Effect of a Terminal Overdeepening on Glacier Hydrology and Flow

Overdeepenings in the bedrock topography beneath glaciers are commonplace. Despite this, the subglacial processes associated with them remain poorly understood. It has been hypothesized that adverse bed gradients can reduce the efficiency of the drainage system and therefore encourage basal sediment to accumulate. To determine to what extent an overdeepening might influence ice flow and the drainage system, a terminal overdeepening at Findelengletscher, Switzerland was targeted. 9 Unmanned Aerial Vehicle (UAV) surveys were carried out, spread across late August and early September 2016, early July 2017 and early September 2017 along with two Ground Penetrating Surveys (GPR) in February and July 2017. An overdeepening with a bed to surface slope ratio above the threshold for glaciohydraulic supercooling with basal sediment layers on its adverse slope was present. Up-glacier Ice flow velocities and spatial ice loss patterns across the meltseason were consistent with drainage system evolution, whilst a less efficient system was present longer at the overdeepening. Findings indicate that drainage, and thus ice flow, at the terminus of Findelengletscher are strongly influenced by the adverse slope. The presence of a more inefficient distributed system at the terminus leads to a reduction in energy also decreases water velocity and, with it, sedimental transport in this location leading to evidence of englacial thrusting at the terminus. It is recommended that bed topography be given consideration when considering rates of sediment erosion and transportation.