The hydrology and dynamics of a glacier overlying a linked-cavity drainage system
This thesis investigates the links between glacier hydrology and ice dynamics at Glacier de Tsanfleuron, a small temperate glacier overlying a linked-cavity system in the Valais Alps, Switzerland. The research results demonstrate that meltwater input to the englacial drainage system is significantly delayed by the supraglacial snowpack with travel velocities through the snowpack (0.08 to 0.32 mh-1) more than an order of magnitude slower than the flow at the water-saturated snow-ice interface (7.7 mh-1 and 12.2 mh-1). Since meltwater delivery is critically influencing subglacial hydrology this has a significant impact on glacier sliding. Tracer return curves obtained from experiments in the subglacial drainage system showed low flow velocities (between 0.02 to 0.05 ms-1) and high dispersivities (23 to 80m) reflecting meltwater routing through an inefficient drainage system. This supports the existence of an inefficient linked-cavity drainage system beneath the present glacier. Results of the subglacial tracer experiments and basic modelling of Nye channel flow velocities indicate that subglacial meltwater travels most of the distance in Nye channels but spends most of the time in cavities. Mean intra-seasonal surface velocities of 4 cm d-1 or 15 m a-1 respectively, were obtained form the survey of a stake network across the glacier. Horizontal surface velocities are generally higher at lower altitudes than at higher altitudes. There was no clear dynamic response (e.g. speed-up events due to increased subglacier water pressure) to seasonal meltwater inputs observed throughout the melt season, although large amounts of meltwater entered the englacial and subglacial systems in July and August. An important finding of the research was the apparent loss of approximately 95% of basal water into the bedrock karst. This is reflected in relatively low proglacial discharges from a limited catchment area.