The effects of basal topography and ice-sheet surface slope in a subglacial glaciofluvial deposition model

Abstract

<p>This work considers the flow of subglacial water and sediment within a channelised drainage system. Focussing on the mechanics of flow within a single channel, we consider the effects of basal topography and the slope of the overlying ice-sheet on the rate of sediment deposition within the channel.</p><p>Previous work in this field has demonstrated how sediment deposition occurs primarily in the final kilometres of the ice sheet, where the overlying ice is comparatively thin and can be expected to exhibit a relatively steep slope. Under these conditions subglacial channel width can be expected to grow rapidly, reducing water flow velocity and therefore sediment carrying capacity. These conditions lead to the deposition of sediment, and the formation of eskers, which may remain as a demarcation of the channel long after the ice sheet as passed.</p><p>By modifying basal topography and ice surface slope and thickness, we demonstrate that sediment deposition is not restricted to the final kilometres of the channel, and may in fact occur at any number of locations within the channel, far from the ice margin. In particular, on the leeside of hills and ridges, or on the upstream slope of a glacial valley. Furthermore, we show how thinner ice profiles enhance upstream sediment deposition, while thicker ice profiles dampen such deposition.</p><p>The dynamics of depositional and erosional zones within the channel do not indicate that these deposits will ordinarily survive the passage of the ice sheet over time; however they provide an interesting mechanism for storage and recycling of sediment within the subglacial drainage system. Furthermore, the presence of basal slopes can be shown to either enhance or dampen the deposition of sediment at the ice margin, affecting the size of eskers that are formed there.</p>