A physically based 3‐D model of ice cliff evolution over debris‐covered glaciers. Issue 12 (22nd December 2016)

• Record Type: Journal Article
• Authors: Buri, Pascal; Miles, Evan S.; Steiner, Jakob F.; Immerzeel, Walter W.; Wagnon, Patrick; Pellicciotti, Francesca
• Is Part Of: Journal of geophysical research. Volume 121:Issue 12(2016)
• Page Start: 2471
• Page End: 2493
• Publication Date: 2016-12-22
• Subjects: ice cliffs -- debris‐covered glaciers -- physically based model of cliff backwasting -- pond‐cliff modeling -- Himalaya -- cliff processes; Geomorphology -- Periodicals; 551.3
• DOI: 10.1002/2016JF004039
• Languages: English
• ISSNs: 2169-9003

Abstract

Abstract: We use high‐resolution digital elevation models (DEMs) from unmanned aerial vehicle (UAV) surveys to document the evolution of four ice cliffs on the debris‐covered tongue of Lirung Glacier, Nepal, over one ablation season. Observations show that out of four cliffs, three different patterns of evolution emerge: (i) reclining cliffs that flatten during the ablation season; (ii) stable cliffs that maintain a self‐similar geometry; and (iii) growing cliffs, expanding laterally. We use the insights from this unique data set to develop a 3‐D model of cliff backwasting and evolution that is validated against observations and an independent data set of volume losses. The model includes ablation at the cliff surface driven by energy exchange with the atmosphere, reburial of cliff cells by surrounding debris, and the effect of adjacent ponds. The cliff geometry is updated monthly to account for the modifications induced by each of those processes. Model results indicate that a major factor affecting the survival of steep cliffs is the coupling with ponded water at its base, which prevents progressive flattening and possible disappearance of a cliff. The radial growth observed at one cliff is explained by higher receipts of longwave and shortwave radiation, calculated taking into account atmospheric fluxes, shading, and the emission of longwave radiation from debris surfaces. The model is a clear step forward compared to existing static approaches that calculate atmospheric melt over an invariant cliff geometry and can be used for long‐term simulations of cliff evolution and to test existing hypotheses about cliffs' survival. Key Points: We use high‐resolution digital elevation models to document the evolution of supraglacial ice cliffs over one ablation season Reclining cliffs that flatten, stable cliffs maintaining a self‐similar geometry, and growing cliffs that expand laterally are observed We develop a 3‐D model of cliff backwasting driven by atmospheric melt, reburial by surrounding debris, and the effect of adjacent ponds