Rain, waves, and short-term evolution of composite seacliffs in southern California

A four-year time series of nine airborne LiDAR surveys were used to assess the roles of wave attack and rainfall on the erosion of 42 km of southern California seacliffs. Nine continuous seacliff sections, separated by coastal lagoon mouths, all show maximum seacliff erosion in the rainiest time period (when wave energy was not particularly elevated), and in most sections the squared correlations between rainfall and erosion time series exceeded 0.8. Although rain and associated subaerial mechanisms such as groundwater seepage triggered most of the observed seacliff failures, wave attack accelerated seacliff erosion, with erosion rates of cliffs exposed to wave attack five times higher than at adjacent cliffs not exposed to waves. The results demonstrate the importance of both waves and rain in the erosion of southern California seacliffs and suggest that the combined influences of marine and subaerial processes accelerate the erosion rate through positive feedbacks.