HR: 13:40h
AN: H43G-01    [Abstracts]
TI: Experimental Insights on Friction at the Base of Geophysical Flows
AU: * Cagnoli, B
EM: cagnoli@seismo.berkeley.edu
AF: University of California, Dept. of Earth and Planetary Science, 307 McCone Hall, Berkeley, CA 94720 United States
AU: Manga, M
EM: manga@seismo.berkeley.edu
AF: University of California, Dept. of Earth and Planetary Science, 307 McCone Hall, Berkeley, CA 94720 United States
AB: We have studied in the laboratory granular mass flows of rock fragments using a high-speed video camera at 2000 frames per second. These flows were generated using beds of pumice fragments positioned on a rough rotating disk whose angular velocity is controlled by a motor. These pumice fragments have an irregular shape and an average sieve diameter equal to 8.75 mm. Our experimental results suggest the validity, on average, of the same Coulomb's relationship between shear and normal forces at the base of granular mass flows irrespective of their Savage number value (the Savage number represents the ratio between grain collision stresses and gravitational grain contact stresses). In Coulomb's law the shear stresses do not depend on the shear rate. We expect the results of our analysis to be valid, for example, in pyroclastic flows, debris flows and rock avalanches. Therefore, our experiments suggest that geophysical flows do not behave as Bagnoldian grain flows and they do not behave as Bingham fluids with a yield strength. Our experiments suggest also that, in natural pyroclastic flows, relatively large pumice fragments can be totally eroded by collisions and turned into the fines that form the overriding ash clouds. In our experiments, the amount of this ash increases when the value of the Savage number increases.
DE: 8414 Eruption mechanisms
DE: 5104 Fracture and flow
DE: 3210 Modeling
DE: 1824 Geomorphology (1625)
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting