Copyright 1999 by the American Geophysical Union.The Colorado Rockfall Simulation Program (CRSP) was developed to provide a statistical analysis of probable rockfall behavior at any given site and to be used as a tool to study the behavior of rockfalls, to determine the need for rockfall mitigation, and to aid in the design of rockfall mitigation.

The discrepancy between calculated velocity data and field estimated velocity data (?220 m/s versus ?110 m/s) is attributed to energy dissipated by the downing of trees and additional entrainment of debris into the atmosphere not included in the calculations. This amount of dust lowered the local atmospheric sound speed to ?220 m/s. The size and location of the first impact are thought to have injected <50 wt % dust into the atmosphere.

Results from the air blast simulations indicate that the second Happy Isles air blast (weak shock wave) traveled with an initial velocity above the local sound speed. The impact pressure (0.5 MPa) is constrained by the kinetic energy of the impact (1010-1012 J) estimated from the seismic energy generated by the impact. The impact velocity (105-107 m/s) is estimated from the Colorado Rockfall Simulation Program that simulates rockfall trajectories. The numerical model simulates the two-dimensional propagation of an air blast through a dusty atmosphere with initial conditions defined by the impact velocity and pressure. From tornadic studies of tree damage, the air blast is estimated to have traveled <108-120 m/s within 50 m from the impact and decreased to <10-20 m/s within 500 m from the impact. Calculated velocities for the air blast from a two-phase, finite difference model are compared to velocities estimated from tree damage. We focus on the dynamic behavior of the second air blast that downed over 1000 trees, destroyed a bridge, demolished a snack bar, and caused one fatality and several injuries. The impacts of the first two events which involved a 550-m free fall, generated seismic waves and atmospheric pressure waves (air blasts). The July 10, 1996, Happy Isles rockfall in Yosemite National Park, California, released 23,000 to 38,000 m3 of granite in four separate events.

Colorado rockfall simulation program