Erosional Landforms on the Dorset Coastline

Introduction

In this leaflet I am going to present my findings about different types of erosion, and at how they take effect different locations. The relevant locations that I have studied are part of the Dorset coastline. These are:

1. Lulworth cove, a bay created through millions of years of erosion.

2. Stairhole, a deep cleft that represents stage 1 of the evolution of the coastline.

3. Durdle door, an arch that will soon collapse and erode away.

Types of Erosion

Erosion is the gradual wearing away of land by water, wind and general weather conditions. The amount of erosion depends on the power of the waves and the rock type. The amount of energy acquired by waves depends upon the wind velocity, the duration of the wind and the distance over which the waves have traveled. This is known as the fetch.

There are two types of erosion that can occur at the coast, these are:

1. Sub-aerial processes (cliff face processes)- These are erosional processes that take place above sea level, affecting the parts of the coastal zone that are not directly influenced by the sea. The processes included in sub-aerial erosion are:

* Freeze-thaw

* Salt crystallization

* Chemical weathering

* Biological weathering

* Human Activity

* Mass movement

2. Marine processes (cliff base processes)- These are erosional processes that occur when the waves collide with the cliff face, these processes determine the main shape of the coast, but not all. The processes included in marine erosion are:

* Abrasion- the process by which small rock particles transported within the waves scour the rock surfaces over which and against which they are carried.

* Attrition- the process by which particles of rock carried by the sea are rounded by knocking into each other and reduced in size.

* Hydraulic Action- erosive action caused as waves force pockets of air into small gaps in the rocks surface where the pressure exerted breaks off small pieces and forces the crack wider.

* Corrosion- the process by which a chemical reaction occurs involving rocks such as chalk and limestone and sea water.

Lulworth Cove

Lulworth cove is a curved bay situated at the very bottom of the United Kingdom, on the Dorset coastline. It is well known for being one of the most well known stretches of coastline in the United Kingdom. It is a prime example of how the land can erode over many years.

In this area all the rocks were formed underneath the waters surface. These rocks include limestone, sands and clays, and chalk. The rocks appear buckled from underneath the water, this is due to the rocks being folded through 50-90 degrees. The coast around Lulworth Cove demonstrates every stage in the development of bays and headlands and how that development is controlled by the underlying geology. Below is a sequence of pictures showing how Lulworth cove and Stairhole were created, and what may happen in the future.

At one time the river running into the cove reached the sea, braking the barrier of hard limestone. This breach meant that the sea was now able to erode the limestone. When the sea reached the softer rocks behind, especially the clay, rapid erosion took place. Then again, once the sea reached the large wall of chalk erosion slowed, forming the curved bay. To the west of Lulworth cove, the sea has been eroding the limestone at Stair Hole and the process of bay formation has begun. In the end Lulworth cove and Stairhole will meet and combine into a larger cove.

Stairhole

Stair hole is a deep cleft, just to the west of Lulworth cove, it is in its early stages in the evolution of the coastline. The

Limestone at this point on the coast is very resistant to erosion, but over a period of time it has been attacked by the sea, forming a cave. Which then evolved into an arch and that is how it still is today. Through these arches and a gap where one has collapsed the sea enters to erode the softer parts of the limestone and shales. This in time will erode and join with Lulworth cove to form an even larger bay.

Durdle Door

Durdle door is an arch, these are created in headlands after erosion has formed caves from either side which eventually meet. The resulting arch is not a permanent feature but will eventually collapse creating landforms called stacks, which in turn will be further eroded to form stumps.

Natural arches such as Durdle Door form as a result of the softer rocks being eroded away behind the hard limestone, allowing the sea to punch through them.

Conclusion

From the information I have found I can see that each of the landforms I have studied are at the same stages in the evolution of the coastline. Lulworth cove and Stairhole are both in the second stage. When they move on into the third stage the two will meet and combine into one large bay. Durdle door is also at the second stage, when it moves into its third stage the landform will erode even more, and the arch will collapse creating a stack.