by Geological Society of America, June 28, 2018 in ScienceDaily
On 27 and 28 September 2017, eight large rockfalls occurred from the southeast face of El Capitan. These rockfalls resulted in one fatality and two serious injuries, and spurred a complicated rescue and temporary closure of the main road exiting Yosemite Valley. In order to manage these challenging events, the National Park Service (NPS) had a critical, immediate need for quantitative information about the sequence of rockfalls and the potential for additional activity.
Using new “structure-from-motion” photogrammetry techniques in conjunction with baseline laser-scanning data, scientists from the NPS, the U.S. Geological Survey, and the University of Lausanne, Switzerland rapidly analyzed these rockfalls. By comparing 3-dimensional (3D) models of the cliff before, during, and after the rockfalls, the researchers were able to pinpoint the exact locations, dimensions, and volumes of the rockfalls, along with the spatial and temporal pattern of their progression up the cliff.