Coastal erosion
Coastal erosion is the loss or displacement of land, or the long-term removal of sediment and rocks along the coastline due to the action of waves, currents, tides, wind-driven water, waterborne ice, or other impacts of storms.[1][2] The landward retreat of the shoreline can be measured and described over a temporal scale of tides, seasons, and other short-term cyclic processes.[3] Coastal erosion may be caused by hydraulic action, abrasion, impact and corrosion by wind and water, and other forces, natural or unnatural.[3]
On non-rocky coasts, coastal erosion results in 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. Over time the coast generally evens out. The softer areas fill up with sediment eroded from hard areas, and rock formations are eroded away.[4] Also erosion commonly happens in areas where there are strong winds, loose sand, and soft rocks. The blowing of millions of sharp sand grains creates a sandblasting effect. This effect helps to erode, smooth and polish rocks. The definition of erosion is grinding and wearing away of rock surfaces through the mechanical action of other rock or sand particles.
According to the IPCC, sea level rise caused by climate change will increase coastal erosion worldwide, significantly changing the coasts and low-lying coastal areas.[5]
Coastal processes[edit]
Hydraulic action[edit]
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[edit]
Attrition occurs when waves cause 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.
Abrasion[edit]
Abrasion, also known as corrasion, 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[edit]
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 moderately high pH, are particularly affected in this way. Wave action also increases the rate of reaction by removing the reacted material.
Pacifica, California coast after major storms in 1997 (resulting from the strongest El Niño on record) destroyed the houses shown above.
Coastal erosion at Torrey Pines State Reserve, California, resulted in the necessary relocation of a scenic overlook.
Erosion of cliffs on the Norfolk coast near Cromer. The coastline along East Anglia's North Sea coast is particularly prone to erosion, and has led to many instances of properties being relocated or destroyed over the course of history.
Tracking[edit]
Storms can cause erosion hundreds of times faster than normal weather. Before-and-after comparisons can be made using data gathered by manual surveying, laser altimeter, or a GPS unit mounted on an ATV.[16] Remote sensing data such as Landsat scenes can be used for large scale and multi year assessments of coastal erosion.[17][18][19] Moreover, geostatistical models can be applied to quantify erosion effects and the natural temporal and spatial evolution of tracked coastal coastal profiles. The results can be used to determine the required temporal and spatial distances between the measured profiles for ecomic tracking.[20]