The work of the sea a.kearon

The Work of the Sea•The sea erodes, transports and deposits material, thereby changing the shape of coast lines.

Waves erode mainly by:1.Hydraulic action (power of the water hitting the shore)2. Abrasion (stones etc. bashed against the shore by the

waves)3. Solution (when certain rocks e.g. chalk are dissolved

by the water)

4. Attrition – the rocks hitting off each other, becoming smooth and well rounded.

5. Compressed air – air and water gets trapped in cracks in rocks, expands and shatters the rock.

Formation of a bay

• Coastlines consist of

hard and soft rock

• The soft rock erodes

more quickly than the

hard rock and a bay is

formed.

Formation of a Headland

• The hard rock in a coastline erodes more slowly than the soft rock

• The hard rock that has not eroded, juts out to the sea, forms a headland

CLIFFS• A cliff is a steep part of the coast

Formation of Cliffs

• A Cliff is formed when– Waves erode the coast and form a small notch.

– The erosion continues until the notch gets bigger.

– The section of rock above the notch cannot be supported anymore and collapses.

– The slope becomes steeper

– A cliff is formed.

– The former base of the cliff remains as a wave cut platform.

Formation of Sea Caves

• A large hole or tunnel at

the base of the Cliff is

called a cave.

• If there is a weak spot

such as a crack or a

joint in the rock, the

waves will attack it and

erode a passage called

a sea cave

Formation of a Blow Hole

• Draw diagram p54

• A blow Hole is a hole which joins the roof of a cave with the surface above.

Transportation by the Sea

• Waves approach the shore at an angle.

• The swash of each wave pushes material up the beach (A-B).

• Because of the slant the backwash drags the material straight down (B-C)

• The process is repeated so the material is transported (moved) along in a zig zag pattern.

Long Shore Drift

Long Shore Drift

A

B

C

Direction of Long Shore Drift

Wave Direction

Sea

How can you stop Long Shore Drift?

• A Groyne is a low wall built into the sea to stop long shore drift.

Sea Deposition

• A beach is a gently sloping area of sand, pebbles or stones along the shore.

• It lies between the high-tide mark and the low-tide mark.

• It is formed by the swash pushing materials up the beach and the weaker backwash pulls finer materials back down.

Formation of a Beach:

A Storm Beach is formed when large stones are deposited at the top of a beach during a storm.

Sand Dunes

• Sand dunes are mounds of sand at the back of a beach.

• Sand dunes are formed because of the wind blowing the sand inland.

Marram Grass

• Marram grass is long, dry and has long roots.

• These roots bind the sand together and protect it from the wind and the rain

The Formation of a SPIT

• A sand spit is a ridge of sand or shingle that juts out into the sea.

• Long shore drift stops when it reaches a bay or sheltered place.

• The material may build up gradually to form a spit.

• Eg. Portmarnock, Co. Dublin

The formation of a SPIT

Formation of a SAND BAR

• A sand bar is a sand spit (explain formation) that stretches across a bay to connect the two sides of the bay.

• The lake behind the sand bar is called a lagoon

• Example: Lady’s Island, Co. Wexford

Formation of a SAND BAR

Formation of a TOMBOLO

• A tombolo is a ridge of sand or shingle that joins an island to the mainland

• A tombolo forms when a sand spit juts out into the sea and links with an island

• Example: Sutton, Co Dublin

Formation of a TOMBOLO