Mass Movement is the downhill movement of cliff material under the influence of gravity. There are a range of different types of mass movement. These are explored below.
Slumping / Rotational Slip
Cliffs formed from boulder clay, material deposited by glacial periods, are susceptible to high rates of coastal erosion. The Holderness Coast is an example of a coastline formed from boulder clay and is the fastest eroding coastline in Europe. The soft boulder clay is quickly eroded through hydraulic action and abrasion. However this is not the only way it is being eroded. Sub-aerial processes, such as rainfall, also cause erosion. This often happens where layers of boulder clay, left behind by melting glaciers, become saturated and cause the cliff to slump. The debris on the beach is then eroded by the sea leaving the cliff exposed once more.
Stage 1 – the soft boulder clay holds rainwater and run-off.
Slumping stage 1
Stage 2 – Waves erode the base of the cliff creating a wave cut notch. The clay becomes saturated and forms a slip plane.
Slumping stage 2
Stage 3 – The weight of the saturated cliff causes it to slump.
Slumping stage 3
The video below shows evidence of slumping at Mappleton, Holderness Coast. The video shows the early stages of the process. Water will percolate down the large crack to lubricate the slip plane. This will cause the land to slump further down.