Coastal and Oceanic Landforms

The main agents responsible for formation of coastal landforms are deposition and erosion, which are the result of waves, tides, and currents. Coastal and oceanic landforms are also heavily dependent on the type of rock present (i.e., the hardness or softness of rock—how resistant/nonresistant it is to erosion). Many coastal and oceanic landforms are listed and described below.

• abyssal fan—underwater structures that look like deltas formed at the end of many large rivers.

• abyssal plain—flat or very gently sloping areas of the deep ocean basin floor.

• arch—a natural formation where a rock arch forms, with a natural passageway underneath. They commonly form where cliffs are subject to erosion from the sea, rivers, or weathering; the processes find weaknesses in rocks and work on them, making them bigger until they break through.

• archipelago—a chain or cluster of islands that are formed tectonically (i.e., by forces and movements within the Earth).

• atoll—an annular reef enclosing a lagoon in which there are no promontories other than reefs and islets composed of reef detritus; in an exclusively morphological sense, a ring-shaped ribbon reef enclosing a lagoon in the center.

• ayre—a body of water divided from the sea by a narrow bar of land.

• barrier bar—a long and narrow (linear) landform within or extending into a body of water, typically composed of sand, silt, or small pebbles.

• bay—an area of water bordered by land on three sides.

• beach—landform along the shoreline of a body of water. A raised beach is an emergent coastal landform, a wave-cut platform raised above the shore line.

• beach cusps—shoreline formations made up of various grades of sediment in an arc pattern.

• beach ridge—a wave-swept or wave-deposited ridge running parallel to a shoreline.

• bight—a bend or curve in the line between land and water, or a large, shallow bay.

• channel—the physical confine of a river, slough, or ocean strait consisting of a bed and banks.

• cliff—a significant, vertical, or near vertical erosion-formed rock exposure.

• coast—where the land meets the sea.

• continental shelf—the undersea extended perimeter of each continent and associated coastal plain.

• coral reef—sea or ocean structures produced by living organisms.

• cove—a circular or oval coastal inlet with a narrow entrance.

• dune—hill of sand built by Aeolian processes.

• estuary—a semienclosed coastal body of water with one or more rivers or streams flowing into it, and with a free connection to the open sea.

• firth—various coastal waters in Scotland.

• fjord—glacier cut U-shaped drowned valley.

• headlands—coastline feature surrounded by water on three sides.

• inlet—a narrow body of water between islands or leading inland from a larger body of water, often leading to an enclosed body of water, such as a bay, lagoon, or marsh.

• isthmus—the narrow strip of land connecting two larger areas of land.

• lagoon—body of comparatively shallow salt or brackish water separated from the deeper sea by a shallow or exposed sandbank, coral ref, or similar feature.

• machair—refers to a fertile, low-lying grassy plain found on some of the northwest coastlines of Ireland and Scotland.

• mid-ocean ridge—an underwater mountain range, typically having a valley known as a rift running along its spine, formed by plate tectonics.

• ocean basin—large geologic basin covered by seawater and well below sea level.

• oceanic trench—narrow topographic depressions of the sea floor that can be hemispheric in length.

• ocean plateau—large, relatively flat submarine region that rises well above the level of the ambient seabed.

• peninsula—a piece of land that is nearly surrounded by water but connected to mainland via an isthmus.

• ria—a drowned river valley.

• river delta—a landform that is created at the mouth of a river where that river flows into an ocean, sea, estuary, lake, reservoir, or another river.

• salt marsh—a type of marsh that is transitional intertidal between land and salty or brackish water.

• sea cave—type of cave formed primarily by the wave action of the sea.

• shoal—a sandbar that is somewhat linear within or extending into a body of water, typically composed of sand, silt, or small pebbles.

• sound—a large sea or ocean inlet larger than a bay, deeper than a bight, and wider than a fjord, or it may identify a narrow sea or ocean channel between two bodies of land.

• spit—a deposition landform off coasts; one end is connected to land and the other far end juts into open water.

• stack—a landform consisting of a steep and often vertical column or columns of rock in the sea near a coast.

• straight—a narrow, navigable channel of water that connects two large navigable bodies of water.

• surge channel—a narrow inlet on a rocky shoreline.

• tombolo (Italian for mound)—a deposition landform in which an island is attached to the mainland by a narrow piece of land such as a spit or bar.

• volcanic arc—a chain of volcanic islands or mountains formed by plate tectonics as an oceanic tectonic plate subducts under another tectonic plate and produces magma.

• wave-cut platform—the narrow, flat area often seen at the base of a sea cliff or along a large lakeshore caused by the action of the waves.