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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.
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.
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.
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]
Since the flint is clearly more weathering- and erosion-resistant than the limestone, it collects on the beach of the chalk cliff and is transported to neighboring areas of the coast by waves and currents during storms and deposited there.
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 ]
Some are more resistant to weathering than the surrounding rock and stand up like walls, while others weather faster and form long narrow depressions. dip slope A geological formation often created by erosion of tilted strata. disconformity A surface that represents missing rock strata but beds above and below that surface are parallel to one ...
Weathering of the chalk has created a characteristic soil known as rendzina. [7] Unlike many soils in which there are easily distinguished layers or soil horizons , a chalk rendzina soil consists of only a shallow dark humus rich surface layer which grades through a lighter brown hillwash containing small pellets of chalk, to the white of the ...