Isle of Purbeck and the nearby coastal areas.

by housejug (student)

The Isle of Purbeck

Introduction

The Isle of Purbeck is in fact a peninsular in the south of England in Dorset. It is a popular tourist attraction because of its coasts and famous landmarks some of which are at the coast and are there as a result of weathering (how the sea and wind erode the rocks and landscapes). The residents main source of income comes from the man-made and natural tourist attractions along the coastline. the coastline is very useful to some of the towns in the isle of Purbeck because it makes the area a popular tourist site and thus a vital part of the area's economy. Many tourists visit Purbeck for its sea sides and erosional landmarks. there are a few well known towns one of which is Studland which is famous for its beach and nature reserves

There is a problem with coastal erosion in this area because the land is made of clay and limestone. These are both soft stones that are easily broken-down by the waves and coastal wind. Some parts of the coast also expose rock with fossils from the Triassic, Jurassic and Cretaceous periods, about 185 million years old.

Erosional Landforms

Old Harry's Rock

Old Harry's rock is a formation of stacks and stumps made of chalk (the reason why they have been so easy to erode) below the cliffs of Ballard directly east of Studland. There were formed by erosion - this could have happened in a variety of ways, but most likely because of the sheer force of the waves smashing against what was originally a cliff face. a fault in the cliff face would be opened up by the force of the waves. to turn into a cave eventually the wave would power through the caves to make an arch when it reached the other side of the cliff face. erosion and gravity would eventually make the top of the arch collapse. Separating the remains of the arch and the cliff face to make a stack. Eventually the waves would bring down the stack and turn it into a stump this is what happened to Old Harry's rock, and the same will happen to Old Harry one day. In local folklore the devil slept on the rocks, hence the name Old Harry because this was another name for the devil.

Studland Bay & Ballard Down

Another landmark near Studland is Ballard down, it is an area of chalk down land between Swanage and Studland. The down was an area of calcareous (Alkaline) grassland for up to a thousand years until WWII when there was a sudden rise in the need for available agricultural land to feed the soldiers. Since the need for agricultural land the Down is now owned by the national trust and has been returned to grassland, to accommodate species of clover plants, flowers and insects, particularly butterflies.

Ballard Down Grassland

Lulworth Cove

Lulworth ...

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Studland Bay & Ballard Down

Ballard Down Grassland

Lulworth Cove

Lulworth is a circular, sheltered bay by the village of west Lulworth on the Jurassic coast world heritage site in Dorset. Lulworth Cove was formed by the sea breaking through a comparatively thin layer of hard Portland Stone that runs parallel to the shoreline. Once through, the waves allowed much softer clays to be eroded away, much slower than the hard rock. When a straight wave hits a barrier with a hole in it, the wave pattern on the other side is semi-circular. The curved waves radiate out from the Cove entrance showing how Lulworth got it’s shape. Like below.

Durdle Door

Durdle is an erosional land form on the Dorset coastline. It is made of Jurassic limestone. You can only reach it on foot. Each year more than 200.000 walkers use the footpath between Lulworth Cove and Durdle Door, making it the busiest stretch in the south west.

Other landforms

Ringsted Bay- is another bay much like Studland

Kimmeridge- The sea has eroded and exposed layer after layer of rock on cliffs of Kimmeridge Bay. These layers are full of fossils from the Jurassic period. Even before Kimmeridge became part of the UNESCO Dorset and East Devon World Heritage Jurassic Coast, an entire stage of the Jurassic Period - the Kimmeridgian was named after it.

Depositional Landform

http://geobytesgcse.blogspot.com/2007/08/coastal-deposition-landforms-features.html

How beaches are formed

Beaches consist of all the material (sand, shingle etc.) that has built up between the high and low tide mark. The main source of beach material is rivers, where fine muds and gravels are deposited at the river mouth. Other sources of beach material include longshore drift (bringing material from elsewhere along the coast); constructive waves and from cliff erosion.

As constructive waves build up beaches, they often form ridges in the beach known as berms. The berm highest up the beach represents the extent to which the water has reached during high tide.

How Bars are formed

These form in the same way as a spit but are created where a spit grows across a bay, joining two headlands. Behind the bar, a lagoon is created, where water has been trapped and the lagoon may gradually be filled in as a salt marsh develops due to it being a low energy zone.

How Tombolos are formed

Tombolos are formed where a spit continues to grow outwards joining land to an offshore island.

How spits are formed

The formation of a spit begins due to a change in the direction of a coastline - the main source of material building up a spit is from longshore drift which brings material from further down the coast. There is a slight drop in energy, and this is where longshore drift deposits material quicker than it is removed. Quickly, a ridge builds up, projecting out of the sea.

The Geology of the area

The area is comprised mostly of clay, gravel, mud and limestone, most of which are easily eroded. This is why there are so many different landforms in the area, it's much easier for the waves to cut into the land and create the things we see there.

Coastal Management of Swanage

Swanage Bay has used Groynes to slow down the effects of longshore drift ( they are replaced regularly ) and used Beach Replenishment ( placing more sand on the beach from another source) .

The groynes were first built in 1925, eighteen of them were reconstructed in 2005-6 at the same time the beach was replenished.

The groynes cost £5000 each to build and replace, and the beach replenishment cost £3500 per metre.

The only drawback of Beach replenishments is the cost. Groynes are very useful for slowing the effects of longshore drift to stop the beach from being carried away, but they are expensive in the numbers required for them to be effective. Neither of these coastal defences are completely successful in defending against floods in Swanage.

Another type of Groyne is a Gabion Groyne. Gabion Groynes are not used in Swanage, they are gabions that are lined up horizontally to the shore and are used as groynes. Steel caged gabions will last 20-25 years, while stainless steel gabions will last much longer.