Modeling channelized and distributed subglacial drainage in two dimensions

Abstract

[1] We present a two-dimensional Glacier Drainage System model (GlaDS) that couples distributed and channelized subglacial water flow. Distributed flow occurs through linked cavities that are represented as a continuous water sheet of variable thickness. Channelized flow occurs through Röthlisberger channels that can form on any of the edges of a prescribed, unstructured network of potential channels. Water storage is accounted for in an englacial aquifer and in moulins, which also act as point sources of water to the subglacial system. Solutions are presented for a synthetic topography designed to mimic an ice sheet margin. For low discharge, all the flow is accommodated in the sheet, whereas for sufficiently high discharge, the model exhibits a channelization instability which leads to the formation of a self-organized channel system. The random orientation of the network edges allows the channel system geometry to be relatively unbiased, in contrast to previous structured grid-based models. Under steady conditions, the model supports the classical view of the subglacial drainage system, with low pressure regions forming around the channels. Under diurnally varying input, water flows in and out of the channels, and a rather complex spatiotemporal pattern of water pressures is predicted. We explore the effects of parameter variations on the channel system topology and mean effective pressure. The model is then applied to a mountain glacier and forced with meltwater calculated by a temperature index model. The results are broadly consistent with our current understanding of the glacier drainage system and demonstrate the applicability of the model to real settings.

Recent Advances in Our Understanding of the Role of Meltwater in the Greenland Ice Sheet System

“…These models, driven by seasonally varying supraglacial meltwater inputs, demonstrate a seasonal evolution in subglacial hydrology from distributed to channelised drainage [70][71][72] which build on the earlier theoretical work of Kamb [61]. There are however disparities between model results [65,70] and evidence from field data [55,62] in terms of the rates at which (or even whether) channels can form and the distance to which they will extend inland from the ice sheet margin.…”

On the reconstruction of palaeo-ice sheets: Recent advances and future challenges

“…More generally, the imprint of meltwater drainage recorded on the bed of former ice sheets is a potentially useful test of numerical models that predict the configuration of the subglacial hydrological system (e.g. Hewitt, 2011;Werder et al, 2013), but which has generally been under-used.…”

Oscillatory subglacial drainage in the absence of surface melt

“…For computational tractability and in keeping with many other similar drainage models (e.g. Werder et al, 2013), we do not impose the upper and lower bounds on water pressure considered in Schoof et al (2012) and Hewitt et al (2012).…”