Sunamura summarized the relationship between cliff erosion and cliff resistance. Weather patterns, sea-level fluctuations, composition of the cliff, and structural dip of the cliff strata control land loss along sea cliffs. Emery and Kuhn , among others, have noted that cliff retreat occurs frequently in the winter in association with storms and high rainfall.
Human activities such as watering lawns and draining septic tanks can artificially increase ground-water levels and either initiate or aggravate slumping at the face of the cliff. Cliff retreat is not necessarily catastrophic and there are many physical and chemical processes that can cause sediment to gradually accumulate in rock debris slopes. An understanding of these processes is important to avoid conducting any activity that would increase slope instability or be ineffective in controlling landslides.
For example, seawalls are commonly constructed on the beach at the bases of sea cliffs to stop slumping when the processes causing the slumping are acting at the top or within the cliff. Skip to main content Skip to table of contents. This service is more advanced with JavaScript available. Beaches and Coastal Geology Edition. Contents Search. Cliff erosion. Authors Authors and affiliations Andrew D. Rockfall occurs when rocks are broken down by freeze-thaw weathering, this loosened material is vulnerable to the elements.
If the rock is at the top of a steep cliff face, it can fall directly to the shore. This can occur more so when a wave cut notch is created at the foot of the cliff by wave action, causing the overhanging rock to be unsupported and more likely to fall. Soil creep is a process operating at the granular scale. It happens on gentle slopes and is noticeable from the wavy surface it produces. Damp soil moves very slowly down the slope as the weight of water pushes it forwards. Rain splash may release soil grains that fall further downslope.
Landslides arise when rocks and unconsolidated material on the cliff face are saturated with water rain or wave-splash. Eventually the material slips down the slope. Stage 1 — the soft boulder clay holds rainwater and run-off. Stage 2 — Waves erode the base of the cliff creating a wave-cut notch. The clay becomes saturated and forms a slip plane. 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. In areas of more resistant cliff material erosion is greatest when waves break at the foot of a cliff.
This causes erosion at the base of the cliff. This creates a wave-cut notch in the base of the cliff. As the notch increases in size, the weight of the cliffs above become too much to support which leads to a landslide. This material will provide temporary protection for the cliff behind. However, once it has been removed by the sea this process will occur again.
Where cliffs are made of more resistant material, wave-cut platforms will be created. An annotated diagram showing the main features of a landslide.
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