Numerical reconstructions of the flow and basal conditions of the Rhine glacier, European Central Alps, at the Last Glacial Maximum
International audience At the Last Glacial Maximum (LGM), the Rhine glacier in the Swiss Alps covered an area of about 16 000 km 2 . As part of an integrative study about the safety of repositories for radioactive waste under ice age conditions in Switzerland, we modeled the Rhine glacier using a th...
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ftccsdartic:oai:HAL:insu-03706501v1 2023-12-17T10:51:01+01:00 Numerical reconstructions of the flow and basal conditions of the Rhine glacier, European Central Alps, at the Last Glacial Maximum Cohen, Denis Gillet-Chaulet, Fabien Haeberli, Wilfried Machguth, Horst Fischer, Urs H. Institut des Géosciences de l’Environnement (IGE) Institut de Recherche pour le Développement (IRD)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes 2016-2019 (UGA 2016-2019 ) 2018 https://insu.hal.science/insu-03706501 https://insu.hal.science/insu-03706501/document https://insu.hal.science/insu-03706501/file/tc-12-2515-2018.pdf https://doi.org/10.5194/tc-12-2515-2018 en eng HAL CCSD Copernicus info:eu-repo/semantics/altIdentifier/doi/10.5194/tc-12-2515-2018 insu-03706501 https://insu.hal.science/insu-03706501 https://insu.hal.science/insu-03706501/document https://insu.hal.science/insu-03706501/file/tc-12-2515-2018.pdf BIBCODE: 2018TCry.12.2515C doi:10.5194/tc-12-2515-2018 http://creativecommons.org/licenses/by/ info:eu-repo/semantics/OpenAccess ISSN: 1994-0424 EISSN: 1994-0416 The Cryosphere https://insu.hal.science/insu-03706501 The Cryosphere, 2018, 12, pp.2515-2544. ⟨10.5194/tc-12-2515-2018⟩ [SDU]Sciences of the Universe [physics] info:eu-repo/semantics/article Journal articles 2018 ftccsdartic https://doi.org/10.5194/tc-12-2515-2018 2023-11-19T00:08:28Z International audience At the Last Glacial Maximum (LGM), the Rhine glacier in the Swiss Alps covered an area of about 16 000 km 2 . As part of an integrative study about the safety of repositories for radioactive waste under ice age conditions in Switzerland, we modeled the Rhine glacier using a thermodynamically coupled three-dimensional, transient Stokes flow and heat transport model down to a horizontal resolution of about 500 m. The accumulation and ablation gradients that roughly reproduced the geomorphic reconstructions of glacial extent and ice thickness suggested extremely cold (T July ∼0 ∘ C at the glacier terminus) and dry (∼10 % to 20 % of today's precipitation) climatic conditions. Forcing the numerical simulations with warmer and wetter conditions that better matched LGM climate proxy records yielded a glacier on average 500 to 700 m thicker than geomorphic reconstructions. Mass balance gradients also controlled ice velocities, fluxes, and sliding speeds. These gradients, however, had only a small effect on basal conditions. All simulations indicated that basal ice reached the pressure melting point over much of the Rhine and Linth piedmont lobes, and also in the glacial valleys that fed these lobes. Only the outer margin of the lobes, bedrock highs beneath the lobes, and Alpine valleys at high elevations in the accumulation zone remained cold based. The Rhine glacier was thus polythermal. Sliding speed estimated with a linear sliding rule ranged from 20 to 100 m a -1 in the lobes and 50 to 250 m a -1 in Alpine valleys. Velocity ratios (sliding to surface speeds) were >80 % in lobes and ∼60 % in valleys. Basal shear stress was very low in the lobes (0.03-0.1 MPa) and much higher in Alpine valleys (>0.2 MPa). In these valleys, viscous strain heating was a dominant source of heat, particularly when shear rates in the ice increased due to flow constrictions, confluences, or flow past large bedrock obstacles, contributing locally up to several watts per square meter but on average 0.03 to 0.2 W ... Article in Journal/Newspaper The Cryosphere Archive ouverte HAL (Hyper Article en Ligne, CCSD - Centre pour la Communication Scientifique Directe) The Cryosphere 12 8 2515 2544 |
institution |
Open Polar |
collection |
Archive ouverte HAL (Hyper Article en Ligne, CCSD - Centre pour la Communication Scientifique Directe) |
op_collection_id |
ftccsdartic |
language |
English |
topic |
[SDU]Sciences of the Universe [physics] |
spellingShingle |
[SDU]Sciences of the Universe [physics] Cohen, Denis Gillet-Chaulet, Fabien Haeberli, Wilfried Machguth, Horst Fischer, Urs H. Numerical reconstructions of the flow and basal conditions of the Rhine glacier, European Central Alps, at the Last Glacial Maximum |
topic_facet |
[SDU]Sciences of the Universe [physics] |
description |
International audience At the Last Glacial Maximum (LGM), the Rhine glacier in the Swiss Alps covered an area of about 16 000 km 2 . As part of an integrative study about the safety of repositories for radioactive waste under ice age conditions in Switzerland, we modeled the Rhine glacier using a thermodynamically coupled three-dimensional, transient Stokes flow and heat transport model down to a horizontal resolution of about 500 m. The accumulation and ablation gradients that roughly reproduced the geomorphic reconstructions of glacial extent and ice thickness suggested extremely cold (T July ∼0 ∘ C at the glacier terminus) and dry (∼10 % to 20 % of today's precipitation) climatic conditions. Forcing the numerical simulations with warmer and wetter conditions that better matched LGM climate proxy records yielded a glacier on average 500 to 700 m thicker than geomorphic reconstructions. Mass balance gradients also controlled ice velocities, fluxes, and sliding speeds. These gradients, however, had only a small effect on basal conditions. All simulations indicated that basal ice reached the pressure melting point over much of the Rhine and Linth piedmont lobes, and also in the glacial valleys that fed these lobes. Only the outer margin of the lobes, bedrock highs beneath the lobes, and Alpine valleys at high elevations in the accumulation zone remained cold based. The Rhine glacier was thus polythermal. Sliding speed estimated with a linear sliding rule ranged from 20 to 100 m a -1 in the lobes and 50 to 250 m a -1 in Alpine valleys. Velocity ratios (sliding to surface speeds) were >80 % in lobes and ∼60 % in valleys. Basal shear stress was very low in the lobes (0.03-0.1 MPa) and much higher in Alpine valleys (>0.2 MPa). In these valleys, viscous strain heating was a dominant source of heat, particularly when shear rates in the ice increased due to flow constrictions, confluences, or flow past large bedrock obstacles, contributing locally up to several watts per square meter but on average 0.03 to 0.2 W ... |
author2 |
Institut des Géosciences de l’Environnement (IGE) Institut de Recherche pour le Développement (IRD)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes 2016-2019 (UGA 2016-2019 ) |
format |
Article in Journal/Newspaper |
author |
Cohen, Denis Gillet-Chaulet, Fabien Haeberli, Wilfried Machguth, Horst Fischer, Urs H. |
author_facet |
Cohen, Denis Gillet-Chaulet, Fabien Haeberli, Wilfried Machguth, Horst Fischer, Urs H. |
author_sort |
Cohen, Denis |
title |
Numerical reconstructions of the flow and basal conditions of the Rhine glacier, European Central Alps, at the Last Glacial Maximum |
title_short |
Numerical reconstructions of the flow and basal conditions of the Rhine glacier, European Central Alps, at the Last Glacial Maximum |
title_full |
Numerical reconstructions of the flow and basal conditions of the Rhine glacier, European Central Alps, at the Last Glacial Maximum |
title_fullStr |
Numerical reconstructions of the flow and basal conditions of the Rhine glacier, European Central Alps, at the Last Glacial Maximum |
title_full_unstemmed |
Numerical reconstructions of the flow and basal conditions of the Rhine glacier, European Central Alps, at the Last Glacial Maximum |
title_sort |
numerical reconstructions of the flow and basal conditions of the rhine glacier, european central alps, at the last glacial maximum |
publisher |
HAL CCSD |
publishDate |
2018 |
url |
https://insu.hal.science/insu-03706501 https://insu.hal.science/insu-03706501/document https://insu.hal.science/insu-03706501/file/tc-12-2515-2018.pdf https://doi.org/10.5194/tc-12-2515-2018 |
genre |
The Cryosphere |
genre_facet |
The Cryosphere |
op_source |
ISSN: 1994-0424 EISSN: 1994-0416 The Cryosphere https://insu.hal.science/insu-03706501 The Cryosphere, 2018, 12, pp.2515-2544. ⟨10.5194/tc-12-2515-2018⟩ |
op_relation |
info:eu-repo/semantics/altIdentifier/doi/10.5194/tc-12-2515-2018 insu-03706501 https://insu.hal.science/insu-03706501 https://insu.hal.science/insu-03706501/document https://insu.hal.science/insu-03706501/file/tc-12-2515-2018.pdf BIBCODE: 2018TCry.12.2515C doi:10.5194/tc-12-2515-2018 |
op_rights |
http://creativecommons.org/licenses/by/ info:eu-repo/semantics/OpenAccess |
op_doi |
https://doi.org/10.5194/tc-12-2515-2018 |
container_title |
The Cryosphere |
container_volume |
12 |
container_issue |
8 |
container_start_page |
2515 |
op_container_end_page |
2544 |
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1785576160946552832 |