how representative are benchmark glaciers?
DESCRIPTION
South Cascade Glacier, WA 1960 USGS 2004 John Scurlock. How representative are benchmark glaciers? Andrew G. Fountain, Mathew Hoffman, Frank Granshaw, Portland State Univ Jon Riedel, National Park Service. - PowerPoint PPT PresentationTRANSCRIPT
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South Cascade Glacier, WA 1960 USGS 2004 John Scurlock
How representative are benchmark glaciers?
Andrew G. Fountain, Mathew Hoffman, Frank Granshaw, Portland State UnivJon Riedel, National Park Service
South Cascade Glacier
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Benchmark Glaciers of the US
Alaska Gulkana -- Alaska Range
Wolverine -- Kenai Range
Continental US South Cascade -- Cascade and Olympic ranges of Washington and Oregon
Our report here on the region around South Cascade Glacier
Meier, 1985
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Dome PeakJohn Scurlock
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MethodsMethods
Aerial Aerial PhotosPhotos
Historic Historic MapsMaps
GIS DatabaseGIS Database
Repeat Repeat PhotograpPhotograp
hyhy
GriddedGriddedClimate Climate
DataData
GlacierInventory
(24K)
Lyell Glacier
www.glaciers.us
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Park Complex
South Cascade Glacier• Original IHD glacier• Monitored since 1959• US Geological Survey• Mass & Water Balance
4 Index Glaciers• Monitored since 1992• Nat. Park Service• Mass balance only
316 Remotely-sensed • 1958, 1998• Area only
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What is a representative glacier?
•Topographic characteristics? area slope elevation aspect
•Location? (any glacier will do)
•Similar climatic response?
Pugh Glacier John Scurlock
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Topographic Characteristics
Benchmark GlacierIndex Glaciers
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
0 1 2 3 4 5 6 7
1998 Area (km2)
Fra
ctio
n o
f gla
cier
s sm
alle
rGlacier Area
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Topographic Characteristics
Elevation, Area, Slope
Benchmark GlacierIndex GlaciersRemotely Sensed Glaciers
0
500
1000
1500
2000
2500
3000
0 2 4 6
Area (km2)
Mea
n E
leva
tion
(m)
0
500
1000
1500
2000
2500
3000
0 20 40 60 80
Mean Slope (deg)
Mean E
levation (m)
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0 50 100 150 200
-60%
-50%
-40%
-30%
-20%
-10%
0%
10%
Are
a C
ha
ng
e
Number
10%
0%
-10%
-20%
-30%
-40%
-50%
-60%
-70%
Fra
ctio
nal
Are
a C
han
ge
Number of Glaciers and Area Change
Area Changes
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-100%
-80%
-60%
-40%
-20%
0%
20%
0 1 2 3 4 5 6 7 8
Glacier Area (km2)
Fra
ctio
nal
Are
a C
han
ge,
195
8-19
98Area Changes
Uncertainty
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From this cursory analysis, both
topographic characteristics
area change
suggest that the benchmark glacier is not representative of the region. And the other index glaciers may be better.
Furthermore, the use of the benchmark glacier would over estimate the glacier change in this region.
John Scurlock
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-3
-2
-1
0
1
2
1960 1970 1980 1990 2000 2010
Year
Ne
t M
as
s B
ala
nc
e (
m w
eq
) South Cascade
Silver
Noisy
North Klawatti
Sandlee
)
Mass Balance Variations
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-30
-25
-20
-15
-10
-5
0
5
10
1950 1960 1970 1980 1990 2000 2010
Year
Cu
mu
lati
ve
Ma
ss
Ba
lan
ce
(m
)
South Cascade
Noisy Creek
Silver Creek
North Klawatti
Sandalee
Blue Glacier
( m
weq
)
Cummulative Mass Change
Mass Balance Variations
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Conclusions
If the example from the North Cascades is typical, probably most benchmark glaciers are not rep- resentative of the regional glaciers, due to the necessary selection criteria (IHD).
- different topographic characteristics - different area/volume changes
Year to year variations in net mass balance are well represented (probably by any glacier). But small differences between glaciers yield large cummulative differences.
The issue is how to transfer mass balance variations from one glacier to another to more accurately depict variations across the region.
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-60%
-50%
-40%
-30%
-20%
-10%
0%
10%
20%
0 10 20 30 40 50 60 70
Glacier Slope (deg)
Are
a C
han
ge,
195
8-19
98
Area Changes
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-60%
-50%
-40%
-30%
-20%
-10%
0%
10%
20%
1000 1500 2000 2500 3000
Glacier Elevation (m)
Are
a C
han
ge,
195
8-19
98