Abstract
AbstractThere exists a need to advance our understanding of debris‐covered glacier surfaces over relatively short timescales due to rapid, climatically induced areal expansion of debris cover at the global scale, and the impact debris has on mass balance. We applied unpiloted aerial vehicle structure‐from‐motion (UAV‐SfM) and digital elevation model (DEM) differencing with debris thickness and debris stability modelling to unravel the evolution of a 0.15 km2 region of the debris‐covered Miage Glacier, Italy, between June 2015 and July 2018. DEM differencing revealed widespread surface lowering (mean 4.1 ± 1.0 m a‐1; maximum 13.3 m a‐1). We combined elevation change data with local meteorological data and a sub‐debris melt model, and used these relationships to produce high resolution, spatially distributed maps of debris thickness. These maps were differenced to explore patterns and mechanisms of debris redistribution. Median debris thicknesses ranged from 0.12 to 0.17 m and were spatially variable. We observed localized debris thinning across ice cliff faces, except those which were decaying, where debris thickened. We observed pervasive debris thinning across larger, backwasting slopes, including those bordered by supraglacial streams, as well as ingestion of debris by a newly exposed englacial conduit. Debris stability mapping showed that 18.2–26.4% of the survey area was theoretically subject to debris remobilization. By linking changes in stability to changes in debris thickness, we observed that slopes that remain stable, stabilize, or remain unstable between periods almost exclusively show net debris thickening (mean 0.07 m a‐1) whilst those which become newly unstable exhibit both debris thinning and thickening. We observe a systematic downslope increase in the rate at which debris cover thickens which can be described as a function of the topographic position index and slope gradient. Our data provide quantifiable insights into mechanisms of debris remobilization on glacier surfaces over sub‐decadal timescales, and open avenues for future research to explore glacier‐scale spatiotemporal patterns of debris remobilization. © 2020 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd
Highlights
Debris‐covered glaciers are common features of glacierized regions and are characterized by a mantle of surface debris in their ablation zones
We focus on a ~0.15km2 area located 3km from the glacier terminus (Figure 1; centroid 45.790° E, 6.857° N) and selected this location primarily for its topographic complexity, which was deemed appropriate for investigating debris redistribution
We record high surface lowering (> 5m a‐1) at the western margin of the depression, a pattern which reflects the lateral expansion of the bowl via backwasting of its steep (> 30°) eastern‐ and southeastern‐facing slopes and coincides with where the debris mantle is locally at its thinnest
Summary
Debris‐covered glaciers are common features of glacierized regions and are characterized by a mantle of surface debris in their ablation zones. Surface debris exerts important controls on glacial ablation and mass balance through its capacity to insulate ice from fluctuations in air temperature where debris cover is continuous, and enhancing ablation where cover is thin and discontinuous (Østrem, 1959; Nakawo et al, 1999; Takeuchi et al, 2000; Benn et al, 2003). Evans and Clague, 1988; Huggel et al, 2005; Deline and Kirkbride, 2009; Uhlmann et al, 2013; Deline et al, 2014, 2015) and the failure of lateral moraines (Nakawo et al, 1986; van Woerkom et al, 2019) can transport debris to a glacier surface.
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