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Volume 28 Issue 8 (August 2018)

GSA Today

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Article, pp. 28–29 | Full Text | PDF (1.9MB)


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Rapid 3-D analysis of rockfalls

Greg M. Stock1, Antoine Guerin2, Nikita Avdievitch1, Brian D. Collins3, Michel Jaboyedoff2

1 National Park Service, Yosemite National Park, El Portal, California 95318, USA
2 Risk Analysis Group, Institute of Earth Sciences, University of Lausanne, Lausanne, Switzerland
3 U.S. Geological Survey, Menlo Park, California 94025, USA


On the afternoon of 27 Sept. 2017, thousands of visitors to Yosemite National Park were enjoying scenic attractions in Yosemite Valley. Dozens of rock climbers were scaling El Capitan, a 900-m-tall granitic cliff famous for its challenging climbing routes. Suddenly, at 13:51 Pacific Standard Time (PST), a rock slab detached from 230 m up the southeast face of El Capitan. Tragically, rock debris struck two rock climbers walking along the base of the cliff, killing one and seriously injuring the other. Over the next three hours, as the park’s search and rescue team worked to extract the climbers, six more rockfalls originating from the new scar pummeled the base of the cliff. The following afternoon at 14:21 PST, a much larger rockfall occurred from the same location. A massive slab fell from just above the previous day’s rockfalls, fragmenting on impact and generating an enormous dust cloud (Fig. 1). A rock fragment struck a vehicle, puncturing the sunroof and injuring the driver, prompting temporary closure of the main road exiting Yosemite Valley. To manage these challenging events, the National Park Service (NPS) had a critical, immediate need for quantitative information regarding the sequence of events and the potential for additional rockfalls.

Manuscript received 17 April 2018. Revised manuscript received 10 May 2018. Manuscript accepted 11 May 2018. Posted 12 June 2018.

©2018, The Geological Society of America. CC-BY-NC.