Coastal Landforms Flashcards
What are cliffs and wave-cut platforms?
1) Cliffs are common coastal landforms- they form as the sea erodes the land. Over time, cliffs retreat due to the action of waves and weathering.
2) Weathering and erosion cause a notch to be formed (eroded rock at bottom of cliff). This develops into a cave.
3) Rock above the cave becomes unstable with nothing to support it, it then collapses.
4) Wave cut platforms are left behind when a cliff is eroded.
How are headlands and bays formed?
1) Headlands and bays form where there are abdns of hard and soft rock at right angles to the shoreline.
2) The soft rock is eroded quickly as it it less dense, therfore forming a bay. The hard rock is eroded less and sticks out as a headland.
How are caves, arches and stacks formed?
1) Weak areas in the rock are eroded to form caves.
2) Caves on the opposite side of a narrow headland may eventually join up to form an arch.
3) When the arch become unbalanced, it collapses and forms a stack.
How is a beach formed?
1) Beaches form when constructive waves deposit sediment on shore- they are a store in the coastal system.
2) Shingle beaches are steep and narrow. Theyre made up of larger particles, while pile up at steep angles. Sand beaches formed from smaller particles are wide and flat.
3) Beaches have disticntive features. Berms are ridges of and and pebbles found at high tide marks.
Runnels are grooves in the sand running parallel to the shore, formed by backwash draining to the sea.
Cusps are crescent-shaped indentations that form on beaches of mixed sand and shingle.
How are spits formed?
Spits tend to form where the coast suddenly changes direction.
1) Longshore dift continues to deposit material across the river mouth, leaving a bank of sand and shingle sticking out at sea. A stright spit that grows parallel out to the coast is called a simple spit.
2) Dominant wind changes may lead to a spit having a curved end.
3) Several curved ends may be abondoned over time, as the waves return to their original direction. A spit that has multiple curved ends resulting from sevral periods of growth is called a compund spit.
4) The area behind the spit is sheltered from the waves and often develops into mudflats and saltmarshes.
How are offshore bars and tombolos formed?
1) Bars are formed when two spits join two headlands together. This can occur across a bay or across a river mouth.
2) A lagoon forms behind the bar
3) Bars can also form off the coast. These may remain partly submerged by the sea- in this case theyre called offshore bars.
4) A bar that connects the shore to an island (often a stack) is called a tombolo
How are barrier islands formed?
1) Barrier islands are long narrow islands of sand or gravel that run parallel to the shore and are detached from it. They tend to form in areas where there is a good supply of sediment, a gentle slope offshore, fairly powerful waves and a small tidal range.
2) Scientists think that they often form after the last ice age ended, when ice melt caused rapid sea level rise. The rising waters flooded the land behind beaches and transported sand offshore, where it was deposited in shallow water, formig islands.
How are sand dunes formed?
1) Sand dunes are formed when sand deposited by longshore drift is moved up the beach by wind.
2) Sand trapped by berms is colonised by plants and grasses, e.g. marram grass. The vegetation stabilises the sand and encourages more sand to accumulate there, forming embryo dunes.
3) Over time, the oldest dunes migrate inland as newer embryo dunes are formed. These mature dunes can reach up to 10m.
How are estuarine mudflats and saltmarshes formed?
1) Mudflats and saltmarshes form in shelted, low energy enviroments, e.g. river esturies or behind spits.
2) As silt and mud are deposited by the river or the tide, muflats develop.
3) The mudflats are colonised by vegetation that can survive the high salt levels and long periods of submergence by tide.
4) The plants trap more mud and silt, and gradually they build upwards to create an area of saltmarsh that remains exposed for longer and longer between tides.
5) Erosion by tidal currents or streams form channels in the surface of mudflats and saltmarshes. These may be permanantly flooded or dry at low tide.
outline the processes which lead to the development of a barrier beach
A barrier beach is usually formed as an extension of a spit (1).
Longshore drift moves sediment along the coastline until there is a change in the coastline (1).
A spit develops, usually in a bay and once the spit develops across the whole bay, a barrier beach forms (1)
