Coasts

Coastal Processes

Like Rivers, coasts have three main processes: erosion, transportation and deposition.

Coastal Erosion

Coastal erosion involves the wearing away of the coastline due to various processes:

• Hydraulic action: This is the erosive power of the water, which removes rock and sand through the constant impact.
• Compressed air: Air becomes trapped in rock cracks by waves. When the waves retreat, the air expands, causing the rock to shatter.
• Abrasion: Pebbles, stones, and rocks are carried by waves and hit against the coastline, breaking off pieces of rock.
• Attrition: Rocks and stones collide with each other as they are carried by waves, becoming smaller and smoother over time until they break into sand.
• Solution: Sea water, which contains salt, slowly dissolves certain types of rocks on the coast.

Coastal Transportation

The sea moves sediment along the coast through a process called longshore drift:

• Waves approach the shore at an angle, moving sediment along the coast in a zig-zag pattern.
• The swash (waves moving up the shore) pushes material up at an angle.
• The backwash (water flowing back down) pulls material back at a right angle.
• This repeated movement causes sand and pebbles to gradually move along the coastline.

Coastal Deposition

Deposition occurs when the sea loses energy and drops the sediment it is carrying:

• Deposition happens in areas where waves slow down, such as shallow water or sheltered bays.
• In summer, waves are weaker, so more material is deposited.

Features of Coastal Erosion: Sea Caves, Arches, Stacks and Stumps

Coastal erosion shapes many unique landforms along the coastline through the processes of hydraulic action, abrasion, attrition, and solution. Below are key features that form due to coastal erosion:

• Notch Formation: Coastal erosion often begins with the formation of a notch at the base of a cliff. Hydraulic action, where the force of the waves hits the rock, creates this indentation. Abrasion, as waves hurl pebbles and sand against the cliff, further deepens the notch.
• Sea Cave: As erosion continues, the notch expands and eventually becomes a sea cave. Hydraulic action and abrasion are key here, gradually hollowing out the rock.
• Sea Arch: When a sea cave continues to be eroded and the waves cut through to the other side of a headland, a sea arch is formed. Compressed air and hydraulic action are particularly important in forcing the rock to give way, creating this open structure.
• Sea Stack: Over time, the roof of the sea arch may become too weak to support itself and collapses. This leaves behind a pillar of rock called a sea stack, isolated from the headland. Attrition further breaks down the collapsed material, leaving the stack standing.
• Sea Stump: Continuous erosion at the base of the sea stack by processes like hydraulic action and abrasion eventually causes it to weaken and collapse, forming a sea stump. This is the final stage in the erosion of a headland feature. Example: An example of these features can be seen at Hook Head, Co. Wexford, where sea caves, arches, stacks, and stumps are all present.

Features of Coastal Deposition: Spits and Tombolos

Coastal deposition occurs when the sea loses energy and drops the material it has been carrying. This process creates various landforms, including sand spits, bars, and tombolos.

Sand Spits

• A sand spit is a long, narrow ridge of sand or shingle that extends from the mainland out into the sea, often across a bay.

• Spits are formed by longshore drift when it reaches a sheltered area such as a bay and deposits material.

• As the energy of the waves decreases, more sediment is deposited, causing the spit to grow.

• Wind and wave action can curve the end of the spit inward, forming a hook shape.

  

• Over time, the spit may continue to grow, eventually forming a sand bar that cuts off a bay from the sea, creating a lagoon (a saltwater lake).

• Example: There is a sand spit at Donegal Golf Course

Tombolos

• A tombolo is a narrow sand or shingle strip connecting an offshore island to the mainland.
• Tombolos are formed when waves approach an island from different directions. As the waves meet, they lose energy and deposit sediment between the island and the mainland.
• Over time, the deposited sediment builds up, creating a sandbar that joins the island to the coast.
• Example: Howth is connected to Dublin by the Sutton tombolo.