The formation of supraglacial debris covers by primary dispersal from transverse englacial debris bands

Abstract

International audience: Glaciological controls on debris cover formation are investigated from the perspective of primary dispersal of supraglacial debris across a melting ice surface. This involves the migration of angled debris septa outcrops across a melting, thinning glacier ablation zone. Three measures of a glacier ' s ability to evacuate supraglacial debris are outlined: (1) a concentration factor describing the focusing of englacial debris into specific supraglacial mass loads; (2) the rate of migration of a septum outcrop relative to the local ice surface; and (3) a downstream velocity differential between a slower septum outcrop and the faster ice surface velocity. Measures (1) and (2) are inversely related, while measure (3) increases down-glacier to explain why slow-moving, thinning ice rapidly becomes debris covered. Data from Glacier d' Estelette (Italian Alps) are used to illustrate these processes, and to explore the potential for debris cover formation and growth in different glaciological environments. The transition from a 'clean ', transport dominated to a debris-covered ablation-dominated glacier is explained by the melting out of more closely-spaced debris septa, in combination with the geometric nteractions of angled septa and ice surface in a field of reducing flow and increasing ablation. The growth and shrinkage of debris covers are most sensitive to glaciological changes at glaciers with gently-dipping debris-bearing foliation, but less sensitive at high-compression glaciers whose termini are constrained by moraine dams and other forms of obstruc- tion. These findings show that a variety of debris-covered glacier types will show a spectrum of response characteristics to negative mass balance. Copyright © 2013 John Wiley & Sons, Ltd

Internal Structure and Current Evolution of Very Small Debris-Covered Glacier Systems Located in Alpine Permafrost Environments

“…At the system scale, atypical characteristics differentiate the study sites from the larger and bare-ice glacier stereotype: the small size of the upslope firn and bare-ice zones and the associated large relative area of debris-covered glacier zones, the existence of marginal rock glaciers and the overall very high amount of debris in comparison with the glacier size. The glacier zones are extensively covered by a coarse-grained debris layer that thickens downglacier due to flux emergence, compressive stress and ice melt (Kirkbride and Deline, 2013). This also explains the debris concentration increase in the glacier margins.…”

“…Two main causes, enhanced by the acceleration of ice melt since the mid-1980s (e.g., Zemp et al, 2015), explain the current extent and thickening of supraglacial debris cover observed in mountainous regions (Kirkbride and Deline, 2013). Firstly, the deglaciation of rockwalls and permafrost degradation increase the debris supply to glacier systems (Bosson et al, 2015;Deline et al, 2015).…”

“…Moreover, the height and surface of the latter can be lopsided in comparison with the restricted glacier surface (Maisch et al, 1999;Grunewald and Scheithauer, 2010). Finally, the debris evacuation can be limited because the weak driving stress of these thin ice masses is commonly reduced by the presence of cold ice (Gilbert et al, 2012) and/or large and possibly frozen sediment accumulations in the distal zone, such as moraine dam (sensu Benn et al, 2003), ice-cored moraines or rock glaciers (Shroder et al, 2000;Kirkbride and Deline, 2013;Bosson et al, 2015).…”

Modeling debris-covered glaciers: response to steady debris deposition

“…As a result complete summer balances from debris-covered glaciers are sparse (WGMS, 2008). Measurements of englacial debris concentrations and distribution are yet more difficult to obtain (e.g., Kirkbride and Deline, 2013). In addition, exploration of century-scale response of debris-covered glaciers is limited by short satellite and observational periods (Bolch et al, 2011).…”

Reduced melt on debris-covered glaciers: investigations from Changri Nup Glacier, Nepal

“…However, the role played by debris on the surface mass balance of glaciers and, in turn, on the glacier response to climate change remains unclear (Kääb et al, 2012). Indeed, this debris layer insulates the glacier surface from the atmosphere when it reaches a sufficient thickness and complicates the response to climate change compared to clean-ice glaciers (Jouvet et al, 2011;Kirkbride and Deline, 2013;Østrem, 1959;Pellicciotti et al, 2015).…”