Rockfall kinematics from massive rock cliffs: Outlier boulders and flyrock from Whitney Portal, California, rockfalls

Environmental and Engineering Geoscience
By: , and 

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Abstract

Geologic conditions and topographic setting are among the most critical factors for assessing rockfall hazards. However, other subtle features of rockfall motion may also govern the runout of rockfall debris, particularly for those sourced from massive cliffs where debris can have substantial momentum during transport. Rocks may undergo collisions with trees and talus boulders, with the latter potentially generating flyrock—launched rock pieces resulting from boulder collisions that follow distinctively different paths than the majority of debris. Collectively, these intricacies of rockfall kinematics may substantially govern the hazards expected from rockfall to both persons and infrastructure located beneath steep cliffs. Here, we investigate the kinematics, including outlier boulder and flyrock trajectories, of seismically triggered rockfalls on 24 June 2020 that damaged campground facilities near Whitney Portal, CA, a heavily used outdoor recreation gateway to the Sierra Nevada mountains. Our results, obtained in part by rockfall runout model simulations, indicate that outlier boulder trajectories resulted from opportunities provided by less steep terrain beyond the talus edge. The influence of trees, initially thought to have served a protective capacity in attenuating rockfall energy, appears to have been negligible for the large boulder volumes (>50 m3) mobilized, although they did potentially deflect the trajectory of flyrock debris. Rockfall outlier boulders from the event were comparable in volume and runout distance to prehistoric boulders located beyond the talus slope, thereby providing some level of confidence in the use of a single rockfall shadow angle for estimating future rockfall hazards at the site.

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Publication type Article
Publication Subtype Journal Article
Title Rockfall kinematics from massive rock cliffs: Outlier boulders and flyrock from Whitney Portal, California, rockfalls
Series title Environmental and Engineering Geoscience
DOI 10.2113/EEG-D-21-00023
Volume 28
Issue 1
Year Published 2022
Language English
Publisher Association of Environmental & Engineering Geologists
Contributing office(s) Geology, Minerals, Energy, and Geophysics Science Center
Description 22 p.
First page 3
Last page 24
Country United States
State California
Other Geospatial Whitney Portal
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