Coastal Landforms and Sea Level Changes Flashcards
How do Cliffs and Wave-cut platforms form?
Cliffs are common coastal landforms - they form as the sea erodes the land. Overtime, cliffs retreat due to the action of waves and weathering.
Weathering and wave erosion cause a notch to form between the high and low water mark. This eventually develops into a cave.
Rock above the caves becomes unstable with nothing to support it, and it collapses.
Wave cut platforms are flat surfaces left behind when a cliff is eroded.
How do headlands and bays form
Headlands and bays form where there are bands of alternating hard rock and soft rock at right angles to the shoreline, discordant coastline.
The soft rock is eroded quickly, forming a bay. The harder rock is eroded less and sticks out as a headland.
What’s a discordant coastline
Discordant coastline occurs where bands of differing rock type run perpendicular to the coast.
What is a concordant coastline
A concordant coastline occurs where the bands of differing rock types run parallel to the coast.
The outer hard provides a protective barrier to erosion of the softer rocks further inland.
How are caves, arches and stacks formed
Some landforms are found in cliffs - these are called cliff profile features
Weak areas in rock (eg joints) are eroded to form caves.
Caves on the opposite sides of a narrow headland may eventually join up to form an arch
When an arch collapses it forms a stack.
Cracks in the cliff appear, small cave forms, arch forms, stack forms and then stump.
What are cliff profile features
landforms found in cliffs
How are beaches formed
They are landforms of deposition
Beaches form when constructive waves deposit sediment on the shore - they are a store in the coastal system.
Shingle beaches are steep and narrow. They’re made up of larger particles, which pile up at steep angles.
Sand beaches, formed from smaller particles, are wide and flat.
Beaches have distinctive features. Berms are ridges of sand and pebbles (about 1 to 2 metres high) found at high tide marks.
Runnels are grooves in the sand running parallel to the shore, formed by the backwash draining to the sea.
Cusps are crescent shaped indentations that form on beaches of mixed sand and shingle
What are berms
Berms are ridges of sand and pebbles (about 1-2 metres high) found at high tide marks.
What are runnels
Runnels are grooves in the sand running parallel to the shore, formed by backwash draining to the sea.
What are cusps
Crescent shaped indentations that form on beaches of mixed sand and shingle.
How do spits form
Spits tend to form where the coast suddenly changes direction eg across river mouths.
Longshore drift continues to deposit material across the river mouth, leaving a bank of sand and shingle sticking out into the sea. A straight spit that grows out roughly parallel to the coast is called a simple spit.
Occasional changes to the dominant wind and wave direction may lead to a spit having a curved end, also known as recurved end.
Over time, several recurved ends may be abandoned as the waves return to their original direction.
A spit that has multiple recurved ends resulting from several periods of growth is called a compound spit.
the area behind the spit is sheltered from the waves and often develops into mudflats and salt marshes.
How do offshore bars and tombolos form
Bars are formed when a spit joins two headlands together. This can occur across a bay or across a river mouth.
A lagoon forms behind the bar.
Bars can also form off the coast when material moves towards the coast (normally as sea level rises). These may remain partly submerged by the sea - in this case they’re called offshore bars.
A bar that connects the shore to an island (often a stack) is called a tombolo.
How do Barrier islands form
Barrier islands (also called barrier beaches) 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’s a good supply of sediment, a gentle slope offshore, fairly powerful waves and a small tidal range.
It’s not exactly clear how barrier islands form, but scientists think that they probably formed after the last ice age needed, when ice melt caused rapid sea level rise. The rising waters flooded the land behind the beaches and transported sand offshore,where it was deposited in shallow water, forming islands.
Another theory is that the islands were originally bars, attached to the coast, which were eroded in sections, causing breaches in the bar.
A lagoon or marsh often forms behind the barrier island, where the coast is sheltered from wave action.
Tell me how sand dunes form
Sand dunes are formed when sand deposited by longshore drift is moved up the beach by the wind. Sand trapped by driftwood or berms is colonised by plants and grasses, eg marram grass. The vegetation stabilises the sand and encourages more sand to accumulate there, forming embryo dunes.
Over time, the oldest dunes migrate inland as newer embryo dunes are formed. These mature dunes can reach heights of up to 10m.
Tell me about the formation of estuarine mudflats and salt marshes
Mudflats and salt marshes form in sheltered, low energy environments eg river estuaries or behind spits.
As silt and mud are deposited by the river or the tide, mudflats develop.
The mudflats are colonised by vegetation that can survive the high salt levels and long periods of submergence by the tide.
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.
Erosion by tidal currents or streams forms channels in the surface of mudflats and salt marshes. These may be permanently flooded or dry at low tide.