Coasts Revision

Salt Marshes & Sand Dunes

• Salt Marshes
• Common in low energy environments of estuaries & sheltered bays
• Slow movement = More material deposited
• Clay particles stick together= Flocculation
• Where they are found;
• Estuaries, Creeks, Behind a Spit (Which sometimes forms across an estuary)
• Impact of Life;
• Plants change the conditions by trapping sediment = Build salt marsh to a higher level
• Sand Dunes
• Where they form;
• Where there is lots of sand & a large area for the sand to dry out
• Onshore winds to blow sand towards land
• Obstacles such a vegetation or shingle ridges = To trap the sand
• Embryo Dunes
• They collect more sand & become larger
• Pioneer plants (e.g sea rocket) are able to colonise the stable dunes & help to hold the sand together
• Yellow Dunes
• Highest & may form a ridge near the dune front with marram grass
• Not fully vegetated & are subject to alteration by wind and waves -> (Blow-outs forming gaps in the line of dunes)
• At high tide or storm conditions = seawater may reach the slacks
• Mature Dunes
• Greater humus content

Formation of a Spit

• Spits form when
• There is a dominant main longshore drift direction
• Plenty of sediment from mass movement and erosion
• There is a gap in the coastline -> Such as estuary or bay
• How its formed
• Longshore drift moves sediment along a coast
• When the sediment reach a gap in the coastline = They are carried for a short while in the same direction -> Until they are deposited on the seabed
• Over time this material is deposited so much = Break the surface of the sea to form a spit
• It shelters the area of sea behind it = Sediment from the sea & rivers are deposited in the calm area
• Eventually salt tolerant plants are able to form mudflat & salt marsh
• As the spit grows longer = Tides, river currents & other wave directions turn the end of the spit into a hook