The Impact of Structure and Lithology on Coastal Landforms

The Impact of Structure and Lithology on Coastal Landforms

"Use examples to explain how the combined impacts of structure and

lithology affect coastal landforms"

With a combination of both structure and lithology, the coastal

landforms are easily affected. Both structure and lithology affect:

- The coastline in plan

- The coastline in profile and

- The distribution of micro features

The coastline in plan

The coastline in plan is mainly determined by structure. It determines

the coastal pattern of headlands, bays, islands and inlets found along

the coast. These are formed by differential erosion which means the

sea waves erode softer rock quicker than the harder and in time the

softer rock is worn away forming gaps in the coastline as we

understand and call coves or bays (Lulworth cove). When eventually the

hard rock is eroded, it can cause an island of hard rock left of the

main land. A key example of this is the needles off the coast of the

island of Wight (see picture beneath).

Needles formed by softer rock being eroded away leaving the hard rock

[IMAGE][IMAGE] The Needles

Lulworth cove was formed by softer rock being eroded back whereas the

hard rock is still prominent.

Lulworth Crumple at Stair Hole

The coastline in section

The main cause of differentiations in cliff profiles and shore

platforms are mostly depicted and dependent on the rock lithology. The

main cause of differentiations of cliff profiles are mainly down to

the fact that certain cliffs erode slower due to the rock types they

consist of. The rock types can affect the rate in which the cliff

erodes and so can many other factors including:

- Salt weathering

- Mechanical wave erosion aided by abrasion (pebbles)

- Bio erosion by boring organisms

- Chemical weathering

- The type of wave reaching the shore

Hard rocks such as granite will erode at a slower rate than soft rocks

and the result of this erosion is that it produces high steep cliffs