Coast
The coast, also known as the coastline, shoreline or seashore, is defined as the area where land meets the ocean,[1] or as a line that forms the boundary between the land and the coastline.[2] Shores are influenced by the topography of the surrounding landscape, as well as by water induced erosion, such as waves. The geological composition of rock and soil dictates the type of shore which is created. The Earth has around 620,000 kilometres (390,000 mi) of coastline. Coasts are important zones in natural ecosystems, often home to a wide range of biodiversity. On land, they harbor important ecosystems such as freshwater or estuarine wetlands, which are important for bird populations and other terrestrial animals. In wave-protected areas they harbor saltmarshes, mangroves or seagrasses, all of which can provide nursery habitat for finfish, shellfish, and other aquatic species.[3][4] Rocky shores are usually found along exposed coasts and provide habitat for a wide range of sessile animals (e.g. mussels, starfish, barnacles) and various kinds of seaweeds. In physical oceanography, a shore is the wider fringe that is geologically modified by the action of the body of water past and present, while the beach is at the edge of the shore, representing the intertidal zone where there is one.[5] Along tropical coasts with clear, nutrient-poor water, coral reefs can often be found between depths of 1–50 meters (3.3–164.0 feet).
According to an atlas prepared by the
However, the economic importance of coasts makes many of these
Because coasts are constantly changing, a coastline's exact
Size
The
The definition of coasts varies. Marine scientists think of the "wet" (aquatic or
While there is general agreement in the scientific community regarding the definition of coast, in the political sphere, the delineation of the extents of a coast differ according to jurisdiction.[citation needed][15] Government authorities in various countries may define coast differently for economic and social policy reasons.
Challenges of precisely measuring the coastline
The
Formation
Tides often determine the range over which sediment is deposited or eroded. Areas with high tidal ranges allow waves to reach farther up the shore, and areas with lower tidal ranges produce deposition at a smaller elevation interval. The tidal range is influenced by the size and shape of the coastline. Tides do not typically cause erosion by themselves; however, tidal bores can erode as the waves surge up the river estuaries from the ocean.[21]: 421
Geologists classify coasts on the basis of
Waves erode coastline as they break on shore releasing their energy; the larger the wave the more energy it releases and the more sediment it moves. Coastlines with longer shores have more room for the waves to disperse their energy, while coasts with cliffs and short shore faces give little room for the wave energy to be dispersed. In these areas, the wave energy breaking against the cliffs is higher, and air and water are compressed into cracks in the rock, forcing the rock apart, breaking it down. Sediment deposited by waves comes from eroded cliff faces and is moved along the coastline by the waves. This forms an
Sediment deposited by rivers is the dominant influence on the amount of sediment located in the case of coastlines that have estuaries.[23] Today, riverine deposition at the coast is often blocked by dams and other human regulatory devices, which remove the sediment from the stream by causing it to be deposited inland. Coral reefs are a provider of sediment for coastlines of tropical islands.[24]
Like the ocean which shapes them, coasts are a dynamic environment with constant change. The Earth's natural processes, particularly sea level rises, waves and various weather phenomena, have resulted in the erosion, accretion and reshaping of coasts as well as flooding and creation of continental shelves and drowned river valleys (rias).
Importance for humans and ecosystems
Human settlements
More and more of the world's people live in coastal regions.
Nations defend their coasts against military invaders, smugglers and illegal migrants. Fixed coastal defenses have long been erected in many nations, and coastal countries typically have a navy and some form of coast guard.
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Fengbin, Hualien
Tourism
Coasts, especially those with beaches and warm water, attract tourists often leading to the development of
Growth management and coastal management can be a challenge for coastal local authorities who often struggle to provide the infrastructure required by new residents, and poor management practices of construction often leave these communities and infrastructure vulnerable to processes like coastal erosion and sea level rise. In many of these communities, management practices such as beach nourishment or when the coastal infrastructure is no longer financially sustainable, managed retreat to remove communities from the coast.
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Houses close to the coast, like these in Tiburon, California, may be especially desirable properties.
Ecosystem services
Estuarine and marine coastal ecosystems are both marine ecosystems. Together, these ecosystems perform the four categories of ecosystem services in a variety of ways: The provisioning services include forest products, marine products, fresh water, raw materials, biochemical and genetic resources. Regulating services include climate regulation as well as waste treatment and disease regulation and buffer zones. Supporting services of coastal ecosystems include nutrient cycling, biologically mediated habitats and primary production. Cultural services of coastal ecosystems include inspirational aspects, recreation and tourism, science and education.
Coasts and their adjacent areas on and offshore are an important part of a local ecosystem. The mixture of fresh water andTypes
Emergent coastline
According to one principle of classification, an emergent coastline is a coastline that has experienced a fall in sea level, because of either a global sea-level change, or local uplift. Emergent coastlines are identifiable by the coastal
Concordant coastline
According to the second principle of classification, a concordant coastline is a coastline where bands of different rock types run parallel to the shore. These rock types are usually of varying resistance, so the coastline forms distinctive landforms, such as coves. Discordant coastlines feature distinctive landforms because the rocks are eroded by the ocean waves. The less resistant rocks erode faster, creating inlets or bay; the more resistant rocks erode more slowly, remaining as headlands or outcroppings.
High and low energy coasts
Parts of a coastline can be categorised as high energy coast or low energy coast. The distinguishing characteristics of a high energy coast are that the average wave energy is relatively high so that erosion of small grained material tends to exceed deposition, and consequently landforms like cliffs, headlands and wave-cut terraces develop.[27] Low energy coasts are generally sheltered from waves, or in regions where the average wind wave and swell conditions are relatively mild. Low energy coasts typically change slowly, and tend to be depositional environments.[28]
High energy coasts are exposed to the direct impact of waves and storms, and are generally erosional environments.[28] High energy storm events can make large changes to a coastline, and can move significant amounts of sediment over a short period, sometimes changing a shoreline configuration.[29]
Destructive and constructive waves
Swash is the shoreward flow after the break, backwash is the water flow back down the beach. The relative strength of flow in the swash and backwash determines what size grains are deposited or eroded. This is dependent on how the wave breaks and the slope of the shore.[30] Depending on the form of the breaking wave, its energy can carry granular material up the beach and deposit it, or erode it by carrying more material down the slope than up it. Steep waves that are close together and break with the surf
Rivieras
Riviera is an Italian word for "shoreline",
As a result of the fame of the Ligurian rivieras, the term came into English to refer to any shoreline, especially one that is sunny, topographically diverse and popular with tourists.
Other coastal categories
- A cliffed coast or abrasion coast is one where marine action has produced steep declivities known as cliffs.
- A flat coast is one where the land gradually descends into the sea.
- A graded shoreline is one where wind and water action has produced a flat and straight coastline.
- A primary coast isone which is mainly undergoing early stage development by major long-term processes such as tectonism and climate change A secondary coast is one where the primary processes have mostly stabilised, and more localised processes have become prominent.[28]
- An erosional coast is on average undergoing erosion, while a depositional coast is accumulating material.[28]
- An active coast is on the edge of a tectonic plate, while a passive coast is usually on a substantial continental shelf or away from a plate edge.[28]
Landforms
The following articles describe some coastal landforms:
Cliff erosion
- Much of the sediment deposited along a coast is the result of erosion of a surrounding Sea cliffs retreat landward because of the constant undercutting of slopes by waves. If the slope/cliff being undercut is made of unconsolidated sediment it will erode at a much faster rate than a cliff made of bedrock.[23]
- A natural arch is formed when a headland is eroded through by waves.
- Sea caves are made when certain rock beds are more susceptible to erosion than the surrounding rock beds because of different areas of weakness. These areas are eroded at a faster pace creating a hole or crevice that, through time, by means of wave action and erosion, becomes a cave.
- A stack is formed when a headland is eroded away by wave and wind action or an arch collapses leaving an offshore remnant.
- A stump is a shortened sea stack that has been eroded away or fallen because of instability.
- Wave-cut notches are caused by the undercutting of overhanging slopes which leads to increased stress on cliff material and a greater probability that the slope material will fall. The fallen debris accumulates at the bottom of the cliff and is eventually removed by waves.
- A wave-cut platform forms after erosion and retreat of a sea cliff has been occurring for a long time. Gently sloping wave-cut platforms develop early on in the first stages of cliff retreat. Later, the length of the platform decreases because the waves lose their energy as they break further offshore.[23][clarification needed]
Coastal features formed by sediment
Coastal features formed by another feature
Other features on the coast
Coastal waters
"Coastal waters" (or "coastal seas") is a rather general term used differently in different contexts, ranging geographically from the waters within a few kilometers of the coast, through to the entire continental shelf which may stretch for more than a hundred kilometers from land.[37] Thus the term coastal waters is used in a slightly different way in discussions of legal and economic boundaries[38] (see territorial waters and international waters) or when considering the geography of coastal landforms or the ecological systems operating through the continental shelf (marine coastal ecosystems). The research on coastal waters often divides into these separate areas too.
The dynamic fluid nature of the ocean means that all components of the whole ocean system are ultimately connected, although certain regional classifications are useful and relevant. The waters of the continental shelves represent such a region.[39] The term "coastal waters" has been used in a wide variety of different ways in different contexts. In European Union environmental management it extends from the coast to just a few nautical miles[40] while in the United States the US EPA considers this region to extend much further offshore.[41][42]
"Coastal waters" has specific meanings in the context of commercial
Similarly, the term
Coastal waters can be threatened by
In geology
The identification of bodies of rock formed from sediments deposited in shoreline and nearshore environments (shoreline and nearshore
Sediments deposited in the shoreface are preserved as lenses of sandstone in which the upper part of the sandstone is coarser than the lower part (a coarsening upwards sequence). Geologists refer to these are parasequences. Each records an episode of retreat of the ocean from the shoreline over a period of 10,000 to 1,000,000 years. These often show laminations reflecting various kinds of tidal cycles.[47]
Some of the best-studied shoreline deposits in the world are found along the former western shore of the
Geologic processes
The following articles describe the various geologic processes that affect a coastal zone:
- Attrition
- Currents
- Denudation
- Deposition
- Erosion
- Flooding
- Longshore drift
- Marine sediments
- Saltation
- Sea level change
- eustatic
- isostatic
- Sedimentation
- Coastal sediment supply
- sediment transport
- solution
- subaerial processes
- suspension
- Tides
- Water waves
- diffraction
- refraction
- wave breaking
- wave shoaling
- Weathering
Wildlife
Animals
Larger animals that live in coastal areas include
There are many kinds of seabirds on various coasts. These include pelicans and cormorants, who join up with terns and oystercatchers to forage for fish and shellfish. There are sea lions on the coast of Wales and other countries.
Coastal fish
Plants
Many coastal areas are famous for their
Threats
Coasts also face many human-induced environmental impacts and coastal development hazards. The most important ones are:
- Pollution which can be in the form of that is contaminating coasts with plastic and other trash.
- Sea level rise, and associated issues like coastal erosion and saltwater intrusion.
Pollution
The pollution of coastlines is connected to marine pollution which can occur from a number of sources: Marine debris (garbage and industrial debris); the transportation of petroleum in tankers, increasing the probability of large oil spills; small oil spills created by large and small vessels, which flush bilge water into the ocean.
Marine pollution
Marine debris
Microplastics
A growing concern regarding plastic pollution in the marine ecosystem is the use of microplastics. Microplastics are beads of plastic less than 5 millimeters wide,[58] and they are commonly found in hand soaps, face cleansers, and other exfoliators. When these products are used, the microplastics go through the water filtration system and into the ocean, but because of their small size they are likely to escape capture by the preliminary treatment screens on wastewater plants.[59] These beads are harmful to the organisms in the ocean, especially filter feeders, because they can easily ingest the plastic and become sick. The microplastics are such a concern because it is difficult to clean them up due to their size, so humans can try to avoid using these harmful plastics by purchasing products that use environmentally safe exfoliates.
Because plastic is so widely used across the planet, microplastics have become widespread in the marine environment. For example, microplastics can be found on sandy beaches[60] and surface waters[61] as well as in the water column and deep sea sediment. Microplastics are also found within the many other types of marine particles such as dead biological material (tissue and shells) and some soil particles (blown in by wind and carried to the ocean by rivers). Population density and proximity to urban centers have been considered the main factors that influence the abundance of microplastics in the environment.Sea level rise due to climate change
Between 1901 and 2018, average global
Global goals
International attention to address the threats of coasts has been captured in Sustainable Development Goal 14 "Life Below Water" which sets goals for international policy focused on preserving marine coastal ecosystems and supporting more sustainable economic practices for coastal communities.[8] Likewise, the United Nations has declared 2021–2030 the UN Decade on Ecosystem Restoration, but restoration of coastal ecosystems has received insufficient attention.[9]
See also
- Bank (geography)
- Beach cleaning
- Coastal and Estuarine Research Federation
- European Atlas of the Seas
- Intertidal zone
- Land reclamation
- List of countries by length of coastline
- List of U.S. states by coastline
- Offshore or Intertidal zone
- Ballantine Scale
- Coastal path
- Shorezone
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Box SYN-1: Sustained warming could lead to severe impacts
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External links
- Woods Hole Oceanographic Institution - organization dedicated to ocean research, exploration, and education