Abstract
Abstract. Glaciers with extensive surface debris cover respond differently to climate forcing than those without supraglacial debris. In order to include debris-covered glaciers in projections of glaciogenic runoff and sea level rise and to understand the paleoclimate proxy recorded by such glaciers, it is necessary to understand the manner and timescales over which a supraglacial debris cover develops. Because debris is delivered to the glacier by processes that are heterogeneous in space and time, and these debris inclusions are altered during englacial transport through the glacier system, correctly determining where, when and how much debris is delivered to the glacier surface requires knowledge of englacial transport pathways and deformation. To achieve this, we present a model of englacial debris transport in which we couple an advection scheme to a full-Stokes ice flow model. The model performs well in numerical benchmark tests, and we present both 2-D and 3-D glacier test cases that, for a set of prescribed debris inputs, reproduce the englacial features, deformation thereof and patterns of surface emergence predicted by theory and observations of structural glaciology. In a future step, coupling this model to (i) a debris-aware surface mass balance scheme and (ii) a supraglacial debris transport scheme will enable the co-evolution of debris cover and glacier geometry to be modelled.
Highlights
All mountain glaciers carry rock and dust material within the ice
These simulations demonstrate the efficiency of our streamlineupwind Petrov–Galerkin (SUPG) algorithm implementation for reducing non-physical spurious oscillations in the solutions and allow us to choose suitable Courant numbers to ensure numerical stability
The debris transport and deformation modelled here reproduces structures analogous to those observed in structural glaciology, where elongated and sometimes cross-cutting debris layers outcrop with a range of dip angles at the glacier surface (Jennings et al, 2014; Goodsell et al, 2005)
Summary
All mountain glaciers carry rock and dust material within the ice. This can originate from gravitational mass movements from the surrounding valley walls, aeolian deposition or basal erosion (Benn and Evans, 2010). In the ablation zone of a glacier, ice flow transports debris towards the glacier surface and surface ice ablation leaves behind a residue of rock material (Fig. 1a). A surface debris cover more than a few centimetres thick inhibits surface ablation of ice and alters glacier runoff, local water resources and contribution to sea level change. It affects glacier dynamics and geometry such that stagnating, low-angled debris-covered ice can survive for longer at lower altitudes than neighbouring clean-ice glaciers (Benn et al, 2012; Anderson and Anderson, 2016). The paleoclimatic signal represented by sediment deposits from a debris-covered glacier is not the same as one from a cleanice glacier
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