Dynamics of granular media.
Granular media are now known to behave neither like fluids or solids, but to have their own complex behavior. Our work in this area is a new initiative, supported by CNES. It is presently concentrated on the behavior of granular systems undergoing shear, like in faults, and the dynamics of landslides.
Granular Mechanics in Faulting.
During shear between two rough surfaces, such as along a fault, asperities on the surfaces are broken off and ground into a layer of crushed granular material. Using a molecular dynamics-type numerical simulation, Aharanov and Sparks have begun to explore shearing as a granulation process in fault zones. The model explores how solid material becomes granulated, and the evolution of shear within this layer. Early results indicate that the initial distribution of heterogeneity within the rock can control the extent of damage to the sliding surfaces, which affects the apparent sliding friction that would be measured.
Sparks, D. W., E. Aharonov, C. Scholz, The development of fault zone features during shear, from discrete numerical models, EOS Trans. Amer. Geophys. 76, 1997.
Flow of dry granular material, with applications to landslides
Laboratory experiments are being desiged and conducted by E. Aharonov, D. Sparks and Columbia Physics undergradate, Lindsey McDevit. This study is motivated by a century long puzzlement over the physical mechanism responsible for long-runout landslides. Long-runout landslides are large-scale landslides which travel much further than expected by simple frictional calculations and are therefore usually described as having an anomalously low friction coefficient. These landslides can be devastating for human settlements in their path.
In these experiments an initially stationary mass of cohesion-less granular material (sand) flows down a curved bed, onto a planar horizontal segment. We are currently exploring relationships between the shape and final position of the material and the initial height and volume of material.
Aharanov and Sparks will organize a special session on Dynamics of Landslides for the AGU Spring Meeting in 1998.