scholarly journals Subglacial Processes at Bondhusbreen, Norway: Preliminary Results

1983 ◽  
Vol 4 ◽  
pp. 91-98 ◽  
Author(s):  
Jon Ove Hagen ◽  
Bjørn Wold ◽  
Olav Liestøl ◽  
Gunnar Østrem ◽  
Johan Ludvig Sollid
Keyword(s):  
Water Pressure ◽  
Water Discharge ◽  
Pressure Sensors ◽  
Hydroelectric Power ◽  
Outlet Glacier ◽  
Running Water ◽  
Order Of Magnitude ◽  
The Difference ◽  
Annual Water Discharge ◽  
Small Channels

Subglacial hydrology, sediment transport, pressure, and temperature have been studied beneath approximately 160 m of ice at Sondhusbreen, an outlet glacier from Folgefonni in south-western Norway.The volume of the mean annual water discharge passing through the study area is about 60x106 m3. Most of this water is diverted into a tunnel system in the rock beneath the glacier and used for hydroelectric power generation. At the beginning of the melt season, this water flows in multiple small channels, but later it collects in one or two main channels. The discharge of eroded material is about 7 600 tonnes a−1. Of this, roughly 90% is transported by running water.Pressure gauges and thermistors were installed at two sites under the glacier. Results from one of the sites indicated that ice can stagnate in some leeward positions, as almost no ice movement was recorded during most of the period of measurement and the pressure distribution was nearly hydrostatic. However, increased water pressure during the summer apparently resulted in the opening of subglacial cavities, adding a local up-glacier component to the flow at this site.At another location, about 20 m up-glacier, non-hydrostatic differential pressures of up to 30 bar were recorded across an artificial dome-shaped obstacle. The flow at this location was more steady, in general, but rather dramatic effects were recorded when a boulder 0.3 m3 in size passed over the obstacle, destroying one of the pressure sensors. This sensor recorded a pressure of 90 bar before failing. The boulder was moving at a speed of about 40 mm d-1, whereas the sliding velocity of the ice was 80 mm d-1. Temperature measurements suggest that the difference in temperature across this obstacle was less than 0.03 deg, or an order of magnitude less than expected. This may mean that water was squeezed out of the ice on the stoss side of the obstacle as suggested by Robin (1976), and thus was not available to warm the lee-side ice by refreezing.

scholarly journals Subglacial Processes at Bondhusbreen, Norway: Preliminary Results

1983 ◽  
Vol 4 ◽  
pp. 91-98 ◽  
Author(s):  
Jon Ove Hagen ◽  
Bjørn Wold ◽  
Olav Liestøl ◽  
Gunnar Østrem ◽  
Johan Ludvig Sollid
Keyword(s):  
Water Pressure ◽  
Water Discharge ◽  
Pressure Sensors ◽  
Hydroelectric Power ◽  
Outlet Glacier ◽  
Running Water ◽  
Order Of Magnitude ◽  
The Difference ◽  
Annual Water Discharge ◽  
Small Channels

Subglacial hydrology, sediment transport, pressure, and temperature have been studied beneath approximately 160 m of ice at Sondhusbreen, an outlet glacier from Folgefonni in south-western Norway.The volume of the mean annual water discharge passing through the study area is about 60x106m3. Most of this water is diverted into a tunnel system in the rock beneath the glacier and used for hydroelectric power generation. At the beginning of the melt season, this water flows in multiple small channels, but later it collects in one or two main channels. The discharge of eroded material is about 7 600 tonnes a−1. Of this, roughly 90% is transported by running water.Pressure gauges and thermistors were installed at two sites under the glacier. Results from one of the sites indicated that ice can stagnate in some leeward positions, as almost no ice movement was recorded during most of the period of measurement and the pressure distribution was nearly hydrostatic. However, increased water pressure during the summer apparently resulted in the opening of subglacial cavities, adding a local up-glacier component to the flow at this site.At another location, about 20 m up-glacier, non-hydrostatic differential pressures of up to 30 bar were recorded across an artificial dome-shaped obstacle. The flow at this location was more steady, in general, but rather dramatic effects were recorded when a boulder 0.3 m3in size passed over the obstacle, destroying one of the pressure sensors. This sensor recorded a pressure of 90 bar before failing. The boulder was moving at a speed of about 40 mm d-1, whereas the sliding velocity of the ice was 80 mm d-1. Temperature measurements suggest that the difference in temperature across this obstacle was less than 0.03 deg, or an order of magnitude less than expected. This may mean that water was squeezed out of the ice on the stoss side of the obstacle as suggested by Robin (1976), and thus was not available to warm the lee-side ice by refreezing.

scholarly journals The Importance of Pressurized Subglacial Water in Separation and Sliding at the Glacier Bed

1983 ◽  
Vol 29 (101) ◽  
pp. 3-19 ◽  
Author(s):  
Robert Bindschadler
Keyword(s):  
Water Pressure ◽  
Water Discharge ◽  
High Water ◽  
Temporal Variations ◽  
Early Summer ◽  
Test Case ◽  
Separation Index ◽  
Order Of Magnitude ◽  
Bed Separation ◽  
Ice Stream B

AbstractThe effect of pressurized subglacial water on the sliding process is examined by a parameter called the “bed separation index”. This index indicates the relative extent of cavity formation by combining the effects of variation of bed-normal stress across undulations (Kamb, 1970) and steady-state water pressure in a Röthlisberger conduit at the glacier bed. Data from three glaciers of widely varying size are used to test the correlation of the bed separation index with inferred sliding rates. For Columbia Glacier and Ice Stream B in West Antarctica it is shown that high water pressure enhances sliding. More complete data from the third test case. Variegated Glacier, are used to compare a number of possible formulations of a “sliding law”. A Weertman-type power law (exponent c. 3), modified for the effect of subglacial water pressure, appears to be most preferable. Other formulations, including the “lubrication factor” hypothesis used by Budd (1975) are tentatively rejected. Consideration of the temporal variations of the “bed separation index” indicate that, on short time scales of days and weeks, variations of water pressure can dominate the sliding process. A rapid order-of-magnitude increase in water discharge causes a hundredfold transient increase in the water pressure. A bi-modal hydraulic regime is revealed for water flow transverse to the direction of main ice flow. This behavior is in accord with the observation of a sudden acceleration of the ice due to increased sliding in early summer or following heavy rainstorms.

Pore water pressure dynamics in a rock slope adjacent to a retreating valley glacier

2020 ◽  
Author(s):  
Marc Hugentobler ◽  
Simon Loew ◽  
Clément Roques
Keyword(s):  
Boundary Conditions ◽  
Pore Water ◽  
Rock Slope ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Water Discharge ◽  
Pressure Sensors ◽  
Swiss Alps ◽  
Special Focus ◽  
Valley Glacier

<p>Rock slope instabilities normally form through long-term strength degradation of initially stable slopes. The rate of progressive damage accumulation in the rock slope is expected to vary over time depending on the current environmental conditions. It is often assumed that glacial retreat, with its increased dynamics in the thermal and hydraulic boundary conditions in combination with mechanical ice unloading induce stresses that cause increased rock mass damage in adjacent slopes. However, direct field measurements to understand these dynamics and to quantify damage are rare.</p><p>In this contribution we present new data of a continuous borehole monitoring system installed in a stable rock slope beside the retreating glacier tongue of the Great Aletsch Glacier (Swiss Alps). Special focus lies on the pore water pressure evolution in order to better understand the origin of the presumably hydro-mechanically forced deformation measured in the study area. We compare data of two borehole pressure sensors installed at 50 m depth in the fractured crystalline rock, pressure fluctuations measured in a sink hole on the glacier close to our study site, and glacial melt water discharge measurements. These data show that the pore pressure variability in the slope is driven by annual snowmelt infiltration cycles, rainfall events, and the connection to the englacial water of the temperate valley glacier. We show that our in-situ measurements provide critical data to improve the understanding of the effects of a retreating valley glacier on the boundary conditions and eventually the stability of an adjacent rock slope.</p>

scholarly journals The Importance of Pressurized Subglacial Water in Separation and Sliding at the Glacier Bed

1983 ◽  
Vol 29 (101) ◽  
pp. 3-19 ◽  
Author(s):  
Robert Bindschadler
Keyword(s):  
Water Pressure ◽  
Water Discharge ◽  
High Water ◽  
Temporal Variations ◽  
Early Summer ◽  
Test Case ◽  
Separation Index ◽  
Order Of Magnitude ◽  
Bed Separation ◽  
Ice Stream B

Abstract The effect of pressurized subglacial water on the sliding process is examined by a parameter called the “bed separation index”. This index indicates the relative extent of cavity formation by combining the effects of variation of bed-normal stress across undulations (Kamb, 1970) and steady-state water pressure in a Röthlisberger conduit at the glacier bed. Data from three glaciers of widely varying size are used to test the correlation of the bed separation index with inferred sliding rates. For Columbia Glacier and Ice Stream B in West Antarctica it is shown that high water pressure enhances sliding. More complete data from the third test case. Variegated Glacier, are used to compare a number of possible formulations of a “sliding law”. A Weertman-type power law (exponent c. 3), modified for the effect of subglacial water pressure, appears to be most preferable. Other formulations, including the “lubrication factor” hypothesis used by Budd (1975) are tentatively rejected. Consideration of the temporal variations of the “bed separation index” indicate that, on short time scales of days and weeks, variations of water pressure can dominate the sliding process. A rapid order-of-magnitude increase in water discharge causes a hundredfold transient increase in the water pressure. A bi-modal hydraulic regime is revealed for water flow transverse to the direction of main ice flow. This behavior is in accord with the observation of a sudden acceleration of the ice due to increased sliding in early summer or following heavy rainstorms.

scholarly journals The Importance of Pressurized Subglacial Water in Separation and Sliding at the Glacier Bed (Abstract only)

1982 ◽  
Vol 3 ◽  
pp. 349-349
Author(s):  
Robert Bindschadler
Keyword(s):  
Water Pressure ◽  
Water Discharge ◽  
Temporal Variations ◽  
Short Time Scale ◽  
Test Case ◽  
Separation Index ◽  
Order Of Magnitude ◽  
Bed Separation ◽  
Ice Stream B ◽  
Basal Shear

The effect of pressurized sub-glacial water on the sliding process is quantified by calculating a “bed separation index”. The water pressure distribution i s calculated assuming the existence of a Rothlisberger channel at the bed. Kamb's formulation is used to describe the variation of normal stress over periodic bed undulations. The hypothesis is that as either basal shear stress or water pressure is increased the extent of ice-bedrock separation (on the down-glacier side of undulations) increases and enhanced sliding occursData from three glaciers of widely varying size are used to test this hypothesis. For Columbia Glacier and “Ice Stream B” the importance of including the effects of water pressure in any “sliding law” are pronounced. More complete data from the third test case, Variegated Glacier, are used to compare a number of possible formulations of sliding law which encompass the above hypothesis. A modified Weertmantype law appears to be most preferable while while some possibilities, including Budd's lubrication factor hypothesis, are tentatively rejected.Consideration of the temporal variations of the “bed separation index” reemphasize that, especially in the short time scale, variations of water pressure can dominate the sliding process. An order of magnitude increase in water discharge causes a hundred fold transient increase in the water pressure.This paper has been accepted for publication in the Journal of Glaciology

scholarly journals The Importance of Pressurized Subglacial Water in Separation and Sliding at the Glacier Bed (Abstract only)

1982 ◽  
Vol 3 ◽  
pp. 349 ◽  
Author(s):  
Robert Bindschadler
Keyword(s):  
Water Pressure ◽  
Water Discharge ◽  
Temporal Variations ◽  
Short Time Scale ◽  
Test Case ◽  
Separation Index ◽  
Order Of Magnitude ◽  
Bed Separation ◽  
Ice Stream B ◽  
Basal Shear

The effect of pressurized sub-glacial water on the sliding process is quantified by calculating a “bed separation index”. The water pressure distribution i s calculated assuming the existence of a Rothlisberger channel at the bed. Kamb's formulation is used to describe the variation of normal stress over periodic bed undulations. The hypothesis is that as either basal shear stress or water pressure is increased the extent of ice-bedrock separation (on the down-glacier side of undulations) increases and enhanced sliding occurs Data from three glaciers of widely varying size are used to test this hypothesis. For Columbia Glacier and “Ice Stream B” the importance of including the effects of water pressure in any “sliding law” are pronounced. More complete data from the third test case, Variegated Glacier, are used to compare a number of possible formulations of sliding law which encompass the above hypothesis. A modified Weertmantype law appears to be most preferable while while some possibilities, including Budd's lubrication factor hypothesis, are tentatively rejected. Consideration of the temporal variations of the “bed separation index” reemphasize that, especially in the short time scale, variations of water pressure can dominate the sliding process. An order of magnitude increase in water discharge causes a hundred fold transient increase in the water pressure. This paper has been accepted for publication in the Journal of Glaciology

scholarly journals Determination of Force Coefficients for a Submerged Rigid Breakwater under the Action of Solitary Waves

Water ◽  
2021 ◽  
Vol 13 (3) ◽  
pp. 315
Author(s):  
Francesco Aristodemo ◽  
Giuseppe Tripepi ◽  
Luana Gurnari ◽  
Pasquale Filianoti
Keyword(s):  
Solitary Waves ◽  
Pressure Sensors ◽  
Wave Forces ◽  
Wave Loads ◽  
Force Coefficients ◽  
Wave Flume ◽  
Physical Tests ◽  
The Difference ◽  
The University ◽  
Semi Empirical

We present an analysis related to the evaluation of Morison and transverse force coefficients in the case of a submerged square barrier subject to the action of solitary waves. To this purpose, two-dimensional experimental research was undertaken in the wave flume of the University of Calabria, in which a rigid square barrier was provided by a discrete battery of pressure sensors to determine the horizontal and vertical hydrodynamic forces. A total set of 18 laboratory tests was carried out by varying the motion law of a piston-type paddle. Owing to the low Keulegan–Carpenter numbers of the tests, the force regime of the physical tests was defined by the dominance of the inertia loads in the horizontal direction and of the lift loads in the vertical one. Through the use of the time series of wave forces and the undisturbed kinematics, drag, horizontal inertia, lift, and vertical inertia coefficients in the Morison and transverse semi-empirical schemes were calculated using time-domain approaches, adopting the WLS1 method for the minimization of the difference between the maximum forces and the linked phase shifts by comparing laboratory and calculated wave loads. Practical equations to calculate these coefficients as a function of the wave non-linearity were introduced. The obtained results highlighted the prevalence of the horizontal forces in comparison with the vertical ones which, however, prove to be fundamental for stability purposes of the barrier. An overall good agreement between the experimental forces and those calculated by the calibrated semi-empirical schemes was found, particularly for the positive horizontal and vertical loads. The analysis of the hydrodynamic coefficients showed a decreasing trend for the drag, horizontal inertia, and lift coefficients as a function of the wave non-linearity, while the vertical inertia coefficient underlined an initial increasing trend and a successive slight decreasing trend.

scholarly journals Discharge of debris from ice at the margin of the Greenland ice sheet

2002 ◽  
Vol 48 (161) ◽  
pp. 192-198 ◽  
Author(s):  
Peter G. Knight ◽  
Richard I. Waller ◽  
Carrie J. Patterson ◽  
Alison P. Jones ◽  
Zoe P. Robinson
Keyword(s):  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
High Rate ◽  
Outlet Glacier ◽  
Tidewater Glaciers ◽  
Sediment Production ◽  
Basal Ice ◽  
Order Of Magnitude ◽  
Sediment Transfer ◽  
A Minor

AbstractSediment production at a terrestrial section of the ice-sheet margin in West Greenland is dominated by debris released through the basal ice layer. The debris flux through the basal ice at the margin is estimated to be 12–45 m3 m−1 a−1. This is three orders of magnitude higher than that previously reported for East Antarctica, an order of magnitude higher than sites reported from in Norway, Iceland and Switzerland, but an order of magnitude lower than values previously reported from tidewater glaciers in Alaska and other high-rate environments such as surging glaciers. At our site, only negligible amounts of debris are released through englacial, supraglacial or subglacial sediment transfer. Glaciofluvial sediment production is highly localized, and long sections of the ice-sheet margin receive no sediment from glaciofluvial sources. These findings differ from those of studies at more temperate glacial settings where glaciofluvial routes are dominant and basal ice contributes only a minor percentage of the debris released at the margin. These data on debris flux through the terrestrial margin of an outlet glacier contribute to our limited knowledge of debris production from the Greenland ice sheet.

scholarly journals An experimental and theoretical investigation of diffusion in a two-phase alloy

1948 ◽  
Vol 192 (1031) ◽  
pp. 575-592 ◽  
Keyword(s):  
Free Energy ◽  
Single Phase ◽  
Phase State ◽  
Theoretical Treatment ◽  
Research Association ◽  
Essential Difference ◽  
Two Phase ◽  
Two Factors ◽  
Order Of Magnitude ◽  
The Difference

The present paper describes an investigation of diffusion in the solid state. Previous experimental work has been confined to the case in which the free energy of a mixture is a minimum for the single-phase state, and diffusion decreases local differences of concentration. This may be called ‘diffusion downhill’. However, it is possible for the free energy to be a minimum for the two-phase state; diffusion may then increase differences of concentration; and so may be called ‘diffusion uphill’. Becker (1937) has proposed a simple theoretical treatment of these two types of diffusion in a binary alloy. The present paper describes an experimental test of this theory, using the unusual properties of the alloy Cu 4 FeNi 3 . This alloy is single phase above 800° C and two-phase at lower temperatures, both the phases being face-centred cubic; the essential difference between the two phases is their content of copper. On dissociating from one phase into two the alloy develops a series of intermediate structures showing striking X-ray patterns which are very sensitive to changes of structure. It was found possible to utilize these results for a quantitative study of diffusion ‘uphill’ and ‘downhill’ in the alloy. The experimental results, which can be expressed very simply, are in fair agreement with conclusions drawn from Becker’s theory. It was found that Fick’s equation, dc / dt = D d2c / dx2 , can, within the limits of error, be applied in all cases, with the modification that c denotes the difference of the measured copper concentration from its equilibrium value. The theory postulates that D is the product of two factors, of which one is D 0f the coefficient of diffusion that would be measured if the alloy were an ideal solid solution. The theory is able to calculate D/D 0 , if only in first approximation, and the experiments confirm this calculation. It was found that in most cases the speed of diffusion—‘uphill’ or ‘downhill’—has the order of magnitude of D 0 . * Now with British Electrical Research Association.

Trapping Effect on the Kinetic Critical Radius in Nucleation and Growth Processes

2014 ◽  
Vol 790-791 ◽  
pp. 97-102
Author(s):  
Zoltán Erdélyi ◽  
Zoltán Balogh ◽  
Gabor L. Katona ◽  
Dezső L. Beke
Keyword(s):  
Critical Nucleus ◽  
Solid Phase ◽  
Kinetic Monte Carlo ◽  
Mean Field ◽  
Transformation Process ◽  
Nucleus Size ◽  
Critical Nucleus Size ◽  
Acta Mater ◽  
Order Of Magnitude ◽  
The Difference

The critical nucleus size—above which nuclei grow, below dissolve—during diffusion controlled nucleation in binary solid-solid phase transformation process is calculated using kinetic Monte Carlo (KMC). If atomic jumps are slower in an A-rich nucleus than in the embedding B-rich matrix, the nucleus traps the A atoms approaching its surface. It doesn’t have enough time to eject A atoms before new ones arrive, even if it would be favourable thermodynamically. In this case the critical nucleus size can be even by an order of magnitude smaller than expected from equilibrium thermodynamics or without trapping. These results were published in [Z. Erdélyi et al., Acta Mater. 58 (2010) 5639]. In a recent paper M. Leitner [M. Leitner, Acta Mater. 60 (2012) 6709] has questioned our results based on the arguments that his simulations led to different results, but he could not point out the reason for the difference. In this paper we summarize our original results and on the basis of recent KMC and kinetic mean field (KMF) simulations we show that Leitner’s conclusions are not valid and we confirm again our original results.

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