Beaches and Islands
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Wikipedia-Article "Beaches"
- For other uses, see Beach (disambiguation).
A beach or strand is a geological formation consisting of loose rock particles such as sand, shingle, cobble, or even shell along the shoreline of a body of water.
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Components
Some geologists consider a beach to be just this shoreline feature of deposited material, but William Bascom (1980) has argued that a beach is the entire system of sand set in motion by waves to a depth of ten meters (30+ feet) or more off ocean coasts. Submerged, longshore bars are therefore also part of the beach. In the Bascom approach, beaches can be viewed as either
- small systems in which the rock material moves onshore, offshore, or alongshore by the forces of waves and currents; or
- geological units of considerable size.
The former are described in detail below; the larger geological units are discussed elsewhere under bars. Both types can be viewed as "beaches."
There are several conspicuous parts to a beach, all of which relate to the processes that form and shape it. That part mostly above water (depending upon tide), and more or less actively influenced by the waves at some point in the tide, is termed the beach berm. The berm is the deposit of material comprising the active shoreline. The berm has a crest (top) and a face — the latter being the slope leading down towards the water from the crest. At the very bottom of the face, there may be a trough, and further seaward one or more longshore bars: slightly raised, underwater embankments formed where the waves first start to break.
The sand deposit may extend well inland from the berm crest, where there may be evidence of one or more older crests (the storm beach) resulting from very large storm waves and beyond the influence of the normal waves. At some point the influence of the waves (even storm waves) on the material comprising the beach stops, and if the particles are small enough (that is, are sand), winds shape the feature. Where wind is the force distributing the grains inland, the deposit behind the beach becomes a dune.
The line between beach and dune is difficult to define in the field. Over any significant period of time, sand is always being exchanged between them. The drift line (the high point of material deposited by waves) is one potential demarcation. This would be the point at which significant wind movement of sand could occur, since the normal waves do not wet the sand beyond this area. However, the drift line is likely to move inland under assault by storm waves.
How beaches are formed
Beaches are deposition landforms, and are the result of wave action by which waves or currents move sand or other loose sediments of which the beach is made as these particles are held in suspension. Alternatively, sand may be moved by saltation (a bouncing movement of large particles). Beach materials come from erosion of rocks offshore, as well as from headland erosion and slumping producing deposits of scree. A coral reef offshore is a significant source of sand particles.
The shape of a beach depends on whether the waves are constructive or destructive, and whether the material is sand or shingle. Constructive waves move material up the beach while destructive waves move the material down the beach. On sandy beaches, the backwash of the waves removes material forming a gently sloping beach. On shingle beaches the swash is dissipated because the large particle size allows percolation, so the backwash is not very powerful, and the beach remains steep. Cusps and horns form where incoming waves divide, depositing sand as horns and scouring out sand to form cusps. This forms the uneven face on some sand shorelines.
There are several beaches which are claimed to be the "World's longest", including Cox's Bazar, Bangladesh (120kms), Fraser Island beach, 90 Mile Beach in Australia and 90 Mile Beach in New Zealand and Long Beach, Washington (which is about 30km). Wasaga Beach, Ontario on Georgian Bay claims to have the world's longest freshwater beach. The Marina Beach at Chennai, India, is the second longest beach in the world.
Beaches and recreation
Beaches have long been a popular attraction for tourism and recreation. Especially popular are seaside resorts and large white sand beaches. Of course, residents and tourists alike use beaches as a place for leisure and sport. The relatively soft formation of sand is comfortable to sit or lie on, and entering and exiting the water is far easier across a sand beach than a rocky shore. The waves present at beaches add to the enjoyment and make the sport of body surfing and related activities possible. One of the many attractions of a sand beach, especially for children, is playing with the sand, building sand castles and other constructs.
Towels and mats are typical beach "furniture". In the Victorian era, many popular beach resorts were equipped with bathing machines because even the all-covering beachware of the period was considered immodest. This social standard still prevails in some Muslim countries. At the other extreme are nude beaches, where no swimware of any kind is compulsory.
Artificial beaches
Some beaches are artificial; they are either permanent or temporary (For examples see Monaco, Paris, Rotterdam, Hong Kong and Singapore).
The soothing qualities of a beach and the pleasant environment offered to the beachgoer are replicated in artificial beaches, such as "beach style" pools with zero-depth entry and wave pools that recreate the natural waves pounding upon a beach. In a zero-depth entry pool, the bottom surface slopes gradually from above water down to depth. Another approach involves so-called urban beaches, a form of public park becoming common in large cities. Urban beaches attempt to mimic natural beaches with fountains that imitate surf and mask city noises, and in some cases can be used as a play park.
Sounds of the beach
Beaches are noted for their sometimes serene stillness and the rhythmic sound made by waves crashing upon the sand. To experience, listen to this sound file sound recording (1.00MB) made on a South Carolina beach at night.
Beaches as habitat
A beach is an unstable environment which exposes plants and animals to harsh conditions. Some small animals burrow into the sand and feed on material deposited by the waves. Crabs, insects and shorebirds feed on these beach dwellers. The endangered Piping Plover and some tern species rely on beaches for nesting. Sea turtles also lay their eggs on ocean beaches. Seagrasses and other beach plants grow on undisturbed areas of the beach and dunes.
See also
- List of beaches
- Beach cricket
- Beach volleyball
- Coast
- Dune buggy
- Nude beach
- Pier
- The Beach Boys
- The Shore
- Urban beach
Reference
- Bascom, W. 1980. Waves and Beaches. Anchor Press/Doubleday, Garden City, New York. 366 p.
External sites
Wikipedia-Article "Islands"
- For other uses, see Island (disambiguation).
An island or isle is any piece of land that is completely surrounded by water. Very small islands are called islets. Although seldom adhered to, it is also proper to call an emergent land feature on an atoll an islet, since an atoll is a type of island. A key or cay is also another name for a relatively small island. Groups of related islands are called archipelagos.
There are three main types of islands: continental islands, river islands, and volcanic islands. There are also some artificial islands.
The word island derives ultimately from the Old English word igland. It was originally spelled phonetically: iland. The letter "s" was added out of the mistaken belief that it derived from isle (< Old French < Latin insula) + land, where no such etymological relationship existed.
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Continental islands
Continental islands are bodies of land that are connected by the continental shelf to a continent. That is, these islands are part of an adjacent continent and are located on the continental shelf of that continent. Examples include Greenland and Sable Island off North America, Barbados and Trinidad off South America, Sicily off Europe, Sumatra and Java off Asia, New Guinea and Tasmania off Australia.
A special type of continental island is the microcontinental island, which results when a continent is rifted. The best example is Madagascar off Africa. The Kerguelen Islands and some of the Seychelles are also examples.
Another subtype is the barrier island: accumulations of sand on the continental shelf.
River islands
River islands occur in river deltas and in large rivers. They are caused by deposition of sediment at points in the flow where the current loses some of its carrying capacity. In essence, they are river bars, isolated in the stream. While some are ephemeral, and may disappear if the river's water volume or speed changes, others are stable and long-lived.
Volcanic islands
Volcanic islands are built by volcanoes. Mid-ocean examples are not geologically part of any continent. One type of volcanic island is found in a volcanic island arc. These islands arise from volcanoes where the subduction of one plate under another is occurring. Examples include the Mariana Islands, the Aleutian Islands, and most of Tonga in the Pacific Ocean. Some of the Lesser Antilles and the South Sandwich Islands are the only Atlantic Ocean examples.
Another type of volcanic island occurs where an oceanic rift reaches the surface. There are two examples: Iceland, which is the world's largest volcanic island, and Jan Mayen—both are in the Atlantic.
The last type of volcanic island are those formed over volcanic hotspots. A hot spot is more or less stationary relative to the moving tectonic plate above it, so a chain of islands results as the plate drifts. Over long periods of time, this type of island is eventually eroded down and "drowned" by isostatic adjustment, becoming a seamount. Plate movement across a hot-spot produces a line of islands oriented in the direction of the plate movement. An example is the Hawaiian Islands, from Hawaii to Kure, which then extends beneath the sea surface in a more northerly direction as the Emperor Seamounts. Another chain with similar orientation is the Tuamotu Archipelago; its older, northerly trend is the Line Islands. The southernmost chain is the Austral Islands, with its northerly trending part the atolls in the nation of Tuvalu. Tristan da Cunha is an example of a hotspot volcano in the Atlantic Ocean.
An atoll is an island formed from a coral reef that has grown on an eroded and submerged volcanic island. The reef rises above the surface of the water and forms a new island. Atolls are typically ring-shaped with a central, shallow lagoon. Examples include the Maldives in the Indian Ocean and Bora Bora in the Pacific.
See also
- List of islands
- List of islands by area
- List of islands by population
- Island nation
- Reef
- Desert island
- Tidal island
- List of artificial islands
- List of divided islands
- Skerry
External links
- Definition of island from United Nations Convention on the Law of the Sea
- Listing of islands from United Nations Island Directory. Very comprehensive listing of all islands in the world with lots of information related to environmental issues.