Yosemite Rock Fall of July 10, 1996

Abstract

At 6:52 pm PDT Wednesday, July 10, 1996, a large block of granite, with an estimated volume of 35,000 to 80,000 cubic yards (27,000 to 62,000 m3), detached from the cliff between Washburn Point and Glacier Point, in Yosemite Valley. The rock mass subsequently slid down a 50-degree inclined shelf on the cliff for approximately 185 m and acquired a velocity of 61 m/s (135 mph), sufficient to launch itself from the cliff. The rock then free-fell ballistically and cleared the remaining 500 m (1,640 feet) of the cliff prior to impacting on the talus slope, about 60 m (200 feet) from its base, in the Happy Isles area of the valley floor in Yosemite National Park. The rock fall was well recorded by 3 UC Berkeley (BDSN) and Caltech (TERRAscope) broadband seismographic stations and 15 short-period seismographic stations (operated by the USGS in Menlo Park and the University of...