Black‐box modeling of the subglacial water system

Murray, Tavi; Clarke, Garry K. C.

doi:10.1029/95jb00671

Cited by 136 publications

(229 citation statements)

References 23 publications

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“…8a). During this event, it is likely that there is a transfer of mechanical support for ice shear stresses from high-water-pressure areas with reduced iceb ed coupling (such as site MA) to adjacent areas characterized by lower water pressures and increased ice^bed coupling (Murray and Clarke, 1995;Fischer and Clarke, 2001). In addition, this region would have experienced increased basal shear stress due to longitudinal coupling with fastermoving ice located 140 m further up-glacier at site MA.…”

Section: Further Discussion Of Patterns Of Bed Deformationmentioning

confidence: 99%

Hydrological controls on patterns of surface, internal and basal motion during three “spring events”: Haut Glacier d’Arolla, Switzerland

et al. 2003

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ABSTRACT. Three early-melt-season high-velocity events (or ''spring events'') occurred on Haut Glacier d' Arolla, Switzerland, during the melt seasons of 1998 and 1999. The events involve enhanced glacier velocity during periods of rapidly increasing bulk discharge in the proglacial stream and high subglacial water pressures. However, differences in spatial patterns of surface velocity, internal ice deformation rates, the spatial extent of high subglacial water pressures and in rates of subglacial sediment deformation suggest different hydrological and mechanical controls. The data from two of the events suggest widespread ice^bed decoupling, particularly along a subglacial drainage axis creating the highest rates of basal motion and ''plug flow'' in the overlying ice. The other event showed evidence of less extensive ice^bed decoupling and sliding along the drainage axis with more mechanical support for ice overburden transferred to areas adjacent to decoupled areas. We suggest that: (1) plug flow may be a common feature on glaciers experiencing locally induced reductions in basal drag; (2) under certain circumstances, enhanced surface motion may be due in part to non-locally forced enhanced bed deformation; and (3) subglacial sediment deformation is confined to a depth of the order of centimetres to decimetres.

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Section: Further Discussion Of Patterns Of Bed Deformationmentioning

confidence: 99%

Hydrological controls on patterns of surface, internal and basal motion during three “spring events”: Haut Glacier d’Arolla, Switzerland

et al. 2003

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“…This result is a reminder that spatial gradients in basal water pressure can locally affect the total stress that ice exerts on the bed (e.g. Murray and Clarke, 1995;Lappegard and others, 2006). In 2001 this effect of water pressure on total normal stress was successfully measured and factored into calculations presented hereinafter; this was not possible for the experiment of 2002, in which the earth-pressure cell rotated.…”

Section: Total Normal Stressesmentioning

confidence: 99%

Soft-bed experiments beneath Engabreen, Norway:regelation infiltration, basal slip and bed deformation

Iverson¹,

Hooyer

Fischer

et al. 2007

J. Glaciol.

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ABSTRACT. To avoid some of the limitations of studying soft-bed processes through boreholes, a prism of simulated till (1.8 m Â Â 1.6 m Â 0.45 m) with extensive instrumentation was constructed in a trough blasted in the rock bed of Engabreen, a temperate glacier in Norway. Tunnels there provide access to the bed beneath 213 m of ice. Pore-water pressure was regulated in the prism by pumping water to it. During experiments lasting 7-12 days, the glacier regelated downward into the prism to depths of 50-80 mm, accreting ice-infiltrated till at rates predicted by theory. During periods of sustained high porewater pressure (70-100% of overburden), ice commonly slipped over the prism, due to a water layer at the prism surface. Deformation of the prism was activated when this layer thinned to a sub-millimeter thickness. Shear strain in the till was pervasive and decreased with depth. A model of slip by ploughing of ice-infiltrated till across the prism surface accounts for the slip that occurred when effective pressure was sufficiently low or high. Slip at low effective pressures resulted from water-layer thickening that increased non-linearly with decreasing effective pressure. If sufficiently widespread, such slip over soft glacier beds, which involves no viscous deformation resistance, may instigate abrupt increases in glacier velocity.

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“…Head gradients at the bed adjacent to the tunnel (where boreholes were assumed to connect) reverse as the main tunnel becomes pressurized and unpressurized on a diurnal cycle and the magnitude of the water-level fluctuations in the boreholes dissipates as the boreholes are farther away from the tunnel. Murray and Clarke (1995) showed that load transfer on Trapridge Glacier, Yukon, Canada, occurred when pressure in the channelized system was high, causing a decrease in water level in unconnected boreholes. This was also observed with further study at Haut Glacier d'Arolla (Gordon and others, 1998).…”

Section: Comparison With Other Borehole Arraysmentioning

confidence: 99%

“…Fountain, 1994;Hubbard and others, 1995;Murray and Clarke, 1995;Smart, 1996;Gordon and others, 1998). They typically exist when at least one borehole has a water level that varies only slightly and is considered isolated from (or unconnected with) the channelized drainage system.…”

Section: Borehole Grid Head Gradientsmentioning

confidence: 99%

“…Investigations on South Cascade Glacier, Wahington, USA, (Fountain, 1994) and Haut Glacier d'Arolla, Switzerland, (Hubbard and others, 1995;Gordon and others, 1998) both concluded that the diurnal fluctuations observed in borehole arrays a few hundred meters wide were caused by a single large drainage tunnel alternating between pressurized and unpressurized states. Murray and Clarke (1995) and Gordon and others (1998) observed that peak water level in connected boreholes corresponded with water-level minimums in boreholes unconnected to the channelized drainage system. Despite the progress made by these studies, the configuration of the drainage system and whether boreholes allow an accurate measure of basal water pressure remains only weakly understood.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Diurnal fluctuations in borehole water levels: configuration of the drainage system beneath Bench Glacier, Alaska, USA

Fudge¹,

Humphrey

Harper

et al. 2008

J. Glaciol.

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Black‐box modeling of the subglacial water system

Cited by 136 publications

References 23 publications

Hydrological controls on patterns of surface, internal and basal motion during three “spring events”: Haut Glacier d’Arolla, Switzerland

Hydrological controls on patterns of surface, internal and basal motion during three “spring events”: Haut Glacier d’Arolla, Switzerland

Soft-bed experiments beneath Engabreen, Norway:regelation infiltration, basal slip and bed deformation

Diurnal fluctuations in borehole water levels: configuration of the drainage system beneath Bench Glacier, Alaska, USA

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