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Half Dome, Yosemite National Park

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Rockfall Year in Review: 2008

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avatar Rockfall Year in Review: 2008
January 12, 2009 04:39PM
Rockfall dramatically influenced human activities in Yosemite Valley in 2008. By far the largest and most consequential rockfalls of 2008 occurred on October 7 and 8 from above the Ledge Trail near Glacier Point. Repeat laser mapping revealed the total volume of these rockfalls to be 5738 cubic meters (17,080 tons). Though not particularly large by Yosemite standards (for comparison, the July 10, 1996 Happy Isles rockfall was about 5 times larger, and the March 10, 1987 Middle Brother rockfall was more than 100 times larger), the October 7 and 8 rockfalls were consequential because of their proximity to Curry Village. Occupied cabins were extensively damaged by rockfall debris and three minor injuries resulted. A comprehensive geologic assessment led to the permanent closure of nearly 300 buildings in the Curry Village area. The other area of notable rockfall in 2008 was El Capitan, where a ~35 cubic meter (104 ton) rockfall occurred from low on the southeast face on July 7, and a ~80 cubic meter (238 ton) rockfall occurred from high on the southwest face on November 4. Other areas experiencing rockfalls in 2008 included Yosemite Falls, Middle Cathedral, the Four Mile Trail, Middle Brother, Washington Column, and Basket Dome. In all, there were 37 documented rockfalls in 2008, with an approximate cumulative volume of 6385 cubic meters (19,003 tons).

It is very likely that there were additional rockfalls in 2008, but these events either were not witnessed or went unreported. If you witness a rockfall of any size, please contact park geologist Greg Stock at (209) 379-1420, or at greg_stock@nps.gov. Predicting rockfalls is not yet possible, but understanding the events that do happen is an important step toward this goal.

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