Flow separation and diurnal variability in the hydrology of Conness Glacier, Sierra Nevada, California, U.S.A.

AbstractA mass-balance approach using hourly discharge and electrical conductivity values measured over a 10 d period during the ablation season was used to separate englacial and subglacial components of the total meltwater discharge from a small alpine glacier in the Sierra Nevada, California, U.S.A. Symmetrical diurnal hydrographs indicate that little delay occurred as water was tranferred through the drainage system. Electrical conductivity (which varied inversely with proglacial discharge) increased abruptly at each daily conductivity maximum, and cross-correlation analysis indicated that subglacial discharge peaked on the rising limb of the englacial hydrograph (about 2 h prior to the englacial peak). This suggests that a translatory flow process operates in which increased water pressure in the englacial system on the rising limb of the diurnal-discharge cycle forced subglacial water from beneath the glacier in advance of short residence-time meltwater. Net radiation dominated the energy balance at the glacier surface, explaining 86% of the variance in proglacial discharge, which was dominated by the englacial flow component.

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

Short term variations of tracer transit speed on alpine glaciers

The Cryosphere ◽

10.5194/tc-4-381-2010 ◽

2010 ◽

Vol 4 (3) ◽

pp. 381-396 ◽

Cited By ~ 16

Author(s):

M. A. Werder ◽

T. V. Schuler ◽

M. Funk

Keyword(s):

Drainage System ◽

Relative Importance ◽

Short Term ◽

Diurnal Variability ◽

Alpine Glacier ◽

Two Component ◽

Transit Speed ◽

Underlying Processes ◽

Diurnal Maximum ◽

Tracer Experiments

Abstract. We first present the results of a series of tracer experiments conducted on an alpine glacier (Gornergletscher, Switzerland) over a diurnal discharge cycle. For these injections, a moulin was used into which an ice marginal lake was draining, providing a relatively constant discharge. The measured tracer transit speeds show two diurnal maxima and minima. These findings are qualitatively different to existing observations from two series of injections conducted at Unteraargletscher (Switzerland) using a moulin fed by supraglacial meltwater having a high diurnal variability, which displayed one diurnal maximum and minimum. We then develop and use a simple two-component model of the glacier drainage system, comprising a moulin and a channel element, to simulate the measured transit speeds for all three injection series. The model successfully reproduces all the observations and shows that the same underlying processes can produce the qualitatively different behaviour depending on the different moulin input discharge regimes. Using the model, we assess the relative importance of the different measurement quantities, show that frequent measurements of moulin input discharge are indispensable and propose an experiment design to monitor the development of the drainage system over several weeks.

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

Glaciohydraulic seismic tremors on an Alpine glacier

The Cryosphere ◽

10.5194/tc-14-287-2020 ◽

2020 ◽

Vol 14 (1) ◽

pp. 287-308 ◽

Cited By ~ 4

Author(s):

Fabian Lindner ◽

Fabian Walter ◽

Gabi Laske ◽

Florent Gimbert

Keyword(s):

Water Flow ◽

Lake Level ◽

Seismic Waves ◽

Water Pressure ◽

Drainage System ◽

Source Tracking ◽

Lake Basin ◽

Flow Measurements ◽

Alpine Glacier ◽

Subsequent Decrease

Abstract. Hydraulic processes impact viscous and brittle ice deformation. Water-driven fracturing as well as turbulent water flow within and beneath glaciers radiate seismic waves which provide insights into otherwise hard-to-access englacial and subglacial environments. In this study, we analyze glaciohydraulic tremors recorded by four seismic arrays installed in different parts of Glacier de la Plaine Morte, Switzerland. Data were recorded during the 2016 melt season including the sudden subglacial drainage of an ice-marginal lake. Together with our seismic data, discharge, lake level, and ice flow measurements provide constraints on glacier hydraulics. We find that the tremors are generated by subglacial water flow, in moulins, and by icequake bursts. The dominating process can vary on sub-kilometer and sub-daily scales. Consistent with field observations, continuous source tracking via matched-field processing suggests a gradual up-glacier progression of an efficient drainage system as the melt season progresses. The ice-marginal lake likely connects to this drainage system via hydrofracturing, which is indicated by sustained icequake signals emitted from the proximity of the lake basin and starting roughly 24 h prior to the lake drainage. To estimate the hydraulics associated with the drainage, we use tremor–discharge scaling relationships. Our analysis suggests a pressurization of the subglacial environment at the drainage onset, followed by an increase in the hydraulic radii of the conduits and a subsequent decrease in the subglacial water pressure as the capacity of the drainage system increases. The pressurization is in phase with the drop in the lake level, and its retrieved maximum coincides with ice uplift measured via GPS. Our results highlight the use of cryo-seismology for monitoring glacier hydraulics.

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

Drainage of the Austre Okstindbreen Ice-dammed Lake, Okstindan, Norway

Journal of Glaciology ◽

10.3189/s0022143000009102 ◽

1988 ◽

Vol 34 (116) ◽

pp. 87-94 ◽

Cited By ~ 1

Author(s):

N. Tvis Knudsen ◽

Wilfred H. Theakstone

Keyword(s):

River Discharge ◽

Heavy Rainfall ◽

Water Pressure ◽

Drainage System ◽

Lake Basin ◽

Glacier Surface ◽

Stage Of Development ◽

Intense Storm ◽

Dammed Lake ◽

Precipitation Changes

AbstractObservations of the discharge, electrical conductivity, cationic content, and isotopic composition of glacier-river water indicate that drainage of the lake dammed at the margin of the glacier Austre Okstindbreen, Okstindan, Norway, is preceded by disruption of the glacier’s drainage system(s). Annual studies over a period of 12 years have demonstrated that intense storm precipitation, changes of ablation conditions, and the stage of development of drainage systems all may play a role in triggering drainage of the ice-dammed lake. Water temperature may influence the course of the outburst. The lake has drained on at least ten occasions in the last 12 years. Three of the events (1979, 1985, and 1986) occurred early in the summer, whilst melting of the winter’s snow cover was contributing substantially to glacier-river discharge: high basal water pressure and rapid sliding may have facilitated disruption of drainage conditions within the glacier. In 1982, the lake drained during a severe storm, in 1977 and 1984 shortly after a period of heavy rainfall. During the 1977 and 1984 events, water under pressure burst up through the glacier surface. The lake basin remained partly filled throughout one summer (1980): in-flow of water was balanced by out-flow into the glacier.

Download Full-text

Glaciofluvial crevasse and conduit fills as indicators of supraglacial dewatering during a surge, Skeiðarárjökull, Iceland

Journal of Glaciology ◽

10.3189/172756500781833232 ◽

2000 ◽

Vol 46 (152) ◽

pp. 25-34 ◽

Cited By ~ 30

Author(s):

Matthew R. Bennett ◽

David Huddart ◽

Richard I. Waller

Keyword(s):

Water Pressure ◽

Drainage System ◽

Active Phase ◽

Glacier Surface ◽

Cavity System ◽

Angle Fractures ◽

High Level ◽

Vertical Fractures

AbstractThis paper documents the glaciological structures associated with the surge of Skeiðarárjökull, Iceland, in 1991. These structures are interpreted as units of stratified ice, low-angle fractures, vertical and sub-vertical fractures (crevasse traces) and thrusts. The inferred thrusts are debris-rich and, unusually, have both down-glacier and up-glacier dips close to the ice margin. Sediment infills consist of either massive sand or horizontally stratified sand units. The most significant debris-rich structures on the glacier surface, however, are supraglacial crevasse and conduit fills, which contain either massive or horizontally stratified silts, sands and granule-gravels. These sediments infill both vertical fractures (relict crevasses) and englacial conduits. At the stratigraphic base of these sediment fills there is evidence of syn-sedimentary deformation, suggesting that sedimentation occurred during crevasse closure and continued thereafter. We argue that these structures relate to an episode of supraglacial meltwater flow during the 1991 surge, caused by the build-up of subglacial water pressure in a linked-cavity system or some similar distributed drainage system beneath the glacier. The development of this high-level drainage route may have helped regulate basal water pressures and therefore the active phase of the surge. The idea that the supraglacial leakage of subglacial water may have played a role in terminating the surge is explored.

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 ◽

10.1017/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.

Download Full-text

Determining the evolution of an alpine glacier drainage system by solving inverse problems

Journal of Glaciology ◽

10.1017/jog.2020.116 ◽

2021 ◽

pp. 1-14

Author(s):

Inigo Irarrazaval ◽

Mauro A. Werder ◽

Matthias Huss ◽

Frederic Herman ◽

Gregoire Mariethoz

Keyword(s):

Field Data ◽

Numerical Models ◽

Water Pressure ◽

Drainage System ◽

Stochastic Approach ◽

Channel Networks ◽

Alpine Glacier ◽

Transit Times ◽

Borehole Water ◽

State Water

Abstract Our understanding of the subglacial drainage system has improved markedly over the last decades due to field observations and numerical modelling. However, integrating data into increasingly complex numerical models remain challenging. Here we infer two-dimensional subglacial channel networks and hydraulic parameters for Gorner Glacier, Switzerland, based on available field data at five specific times (snapshots) across the melt season of 2005. The field dataset is one of the most complete available, including borehole water pressure, tracer experiments and meteorological variables. Yet, these observations are still too sparse to fully characterize the drainage system and thus, a unique solution is neither expected nor desirable. We use a geostatistical generator and a steady-state water flow model to produce a set of subglacial channel networks that are consistent with measured water pressure and tracer-transit times. Field data are used to infer hydraulic and morphological parameters of the channels under the assumption that the location of channels persists during the melt season. Results indicate that it is possible to identify locations where subglacial channels are more likely. In addition, we show that different network structures can equally satisfy the field data, which support the use of a stochastic approach to infer unobserved subglacial features.

Download Full-text