# Mass Balance: Theory and Application Steve Wilson South Cascade Glacier - 1928.

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Mass Balance: Theory and Application Steve Wilson South Cascade Glacier - 1928

Outline Basics Methods – Stratigraphic Annual – Hydrologic – Photogrammetric – Flux Gate (Ice Sheets) South Cascade Glacier – Comparative Methods – Dynamics

Mass Balance Basics “Wavering between the profit and the loss.” -T.S. Eliot, Ash Wednesday The bank account model B n vs. b n Measurements made twice a year Net balance (~October 1) Winter balance (~May 1) Summer balance (calculate)

Stratigraphic Method Similar to annual mass balance method Direct measurement of accumulation and ablation Very labor intensive

Terminology Stratigraphic balance vs. annual balance Mass balance is a time transgressive process using time dependent variables and methods from Mayo et al. (1972)

Measurement Tools Selecting representative points Mapping transient snow line Measurement tools Surface area estimations R. Hock (2008) Calculated mass balance can depend on glacier outlines, number of measurements, human error, and other factors.

Measurement Points Established positions Stakes/pits should cover even elevation distribution Account for velocity from Kaser et al. (2003)

Transient Snow Line Early SeasonLate Season

ELA Low ELA/sharply defined High ELA/sharply defined ELA separated from ice by old firn +B n Increased accumulation following years of –B n B n more negative than in preceding years

Measurement Tools Probes, stakes, pits, and cores Material properties from Kaser et al. (2003)

Surface Area 19921993

Hydrologic Method – (square = Δ) Where is the glacier? Accounts for internal water storage Primarily used in conjunction with other methods from Krimmel (1995)

Photogrammetric Method Requires high accuracy Works on ice, difficult on snow Elevation change at a specific point due to multiple processes Timing is critical Still requires snow/firn densities

Flux Gate Primarily used on ice sheets Accumulation – Total accumulation over grounded ice Ablation – Annual ice flux across grounding line

South Cascade Glacier Benchmark Glacier Multiple mass balance methods used and compared Long term glaciological and meteorological records

Internal Consistency Meier and Tangborn (1965) use three methods on South Cascade Glacier – (squares = Δ) Photogrammetric values and directly measured balance should be equal Can be checked against hydrologic data to check for consistency or water storage

Emergence Velocity Describes relationship between net balance, flow, and thickness changes Submergence in the accumulation area Emergence in the ablation area Crossover point=equilibrium ELA

Be careful where you dig!!! The End

References Fountain, A.G., Krimmel, R.M., Trabant, D.C., A Strategy for Monitoring Glaciers: United States Geological Survey, Circular 1132, 25 p. Hock, R., Hulth, J., Pettersson, R., 2008, Mass Balance of Storglacieren: American Geophysical Union, Fall Meeting 2008, abstract #C11D-0527 Kaser, G., Fountain, A.G., Jansson, P., 2003, A Manual for Monitoring the Mass Balance of Mountain Glaciers: Technical Documents in Hydrology, UNESCO, no. 59, 137 p. Krimmel, R.M., 1995, Water, ice, and meteorological measurements at South Cascade Glacier, Washington, 1994 balance year: U.S. Geological Survey Water-Resources Investigations Report 95-4162, 41 p. Krimmel, R.M., 1994, Runoff, precipitation, mass balance, and ice velocity measurements at South Cascade Glacier, Washington, 1993 balance year: U.S. Geological Survey Water-Resources Investigations Report 94-4139, 34 p. Krimmel, R.M., 1993, Mass balance, meteorological, and runoff measurements at South Cascade Glacier, Washington, 1992 balance year: U.S. Geological Survey Open-File Report 93-640, 38 p. Mayo, L.R., Meier, M.F., and Tangborn, W.V., 1972, A System to Combine Stratigraphic and Annual Mass Balance Systems: A Contribution to the International Hydrological Decade: Journal of Glaciology, v. 11, no. 61, p. 3-14. Meier, M.F., and Tangborn, W.V., 1965, Net budget and flow of South Cascade Glacier, Washington: Journal of Glaciology, v. 5, no. 41, p. 547-566. Paterson, W.S.B., 1994, the Physics of Glaciers, Third Edition: Butterworth-Heinemann, Oxford, pp. 26-52.