The debris on the beach is then eroded by the sea leaving the cliff exposed once more. An annotated diagram showing the main features of slumping. 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.
The image below shows a landslide at West Bay , Dorset. A rockfall involves fragments of rock breaking away from the cliff face, often due to freeze-thaw weathering. An annotated diagram showing the main features of a rock fall. This is when salt crystals are deposited in cracks and over time the salt accumulates and applies pressure to the crack similar to freeze-thaw weathering.
Wetting and drying is common along coastlines. Clay-rich rocks are prone to expand when they are wet and contract when they dry. This results in cracks which are vulnerable to both freeze-thaw and salt crystallisation. Biological weathering is mechanical when there is a physical effect. An example of this is when growing plant roots widen cracks as does the leverage created by bushes and trees swaying in strong winds.
Burrowing animals and nesting birds excavate material in partially weathered and eroded cliffs. Chemical weathering involves decomposition of rocks literally, changing the minerals. Chemical weathering occurs as a result of a weak chemical reaction between water and rock.
Rainwater mixed with carbon dioxide in the atmosphere forms Carbonic acid. This then reacts with calcium carbonate in limestone to form calcium bicarbonate. Bicarbonate is soluble in water and the limestone gets weathered when carbonation occurs. Mass movement is the movement of material downslope as the result of gravity. This can be a slow process in the case of soil creep or fast in the case of rockfalls.
Water commonly acts as a lubricant in mass movement. Soil creep is a slow but continuous process. It typically occurs on most slopes over 5 degrees. Soil creep rarely exceeds speeds of 1cm per year.
Creep occurs as the result of repeated expansion and contraction of material. Cycles of freeze-thaw heave particles upon freezing and allow them to fall further downslope when the ice melts. Alternating hydration and dehydration have the same effect.
Earth flows tend to be faster than slow creep but less sporadic. The slope material liquefies and runs out, forming a bowl or depression at the head. The flow itself is elongate and usually occurs in fine-grained materials or clay-bearing rocks on moderate slopes and under saturated conditions.
However, dry flows of granular material are also possible. Company Reg no: VAT reg no Main menu. Subjects Shop Courses Live Jobs board. View shopping cart. View mytutor2u. Account Shopping cart Logout. Explore Geography Geography Search. Explore Blog Reference library Collections Shop. Share: Facebook Twitter Email Print page.
Rockfall Rockfall occurs when rocks are broken down by freeze-thaw weathering, this loosened material is vulnerable to the elements. Soil creep Soil creep is a process operating at the granular scale.
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