Abstract
Supraglacial debris is known to strongly influence the distribution of glacier surface melt. Since melt inputs drive the formation and evolution of glacial drainage systems, it should follow that the drainage systems of debris-covered glaciers will differ from those of debris-free glaciers. This would have implications for the proglacial runoff regime, subglacial erosion and glacier dynamics. This paper presents analysis of return curves from 33 successful dye injections into the extensively debris-covered Miage Glacier, Italian Alps. It demonstrates that the spatial distribution of supraglacial debris influences the structure and seasonal evolution of the glacial drainage system. Where the debris cover is continuous, melt is lower and the surface topography is chaotic, with many small supraglacial catchments. These factors result in an inefficient englacial/subglacial drainage network beneath continuous debris, which drains to the conduit system emanating from the upper ablation zone. Melt rates are high in areas of clean and dirty ice above the continuous debris. Runoff from these areas is concentrated by inter-moraine troughs into large supraglacial streams, which encourages the early-season development of an efficient englacial/subglacial conduit system downstream of this area. Drainage efficiency from the debris-covered area increases over the melt season but dye-trace transit velocity remains lower than from moulins on the upper glacier. Future runoff models should account for the influence of supraglacial debris on the hydrological system.
Highlights
Background very variableQsQs us us type (m2) V AdD 0.44 AdD 2.06 0.17 AdD 8.14 0.874† 0.888† 0.147 AdD 0.50 Sep2011 11:19:35
On the heavily debris-covered lower tongue the debris cover resulted in hummocky topography and consistently small supraglacial catchments (Figs. 2, 3b and Table 4)
Supraglacial streams were difficult to find in this region of the glacier and there was a lack of well-defined moulins
Summary
Background data attached to a large, stable boulder (see Table 2 for details). The Onset HOBO pressure data were compensated using air pressure data from Mont de la Saxe, 7.6 km from the gauging station. The use of a single rating curve for the whole period was justified by the correspondence of gaugings from different field visits Supraglacial streams and their catchments were defined by applying Arnold’s (2010) lake and catchment identification algorithm (LCIA) to a digital elevation model (DEM). Salt dilution gauging was performed using a portable conductivity probe (Table 2), where the dilution gauging velocity was the distance between injection and detection points divided by the time between injection and peak of the concentration curve This gives a better measure of velocity than is provided by the float method. Streams injected in this area include S12 (the main stream draining the eastern side of the upper glacier, Supplementary Fig. 1a) and S14 (the main stream draining the western side of the upper glacier, Supplementary Fig. 1b). The crevassed, debris-covered lateral moraines had smaller supraglacial catchments due to the enechelon crevasses intersecting surface runoff
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