Structure and stability of the former subglacial drainage system of the glacier De Tsanfleuron, Switzerland

Abstract

A well-developed subglacial drainage system consisting of large cavities developed in the lee of bedrock steps connected together by a network of Nye channels is exposed on an area of recently deglaciated limestone bedrock in front of Glacier de Tsanfleuron, Switzerland. This system covers some 51 per cent of the bedrock surface area, and is believed to have transported the bulk of supraglacially-derived meltwaters through the glacier. Using the cavity hydraulics model of Kamb (1987), it is shown that the geometry of the system rendered it stable against collapse by meltback of channel roofs into a tunnel-dominated system. For likely combinations of glacier gepmetry and meltwater discharge, the steady state water pressure in this system would have been only a small fraction of that required for flotation, and for discharges of less than about 05-5 m3 s-water would have flowed at atmospheric pressure. The system appears to have adjusted to varying discharges by a combination of varying water pressure and changing the total cross-sectional area of flow by altering the number of active channels connecting cavities. Glacier sliding velocity would have been independent of meltwater discharge for discharges at which water flowed at atmospheric pressure, but would have risen with increasing discharge for higher flows. Velocities on the order of 0.1 m d-are predicted for a realistic range of discharges and effective pressures, and these are believed to be plausible. Episodes of enhanced sliding in glaciers with similar drainage systems could be triggered by a rise in meltwater discharge across the threshold between flows at atmospheric pressure and flow under pressure from the glacier.

Potential subglacial lake locations and meltwater drainage pathways beneath the Antarctic and Greenland ice sheets

“…Röthlisberger, 1972;Walder and Hallet, 1979;Nienow et al, 1998); (ii) distributed networks of passageways and cavities (e.g. Lliboutry, 1979;Kamb, 1987;Sharp et al, 1989); (iii) thin water films (e.g. Hallet, 1979;Lappegard et al, 2006); and (iv) Darcian flow through sediments (e.g.…”

The development of a late Weichselian - early Holocene subaqueous ice-contact fan, Teikangas, SW Finland

“…Shreve 1972). Therefore, it is suggested that a linked cavity system (Walder 1986, Sharp et al 1989) and/or subglacial water sheetflow (Weertman 1972, Alley et al 1987, rather than a well-defined major channel, could be responsible for the supply of meltwater and sediment to the ice-grounding line in the present case. Smaller subglacial conduits are more unstable than large ones, and thus might have switched their position several times during the development of the Teikangas fan.…”

Glacier Biogeochemistry

“…Formerly glaciated limestone bedrock surface at the Glacier de Tsanfleuron, Switzerland, showing dissolution furrowing (1) on the upstream side of a bedrock bump where pressure-induced melting would have occurred, and subglacial calcite precipitation (2) on the downstream side where low pressures, refreezing and solute concentration would have occurred. Glacier flow was from left to right (modified from Sharp et al,1989).…”

“…Detailed geomorphological map of an area of the recently deglaciated bed of Glacier de Tsanfleuron, Switzerland, showing the distribution of formerly water-filled leeside cavities, Nye channels incised into bedrock, and depressions filled with calcite precipitates (from Sharp et al,1989).…”