Depositional landforms

DEPOSITIONAL LANDFORMS

ABIN V ARKKATTU

Spit• A Spit is a long, narrow

accumulation of sand or shingle, one end attached to the land the other projecting out to sea or across a river estuary. Many spits have hooked or curved ends. They are formed where longshore drift moves large quantities of sand & shingle along the coast & where the coastline suddenly changes direction to leave a shallow sheltered area of water. In the diagram X to Y represents the original coastline.

Da Nong, Vietnam

Spit• As the fetch & prevailing winds

are from the south west, in this diagram, longshore drift will be moved eastward along the coastline. At headland X the coastline changes direction & shingle will be deposited in water sheltered by the headland (B). Further deposition of sand enables the feature to build up to sea level (C) & extends its length (D). The spits growth is limited by river currents scouring its end & transporting sediment out to sea. Spurn point.

Spit (Salt Marsh)• Behind the spit a quiet

tranquil lagoon forms & sediment (brought in both by sea currents & from rivers) is deposited there. Eventually the sediment builds up to sea level & a Salt marsh forms.

Hooked (Recurved) Spit

• Occasionally storms come in from the south east or east & move sediment in a different direction forming the curve or hook (E).When the wind returns to normal the spit resumes its growth eastward (F). Sand is blown on land (G), forming sand dunes.

• Hurst Castle Spit, Hants.

Hooked (Recurved) Spit

The hooks & salt Marsh are well displayed on the slide above.

Animation

Double Spit

• Formed from a breach of a pre existing spit or bar.

• Usually by a river or storm.

• Christchurch Harbour, Dorset

• Laudhelm Beach, Maine.

Barrier Beach (Bar)

• The spits growth is limited by river currents scouring its end & transporting sediment out to sea. If there is no river the spit may grow across the estuary and form a Bar.

• Slapton Sands, Devon

Barrier Island

• These are formed by rising sea level. As the sea rose at the end of the last ice age large quantities of sediment (beach) were pushed upward in front of the rising sea level (bulldozerisation), forming a ridge or island.

• The barriers move inland by “overwash” as sediment is eroded off the seaward side of the barrier & redeposited on the landward side.

• North Carolina, USA.

Barrier Island

Wave Refraction• As waves approach the

coastline, they come in contact with the sea bed & slow down, this happens first off the headlands.

• The wave is still in deep water off the bays.

• The wave is therefore bent.• The energy is concentrated

on the headlands (erosion)• Energy is dissipated in the

bays (deposition)

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Tombolo

• The waves are refracted around the island & set up 2 opposing LSD directions.

• These merge behind the island & sand is deposited linking the mainland & the island

• Goat Island, California• San Antonia, Costa Rica

Tombolo• Hafun Penninsula,

Somalia• St. Ninian Island,

Western Scotland.

LSD

LSD

Cuspate Foreland• A complex structure formed in a variety of ways• Deposition behind a spit.• LSD in 2 directions (Tombolo)

• Dungeness, Kent.

Bayhead Beach

• In bays there is little energy (wave refraction).

• Sediment that drifts in is trapped & a beach develops.

• Pett Levels, Kent.