Feedback Between Coastal Erosion Processes And Landslide Activity On The Oregon Coast

Erosive processes have long been considered a forcing component on the activity of landslides, although there has been limited quantitative characterization of the feedbacks between the processes that result in erosion or retreat of seacliffs. Considering the impacts of global environmental changes, it is critical characterize the feedbacks between these erosional processes and landslide activity now. Through this, we are better-positioned to understand (1) what geomorphic factors dictate controls on coastal landslide activity - precipitation, erosion or some combination, (2) how changes in forcing conditions may amplify landslide activity in the coastal environment, and (3) how these changes may alter coastal landslide activity.

Quantifying the velocity, volume, and kinematics of coastal slow-moving landslides is crucial for hazard prediction and landscape evolution. We assess the sensitivity of coastal instability with observed seasonal oscillations of erosional processes and groundwater changes to investigate and isolate the relative influence of each destabilizing process. These analyses are performed using a simple and widely applicable methodology, which constrains landslide 3D deformation through a conservation of mass approach, where activity is defined by evolving three-dimensional slope stability analyses subject to evolving landslide and seacliff geometry over time. Using data from repeat lidar acquisitions of seacliff erosion, we estimate the rate and exposure of seacliff erosion and bracket the evolution of landslide activity under a range of conditions.

A focus is placed on the Arizona Inn landslide, a coastal landslide located on southern Oregon coast. The rate of landslide advance and its potential for constant movement related to the hydrological triggering factors has been previously investigated, but the landside sensitivity to toe erosion is not well-quantified. Albeit the sensitivity to pore-water pressures oscillations is usually found as a primary driver for landslide movements at the site, there is significant, non-linear sensitivity to erosion rate. These conditions are of paramount importance, as increasingly extreme storm events may magnify landslide activity in coastal environments not just from precipitation, but localized erosion and undercutting.