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Bank (topography)

Bank (topography)

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A bank, sometimes referred to as a fishing bank, is an area on the continental shelf
Continental shelf
The continental shelf is the extended perimeter of each continent and associated coastal plain. Much of the shelf was exposed during glacial periods, but is now submerged under relatively shallow seas and gulfs, and was similarly submerged during other interglacial periods. The continental margin,...

 which is shallow compared to its surrounding area, such as a shoal
Shoal
Shoal, shoals or shoaling may mean:* Shoal, a sandbank or reef creating shallow water, especially where it forms a hazard to shipping* Shoal draught , of a boat with shallow draught which can pass over some shoals: see Draft...

 or the top of an underwater hill
Seamount
A seamount is a mountain rising from the ocean seafloor that does not reach to the water's surface , and thus is not an island. These are typically formed from extinct volcanoes, that rise abruptly and are usually found rising from a seafloor of depth. They are defined by oceanographers as...

. Somewhat like continental slopes, ocean banks slopes can upwell
Upwelling
Upwelling is an oceanographic phenomenon that involves wind-driven motion of dense, cooler, and usually nutrient-rich water towards the ocean surface, replacing the warmer, usually nutrient-depleted surface water. The increased availability in upwelling regions results in high levels of primary...

 as tidal and other flows intercept them, resulting sometimes in nutrient rich currents. Because of this, some large banks, such as Dogger Bank
Dogger Bank
Dogger Bank is a large sandbank in a shallow area of the North Sea about off the east coast of England. It extends over approximately , with its dimensions being about long and up to broad. The water depth ranges from 15 to 36 metres , about shallower than the surrounding sea. It is a...

 and the Grand Banks of Newfoundland, are among the richest fishing grounds in the world.

There are some banks that were reported in the 19th century by navigators, such as Wachusett Reef
Wachusett Reef
Captain Lambert of the ship Wachusett reported that on June 4, 1899 he passed over a reef which appeared to be of coral formation in approximately latitude . The reef appeared to be about 500 feet wide. The bottom showed of a dark gray color with deep blue on both sides of the reef...

, whose existence is doubtful.

Types


Ocean banks may be of volcanic
Volcano
2. Bedrock3. Conduit 4. Base5. Sill6. Dike7. Layers of ash emitted by the volcano8. Flank| 9. Layers of lava emitted by the volcano10. Throat11. Parasitic cone12. Lava flow13. Vent14. Crater15...

 nature. Banks may be carbonate
Carbonate platform
A carbonate platform is a sedimentary body which possesses topographic relief, and is composed of autochthonous calcareous deposits . Platform growth is mediated by sessile organisms whose skeletons build up the reef or by organisms which induce carbonate precipitation through their metabolism...

 or terrigenous. In tropical areas some banks are submerged atoll
Atoll
An atoll is a coral island that encircles a lagoon partially or completely.- Usage :The word atoll comes from the Dhivehi word atholhu OED...

s. As they are not associated with any landmass
Landmass
A landmass is a contiguous area of land surrounded by ocean. Although it may be most often written as one word to distinguish it from the usage "land mass"—the measure of land area—it is also used as two words.Landmasses include:*supercontinents...

, banks have no outside source of sediments.
Carbonate banks are typically platforms, rising from the ocean depths, whereas terrigenous banks are elevated sedimentary deposits.

Seamount
Seamount
A seamount is a mountain rising from the ocean seafloor that does not reach to the water's surface , and thus is not an island. These are typically formed from extinct volcanoes, that rise abruptly and are usually found rising from a seafloor of depth. They are defined by oceanographers as...

s, by contrast, are mountains, of volcanic
Volcano
2. Bedrock3. Conduit 4. Base5. Sill6. Dike7. Layers of ash emitted by the volcano8. Flank| 9. Layers of lava emitted by the volcano10. Throat11. Parasitic cone12. Lava flow13. Vent14. Crater15...

 origin, rising from the deep sea
Deep sea
The deep sea, or deep layer, is the lowest layer in the ocean, existing below the thermocline and above the seabed, at a depth of 1000 fathoms or more. Little or no light penetrates this part of the ocean and most of the organisms that live there rely for subsistence on falling organic matter...

, and are steeper, and higher in comparison to the surrounding seabed
Seabed
The seabed is the bottom of the ocean.- Ocean structure :Most of the oceans have a common structure, created by common physical phenomena, mainly from tectonic movement, and sediment from various sources...

. Examples are Pioneer and Guide Seamounts, west of the Farallon Islands
Farallon Islands
The Farallon Islands, or Farallones , are a group of islands and sea stacks in the Gulf of the Farallones, off the coast of San Francisco, California, USA. They lie outside the Golden Gate and south of Point Reyes, and are visible from the mainland on clear days...

. The Pioneer Seamount has a depth of 1,000 meters, In other cases, parts of a bank may reach above the water surface, thereby forming island
Island
An island or isle is any piece of sub-continental land that is surrounded by water. Very small islands such as emergent land features on atolls can be called islets, cays or keys. An island in a river or lake may be called an eyot , or holm...

s.

Important banks


The largest banks in the world are:
  1. Grand Banks of Newfoundland (280,000 km²) - terrigenous bank
  2. Great Bahama Bank (95,798.12 km², has islands, area without islands)
  3. Saya de Malha (35,000 km², excluding the separate North bank, least depth 7 m)
  4. Seychelles Bank (31,000 km², including islands of 266 km²)
  5. Georges Bank
    Georges Bank
    Georges Bank is a large elevated area of the sea floor which separates the Gulf of Maine from the Atlantic Ocean and is situated between Cape Cod, Massachusetts and Cape Sable Island, Nova Scotia ....

     (28,800 km²) - terrigenous bank
  6. Lansdowne Bank
    Lansdowne Bank
    Lansdowne Bank, sometimes called Landsdowne Bank, is an extensive submerged bank located between the main island of New Caledonia and the Chesterfield Islands, in the easternmost part of the Coral Sea. It covers an area of 21,000 km², making it one of the largest banks of the world , has general...

     (21,000 km², west of New Caledonia
    New Caledonia
    New Caledonia is a special collectivity of France located in the southwest Pacific Ocean, east of Australia and about from Metropolitan France. The archipelago, part of the Melanesia subregion, includes the main island of Grande Terre, the Loyalty Islands, the Belep archipelago, the Isle of...

    , least depth 3.7 m)
  7. Dogger Bank
    Dogger Bank
    Dogger Bank is a large sandbank in a shallow area of the North Sea about off the east coast of England. It extends over approximately , with its dimensions being about long and up to broad. The water depth ranges from 15 to 36 metres , about shallower than the surrounding sea. It is a...

     (17,600 km², least depth 13 m)
  8. Little Bahama Bank (14,260.64 km², has islands, area without islands)
  9. Great Chagos Bank
    Great Chagos Bank
    The Great Chagos Bank, in the Chagos Archipelago, about South of the Maldives, is the largest atoll structure in the world, with a total area of . The Atoll is administered by the UK through the BIOT.-Islands:...

     (12,642 km², including islands of 4.5 km²)
  10. Reed Bank, Spratly Islands
    Spratly Islands
    The Spratly Islands are a group of more than 750 reefs, islets, atolls, cays and islands in the South China Sea. The archipelago lies off the coasts of the Philippines and Malaysia , about one third of the way from there to southern Vietnam. They comprise less than four square kilometers of land...

     (8,866 km², least depth 9 m)
  11. Caicos Bank, Caicos Islands (7,680 km², including islands of 589.5 km²)
  12. Macclesfield Bank
    Macclesfield Bank
    Macclesfield Bank or Zhongsha Islands is an elongated sunken atoll of underwater reefs and shoals in the South China Sea and part of the disputed South China Sea Islands, centred around , east of the Paracel Islands. Its length exceeds southwest-northeast, with a maximal width of more than...

     (6,448 km², least depth 9.2 m)
  13. North Bank or Ritchie Bank (5,800 km², north of Saya de Malha, least depth <10 m)
  14. Cay Sal Bank
    Cay Sal Bank
    Cay Sal Bank is the third largest and the westernmost of the Bahama Banks. It is located between 23º27'N - 24º10'N and 079º25'W – 080º35'W...

     (5,226.73 km², including islands of 14,87 km²)
  15. Rosalind Bank
    Rosalind Bank
    Rosalind Bank, also called Rosalinda or Rosa Linda Bank, is a large, completely submerged atoll that lies with its southern extremity 269 km ENE of Cabo Gracias a Dios, at . It is the culmination of an area of coral reef some 300 km long that is stretching out eastward from Cabo Gracias a Dios...

    (4,500 km², lest depth 7.3 m)

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