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 Bn vs. bn 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 from Kaser et al. (2003) • Established positions • Stakes/pits should cover even elevation distribution • Account for velocity
Transient Snow Line Early Season Late Season
ELA • Low ELA/sharply defined • High ELA/sharply defined • ELA separated from ice by old firn • +Bn • Increased accumulation following years of –Bn • Bn more negative than in preceding years
Measurement Tools • Probes, stakes, pits, and cores • Material properties from Kaser et al. (2003)
Surface Area 1992 1993
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
The End Be careful where you dig!!!
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.