scholarly journals An integrated modelling approach to understanding subglacial hydraulic release events

2000 ◽  
Vol 31 ◽  
pp. 222-228 ◽  
Author(s):  
Gwenn E. Flowers ◽  
Garry K. C. Clarke
Keyword(s):  
Water Pressure ◽  
Water Storage ◽  
Drainage System ◽  
High Water ◽  
Integrated Modelling ◽  
Glacier Motion ◽  
Bear Witness ◽  
Modelling Approach ◽  
Subglacial Drainage

AbstractOutbursts of subglacial water from numerous alpine glaciers have been observed and documented. Such events tend to occur in spring and are thus attributed to an inability of the winter subglacial drainage system (characterized by high water pressure and low capacity) to accommodate a sudden and profuse influx of surface meltwater. Prior to a release event, bursts of glacier motion are common, and the release then precipitates the restoration of summer plumbing that damps or terminates surface acceleration. The events bear witness to the importance of interactions between surface melt, runoff, en-glacial water storage and internal routing, in addition to subglacial drainage morphology. Using a distributed numerical model to simultaneously solve surficial, englacial and subglacial water-transport equations, we investigate the role of these components in a hydro-mechanical event observed at Trapridge Glacier, YukonTerritory, Canada, in July 1990.

scholarly journals Channelized subglacial drainage over a deformable bed

1994 ◽  
Vol 40 (134) ◽  
pp. 3-15 ◽  
Author(s):  
Joseph S. Walder ◽  
Andrew Fowler
Keyword(s):  
Water Pressure ◽  
Ice Sheets ◽  
Drainage System ◽  
West Antarctica ◽  
Plausible Assumption ◽  
Basal Ice ◽  
Ice Stream B ◽  
Steep Slopes ◽  
Subglacial Drainage

AbstractWe develop theoretically a description of a possible subglacial drainage mechanism for glaciers and ice sheets moving over saturated, deformable till. The model is based on the plausible assumption that flow of water in a thin film at the ice-till interface is unstable to the formation of a channelized drainage system, and is restricted to the case in which meltwater cannot escape through the till to an underlying aquifer. In describing the physics of such channelized drainage, we have generalized and extended Röthlisberger’s model of channels cut into basal ice to include “canals” cut into the till, paying particular attention to the role of sediment properties and the mechanics of sediment transport. We show that sediment-floored Röthlisberger (R) channels can exist for high effective pressures, and wide, shallow, ice-roofed canals cut into the till for low effective pressures. Canals should form a distributed, non-arborescent system, unlike R channels. For steep slopes typical of alpine glaciers, both drainage systems can exist, but with the water pressure lower in the R channels than in the canals; the canal drainage should therefore be unstable in the presence of channels. For small slopes typical of ice sheets, only canals can exist and we therefore predict that, if channelized meltwater flow occurs under ice sheets moving over deformable till, it takes the form of shallow, distributed canals at low effective pressure, similar to that measured at Ice Stream B in West Antarctica. Geologic evidence derived from land forms and deposits left by the Pleistocene ice sheets in North America and Europe is also consistent with predictions of the model.

scholarly journals Water storage and subglacial drainage conditions inferred from borehole measurements on Gornergletscher, Valais, Switzerland

1996 ◽  
Vol 42 (141) ◽  
pp. 233-248 ◽  
Author(s):  
Almut Iken ◽  
Kristian Fabri ◽  
Martin Funk
Keyword(s):  
Cross Sections ◽  
Water Pressure ◽  
Water Storage ◽  
Drainage System ◽  
Water Levels ◽  
Sediment Layer ◽  
Northern Margin ◽  
Upstream Side ◽  
Different Depths ◽  
Subglacial Drainage

AbstractMeasurements of change in length of a borehole, or displacements of poles and of subglacial Water pressure were combined with drainage tests and electrode tests in boreholes, in experiments near the northern margin of Gornergletscher, Valais, Switzerland, at the upstream side of an overdeepening. The measurements suggest that the subglacial drainage system consisted of discrete conduits at that location, presumably linked cavities on “clean” bedrock. Changes in subglacial water pressure were followed by variations in subglacial water storage, together with similar variations in elevation of a pole. The variations in subglacial water storage caused changes in cross-sections of subglacial passageways and thereby changed the frequencies of slug-test oscillations. Similar experiments conducted near the center line of the glacier revealed different subglacial conditions: impeded drainage through a sediment layer, and different depths of water levels in different boreholes. These results are discussed in relation to previous studies.

scholarly journals Surge dynamics and lake outbursts of Kyagar Glacier, Karakoram

2016 ◽  
Author(s):  
Vanessa Round ◽  
Silvan Leinss ◽  
Matthias Huss ◽  
Christoph Haemmig ◽  
Irena Hajnsek
Keyword(s):  
Water Pressure ◽  
Thickness Distribution ◽  
Drainage System ◽  
High Water ◽  
Surface Velocity ◽  
Glacier Surface ◽  
Lake Volume ◽  
Lake Formation ◽  
Landsat Satellite ◽  
Subglacial Drainage

Abstract. The recent surge cycle of Kyagar Glacier, in the Chinese Karakoram, caused formation of an ice-dammed lake and subsequent glacial lake outburst floods (GLOFs) exceeding 50 and 40 million m3 in 2015 and 2016, respectively. GLOFs from Kyagar Glacier reached double this size in 2002 and earlier, but the role of glacier surging in GLOF formation was previously unrecognised. We present an integrative analysis of the glacier surge dynamics from 2011 to 2016, assessing surge mechanisms and evaluating the surge cycle impact on GLOFs. Over 80 glacier surface velocity fields were created from TanDEM-X, Sentinel-1A and Landsat satellite data. Changes in ice thickness distribution were revealed by a time series of TanDEM-X DEMs. The analysis shows that during a quiescence phase lasting at least 14 years, ice mass built up in a reservoir area at the top of the glacier tongue and the terminus thinned by up to 100 m, but in the two years preceding the surge this pattern reversed. The surge clearly initiated with the onset of the 2014 melt season, and in the following 15 months velocity evolved in a manner consistent with a hydrologically-controlled surge mechanism with dramatic accelerations coinciding with melt seasons, winter deceleration accompanied by subglacial drainage, and rapid surge termination following the 2015 GLOF. Rapid basal motion during surging is seemingly controlled by high water pressure caused by input of surface water into either an inefficient subglacial drainage system or unstable subglacial till. Over 60 m of thickening at the terminus caused potential lake volume to increase more than 40-fold since surge onset, to currently more than 70 million m3, indicating that lake formation should be carefully monitored to anticipate large GLOFs in the near future.

scholarly journals Channelized subglacial drainage over a deformable bed

1994 ◽  
Vol 40 (134) ◽  
pp. 3-15 ◽  
Author(s):  
Joseph S. Walder ◽  
Andrew Fowler
Keyword(s):  
Water Pressure ◽  
Ice Sheets ◽  
Drainage System ◽  
West Antarctica ◽  
Plausible Assumption ◽  
Basal Ice ◽  
Ice Stream B ◽  
Steep Slopes ◽  
Subglacial Drainage

AbstractWe develop theoretically a description of a possible subglacial drainage mechanism for glaciers and ice sheets moving over saturated, deformable till. The model is based on the plausible assumption that flow of water in a thin film at the ice-till interface is unstable to the formation of a channelized drainage system, and is restricted to the case in which meltwater cannot escape through the till to an underlying aquifer. In describing the physics of such channelized drainage, we have generalized and extended Röthlisberger’s model of channels cut into basal ice to include “canals” cut into the till, paying particular attention to the role of sediment properties and the mechanics of sediment transport. We show that sediment-floored Röthlisberger (R) channels can exist for high effective pressures, and wide, shallow, ice-roofed canals cut into the till for low effective pressures. Canals should form a distributed, non-arborescent system, unlike R channels. For steep slopes typical of alpine glaciers, both drainage systems can exist, but with the water pressure lower in the R channels than in the canals; the canal drainage should therefore be unstable in the presence of channels. For small slopes typical of ice sheets, only canals can exist and we therefore predict that, if channelized meltwater flow occurs under ice sheets moving over deformable till, it takes the form of shallow, distributed canals at low effective pressure, similar to that measured at Ice Stream B in West Antarctica. Geologic evidence derived from land forms and deposits left by the Pleistocene ice sheets in North America and Europe is also consistent with predictions of the model.

scholarly journals Surge dynamics and lake outbursts of Kyagar Glacier, Karakoram

2017 ◽  
Vol 11 (2) ◽  
pp. 723-739 ◽  
Author(s):  
Vanessa Round ◽  
Silvan Leinss ◽  
Matthias Huss ◽  
Christoph Haemmig ◽  
Irena Hajnsek
Keyword(s):  
Water Pressure ◽  
Thickness Distribution ◽  
Drainage System ◽  
High Water ◽  
Surface Velocity ◽  
Glacier Surface ◽  
Lake Volume ◽  
Lake Formation ◽  
Landsat Satellite ◽  
Subglacial Drainage

Abstract. The recent surge cycle of Kyagar Glacier, in the Chinese Karakoram, caused formation of an ice-dammed lake and subsequent glacial lake outburst floods (GLOFs) exceeding 40 million m3 in 2015 and 2016. GLOFs from Kyagar Glacier reached double this size in 2002 and earlier, but the role of glacier surging in GLOF formation was previously unrecognised. We present an integrative analysis of the glacier surge dynamics from 2011 to 2016, assessing surge mechanisms and evaluating the surge cycle impact on GLOFs. Over 80 glacier surface velocity fields were created from TanDEM-X (TerraSAR-X add-on for Digital Elevation Measurement), Sentinel-1A, and Landsat satellite data. Changes in ice thickness distribution were revealed by a time series of TanDEM-X elevation models. The analysis shows that, during a quiescence phase lasting at least 14 years, ice mass built up in a reservoir area at the top of the glacier tongue, and the terminus thinned by up to 100 m, but in the 2 years preceding the surge onset this pattern reversed. The surge initiated with the onset of the 2014 melt season, and in the following 15 months velocity evolved in a manner consistent with a hydrologically controlled surge mechanism. Dramatic accelerations coincided with melt seasons, winter deceleration was accompanied by subglacial drainage, and rapid surge termination occurred following the 2015 GLOF. Rapid basal motion during the surge is seemingly controlled by high water pressure, caused by input of surface water into either an inefficient subglacial drainage system or unstable subglacial till. The potential lake volume increased to more than 70 million m3 by late 2016, as a result of over 60 m of thickening at the terminus. Lake formation and the evolution of the ice dam height should be carefully monitored through remote sensing to anticipate large GLOFs in the near future.

scholarly journals Water storage and subglacial drainage conditions inferred from borehole measurements on Gornergletscher, Valais, Switzerland

1996 ◽  
Vol 42 (141) ◽  
pp. 233-248 ◽  
Author(s):  
Almut Iken ◽  
Kristian Fabri ◽  
Martin Funk
Keyword(s):  
Cross Sections ◽  
Water Pressure ◽  
Water Storage ◽  
Drainage System ◽  
Water Levels ◽  
Sediment Layer ◽  
Northern Margin ◽  
Upstream Side ◽  
Different Depths ◽  
Subglacial Drainage

AbstractMeasurements of change in length of a borehole, or displacements of poles and of subglacial Water pressure were combined with drainage tests and electrode tests in boreholes, in experiments near the northern margin of Gornergletscher, Valais, Switzerland, at the upstream side of an overdeepening. The measurements suggest that the subglacial drainage system consisted of discrete conduits at that location, presumably linked cavities on “clean” bedrock. Changes in subglacial water pressure were followed by variations in subglacial water storage, together with similar variations in elevation of a pole. The variations in subglacial water storage caused changes in cross-sections of subglacial passageways and thereby changed the frequencies of slug-test oscillations. Similar experiments conducted near the center line of the glacier revealed different subglacial conditions: impeded drainage through a sediment layer, and different depths of water levels in different boreholes. These results are discussed in relation to previous studies.

scholarly journals Large-scale integrated subglacial drainage around the former Keewatin Ice Divide, Canada reveals interaction between distributed and channelised systems

2020 ◽  
Author(s):  
Emma L. M. Lewington ◽  
Stephen J. Livingstone ◽  
Chris D. Clark ◽  
Andrew J. Sole ◽  
Robert D. Storrar
Keyword(s):  
Spatial Distribution ◽  
Dynamic Response ◽  
Large Scale ◽  
Water Pressure ◽  
Pressure Fluctuations ◽  
Drainage System ◽  
Different Types ◽  
Form Part ◽  
Subglacial Meltwater ◽  
Subglacial Drainage

Abstract. We identify and map traces of subglacial meltwater drainage around the former Keewatin Ice Divide, Canada from ArcticDEM data. Meltwater tracks, tunnel valleys and esker splays exhibit several key similarities, including width, spacing, their association with eskers and transitions to and from different types, which together suggest they form part of an integrated drainage signature. We collectively term these features 'meltwater corridors' and propose a new model for their formation, based on observations from contemporary ice masses, of pressure fluctuations surrounding a central conduit. We suggest that eskers record the imprint of a central conduit and meltwater corridors the interaction with the surrounding distributed drainage system. The widespread aerial coverage of meltwater corridors (5–36 % of the bed) provides constraints on the extent of basal uncoupling induced by basal water pressure fluctuations and variations in spatial distribution and evolution of the subglacial drainage system, which will modulate the ice dynamic response.

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 Oscillatory subglacial drainage in the absence of surface melt

2014 ◽  
Vol 8 (3) ◽  
pp. 959-976 ◽  
Author(s):  
C. Schoof ◽  
C. A Rada ◽  
N. J. Wilson ◽  
G. E. Flowers ◽  
M. Haseloff
Keyword(s):  
Water Pressure ◽  
Drainage System ◽  
Yukon Territory ◽  
Strongly Correlated ◽  
Pressure Oscillations ◽  
Power Failure ◽  
Multiple Data ◽  
Data Loggers ◽  
Diurnal Cycling ◽  
Subglacial Drainage

Abstract. The presence of strong diurnal cycling in basal water pressure records obtained during the melt season is well established for many glaciers. The behaviour of the drainage system outside the melt season is less well understood. Here we present borehole observations from a surge-type valley glacier in the St Elias Mountains, Yukon Territory, Canada. Our data indicate the onset of strongly correlated multi-day oscillations in water pressure in multiple boreholes straddling a main drainage axis, starting several weeks after the disappearance of a dominant diurnal mode in August 2011 and persisting until at least January 2012, when multiple data loggers suffered power failure. Jökulhlaups provide a template for understanding spontaneous water pressure oscillations not driven by external supply variability. Using a subglacial drainage model, we show that water pressure oscillations can also be driven on a much smaller scale by the interaction between conduit growth and distributed water storage in smaller water pockets, basal crevasses and moulins, and that oscillations can be triggered when water supply drops below a critical value. We suggest this in combination with a steady background supply of water from ground water or englacial drainage as a possible explanation for the observed wintertime pressure oscillations.

scholarly journals The Uplift of Unteraargletscher at the Beginning of the Melt Season—A Consequence of Water Storage at the Bed?

1983 ◽  
Vol 29 (101) ◽  
pp. 28-47 ◽  
Author(s):  
A. Iken ◽  
H. Röthlisberger ◽  
A. Flotron ◽  
W. Haeberli
Keyword(s):  
Water Pressure ◽  
Storage System ◽  
Water Storage ◽  
High Water ◽  
Early Summer ◽  
Upward Movement ◽  
Drainage Channels ◽  
Summer Maximum ◽  
Cavity Development ◽  
The Times

Abstract Results of systematic movement studies carried out by means of an automatic camera on Unteraargletscher since 1969 are discussed together with supplementary theodolite measurements made at shorter intervals and over a longer section of the glacier. In addition to the typical spring/early summer maximum of velocity known from other glaciers, an upward movement of up to 0.6 m has been recorded at the beginning of the melt season. It was followed, after a few fluctuations of the vertical velocity, by an equal but slower downward movement which continued at an almost constant rate for about three months. Possible explanations of the uplift are discussed, the most satisfactory explanation being water storage at the bed. The observations then suggest that this storage system is efficiently connected with the main subglacial drainage channels only during times of very high water pressure in the channels. Detailed measurements showed that the times of maximum horizontal velocity coincided with the times of maximum upward velocity rather than with the times when the elevation of the surveyed poles had reached a maximum. On the basis of the hypothesis of water storage at the bed this finding means that the sliding velocity is influenced mainly by the subglacial water pressure and the actual, transient stage of cavity development, while the amount of stored water is of lesser influence.

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