Davidson Seamount is an underwater volcano located off the coast of Central California, 80 miles (129 km) southwest of Monterey and 75 mi (121 km) west of San Simeon. At 26 mi (42 km) long and 8 mi (13 km) wide, it is one of the largest known seamounts in the world. From base to crest, the seamount is 7,480 feet (2,280 m) tall, yet its summit is still 4,101 ft (1,250 m) below the sea surface. The seamount is biologically diverse, with 237 species and 27 types of deep-sea coral having been identified.
In the image on the left is the Ely Seamount in the Gulf of Alaska. "Geomorphic and age data [have been documented] for the Dellwood, Denson, Dickins, Giacomini, and Ely seamounts, the Tsimshian Seachannel, and the southern Juan de Fuca Ridge with Brown Bear, Bear Cub, Grizzly Bear, and Cobb seamounts." For the Ely Seamount note the circularity and the hole in the center of the seamount.
Theoretical seamounts edit
Def. a "flat-topped seamount" is called a guyot.
Seamounts are defined as independent features that rise to at least 1,000 metres (3,300 ft) above the seafloor, characteristically of conical form.
The peaks are often found hundreds to thousands of meters below the surface, and are therefore considered to be within the deep sea.
During their evolution over geologic time, the largest seamounts may reach the sea surface where wave action erodes the summit to form a flat surface, but after they have subsided and sunk below the sea surface such flat-top seamounts are called "guyots" or "tablemounts".
The Earth's oceans contain more than 14,500 identified seamounts of which 9,951 seamounts and 283 guyots, covering a total area of 8,796,150 square kilometres (3,396,210 sq mi), have been mapped.
Antarctic Ocean seamounts edit
Note the location of the South Shetland Islands off the coast near the end of the Antarctic Peninsula.
Pacific-Antarctic Ridge edit
The Pacific-Antarctic Ridge (PAR) is a divergent tectonic plate boundary located on the seafloor of the South Pacific Ocean, separating the Pacific Plate from the Antarctic Plate. It is regarded as the southern section of the East Pacific Rise in some usages, generally south of the Challenger Fracture Zone and stretching to the Macquarie Triple Junction south of New Zealand.
Wordie Seamount edit
Wordie Seamount is located at Lua error: callParserFunction: function "#coordinates" was not found., which is 37 km south of Gibbs Island in the South Shetland Islands.
Arctic Ocean seamounts edit
The Arctic Ocean has only 16 seamounts and no guyots.
Atlantic Ocean seamounts edit
Morphometry of the Concepcion Bank shows evidence of geological and biological processes on a large volcanic seamount of the Canary Islands Seamount Province. Bathymetry of Concepcion Bank and surrounding deep seafloor.
(A) Bathymetric map from multibeam data (bright colours) and GEBCO (dull colours). The dashed lines delimit the three SWNW oriented parallel depth sectors.
(B) Bathymetric cross section along a SE-NW direction. Significant changes in slope are indicated. See location in A. Vertical exaggeration is 14:1. Summit location is indicated by a black triangle with a label showing its depth in meters.
Atlantis Seamount edit
Numerous freshwater diatoms likely deposited as sediment in fresh water lakes have been found on the Mid-Atlantic Ridge from several cores that were taken over 900 km distance from the coast of Equatorial West Africa that may be evidence that the area was islands 10 – 12,000 years ago, where the diatoms were later inundated under 3 km of sea water..
At 37 degrees North the Atlantis seamount located on the Mid-Atlantic Ridge is flat topped at a depth of around 180 fathoms and has a current-rippled sand or cobbled surface, where around a ton of limestone cobbles have been brought up from the summit, which gave a radiocarbon date of 12,000+/- 900 years and that the limestone was lithified in a location above the water and that this is evidence that the seamount had once been an island but was submerged in the last 12,000 years.
The Seewarte Seamounts, also known as the Seewarte Seamount Chain, Atlantis-Great Meteor Seamount Chain and the Atlantis-Plato-Cruiser-Great Meteor Seamount Group, is a north-south trending group of extinct submarine volcanoes in the northern Atlantic Ocean south-southeast of the Corner Rise Seamounts.
The Seewarte Seamounts have been interpreted to have formed as a result of the African Plate traveling over the New England hotspot.
The Seewarte Seamounts include:
- Closs Seamount
- Little Meteor Seamount
- Great Meteor Seamount
- Hyères Seamount
- Irving Seamount
- Cruiser Tablemount
- Plato Seamount
- Atlantis Seamount
- Tyro Seamount.
Bear Seamount edit
The Bear Seamount is a guyot or flat-topped underwater volcano in the Atlantic Ocean, the oldest of the New England Seamounts, which was active more than 100 million years ago, formed when the North American Plate moved over the New England hotspot.
Coral Patch Seamount edit
Bathymetric map of the Coral Patch Seamount covers an area of 560 km2 and a water depth range between 560 and 2660 m (Mercator projection, 5 times exaggerated, shaded relief). Displayed are the ENE-WSW elongated summit and the northern and southern flanks of the seamount, the latter being incised by several canyon-like structures. Inserted box shows video-surveyed area (white lines indicate survey tracks) at the south-western top. Pink stars indicate ROV samples (a, b, c) and pink dots indicate position of Van Veen grab samples (91, 92) collected during R/V VICTOR HENSEN cruise VH97.
Iberian margins edit
In the image on the left, sea level during the last glaciation is likely at or above the yellow contour band.
The image on the right shows a larger area of the Iberian margins in which the features in left image occur.
Indian Ocean seamounts edit
The largest mean seamount size occurs in the Indian Ocean.
Christmas Island Seamounts edit
Christmas Island is located at 10°29'S 105°38'E, near Indonesia.
Height is up to 4,500 metres (14,800 ft)
Age is 47 to 136 Ma.
The Christmas Island Seamount Province (aka Christmas Island Seamounts) is an unusual seamount (submarine volcano) formation named for Christmas Island that is also part of the chain. The province consists of more than 50 seamounts, up to 4,500 metres (14,800 ft) in height, within a 1,080,000 square kilometres (417,000 sq mi) area.
Unlike most seamount groups, the Christmas Island seamount formation does not form a long hotspot-based chain of increasingly older volcanoes, instead being a scattered grouping of volcanoes within a large radius. The Christmas Island area does not exhibit the hotspot chain formation that most seamount groups have, nor does it run perpendicular to a local rift zone, instead lying roughly parallel to the edge of the Australian Plate. Many of the seamounts are flat-topped guyots, showing that at one point the province was likely a group of active volcanic islands, before it was slowly eroded to its current subsurface level.
Rock samples tested for Argon-argon dating (40Ar/39Ar), strontium, neodymium, hafnium and lead to determine its age and origin found that the rock of the seamounts was more similar to continental than oceanic crust, particularly resembling northwest Australian crust. The seamounts were found to be 47 to 136 million years old, decreasing in age from east to west, and at most 25 million years younger than the crust surrounding them. Plate reconstructions based on these dates showed that the seamounts formed where West Burma separated from Australia and India, during the breakup of Gondwana, approximately 150 million years ago. The seamounts may have been made of recycled, delaminated continental crust enriched in mantle material that was rising beneath the mid-ocean ridge forming at the time, and that this may be a relatively common process in shallow-basin areas.
The island is about 19 kilometres (12 mi) in greatest length and 14.5 kilometres (9.0 mi) in breadth. The total land area is 135 square kilometres (52 sq mi), with 138.9 kilometres (86.3 mi) of coastline. The island is the flat summit of an underwater mountain more than 4,500 metres (14,800 ft) high, which rises from about 4,200 metres (13,780 ft) below the sea and only about 300 m (984 ft) above it.
The mountain was originally a volcano, and some basalt is exposed in places such as The Dales and Dolly Beach, but most of the surface rock is limestone accumulated from coral growth. The karst terrain supports numerous anchialine caves. The summit of this mountain peak is formed by a succession of Tertiary limestones ranging in age from the Eocene or Oligocene up to recent reef deposits, with intercalations of volcanic rock in the older beds.
Steep cliffs along much of the coast rise abruptly to a central plateau. Elevation ranges from sea level to 361 metres (1,184 ft) at Murray Hill. The island is mainly tropical rainforest, 63% of which is national parkland. The narrow fringing reef surrounding the island poses a maritime hazard.
Christmas Island lies 2,600 kilometres (1,600 mi) northwest of Perth, Western Australia, 350 kilometres (220 mi) south of Indonesia, 975 km (606 mi) ENE of the Cocos (Keeling) Islands, and 2,748 km (1,708 mi) west of Darwin, Northern Territory. Its closest point to the Australian mainland is 1,560 km (970 mi) from the town of Exmouth, Western Australia.
Mediterranean and Black Seas seamounts edit
The Mediterranean and Black seas together have only 23 seamounts and 2 guyots.
Pacific Ocean seamounts edit
The largest seamount has an area of 15,500 square kilometres (6,000 sq mi) and it occurs in the North Pacific. Guyots cover a total area of 707,600 square kilometres (273,200 sq mi) and have an average area of 2,500 square kilometres (970 sq mi), more than twice the average size of seamounts. Nearly 50% of guyot area and 42% of the number of guyots occur in the North Pacific Ocean, covering 342,070 square kilometres (132,070 sq mi). The largest three guyots are all in the North Pacific: the Kuko Guyot (estimated 24,600 square kilometres (9,500 sq mi)), Suiko Guyot (estimated 20,220 square kilometres (7,810 sq mi)) and the Pallada Guyot (estimated 13,680 square kilometres (5,280 sq mi)).
The Louisville Ridge, aka the Louisville Seamount Chain, is an underwater chain of over 70 seamounts located in the Southwest portion of the Pacific Ocean. As one of the longest seamount chains on Earth it stretches some 4,300 kilometres (2,700 mi) from the Pacific-Antarctic Ridge northwest to the Tonga-Kermadec Trench, where it subducts under the Indo-Australian Plate as part of the Pacific Plate. The chain may have been formed by movement of the Pacific Plate over the Louisville hotspot or by leakage of magma from the shallow mantle up through the Eltanin fracture zone, which it follows closely.
Depth-sounding data first revealed the existence of the seamount chain in 1972. "The Louisville Ridge was first detected in 1972 using depth soundings collected along random ship crossings of the South Pacific. Six years later the full extent of this chain was revealed by a radar altimeter aboard the Seasat (NASA) spacecraft."
The Louisville Ridge includes the following:
- Burton Seamount
- Currituck Seamount
- Danseur Seamount
- Darvin Guyot
- Forde Seamount
- Louisville Seamount
- Osbourn Seamount
- Pierson Seamount
- Rumyantsev Seamount
- Seafox Seamount
- Trobriant Seamount
- Valerie Guyot
- Vostok Seamount.
Axial Seamount edit
The Axial Seamount (aka Coaxial Seamount or Axial Volcano) is a seamount and submarine volcano located on the Juan de Fuca Ridge, approximately 480 kilometres (298 mi) west of Cannon Beach, Oregon, standing 1,100 metres (3,609 ft) high.
The Axial Seamount is the youngest volcano and current eruptive center of the Cobb–Eickelberg Seamount chain, a chain of seamounts that terminates south of Alaska. Axial lies where the chain intersects with the Juan de Fuca Ridge, approximately 480 kilometres (298 mi) west of Oregon. It is a product of the Cobb hotspot, but now sits on an ocean spreading center between the Juan de Fuca Plate and the North American Plate, offset by the Blanco Fracture Zone to the south and a mid-ocean ridge-built triple junction to the north.
The chain may have been formed over millions of years by the now-inactive Cobb hotspot and is older than the mid-ocean ridge it bisects. Between 200,000 and 700,000 years ago, the hotspot was encroached by the tectonic spreading center, displacing it by as much as 20 kilometres (12 mi) and building up the 500 kilometres (311 mi) long Juan de Fuca Ridge. At least 7 spreading centers have been recognized, and plate measurements near Axial show that the ridge is separating at a rate of 6 centimetres (2 in) per year,[n 1] producing a complex system of oceanic basins and ridges. However, the high density of the chain's overlapping seamounts is incompatible with such an origin, as a hotspot would form a well organized, widely spaced chain.
Basins around the volcano increase its irregularity, making it unusually complex (most seamounts of roughly the same size are circular or flattened in shape.)
The Axial Seamount's summit is marked by an unusual rectangular caldera, 3 by 8 kilometres (2 mi × 5 mi) in area, ~3° in slope, and breached on the southeast side. The area is offset by the two rift zones and defined on three sides by boundary faults up to 150 metres (492 ft) deep. The caldera is roughly 50 metres (164 ft) deeper at the north side then it is in the south. Flows within the caldera consist mostly of sheet flows pocketed by lava ponds and pit craters. Less common are pillow lavas; their arrangement along the caldera walls suggests that they were an important component in the volcano's early growth. There are several lava dome-like structures within the caldera with heights of 100–300 metres (328–984 ft). There are several small volcanic craters within the region, the largest of which, the D.D. Cone, is 2 kilometres (1 mi) in diameter and 100 metres (328 ft) in relief. However, most of the features do not range over 30 to 40 metres (98 to 131 ft) deep and 1 km (1 mi) across.
The northern rift zone of Axial Seamount is a 5 kilometres (3 mi) long ridge running 10 to 20 degrees northeast of the main caldera. The rift is pocketed by multiple fissures, 100–200 metres (328–656 ft) in length, as far as 7 kilometres (4 mi) from Axial Volcano's center, and reaching up to 400 metres (1,312 ft) long and 20 metres (66 ft) deep. The area contains high amounts of volcanic glass; a major eruption is still visible in the form of an elongated glassy lava flow extending off the caldera wall, east of the main rift line. Dives in 1983 found extensive low-temperature hydrothermal venting at the northern half of the fissure. The shorter, newer southern rift zone consists of a topographically plunging rift, surrounding by subtle, discontinuous faults. Camera tows along the southern flank reveal that the area is built of delineated sheet flows, small lava ponds, and lava channels.
The youngest of the flows on Axial Seamount are aligned along the two rift zones, followed by flows inside the summit caldera; the oldest appear to originate from directly around the caldera, where most of the basalt is completely covered in accumulated sediment. This suggests a bilateral growth pattern, a trend also found in Hawaii hotspot volcanics and other well-known seamounts, for instance Jasper Seamount.
The Axial Seamount's growth has intersected the growth of many of the smaller seamounts around it. The largest of these is Brown Bear Seamount, to which it is connected by a narrow ridge running roughly perpendicular to its western caldera wall. However, little evidence of interactions between the two seamounts has been found. On the other hand, Axial Seamount's southern rift zone bisects Vance Seamount by as much as 30 kilometres (19 mi), creating a zone of intense fissuring at the northern edge of the smaller volcano.[n 2] Interactions with Cobb Seamount to the north are more complex, forming an unusual "bent spreading center." In addition there are four smaller structures directly east, north, and south of Axial.
Cross Seamount edit
Cross Seamount is a seamount far southwest of the Hawaii archipelago that is one of the numerous seamounts surrounding Hawaii, although unrelated to the Hawaiian hotspot.
Main line seamounts edit
One of the Main Line Islands seamount chain is the Horizon Guyot at Coordinates 19°07.9′N 169°27.6′W in the Mid-Pacific Mountains.
See also edit
- Antarctic continental shelves
- Arctic continental shelves
- Mediterranean continental shelves
- North Sea continental shelves
- North east American continental shelves
- North west African continental shelves
- Pole star project/Equatorials
- South east African continental shelves
- South East Asian continental shelves
- South west African continental shelves
- West American continental shelves
- West European continental shelves
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