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COASTAL DEPOSITION

How Deposition takes Place When waves don’t have much energy they drop their load.

This happens mainly when:

A bay is sheltered (no wind to give the wave energy).

The shore is sloped (harder for the wave to move uphill).

How is a bay

formed ?Sheltered Bays + Gentle Slope = Deposition

Features of Coastal Deposition

Beaches and storm beaches Spits Bars Lagoons Tombolos

BarLagoon Tombol

o

Spit

Sheltered Bay

Longshore drift

Beaches F A beach is the area between high tide and

low tide and it consists of sand and shingle.

E Beaches are formed by constructive waves depositing material. When waves break the

swash carries its load up the shore. The weak backwash drags some of the finer material down the shore.

E Rosses Point, Co. Sligo

Storm Beaches F A storm beach is a beach consisting of large rocks

and stones above normal high tide level.

E They are formed when the swash is strong enough to hurl the large stones up past the normal level of the beach where they remain.

E Greystones, Co. WicklowKilliney Beach, Co. Dublin

Cliffs

Beach

Some material comes from the river system

Destructive waves attack

the coast

Transportation of sediment by Longshore drift

LEARNING OUTCOMES TUESDAY 8TH

The formation of a sea spit , sea bar , lagoon and tombolo

Quickly revise beaches

Low ti

de m

ark

High

tide

mar

k

Coarser Material Fine

Material

Silt

Storm Beach

Sandy Beach

Constructive Waves

Headland

Storm Beach

What other features can

you see ?

BarLagoon Tombol

o

Spit

Sheltered Bay

Longshore drift

Spits F A spit is a ridge of sand or shingle that is connected to

the land at one end and extends into the bay or estuary at the other.

E Sand spits are formed by longshore drift. When it reaches a bay or sheltered area the waves lose energy and deposit their load on the seabed. These deposits build up above the level of the water. As this continues a spit is formed.

E Tramore, Co. Waterford

Clew Bay, Co. Mayo

Headland (hard-rock)

Salt Marsh behind a

spit

Spit

Curve caused by

wind direction

Spit stopped by

a river estuary

Prevailing wind

direction

Change in wind

direction

Direction of longshore drift

http://www.ngfl-cymru.org.uk/vtc/transport_deposit/eng/Introduction/MainSessionPart3.htm

BarLagoon Tombol

o

Spit

Sheltered Bay

Longshore drift

SAND BARS

F A bar is a narrow ridge of sand or shingle which seals off the mouth of a bay.

E A bar is formed when a spit connects two headlands.

E Our Lady’s Island Lake, Co. Wexford

LAGOON

F A lagoon is a body of water behind a sand bar.

E As the bar connects two headlands it traps a body of water behind it called a lagoon. Over time this lagoon will dry or silt up.

E Our Lady’s Island Lake, Co. WexfordLough Gill, Co. Kerry

Lagoon :Area of water cut off by a sand bar Old bay

Sand Bar formed when a spit grows across a bay,

joining the two headlands

http://www.youtube.com/watch?NR=1&v=3Y8AkkB3GdA&feature=endscreen

BarLagoon Tombol

o

Spit

Sheltered Bay

Longshore drift

TOMBOLO

F A tombolo is a ridge of sand or shingle connecting an island to the mainland.

E A sand spit extends outwards from the mainland due to long shore drift and sometimes it links with an island.

E The Sutton tombolo links Howth Head with the mainland.

Beaches

Sand Dunes

Marram Grass

Storm Beach