Equilibrium Line Altitudes & Mass Balance

Home , Cirque, Glacier morphology, Moraine

Equilibrium Line Altitudes Christopher Mira, Class of 2004 in Alaska & Mass Balance

Mass Balance Economy of Glaciers •describes input/output relationship of snow, ﬁrn Regional Energy balance and ice. Climate •difference between Net Mass accumulation and ablation Balance is the net mass balance •Balance year is interval between time of minimum Quaternary mass balance one year to Composite ASTER image showing retreat of the Studies Gangotri Glacier terminus in the Garhwal Glacial the mimimum the next year Himalaya since 1780. Glacier retreat boundaries courtesy of the Land Processes Distributed Active response Archive Center. http://nsidc.org/data/ g10002.html Geologic Record time Equilibrium means glacier has to transfer mass from above to Landforms/deposts below the ELA; or net retreat or advance with negative or positive mass balance.

1 How does a glacier’s Glacial response time morphology and elevation profile = f (length of the flow path and rate of flow) influence response time? What controls these parameters?

Make a list……

From Bill Locke, Bozeman

At any point on the glacier

bn = bw + bs

• Where

bn= net balance

bw= winter

bs = summer balance Columbia Glacier, Cascades -may be + or - depending on the yearly conditions Lemon Creek, Cascades

Miller and Pelto, 1999

2 bn bs In the ﬁeld - dig snow pits bw

Elevation ELA

(-) Ablation 0 (+) Accumulation Area km2

• Stainless cylinders Back lit b x area = balance (B ) • 500 cm 3 n net Steady state glacier = ~65% accum area • Calculate volume of What are the consequences of a rise or fall of the ELA? snow accumulated in

meters of H2O equivalent

Equilibrium Line Altitude (ELA) controlled by 1. temperature 2. latitude 3. altitude 4. aspect 5. continentality

ELA south facing

ELA north facing

Elevation --> Rainbow Glacier, Cascades, 1979 Rainbow Glacier, Cascades, 1988

3 SOUTH CASCADE GLACIER CHANGES THROUGH TIME CACHE COL GLACIER

1960

1979 1916 1966 1991 http://www.nichols.edu/departments/glacier/cache.htm http://www.nichols.edu/departments/glacier/index.html

McCall Glacier, located in Arctic National Wildlife Refuge Alaska, has the longest history of scientiﬁc observation for any U.S. Arctic Glacier. Observations began with International Geophysical Year in 1957-58 (pre-dating the Refuge). 1937 2006 Bradford Washburn David Arnold http://www.uaf.edu/water/faculty/nolan/mccall/index.htm

4 Reconstructing Paleo ELAs pg. 83-85 B&E

• Cirque Floor Elevations – Why is this a bad idea? • Toe to Headwall Area Ratio (THAR) – Median elevation of 0.5, 0.6, 0.4 as ELA • Maximum altitude of Lateral Moraine – Lateral moraines only below ELA – Problem of preservation; does it = steady state? • Area Accumulation Ratio (AAR) – Ratio of Accumulation Area/total area – Assume steady at ~0.65 +/- 0.5; < .5 = neg mass balance and >0.7 is positive mass balance.

Athabasca Glacier Canada Note lateral moraines

5 Glacier Morphology -shape, elevation range

No Topographic Control Ice Sheets Ice caps Highland Ice caps Topographic Controlled Response time to Valley Glaciers change in mass balance Cirque Glaciers will vary Sidewall Glaciers Spreading Ice Bodies f(length ﬂow line, velocity of ice) Ice Shelves Ice Streams Piedmont Glaciers http://instaar.colorado.edu/QGISL/paleo_ela.html

Antarctica in the world

6 Valley Glaciers

ELA at time 1

ELA at time 0

Alley et al, 2007; Alley et al, in review

Cirque Glaciers

ELA at time 1

ELA at time 0

7 Piedmont Glaciers - Ellesmere Island (Evans)

R. Powell, NIU,

8 Columbia Time Lapse.mpg

easterbrook

Tad Pfeffer USGS

9 Ice Floating Ice shelves Streams: Zones of fast ﬂow

Angelika Humbert http://environmentalresearchweb.org/cws/article/opinion/36126

ANDRILL Glaciology homework Drilling into the sediments beneath the Ross • See hand outs Ice shelf

Andrill.org