Coast
The coast is defined as that part of the land adjoining or near the ocean or its saltwater arms.[1] A precise line that can be called a coastline cannot be determined due to the process of tides. The term "coastal zone" can be used instead, which is a spatial zone where interaction of the sea and land processes occurs.[2]
A pelagic coast refers to a coast which fronts the open ocean, as opposed to a more sheltered coast in a gulf or bay. A shore, on the other hand, can refer to parts of the land which adjoin any large body of water, including oceans (sea shore) and lakes (lake shore). Similarly, the somewhat related term "bank" refers to the land alongside or sloping down to a river (riverbank) or of a body of water smaller than a lake. "Bank" is also used in some parts of the world to refer to an artificial ridge of earth intended to retain the water of a river or pond. In other places this may be called a levee.
While many scientific experts might agree on a common definition of the term "coast", the delineation of the inland extents of a coast differ according to jurisdiction, with many scientific and government authorities in various countries differing for economic and social policy reasons.
Formation of Coasts
The main agents responsible for deposition and erosion along coastlines are waves, tides and rivers. The formation of coasts is also heavily influenced by their lithology. The harder the material the less likely it is to erode. Variants in the rock create different-shaped coastlines.
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 river estuaries from the ocean.[3]
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.
Sediment deposited by rivers is the dominant influence on the amount of sediment located on a coastline.[4] 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.
Environmental importance
The coast and its adjacent areas on and off shore is an important part of a local ecosystem as the mixture of fresh water and salt water in estuaries provides many nutrients for marine life. Salt marshes and beaches also support a diversity of plants, animals, and insects crucial to the food chain.
Like the ocean which shapes them, coasts are a dynamic environment with constant change. The earth's natural processes, particularly sea level rise, 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).
The high level of biodiversity creates a high level of biological activity, which has attracted human activity for thousands of years. Due to extraordinary population growth in the 20th century, tremendous pressures have been placed on the planet’s ecosystems. With a larger population we must provide more housing, energy, and food. The problem exists both in the concentration of people in coastal areas and their sheer numbers. In the Mancote Mangroves of St. Lucia, harvesting mangrove for timber and clearing for fishing drove the mangrove forests to dangerously low levels. This disruption resulted in a loss of habitat and spawning ground for marine life that was unique to the area. These mangrove forests also helped to stabilize the coastlines. St. Lucia was faced with a huge mess and fortunately have been able to make great conservation efforts since the 80’s that has partially restored the ecosystem functioning.
Human impacts
Coasts also face many environmental challenges relating to human-induced impacts. The human influence on climate change is thought to be a contributing factor of an accelerated trend in sea level rise which threatens coastal habitat as natural systems struggle to adapt faster. Human development of coastal land, particularly for recreational or industrial uses are similarly threatened by sea level rise, but also contribute to aesthetic problems of land use and reduced natural coastal habitat.
Pollution is an ongoing concern along coasts with garbage and industrial debris littering beaches and sometimes entire coasts, requiring government agencies to make frequent use of beach cleaners and other volunteer cleanup efforts. The transportation of petroleum in tankers is a major hazard both for the open ocean and along coasts, particularly when large oil spills occur. Another major hazard for coastal marine life is the large number of small oil spills created by large and small vessels powered by petroleum which flush bilge water directly into the ocean.
Both the terms coast and coastal are often used to describe a geographic location or region. For example, New Zealand's West Coast, or the East and West Coasts of the United States.
A large part of the global population inhabits areas near a coast, partly to take advantage of marine resources such as fish, but more importantly to participate in seaborne trade with other nations. Many of the world's major cities that have developed in recent centuries were built on or near good harbours and have large port facilities to take advantage of marine transportation. Jurisdictions which are landlocked and have no coast are often at an economic disadvantage with overseas trade being more difficult; sometimes being forced to go to extravagant measures such as building canals to permit ocean-going vessels to travel inland.
Coasts, especially those with beaches and warm water are also an important draw for tourists. Starting in the mid-nineteenth century, seaside resorts around the world expanded to meet the increasing tourist demand for leisure time on sea coasts. In many island nations such as those of the Mediterranean, South Pacific and Caribbean, tourism by those who come to enjoy the coast is central to the economy. Coasts are popular destinations because of recreational activities such as swimming, fishing, surfing, boating, and sunbathing. Growth management can be a challenge for coastal local authorities who often struggle to provide the infrastructure required by new residents seeking seachange lifestyles.
Many tourists and residents also enjoy the salt air by the sea coast which some consider to have health benefits. Coastal weather is heavily influenced by the ocean and while this can sometimes result in dangerous storms such as Nor'easters and hurricanes, the coastal climate is often cooler and more temperate than corresponding inland areas. Consequently tourists from areas experiencing extremely warm and humid weather seek coastal areas for these reasons.
Fisheries have lost much of their capacity to produce fish due to habitat degradation, and overfishing. Overharvesting, trawling, bycatch and climate change are among some of the major pressures on fisheries. Since the growth of the global fishing enterprise since the 1950’s, intensive fishing has gone from a few concentrated areas to encompass nearly all fisheries. Not only is over fishing a problem but the technology involved creates even greater destruction. Trawling, or bottom dragging, is used for catching shrimp and other bottom dwelling species. This scraping of the ocean floor is devastating to coral, sponges and other long-lived species that do not recover quickly. This destruction alters the functioning of the ecosystem and can permanently alter species composition and biodiversity. Bycatch is the result of capturing unintended species in the course of fishing. Of this unintended catch most is discarded back into the ocean and dies from injuries or exposure. Bycatch represents approximately ¼ of all marine catch. In the case of shrimp capture, the amount of bycatch is five times larger than the amount of shrimp caught.
The coast is often a crucial defensive frontier, both for warding off military invaders but also smugglers and illegal migrants. Coastal defenses have thus long been erected in many nations. Most coastal countries also have a navy and some form of coast guard.
Types of coast
An emergent coastline is a coastline which 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 landforms, which are above the high tide mark, such as raised beaches. Alternatively, a submergent coastline is a coastline which has experienced a rise in sea level, due to a global sea level change, local subsidence, or isostatic rebound. Submergent coastlines are identifiable by their submerged, or "drowned" landforms, such as rias (drowned valleys) and fjords.
A concordant coastline is a coastline where bands of different rock types run parallel to the shore. These rock types are usually of alternating resistance, so the coastline forms distinctive landforms, such as coves. A discordant coastline is a type of coastline formed when rock types of alternating resistance run perpendicular to the shore. Discordant coastlines feature distinctive landforms because the rocks are eroded by ocean waves. The less resistant rocks erode faster, creating inlets or bays; the more resistant rocks erode more slowly, remaining as headlands or outcroppings.
Coastal landforms and features
Cliff erosion
- Much of the sediment deposited along a coast is the result of erosion of a surrounding Cliff, or bluff. 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 then a cliff made of bedrock. (Easterbrook 1999).
- A Natural arch is formed when a sea stacks 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 crevasse 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.
- A Stump is a shortened sea stacks 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 off shore (Easterbrook 1999).
Rivers on the coastline
Coastal features formed by sediment
Coastal features formed by another feature
Other features on the coast
Coastal processes
The following articles describe the various geologic processes that affect a coastal zone:
Wildlife
Animals
Animals living along the coast vary enormously, some live along coasts to nest like puffins, sea turtles and rockhopper penguins. Sea snails and various kinds of barnacles live on the coast and scavenge on food deposited by the sea. Most coastal animals are used to humans in developed areas, such as dolphins and seagulls who eat food thrown for them by tourists. Since the coastal areas are all part of the littoral zone, there is a profusion of marine life found just off-coast.
There are many kinds of seabirds on the coast. Pelicans and cormorants join up with terns and oystercatchers to forage for fish and shellfish on the coast.
Plants
Coastal areas are famous for their kelp beds. Kelp is a fast growing seaweed that grows up to a metre a day. Corals and anemones are true animals, but live a similar lifestyle as plants do.
The coastline problem
At some time in the years immediately preceding 1951, Lewis Fry Richardson in researching the possible effect of border lengths on the probability of war noticed that the Portuguse reported their measured border with Spain to be 987 km, but the Spanish reported it to be 1214 km. This was the beginning of the coastline problem, which is how to arrive at an estimate of a boundary that is infinite.[5]
The prevailing method of estimating a border (or coastline) was to lay off n equal straight-line segments of length l with dividers on a map or aerial photograph. Each end of the segment must be on the boundary. Investigating the discrepancies in border estimation Richardson discovered what is now termed the Richardson Effect: the sum of the segments is inversely proportional to the common length of the segments. In effect, the shorter the ruler, the longer the measured border; thus, the Spanish and Portuguese geographers were using different-length rulers.
Notes
- ^ "Coast" (html). The American Heritage® Dictionary of the English Language: Fourth Edition. 2000. Retrieved 2008-12-11.
- ^ Nelson, Stephen A. (2007). "Coastal Zones" (html). Retrieved 2008-12-11.
- ^ Davidson (2002), p.421.
- ^ Easterbrook (1999).
- ^ Drazin (1993), "Fractals", in Ashford, Oliver M.; Charnock, H.; Drazin, P. G.; Hunt, J. C.; Smoker, P.; Sutherland, Ian (eds.), The Collected Papers of Lewis Fry Richardson:, vol. 1, Meteorology and numerical analysis, Cambridge University Press (CUP) Archive, pp. 45–46, ISBN 0521382971, ISBN 9780521382977
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References
- Burke, Lauretta A.; Kura, Yumiko; Kassem, Ken; Revenga, Carmen; Spalding, Mark; McAllister, Don (2001), "Coastal Ecosystems" (PDF), in Hutter, Carolynne (ed.), Pilot Analysis of Global Ecosystems, World Resources Institute, ISBN 1-56973-458-5
- United Nations Development Programme, United Nations Environment Programme, World Bank, World Resources Institute. “Taking Stock of Ecosystems.” World Resources 2000-2001. Pg 69-86. World Resources Institute Washington D.C.
- United Nations Development Programme, United Environment Programme, World Bank, World Resources Institute. “Village By Village.” World Resources 2005. Pg 144-151. World Resources Institute Washington D.C.
- United Nations Development Programme, United Environment Programme, World Bank, World Resources Institute. “Threats to Coastal Ecosystems. World Resources 1996-97. World Resources Institute. 22 May 2007 <http://pubs.wri.org/pubs_content_text.cfm?ContentID=799>
- Davidson, Jon P. (2002). Exploring Earth: An Introduction to Physical Geology. Upper Saddle River, NJ: Prentice-Hall Inc. ISBN 0130183725, ISBN 9780130183729.
{{cite book}}: Unknown parameter|coauthors=ignored (|author=suggested) (help) - Easterbrook, Don J. (1999). Surface Processes and Landforms (2 ed.). Upper Saddle River, NJ: Prentice-Hall Inc. ISBN 0138609586, ISBN 9780138609580.
- Haslett, Simon K. (2000). Coastal Systems. introduction to environment. New York: Routledge. ISBN 0415213029, ISBN 9780415213028.
See also
External links
- UK Coast Guide
- "Wild Coast USA" (html). Sierra Club. Retrieved 2008-12-11.
- "Data Explorer" (html). NOAA's National Ocean Service. Retrieved 2008-12-11.