The Hooskanaden Landslide: historic and recent surge behavior of an active earthflow on the Oregon Coast
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Stefano Alberti I Andrew Senogles I Kara Kingen I Adam Booth I Pete Castro I Jill DeKoekkoek I Kira Glover-Cutter I Curran Mohney I Michael Olsen I Ben Leshchinsky
The Hooskanaden Landslide: historic and recent surge behavior of an active earthflow on the Oregon Coast
Abstract This paper presents an analysis of the Hooskanaden Landslide, an earthflow, which experienced a dramatic surge event beginning on February 24, 2019, closing US Highway 101 near mile point 343.5 for nearly 2 weeks. This ~ 1 km long surge event resulted in horizontal displacements of up to 45 m and uplift of 6 m at the toe located on a gravel beach adjacent to the Pacific Ocean. The Hooskanaden Landslide, likely active since the eighteenth century, exhibits regular activity with a recurrence interval of major surge events of approximately every 20 years, transitioning from slow to relatively rapid velocities. During the 2019 event, maximum displacement rates of approximately 60 cm/ h were observed, slowly decreasing to 15 cm/h for a sustained period of approximately 2 weeks before the eventual return to baseline conditions (< 0.02 cm/h). Keywords Landslide . Earthflow . Surge . Landslide activity Introduction Landslides have major environmental, economic and social impacts worldwide (e.g., Clague et al. 2012; Froude and Petley 2018). Between 2004 and 2016, 4862 fatal landslides were recorded, resulting in a total of 55,997 fatalities (Froude and Petley 2018). The United States Geological Survey estimates that landslides cause 25–50 deaths and $3.5 billion in damage on an annual basis within the US (USGS 2004). Regionally, the coastal mountain ranges of California, Oregon, and Washington experience some of the most frequent and expansive landslide activity owing to frequent storms, steep terrain, and weak lithologies (e.g., USGS 2004; Wilson and Fischetti 2010; Booth and Roering 2011; Roering et al. 2015). With approximately 32 million people living along the Pacific coastline in the USA, these coastal landslides result in major economic and social impacts due to frequent road closures that can hinder commerce and isolated communities (WAlbritton and Dokken 2001; Leshchinsky et al. 2018). Given the magnitude of many of these slope failures, direct countermeasures such as avoidance are often economically infeasible due to lack of available right-of-way and/or harsh terrain. Characterizing mechanisms and timing of coastal landslides is an essential first step towards managing the extent of the impacts of these failures (Leshchinsky et al. 2017; Francioni et al. 2018). Coastal landslides occur in response to a variety of disturbances and are highly dependent on localized environmental conditions and litho-structural predisposition (Hungr et al. 2014). The Oregon Coast is scattered with hundreds of large active landslides (Leshchinsky et al. 2018) that may be categorized as earthflows or compound failures (Hungr et al. 2014), both of which are associated with thin-bedded, weak lithologies, significant winter precipitation, and intensive sea cliff e
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