Publication Date:
2016-11-17
Description:
We determine the geodetic mass balance of surge-type Black Rapids Glacier, Alaska, for the time periods 1980–2001 and 2001–2010 by combining modern InSAR-derived DEMs, DEMs derived from archival aerial imagery, laser altimetry data and in-situ surface elevation measurements. Our analysis accounts for both the large rockslides and terrain displacements caused by the 2002 M 7.9 earthquake on the Denali fault, which runs through Black Rapids Glacier. To estimate uncertainties we apply Monte Carlo simulations. For the earthquake-triggered rockslides we find a volume of 56.62±2.86 × 10 6 m 3 , equivalent to an average debris thickness of 4.44±0.24 m across the 11.7 km 2 deposit area on the glacier. Terrain displacement due to the earthquake corresponds to an apparent glacier volume change of –53.1×10 6 m 3 , which would cause an apparent specific mass balance of –0.19 m w.e. if not taken into account. The geodetic mass balance of Black Rapids Glacier is –0.48±0.07 m w.e. a −1 for the entire 30 year period, but more negative for the period 2001–2010 (–0.64±0.11 m w.e. a −1 ) than the period 1980–2001 (–0.42±0.11 m w.e. a −1 ), in agreement with trends indicated by in-situ mass balance measurements. Elevation data indicate no net thickening of the surge reservoir between 1980 and 2010, in contrast to what is expected during the quiescent phase. A surge of Black Rapids Glacier in the near future is thus considered unlikely.
Print ISSN:
0148-0227
Topics:
Geosciences
,
Physics
