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GEOREF RECORD

Landslides along the Winter Rim Fault, Summer Lake, Oregon

Thomas C. Badger and Robert J. Watters
Landslides along the Winter Rim Fault, Summer Lake, Oregon (in Volcanoes to vineyards; geologic field trips through the dynamic landscape of the Pacific Northwest, Jim E. O'Connor (editor), Rebecca J. Dorsey (editor) and Ian P. Madin (editor))
Field Guide (Geological Society of America) (December 2009) 15: 203-220

Abstract

The field trip guide describes nine stops that examine the mechanisms and timing of some of the abundant and often gigantic landslides that occur along the Winter Ridge-Slide Mountain escarpment in south-central Oregon. Subsidence of Summer Lake basin, situated in the northwestern Basin and Range Province, has exposed a kilometer-thick Neogene sequence of dense volcanic flow rocks overlying very weak tuffaceous sedimentary rocks in the bounding escarpment. Subsidence is accommodated on the 58-km-long Winter Rim fault system, a normal fault which is capable of producing Mw nearly equal 7 earthquakes with near-field, maximum horizontal acceleration approaching 1 g on the bedrock footwall. Gigantic rock slides cubic kilometers in volume scallop the southwestern portion of the escarpment, and their deposits run out as rock avalanches several kilometers onto the basin floor. Limit-equilibrium slope stability analyses support observations that these gigantic bedrock landslides initiate within the weak tuffaceous sedimentary rocks along shallow, east-dipping, planar failure surfaces one to two kilometers in length; are insensitive to groundwater fluctuations; and, are stable under static conditions. Strong ground motions appear requisite to trigger landsliding and are necessary to replicate the long, shallow failure surfaces. Landslide, colluvial, and lacustrine deposits on the hanging wall have undergone widespread post-emplacement deformation, which may involve large-scale seismogenic lateral spreading and flow sliding controlled by the saturated, fine-grained basin fill.


ISSN: 2333-0937
EISSN: 2333-0945
Serial Title: Field Guide (Geological Society of America)
Serial Volume: 15
Title: Landslides along the Winter Rim Fault, Summer Lake, Oregon
Title: Volcanoes to vineyards; geologic field trips through the dynamic landscape of the Pacific Northwest
Author(s): Badger, Thomas C.Watters, Robert J.
Author(s): O'Connor, Jim E.editor
Author(s): Dorsey, Rebecca J.editor
Author(s): Madin, Ian P.editor
Affiliation: Washington State Department of Transportation, Olympia, WA, United States
Affiliation: U. S. Geological Survey, Portland, OR, United States
Pages: 203-220
Published: 200912
Text Language: English
Publisher: Geological Society of America, Boulder, CO, United States
References: 44
Accession Number: 2010-060160
Categories: Geomorphology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. sects., sketch map
N42°42'00" - N43°00'00", W120°55'00" - W120°34'60"
Secondary Affiliation: University of Oregon, USA, United StatesOregon Department of Geology and Mineral Industries, USA, United StatesUniversity of Nevada, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2019, American Geosciences Institute. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 201033
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