You are here:

Offshore water: Coastal Processes

Offshore water: Coastal Processes

​There are various coastal processes in play which are always in action and these have shaped the coastlines of the world and are responsible for some of the resulting landforms formed. These are coastal erosion, transportation and deposition. The island of Ireland is no stranger to these processes (having over 1450 km of coastline) and they, along with the underlying geology, are responsible for some our coastal landmarks e.g. Bridges of Ross and Cliffs of Moher, Co Clare; Curracloe Strand Beach, Co Wexford; Rosses Point, Co Sligo; and Dingle, Co Kerry.

Geological Survey Ireland is involved in a series of projects which monitors coastal erosion and the susceptibility of the Irish coast. These include the Coastal Vulnerability Index (more info here) and Coastal Erosion from Space (more info here). This data can help policy makers plan for things such as future sea-level rise.

Before learning about the different coastal processes, here a few key terms:

  • Swash = waves moving up the beach and towards the land
  • Backwash = waves moving down the beach and back to the sea
  • Destructive waves = higher rather than long, backwash stronger than swash, carry material out to sea.
  • Constructive waves = longer rather than high, swash stronger than backwash, carry material to beach and deposit it.

Coastal erosion

This is where the land is eroded by the sea and usually involves destructive waves. It is usually the base of the cliff which is eroded, and as there is nothing to support the top part, it crumbles and collapses into the sea.

Processes include:

  • Corrasion – beach material (e.g. stones and pebbles) picked up by waves slam/crash into the base of cliffs
  • Abrasion – beach material (e.g. stone and pebbles) grind along rocks, acting like sandpaper. The rock eventually becomes smooth.
  • Hydraulic action – air from waves hitting the base of cliffs is trapped and compressed in the cracks of the rocks and causes it to expand. Repeated action causes material to break away.
  • Attrition – waves cause beach material (e.g. stone and pebbles) to collide and chip against one another, causing them to break apart, and become smaller and more rounded particles.
  • Corrosion/ solution – weak acids in seawater react with certain rocks, such as limestone and chalk, and erode them by dissolving them.

Resulting landforms: cliffs (e.g. cliffs of Moher, Co Clare); headlands and bays (e.g. Bray Head, Co Dublin); caves-arches-stacks-stumps (e.g. Great Pollet Sea Arch, Co Donegal).

More details about coastal erosion as a natural hazard can be found in the Topics section.

Coastal transportation

This is where beach material is transported in the sea and along the coast. This is mainly done by longshore drift, but there are also other ways to move beach material.

Longshore drift is when waves move in the direction of the prevailing wind at an angle to the beach. The swash, which carries the material, follows this same angle, but the backwash moves material vertically down the beach. This allows for material to be eroded from one side of the beach and to be deposited at the other. Examples of such deposition features are spits, such as Inch Strand, Co Kerry and Bannow Bay Spit, Co Wexford.

The other ways beach material can be moved are:

  • Traction – beach material rolls along the sea floor
  • Saltation – beach material bounces along the sea floor
  • Suspension – beach material is suspended within the water column and moved by the waves
  • Solution – beach material is dissolved in the sea water and moved by the waves

Coastal deposition

This is where beach material is deposited, builds up over time and usually involves constructive waves.

Resulting landforms: beaches (any beach in Ireland, can be sand, rocks, pebbles); spits (e.g. Inch Strand, Co Kerry and Bannow Bay Spit, Co Wexford).