Abstract
AbstractContinuous surface debris cover strongly reduces the ablation of glaciers, but high melt rates may occur at ice cliffs that are too steep to hold debris. This study assesses the contribution of ice-cliff backwasting to total ablation of Miage glacier, Mont Blanc massif, Italy, in 2010 and 2011, based on field measurements, physical melt models and mapping of ice cliffs using a high-resolution (1 m) digital elevation model (DEM). Short-term model calculations closely match the measured melt rates. A model sensitivity analysis indicates that the effects of cliff slope and albedo are more important for ablation than enhanced longwave incidence from sun-warmed debris or reduced turbulent fluxes at sheltered cliff bases. Analysis of the DEM indicates that ice cliffs account for at most 1.3% of the 1 m pixels in the glacier’s debris-covered zone, but application of a distributed model indicates that ice cliffs account for ~7.4% of total ablation. We conclude that ice cliffs make an important contribution to the ablation of debris-covered glaciers, even when their spatial extent is very small.
Highlights
Debris-covered glaciers are found in most glacierized mountains and are extensive in the high Asian ranges, Alaska and the Andes (Kirkbride, 2011)
This paper describes an assessment of the contribution of backwasting to total ablation of Miage glacier (4584703000 N, 685200000 E; Fig. 1a), a well-studied debris-covered glacier on the southwestern side of the Mont Blanc massif, Italy (e.g. Foster and others, 2012)
We argue that these effects will be small for an ice cliff because the area of exposed ice is small relative to the surrounding debris cover, and the wind will usually quickly replenish the air in contact with the ice
Summary
Debris-covered glaciers are found in most glacierized mountains and are extensive in the high Asian ranges, Alaska and the Andes (Kirkbride, 2011). Some researchers have shown that the process of backwasting on localized ice cliffs could make a large net contribution to total ablation of debris-covered glaciers (Sakai and others, 2002; Han and others 2010). These cliffs are likely to show enhanced melt rates relative to cliffs on clean glaciers because they have reduced ice albedos due to deposition of fine debris, and are in close proximity to warm debris layers that emit longwave radiation and raise ambient air temperature through convection (Brock and others, 2010). In a further advance on previous work, a highresolution digital elevation model (DEM) derived from an airborne lidar survey is used to identify ice cliffs across the glacier’s debris-covered zone to estimate their overall contribution to ablation
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