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| Titel |
Non-linear till waves |
| VerfasserIn |
Gwendolyn J. M. C. Leysinger-Vieli, G. Hilmar Gudmundsson |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250035480
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| Zusammenfassung |
| The advance of a glacier over a deforming sediment layer is analysed numerically. We treat this
problem as a contact problem involving two slowly-deforming viscous bodies. The surface evolution of
both bodies, and that of the contact interface between them, is followed in time. Using various
different till rheologies we show how the mode of advance depends on the relative effective
viscosities of ice and till. Three modes of advances are observed: 1) overriding, where the glacier
advances through ice deformation only and without deforming the sediment; 2) plug-flow, where the
sediment is strongly deformed, the ice moves forward as a block and a bulge is built in front of the
glacier; and 3) mixed-flow, where the glacier overrides deforming sediment. An inverse depth-age
relationship is obtained for a glacier advance by both overriding and mixed-flow. An additional
model experiment, using a till with near plastic rheology, shows that the contrast in effective
viscosity between ice and till is the single most important model parameter defining the mode of
advance and the resulting thickness distribution of the till. Furthermore, the model calculations
imply that measurements of sediment thickness and sediment deformation taken closely to the glacier
front significantly overestimate the average sediment thickness and displacement due to sediment
deformation. A sediment bulge is formed in front of the glacier given sufficiently large contrast in
effective viscosity between ice and till. During glacier advance, the bulge quickly reaches a
steady state form strongly resembling single-crested push moraines. Inspection of particle paths
within the sediment bulge, shows the material particle of the till to travel at different speed to
that of the bulge itself, and the push moraine to advance as a form-conserving non-linear wave. |
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