scholarly journals Longitudinal coupling in ice flow across a subglacial ridge

1997 ◽  
Vol 24 ◽  
pp. 169-174 ◽  
Author(s):  
Peter Jansson
Keyword(s):  
Numerical Model ◽  
Flow Regime ◽  
Field Data ◽  
Water Pressure ◽  
Drastic Change ◽  
Surface Velocity ◽  
Northern Sweden ◽  
Ice Flow ◽  
Bedrock Topography ◽  
Velocity Variations

A transverse bedrock ridge, or riegel, in the bedrock topography under Storglaciären, northern Sweden, induces a drastic change in flow regime. The part of the glacier located downstream of the riegel exhibits velocity variations correlated to water-pressure variations under this part of the glacier. Similar velocity variations are also observed up-glacier from the riegel despite a lack of significant water-pressure variations there. Field data and a numerical model suggest that the variations in surface velocity observed on the glacier upstream of the riegel are a result of pulling from down-glacier through longitudinal coupling across the riegel.

scholarly journals Longitudinal coupling in ice flow across a subglacial ridge

1997 ◽  
Vol 24 ◽  
pp. 169-174 ◽  
Author(s):  
Peter Jansson
Keyword(s):  
Numerical Model ◽  
Flow Regime ◽  
Field Data ◽  
Water Pressure ◽  
Drastic Change ◽  
Surface Velocity ◽  
Northern Sweden ◽  
Ice Flow ◽  
Bedrock Topography ◽  
Velocity Variations

A transverse bedrock ridge, or riegel, in the bedrock topography under Storglaciären, northern Sweden, induces a drastic change in flow regime. The part of the glacier located downstream of the riegel exhibits velocity variations correlated to water-pressure variations under this part of the glacier. Similar velocity variations are also observed up-glacier from the riegel despite a lack of significant water-pressure variations there. Field data and a numerical model suggest that the variations in surface velocity observed on the glacier upstream of the riegel are a result of pulling from down-glacier through longitudinal coupling across the riegel.

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

1986 ◽  
Vol 32 (110) ◽  
pp. 101-119 ◽  
Author(s):  
Almut Iken ◽  
Robert A. Bindschadler
Keyword(s):  
Functional Relationship ◽  
Water Pressure ◽  
Drainage System ◽  
High Water ◽  
Water Levels ◽  
Surface Velocity ◽  
Glacier Surface ◽  
Measured Velocity ◽  
Sliding Mechanism ◽  
Velocity Variations

AbstractDuring 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.

scholarly journals The ice thickness distribution of Flask Glacier, Antarctic Peninsula, determined by combining radio-echo soundings, surface velocity data and flow modelling

2013 ◽  
Vol 54 (63) ◽  
pp. 18-24 ◽  
Author(s):  
Daniel Farinotti ◽  
Hugh Corr ◽  
G.Hilmar Gudmundsson
Keyword(s):  
Antarctic Peninsula ◽  
Thickness Distribution ◽  
Surface Velocity ◽  
Ice Thickness ◽  
Ice Shelf ◽  
Ice Flow ◽  
Ice Volume ◽  
Flow Modelling ◽  
Bedrock Topography ◽  
Sparse Measurements

AbstractAn interpolated bedrock topography is presented for Flask Glacier, one of the tributaries of the remnant part of the Larsen B ice shelf, Antarctic Peninsula. The ice thickness distribution is derived by combining direct but sparse measurements from airborne radio-echo soundings with indirect estimates obtained from ice-flow modelling. The ice-flow model is applied to a series of transverse profiles, and a first estimate of the bedrock is iteratively adjusted until agreement between modelled and measured surface velocities is achieved. The adjusted bedrock is then used to reinterpret the radio-echo soundings, and the recovered information used to further improve the estimate of the bedrock itself. The ice flux along the glacier center line provides an additional and independent constraint on the ice thickness. The resulting bedrock topography reveals a glacier bed situated mainly below sea level with sections having retrograde slope. The total ice volume of 120 ±15 km3 for the considered area of 215 km2 corresponds to an average ice thickness of 560 ± 70 m.

scholarly journals Water pressure and basal sliding on Storglaciären, northern Sweden

1995 ◽  
Vol 41 (138) ◽  
pp. 232-240 ◽  
Author(s):  
Peter Jansson
Keyword(s):  
Water Pressure ◽  
Surface Velocity ◽  
Northern Sweden ◽  
Overburden Pressure ◽  
Weakly Coupled ◽  
Basal Sliding ◽  
Order Of Magnitude ◽  
Image Position ◽  
Hydraulic Jacking ◽  
Small Valley

AbstractThe subglacial hydrology of the ablation area of Storglaciären, a small valley glacier in northern Sweden, is dramatically affected by a subglacial ridge, or riegel. Water pressures above this riegel are relatively constant, while down-glacier from it they vary significantly. The lower part of the glacier accelerates in response to peaks in basal water pressure. The upper part may be weakly coupled to the lower part during these peaks.A power-law fit of observed basal water pressures and measured surface velocities yieldswhereusis the surface velocity andPEis the effective water pressure (ice overburden pressure minus subglacial water pressure). Data from Findelengletscher, reported by Iken and Bindschadler (1986), yield an identical exponent and a coefficient one order of magnitude larger. The similar exponent implies that the process producing the velocity variations on both glaciers is similar. The variations in velocity are inferred to be due to hydraulic jacking on both glaciers.

scholarly journals Surface Velocity Determination on Large Polar Glaciers by Aerial Photogrammetry

1986 ◽  
Vol 8 ◽  
pp. 22-26 ◽  
Author(s):  
H. H. Brecher
Keyword(s):  
Strain Rate ◽  
Flow Regime ◽  
Surface Velocity ◽  
Control Points ◽  
West Antarctica ◽  
Ice Flow ◽  
Elapsed Time ◽  
Aerial Photogrammetry ◽  
Ice Surface ◽  
Ice Stream B

Aerial photogrammetric block triangulation, a standard and well-developed technique for extending accurate control for mapping into the interior of a region from a few points of known position on its perimeter, can be readily adapted to determine surface velocities on bodies of ice which are too large, and often too crevassed, to be studied effectively by conventional ground surveying. Velocities are calculated from the changes in positions of the same natural surface features determined from photography of two (or more) epochs and the elapsed time. This method is capable of providing many uniformly-spaced measurements over the whole, moving, ice surface, thus allowing the production of maps of velocity and strain-rate, which are valuable in analyzing the ice-flow regime. Results from measurements completed some years ago on Byrd Glacier, one of the largest outlet glaciers from the East Antarctic plateau, are presented as an example of what the method can yield. By means of Doppler satellite surveying, relative positions of control points for each photography epoch can be determined with sub-meter accuracy, making the technique suitable also in regions where no fixed land features exist. A brief description of a project under way in such an area, on Ice Stream B in West Antarctica, is given.

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

1986 ◽  
Vol 32 (110) ◽  
pp. 101-119 ◽  
Author(s):  
Almut Iken ◽  
Robert A. Bindschadler
Keyword(s):  
Functional Relationship ◽  
Water Pressure ◽  
Drainage System ◽  
High Water ◽  
Water Levels ◽  
Surface Velocity ◽  
Glacier Surface ◽  
Measured Velocity ◽  
Sliding Mechanism ◽  
Velocity Variations

AbstractDuring 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.

scholarly journals Water pressure and basal sliding on Storglaciären, northern Sweden

1995 ◽  
Vol 41 (138) ◽  
pp. 232-240 ◽  
Author(s):  
Peter Jansson
Keyword(s):  
Water Pressure ◽  
Surface Velocity ◽  
Northern Sweden ◽  
Overburden Pressure ◽  
Weakly Coupled ◽  
Basal Sliding ◽  
Order Of Magnitude ◽  
Image Position ◽  
Hydraulic Jacking ◽  
Small Valley

AbstractThe subglacial hydrology of the ablation area of Storglaciären, a small valley glacier in northern Sweden, is dramatically affected by a subglacial ridge, or riegel. Water pressures above this riegel are relatively constant, while down-glacier from it they vary significantly. The lower part of the glacier accelerates in response to peaks in basal water pressure. The upper part may be weakly coupled to the lower part during these peaks.A power-law fit of observed basal water pressures and measured surface velocities yieldswhere us is the surface velocity and PE is the effective water pressure (ice overburden pressure minus subglacial water pressure). Data from Findelengletscher, reported by Iken and Bindschadler (1986), yield an identical exponent and a coefficient one order of magnitude larger. The similar exponent implies that the process producing the velocity variations on both glaciers is similar. The variations in velocity are inferred to be due to hydraulic jacking on both glaciers.

scholarly journals Surface speed and frontal ablation of Kronebreen and Kongsbreen, NW-Svalbard, from SAR offset tracking

2014 ◽  
Vol 8 (6) ◽  
pp. 6193-6233 ◽  
Author(s):  
T. Schellenberger ◽  
T. Dunse ◽  
A. Kääb ◽  
J. Kohler ◽  
C. H. Reijmer
Keyword(s):  
Water Pressure ◽  
Velocity Fields ◽  
Surface Velocity ◽  
Gps Measurements ◽  
Ice Flow ◽  
Area Loss ◽  
Continuous Gps ◽  
Offset Tracking ◽  
Frontal Ablation ◽  
Data Surface

Abstract. Kronebreen and Kongsbreen are among the fastest flowing glaciers on Svalbard, and therefore important contributors to glacier mass loss from the archipelago through frontal ablation. Here, we present a time series of area-wide surface velocity fields from April 2012 to December 2013 based on offset tracking on repeat high-resolution Radarsat-2 Ultrafine data. Surface speeds reached up to 3.2 m d−1 near the calving front of Kronebreen in summer 2013 and 2.7 m d−1 at Kongsbreen in late autumn 2012. Additional velocity fields from Radarsat-1, Radarsat-2 and TerraSAR-X data since December 2007 together with continuous GPS measurements on Kronebreen since September 2008 revealed complex patterns in seasonal and interannual speed evolution. Part of the ice-flow variations seem closely linked to the amount and timing of surface melt water production and rainfall, both of which are known to have a strong influence on the basal water pressure and lubrication. In addition, terminus retreat and the associated reduction in backstress appear to have influenced the speed close to the calving front, especially at Kongsbreen in 2012 and 2013. Since 2007, Kongsbreen retreated up to 1800 m, corresponding to a total area loss of 2.5 km2. In 2011 the retreat of Kronebreen of up to 850 m, responsible for a total area loss of 2.8 km2, was triggered after a phase of stable terminus position since ~1990. The retreat is an important component of the mass balance of both glaciers, in which frontal ablation is the largest component. Total frontal ablation between April 2012 and December 2013 was estimated to 0.21–0.25 Gt a−1 for Kronebreen and 0.14–0.16 Gt a−1 for Kongsbreen.

scholarly journals Surface Velocity Determination on Large Polar Glaciers by Aerial Photogrammetry

1986 ◽  
Vol 8 ◽  
pp. 22-26 ◽  
Author(s):  
H. H. Brecher
Keyword(s):  
Strain Rate ◽  
Flow Regime ◽  
Surface Velocity ◽  
Control Points ◽  
West Antarctica ◽  
Ice Flow ◽  
Elapsed Time ◽  
Aerial Photogrammetry ◽  
Ice Surface ◽  
Ice Stream B

Aerial photogrammetric block triangulation, a standard and well-developed technique for extending accurate control for mapping into the interior of a region from a few points of known position on its perimeter, can be readily adapted to determine surface velocities on bodies of ice which are too large, and often too crevassed, to be studied effectively by conventional ground surveying. Velocities are calculated from the changes in positions of the same natural surface features determined from photography of two (or more) epochs and the elapsed time. This method is capable of providing many uniformly-spaced measurements over the whole, moving, ice surface, thus allowing the production of maps of velocity and strain-rate, which are valuable in analyzing the ice-flow regime. Results from measurements completed some years ago on Byrd Glacier, one of the largest outlet glaciers from the East Antarctic plateau, are presented as an example of what the method can yield. By means of Doppler satellite surveying, relative positions of control points for each photography epoch can be determined with sub-meter accuracy, making the technique suitable also in regions where no fixed land features exist. A brief description of a project under way in such an area, on Ice Stream B in West Antarctica, is given.

scholarly journals Surface speed and frontal ablation of Kronebreen and Kongsbreen, NW Svalbard, from SAR offset tracking

2015 ◽  
Vol 9 (6) ◽  
pp. 2339-2355 ◽  
Author(s):  
T. Schellenberger ◽  
T. Dunse ◽  
A. Kääb ◽  
J. Kohler ◽  
C. H. Reijmer
Keyword(s):  
Water Pressure ◽  
Back Stress ◽  
Velocity Fields ◽  
Surface Velocity ◽  
Ice Flow ◽  
Area Loss ◽  
Continuous Gps ◽  
Offset Tracking ◽  
Frontal Ablation ◽  
Data Surface

Abstract. Kronebreen and Kongsbreen are among the fastest-flowing glaciers on Svalbard and, therefore, important contributors to the total dynamic mass loss from the archipelago. Here, we present a time series of area-wide surface velocity fields from April 2012 to December 2013 based on offset tracking on repeat high-resolution Radarsat-2 Ultrafine data. Surface speeds reached up to 3.2 m d−1 near the calving front of Kronebreen in summer 2013 and 2.7 m d−1 at Kongsbreen in late autumn 2012. Additional velocity fields from Radarsat-1, Radarsat-2 and TerraSAR-X data since December 2007 together with continuous GPS measurements on Kronebreen since September 2008 revealed complex patterns in seasonal and interannual speed evolution. Part of the ice-flow variations seem closely linked to the amount and timing of surface meltwater production and rainfall, both of which are known to have a strong influence on the basal water pressure and hence basal lubrication. In addition, terminus retreat and the associated reduction in back stress appear to have influenced the speed close to the calving front, especially at Kongsbreen in 2012 and 2013. Since 2007, Kongsbreen retreated up to 1800 m, corresponding to a total area loss of 2.5 km2. In 2011 the retreat of Kronebreen of up to 850 m, responsible for a total area loss of 2.8 km2, was triggered after a phase of stable terminus position since ~ 1990. Retreat is an important component of the mass balance of both glaciers, in which frontal ablation is the largest component. Total frontal ablation between April 2012 and December 2013 was estimated to 0.21–0.25 Gt a−1 for Kronebreen and 0.14–0.16 Gt a−1 for Kongsbreen.

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