HR: 0800h
AN: H41B-0292    [Abstracts]
TI: Experimental Investigation of Unconfined Granular Flows Along an Incline : When do Levees Form?
AU: * Deboeuf, S
EM: deboeuf@ipgp.jussieu.fr
AF: Institut de Physique du Globe de Paris / Departement de Modelisation Physique et Numerique, 4 place Jussieu, Paris, 75252 France
AU: Lajeunesse, E
EM: lajeunes@ipgp.jussieu.fr
AF: Institut de Physique du Globe de Paris / Laboratoire de Dynamique des Systemes Geologiques, 4 place Jussieu, Paris, 75252 France
AU: Dauchot, O
EM: dauchot@cea.fr
AF: Commissariat a l'Energie Atomique / Service de Physique de l'Etat Condense, L'Orme des Merisiers, Gif sur Yvette, 91191 France
AB: Natural granular flows such as rock avalanches, debris flows or pyroclastic flows are known to spontaneously channelize through the formation of levees along their sides. We report in this paper the results of laboratory experiments aimed at understanding this phenomenon in a simple flow geometry. The experiment consists in releasing granular material on a rough inclined plane at a constant mass flow rate. The resulting unconfined granular coulee has the shape of a finger descending the slope. Using image analysis, we measure the time evolution of both the flow morphological characteristics (width and thickness) and the surface velocity field for different values of the mass flow rate and the slope angle. Surface velocity measurements reveal the presence of static zones along the sides of the flow. Our main observation is that although the input mass flow rate remains constant during the whole experiment, the coulee never reaches a stationary state. On the contrary, the flow morphological characteristics constantly evolve with time : the granular flow slowly enlarges while its thickness decreases. If the flow is maintained for a sufficiently long time, it finally distabilizes leading to the formation of a wavy pattern along the sides of the coulee. As a result of this non-stationary flow dynamics, the final deposit morphology strongly depends on the duration of the flow. If the flow duration is short, the deposit exhibits a classical levees/channel morphology. However the levee thickness progressively decreases when the flow duration is increased. In the case of a very long flow, the levees eventually vanish. Systematic comparisons between numerical and experimental modelisations, especially on the transient dynamics of the levees/channel morphology might provide new constraints on the frictionnal constitutive behaviour of avalanches.
DE: 5104 Fracture and flow
DE: 1815 Erosion and sedimentation
DE: 1824 Geomorphology (1625)
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting