Mass Balance: Theory and Application

# Mass Balance: Theory and Application

## Mass Balance: Theory and Application

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##### Presentation Transcript

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

2. South Cascade Glacier - 2004

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

4. 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)

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

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

7. from Mayo et al. (1972)

8. 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.

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

10. Transient Snow Line Early Season Late Season

11. 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

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

13. Surface Area 1992 1993

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

15. 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

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

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