Coastal landforms Flashcards
Cliffs
Common coastal landforms that form as the sea erodes the land.
Over time they retreat.
Wave cut notch
They form at the high water mark of cliffs due to weathering and erosion.
They eventually develop into caves.
Wave cut platforms
Flat surfaces left behind when a cave collapses and the cliff then retreats.
Headlands and bays
Features that form at discordant coastlines, as alternating hard and soft rock erode at different rates.
For example the Isle of Purbeck in Dorset is made up of Studland Bay (soft rock), Ballard Point (hard rock), Swanage Bay (soft rock) and Durlston Head (hard rock).
Caves, arches and stacks
Examples of cliff profile features. Joints in rocks are eroded to form caves. Caves either side of a narrow headland may join up to form and arch. When the arch collapses it leaves a stack.
e.g. Old Harry Rocks in Dorset
Beaches
Formed when constructive waves deposit sediment on the shore.
Shingle beaches are steep and narrow as they are made of larger particles which pile up at steep angles.
Sand beaches, formed by smaller particles are wide and flat.
Summer beaches are steeper because there are more constructive waves.
Cusps
Crescent-shaped indentations that form on beaches of mixed sand and shingle. Swash is concentrated in the small bay and a stronger back wash moves sediment down the beach.
Ridges and runnels
Features that form parallel to the shoreline in the foreshore. Ridges are raised above the adjacent shore and dip into runnels. They form by backwash draining back into the sea. They form on beaches with shallow gradients.
Berms
Ridges of sand and pebbles that are about 1-2 metres high and are found at high tide marks.
Spits
Formed when the coast suddenly changes direction e.g. across river mouths and sediment is deposited by longshore drift.
They are long, narrow deposits of sand and shingle that extend into the sea.
Simple spits are straight and roughly parallel to the coast.
Spits with recurved ends occur when there is a change in dominant wind and wave direction.
A compound spit has multiple recurved ends that form as the waves return to their original direction.
Bars
When a spit extends across a bay and rejoins the coast on the opposite shore. A lagoon forms behind the bar.
Offshore bar
When a bar forms off the coast as material moves towards the coast. They remain partly submerged by the sea.
Tombolo
A bar that connects the shore to an offshore island.
e.g. St Ninian’s Isle in the Shetland Islands.
Barrier beach
A general term for any beach that shelters the coast.
Barrier islands
Long, narrow deposits of sand or gravel that run parallel to the shore, but are detached from it.
e.g. Horn Island in Mississippi.
Conditions for barrier islands
They tend to form in areas with a good supply of sediment, a gentle slope offshore, fairly powerful waves and a small tidal range.
How do barrier islands form?
It is not exactly clear how they are formed but scientists believe that they probably formed after the last ice age when there was rapid sea level rise. The rising water flooded land behind the beaches and transported sand offshore, where is was deposited in in shallow water, forming islands. Another theory is that they were originally bars that have been eroded.
Sand dunes
Formed when sand deposited by longshore drift is moved up the beach by wind.
Sand trapped by driftwood or berms is colonised by plant and grasses e.g. marram grass. The vegetation stabilises the sand and encourages more sand to accumulate there, forming embryo dunes.
Over time the older dunes migrate inland as newer ones are formed.
Mature dunes can reach up to 10m.
Estuarine mudflats
They form in sheltered, low energy environments, e.g. behind spits as tidal currents here are slower.
As silt and mud are deposited, mudflats develop.
They are colonised by salt-tolerant vegetation.
As more mud and silt settles, the mudflat gradually builds up so it is exposed for longer between high tides.
The closer inland you go, the more exposure there is so the less salt-tolerant the plants are.
Saltmarshes
As more sediment accumulates, mudflats transform into saltmarshes. Here, only spring tides submerge the intertidal shore so there is a more dense coverage of vegetation.
