Computer Science – Sound
Scientific paper
Dec 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agufm.h32a0295m&link_type=abstract
American Geophysical Union, Fall Meeting 2001, abstract #H32A-0295
Computer Science
Sound
1815 Erosion And Sedimentation, 1824 Geomorphology (1625), 3210 Modeling, 5415 Erosion And Weathering
Scientific paper
The high mobility exhibited by long runout landslides remains a geologic puzzle. In 1979 I proposed that the presence of strong internal vibrations could fluidize the rock debris composing such a landslide, and permit very large volumes of rock debris (more than 106 m3) to flow with a low coefficient of friction. Numerical simulations by Campbell in 1995 verified that a low friction mode of motion is theoretically possible but their time resolution was insufficient to validate my proposed mechanism. Since my initial proposal I performed laboratory studies of vibrated granular materials that support the rheology predicted by acoustic fluidization theory. I now report theoretical studies that apply this rheologic law to the steady flow of granular material down an incline of uniform slope. Although numerical solutions of the resulting highly nonlinear equations are generally necessary, a simple analytic solution is possible when the sound waves in the landslide propagate only short distances compared to the thickness of the slide mass. This solution shows that sustained flow is possible if a "regeneration parameter" equal to 1/2 Q e sin2 θ is equal to about 1. In this equation Q denotes the rate of energy absorption by inelastic processes, e is the vibrational energy generation efficiency, and θ is the (constant) slope. For plausible values of these parameters the critical slope on which steady sliding is possible is between 7 and 11 degrees, far lower than permitted by the static coefficient of friction. These slopes are similar to those observed for long runout landslides on the Earth, Venus, Mars and Io. The solution also shows that the velocity-depth profile is close to parabolic. Although a basal shear concentration has been reported for the Blackhawk landslide (which also possesses a basal layer of fine sand), more uniform shear is inferred in homogeneous slide masses. Campbell's numerical simulations also exhibit a parabolic velocity profile through the slide mass, in agreement with the analytical solution for acoustically fluidized flow.
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