scholarly journals Quantification of seasonal and diurnal dynamics of subglacial channels using seismic observations on an Alpine glacier

2020 ◽  
Vol 14 (5) ◽  
pp. 1475-1496 ◽  
Author(s):  
Ugo Nanni ◽  
Florent Gimbert ◽  
Christian Vincent ◽  
Dominik Gräff ◽  
Fabian Walter ◽  
...  
Keyword(s):  
Pressure Gradient ◽  
Water Discharge ◽  
Drainage System ◽  
Fold Increase ◽  
Hydraulic Pressure ◽  
Hydraulic Radius ◽  
Sliding Speed ◽  
Alpine Glacier ◽  
Basal Sliding ◽  
Potential Link

Abstract. Water flowing below glaciers exerts a major control on glacier basal sliding. However, our knowledge of the physics of subglacial hydrology and its link with sliding is limited because of lacking observations. Here we use a 2-year-long dataset made of on-ice-measured seismic and in situ-measured glacier basal sliding speed on Glacier d'Argentière (French Alps) to investigate the physics of subglacial channels and its potential link with glacier basal sliding. Using dedicated theory and concomitant measurements of water discharge, we quantify temporal changes in channels' hydraulic radius and hydraulic pressure gradient. At seasonal timescales we find that hydraulic radius and hydraulic pressure gradient respectively exhibit a 2- and 6-fold increase from spring to summer, followed by comparable decrease towards autumn. At low discharge during the early and late melt season channels respond to changes in discharge mainly through changes in hydraulic radius, a regime that is consistent with predictions of channels' behaviour at equilibrium. In contrast, at high discharge and high short-term water-supply variability (summertime), channels undergo strong changes in hydraulic pressure gradient, a behaviour that is consistent with channels behaving out of equilibrium. This out-of-equilibrium regime is further supported by observations at the diurnal scale, which prove that channels pressurize in the morning and depressurize in the afternoon. During summer we also observe high and sustained basal sliding speed, which supports that the widespread inefficient drainage system (cavities) is likely pressurized concomitantly with the channel system. We propose that pressurized channels help sustain high pressure in cavities (and therefore high glacier sliding speed) through an efficient hydraulic connection between the two systems. The present findings provide an essential basis for testing the physics represented in subglacial hydrology and glacier sliding models.

scholarly journals Seasonal and Diurnal Dynamics of Subglacial Channels: Observations Beneath an Alpine Glacier

2019 ◽  
Author(s):  
Ugo Nanni ◽  
Florent Gimbert ◽  
Christian Vincent ◽  
Dominik Gräff ◽  
Fabian Walter ◽  
...  
Keyword(s):  
Pressure Gradient ◽  
Water Discharge ◽  
Drainage System ◽  
Fold Increase ◽  
Hydraulic Pressure ◽  
Hydraulic Radius ◽  
Ice Dynamics ◽  
Alpine Glacier ◽  
Basal Sliding ◽  
Potential Link

Abstract. Water flowing below glaciers exerts a major control on glacier basal sliding speeds. However, our knowledge on the physics of subglacial hydrology and its link with sliding is limited by lacking observations. Here we use a two-year long dataset made of on-ice measured seismic and in-situ measured glacier basal sliding speed records on the Glacier d’Argentière (French Alps) to investigate the physics of subglacial channels and its potential link with glacier basal sliding. Using dedicated theory and concomitant measurements of water discharge, we quantify temporal changes in channels hydraulic radius and hydraulic pressure gradient. At seasonal timescales we observe, for the first time, that hydraulic radius and hydraulic pressure gradient present a four-fold increase from spring to summer, followed by a comparable decrease towards autumn. At low discharge during the early and late melt season channels respond to changes in discharge mainly through changes in hydraulic radius, a regime that is consistent with predictions of channels behaving at equilibrium. In contrast, at high discharge and high short-term water-supply variability (summertime), channels undergo strong changes in hydraulic pressure gradient, a behavior that is consistent with channels being out-of-equilibrium. This out-of-equilibrium regime is further supported by observations at the diurnal scale, which demonstrate that channels pressurize in the morning and depressurize in the afternoon. During summer we also observe high and sustained basal sliding speeds, supporting that the widespread inefficient drainage system (cavities) is likely pressurized concomitantly with the channel-system. We propose that pressurized channels help sustain high pressure in cavities (and therefore high glacier sliding speeds) through an efficient hydraulic connection between the two systems. Using the two regimes herein observed in channels seasonal-dynamics as constraints for subglacial hydrology/ice dynamics models may allow to strengthen our knowledge on the physics of subglacial processes.

scholarly journals Variations in the Sliding of a Temperate Glacier

1974 ◽  
Vol 13 (69) ◽  
pp. 349-369 ◽  
Author(s):  
Steven M. Hodge
Keyword(s):  
Water Discharge ◽  
Ice Flow ◽  
Sliding Speed ◽  
Temporary Storage ◽  
State Of Stress ◽  
Basal Sliding ◽  
Internal Deformation ◽  
Pressure Melting ◽  
Glacier Flow ◽  
Basal Shear

Detailed measurements of the positions of stakes along the center-line of the lower Nisqually Glacier were made over a period of two years. Variations in the basal sliding speed were calculated from the measured changes in surface speed, surface slope, and thickness, using the glacier flow model of Nye (1952) and allowing for the effect of the valley walls, longitudinal stress gradients, and uncertainties in the flow law of ice. The flow is predominantly by basal sliding and has a pronounced seasonal variation of approximately ±25%. Internal deformation contributes progressively less to the total motion with distance up-glacier. Neither the phase nor the magnitude of the seasonal velocity fluctuations can be accounted for by seasonal variations in the state of stress within the ice or at the bed, and the variations do not correlate directly with the melt-water discharge from the terminus. A seasonal wave in the ice flow travels down the glacier at a speed too high for propagation by internal deformation or the pressure melting/enhanced creep mechanism of basal sliding.The rate of sliding appears to be determined primarily by the amount of water in temporary storage in the glacier. The peak in sliding speed occurs, on the average, at the same time as the maximum liquid water storage of the South Cascade Glacier. The data support the idea that glaciers store water in the fall, winter and spring and then release it in the summer. This temporary storage may be greatest near the equilibrium line. The amount of stored water may increase over a period of years and be released catastrophically as a jökulhlaup. Any dependence of sliding on the basal shear stress is probably masked by the effect of variations in the hydrostatic pressure of water having access to the bed.

Variations in the Sliding of a Temperate Glacier

1974 ◽  
Vol 13 (69) ◽  
pp. 349-369 ◽  
Author(s):  
Steven M. Hodge
Keyword(s):  
Water Discharge ◽  
Ice Flow ◽  
Sliding Speed ◽  
Temporary Storage ◽  
State Of Stress ◽  
Basal Sliding ◽  
Internal Deformation ◽  
Pressure Melting ◽  
Glacier Flow ◽  
Basal Shear

Detailed measurements of the positions of stakes along the center-line of the lower Nisqually Glacier were made over a period of two years. Variations in the basal sliding speed were calculated from the measured changes in surface speed, surface slope, and thickness, using the glacier flow model of Nye (1952) and allowing for the effect of the valley walls, longitudinal stress gradients, and uncertainties in the flow law of ice. The flow is predominantly by basal sliding and has a pronounced seasonal variation of approximately ±25%. Internal deformation contributes progressively less to the total motion with distance up-glacier. Neither the phase nor the magnitude of the seasonal velocity fluctuations can be accounted for by seasonal variations in the state of stress within the ice or at the bed, and the variations do not correlate directly with the melt-water discharge from the terminus. A seasonal wave in the ice flow travels down the glacier at a speed too high for propagation by internal deformation or the pressure melting/enhanced creep mechanism of basal sliding. The rate of sliding appears to be determined primarily by the amount of water in temporary storage in the glacier. The peak in sliding speed occurs, on the average, at the same time as the maximum liquid water storage of the South Cascade Glacier. The data support the idea that glaciers store water in the fall, winter and spring and then release it in the summer. This temporary storage may be greatest near the equilibrium line. The amount of stored water may increase over a period of years and be released catastrophically as a jökulhlaup. Any dependence of sliding on the basal shear stress is probably masked by the effect of variations in the hydrostatic pressure of water having access to the bed.

scholarly journals Changing friction at the base of an Alpine glacier

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Dominik Gräff ◽  
Fabian Walter
Keyword(s):  
Drainage System ◽  
Normal Stresses ◽  
Stick Slip ◽  
Ice Flow ◽  
Alpine Glacier ◽  
Repeating Earthquakes ◽  
Tectonic Faults ◽  
Basal Sliding ◽  
Rate And State Friction ◽  
Local Shear

AbstractRepeating earthquakes are a global phenomenon of tectonic faults. Multiple ruptures on the same fault asperities lead to nearly identical waveforms characteristic for these seismic events. We identify their microseismic counterparts beneath an Alpine glacier, where basal sliding accounts for a significant amount of ice flow. In contrast to tectonic faults, Alpine glacier beds are subject to large variations in sliding velocity and effective normal stresses. This leads to inter- and sub-seasonal variations in released seismic moment from stick–slip asperities, which we explain with the rate-and-state friction formalism. During summer, numerically modelled effective normal stresses at asperities are three times higher than in winter, which increases the local shear resistance by the same factor. Stronger summer asperities therefore tend to form in bed regions well connected to the efficient subglacial drainage system. Moreover, asperities organise themselves into a state of subcriticality, transferring stresses between each other. We argue that this seismic stick–slip behavior has potentially far-reaching consequences for glacier sliding and in particular for catastrophic failure of unstable ice masses.

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.

scholarly journals Short term variations of tracer transit speed on alpine glaciers

2010 ◽  
Vol 4 (3) ◽  
pp. 381-396 ◽  
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.

Intrapleural liquid flow down a gravity-dependent hydraulic pressure gradient

1988 ◽  
Vol 64 (2) ◽  
pp. 577-584 ◽  
Author(s):  
G. Miserocchi ◽  
D. Negrini ◽  
M. Pistolesi ◽  
C. R. Bellina ◽  
M. C. Gilardi ◽  
...  
Keyword(s):  
Pressure Gradient ◽  
Time Course ◽  
Sudden Change ◽  
Vertical Movement ◽  
Rate Of Change ◽  
Large Field ◽  
Liquid Volume ◽  
Hydraulic Pressure ◽  
Albumin Clearance ◽  
Turning Maneuver

We studied the vertical movement of 2 mg technetium-labeled albumin injected intrapleurally in 0.5 ml saline (15% of pleural liquid volume) in eight spontaneously breathing anesthetized dogs subject to a sudden change in posture (prone to supine or vice versa). The albumin movements were evaluated through a large field gamma camera placed laterally to the animal and detecting total (AT) and regional activities from two superimposed equal areas (At and Ab, top and bottom, respectively). The At/Ab ratio decreased from 2.1 to 1.3 in four animals up to 20 min from the change in posture and from 0.9 to 0.5 in four more animals studied from 50 to 90 min from turning maneuver. The rate of change in At and Ab was similar in the two groups of animals and unaffected by the acquisition posture. AT decreased by 7.7 and 3.5% for the two groups, respectively, reflecting albumin clearance from the pleural space. The opposite time course of regional activities and the independence of their rate of change of the At/Ab ratio and of the animal posture suggest a top-to-bottom albumin transfer occurring through a bulk flow of liquid estimated at 0.006 ml.kg-1.h-1. The data are consistent with a measured vertical pleural liquid pressure gradient that does not reflect a hydrostatic condition.

Intrapleural fluid movements described by a porous flow model

1992 ◽  
Vol 73 (6) ◽  
pp. 2511-2516 ◽  
Author(s):  
G. Miserocchi ◽  
D. Venturoli ◽  
D. Negrini ◽  
M. C. Gilardi ◽  
R. Bellina
Keyword(s):  
Porous Medium ◽  
Gamma Camera ◽  
Flow Model ◽  
Pleural Space ◽  
Interstitial Tissue ◽  
Hydraulic Pressure ◽  
Pressure Gradients ◽  
Hydraulic Radius ◽  
Porous Flow ◽  
Anesthetized Dogs

We injected technetium-labeled albumin (at a concentration similar to that of the pleural fluid) in the costal region of anesthetized dogs (n = 13) either breathing spontaneously or apneic. The decay rate of labeled activity at the injection site was studied with a gamma camera placed either in the anteroposterior (AP) or laterolateral (LL) projection. In breathing animals (respiratory frequency approximately 10 cycles/min), 10 min after the injection the activity decreased by approximately 50% on AP and approximately 20% on LL imaging; in apneic animals the corresponding decrease in activity was reduced to approximately 15 and approximately 3%, respectively. We considered label translocation from AP and LL imaging as a result of bulk flows of liquid along the costomediastinal and gravity-dependent direction, respectively. We related intrapleural flows to the hydraulic pressure gradients existing along these two directions and to the geometry of the pleural space. The pleural space was considered as a porous medium partially occupied by the mesh of microvilli protruding from mesothelial cells. Solution of the Kozeny-Carman equation for the observed flow velocities and pressure gradients yielded a mean hydraulic radius of the pathways followed by the liquid ranging from 2 to 4 microns. The hydraulic resistivity of the pleural space was estimated at approximately 8.5 x 10(5) dyn.s.cm-4, five orders of magnitude lower than that of interstitial tissue.

scholarly journals ANALISA PERENCANAAN SISTEM DRAINASE DALAM UPAYA PENANGGULANGAN BANJIR DI KECAMATAN GANDUSARI KABUPATEN TRENGGALEK

2019 ◽  
Vol 2 (1) ◽  
pp. 131
Author(s):  
Rizqi Dwi Prasetyo ◽  
Yosef Cahyo ◽  
Ahmad Ridwan
Keyword(s):  
Water Discharge ◽  
Drainage System ◽  
Domestic Wastewater ◽  
Channel Height ◽  
Construction Costs ◽  
Flood Prevention ◽  
Dirty Water ◽  
Rainwater Runoff ◽  
The Cost ◽  
The Ideal

In industrial areas or densely populated settlements, generally found channels that function besides to drain rainwater as well as to discharge domestic wastewater or dirty water from households. Drainage systems are often the main problem in the occurrence of flooding. It is necessary to analyze how their performance and resistance to flooding in the District of Gandusari, Trenggalek Regency. For analysis of drainage system planning in flood prevention efforts, the authors used the Van-Breun and Mononobe calculation methods to determine the number of incoming water discharge, the ideal dimension of the channel to accommodate the inlet discharge channel, and calculate the cost budget plan (RAB) of the builder. From the analysis, results obtained a cumulative discharge of rainwater, and dirty water entering the drainage amounted to 0.4695 m3 / sec. From the calculation, the ideal dimensions of the drainage can be obtained to be able to accommodate rainwater runoff and dirty water discharge using square channels, where the 1.5 m channel height is all added to the water level of 0.2 m and 0.7 m in width 500 m. While the budget plan for the construction costs is Rp. 794,048,000.00 -Di daerah industri atau pemukiman padat penduduk umumnya ditemukan saluran yang berfungsi selain untuk mengalirkan air hujan juga sekaligus untuk pembuangan air limbah domestik ataupun air kotor dari rumah tangga. System drainase sering menjadi pokok masalah dalam terjadinya banjir, maka perlu di Analisa bagaimana kinerjanya dan ketahanan terhadap banjir di Kecamatan Gandusari Kabupaten Trenggalek. Untuk analisis perencanaan sistem drainase dalam upaya penanggulangan banjir penulis menggunakan metode perhitungan Van-Breun dan Mononobe untuk mengetahui angka debit air yang masuk, dimensi ideal saluran untuk menampung saluran debit air masuk dan menghitung rencana anggaran biaya (RAB) pembangunanya. Dari hasil analisa didapatkan debit komulatif air hujan dan air kotor yang masuk ke drainase sebesar 0.4695 m3/detik. Dari perhitungan didapatkan dimensi saluran drainase yang ideal agar mampu menampung limpasan air hujan dan debit air kotor dengan menggunakan saluran berbentuk persegi, dimana tinggi saluran 1,5 m semuanya ditambahkan dengan tinggi jagaan air sebesar 0,2 m dan lebar 0,7 m dengan panjang 500 m. Sedangkan rencana Anggaran Biaya pembangunannya sebesar Rp. 794.048.000,00,-

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.

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