Surge dynamics and lake outbursts of Kyagar Glacier, Karakoram

The Cryosphere ◽

10.5194/tc-11-723-2017 ◽

2017 ◽

Vol 11 (2) ◽

pp. 723-739 ◽

Cited By ~ 37

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.

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

Journal of Glaciology ◽

10.3189/s0022143000006936 ◽

1986 ◽

Vol 32 (110) ◽

pp. 101-119 ◽

Cited By ~ 35

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.

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

Journal of Glaciology ◽

10.1017/s0022143000006936 ◽

1986 ◽

Vol 32 (110) ◽

pp. 101-119 ◽

Cited By ~ 376

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.

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Short-term velocity and water-pressure variations down-glacier from a riegel, Storglaciären, Sweden

Journal of Glaciology ◽

10.3189/s0022143000002689 ◽

1998 ◽

Vol 44 (147) ◽

pp. 359-367 ◽

Cited By ~ 1

Author(s):

Brian Hanson ◽

Roger LeB. Hooke ◽

Edmund M. Grace

Keyword(s):

Water Pressure ◽

Spatial Coherence ◽

Drainage System ◽

Pressure Rise ◽

Surface Velocity ◽

Storm Events ◽

Pressure Cycle ◽

Large Water ◽

Local Water ◽

Subglacial Drainage

AbstractDuring the 1991 94 summer held seasons, time-correlated measure-merits of water pressure and surface speed were made over and down-glacier from a major riegel on Storglaciären, Sweden. Measurements were made at sub-hourly time-scales in order to discern details in the diurnal cycle. Large water-input events, typically associated with rain storms, produced coherent, lagged surface-velocity responses that could be understood in terms of till deformation or decoupling, and these have been discussed elsewhere. The consequences of smaller diurnal water-pressure events w ere more enigmatic, in that acceleration of ice flow generally preceded the onset of the local water-pressure rise. From consideration of these data and other work done on the hydrology of Storglaciären, we infer that the ice in this area is generally pushed from behind via a relaxation in extensional strain across the riegel. Hence, accelerations occur in response to increases in water pressure that occur up-glacier and that precede local water-pressure rises. In addition, following a period of large storm events, surface speeds became more spatially coherent and were in phase with the diurnal water-pressure cycle. This suggests that the large water-pressure events lead to a spatially more homogeneous subglacial drainage system. Sliding laws need to take into account such temporal changes in spatial coherence of the subglacial drainage system.

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An integrated modelling approach to understanding subglacial hydraulic release events

Annals of Glaciology ◽

10.3189/172756400781820471 ◽

2000 ◽

Vol 31 ◽

pp. 222-228 ◽

Cited By ~ 16

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.

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Seasonal variations in ice deformation and basal motion across the tongue of Haut Glacier d’Arolla, Switzerland

Annals of Glaciology ◽

10.3189/172756403781816455 ◽

2003 ◽

Vol 36 ◽

pp. 157-167 ◽

Cited By ~ 21

Author(s):

Ian Willis ◽

Douglas Mair ◽

Bryn Hubbard ◽

Peter Nienow ◽

Urs H. Fischer ◽

...

Keyword(s):

Surface Deformation ◽

Water Pressure ◽

Drainage System ◽

System Structure ◽

Glacier Surface ◽

Changing Patterns ◽

Internal Deformation ◽

Internal Velocity ◽

Subglacial Drainage

AbstractRecords of surface motion, englacial tilt and repeat inclinometry are used to determine patterns of surface, internal and basal motion across the tongue of Haut Glacier d’Arolla, Switzerland, over temporal scales ranging from days to months. Findings are interpreted with reference to contemporaneous measurements of subglacial water pressures, and prior knowledge of the glacier’s subglacial drainage-system structure. Long-term inclinometry results show pronounced extrusion flow over a subglacial drainage axis, with basal velocities up to twice those measured at the glacier surface. Deformation profiles are more conventional away from the drainage axis, with basal velocities ∼60–70% of surface velocities. Comparison of long-term tilt rates from repeat inclinometry and englacial tiltmeters shows close correspondence. Englacial tiltmeter data are used to reconstruct internal velocity profiles and to split surface velocities into internal deformation and basal motion contributions over spring, summer and autumn/winter periods. Although, spatial patterns of surface movement are similar between periods, patterns of internal and basal motion are not. Results are interpreted in terms of the location of sticky and slippery spots, with temporally changing patterns of basal drag reflecting changing distributions of water pressure.

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Short-term velocity and water-pressure variations down-glacier from a riegel, Storglaciären, Sweden

Journal of Glaciology ◽

10.1017/s0022143000002689 ◽

1998 ◽

Vol 44 (147) ◽

pp. 359-367 ◽

Cited By ~ 21

Author(s):

Brian Hanson ◽

Roger LeB. Hooke ◽

Edmund M. Grace

Keyword(s):

Water Pressure ◽

Spatial Coherence ◽

Drainage System ◽

Pressure Rise ◽

Surface Velocity ◽

Storm Events ◽

Pressure Cycle ◽

Large Water ◽

Local Water ◽

Subglacial Drainage

AbstractDuring the 1991 94 summer held seasons, time-correlated measure-merits of water pressure and surface speed were made over and down-glacier from a major riegel on Storglaciären, Sweden. Measurements were made at sub-hourly time-scales in order to discern details in the diurnal cycle. Large water-input events, typically associated with rain storms, produced coherent, lagged surface-velocity responses that could be understood in terms of till deformation or decoupling, and these have been discussed elsewhere. The consequences of smaller diurnal water-pressure events w ere more enigmatic, in that acceleration of ice flow generally preceded the onset of the local water-pressure rise. From consideration of these data and other work done on the hydrology of Storglaciären, we infer that the ice in this area is generally pushed from behind via a relaxation in extensional strain across the riegel. Hence, accelerations occur in response to increases in water pressure that occur up-glacier and that precede local water-pressure rises. In addition, following a period of large storm events, surface speeds became more spatially coherent and were in phase with the diurnal water-pressure cycle. This suggests that the large water-pressure events lead to a spatially more homogeneous subglacial drainage system. Sliding laws need to take into account such temporal changes in spatial coherence of the subglacial drainage system.

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Short-term Variations in Strain and Surface Tilt on Storglaciären, Kebnekaise, Northern Sweden

Journal of Glaciology ◽

10.3189/s0022143000004512 ◽

1989 ◽

Vol 35 (120) ◽

pp. 201-208 ◽

Cited By ~ 29

Author(s):

Peter Jansson ◽

Roger LeB. Hooke

Keyword(s):

Water Pressure ◽

High Water ◽

Ice Thickness ◽

Gradual Change ◽

Short Term ◽

Glacier Surface ◽

Vertical Movements ◽

Bed Topography ◽

The Waves ◽

Local Uplift

AbstractTiltmeters that can detect changes in slope of a glacier surface as small as 0.1 μ rad have been used on Storglaciären. The records obtained to date have been from the upper part of the ablation area, where the bed of the glacier is overdeepened. A total of 82 d of records has been obtained for various time periods between early June and early September.There is generally a gradual change in inclination of the glacier surface over periods of several days, but these changes do not appear to be systematic. In particular, they are not consistent with vertical movements of stakes located 2–3 ice thicknesses away from the tiltmeters. This suggests that the tiltmeters are sensing disturbances over areas with diameters comparable to the local ice thickness.Superimposed on these trends are diurnal signals suggesting rises and falls of the surface just up-glacier from the riegel that bounds the overdeepening on its down-glacier end. These may be due to waves of high water pressure originating in a crevassed area near the equilibrium line. If this interpretation is correct, the waves apparently move down-glacier at speeds of 20–60 m h−1and become sufficiently focused, either by the bed topography or by conduit constrictions, to result in local uplift of the surface. Also observed are abrupt tilts towards the glacier center line shortly after the beginning of heavy rainstorms. These appear to be due to longitudinal stretching as the part of the glacier below the riegel accelerates faster than that above. Water entering the glacier by way of a series of crevasses over the riegel is believed to be responsible for this differential acceleration. In June 1987, a dramatic event was registered, probably reflecting the initial summer acceleration of the glacier.

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

10.5194/tc-2020-10 ◽

2020 ◽

Cited By ~ 1

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 &apos;meltwater corridors&apos; 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.

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Oscillatory subglacial drainage in the absence of surface melt

The Cryosphere ◽

10.5194/tc-8-959-2014 ◽

2014 ◽

Vol 8 (3) ◽

pp. 959-976 ◽

Cited By ~ 31

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.

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