At present, the most widely accepted hypothesis for the transition from mudsliding to deep-seated rotational slipping as the dominant agent of mass transport in actively eroding clay cliffs is that the transition depends on the rate of marine erosion at the toe of the slope. This paper explores an alternative theory, that the transition from one type of behaviour to another depends largely on the nature of the materials at the crest of the slope and to a lesser, but still important, extent on the groundwater hydrology.
The main argument behind this alternative theory is that the presence of stronger soil strata at the crest of the slope inhibits the mudslide behaviour that would otherwise occur and hence form a toe-protecting ‘mudslide barrier’. This allows marine action to erode the toe of the slope directly, causing it to be oversteepened, and ultimately precipitates a deep-seated rotational landslide. Where the coastal cliffs are capped with thick, hard and jointed caprock the slides tend to be of the multiple rotational kind.