Coastal Features Flashcards
Wave Cut Platform
The sea attacks a weakness in the base of the cliff, for example, joints, faults or cracks in cliffs
A wave-cut notch is created by erosional processes such as hydraulic action and abrasion.
The rock above overhangs over the notch and, as erosion continues, the notch enlarges until the unsupported overhang collapses due to the weight.
The new cliff face is then eroded and through time, the cliff retreats inland, leaving a gently-sloping rocky surface called a wave-cut platform, which extends out to sea away from the cliff.
The platform is abraded by rock materials, with rock pools and pot holes forming, evident at low tide
Headland and Bay
Cliffs along the coastline do not erode at the same pace. When a stretch of coastline is formed from different types of rock, headlands and bays can form.
Bands of soft rock such as sand and clay are weaker, therefore they can be eroded more quickly than those of more resistant rock, such as chalk. This process forms bays.
The harder sandstone areas are more resistant to erosion and jut out into the sea to form exposed headlands.
Headlands and bays often form in areas with a discordant coastline where alternate bands of rock are found at right angles to the coast.
Sandy beaches are often found the sheltered bays where waves lose energy, and their capacity to transport material decreases resulting in material being deposited.
Sand Spit
Sand spits are formed by the process of longshore drift of sediment.
Swash is where waves, driven by prevailing wind push material up the beach at an angle.
The returning backwash is dragged back by gravity down the beach at right angles.
The spits forms when there is a change in direction on a coastline allowing a sheltered area for deposition.
Over time, material slowly builds up to appear above the water.
The spit develops as long as the supply of deposits is greater than the amount of erosion.
The shape can become hooked or curved at the end in response to changes in wind direction/currents.
A salt marsh may form in a sheltered area behind a sand spit.
Sand Bar
Sandbars usually begin forming underwater.
As waves break, this pulls material from the shoreline, migrating further into the ocean.
The deposition features are caused by the process of longshore drift, where waves, driven by the prevailing wind, push material up the beach; known as the swash.
The returning backwash is dragged back by gravity down the beach at right angles
The bar is formed when a spit grows across the entrance to a bay, connecting two headlands, enclosing a sheltered lagoon behind it
This happens when there is no strong flow of water from a river into the sea and through time, this stagnant lagoon water is infilled by deposition.
Bars form when there is a change in direction on a coastline, which allows a sheltered area for deposition.
During heavy storms, large waves can build sandbars far from shore, until they rise above the water’s surface.
A large sandbar is called a barrier island.
Tombolo
Deposition is caused by the process of longshore drift, where waves, driven by the prevailing wind, push material up the beach; known as the swash.
Material is pushed up onto beaches at an angle when the swash brings it onto the coastline at a 45 degree angle.
The backwash takes it back out towards the sea at a right angle to the coast.
Eventually, when enough sediment has built up, the beach shoreline, known as a spit, will connect with an island and form a tombolo.
A tombolo is formed when a spit extends out from the mainland, connecting to an island.
St Ninian’s Isle off the coast of Shetland is connected by the largest tombolo in the UK.
Crack to Stack
Cracks at the base of the headland within the inter- tidal zone become exposed through hydraulic action, which pressurises air, forcing the crack to widen.
Cracks are further widened by weathering processes such as salt crystallisation 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 affects all three sides of the headland. If two caves are aligned the waves may cut through to form an arch. Wave- cut notches widen 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 sack will collapse to form a stump. The broken material is further eroded through attrition and transported away to be deposited within the bay.
