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Article
Sliding of ice past an obstacle at Engabreen, Norway
Journal of Glaciology
  • Denis Cohen, University of Minnesota-Twin Cities
  • Roger LeB. Hooke, University of Maine
  • Neal R. Iverson, Iowa State University
  • Jack Kohler, Norwegian Water Resources and Energy Administration
Document Type
Article
Disciplines
Publication Version
Published Version
Publication Date
12-1-2000
DOI
10.3189/172756500781832747
Abstract

At Engabreen, Norway, an instrumented panel containing a decimetric obstacle was mounted flush with the bed surface beneath 210 m of ice. Simultaneous measurements of normaland shear stresses, ice velocity and temperature were obtained as dirty basal ice flowed past the obstacle. Our measurements were broadly consistent with ice thickness, flow conditions and bedrock topography near the site of the experiment. Ice speed 0.45 m above the bed was about 130 mm d–1, much less than the surface velocity of 800 mm d–1. Average normalstress on the panelwas 1.0–1.6 MPa, smaller than the expected ice overburden pressure. Normal stress was larger and temperature was lower on the stoss side than on the lee side, in accord with flow dynamics and equilibrium thermodynamics. Annualdifferences in normal stresses were correlated with changes in sliding speed and ice-flow direction. These temporal variations may have been caused by changes in ice rheology associated with changes in sediment concentration, water content or both. Temperature and normalstress were generally correlated, except when clasts presumably collided with the panel. Temperature gradients in the obstacle indicated that regelation was negligible, consistent with the obstacle size. Melt rate was about 10% of the sliding speed. Despite high sliding speed, no significant ice/bed separation was observed in the lee of the obstacle. Frictional forces between sediment particles in the ice and the panel, estimated from Hallet's (1981) model, indicated that friction accounted for about 5% of the measured bed-parallel force. This value is uncertain, as friction theories are largely untested. Some of these findings agree with sliding theories, others do not.

Comments

This article is from Journal of Glaciology 46 (2000): 599, doi:10.3189/172756500781832747. Posted with permission.

Rights
Creative Commons Attribution license.
Copyright Owner
International Glaciological Society
Language
en
File Format
application/pdf
Citation Information
Denis Cohen, Roger LeB. Hooke, Neal R. Iverson and Jack Kohler. "Sliding of ice past an obstacle at Engabreen, Norway" Journal of Glaciology Vol. 46 Iss. 155 (2000) p. 599 - 610
Available at: http://works.bepress.com/neal-iverson/42/