The coast, also known as the coastline or seashore, is defined as the area where land meets the sea or ocean, or as a line that forms the boundary between the land and the ocean
or a lake
. Earth has around of coastline. Because coasts are constantly changing, a coastline's exact perimeter
cannot be determined; this measurement challenge is called the coastline paradox
. The term ''coastal zone'' is used to refer to a region where interactions of sea and land processes occur. Both the terms ''coast'' and ''coastal'' are often used to describe a geographic location or region located on a coastline (e.g., New Zealand's West Coast
, or the East
, and Gulf Coast
of the United States
Coasts are important zones in natural ecosystems, often home to a wide range of biodiversity, and important zones such as wetlands which are important for bird populations or mangroves
which provide nursery habitat
for fish or other aquatic species. Some coasts fronts on the open ocean and are called ''pelagic
coast'' while other coasts are more sheltered coast in a gulf
. A shore
, on the other hand, may refer to parts of land adjoining any large body of water, including oceans (seashore) and lakes (lake shore).
While there is general agreement in the scientific community regarding the definition of a coast, in the political sphere, the delineation of the extents of a coast differ according to jurisdiction
. Government authorities in various countries may define coast differently for economic and social policy reasons. According to a United Nations
atlas, 44% of all people live within of the sea.
Because of their importance in society and high concentration of population, the coast is important for major parts of the global food and economic system. Important human activities happen in port cities
, and other spaces beaches
and seaside resort
s which are used for tourism.
However, the economic importance of coasts makes many of these communities vulnerable to climate change
which causes changes in extreme weather
and sea level rise
and related issues such as coastal erosion
, saltwater intrusion
and coastal flooding
Other coastal issues, such as marine pollution
and marine ecosystem destruction, further complicate the human uses of the coast and threaten coastal ecosystems.
International attention to these issues has been captured in Sustainable Development Goal 14
"Life Below Water" which sets goals for international policy focused on preserving coastal ecosystems and supporting more sustainable economic practices
for coastal communities.
[United Nations (2017) Resolution adopted by the General Assembly on 6 July 2017, Work of the Statistical Commission pertaining to the 2030 Agenda for Sustainable Development]
s 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 bore
s can erode as the waves surge up river estuaries
from the ocean.
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. 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 rise
s, waves and various weather
phenomena, have resulted in the erosion
and reshaping of coasts as well as flooding and creation of continental shelves
and drowned river valleys (ria
Coasts and their adjacent areas on and off shore are an important part of a local ecosystem
. The mixture of fresh water
and salt water
) in estuaries provides many nutrients for marine life
. Salt marsh
es and beach
es 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.
Coasts also create essential material for organisms to live by, including estuaries, wetland
, coral reef
s, and mangrove
s. They support 85 percent of U.S. migratory birds. Coasts also provide a habitat for sea turtles, marine mammals, and coral reefs.
Human uses of coasts
More and more of the world's people live in coastal regions. Many major cities are on or near good harbor
s and have port
facilities. Some landlocked
places have achieved port status by building canal
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
File:花蓮新社梯田.jpg|Paddy fields by the coast of Fengbin, Hualien
File:170209 219 R.jpg|Coastline of Barcelona as viewed from Port Fòrum, with Montjuïc and Port Vell can also be seen.
Coasts, especially those with beaches and warm water, attract tourists often leading to the development of seaside resort
communities. In many island nation
s such as those of the Mediterranean
, South Pacific Ocean
, tourism is central to the economy
. Coasts offer recreational activities such as swimming, fishing, surfing, boating, and sunbathing
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.
File:Maarianhamina SNV10312 -2B.jpg| A passenger car ferry arrives to the coast of Mariehamn, Åland.
File:Tiburon.jpg|Houses close to the coast, like these in Tiburon, California, may be especially desirable properties.
Threats to a coast
Coasts also face many human-induced environmental impacts
. principal among which are sea level rise, and associated issues like coastal erosion
and saltwater intrusion
, and pollution, such as oil spills
or marine debris
contaminating coasts with plastic and other trash.
can occur from a number of sources: garbage and industrial debris
; the transportation of petroleum
, increasing the probability of large oil spill
s; small oil spills created by large and small vessels, which flush bilge
water into the ocean.
Fishing has declined due to habitat degradation
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
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.
File:Marbleheadcoastline.jpg|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.
File:Beach at Msasani Bay, Dar es Salaam, Tanzania.JPG|This stretch of coast in Tanzania's capital Dar es Salaam serves as a public waste dump.
File:Aquatic Dead Zones.jpg|Dead zones occur when phosphorus and nitrogen from fertilizers cause excessive growth of microorganisms, which depletes oxygen and kills fauna.
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 landform
s, which are above the high tide mark, such as raised beach
es. 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 ria
s (drowned valleys) and fjord
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 wave
s. The less resistant rocks erode faster, creating inlet
s or bay
; the more resistant rocks erode more slowly, remaining as headland
s or outcrop
Other coastal categories
* A cliffed coast
or abrasion coast is one where marine action has produced steep declivities known as cliff
* 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.
The following articles describe some coastal landforms:
* Much of the sediment deposited along a coast is the result of erosion of a surrounding cliff
, or bluff. Sea cliff
s 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.
* A natural arch
is formed when a headland is eroded through by waves.
* Sea cave
s 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.
Coastal features formed by sediment
* Beach cusps
* Raised beach
* Cuspate foreland
* Dune system
* Strand plain
* Surge channel
Coastal features formed by another feature
* Salt marsh
Other features on the coast
* Concordant coastline
* Discordant coastline
* Island arc
The following articles describe the various geologic processes that affect a coastal zone:
* Longshore drift
* Sea level change
* Coastal sediment supply
** sediment transport
* Water waves
** wave breaking
** wave shoaling
Animals that live in coastal areas include puffin
s, sea turtle
s and rockhopper penguin
s, among many others. Sea snails
and various kinds of barnacle
s live on the coast and scavenge on food deposited by the sea. Most coastal animals are used to humans in developed areas, such as dolphin
s 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, including sessile
animals such as coral
s and sea anemone
There are many kinds of seabird
s on various coasts. These include pelican
s and cormorant
s, who join up with tern
s and oystercatcher
s to forage for fish and shellfish. There are sea lion
s on the coast of Wales
and other countries.
Many coastal areas are famous for their kelp
beds. Kelp is a fast-growing seaweed
that grows up to a metre a day. Mangroves
es and salt marsh
are important coastal vegetation types in tropical and temperate environments respectively.
is another type of coastal vegetation.
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.
The prevailing method of estimating the length of a border (or coastline) was to lay out ''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; the Spanish and Portuguese geographers were simply using different-length rulers.
The result most astounding to Richardson is that, under certain circumstances, as ''ℓ'' 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. His own definition of the new figure serving as the basis for his study is:
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 "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:
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:
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.
* Ballantine scale
* Coastal and Estuarine Research Federation
* Coastal biogeomorphology
* Coastal development hazards
* Coastline of the North Sea
* European Atlas of the Seas
* How Long Is the Coast of Britain? Statistical Self-Similarity and Fractional Dimension
* Land reclamation
* List of beaches
* List of countries by length of coastline
* List of U.S. states by coastline
* Marine debris
* National Oceanic and Atmospheric Administration Climate and Societal Interactions Program
* Nautical chart
* Pole of inaccessibility
* Seaside resort
Category:Coastal and oceanic landforms
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