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%

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

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)

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

-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

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

-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

-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

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.

-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

-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