Modeling the Feedbacks Between Surface Ablation and Morphological Variations on the Debris-Covered Baltoro Glacier in the Central Karakoram

Published in Geomorphology, Huo, D., Bishop, M. P., Young, B. W. & Chi, Z., 2021

Abstract: Recent studies show that many debris-covered glaciers exhibit high-magnitude differential thinning despite the presence of supraglacial debris. Existing studies have not adequately explored the variability in surface ablation, morphology, and related feedback mechanisms that incorporate topographically controlled surface irradiance and debris transport. In this study, we address these issues using a radiation-driven surface ablation model that more fully characterizes ablation dynamics by accounting for temporally-linked radiative forcing, surface geomorphological evolution and gravitational debris flux. Simulation results based on Baltoro Glacier in the central Karakoram indicate the following: 1) A debris-covered glacier can exhibit high spatial variability in surface ablation due to heterogeneous debris thickness and debris transport. A bare-ice glacier given similar initial conditions, has higher overall ablation but exhibits much less variability. 2) The topographic influence on surface ablation is non-negligible because glacier-surface topography controls irradiance and gravitational debris flux. The overall ablation on a debris-covered glacier tends to increase in response to high-frequency topographic variations due to the larger area with thin debris cover. In contrast, a bare-ice glacier exhibits decreased overall ablation in response to high-frequency topographic variations due to its high sensitivity to topographic shading. 3) Gravity-driven surface debris flux plays an important role in local debris thickness redistribution, which regulates ablation rates over the ablation season. 4) Surface ablation dynamics on a debris-covered glacier is regulated by active system couplings and feedbacks between surface morphology, melt and debris transport. Consequently, certain locations on a debris-covered glacier may be more sensitive to radiative forcing than previously thought. Simulation results suggest that nonlinear feedback responses may permit debris-covered glacier subsystems to be very sensitive to radiative forcing, thereby causing significant morphological changes to the glacier surface.

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