger Hoffman and SteveDorsch contributed GIS and cartographic expertise Finallywe want to acknowledge Richard Spicer for the valuablebaseline he created on the status of Olympic glaciers in theearly 1980s

REFERENCESAllen CR Kamb WB Meier MF and Sharp RP (1960) Structure ofthe lower Blue Glacier Washington J Geol 68(6) 601ndash625

Bolch T Menounos B andWheate R (2010) Landsat-based inventoryof glaciers in western Canada 1985ndash2005 Remote SensEnviron 114(1) 127ndash137 (doi 101016jrse200908015)

Conway H Rasmussen LA and Marshall HP (1999) Annual massbalance of Blue Glacier USA 1955ndash97 Geogr Ann A 81(4)509ndash520

Davey CA Redmond KT and Simeral DB (2006) Weather andclimate inventory National Park Service North Coast andCascades Network (National Resource Technical Report NPSNCCNNRTR-2006010) National Resource Program CenterFort Collins CO

De Woul M and Hock R (2005) Static mass-balance sensitivity ofArctic glaciers and ice caps using a degree-day approach AnnGlaciol 42 217ndash224 (doi 103189172756405781813096)

Elsner MM and 8 others (2010) Implications of 21st-century climatechange for the hydrology of Washington State Climatic Change102(1ndash2) 225ndash260 (doi 101007s10584-010-9855-0)

Granshaw FD and Fountain AG (2006) Glacier change (1958ndash1998) in the North Cascades National Park ComplexWashington USA J Glaciol 52(177) 251ndash256 (doi 103189172756506781828782)

Halofsky JE Peterson DL OrsquoHalloran KA and Hoffman CH eds(2011) Adapting to climate change at Olympic National Forestand Olympic National Park (Gen Tech Rep PNW-GTR-844)Pacific Northwest Research Station US Department of Agricul-ture Portland OR httpwwwtreesearchfsfeduspubs38702

Heroux P and Kouba J (2001) GPS precise point positioning usingIGS orbit products Phys Chem Earth 26(6ndash8) 573ndash578

Heusser CJ (1957) Variations of Blue Hoh and White Glaciersduring recent centuries Arctic 10(3) 139ndash150 (doi 1014430arctic3761)

Hodge SM (1974) Variations in the sliding of a temperate glacierJ Glaciol 13(69) 349ndash369

Hodson A and 7 others (2008) Glacial ecosystems Ecol Monogr78(1) 41ndash67 (doi 10189007-01871)

Hubley RC (1956) Glaciers of the Washington Cascade andOlympic Mountains their present activity and its relation tolocal climatic trends J Glaciol 2(19) 669ndash674 (doi 103189002214356793701938)

Josberger EG Bidlake WR March RS and Kennedy BW (2007)Glacier mass-balance fluctuations in the Pacific Northwest andAlaska USA Ann Glaciol 46 291ndash296 (doi 103189172756407782871314)

LaChapelle ER (1965) The mass budget of Blue Glacier Washing-ton J Glaciol 5(41) 609ndash623

Malcomb NL and Wiles GC (2013) Tree-ring-based reconstructionsof North American glacier mass balance through the Little IceAge contemporary warming transition Quat Res 79(2)123ndash137 (doi 101016jyqres201211005)

Mantua NJ Hare SR Zhang Y Wallace JM and Francis RC (1997) APacific interdecadal climate oscillation with impacts on salmonproduction Bull Am Meteorol Soc 78(6) 1069ndash1079 (doi1011751520-0477(1997)078lt1069APICOWgt20CO2)

Mantua N Tohver I and Hamlet A (2010) Climate change impactson streamflow extremes and summertime stream temperatureand their possible consequences for freshwater salmon habitatin Washington State Climatic Change 102(1ndash2) 187ndash223 (doi101007s10584-010-9845-2)

Matthes FE (1946) Report of Committee on Glaciers 1945 Eos27(2) 219ndash233

Meier MF (1961) Distribution and variations of glaciers in theUnited States exclusive of Alaska IASH Publ 54 (GeneralAssembly of Helsinki 1960 ndash Snow and Ice) 420ndash429

Mote PW and Salatheacute EP Jr (2010) Future climate in the PacificNorthwest Climatic Change 102(1ndash2) 29ndash50 (doi 101007s10584-010-9848-z)

Nolin AW and Daly C (2006) Mapping lsquoat riskrsquo snow in thePacific Northwest J Hydromet 7(5) 1164ndash1171 (doi 101175JHM5431)

PRISM Group (2006) United States average monthly and annualprecipitation 1971ndash2000 Oregon State University CorvallisOR httpprismoregonstateedu

Rasmussen LA and Conway H (2001) Estimating South CascadeGlacier (Washington USA) mass balance from a distant radio-sonde and comparison with Blue Glacier J Glaciol 47(159)579ndash588 (doi 103189172756501781831873)

Rasmussen LA and Wenger JM (2009) Upper-air model of summerbalance on Mount Rainier USA J Glaciol 55(192) 619ndash624(doi 103189002214309789471012)

Rasmussen LA Conway H and Hayes PS (2000) The accumulationregime of Blue Glacier USA 1914ndash96 J Glaciol 46(153)326ndash334 (doi 103189172756500781832846)

Riedel JR Burrows RA and Wenger JM (2008) Long-term monitoringof small glaciers at North Cascades National Park a prototypepark model for the North Coast and Cascades Network (NaturResour Rep NPSNCCNNRR-2008066) National Park ServiceFort Collins CO

Spicer RC (1986) Glaciers in the Olympic Mountains Washingtonpresent distribution and recent variations (PhD thesis Uni-versity of Washington)

Tabor RW and Cady WM (1978) Geologic map of the OlympicPeninsula Washington (Misc Inv Map 994) US GeologicalSurvey Reston VA

MS received 19 July 2014 and accepted in revised form 11 September 2014

Riedel and others Glaciers in the Olympic Mountains16

more) smaller glaciers For example continued climatewarming will eventually lead Blue Glacier to divideWe identified 083 km2 of debris-covered ice half of

which is on Blue and Black Glaciers on Mount OlympusSpicer (1986) identified 12 lsquorock glaciersrsquo in a previousinventory but we did not track changes in them indi-vidually The presence of debris-covered ice is expected toincrease as the climate warms glaciers thin and in somecases glacier flow velocities decline Debris cover of morethan a few centimeters can dramatically slow melting andin the future many of the Peninsularsquos glaciers may becomerock glaciers Heusser (1957) noted that debris cover onlower White and Hoh Glaciers slowed recession in the early20th century Ferry Glacier was one of the 50 largest glaciersin the Olympics Mountains in 1980 with an area of

017 km2 but by 2009 what remained of the glacier wascovered by a rockfall making it difficult to determine howmuch if any ice remainsAll the glaciers counted in a previous inventory have

decreased in size in the past 30 years and our countrepresents a decrease of 82 glaciers from the 266 noted in1980 (Fig 2 Spicer 1986) Total glacier cover now standsat 3020 095 km2 not including features smaller than001 km2 Uncertainty associated with the 1m resolution ofthe NAIP imagery is compounded by shadows and debriscover and varies substantially between glaciers largerglaciers have ten times the uncertainty of smaller glaciers(Table 1) Total uncertainty represents only 6 of the totalestimated change in glacier area not enough to affect theconclusion that glaciers are in rapid decline

Fig 4 Histogram of the number of glaciers by size category note size of categories changes Perennial snow and ice features lt001 km2 notshown

Table 1 Area (km2) of select glaciers at various times in the past century Data for 1980 and early 20th century from Spicer (1986) SeeFigure 2 for locations

Glacier (mountainndashaspect) Little Ice Age maximum Early 20th century 1980 2009 Change 1980ndash2009

(photograph date) ( error)

West of the Elwha valleyBlue (OlympusndashNE) 717 561(1899) 61 535 (0079) ndash12

Humes (OlympusndashE) 263 202 (1907) 185 148 (0088) ndash20

Hoh (OlympusndashNE) 807 54 (1933) 489 403 (0055) ndash18

White (TomndashN) 779 512 (1924) 469 390 (0055) ndash17

Jeffers (OlympusndashSE) 281 na 08 031 (0127) ndash61

Hubert (OlympusndashSW) 239 na 110 071 (0058) ndash35

Carrie (BaileysndashNE) na na 098 062 (0011) ndash37

East of the Elwha valleyChristie (ChristiendashN) na na 02 0099 (0003) ndash51

Lillian (McCartneyndashN) na na 014 0029 (0001) ndash21

Cameron (Cameron) na na 016 0103 (0003) ndash36

Anderson (AndersonndashS) 158 122 (1927) 061 014 (0003) ndash77

Eel (AndersonndashN) 230 177 (1920) 111 085 (0008) ndash23

Total eight named glaciers 3474 na 2115 1677 21

OLYM total na 6657 4594 3020 (0945) ndash34

Based on aerial photographs taken between 1976 and 1982

Riedel and others Glaciers in the Olympic Mountains 11

Combined glacier area decreased by 157 km2 from 1980(459 km2) to 2009 (302 km2) a loss of 34 (Table 1 Spicer1986) Mean glacier area decreased from 017 km2 in 1980 to011 km2 in 2009 In 1980 eight of 266 glaciers were gt1 km2

(Spicer 1986) there are now only four that exceed that size(Blue Hoh White and Humes glaciers) All of these glaciersare on Mount Olympus the highest mountain on thePeninsula located on the windward (wet) west side of the

Olympic Mountains (Figs 2 and 5) Other clusters of glaciersin the 005ndash02 km2 size range occur in the Bailey Range andon Mount Christie and Mount Anderson (Fig 2) Thesesummits are all either on the wetter windward side of therange (Baileys) or benefit from storms that penetrate deep intothe mountains along the Quinnault RiverAspect and distance inland from the Pacific moisture

source have had a strong influence on glacier response to the

Fig 5 Change in glacier extent on Mount Olympus (a) and Mount Anderson (b) from AD1980 to present

Riedel and others Glaciers in the Olympic Mountains12

warming climate Glaciers in the eastern part of the Peninsulaand those that face south lost more area than those facingnorth and on the wetter windward slope (Table 1) Glacierlosses were most pronounced in the drier northeastern part ofthe Peninsula where for example little remains of LillianGlacier on McCartney Peak (Fig 6) For the most partglaciers east of the Elwha River now exist almost exclusivelyon shaded northern aspects where melting is slower and theymay benefit from secondary sources of accumulation (egwind redeposition and snow avalanche)The influence of aspect is well illustrated on Mount

Anderson Since 1980 Anderson Glacier has lost 77 of itsarea compared with a 23 loss for adjacent north-facing EelGlacier (Table 1 Figs 5 and 7) Aspect is also a critical factorto glacier status on Mount Olympus where southeast-facingJeffers Glacier shrank by 61 in 30 years while north-facing Hoh and White Glaciers declined by 17ndash18 (Fig 5)North-facing glaciers east of the Elwha lost 21ndash51 of theirarea in 30 years whereas the north-facing glaciers on MountOlympus lost 12ndash20 over the same period Glaciers in theBailey Range with north aspects had area losses comparablewith glaciers on the south side of Olympus and with north-facing glaciers east of the Elwha (eg Carrie GlacierTable 1)The rate of ice loss for six glaciers from AD1900 to 1980

was 026 km2 andash1 although this included a period of positivebalance at Blue Glacier from 1959 to 1975 (Hubley 1956Spicer 1986 Rasmussen and Conway 2001) Since 1980the rate of decline in combined ice extent across theOlympic Mountains doubled to 054 km2 andash1 Acceleratingdecline of glacier area is also reflected in strongly negative

cumulative balance on Blue Glacier since the mid-1980s(Rasmussen and Conway 2001)Decline in glacier area in recent decades on the Olympic

Peninsula exceeds losses east of the FraserndashPuget lowlandsIn the southern Coast Mountains of British Columbia glacierarea declined 10 from 1985 to 2005 (Bolch and others2010) while Granshaw and Fountain (2006) estimated lossof glaciers in the North Cascades National Park over a40 year period ending in 1998 at 7 The more rapid lossof glaciers in the Olympics is more comparable with theobserved loss of 20 over a similar period on VancouverIsland (Bolch and others 2010) Rapid loss of glaciers incoastal ranges is likely due to their sensitivity to changes intemperature that strongly influence spring ablation andearly-fall accumulation (LaChapelle 1965) Accumulatingevidence indicates that the recent loss of glacier area andvolume through multiple decades for all glaciers in thePacific Northwest has not occurred since at least AD 1694(Malcomb and Wiles 2013)Glacier area measurements were combined with surface

elevation profiles to assess thickness changes from 1987 to2010 for four of the largest glaciers in the OlympicMountains (Table 2) Only Blue Glacier has ice thicknessdata and a known glacier volume (Allen and others 1960)the other glacier volumes were estimated assuming anaverage ice thickness and by the ratio of the glacierrsquos area to

Fig 6 Changes in Lillian Glacier on McCartney Peak from 1905 (aNPS photograph) to the present (b photograph by J McLean)

Fig 7 Changes in Anderson Glacier from 1936 (a photograph byA Curtis) to the present (b photograph by R Hoffman)

Riedel and others Glaciers in the Olympic Mountains 13

Blue Glacierrsquos area Blue Glacier on Mount Olympus hadthe largest volume loss since 1987 because it has the largestarea The largest percent change however was for south-facing Humes Glacier at ndash22 while north-facing Blue andHoh Glaciers lost 15 and 16 respectively (Table 2) Inaddition to its aspect Humes Glacier had the mostsignificant volume reduction because it is at a lowerelevation than its neighbors Hoh Blue and White glaciersFurther to the east north-facing Eel Glacier has lost 14 ofits volume (0013 km3) since 1987Even with a 34 decline in area and 20 decline in

volume in the last 30 years glaciers continue to providesignificant amounts of water to streams on the OlympicPeninsula We used the hypsometry of glaciers and summer-melt versus elevation curves from the PDD model toestimate glacial contribution to summer streamflow forthree large basins that represent a range in climate andglacial cover (Table 3 Figs 8 and 9) As shown in Figure 8the model accurately reproduced the amount of summermelt as measured by melt stakes at two locations The modeland melt data also show that summer melt at 1500m variesby 20ndash25 (1m) between extreme years with lessvariability at higher elevations Model error at 1500m is050mwe andash1 (r2 = 068) based on the residual mean sumof errors at 2050m it is 028mwe andash1 (r2 = 076) Thesevalues represent an error of 10 in the total summermelt estimateAbout 66 of the glacier-covered landscape in the

Olympic Mountains is found in the Hoh River watershed

(20 km2) more than half of the remaining glacial cover is inthe Queets and Elwha watersheds (Fig 2) Based on thePDD model and basin-wide glacier hypsometry glacierscurrently provide 63ndash797106m3 of water to the HohRiver annually from 1 May to 30 September In the Elwhawatershed glaciers provide 12ndash1513 106m3 of sum-mer runoff while in the Dungeness basin they provide 25ndash31028106m3 The other large watersheds on theOlympic Peninsula have lt5 glacial contribution tosummer streamflow Given a 20 loss in glacier volumeglacial runoff on the Peninsula has decreased a similaramount in the past 30 yearsOur PDD model estimates of glacial runoff combine

snow firn and ice contributions but we recognize that theyare likely dominated by snowmelt LaChapelle (1965)suggested snowmelt was 16 and 42 times firn and icemelt on Blue Glacier in 1958 and 1962 respectively andthat ice melt occurred primarily in September and OctoberGiven reduced winter accumulation in the last 50 years anda longer melt season (Rasmussen and Conway 2001) thesnow to firnice melt ratios are now probably smallerThe volume loss calculations allowed us to assess the

glacier ice (not snow or firn) contribution to summerstreamflow in the Hoh basin (Tables 2 and 3) Volumeof ice loss for Hoh and Blue Glaciers averaged 63106m3we andash1 from 1987 to 2010 assuming a similarcontribution from the other 1065 km2 of glaciers in the Hohvalley the 23 year average annual glacial ice ablation is117 106m3we Using the PDD model estimate of an

Table 3 Range of modern glacial ice snow and firn contribution tosummer (1 Mayndash30 September) streamflow for three rivers

Watershed Basin

area

Glacier

area

Glacial runoff Total summer

runoff

2010 low 2009 high

km2 km2 106 m3 106 m3

Hoh 655 2003 63 79 89ndash154

Elwha 697 372 12 15 25ndash40

Dungeness 404 113 245 308 30ndash38

Includes snow firn and ice

Fig 8 Degree-day model of Blue Glacier summer balance (dashedline) used to estimate range in glacier runoff Measured values(square and diamond) from Conway and others (1999)

Fig 9 Modern range in summer (1 Mayndash30 September) glacialrunoff for three Olympic Peninsula watersheds determined by aPDD model for negative (2009) and positive (2010) net mass-balance years Runoff includes snow firn and ice from glaciers ineach basin Percentage of basin above gage site covered by glaciersshown in parentheses

Table 2 Volume change estimates for four glaciers 1987ndash2010Volume changes are not adjusted to water equivalence

Glacier Area 2009 Volume 2010 Volume loss

1987ndash2009

Change

1987ndash2010

km2 km3 km3

Hoh 403 049 0078 ndash16

Blue 535 057 0084 ndash15

Humes 148 017 0038 ndash22

Eel 085 009 0013 ndash14

Volume and change estimates less certain due to lack of ice radarmeasurements

Riedel and others Glaciers in the Olympic Mountains14

average annual total glacier summer contribution of71106m3we for the Hoh River the ice fractioncontributed 16 of total glacier runoff for MayndashSeptem-ber mostly late in the melt seasonEstimates of glacier volume loss and results from the

glacial runoff model highlight the importance of glaciers tolate-summer streamflow at the Hoh River gaging station nearForks (Fig 1) Comparing the streamflow data with the PDDmodel results glacial snow firn and ice contribute 359ndash397106m3we or 18ndash30 of total streamflow forAugustndashSeptember compared with 9ndash15 for the entiremelt seasonVolume change estimates also provide a means to assess

the glacial ice (not snow and firn) contribution to late-summer streamflow assuming that all the volume loss wasice that melted in August and September The averageAugustndashSeptember discharge in the lower Hoh River for thepast 23 years is 160 106m3 Based on the 23 year volumeloss estimate of average annual icemelt of 117 106m3wefor the Hoh basin glacier ice provided 7 of the dischargeon the lower Hoh River and 31 of the total glaciercontribution (including snow and firn) Although a smallfraction of total streamflow the glacier ice contributionoccurs when the contribution from snow and firn melt hasdeclined and summer rainfall is minimal and represents theaverage minimum reduction of AugustndashSeptember stream-flow that would occur in the lower Hoh River in the future ifglaciers disappeared The importance of this lsquofossilrsquo water ismagnified during summers when the previous winterrsquossnowfall is low and will become more critical in the futureas the snowpack declinesThe marked loss of glaciers on the Olympic Peninsula in

the past 30 years is largely a result of a 1degC rise in meanannual temperature (Rasmussen and Conway 2001) andillustrates how sensitive these relatively small thin low-elevation temperate glaciers are to climate change Thistemperature increase has directly increased the summermelt rate lengthened the melt season and decreased theduration of the accumulation season resulting in less wintersnow accumulation LaChapelle (1965) notes that theelevation of the freezing level is particularly important inearly fall as it controls how much precipitation falls as snowwhile Rasmussen and others (2000) suggest that springweather is a more important influence on ablation Coolcloudy conditions that often prevail in spring in thismaritime climate lead to lower melt rates at the time ofthe summer solstice particularly during the wet and coldphases of the Southern Oscillation and Pacific DecadalOscillation Recent climate warming appears stronger inwinter at Blue Glacier where average winter temperaturehas risen 3degC in the past half-century (Rasmussen andothers 2000) As a result average winter snow accumu-lation has decreased 500mm near 1500m at the glacierterminus since 1948 (Rasmussen and others 2000)Most of the glaciers on the Peninsula are currently not in

equilibrium with the present climate and are expected tocontinue to shrink in the near future even if accumulationincreases and temperature stops rising In the next severaldecades glaciers are likely to continue to disappear rapidlybased on projected future temperature increases of severaldegrees in the next 70 years Mote and Salatheacute (2010)estimate that mean annual temperature in Washington Statewill increase by at least 12degC by 2040 and at least 28degC by2080 Future temperature increases may be even higher near

the elevation of glaciers given positive feedback mechan-isms Further it is possible that the periodic increases inprecipitation associatedwith the cool wet phase of the PacificDecadal Oscillationmay havewaned in the past few decadeswith a warming climate (Josberger and others 2007)The preponderance of small glaciers remaining on the

Peninsula (145 of 184 are lt01 km2) means that most arevulnerable to melting away completely in the near future(Fig 2) The glaciers most threatened by future climatewarming are generally those that face south in the drier andwarmer climate prevalent on the eastern side of thePeninsula Glaciers on the northeast part of the mountainson Mount Deception McCartney Peak and Cameron Peakmay be the most threatened due to their isolation fromPacific moisture and climate model projections of highersummer potential evapotranspiration that could translate tohigher summer melt rates (Elsner and others 2010) Glacierson the northern side of the Bailey Range and in theheadwaters of the Queets and Elwha Rivers should fareslightly better because of their proximity to large valleys thatfunnel moisture from the Pacific Ocean However theiraccumulation zones are several hundred meters lower thanthose on the large glaciers of Mount Olympus If the climatewarms at the projected rates it is likely that within a centuryglaciers in the Olympic Mountains will be confined to theMount Olympus massifLoss of glaciers due to warming climate has several

significant implications for the Olympic Peninsula includ-ing loss of glacial habitat exposure of vast areas of looseglacial sand and gravel higher summer stream temperaturesand lower late-summer flows in most watersheds Decline inglacier meltwater production will exacerbate changes inaquatic habitat associated with a warming climate Mantuaand others (2010) identified summer temperature andstreamflow as critical physical habitat features for salmonLoss of glaciers will reduce summer streamflow andcontribute to higher summer stream temperatures to thedetriment of species such as the bull trout (Salvelinusconfluentus) (Halofsky and others 2011) Other ecosystemswill also be affected by the loss of glaciers For examplealpine food webs will be diminished by the loss of speciessuch as the ice worm which is preyed upon by rosy finchesand other alpine species

CONCLUSIONSThe glacier geospatial database we developed provides animportant benchmark for assessing glacier extent and glacialrunoff changes in the Olympic Mountains for the past30 years and into the future The combined area of allglaciers has decreased 34 in the past 30 years with ice lossaccelerating to a rate more than twice as fast as that from1900 to 1980 Only four of the 184 remaining glaciers aregt1 km2 in area Glaciers on the southern side of themountains at lower elevations and in the northeastern partof the Peninsula exhibited the greatest area and volume lossesand are the most likely to disappear in the next centuryGlacier decline in the past 30 years in the Olympics is greaterthan in the Cascades and southern Coast Mountains but iscomparable with Vancouver Island Based on ice volumelosses glacial contribution to summer streamflow hasdeclined 20 in the past 30 years but remains significantfor the Hoh River at 63ndash797106m3 andash1 Glaciers con-tribute lt5 to summer streamflow in all other large

Riedel and others Glaciers in the Olympic Mountains 15

watersheds in the Olympic Mountains Delivery of this coldfresh water to streams becomes more critical in the latesummer when rainfall is minimal and snowmelt hasdeclined On the lower Hoh River glacial ice contributes7 of the AugustndashSeptember streamflow which representsthe minimum reduction in flow that would occur if all theglaciers melted away Continued loss of glaciers will directlyimpact aquatic ecosystems through higher stream tempera-tures and lower summer base flows

ACKNOWLEDGEMENTSWe thank the US National Park Service Climate ChangeProgram for funding this research and Olympic and NorthCascades national parks and Portland State University for in-kind support Sharon Brady Roger Hoffman and SteveDorsch contributed GIS and cartographic expertise Finallywe want to acknowledge Richard Spicer for the valuablebaseline he created on the status of Olympic glaciers in theearly 1980s

REFERENCESAllen CR Kamb WB Meier MF and Sharp RP (1960) Structure ofthe lower Blue Glacier Washington J Geol 68(6) 601ndash625

Bolch T Menounos B andWheate R (2010) Landsat-based inventoryof glaciers in western Canada 1985ndash2005 Remote SensEnviron 114(1) 127ndash137 (doi 101016jrse200908015)

Conway H Rasmussen LA and Marshall HP (1999) Annual massbalance of Blue Glacier USA 1955ndash97 Geogr Ann A 81(4)509ndash520

Davey CA Redmond KT and Simeral DB (2006) Weather andclimate inventory National Park Service North Coast andCascades Network (National Resource Technical Report NPSNCCNNRTR-2006010) National Resource Program CenterFort Collins CO

De Woul M and Hock R (2005) Static mass-balance sensitivity ofArctic glaciers and ice caps using a degree-day approach AnnGlaciol 42 217ndash224 (doi 103189172756405781813096)

Elsner MM and 8 others (2010) Implications of 21st-century climatechange for the hydrology of Washington State Climatic Change102(1ndash2) 225ndash260 (doi 101007s10584-010-9855-0)

Granshaw FD and Fountain AG (2006) Glacier change (1958ndash1998) in the North Cascades National Park ComplexWashington USA J Glaciol 52(177) 251ndash256 (doi 103189172756506781828782)

Halofsky JE Peterson DL OrsquoHalloran KA and Hoffman CH eds(2011) Adapting to climate change at Olympic National Forestand Olympic National Park (Gen Tech Rep PNW-GTR-844)Pacific Northwest Research Station US Department of Agricul-ture Portland OR httpwwwtreesearchfsfeduspubs38702

Heroux P and Kouba J (2001) GPS precise point positioning usingIGS orbit products Phys Chem Earth 26(6ndash8) 573ndash578

Heusser CJ (1957) Variations of Blue Hoh and White Glaciersduring recent centuries Arctic 10(3) 139ndash150 (doi 1014430arctic3761)

Hodge SM (1974) Variations in the sliding of a temperate glacierJ Glaciol 13(69) 349ndash369

Hodson A and 7 others (2008) Glacial ecosystems Ecol Monogr78(1) 41ndash67 (doi 10189007-01871)

Hubley RC (1956) Glaciers of the Washington Cascade andOlympic Mountains their present activity and its relation tolocal climatic trends J Glaciol 2(19) 669ndash674 (doi 103189002214356793701938)

Josberger EG Bidlake WR March RS and Kennedy BW (2007)Glacier mass-balance fluctuations in the Pacific Northwest andAlaska USA Ann Glaciol 46 291ndash296 (doi 103189172756407782871314)

LaChapelle ER (1965) The mass budget of Blue Glacier Washing-ton J Glaciol 5(41) 609ndash623

Malcomb NL and Wiles GC (2013) Tree-ring-based reconstructionsof North American glacier mass balance through the Little IceAge contemporary warming transition Quat Res 79(2)123ndash137 (doi 101016jyqres201211005)

Mantua NJ Hare SR Zhang Y Wallace JM and Francis RC (1997) APacific interdecadal climate oscillation with impacts on salmonproduction Bull Am Meteorol Soc 78(6) 1069ndash1079 (doi1011751520-0477(1997)078lt1069APICOWgt20CO2)

Mantua N Tohver I and Hamlet A (2010) Climate change impactson streamflow extremes and summertime stream temperatureand their possible consequences for freshwater salmon habitatin Washington State Climatic Change 102(1ndash2) 187ndash223 (doi101007s10584-010-9845-2)

Matthes FE (1946) Report of Committee on Glaciers 1945 Eos27(2) 219ndash233

Meier MF (1961) Distribution and variations of glaciers in theUnited States exclusive of Alaska IASH Publ 54 (GeneralAssembly of Helsinki 1960 ndash Snow and Ice) 420ndash429

Mote PW and Salatheacute EP Jr (2010) Future climate in the PacificNorthwest Climatic Change 102(1ndash2) 29ndash50 (doi 101007s10584-010-9848-z)

Nolin AW and Daly C (2006) Mapping lsquoat riskrsquo snow in thePacific Northwest J Hydromet 7(5) 1164ndash1171 (doi 101175JHM5431)

PRISM Group (2006) United States average monthly and annualprecipitation 1971ndash2000 Oregon State University CorvallisOR httpprismoregonstateedu

Rasmussen LA and Conway H (2001) Estimating South CascadeGlacier (Washington USA) mass balance from a distant radio-sonde and comparison with Blue Glacier J Glaciol 47(159)579ndash588 (doi 103189172756501781831873)

Rasmussen LA and Wenger JM (2009) Upper-air model of summerbalance on Mount Rainier USA J Glaciol 55(192) 619ndash624(doi 103189002214309789471012)

Rasmussen LA Conway H and Hayes PS (2000) The accumulationregime of Blue Glacier USA 1914ndash96 J Glaciol 46(153)326ndash334 (doi 103189172756500781832846)

Riedel JR Burrows RA and Wenger JM (2008) Long-term monitoringof small glaciers at North Cascades National Park a prototypepark model for the North Coast and Cascades Network (NaturResour Rep NPSNCCNNRR-2008066) National Park ServiceFort Collins CO

Spicer RC (1986) Glaciers in the Olympic Mountains Washingtonpresent distribution and recent variations (PhD thesis Uni-versity of Washington)

Tabor RW and Cady WM (1978) Geologic map of the OlympicPeninsula Washington (Misc Inv Map 994) US GeologicalSurvey Reston VA

MS received 19 July 2014 and accepted in revised form 11 September 2014

Riedel and others Glaciers in the Olympic Mountains16

Combined glacier area decreased by 157 km2 from 1980(459 km2) to 2009 (302 km2) a loss of 34 (Table 1 Spicer1986) Mean glacier area decreased from 017 km2 in 1980 to011 km2 in 2009 In 1980 eight of 266 glaciers were gt1 km2

(Spicer 1986) there are now only four that exceed that size(Blue Hoh White and Humes glaciers) All of these glaciersare on Mount Olympus the highest mountain on thePeninsula located on the windward (wet) west side of the

Olympic Mountains (Figs 2 and 5) Other clusters of glaciersin the 005ndash02 km2 size range occur in the Bailey Range andon Mount Christie and Mount Anderson (Fig 2) Thesesummits are all either on the wetter windward side of therange (Baileys) or benefit from storms that penetrate deep intothe mountains along the Quinnault RiverAspect and distance inland from the Pacific moisture

source have had a strong influence on glacier response to the

Fig 5 Change in glacier extent on Mount Olympus (a) and Mount Anderson (b) from AD1980 to present

Riedel and others Glaciers in the Olympic Mountains12

warming climate Glaciers in the eastern part of the Peninsulaand those that face south lost more area than those facingnorth and on the wetter windward slope (Table 1) Glacierlosses were most pronounced in the drier northeastern part ofthe Peninsula where for example little remains of LillianGlacier on McCartney Peak (Fig 6) For the most partglaciers east of the Elwha River now exist almost exclusivelyon shaded northern aspects where melting is slower and theymay benefit from secondary sources of accumulation (egwind redeposition and snow avalanche)The influence of aspect is well illustrated on Mount

Anderson Since 1980 Anderson Glacier has lost 77 of itsarea compared with a 23 loss for adjacent north-facing EelGlacier (Table 1 Figs 5 and 7) Aspect is also a critical factorto glacier status on Mount Olympus where southeast-facingJeffers Glacier shrank by 61 in 30 years while north-facing Hoh and White Glaciers declined by 17ndash18 (Fig 5)North-facing glaciers east of the Elwha lost 21ndash51 of theirarea in 30 years whereas the north-facing glaciers on MountOlympus lost 12ndash20 over the same period Glaciers in theBailey Range with north aspects had area losses comparablewith glaciers on the south side of Olympus and with north-facing glaciers east of the Elwha (eg Carrie GlacierTable 1)The rate of ice loss for six glaciers from AD1900 to 1980

was 026 km2 andash1 although this included a period of positivebalance at Blue Glacier from 1959 to 1975 (Hubley 1956Spicer 1986 Rasmussen and Conway 2001) Since 1980the rate of decline in combined ice extent across theOlympic Mountains doubled to 054 km2 andash1 Acceleratingdecline of glacier area is also reflected in strongly negative

cumulative balance on Blue Glacier since the mid-1980s(Rasmussen and Conway 2001)Decline in glacier area in recent decades on the Olympic

Peninsula exceeds losses east of the FraserndashPuget lowlandsIn the southern Coast Mountains of British Columbia glacierarea declined 10 from 1985 to 2005 (Bolch and others2010) while Granshaw and Fountain (2006) estimated lossof glaciers in the North Cascades National Park over a40 year period ending in 1998 at 7 The more rapid lossof glaciers in the Olympics is more comparable with theobserved loss of 20 over a similar period on VancouverIsland (Bolch and others 2010) Rapid loss of glaciers incoastal ranges is likely due to their sensitivity to changes intemperature that strongly influence spring ablation andearly-fall accumulation (LaChapelle 1965) Accumulatingevidence indicates that the recent loss of glacier area andvolume through multiple decades for all glaciers in thePacific Northwest has not occurred since at least AD 1694(Malcomb and Wiles 2013)Glacier area measurements were combined with surface

elevation profiles to assess thickness changes from 1987 to2010 for four of the largest glaciers in the OlympicMountains (Table 2) Only Blue Glacier has ice thicknessdata and a known glacier volume (Allen and others 1960)the other glacier volumes were estimated assuming anaverage ice thickness and by the ratio of the glacierrsquos area to

Fig 6 Changes in Lillian Glacier on McCartney Peak from 1905 (aNPS photograph) to the present (b photograph by J McLean)

Fig 7 Changes in Anderson Glacier from 1936 (a photograph byA Curtis) to the present (b photograph by R Hoffman)

Riedel and others Glaciers in the Olympic Mountains 13

Blue Glacierrsquos area Blue Glacier on Mount Olympus hadthe largest volume loss since 1987 because it has the largestarea The largest percent change however was for south-facing Humes Glacier at ndash22 while north-facing Blue andHoh Glaciers lost 15 and 16 respectively (Table 2) Inaddition to its aspect Humes Glacier had the mostsignificant volume reduction because it is at a lowerelevation than its neighbors Hoh Blue and White glaciersFurther to the east north-facing Eel Glacier has lost 14 ofits volume (0013 km3) since 1987Even with a 34 decline in area and 20 decline in

volume in the last 30 years glaciers continue to providesignificant amounts of water to streams on the OlympicPeninsula We used the hypsometry of glaciers and summer-melt versus elevation curves from the PDD model toestimate glacial contribution to summer streamflow forthree large basins that represent a range in climate andglacial cover (Table 3 Figs 8 and 9) As shown in Figure 8the model accurately reproduced the amount of summermelt as measured by melt stakes at two locations The modeland melt data also show that summer melt at 1500m variesby 20ndash25 (1m) between extreme years with lessvariability at higher elevations Model error at 1500m is050mwe andash1 (r2 = 068) based on the residual mean sumof errors at 2050m it is 028mwe andash1 (r2 = 076) Thesevalues represent an error of 10 in the total summermelt estimateAbout 66 of the glacier-covered landscape in the

Olympic Mountains is found in the Hoh River watershed

(20 km2) more than half of the remaining glacial cover is inthe Queets and Elwha watersheds (Fig 2) Based on thePDD model and basin-wide glacier hypsometry glacierscurrently provide 63ndash797106m3 of water to the HohRiver annually from 1 May to 30 September In the Elwhawatershed glaciers provide 12ndash1513 106m3 of sum-mer runoff while in the Dungeness basin they provide 25ndash31028106m3 The other large watersheds on theOlympic Peninsula have lt5 glacial contribution tosummer streamflow Given a 20 loss in glacier volumeglacial runoff on the Peninsula has decreased a similaramount in the past 30 yearsOur PDD model estimates of glacial runoff combine

snow firn and ice contributions but we recognize that theyare likely dominated by snowmelt LaChapelle (1965)suggested snowmelt was 16 and 42 times firn and icemelt on Blue Glacier in 1958 and 1962 respectively andthat ice melt occurred primarily in September and OctoberGiven reduced winter accumulation in the last 50 years anda longer melt season (Rasmussen and Conway 2001) thesnow to firnice melt ratios are now probably smallerThe volume loss calculations allowed us to assess the

glacier ice (not snow or firn) contribution to summerstreamflow in the Hoh basin (Tables 2 and 3) Volumeof ice loss for Hoh and Blue Glaciers averaged 63106m3we andash1 from 1987 to 2010 assuming a similarcontribution from the other 1065 km2 of glaciers in the Hohvalley the 23 year average annual glacial ice ablation is117 106m3we Using the PDD model estimate of an

Table 3 Range of modern glacial ice snow and firn contribution tosummer (1 Mayndash30 September) streamflow for three rivers

Watershed Basin

area

Glacier

area

Glacial runoff Total summer

runoff

2010 low 2009 high

km2 km2 106 m3 106 m3

Hoh 655 2003 63 79 89ndash154

Elwha 697 372 12 15 25ndash40

Dungeness 404 113 245 308 30ndash38

Includes snow firn and ice

Fig 8 Degree-day model of Blue Glacier summer balance (dashedline) used to estimate range in glacier runoff Measured values(square and diamond) from Conway and others (1999)

Fig 9 Modern range in summer (1 Mayndash30 September) glacialrunoff for three Olympic Peninsula watersheds determined by aPDD model for negative (2009) and positive (2010) net mass-balance years Runoff includes snow firn and ice from glaciers ineach basin Percentage of basin above gage site covered by glaciersshown in parentheses

Table 2 Volume change estimates for four glaciers 1987ndash2010Volume changes are not adjusted to water equivalence

Glacier Area 2009 Volume 2010 Volume loss

1987ndash2009

Change

1987ndash2010

km2 km3 km3

Hoh 403 049 0078 ndash16

Blue 535 057 0084 ndash15

Humes 148 017 0038 ndash22

Eel 085 009 0013 ndash14

Volume and change estimates less certain due to lack of ice radarmeasurements

Riedel and others Glaciers in the Olympic Mountains14

average annual total glacier summer contribution of71106m3we for the Hoh River the ice fractioncontributed 16 of total glacier runoff for MayndashSeptem-ber mostly late in the melt seasonEstimates of glacier volume loss and results from the

glacial runoff model highlight the importance of glaciers tolate-summer streamflow at the Hoh River gaging station nearForks (Fig 1) Comparing the streamflow data with the PDDmodel results glacial snow firn and ice contribute 359ndash397106m3we or 18ndash30 of total streamflow forAugustndashSeptember compared with 9ndash15 for the entiremelt seasonVolume change estimates also provide a means to assess

the glacial ice (not snow and firn) contribution to late-summer streamflow assuming that all the volume loss wasice that melted in August and September The averageAugustndashSeptember discharge in the lower Hoh River for thepast 23 years is 160 106m3 Based on the 23 year volumeloss estimate of average annual icemelt of 117 106m3wefor the Hoh basin glacier ice provided 7 of the dischargeon the lower Hoh River and 31 of the total glaciercontribution (including snow and firn) Although a smallfraction of total streamflow the glacier ice contributionoccurs when the contribution from snow and firn melt hasdeclined and summer rainfall is minimal and represents theaverage minimum reduction of AugustndashSeptember stream-flow that would occur in the lower Hoh River in the future ifglaciers disappeared The importance of this lsquofossilrsquo water ismagnified during summers when the previous winterrsquossnowfall is low and will become more critical in the futureas the snowpack declinesThe marked loss of glaciers on the Olympic Peninsula in

the past 30 years is largely a result of a 1degC rise in meanannual temperature (Rasmussen and Conway 2001) andillustrates how sensitive these relatively small thin low-elevation temperate glaciers are to climate change Thistemperature increase has directly increased the summermelt rate lengthened the melt season and decreased theduration of the accumulation season resulting in less wintersnow accumulation LaChapelle (1965) notes that theelevation of the freezing level is particularly important inearly fall as it controls how much precipitation falls as snowwhile Rasmussen and others (2000) suggest that springweather is a more important influence on ablation Coolcloudy conditions that often prevail in spring in thismaritime climate lead to lower melt rates at the time ofthe summer solstice particularly during the wet and coldphases of the Southern Oscillation and Pacific DecadalOscillation Recent climate warming appears stronger inwinter at Blue Glacier where average winter temperaturehas risen 3degC in the past half-century (Rasmussen andothers 2000) As a result average winter snow accumu-lation has decreased 500mm near 1500m at the glacierterminus since 1948 (Rasmussen and others 2000)Most of the glaciers on the Peninsula are currently not in

equilibrium with the present climate and are expected tocontinue to shrink in the near future even if accumulationincreases and temperature stops rising In the next severaldecades glaciers are likely to continue to disappear rapidlybased on projected future temperature increases of severaldegrees in the next 70 years Mote and Salatheacute (2010)estimate that mean annual temperature in Washington Statewill increase by at least 12degC by 2040 and at least 28degC by2080 Future temperature increases may be even higher near

the elevation of glaciers given positive feedback mechan-isms Further it is possible that the periodic increases inprecipitation associatedwith the cool wet phase of the PacificDecadal Oscillationmay havewaned in the past few decadeswith a warming climate (Josberger and others 2007)The preponderance of small glaciers remaining on the

Peninsula (145 of 184 are lt01 km2) means that most arevulnerable to melting away completely in the near future(Fig 2) The glaciers most threatened by future climatewarming are generally those that face south in the drier andwarmer climate prevalent on the eastern side of thePeninsula Glaciers on the northeast part of the mountainson Mount Deception McCartney Peak and Cameron Peakmay be the most threatened due to their isolation fromPacific moisture and climate model projections of highersummer potential evapotranspiration that could translate tohigher summer melt rates (Elsner and others 2010) Glacierson the northern side of the Bailey Range and in theheadwaters of the Queets and Elwha Rivers should fareslightly better because of their proximity to large valleys thatfunnel moisture from the Pacific Ocean However theiraccumulation zones are several hundred meters lower thanthose on the large glaciers of Mount Olympus If the climatewarms at the projected rates it is likely that within a centuryglaciers in the Olympic Mountains will be confined to theMount Olympus massifLoss of glaciers due to warming climate has several

significant implications for the Olympic Peninsula includ-ing loss of glacial habitat exposure of vast areas of looseglacial sand and gravel higher summer stream temperaturesand lower late-summer flows in most watersheds Decline inglacier meltwater production will exacerbate changes inaquatic habitat associated with a warming climate Mantuaand others (2010) identified summer temperature andstreamflow as critical physical habitat features for salmonLoss of glaciers will reduce summer streamflow andcontribute to higher summer stream temperatures to thedetriment of species such as the bull trout (Salvelinusconfluentus) (Halofsky and others 2011) Other ecosystemswill also be affected by the loss of glaciers For examplealpine food webs will be diminished by the loss of speciessuch as the ice worm which is preyed upon by rosy finchesand other alpine species

CONCLUSIONSThe glacier geospatial database we developed provides animportant benchmark for assessing glacier extent and glacialrunoff changes in the Olympic Mountains for the past30 years and into the future The combined area of allglaciers has decreased 34 in the past 30 years with ice lossaccelerating to a rate more than twice as fast as that from1900 to 1980 Only four of the 184 remaining glaciers aregt1 km2 in area Glaciers on the southern side of themountains at lower elevations and in the northeastern partof the Peninsula exhibited the greatest area and volume lossesand are the most likely to disappear in the next centuryGlacier decline in the past 30 years in the Olympics is greaterthan in the Cascades and southern Coast Mountains but iscomparable with Vancouver Island Based on ice volumelosses glacial contribution to summer streamflow hasdeclined 20 in the past 30 years but remains significantfor the Hoh River at 63ndash797106m3 andash1 Glaciers con-tribute lt5 to summer streamflow in all other large

Riedel and others Glaciers in the Olympic Mountains 15

watersheds in the Olympic Mountains Delivery of this coldfresh water to streams becomes more critical in the latesummer when rainfall is minimal and snowmelt hasdeclined On the lower Hoh River glacial ice contributes7 of the AugustndashSeptember streamflow which representsthe minimum reduction in flow that would occur if all theglaciers melted away Continued loss of glaciers will directlyimpact aquatic ecosystems through higher stream tempera-tures and lower summer base flows

ACKNOWLEDGEMENTSWe thank the US National Park Service Climate ChangeProgram for funding this research and Olympic and NorthCascades national parks and Portland State University for in-kind support Sharon Brady Roger Hoffman and SteveDorsch contributed GIS and cartographic expertise Finallywe want to acknowledge Richard Spicer for the valuablebaseline he created on the status of Olympic glaciers in theearly 1980s

REFERENCESAllen CR Kamb WB Meier MF and Sharp RP (1960) Structure ofthe lower Blue Glacier Washington J Geol 68(6) 601ndash625

Bolch T Menounos B andWheate R (2010) Landsat-based inventoryof glaciers in western Canada 1985ndash2005 Remote SensEnviron 114(1) 127ndash137 (doi 101016jrse200908015)

Conway H Rasmussen LA and Marshall HP (1999) Annual massbalance of Blue Glacier USA 1955ndash97 Geogr Ann A 81(4)509ndash520

Davey CA Redmond KT and Simeral DB (2006) Weather andclimate inventory National Park Service North Coast andCascades Network (National Resource Technical Report NPSNCCNNRTR-2006010) National Resource Program CenterFort Collins CO

De Woul M and Hock R (2005) Static mass-balance sensitivity ofArctic glaciers and ice caps using a degree-day approach AnnGlaciol 42 217ndash224 (doi 103189172756405781813096)

Elsner MM and 8 others (2010) Implications of 21st-century climatechange for the hydrology of Washington State Climatic Change102(1ndash2) 225ndash260 (doi 101007s10584-010-9855-0)

Granshaw FD and Fountain AG (2006) Glacier change (1958ndash1998) in the North Cascades National Park ComplexWashington USA J Glaciol 52(177) 251ndash256 (doi 103189172756506781828782)

Halofsky JE Peterson DL OrsquoHalloran KA and Hoffman CH eds(2011) Adapting to climate change at Olympic National Forestand Olympic National Park (Gen Tech Rep PNW-GTR-844)Pacific Northwest Research Station US Department of Agricul-ture Portland OR httpwwwtreesearchfsfeduspubs38702

Heroux P and Kouba J (2001) GPS precise point positioning usingIGS orbit products Phys Chem Earth 26(6ndash8) 573ndash578

Heusser CJ (1957) Variations of Blue Hoh and White Glaciersduring recent centuries Arctic 10(3) 139ndash150 (doi 1014430arctic3761)

Hodge SM (1974) Variations in the sliding of a temperate glacierJ Glaciol 13(69) 349ndash369

Hodson A and 7 others (2008) Glacial ecosystems Ecol Monogr78(1) 41ndash67 (doi 10189007-01871)

Hubley RC (1956) Glaciers of the Washington Cascade andOlympic Mountains their present activity and its relation tolocal climatic trends J Glaciol 2(19) 669ndash674 (doi 103189002214356793701938)

Josberger EG Bidlake WR March RS and Kennedy BW (2007)Glacier mass-balance fluctuations in the Pacific Northwest andAlaska USA Ann Glaciol 46 291ndash296 (doi 103189172756407782871314)

LaChapelle ER (1965) The mass budget of Blue Glacier Washing-ton J Glaciol 5(41) 609ndash623

Malcomb NL and Wiles GC (2013) Tree-ring-based reconstructionsof North American glacier mass balance through the Little IceAge contemporary warming transition Quat Res 79(2)123ndash137 (doi 101016jyqres201211005)

Mantua NJ Hare SR Zhang Y Wallace JM and Francis RC (1997) APacific interdecadal climate oscillation with impacts on salmonproduction Bull Am Meteorol Soc 78(6) 1069ndash1079 (doi1011751520-0477(1997)078lt1069APICOWgt20CO2)

Mantua N Tohver I and Hamlet A (2010) Climate change impactson streamflow extremes and summertime stream temperatureand their possible consequences for freshwater salmon habitatin Washington State Climatic Change 102(1ndash2) 187ndash223 (doi101007s10584-010-9845-2)

Matthes FE (1946) Report of Committee on Glaciers 1945 Eos27(2) 219ndash233

Meier MF (1961) Distribution and variations of glaciers in theUnited States exclusive of Alaska IASH Publ 54 (GeneralAssembly of Helsinki 1960 ndash Snow and Ice) 420ndash429

Mote PW and Salatheacute EP Jr (2010) Future climate in the PacificNorthwest Climatic Change 102(1ndash2) 29ndash50 (doi 101007s10584-010-9848-z)

Nolin AW and Daly C (2006) Mapping lsquoat riskrsquo snow in thePacific Northwest J Hydromet 7(5) 1164ndash1171 (doi 101175JHM5431)

PRISM Group (2006) United States average monthly and annualprecipitation 1971ndash2000 Oregon State University CorvallisOR httpprismoregonstateedu

Rasmussen LA and Conway H (2001) Estimating South CascadeGlacier (Washington USA) mass balance from a distant radio-sonde and comparison with Blue Glacier J Glaciol 47(159)579ndash588 (doi 103189172756501781831873)

Rasmussen LA and Wenger JM (2009) Upper-air model of summerbalance on Mount Rainier USA J Glaciol 55(192) 619ndash624(doi 103189002214309789471012)

Rasmussen LA Conway H and Hayes PS (2000) The accumulationregime of Blue Glacier USA 1914ndash96 J Glaciol 46(153)326ndash334 (doi 103189172756500781832846)

Riedel JR Burrows RA and Wenger JM (2008) Long-term monitoringof small glaciers at North Cascades National Park a prototypepark model for the North Coast and Cascades Network (NaturResour Rep NPSNCCNNRR-2008066) National Park ServiceFort Collins CO

Spicer RC (1986) Glaciers in the Olympic Mountains Washingtonpresent distribution and recent variations (PhD thesis Uni-versity of Washington)

Tabor RW and Cady WM (1978) Geologic map of the OlympicPeninsula Washington (Misc Inv Map 994) US GeologicalSurvey Reston VA

MS received 19 July 2014 and accepted in revised form 11 September 2014

Riedel and others Glaciers in the Olympic Mountains16

warming climate Glaciers in the eastern part of the Peninsulaand those that face south lost more area than those facingnorth and on the wetter windward slope (Table 1) Glacierlosses were most pronounced in the drier northeastern part ofthe Peninsula where for example little remains of LillianGlacier on McCartney Peak (Fig 6) For the most partglaciers east of the Elwha River now exist almost exclusivelyon shaded northern aspects where melting is slower and theymay benefit from secondary sources of accumulation (egwind redeposition and snow avalanche)The influence of aspect is well illustrated on Mount

Anderson Since 1980 Anderson Glacier has lost 77 of itsarea compared with a 23 loss for adjacent north-facing EelGlacier (Table 1 Figs 5 and 7) Aspect is also a critical factorto glacier status on Mount Olympus where southeast-facingJeffers Glacier shrank by 61 in 30 years while north-facing Hoh and White Glaciers declined by 17ndash18 (Fig 5)North-facing glaciers east of the Elwha lost 21ndash51 of theirarea in 30 years whereas the north-facing glaciers on MountOlympus lost 12ndash20 over the same period Glaciers in theBailey Range with north aspects had area losses comparablewith glaciers on the south side of Olympus and with north-facing glaciers east of the Elwha (eg Carrie GlacierTable 1)The rate of ice loss for six glaciers from AD1900 to 1980

was 026 km2 andash1 although this included a period of positivebalance at Blue Glacier from 1959 to 1975 (Hubley 1956Spicer 1986 Rasmussen and Conway 2001) Since 1980the rate of decline in combined ice extent across theOlympic Mountains doubled to 054 km2 andash1 Acceleratingdecline of glacier area is also reflected in strongly negative

cumulative balance on Blue Glacier since the mid-1980s(Rasmussen and Conway 2001)Decline in glacier area in recent decades on the Olympic

Peninsula exceeds losses east of the FraserndashPuget lowlandsIn the southern Coast Mountains of British Columbia glacierarea declined 10 from 1985 to 2005 (Bolch and others2010) while Granshaw and Fountain (2006) estimated lossof glaciers in the North Cascades National Park over a40 year period ending in 1998 at 7 The more rapid lossof glaciers in the Olympics is more comparable with theobserved loss of 20 over a similar period on VancouverIsland (Bolch and others 2010) Rapid loss of glaciers incoastal ranges is likely due to their sensitivity to changes intemperature that strongly influence spring ablation andearly-fall accumulation (LaChapelle 1965) Accumulatingevidence indicates that the recent loss of glacier area andvolume through multiple decades for all glaciers in thePacific Northwest has not occurred since at least AD 1694(Malcomb and Wiles 2013)Glacier area measurements were combined with surface

elevation profiles to assess thickness changes from 1987 to2010 for four of the largest glaciers in the OlympicMountains (Table 2) Only Blue Glacier has ice thicknessdata and a known glacier volume (Allen and others 1960)the other glacier volumes were estimated assuming anaverage ice thickness and by the ratio of the glacierrsquos area to

Fig 6 Changes in Lillian Glacier on McCartney Peak from 1905 (aNPS photograph) to the present (b photograph by J McLean)

Fig 7 Changes in Anderson Glacier from 1936 (a photograph byA Curtis) to the present (b photograph by R Hoffman)

Riedel and others Glaciers in the Olympic Mountains 13

Blue Glacierrsquos area Blue Glacier on Mount Olympus hadthe largest volume loss since 1987 because it has the largestarea The largest percent change however was for south-facing Humes Glacier at ndash22 while north-facing Blue andHoh Glaciers lost 15 and 16 respectively (Table 2) Inaddition to its aspect Humes Glacier had the mostsignificant volume reduction because it is at a lowerelevation than its neighbors Hoh Blue and White glaciersFurther to the east north-facing Eel Glacier has lost 14 ofits volume (0013 km3) since 1987Even with a 34 decline in area and 20 decline in

volume in the last 30 years glaciers continue to providesignificant amounts of water to streams on the OlympicPeninsula We used the hypsometry of glaciers and summer-melt versus elevation curves from the PDD model toestimate glacial contribution to summer streamflow forthree large basins that represent a range in climate andglacial cover (Table 3 Figs 8 and 9) As shown in Figure 8the model accurately reproduced the amount of summermelt as measured by melt stakes at two locations The modeland melt data also show that summer melt at 1500m variesby 20ndash25 (1m) between extreme years with lessvariability at higher elevations Model error at 1500m is050mwe andash1 (r2 = 068) based on the residual mean sumof errors at 2050m it is 028mwe andash1 (r2 = 076) Thesevalues represent an error of 10 in the total summermelt estimateAbout 66 of the glacier-covered landscape in the

Olympic Mountains is found in the Hoh River watershed

(20 km2) more than half of the remaining glacial cover is inthe Queets and Elwha watersheds (Fig 2) Based on thePDD model and basin-wide glacier hypsometry glacierscurrently provide 63ndash797106m3 of water to the HohRiver annually from 1 May to 30 September In the Elwhawatershed glaciers provide 12ndash1513 106m3 of sum-mer runoff while in the Dungeness basin they provide 25ndash31028106m3 The other large watersheds on theOlympic Peninsula have lt5 glacial contribution tosummer streamflow Given a 20 loss in glacier volumeglacial runoff on the Peninsula has decreased a similaramount in the past 30 yearsOur PDD model estimates of glacial runoff combine

snow firn and ice contributions but we recognize that theyare likely dominated by snowmelt LaChapelle (1965)suggested snowmelt was 16 and 42 times firn and icemelt on Blue Glacier in 1958 and 1962 respectively andthat ice melt occurred primarily in September and OctoberGiven reduced winter accumulation in the last 50 years anda longer melt season (Rasmussen and Conway 2001) thesnow to firnice melt ratios are now probably smallerThe volume loss calculations allowed us to assess the

glacier ice (not snow or firn) contribution to summerstreamflow in the Hoh basin (Tables 2 and 3) Volumeof ice loss for Hoh and Blue Glaciers averaged 63106m3we andash1 from 1987 to 2010 assuming a similarcontribution from the other 1065 km2 of glaciers in the Hohvalley the 23 year average annual glacial ice ablation is117 106m3we Using the PDD model estimate of an

Table 3 Range of modern glacial ice snow and firn contribution tosummer (1 Mayndash30 September) streamflow for three rivers

Watershed Basin

area

Glacier

area

Glacial runoff Total summer

runoff

2010 low 2009 high

km2 km2 106 m3 106 m3

Hoh 655 2003 63 79 89ndash154

Elwha 697 372 12 15 25ndash40

Dungeness 404 113 245 308 30ndash38

Includes snow firn and ice

Fig 8 Degree-day model of Blue Glacier summer balance (dashedline) used to estimate range in glacier runoff Measured values(square and diamond) from Conway and others (1999)

Fig 9 Modern range in summer (1 Mayndash30 September) glacialrunoff for three Olympic Peninsula watersheds determined by aPDD model for negative (2009) and positive (2010) net mass-balance years Runoff includes snow firn and ice from glaciers ineach basin Percentage of basin above gage site covered by glaciersshown in parentheses

Table 2 Volume change estimates for four glaciers 1987ndash2010Volume changes are not adjusted to water equivalence

Glacier Area 2009 Volume 2010 Volume loss

1987ndash2009

Change

1987ndash2010

km2 km3 km3

Hoh 403 049 0078 ndash16

Blue 535 057 0084 ndash15

Humes 148 017 0038 ndash22

Eel 085 009 0013 ndash14

Volume and change estimates less certain due to lack of ice radarmeasurements

Riedel and others Glaciers in the Olympic Mountains14

average annual total glacier summer contribution of71106m3we for the Hoh River the ice fractioncontributed 16 of total glacier runoff for MayndashSeptem-ber mostly late in the melt seasonEstimates of glacier volume loss and results from the

glacial runoff model highlight the importance of glaciers tolate-summer streamflow at the Hoh River gaging station nearForks (Fig 1) Comparing the streamflow data with the PDDmodel results glacial snow firn and ice contribute 359ndash397106m3we or 18ndash30 of total streamflow forAugustndashSeptember compared with 9ndash15 for the entiremelt seasonVolume change estimates also provide a means to assess

the glacial ice (not snow and firn) contribution to late-summer streamflow assuming that all the volume loss wasice that melted in August and September The averageAugustndashSeptember discharge in the lower Hoh River for thepast 23 years is 160 106m3 Based on the 23 year volumeloss estimate of average annual icemelt of 117 106m3wefor the Hoh basin glacier ice provided 7 of the dischargeon the lower Hoh River and 31 of the total glaciercontribution (including snow and firn) Although a smallfraction of total streamflow the glacier ice contributionoccurs when the contribution from snow and firn melt hasdeclined and summer rainfall is minimal and represents theaverage minimum reduction of AugustndashSeptember stream-flow that would occur in the lower Hoh River in the future ifglaciers disappeared The importance of this lsquofossilrsquo water ismagnified during summers when the previous winterrsquossnowfall is low and will become more critical in the futureas the snowpack declinesThe marked loss of glaciers on the Olympic Peninsula in

the past 30 years is largely a result of a 1degC rise in meanannual temperature (Rasmussen and Conway 2001) andillustrates how sensitive these relatively small thin low-elevation temperate glaciers are to climate change Thistemperature increase has directly increased the summermelt rate lengthened the melt season and decreased theduration of the accumulation season resulting in less wintersnow accumulation LaChapelle (1965) notes that theelevation of the freezing level is particularly important inearly fall as it controls how much precipitation falls as snowwhile Rasmussen and others (2000) suggest that springweather is a more important influence on ablation Coolcloudy conditions that often prevail in spring in thismaritime climate lead to lower melt rates at the time ofthe summer solstice particularly during the wet and coldphases of the Southern Oscillation and Pacific DecadalOscillation Recent climate warming appears stronger inwinter at Blue Glacier where average winter temperaturehas risen 3degC in the past half-century (Rasmussen andothers 2000) As a result average winter snow accumu-lation has decreased 500mm near 1500m at the glacierterminus since 1948 (Rasmussen and others 2000)Most of the glaciers on the Peninsula are currently not in

equilibrium with the present climate and are expected tocontinue to shrink in the near future even if accumulationincreases and temperature stops rising In the next severaldecades glaciers are likely to continue to disappear rapidlybased on projected future temperature increases of severaldegrees in the next 70 years Mote and Salatheacute (2010)estimate that mean annual temperature in Washington Statewill increase by at least 12degC by 2040 and at least 28degC by2080 Future temperature increases may be even higher near

the elevation of glaciers given positive feedback mechan-isms Further it is possible that the periodic increases inprecipitation associatedwith the cool wet phase of the PacificDecadal Oscillationmay havewaned in the past few decadeswith a warming climate (Josberger and others 2007)The preponderance of small glaciers remaining on the

Peninsula (145 of 184 are lt01 km2) means that most arevulnerable to melting away completely in the near future(Fig 2) The glaciers most threatened by future climatewarming are generally those that face south in the drier andwarmer climate prevalent on the eastern side of thePeninsula Glaciers on the northeast part of the mountainson Mount Deception McCartney Peak and Cameron Peakmay be the most threatened due to their isolation fromPacific moisture and climate model projections of highersummer potential evapotranspiration that could translate tohigher summer melt rates (Elsner and others 2010) Glacierson the northern side of the Bailey Range and in theheadwaters of the Queets and Elwha Rivers should fareslightly better because of their proximity to large valleys thatfunnel moisture from the Pacific Ocean However theiraccumulation zones are several hundred meters lower thanthose on the large glaciers of Mount Olympus If the climatewarms at the projected rates it is likely that within a centuryglaciers in the Olympic Mountains will be confined to theMount Olympus massifLoss of glaciers due to warming climate has several

significant implications for the Olympic Peninsula includ-ing loss of glacial habitat exposure of vast areas of looseglacial sand and gravel higher summer stream temperaturesand lower late-summer flows in most watersheds Decline inglacier meltwater production will exacerbate changes inaquatic habitat associated with a warming climate Mantuaand others (2010) identified summer temperature andstreamflow as critical physical habitat features for salmonLoss of glaciers will reduce summer streamflow andcontribute to higher summer stream temperatures to thedetriment of species such as the bull trout (Salvelinusconfluentus) (Halofsky and others 2011) Other ecosystemswill also be affected by the loss of glaciers For examplealpine food webs will be diminished by the loss of speciessuch as the ice worm which is preyed upon by rosy finchesand other alpine species

CONCLUSIONSThe glacier geospatial database we developed provides animportant benchmark for assessing glacier extent and glacialrunoff changes in the Olympic Mountains for the past30 years and into the future The combined area of allglaciers has decreased 34 in the past 30 years with ice lossaccelerating to a rate more than twice as fast as that from1900 to 1980 Only four of the 184 remaining glaciers aregt1 km2 in area Glaciers on the southern side of themountains at lower elevations and in the northeastern partof the Peninsula exhibited the greatest area and volume lossesand are the most likely to disappear in the next centuryGlacier decline in the past 30 years in the Olympics is greaterthan in the Cascades and southern Coast Mountains but iscomparable with Vancouver Island Based on ice volumelosses glacial contribution to summer streamflow hasdeclined 20 in the past 30 years but remains significantfor the Hoh River at 63ndash797106m3 andash1 Glaciers con-tribute lt5 to summer streamflow in all other large

Riedel and others Glaciers in the Olympic Mountains 15

watersheds in the Olympic Mountains Delivery of this coldfresh water to streams becomes more critical in the latesummer when rainfall is minimal and snowmelt hasdeclined On the lower Hoh River glacial ice contributes7 of the AugustndashSeptember streamflow which representsthe minimum reduction in flow that would occur if all theglaciers melted away Continued loss of glaciers will directlyimpact aquatic ecosystems through higher stream tempera-tures and lower summer base flows

ACKNOWLEDGEMENTSWe thank the US National Park Service Climate ChangeProgram for funding this research and Olympic and NorthCascades national parks and Portland State University for in-kind support Sharon Brady Roger Hoffman and SteveDorsch contributed GIS and cartographic expertise Finallywe want to acknowledge Richard Spicer for the valuablebaseline he created on the status of Olympic glaciers in theearly 1980s

REFERENCESAllen CR Kamb WB Meier MF and Sharp RP (1960) Structure ofthe lower Blue Glacier Washington J Geol 68(6) 601ndash625

Bolch T Menounos B andWheate R (2010) Landsat-based inventoryof glaciers in western Canada 1985ndash2005 Remote SensEnviron 114(1) 127ndash137 (doi 101016jrse200908015)

Conway H Rasmussen LA and Marshall HP (1999) Annual massbalance of Blue Glacier USA 1955ndash97 Geogr Ann A 81(4)509ndash520

Davey CA Redmond KT and Simeral DB (2006) Weather andclimate inventory National Park Service North Coast andCascades Network (National Resource Technical Report NPSNCCNNRTR-2006010) National Resource Program CenterFort Collins CO

De Woul M and Hock R (2005) Static mass-balance sensitivity ofArctic glaciers and ice caps using a degree-day approach AnnGlaciol 42 217ndash224 (doi 103189172756405781813096)

Elsner MM and 8 others (2010) Implications of 21st-century climatechange for the hydrology of Washington State Climatic Change102(1ndash2) 225ndash260 (doi 101007s10584-010-9855-0)

Granshaw FD and Fountain AG (2006) Glacier change (1958ndash1998) in the North Cascades National Park ComplexWashington USA J Glaciol 52(177) 251ndash256 (doi 103189172756506781828782)

Halofsky JE Peterson DL OrsquoHalloran KA and Hoffman CH eds(2011) Adapting to climate change at Olympic National Forestand Olympic National Park (Gen Tech Rep PNW-GTR-844)Pacific Northwest Research Station US Department of Agricul-ture Portland OR httpwwwtreesearchfsfeduspubs38702

Heroux P and Kouba J (2001) GPS precise point positioning usingIGS orbit products Phys Chem Earth 26(6ndash8) 573ndash578

Heusser CJ (1957) Variations of Blue Hoh and White Glaciersduring recent centuries Arctic 10(3) 139ndash150 (doi 1014430arctic3761)

Hodge SM (1974) Variations in the sliding of a temperate glacierJ Glaciol 13(69) 349ndash369

Hodson A and 7 others (2008) Glacial ecosystems Ecol Monogr78(1) 41ndash67 (doi 10189007-01871)

Hubley RC (1956) Glaciers of the Washington Cascade andOlympic Mountains their present activity and its relation tolocal climatic trends J Glaciol 2(19) 669ndash674 (doi 103189002214356793701938)

Josberger EG Bidlake WR March RS and Kennedy BW (2007)Glacier mass-balance fluctuations in the Pacific Northwest andAlaska USA Ann Glaciol 46 291ndash296 (doi 103189172756407782871314)

LaChapelle ER (1965) The mass budget of Blue Glacier Washing-ton J Glaciol 5(41) 609ndash623

Malcomb NL and Wiles GC (2013) Tree-ring-based reconstructionsof North American glacier mass balance through the Little IceAge contemporary warming transition Quat Res 79(2)123ndash137 (doi 101016jyqres201211005)

Mantua NJ Hare SR Zhang Y Wallace JM and Francis RC (1997) APacific interdecadal climate oscillation with impacts on salmonproduction Bull Am Meteorol Soc 78(6) 1069ndash1079 (doi1011751520-0477(1997)078lt1069APICOWgt20CO2)

Mantua N Tohver I and Hamlet A (2010) Climate change impactson streamflow extremes and summertime stream temperatureand their possible consequences for freshwater salmon habitatin Washington State Climatic Change 102(1ndash2) 187ndash223 (doi101007s10584-010-9845-2)

Matthes FE (1946) Report of Committee on Glaciers 1945 Eos27(2) 219ndash233

Meier MF (1961) Distribution and variations of glaciers in theUnited States exclusive of Alaska IASH Publ 54 (GeneralAssembly of Helsinki 1960 ndash Snow and Ice) 420ndash429

Mote PW and Salatheacute EP Jr (2010) Future climate in the PacificNorthwest Climatic Change 102(1ndash2) 29ndash50 (doi 101007s10584-010-9848-z)

Nolin AW and Daly C (2006) Mapping lsquoat riskrsquo snow in thePacific Northwest J Hydromet 7(5) 1164ndash1171 (doi 101175JHM5431)

PRISM Group (2006) United States average monthly and annualprecipitation 1971ndash2000 Oregon State University CorvallisOR httpprismoregonstateedu

Rasmussen LA and Conway H (2001) Estimating South CascadeGlacier (Washington USA) mass balance from a distant radio-sonde and comparison with Blue Glacier J Glaciol 47(159)579ndash588 (doi 103189172756501781831873)

Rasmussen LA and Wenger JM (2009) Upper-air model of summerbalance on Mount Rainier USA J Glaciol 55(192) 619ndash624(doi 103189002214309789471012)

Rasmussen LA Conway H and Hayes PS (2000) The accumulationregime of Blue Glacier USA 1914ndash96 J Glaciol 46(153)326ndash334 (doi 103189172756500781832846)

Riedel JR Burrows RA and Wenger JM (2008) Long-term monitoringof small glaciers at North Cascades National Park a prototypepark model for the North Coast and Cascades Network (NaturResour Rep NPSNCCNNRR-2008066) National Park ServiceFort Collins CO

Spicer RC (1986) Glaciers in the Olympic Mountains Washingtonpresent distribution and recent variations (PhD thesis Uni-versity of Washington)

Tabor RW and Cady WM (1978) Geologic map of the OlympicPeninsula Washington (Misc Inv Map 994) US GeologicalSurvey Reston VA

MS received 19 July 2014 and accepted in revised form 11 September 2014

Riedel and others Glaciers in the Olympic Mountains16

Blue Glacierrsquos area Blue Glacier on Mount Olympus hadthe largest volume loss since 1987 because it has the largestarea The largest percent change however was for south-facing Humes Glacier at ndash22 while north-facing Blue andHoh Glaciers lost 15 and 16 respectively (Table 2) Inaddition to its aspect Humes Glacier had the mostsignificant volume reduction because it is at a lowerelevation than its neighbors Hoh Blue and White glaciersFurther to the east north-facing Eel Glacier has lost 14 ofits volume (0013 km3) since 1987Even with a 34 decline in area and 20 decline in

volume in the last 30 years glaciers continue to providesignificant amounts of water to streams on the OlympicPeninsula We used the hypsometry of glaciers and summer-melt versus elevation curves from the PDD model toestimate glacial contribution to summer streamflow forthree large basins that represent a range in climate andglacial cover (Table 3 Figs 8 and 9) As shown in Figure 8the model accurately reproduced the amount of summermelt as measured by melt stakes at two locations The modeland melt data also show that summer melt at 1500m variesby 20ndash25 (1m) between extreme years with lessvariability at higher elevations Model error at 1500m is050mwe andash1 (r2 = 068) based on the residual mean sumof errors at 2050m it is 028mwe andash1 (r2 = 076) Thesevalues represent an error of 10 in the total summermelt estimateAbout 66 of the glacier-covered landscape in the

Olympic Mountains is found in the Hoh River watershed

(20 km2) more than half of the remaining glacial cover is inthe Queets and Elwha watersheds (Fig 2) Based on thePDD model and basin-wide glacier hypsometry glacierscurrently provide 63ndash797106m3 of water to the HohRiver annually from 1 May to 30 September In the Elwhawatershed glaciers provide 12ndash1513 106m3 of sum-mer runoff while in the Dungeness basin they provide 25ndash31028106m3 The other large watersheds on theOlympic Peninsula have lt5 glacial contribution tosummer streamflow Given a 20 loss in glacier volumeglacial runoff on the Peninsula has decreased a similaramount in the past 30 yearsOur PDD model estimates of glacial runoff combine

snow firn and ice contributions but we recognize that theyare likely dominated by snowmelt LaChapelle (1965)suggested snowmelt was 16 and 42 times firn and icemelt on Blue Glacier in 1958 and 1962 respectively andthat ice melt occurred primarily in September and OctoberGiven reduced winter accumulation in the last 50 years anda longer melt season (Rasmussen and Conway 2001) thesnow to firnice melt ratios are now probably smallerThe volume loss calculations allowed us to assess the

glacier ice (not snow or firn) contribution to summerstreamflow in the Hoh basin (Tables 2 and 3) Volumeof ice loss for Hoh and Blue Glaciers averaged 63106m3we andash1 from 1987 to 2010 assuming a similarcontribution from the other 1065 km2 of glaciers in the Hohvalley the 23 year average annual glacial ice ablation is117 106m3we Using the PDD model estimate of an

Table 3 Range of modern glacial ice snow and firn contribution tosummer (1 Mayndash30 September) streamflow for three rivers

Watershed Basin

area

Glacier

area

Glacial runoff Total summer

runoff

2010 low 2009 high

km2 km2 106 m3 106 m3

Hoh 655 2003 63 79 89ndash154

Elwha 697 372 12 15 25ndash40

Dungeness 404 113 245 308 30ndash38

Includes snow firn and ice

Fig 8 Degree-day model of Blue Glacier summer balance (dashedline) used to estimate range in glacier runoff Measured values(square and diamond) from Conway and others (1999)

Fig 9 Modern range in summer (1 Mayndash30 September) glacialrunoff for three Olympic Peninsula watersheds determined by aPDD model for negative (2009) and positive (2010) net mass-balance years Runoff includes snow firn and ice from glaciers ineach basin Percentage of basin above gage site covered by glaciersshown in parentheses

Table 2 Volume change estimates for four glaciers 1987ndash2010Volume changes are not adjusted to water equivalence

Glacier Area 2009 Volume 2010 Volume loss

1987ndash2009

Change

1987ndash2010

km2 km3 km3

Hoh 403 049 0078 ndash16

Blue 535 057 0084 ndash15

Humes 148 017 0038 ndash22

Eel 085 009 0013 ndash14

Volume and change estimates less certain due to lack of ice radarmeasurements

Riedel and others Glaciers in the Olympic Mountains14

average annual total glacier summer contribution of71106m3we for the Hoh River the ice fractioncontributed 16 of total glacier runoff for MayndashSeptem-ber mostly late in the melt seasonEstimates of glacier volume loss and results from the

glacial runoff model highlight the importance of glaciers tolate-summer streamflow at the Hoh River gaging station nearForks (Fig 1) Comparing the streamflow data with the PDDmodel results glacial snow firn and ice contribute 359ndash397106m3we or 18ndash30 of total streamflow forAugustndashSeptember compared with 9ndash15 for the entiremelt seasonVolume change estimates also provide a means to assess

the glacial ice (not snow and firn) contribution to late-summer streamflow assuming that all the volume loss wasice that melted in August and September The averageAugustndashSeptember discharge in the lower Hoh River for thepast 23 years is 160 106m3 Based on the 23 year volumeloss estimate of average annual icemelt of 117 106m3wefor the Hoh basin glacier ice provided 7 of the dischargeon the lower Hoh River and 31 of the total glaciercontribution (including snow and firn) Although a smallfraction of total streamflow the glacier ice contributionoccurs when the contribution from snow and firn melt hasdeclined and summer rainfall is minimal and represents theaverage minimum reduction of AugustndashSeptember stream-flow that would occur in the lower Hoh River in the future ifglaciers disappeared The importance of this lsquofossilrsquo water ismagnified during summers when the previous winterrsquossnowfall is low and will become more critical in the futureas the snowpack declinesThe marked loss of glaciers on the Olympic Peninsula in

the past 30 years is largely a result of a 1degC rise in meanannual temperature (Rasmussen and Conway 2001) andillustrates how sensitive these relatively small thin low-elevation temperate glaciers are to climate change Thistemperature increase has directly increased the summermelt rate lengthened the melt season and decreased theduration of the accumulation season resulting in less wintersnow accumulation LaChapelle (1965) notes that theelevation of the freezing level is particularly important inearly fall as it controls how much precipitation falls as snowwhile Rasmussen and others (2000) suggest that springweather is a more important influence on ablation Coolcloudy conditions that often prevail in spring in thismaritime climate lead to lower melt rates at the time ofthe summer solstice particularly during the wet and coldphases of the Southern Oscillation and Pacific DecadalOscillation Recent climate warming appears stronger inwinter at Blue Glacier where average winter temperaturehas risen 3degC in the past half-century (Rasmussen andothers 2000) As a result average winter snow accumu-lation has decreased 500mm near 1500m at the glacierterminus since 1948 (Rasmussen and others 2000)Most of the glaciers on the Peninsula are currently not in

equilibrium with the present climate and are expected tocontinue to shrink in the near future even if accumulationincreases and temperature stops rising In the next severaldecades glaciers are likely to continue to disappear rapidlybased on projected future temperature increases of severaldegrees in the next 70 years Mote and Salatheacute (2010)estimate that mean annual temperature in Washington Statewill increase by at least 12degC by 2040 and at least 28degC by2080 Future temperature increases may be even higher near

the elevation of glaciers given positive feedback mechan-isms Further it is possible that the periodic increases inprecipitation associatedwith the cool wet phase of the PacificDecadal Oscillationmay havewaned in the past few decadeswith a warming climate (Josberger and others 2007)The preponderance of small glaciers remaining on the

Peninsula (145 of 184 are lt01 km2) means that most arevulnerable to melting away completely in the near future(Fig 2) The glaciers most threatened by future climatewarming are generally those that face south in the drier andwarmer climate prevalent on the eastern side of thePeninsula Glaciers on the northeast part of the mountainson Mount Deception McCartney Peak and Cameron Peakmay be the most threatened due to their isolation fromPacific moisture and climate model projections of highersummer potential evapotranspiration that could translate tohigher summer melt rates (Elsner and others 2010) Glacierson the northern side of the Bailey Range and in theheadwaters of the Queets and Elwha Rivers should fareslightly better because of their proximity to large valleys thatfunnel moisture from the Pacific Ocean However theiraccumulation zones are several hundred meters lower thanthose on the large glaciers of Mount Olympus If the climatewarms at the projected rates it is likely that within a centuryglaciers in the Olympic Mountains will be confined to theMount Olympus massifLoss of glaciers due to warming climate has several

significant implications for the Olympic Peninsula includ-ing loss of glacial habitat exposure of vast areas of looseglacial sand and gravel higher summer stream temperaturesand lower late-summer flows in most watersheds Decline inglacier meltwater production will exacerbate changes inaquatic habitat associated with a warming climate Mantuaand others (2010) identified summer temperature andstreamflow as critical physical habitat features for salmonLoss of glaciers will reduce summer streamflow andcontribute to higher summer stream temperatures to thedetriment of species such as the bull trout (Salvelinusconfluentus) (Halofsky and others 2011) Other ecosystemswill also be affected by the loss of glaciers For examplealpine food webs will be diminished by the loss of speciessuch as the ice worm which is preyed upon by rosy finchesand other alpine species

CONCLUSIONSThe glacier geospatial database we developed provides animportant benchmark for assessing glacier extent and glacialrunoff changes in the Olympic Mountains for the past30 years and into the future The combined area of allglaciers has decreased 34 in the past 30 years with ice lossaccelerating to a rate more than twice as fast as that from1900 to 1980 Only four of the 184 remaining glaciers aregt1 km2 in area Glaciers on the southern side of themountains at lower elevations and in the northeastern partof the Peninsula exhibited the greatest area and volume lossesand are the most likely to disappear in the next centuryGlacier decline in the past 30 years in the Olympics is greaterthan in the Cascades and southern Coast Mountains but iscomparable with Vancouver Island Based on ice volumelosses glacial contribution to summer streamflow hasdeclined 20 in the past 30 years but remains significantfor the Hoh River at 63ndash797106m3 andash1 Glaciers con-tribute lt5 to summer streamflow in all other large

Riedel and others Glaciers in the Olympic Mountains 15

watersheds in the Olympic Mountains Delivery of this coldfresh water to streams becomes more critical in the latesummer when rainfall is minimal and snowmelt hasdeclined On the lower Hoh River glacial ice contributes7 of the AugustndashSeptember streamflow which representsthe minimum reduction in flow that would occur if all theglaciers melted away Continued loss of glaciers will directlyimpact aquatic ecosystems through higher stream tempera-tures and lower summer base flows

ACKNOWLEDGEMENTSWe thank the US National Park Service Climate ChangeProgram for funding this research and Olympic and NorthCascades national parks and Portland State University for in-kind support Sharon Brady Roger Hoffman and SteveDorsch contributed GIS and cartographic expertise Finallywe want to acknowledge Richard Spicer for the valuablebaseline he created on the status of Olympic glaciers in theearly 1980s

REFERENCESAllen CR Kamb WB Meier MF and Sharp RP (1960) Structure ofthe lower Blue Glacier Washington J Geol 68(6) 601ndash625

Bolch T Menounos B andWheate R (2010) Landsat-based inventoryof glaciers in western Canada 1985ndash2005 Remote SensEnviron 114(1) 127ndash137 (doi 101016jrse200908015)

Conway H Rasmussen LA and Marshall HP (1999) Annual massbalance of Blue Glacier USA 1955ndash97 Geogr Ann A 81(4)509ndash520

Davey CA Redmond KT and Simeral DB (2006) Weather andclimate inventory National Park Service North Coast andCascades Network (National Resource Technical Report NPSNCCNNRTR-2006010) National Resource Program CenterFort Collins CO

De Woul M and Hock R (2005) Static mass-balance sensitivity ofArctic glaciers and ice caps using a degree-day approach AnnGlaciol 42 217ndash224 (doi 103189172756405781813096)

Elsner MM and 8 others (2010) Implications of 21st-century climatechange for the hydrology of Washington State Climatic Change102(1ndash2) 225ndash260 (doi 101007s10584-010-9855-0)

Granshaw FD and Fountain AG (2006) Glacier change (1958ndash1998) in the North Cascades National Park ComplexWashington USA J Glaciol 52(177) 251ndash256 (doi 103189172756506781828782)

Halofsky JE Peterson DL OrsquoHalloran KA and Hoffman CH eds(2011) Adapting to climate change at Olympic National Forestand Olympic National Park (Gen Tech Rep PNW-GTR-844)Pacific Northwest Research Station US Department of Agricul-ture Portland OR httpwwwtreesearchfsfeduspubs38702

Heroux P and Kouba J (2001) GPS precise point positioning usingIGS orbit products Phys Chem Earth 26(6ndash8) 573ndash578

Heusser CJ (1957) Variations of Blue Hoh and White Glaciersduring recent centuries Arctic 10(3) 139ndash150 (doi 1014430arctic3761)

Hodge SM (1974) Variations in the sliding of a temperate glacierJ Glaciol 13(69) 349ndash369

Hodson A and 7 others (2008) Glacial ecosystems Ecol Monogr78(1) 41ndash67 (doi 10189007-01871)

Hubley RC (1956) Glaciers of the Washington Cascade andOlympic Mountains their present activity and its relation tolocal climatic trends J Glaciol 2(19) 669ndash674 (doi 103189002214356793701938)

Josberger EG Bidlake WR March RS and Kennedy BW (2007)Glacier mass-balance fluctuations in the Pacific Northwest andAlaska USA Ann Glaciol 46 291ndash296 (doi 103189172756407782871314)

LaChapelle ER (1965) The mass budget of Blue Glacier Washing-ton J Glaciol 5(41) 609ndash623

Malcomb NL and Wiles GC (2013) Tree-ring-based reconstructionsof North American glacier mass balance through the Little IceAge contemporary warming transition Quat Res 79(2)123ndash137 (doi 101016jyqres201211005)

Mantua NJ Hare SR Zhang Y Wallace JM and Francis RC (1997) APacific interdecadal climate oscillation with impacts on salmonproduction Bull Am Meteorol Soc 78(6) 1069ndash1079 (doi1011751520-0477(1997)078lt1069APICOWgt20CO2)

Mantua N Tohver I and Hamlet A (2010) Climate change impactson streamflow extremes and summertime stream temperatureand their possible consequences for freshwater salmon habitatin Washington State Climatic Change 102(1ndash2) 187ndash223 (doi101007s10584-010-9845-2)

Matthes FE (1946) Report of Committee on Glaciers 1945 Eos27(2) 219ndash233

Meier MF (1961) Distribution and variations of glaciers in theUnited States exclusive of Alaska IASH Publ 54 (GeneralAssembly of Helsinki 1960 ndash Snow and Ice) 420ndash429

Mote PW and Salatheacute EP Jr (2010) Future climate in the PacificNorthwest Climatic Change 102(1ndash2) 29ndash50 (doi 101007s10584-010-9848-z)

Nolin AW and Daly C (2006) Mapping lsquoat riskrsquo snow in thePacific Northwest J Hydromet 7(5) 1164ndash1171 (doi 101175JHM5431)

PRISM Group (2006) United States average monthly and annualprecipitation 1971ndash2000 Oregon State University CorvallisOR httpprismoregonstateedu

Rasmussen LA and Conway H (2001) Estimating South CascadeGlacier (Washington USA) mass balance from a distant radio-sonde and comparison with Blue Glacier J Glaciol 47(159)579ndash588 (doi 103189172756501781831873)

Rasmussen LA and Wenger JM (2009) Upper-air model of summerbalance on Mount Rainier USA J Glaciol 55(192) 619ndash624(doi 103189002214309789471012)

Rasmussen LA Conway H and Hayes PS (2000) The accumulationregime of Blue Glacier USA 1914ndash96 J Glaciol 46(153)326ndash334 (doi 103189172756500781832846)

Riedel JR Burrows RA and Wenger JM (2008) Long-term monitoringof small glaciers at North Cascades National Park a prototypepark model for the North Coast and Cascades Network (NaturResour Rep NPSNCCNNRR-2008066) National Park ServiceFort Collins CO

Spicer RC (1986) Glaciers in the Olympic Mountains Washingtonpresent distribution and recent variations (PhD thesis Uni-versity of Washington)

Tabor RW and Cady WM (1978) Geologic map of the OlympicPeninsula Washington (Misc Inv Map 994) US GeologicalSurvey Reston VA

MS received 19 July 2014 and accepted in revised form 11 September 2014

Riedel and others Glaciers in the Olympic Mountains16

average annual total glacier summer contribution of71106m3we for the Hoh River the ice fractioncontributed 16 of total glacier runoff for MayndashSeptem-ber mostly late in the melt seasonEstimates of glacier volume loss and results from the

glacial runoff model highlight the importance of glaciers tolate-summer streamflow at the Hoh River gaging station nearForks (Fig 1) Comparing the streamflow data with the PDDmodel results glacial snow firn and ice contribute 359ndash397106m3we or 18ndash30 of total streamflow forAugustndashSeptember compared with 9ndash15 for the entiremelt seasonVolume change estimates also provide a means to assess

the glacial ice (not snow and firn) contribution to late-summer streamflow assuming that all the volume loss wasice that melted in August and September The averageAugustndashSeptember discharge in the lower Hoh River for thepast 23 years is 160 106m3 Based on the 23 year volumeloss estimate of average annual icemelt of 117 106m3wefor the Hoh basin glacier ice provided 7 of the dischargeon the lower Hoh River and 31 of the total glaciercontribution (including snow and firn) Although a smallfraction of total streamflow the glacier ice contributionoccurs when the contribution from snow and firn melt hasdeclined and summer rainfall is minimal and represents theaverage minimum reduction of AugustndashSeptember stream-flow that would occur in the lower Hoh River in the future ifglaciers disappeared The importance of this lsquofossilrsquo water ismagnified during summers when the previous winterrsquossnowfall is low and will become more critical in the futureas the snowpack declinesThe marked loss of glaciers on the Olympic Peninsula in

the past 30 years is largely a result of a 1degC rise in meanannual temperature (Rasmussen and Conway 2001) andillustrates how sensitive these relatively small thin low-elevation temperate glaciers are to climate change Thistemperature increase has directly increased the summermelt rate lengthened the melt season and decreased theduration of the accumulation season resulting in less wintersnow accumulation LaChapelle (1965) notes that theelevation of the freezing level is particularly important inearly fall as it controls how much precipitation falls as snowwhile Rasmussen and others (2000) suggest that springweather is a more important influence on ablation Coolcloudy conditions that often prevail in spring in thismaritime climate lead to lower melt rates at the time ofthe summer solstice particularly during the wet and coldphases of the Southern Oscillation and Pacific DecadalOscillation Recent climate warming appears stronger inwinter at Blue Glacier where average winter temperaturehas risen 3degC in the past half-century (Rasmussen andothers 2000) As a result average winter snow accumu-lation has decreased 500mm near 1500m at the glacierterminus since 1948 (Rasmussen and others 2000)Most of the glaciers on the Peninsula are currently not in

equilibrium with the present climate and are expected tocontinue to shrink in the near future even if accumulationincreases and temperature stops rising In the next severaldecades glaciers are likely to continue to disappear rapidlybased on projected future temperature increases of severaldegrees in the next 70 years Mote and Salatheacute (2010)estimate that mean annual temperature in Washington Statewill increase by at least 12degC by 2040 and at least 28degC by2080 Future temperature increases may be even higher near

the elevation of glaciers given positive feedback mechan-isms Further it is possible that the periodic increases inprecipitation associatedwith the cool wet phase of the PacificDecadal Oscillationmay havewaned in the past few decadeswith a warming climate (Josberger and others 2007)The preponderance of small glaciers remaining on the

Peninsula (145 of 184 are lt01 km2) means that most arevulnerable to melting away completely in the near future(Fig 2) The glaciers most threatened by future climatewarming are generally those that face south in the drier andwarmer climate prevalent on the eastern side of thePeninsula Glaciers on the northeast part of the mountainson Mount Deception McCartney Peak and Cameron Peakmay be the most threatened due to their isolation fromPacific moisture and climate model projections of highersummer potential evapotranspiration that could translate tohigher summer melt rates (Elsner and others 2010) Glacierson the northern side of the Bailey Range and in theheadwaters of the Queets and Elwha Rivers should fareslightly better because of their proximity to large valleys thatfunnel moisture from the Pacific Ocean However theiraccumulation zones are several hundred meters lower thanthose on the large glaciers of Mount Olympus If the climatewarms at the projected rates it is likely that within a centuryglaciers in the Olympic Mountains will be confined to theMount Olympus massifLoss of glaciers due to warming climate has several

significant implications for the Olympic Peninsula includ-ing loss of glacial habitat exposure of vast areas of looseglacial sand and gravel higher summer stream temperaturesand lower late-summer flows in most watersheds Decline inglacier meltwater production will exacerbate changes inaquatic habitat associated with a warming climate Mantuaand others (2010) identified summer temperature andstreamflow as critical physical habitat features for salmonLoss of glaciers will reduce summer streamflow andcontribute to higher summer stream temperatures to thedetriment of species such as the bull trout (Salvelinusconfluentus) (Halofsky and others 2011) Other ecosystemswill also be affected by the loss of glaciers For examplealpine food webs will be diminished by the loss of speciessuch as the ice worm which is preyed upon by rosy finchesand other alpine species

CONCLUSIONSThe glacier geospatial database we developed provides animportant benchmark for assessing glacier extent and glacialrunoff changes in the Olympic Mountains for the past30 years and into the future The combined area of allglaciers has decreased 34 in the past 30 years with ice lossaccelerating to a rate more than twice as fast as that from1900 to 1980 Only four of the 184 remaining glaciers aregt1 km2 in area Glaciers on the southern side of themountains at lower elevations and in the northeastern partof the Peninsula exhibited the greatest area and volume lossesand are the most likely to disappear in the next centuryGlacier decline in the past 30 years in the Olympics is greaterthan in the Cascades and southern Coast Mountains but iscomparable with Vancouver Island Based on ice volumelosses glacial contribution to summer streamflow hasdeclined 20 in the past 30 years but remains significantfor the Hoh River at 63ndash797106m3 andash1 Glaciers con-tribute lt5 to summer streamflow in all other large

Riedel and others Glaciers in the Olympic Mountains 15

watersheds in the Olympic Mountains Delivery of this coldfresh water to streams becomes more critical in the latesummer when rainfall is minimal and snowmelt hasdeclined On the lower Hoh River glacial ice contributes7 of the AugustndashSeptember streamflow which representsthe minimum reduction in flow that would occur if all theglaciers melted away Continued loss of glaciers will directlyimpact aquatic ecosystems through higher stream tempera-tures and lower summer base flows

ACKNOWLEDGEMENTSWe thank the US National Park Service Climate ChangeProgram for funding this research and Olympic and NorthCascades national parks and Portland State University for in-kind support Sharon Brady Roger Hoffman and SteveDorsch contributed GIS and cartographic expertise Finallywe want to acknowledge Richard Spicer for the valuablebaseline he created on the status of Olympic glaciers in theearly 1980s

REFERENCESAllen CR Kamb WB Meier MF and Sharp RP (1960) Structure ofthe lower Blue Glacier Washington J Geol 68(6) 601ndash625

Bolch T Menounos B andWheate R (2010) Landsat-based inventoryof glaciers in western Canada 1985ndash2005 Remote SensEnviron 114(1) 127ndash137 (doi 101016jrse200908015)

Conway H Rasmussen LA and Marshall HP (1999) Annual massbalance of Blue Glacier USA 1955ndash97 Geogr Ann A 81(4)509ndash520

Davey CA Redmond KT and Simeral DB (2006) Weather andclimate inventory National Park Service North Coast andCascades Network (National Resource Technical Report NPSNCCNNRTR-2006010) National Resource Program CenterFort Collins CO

De Woul M and Hock R (2005) Static mass-balance sensitivity ofArctic glaciers and ice caps using a degree-day approach AnnGlaciol 42 217ndash224 (doi 103189172756405781813096)

Elsner MM and 8 others (2010) Implications of 21st-century climatechange for the hydrology of Washington State Climatic Change102(1ndash2) 225ndash260 (doi 101007s10584-010-9855-0)

Granshaw FD and Fountain AG (2006) Glacier change (1958ndash1998) in the North Cascades National Park ComplexWashington USA J Glaciol 52(177) 251ndash256 (doi 103189172756506781828782)

Halofsky JE Peterson DL OrsquoHalloran KA and Hoffman CH eds(2011) Adapting to climate change at Olympic National Forestand Olympic National Park (Gen Tech Rep PNW-GTR-844)Pacific Northwest Research Station US Department of Agricul-ture Portland OR httpwwwtreesearchfsfeduspubs38702

Heroux P and Kouba J (2001) GPS precise point positioning usingIGS orbit products Phys Chem Earth 26(6ndash8) 573ndash578

Heusser CJ (1957) Variations of Blue Hoh and White Glaciersduring recent centuries Arctic 10(3) 139ndash150 (doi 1014430arctic3761)

Hodge SM (1974) Variations in the sliding of a temperate glacierJ Glaciol 13(69) 349ndash369

Hodson A and 7 others (2008) Glacial ecosystems Ecol Monogr78(1) 41ndash67 (doi 10189007-01871)

Hubley RC (1956) Glaciers of the Washington Cascade andOlympic Mountains their present activity and its relation tolocal climatic trends J Glaciol 2(19) 669ndash674 (doi 103189002214356793701938)

Josberger EG Bidlake WR March RS and Kennedy BW (2007)Glacier mass-balance fluctuations in the Pacific Northwest andAlaska USA Ann Glaciol 46 291ndash296 (doi 103189172756407782871314)

LaChapelle ER (1965) The mass budget of Blue Glacier Washing-ton J Glaciol 5(41) 609ndash623

Malcomb NL and Wiles GC (2013) Tree-ring-based reconstructionsof North American glacier mass balance through the Little IceAge contemporary warming transition Quat Res 79(2)123ndash137 (doi 101016jyqres201211005)

Mantua NJ Hare SR Zhang Y Wallace JM and Francis RC (1997) APacific interdecadal climate oscillation with impacts on salmonproduction Bull Am Meteorol Soc 78(6) 1069ndash1079 (doi1011751520-0477(1997)078lt1069APICOWgt20CO2)

Mantua N Tohver I and Hamlet A (2010) Climate change impactson streamflow extremes and summertime stream temperatureand their possible consequences for freshwater salmon habitatin Washington State Climatic Change 102(1ndash2) 187ndash223 (doi101007s10584-010-9845-2)

Matthes FE (1946) Report of Committee on Glaciers 1945 Eos27(2) 219ndash233

Meier MF (1961) Distribution and variations of glaciers in theUnited States exclusive of Alaska IASH Publ 54 (GeneralAssembly of Helsinki 1960 ndash Snow and Ice) 420ndash429

Mote PW and Salatheacute EP Jr (2010) Future climate in the PacificNorthwest Climatic Change 102(1ndash2) 29ndash50 (doi 101007s10584-010-9848-z)

Nolin AW and Daly C (2006) Mapping lsquoat riskrsquo snow in thePacific Northwest J Hydromet 7(5) 1164ndash1171 (doi 101175JHM5431)

PRISM Group (2006) United States average monthly and annualprecipitation 1971ndash2000 Oregon State University CorvallisOR httpprismoregonstateedu

Rasmussen LA and Conway H (2001) Estimating South CascadeGlacier (Washington USA) mass balance from a distant radio-sonde and comparison with Blue Glacier J Glaciol 47(159)579ndash588 (doi 103189172756501781831873)

Rasmussen LA and Wenger JM (2009) Upper-air model of summerbalance on Mount Rainier USA J Glaciol 55(192) 619ndash624(doi 103189002214309789471012)

Rasmussen LA Conway H and Hayes PS (2000) The accumulationregime of Blue Glacier USA 1914ndash96 J Glaciol 46(153)326ndash334 (doi 103189172756500781832846)

Riedel JR Burrows RA and Wenger JM (2008) Long-term monitoringof small glaciers at North Cascades National Park a prototypepark model for the North Coast and Cascades Network (NaturResour Rep NPSNCCNNRR-2008066) National Park ServiceFort Collins CO

Spicer RC (1986) Glaciers in the Olympic Mountains Washingtonpresent distribution and recent variations (PhD thesis Uni-versity of Washington)

Tabor RW and Cady WM (1978) Geologic map of the OlympicPeninsula Washington (Misc Inv Map 994) US GeologicalSurvey Reston VA

MS received 19 July 2014 and accepted in revised form 11 September 2014

Riedel and others Glaciers in the Olympic Mountains16

watersheds in the Olympic Mountains Delivery of this coldfresh water to streams becomes more critical in the latesummer when rainfall is minimal and snowmelt hasdeclined On the lower Hoh River glacial ice contributes7 of the AugustndashSeptember streamflow which representsthe minimum reduction in flow that would occur if all theglaciers melted away Continued loss of glaciers will directlyimpact aquatic ecosystems through higher stream tempera-tures and lower summer base flows

ACKNOWLEDGEMENTSWe thank the US National Park Service Climate ChangeProgram for funding this research and Olympic and NorthCascades national parks and Portland State University for in-kind support Sharon Brady Roger Hoffman and SteveDorsch contributed GIS and cartographic expertise Finallywe want to acknowledge Richard Spicer for the valuablebaseline he created on the status of Olympic glaciers in theearly 1980s

REFERENCESAllen CR Kamb WB Meier MF and Sharp RP (1960) Structure ofthe lower Blue Glacier Washington J Geol 68(6) 601ndash625

Bolch T Menounos B andWheate R (2010) Landsat-based inventoryof glaciers in western Canada 1985ndash2005 Remote SensEnviron 114(1) 127ndash137 (doi 101016jrse200908015)

Conway H Rasmussen LA and Marshall HP (1999) Annual massbalance of Blue Glacier USA 1955ndash97 Geogr Ann A 81(4)509ndash520

Davey CA Redmond KT and Simeral DB (2006) Weather andclimate inventory National Park Service North Coast andCascades Network (National Resource Technical Report NPSNCCNNRTR-2006010) National Resource Program CenterFort Collins CO

De Woul M and Hock R (2005) Static mass-balance sensitivity ofArctic glaciers and ice caps using a degree-day approach AnnGlaciol 42 217ndash224 (doi 103189172756405781813096)

Elsner MM and 8 others (2010) Implications of 21st-century climatechange for the hydrology of Washington State Climatic Change102(1ndash2) 225ndash260 (doi 101007s10584-010-9855-0)

Granshaw FD and Fountain AG (2006) Glacier change (1958ndash1998) in the North Cascades National Park ComplexWashington USA J Glaciol 52(177) 251ndash256 (doi 103189172756506781828782)

Halofsky JE Peterson DL OrsquoHalloran KA and Hoffman CH eds(2011) Adapting to climate change at Olympic National Forestand Olympic National Park (Gen Tech Rep PNW-GTR-844)Pacific Northwest Research Station US Department of Agricul-ture Portland OR httpwwwtreesearchfsfeduspubs38702

Heroux P and Kouba J (2001) GPS precise point positioning usingIGS orbit products Phys Chem Earth 26(6ndash8) 573ndash578

Heusser CJ (1957) Variations of Blue Hoh and White Glaciersduring recent centuries Arctic 10(3) 139ndash150 (doi 1014430arctic3761)

Hodge SM (1974) Variations in the sliding of a temperate glacierJ Glaciol 13(69) 349ndash369

Hodson A and 7 others (2008) Glacial ecosystems Ecol Monogr78(1) 41ndash67 (doi 10189007-01871)

Hubley RC (1956) Glaciers of the Washington Cascade andOlympic Mountains their present activity and its relation tolocal climatic trends J Glaciol 2(19) 669ndash674 (doi 103189002214356793701938)

Josberger EG Bidlake WR March RS and Kennedy BW (2007)Glacier mass-balance fluctuations in the Pacific Northwest andAlaska USA Ann Glaciol 46 291ndash296 (doi 103189172756407782871314)

LaChapelle ER (1965) The mass budget of Blue Glacier Washing-ton J Glaciol 5(41) 609ndash623

Malcomb NL and Wiles GC (2013) Tree-ring-based reconstructionsof North American glacier mass balance through the Little IceAge contemporary warming transition Quat Res 79(2)123ndash137 (doi 101016jyqres201211005)

Mantua NJ Hare SR Zhang Y Wallace JM and Francis RC (1997) APacific interdecadal climate oscillation with impacts on salmonproduction Bull Am Meteorol Soc 78(6) 1069ndash1079 (doi1011751520-0477(1997)078lt1069APICOWgt20CO2)

Mantua N Tohver I and Hamlet A (2010) Climate change impactson streamflow extremes and summertime stream temperatureand their possible consequences for freshwater salmon habitatin Washington State Climatic Change 102(1ndash2) 187ndash223 (doi101007s10584-010-9845-2)

Matthes FE (1946) Report of Committee on Glaciers 1945 Eos27(2) 219ndash233

Meier MF (1961) Distribution and variations of glaciers in theUnited States exclusive of Alaska IASH Publ 54 (GeneralAssembly of Helsinki 1960 ndash Snow and Ice) 420ndash429

Mote PW and Salatheacute EP Jr (2010) Future climate in the PacificNorthwest Climatic Change 102(1ndash2) 29ndash50 (doi 101007s10584-010-9848-z)

Nolin AW and Daly C (2006) Mapping lsquoat riskrsquo snow in thePacific Northwest J Hydromet 7(5) 1164ndash1171 (doi 101175JHM5431)

PRISM Group (2006) United States average monthly and annualprecipitation 1971ndash2000 Oregon State University CorvallisOR httpprismoregonstateedu

Rasmussen LA and Conway H (2001) Estimating South CascadeGlacier (Washington USA) mass balance from a distant radio-sonde and comparison with Blue Glacier J Glaciol 47(159)579ndash588 (doi 103189172756501781831873)

Rasmussen LA and Wenger JM (2009) Upper-air model of summerbalance on Mount Rainier USA J Glaciol 55(192) 619ndash624(doi 103189002214309789471012)

Rasmussen LA Conway H and Hayes PS (2000) The accumulationregime of Blue Glacier USA 1914ndash96 J Glaciol 46(153)326ndash334 (doi 103189172756500781832846)

Riedel JR Burrows RA and Wenger JM (2008) Long-term monitoringof small glaciers at North Cascades National Park a prototypepark model for the North Coast and Cascades Network (NaturResour Rep NPSNCCNNRR-2008066) National Park ServiceFort Collins CO

Spicer RC (1986) Glaciers in the Olympic Mountains Washingtonpresent distribution and recent variations (PhD thesis Uni-versity of Washington)

Tabor RW and Cady WM (1978) Geologic map of the OlympicPeninsula Washington (Misc Inv Map 994) US GeologicalSurvey Reston VA

MS received 19 July 2014 and accepted in revised form 11 September 2014

Riedel and others Glaciers in the Olympic Mountains16