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Characterization and dynamic analysis of the Devils Castle rock avalanche, Alta, Utah


Rock avalanches are large-magnitude mass movements with high mobility and fluid-like runout; however, because of their scarcity, little information is typically available to describe the hazard posed by these events. Geologic records thus provide key data regarding rock avalanche size, timing, and dynamics. Here we present a detailed case history analysis of the Devils Castle rock avalanche located near the town of Alta in the Wasatch Mountains of Utah. The deposit is approximately 1.5 km in length with a Fahrboeschung angle of 14 degrees (height-to-length ratio = 0.25). Through topographic reconstruction, we calculated a deposit volume of 1.7 million m (super 3) with a maximum thickness of 25 m and an average thickness of 7 m. Cosmogenic surface exposure dating of six deposit boulders indicates a failure age of 14.4 + or - 1.0 ka. The Devils Castle headwall displays no obvious evidence indicating precise source location and geometry; therefore, we reconstructed two plausible source volumes and performed numerical runout simulations for each. Results agree well with mapped deposit boundaries for both source scenarios; however, the east source model better represents material and dynamic characteristics of the deposit observed in the field. While the region is seismically active, the Late Pleistocene age for the rock avalanche precludes ascribing direct correlation with any currently known surface-rupturing paleoearthquakes. We identified and describe five similar events in the region highlighting the extent of the potential hazard. Individual case history analyses such as this allow us to better understand the processes and controls of large-scale mass movements in the region.

ISSN: 1078-7275
EISSN: 1558-9161
Coden: ENGEA9
Serial Title: Environmental & Engineering Geoscience
Serial Volume: 26
Serial Issue: 2
Title: Characterization and dynamic analysis of the Devils Castle rock avalanche, Alta, Utah
Affiliation: University of Utah, Department of Geology and Geophysics, Salt Lake City, UT, United States
Pages: 201-215
Published: 20200121
Text Language: English
Publisher: Geological Society of America, Association of Engineering Geologists, College Station, TX, United States
Number of pages: 16
References: 65
Accession Number: 2020-061294
Categories: Environmental geologyEngineering geology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 3 tables, geol. sketch maps
N40°34'00" - N40°34'60", W111°37'60" - W111°35'60"
Secondary Affiliation: Utah Geological Survey, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2020, American Geosciences Institute. Abstract, Copyright, Association of Engineering Geologists and the Geological Society of America. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 202038
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