DEPOSITIONAL LANDFORMS Flashcards
wave type
constructive waves
depositional landforms
(beaches, recurved and double spits, offshore bars, barrier beaches and bars, tombolos and cuspate forelands), which can be stabilised by plant succession.
what is depostrion
Deposition occurs when waves no longer have sufficient energy to continue to transport material
why might deposition occur
This loss of energy might be due to:
the wind dropping
resistance by obstruction, e.g. a groyne or headland
dissipation of energy through refraction
types of deposition
Gravity settling
Flocculation
desribe Flocculation
a depositional process that is important for very small particles, such as clay, which are so small that they will remain suspended in water. Clay particles clump together through electrical or chemical attraction, and become large enough to sink.
descrube gravity setling
occurs when the energy of transporting water becomes too low to move sediment. Large sediment will be deposited first, followed by smaller sediment (pebbles -> sand -> silt)
how are beaches formed
Beaches are accumulations of sand and/or shingle found in the foreshore and backshore zones.
They’re produced by material deposited by constructive waves
The swash has the strength to carry material up the beach, but the backwash only has enough energy to transport some of the material back down the beach, leaving the remainder deposited
ho atre spitss formed
Spits are linear ridges of sand or shingle beach stretching into the sea beyond a turn in the coastline but connected to the land at one end
They form on drift-aligned coastlines, where the coastline changes direction
At the turn, longshore drift continues in the original direction, but its energy is dispersed, lost as the wave refracts and the current spreads, leading to deposition on the sea bed.
Over time, sufficient sediment is deposited to break the surface, extending the beach into the sea as a spit
The process continues until equilibrium is reached at the distal end (seaward end) of the spit, between deposition and erosion by waves or the existing river current.
formation o foffshore bars
Offshore bars are ridges of sand or shingle running parallel to the coast in an offshore zone.
They form from sediment eroded by destructive waves and carried seawards by backwash.
The sediment is deposited at the boundary of the offshore and nearshore zone, where the orbit of water particles ceases to reach the seabed, halting the transport offshore.
They are also called breakpoint bars because the offshore/nearshore boundary is where waves first begin to break.
They can sometimes be exposed by neap tide.
They are used:
to construct wind farms
e.g. Scroby Sands in Norfolk
as a source of sand for beach nourishment
for shingle dredging for construction material
tombolo formation
Tombolos
Tomobolos are linear ridges (or bar) of sand and shingle connecting an offshore island to the coastline of the mainland.
Two ways they can form are:
On drift aligned coastlines, when longshore drift builds a spit out from land until it contacts with an offshore island.
On swash aligned coasts when there is wave refraction around both sides of the island.
This causes a collision of wave fronts on the landward side, cancelling each other out and producing a zone of still, calm water where deposition occurs, between the island and the coast.
Oppositional longshore currents may play a role, in which case the depositional feature is similar to a spit.
E.g. St Ninian’s tombolo on the Shetland Islands
The tombolo connecting Portland Bill to the mainland in Dorset.
why are deposition landforms unsable
They are made of unconsolidated material
They are dynamic as they lose material transported by waves, tides, currents and wind.
how are depositional landforms stabalised
They are stabilised by plant succession, which binds the loose sediment together and encourages further deposition.
Plant succession on sand dunes is psammosere.
Plant succession on salt marsh is halosere.
how do plandt cionsidate materoal
Plant roots hold sediment together
Their leaves/stems slow water and wind flow reducing erosion and encouraging further deposition
