Feedback thresholds between coastal retreat and landslide activity

Erosive processes have long been considered an important control on landslide activity in coastal environments. Despite its importance and numerous coastal failures in recent years, there has been limited quantitative characterization of the feedbacks between coastal erosion and the commensurate advance of active landslides. Quantitatively understanding the role of erosion as a control on the advance of coastal landslides is imperative from both hazard assessment and geomorphic perspectives, particularly considering future projections of increased erosion from sea level rise. Using a three-dimensional slope stability model coupled with a mass conserving finite difference analysis, we constrain landslide advance in response to erosion and evolving landslide geometry. We identified an inversely proportional relationship between landslide volume and magnitude of advance for a given level of toe retreat. Landslide aspect ratio and geometry may exert a second-order control on sensitivity of advance to coastal erosion. Further, in comparison to observed landslide advance of three well-characterized landslides in Oregon, the proposed relationships provide insights towards the relative importance of erosion versus other disturbances, such as groundwater rise. Our findings provide insight towards the dynamics of landslides in coastal environments to advance regional coastal landslide hazard and risk assessments.