Process-based Empirical Prediction of Landslides in Weakly Lithified Coastal Cliffs

ABSTRACT: Coastal landslides in weakly lithified sediment are a common occurrence in many parts of the world, including the west coast of the United States. Here, geologically young (Quaternary), marine terrace deposits form steep, near vertical cliff exposures up to 30 m in height and extend for many kilometers along the coastlines of the states of California, Oregon, and Washington. A comprehensive research study begun in 2001 documented and monitored the effects of winter storms on several sections of cliff south of San Fran-cisco, California, USA. We present the results of five seasons (2001-2006) of weekly observations of these cliffs, documenting failure occurrences, modes, and mechanisms along a 1.5 km stretch of coast, and correlate these with storm event precipitation totals and storm-induced ocean wave run-up heights. We utilize the re-sults of the correlations to outline thresholds for the likelihood of cliff failure in order to form a process-based, short-term, methodology for landslide prediction. The methodology is generalized for long-term (de-cadal) predictions of landslide occurrence based on rates of sea-level rise, and possible changes in precipita-tion.