snow / ice / climate i energy and mass “the essence of glaciology” “the essence of...
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Snow / Ice / Climate ISnow / Ice / Climate IEnergy and MassEnergy and Mass
““The Essence of Glaciology”The Essence of Glaciology” Processes of:Processes of:
accumulation – precipitationaccumulation – precipitation ablation – melt, sublimation, calvingablation – melt, sublimation, calving
wind & avalanche can affect eitherwind & avalanche can affect either
Transformation of snow Transformation of snow firn firn ice ice takes time – depends on mass, temperature, takes time – depends on mass, temperature,
etcetc Balance of acc & abl Balance of acc & abl energy budget energy budget
Energy and MassEnergy and Mass The annual The annual energy budgetenergy budget of a of a
glacier is the sum of inputs minus the glacier is the sum of inputs minus the sum of outputs ± changes in storage.sum of outputs ± changes in storage.
The annual The annual mass budgetmass budget of a glacier of a glacier is the is the specificspecific (at-a-point) budget (at-a-point) budget times the area to which it applies, times the area to which it applies, summed across the entire glacier:summed across the entire glacier:
BBnn = = ΣΣ(1-i) (1-i) (b(bnini x A x Aii))
Energy BudgetEnergy Budget
INPUTSINPUTS OUTPUTSOUTPUTS Solar (short-wave) radiationSolar (short-wave) radiation Reflection [albedo]Reflection [albedo] Long-wave radiationLong-wave radiation Long-waveLong-wave Conduction (air)Conduction (air) ConductionConduction Conduction (ground)Conduction (ground) Convection (air) [sensible]Convection (air) [sensible] ConvectionConvection Latent heatLatent heat Latent heatLatent heat
Condensation, freezingCondensation, freezing Evaporation, melt Evaporation, melt ?? energy from sliding/friction, water flow ??? energy from sliding/friction, water flow ?
Energy Balance?Energy Balance?
Varies with position on a glacier, time Varies with position on a glacier, time of day, season, cloud cover, wind …of day, season, cloud cover, wind …
Convection often estimated by Convection often estimated by difference (assuming balance)difference (assuming balance)
““Balance” implies no change in Balance” implies no change in storage (temperature)storage (temperature)
Studies are rare because of difficulty.Studies are rare because of difficulty.
Examples of Energy Examples of Energy BudgetsBudgets
SpecificSpecific Mass Budget – Mass Budget – StratigraphicStratigraphic
Most commonly, End Of Summer to EOSMost commonly, End Of Summer to EOS Uses old snow / firn / ice as a markerUses old snow / firn / ice as a marker
Specific Mass Budget Specific Mass Budget ProtocolsProtocols
Stakes = aluminum conduit melted into iceStakes = aluminum conduit melted into ice Winter balance (bWinter balance (bww))
bbww = depth of snow x density (= “water = depth of snow x density (= “water equivalent”)equivalent”)
Summer balance (bSummer balance (bSS)) bbss = b = bn n – b– bww (accumulation area) (accumulation area) bbss = b = bww + lost ice times 0.917 (ablation area) + lost ice times 0.917 (ablation area)
Firn line, bFirn line, bnn = 0 = 0 Equilibrium line altitude (ELA), bEquilibrium line altitude (ELA), bnn = 0 = 0
Specific Mass Budget Specific Mass Budget TrendsTrends
Accumulation often Accumulation often increases slightly increases slightly with increasing with increasing altitude above the altitude above the ELA.ELA.
@ ELA, b@ ELA, bnn = 0 = 0 Ablation increases Ablation increases
rapidly with rapidly with decreasing altitude decreasing altitude below the ELA.below the ELA. (+)(-)
Mass Exchange (m H2O)
Summer budget (bs)
Netbudget
(bn)
Winterbudget
(bw)
Specific Mass Budget with Specific Mass Budget with ClimateClimate
““Accumulation gradient” Accumulation gradient” = = ΔΔmassmassaccacc//ΔΔelevationelevation= mm= mmH2OH2O/m/melevationelevation
““Ablation gradient”Ablation gradient”= = ΔΔmassmassabl abl //ΔΔelevationelevation= mm= mmH2OH2O/m/melevationelevation
““Activity gradient”Activity gradient”= gradient @ ELA= gradient @ ELA
Maritime = high Maritime = high activity gradientactivity gradient
Continental = low A.G.Continental = low A.G.
Specific Mass Budget with Specific Mass Budget with ClimateClimate
““Accumulation gradient” Accumulation gradient” = = ΔΔmassmassaccacc//ΔΔelevationelevation= mm= mmH2OH2O/m/melevationelevation
““Ablation gradient”Ablation gradient”= = ΔΔmassmassabl abl //ΔΔelevationelevation= mm= mmH2OH2O/m/melevationelevation
““Activity gradient”Activity gradient”= gradient @ ELA= gradient @ ELA
Maritime = high Maritime = high activity gradientactivity gradient
Continental = low A.G.Continental = low A.G.
Why is the ablation gradient >>Why is the ablation gradient >>the accumulation gradient?the accumulation gradient?
Accumulation = Accumulation = f (precip)f (precip)
Ablation = f (melt)Ablation = f (melt) Melt = f (T, albedo)Melt = f (T, albedo)
snow ~ 0.9snow ~ 0.9 ice ~0.5ice ~0.5 debris ~ 0.2, BUT debris ~ 0.2, BUT
can also insulatecan also insulate
other reasons?other reasons?
Specific Mass Budget with Specific Mass Budget with TimeTime
Remarkably Remarkably consistent!consistent!
Shape = Shape = f f
(climate)(climate) Position = Position = f f
(weather)(weather)
Snow / Ice / Climate IISnow / Ice / Climate IISnowlines – Space and TimeSnowlines – Space and Time
Snowlines and their many definitionsSnowlines and their many definitions Estimating bEstimating bnn = 0 = 0
Contemporary controls on snowlinesContemporary controls on snowlines local climate / weather and topographylocal climate / weather and topography
Spatial variabilitySpatial variability Temporal variabilityTemporal variability Pleistocene snowlines and climatesPleistocene snowlines and climates
Snowlines I – Cirque FloorsSnowlines I – Cirque Floors
Permanent snowfields? No – glaciers!Permanent snowfields? No – glaciers! Cirque floor elevationsCirque floor elevations
Maximum erosion at minimum sizeMaximum erosion at minimum size Problems = size, timingProblems = size, timing
Snowlines II – Lateral Snowlines II – Lateral MorainesMoraines
Highest laterals = initiation of depositionHighest laterals = initiation of deposition[discuss more with “glacier flow” ?][discuss more with “glacier flow” ?] Problem = postglacial slope erosion/removalProblem = postglacial slope erosion/removal
Snowlines III –Snowlines III –Glaciation ThresholdGlaciation Threshold
True True “snowline”“snowline”
Problems = Problems = manymany Area?Area? Topography?Topography? Summits > Summits >
glacier glacier elevationselevations
Snowlines IV – THARSnowlines IV – THAR
Toe-headwall altitude ratioToe-headwall altitude ratio Requires reconstructionRequires reconstruction Assumes known “correct” ratio – 40%?Assumes known “correct” ratio – 40%?
Snowlines V – AARSnowlines V – AAR Accumulation Accumulation
area ratioarea ratio Requires Requires
complete complete reconstructionreconstruction
Assumes Assumes correct correct ratio .55–.60–.6ratio .55–.60–.65 ?5 ?
[topo map method][topo map method]
Snowline ComparisonsSnowline Comparisons
Meierding Meierding (1982)(1982) CO Front RangeCO Front Range tried many tried many
ratiosratios
Locke (1990)Locke (1990) MontanaMontana small glacierssmall glaciers s.d. ~ 350 ms.d. ~ 350 m
CF (n=12)CF (n=12) 3161 m3161 m
LM (45)LM (45) 31883188
GT (13)GT (13) 33883388
THAR (24)THAR (24) 3161 3161 (40%)(40%)
AAR (24)AAR (24) 3163 3163 (65%)(65%)CF CF
(n=400)(n=400)2347 m2347 m
LM (321)LM (321) 21212121
THAR THAR (330)(330)
2355 2355 (40%)(40%)
AAR (264)AAR (264) 2353 2353 (65%)(65%)
ELA = ELA = representative?representative?
Many studies say Many studies say so!so! e.g., Sutherland e.g., Sutherland
(1984)(1984) ELA balance ELA balance
represents represents averageaverage winter balance for winter balance for entire glacierentire glacier
Measure once – use a Measure once – use a lot!lot!
Glacial Glacial ClimatesClimates
Glaciers exist Glaciers exist only in a only in a narrow range narrow range of climatesof climates = f(winter = f(winter
ppt and ppt and summer T)summer T)
= f(P, T, and = f(P, T, and continentalitcontinentalityy
Glacial Glacial ClimatesClimates
Controls on Snowlines I – Controls on Snowlines I – LatitudeLatitude
Latitude Latitude ≈ temperature (treeline)≈ temperature (treeline) highest near equatorhighest near equator
Latitude ≠ precipitation (snowlines)Latitude ≠ precipitation (snowlines) saddle near equatorsaddle near equator
Weak gradients (<1 m/km)Weak gradients (<1 m/km)
Controls II – Controls II – ContinentaliContinentali
tyty Lowest near Lowest near
moisture moisture sourcesource
Higher inlandHigher inland Strong Strong
gradientsgradients up to 10 up to 10
m/kmm/km
No Hem No Hem GlaciersGlaciers
Latitude?Latitude? ContinentaliContinentali
tyty Ocean Ocean
currentscurrents Local Local
precipitatioprecipitationn
Temporal ResolutionTemporal Resolution
Glaciers respond at annual to decadal Glaciers respond at annual to decadal scalesscales
Temporal InconsistencyTemporal Inconsistency
Not all glaciers respond similarlyNot all glaciers respond similarly Not even glaciers in the same region!Not even glaciers in the same region!
Temporal InconsistencyTemporal Inconsistency
Not all glaciers respond similarlyNot all glaciers respond similarly Not even glaciers in the same region!Not even glaciers in the same region!
PleistocenePleistoceneSnowlinesSnowlines
II
SierraSierraNevadaNevada Note effects ofNote effects of
subtropical high &subtropical high &rain shadowrain shadow
Wahrhaftig and Birman, 1965
Pleistocene Pleistocene Snowlines Snowlines
IIII US WestUS West
(Porter et (Porter et al. 1983)al. 1983)
Effects of:Effects of: SubT HighSubT High WesterliesWesterlies Storm Storm
trackstracks OrographyOrography
Pleistocene Pleistocene Snowlines Snowlines
IIII
Montana Montana Climate & Climate & GlaciersGlaciers
GlaciersGlaciers Inferred air Inferred air
mass mass movementmovement
ResidualsResiduals Inferred Inferred
causescauses
MT/ID MT/ID PaleoclimatPaleoclimat
ee Complex Complex
pattern!pattern! More More
detailed detailed than modern than modern weather weather stations stations andand SNOTEL SNOTEL sites!sites!
Spatial Spatial ResolutionResolution
Humlum (1985)Humlum (1985) West GreenlandWest Greenland Local data are Local data are
consistentconsistent Needs no Needs no
smoothingsmoothing High resolution!High resolution!