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| Titel |
Landslide boost from entrainment of erodible material along the slope |
| VerfasserIn |
M. Farin, A. Mangeney, O. Roche, I. R. Ionescu, O. Hungr |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250061496
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| Zusammenfassung |
| Landslides, debris flows, pyroclastic flows and avalanches are natural hazards that threaten
life and property in mountainous, volcanic, coastal and seismically-active areas. The granular
mass tends to accelerate as gravity pulls it down the slope and will decelerate on more gentle
slopes, where frictional forces that dissipate energy can overcome the driving forces. The
entrainment of underlying sediments or debris into the gravitational granular flows is
suspected to be critical to their dynamics, but direct measurement of material entrainment in
natural flows is very difficult. Nevertheless, qualitative and quantitative field observations
suggest that material entrainment can either increase or decrease flow velocity and
deposit extent, depending on the geological setting and the type of gravitational
flow.
We present laboratory experiments of granular column collapse over an inclined plane
covered by an erodible bed, designed to mimic erosion processes of natural flows traveling
over deposits built up by earlier events. The controlling parameters are the inclination of the
plane, the aspect ratio of the granular column released and the thickness of the erodible layer.
The avalanche excavates the erodible layer immediately at the flow front, behind
which waves traveling downstream help removing grains from the erodible bed are
observed. We show that erosion processes increases the flow mobility (i. e. runout)
by up to 25% over slopes with inclination close to the repose angle of the grains.
Erosion efficiency is shown to strongly depend on the slope and on the nature of the
erodible bed (i. e. degree of compaction): erosion effects are smaller as the compaction
of the erodible granular bed increases. The excavation depth first increases and
stabilizes to a critical value, and finally decreases when increasing the thickness of
the erodible bed. We demonstrate that the increase of mass of the flowing grains
caused by entrainment of the erodible layer is not enough to explain the observed
increase in velocity and runout of the granular mass. Finally, numerical simulations
using a 2D hydrodynamic model and a 3D visco-plastic model are performed to
obtain insight into the physical processes at work during entrainment processes. |
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