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Bathymetry

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Beneath the smooth ocean surface extends an underwater landscape as complex as anything you might find on land. While the ocean has an average depth of 3.7 km (2.3 mi), the shape and depth of the seafloor is complex. The topography of the ocean floor is described in terms of bathymetry. This field describes the major bathymetric features found on the ocean floor. The profile of the ocean floor includes seven major features extending from the shoreline. Specific bathymetric features associated with each of the following categories are listed for each ocean.

  • The Continental Shelf, a rather flat area of the sea floor adjacent to the coast that gradually slopes down from the shore to water depths of about 200 m (660 ft). It is narrow or nearly nonexistent in some places; in others, it extends for hundreds of miles. The waters along the continental shelf are usually productive in both plant and animal life, both from sunlight and nutrients from ocean upwelling and terrestrial runoff.
  • The Continental Slope is where the bottom drops off more rapidly until it meets the deep-sea floor (Abyssal Plain) at about 3,200 m (10,500 ft) water depth. The deep waters of the Continental Slope are characterized by cold temperatures, low light conditions, and very high pressures. Sunlight does not penetrate to these depths, having been absorbed or reflected in the water above. The continental slope can be indented by submarine canyons, often associated with the outflow of major rivers. Another feature of the continental slope are alluvial fans or cones of sediments carried downstream to the ocean by major rivers and deposited down the slope.
  • The Abyssal Plains, at depths of over 3,000 m (10,000 ft) and covering 70% of the ocean floor, are the largest habitat on earth. Sunlight does not penetrate to the sea floor, making these deep, dark ecosystems less productive than those along the continental shelf. But despite their name, these “plains” are not uniformly flat. They are interrupted by features like hills, valleys, and seamounts.
  • The Mid-ocean Ridge, rising up from the Abyssal Plain, is an underwater mountain range, over 64,000 km (40,000 mi) long, rising to an average depth of 2,400 m (8,000 ft). Mid-ocean ridges form at divergent plate boundaries where two tectonic plates are moving apart and new crust is created by magma pushing up from the mantle. Tracing their way around the global ocean, this system of underwater volcanoes forms the longest mountain range on Earth.
  • Seamounts are submarine mountains at least 1,000 m (3,300 ft) high formed from individual volcanoes on the ocean floor. They are distinct from the plate-boundary volcanic system of the mid-ocean ridges, because seamounts tend to be circular or conical. A circular collapse caldera is often centered at the summit, evidence of a magma chamber within the volcano. Flat topped seamounts are known as Guyots. Long chains of seamounts are often fed by "hot spots" in the deep mantle. These hot spots are associated with stationary plumes of molten rock rising from deep within the Earth's mantle. These hot spot plumes melt through the overlying tectonic plate as it moves and supplies magma to the active volcanic island at the end of the chain of volcanic islands and seamounts.
  • Ocean Trenches are the deepest parts of the ocean floor and are created by the process of subduction. Trenches form along convergent boundaries where tectonic plates are moving toward each other, and one plate sinks (is subducted) under another. The location where the sinking of a plate occurs is called a subduction zone. Subduction can occur when oceanic crust collides with and sinks under (subducts) continental crust resulting in volcanic, seismic, and mountain-building processes. Subduction can also occur in the convergence of two oceanic plates where one will sink under the other and in the process create a deep ocean trench. Subduction processes in oceanic-oceanic plate convergence also result in the formation of volcanoes. Over millions of years, the erupted lava and volcanic debris pile up on the ocean floor until a submarine volcano rises above sea level to form a volcanic island. Such volcanoes are typically strung out in chains called island arcs. As the name implies, volcanic island arcs, which closely parallel the trenches, are generally curved.
  • Atolls are the remains of dormant volcanic islands. In warm tropical oceans, coral colonies establish themselves on the margins of the island. Then, over time, the high elevation of the island collapses and erodes away to sea level leaving behind an outline of the island in the form of the fringing coral reef. The resulting low island is typified by the coral reef surrounding a low elevation of sand and coral above sea level with an interior shallow lagoon. Often times the remaining dry land is broken into a ring of islets. Some lagoons can be hundreds of square kilometers. It may take as long as 300,000 years for an atoll formation to occur. Guyots are submerged atoll structures, which explains why they are flat topped seamounts.

  • Atlantic Ocean

    continental shelf: The continental shelf (see Figure 1), a rather flat area of the sea floor adjacent to the coast that gradually slopes down from the shore to water depths of about 200 m (660 ft). Dimensions can vary: they may be narrow or nearly nonexistent in some places or extend for hundreds of miles in others. The waters along the continental shelf are usually productive in both plant and animal life, both from sunlight and nutrients from ocean upwelling and terrestrial runoff. The passive margins of the Atlantic Ocean provide for wide continental shelves in North America, Northwest Europe, and the southern coast of South America. The following are examples of features found on the continental shelf of the Atlantic Ocean.

    Blake Plateau (Figure 5)
    Celtic Shelf (Figure 2)
    Dogger Bank (Figure 2)
    Flemish Cap (Figure 2)
    Falkland Plateau (Figure 3)
    Grand Banks of Newfoundland (Figure 2)
    Great Bahama Bank (Figure 5)
    Little Bahama Bank (Figure 5)
    Tunisian Plateau (Figure 4)
    Yacatan Shelf (Figure 5)



    continental slope: The continental slope (see Figure 1) is where the ocean bottom drops off more rapidly until it meets the deep-sea floor (abyssal plain) at about 3,200 m (10,500 ft) water depth. The deep waters of the continental slope are characterized by cold temperatures, low light conditions, and very high pressures. Sunlight does not penetrate to these depths, having been absorbed or reflected in the water above. The continental slope can be indented by submarine canyons, often associated with the outflow of major rivers. Another feature of the continental slope are alluvial fans or cones of sediments carried downstream to the ocean by major rivers and deposited down the slope. The following are examples of features found on the continental slope of the Atlantic Ocean.

    Amazon Cone (Figure 3)
    Congo Fan (Figure 3)
    Hudson Canyon (Figure 5)
    Mississippi Fan (Figure 5)



    abyssal plains: The abyssal plains (see Figure 1), at depths of over 3,000 m (10,000 ft) and covering 70% of the ocean floor, are the largest habitat on earth. Sunlight does not penetrate to the sea floor, making these deep, dark ecosystems less productive than those along the continental shelf. Despite their name, these “plains” are not uniformly flat; they are interrupted by features like hills, valleys, and seamounts. The following are examples of features found on the abyssal plains of the Atlantic Ocean.

    Angola Basin (Figure 3)
    Agulhas Basin (Figure 3)
    Argentine Basin (Figure 3)
    Brazil Basin (Figure 3)
    Canary Basin (Figure 2)
    Cape Basin (Figure 3)
    Colombia Basin (Figure 2)
    Labrador Basin (Figure 2)
    Mexico Basin (Figure 2)
    Newfoundland Basin (Figure 2)
    North American Basin (Figure 2)
    Venezuela Basin (Figure 2)
    West European Basin (Figure 2)



    mid-ocean ridge: The mid-ocean ridge (see Figure 1), rising up from the abyssal plain, is an underwater mountain range, over 64,000 km (40,000 mi) long, rising to an average depth of 2,400 m (8,000 ft). Mid-ocean ridges form at divergent plate boundaries where two tectonic plates are moving apart and new crust is created by magma pushing up from the mantle. Tracing their way around the global ocean, this system of underwater volcanoes forms the longest mountain range on Earth. Fracture Zones are linear transform faults that develop perpendicular to the line of the mid-ocean ridge which can offset the ridge line and divide it into segments.The Charlie-Gibbs Fracture Zone displaces the mid-ocean ridge 350 km to the west separating the Mid-Atlantic Ridge from the Reykjanes Ridge. The Romanche Fracture Zone, located near the Equator, offsets the Mid-Atlantic Ridge 900 km and is considered the dividing line between the North and South Atlantic Oceans. The following are examples of mid-ocean ridges found on the floor of the Atlantic Ocean.

    East Mediterranean Ridge (Figure 4)
    Mid-Atlantic Ridge (Figures 2, 3)
    Reykjanes Ridge (Figure 2)



    seamounts: Seamounts (see Figure 1) are submarine mountains at least 1,000 m (3,300 ft) high formed from individual volcanoes on the ocean floor. They are distinct from the plate-boundary volcanic system of the mid-ocean ridges, because seamounts tend to be circular or conical. A circular collapse caldera is often centered at the summit, evidence of a magma chamber within the volcano. Flat topped seamounts are known as guyots. Long chains of seamounts are often fed by "hot spots" in the deep mantle. These hot spots are associated with stationary plumes of molten rock rising from deep within the Earth's mantle. These hot spot plumes melt through the overlying tectonic plate as it moves and supplies magma to the active volcanic island at the end of the chain of volcanic islands and seamounts. The following are examples of seamounts found on the floor of the Atlantic Ocean.

    Bermuda Rise (Figure 2)
    Cape Verde Plateau (Figure 2)
    New England Seamounts (Figure 2)
    Rio Grande Plateau (Figure 3)
    Rockall Plateau (Figure 2)



    ocean trenches: Ocean trenches (see Figure 1) are the deepest parts of the ocean floor and are created by the process of subduction. Trenches form along convergent boundaries where tectonic plates are moving toward each other, and one plate sinks (is subducted) under another. The location where the sinking of a plate occurs is called a subduction zone. Subduction can occur when oceanic crust collides with and sinks under (subducts) continental crust resulting in volcanic, seismic, and mountain-building processes. Subduction can also occur in the convergence of two oceanic plates where one will sink under the other and in the process create a deep ocean trench. Subduction processes in oceanic-oceanic plate convergence also result in the formation of volcanoes. Over millions of years, the erupted lava and volcanic debris pile up on the ocean floor until a submarine volcano rises above sea level to form a volcanic island. Such volcanoes are typically strung out in chains called island arcs. As the name implies, volcanic island arcs, which closely parallel the trenches, are generally curved. The following are examples of ocean trenches found on the floor of the Atlantic Ocean.

    Cayman Trench (Caribbean Sea) (Figure 2)
    Hellenic Trench (Mediterranean Sea) (Figure 4)
    Puerto Rico Trench (Figure 2); note - deepest point in the Atlantic Ocean
    South Sandwich Trench (South Atlantic) (Figure 3)



    atolls: Atolls are the remains of dormant volcanic islands. In warm tropical oceans, coral colonies establish themselves on the margins of the island. Then, over time, the high elevation of the island collapses and erodes away to sea level leaving behind an outline of the island in the form of the fringing coral reef. The resulting low island is typified by the coral reef surrounding a low elevation of sand and coral above sea level with an interior shallow lagoon. Often times the remaining dry land is broken into a ring of islets. Some lagoons can be hundreds of square kilometers. It may take as long as 300,000 years for an atoll formation to occur. Guyots are submerged atoll structures, which explains why they are flat topped seamounts. The following are examples of atolls found in the Atlantic Ocean

    Rocas Atoll (Brazil); note - the only atoll in the South Atlantic

  • Indian Ocean

    continental shelf:

    The continental shelf (see Figure 1), a rather flat area of the sea floor adjacent to the coast that gradually slopes down from the shore to water depths of about 200 m (660 ft). Dimensions can vary: they may be narrow or nearly nonexistent in some places or extend for hundreds of miles in others. The waters along the continental shelf are usually productive in both plant and animal life, both from sunlight and nutrients from ocean upwelling and terrestrial runoff. The following are examples of features found on the continental shelf of the Indian Ocean (see Figure 2).

    Exmouth Plateau
    Indus Canyon
    The Swatch of No Ground/Ganges Canyon (Bay of Bengal)
    Sunda Shelf



    continental slope:

    The continental slope (see Figure 1) is where the ocean bottom drops off more rapidly until it meets the deep-sea floor (abyssal plain) at about 3,200 m (10,500 ft) water depth. The deep waters of the continental slope are characterized by cold temperatures, low light conditions, and very high pressures. Sunlight does not penetrate to these depths, having been absorbed or reflected in the water above. The continental slope can be indented by submarine canyons, often associated with the outflow of major rivers. Another feature of the continental slope are alluvial fans or cones of sediments carried downstream to the ocean by major rivers and deposited down the slope. The following are examples of features found on the continental slope of the Indian Ocean (see Figure 2).

    Bengal Fan
    Indus Fan



    abyssal plains:

    The abyssal plains (see Figure 1), at depths of over 3,000 m (10,000 ft) and covering 70% of the ocean floor, are the largest habitat on earth. Sunlight does not penetrate to the sea floor, making these deep, dark ecosystems less productive than those along the continental shelf. Despite their name, these “plains” are not uniformly flat; they are interrupted by features like hills, valleys, and seamounts. The following are examples of features found on the abyssal plains of the Indian Ocean (see Figure 2).

    Arabian Basin
    Crozet Basin
    Madagascar Basin
    Mid-Indian Basin
    Mozambique Basin
    Wharton Basin



    mid-ocean ridge:

    The mid-ocean ridge (see Figure 1), rising up from the abyssal plain, is an underwater mountain range, over 64,000 km (40,000 mi) long, rising to an average depth of 2,400 m (8,000 ft). Mid-ocean ridges form at divergent plate boundaries where two tectonic plates are moving apart and new crust is created by magma pushing up from the mantle. Tracing their way around the global ocean, this system of underwater volcanoes forms the longest mountain range on Earth. Fracture Zones are linear transform faults that develop perpendicular to the line of the mid-ocean ridge which can offset the ridge line and divide it into segments. The following are examples of mid-ocean ridges found on the floor of the Indian Ocean (see Figure 2).

    Central Indian Ridge
    Davie Ridge
    Southeast Indian Ridge
    Southwest Indian Ridge



    seamounts:

    Seamounts (see Figure 1) are submarine mountains at least 1,000 m (3,300 ft) high formed from individual volcanoes on the ocean floor. They are distinct from the plate-boundary volcanic system of the mid-ocean ridges, because seamounts tend to be circular or conical. A circular collapse caldera is often centered at the summit, evidence of a magma chamber within the volcano. Flat topped seamounts are known as guyots. Long chains of seamounts are often fed by "hot spots" in the deep mantle. These hot spots are associated with stationary plumes of molten rock rising from deep within the Earth's mantle. These hot spot plumes melt through the overlying tectonic plate as it moves and supplies magma to the active volcanic island at the end of the chain of volcanic islands and seamounts. The following are examples of seamounts found on the floor of the Indian Ocean (see Figure 2).

    Andaman-Nicobar Ridge
    Chagos-Laccadive Ridge
    Kerguelen Plateau
    Madagascar Plateau
    Mascarene Plateau
    Mozambique Plateau
    Ninetyeast Ridge



    ocean trenches:

    Ocean trenches (see Figure 1) are the deepest parts of the ocean floor and are created by the process of subduction. Trenches form along convergent boundaries where tectonic plates are moving toward each other, and one plate sinks (is subducted) under another. The location where the sinking of a plate occurs is called a subduction zone. Subduction can occur when oceanic crust collides with and sinks under (subducts) continental crust resulting in volcanic, seismic, and mountain-building processes. Subduction can also occur in the convergence of two oceanic plates where one will sink under the other and in the process create a deep ocean trench. Subduction processes in oceanic-oceanic plate convergence also result in the formation of volcanoes. Over millions of years, the erupted lava and volcanic debris pile up on the ocean floor until a submarine volcano rises above sea level to form a volcanic island. Such volcanoes are typically strung out in chains called island arcs. As the name implies, volcanic island arcs, which closely parallel the trenches, are generally curved. The following are examples of ocean trenches found on the floor of the Indian Ocean (see Figure 2).

    Java/Sunda Trench; note - deepest point in the Indian Ocean



    atolls:

    Atolls (see Figure 1) are the remains of dormant volcanic islands. In warm tropical oceans, coral colonies establish themselves on the margins of the island. Then, over time, the high elevation of the island collapses and erodes away to sea level leaving behind an outline of the island in the form of the fringing coral reef. The resulting low island is typified by the coral reef surrounding a low elevation of sand and coral above sea level with an interior shallow lagoon. Often times the remaining dry land is broken into a ring of islets. Some lagoons can be hundreds of square kilometers. It may take as long as 300,000 years for an atoll formation to occur. Guyots are submerged atoll structures, which explains why they are flat topped seamounts. The following are examples of atolls found in the Indian Ocean (see Figure 2).

    Bassas da India
    Chagos Archipelago/Diego Garcia
    Europa Island
    Juan de Nova Island
    Lakshadweep Islands
    Maldive Islands
    Seychelles

  • Pacific Ocean

    continental shelf: The continental shelf (see Figure 1), a rather flat area of the sea floor adjacent to the coast that gradually slopes down from the shore to water depths of about 200 m (660 ft). Dimensions can vary: they may be narrow or nearly nonexistent in some places or extend for hundreds of miles in others. The waters along the continental shelf are usually productive in both plant and animal life, both from sunlight and nutrients from ocean upwelling and terrestrial runoff. The following are examples of features found on the continental shelf of the Pacific Ocean.

    Arafura Shelf (Figure 4B)
    Sahul Shelf (Figure 4B)
    Sunda Shelf (Figure 4B)
    Taiwan Banks (Figure 4B)



    continental slope: The continental slope (see Figure 1) is where the ocean bottom drops off more rapidly until it meets the deep-sea floor (abyssal plain) at about 3,200 m (10,500 ft) water depth. The deep waters of the continental slope are characterized by cold temperatures, low light conditions, and very high pressures. Sunlight does not penetrate to these depths, having been absorbed or reflected in the water above. The continental slope can be indented by submarine canyons, often associated with the outflow of major rivers. Another feature of the continental slope are alluvial fans or cones of sediments carried downstream to the ocean by major rivers and deposited down the slope. The following are examples of features found on the continental slope of the Pacific Ocean.

    Pribilof Canyon (Figure 2)
    Zhemchug Canyon (Figure 2); note - deepest submarine canyon



    abyssal plains: The abyssal plains (see Figure 1), at depths of over 3,000 m (10,000 ft) and covering 70% of the ocean floor, are the largest habitat on earth. Sunlight does not penetrate to the sea floor, making these deep, dark ecosystems less productive than those along the continental shelf. Despite their name, these “plains” are not uniformly flat; they are interrupted by features like hills, valleys, and seamounts. The following are examples of features found on the abyssal plains of the Pacific Ocean.

    Aleutian Basin (Figure 2)
    Central Pacific Basin (Figure 2)
    Northeast Pacific Basin (Figure 2)
    Northwest Pacific Basin (Figure 2)
    Philippine Basin (Figure 4)
    Southwest Pacific Basin (Figure 4)
    Tasman Basin (Figure 4)



    mid-ocean ridge: The mid-ocean ridge (see Figure 1), rising up from the abyssal plain, is an underwater mountain range, over 64,000 km (40,000 mi) long, rising to an average depth of 2,400 m (8,000 ft). Mid-ocean ridges form at divergent plate boundaries where two tectonic plates are moving apart and new crust is created by magma pushing up from the mantle. Tracing their way around the global ocean, this system of underwater volcanoes forms the longest mountain range on Earth. Fracture Zones are linear transform faults that develop perpendicular to the line of the mid-ocean ridge which can offset the ridge line and divide it into segments. The following are examples of mid-ocean ridges found on the floor of the Pacific Ocean.

    East Pacific Rise (Figure 3)
    Pacific-Antarctic Ridge (Figure 3)



    seamounts: Seamounts (see Figure 1) are submarine mountains at least 1,000 m (3,300 ft) high formed from individual volcanoes on the ocean floor. They are distinct from the plate-boundary volcanic system of the mid-ocean ridges, because seamounts tend to be circular or conical. A circular collapse caldera is often centered at the summit, evidence of a magma chamber within the volcano. Flat topped seamounts are known as guyots. Long chains of seamounts are often fed by "hot spots" in the deep mantle. These hot spots are associated with stationary plumes of molten rock rising from deep within the Earth's mantle. These hot spot plumes melt through the overlying tectonic plate as it moves and supplies magma to the active volcanic island at the end of the chain of volcanic islands and seamounts. The following are examples of seamounts found on the floor of the Pacific Ocean.

    Caroline Seamounts (Figure 4B)
    East Mariana Ridge (Figure 4)
    Emperor Seamount Chain (Figure 2)
    Hawaiian Ridge (Figure 2)
    Lord Howe Seamount Chain (Figure 4)
    Louisville Ridge (Figure 4)
    Kapingamarangi (Ontong-Java) Rise (Figure 4B); note - largest submarine plateau
    Macclesfield Bank (Figure 4B)
    Marshall Seamounts (Figure 2)
    Magellan Seamounts (Figure 2)
    Mid-Pacific Seamounts (Figure 2)
    Reed Tablemount (Figure 4B)
    Shatsky Rise (Figure 2); note - third largest submarine plateau
    Tonga-Kermadec Ridge (Figure 4)



    ocean trenches: Ocean trenches (see Figure 1) are the deepest parts of the ocean floor and are created by the process of subduction. Trenches form along convergent boundaries where tectonic plates are moving toward each other, and one plate sinks (is subducted) under another. The location where the sinking of a plate occurs is called a subduction zone. Subduction can occur when oceanic crust collides with and sinks under (subducts) continental crust resulting in volcanic, seismic, and mountain-building processes. Subduction can also occur in the convergence of two oceanic plates where one will sink under the other and in the process create a deep ocean trench. Subduction processes in oceanic-oceanic plate convergence also result in the formation of volcanoes. Over millions of years, the erupted lava and volcanic debris pile up on the ocean floor until a submarine volcano rises above sea level to form a volcanic island. Such volcanoes are typically strung out in chains called island arcs. As the name implies, volcanic island arcs, which closely parallel the trenches, are generally curved. The following are examples of ocean trenches found on the floor of the Pacific Ocean.

    Aleutian Trench (Figure 2)
    Chile Trench (Figure 3)
    Izu-Ogasawara Trench (Figure 2)
    Japan Trench (Figure 2)
    Kermadec Trench (Figure 3, 4)
    Kuril-Kamchatka Trench (Figure 2)
    Manus Trench (Figure 4)
    Mariana Trench (Figure 2, 4); note - deepest ocean trench
    Middle America Trench (Figure 3)
    Nansei-Shoto Trench (Figure 4B)
    Palau Trench (Figure 2, 4)
    Philippine Trench (Figure 4)
    Peru-Chile Trench (Figure 3)
    South New Hebrides Trench (Figure 4)
    Tonga Trench (Figure 3, 4)
    Yap Trench (Figure 2, 4)



    atolls: Atolls are the remains of dormant volcanic islands. In warm tropical oceans, coral colonies establish themselves on the margins of the island. Then, over time, the high elevation of the island collapses and erodes away to sea level leaving behind an outline of the island in the form of the fringing coral reef. The resulting low island is typified by the coral reef surrounding a low elevation of sand and coral above sea level with an interior shallow lagoon. Often times the remaining dry land is broken into a ring of islets. Some lagoons can be hundreds of square kilometers. It may take as long as 300,000 years for an atoll formation to occur. Guyots are submerged atoll structures, which explains why they are flat topped seamounts. The following are examples of atolls found in the Pacific Ocean; for more information see the following entries in The World Factbook.

    Federated States of Micronesia
    French Polynesia
    Kiribati
    Marshall Islands
    Midway Island
    Tonga
    Tuvalu
    US Pacific Island Wildlife Refuges
    Vanuatu
    Wake Island