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Chalk is a soft, white, porous, sedimentary carbonate rock.It is a form of limestone composed of the mineral calcite and originally formed deep under the sea by the compression of microscopic plankton that had settled to the sea floor.
Physical weathering, also called mechanical weathering or disaggregation, is the class of processes that causes the disintegration of rocks without chemical change. Physical weathering involves the breakdown of rocks into smaller fragments through processes such as expansion and contraction, mainly due to temperature changes.
Cliffs are usually composed of rock that is resistant to weathering and erosion. The sedimentary rocks that are most likely to form cliffs include sandstone, limestone, chalk, and dolomite. Igneous rocks such as granite and basalt also often form cliffs.
Such erosion landscapes are known as karsts. Limestone is less resistant to erosion than most igneous rocks, but more resistant than most other sedimentary rocks. It is therefore usually associated with hills and downland, and occurs in regions with other sedimentary rocks, typically clays. [85] [86]
Coastal erosion may be caused by hydraulic action, abrasion, impact and corrosion by wind and water, and other forces, natural or unnatural. [3] On non-rocky coasts, coastal erosion results in rock formations in areas where the coastline contains rock layers or fracture zones with varying resistance to erosion.
The chalk outcrop at Flamborough Head in the north produces a headland relatively resistant to coastal erosion whilst the coastline south of this at such places as Mappleton and Hornsea with their soft glacial deposits are vulnerable.
On a cliffed coast made up of material which is only fairly or even hardly resistant to erosion no wave-cut platform but a beach is formed in front of the sea cliff. If waves carve notches at a narrow point on both sides of a promontory on the rocky cliffed coast, a natural arch may be formed. [ 4 ]
Forming the back of the cove is a 250-metre-wide (820 ft) band of chalk, which is considerably more resistant than the clays and sands, but less resistant than the limestones. The entrance to the cove is a narrow gap in the limestone bands, formed by wave action and weathering. The wide part of the cove is where the weak clays and greensands ...