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

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.

Download Full-text

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.

Download Full-text

Interaction between water pressure in the basal drainage system and discharge from an Alpine glacier before and during a rainfall-induced subglacial hydrological event

Annals of Glaciology ◽

10.3189/s0260305500012325 ◽

1997 ◽

Vol 24 ◽

pp. 288-292 ◽

Cited By ~ 1

Author(s):

Andrew P. Barrett ◽

David N. Collins

Keyword(s):

Water Level ◽

Water Pressure ◽

Drainage System ◽

Water Levels ◽

Drainage Network ◽

Alpine Glacier ◽

Hydraulic Conditions ◽

Borehole Water ◽

Progressive Growth ◽

Resultant Increase

Combined measurements of meltwater discharge from the portal and of water level in a borehole drilled to the bed of Findelengletscher, Switzerland, were obtained during the later part of the 1993 ablation season. A severe storm, lasting from 22 through 24 September, produced at least 130 mm of precipitation over the glacier, largely as rain. The combined hydrological records indicate periods during which the basal drainage system became constricted and water storage in the glacier increased, as well as phases of channel growth. During the storm, water pressure generally increased as water backed up in the drainage network. Abrupt, temporary falls in borehole water level were accompanied by pulses in portal discharge. On 24 September, whilst borehole water level continued to rise, water started to escape under pressure with a resultant increase in discharge. As the drainage network expanded, a large amount of debris was flushed from a wide area of the bed. Progressive growth in channel capacity as discharge increased enabled stored water to drain and borehole water level to fall rapidly. Possible relationships between observed borehole water levels and water pressures in subglacial channels are influenced by hydraulic conditions at the base of the hole, distance between the hole and a channel, and the nature of the substrate.

Download Full-text

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.

Download Full-text

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.

Download Full-text

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.

Download Full-text

Modelling the evolution of subglacial tunnels due to varying water input

Journal of Glaciology ◽

10.1017/s002214300000201x ◽

1998 ◽

Vol 44 (148) ◽

pp. 485-497 ◽

Cited By ~ 21

Author(s):

Paul M. Cutler

Keyword(s):

Water Pressure ◽

Drainage System ◽

Water Levels ◽

Initial Shape ◽

Initial Area ◽

Physically Based ◽

Dimensional Finite Element ◽

Borehole Water ◽

Low Tunnels ◽

Tunnel Cross Section

AbstractThe time evolution of a subglacial tunnel cross-section is examined usine a two-dimensional finite-element ice-flow model coupled to an idealized drainage system. Simulations are driven by physically based calculations of surface water-input variations at Slorgiaciaren, Sweden. Highlights of the model are its ability to handle unsteady conditions and irregular tunnel shapes. Agreement between modelled water pressure and borehole water levels is good. The following conclusions are reached: (i) Tunnels adapt to fluctuating inflow on time-scales of days. Storms, during which effective pressure ranges from 0 to 0.9 MPa, cause significant adjustments but daily fluctuations due solely to melt-water inflow are minor, (ii) Open-channel flow may become commonplace late in the ablation season, (iii) Initial tunnel shape influences subsequent tunnel evolution and seasonal water-pressure variation. Over the course of a summer, tunnels retain some of their initial shape, though in all experiments the width-to-height ratio increased with time, (iv) Tunnel contraction forms broad low tunnels. However, (v) given two tunnels of equal initial area, the higher narrower one expands more rapidly. Thus, more semi-circular tunnels may capture How from broader neighbours early in the summer.

Download Full-text

Interaction between water pressure in the basal drainage system and discharge from an Alpine glacier before and during a rainfall-induced subglacial hydrological event

Annals of Glaciology ◽

10.1017/s0260305500012325 ◽

1997 ◽

Vol 24 ◽

pp. 288-292 ◽

Cited By ~ 11

Author(s):

Andrew P. Barrett ◽

David N. Collins

Keyword(s):

Water Level ◽

Water Pressure ◽

Drainage System ◽

Water Levels ◽

Drainage Network ◽

Alpine Glacier ◽

Hydraulic Conditions ◽

Borehole Water ◽

Progressive Growth ◽

Resultant Increase

Combined measurements of meltwater discharge from the portal and of water level in a borehole drilled to the bed of Findelengletscher, Switzerland, were obtained during the later part of the 1993 ablation season. A severe storm, lasting from 22 through 24 September, produced at least 130 mm of precipitation over the glacier, largely as rain. The combined hydrological records indicate periods during which the basal drainage system became constricted and water storage in the glacier increased, as well as phases of channel growth. During the storm, water pressure generally increased as water backed up in the drainage network. Abrupt, temporary falls in borehole water level were accompanied by pulses in portal discharge. On 24 September, whilst borehole water level continued to rise, water started to escape under pressure with a resultant increase in discharge. As the drainage network expanded, a large amount of debris was flushed from a wide area of the bed. Progressive growth in channel capacity as discharge increased enabled stored water to drain and borehole water level to fall rapidly. Possible relationships between observed borehole water levels and water pressures in subglacial channels are influenced by hydraulic conditions at the base of the hole, distance between the hole and a channel, and the nature of the substrate.

Download Full-text

Investigating Spatio-temporal Changes in Subglacial Hydrology from Dense Array Seismology.

10.5194/egusphere-egu2020-10710 ◽

2020 ◽

Author(s):

Ugo Nanni ◽

Florent Gimbert ◽

Philippe Roux ◽

Albanne Lecointre

Keyword(s):

Water Flow ◽

Seismic Noise ◽

Water Pressure ◽

Noise Analysis ◽

Drainage System ◽

Dense Array ◽

Noise Sources ◽

Spatio Temporal ◽

Surrounding Areas ◽

Subglacial Drainage

Subglacial hydrology strongly modulates glacier basal sliding, and thus likely exerts a major control on ice loss and sea-level rise. However, the limited direct and spatialized observations of the subglacial drainage system make difficult to assess the physical processes involved in its development. Recent work shows that detectable seismic noise is generated by subglacial water flow, such that seismic noise analysis may be used to retrieve the physical properties of subglacial channelized water flow. Yet, investigating the spatial organisation of the drainage system (e.g. channels numbers and positions) together with its evolving properties (e.g. pressure conditions) through seismic observations remains to be done. The objective of this study is to bring new insights on the subglacial hydrology spatio-temporal dynamics using dense array seismic observations.We use 1-month long ground motion records at a hundred of sensors deployed on the Argenti&#232;re Glacier (French Alps) during the onset of the melt season, when the subglacial drainage system is expected to strongly evolve in response to the rapidly increasing water input. We conduct a multi-method approach based on the analysis of both amplitude and phase maps of seismic signals. We observe characteristic spatial patterns, consistent across those independent approaches, which we attribute to the underlying subglacial drainage system.The phase-driven approach shows seismic noise sources that focuses in the along-flow direction as the water input increases. We identify this evolution as the development of the main subglacial channel whose position is coherent with the one expected from hydraulic potential calculations. During periods of rapid changes in water input (5 days over 31) and concomitant glacier acceleration the amplitude-driven approach shows spatial pattern highly consistent with the seismic noise sources location. At this time, we suggest that the spatial variations in the amplitude are representative of the water pressure conditions in subglacial channels and surrounding areas. Our spatialized observations therefore reveal the spatio-temporal evolution of the subglacial drainage system together with its changing pressure conditions. We observe, for instance, that channels develop at the very onset of the melt-season and rapidly capture the water from surrounding areas. Such unique observations may allow to better constrain the physics of subglacial water flow and therefore strengthen our knowledge on the dynamics of subglacial environments.

Download Full-text

Borehole water-level variations and the structure of the subglacial hydrological system of Haut Glacier d’Arolla, Valais, Switzerland

Journal of Glaciology ◽

10.3189/s0022143000034894 ◽

1995 ◽

Vol 41 (139) ◽

pp. 572-583 ◽

Cited By ~ 7

Author(s):

B. P. Hubbard ◽

M. J. Sharp ◽

I. C. Willis ◽

M. K. Nielsen ◽

C. C. Smart

Keyword(s):

Distributed System ◽

Water Pressure ◽

Drainage System ◽

Late Summer ◽

Variable Pressure ◽

Sediment Layer ◽

Drainage Channels ◽

Hydrological System ◽

Borehole Water ◽

Water Level Variations

AbstractLate-summer subglacial water pressures have been measured in a dense array of boreholes in the ablation area of Haut Glacier d’Arolla, Switzerland. Interpolated surfaces of minimum diurnal water pressure and diurnal water-pressure variation suggest the presence of a subglacial channel within a more widespread, distributed drainage system. The channel flows along the centre of a variable pressure axis (VPA), some tens of metres wide, that is characterized by low minimum diurnal water pressures (frequently atmospheric) and high diurnal water-pressure variations. These characteristics are transitional over a lateral distance of c. 70 m to higher and more stable subglacial water pressures in the adjacent distributed system. Water-pressure variations recorded in boreholes located close to the centre of the VPA reflect the delivery of surface-derived meltwater to the glacier bed and result in a diurnally reversing, transverse hydraulic gradient that drives water out from the channel into the distributed system during the afternoon and back to the channel overnight. Subglacial observations suggest that such flow occurs through a vertically confined sediment layer. Borehole turbidity records indicate that the resulting diurnal water flows are responsible for the mobilization and transport of fine debris in suspension. Analysis of the propagation velocity and amplitude attenuation cf the diurnal pressure waves suggests that the hydraulic conductivity of the sediment layer decreases exponentially with distance from the channel, falling from c. 10−4 m s−1 at the channel boundary to c. 10−7 m s−1 70 m away. These apparent hydraulic conductivities are consistent with Darcian flow through clean sand and typical glacial till, respectively.We suggest that fine material is systematically flushed from basal sediments located adjacent to large, melt-season drainage channels beneath warm-based glaciers. This process may have important implications for patterns of glacier erosion, hydro-chemistry and dynamics.

Download Full-text