dorset

• -Swanage Bay: the cliffs backing Swanage Bay are made

  of clay, which is a soft rock. Towards the northern end of

  the bay the cliffs are covered in vegetation, stabilising them

  and protecting them from erosion. Elsewhere, the cliffs are

  not covered by vegetation, so wet weather weakens them

  causing slumps. Longshore drift affects the bay carrying

  material (mainly gravel) from the south to the north of the

  beach. Erosion is the dominant process in the bay with the

  beach losing material year on year.
• -The Foreland, Old Harry and his Wife: in between the

  two bays (Studland and Swanage Bays) is a headland

  named the Foreland. This is made of chalk which is a

  harder rock. An arch at the end of the headland has

  collapsed to form a stack called Old Harry and a stump

  called Old Harry's Wife. Chemical weathering and erosion is

  gradually wearing them down. Biological weathering caused

  by the vegetation on the top of the headland is also

  breaking up the rock.
• -Durdle door: this is an arch which has formed on a hard

  limestone headland. Erosion by waves opened up a crack in

  the headland, which then became a cave and eventually an

  arch. The arch is gradually being worn away by mechanical,

  chemical and biological weathering.
• -Lulworth Cove: this is a cove formed when a gap was

  eroded in a band of limestone. Behind the limestone is a

  layer of clay which is softer so more easily eroded. The

  limestone cliffs forming the back wall of the cove are

  vulnerable to mass movement and sometimes experience

  small slides and slumps.
• -Chesil Beach: this is a tombolo 3 (a spit, which connects the mainland to an island). It connects the Isle of Portland to

  the mainland. It has been created by longshore drift. Behind

  Chesil Beach is a lagoon 4 called The Fleet Lagoon.
• The geology and recent glacials and interglacials have

  helped shape the coastline over the long term. The more

  resistant Jurassic limestones (Portland and Purbeck) have

  been folded so that they dip very steeply landwards, as

  tectonic forces crumpled the rocks of what is now Dorset

  some 65 million years ago.
• During the ice age the Dorset coastline was not covered by

  ice, but was intensely cold with the land frozen to great

  depth and sea level 120 metres below the present day. As

  the ice receded (approx. 11,700 years ago) and the frozen

  land thawed, vast quantities of water were released from ice

  melt. Fast-flowing rivers made their way to the sea, cutting

  through all the rocks, including the resistant Jurassic

  limestones. This helped the sea break through the resistant

  rocks and form coves and bays 2 . As sea level gradually

  rose, eventually wave action producing today’s landscape.
• Dorset’s location means that it is exposed to south westerly

  prevailing winds which bring storms to the UK from the

  Atlantic Ocean. These are high energy, destructive waves

  which increase erosion on the coastline. Hydraulic action

  and abrasion increase during these storms and erode the

  base of cliffs. This then can lead to instability in the cliff line

  and mass movement.
• The limestones and chalks are also vulnerable to solution where seawater chemically reacts with the rock, causing it to dissolve. In places where the limestone has been broken through (as discussed earlier as a result of glacial meltwaters), the less resistant Greensand

  and Wealdon sands and clays have been worn away at a

  faster rate by hydraulic action and abrasion, forming bays

  such as Lulworth cove.
• The Dorset coast receives relatively low amounts of rainfall,

  but it can experience very wet winters with heavy rainfall

  during storms. Chalk and limestone are both vulnerable to

  weathering through carbonation. Prolonged heavy rainfall

  causes clay to become heavier, softer and more slippery,

  making mass movement more likely. During the winter

  rainfall there are often slides and slumps on the cliffs.
• Dorset has warm and dry summers (around 21℃ in July)and

  mild wet winters (average a minimum in January of 3℃).

  Salt weathering is the dominant form of mechanical

  weathering especially in the summer. This is because warm

  temperatures cause sea water to evaporate from rocks

  quickly, leaving a buildup of salt crystals in tiny cracks in the

  rocks. Mild winters mean freeze thaw weathering is rare as

  temperatures rarely oscillate around 0℃.