Intra-annual variations in glacier motion: a review

1995 ◽  
Vol 19 (1) ◽  
pp. 61-106 ◽  
Author(s):  
Ian C. Willis
Keyword(s):  
Drainage System ◽  
Vertical Motion ◽  
System Structure ◽  
Longitudinal Stress ◽  
Stress Gradients ◽  
Annual Variations ◽  
Bed Deformation ◽  
Longitudinal Extension ◽  
Glacier Motion ◽  
Subglacial Drainage

Variations in glacier horizontal and vertical motion occur at a variety of intra-annual timescales: monthly, daily and even hourly. These variations have been identified from measurements made both beneath and on the surface of glaciers. They must be associated with variations in basal motion rather than changes in internal ice-deformation rates. Variations in basal motion result from changes in sliding rates over a 'hard bed' (i.e., rigid bedrock) or changes in deformation rates within a 'soft bed' (i.e., unlithified permeable till). Changes in both sliding and bed deformation rates are related to variations in subglacial water pressures and therefore depend critically on the structure of the subglacial drainage system and the hydraulics of individual drainage passageways. Thus changes in subglacial drainage system structure and drainage passageway hydraulics can cause intra-annual variations in glacier motion. However, intra-annual variations in glacier motion will also be influenced by variations in longitudinal stress gradients as a result of changes in the rate of longitudinal extension and compression.

scholarly journals An integrated modelling approach to understanding subglacial hydraulic release events

2000 ◽  
Vol 31 ◽  
pp. 222-228 ◽  
Author(s):  
Gwenn E. Flowers ◽  
Garry K. C. Clarke
Keyword(s):  
Water Pressure ◽  
Water Storage ◽  
Drainage System ◽  
High Water ◽  
Integrated Modelling ◽  
Glacier Motion ◽  
Bear Witness ◽  
Modelling Approach ◽  
Subglacial Drainage

AbstractOutbursts of subglacial water from numerous alpine glaciers have been observed and documented. Such events tend to occur in spring and are thus attributed to an inability of the winter subglacial drainage system (characterized by high water pressure and low capacity) to accommodate a sudden and profuse influx of surface meltwater. Prior to a release event, bursts of glacier motion are common, and the release then precipitates the restoration of summer plumbing that damps or terminates surface acceleration. The events bear witness to the importance of interactions between surface melt, runoff, en-glacial water storage and internal routing, in addition to subglacial drainage morphology. Using a distributed numerical model to simultaneously solve surficial, englacial and subglacial water-transport equations, we investigate the role of these components in a hydro-mechanical event observed at Trapridge Glacier, YukonTerritory, Canada, in July 1990.

scholarly journals Seasonal variations in ice deformation and basal motion across the tongue of Haut Glacier d’Arolla, Switzerland

2003 ◽  
Vol 36 ◽  
pp. 157-167 ◽  
Author(s):  
Ian Willis ◽  
Douglas Mair ◽  
Bryn Hubbard ◽  
Peter Nienow ◽  
Urs H. Fischer ◽  
...  
Keyword(s):  
Surface Deformation ◽  
Water Pressure ◽  
Drainage System ◽  
System Structure ◽  
Glacier Surface ◽  
Changing Patterns ◽  
Internal Deformation ◽  
Internal Velocity ◽  
Subglacial Drainage

AbstractRecords of surface motion, englacial tilt and repeat inclinometry are used to determine patterns of surface, internal and basal motion across the tongue of Haut Glacier d’Arolla, Switzerland, over temporal scales ranging from days to months. Findings are interpreted with reference to contemporaneous measurements of subglacial water pressures, and prior knowledge of the glacier’s subglacial drainage-system structure. Long-term inclinometry results show pronounced extrusion flow over a subglacial drainage axis, with basal velocities up to twice those measured at the glacier surface. Deformation profiles are more conventional away from the drainage axis, with basal velocities ∼60–70% of surface velocities. Comparison of long-term tilt rates from repeat inclinometry and englacial tiltmeters shows close correspondence. Englacial tiltmeter data are used to reconstruct internal velocity profiles and to split surface velocities into internal deformation and basal motion contributions over spring, summer and autumn/winter periods. Although, spatial patterns of surface movement are similar between periods, patterns of internal and basal motion are not. Results are interpreted in terms of the location of sticky and slippery spots, with temporally changing patterns of basal drag reflecting changing distributions of water pressure.

scholarly journals Stable oxygen isotope variability in two contrasting glacier river catchments in Greenland

2016 ◽  
Vol 20 (3) ◽  
pp. 1197-1210 ◽  
Author(s):  
Jacob C. Yde ◽  
Niels T. Knudsen ◽  
Jørgen P. Steffensen ◽  
Jonathan L. Carrivick ◽  
Bent Hasholt ◽  
...  
Keyword(s):  
Oxygen Isotope ◽  
Peak Flow ◽  
Drainage System ◽  
Greenland Ice Sheet ◽  
System Structure ◽  
Stable Oxygen Isotope ◽  
Run Off ◽  
Stable Oxygen ◽  
The Mean ◽  
Subglacial Drainage

Abstract. Analysis of stable oxygen isotope (δ18O) characteristics is a useful tool to investigate water provenance in glacier river systems. In order to attain knowledge on the diversity of δ18O variations in Greenlandic rivers, we examined two contrasting glacierised catchments disconnected from the Greenland Ice Sheet (GrIS). At the Mittivakkat Gletscher river, a small river draining a local temperate glacier in southeast Greenland, diurnal oscillations in δ18O occurred with a 3 h time lag to the diurnal oscillations in run-off. The mean annual δ18O was −14.68 ± 0.18 ‰ during the peak flow period. A hydrograph separation analysis revealed that the ice melt component constituted 82 ± 5 % of the total run-off and dominated the observed variations during peak flow in August 2004. The snowmelt component peaked between 10:00 and 13:00 local time, reflecting the long travel time and an inefficient distributed subglacial drainage network in the upper part of the glacier. At the Kuannersuit Glacier river on the island Qeqertarsuaq in west Greenland, the δ18O characteristics were examined after the major 1995–1998 glacier surge event. The mean annual δ18O was −19.47 ± 0.55 ‰. Despite large spatial variations in the δ18O values of glacier ice on the newly formed glacier tongue, there were no diurnal oscillations in the bulk meltwater emanating from the glacier in the post-surge years. This is likely a consequence of a tortuous subglacial drainage system consisting of linked cavities, which formed during the surge event. Overall, a comparison of the δ18O compositions from glacial river water in Greenland shows distinct differences between water draining local glaciers and ice caps (between −23.0 and −13.7 ‰) and the GrIS (between −29.9 and −23.2 ‰). This study demonstrates that water isotope analyses can be used to obtain important information on water sources and the subglacial drainage system structure that is highly desired for understanding glacier hydrology.

scholarly journals Changes in geometry and subglacial drainage derived from digital elevation models: Unteraargletscher, Switzerland, 1927–97

2005 ◽  
Vol 40 ◽  
pp. 20-24 ◽  
Author(s):  
Urs H. Fischer ◽  
André Braun ◽  
Andreas Bauder ◽  
Gwenn E. Flowers
Keyword(s):  
Water Flow ◽  
Digital Elevation Models ◽  
Drainage System ◽  
System Structure ◽  
Water Drainage ◽  
Drainage Pattern ◽  
Glacier Surface ◽  
Digital Elevation ◽  
Bed Changes ◽  
Subglacial Drainage

AbstractDigital elevation models of the bed and surface of Unteraargletscher, Switzerland, are used to reconstruct the theoretical pattern of basal water drainage for the years 1927, 1947, 1961 and 1997, during which period the glacier was thinning and receding. The theoretical drainage pattern for 1997 compares well, in a broad sense, with the locations of active moulins and the hydraulic connection status of boreholes drilled to the glacier bed. Changes in the basal water-flow pattern over the period 1927–97 that are revealed by the theoretical reconstructions of the subglacial drainage system structure are likely to have resulted from changes in glacier geometry. Concurrent with the retreat and thinning of the glacier, the height of medial moraines increased, probably due to the insulating effect of the debris cover reducing the melt of the underlying ice. This increase of moraine heights has led to the formation of hydraulic barriers at the glacier bed such that water flow has become channelized beneath the ice along drainage axes that parallel the course of the medial moraines on the glacier surface.

Subglacial drainage system structure and morphology of Brewster Glacier, New Zealand

2009 ◽  
Vol 23 (3) ◽  
pp. 384-396 ◽  
Author(s):  
Ian Willis ◽  
Wendy Lawson ◽  
Ian Owens ◽  
Bob Jacobel ◽  
Jenny Autridge
Keyword(s):  
New Zealand ◽  
Drainage System ◽  
System Structure ◽  
Structure And Morphology ◽  
Subglacial Drainage

Longitudinal extension of the pulmonary trunk during breathing in young rabbits: a possible factor in elastin fragmentation

1976 ◽  
Vol 54 (2) ◽  
pp. 113-117
Author(s):  
Paul H. Smith
Keyword(s):  
Pulmonary Arteries ◽  
Pulmonary Trunk ◽  
Corrosion Casts ◽  
Longitudinal Stress ◽  
Longitudinal Extension ◽  
Silicone Polymer

Corrosion casts of the pulmonary trunk and major branches of the pulmonary arteries of 39 rabbits were made from a silicone polymer. In half of the rabbits the casts were made with the lungs expanded and half with the lungs collapsed. The length of various segments of the casts were measured from magnified photographs. It was found that in rabbits less than 23 days old the pulmonary trunk is significantly longer when the lungs are expanded than when they are collapsed. This suggests that a repeated longitudinal extension of the vessel occurs during breathing. This effect disappears after 30 days of age, possibly because of elastin fragmentation. Between the ages of 23 and 30 days the growth in length and diameter of the pulmonary trunk undergoes a rapid acceleration. This may also be the result of elastin fragmentation. Whereas it may be that repeated longitudinal stress in the pulmonary trunk during breathing causes elastin in its media to fragment, one cannot exclude the possibility that other factors such as growth are responsible.

scholarly journals Abrupt glacier motion and reorganization of basal shear stress following the establishment of a connected drainage system

2001 ◽  
Vol 47 (158) ◽  
pp. 472-480 ◽  
Author(s):  
Jeffrey L. Kavanaugh ◽  
Garry K. C. Clarke
Keyword(s):  
Pressure Sensors ◽  
Drainage System ◽  
Yukon Territory ◽  
Stable Configuration ◽  
Drainage Patterns ◽  
Pressure Pulses ◽  
Gradual Failure ◽  
Basal Shear ◽  
Pressure Changes ◽  
Glacier Motion

AbstractThree episodes of strong basal motion occurred at Trapridge Glacier, Yukon Territory, Canada, on 11 June 1995 following the establishment of a connected subglacial drainage system. Responses to these “spring events” are noted in the records for 42 instruments and were recorded throughout the ∼60 000 m2 study area. Strong basal motion during the events is indicated by ploughmeter, load-bolt and vertical-strain records, and abrupt pressure changes in several transducer records denote damage caused by extreme pressure pulses. These pressure pulses, generated by the abrupt basal motion, also resulted in the failure of seven pressure sensors. Records for pressure, turbidity and conductivity sensors indicate that basal drainage patterns did not change significantly during the events. Geophone records suggest that the episodes of basal motion were precipitated by the gradual failure of a “sticky spot” following hydraulic connection of part of the study area. This failure resulted in the transfer of basal stress to the unconnected region of the bed during the course of the events. No evidence for strong basal motion is seen in the instrument records for several weeks following the events, suggesting that the mechanical adjustments resulted in a stable configuration of basal stresses. This event illustrates how unstable situations can be quickly accommodated by mechanical adjustments at the glacier bed.

scholarly journals Large-scale integrated subglacial drainage around the former Keewatin Ice Divide, Canada reveals interaction between distributed and channelised systems

2020 ◽  
Author(s):  
Emma L. M. Lewington ◽  
Stephen J. Livingstone ◽  
Chris D. Clark ◽  
Andrew J. Sole ◽  
Robert D. Storrar
Keyword(s):  
Spatial Distribution ◽  
Dynamic Response ◽  
Large Scale ◽  
Water Pressure ◽  
Pressure Fluctuations ◽  
Drainage System ◽  
Different Types ◽  
Form Part ◽  
Subglacial Meltwater ◽  
Subglacial Drainage

Abstract. We identify and map traces of subglacial meltwater drainage around the former Keewatin Ice Divide, Canada from ArcticDEM data. Meltwater tracks, tunnel valleys and esker splays exhibit several key similarities, including width, spacing, their association with eskers and transitions to and from different types, which together suggest they form part of an integrated drainage signature. We collectively term these features 'meltwater corridors' and propose a new model for their formation, based on observations from contemporary ice masses, of pressure fluctuations surrounding a central conduit. We suggest that eskers record the imprint of a central conduit and meltwater corridors the interaction with the surrounding distributed drainage system. The widespread aerial coverage of meltwater corridors (5–36 % of the bed) provides constraints on the extent of basal uncoupling induced by basal water pressure fluctuations and variations in spatial distribution and evolution of the subglacial drainage system, which will modulate the ice dynamic response.

scholarly journals Longitudinal Stress Gradients and Basal Shear Stress of a Temperate Valley Glacier

1979 ◽  
Vol 24 (90) ◽  
pp. 507-508 ◽  
Author(s):  
Robert Bindschadler
Keyword(s):  
Shear Stress ◽  
Strain Rate ◽  
Field Data ◽  
Numerical Models ◽  
Lateral Strain ◽  
Longitudinal Stress ◽  
Base Shear ◽  
Stress Gradients ◽  
Valley Glacier ◽  
Image Position

AbstractFor the first time field data from a temperate valley glacier, the Variegated Glacier, are used to investigate the behavior of longitudinal stress gradients predicted by the relation(1)whereHis the local depth, andysandybare the surface and bed elevations respectively. This equation is similar to one derived by Budd (1970) for plane strain-rate, to evaluate the importance of longitudinal stress gradients, but a shape factorfis included to account approximately for lateral strain-rate gradients. Predictive numerical models of valley glaciers require the local base shear stress to be known as accurately as possible. It has been argued on theoretical grounds that whenTis averaged over distances of more than five to ten times the depth, this term is negligible. At larger averaging scales, 2Gcan then be considered a correction to the simple geometric expression of base stress due to the presence of longitudinal stress gradients. Field data of velocity and geometry are used to evaluate the terms of Equation (1), whereτband 2Gare estimated asandat intervals of 100 m,Usis the measured surface center-line velocity,Aandnare the flow-law parameters, andis the surface longitudinal strain-rate. The expression for 2Gis an approximation proposed by Budd (1970).

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