Dynamics and legacy of 4.8 ka rock avalanche that dammed Zion Canyon, Utah, USA

GSA Today

Jeffrey R. Moore³  Jessica J. Castleton³  Susan Ivy-Ochs²  Jordan Aaron¹  Marcus Christl² 

[1] University of British Columbia, Dept. of Earth, Ocean and Atmospheric Sciences, 2020-2207 Main Hall, Vancouver, Canada V6T 1Z4$$;Laboratory of Ion Beam Physics, ETH Zurich, Otto-Stern-Weg 5, 8093 Zurich, Switzerland$$;University of Utah, Dept. of Geology and Geophysics, 115 South 1460 East, Salt Lake City, Utah 84112, USA$$

关键词: Fire safety;    fatal fires;    smoke alarms;   

DOI  :  10.1130/GSATG269A.1

学科分类：地质学

来源: Geological Society of America

【 摘 要 】

The Sentinel rock avalanche blocked the mouth of Zion Canyon,Utah, USA, over a distance of 3.3 km and created a large lake that filled the canyonfloor with sediment, transforming this iconic desert landscape. However, key questionsremain regarding the size, timing, and dynamics, as well as the geomorphic effectsof this prominent landslide. Reconstructing topography before and after the failure,we calculate an original deposit volume of 286 million m3 with maximumthickness of 200 m. New cosmogenic nuclide surface exposure ages of 12 bouldersfrom across the deposit reveal a mean age of 4.8 ± 0.4 ka and are consistent withsingle-event emplacement. Results of 3D numerical runout simulations agree wellwith mapped deposit boundaries and thickness, affirming our hypothesized failurescenario and indicating an average runout velocity of 50 m/s. Following partialbreach of the landslide dam, we estimate that water levels stabilized for ~700 yruntil the lake filled with sediment. Deposited lacustrine clays reveal a periodwhen Zion Canyon was filled by the 3 km2 Sentinel Lake extending morethan 7 km upstream. Today the Virgin River incises alluvial and lacustrine depositsstill stranded behind remnants of the rock avalanche dam, attesting to the long-lastinggeomorphic and ecological impacts of large landslides in steep desert landscapes.

【 授权许可】

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