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| Titel |
Basal conditions and flow dynamics of the Rhine glacier, Alps, at the Last Glacial Maximum |
| VerfasserIn |
Denis Cohen, Fabien Gillet-Chaulet, Thomas Zwinger, Horst Machguth, Wilfried Haeberli, Urs H. Fischer |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250125142
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| Publikation (Nr.) |
 EGU/EGU2016-4679.pdf |
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| Zusammenfassung |
| The safe disposal of radioactive wastes in deep geological repositories requires their
containment and isolation for up to one million years. In Switzerland, repositories are
planned in the northern Swiss lowlands near the marginal zone of the former Rhine glacier
that repeatedly formed two extensive piedmont lobes (the Rhine and Linth lobes) over the
Swiss Plateau. Future ice-age conditions may thus impact the repositories due to
erosion by glaciers, permafrost conditions, and changes in groundwater fluxes. We
use the Last Glacial Maximum (LGM) as a representative future ice-age scenario
over northern Switzerland and model the Rhine glacier at the LGM using a full
three-dimensional, thermo-mechanical model that solves Stokes flow in ice and the heat
equation in both ice and rock. Permafrost in rocks and sediments is implemented using an
effective heat capacity formulation. The Rhine glacier at the LGM is one of the
best studied paleo-glacier with geomorphic reconstructions of terminal moraines,
equilibrium lines, provenance of erratics, till extent and provenance, and evidences of
cold vs warm subglacial environments. These data are compared with modeled
ice ice thickness, cold vs warm basal condition, and flow paths. Numerical results
indicate that LGM modeled ice extent and ice thickness are not fully consistent with
geomorphic reconstructions and known climate proxies: ice is either too thick in the
accumulation zone or summer temperatures are too cold at the terminus. Simulations
with different climate parameters all indicate, however, that the beds of the Rhine
and Linth lobes were at the melting temperature except above local topographic
highs and along a thin marginal zone. Sliding speed was highest along topographic
lows with ice moving at 20 to 80 m a−1 depending on mass balance gradients.
Basal shear stress was low (< 30 kPa). Melt water was probably abundant due to
above-freezing temperatures in summer. Thus, melt water was likely routed over large
fractions of the bed. These conditions indicate the possibility of erosion by ice
through the process of quarrying and by subglacial fluvial action both of which
are thought to be responsible for the many overdeepenings present in the Swiss
Plateau. |
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