Laterally varying basal conditions beneath ice Streams B and C, West Antarctica

Atre, Shashank R.; Bentley, Charles R.

doi:10.3189/s0022143000016403

Cited by 37 publications

(75 citation statements)

References 21 publications

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“…\\ie argue that an unconsolidated till at the bed of Ice Stream C that permitted fast ice flow 130 a ago would likely still exist. Supporting these theoretical considerations is the discovery of a 20 km wide band of presumed dilatanl till beneath Ice Stream C flanked by till of indeterminate dilatancy (Atre and Bentley, 1993). These results arc from an analysis of the phase-reversals of reflections from the bed during an explosive-source seismic profile on Icc Stream C.…”

Section: Introductionmentioning

confidence: 77%

Ice Stream C, Antarctica, sticky spots detected by microearthquake monitoring

Anandakrishnan

Alley

1994

A. Glaciology.

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Microearthquakes at the base of slow-moving Ice Stream C occur many times more frequently than at the base of fast-moving Ice Stream B. We suggest that the microearthquake source sites are so-called “sticky spots”, defined as limited zones of stronger Subglacial material interspersed within a weaker matrix. The fault-plane area of the microearthquakes (O (102m2)) is therefore a measure of the size of the sticky spots. The spatial density of the microearthquakes (O (10 km-2)) is a measure of the distribution of sticky spots. The average stress drop associated with these microearthquakes is consistent with an ice-stream bed model of weak subglacial till interspersed with stronger zones that support much or all of the basal shear stress. We infer a weak inter-sticky-spot material by the large distances (O (103 m)), relative to fault radius, to which the microearthquake stress change is transmitted.

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Section: Introductionmentioning

confidence: 77%

Ice Stream C, Antarctica, sticky spots detected by microearthquake monitoring

Anandakrishnan

Alley

1994

A. Glaciology.

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“…We then provide our interpretation of each of the bed forms. King and others (2004) showed that the material forming the bed of the ice stream over the majority of the area was dilatant till (Atre and Bentley, 1993;Smith, 1997a, b), i.e. soft water-saturated material undergoing active deformation due to shear between the mobile ice above and more consolidated sediment beneath.…”

Section: Discussionmentioning

confidence: 99%

Seismic and radar observations of subglacial bed forms beneath the onset zone of Rutford Ice Stream, Antarctica

King¹,

Woodward

Smith³

2007

J. Glaciol.

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ABSTRACT. We present seismic and radar data from the onset region of Rutford Ice Stream, West Antarctica, which show the form and internal structure of a variety of bed forms beneath an active ice stream. The ice flow in the area of our survey accelerates from 72 to >200 m a -1 , the ice is 2200-3200 m thick, and the bed of the ice stream lies up to 2000 m below present sea level. We have imaged the internal structure of the bed forms with seismic reflection techniques and also observed radar reflections from below the bed in some circumstances. We observed a transverse moraine 2 km wide and 1.5 km long beneath the slower-flowing part of the ice stream, which we interpret to be composed of unconsolidated sediment undergoing active deformation near the ice-sediment interface. We observed drumlins of classical form with elongation ratios of between 1 : 1.5 and 1 : 4.0 where the surface flow speed exceeded 95 m a -1 . The conformity of the internal structure of the bed forms with the ice base suggests that the bed forms are active depositional features in congruence with the observation of a contemporary drumlin-forming episode in the distal part of the same ice stream. These observations provide the first direct evidence of the association between ice-stream flow speed and bed-form shape.

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“…Considering a seismic velocity in ice of 3630 m s À1 near the glacier bed and a density of 917 kg m À3 , the acoustic impedance for ice Z i would be 3.33Â10 6 kg m À2 s À1 , which would lead to an acoustic impedance of the bed material Z b of 4.5Â10 6 kg m À2 s À1 . According to data from Smith (1997), Atre and Bentley (1993) and references therein, this acoustic impedance would correspond to a porosity of the subglacial material b0.30, that could be interpreted as lodged till or poorly lithified sedimentary rock (non-deforming sediments) underneath this section of the glacier. The presence of these subglacial sediments is confirmed by the stacked section for L8 (Fig.…”

Section: Northwest Southeastmentioning

confidence: 99%