Submarine canyon

A submarine canyon is a steep-sided valley cut into the seabed of the continental slope, sometimes extending well onto the continental shelf, having nearly vertical walls, and occasionally having canyon wall heights of up to 5 km, from canyon floor to canyon rim, as with the Great Bahama Canyon.[1] Just as above-sea-level canyons serve as channels for the flow of water across land, submarine canyons serve as channels for the flow of turbidity currents across the seafloor. Turbidity currents are flows of dense, sediment laden waters that are supplied by rivers, or generated on the seabed by storms, submarine landslides, earthquakes, and other soil disturbances. Turbidity currents travel down slope at great speed (as much as 70 km/h), eroding the continental slope and finally depositing sediment onto the abyssal plain, where the particles settle out.[2]

About 3% of submarine canyons include shelf valleys that have cut transversely across continental shelves, and which begin with their upstream ends in alignment with and sometimes within the mouths of large rivers, such as the Congo River and the Hudson Canyon. About 28.5% of submarine canyons cut back into the edge of the continental shelf, whereas the majority (about 68.5%) of submarine canyons have not managed at all to cut significantly across their continental shelves, having their upstream beginnings or "heads" on the continental slope, below the edge of continental shelves.[3]

The formation of submarine canyons is believed to occur as the result of at least two main process: 1) erosion by turbidity current erosion; and 2) slumping and mass wasting of the continental slope. While at first glance, the erosion patterns of submarine canyons may appear to mimic those of river-canyons on land, due to the markedly different erosion processes that have been found to take place underwater at the soil/ water interface, several notably different erosion patterns have been observed in the formation of typical submarine canyons.[2][4]

Many canyons have been found at depths greater than 2 km below sea level. Some may extend seawards across continental shelves for hundreds of kilometres before reaching the abyssal plain. Ancient examples have been found in rocks dating back to the Neoproterozoic.[5] Turbidites are deposited at the downstream mouths or ends of canyons, building an abyssal fan.

CanyonsbathyLG USGS
Shaded relief image of seven submarine canyons imaged on the continental slope off New York, using multibeam echosounder data, the Hudson Canyon is the furthest to the left
Canyons off LA
Perspective view shaded relief image of the San Gabriel and Newport submarine canyons off Los Angeles
Congo canyon
The Congo Canyon off southwestern Africa, about 300 km visible in this view
Porcupine Biscay canyons
Heavily canyoned northern margin to the Biscay abyssal plain, with the Whittard Canyon highlighted
Beringian Margin canyons
Bering Sea showing the larger of the submarine canyons that cut the margin
Submarine canyon
Sketch showing the main elements of a submarine canyon

Characteristics

Submarine canyons are more common on the steep slopes found on active margins compared to those on the gentler slopes found on passive margins.[6] They show erosion through all substrates, from unlithified sediment to crystalline rock. Canyons are steeper, shorter, more dendritic and more closely spaced on active than on passive continental margins.[3] The walls are generally very steep and can be near vertical. The walls are subject to erosion by bioerosion, or slumping. There are an estimated 9,477 submarine canyons on Earth, covering about 11% of the continental slope.[7]

Examples

Formation

Different mechanisms have been proposed for the formation of submarine canyons. Their primary causes have been subject to debate since the early 1930s.[11]

An early and obvious theory was that the canyons present today were carved during glacial times, when sea level was about 125 meters below present sea level, and rivers flowed to the edge of the continental shelf. However, while many (but not all) canyons are found offshore from major rivers, subaerial river erosion cannot have been active to the water depths as great as 3000 meters where canyons have been mapped, as it is well established (by many lines of evidence) that sea levels did not fall to those depths.

The major mechanism of canyon erosion is thought to be turbidity currents and underwater landslides. Turbidity currents are dense, sediment-laden currents which flow downslope when an unstable mass of sediment that has been rapidly deposited on the upper slope fails, perhaps triggered by earthquakes. There is a spectrum of turbidity- or density-current types ranging from "muddy water" to massive mudflow, and evidence of both these end members can be observed in deposits associated with the deeper parts of submarine canyons and channels, such as lobate deposits (mudflow) and levees along channels.

Mass wasting, slumping, and submarine landslides are forms of slope failures (the effect of gravity on a hillslope) observed in submarine canyons. Mass wasting is the term used for the slower and smaller action of material moving downhill. Slumping is generally used for rotational movement of masses on a hillside. Landslides, or slides, generally comprise the detachment and displacement of sediment masses.

It is now understood that many mechanisms of submarine canyon creation have had effect to greater or lesser degree in different places, even within the same canyon, or at different times during a canyon's development. However, if a primary mechanism must be selected, the downslope lineal morphology of canyons and channels and the transportation of excavated or loose materials of the continental slope over extensive distances require that various kinds of turbidity or density currents act as major participants.

In addition to the processes described above, submarine canyons that are especially deep may form by another method. In certain cases, a sea with a bed significantly below sea level is cut off from the larger ocean to which it is usually connected. The sea which is normally repleted by contact and inflow from the ocean is now no longer replenished and hence dries up over a period of time, which can be very short if the local climate is arid. In this scenario, rivers that previously flowed into the sea at a sea level elevation now can cut far deeper into the bottom of the bed now exposed. The Messinian Salinity Crisis is an example of this phenomenon; between five and six million years ago, the Mediterranean Sea became isolated from the Atlantic Ocean and evaporated away in roughly a thousand years. During this time, the Nile River delta, among other rivers, extended far beyond its present location, both in depth and length. In a cataclysmic event, the Mediterranean sea basin was flooded. One relevant consequence is that the submarine canyons eroded are now far below the present sea level.

See also

References

  1. ^ Shepard, F.P., 1963. Submarine Geology. Harper & Row, New York
  2. ^ a b Continental Margin Sedimentation: From Sediment Transport to Sequence Stratigraphy (Special Publication 37 of the IAS) March 2009, by Charles Nittroeur, pg 372.
  3. ^ a b Harris, P.T., Whiteway, T., 2011. Global distribution of large submarine canyons: geomorphic differences between active and passive continental margins. Marine Geology 285, 69–86.
  4. ^ Submarine Canyon Archived 2016-03-07 at the Wayback Machine by Richard Strickland, 2004
  5. ^ Giddings, J.A.; Wallace M.W.; Haines P.W.; Mornane K. (2010). "Submarine origin for the Neoproterozoic Wonoka canyons, South Australia". Sedimentary Geology. Elsevier. 223 (1–2): 35–50. Bibcode:2010SedG..223...35G. doi:10.1016/j.sedgeo.2009.10.001.
  6. ^ Harris, P.T. (2011). "Seafloor Geomorphology–Coast, Shelf, and Abyss". In Harris P.T. & Baker E.K. (ed.). Seafloor Geomorphology as Benthic Habitat: GeoHAB Atlas of Seafloor Geomorphic Features and Benthic Habitats. Elsevier. pp. 125–127. ISBN 978-0-12-385141-3. Retrieved 26 January 2012.
  7. ^ Harris, P.T., MacMillan-Lawler, M., Rupp, J., Baker, E.K., 2014. Geomorphology of the oceans. Marine Geology 352, 4–24.
  8. ^ Sánchez, F., Cartes, J.E. and Papiol, V., 2014, "Sistema de Cañones Submarinos de Avilés". Áreas de estudio del proyecto LIFE+ INDEMARES
  9. ^ Arthur Newell Strahler, Physical Geography. New York: John Wiley & Sons, Inc., 1960, Second Edition, p. 290
  10. ^ https://oceanexplorer.noaa.gov/explorations/16carolina/welcome.html
  11. ^ Shepard, Francis P. (1936). "The Underlying Causes of Submarine Canyons". Proceedings of the National Academy of Sciences of the United States of America. 22 (8): 496–502. Bibcode:1936PNAS...22..496S. doi:10.1073/pnas.22.8.496. PMC 1079213.
Acanthopolymastia bathamae

Acanthopolymastia bathamae is a species of demosponge belonging to the family Polymastiidae. It is only known from the Papanui Submarine Canyon off Dunedin, South Island, New Zealand.

This is a small, cream-coloured hemispherical sponge up to 8 mm in diameter. Its texture is soft and velvety with a single central papilla up to 7 mm in height.

Amazon Canyon

The Amazon Canyon is a submarine canyon within the Amazon Fan in the Atlantic Ocean, located approximately 200 mi (322 km) from the mouth of the Amazon River, near South America. It covers an area of 2,250 km2 (870 sq mi). It was formed in the mid to late Miocene period. The canyon is believed to have formed through mass failures, and subsequently evolved through underwater erosion. Because of its relatively small size, the canyon has been extensively mapped.

Astoria Canyon

Astoria Canyon is a submarine canyon 10 miles (16 km) offshore from the mouth of the Columbia River.

Bowie Canyon

The Bowie Canyon is a submarine canyon located in the Bering Sea. It is a submerged line of demarkation between the Bowers Ridge and the Aleutian Ridge. At its deepest point, it is 1.3 miles deep. It is named after American geodetic engineer, William Bowie.

Carmel Pinnacles State Marine Reserve

Carmel Pinnacles State Marine Reserve (SMR) is a marine protected area in Carmel Bay including a unique underwater pinnacle formation with adjacent kelp forest, submarine canyon head, and surfgrass. Carmel Bay is adjacent to the city of Carmel-by-the-Sea and is near Monterey, on California’s central coast.

Congo Canyon

Congo Canyon is a submarine canyon found at the end of the Congo River in Africa. It is one of the largest submarine canyons in the world.

Danube Canyon

The Danube Canyon (also known as the Viteaz Canyon) is a large submarine canyon which indents the shelf in the northwestern part of the Black Sea. It developed seawards during the late Pleistocene seaward along the Danube valley.The canyon continues into the most recent central channel in the relict Danube fan at the bottom of the Black Sea and has been the major route of the transport of the deposit from Danube river to the Danube fan.

Near the shelf break zone the canyon is approximately 350m deep.

Delgada Submarine Canyon

The Delgada Submarine Canyon is an underwater submarine canyon located off the King Range in Northern California. A million cubic meters of sediment fall into this canyon and another canyon each year. One end is near the coastline, close to Shelter Cove, part of the Lost Coast of California. The Delgada deep-sea fan is located at the mouth of the canyon.It was originally created 10 million years ago from the San Francisco Bay drainage, and is today one of the largest geological features off the shores of North America.

The canyon's depth is 182 metres (597 ft) 1 kilometre (0.62 mi) off the coast. At a distance of 14 miles (23 km) offshore, it is 3,000 feet (910 m). The canyon follows an underwater mountain that does not have gullies. Most canyons do not do this, indicating that it has been shifted by seismic activity.

Great Bahama Canyon

The Great Bahama Canyon is a V-shaped submarine canyon system in the Bahamas that cuts between the Abaco Islands to the north and Eleuthera island to the south. It separates the Bahama Banks and forms one of the deepest underwater canyon systems known. There are three branches: the Tongue of the Ocean running south between Andros and New Providence, and the northeast and northwest Providence Channel. The canyon walls reach heights of 5 kilometres (3 mi); taller than any canyon walls on land. This canyon system has remained open through a process of submarine erosion.

Mississippi Canyon

The Mississippi Canyon is an undersea canyon, part of the Mississippi Submarine Valley in the North-central Gulf of Mexico, south of Louisiana. According to the U.S. Geological Survey GLORIA Mapping Program, it is the dominant feature of the north-central Gulf of Mexico. According to GCAGS Transactions, it has an average width of 8 kilometres (5.0 mi), and a length of 120 kilometres (75 mi). The US Minerals Management Service (MMS) applies the name Mississippi Canyon to numbered federal oil and gas lease blocks over a large offshore area centered on, but mostly outside, the submarine canyon.

Monterey Bay Aquarium Research Institute

The Monterey Bay Aquarium Research Institute (MBARI) is a private, non-profit oceanographic research center in Moss Landing, California. MBARI was founded in 1987 by David Packard, and is primarily funded by the David and Lucile Packard Foundation. Christopher Scholin serves as the institute's president and chief executive officer, managing a work force of approximately 220 scientists, engineers, and operations and administrative staff.

At MBARI, scientists and engineers work together to develop new tools and methods for studying the ocean. Long-term funding from the David and Lucile Packard Foundation allows the institute to take on studies that traditional granting institutions may be reluctant to sponsor. Part of David Packard's charge for MBARI was to "Take risks. Ask big questions. Don't be afraid to make mistakes; if you don't make mistakes, you're not reaching far enough."

MBARI's campus in Moss Landing is located near the center of Monterey Bay, at the head of the Monterey Canyon. Monterey Bay is one of the most biologically diverse bodies of waters in the world, and the underlying submarine canyon is one of the deepest underwater canyons along the continental United States. With this 4,000-meter-deep submarine canyon only a few ship-hours from their base of operations, institute scientists enjoy an advantageous proximity to this natural, deep-sea "laboratory".

MBARI is not open to the general public, but it has an open house once a year. Although MBARI is a sister institution to the Monterey Bay Aquarium, the two organizations have entirely separate management and funding.

Monterey Canyon

Monterey Canyon, or Monterey Submarine Canyon, is a submarine canyon in Monterey Bay, California with steep canyon walls measuring a full 1 mile in height from bottom to top, which height/depth rivals the depth of the Grand Canyon itself. It is the largest such submarine canyon along the West coast of the North American continent, and was formed by the underwater erosion process known as turbidity current erosion. Many questions remain unresolved regarding the exact nature of its origins, and as such it is the subject of several ongoing geological and marine life studies being carried out by scientists stationed at the nearby Monterey Bay Aquarium Research Institute, the Moss Landing Marine Laboratories, and other oceanographic institutions.

Monterey Canyon begins at Moss Landing, California, which is situated along the middle of the coast of Monterey Bay, and extends horizontally 95 mi (153 km) under the Pacific Ocean where it terminates at the Monterey Canyon submarine fan, reaching depths of up to 3,600 m (11,800 ft) below surface level at its downstream mouth. It is a part of the greater Monterey Bay Canyon System, which consists of Monterey, Soquel and Carmel Canyons. The canyon's depth and nutrient availability (due to the regular influx of nutrient-rich sediment) provide a habitat suitable for many marine life forms.

The Soquel Canyon State Marine Conservation Area protects a side-branch of the Monterey Submarine Canyon. Like an underwater park, this marine protected area helps conserve ocean wildlife and marine ecosystems.

Navarin Canyon

The Navarin Canyon is a submarine canyon in the Bering Sea. It is just as wide but less than half as deep as the Zhemchug Canyon, which is the largest canyon in the world.The Navarin Canyon is the third-largest to cut through the Beringian margin. It is the second-largest in area. Though these canyons were not directly formed by rivers, it is postulated that when the sea level was low during the Ice Ages, rivers such as the Yukon and the Kuskokwim may have shaped in part the heads of these canyons. At the shelf break, it is approximately 100 kilometres (62 mi) wide.

Quileute Canyon

Quileute Canyon (also Quillayute Canyon) is a submarine canyon, off of Washington State, United States.

Soquel Canyon State Marine Conservation Area

Soquel Canyon State Marine Conservation Area (SMCA) is an offshore marine protected area in Monterey Bay. Monterey Bay is on California’s central coast with the city of Monterey at its south end and the city of Santa Cruz at its north end. The SMCA covers 23.41 square miles (60.6 km2). Within the SMCA, fishing and taking of any living marine resources is prohibited except the commercial and recreational take of pelagic finfish.

Taiaroa (coral)

Taiaroa is a genus of deep-water, solitary marine octocorals in the family Taiaroidae. Taiaroa is monotypic in the family Taiaroidae and contains a single species, Taiaroa tauhou. The species was first described by the marine zoologists Frederick M. Bayer and Katherine Margaret Muzik in 1976. The scientific name derives from "Taiaroa", the submarine canyon off New Zealand in which the first specimens were found and "tauhou", the Maori word for "strange".

Titanic Canyon

Titanic Canyon is a submarine canyon located south of the Grand Banks of Newfoundland, Canada. Its name was proposed in 1991 by marine geologist Alan Ruffman for the remembrance of British passenger liner RMS Titanic, the wreck of which lies about 34 km (21 mi) south of the head of Titanic Canyon on its eastern slope.

Toms Canyon impact crater

The Toms Canyon impact crater is a probable impact crater where one or more asteroids struck the Atlantic continental shelf, about 100 miles (160 km) east of Atlantic City, New Jersey. The submarine canyon is the drowned glacial-age mouth of Toms River.

The crater dates to the late Eocene geological time period (about 35 million years ago), and may have been formed by the same event as the larger Chesapeake Bay impact crater (and possibly the Popigai crater in Siberia), 200 miles (320 km) to the southwest at the mouth of Chesapeake Bay, also dating to the late Eocene.

Seismic reflection profiles, studied by USGS scientists, show that the crater was formed by an object or objects which struck from the southwest at a glancing angle and formed a long, oval crater. Since impact, sediment filled part of the crater, giving it its present triangular shape.

Zhemchug Canyon

Zhemchug Canyon is an underwater canyon located in the middle of the Bering Sea. This submarine canyon is the deepest and is tied for widest canyon in the ocean.

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