coastal landforms Flashcards
what are coastal landforms which are created by erosion
-cliffs and wave-cut platforms
-headlands and bays
-caves, arches, stacks and stumps
what are cliffs and wave-cut platforms
- cliffs are the most common coastal landform and they form due to erosion by the sea, over time the cliffs begin to retreat due to erosion and weathering.
-> this can cause issues for people who live in coastal areas as it can put their livelihoods at risk - wave-cut platforms are caused by weathering and erosion. this erosion causes a notch to be formed in a cliff face at the high water mark, eventually this notch will become a cave
- the rock above the cave become unstable as it is not supported and collapses through mass movement
- the wave-cut platform is then left behind where the cliff is eroded
what are headlands and bays
- headlands and bays form where there are bands of alternating bands of soft and hard rock at a right angle to the coastline
- the band of soft rock is then eroded away quickly which forms the bay, the harder rock is more resistant and creates a headland
what are caves, arches, stacks and stumps
- the landform in a cliff is known as a cliff profile feature
- the weaker areas in the rocks (joints) are eroded and become caves
- caves on opposite sides of a narrow headland may form an arch
- when the arch collapses it creates a stack
- stack is eventually eroded into a stump
what are coastal landforms of deposition
- beaches
- spits
- offshore bars and tombolos
- barrier islands
- sand dunes
- mudflats and saltmarshes
how is a beach formed
- through constructive waves depositing sediment onto the shore
- there are two types of beaches, sand and shingle, shingle beaches are steep and narrow whereas sand beaches are wide and flat
- beaches have many distinctive features like berms and ridges which are around 1-2m high which are found at high tide marks. there are also runnels which are grooves that run parallel to the shore and are formed by backwash draining into the sea, cusps are crescent shaped indentations that form on beaches made of both sand and shingle
how are spits formed
spits form due to a change in the direction of the coastline, such as across river mouths
- longshore drift deposits material across a river mouth and leaves a bank of sand and shingle sticking out into the sea. a straight spit that grows parallel to the sea is called a simple spit
- occasional changes to the dominant wind and wave direction may lead to a spit having a curved end (recurved)
- compound spits can also be formed where is has multiple recurved ends from different periods of growth
- the area behind a spit is sheltered from the waves and develops into mudflats and saltmarshes
how are offshore bars and tombolos formed
- bars are formed when a spit joins across two headlands, this can occur either at a bay or river mouth
- lagoon forms behind a bar
- bars are also able to form off the coast when material moves towards the coast, these may remain partially submerged by the sea, this is when it is known as an offshore bar
4, bar that connects a bay to an island is a tombolo
how are barrier islands formed
a barrier island or a barrier beach are long narrow islands of sand or gravel that run parallel to the shore and are detached from it. they form in areas where there is a good supply of sediment, with a gentle slope offshore fairly powerful waves and a small tidal range. we do not know how they are formed but scientists think after the last ice age ended when the ice melt caused a rapid sea level rise the rising water flooded land behind beaches and transported the sand offshore where it was deposited and formed islands.
how are sand dunes formed
formed when sand is deposited by longshore drift is moved up the beach by the wind. the sand is trapped by driftwood or berms and is colonised by plays and grasses. these plants stabilise the sand and encourages more sand to collect there, forming a dune
how are saltmarshes and mudflats formed
-form in sheltered low-energy environments, like in an estuary or behind a spit
-as silt and mud are deposited by the river or the tide the mudflat develops
-mudflats become colonised by salt tolerant vegetation
-plants trap more mud and silt, gradually they build upwards to create the area of a saltmarsh that remains exposed for longer periods between tides
-erosion by tidal currents or streams forms channels in the surface of mudflats and saltmarshes. they may be either permanently flooded or dry at low tide
