scholarly journals The Importance of Pressurized Subglacial Water in Separation and Sliding at the Glacier Bed (Abstract only)

1982 ◽  
Vol 3 ◽  
pp. 349-349
Author(s):  
Robert Bindschadler
Keyword(s):  
Water Pressure ◽  
Water Discharge ◽  
Temporal Variations ◽  
Short Time Scale ◽  
Test Case ◽  
Separation Index ◽  
Order Of Magnitude ◽  
Bed Separation ◽  
Ice Stream B ◽  
Basal Shear

The effect of pressurized sub-glacial water on the sliding process is quantified by calculating a “bed separation index”. The water pressure distribution i s calculated assuming the existence of a Rothlisberger channel at the bed. Kamb's formulation is used to describe the variation of normal stress over periodic bed undulations. The hypothesis is that as either basal shear stress or water pressure is increased the extent of ice-bedrock separation (on the down-glacier side of undulations) increases and enhanced sliding occursData from three glaciers of widely varying size are used to test this hypothesis. For Columbia Glacier and “Ice Stream B” the importance of including the effects of water pressure in any “sliding law” are pronounced. More complete data from the third test case, Variegated Glacier, are used to compare a number of possible formulations of sliding law which encompass the above hypothesis. A modified Weertmantype law appears to be most preferable while while some possibilities, including Budd's lubrication factor hypothesis, are tentatively rejected.Consideration of the temporal variations of the “bed separation index” reemphasize that, especially in the short time scale, variations of water pressure can dominate the sliding process. An order of magnitude increase in water discharge causes a hundred fold transient increase in the water pressure.This paper has been accepted for publication in the Journal of Glaciology

scholarly journals The Importance of Pressurized Subglacial Water in Separation and Sliding at the Glacier Bed (Abstract only)

1982 ◽  
Vol 3 ◽  
pp. 349 ◽  
Author(s):  
Robert Bindschadler
Keyword(s):  
Water Pressure ◽  
Water Discharge ◽  
Temporal Variations ◽  
Short Time Scale ◽  
Test Case ◽  
Separation Index ◽  
Order Of Magnitude ◽  
Bed Separation ◽  
Ice Stream B ◽  
Basal Shear

The effect of pressurized sub-glacial water on the sliding process is quantified by calculating a “bed separation index”. The water pressure distribution i s calculated assuming the existence of a Rothlisberger channel at the bed. Kamb's formulation is used to describe the variation of normal stress over periodic bed undulations. The hypothesis is that as either basal shear stress or water pressure is increased the extent of ice-bedrock separation (on the down-glacier side of undulations) increases and enhanced sliding occurs Data from three glaciers of widely varying size are used to test this hypothesis. For Columbia Glacier and “Ice Stream B” the importance of including the effects of water pressure in any “sliding law” are pronounced. More complete data from the third test case, Variegated Glacier, are used to compare a number of possible formulations of sliding law which encompass the above hypothesis. A modified Weertmantype law appears to be most preferable while while some possibilities, including Budd's lubrication factor hypothesis, are tentatively rejected. Consideration of the temporal variations of the “bed separation index” reemphasize that, especially in the short time scale, variations of water pressure can dominate the sliding process. An order of magnitude increase in water discharge causes a hundred fold transient increase in the water pressure. This paper has been accepted for publication in the Journal of Glaciology

scholarly journals The Importance of Pressurized Subglacial Water in Separation and Sliding at the Glacier Bed

1983 ◽  
Vol 29 (101) ◽  
pp. 3-19 ◽  
Author(s):  
Robert Bindschadler
Keyword(s):  
Water Pressure ◽  
Water Discharge ◽  
High Water ◽  
Temporal Variations ◽  
Early Summer ◽  
Test Case ◽  
Separation Index ◽  
Order Of Magnitude ◽  
Bed Separation ◽  
Ice Stream B

AbstractThe effect of pressurized subglacial water on the sliding process is examined by a parameter called the “bed separation index”. This index indicates the relative extent of cavity formation by combining the effects of variation of bed-normal stress across undulations (Kamb, 1970) and steady-state water pressure in a Röthlisberger conduit at the glacier bed. Data from three glaciers of widely varying size are used to test the correlation of the bed separation index with inferred sliding rates. For Columbia Glacier and Ice Stream B in West Antarctica it is shown that high water pressure enhances sliding. More complete data from the third test case. Variegated Glacier, are used to compare a number of possible formulations of a “sliding law”. A Weertman-type power law (exponent c. 3), modified for the effect of subglacial water pressure, appears to be most preferable. Other formulations, including the “lubrication factor” hypothesis used by Budd (1975) are tentatively rejected. Consideration of the temporal variations of the “bed separation index” indicate that, on short time scales of days and weeks, variations of water pressure can dominate the sliding process. A rapid order-of-magnitude increase in water discharge causes a hundredfold transient increase in the water pressure. A bi-modal hydraulic regime is revealed for water flow transverse to the direction of main ice flow. This behavior is in accord with the observation of a sudden acceleration of the ice due to increased sliding in early summer or following heavy rainstorms.

scholarly journals The Importance of Pressurized Subglacial Water in Separation and Sliding at the Glacier Bed

1983 ◽  
Vol 29 (101) ◽  
pp. 3-19 ◽  
Author(s):  
Robert Bindschadler
Keyword(s):  
Water Pressure ◽  
Water Discharge ◽  
High Water ◽  
Temporal Variations ◽  
Early Summer ◽  
Test Case ◽  
Separation Index ◽  
Order Of Magnitude ◽  
Bed Separation ◽  
Ice Stream B

Abstract The effect of pressurized subglacial water on the sliding process is examined by a parameter called the “bed separation index”. This index indicates the relative extent of cavity formation by combining the effects of variation of bed-normal stress across undulations (Kamb, 1970) and steady-state water pressure in a Röthlisberger conduit at the glacier bed. Data from three glaciers of widely varying size are used to test the correlation of the bed separation index with inferred sliding rates. For Columbia Glacier and Ice Stream B in West Antarctica it is shown that high water pressure enhances sliding. More complete data from the third test case. Variegated Glacier, are used to compare a number of possible formulations of a “sliding law”. A Weertman-type power law (exponent c. 3), modified for the effect of subglacial water pressure, appears to be most preferable. Other formulations, including the “lubrication factor” hypothesis used by Budd (1975) are tentatively rejected. Consideration of the temporal variations of the “bed separation index” indicate that, on short time scales of days and weeks, variations of water pressure can dominate the sliding process. A rapid order-of-magnitude increase in water discharge causes a hundredfold transient increase in the water pressure. A bi-modal hydraulic regime is revealed for water flow transverse to the direction of main ice flow. This behavior is in accord with the observation of a sudden acceleration of the ice due to increased sliding in early summer or following heavy rainstorms.

scholarly journals The role of bed separation and friction in sliding over an undeformable bed

1992 ◽  
Vol 38 (128) ◽  
pp. 77-92 ◽  
Author(s):  
Jürg Schweizer ◽  
Almut Iken
Keyword(s):  
Shear Stress ◽  
Functional Relationship ◽  
Water Pressure ◽  
Important Variable ◽  
Sliding Velocity ◽  
Sliding Motion ◽  
Basal Ice ◽  
Bed Separation ◽  
Basal Shear

AbstractThe classic sliding theories usually assume that the sliding motion occurs frictionlessly. However, basal ice is debris-laden and friction exists between the substratum and rock particles embedded in the basal ice. The influence of debris concentration on the sliding process is investigated. The actual conditions where certain types of friction apply are defined, the effect for the case of bed separation due to a subglacial water pressure is studied and consequences for the sliding law are formulated. The numerical modelling of the sliding of an ice mass over an undulating bed, including the effect of both the subglacial water pressure and the friction, is done by using the finite-clement method. Friction, seen as a reduction of the driving shear stress due to gravity, can be included in existing sliding laws which should contain the critical pressure as an important variable. An approximate functional relationship between the sliding velocity, the effective basal shear stress and the subglacial water pressure is given.

scholarly journals The role of bed separation and friction in sliding over an undeformable bed

1992 ◽  
Vol 38 (128) ◽  
pp. 77-92 ◽  
Author(s):  
Jürg Schweizer ◽  
Almut Iken
Keyword(s):  
Shear Stress ◽  
Functional Relationship ◽  
Water Pressure ◽  
Important Variable ◽  
Sliding Velocity ◽  
Sliding Motion ◽  
Basal Ice ◽  
Bed Separation ◽  
Basal Shear

AbstractThe classic sliding theories usually assume that the sliding motion occurs frictionlessly. However, basal ice is debris-laden and friction exists between the substratum and rock particles embedded in the basal ice. The influence of debris concentration on the sliding process is investigated. The actual conditions where certain types of friction apply are defined, the effect for the case of bed separation due to a subglacial water pressure is studied and consequences for the sliding law are formulated. The numerical modelling of the sliding of an ice mass over an undulating bed, including the effect of both the subglacial water pressure and the friction, is done by using the finite-clement method. Friction, seen as a reduction of the driving shear stress due to gravity, can be included in existing sliding laws which should contain the critical pressure as an important variable. An approximate functional relationship between the sliding velocity, the effective basal shear stress and the subglacial water pressure is given.

scholarly journals Water-pressure Coupling of Sliding and Bed Deformation: II. Velocity-Depth Profiles

1989 ◽  
Vol 35 (119) ◽  
pp. 119-129 ◽  
Author(s):  
R.B. Alley
Keyword(s):  
Size Range ◽  
Water Pressure ◽  
Effective Pressure ◽  
West Antarctica ◽  
Depth Profiles ◽  
Bed Deformation ◽  
Melt Water ◽  
Ice Stream B ◽  
Basal Shear ◽  
Theoretical Analyses

AbstractBasal motion of a glacier resting on an unconsolidated bed can arise from sliding between ice and bed, ploughing of clasts through the upper layer of the bed, pervasive deformation of the bed, or shearing across discrete planes in the bed. Theoretical analyses and limited observations of soft-bedded glaciers not dominated by supply of channelized melt water from the surface suggest that sliding will be slow if the bed contains abundant clasts in the 1–10 mm size range, and that high velocities by ploughing are unlikely though possible. Pervasive deformation usually will account for 60–100% of the basal velocity, and the strain-rate will be proportional to the basal shear stress and inversely proportional to the square or cube of the effective pressure. These hypotheses are based on results of part I in this series, and allow modeling of Ice Stream B, West Antarctica, in part III of this series.

scholarly journals Basal Sliding and Bed Separation: Is There a Connection?

1979 ◽  
Vol 23 (89) ◽  
pp. 407-408 ◽  
Author(s):  
Robert Bindschadler
Keyword(s):  
Shear Stress ◽  
Normal Stress ◽  
Water Pressure ◽  
Simple Relationship ◽  
Sliding Velocity ◽  
Separation Parameter ◽  
Basal Sliding ◽  
Bed Separation ◽  
Image Position ◽  
Basal Shear

Abstract Analysis of field data from Variegated Glacier supports the conclusion of Meier (1968) that no simple relationship between basal shear stress and sliding velocity can be found. On the other hand, an index of bed separation is defined and evaluated that correlates very well with the longitudinal variation of summer sliding velocity inferred for Variegated Glacier. This bed separation parameter is defined as where τ is the basal shear stress and is proportional to the drop in normal stress on the down-glacier side of bedrock bumps and N eff is the effective normal stress equal to the overburden stress minus the subglacial water pressure. The water-pressure distribution is calculated assuming water flow to be confined in subglacial Röthlisberger conduits. The excellent agreement between the longitudinal profiles of I and sliding velocity suggests that calculations of the variation of bed separation can be used to deduce the variation of sliding velocity in both space and time. Further, it is possible that a functional relationship can be developed that adequately represents the geometric controls on basal sliding to permit accurate predictions of sliding velocities.

scholarly journals Basal Sliding and Bed Separation: Is There a Connection?

1979 ◽  
Vol 23 (89) ◽  
pp. 407-408
Author(s):  
Robert Bindschadler
Keyword(s):  
Shear Stress ◽  
Normal Stress ◽  
Water Pressure ◽  
Simple Relationship ◽  
Sliding Velocity ◽  
Separation Parameter ◽  
Basal Sliding ◽  
Bed Separation ◽  
Image Position ◽  
Basal Shear

AbstractAnalysis of field data from Variegated Glacier supports the conclusion of Meier (1968) that no simple relationship between basal shear stress and sliding velocity can be found. On the other hand, an index of bed separation is defined and evaluated that correlates very well with the longitudinal variation of summer sliding velocity inferred for Variegated Glacier. This bed separation parameter is defined as where τ is the basal shear stress and is proportional to the drop in normal stress on the down-glacier side of bedrock bumps and Neff is the effective normal stress equal to the overburden stress minus the subglacial water pressure. The water-pressure distribution is calculated assuming water flow to be confined in subglacial Röthlisberger conduits. The excellent agreement between the longitudinal profiles of I and sliding velocity suggests that calculations of the variation of bed separation can be used to deduce the variation of sliding velocity in both space and time. Further, it is possible that a functional relationship can be developed that adequately represents the geometric controls on basal sliding to permit accurate predictions of sliding velocities.

scholarly journals Subglacial Processes at Bondhusbreen, Norway: Preliminary Results

1983 ◽  
Vol 4 ◽  
pp. 91-98 ◽  
Author(s):  
Jon Ove Hagen ◽  
Bjørn Wold ◽  
Olav Liestøl ◽  
Gunnar Østrem ◽  
Johan Ludvig Sollid
Keyword(s):  
Water Pressure ◽  
Water Discharge ◽  
Pressure Sensors ◽  
Hydroelectric Power ◽  
Outlet Glacier ◽  
Running Water ◽  
Order Of Magnitude ◽  
The Difference ◽  
Annual Water Discharge ◽  
Small Channels

Subglacial hydrology, sediment transport, pressure, and temperature have been studied beneath approximately 160 m of ice at Sondhusbreen, an outlet glacier from Folgefonni in south-western Norway.The volume of the mean annual water discharge passing through the study area is about 60x106 m3. Most of this water is diverted into a tunnel system in the rock beneath the glacier and used for hydroelectric power generation. At the beginning of the melt season, this water flows in multiple small channels, but later it collects in one or two main channels. The discharge of eroded material is about 7 600 tonnes a−1. Of this, roughly 90% is transported by running water.Pressure gauges and thermistors were installed at two sites under the glacier. Results from one of the sites indicated that ice can stagnate in some leeward positions, as almost no ice movement was recorded during most of the period of measurement and the pressure distribution was nearly hydrostatic. However, increased water pressure during the summer apparently resulted in the opening of subglacial cavities, adding a local up-glacier component to the flow at this site.At another location, about 20 m up-glacier, non-hydrostatic differential pressures of up to 30 bar were recorded across an artificial dome-shaped obstacle. The flow at this location was more steady, in general, but rather dramatic effects were recorded when a boulder 0.3 m3 in size passed over the obstacle, destroying one of the pressure sensors. This sensor recorded a pressure of 90 bar before failing. The boulder was moving at a speed of about 40 mm d-1, whereas the sliding velocity of the ice was 80 mm d-1. Temperature measurements suggest that the difference in temperature across this obstacle was less than 0.03 deg, or an order of magnitude less than expected. This may mean that water was squeezed out of the ice on the stoss side of the obstacle as suggested by Robin (1976), and thus was not available to warm the lee-side ice by refreezing.

scholarly journals Subglacial Processes at Bondhusbreen, Norway: Preliminary Results

1983 ◽  
Vol 4 ◽  
pp. 91-98 ◽  
Author(s):  
Jon Ove Hagen ◽  
Bjørn Wold ◽  
Olav Liestøl ◽  
Gunnar Østrem ◽  
Johan Ludvig Sollid
Keyword(s):  
Water Pressure ◽  
Water Discharge ◽  
Pressure Sensors ◽  
Hydroelectric Power ◽  
Outlet Glacier ◽  
Running Water ◽  
Order Of Magnitude ◽  
The Difference ◽  
Annual Water Discharge ◽  
Small Channels

Subglacial hydrology, sediment transport, pressure, and temperature have been studied beneath approximately 160 m of ice at Sondhusbreen, an outlet glacier from Folgefonni in south-western Norway.The volume of the mean annual water discharge passing through the study area is about 60x106m3. Most of this water is diverted into a tunnel system in the rock beneath the glacier and used for hydroelectric power generation. At the beginning of the melt season, this water flows in multiple small channels, but later it collects in one or two main channels. The discharge of eroded material is about 7 600 tonnes a−1. Of this, roughly 90% is transported by running water.Pressure gauges and thermistors were installed at two sites under the glacier. Results from one of the sites indicated that ice can stagnate in some leeward positions, as almost no ice movement was recorded during most of the period of measurement and the pressure distribution was nearly hydrostatic. However, increased water pressure during the summer apparently resulted in the opening of subglacial cavities, adding a local up-glacier component to the flow at this site.At another location, about 20 m up-glacier, non-hydrostatic differential pressures of up to 30 bar were recorded across an artificial dome-shaped obstacle. The flow at this location was more steady, in general, but rather dramatic effects were recorded when a boulder 0.3 m3in size passed over the obstacle, destroying one of the pressure sensors. This sensor recorded a pressure of 90 bar before failing. The boulder was moving at a speed of about 40 mm d-1, whereas the sliding velocity of the ice was 80 mm d-1. Temperature measurements suggest that the difference in temperature across this obstacle was less than 0.03 deg, or an order of magnitude less than expected. This may mean that water was squeezed out of the ice on the stoss side of the obstacle as suggested by Robin (1976), and thus was not available to warm the lee-side ice by refreezing.

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