Wave Cut Platform Formation Fig 18.4 p301 Add in the Retreating cliff lines The sea uses its four erosion methods during high and low tide to create a notch. This means the cliff above is unsupported and collapses – retreating inland. This process is called ‘UNDERCUTTING’. The cliff is vertical and steep.

Cliffs & Wave Cut Platforms - Cliffs are formed when destructive waves attack the bottom of the rock face between high and low water mark. - The area under attack is eroded using the major processes of coastal erosion. - Points of weakness, such as faults and joints are attacked most, and eventually a wave-cut notch is gouged out.

The rock above overhangs the notch, and as it is cut deeper into the rock, gravity causes the overhanging rock to collapse. - The loose rocks are removed by the sea and transported along the coast by long shore drift. - The whole process of undercutting the cliff begins again. - As the cliff is eroded backwards it leaves behind a wave-cut platform, at the level of the low water mark. - This platform is rarely eroded, as the waves energy is concentrated on eroding the area between the high and low water mark, and not the rock that is underneath them.

Model Answer Erosion Headland Formation A cave is formed in the rock as various processes of coastal erosion operate on it. Hydraulic action (which involved mini explosions of air under water) eats out the notch to form a cave. A cave is eroded further by the processes of attrition, corrosion (solution) abrasion and scouring. This eventually forms an arch. Over time the arch weakens and collapses leaving an stack. The stack erodes over time to form a stump.

                                                                   

Caves, Arches, Stacks and Stumps - Mainly seen on headlands. - Waves start by attacking the main points of weakness in the rock: the joints and faults. - A point of weakness is increased in size until it becomes a cave. - The waves continue to attack the cave, which finally results in an arch being formed through the headland. - The arch is attacked both by coastal erosion and sub-aerial erosion and finally the roof of the arch falls into the sea. - This leaves behind a stack, which is then slowly eroded down to become a stump.

OLD HARRY

Model Answers Rock Types Sheet 1a) The slate rock must be harder (more resistant) than the sandstone as it sticks out on the coastline as headlands (2) 1b) The limestone must be harder than the sands and clays because although the limestone is closer to the sea, and therefore more easily eroded, the sands and clays have been eroded BEHIND the limestone to form coves – eg Lulworth cove (2) 2a) Headlands are sections of rock jutting out into the sea – whereas bays are indentations into the coastline where the sea has eaten it away (2) 2b) Arches look like headlands except they have a hole at the base and stumps are large towers or columns of rock sticking out of the sea 3a) Erosion occurs in both headlands and bays. As the headlands are made up of hard rock they are eroded more slowly. Processes such as hydraulic action and abrasion will be important in their formation. Bays will be eroded more quickly as they are made of softer rock. Material eroded at the headland cliffs will also be transported to the bays 3 b) First of all hydraulic action attacks small notches in the cliff face. Over time – this is enlarged

..to form an arch. The arch is then eroded until the top collapses away forming a stack. Erosion from the sea then leads to the stack collapsing forming a stump. (6) 4. In Devon = DISCORDANT COASTLINE = the rocks lie at right angles to the sea. This forms headlands (on the resistant rock - SLATE) and bays (on the weaker rock - SANDSTONE). In Dorset = CONCORDANT COASTLINE = rocks lie parallel to the sea. This forms isolated parallel rock features in the limestone and coves behind in the weaker sands and clays. (9) 5. Devon = headlands will get more PRONOUNCED as the bays will be eroded at a quicker rate Dorset = the weak rock behind the limestone (sands and clays) will be eaten out even more to form very large coves. Some of the coves may join up with each other too. The limestone (which is more resistant) will slowly get eaten away and will end up as isolated rock outcrops in the sea – standing alone (5)