scholarly journals Surface “waves” on Byrd Glacier, Antarctica

2003 ◽  
Vol 15 (4) ◽  
pp. 547-555 ◽  
Author(s):  
D. REUSCH ◽  
T. HUGHES
Keyword(s):  
Surface Waves ◽  
Wave Train ◽  
Water Pressure ◽  
Force Balance ◽  
Surface Slope ◽  
Ice Shelf ◽  
Overburden Pressure ◽  
Ross Ice Shelf ◽  
Bed Topography ◽  
Catchment Areas

Byrd Glacier has one of the largest ice catchment areas in Antarctica, delivers more ice to the Ross Ice Shelf than any other ice stream, and is the fastest of these ice streams. A force balance, combined with a mass balance, demonstrates that stream flow in Byrd Glacier is transitional from sheet flow in East Antarctica to shelf flow in the Ross Ice Shelf. The longitudinal pulling stress, calculated along an ice flowband from the force balance, is linked to variations of ice thickness, to the ratio of the basal water pressure to the ice overburden pressure where Byrd Glacier is grounded, and is reduced by an ice-shelf buttressing stress where Byrd Glacier is floating. Longitudinal tension peaks at pressure-ratio maxima in grounded ice and close to minima in the ratio of the pulling stress to the buttressing stress in floating ice. The longitudinal spacing of these tension peaks is rather uniform and, for grounded ice, the peaks occur at maxima in surface slope that have no clear relation to the bed slope. This implies that the maxima in surface slope constitute a “wave train” that is related to regular variations in ice-bed coupling, not primarily to bed topography. It is unclear whether these surface “waves” are “standing waves” or are migrating either upslope or downslope, possibly causing the grounding line to either retreat or advance. Deciding which is the case will require obtaining bed topography in the map plane, a new map of surface topography, and more sophisticated modeling that includes ice flow linked to subglacial hydrology in the map plane.

scholarly journals Water Pressure in Intra- and Subglacial Channels

1972 ◽  
Vol 11 (62) ◽  
pp. 177-203 ◽  
Author(s):  
Hans Röthlisberger
Keyword(s):  
Sediment Load ◽  
Water Pressure ◽  
Drainage System ◽  
Water Layer ◽  
Frictional Heat ◽  
Overburden Pressure ◽  
Bed Topography ◽  
Water Head ◽  
Local Topography ◽  
Dependent Flow

AbstractWater flowing in tubular channels inside a glacier produces frictional heat, which causes melting of the ice walls. However the channels also have a tendency to close under the overburden pressure. Using the equilibrium equation that at every cross-section as much ice is melted as flows in, differential equations are given for steady flow in horizontal, inclined and vertical channels at variable depth and for variable discharge, ice properties and channel roughness. It is shown that the pressure decreases with increasing discharge, which proves that water must flow in main arteries. The same argument is used to show that certain glacier lakes above long flat valley glaciers must form in times of low discharge and empty when the discharge is high, i.e. when the water head in the subglacial drainage system drops below the lake level. Under the conditions of the model an ice mass of uniform thickness does not float, i.e. there is no water layer at the bottom, when the bed is inclined in the down-hill direction, but it can float on a horizontal bed if the exponentnof the law for the ice creep is small. It is further shown that basal streams (bottom conduits) and lateral streams at the hydraulic grade line (gradient conduits) can coexist. Time-dependent flow, local topography, ice motion, and sediment load are not accounted for in the theory, although they may strongly influence the actual course of the water. Computations have been carried out for the Gornergletscher where the bed topography is known and where some data are available on subglacial water pressure.

scholarly journals Quantifying the Jakobshavn Effect: Jakobshavn Isbrae, Greenland, compared to Byrd Glacier, Antarctica

2014 ◽  
Vol 8 (2) ◽  
pp. 2043-2118
Author(s):  
T. Hughes ◽  
A. Sargent ◽  
J. Fastook ◽  
K. Purdon ◽  
J. Li ◽  
...  
Keyword(s):  
Ice Sheets ◽  
Greenland Ice Sheet ◽  
Force Balance ◽  
Ice Age ◽  
Ice Shelf ◽  
Ice Streams ◽  
Ross Ice Shelf ◽  
Ice Stream ◽  
Visual Understanding ◽  
Subglacial Lakes

Abstract. The Jakobshavn Effect is a series of positive feedback mechanisms that was first observed on Jakobshavn Isbrae, which drains the west-central part of the Greenland Ice Sheet and enters Jakobshavn Isfjord at 69°10'. These mechanisms fall into two categories, reductions of ice-bed coupling beneath an ice stream due to surface meltwater reaching the bed, and reductions in ice-shelf buttressing beyond an ice stream due to disintegration of a laterally confined and locally pinned ice shelf. These uncoupling and unbuttressing mechanisms have recently taken place for Byrd Glacier in Antarctica and Jakobshavn Isbrae in Greenland, respectively. For Byrd Glacier, no surface meltwater reaches the bed. That water is supplied by drainage of two large subglacial lakes where East Antarctic ice converges strongly on Byrd Glacier. Results from modeling both mechanisms are presented here. We find that the Jakobshavn Effect is not active for Byrd Glacier, but is active for Jakobshavn Isbrae, at least for now. Our treatment is holistic in the sense it provides continuity from sheet flow to stream flow to shelf flow. It relies primarily on a force balance, so our results cannot be used to predict long-term behavior of these ice streams. The treatment uses geometrical representations of gravitational and resisting forces that provide a visual understanding of these forces, without involving partial differential equations and continuum mechanics. The Jakobshavn Effect was proposed to facilitate terminations of glaciation cycles during the Quaternary Ice Age by collapsing marine parts of ice sheets. This is unlikely for the Antarctic and Greenland ice sheets, based on our results for Byrd Glacier and Jakobshavn Isbrae, without drastic climate warming in high polar latitudes. Warming would affect other Antarctic ice streams already weakly buttressed or unbuttressed by an ice shelf. Ross Ice Shelf would still protect Byrd Glacier.

scholarly journals Water Pressure in Intra- and Subglacial Channels

1972 ◽  
Vol 11 (62) ◽  
pp. 177-203 ◽  
Author(s):  
Hans Röthlisberger
Keyword(s):  
Sediment Load ◽  
Water Pressure ◽  
Drainage System ◽  
Water Layer ◽  
Frictional Heat ◽  
Overburden Pressure ◽  
Bed Topography ◽  
Water Head ◽  
Local Topography ◽  
Dependent Flow

AbstractWater flowing in tubular channels inside a glacier produces frictional heat, which causes melting of the ice walls. However the channels also have a tendency to close under the overburden pressure. Using the equilibrium equation that at every cross-section as much ice is melted as flows in, differential equations are given for steady flow in horizontal, inclined and vertical channels at variable depth and for variable discharge, ice properties and channel roughness. It is shown that the pressure decreases with increasing discharge, which proves that water must flow in main arteries. The same argument is used to show that certain glacier lakes above long flat valley glaciers must form in times of low discharge and empty when the discharge is high, i.e. when the water head in the subglacial drainage system drops below the lake level. Under the conditions of the model an ice mass of uniform thickness does not float, i.e. there is no water layer at the bottom, when the bed is inclined in the down-hill direction, but it can float on a horizontal bed if the exponent n of the law for the ice creep is small. It is further shown that basal streams (bottom conduits) and lateral streams at the hydraulic grade line (gradient conduits) can coexist. Time-dependent flow, local topography, ice motion, and sediment load are not accounted for in the theory, although they may strongly influence the actual course of the water. Computations have been carried out for the Gornergletscher where the bed topography is known and where some data are available on subglacial water pressure.

scholarly journals Timing of stagnation of Ice Stream C, West Antarctica, from short-pulse radar studies of buried surface crevasses

1993 ◽  
Vol 39 (133) ◽  
pp. 553-561 ◽  
Author(s):  
Rory Retzlaff ◽  
Charles R. Bentley
Keyword(s):  
Short Pulse ◽  
Water Pressure ◽  
West Antarctica ◽  
Ice Shelf ◽  
Ice Streams ◽  
Ross Ice Shelf ◽  
Pulse Radar ◽  
West Antarctic ◽  
Ice Stream ◽  
Inland Ice

AbstractFive short-pulse radar profiles were run across the edge of inactive Ice Stream C, one of the “Ross” ice streams that flows from the West Antarctic inland ice sheet into the Ross Ice Shelf. Scatter from buried crevasses, which we presume were at the surface of the ice stream when it was active, creates hyperbolae on the radar records. A density-depth curve and local accumulation rates were used to convert the picked travel times of the apices of the hyperbolae into stagnation ages for the ice stream. Stagnation ages are 130 ± 25 year for the three profiles farthest downstream and marginally less (100 ± 30 year) for the fourth. The profile farthest upstream shows a stagnation age of only ~30 year. We believe that these results indicate a “wave” of stagnation propagating at a diminishing speed upstream from the mouth of the ice stream, and we suggest that the stagnation process involves a drop in water pressure at the bed due to a conversion from sheet flow to channelized water flow.

scholarly journals Hydraulic run-away: a mechanism for thermally regulated surges of ice sheets

1995 ◽  
Vol 41 (139) ◽  
pp. 554-561 ◽  
Author(s):  
A. C. Fowler ◽  
Clare Johnson
Keyword(s):  
Drainage Basin ◽  
Water Pressure ◽  
Ice Sheets ◽  
Ice Shelf ◽  
Coupled Flow ◽  
Ice Streams ◽  
Ross Ice Shelf ◽  
Physically Based ◽  
Parameterized Model ◽  
Confined Flows

AbstractBy using a simple parameterized model of thermomechanically coupled flow in cold ice sheets, together with a physically based sliding law which includes a description of basal drainage, we show that relationships between ice flux and ice thickness can realistically be multi-valued, and hence that hydraulically induced surges can occur. We term this mechanism hydraulic run-away, as it relies on the positive feed-back between sliding velocity and basal melt production. For this feedback to operate, it is essential that water pressure increases with water storage. This is consistent with various recent ideas concerning drainage, under ice sheets, be it through a system of canals, a distnbuted film or a subglacial aquifer. For confined flows, such as valley glaciers (e.g. Trapridge Glacier) or topographically constrained ice streams (e.g. Hudson Strait in the Laurentide ice sheet), which are underlain by sufficiently deformable sediment, we can expect thermally regulated surges to occur, while in a laterally unconfined drainage basin (such as that which flows into the Ross Ice Shelf), we might expect ice streams to develop.

scholarly journals The sliding velocity over a sinusoidal bed at high water pressure

1998 ◽  
Vol 44 (147) ◽  
pp. 379-382 ◽  
Author(s):  
Martin Truffer ◽  
Almut Iken
Keyword(s):  
Contact Area ◽  
Critical Pressure ◽  
Water Pressure ◽  
Wave Length ◽  
High Water ◽  
Force Balance ◽  
Sliding Velocity ◽  
Pressurized Water ◽  
Overburden Pressure ◽  
Basal Shear

AbstractUnder idealized conditions, when pressurized water has access to all low-pressure areas at the glacier bed, a sliding instability exists at a critical pressure,pc,well below the overburden pressure,p0.The critical pressure is given by, wherelis the wave length andais the amplitude of a sinusoidal bedrock, andTis the basal shear stress. When the subglacial water pressure, pw, approaches this critical value, the area of ice-bed contact,△l,becomes very small and the pressure on the contact area becomes very large. This pressure is calculated from a force balance and the corresponding rate of compression is obtained using Glen’s flow law for ice. On the assumption that compression in the vicinity of the contact area occurs over a distance of the order of the size of this area,Δl,a deformational velocity is estimated. The resultant sliding velocity shows the expected instability at the critical water pressure. The dependency on other parameters, such as wavelengthland roughnessa/l,was found to be the same as for sliding without bed separation.

scholarly journals Hydraulic run-away: a mechanism for thermally regulated surges of ice sheets

1995 ◽  
Vol 41 (139) ◽  
pp. 554-561 ◽  
Author(s):  
A. C. Fowler ◽  
Clare Johnson
Keyword(s):  
Drainage Basin ◽  
Water Pressure ◽  
Ice Sheets ◽  
Ice Shelf ◽  
Coupled Flow ◽  
Ice Streams ◽  
Ross Ice Shelf ◽  
Physically Based ◽  
Parameterized Model ◽  
Confined Flows

Abstract By using a simple parameterized model of thermomechanically coupled flow in cold ice sheets, together with a physically based sliding law which includes a description of basal drainage, we show that relationships between ice flux and ice thickness can realistically be multi-valued, and hence that hydraulically induced surges can occur. We term this mechanism hydraulic run-away, as it relies on the positive feed-back between sliding velocity and basal melt production. For this feedback to operate, it is essential that water pressure increases with water storage. This is consistent with various recent ideas concerning drainage, under ice sheets, be it through a system of canals, a distnbuted film or a subglacial aquifer. For confined flows, such as valley glaciers (e.g. Trapridge Glacier) or topographically constrained ice streams (e.g. Hudson Strait in the Laurentide ice sheet), which are underlain by sufficiently deformable sediment, we can expect thermally regulated surges to occur, while in a laterally unconfined drainage basin (such as that which flows into the Ross Ice Shelf), we might expect ice streams to develop.

scholarly journals Timing of stagnation of Ice Stream C, West Antarctica, from short-pulse radar studies of buried surface crevasses

1993 ◽  
Vol 39 (133) ◽  
pp. 553-561 ◽  
Author(s):  
Rory Retzlaff ◽  
Charles R. Bentley
Keyword(s):  
Short Pulse ◽  
Water Pressure ◽  
West Antarctica ◽  
Ice Shelf ◽  
Ice Streams ◽  
Ross Ice Shelf ◽  
Pulse Radar ◽  
West Antarctic ◽  
Ice Stream ◽  
Inland Ice

AbstractFive short-pulse radar profiles were run across the edge of inactive Ice Stream C, one of the “Ross” ice streams that flows from the West Antarctic inland ice sheet into the Ross Ice Shelf. Scatter from buried crevasses, which we presume were at the surface of the ice stream when it was active, creates hyperbolae on the radar records. A density-depth curve and local accumulation rates were used to convert the picked travel times of the apices of the hyperbolae into stagnation ages for the ice stream. Stagnation ages are 130 ± 25 year for the three profiles farthest downstream and marginally less (100 ± 30 year) for the fourth. The profile farthest upstream shows a stagnation age of only ~30 year. We believe that these results indicate a “wave” of stagnation propagating at a diminishing speed upstream from the mouth of the ice stream, and we suggest that the stagnation process involves a drop in water pressure at the bed due to a conversion from sheet flow to channelized water flow.

scholarly journals Ice velocity changes in the Ross and Ronne sectors observed using satellite radar data from 1997 and 2009

2012 ◽  
Vol 6 (5) ◽  
pp. 1019-1030 ◽  
Author(s):  
B. Scheuchl ◽  
J. Mouginot ◽  
E. Rignot
Keyword(s):  
Order Effects ◽  
Strong Impact ◽  
Ice Shelf ◽  
Ice Streams ◽  
Dynamic Changes ◽  
Ice Shelves ◽  
Ross Ice Shelf ◽  
Catchment Areas ◽  
Ice Velocity ◽  
The Antarctic

Abstract. We report changes in ice velocity of a 6.5 million km2 region around South Pole encompassing the Filchner-Ronne and Ross Ice Shelves and a significant portion of the ice streams and glaciers that constitute their catchment areas. Using the first full interferometric synthetic aperture radar (InSAR) coverage of the region completed in 2009 and partial coverage acquired in 1997, we processed the data to assemble a comprehensive map of ice speed changes between those two years. On the Ross Ice Shelf, our results confirm a continued deceleration of Mercer and Whillans Ice Streams with a 12-yr velocity difference of −50 m yr−1 (−16.7%) and −100 m yr−1 (−25.3%) at their grounding lines. The deceleration spreads 450 km upstream of the grounding line and more than 500 km onto the shelf, beyond what was previously known. Ross and Filchner Ice Shelves exhibit signs of pre-calving events, representing the largest observed changes, with an increase in speed in excess of +100 m yr−1 in 12 yr. Other changes in the Ross Ice Shelf region are less significant. The observed changes in glacier speed extend on the Ross Ice Shelf along the ice streams' flow lines. Most tributaries of the Filchner-Ronne Ice Shelf show a modest deceleration or no change between 1997 and 2009. Slessor Glacier shows a small deceleration over a large sector. No change is detected on the Bailey, Rutford, and Institute Ice Streams. On the Filchner Ice Shelf itself, ice decelerated rather uniformly with a 12-yr difference in speed of −50 m yr−1, or −5% of its ice front speed, which we attribute to a 12 km advance in its ice front position. Our results show that dynamic changes are present in the region. They highlight the need for continued observation of the area with a primary focus on the Siple Coast. The dynamic changes in Central Antarctica between 1997 and 2009 are generally second-order effects in comparison to losses on glaciers in the Bellingshausen and Amundsen Seas region and on the Antarctic Peninsula. We therefore conclude that the dynamic changes shown here do not have a strong impact on the mass budget of the Antarctic continent.

scholarly journals The sliding velocity over a sinusoidal bed at high water pressure

1998 ◽  
Vol 44 (147) ◽  
pp. 379-382
Author(s):  
Martin Truffer ◽  
Almut Iken
Keyword(s):  
Contact Area ◽  
Critical Pressure ◽  
Water Pressure ◽  
Wave Length ◽  
High Water ◽  
Force Balance ◽  
Sliding Velocity ◽  
Pressurized Water ◽  
Overburden Pressure ◽  
Basal Shear

AbstractUnder idealized conditions, when pressurized water has access to all low-pressure areas at the glacier bed, a sliding instability exists at a critical pressure, pc, well below the overburden pressure, p0. The critical pressure is given by , where l is the wave length and a is the amplitude of a sinusoidal bedrock, and T is the basal shear stress. When the subglacial water pressure, pw, approaches this critical value, the area of ice-bed contact, △l, becomes very small and the pressure on the contact area becomes very large. This pressure is calculated from a force balance and the corresponding rate of compression is obtained using Glen’s flow law for ice. On the assumption that compression in the vicinity of the contact area occurs over a distance of the order of the size of this area, Δl, a deformational velocity is estimated. The resultant sliding velocity shows the expected instability at the critical water pressure. The dependency on other parameters, such as wavelength l and roughness a/l, was found to be the same as for sliding without bed separation.

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