Coast and Shore

Coasts mark the area where dry land meets oceans or other large bodies of water. They are one of the most active environments found on Earth. The coastal landscape is ever-changing. It reflects the conflicting processes of erosion (the gradual wearing away of Earth surfaces through the action of wind and water) and deposition (the accumulation and building up of natural materials). It is a landscape that is affected by the interactions of Earth, the Moon, and the Sun.

Coasts are among the most beautiful and inspiring landscapes on the planet, whether they are scenes of torrential storms or serene calm. Throughout recorded history, humans have sought to live on or near coasts. Although coasts account for only 10 percent of Earth's land surface, they serve as home to two-thirds of the world's human population.

The shape of the land

Coast and shore, coastline and shoreline, are commonly used in place of each other. Technically, they are different areas along a coastal landscape. The line that marks the boundary between water and land is the shoreline. It constantly fluctuates because of the regular action of waves and tides. The shore is that strip of ground bordering a body of water that is alternately covered or exposed by waves or tides. The boundaries of the shore are marked by the shoreline at its farthest seaward (low tide) and farthest landward (high tide).

Tide is the periodic rising and falling of water in oceans and other large bodies of water in response to the gravitational attraction of the Moon and the Sun upon Earth. Although the Sun is larger than the Moon, the Moon is closer to Earth and, therefore, its gravitational force is approximately 2.2 times greater. The gravitational pull of the Moon creates two types of tides: high and low. A tidal bulge occurs in the oceans on

the side of Earth nearest the Moon; at the same time, a second tidal bulge occurs on the opposite side of Earth. This second bulge forms because the force of the Moon's gravity pulls the solid body of Earth slightly away from the water on Earth's far side. These bulges are high tides. The areas between the tidal bulges experience low tide.

As Earth rotates, the tides move over its surface. It takes approximately 24 hours and 50 minutes for a given point on Earth to make a complete cycle relative to the Moon, and two lunar tidal cycles occur during this time. Thus, the average time between high tides is 12 hours and 25 minutes. This is a generalized explanation of tides. They do not move evenly and predictably over Earth's surface. Variations in the depth of the oceans and the distribution of landmasses combine with other factors to produce highly complex tidal behavior.

The coast and coastline begin where the shore ends at its high tide mark (farthest landward). The line between the coast and the shore at high tide is the coastline. The coast extends landward from the coastline to the first major change in terrain features, which may be miles inland. This could be a highland or a forest or some other type of terrain. Sometimes, the change between the coast and the adjacent terrain is not so distinct.

Coast and shore: Words to Know

Backshore zone:

The area of a beach normally affected by waves only during a storm at high tide.

Backwash:

The return flow of water to the ocean following the swash of a wave.

Bar:

A ridge or mound of sand or gravel that lies partially or completely underwater a short distance from and parallel to a beach; also commonly known as a sand bar.

Barrier island:

A bar that has been built up so that it rises above the normal high tide level.

Bay:

A body of water in a curved inlet between headlands.

Beach:

A deposit of loose material on shores that is moved by waves, tides, and, sometimes, winds.

Beach drift:

The downwind movement of sand along a beach as a result of the zigzag pattern created by swash and backwash.

Berm:

A distinct mound of sand or gravel running parallel to the shoreline that divides the foreshore zone from the backshore zone of a beach.

Cliff:

A high, steep face of rock.

Coast:

A strip of land that extends landward from the coastline to the first major change in terrain features.

Coastline:

The boundary between the coast and the shore.

Emergent coast:

A coast in which land formerly under water has gradually risen above sea level through geologic uplift of the land or has been exposed because of a drop in sea level.

Erosion:

The gradual wearing away of Earth surfaces through the action of wind and water.

Foreshore zone:

The area of a beach between the ordinary low tide mark and the high tide mark.

Headland:

An elevated area of hard rock that projects out into an ocean or other large body of water.

Longshore current:

An ocean current that flows close and almost parallel to the shoreline and is caused by the angled rush of waves toward the shore.

Longshore drift:

The movement of sand and other material along a shoreline in the longshore current.

Sea arch:

An arch created by the erosion of weak rock in a sea cliff through wave action.

Sea stack:

An isolated column of rock, the eroded remnant of a sea arch, located in the ocean a short distance from the shoreline.

Shore:

The strip of ground bordering a body of water that is alternately covered or exposed by waves or tides.

Shoreline:

The fluctuating line between water and the shore.

Spit:

A long, narrow deposit of sand or gravel that projects from land into open water.

Submergent coast:

A coast in which formerly dry land has been gradually flooded, either by land sinking or by sea level rising.

Swash:

The rush of water up the shore after the breaking of a wave.

Tide:

The periodic rising and falling of water in oceans and other large bodies of water that results from the gravitational attraction of the Moon and the Sun upon Earth.

Tombolo:

A mound of sand or other beach material that rises above the water to connect an offshore island to the shore or to another island.

Wave crest:

The highest part of a wave.

Wave-cut notch:

An indentation produced by wave erosion at the base of a sea cliff.

Wave-cut platform:

A horizontal bench of rock formed beneath the waves at the base of a sea cliff as it retreats because of wave erosion.

Wave height:

The vertical distance between the wave crest and the wave trough.

Wavelength:

The horizontal distance between two wave crests or troughs.

Wave trough:

The lowest part of a wave form between two crests.

Coasts are generally classified into two types: emergent and submergent. Emergent coasts are those in which land formerly under water has gradually risen above sea level through geologic uplift of the land or has been exposed because of a drop in sea level. Currently, sea level around the world is rising by an average of 0.1 inch (0.25 centimeter) per year because glaciers and ice sheets are melting due to global warming (an increase in the world's temperatures thought to be caused, in part, by the burning of fossil fuels and the depletion of the ozone layer). So an emergent coast in the present-day is one that is rising on average more than 0.1 inch (0.25 centimeter) per year. Coasts along Scandinavia, New England, California, and Hawaii are examples of emergent coasts. Submergent coasts are those in which formerly dry land has been gradually flooded, either by land sinking or by sea level rising. Coasts along the southeast Atlantic and the Gulf of Mexico are examples of submergent coasts.

Coastal landscapes may be broadly divided into rocky cliffs and sandy beaches and dunes. All coasts experience a combination of erosion and deposition to varying degrees. Emergent coasts are typically dominated by cliffs or high, steep faces of rock. Because the land is rising in these areas, its landforms are subject to erosion. As waves break against a cliff, certain features are formed, depending on the hardness of the rock. Initially, wave action may cut an indentation, called a wave-cut notch, at the base of the cliff. When the notch becomes larger, rock in the cliff face above the notch loses support and falls into the water where it is broken up by the action of the waves. This process continues and the cliff slowly retreats inland. As it does so, a horizontal bench of rock remains beneath the waves at high tide where the cliff once stood. This feature is called a wave-cut platform. Over time, as the land continues to rise, this platform may be elevated and a new cliff face formed.

The Literary Landscape

"At the foot of this cliff a great ocean beach runs north and south unbroken, mile lengthening into mile. Solitary and elemental, unsullied and remote, visited and possessed by the outer sea, these sands might be the end or the beginning of a world. Age by age, the sea here gives battle to the land; age by age, the earth struggles for her own, calling to her defense her energies and her creations, bidding her plants steal down upon the beach, and holding the frontier sands in a net of grass and roots which the storms wash free."

—Henry Beston, The Outermost House: A Year of Life on the Great Beach of Cape Cod, 1928.

In areas where cliff rock is alternately hard and soft, headlands and bays may form. A headland is an elevated area of hard rock that projects out into an ocean or other large body of water. When soft rock is eroded away between headlands, a curved inlet that holds a body of water known as a bay forms. Because of its location, a headland receives the brunt of

wave attack (wave energy is spread out and weaker in bays). Erosion by water and wind may create distinct features such as sea caves, sea arches, and sea stacks in a headland. Sea caves arise when waves hollow out weak areas of rock in headlands. Waves may then erode the cave through the headland, or caves on either side of the headland may meet. In either case, a sea arch is formed. Erosion of the arch continues until its top portion collapses, leaving a column of hard rock known as a sea stack standing detached from the sea cliff. Continual wave erosion eventually reduces the stack into a stump.

Beaches occur when sand, gravel, and other loose material are deposited by waves along a shore. A beach extends landward from the shoreline at low tide to the shoreline at high tide during storms, when waves are at their highest. In general, a beach is a sandy shore. Beaches are commonly divided into two zones: the foreshore zone and the back-shore zone. The foreshore zone is the area between the ordinary low tide mark and the ordinary high tide mark. The backshore zone is the area normally affected by waves only during a storm at high tide. Behind the back-shore zone may be cliffs, vegetation, or dunes created by winds moving

sand from the beach. Commonly separating the two zones is a distinct mound of sand or gravel, called a berm, that runs parallel to the shoreline. It is created by the action of waves and tides.

Wave activity keeps sand and other loose material in constant motion. As a consequence, it can create other features along the shore, such as spits, bars, barrier islands, and tombolos. A spit is a long, narrow deposit of sand or gravel that projects from land into open water. Spits normally form at the mouth of a bay and curve inward. If a spit extends across the entire mouth of a bay, it is called a baymouth bar or bay barrier. A bar, commonly known as a sand bar, is a ridge or mound of sand or gravel that lies partially or completely underwater a short distance from and parallel to a beach. If more sand is deposited on the bar so that it rises above the normal high tide level, the bar becomes a barrier island. Barrier islands range in length from 1.8 to 62 miles (3 to 100 kilometers) and in width from 0.6 to 1.8 miles (1 to 3 kilometers). Separated from the shore by a shallow body of water known as a lagoon, a barrier island often helps protect the shore from the full force of waves. The East Coast of the United States from Massachusetts to Florida is noted for its system of barrier islands. A mound of sand or other beach material that rises above the water to connect an offshore island to the shore or to another island is called a tombolo (pronounced TOM-beh-low).

Forces and changes: Construction and destruction

Coasts and shores are constantly changing. The shoreline moves with the waves and the tides. Rock is eroded away, and gravel and sand are deposited onshore, only to be swept back offshore. Storms batter coasts, and tides flood areas on a daily basis. The premiere forces that shape the coastal landscape, however, are waves.

Breaking waves exert great force. A 10-foot (3-meter) wave can produce a force of 30 pounds per square inch (2.1 kilograms per square centimeter). In addition to the pressure exerted by their impact, waves erode by scouring rock cliffs and other coastal features with rock fragments they carry.

Waves

Most waves get energy and motion from the wind. Wind blowing over the surface of an ocean or other large water body creates friction along that surface, producing tiny ripples. Further pushed by the wind, these ripples combine and increase in size. The size of waves depends on the strength of the winds, the length of the time the winds blow, and the distance of open water across which the winds blow. Large waves may be created by strong winds blowing for long periods of time across large areas of water.

The highest part of a wave is called the wave crest. The lowest part of a wave between two crests is the wave trough. The vertical distance between the wave crest and the wave trough is the wave height. The horizontal distance between two wave crests or troughs is the wavelength. As a wave travels across an ocean or other body of water, the water particles in the wave move in circular patterns, in loops. These loops extend down underneath the surface of the water only one-half the distance of the wavelength. Water beneath that is not disturbed by wave motion. As the wave form advances across the surface, its energy moves forward, not the water itself. The water particles in the loops essentially return to their original position after the wave has passed.

As a wave enters shallow water near a shoreline, the lower loops in the wave begin to drag on the bottom. This causes the wave to slow down. As it does so, its wavelength decreases and its height increases. When the wave can no longer support its height, the wave breaks. Most of the energy it has carried across the ocean is then transferred into the churning, turbulent water known as surf. The powerful surf either crashes into a cliff or runs up a beach. The water moving up the beach is known as swash; the return flow toward the ocean is called the backwash. The speed of the swash is greater than that of the backwash.

Angled waves and drifting sand

Most of the sand and other sediments making up a beach come from weathered and eroded rock from the mainland that is deposited by rivers at the coast. Material eroded from cliffs at the head of a beach itself may

Bay of Fundy

Lying between New Brunswick and Nova Scotia, Canada, is an inlet of the Atlantic Ocean known as the Bay of Fundy. Measuring about 50 miles (80 kilometers) wide where its mouth meets the Atlantic, the somewhat funnel-shaped bay extends about 170 miles (270 kilometers) to the northeast. At its head it splits into two narrow bays, Chignecto Bay and Minas Basin.

The bay is famous for its tidal range. High and low tide alternate in the bay every 6 hours and 13 minutes. With each tide, 24 cubic miles (100 cubic kilometers) of water flushes through the Bay of Fundy, an amount equal to the daily discharge of all the world's rivers. The average range between high tide and low tide of oceans around the world is 3 feet (1 meter). In the Bay of Fundy, the average is 30 feet (10 meters). In Minas Basin, the difference between high tide and low tide can be as much as 52.5 feet (16 meters).

The reason tides rise and fall to such a great extent in the Bay of Fundy is primarily because of its shape. It tapers significantly at its head, and water flowing into the bay rises in response to this constriction. Also, water flows through the entire bay at the same rate that it enters the bay's mouth from the Atlantic Ocean.

form the beach. Beach sand may also contain fragments of smoothed and rounded shells of marine creatures, such as clams. Tropical beaches often consist entirely of shell and coral fragments. Beaches in areas of volcanic activity, such as Hawaii, can be black since the sand is created by the erosion of volcanic rock. Because sand is in constant motion, beaches are often referred to as "rivers of sand." Depending on the action of waves, sand on a beach may travel along the shore hundreds of feet a day.

When waves approach a shoreline, they rarely do so parallel or straight on. Most often, they do so at a slight angle. After a wave breaks, the swash runs up the shore at that slight angle. Because of gravity, however, the back-wash runs straight back to the water directly, without any angle. As a result, the water moves the sand along the beach downwind in a zigzag pattern. This movement is known as beach drift. In addition to beach drift, sand and other sediment is transported downwind along the beach in the longshore current, a current formed by the angled rush of waves that runs close to and almost parallel to the shoreline. The movement of material in this current is known as longshore drift. Over long periods of time, beach drift and long-shore drift may combine to transport sand and other material great distances, eventually forming coastal features such as spits.

Beaches are not fixed features; they are dynamic environments. They expand and contract depending on wave conditions. In winter and during storms, when wind and wave action are more powerful and frequent, erosion often reduces the size of beaches. In summer and during calm weather, gentle waves deposit sand, creating wider beaches. All sandy landforms along a coast—spits, bars, barrier islands, tombolos—are subject to the erosional or depositional action of waves.

Although they do not change as quickly, rocky coasts will eventually change. An irregular coastline of headlands and bays will be straightened by erosion. Wave action will cut away at headlands, quickly break up rock debris and other material, then deposit it along the shoreline of the bay.

Spotlight on famous forms

Cape Cod, Massachusetts

On the East Coast of the United States, just south of Boston, Massachusetts, a large peninsula resembling a flexed arm extends 60 miles (96.5 kilometers) into the Atlantic Ocean (a peninsula is a piece of land that projects from a mainland into a body of water). Considered a premiere vacation resort, Cape Cod features the longest uninterrupted sandy shore in New England.

Cape Cod was formed more than 15,000 years ago by glaciers that covered the area, deposited sediment, then retreated. Ever since, waves

and currents near the shore have shaped and reshaped the peninsula. They continue to do so in the present, transporting sand along the shore to create a variety of coastal landforms, including chains of barrier islands, curved spits, and dunes. Cape Cod's wide sandy beaches are maintained by material that is eroded from cliffs that border the beaches.

During calm summer months, the amount of beach material that is eroded is equal to the amount that is deposited. In winter months, dominated by severe storms from the northeast, erosion takes over. Prevailing waves drag away sand and other material. Overall, land is lost. On average, the cliffs retreat by 3 feet (1 meter) every year. Structures such as walls and jetties built to protect housing and other development from erosion actually increased its rate. To protect this delicate environment from further development, over 43,600 acres (17,440 hectares) along the outer portion of Cape Cod were designated a national seashore in 1961.

Oregon coast

The coast of Oregon along the Pacific Ocean is noted for sheer cliffs, jagged sea stacks and arches, wave-battered headlands, and long sandy beaches. It is a battleground where land and ocean meet. Wind-driven waves that have traveled 6,000 miles (9,654 kilometers) from Japan—the longest stretch of open ocean in the Northern Hemisphere—crash into the coast unhindered by barrier islands or other features.

This emergent coast has been sculpted by pounding waves that create some of the most violent surf anywhere. The erosive process of the surf takes many years to produce noticeable results, but its force is relentless. Due to erosion, the rocky coast has retreated inland. Evidence of this are the numerous sea stacks jutting from the ocean along much of the coast.

Many of the sea stacks have been given names: Cathedral Rock, Elephant Rock, Face Rock, and the Cat and Kittens. Among the famous sea stacks lining the coast is Haystack Rock, which lies offshore near the town of Cannon Beach. One of the largest free-standing rocks in the world, it towers 235 feet (72 meters) above sea level. It is composed of basalt, a dark, dense volcanic rock. Some 10,000 years ago, Haystack Rock was once part of Tillamook Head (pronounced TIL-ah-muhk), a headland that rises to a height of more than 1,000 feet (305 meters) above sea level.

White Cliffs of Dover, England

Celebrated in literature, song, and film, the White Cliffs of Dover have been an important part of England's natural and social history. Located on the southeast coast of England facing the English Channel, the more than 300-foot-high (91-meter-high) cliffs have provided a natural barrier to foreign invaders throughout history. For English aircrews that flew bombing missions over Europe during World War II (1939–45), the cliffs were the first part of England they saw upon their return. They represented safety.

The cliffs are composed of chalk, which is a particular type of limestone that forms a brilliant white rock formation. Limestone is a sedimentary rock, or rock formed by the accumulation and compression of sediment, which may consist of rock fragments, remains of microscopic organisms, and minerals. Chalk is formed mainly from coccoliths (pronounced COKE-ah-liths), the fossilized remains of tiny, single-celled marine organisms. The coccoliths that form the cliffs were first laid down more than 100 million years ago over a large area of shallow sea, eventually piling into layers.

Before the last ice age some 10,000 years ago, England and France were linked by a chalk landmass. Over time, as sea levels rose, tidal movements eroded the mass, creating the English Channel. Layers of chalk still lie under the seabed of the channel, which has an average depth of 360 feet (110 meters). White cliffs along the French coast match the White Cliffs of Dover. Chalk is a soft rock, and the cliffs naturally erode as waves cut into lower levels while rain seeps into and weakens upper levels. On average, the cliffs are receding at a rate of 0.5 inch (1.3 centimeter) a year.

For More Information

Books

Bird, Eric. Coastal Geomorphology: An Introduction. New York: John Wiley and Sons, 2000.

Davis, Richard A., Jr. The Evolving Coast. New York: W. H. Freeman, 1997.

Haslett, Simon. Coastal Systems. New York: Routledge, 2001.

Hecht, Jeff. Shifting Shores: Rising Seas, Retreating Coastlines. New York: Atheneum, 1990.

Web Sites

"Coastal and Marine Geology Program." U.S. Geological Survey. http://marine.usgs.gov/index.html (accessed on August 14, 2003).

"The Coastal Scene: Oceanography from the Space Shuttle." Goddard Space Flight Center, National Aeronautics and Space Administration. http://daac.gsfc.nasa.gov/CAMPAIGN_DOCS/OCDST/shuttle_oceanography_web/oss_4.html (accessed on August 14, 2003).

"Park Geology Tour of Shoreline Geology." National Park Service, Geologic Resources Division. http://www2.nature.nps.gov/grd/tour/coastal.htm (accessed on August 14, 2003).

"Where Parks Meet the Sea." U.S. Geological Survey and the National Park Service. http://www2.nature.nps.gov/grd/usgsnps/sea/sea.html (accessed on August 14, 2003).

COAST AND GEODETIC SURVEY

COAST AND GEODETIC SURVEY. The Coast and Geodetic Survey was born in 1807 when Congress, on the initiative of President Thomas Jefferson, passed a law authorizing "a survey to be taken of the coasts of the United States." The Survey, originally called the Coast Survey, was—for the first time in the history of the new nation—"to designate the islands and shoals, with the roads and places of anchorage, within twenty leagues of any part of the shores of the United States.…" The Survey, using new scientific methods, would be responsible for producing accurate charts of these features and would also identify other key characteristics of what can roughly be defined as the coastal zones of the United States. As the nation grew, new areas such as Florida, Texas, the Pacific Coast, and Alaska were added to the Survey's growing mission.

Historians agree that the Coast Survey led American science away from the older descriptive methods to the modern methods of statistical analysis and the prediction of future states of natural phenomena based on mathematical modeling. Virtually all branches of science, including the social and biological sciences, have adapted similar methodologies and similar techniques in their quest for scientific truth. (National Oceanic and Atmospheric Administration, "Comments on the Archive of the Coast and Geodetic Survey," 1991).

The survey was placed under the jurisdiction of the Treasury Department but its gestation and evolution were complicated and politicized from the outset. A Swiss immigrant to the United States, the geodesist and mathematician Ferdin and Rudolph Hassler, was selected to head the Survey. He left for Europe in 1811 to secure the necessary scientific books, instruments, and knowledgeable expertise necessary for conducting a massive, complex, and accurate survey of the coastal areas of the United States. None of these necessities was available in America at that time. Hassler remained in Europe until 1815 and it was not until 1816 that Congress appropriated the funds for the survey. Hassler was officially made superintendent of the survey in 1816. However, in 1818 Congress changed the law and specified that only military and naval officers could be employed in the survey, neither of which Hassler was. The instruments and management of the project were turned over to the Navy Department.

In 1832 Congress reactivated the original 1807 legislation placing the Survey in the Treasury Department, and Hassler was again appointed superintendent. The tensions between military and civilian control of the Survey continued. In 1834 the Survey was again transferred to the Department of the Navy, but after repeated protests from Hassler it was once more returned to the jurisdiction of the Treasury Department in 1836. Further efforts to move the Survey to naval jurisdiction continued until 1882.

After the death of Hassler in 1843, Alexander Dallas Bache, a great-grandson of Benjamin Franklin, took over as superintendent of the Coast Survey. Bache built on the strong foundation that had been created, and is credited with developing the Survey into the first real scientific organization in the federal government. He became a leader in the American Association for the Advancement of Science and was a founding member of the National Academy of Sciences.

The scope and flair of the Survey is captured in the following description taken from an analysis of its annual reports:

The Survey was continental in scope, tying together east and west coasts by an invisible transcontinental network of triangles while leading American commerce by means of precise nautical charting surveys into the ports of our Atlantic, Gulf, and Pacific shores. Storms, mountains, dust, mud, deserts, wild beasts, heat and cold; all were the companions of the Coast Surveyors. They engaged in a great physical adventure that is little known and little understood. Beyond the romance of the Coast Surveyors, there was an enduring intellectual adventure as the field men and the office force of the Coast Survey engaged in a fascinating quest for the ultimate limits of accuracy of scientific measurement. They were seekers of scientific "truth." No effort was too great or hardship too onerous to overcome in this quest. The perseverance and fortitude of the field men was matched by the office force of mathematicians, physicists, geodesists, astronomers, instrument-makers, draftsmen, engravers, and pressmen. These men and women (the Coast Survey hired women professionals as early as 1845) helped push back the limits of astronomic measures, designed new and more accurate observational instruments for sea and land surveying, developed new techniques for the mathematical analysis of the mountains of data obtained by the field parties, and further refined techniques of error analysis and mitigation. (National Oceanic and Atmospheric Administration, "Comments on the Archive of the Coast and Geodetic Survey," 1991)

In 1878 the program was officially renamed the Coast and Geodetic Survey. In 1903 it was transferred to the Department of Commerce and Labor and it remained in Commerce after Labor became a separate cabinet department in 1913. In 1920 the title "superintendent" was changed to "director."

In 1965 the Coast and Geodetic Survey became part of the Environmental Science Services Administration (ESSA), which also incorporated the Weather Bureau and the National Bureau of Standards' Central Radio Propagation Laboratory. When the National Oceanic and Atmospheric Administration (NOAA) was created in 1970 as a new entity within the Department of Commerce, ESSA and thus the Survey became part of NOAA.

The Survey is considered to have been one of the major birthplaces of modern American science, including many disciplines not generally associated with geodesy and hydrology. Its creation is a cornerstone of the rapid growth of science and technology and of the development of natural resources for commercial use in the United States.

BIBLIOGRAPHY

Dracup, Joseph F. The United States Horizontal Control Network, 1816–1976. Rockville, Md.: National Oceanic and Atmospheric Administration, n.d.

National Oceanic and Atmospheric Administration. "Comments on the Archive of the Coast and Geodetic Survey." Available at http://www.lib.noaa.gov.

National Oceanic and Atmospheric Administration. "Functions of the Coast Survey and the Coast and Geodetic Survey." Updated February 17, 2000. Available at http://www.lib.noaa.gov.

U.S. Department Commerce. U.S. Coast and Geodetic Survey: 150 Years of Service, 1807–1957. Washington, D.C., 1957.

Wright, A. Joseph, and Elliot B. Roberts. The Coast and Geodetic Survey, 1807–1957: 150 Years of History. Washington, D.C.: U.S. Department of Commerce, 1957.

Steffen W.Schmidt

See alsoGeological Survey, U.S.

Coast and beach

The coast and beach, where the continents meet the ocean, are everchanging environments where the conflicting processes of erosion (wearing away) and sedimentation (building up) take place. Coast is the land that borders an ocean or large body of water. Beach refers to a much smaller land region, usually just the area directly affected by wave action.

Coasts

Coasts are generally classified into two types: emergent and submergent. Emergent coasts are those that are formed when sea level declines. Areas that were once covered by the sea emerge and form part of the landscape. This new land area, which was once protected underwater, is now attacked by waves and eroded. If the new land is a cliff, waves may undercut it, eventually causing the top portions of the cliff to fall into the sea. When this happens, the beach is extended at its base. Along emergent coast shorelines the water level is quite shallow for some distance offshore. Much of the coast along California is emergent coast.

Submergent coasts are those that are formed when sea level rises, flooding formerly exposed land areas. Valleys near coastal areas that had been carved out by rivers become estuaries, or arms of the sea that extend inland to meet the mouth of a river, for example, Chesapeake Bay in Virginia and Maryland. Hilly terrains become collections of islands, such as those off the coast of Maine.

Beaches

Most of the sand and other sediments making up a beach are supplied by weathered and eroded rock from the mainland that is deposited by rivers at the coast. At the beach, wave action moves massive amounts of sand. As waves approach shallow water, they slow down because of friction with the bottom. They then become steeper and finally break. It is during this slowing and breaking that sand gets transported.

Words to Know

Emergent coast: A coast that is formed when sea level declines and is characterized by wave-cut cliffs and formerly underwater beaches.

Longshore drift: Movement of sand parallel to the shore, caused by slowing and breaking waves approaching the shore at an angle.

Submergent coast: A coast that is formed when sea level rises and is characterized by drowned river valleys.

When a breaking wave washes up onto the beach, it does so at a slight angle, moving sand both toward and slightly down the beach. When the water sloshes back, it does so directly, without any angle. As a result, the water moves the sand along the beach in a zigzag pattern. This is called longshore drift. The magnitude and direction of longshore drift depends on the strength of the waves and the angle at which they approach, and these may vary with the season.

Barrier islands

A barrier island is a long, thin, sandy stretch of land that lies parallel to a mainland coast. Between the barrier island and the mainland is a calm, protected water body such as a lagoon or bay. If the coastline has a broad, gentle slope, strong waves and other ocean currents carry sand offshore and then deposit it, creating these islands. In the United States, most barrier islands are found along the Gulf Coast and the Atlantic Coast as far north as Long Island, New York.

Sand being moved by longshore drift and being replenished on beaches by eroding highlands is a natural, constant cycle. Beaches erode, however, when humans intervene in the cycle, often by building on coastal land. Two methods used to remedy beach erosion include pumping sand onto beaches from offshore and building breakwaters away from shore to stop longshore drift.

[See also Erosion; Ocean; Tides ]

coast land bordering an ocean or other large body of water. The line of contact between the land and water surfaces is called the shoreline. It fluctuates with the waves and tides. Sometimes the terms coast and shore are used synonymously, but often shore is interpreted to mean only the zone between the shorelines at high tide and low tide, and coast indicates a strip of land of indefinite width landward of the shore. Classically, coasts have been designated as submergent if they resulted from a rise in the relative sea level and emergent if they resulted from a decline. Young submergent coasts usually are irregular and have deep water offshore and many good harbors, either bays or estuaries. Much of the coast of New England and most of the Atlantic coast of Europe are young submergent coasts according to this classification scheme. Gradually the submergent coast, subjected to erosive attacks of the ocean and other agents, becomes mature. Headlands are worn back to form cliffs, at the base of which deposits of eroded material accumulate as fringing beaches; spits and bars also grow up from material that is carried by currents and deposited in deeper water. The shoreline is called mature when it is smooth, the headlands having been cut away and the bays either filled up or closed off by spits. Emergent shorelines usually have shallow water for some distance offshore. Such shorelines are found along the Atlantic coast of the SE United States and along part of the coast of Argentina, near the Río de la Plata. This classification system does not adequately describe many coasts, partly because many of them exhibit features of both submergence and emergence. Because of these and other problems a classification system that is based on the most recent and predominant geologic agent forming the coast has become popular. Under this scheme, there are essentially two major types of coasts. Primary coasts are youthful coasts formed where the sea rests against a land mass whose topography was formed by terrestrial agents. These coasts include land erosion coasts (Maine), volcanic coasts (Hawaii), deposition coasts (Nile Delta coast), and fault coasts (Red Sea). Secondary coasts are formed chiefly and most recently by marine agents, and may even be primary coasts that have been severely modified by wave action. These coasts include wave erosion coasts, marine deposition coasts, and coasts built by organisms (reefs and mangrove coasts). The nature of the coastline of a country or a state is an important factor in its economic development because it relates to defense, fishing, recreation, and overseas commerce.

Bibliography: See C. A. M. King, Beaches and Coasts (2d ed. 1972).

coast / kōst/ • n. 1. the part of the land near the sea; the edge of the land. ∎  (the Coast) the Pacific coast of North America. 2. a run or movement in or on a vehicle without the use of power. • v. 1. [intr.] (of a person or vehicle) move easily without using power: the engines stopped, and the craft coasted along. ∎  act or make progress without making much effort: he coasted to victory. ∎  slide down a snowy hill on a sled. 2. [intr.] sail along the coast, esp. in order to carry cargo. PHRASES: the coast is clear there is no danger of being observed or caught.

coast †tract, region XIII; †quarter, direction; †side; sea-shore XIV; (N. Amer.) toboggan slide XVIII. ME. cost(e) — OF. coste (mod. côte) :- L. costa rib, flank, side.
So coast vb. †keep or move by the side or coast of; †border upon XIV; †traverse, scour XV; (U.S.) slide down a slope on a sled (also in transf. use) XIX.

COAST Abbr. for Cambridge Optical Aperture Synthesis Telescope.

coast •boast, coast, ghost, host, most, oast, post, roast, toast •backmost • headmost • leftmost •endmost • midmost • hindmost •rightmost • topmost • foremost •almost • northernmost • downmost •outmost • southernmost • upmost •utmost • rearmost • lowermost •undermost • innermost • uppermost •aftermost •centremost (US centermost) •westernmost • easternmost •bottommost • outermost • uttermost •nethermost • furthermost •lamp post • bedpost • gatepost •Freepost • impost • guidepost •milepost • signpost • doorpost •outpost • goalpost • newel post •fingerpost • sternpost