Coastal Erosion Facts

Water is not given enough credit for the role it plays in shaping Earth. Tectonic plates and volcanic eruptions are often cited as the culprits for most land features, but it is water and wave action that shapes and constantly reshapes the coastlines of our world.

When a wave crashes on the shore it carries sediments that are suspended in the water, and it pushes larger sediments along the ground too. When a wave recedes it also takes sediment with it and this is rarely done at an equal rate.

If a wave deposits more sediment than it takes away it builds up, causing coastlines to extend. Alternatively, when more sediment is being removed than added, the coastline recedes or erodes. Coastal erosion is responsible for some of the most amazing landforms we know today from the Twelve Apostles in Australia to the White Cliffs of Dover in England.

The type of coastline that is created from erosion varies greatly depending on any number of factors including the strength of the wave action and wind, sediment composition of the coastline and the types of rock in the vicinity.

Coastal erosion is a very slow process taking hundreds of years, but scientists believe that climate change is speeding things up. Climate change has caused a rise in sea levels and storm frequency and severity – both of which play a key role in erosion. Indeed, the UK’s Environment Agency has estimated that the British coastline could erode anywhere from 67-175 metres {220-575 feetlover the next 100 years.

More than one way to wear a rock…

Corrosion – This chemical-based erosion occurs only with certain types of rock such as chalk or limestone, which are high in calcite. The acidity of the seawater causes a chemical reaction in the mineral, eating away at it.

Abrasion – This occurs when the sediment suspended in the water (eg sand) is thrown against the shore by waves. The sediments grind against the land, weakening the structural integrity of the coastline.

Hydraulic action – Wave action compresses tiny air pockets within the rock, which eventually causes cracks to form. The cracks get bigger and bigger over many years and eventually develop into caves and so on.

Attrition – Continued wave action hurls stones and other material at the land, which smooths and breaks up the rocks on the coast, dislodging them from. These in turn collide with other rocks on the shore.

The different shapes of coastlines

Bay – Bays are inlets of water that form between headlands. They have low-energy wave action.

Atoll – Atolls can be ring or horseshoe-shaped coral reefs surrounding an inner lagoon. They are formed when a fringing reef develops around an island; the island gradually subsides into the water due to erosion.

Delta – These occur where a river flows into another body of water like the ocean. The river’s flow, which carries sediment, is stemmed so the sediment builds up around the river mouth.

Fjord – A narrow inlet of water surrounded by a steep shoreline. Fjords form when a glacier cuts a deep valley into bedrock. The glacier recedes and the valley floods with water.

Fringing reef – Fringing reefs are coral reefs that develop around an island, creating – as the name suggests-a fringe. Coral polyps build on top of one another to form huge living structures.

Blowhole – These occur when a sea cave is developing and a small hole forms on top of the headland. Wave action forces water up through the hole, up to several metres high.