Topic3(3)-Coastal Landforms Flashcards
Cliffs and wave-cut platforms
-how are they formed
- Cliffs form as sea erodes the land
- over time, cliff retreats due to the action of waves and weathering
- weathering and wave erosion causes a notch at higher water mark, developing into a cave
- rocks above cave become unstable, so collapses
- wave-cut platforms and flat surfaces are left behind when cliff is further eroded
Headlands and Bays
-how do they form
- when there are bands of alternating soft and hard rock at right angles to the shoreline
- soft rock is eroded quickly,forming a bay
- hard rock is eroded less and sticks out as a headland
Caves, arches and stacks
-how are they formed
- they are cliff profile features
- weak areas in rock are eroded to form caves
- caves on opposite sides of a narrow headland may eventually join up to form an arch
- when an arch collapses it forms a stack
Name 3 sets of coastal landforms caused by erosion
1) cliffs and wave cut platforms
2) bays and headlands
3) caves, arches and stacks
Name 6 sets of coastal landforms caused by deposition
1) beaches
2) spits
3) offshore bars and tombolos
4) barrier island
5) sand dunes
6) estuarine mudflats and saltmarshes
Beaches
- how are they formed
- features
- formed when constructive waves deposit sediment on the shore (store)
- Berms and Ridges of sand and pebbles are found at high tide marks
- Runnels are grooves in the sand running parallel to shore, formed by backwash draining to the sea
- Cusps are crescent-shaped indentations that form on both beach types
What are the 2 types of beach?
1) Shingle beaches
2) Sand beaches
Shingle beaches
- steep and narrow
- made up of larger particles (piled at steeper angles)
Sand beaches
- formed from smaller particles
- wide and flat
Spits
-how are they formed
- tend to form where the coast suddenly changes direction
- longshore drift continues to deposit material across river mouth, leaving a bank of sand and shingle sticking out to sea
- occasional changes in dominant wind and wave direction may lead to curved end
- the area behind the spit is sheltered from waves so often develops into mudflats and saltmarshes
What are the two types of Spits
1) Simple spits (no recurved end) just straight
2) Compound spits(multiple recurved ends)
Offshore bars and tombolos
-how are they formed
- bars are formed when a spit joins 2 headlands together (can occur over a bay or river mouth)
- a lagoon forms behind a bar
- bars can also form off the coast when material moves towards the coast (as sea level rises)
- these may remain partially submerged so would be called offshore bars
What is an offshore bar
Bars which form off the coast and remain partially submerged by the sea, usually due to sea level rise
What is a tombolo
A bar that connects the shore to an island (often a stack)
E.G. St Ninians Isle in the Shetland Islands
Barrier islands (Barrier beaches) -what are they
-long, narrow islands of sand or gravel that run parallel to the shore and are detached
-tend to form in areas with a good sediment supply, a gentle slope offshore, fairly powerful waves and a small tidal range
E.G. Horn Island in Mississippi, USA
Theories of how barrier beaches are formed
- scientists think they probably formed after the last ice age ended, when ice melt caused rapid sea level rise
- the waters flooded the land behind beaches and transported sand offshore, where it was deposited in shallow water, forming island
- another theory is the islands were originally bars which were eroded in sections
What is normally found behind a barrier beach
Lagoons or marshes (sheltered)
How are Sand dunes formed
- when sand deposited by longshore drift is moved up the beach by wind
- sand is trapped by driftwood/berms and colonised by plants and grasses e.g. marram grass
- vegetation stabilises sand and encourages more sand to accumulate there, forming embryo dunes
Where do the oldest dunes migrate?
Inland, as newer embryo dunes are formed. These mature dunes can reach heights of up to 10m
Where do Estuarine mudflats and saltmarshes form?
In sheltered, low-energy environments (e.g. behind spits, river estuaries)
How are mudflats formed
Silt and mud are deposited by the river or tide.
What does vegetation colonising do to mudflats
Allows them to survive high salt levels and long periods of submergence by the tide
How do saltmarshes form
Plants which colonise mudflats trap more mud and silt, and gradually build up to create an area of saltmarsh that remains exposed for longer between tides
What can erosion do to mudflats and saltmarshes
Erosion from currents or streams form channels
These may be permanently flooded or dry at low tide
