UMass Amherst GEO-SCI 563 - Equilibrium Line Altitudes & Mass Balance

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1!Christopher Mira, Class of 2004 in Alaska! Equilibrium Line Altitudes & Mass Balance!Composite ASTER image showing retreat of the Gangotri Glacier terminus in the Garhwal Himalaya since 1780. Glacier retreat boundaries courtesy of the Land Processes Distributed Active Archive Center. http://nsidc.org/data/g10002.html!Mass Balance!• describes input/output relationship of snow, firn and ice.!• difference between accumulation and ablation is the net mass balance!• Balance year is interval between time of minimum mass balance one year to the mimimum the next year!Equilibrium means glacier has to transfer mass from above to below the ELA; or net retreat or advance with negative or positive mass balance. !Economy of Glaciers!Regional Climate!Energy balance!Net Mass Balance!Glacial response time!Geologic Record!Landforms/deposts!Quaternary Studies!2!From Bill Locke, Bozeman!How does a glacier’s morphology and elevation profile influence response time?!= f (length of the flow path and rate of flow)!Glacial response time!What controls these parameters? !Make a list……! At any point on the glacier"bn = bw + bs!• Where!bn= net balance!bw= winter!bs = summer balance!-may be + or - depending on the yearly conditions!Lemon Creek, Cascades!Columbia Glacier, Cascades!Miller and Pelto, 1999!3!In the field - dig snow pits!• Stainless cylinders!• 500 cm 3!• Calculate volume of snow accumulated in meters of H2O equivalent!Back lit!bn x area = balance (Bnet)!Steady state glacier = ~65% accum area!What are the consequences of a rise or fall of the ELA?!(-) Ablation! (+) Accumulation!Elevation !bw!bs!bn!0!Area km2!ELA!Equilibrium Line Altitude (ELA)!!controlled by !1. temperature!2. ! latitude!3. ! altitude!4. ! aspect!5. ! continentality!Elevation -->!ELA south facing!ELA north facing!Rainbow Glacier, Cascades, 1979!Rainbow Glacier, Cascades, 1988!4!http://www.nichols.edu/departments/glacier/cache.htm!CACHE COL GLACIER 1916!1966!SOUTH CASCADE GLACIER CHANGES THROUGH TIME 1960!1979!1991!http://www.nichols.edu/departments/glacier/index.html!1937 "Bradford Washburn!2006 "David Arnold!http://www.uaf.edu/water/faculty/nolan/mccall/index.htm!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).!5!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!6!http://instaar.colorado.edu/QGISL/paleo_ela.html! Glacier Morphology -shape, elevation range!No Topographic Control!!Ice Sheets!!Ice caps!!Highland Ice caps!Topographic Controlled!!Valley Glaciers!!Cirque Glaciers!!Sidewall Glaciers!Spreading Ice Bodies!!Ice Shelves!!Ice Streams!!Piedmont Glaciers!Response time to change in mass balance will vary !!f(length flow line, velocity of ice)!Antarctica in the world7!Alley et al, 2007; Alley et al, in review!Valley Glaciers!ELA at time 0!ELA at time 1!Cirque Glaciers!ELA at time 0!ELA at time 1!8!Piedmont Glaciers - Ellesmere Island (Evans)!R. Powell, NIU, !9!easterbrook!Columbia Time Lapse.mpg Tad Pfeffer!USGS !10!Ice Streams:!Zones of fast flow!Floating Ice shelves !Angelika Humbert http://environmentalresearchweb.org/cws/article/opinion/36126!ANDRILL!Drilling into the sediments beneath the Ross Ice shelf!Andrill.org!Glaciology homework!• See hand outs


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UMass Amherst GEO-SCI 563 - Equilibrium Line Altitudes & Mass Balance

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