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Surface roughness dating of long-runout landslides near Oso, Washington (USA), reveals persistent postglacial hillslope instability

Sean Richard LaHusen, Alison R. Duvall, Adam M. Booth and David R. Montgomery
Surface roughness dating of long-runout landslides near Oso, Washington (USA), reveals persistent postglacial hillslope instability
Geology (Boulder) (February 2016) 44 (2): 111-114

Abstract

Establishing regional landslide chronologies is necessary to advance from hazard recognition to risk assessment, and to understand the evolution of landslide-prone terrain. Despite recent advances in landslide mapping due to the availability of high-resolution lidar imagery, estimating the timing of slope failures remains a challenge. Here we present a new integrated approach to dating landslides on a regional scale by augmenting quantitative surface roughness analysis with radiocarbon dating and numerical landscape modeling. We calibrate a roughness-age curve, which we use to date 25 deep-seated landslides in glacial sediment surrounding the catastrophic A.D. 2014 Oso landslide along the North Fork Stillaguamish River in Washington State (USA). Lidar bare-earth images show a high density of long-runout landslides in this region. Using our roughness-age curve, we estimate an average Holocene landslide frequency of 1 every 140-500 yr, and show that the 2014 Oso landslide was the latest event in an active history of slope failures throughout the Holocene. With each landslide, substantial sediment is delivered to the North Fork Stillaguamish River, driving shifts in the active channel that ultimately affect the pattern of landslides across the valley. The high frequency of landslides in this area, where river incision and isostatic uplift rates have dropped dramatically since peaking soon after ice retreated from the region, shows that landscapes inundated by glacial sediment do not require dramatic changes in base level to remain highly unstable for tens of thousands of years.


ISSN: 0091-7613
EISSN: 1943-2682
Coden: GLGYBA
Serial Title: Geology (Boulder)
Serial Volume: 44
Serial Issue: 2
Title: Surface roughness dating of long-runout landslides near Oso, Washington (USA), reveals persistent postglacial hillslope instability
Affiliation: University of Washington, Department of Earth and Space Sciences, Seattle, WA, United States
Pages: 111-114
Published: 201602
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 28
Accession Number: 2016-025670
Categories: Quaternary geologyGeochronology
Document Type: Serial
Bibliographic Level: Analytic
Annotation: GSA Data Repository item 2016029
Illustration Description: illus. incl. geol. sketch maps
N48°16'00" - N48°16'60", W121°52'00" - W121°50'60"
Secondary Affiliation: Portland State University, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 201613
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