The coast, also known as the coastline or seashore, is the area where land meets the sea or ocean,[1] or a line that forms the boundary between the land and the ocean or a lake.[2] A precise line that can be called a coastline cannot be determined due to the Coastline paradox.

The term coastal zone is a region where interaction of the sea and land processes occurs.[3] 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. Edinburgh for example is a city on the coast of Great Britain.

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 land adjoining any large body of water, including oceans (sea shore) and lakes (lake shore). Similarly, the somewhat related term "[stream bed/bank]" refers to the land alongside or sloping down to a river (riverbank) or 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 extents of a coast differ according to jurisdiction, with many scientific and government authorities in various countries differing for economic and social policy reasons. According to the UN atlas, 44% of people live within 150 kilometres (93 miles) of the sea.[4]

Knight's Point, West Coast
Rugged coastline of the West Coast Region of New Zealand


Porto Covo pano April 2009-4
Atlantic rocky coastline, showing a surf area. Porto Covo, west coast of Portugal

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.[5]

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 abrasion or cliffed coast.

Sediment deposited by rivers is the dominant influence on the amount of sediment located on a coastline.[6] 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.

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).

Environmental importance

Somalia 16.08.2009 08-30-13
Somalia has the longest coastline in Africa

The coast and its adjacent areas on and off shore are an important part of a local ecosystem: the mixture of fresh water and salt water (brackish 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.

The high level of biodiversity creates a high level of biological activity, which has attracted human activity for thousands of years.

Human impacts

Human uses of coasts

The CHW system
The Coastal Hazard Wheel system published by UNEP for global coastal management
A settled coastline in Marblehead, Massachusetts. Once a fishing port, the harbor is now dedicated to tourism and pleasure boating. Observe that the sand and rocks have been darkened by oil slick up to the high-water line.
Beach at Msasani Bay, Dar es Salaam, Tanzania
This stretch of coast in Tanzania's capital Dar es Salaam serves as a public waste dump.
Houses close to the coast, like these in Tiburon, California, may be especially desirable properties.
View of sea coast from top of a hill at Visakhapatnam in India

More and more of the world's people live in coastal regions.[7] Many major cities are on or near good harbors and have port facilities. Some landlocked places have achieved port status by building canals.

The coast is a frontier that nations have typically defended 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.

Coasts, especially those with beaches and warm water, attract tourists. In many island nations such as those of the Mediterranean, South Pacific and Caribbean, tourism is central to the economy. Coasts offer 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.

Threats to a coast

Coasts also face many human-induced environmental impacts. The human influence on climate change is thought to contribute to an accelerated trend in sea level rise which threatens coastal habitats.

Pollution can occur from a number of sources: 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.

Fishing has declined due to habitat degradation, overfishing, trawling, bycatch and climate change. Since the growth of global fishing enterprises after the 1950s, intensive fishing has spread from a few concentrated areas to encompass nearly all fisheries. The scraping of the ocean floor in bottom dragging 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, the capture of unintended species in the course of fishing, is typically returned to the ocean only to die from injuries or exposure. Bycatch represents about a quarter of all marine catch. In the case of shrimp capture, the bycatch is five times larger than the shrimp caught.

It is believed that melting Arctic ice will cause sea levels to rise and flood coastal areas.


Extraordinary population growth in the 21st century has placed stress on the planet's ecosystems. For example, on Saint Lucia, harvesting mangrove for timber and clearing for fishing reduced the mangrove forests, resulting in a loss of habitat and spawning grounds for marine life that was unique to the area. These forests also helped to stabilize the coastline. Conservation efforts since the 1980s have partially restored the ecosystem.


According to one principle of classification, 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. In contrast, a submergent coastline is one where the sea level has risen, 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.

According to a 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 ocean waves. The less resistant rocks erode faster, creating inlets or bay; the more resistant rocks erode more slowly, remaining as headlands or outcroppings.

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.


Accreting coast Image6
Coastal landforms. The feature shown here as a bay would, in certain (mainly southern) parts of Britain, be called a cove. That between the cuspate foreland and the tombolo is a British bay.

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 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.[6]
  • 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.
  • 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 off shore.[6]

Coastal features formed by sediment

Coastal features formed by another feature

Other features on the coast

Geologic processes

The following articles describe the various geologic processes that affect a coastal zone:



Some of the animals live along a typical coast. There are animals 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. There are sea lions on the coast of Wales and other countries.


Coastal areas are famous for their kelp beds. Kelp is a fast-growing seaweed that grows up to a metre a day. Corals and sea anemones are true animals, but live a lifestyle similar to that of plants. Mangroves, seagrasses and salt marsh are important coastal vegetation types in tropical and temperate environments respectively.


Coastline problem

Shortly before 1951, Lewis Fry Richardson, in researching the possible effect of border lengths on the probability of war, noticed that the Portuguese reported their measured border with Spain to be 987 km, but the Spanish reported it as 1214 km. This was the beginning of the coastline problem, which is a mathematical uncertainty inherent in the measurement of boundaries that are irregular.[8]

The prevailing method of estimating the length of a border (or coastline) was to lay out n equal straight-line segments of length 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; the Spanish and Portuguese geographers were simply using different-length rulers.

The result most astounding to Richardson is that, under certain circumstances, as approaches zero, the length of the coastline approaches infinity. Richardson had believed, based on Euclidean geometry, that a coastline would approach a fixed length, as do similar estimations of regular geometric figures. For example, the perimeter of a regular polygon inscribed in a circle approaches the circumference with increasing numbers of sides (and decrease in the length of one side). In geometric measure theory such a smooth curve as the circle that can be approximated by small straight segments with a definite limit is termed a rectifiable curve.

Measuring a coastline

More than a decade after Richardson completed his work, Benoit Mandelbrot developed a new branch of mathematics, fractal geometry, to describe just such non-rectifiable complexes in nature as the infinite coastline.[9] His own definition of the new figure serving as the basis for his study is:[10]

I coined fractal from the Latin adjective fractus. The corresponding Latin verb frangere means "to break:" to create irregular fragments. It is therefore sensible ... that, in addition to "fragmented" ... fractus should also mean "irregular."

A key property of the fractal is self-similarity; that is, at any scale the same general configuration appears. A coastline is perceived as bays alternating with promontories. In the hypothetical situation that a given coastline has this property of self-similarity, then no matter how greatly any one small section of coastline is magnified, a similar pattern of smaller bays and promontories superimposed on larger bays and promontories appears, right down to the grains of sand. At that scale the coastline appears as a momentarily shifting, potentially infinitely long thread with a stochastic arrangement of bays and promontories formed from the small objects at hand. In such an environment (as opposed to smooth curves) Mandelbrot asserts[9] "coastline length turns out to be an elusive notion that slips between the fingers of those who want to grasp it."

There are different kinds of fractals. A coastline with the stated property is in "a first category of fractals, namely curves whose fractal dimension is greater than 1." That last statement represents an extension by Mandelbrot of Richardson's thought. Mandelbrot's statement of the Richardson Effect is:[11]

where L, coastline length, a function of the measurement unit, ε, is approximated by the expression. F is a constant and D is a parameter that Richardson found depended on the coastline approximated by L. He gave no theoretical explanation but Mandelbrot identified D with a non-integer form of the Hausdorff dimension, later the fractal dimension. Rearranging the right side of the expression obtains:

where Fε−D must be the number of units ε required to obtain L. The fractal dimension is the number of the dimensions of the figure being used to approximate the fractal: 0 for a dot, 1 for a line, 2 for a square. D in the expression is between 1 and 2, for coastlines typically less than 1.5. The broken line measuring the coast does not extend in one direction nor does it represent an area, but is intermediate. It can be interpreted as a thick line or band of width 2ε. More broken coastlines have greater D and therefore L is longer for the same ε. Mandelbrot showed that D is independent of ε.

See also


  1. ^ "Coast". The American Heritage Dictionary of the English Language: Fourth Edition. 2000. Archived from the original on 2009-02-01. Retrieved 2008-12-11.
  2. ^ The Merriam-Webster Dictionary Internet edition. Retrieved 2015-06-13.
  3. ^ Nelson, Stephen A. (2007). "Coastal Zones". Retrieved 2008-12-11.
  4. ^ "UN Atlas". Archived from the original on 2 November 2013. Retrieved 31 October 2013.
  5. ^ Davidson (2002), p.421.
  6. ^ a b c Easterbrook (1999).
  7. ^ Goudarzi, Sara (July 18, 2006). "Flocking to the Coast: World's Population Migrating into Danger". Live Science. Retrieved 2008-12-14.
  8. ^ Drazin, P. G. (1993). "Fractals". The Collected Papers of Lewis Fry Richardson: Meteorology and numerical analysis. By Richardson, Lewis Fry. Ashford, Oliver M.; Charnock, H.; Drazin, P. G.; et al. (eds.). 1. Cambridge University Press. pp. 45–46. ISBN 0-521-38297-1.
  9. ^ a b Mandelbrot (1983) page 28.
  10. ^ Mandelbrot (1983), page 1.
  11. ^ Mandelbrot (1983), pages 29–31.


  • 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 978-1-56973-458-2. Archived from the original (PDF) on 2003-04-08.
  • Davidson, Jon P.; Reed, Walter E.; Davis, Paul M. (2002). Exploring Earth: An Introduction to Physical Geology. Upper Saddle River, NJ: Prentice-Hall Inc. ISBN 978-0-13-018372-9.
  • Easterbrook, Don J. (1999). Surface Processes and Landforms (2 ed.). Upper Saddle River, NJ: Prentice-Hall Inc. ISBN 978-0-13-860958-0.
  • Haslett, Simon K. (2009). Coastal Systems (2nd Edition). introduction to environment. New York: Routledge. ISBN 978-0-415-44060-8.
  • Mandelbrot, Benoit B. "II.5 How long is the coast of Britain?". The Fractal Geometry of Nature. Macmillan. pp. 25–33. ISBN 978-0-7167-1186-5.

External links

East Coast of the United States

The East Coast of the United States, also known as the Eastern Seaboard, the Atlantic Coast, and the Atlantic Seaboard, is the coastline along which the Eastern United States meets the North Atlantic Ocean. The coastal states that have shoreline on the Atlantic Ocean are, from north to south, Maine, New Hampshire, Massachusetts, Rhode Island, Connecticut, New York, New Jersey, Delaware, Maryland, Virginia, North Carolina, South Carolina, Georgia, and Florida.

Gold Coast, Queensland

The Gold Coast is a coastal city in the Australian state of Queensland, approximately 66 kilometres (41 mi) south-southeast of the state capital Brisbane and immediately north of the border with New South Wales. With a census-estimated 2016 population of 638,090, the Gold Coast is the sixth-largest city in Australia, making it the largest non-capital city, and Queensland's second-largest city.The Gold Coast region remained largely uninhabited by Europeans until 1823 when explorer John Oxley landed at Mermaid Beach. The hinterland's red cedar supply attracted people to the area in the mid-19th century. Later in 1875, Southport was surveyed and established and grew a reputation as a secluded holiday destination for wealthy Brisbane residents.

After the establishment of the Surfers Paradise Hotel in the late 1920s, the Gold Coast region grew significantly. The area boomed in the 1980s as a leading tourist destination and in 1994, the City of Gold Coast local government area was expanded to encompass the majority of the Gold Coast's metropolitan area, becoming the second most populous local government area in Australia after the City of Brisbane.

Today, the Gold Coast is a major tourist destination with its sunny subtropical climate and has become widely known for its surfing beaches, high-rise dominated skyline, theme parks, nightlife, and rainforest hinterland. The city is part of the nation's entertainment industry with television productions and a major film industry. The city hosted the 21st Commonwealth Games which ran from 4 to 15 April 2018.

Ivory Coast

Ivory Coast or Côte d'Ivoire, officially the Republic of Côte d'Ivoire, is a country located on the south coast of West Africa. Ivory Coast's political capital is Yamoussoukro in the centre of the country, while its economic capital and largest city is the port city of Abidjan. It borders Guinea and Liberia to the west, Burkina Faso and Mali to the north, Ghana to the east, and the Gulf of Guinea (Atlantic Ocean) to the south.

Before its colonization by Europeans, Ivory Coast was home to several states, including Gyaaman, the Kong Empire, and Baoulé. The area became a protectorate of France in 1843 and was consolidated as a French colony in 1893 amid the European scramble for Africa. It achieved independence in 1960, led by Félix Houphouët-Boigny, who ruled the country until 1993. Relatively stable by regional standards, Ivory Coast established close political and economic ties with its West African neighbors while at the same time maintaining close relations to the West, especially France. Ivory Coast experienced a coup d'état in 1999 and two religiously-grounded civil wars, first between 2002 and 2007 and again during 2010–2011. In 2000, the country adopted a new constitution.Ivory Coast is a republic with strong executive power vested in its president. Through the production of coffee and cocoa, the country was an economic powerhouse in West Africa during the 1960s and 1970s, though it went through an economic crisis in the 1980s, contributing to a period of political and social turmoil. Only around 2014 has GDP per capita in the country again reached the level of its peak in the 1970s. In the 21st century, the Ivorian economy is largely market-based and still relies heavily on agriculture, with smallholder cash-crop production being dominant.The official language is French, with local indigenous languages also widely used, including Baoulé, Dioula, Dan, Anyin, and Cebaara Senufo. In total there are around 78 languages spoken in Ivory Coast. There are large populations of Muslims, Christians (primarily Roman Catholics) and various indigenous religions.

United States Armed Forces

The United States Armed Forces are the military forces of the United States of America. It consists of the Army, Marine Corps, Navy, Air Force, and Coast Guard. The President of the United States is the Commander-in-Chief of the Armed Forces and forms military policy with the Department of Defense (DoD) and Department of Homeland Security (DHS), both federal executive departments, acting as the principal organs by which military policy is carried out. All five armed services are among the seven uniformed services of the United States.From the time of its inception, the U.S. Armed Forces played a decisive role in the history of the United States. A sense of national unity and identity was forged as a result of victory in the First Barbary War and the Second Barbary War. Even so, the founders of the United States were suspicious of a permanent military force. It played a critical role in the American Civil War, continuing to serve as the armed forces of the United States, although a number of its officers resigned to join the military of the Confederate States. The National Security Act of 1947, adopted following World War II and during the Cold War's onset, created the modern U.S. military framework. The Act established the National Military Establishment, headed by the Secretary of Defense; and created the Department of the Air Force and the National Security Council. It was amended in 1949, renaming the National Military Establishment the Department of Defense, and merged the cabinet-level Department of the Army, Department of the Navy, and Department of the Air Force, into the Department of Defense.

The U.S. Armed Forces are one of the largest militaries in terms of the number of personnel. It draws its personnel from a large pool of paid volunteers. Although conscription has been used in the past in various times of both war and peace, it has not been used since 1973, but the Selective Service System retains the power to conscript males, and requires that all male citizens and residents residing in the U.S. between the ages of 18–25 register with the service. On February 22, 2019, however, a federal judge ruled that registering only males for Selective Service is unconstitutional.

As of 2017, the U.S. spends about US$610 billion annually to fund its military forces and Overseas Contingency Operations. Put together, the U.S. constitutes roughly 40 percent of the world's military expenditures. The U.S. Armed Forces has significant capabilities in both defense and power projection due to its large budget, resulting in advanced and powerful technologies which enables a widespread deployment of the force around the world, including around 800 military bases outside the United States. The U.S. Air Force is the world's largest air force, the U.S. Navy is the world's largest navy by tonnage, and the U.S. Navy and the U.S. Marine Corps combined are the world's second largest air arm. In terms of size, the U.S. Coast Guard is the world's 12th largest naval force.

United States Coast Guard

The United States Coast Guard (USCG) is the coastal defense and maritime law enforcement branch of the United States Armed Forces and one of the country's seven uniformed services. The Coast Guard is a maritime, military, multi-mission service unique among the U.S. military branches for having a maritime law enforcement mission (with jurisdiction in both domestic and international waters) and a federal regulatory agency mission as part of its mission set. It operates under the U.S. Department of Homeland Security during peacetime, and can be transferred to the U.S. Department of the Navy by the U.S. President at any time, or by the U.S. Congress during times of war. This has happened twice: in 1917, during World War I, and in 1941, during World War II.Created by Congress on 4 August 1790 at the request of Alexander Hamilton as the Revenue-Marine, it is the oldest continuous seagoing service of the United States. As Secretary of the Treasury, Hamilton headed the Revenue-Marine, whose original purpose was collecting customs duties in the nation's seaports. By the 1860s, the service was known as the U.S. Revenue Cutter Service and the term Revenue-Marine gradually fell into disuse.The modern Coast Guard was formed by a merger of the Revenue Cutter Service and the U.S. Life-Saving Service on 28 January 1915, under the U.S. Department of the Treasury. As one of the country's five armed services, the Coast Guard has been involved in every U.S. war from 1790 to the Iraq War and the War in Afghanistan.The Coast Guard has 40,992 men and women on active duty, 7,000 reservists, 31,000 auxiliarists, and 8,577 full-time civilian employees, for a total workforce of 87,569. The Coast Guard maintains an extensive fleet of 243 coastal and ocean-going patrol ships, tenders, tugs and icebreakers called "cutters", and 1650 smaller boats, as well as an extensive aviation division consisting of 201 helicopters and fixed-wing aircraft. While the U.S. Coast Guard is the smallest of the U.S. military service branches in terms of membership, the U.S. Coast Guard by itself is the world's 12th largest naval force.

West Coast of the United States

The West Coast or Pacific Coast is the coastline along which the continental Western United States meets the North Pacific Ocean. As a region, this term most often refers to the coastal states of California, Oregon, Washington, and Alaska. More specifically, it refers to an area defined on the east by the Alaska Range, Cascade Range, Sierra Nevada, and Mojave Desert, and on the west by the Pacific Ocean. The United States Census groups the five states of California, Oregon, Washington, Alaska, and Hawaii together as the Pacific States division.


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