Abstract
Ice cliffs are common on debris‐covered glaciers and have relatively high melt rates due to their direct exposure to incoming radiation. Previous studies have shown that their number and relative area can change considerably from year to year, but this variability has not been explored, in part because available cliff observations are irregular. Here, we systematically mapped and tracked ice cliffs across four debris‐covered glaciers in High Mountain Asia for every late ablation season from 2009 to 2019 using high‐resolution multi‐spectral satellite imagery. We then quantified the processes occurring at the feature scale to train a stochastic birth‐death model to represent the cliff population dynamics. Our results show that while the cliff relative area can change by up to 20% from year to year, the natural long‐term variability is constrained, thus defining a glacier‐specific cliff carrying capacity. In a subsequent step, the inclusion of external drivers related to climate, glacier dynamics, and hydrology highlights the influence of these variables on the cliff population dynamics, which is usually not a direct one due to the complexity and interdependence of the processes taking place at the glacier surface. In some extreme cases (here, a glacier surge), these external drivers may lead to a reorganization of the cliffs at the glacier surface and a change in the natural variability. These results have implications for the melt of debris‐covered glaciers, in addition to showing the high rate of changes at their surface and highlighting some of the links between cliff population and glacier state.
Highlights
Debris-covered glaciers are widespread in all mountain ranges around the globe (Herreid & Pellicciotti, 2020b; Scherler et al, 2018) and especially in High Mountain Asia (HMA), where half of the glaciers larger than 2 km2 have more than 5% of their total area covered by a layer of rock debris (Herreid & Pellicciotti, 2020b) varying in thickness from centimeter to meter scale
The inclusion of external drivers related to climate, glacier dynamics, and hydrology highlights the influence of these variables on the cliff population dynamics, which is usually not a direct one due to the complexity and interdependence of the processes taking place at the glacier surface
Of values except for year 2012 for the cliff relative area in Urdok (Figure 5). This variability range is characterized by a standard deviation that is between 12% and 20% of the mean value after 10 years for both cliff relative area and number
Summary
Debris-covered glaciers are widespread in all mountain ranges around the globe (Herreid & Pellicciotti, 2020b; Scherler et al, 2018) and especially in High Mountain Asia (HMA), where half of the glaciers larger than 2 km have more than 5% of their total area covered by a layer of rock debris (Herreid & Pellicciotti, 2020b) varying in thickness from centimeter to meter scale These glaciers are often characterized by undulating, hummocky topography (Bartlett et al, 2020) and their surface is punctuated by supraglacial ponds, streams, and ice cliffs. Ice cliff formation has been suggested to be triggered by several possible mechanisms, including the collapse of englacial conduits (Benn et al, 2012; Immerzeel et al, 2014; Reid & Brock, 2014; Sakai & Takeuchi, 2000; Watson, Quincey, Carrivick & Smith, 2017; Watson, Quincey, Smith, et al, 2017; Westoby et al, 2020); slope oversteepening, for example from differential melt under the debris (Sakai et al, 1998; Sharp, 1949; Westoby et al, 2020); crevasse opening (Reid & Brock, 2014); undercutting by supraglacial ponds or streams (Moore, 2018; Nicholson et al, 2018); and melt enhancement at pond margins (Miles, Steiner, et al, 2017; Miles, Willis, et al, 2017; Röhl, 2006, 2008; Sakai & Takeuchi, 2000) that may sometimes lead to accelerated steepening from calving (Benn et al, 2012; Immerzeel et al, 2014; Röhl, 2006, 2008)
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