Triggering Mechanisms for Catastrophic Rock Falls from Glacier Point Cliffs, Yosemite National Park, California

摘要

Since 1857, more than 519 rock falls, rock slides, and other slope movements have been recorded within the boundaries of Yosemite National Park. More than 330 of them originated on the steep glacially-carved granite walls of Yosemite Valley, known for its spectacular beauty. Rock falls in the park have not just caused property damage but have injured at least 62 people and killed 12 others. Detailed historical studies compiled by Yosemite National Park in cooperation with the U.S. Geological Survey are useful for evaluating past events and for identifying trends and changes in rock fall behavior. The cliffs below Glacier Point experienced limited rock fall activity until 1996 when a spectacular rock fall with its resulting air blast leveled trees causing numerous injuries to tourists and one fatality. As additional rock falls caused more injuries and another fatality in the months and years that followed, scientific evidence grew linking the increased rock fall activity to redevelopment of land along the Glacier Point rim and to wastewater disposal associated with the revitalized visitors' facilities. Yosemite National Park dismisses the evidence and conclusions citing, among other things, a belief that wastewater is insignificant compared to natural precipitation and snowmelt. Some of the scientific and engineering facts are presented.