Coastal erosion

Many stretches of the East Anglia, England coastline are prone to heavy levels of erosion, such as this, the collapsed section of cliffs at Hunstanton, Norfolk.

Coastal erosion is the wearing away of land and the removal of beach or dune sediments by wave action, tidal currents, wave currents, or drainage (see also beach evolution). Waves, generated by storms, wind, or fast moving motor craft, cause coastal erosion, which may take the form of long-term losses of sediment and rocks, or merely the temporary redistribution of coastal sediments; erosion in one location may result in accretion nearby. The study of erosion and sediment redistribution is called 'coastal morphodynamics'. It may be caused by hydraulic action, abrasion, impact and corrosion.

On non-rocky coasts, coastal erosion results in dramatic (or non-dramatic) rock formations in areas where the coastline contains rock layers or fracture zones with varying resistance to erosion. Softer areas become eroded much faster than harder ones, which typically result in landforms such as tunnels, bridges, columns, and pillars.

Contents

Examples

An example of coastline erosion is in north Wales where over years of the sea beating at the cliffs the houses on top have begun collapsing into the sea. With some of them you can even see inside as the entire backs of some of the houses have come off and have been launched over the clifftop that has been torn through by the ferocious sea.

Dunwich, the capital of the English medieval wool trade, disappeared over the period of a few centuries due to redistribution of sediment by waves. Human interference can also increase coastal erosion: Hallsands in Devon, England, was a coastal village that washed away overnight, an event possibly exacerbated by dredging of shingle in the bay in front of it.

The California coast, which has soft cliffs of sedimentary rock and is heavily populated, regularly has incidents of housing damage as cliffs erode. Damage in Pacifica is shown at left. Devil's Slide, Santa Barbara and Malibu are regularly affected.

The Holderness coastline on the east coast of England, just north of the Humber Estuary, is the fastest eroding coastline in Europe due to its soft clay cliffs and powerful waves. Groynes and other artificial measures to keep it under control has only accelerated the process further down the coast, because longshore drift starves the beaches of sand, leaving them more exposed. The White Cliffs of Dover have also been affected.

Wave action

Hydraulic action

Hydraulic action occurs when waves striking a cliff face compress air in cracks on the cliff face. This exerts pressure on the surrounding rock, and can progressively splinter and remove pieces. Over time, the cracks can grow, sometimes forming a cave. The splinters fall to the sea bed where they are subjected to further wave action.

Attrition

Attrition occurs when waves causes loose pieces of rock debris (scree) to collide with each other, grinding and chipping each other, progressively becoming smaller, smoother and rounder. Scree also collides with the base of the cliff face, chipping small pieces of rock from the cliff or have a corrasion (abrasion) effect, similar to sandpapering.

Corrasion and corrosion

Corrasion (abrasion) occurs when waves break on cliff faces and slowly erode it. As the sea pounds cliff faces it also uses the scree from other wave actions to batter and break off pieces of rock from higher up the cliff face which can be used for this same wave action and attrition.

Corrosion or solution/chemical weathering occurs when the sea's pH (anything below pH 7.0) corrodes rocks on a cliff face. Limestone cliff faces, which have a high pH, are particularly affected in this way. Wave action also increases the rate of reaction by removing the reacted material.

Factors that influence erosion rates

Primary factors

The ability of waves to cause erosion of the cliff face depends on many factors.

The hardness or ‘erodibility’ of sea-facing rocks is controlled by the rock strength and the presence of fissures, fractures, and beds of non-cohesive materials such as silt and fine sand.

The rate at which cliff fall debris is removed from the foreshore depends on the power of the waves crossing the beach. This energy must reach a critical level to remove material from the debris lobe. Debris lobes can be very persistent and can take many years to completely disappear.

Beaches dissipate wave energy on the foreshore and provide a measure of protection to the adjoining land.

The stability of the foreshore, or its resistance to lowering. Once stable, the foreshore should widen and become more effective at dissipating the wave energy, so that fewer and less powerful waves reach beyond it. The provision of updrift material coming onto the foreshore beneath the cliff helps ensure a stable beach.

The adjacent bathymetry, or configuration of the seafloor, controls the wave energy arriving at the coast, and can have an important influence on the rate of cliff erosion. Shoals and bars offer protection from wave erosion by causing storm waves to break and dissipate their energy before reaching the shore. Given the dynamic nature of the seafloor, changes in the location of shoals and bars may cause the locus of beach or cliff erosion to change position along the shore.[1]


Secondary factors

  • Weathering and transport slope processes
  • Slope hydrology
  • Vegetation
  • Cliff foot erosion
  • Cliff foot sediment accumulation
  • Resistance of cliff foot sediment to attrition and transport

Tertiary factors

  • Resource extraction
  • Coastal management

See also

External links

Images:

References


Wikimedia Foundation. 2010.

Look at other dictionaries:

  • Coastal sediment supply — is the transport of sediment to the beach environment by both fluvial and aeolian transport. While aeolian transport plays a role in the overall sedimentary budget for the coastal environment, it is paled in comparison to the fluvial supply which …   Wikipedia

  • Coastal flood — Coastal flooding occurs when normally dry, low lying land is flooded by sea water.[1] The extent of coastal flooding is a function of the elevation inland flood waters penetrate which is controlled by the topography of the coastal land exposed to …   Wikipedia

  • Coastal geography — is the study of the dynamic interface between the ocean and the land, incorporating both the physical geography (i.e coastal geomorphology, geology and oceanography) and the human geography (sociology and history) of the coast. It involves an… …   Wikipedia

  • Coastal management — This article is about coastal management aimed to prevent erosion and flooding. For broader management issues, see Integrated coastal zone management. Oosterscheldekering sea wall, the Netherlands. In some jurisdictions the terms sea defense and… …   Wikipedia

  • Coastal development hazards — A coastal development hazard can be defined as the likelihood of an event or incident occurring multiplied by the seriousness of the event or incident if it occurred. The seriousness is controlled by how vulnerable the adversely affected party… …   Wikipedia

  • erosion — erosional, adj. /i roh zheuhn/, n. 1. the act or state of eroding; state of being eroded. 2. the process by which the surface of the earth is worn away by the action of water, glaciers, winds, waves, etc. [1535 45; < L erosion (s. of erosio). See …   Universalium

  • erosion — noun ADJECTIVE ▪ serious, severe, significant ▪ Acid rain has caused severe erosion on the hillside. ▪ further ▪ He risks further erosion of his support among voters …   Collocations dictionary

  • coastal — adjective 1. of or relating to a coast (Freq. 1) coastal erosion • Pertains to noun: ↑coast • Derivationally related forms: ↑coast 2. located on or near or bordering on a coast (Freq. 1) …   Useful english dictionary

  • Erosion du littoral — Érosion du littoral 75% environ du trait de côte européen régresse significativement et parfois rapidement, parfois naturellement, parfois suite aux activités humaines, ici sur l île d Héligoland (Allemagne) L érosion du littoral est un phénomène …   Wikipédia en Français

  • Érosion côtière — Érosion du littoral 75% environ du trait de côte européen régresse significativement et parfois rapidement, parfois naturellement, parfois suite aux activités humaines, ici sur l île d Héligoland (Allemagne) L érosion du littoral est un phénomène …   Wikipédia en Français


Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”

We are using cookies for the best presentation of our site. Continuing to use this site, you agree with this.