Pressure-Melting Effects in Basal Ice of Temperate Glaciers: Laboratory Studies and Field Observations Under Glacier D’Argentière

Goodman, D. J.; King, Geoffrey; Millar, D. H. M.; Robin, G. de Q.

doi:10.3189/s0022143000029889

Cited by 23 publications

(20 citation statements)

References 13 publications

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“…* The field observations of Goodman (Goodman and others, 1979) suggest that the j erking movement of the glacier seems to be responsible for the strain variations observed and measured in the rock a few metres under the interface.…”

Section: Ill Subglacial Drainage Characteristicsmentioning

confidence: 99%

The Nature of the Ice-Rock Interface: The Results of Investigation on 20000m2 of the Rock Bed of Temperate Glaciers

Vivian¹

1980

J. Glaciol.

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This paper reviews the results of 10 years study of the only four subglacial sites which are permanently accessible due to activity by hydro-electrical companies. All the sites occur beneath temperate ice. The first part is devoted to the study of the ice-rock interface as a glaciological phenomenon, and emphasizes the dynamic conditions for separation of the ice from the rock bed. This glaciological cavitation phenomenon occurs when tan α >Vi/Hi. Another phenomenon, “regressive cavitation” refers to the existence up-stream of the large permanent cavities, of a series of small cavities which although they are not permanent are fundamentally important because they control the subglacial water drainage allowing the water to penetrate new routes. The second part analyses the sliding movement of the ice on the rock bed. The deformation of the cavities depends mainly on variations in the velocity of the glacier. The sliding velocity measured at the interface accounts for 60 to 80% of the surface movement of the glacier; 80 to 90% of the surface velocity movement is attained a few metres above the glacier-bed interface. The third part describes the characteristics of subglacial drainage which are necessary to understand the nature of the ice-rock interface. The fourth part is devoted to the precise description of the different types of interface as they appeared in the subglacial sites.

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Section: Ill Subglacial Drainage Characteristicsmentioning

confidence: 99%

The Nature of the Ice-Rock Interface: The Results of Investigation on 20000m2 of the Rock Bed of Temperate Glaciers

Vivian¹

1980

J. Glaciol.

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“…Considering other direct observations of stick-slip sliding at the base of glaciers (e.g. beneath Glacier d’Argentière, France (Goodman and others, 1979), and Trapridge Glacier, Canada (Fischer and Clarke, 1997)), it seems reasonable to expect seismic signals also from deformational processes occurring at or near the base of temperate mountain glaciers.…”

Section: Introductionmentioning

confidence: 99%

Evidence for deep icequakes in an Alpine glacier

et al. 2000

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To obtain more reliable information about the focal-depth distribution of icequakes, in April 1997 we operated an array of seven portable digital seismographs on Unteraargletscher, central Swiss Alps. Over 5000 events were detected by at least two instruments during the 9 day recording period. P-wave velocities (3770 m s^1) were determined from several calibration shots detonated at the glacier surface as well as in a 49 m deep borehole, whereas S-wave velocities (1860 m s^1) were derived from a simultaneous inversion for V p /V s applied to 169 icequakes. So far, hypocentral locations have been calculated for over 300 icequakes. Besides confirming the occurrence of shallow events associated with the opening of crevasses, our results show that a small but significant fraction of the hypocenters are located at or near the glacier bed. One event was found at an intermediate depth of about 120 m. Three-dimensional particle-motion diagrams of both explosions and icequakes clearly demonstrate that all vertical component seismograms from shallow sources are dominated by the Rayleigh wave. On the other hand, for events occurring at depths greater than about 40 m, the Rayleigh wave disappears almost entirely. Therefore, a qualitative analysis of the signal character provides direct information on the focal depth of an event and was used as an independent check of the locations obtained from traditional arrival-time inversions. Thus, our results demonstrate that deep icequakes do occur and that simple rheological models, according to which brittle deformation is restricted to the uppermost part of a glacier, may need revision.

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“…Robin (1976) suggests that pressure melting within the basal ice mass, as distinct from processes at the ice-bedrock interface, may be responsible for the formation of excess water in zones of high-pressure ice upstream of glacier-bed obstacles and that this water is squeezed out of the ice by the pressure. Goodman and others (1979) have published another paper which justifies some of the speculations made. It is difficult to say that our chemical studies demonstrate the occurrence of the Robin effect, although we think the squeezed water must have a local origin in the basal part of the glacier.…”

Section: Formation Of the Basal Ice Layermentioning

confidence: 65%

Basal Freezing of Squeezed Water: Its Influence on Glacier Erosion

Souchez¹,

Tison²

1981

Ann. Glaciol.

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The basal ice layer aT Glaci~r de TsidjioreNouve in the Swiss Alps consists of debris bands and associated clear ice lenses. This layer is due to refreezing of squeezed water at the sale of the glacier, as evidenced by the chemical properties of the ice. Active erosion processes include entrainment of debris in the basal ice layer and abrasion on rock protuberances immediately down-glacier. The formation of the basal ice layer requires that the temperature of the squeezed water, which is determined by the pressure-melting point within the basal ice, should be below the freezing temperature of the pore water in the subglacial debris layer. This would be the case if the pore water were at a pressure lower than the basal ice pressure.

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Pressure-Melting Effects in Basal Ice of Temperate Glaciers: Laboratory Studies and Field Observations Under Glacier D’Argentière

Cited by 23 publications

References 13 publications

The Nature of the Ice-Rock Interface: The Results of Investigation on 20000m2 of the Rock Bed of Temperate Glaciers

The Nature of the Ice-Rock Interface: The Results of Investigation on 20000m2 of the Rock Bed of Temperate Glaciers

Evidence for deep icequakes in an Alpine glacier

Basal Freezing of Squeezed Water: Its Influence on Glacier Erosion

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