EGU21-15674
https://doi.org/10.5194/egusphere-egu21-15674
EGU General Assembly 2021
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Debris cover and the thinning of Kennicott Glacier, Alaska

Leif S. Anderson1,2,3, William H. Armstrong3,4, Robert S. Anderson3, and Dirk Scherler2,5
Leif S. Anderson et al.
  • 1University of Lausanne, Institute of Earth Surface Dynamics, Lausanne, Switzerland (leif.anderson@unil.ch)
  • 2Helmoholz Centre Potsdam, GFZ German Centre for Geoscience Research, Potsdam, Germany
  • 3University of Colorado, Department of Geological Science and Institute of Arctic and Alpine Research, Boulder, Colorado, USA
  • 4Appalachian State University, Department of Geological and Environmental Science, Boone, North Carolina, USA
  • 5Freie Universität, Institute for Geological Science, Berlin, Germany

Many glaciers in High Mountain Asia are experiencing the debris-cover anomaly. The Kennicott Glacier, a large Alaskan Glacier, is also thinning most rapidly under debris cover. This contradiction has been explained by melt hotspots, such as ice cliffs, streams, or ponds scattered within the debris cover or by declining ice flow in time. We collected abundant in situ measurements of debris thickness, sub-debris melt, and ice cliff backwasting, allowing for extrapolation across the debris-covered tongue. A newly developed automatic ice cliff delineation method is the first to use only optical satellite imagery. The adaptive binary threshold method accurately estimates ice cliff coverage even where ice cliffs are small and debris color varies. We also develop additional remotely-sensed datasets of ice dynamical variables, other melt hot spots, and glacier thinning.

Kennicott Glacier exhibits the highest fractional area of ice cliffs (11.7 %) documented to date. Ice cliffs contribute 26 % of total melt across the glacier tongue. Although the relative importance of ice cliffs to area-average melt is significant, the absolute area-averaged melt is dominated by debris. At Kennicott Glacier, glacier-wide melt rates are not maximized in the zone of maximum thinning. Declining ice discharge through time therefore explains the rapid thinning. Through this study, Kennicott Glacier is the first glacier in Alaska, and the largest glacier globally, where melt across its debris-covered tongue has been rigorously quantified.

We also carefully explore the relationship between debris, melt hotspots, ice dynamics, and thinning across the debris-covered tongue. In doing so we reveal a chain of linked processes that can explain the striking patterns expressed on the debris-covered tongue of Kennicott Glacier.

How to cite: Anderson, L. S., Armstrong, W. H., Anderson, R. S., and Scherler, D.: Debris cover and the thinning of Kennicott Glacier, Alaska, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15674, https://doi.org/10.5194/egusphere-egu21-15674, 2021.

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