Origin of a washboard moraine of the Des Moines Lobe inferred from sediment properties
International audience Geometric characteristics of the washboard moraines of the Des Moines Lobe (DML) of the Laurentide ice sheet agree with their proposed origin as crevasse-squeeze ridges, but study of their sediments is required to help further test this hypothesis. A 70-m-long, 3-5 m high sect...
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ftsorbonneuniv:oai:HAL:insu-03579364v1 2023-11-12T04:16:27+01:00 Origin of a washboard moraine of the Des Moines Lobe inferred from sediment properties Ankerstjerne, Suzanne Iverson, Neal R. Lagroix, France Institut de Physique du Globe de Paris (IPGP) Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris Diderot - Paris 7 (UPD7)-Université de La Réunion (UR)-Institut de Physique du Globe de Paris (IPG Paris)-Centre National de la Recherche Scientifique (CNRS) 2015 https://insu.hal.science/insu-03579364 https://doi.org/10.1016/j.geomorph.2015.07.019 en eng HAL CCSD Elsevier info:eu-repo/semantics/altIdentifier/doi/10.1016/j.geomorph.2015.07.019 insu-03579364 https://insu.hal.science/insu-03579364 BIBCODE: 2015Geomo.248.452A doi:10.1016/j.geomorph.2015.07.019 ISSN: 0169-555X Geomorphology https://insu.hal.science/insu-03579364 Geomorphology, 2015, 248, pp.452-463. ⟨10.1016/j.geomorph.2015.07.019⟩ Glacier Moraine Till Fabric Preconsolidation [SDU]Sciences of the Universe [physics] info:eu-repo/semantics/article Journal articles 2015 ftsorbonneuniv https://doi.org/10.1016/j.geomorph.2015.07.019 2023-10-24T22:36:43Z International audience Geometric characteristics of the washboard moraines of the Des Moines Lobe (DML) of the Laurentide ice sheet agree with their proposed origin as crevasse-squeeze ridges, but study of their sediments is required to help further test this hypothesis. A 70-m-long, 3-5 m high section through a moraine ridge in central Iowa revealed till with irregular, isolated lenses of silt, sand, and gravel that dip to varying extents upglacier. The texture and density of the till are like those of the basal till of the DML studied elsewhere in Iowa, and preconsolidation pressures determined from tests on till and silt of the ridge indicate that it developed subglacially rather than at the glacier margin. Preconsolidation pressures additionally demonstrate that pore-water pressures in the bed supported most of the glacier's weight, which would have contributed to till mobility. Fabrics based on the anisotropy of magnetic susceptibility of 3125 intact till specimens collected at 125 locations in the section indicate two end-member states of strain that varied with location in the ridge and caused sediment mounding: simple shear that was directed downglacier along shear planes inclined upglacier, together with pure shear where an overlying crevasse allowed the sediment bed to extend upward and laterally. Meltwater that likely flowed along the crevasse deposited sorted sediments that were incorporated in till, deformed, and rotated. This positive test of the crevasse-squeeze hypothesis indicates that the DML was in longitudinal extension near its margin, reinforcing previous arguments that the lobe surged. The predominance of fabrics caused by simple shear demonstrates that crevasse filling was underway before the surge had fully halted. This study should prompt caution in using similar transverse ridges, such as those geophysically imaged in some submarine glacier forefields, as indicators of retreat rates. Article in Journal/Newspaper DML Ice Sheet HAL Sorbonne Université Moraine Ridge ENVELOPE(168.050,168.050,-72.300,-72.300) Geomorphology 248 452 463 |
institution |
Open Polar |
collection |
HAL Sorbonne Université |
op_collection_id |
ftsorbonneuniv |
language |
English |
topic |
Glacier Moraine Till Fabric Preconsolidation [SDU]Sciences of the Universe [physics] |
spellingShingle |
Glacier Moraine Till Fabric Preconsolidation [SDU]Sciences of the Universe [physics] Ankerstjerne, Suzanne Iverson, Neal R. Lagroix, France Origin of a washboard moraine of the Des Moines Lobe inferred from sediment properties |
topic_facet |
Glacier Moraine Till Fabric Preconsolidation [SDU]Sciences of the Universe [physics] |
description |
International audience Geometric characteristics of the washboard moraines of the Des Moines Lobe (DML) of the Laurentide ice sheet agree with their proposed origin as crevasse-squeeze ridges, but study of their sediments is required to help further test this hypothesis. A 70-m-long, 3-5 m high section through a moraine ridge in central Iowa revealed till with irregular, isolated lenses of silt, sand, and gravel that dip to varying extents upglacier. The texture and density of the till are like those of the basal till of the DML studied elsewhere in Iowa, and preconsolidation pressures determined from tests on till and silt of the ridge indicate that it developed subglacially rather than at the glacier margin. Preconsolidation pressures additionally demonstrate that pore-water pressures in the bed supported most of the glacier's weight, which would have contributed to till mobility. Fabrics based on the anisotropy of magnetic susceptibility of 3125 intact till specimens collected at 125 locations in the section indicate two end-member states of strain that varied with location in the ridge and caused sediment mounding: simple shear that was directed downglacier along shear planes inclined upglacier, together with pure shear where an overlying crevasse allowed the sediment bed to extend upward and laterally. Meltwater that likely flowed along the crevasse deposited sorted sediments that were incorporated in till, deformed, and rotated. This positive test of the crevasse-squeeze hypothesis indicates that the DML was in longitudinal extension near its margin, reinforcing previous arguments that the lobe surged. The predominance of fabrics caused by simple shear demonstrates that crevasse filling was underway before the surge had fully halted. This study should prompt caution in using similar transverse ridges, such as those geophysically imaged in some submarine glacier forefields, as indicators of retreat rates. |
author2 |
Institut de Physique du Globe de Paris (IPGP) Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris Diderot - Paris 7 (UPD7)-Université de La Réunion (UR)-Institut de Physique du Globe de Paris (IPG Paris)-Centre National de la Recherche Scientifique (CNRS) |
format |
Article in Journal/Newspaper |
author |
Ankerstjerne, Suzanne Iverson, Neal R. Lagroix, France |
author_facet |
Ankerstjerne, Suzanne Iverson, Neal R. Lagroix, France |
author_sort |
Ankerstjerne, Suzanne |
title |
Origin of a washboard moraine of the Des Moines Lobe inferred from sediment properties |
title_short |
Origin of a washboard moraine of the Des Moines Lobe inferred from sediment properties |
title_full |
Origin of a washboard moraine of the Des Moines Lobe inferred from sediment properties |
title_fullStr |
Origin of a washboard moraine of the Des Moines Lobe inferred from sediment properties |
title_full_unstemmed |
Origin of a washboard moraine of the Des Moines Lobe inferred from sediment properties |
title_sort |
origin of a washboard moraine of the des moines lobe inferred from sediment properties |
publisher |
HAL CCSD |
publishDate |
2015 |
url |
https://insu.hal.science/insu-03579364 https://doi.org/10.1016/j.geomorph.2015.07.019 |
long_lat |
ENVELOPE(168.050,168.050,-72.300,-72.300) |
geographic |
Moraine Ridge |
geographic_facet |
Moraine Ridge |
genre |
DML Ice Sheet |
genre_facet |
DML Ice Sheet |
op_source |
ISSN: 0169-555X Geomorphology https://insu.hal.science/insu-03579364 Geomorphology, 2015, 248, pp.452-463. ⟨10.1016/j.geomorph.2015.07.019⟩ |
op_relation |
info:eu-repo/semantics/altIdentifier/doi/10.1016/j.geomorph.2015.07.019 insu-03579364 https://insu.hal.science/insu-03579364 BIBCODE: 2015Geomo.248.452A doi:10.1016/j.geomorph.2015.07.019 |
op_doi |
https://doi.org/10.1016/j.geomorph.2015.07.019 |
container_title |
Geomorphology |
container_volume |
248 |
container_start_page |
452 |
op_container_end_page |
463 |
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1782333528744132608 |