scholarly journals Glaciohydraulic seismic tremors on an Alpine glacier

2020 ◽  
Vol 14 (1) ◽  
pp. 287-308 ◽  
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.

scholarly journals Glaciohydraulic seismic tremors on an Alpine glacier

2019 ◽  
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 upglacier 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 hours 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.

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

1997 ◽  
Vol 24 ◽  
pp. 288-292 ◽  
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.

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

1997 ◽  
Vol 24 ◽  
pp. 288-292 ◽  
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.

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

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

<p>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.</p><p>We use 1-month long ground motion records at a hundred of sensors deployed on the Argentière 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.</p><p>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.</p>

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

1988 ◽  
Vol 34 (116) ◽  
pp. 87-94 ◽  
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.

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

1993 ◽  
Vol 39 (132) ◽  
pp. 216-222 ◽  
Author(s):  
Scott A. Lecce
Keyword(s):  
Electrical Conductivity ◽  
Sierra Nevada ◽  
Water Pressure ◽  
Drainage System ◽  
Flow Process ◽  
Glacier Surface ◽  
Diurnal Variability ◽  
Alpine Glacier ◽  
Cross Correlation Analysis ◽  
Mass Balance Approach

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.

scholarly journals Interactions between Lake-Level Fluctuations and Waterlogging Disasters around a Large-Scale Shallow Lake: An Empirical Analysis from China

Water ◽  
2019 ◽  
Vol 11 (2) ◽  
pp. 318 ◽  
Author(s):  
Zongzhi Wang ◽  
Kun Wang ◽  
Kelin Liu ◽  
Liang Cheng ◽  
Lihui Wang ◽  
...  
Keyword(s):  
Hydrodynamic Model ◽  
Lake Level ◽  
Large Scale ◽  
Drainage System ◽  
Flood Routing ◽  
Lake Basin ◽  
Rainfall Events ◽  
One Dimensional ◽  
Lake Level Fluctuations ◽  
Pumping Stations

Waterlogging disasters in the lakeside areas of shallow lakes that located in plain regions are sensitive to lake-level fluctuations. However, there are very few studies on the influences of lake-level fluctuations on waterlogged lakeside areas from a large lake basin perspective. This paper proposes an integrated hydrodynamic model employing the MIKE software to contribute to the existing literature by filling the gap constituted by the lack of an estimation of the impacts of lake-level fluctuations on waterlogging disasters by relevant models. First, a coupled one-dimensional and two-dimensional hydrodynamic model is established to simulate the waterlogging routing in the lakeside area around Nansi Lake (NL) in addition to the flood routing in NL and its tributaries. Second, the model is calibrated and verified by two measured flood events in July 2007 and July 2008; the results indicate that the model can correctly simulate the drainage process of pumping stations in the lakeside area, as well as the interactions between the waterlogging drainage and lake-level fluctuations. Third, the process of waterlogging in the lakeside area of NL is simulated under different rainfall events and initial lake-level conditions. Fourth, based on the results of the model, this paper illustrates the influences of lake-level fluctuations on the waterlogged area around the lake, as well as the different responses of waterlogging in different areas to lake-level fluctuations in NL and the main cause for these differences. Finally, based on the results of the model, this paper presents some implications for waterlogging simulations and drainage system design.

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

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.

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

1988 ◽  
Vol 34 (116) ◽  
pp. 87-94 ◽  
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

Abstract Observations 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.

scholarly journals Seasonal Development of Subglacial Drainage and Suspended Sediment Delivery to Melt Waters Beneath an Alpine Glacier

1989 ◽  
Vol 13 ◽  
pp. 45-50 ◽  
Author(s):  
David N. Collins
Keyword(s):  
Suspended Sediment ◽  
Water Pressure ◽  
Drainage System ◽  
Sediment Concentration ◽  
Sediment Flux ◽  
Seasonal Development ◽  
Sediment Delivery ◽  
Alpine Glacier ◽  
Run Off ◽  
Subglacial Drainage

During the ablation seasons of 1983 and 1987, measurements of discharge and suspended sediment concentration of melt waters draining from Gornergletscher, Switzerland, were obtained at hourly intervals, permitting estimation of total daily sediment flux. Seasonal patterns of variation in sediment flux are interpreted in terms of development of the subglacial drainage network. Variations in flux relate to contrasting temporal patterns of run-off, and the differing incidence of subglacial hydrological events in the 2 years. During such events, in which basal water pressure is raised, large areas of previously hydraulically isolated sub-sole are integrated with flow, releasing quantities of sediment from basal storage. Several types of event are identified, arising during periods of generally increasing discharge in the early ablation season, resulting from temporary blocking of subglacial passageways or from outbursts emptying a marginal, ice-dammed lake, and related to rain-induced floods. Flow spreads out over the glacier bed as pressure increases, suggesting that the basal drainage system consists of a diffuse network of many linked cavities rather than fewer major conduits, particularly at the start of the season. A distributed cavity system may be simplified to fewer conduits, dimensions of cavities may enlarge or the area of bed over which cavities are developing may be expanded to supply debris to melt waters during events. Different partial areas of sub-sole become progressively integrated with flow during sequences of hydrological events. Later in summer, melt waters are confined to basal areas within which only limited sediment remains available for acquisition.

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