Chapter 10: The Sea

Question 1

Waves

Answer 1

The sea is constantly shaping the coastline. Waves erode, transport and deposit material along the coast.
Waves are formed by wind moving across the surface of the sea. The distance of open sea over which the wind blows is called the fetch. Waves with a greater fetch are stronger.
When waves reach shallow water, the front of the waves comes in contact with the seabed, causing it to break as it moves towards the short.
When a wave breaks, the water that rushes up the beach is known as the swash. The water that returns back down the beach is known as the backlash.

Question 2

Two types of waves

Answer 2

Constructive waves

Destructive waves

Question 3

Construction waves

Answer 3

Waves in which the swash is greater than the backwash. Constructive waves deposit material.

Question 4

Destructive waves

Answer 4

Waves in which the backwash is greater than the swash. Destructive waves erode material and carry it away.

Question 5

Processes of coastal erosion

Answer 5

Hydraulic action
Abrasion
Compression
Solution
Attrition

Question 6

Coastal erosion: Hydraulic action

Answer 6

The physical force of the waves breaks material off the coastline. During a storm, waves are stronger and their ability to erode increases.

Question 7

Coastal erosion: Abrasion

Answer 7

Loose material (rocks and sand) is thrown against the coastline by waves. This action breaks more material off the coastline

Question 8

Coastal erosion: Compression

Answer 8

When waves crash against a cliff, air gets trapped in the cracks and joints on the cliff face and becomes compressed. When the waves retreat, the pressure is suddenly released. This process of compression and release happens repeatedly until the rock eventually shatters

Question 9

Coastal Erosion: Solution

Answer 9

Some rocks, such as limestone and chalk, are dissolved by water.

Question 10

Coastal erosion: Attrition

Answer 10

The stones that are carried in the water are constantly hitting against each other. Over time, they become worn down, smooth and rounded. This can eventually lead to the formation of sand

Question 11

Bays and headlands

Answer 11

A bay is a curved area where the waves have eroded the coastline. A headland is an area of hard rock jutting into the sea
Formation
The coastline is made up of hard rock and soft rock. As waves crash against the coastline, soft rock such as limestone is eroded faster than hard rock such as basalt.
The processes of hydraulic action, abrasion, compression and sometimes, solution erode the softer rock to form a bay.
The harder rock stands out on either side of the bay to form headlands.
Sometimes beaches form in bays.
Example of a bay: Dublin Bay
Examples of a headland: Bray Head

Question 12

Sea Cliffs

Answer 12

A sea cliff is a vertical or steep slope on the coastline. They can be seen on OS maps where contour lines along the coast are very close together.

Question 13

Formation of a Sea Cliff

Answer 13

Waves erode a notch at a line of weakness on the coastline between the high-water mark and the low-water mark. Over time, this notch grows larger due to the hydraulic action of the waves.
Undercutting then occurs
The rock above the notch is called the overhang. It is left without support and eventually collapses.
As the sea erodes further and the rock it erodes get higher, a cliff is formed.
The processes of compression and abrasion constantly erode the cliff so that it retreats into the coastline.
The rock that is left at the former base of the cliff is called a wave-cut platform. Material eroded from the new cliff face is then deposited on top of this platform to form a wave-built terrace
Example: Cliff of Moher in Co. Claire

Question 14

Sea caves

Answer 14

A sea cave is a tunnel at the base of a cliff.

Question 15

Sea arches

Answer 15

A sea arch is an arch-shaped tunnel that stretches through a headland.

Question 16

Sea stacks and stumps

Answer 16

A sea stack is a pillar of rock cut off from the cliff or headland and left standing on its own.

Question 17

Blowholes

Answer 17

A blowhole is a passage that links the surface of the cliff top with the roof of a sea cave. They can be seen on OS maps as small blue circles near the coast.

Question 18

Formation of Blowholes

Answer 18

When waves crash into a sea cave, air is trapped and compressed inside, causing the rock in the roof of the sea cave to shatter. The rock eventually collapses, forming a blowhole. During stormy weather conditions, sea spray can be seem coming out of the blowhole
Examples of blowholes: The Two Pistols and McSwyne’s Gun on the Co. Donegal coast.

Question 19

Longshort Drift

Answer 19

The material transported by waves, such as sand, shingle, mud and eroded material, is called the load. The movement of the load along the coastline is called longshore drift.

Question 20

Longshort drift involves two steps

Answer 20

1. Waves approach and move up the shore at an angle (matching the direction of the prevailing wind). When a wave breaks, the swash moves the load up the shore at an angle and deposits some material there, and so the material is move along the shore.
2. The backwash carries material back down the shore. This movement follows the slope of the beach, and is usually in a straight line.

The process is repeated over and over, resulting in the gradual movement of material along the shore in a zigzag fashion.

Question 21

Beaches

Answer 21

A beach is a build-up of sand and shingle (small pebbles) that have been deposited by constructive waves between the high-water and low-water marks. They are yellow on OS maps.

Question 22

Formation of Beaches

Answer 22

When wave break, they lose energy and are unable to carry their load. The swash carries material up the shore and deposit it.
The waves are unable to carry all the material back because the backwash is weaker than the swash.
The heaviest material is dropped first, and the finer material is carried closer to the shoreline. Over time, this material builds up to form a beach.
During storms, waves are stronger and are able to carry heavier material such as boulders and rocks. This heavy material is then deposited above the high-water line. This creates a storm beach.
Examples: Greystones in Co. Wicklow
Example of storm beach: Kilkee, Co. Claire.

Question 23

Sand Dunes

Answer 23

Sand dunes are a build-up of sand at the back of the beach above the high-tide level

Question 24

Sand spits

Answer 24

A sand split is a long ridge of sand or shingle that stretches across a bay and is connected to one side of the bay.

Question 25

Lagoons

Answer 25

A lagoon is an area of water that has been cut off from the sea by a sandbar.

Question 26

Tombolos

Answer 26

A tombolo is a ridge of sand that connects the mainland to an island.

Question 27

How people interact with the sea

Answer 27

Food supply
Transport
Recreation

Question 28

Coastal protection

Answer 28

Sea walls
Rock armour
Groynes
Gabions

Question 29

Sea walls

Answer 29

Sea walls break the power of incoming waves, and their curved tops push waves back out to sea. During storms, these concrete walls can be damaged and may need repair.
Examples: Salthill, Co. Galway.

Question 30

Rock armour

Answer 30

These are large boulders at the base of cliff or in front of sand dunes. When a wave breaks, it hits the rock armour and loses energy. This reduces the erosion of the coastline. Rock armour is used to protect the coastline at Tramore in Co. Waterford

Question 31

Groynes

Answer 31

Groynes are concrete or wooden structures built at right angles to the coastline. They extend down the shoreand into the sea. They are designed to trap sediment carried by longshore drift. This ensures that sand builds up on the beach rather than being removed from it. Groynes can have a negative impact, however. If sand is trapped in one place, it means that further down the coastline there is nothing to deposit, and rhe waves have more power to erode.

Question 32

Gabions

Answer 32

Gabions are wire cages filled with small stones. They are placed in front of beaches or sand dunes to break the power of the waves and slow down erosion. Gabions are used to protect the beach at Lahinch in Co. Galway.