Landforms of deposition Flashcards
What are some landforms of deposition
Beaches
Spits, bars, tombolos
Sand dune
Salt marsh
What is a beach
accumulation of material deposited by waves
What factors define a beach
sediment size
wave type
wave angle
What are the 4 types of beaches
Shingle or Sand
Drift or swash
Describe shingle and sand beaches
Shingle has a high percolation rate, so there is lots of swash but no backwash, making them steep and narrow
Sand has a low percolation rate, so there is lots of swash and backwash so is more flat and wide
Describe drift and swash beaches
Drift beaches are parallel to the shoreline and have lots of sediment transported along them (regular coast)
Swash beaches are parallel to the wave crests and do not have lots of sediment transportation (irregular coastline)
What are some features of a beach
Berms - (ridges of sand and pebble found at high tide marks, by deposition)
Runnels - (grooves in sand parallel to shore, by backwash)
Cusps
What are cusps and how are they made
Crescent shaped indentations
Form on mixed beaches with a large tidal range, and waves parallel to beach
Sides channel swash into the centre, strong backwash moves through centre, deepens cusp and makes rip current
What is a spit
Long narrow piece of land with one end to the main land and the other jutting out to sea
How are spits formed
1.Sand deposited in sheltered water (longshore drift)
- Feature projects, storm build up more material for greater permanence
- Eventually is stopped by deep water
- Distal end curves toward land due to wave refraction and second most dominant wind
What is a bar and how do they form
A bar is when a spit connects to 2 headlands , creating a lagoon behind it
What is a tombolo and how do they form
A tombolo is when a beach extends outwards to join an offshore island
What is a barrier island and how do they form
Elongated bank of deposited sand/shingle parallel to the coastline but not submerged by high tide. If sand dunes develop, it becomes a barrier island rather than a barrier beach. Often the sheltered area becomes a lagoon or coastal marsh
Although they make up 13% of the worlds coastline, their origin is unknown, although some say they are submerged beach ridges
What is a sand dune
Accumulation of sand shaped into a mound by the wind
What conditions do sand dunes need to form
Constructive waves
Abundant sand on a gentle profile
Prevailing onshore winds
High tidal range
VEGETATION
Why are plants so important for sand dunes
Make more sand accumulate
Roots fix sand into place
Reduces wind speed close to surface
Give an example of a key plant for sand dunes and some qualities of it
marram grass
1. Spreads rapidly
2. Long roots to touch water table
3. Silver leaves reflect heat
4. Leaves fold to retain moisture
What are the 4 stages of dune development
Embryo (hummocky)
Fore/Yellow
Grey
How do embryo dunes form
Sand trapped by obstacles like driftwood. They grow upwards through accumulating sand and stabilise the surface. The growth of plants leads to hummocky dunes, where the addition of organic matter (marram grass) creates water retention
What happens at fore, yellow and grey dunes
Upward growth of embryo dunes keeps them out of reach of storm tides, meaning they can grow tall. At first they appear yellow due to lack of organic matter, but as plants grow they become more grey, and more fixed
What happens at dune heaths
Ridges start to stick out, of the grey and yellow dunes which cuts off the sand supply, so the features become smaller
What are some features of sand dunes
Dune slack - depressions in the sand dune near the water table leading to damp conditions
Blowout - Bare area of dune caused by erosion
What are mudflats
A coastal wetland
What conditions are required for a mudflat to form
Sheltered shoreline
Mix of fresh and salt water (estuary)
Lots of material (silt and clay)
Low lying, submerged at high tide
How are mudflats developed
- Sea water an river water meet, bringing together fine sediments
- The 2 flows settle out suspension through flocculation (particles aggregate together to form larger particles) and they sink to the sea bed
- Over time the sediment builds, and at low tide the mud is exposed
What are salt marshes
Coastal grassland
What conditions are required for a salt marsh to form
The same as mudflats but with VEGETATION
Give an example of key halophyte for a salt marsh to form (not algae)
Spartina grass
Has a 2 root system
- One root is fine and binds mud
- One root is thick and deep to anchor it
- Tall so they don’t drown
Give another example of a key halophyte for a salt marsh to form
Algae has…
1. High salinity
2. High turbidity
3. Long inundated periods
4. Low oxygen levels
Allowing it to slow currents and deposit material
How (in long) do salt marshes develop
1.Mudflats develop and algae grows on them , building material
- Low marsh areas become colonised by pioneer plants like Spartina,
- High marsh areas are completely covered by pioneer plants, creating a dense 15cm thick mat of vegetation and allows soil to develop
- More and more mud builds and it grows below the water level
What are the 2 types of spits
Simple
Compound - mini spits and recurved ridges within
