scholarly journals Of isbræ and ice streams

2003 ◽  
Vol 36 ◽  
pp. 66-72 ◽  
Author(s):  
Martin Truffer ◽  
Keith A. Echelmeyer
Keyword(s):  
Ice Sheet ◽  
Shear Zones ◽  
West Antarctica ◽  
Ice Streams ◽  
Ice Flow ◽  
Bed Topography ◽  
Ice Stream ◽  
Fast Ice ◽  
Fast Flow ◽  
End Members

AbstractFast-flowing ice streams and outlet glaciers provide the major avenues for ice flow from past and present ice sheets. These ice streams move faster than the surrounding ice sheet by a factor of 100 or more. Several mechanisms for fast ice-stream flow have been identified, leading to a spectrum of different ice-stream types. In this paper we discuss the two end members of this spectrum, which we term the “ice-stream” type (represented by the Siple Coast ice streams in West Antarctica) and the “isbræ” type (represented by Jakobshavn Isbræ in Greenland). The typical ice stream is wide, relatively shallow (∼1000 m), has a low surface slope and driving stress (∼10 kPa), and ice-stream location is not strongly controlled by bed topography. Fast flow is possible because the ice stream has a slippery bed, possibly underlain by weak, actively deforming sediments. The marginal shear zones are narrow and support most of the driving stress, and the ice deforms almost exclusively by transverse shear. The margins seem to be inherently unstable; they migrate, and there are plausible mechanisms for such ice streams to shut down. The isbræ type of ice stream is characterized by very high driving stresses, often exceeding 200 kPa. They flow through deep bedrock channels that are significantly deeper than the surrounding ice, and have steep surface slopes. Ice deformation includes vertical as well as lateral shear, and basal motion need not contribute significantly to the overall motion. The marginal shear zone stend to be wide relative to the isbræ width, and the location of isbræ and its margins is strongly controlled by bedrock topography. They are stable features, and can only shut down if the high ice flux cannot be supplied from the adjacent ice sheet. Isbræs occur in Greenland and East Antarctica, and possibly parts of Pine Island and Thwaites Glaciers, West Antarctica. In this paper, we compare and contrast the two types of ice streams, addressing questions such as ice deformation, basal motion, subglacial hydrology, seasonality of ice flow, and stability of the ice streams.

scholarly journals Ice stream or not? Radio-echo sounding of Carlson Inlet, West Antarctica

2011 ◽  
Vol 5 (4) ◽  
pp. 907-916 ◽  
Author(s):  
E. C. King
Keyword(s):  
West Antarctica ◽  
Ice Streams ◽  
Basal Resistance ◽  
Bed Topography ◽  
Ice Stream ◽  
Time Period ◽  
Adjacent Part ◽  
Radio Echo Sounding ◽  
History Of ◽  
Fast Flow

Abstract. The Antarctic Ice Sheet loses mass to the surrounding ocean mainly by drainage through a network of ice streams: fast-flowing glaciers bounded on either side by ice flowing one or two orders of magnitude more slowly. Ice streams flow despite low driving stress because of low basal resistance but are known to cease flowing if the basal conditions change, which can take place when subglacial sediment becomes dewatered by freezing or by a change in hydraulic pathways. Carlson Inlet, Antarctica has been interpreted as a stagnated ice stream, based on surface and basal morphology and shallow radar reflection profiling. To resolve the question of whether the flow history of Carlson Inlet has changed in the past, I conducted a ground-based radar survey of Carlson Inlet, the adjacent part of Rutford Ice Stream, and Talutis Inlet, West Antarctica. This survey provides details of the internal ice stratigraphy and allows the flow history to be interpreted. Tight folding of isochrones in Rutford Ice Stream and Talutis Inlet is interpreted to be the result of lateral compression during convergent flow from a wide catchment into a narrow, fast-flowing trunk. In contrast, the central part of Carlson Inlet has gently-folded isochrones that drape over the bed topography, suggestive of local accumulation and slow flow. A 1-D thermo-mechanical model was used to estimate the age of the ice. I conclude that the ice in the centre of Carlson Inlet has been near-stagnant for between 3500 and 6800 yr and that fast flow has not occurred there during that time period.

scholarly journals New and improved determinations of velocity of Ice Streams B and C, West Antarctica

1993 ◽  
Vol 39 (133) ◽  
pp. 483-590 ◽  
Author(s):  
I. M. Whillans ◽  
C.J. Van Der Veen
Keyword(s):  
Stream Flow ◽  
West Antarctica ◽  
Ice Shelf ◽  
Ice Streams ◽  
Ice Flow ◽  
Ice Stream ◽  
Fast Ice ◽  
Ice Stream B ◽  
Shelf Flow ◽  
Streaming Flow

AbstractMeasurements of velocity have been made on and next to Ice Streams Β and C, West Antarctica. The results are more precise than previous work and constitute a 93% increase in the number of values. These velocities are used to describe the confluence of flow into the ice streams and the development of fast ice-stream flow. The onset of fast-streaming flow occurs in many separate tributaries that coalesce down-glacier into the major ice streams. For those inter-stream ridges that have been studied, the flow is consistent with steady state. Along Ice Stream B, gradients in longitudinal stress offer little resistance to the ice flow. The transition from basal-drag control to ice-shelf flow is achieved through reduced drag at the glacier base and increased resistance associated with lateral drag. Velocities in the trunk of Ice Stream C are nearly zero but those at the up-glacial head are similar to those at the head of Ice Stream B.

scholarly journals New and improved determinations of velocity of Ice Streams B and C, West Antarctica

1993 ◽  
Vol 39 (133) ◽  
pp. 483-590 ◽  
Author(s):  
I. M. Whillans ◽  
C.J. Van Der Veen
Keyword(s):  
Stream Flow ◽  
West Antarctica ◽  
Ice Shelf ◽  
Ice Streams ◽  
Ice Flow ◽  
Ice Stream ◽  
Fast Ice ◽  
Ice Stream B ◽  
Shelf Flow ◽  
Streaming Flow

Abstract Measurements of velocity have been made on and next to Ice Streams Β and C, West Antarctica. The results are more precise than previous work and constitute a 93% increase in the number of values. These velocities are used to describe the confluence of flow into the ice streams and the development of fast ice-stream flow. The onset of fast-streaming flow occurs in many separate tributaries that coalesce down-glacier into the major ice streams. For those inter-stream ridges that have been studied, the flow is consistent with steady state. Along Ice Stream B, gradients in longitudinal stress offer little resistance to the ice flow. The transition from basal-drag control to ice-shelf flow is achieved through reduced drag at the glacier base and increased resistance associated with lateral drag. Velocities in the trunk of Ice Stream C are nearly zero but those at the up-glacial head are similar to those at the head of Ice Stream B.

scholarly journals Identifying fast ice flow from landform assemblages in the geological record: a discussion

1999 ◽  
Vol 28 ◽  
pp. 59-66 ◽  
Author(s):  
Jane K. Hart
Keyword(s):  
Ice Sheet ◽  
Sediment Supply ◽  
Coarse Grained ◽  
Ice Streams ◽  
Ice Flow ◽  
Land Form ◽  
Tidewater Glaciers ◽  
Fine Grained ◽  
Fast Ice ◽  
Fast Flow

AbstractDifferent types of fast ice flow (both spatial and temporal) in valley glaciers (surging glaciers, tidewater glaciers and deforming-bed glaciers) and ice sheets (ice streams and deforming-bed ice-sheet flow) are discussed briefly. Although there are unlikely to be any specific individual landforms associated with fast ice flow, there may be landform assemblages.At valley glacier scale, it is suggested that there are two landform assemblages: (1) an ice-thrust type, dominated by bulldozed push moraines and hummocky moraines (associated with glaciers with a high supraglacial sediment supply, a coarse-grained substrate and a coarse-grained proglacial sediment wedge); and (2) a bed-flow type dominated by “squeeze” push moraines, flutes and drumlins (associated with glaciers with a low supra- glacial sediment supply and fine-grained substrate). The ice-thrust type alone is only associated with discontinuous fast flow (on both rigid and deforming beds); whilst the bed-flow type is associated with both continuous and discontinuous fast flow.It is suggested that these two landform assemblages may also be indicative of fast ice flow at ice-sheet scale, in particular the bed-flow style. If that is the case, then discontinuous fast ice flow may be indicated by the ice-thrust landform assemblage and the bed-flow style where drumlins are present.It is also suggested that specific evidence for ice streams includes the distinctive land-form assemblages within valley or fan-like locations, and a predictable pattern of velocity reflected by drumlin elongation ratios.

scholarly journals Ice stream or not? Radio-echo sounding of Carlson Inlet, West Antarctica

2011 ◽  
Vol 5 (2) ◽  
pp. 1219-1238
Author(s):  
E. C. King
Keyword(s):  
West Antarctica ◽  
Ice Streams ◽  
Basal Resistance ◽  
Bed Topography ◽  
Ice Stream ◽  
Time Period ◽  
Adjacent Part ◽  
Radio Echo Sounding ◽  
History Of ◽  
Fast Flow

Abstract. The Antarctic Ice Sheet loses mass to the surrounding ocean mainly by drainage through a network of ice streams: fast-flowing glaciers bounded on either side by ice flowing one or two orders of magnitude more slowly. Ice streams flow despite low driving stress because of low basal resistance but are known to cease flowing if the basal conditions change, which can take place when subglacial sediment becomes dewatered by freezing or by a change in hydraulic pathways. Carlson Inlet, Antarctica has been interpreted as a stagnated ice stream, based on surface and basal morphology and shallow radar reflection profiling. To resolve the question of whether the flow history of Carlson Inlet has changed in the past, I conducted a ground-based radar survey of Carlson Inlet, the adjacent part of Rutford Ice Stream, and Talutis Inlet, West Antarctica. This survey provides details of the internal ice stratigraphy and allows the flow history to be interpreted. Tight folding of isochrones in Rutford Ice Stream and Talutis Inlet is interpreted to be the result of lateral compression during convergent flow from a wide catchment into a narrow, fast-flowing trunk. In contrast, the central part of Carlson Inlet has gently-folded isochrones that drape over the bed topography, suggestive of local accumulation and slow flow. A 1-D thermo-mechanical model was used to estimate the age of the ice. I conclude that the ice in the centre of Carlson Inlet has been near-stagnant for between 3500 and 6800 years and that fast flow has not occurred there during that time period.

scholarly journals Thermomechanical modelling of the Scandinavian ice sheet: implications for ice-stream formation

1999 ◽  
Vol 28 ◽  
pp. 83-89 ◽  
Author(s):  
A. J. Payne ◽  
D.J. Baldwin
Keyword(s):  
Three Dimensional ◽  
Ice Sheet ◽  
Ice Streams ◽  
Ice Flow ◽  
Low Viscosity ◽  
Ice Stream ◽  
Scandinavian Ice Sheet ◽  
The Baltic ◽  
Stream Formation ◽  
Initial Results

AbstractThis work attempts to explain the fan-like landform assemblages observed in satellite images of the area covered by the former Scandinavian ice sheet (SIS). These assemblages have been interpreted as evidence of large ice streams within the SIS. If this interpretation is correct, then it calls into doubt current theories on the formation of ice streams. These theories regard soft sediment and topographic troughs as being the key determinants of ice-stream location. Neither can be used to explain the existence of ice streams on the flat, hard-rock area of the Baltic Shield. Initial results from a three-dimensional, thermomechanical ice-sheet model indicate that interactions between ice flow, form and temperature can create patterns similar to those mentioned above. The model uses a realistic, 20 km resolution gridded topography and a simple parameterization of accumulation and ablation. It produces patterns of maximum ice-sheet extent, which are similar to those reconstructed from the area’s glacial geomorphology. Flow in the maximum, equilibrium ice sheet is dominated by wedges of warm, low-viscosity, fast-flowing ice. These are separated by areas of cold, slow-flowing ice. This patterning appears to develop spontaneously as the modelled ice sheet grows.

scholarly journals Deformation in Rutford Ice Stream, West Antarctica: measuring shear-wave anisotropy from icequakes

2013 ◽  
Vol 54 (64) ◽  
pp. 105-114 ◽  
Author(s):  
S.R. Harland ◽  
J.-M. Kendall ◽  
G.W. Stuart ◽  
G.E. Lloyd ◽  
A.F. Baird ◽  
...  
Keyword(s):  
Shear Wave ◽  
Flow Direction ◽  
Transversely Isotropic ◽  
Shear Wave Splitting ◽  
Ice Crystal ◽  
West Antarctica ◽  
Ice Streams ◽  
Ice Flow ◽  
Ice Stream ◽  
Wave Splitting

Abstract Ice streams provide major drainage pathways for the Antarctic ice sheet. The stress distribution and style of flow in such ice streams produce elastic and rheological anisotropy, which informs ice-flow modelling as to how ice masses respond to external changes such as global warming. Here we analyse elastic anisotropy in Rutford Ice Stream, West Antarctica, using observations of shear-wave splitting from three-component icequake seismograms to characterize ice deformation via crystal-preferred orientation. Over 110 high-quality measurements are made on 41 events recorded at five stations deployed temporarily near the ice-stream grounding line. To the best of our knowledge, this is the first well-documented observation of shear-wave splitting from Antarctic icequakes. The magnitude of the splitting ranges from 2 to 80 ms and suggests a maximum of 6% shear-wave splitting. The fast shear-wave polarization direction is roughly perpendicular to ice-flow direction. We consider three mechanisms for ice anisotropy: a cluster model (vertical transversely isotropic (VTI) model); a girdle model (horizontal transversely isotropic (HTI) model); and crack-induced anisotropy (HTI model). Based on the data, we can rule out a VTI mechanism as the sole cause of anisotropy – an HTI component is needed, which may be due to ice crystal a-axis alignment in the direction of flow or the alignment of cracks or ice films in the plane perpendicular to the flow direction. The results suggest a combination of mechanisms may be at play, which represent vertical variations in the symmetry of ice crystal anisotropy in an ice stream, as predicted by ice fabric models.

scholarly journals Is Ice-Stream Evolution Revealed By Satellite Imagery?

1990 ◽  
Vol 14 ◽  
pp. 273-277 ◽  
Author(s):  
S.N. Stephenson ◽  
R.A. Bindschadler
Keyword(s):  
Stream Flow ◽  
Temporal Evolution ◽  
Thematic Mapper ◽  
Landsat Thematic Mapper ◽  
West Antarctica ◽  
Ice Streams ◽  
Ice Flow ◽  
Ice Shelves ◽  
Ice Stream ◽  
Grounding Line

Ten Landsat Thematic Mapper images together show Ice Streams E, D and most of Ice Stream C on Siple Coast, West Antarctica. The images are interpreted to reveal aspects of both spatial and temporal evolution of the ice streams. Onset of ice-stream flow appears to occur at distributed sites within the ice-stream catchment, and the apparent enhanced flow continues in channels until they join, forming the main ice stream. Most crevassing on these ice streams is associated with features of horizontal dimensions between 5 and 20 km. We suggest these features are caused by bed structures which may be an important source of restraint to ice flow, similar to ice rumples on ice shelves. A pattern of features near the grounding line of the now-stagnant Ice Stream C are interpreted as having formed because there was a period of reduced flux before the ice stream stopped.

scholarly journals Is Ice-Stream Evolution Revealed By Satellite Imagery?

1990 ◽  
Vol 14 ◽  
pp. 273-277 ◽  
Author(s):  
S.N. Stephenson ◽  
R.A. Bindschadler
Keyword(s):  
Stream Flow ◽  
Temporal Evolution ◽  
Thematic Mapper ◽  
Landsat Thematic Mapper ◽  
West Antarctica ◽  
Ice Streams ◽  
Ice Flow ◽  
Ice Shelves ◽  
Ice Stream ◽  
Grounding Line

Ten Landsat Thematic Mapper images together show Ice Streams E, D and most of Ice Stream C on Siple Coast, West Antarctica. The images are interpreted to reveal aspects of both spatial and temporal evolution of the ice streams. Onset of ice-stream flow appears to occur at distributed sites within the ice-stream catchment, and the apparent enhanced flow continues in channels until they join, forming the main ice stream. Most crevassing on these ice streams is associated with features of horizontal dimensions between 5 and 20 km. We suggest these features are caused by bed structures which may be an important source of restraint to ice flow, similar to ice rumples on ice shelves. A pattern of features near the grounding line of the now-stagnant Ice Stream C are interpreted as having formed because there was a period of reduced flux before the ice stream stopped.

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