HR: 0830h
AN: H31C-0479    [PDF]
TI: Rock avalanches revisited: New insights into catastrophic event triggering through experimental physics
AU: Losert, W
EM: wlosert@glue.umd.edu
AF: Dept. of Physics, IPST and IREAP, Univ. of Maryland, College Park, MD 20742-3511 United States
AU: * Friedmann, J
EM: juliof@geol.umd.edu
AF: Dept. of Geology, Univ. Maryland, College Park, MD 20742-4211 United States
AB: Rock avalanches remain among the largest and most devastating of mass-wasting phenomena, and are responsible for the fragmentation and transport of significant rock volumes from mountains to basins. Many aspects of their physics remain poorly understood, including triggering, transport, long run-out, and deposition. Recent experiments in granular physics suggest that many phenomena and features simply reflect the non-linear nature of granular flows. These effects are captured using high-speed cameras ($>$3000 frames/second) and particle tracking to map out the velocity field during flow initiation, transport, and cessation. A series of experiments suggest that the peculiarities of granular physics explain many features within rock avalanches, including long run-out, inverse grading, preservation of inherited stratigraphy, shear band occurrence, morphology, and flow initiation. To date, long run out has not yet been reproduced despite many attempts and configurations. Examples from the Blackhawk landslide, Frank landslide, Sherman Glacier, and others are discussed and compared to results from laboratory experiments. This work supports several new conclusions. First, flow triggering may depend on the history and geometry of earlier shear. This is due to subtle anisotropies in the granular framework that affect the initial collapse of the bulk granular framework. Second, the plug-like rheology of sheared granular material is consistent with many observations of rock-avalanche features without special mechanisms (e.g., air lubrication, frictional melting, acoustic fluidization). Third, the morphology of the flow (e.g., longitudinal and lateral ridges) may reflect the flow dynamics over a range of conditions, and may be more generic than previously though. If correct, then these conclusions can be used to create better hazard maps and more accurate risk characterizations than currently deployed. Moreover, they suggest caution in the interpretation ancient physical phenomena, especially from geomorphological data alone, before the physics of granular flows are better understood and applied in context.
DE: 1815 Erosion and sedimentation
DE: 1824 Geomorphology (1625)
DE: 1899 General or miscellaneous
DE: 5120 Plasticity, diffusion, and creep
DE: 7223 Seismic hazard assessment and prediction
SC: Hydrology [H]
MN: 2003 Fall Meeting