Flow mechanism of the Des Moines lobe of the Laurentide ice sheet
Rapid flow of the Des Moines lobe of the Laurentide ice sheet may have been related to its unlithified substrate. New reconstructions of the lobe, based on moraine elevations, sediment subsidence during moraine deposition, and flow-direction indicators, indicate that the lobe may have been ~3 times...
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ftiowastateuniv:oai:lib.dr.iastate.edu:ge_at_pubs-1147 2023-05-15T16:40:30+02:00 Flow mechanism of the Des Moines lobe of the Laurentide ice sheet Hooyer, Thomas S. Iverson, Neal R. 2002-12-01T08:00:00Z application/pdf https://lib.dr.iastate.edu/ge_at_pubs/140 https://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=1147&context=ge_at_pubs en eng Iowa State University Digital Repository https://lib.dr.iastate.edu/ge_at_pubs/140 https://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=1147&context=ge_at_pubs Creative Commons Attribution license. CC-BY Geological and Atmospheric Sciences Publications Geomorphology Glaciology text 2002 ftiowastateuniv 2021-08-28T22:47:13Z Rapid flow of the Des Moines lobe of the Laurentide ice sheet may have been related to its unlithified substrate. New reconstructions of the lobe, based on moraine elevations, sediment subsidence during moraine deposition, and flow-direction indicators, indicate that the lobe may have been ~3 times thicker than in previous reconstructions. Nevertheless, implied basal shear stresses are <15 kPa, so internal ice deformation was not significant. Instead, the lobe likely moved by a combination of sliding, plowing of particles through the bed surface, and bed shear. Consolidation tests on basal till yield preconsolidation stresses of 125-300 kPa, so effective normal stresses on the bed were small. A model of sliding and plowing indicates that at such stresses most particles gripped by the ice may have plowed easily through the till bed, resulting in too small a shear traction on the bed to shear it at depth. Consistent with this prediction, measurements of orientations of clasts in basal till yield a weak fabric, implying pervasive bed shear strain less than ~2, although some stronger fabrics have been reported by others. We infer, tentatively, that movement was principally at the bed surface by plowing. Text Ice Sheet Digital Repository @ Iowa State University |
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Open Polar |
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Digital Repository @ Iowa State University |
op_collection_id |
ftiowastateuniv |
language |
English |
topic |
Geomorphology Glaciology |
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Geomorphology Glaciology Hooyer, Thomas S. Iverson, Neal R. Flow mechanism of the Des Moines lobe of the Laurentide ice sheet |
topic_facet |
Geomorphology Glaciology |
description |
Rapid flow of the Des Moines lobe of the Laurentide ice sheet may have been related to its unlithified substrate. New reconstructions of the lobe, based on moraine elevations, sediment subsidence during moraine deposition, and flow-direction indicators, indicate that the lobe may have been ~3 times thicker than in previous reconstructions. Nevertheless, implied basal shear stresses are <15 kPa, so internal ice deformation was not significant. Instead, the lobe likely moved by a combination of sliding, plowing of particles through the bed surface, and bed shear. Consolidation tests on basal till yield preconsolidation stresses of 125-300 kPa, so effective normal stresses on the bed were small. A model of sliding and plowing indicates that at such stresses most particles gripped by the ice may have plowed easily through the till bed, resulting in too small a shear traction on the bed to shear it at depth. Consistent with this prediction, measurements of orientations of clasts in basal till yield a weak fabric, implying pervasive bed shear strain less than ~2, although some stronger fabrics have been reported by others. We infer, tentatively, that movement was principally at the bed surface by plowing. |
format |
Text |
author |
Hooyer, Thomas S. Iverson, Neal R. |
author_facet |
Hooyer, Thomas S. Iverson, Neal R. |
author_sort |
Hooyer, Thomas S. |
title |
Flow mechanism of the Des Moines lobe of the Laurentide ice sheet |
title_short |
Flow mechanism of the Des Moines lobe of the Laurentide ice sheet |
title_full |
Flow mechanism of the Des Moines lobe of the Laurentide ice sheet |
title_fullStr |
Flow mechanism of the Des Moines lobe of the Laurentide ice sheet |
title_full_unstemmed |
Flow mechanism of the Des Moines lobe of the Laurentide ice sheet |
title_sort |
flow mechanism of the des moines lobe of the laurentide ice sheet |
publisher |
Iowa State University Digital Repository |
publishDate |
2002 |
url |
https://lib.dr.iastate.edu/ge_at_pubs/140 https://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=1147&context=ge_at_pubs |
genre |
Ice Sheet |
genre_facet |
Ice Sheet |
op_source |
Geological and Atmospheric Sciences Publications |
op_relation |
https://lib.dr.iastate.edu/ge_at_pubs/140 https://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=1147&context=ge_at_pubs |
op_rights |
Creative Commons Attribution license. |
op_rightsnorm |
CC-BY |
_version_ |
1766030906044186624 |