20. Bluff erosion and land loss tends to be episodic. Eroding bluffs tend to follow a cycle of toe erosion (A to B), with sediment removed by waves, coastal flooding, and tidal action. Toe erosion can lead to minor slumps and soil loss across the surface of the seaward face of the bluff. Prolonged undercutting can lead to internal movement underground (B to C) which results in a landslide. Landslides involve the internal failure of a thick sequence of sediments that lack sufficient strength to rise above the sea. Some landslides are small and involve a single block and others can involve a sequence of blocks that slide and rotate on several curved planes of failure (black lines in C). Sediment that moves out across the intertidal zone leaves an uneven surface, often covered with terrestrial vegetation, that subsequently comes under wave and tidal scour (C to D). The landslide toe can be gradually eroded over years to decades as sediment is washed away and deposited in other tidal flats or below the low tide line (D to A). Depending on the scale of the mass movement and the strength of coastal processes, the cycle can take years to be completed. Sometimes shorelines adjacent to landslides become more unstable after a landslide has occurred nearby. So shoreline instability may propagate along the coast after a landslide. (Graphic from MGS Coastal Landslide Hazards map; modified from Kelley and others, 1989)