Coastal Features Flashcards
1
Q
Wave Cut Platform
A
- Wave erosion is greatest when large waves break against the foot of a cliff. This is known as abrasion and occurs when material carried by the sea is hurled at cliffs by waves causing them to be worn down.
- With wave energy at its maximum, the waves undercut the foot of the cliff to form a wave-cut notch. This may be further eroded by hydraulic action. This is when air is compressed in cracks causing a small explosion and the rock breaks apart.
- Over a period of time the notch enlarges until the cliff above is left unsupported and collapses. Weak acids in the water may also slowly dissolve the rocks wearing them away - known as corrosion.
- As this process is repeated, the cliff retreats.
- The gently sloping expanse of rock marking the foot of the retreating cliff is called a wave-cut platform. These are exposed at low tide but covered at high tide. They often slope at an angle of less than 5°.
2
Q
Headland and Bay
A
The soft rock is eroded further by waves approaching the shore (eg.clay, sand, gravel). The soft rock is eroded by abrasion (when rocks are hurled at the cliff and break off bits of rock) and hydraulic action (air is compressed in cracks and a small explosion loosens rock). Weak acids/salt also dissolves the rock and washes the particles away. Hard rock is left sticking out into the sea - known as headlands - as it is more resistent to erosion. The area between headlands - known as bays - is an area of sheltered water. Bays are formed due to the rapid erosion of less resistent rock.
3
Q
Cave-Arch-Stack
A
- Cracks at the base of the headland within the inter-tidal zone become exposed through hydraulic action, which pressurizes air, forcing the crack to widen.
- Cracks are further widened by weathering processes such as salt crystalization and wet and dry weathering that affects chalk.
- Over time the cracks widen and develop as wave-cut notches. Further processes of abrasion and hydraulic action will deepen the notch to form caves.
- As a result of wave refraction, which distorts the wave direction, destructive waves concentrate their energy on the sides. This deepens the cave.
- Wave refraction effects all three sides of the headland. If two caves are aligned the waves may cut through to form an arch. Wave-cut notches widens the base of the arch.
- Vertical joints are exposed by tall breakers associated with destructive waves. Joints can also be weathered from above such as through carbonation in limestone. Here blowholes may form.
- Over time the arch becomes unstable and collapses under its own weight to form a pillar of rock, called a stack. A good example is Old Harry along the dorset coast.
- The stack is further eroded at its base creating new wave-cut notches. Sub-aerial processes continue to weaken the stack from above.
- Eventually the exposed stack will collapse to form a stump. The broken material is further eroded through attrition (this is when materials carried along the sea hit against each other causing them to get smaller and smoother) and transported away to be deposited within the bay.
4
Q
Spit
A
- Prevailing wind powers process of longshore drift (the prevailing wind makes waves wash onto the beach at an angle, the waves return to the sea at 45° known as backwash where material is then returned, small material will be carried the furthest) which moves material along the coastline.
- Coastline changes shape (bay,river,estuary) but lingshore drift contiues out beyond it depositing sand in the calmer, shallower water where the river current and waves counteract against eachother.
- Short term changes in wind direction cause the spit tohave a hooked end. This can happen several times leading to ‘recurved laterals’.
- The force of the river bringing water down to its mouth means that the spit cannot join to the other side of the estuary.
- Behind the spit, silts carried by the river collect. This is a low energy zoneso they are not washed away by the current. Plants colonise the area and a salt marsh develops.
5
Q
Bar
A
- Prevailing wind powers process of longshore drift (the prevailing wind makes waves wash onto the beach at an angle, the waves return to the sea at 45° known as backwash where material is then returned, small material will be carried the furthest) which moves material along the coastline.
- Coastline changes shape (bay,river,estuary) but lingshore drift contiues out beyond it depositing sand in the calmer, shallower water where the river current and waves counteract against eachother.
- Short term changes in wind direction cause the spit tohave a hooked end. This can happen several times leading to ‘recurved laterals’.
- The force of the river bringing water down to its mouth means that the spit cannot join to the other side of the estuary.
- Behind the spit, silts carried by the river collect. This is a low energy zoneso they are not washed away by the current. Plants colonise the area and a salt marsh develops.
- A bar is a spit that joins two headlands together.
6
Q
Tombolo
A
- Prevailing wind powers process of longshore drift (the prevailing wind makes waves wash onto the beach at an angle, the waves return to the sea at 45° known as backwash where material is then returned, small material will be carried the furthest) which moves material along the coastline.
- Coastline changes shape (bay,river,estuary) but lingshore drift contiues out beyond it depositing sand in the calmer, shallower water where the river current and waves counteract against eachother.
- Short term changes in wind direction cause the spit tohave a hooked end. This can happen several times leading to ‘recurved laterals’.
- The force of the river bringing water down to its mouth means that the spit cannot join to the other side of the estuary.
- Behind the spit, silts carried by the river collect. This is a low energy zoneso they are not washed away by the current. Plants colonise the area and a salt marsh develops.
- A tombolo is a spit connecting the mainland to an island.
