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| Titel |
Fundamental changes of granular flows dynamics, deposition and erosion processes at high slope angles: insights from laboratory experiments. |
| VerfasserIn |
Maxime Farin, Anne Mangeney, Olivier Roche |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250086254
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| Publikation (Nr.) |
 EGU/EGU2014-83.pdf |
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| Zusammenfassung |
| Geophysical granular flows commonly interact with their substrate in various ways depending
on the mechanical properties of the underlying material. Granular substrates, resulting
from deposition of earlier flows or various geological events, are often eroded by
avalanches [see Hungr and Evans, 2004 for review]. The entrainment of underlying
debris by the flow is suspected to affect flow dynamics because qualitative and
quantitative field observations suggest that it can increase the flow velocity and
deposit extent, depending on the geological setting and flow type [Sovilla et al.,
2006; Iverson et al., 2011]. Direct measurement of material entrainment in nature,
however, is very difficult. We conducted laboratory experiments on granular column
collapse over an inclined channel with and without an erodible bed of granular
material. The controlling parameters were the channel slope angle, the granular
column volume and its aspect ratio (i.e. height over length), the inclination of the
column with respect to the channel base, the channel width, and the thickness and
compaction of the erodible bed. For slope angles below a critical value θc, between
10° and 16°, the runout distance rf is proportional to the initial column height h0
and is unaffected by the presence of an erodible bed. On steeper slopes, the flow
dynamics change fundamentally since a last phase of slow propagation develops
at the end of the flow front deceleration, and prolongates significantly the flow
duration. This phase has similar characteristics that steady, uniform flows. The slow
propagation phase lasts longer for increasing slope angle, column volume, column
inclination with respect to the slope, and channel width, and for decreasing column
aspect ratio. It is however independent of the maximum front velocity and, on an
erodible bed, of the maximum depth of excavation within the bed. Both on rigid and
erodible beds, the increase of the slow propagation phase duration has a crucial effect
on the granular flows dynamics and deposition. (i) Over a rigid bed, as the slow
propagation phase lasts longer, the normalized runout distance rf-h0 is greater for a given
slope angle and the front of the flow deposit becomes steeper. (ii) Over an erodible
bed, increasing the duration of the slow phase causes the bed excavation to lasts
longer and leads to the increase of the runout distance compared with the case on the
rigid bed being greater; this is even more significant as the bed is less compact. |
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