Velocity pattern in a transect across Ice Stream B, Antarctica

Abstract

Repeat aerial photography is used to obtain closely spaced measurements of velocity and elevation over a complete transect of Ice Stream tributary B2, including the shear margins, the fast ice of the ice stream and several unusual features, as well as the UpB camp. Persistent features, mainly crevasses, are tracked to provide 1541 values of velocity and 1933 values of elevation. These are used to describe ice flow in the ice stream. Within the ice stream, the dominant velocity gradient is lateral shear. Crevasse patterns are studied in relation to measured velocity gradients. Crevasses intersect one another at acute angles, indicating that their origin is deeper than the depth to which crevasses penetrate. One feature within the ice stream seems to be a raft of stiff ice. Others are crevasse trains. Also, there are spreading ridges, perhaps due to upwelling ice. There is no evidence of large sticky spots within the studied transect, i.e. no steep surface slopes with associated surface stretching just up-glacier and surface compression down-glacier.

Grain‐scale processes, folding, and stratigraphic disturbance in the GISP2 ice core

“…If such organized polygonization occurs at a depth where the Waddington et al [1995] folding criterion is satisfied, then striping and folding would be initiated. The hypothesis of vein recrystallization of Whillans et al [1993] is similar to our speculation on organized polygonization; however, the initially small angles observed between stripe and nonstripe c axes suggest to us that progressive subgrain rotation is involved.…”

Are long subglacial bedforms indicative of fast ice flow?

“…5 also indicates that bedforms tend to be more elongated towards the central axis of the ow-set away from the southern lateral margin. This concurs with observations on contemporary ice streams, where side drag is imposed by the slower moving ice outside the margins (Whillans et al 1993). Making inferences from internal variations of elongation ratio within an isochronous ow pattern appears to be valid, but comparing elongation ratios between separate ow-sets may not be so informative.…”

Megagrooves and streamlined bedrock in NW Scotland: The role of ice streams in landscape evolution

“…Stokes and Clark, 2003) and consistent with velocity profiles from Antarctic ice streams (Whillans et al, 1993;Paterson, 1994).…”

“…We speculate that undulations set up at the ice sheetbedrock interface, possibly in response to longitudinal driving-stress variations, may concentrate debris into linear bands. Several workers have reported the presence of flow-parallel debris bands near ice-stream beds, in the form of englacial flow stripes or debris-rich basal crevasses (Jezek and Bentley, 1983;Whillans et al, 1993;Catania et al, 2005). It is conceivable that focused glacial erosion by basal debris locked in flow-parallel bands is responsible for carving large-scale bedrock grooves.…”