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On the run-out distance of geophysical gravitational flows: Insight from fluidized granular collapse experiments

Roche, O. and Attali, M. and Mangeney, A. and Lucas, A. (2011) On the run-out distance of geophysical gravitational flows: Insight from fluidized granular collapse experiments. Earth and Planetary Science Letters, 311 (3-4). pp. 375-385. ISSN 0012-821X.

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We present the results of laboratory experiments on the emplacement of gravitational granular flows generated from axisymmetrical release of columns of fine (~75 μm) or coarse (~330 μm) particles initially fluidized with air. Internal friction is first negligible in the granular columns and then increases as pore pressure diffuses within the propagating flows, which are thus characterized by a mean friction lower than that of dry (i.e., non fluidized) flows. For columns of height-to-radius ratios a ≈ 0.2–30, we identify the modes of flow propagation and the scaling laws that characterize the morphology of the resulting deposits. Here we show that the normalized run-out distance of the initially fluidized flows scales as a power law of a (i.e., λa^n), thus demonstrating that this scaling law is not only typical of dry granular flows, as claimed in the literature. Fluidization reduces contacts between the grains and thus effective energy dissipation. Its effect increases the coefficient λ compared to dry flows but it has no influence on the exponent n that decreases from 1 to 1/2 at increasing a, mainly due to axisymmetrical spreading as shown by earlier works on dry coarse particles, except for the initially dry flows of fine particles at a > ~2 as it decreases to ~2/3. In this latter case the flows could experience (partial) auto fluidization as their normalized flow run-out is equal to that of their initially fluidized counterparts at a > ~4. The auto fluidization mechanism, supported by other recent experimental works, is particularly appealing to account for the long run-out distance of natural dense gas–particle mixtures such as pyroclastic flows. At high a, fluidization also affects the generation of surface waves with clear signatures on the deposits. We compare our experimental results with published data on Valles Marineris landslides (Mars) whose emplacement mechanisms are controversial. These natural events are characterized by values of λ higher than that of the laboratory flows, including those with low friction. This shows that some mechanism and/or scale effects promoted energy dissipation for the VM landslides that was significantly smaller than for typical dry frictional granular materials, as suggested by Lucas and Mangeney (2007).

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Additional Information:© 2011 Elsevier B.V. Received 10 February 2011. Revised 12 September 2011. Accepted 14 September 2011. Available online 21 October 2011. Editor: Y. Ricard. Eric Lajeunesse communicated his data on Valles Marineris landslides. This work was supported by the Institut de Recherche pour le Développement (IRD, France), and the ANR Volbiflo and Planeteros projects (France). The paper benefited from useful comments of three anonymous reviewers.
Funding AgencyGrant Number
Institut de Recherche pour le Développment (IRD) (France)UNSPECIFIED
Agence Nationale pour la Recherche (ANR) (France)UNSPECIFIED
Subject Keywords:granular flow; rock avalanche; Valles Marineris landslides; pyroclastic flow; run-out; experimental scaling law
Issue or Number:3-4
Record Number:CaltechAUTHORS:20120223-095445294
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Official Citation:O. Roche, M. Attali, A. Mangeney, A. Lucas, On the run-out distance of geophysical gravitational flows: Insight from fluidized granular collapse experiments, Earth and Planetary Science Letters, Volume 311, Issues 3–4, 15 November 2011, Pages 375-385, ISSN 0012-821X, 10.1016/j.epsl.2011.09.023.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:29435
Deposited By: Tony Diaz
Deposited On:23 Feb 2012 21:07
Last Modified:03 Oct 2019 03:41

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