Rapid Glacier sliding, reverse ice motion and subglacial water pressure during an autumn rainstorm

  • Fudge T
  • Harper J
  • Humphrey N
 et al. 
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Abstract

Measurements of basal water pressure from 15 boreholes located at
both local (tens of meters) and regional (kilometers) length scales
were used to elucidate the pressure/sliding relationship during an
autumn rapid motion event on Bench Glacier, Alaska, USA. The 8 day
event had two distinct phases, each with a ten-fold speed-up with
respect to winter velocity. The water pressure in all 15 boreholes
varied synchronously during the speed-up. The first phase of rapid
sliding began after a peak in basal water pressure and continued
while the pressure was elevated and stable, or decreasing. The second
phase of rapid sliding occurred when the basal water pressure was
low but increasing, and terminated before the pressure peaked. Pressure
and velocity do not appear unrelated, but the pressure/sliding relationship
was not consistently linked to increasing, decreasing or a critical
water pressure. The pressure variations and sliding accelerations
are a response to a warm rainstorm, although equally large input
events occurred in weeks prior with no apparent response. Drainage
system evolution therefore appears to play a key role in both the
acceleration and the pressure/velocity relationship. Basal cavity
dynamics are likely responsible for three episodes of reverse (up-valley)
motion observed after enhanced sliding.

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Authors

  • T. J. Fudge

  • J. T. Harper

  • N. F. Humphrey

  • W. T. Pfeffer

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