Land forms on the coast are created or formed as a
result of wave processes such as corrasion/abrasion, hydraulic, solution and
attrition. These processes erode the coast and the material is transported and
deposited along the coastline. As a result of these processes affecting the
coastline, a number of landforms are created. We can categorize the landforms
into two categories: features of erosion and features of deposition.
Features of erosion include cliffs, notches, wave-cut platforms, stacks and headlands
and bays, caves, arches. While features of deposition include beaches, spits,
tombolos, bars, etc.
The diagram below show features typical to coastal
erosion. There are cliffs, caves headland, etc. The waves attack the weak areas
of the rock and leave the resistant areas to form the different features.
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| Coastal Landforms |
Cliffs,
Notches and Wave-cut Platforms
Cliffs are steep rocky faces, often
nearly vertical facing the sea. Some are often high depending on the height of
the land forming the coast. A cliff is formed as the waves erode the base of
the coast and forms a wave-cut notch. After years of erosion, the notch gets
deeper and deeper until the overlying cliff can no longer supports it own
weight and collapses.
As the erosion continues, a wave cut notch or notch is cut into the base of the cliff. The
notch is either created by wave action or by bioerosion.
Cliffs undercut by notches may eventually collapse
and the shoreline will recede (go back) inland to form a wave-cut platform. Wave-cut platforms are usually scraped and
smoothed by abrasion. At high tide the platform is covered and is seen at low
tide.
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| Diagrams showing how cliffs, notches and wave-cut platforms are formed. |
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| Diagram showing how cliffs, notches and wave-cut platforms are formed. |
Headlands
and Bays
Along
the coastline, all areas are not vulnerable to erosion. Some areas of land that
juts out into the ocean come under attack by waves more than indented areas.
These points are called headlands and the indented areas between two headlands
are called bays. A headland is a
section of rocky coastline that protrudes into the sea while a bay is an indentation in the coastline
usually found between two headlands. Headlands are formed when the presence of
hard and soft rock line the coastline.
Erosion occurs at different rates, that is, the soft rock eg. shale is
eroded faster than the harder, resistant rock eg. chalk. Where the more
resistant harder rock is left it sticks out into the sea forming a headland and
where the erosion of the soft rock is fast, it forms a bay.
Caves,
Arches, Stacks and Stumps
In a headland, processes of erosion are usually active
where there are joints or faults. Wave energy work on these areas and gouge or
hollow them out to form caves. In due course, the erosion may lead to two back
to back caves breaking through the headland, forming an arch. Gradually, the
arch is enlarged by erosion and weathering. Eventually, the roof collapses and
forms a pillar of rock called a stack. The stack is then eroded and shrinks to
form a stump.
Read More: Caves occur
when waves force their way into cracks in the cliff face. The water contains
sand and other materials that grind away at the rock until the cracks become a
cave. Hydraulic action is the
predominant process. If the cave is formed in a headland, it may eventually
break through to the other side forming an arch. The
arch will gradually become bigger until it can no longer support the top of the
arch. When the arch collapses, it
leaves the headland on one side and a stack (a tall
column of rock) on the other. The stack will be attacked at the base in the
same way that a wave-cut notch is formed. This weakens the structure and it will
eventually collapse to form
a stump. One
of the best examples in Britain is Old Harry Rocks, a stack found off a
headland in the Isle of Purbeck.
RETRIEVE FROM>>>http://www.bbc.co.uk/schools/gcsebitesize/geography/coasts/erosional_landforms_rev3.shtml
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| Diagram showing the formation of caves, arches, stacks and stump. |
