The work of the Sea
The sea, like rivers, erodes, transports and deposits. As a result
of this many features are formed.
Waves
Waves are formed when wind blows across the surface of the
water. This causes the water to move in a circular motion. This
is why the Crest (Top) curls over before it breaks. A good
example of this is surfers in a tunnel of water.
Ways in which waves erode
1. Hydraulic action The force of the water pounding against
the coast.
2. Compression
Air trapped by the waves causes the rock
to shatter.
3. Abrasion
Rocks/stones carried by the sea crashing
against the coast.
4. Attrition
Rocks/stones hitting and rubbing off each
other to create sand and pebbles.
Features formed by Sea Erosion
Sea Cliffs
Sea cliffs are formed as a result of Hydraulic Action. As the
waves pound against the coast a notch is formed. As the notch
gets deeper the overhanging rock becomes unstable and
collapses to form a cliff. A level stretch of rock is formed at the
base called a wave cut platform, while the fallen rubble in front
of this is called a wave built terrace.
Examples: Cliffs of Moher, Co.Clare.
1
Bays
A Bay is a wide, curved opening into the coast. It is formed
where areas of hard rock and soft rock lie side by side. The soft
rock erodes faster to form a bay shape. Sandy beaches are often
found on the inside of bays.
Example: Donegal Bay.
Headlands
A Headland is formed in the same way as a bay only that it is
the hard, resistant rock that is left behind that makes up the
headland. A piece of land that juts further out into the sea than
the land around it is a headland.
Example: Malin Head, Co.Donegal.
Sea Caves
A Sea Cave is a long tunnel shape on a Sea Cliff. It gets lower
and narrower the further into the cliff it goes. Waves find a
weak spot at the base of the cliff and gradually erodes it until a
cave is formed.
Example: Bundoran, Co. Donegal.
Sea Arch
A Sea Arch is an arch-shaped tunnel through a headland. It is
formed as a result of a cave eroding right through to the other
side of a (narrow) headland.
Example: Bundoran, Co.Donegal.
Sea Stack
A Sea Stack is a pillar of rock that stands alone just off the
coast. It is formed when the roof of a Sea Arch collapses into the
sea. The Sea Stack is totally surrounded by water. On an
ordnance survey map they are always found just off the coast
and are referred to as ‘rocks’. A sea stump is a worn down stack.
Example: Bundoran, Co. Donegal.
2
Blowholes
A Blowhole is a hole on the mainland that forms above a Sea
Cave. It is formed by Compression. Air gets trapped in a cave
by waves and causes small rock particles to shatter. Over a
period of time the roof will eventually break through to the
surface and form a blowhole. It is called a blowhole as water
often sprays up out of it.
Example: ‘McSweeney’s Gun’, Co.Donegal.
Transport by the Sea
Waves carry the seas’ load in two ways/directions.
 Up and down the shore by the Swash and Backswash.
 Along the shore by Longshore Drift.
Waves approach the coast at an acute angle (roughly 45). As a
result of this the material that has been deposited on a beach is
constantly being moved across to one side (in a zig-zag pattern).
This results in a build up of sand at one end of the beach.
Deposition occurs mainly in sheltered areas like bays and areas
of shallow water. The lighter material (sand) is found closer to
the sea while the shingle (sand and pebbles) are found further up
the beach and would have been deposited during storms, hence
the name Storm Beach.
3
Features formed by Sea Deposition
Beaches
Beaches are formed when waves that are carrying sand/pebbles
break when they reach the shore. When they break they lose
their power and so drop whatever they were carrying. Beaches
are usually found on the inside of bays. The material is usually
sorted in layers. Heavier material found further up the beach and
sand found closer to the waters edge. On an ordnance survey
map beaches appear as yellow.
Sand Dunes
Sand dunes are formed when sea breezes blow the dry sand off a
beach and on to the land behind it. After some time the sand
accumulates to form sand dunes. Marram grass helps to bind the
dunes together.
Sand Spit
A sand spit is a narrow ridge of sand that juts out into the sea
but is connected to the land at one end. It is formed as a result of
a beach extending out into a bay. The sand which had been
carried by Longshore Drift eventually builds up to form a sand
spit.
Example: Portmarnock, Co.Dublin.
Sand Bar
A Sand Bar is a beach or sand spit that stretches right across a
bay and seals part of it off from the rest of the bay. The trapped
water that has been cut off is now referred to as a Lagoon.
Example: Lady’s Island Lake, Co.Wexford.
4
Tombolos
A Tombolo is a narrow ridge of material that joins an offshore
island to the mainland.
Example: Howth, in Co.Dublin used to be an island until a
tombolo joined it to the mainland.
People and the Sea
Ways in which the sea helps people
1.
2.
3.
4.
Useful for tourism and leisure activities.
Provide fish for food etc.
The sea floor provides a lot of fossil fuels.Oil,Gas,Coal etc
Wave power. Provides electricity.
Ways in which the sea harms people
1. Land and property may be lost due to Erosion.
2. Low lying areas may become flooded. E.g. Holland,
Bangladesh.
3. May increase the damage caused by pollution i.e.
Waves/currents spreading oil spills over vast distances.
Ways of defending against the Sea
 Strong concrete Sea Walls or large boulders to break
waves and reduce erosion.
 Breakwaters to reduce erosion in the area sheltered
by it.
 Groynes (Concrete or Wooden) to reduce Longshore
Drift.
 Dredge harbours to get rid of sand deposited as a
result of Longshore Drift.
5
6