Ivy-Ochs Susan
Datierung des Bleis Marscha Blockgletschers (Val d’Err)
Project Number: CH-7301
| Project Type: |
Master |
| Project Duration: |
09/01/2018 - 10/12/2018 project completed |
| Funding Source: |
other , |
| Leading Institution: |
Geologisches Institut, ETH Zürich |
| Project Leader: |
Prof. Susan Ivy-Ochs
Senior Research Scientist/Lecturer (Quaternary Geologist)
Labor für Ionenstrahlphysik, 10Be / 26Al / 36Cl-Analysen
Institut für Teilchenphysik (IPP)
ETH Zürich
HPK H27
Otto-Stern-Weg 5
8093 Zürich
Phone: +41 (0) 44 633 38 86 ; +41 (0) 44 633 65 07
FAX: +41 (0) 44 633 10 67
e-Mail: ivy(at)phys.ethz.ch
http://www.ams.ethz.ch |
Research Areas:
Disciplines:
Abstract:
We attempt to reconstruct the formation of the Bleis Marscha rockglacier in the Val d’Err, Grisons (Switzerland) with terrestrial cosmogenic surface exposure dating, aerial image correlation and numerical modelling. The Bleis Marscha rockglacier is a 1200 m long, multi-unit talus rockglacier with an active upper part that overrides a lower part. Lichen-covered boulders, vegetated, stabilized slopes, and signs of settling suggest that the parts below ?2500 m a.s.l. are relict. Internal front scarps separate the rockglacier into different units, each with its own activity phase. Morphological evidence suggests that the rockglacier began forming in the earliest Holocene. Surface exposure dating with cosmogenic 10Be and 36Cl places a temporal framework (ka scale) on rockglacier movement periods. On the presently active part, the exposure ages correlate well with distance from the source and can be addressed as minimal travel times. The oldest age above the internal main scarp suggests that the late Holocene activity period initiated not after 2.8±0.2 ka. The exposure ages on the relict part below have a larger scatter in the order of centuries, suggesting that disturbances (intermittent boulder instabilities, self-shielding caused by boulder rotation) affecting the nuclide inventories are more important during inactivation and collapse. This apparent rejuvenation explains both the tendentially “too-young” ages and the large spread. The oldest age, interpreted as (rough) inactivity age, suggests that first generation of the Bleis Marscha rockglacier initiated in the late Younger Dryas and ceased its activity around 9.0±0.6 ka. Feature-tracking analysis of bi-temporal (2003-2012) orthophotos constrains the present horizontal surface velocity field. An illumination-invariant method for correlating orthophoto-derived orientation images yielded reliable displacements on the rugged rockglacier surface. The image correlation results support the subdivision of the Bleis Marscha rockglacier in an active upper part, characterised by moderate to high surface velocities controlled by the topography on a 100-m scale, and a relict, collapsing lower part, characterised by an irregular surface velocity field strongly coupled to the small-scale topography (“effet camembert”). The degree of correlation between morphology and surface creep field indicates the dynamic state of the rockglacier. Present-day dynamics are numerically modelled using a two-dimensional finite-element approach to gain insights into the mechanical and material properties. The influence of the mechanical layering (boulder mantle, rockglacier core and low-viscosity basal shear layer) on stress distribution and deformation is explored. In an inverse problem constrained with the surface velocity data, the viscosity structure of the rockglacier is inferred. Surface velocities of up to 30 cm a?1 on the apparently relict part could only be numerically reproduced assuming a considerable fraction of ice and/or water that weakens the material. The subsurface ice either has been preserved throughout the Holocene or has reformed more recently. Although the model assumes a Newtonian, incompressible rheology, the typical strain localisation towards the basal shear zone resulting from non-linear deformation mechanisms could be emulated (reproduced “by appearance”) with the prescribed viscosity layering.
Publications:
Conference Poster
Last update: 7/27/22
Source of data: ProClim- Research InfoSystem (1993-2024)
Update the data of project: CH-7301
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