How representative are benchmark glaciers?
description
Transcript of How representative are benchmark glaciers?
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
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
Dome PeakJohn Scurlock
MethodsMethods
Aerial Aerial PhotosPhotos
Historic Historic MapsMaps
GIS DatabaseGIS Database
Repeat Repeat PhotograpPhotograp
hyhy
GriddedGriddedClimate Climate
DataData
GlacierInventory
(24K)
Lyell Glacier
www.glaciers.us
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
What is a representative glacier?
•Topographic characteristics? area slope elevation aspect
•Location? (any glacier will do)
•Similar climatic response?
Pugh Glacier John Scurlock
Topographic Characteristics
Benchmark GlacierIndex Glaciers
0%
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0 1 2 3 4 5 6 7
1998 Area (km2)
Fra
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s sm
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rGlacier Area
Topographic Characteristics
Elevation, Area, Slope
Benchmark GlacierIndex GlaciersRemotely Sensed Glaciers
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Area (km2)
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leva
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Mean Slope (deg)
Mean E
levation (m)
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Number of Glaciers and Area Change
Area Changes
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Glacier Area (km2)
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Uncertainty
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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1960 1970 1980 1990 2000 2010
Year
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t M
as
s B
ala
nc
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m w
eq
) South Cascade
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Noisy
North Klawatti
Sandlee
)
Mass Balance Variations
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1950 1960 1970 1980 1990 2000 2010
Year
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mu
lati
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ss
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lan
ce
(m
)
South Cascade
Noisy Creek
Silver Creek
North Klawatti
Sandalee
Blue Glacier
( m
weq
)
Cummulative Mass Change
Mass Balance Variations
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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Glacier Slope (deg)
Are
a C
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Area Changes
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1000 1500 2000 2500 3000
Glacier Elevation (m)
Are
a C
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ge,
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