Despositional Landforms Flashcards
Spit
This is a long, narrow strip of land which is formed when longshore drift causes the beach to extend out to sea, usually due to a change in direction of the coastline
The sediment projection can create a salt marsh due to the sheltered, saline environment where water flow speed is lower so disposition of finer sediments can occur
Length of the spit depends on any changing currents or rivers which will prevent sediment from being deposited meaning a spit can never extend across an estuary
Change in wind or wave direction can cause the end of the spit to curve (recurved spit) and overtime may have multiple recurved tips (compound spit)
Tombolo
A tombolo is a bar or beach that that connects the mainland to an offshore island and is formed due to wave refraction off the coastal island, reducing wave velocity, leading to deposition of sediments. They may be covered at high tide if low lying
Barrier Beach/ Bar
A barrier beach occurs when a beach or spit extents across a bay to join two headlands. This traps water behind it leading to formation of a brackish lagoon which is separated from the sea. If a barrier beach becomes separated from the mainland it becomes a barrier island. They are common in areas with low tidal ranges and can be very large.
Offshore bars
An offshore region where sand is deposited as the waves don’t have enough energy to carry the sediment to shore. They can be formed when the waves break early and instantly deposit sediment as a loose sediment offshore bar
They can also be formed when backwash from destructive waves removing sediment from a beach
Plant succession
A vegetation succession is a plant community that changes over time.
Sand dunes 5 steps
Obstacles such as drift wood get dropped on the beach
The wind blows sand up the beach which gets trapped on the obstacle
Colonising pioneer plants like marram grass grow on the dune and stabilise it with their roots and trap more sand
This creates an embryo dune
As the plants die they add organic matter to the soil and improve it so other plants can grow which will change the environment progressively
Sand dune 5 stages lead to a deine structure involving different types of dunes
Embryo dunes - upper beach area where sand starts to accumulate around a small obstacle
Yellow dunes - as more sand accumulates and the dune grows, vegetation may develop on the upper and back dune surfaces which stabilises the dune
Grey dunes - sand develops into soil with lots of moisture and nutrients we vegetation dies enabling more varied plant growth
Dune slack - the water table rises close to the surface or water is trapped between hollows between dunes during storms allowing the development of moisture loving plants
Heath and Woodland - sandy soils develop as there is greater nutrients content allowing for less brackish plants to thrive and trees will grow
Salt marsh
A coastal wetland ground in the intertidal zone where mud and silt accumulate in sheltered grass like estuaries or behind spits. Covered in salt tolerant plants like grasses and shrubs and is regularly flooded by tides
Salt marsh succession
Algal stage - gut weed and blue green algae establish as they can grow on bare mud which their roots help to bind together
Pioneer stage - cord grass and glasswort grow, their roots begin to stabilise the mud allowing the estuarine to grow
Establishment stage - salt marsh grass and sea asters grow creating a carpet of vegetation and so the height of the salt marsh increases
Stabilisation - sea thrift, scurvy grass and sea lavender grow and so salt deart ever gets submerged beneath the marsh
Climax vegetation- rush, sedge and red fescue grass grow since the salt marsh is only submerged once or twice a year
Beaches
A despositional landform that stretches from roughly the low tide to the high tide line and is created when sediment is deposited near the coastline when waves lose energy. Beach accretion builds up the beach by constructive waves but beach excavation occurs with destructive waves removing sediment from the beach.
Beaches - awash aligned and drift aligned
Swash aligned - wave crests approach perpendicular to coast so there is limited longshore drift. Sediment doesn’t travel far along the beach. Wave refraction may reduce the speed of high energy waves leading to the formation of a shingle beach with larger sediment
Drift aligned - waves approach at a significant angle so longshore drift causes the sediment to travel far along the beach which may lead to the formation of a spit at the end of a beach. Larger sediment at the start of the beach but smaller sediment at the end of the beach
Features of beach - Ridges and Runnels
Series of ridges and troughs running parallel to the coastline bear the low water mark. Ridges formed by deposition during backwash and the runnels are formed when water runs back to the ocean
Features of beach - Ripples
Relatively small elongated ridges that form on the beach
Formed by waves and currents flowing across loose sand which is dragged along the bottom and is piled up
Features of beach - Cusps
Semi circular shaped depressions with coarser material around the edge and finer materials in the middle
Formed by the waves reaching the same point and backwash scouring out the finer materials in the centre
Features of beach - berms
A series of small ridges that form near the high tide mark.
Deposited by the swash of constructive waves
