Combined measurements of Subglacial Water Pressure and Surface Velocity of Findelengletscher, Switzerland: Conclusions about Drainage System and Sliding Mechanism

Abstract

During the snow-melt season of 1982, basal water pressure was recorded in 11 bore holes communicating with the subglacial drainage system. In most of these holes the water levels were at approximately the same depth (around 70 m below surface). The large variations of water pressure, such as diurnal variations, were usually similar at different locations and in phase. In two instances of exceptionally high water pressure, however, systematic phase shifts were observed; a wave of high pressure travelled down-glacier with a velocity of approximately 100 m/h.The glacier-surface velocity was measured at four lines of stakes several times daily. The velocity variations correlated with variations in subglacial water pressure. The functional relationship of water pressure and velocity suggests that fluctuating bed separation was responsible for the velocity variations. The empirical functional relationship is compared to that of sliding over a perfectly lubricated sinusoidal bed. On the basis of the measured velocity-pressure relationship, this model predicts a reasonable value of bed roughness but too high a sliding velocity and unstable sliding at too low a water pressure. The main reason for this disagreement is probably the neglect of friction from debris in the sliding model.The measured water pressure was considerably higher than that predicted by the theory of steady flow through straight cylindrical channels near the glacier bed. Possible reasons are considered. The very large disagreement between measured and predicted pressure suggests that no straight cylindrical channels may have existed.

Observations: Cryosphere

“…• A common worry regarding ice wastage is that in summer surficial meltwater will penetrate through crevasses to lubricate faster flow at the base of the glacier (Iken and Bindschadler, 1986;Mair et al, 2002;Truffer et al, 2005;Bamber et al, 2007;Bartholomaus et al, 2008;van de Wal et al, 2008;Shepherd et al, 2009;Schoof, 2010;Sundal et al, 2011). Given that much glacier flow occurs by intracrystalline plastic processes, this worry is based on the speculative assumption of additional flow by sliding along the glacier-bedrock contact.…”

Subglacial flood path development during a rapidly rising jökulhlaup from the western Skaftá cauldron, Vatnajökull, Iceland

“…Subglacial accumulation of water has been observed or inferred at many locations on large and small glaciers and found to be associated with substantial increases in ice flow velocities (e.g. Iken and Bindschadler, 1986;Fudge and others, 2009;Magnússon and others, 2011). Jökulhlaups provide one of the best opportunities to study the response of the subglacial hydraulic system to large and sudden variations in water flow, and lessons learned from studies of jökulhlaups may be useful for understanding variations in basal sliding and ice flow in glaciers and ice sheets in general (Bell, 2008).…”

Spatially distributed runoff at the grounding line of a large Greenlandic tidewater glacier inferred from plume modelling

“…The relationship between subglacial hydrology and ice velocity has long been studied at alpine glaciers (Iken and Bindschadler, 1986) and more recently at land-terminating glaciers in Greenland (e.g. Bartholomew and others, 2010).…”