Purbeck Coast - Processes

This is an essay that I have written and then drawn pictures of the processes. Has examples of locations and landforms as well

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  • Created on: 05-02-15 15:11
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Introduction
This leaflet has been designed to help the general public to understand what is happening
on the Purbeck coast and how landforms have been created through specific processes and
features of the coast. I have outlined the main causes and features of coastal processes and
how these relate to specific case studies on the Purbeck Coast.
The geology of rocks and soils plays a specific role on how the coastline is shaped. Other
factors such as erosion and the process of longshore drift changes that shape. Dorset is
known for having a diverse coastline with many features and some of these include: Durdle
Door, Lulworth Cove, Old Harry's Rocks and Swanage Bay.
The Geology of Purbeck
Geology is the term used to describe the combinations of rocks and soils
located in a certain area. The geology of Purbeck is hugely set around the
formation of hard and soft rock. These have formed a discordant coastline to the east and a
concordant coastline to the south. This means that along the east of the county, the bands
of rock are placed at 90 degrees to the sea and are alternating between types. A concordant
coastline is where one type of rock covers the frontage to the sea but further layers of rock
are placed behind this. These are shown, along with the rock types present, in figure 1.
These different bands of rock can lead to differential erosion, which means that the soft
rock will get eroded away before the hard rock and leave bays and headlands on the
coastline.
The geology is important in understanding how many of the landforms and sites along the
Purbeck coast were firstly made vulnerable and then had the effects of the coast put upon it
to create these stunning pieces of natural beauty. One influence on the coastal features is
the difference between soft and hard rock. To the eye these could look quite similar but
they have different characteristics and act in very different ways.

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Erosion
Erosion is one of the main contributing factors
for coastal features. It is the first part of
longshore drift which in simple terms picks
sediment up from one part of the beach and
moves it down the coast to be deposited. The
erosion can happen in one or more of four
ways; it can be rubbed against another rock and
the load grinds away. This is known as attrition
and ends in sandy sediment. Another common
type of erosion is hydraulic action.…read more

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Transport
Transport is the movement of the
eroded material before it is deposited.
Transport is usually by the sea water. It
moves up and down the beach
diagonally. The swash is where the wav
moves out towards the land. This is
done at an angle depending on the
location and therefore the prevailing
wind. The backwash is where the water
is drawn back into the sea at a right
angle to the water.…read more

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Mass movement is where large areas of rock
are moved because of a process. Slumping is
a very common cause of movement and is
often referred to as a rotational slip. The
geology of the rock is also partly behind this
landform as well. When two different rock
types are placed together there is a
difference in permeability. This means the
amount of water that can saturate through
the rocks.…read more

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One example of this is Lulworth Cove. It is
located in the Jurassic Heritage site in the
village of Lulworth. The cove has formed
because of the concordant coastline. The
rocks that provide more resistance towards
erosion are still present and are shaped in
rows. The softer Purbeck limestone and less
resistant clays have been eroded by hydraulic
action. The back of the cove is made up of
chalk and is liable to slumping because of the
permeable rocks. This reduces the coastline
further.…read more

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This piece of rock was battered by differential erosion and came through a series
of events. To start with the hydraulic action of the waves would cause cracks to form in the
soft rock. This crack would then widen to create a cave. These can be seen all along the
Dorset coastline and will continue to erode over time. The back of the cave will collapse and
an arch will appear. This is what has occurred at the Durdle Door.…read more

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