undercliff

The undercliff is that mass of rock jumbled at the base of a standing cliff, or it can be a subsidiary cliff formed by fallen material and then trimmed to a vertical profile by waves or other action: a slump of mud, or the collapse of eroded gullies on a cliff face. The action of waves against a sea cliff, or a soft lower stratum being eroded by wind or water faster than what lies above, can also lead to collapse. The undercliff is often an area of jumbled, tilted, slumped, and highly unstable material that protects the remaining cliff from further erosion.

Kim Stafford