coastal processes

HYDRAULIC ACTION: waves enter faults in coastline, compressing the air within. when the wave retreats the air expands quickly causing a minor explosion.

ABRASION: waves throw particles against the rock at high velocity.

ATTRITION: material carried by waves bumping into each other becoming smoothed and broken down into smaller pieces.

SOLUTION: chemical action of the seawater (contains carbonic acid) the acids slowly dissolve rocks along the coastline, particularly alkaline rocks like limestone and chalk.

SUSPENSION: tiny particles of sediment carried (in suspension) in the sea's currents.

SALTATION: smaller stones/pebbles picked up and dropped, results in skipping motion

SOLUTION: dissolved chemicals carried along

TRACTION: large stones/boulders rolled along the seabed

LONGSHORE DRIFT:

• waves approach shore at an angle
• material pushed up beach by swash (same direction as approach)
• backwash drags material down steepest gradient at right angles to shoreline
• over period of time sediment moved in zigzag motion down coast by saltation and traction
• if material carried for a while it becomes smaller, more rounded and better sorted
• deposition of this material then occurs in sheltered areas or where direction of coastline changes abruptly

FREEZE-THAW: process whereby water repeatedly freezes and melts within joints/faults in the rock. As water percolates into the faults it freezes causing expansion (by up to 9%) putting presure on the rock. Scree breaks off at bare and rocky cliffs.

BIOLOGICAL: weathering resulting from organic agents (eg tree roots/rabbit burrows etc). Plants can prise apart rocks (with their roots) causing them to crack. Animals like piddocks (like clams) also burrow into the rock.

CHEMICAL: weathering of rocks by chemicals. CaCO3 in rocks like limestone dissolved by water and CO2 in air reacting (forms carbonic acid)

SALT: physical weathing of rocks. Salt crystals left behind after seawater evapourates. Can grow over time and cause cracks to form (like ice).

SOIL CREEP: (slowest form of m.m.) Heavy rain, freeze-thaw weathering and long wet periods can all move the soil in a net downslope movement of less than 1cm a year.

LANDSLIDE: rapid movement of detached slabs of rock down the cliff face

MUDFLOWS: faster movements occur on steeper slopes which are saturated (with water). Fast, most likely to be found on unconsolidated material after heavy rainfall.

ROTATIONAL SLIP: common coastal landslips in weak rocks, eg. sands and clays

ROCKFALL: rapid movements found where slopes exceed 40 degrees. Indivual rocks fall off a cliff face (often due to freeze-thaw)