Coastal Landscape Notes

Página 1

Cliffs

One of the most common features of a coastline is a cliff. Cliffs are shaped as a result of erosion and weathering.

Steep cliffs are formed where the land consists of hard, more resistant rock - such as chalk. The hard rock weathers and erodes slowly.

Igneous rocks such as granite and basalt from rugged vertical cliffs - such as those found along the Cornish Atlantic coast. Granite can withstand the constant pounding from the Atlantic storm waves.

If cliffs are steep, the removal of material at its base is greater than the supply.

Sedimentary rocks have been laid down in distinct layers - strata - and this may dip towards or away from the sea.

Softer rocks, such as clay and shale, erode and weather more easily and therefore create gentle sloping cliffs. Sub-aerial processes can contribute more to erosion than marine processes, leading to mass movements such as sliding, slumping and falls.

If cliffs are shallow, the supply of material is greater than the removal.

UNDERCUTTING, COLLAPSE, RETREAT.

Process

1) Weather weakens the top of the cliff

2) The sea attacks the base of the cliff forming a wave-cut notch.

3) The notch increases in size causing the cliff to collapse.

4) The backwash carries the rubble towards the sea forming a wave-cut platform

5) The process repeats and the cliff continues to retreat.

Página 2

Shore Platforms (Wave-cut Platforms)

Wave cut notches are small indents at the base of cliffs, formed when the wave is undercut by the sea. When waves break on cliffs, all the energy is focused to one point and therefore the cliff experiences erosion - corrosion. As the cliff is being undercut, a wave cut notch will start to form. The section above the wave cut notch will start to hang over - however will eventually collapse.

The process will repeat and eventually the cliff will being to 'retreat'.

As the cliff retreats, a gentle platform is left behind. It is heavily scarred due to the erosion from transportation of rock across it.

The platform typically has a gradient of less than 4 degrees, therefore it is only fully exposed at low tide. As the platform grows, the waves will have to travel further to reach the cliff - therefore the will lost more and more of their energy. Waves tend to break earlier before they can erode the cliff. This reduces the amount of erosion the waves can perform on the cliff.

Shallow water causes the waves to drag, therefore waves will break further out. This leads to the undercutting, collapsing and retreating process to stop.

Página 3

Bays and Headlands

Headlands are formed when the sea attacks a section of the coast with alternating sections of soft and hard rock.

The bands of soft rock, containing sand and clay, erode more quickly that those of a more resistant rock such as chalk.

Therefore the areas of hard rock are left sticking out - headlands.

The areas of soft eroded rock are called bays.

Geology is the study of the types of rocks that make up the earths crust. Coastlines, where the geology alternates between strata of hard and soft rock are known as discordant coastlines.

A concordant coastline has the same type of rock along - however along its length. Therefore concordant coastlines tend to have fewer bays and headlands.

As the bay starts to develop, wave refraction occurs around the headlands - increasing the erosion of headlands by reducing the development of the bay due to loss of energy.

Sun-aerial weathering, such as corrosion, begins to weather the bay - furthering its development.

Bays are sandy because wave refraction and longshore drift push sediment into them.

Página 4

Geos and Blowholes

A blowhole forms in a cave. As the cave moves inland, the roof above is weakened and therefore caves crash into the cave and can be reflected up on the roof causing erosion. At the same time, weathering on the roof will also help weaken the structure therefore water will eventually be able to breakthrough - causing a blowhole.

Where erosion hollows out enough material along a wave cut platform, a steep sided inlet called a geo may form.

Página 5

Caves, Arches, Stack and Stumps.

Caves occur when waves force their way into cracks in the face of the cliff. The water contains sand and other materials that wear away the rock until it cracks - resulting in a cave. Corrosion and hydraulic action are the two main processes which cause this development.

It the cave is formed in a headland, it may eventually wear away and break through to the other side - forming an arch. The arch will eventually become bigger until no more material can support the top of the arch. This makes the roof of the arch vulnerable to weathering such as salt crystallisation and biological weathering.

When it collapses it leaves the headland on one side, and a stack on the other.

The stack will be attack at the base - in the same way that a wave-cut notch is formed. Therefore the structure is weakened and eventually the stack will collapse and form a stump.