Coastal Landforms Presentation Written and Presented by Lisa Eggo and Gemma Pattinson
Coasts • Formation • A beach is one of the most dynamic features on earth, located between the cliff line and sea at the coast. It changes twice a day with the tides, so it is never the same from one day to the next. Beaches are found along coastlines where eroded material in the sea has been deposited for example in bays between headlands. Beaches form by the action of rivers (as they bring in the material-fine sand and mud), waves, currents, tides and wind and they are covered with sand or gravel. Beaches contain a wide variety of sediment sizes from fine sands to shingles. The size and character of the beach and the slope of the beach are related to the forces to which the beach is exposed and the type of material available. The beach is the area between the lowest spring tide level and the point reached by the storm waves in the highest tides. Every beach is different but they are usually made up of material deposited on a wave-cut platform. This material is deposited as friction slows down the waves, which drop the sediment they are carrying. These waves are described as constructive because their speed up the beach (swash) is greater than their retreat (backwash). This causes material to accumulate. Most beaches will be found in bays and are formed from materials eroded from surrounding headlands. Because of the shape of the bay, the beaches are not affected by the coastal movement of material. Beaches formed in front of a line of roughly straight cliffs tend to be much more affected by longshore drift.
Sandunes • Not strictly a feature resulting directly from marine action, but the blowing of sand from a beach inland. • Conditions for formation: • 1. Strong on-shore winds. • 2. Large expanses of dry sand (spits, cuspate forlands, bays). • 3. Obstacles to limit sand movement. • Sand movement (saltation): • Is helped or hindered by: • 1. Wind velocity. • 2. Grain size and shape. • 3. Dampness of sand. • 4. An obstacle present around which deposition of sand occurs and vegetation grows.
Sand dunes Continued….. Large obsticles-in this case plants too hinder movement of sand Strong onshore winds cause the movement of and across the beach Large quantites of sand needed too form san dune
Spits Formation • A spit is a permanent landform resulting from marine deposition and formed by the processes of longshore drift. A spit can be identified as a long narrow accumulation of sand or shingle with one end attached to the land and the other projecting at a narrow angle either into the sea or across a river estuary. At the end of a spit there are usually some hooks or a curved end formed by frequent strong winds from another direction. • Spits are formed by the interruption of long shore drift, due to the wave interaction with tides, currents, or a bend in the coastline. The consequent decrease in wave energy causes more material to be deposited than is transported down the coast, building up a finger of sand that points in the direction of the longshore drift. Deposition in the water behind a spit may result in the formation of a salt marsh. • Processes involved in the formation • As I have already identified spits tend to be formed due to longshore drift. Longshore drift moves large amounts of material (sand and shingle) along the coast, where the coastline suddenly changes direction to leave a shallow, sheltered area of water. • When a wave breaks at a sloping angle due to the prevailing winds, pebbles are carried up the beach in the direction of the wave (swash). The wave draws back at right angles to the beach (backwash), carrying some pebbles with it. In this way, material moves in a zigzag fashion along a beach. • Longshore drift is responsible for the erosion of beaches and the formation of spits. Attempts are often made to halt longshore drift by constructing barriers, or groynes, at right angles to the shore.