Wave-cut platform

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Wave-cut platform at Southerndown, South Wales, UK Wavecut platform southerndown pano.jpg
Wave-cut platform at Southerndown, South Wales, UK

A wave-cut platform, shore platform, coastal bench, or wave-cut cliff is the narrow flat area often found at the base of a sea cliff or along the shoreline of a lake, bay, or sea that was created by erosion. Wave-cut platforms are often most obvious at low tide when they become visible as huge areas of flat rock. Sometimes the landward side of the platform is covered by sand, forming the beach, and then the platform can only be identified at low tides or when storms move the sand.

Lake A body of relatively still water, in a basin surrounded by land

A lake is an area filled with water, localized in a basin, surrounded by land, apart from any river or other outlet that serves to feed or drain the lake. Lakes lie on land and are not part of the ocean, and therefore are distinct from lagoons, and are also larger and deeper than ponds, though there are no official or scientific definitions. Lakes can be contrasted with rivers or streams, which are usually flowing. Most lakes are fed and drained by rivers and streams.

Bay A recessed, coastal body of water connected to an ocean or lake

A bay is a recessed, coastal body of water that directly connects to a larger main body of water, such as an ocean, a lake, or another bay. A large bay is usually called a gulf, sea, sound, or bight. A cove is a type of smaller bay with a circular inlet and narrow entrance. A fjord is a particularly steep bay shaped by glacial activity.

Sea Large body of salt water

The sea, the world ocean or simply the ocean is the connected body of salty water that covers over 70% of Earth's surface. It moderates Earth's climate and has important roles in the water cycle, carbon cycle, and nitrogen cycle. It has been travelled and explored since ancient times, while the scientific study of the sea—oceanography—dates broadly from the voyages of Captain James Cook to explore the Pacific Ocean between 1768 and 1779. The word sea is also used to denote smaller, partly landlocked sections of the ocean and certain large, entirely landlocked, saltwater lakes, such as the Caspian Sea and the Dead Sea.

Contents

Formation

The formation of a wave cut platform Wave cut platform.png
The formation of a wave cut platform

Wave-cut platforms form when destructive waves hit against the cliff face, causing an undercut between the high and low water marks, mainly as a result of abrasion, corrosion and hydraulic action, creating a wave-cut notch. This notch then enlarges into a cave. The waves undermine this portion until the roof of the cave cannot hold due to the pressure and freeze-thaw or biological weathering acting on it, and collapses, resulting in the cliff retreating landward. The base of the cave forms the wave-cut platform as attrition causes the collapsed material to be broken down into smaller pieces, while some cliff material may be washed into the sea. This may be deposited at the end of the platform, forming an off-shore terrace.

Corrosion Gradual destruction of materials by chemical reaction with its environment

Corrosion is a natural process that converts a refined metal into a more chemically-stable form such as oxide, hydroxide, or sulfide. It is the gradual destruction of materials by chemical and/or electrochemical reaction with their environment. Corrosion engineering is the field dedicated to controlling and stopping corrosion.

Hydraulic action

Hydraulic action is the erosion that occurs when the motion of water against a rock surface produces mechanical weathering. Most generally, it is the ability of moving water to dislodge and transport rock particles. Within this rubric are a number of specific erosional processes, including abrasion, attrition, corrasion, saltation, and scouring (downcutting). Hydraulic action is distinguished from other types of water facilitated erosion, such as static erosion where water leaches salts and floats off organic material from unconsolidated sediments, and from chemical erosion more often called chemical weathering. It is a mechanical process, in which the moving water current flows against the banks and bed of a river, thereby removing rock particles.

Because of the continual wave action, a wave-cut platform represents an extremely hostile environment and only the toughest of organisms can utilize such a niche.

Organism Any individual living physical entity

In biology, an organism is any individual entity that propagates the properties of life. It is a synonym for "life form".

Ecological niche The fit of a species living under specific environmental conditions.

In ecology, a niche is the match of a species to a specific environmental condition. It describes how an organism or population responds to the distribution of resources and competitors and how it in turn alters those same factors. "The type and number of variables comprising the dimensions of an environmental niche vary from one species to another [and] the relative importance of particular environmental variables for a species may vary according to the geographic and biotic contexts".

Use of ancient examples

Ancient wave-cut platforms provide evidence of past sea and lake levels. Raised and abandoned platforms, sometimes found behind modern beaches, are evidence of higher sea levels in the geological past, [1] and have been used to identify areas of isostatic adjustment. By using scientific dating methods, or examination of marine fossils found on the platform, it is possible to work out when the platform was formed, thus giving geographers and geologists information about sea levels at known times in the past. This has been used in the United Kingdom and other previously glaciated areas to calculate the rate at which land is rising now that it is no longer covered in ice.

Where the coastline itself is changing due to seismic action, there may be a series of platforms showing earlier sea levels and indicating the amount of uplift caused by various earthquakes.

Earthquake Shaking of the surface of the earth caused by a sudden release of energy in the crust

An earthquake is the shaking of the surface of the Earth, resulting from the sudden release of energy in the Earth's lithosphere that creates seismic waves. Earthquakes can range in size from those that are so weak that they cannot be felt to those violent enough to toss people around and destroy whole cities. The seismicity, or seismic activity, of an area is the frequency, type and size of earthquakes experienced over a period of time. The word tremor is also used for non-earthquake seismic rumbling.

Usage of term 'wave-cut'

According to Trenhaile, [2] Sunamura, [3] and Massalink and Hughes, [4] the term 'wave-cut platform' should no longer be used as it assumes that shore platforms are the result of wave action, which is not always true. Shore platforms, like comparable river and lake platforms, are erosional features that develop when removal of saprock and other debris by waves and currents leaves behind a bedrock surface below the water table. [5]

See also

Related Research Articles

Coast Area where land meets the sea or ocean

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

Lagoon A shallow body of water separated from a larger body of water by barrier islands or reefs

A lagoon is a shallow body of water separated from a larger body of water by barrier islands or reefs. Lagoons are commonly divided into coastal lagoons and atoll lagoons. They have also been identified as occurring on mixed-sand and gravel coastlines. There is an overlap between bodies of water classified as coastal lagoons and bodies of water classified as estuaries. Lagoons are common coastal features around many parts of the world.

Coastal erosion The loss or displacement of land along the coastline due to the action of waves, currents, tides. wind-driven water, waterborne ice, or other impacts of storms

Coastal erosion is the loss or displacement of land, or the long-term removal of sediment and rocks along the coastline due to the action of waves, currents, tides, wind-driven water, waterborne ice, or other impacts of storms. The landward retreat of the shoreline can measured and described over a temporal scale of tides, seasons, and other short-term cyclic processes. Coastal erosion may be caused by hydraulic action, abrasion, impact and corrosion by wind and water, and other forces, natural or unnatural.

Hạ Long Bay bay

Ha Long Bay is a UNESCO World Heritage Site and popular travel destination in Quang Ninh Province, Vietnam. The name Hạ Long means "descending dragon". Administratively, the bay belongs to Ha Long City, Cam Pha City, and is a part of Van Don District. The bay features thousands of limestone karsts and isles in various shapes and sizes. Ha Long Bay is a center of a larger zone which includes Bai Tu Long Bay to the northeast, and Cat Ba Island to the southwest. These larger zones share a similar geological, geographical, geomorphological, climate, and cultural characters.

Stack (geology) A geological landform consisting of a steep and often vertical column or columns of rock in the sea near a coast, formed by wave erosion

A stack or sea stack is a geological landform consisting of a steep and often vertical column or columns of rock in the sea near a coast, formed by wave erosion. Stacks are formed over time by wind and water, processes of coastal geomorphology. They are formed when part of a headland is eroded by hydraulic action, which is the force of the sea or water crashing against the rock. The force of the water weakens cracks in the headland, causing them to later collapse, forming free-standing stacks and even a small island. Without the constant presence of water, stacks also form when a natural arch collapses under gravity, due to sub-aerial processes like wind erosion. Erosion causes the arch to collapse, leaving the pillar of hard rock standing away from the coast—the stack. Eventually, erosion will cause the stack to collapse, leaving a stump. Stacks can provide important nesting locations for seabirds, and many are popular for rock climbing.

Both headland and bay are two coastal features that are related and often found on the same coastline. A bay is a body of water—usually seawater and sometimes fresh water— mostly surrounded by land, whereas a headland is surrounded by water on three sides. Headlands are characterized by breaking waves, rocky shores, intense erosion and steep sea cliffs. Bays generally have less wave activity and typically have sandy beaches. Headlands and bays form on discordant coastlines, where the land consists of bands of rock of alternating resistance that run perpendicular to the coast.

Raised beach A beach or wave-cut platform raised above the shoreline by a relative fall in the sea level

A raised beach, coastal terrace, or perched coastline is a relatively flat, horizontal or gently inclined surface of marine origin, mostly an old abrasion platform which has been lifted out of the sphere of wave activity. Thus, it lies above or under the current sea level, depending on the time of its formation. It is bounded by a steeper ascending slope on the landward side and a steeper descending slope on the seaward side. Due to its generally flat shape it is often used for anthropogenic structures such as settlements and infrastructure.

Coastal geography The study of the region between the ocean and the land

Coastal geography is the study of the constantly changing region between the ocean and the land, incorporating both the physical geography and the human geography of the coast. It includes understanding coastal weathering processes, particularly wave action, sediment movement and weather, and the ways in which humans interact with the coast

Coastal management

Coastal management is defence against flooding and erosion, and techniques that stop erosion to claim lands.

Swash A turbulent layer of water that washes up on the beach after an incoming wave has broken

Swash, or forewash in geography, is a turbulent layer of water that washes up on the beach after an incoming wave has broken. The swash action can move beach materials up and down the beach, which results in the cross-shore sediment exchange. The time-scale of swash motion varies from seconds to minutes depending on the type of beach. Greater swash generally occurs on flatter beaches. The swash motion plays the primary role in the formation of morphological features and their changes in the swash zone. The swash action also plays an important role as one of the instantaneous processes in wider coastal morphodynamics.

Terrace (geology) A step-like landform

In geology, a terrace is a step-like landform. A terrace consists of a flat or gently sloping geomorphic surface, called a tread, that is typically bounded one side by a steeper ascending slope, which is called a "riser" or "scarp." The tread and the steeper descending slope together constitute the terrace. Terraces can also consist of a tread bounded on all sides by a descending riser or scarp. A narrow terrace is often called a bench.

St Bees Head cape

St Bees Head is a headland on the North West coast of the English county of Cumbria and is named after the nearby village of St Bees.

Abrasion (geology)

Abrasion is a process of erosion which occurs when material being transported wears away at a surface over time. It is the process of friction caused by scuffing, scratching, wearing down, marring, and rubbing away of materials. The intensity of abrasion depends on the hardness, concentration, velocity and mass of the moving particles. Abrasion generally occurs four ways. Glaciation slowly grinds rocks picked up by ice against rock surfaces. Solid objects transported in river channels make abrasive surface contact with the bed and walls. Objects transported in waves breaking on coastlines cause abrasion. And, finally, abrasion can be caused by wind transporting sand or small stones against surface rocks.

Cuspate foreland Geographical features found on coastlines and lakeshores that are created primarily by longshore drift

Cuspate forelands, also known as cuspate barriers or nesses in Britain, are geographical features found on coastlines and lakeshores that are created primarily by longshore drift. Formed by accretion and progradation of sand and shingle, they extend outwards from the shoreline in a triangular shape. Some cuspate forelands may be stabilised by vegetation, while others may migrate down the shoreline. Because some cuspate forelands provide an important habitat for many flora and fauna, effective management is required to reduce the impacts from both human activities and physical factors such as climate change and sea level rise.

The shoreline is where the land meets the sea and it is continually changing. Over the long term, the water is eroding the land. Beaches represent a special case, in that they exist where sand accumulated from the same processes that strip away rocky and sedimentary material. That is, they can grow as well as erode. River deltas are another exception, in that silt that erodes up river can accrete at the river's outlet and extend ocean shorelines. Catastrophic events such as tsunamis, hurricanes and storm surges accelerate beach erosion, potentially carrying away the entire sand load. Human activities can be as catastrophic as hurricanes, albeit usually over a longer time interval.

Bench (geology) A long, relatively narrow land bounded by distinctly steeper slopes above and below

In geomorphology, geography and geology, a bench or benchland is a long, relatively narrow strip of relatively level or gently inclined land that is bounded by distinctly steeper slopes above and below it. Benches can be of different origins and created by very different geomorphic processes.

A raised shoreline is an ancient shoreline exposed above current water level. These landforms are formed by a relative change in sea level due to global sea level rise, isostatic rebound, and/or tectonic uplift. These surfaces are usually exposed above modern sea level when a heavily glaciated area experiences a glacial retreat, causing water levels to rise. This area will then experience post-glacial rebound, effectively raising the shoreline surface.
Examples of raised shorelines can be found along the coasts of formerly glaciated areas in Ireland and Scotland, as well as in North America. Raised shorelines are exposed at various locations around the Puget Sound of Washington State.

Cliffed coast A form of coast where the action of marine waves has formed steep cliffs that may or may not be precipitous

A cliffed coast, also called an abrasion coast, is a form of coast where the action of marine waves has formed steep cliffs that may or may not be precipitous. It contrasts with a flat or alluvial coast.

Flat coast Shoreline where the land descends gradually into the sea

At a flat coast or flat shoreline, the land descends gradually into the sea. Flat coasts can be formed either as a result of the sea advancing into gently-sloping terrain or through the abrasion of loose rock. They may be basically divided into two parallel strips: the shoreface and the beach.

References

  1. Wilson, M.A., Curran, H.A. and White, B. 1998: Paleontological evidence of a brief global sea-level event during the last interglacial. Lethaia 31: 241-250. "Archived copy" (PDF). Archived from the original (PDF) on 2011-01-12. Retrieved 2009-10-28.CS1 maint: archived copy as title (link)
  2. Trenhaile, A. S. 1987: The Geomorphology of Rock Coasts. (Oxford University Press, Oxford, U.K.) 393 pp.
  3. Sunamura, T., 1992. Geomorphology of rocky coasts. New York: John Wiley.
  4. Masselink, G and Hughes, M. 2003. Introduction to Coastal Processes and Geomorphology. Hodder Arnold
  5. Retallack, G.J. and Roering, J.J. 2012: Wave-cut or water-table platforms of rocky coasts and rivers? GSA Today 22(6), 4-9.