Seamount

This is a good article. Click here for more information.
Source: Wikipedia, the free encyclopedia.
For active seamounts, see Submarine volcano.
Marine habitats
Bear Seamount
Coastal habitats
Ocean surface
Open ocean
Sea floor

A seamount is a large submarine landform that rises from the ocean floor without reaching the water surface (sea level), and thus is not an island, islet, or cliff-rock. Seamounts are typically formed from extinct volcanoes that rise abruptly and are usually found rising from the seafloor to 1,000–4,000 m (3,300–13,100 ft) in height. They are defined by oceanographers as independent features that rise to at least 1,000 m (3,281 ft) above the seafloor, characteristically of conical form.[1] The peaks are often found hundreds to thousands of meters below the surface, and are therefore considered to be within the deep sea.[2] 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. After they have subsided and sunk below the sea surface such flat-top seamounts are called "guyots" or "tablemounts".[1]

Earth's oceans contain more than 14,500 identified seamounts,[3] of which 9,951 seamounts and 283 guyots, covering a total area of 8,796,150 km2 (3,396,210 sq mi), have been mapped[4] but only a few have been studied in detail by scientists. Seamounts and guyots are most abundant in the North Pacific Ocean, and follow a distinctive evolutionary pattern of eruption, build-up, subsidence and erosion. In recent years, several active seamounts have been observed, for example Kamaʻehuakanaloa (formerly Lōʻihi) in the Hawaiian Islands.

Because of their abundance, seamounts are one of the most common marine ecosystems in the world. Interactions between seamounts and underwater currents, as well as their elevated position in the water, attract plankton, corals, fish, and marine mammals alike. Their aggregational effect has been noted by the commercial fishing industry, and many seamounts support extensive fisheries. There are ongoing concerns on the negative impact of fishing on seamount ecosystems, and well-documented cases of stock decline, for example with the orange roughy (Hoplostethus atlanticus). 95% of ecological damage is done by bottom trawling, which scrapes whole ecosystems off seamounts.

Because of their large numbers, many seamounts remain to be properly studied, and even mapped. Bathymetry and satellite altimetry are two technologies working to close the gap. There have been instances where naval vessels have collided with uncharted seamounts; for example, Muirfield Seamount is named after the ship that struck it in 1973. However, the greatest danger from seamounts are flank collapses; as they get older, extrusions seeping in the seamounts put pressure on their sides, causing landslides that have the potential to generate massive tsunamis.

Geography

Bathymetric mapping of part of Davidson Seamount. The dots indicate significant coral nurseries.

Seamounts can be found in every

ocean basin in the world, distributed extremely widely both in space and in age. A seamount is technically defined as an isolated rise in elevation of 1,000 m (3,281 ft) or more from the surrounding seafloor, and with a limited summit area,[5] of conical form.[1] There are more than 14,500 seamounts.[3] In addition to seamounts, there are more than 80,000 small knolls, ridges and hills less than 1,000 m in height in the world's oceans.[4]

Most seamounts are volcanic in origin, and thus tend to be found on

Pallada Guyot (estimated 13,680 km2 (5,280 sq mi)).[4]

Grouping

"Seamount chain" redirects here. For a broader coverage of this topic, see Undersea mountain range.

Seamounts are often found in groupings or submerged

Emperor Seamounts, an extension of the Hawaiian Islands. Formed millions of years ago by volcanism, they have since subsided far below sea level. This long chain of islands and seamounts extends thousands of kilometers northwest from the island of Hawaii
.

Distribution of seamounts and guyots in the North Pacific
Distribution of seamounts and guyots in the North Atlantic

There are more seamounts in the Pacific Ocean than in the Atlantic, and their distribution can be described as comprising several elongate chains of seamounts superimposed on a more or less random background distribution.

Cape Verde Islands. The mid-Atlantic ridge and spreading ridges in the Indian Ocean are also associated with abundant seamounts.[7]
Otherwise, seamounts tend not to form distinctive chains in the Indian and Southern Oceans, but rather their distribution appears to be more or less random.

Isolated seamounts and those without clear volcanic origins are less common; examples include Bollons Seamount, Eratosthenes Seamount, Axial Seamount and Gorringe Ridge.[8]

If all known seamounts were collected into one area, they would make a landform the size of Europe.[9] Their overall abundance makes them one of the most common, and least understood, marine structures and biomes on Earth,[10] a sort of exploratory frontier.[11]

Geology

Geochemistry and evolution

Magma conduit 6. Magma chamber 7. Dike 8. Pillow lava) Click to enlarge

Most seamounts are built by one of two volcanic processes, although some, such as the

viscous eruptions.[11]

All volcanic seamounts follow a particular pattern of growth, activity, subsidence and eventual extinction. The first stage of a seamount's evolution is its early activity, building its flanks and core up from the sea floor. This is followed by a period of intense volcanism, during which the new volcano erupts almost all (e.g. 98%) of its total magmatic volume. The seamount may even grow above sea level to become an

subduction zone. Here it is subducted under the plate margin and ultimately destroyed, but it may leave evidence of its passage by carving an indentation into the opposing wall of the subduction trench. The majority of seamounts have already completed their eruptive cycle, so access to early flows by researchers is limited by late volcanic activity.[11]

Ocean-ridge volcanoes in particular have been observed to follow a certain pattern in terms of eruptive activity, first observed with

Hawaiian seamounts but now shown to be the process followed by all seamounts of the ocean-ridge type. During the first stage the volcano erupts basalt of various types, caused by various degrees of mantle melting. In the second, most active stage of its life, ocean-ridge volcanoes erupt tholeiitic to mildly alkalic basalt as a result of a larger area melting in the mantle. This is finally capped by alkalic flows late in its eruptive history, as the link between the seamount and its source of volcanism is cut by crustal movement. Some seamounts also experience a brief "rejuvenated" period after a hiatus of 1.5 to 10 million years, the flows of which are highly alkalic and produce many xenoliths.[11]

In recent years, geologists have confirmed that a number of seamounts are active undersea volcanoes; two examples are

Manu'a Group (Samoa).[8]

Lava types

Pillow lava, a type of basalt flow that originates from lava-water interactions during submarine eruptions[13]

The most apparent lava flows at a seamount are the eruptive flows that cover their flanks, however

igneous intrusions, in the forms of dikes and sills, are also an important part of seamount growth. The most common type of flow is pillow lava, named so after its distinctive shape. Less common are sheet flows, which are glassy and marginal, and indicative of larger-scale flows. Volcaniclastic sedimentary rocks dominate shallow-water seamounts. They are the products of the explosive activity of seamounts that are near the water's surface, and can also form from mechanical wear of existing volcanic rock.[11]

Structure

Seamounts can form in a wide variety of tectonic settings, resulting in a very diverse structural bank. Seamounts come in a wide variety of structural shapes, from conical to flat-topped to complexly shaped.[11] Some are built very large and very low, such as Koko Guyot[14] and Detroit Seamount;[15] others are built more steeply, such as Kamaʻehuakanaloa Seamount[16] and Bowie Seamount.[17] Some seamounts also have a carbonate or sediment cap.[11]

Many seamounts show signs of

intrusive activity, which is likely to lead to inflation, steepening of volcanic slopes, and ultimately, flank collapse.[11] There are also several sub-classes of seamounts. The first are guyots, seamounts with a flat top. These tops must be 200 m (656 ft) or more below the surface of the sea; the diameters of these flat summits can be over 10 km (6.2 mi).[18] Knolls are isolated elevation spikes measuring less than 1,000 meters (3,281 ft).[clarification needed] Lastly, pinnacles are small pillar-like seamounts.[5]

Ecology

Ecological role of seamounts

Animations depicting current flow over seamounts and ridges.

Seamounts are exceptionally important to their biome ecologically, but their role in their environment is poorly understood. Because they project out above the surrounding sea floor, they disturb standard water flow, causing eddies and associated hydrological phenomena that ultimately result in water movement in an otherwise still ocean bottom. Currents have been measured at up to 0.9 knots, or 48 centimeters per second. Because of this upwelling seamounts often carry above-average plankton populations, seamounts are thus centers where the fish that feed on them aggregate, in turn falling prey to further predation, making seamounts important biological hotspots.[5]

Seamounts provide habitats and spawning grounds for these larger animals, including numerous fish. Some species, including

blackstripe cardinalfish (Apogon nigrofasciatus), have been shown to occur more often on seamounts than anywhere else on the ocean floor. Marine mammals, sharks, tuna, and cephalopods all congregate over seamounts to feed, as well as some species of seabirds when the features are particularly shallow.[5]

bubblegum coral (Paragorgia arborea) on the crest of Davidson Seamount. These are two species attracted to the seamount; Paragorgia arborea in particular grows in the surrounding area as well, but nowhere near as profusely.[19]

Seamounts often project upwards into shallower zones more hospitable to sea life, providing

biogeographical interest. As they are formed from volcanic rock, the substrate is much harder than the surrounding sedimentary deep sea floor. This causes a different type of fauna to exist than on the seafloor, and leads to a theoretically higher degree of endemism.[20] However, recent research especially centered at Davidson Seamount suggests that seamounts may not be especially endemic, and discussions are ongoing on the effect of seamounts on endemicity. They have, however, been confidently shown to provide a habitat to species that have difficulty surviving elsewhere.[21][22]

The volcanic rocks on the slopes of seamounts are heavily populated by

tropical zones extensive coral growth results in the formation of coral atolls late in the seamount's life.[22][24]

In addition soft sediments tend to accumulate on seamounts, which are typically populated by

Xenophyophores have also been found. They tend to gather small particulates and thus form beds, which alters sediment deposition and creates a habitat for smaller animals.[5] Many seamounts also have hydrothermal vent communities, for example Suiyo[25] and Kamaʻehuakanaloa seamounts.[26] This is helped by geochemical exchange between the seamounts and the ocean water.[11]

Seamounts may thus be vital stopping points for some migratory animals, specifically whales. Some recent research indicates whales may use such features as navigational aids throughout their migration.[27] For a long time it has been surmised that many pelagic animals visit seamounts as well, to gather food, but proof of this aggregating effect has been lacking. The first demonstration of this conjecture was published in 2008.[28]

Fishing

The effect that seamounts have on fish populations has not gone unnoticed by the commercial fishing industry. Seamounts were first extensively fished in the second half of the 20th century, due to poor management practices and increased fishing pressure seriously depleting stock numbers on the typical fishing ground, the continental shelf. Seamounts have been the site of targeted fishing since that time.[29]

Nearly 80 species of fish and shellfish are commercially harvested from seamounts, including

red snapper (Lutjanus campechanus), tuna (Scombridae), Orange roughy (Hoplostethus atlanticus), and perch (Percidae).[5]

Conservation

Because of overfishing at their seamount spawning grounds, stocks of orange roughy (Hoplostethus atlanticus) have plummeted; experts say that it could take decades for the species to restore itself to its former numbers.[29]

The ecological conservation of seamounts is hurt by the simple lack of information available. Seamounts are very poorly studied, with only 350 of the estimated 100,000 seamounts in the world having received sampling, and fewer than 100 in depth.[30] Much of this lack of information can be attributed to a lack of technology,[clarification needed] and to the daunting task of reaching these underwater structures; the technology to fully explore them has only been around the last few decades. Before consistent conservation efforts can begin, the seamounts of the world must first be mapped, a task that is still in progress.[5]

Overfishing is a serious threat to seamount ecological welfare. There are several well-documented cases of fishery exploitation, for example the

pelagic armorhead (Pseudopentaceros richardsoni) near Japan and Russia.[5] The reason for this is that the fishes that are targeted over seamounts are typically long-lived, slow-growing, and slow-maturing. The problem is confounded by the dangers of trawling, which damages seamount surface communities, and the fact that many seamounts are located in international waters, making proper monitoring difficult.[29] Bottom trawling in particular is extremely devastating to seamount ecology, and is responsible for as much as 95% of ecological damage to seamounts.[31]

earrings
of this type are often made from coral harvested off seamounts.

Corals from seamounts are also vulnerable, as they are highly valued for making jewellery and decorative objects. Significant harvests have been produced from seamounts, often leaving coral beds depleted.[5]

Individual nations are beginning to note the effect of fishing on seamounts, and the

CenSeam, a Census of Marine Life project formed in 2005. CenSeam is intended to provide the framework needed to prioritise, integrate, expand and facilitate seamount research efforts in order to significantly reduce the unknown and build towards a global understanding of seamount ecosystems, and the roles they have in the biogeography, biodiversity, productivity and evolution of marine organisms.[30][32]

Possibly the best ecologically studied seamount in the world is

marine sanctuary, a motion that was granted in 2008 as part of the Monterey Bay National Marine Sanctuary.[33] Much of what is known about seamounts ecologically is based on observations from Davidson.[19][28] Another such seamount is Bowie Seamount, which has also been declared a marine protected area by Canada for its ecological richness.[34]

Exploration

satellite altimeter TOPEX/Poseidon (left) and its follow-on mission Jason-1

The study of seamounts has been hindered for a long time by the lack of technology. Although seamounts have been sampled as far back as the 19th century, their depth and position meant that the technology to explore and sample seamounts in sufficient detail did not exist until the last few decades. Even with the right technology available,[clarification needed] only a scant 1% of the total number have been explored,[9] and sampling and information remains biased towards the top 500 m (1,640 ft).[5] New species are observed or collected and valuable information is obtained on almost every submersible dive at seamounts.[10]

Before seamounts and their oceanographic impact can be fully understood, they must be mapped, a daunting task due to their sheer number.[5] The most detailed seamount mappings are provided by multibeam echosounding (sonar), however after more than 5000 publicly held cruises, the amount of the sea floor that has been mapped remains minuscule. Satellite altimetry is a broader alternative, albeit not as detailed, with 13,000 catalogued seamounts; however this is still only a fraction of the total 100,000. The reason for this is that uncertainties in the technology limit recognition to features 1,500 m (4,921 ft) or larger. In the future, technological advances could allow for a larger and more detailed catalogue.[24]

Observations from CryoSat-2 combined with data from other satellites has shown thousands of previously uncharted seamounts, with more to come as data is interpreted.[35][36][37][38]

Deep-sea mining

Seamounts are a possible future source of economically important metals. Even though the ocean makes up 70% of Earth's surface area, technological challenges have severely limited the extent of deep sea mining. But with the constantly decreasing supply on land, some mining specialists see oceanic mining as the destined future, and seamounts stand out as candidates.[39]

Seamounts are abundant, and all have metal resource potential because of various enrichment processes during the seamount's life. An example for

sulfate, sulfur, hydrothermal manganese oxide, and phosphorite[41] (the latter especially in parts of Micronesia) are all mineral resources that are deposited upon or within seamounts. However, only the first two have any potential of being targeted by mining in the next few decades.[39]

Dangers

USS San Francisco in dry dock in Guam in January 2005, following its collision with an uncharted seamount. The damage was extensive and the submarine was just barely salvaged.[42]
See also: Landslide § Causing tsunamis, and Landslide § Prehistoric submarine landslides

Some seamounts have not been mapped and thus pose a navigational danger. For instance, Muirfield Seamount is named after the ship that hit it in 1973.[43] More recently, the submarine USS San Francisco ran into an uncharted seamount in 2005 at a speed of 35 knots (40.3 mph; 64.8 km/h), sustaining serious damage and killing one seaman.[42]

One major seamount risk is that often, in the late of stages of their life,

Vlinder Seamount resulted in a pronounced headwall scarp and a field of debris up to 6 km (4 mi) away.[11] A catastrophic collapse at Detroit Seamount flattened its whole structure extensively.[15] Lastly, in 2004, scientists found marine fossils 61 m (200 ft) up the flank of Kohala mountain in Hawaii. Subsidation analysis found that at the time of their deposition, this would have been 500 m (1,640 ft) up the flank of the volcano,[44] far too high for a normal wave to reach. The date corresponded with a massive flank collapse at the nearby Mauna Loa, and it was theorized that it was a massive tsunami, generated by the landslide, that deposited the fossils.[45]

See also

References

  1. ^ a b c IHO, 2008. Standardization of Undersea Feature Names: Guidelines Proposal form Terminology, 4th ed. International Hydrographic Organization and Intergovernmental Oceanographic Commission, Monaco.
  2. ^ Nybakken, James W. and Bertness, Mark D., 2008. Marine Biology: An Ecological Approach. Sixth Edition. Benjamin Cummings, San Francisco
  3. ^ a b Watts, T. (August 2019). "Science, Seamounts and Society". Geoscientist: 10–16.
  4. ^
    doi:10.1016/j.margeo.2014.01.011
    .
  5. ^ a b c d e f g h i j k l "Seamount". Encyclopedia of Earth. December 9, 2008. Retrieved 24 July 2010.
  6. ^
    doi:10.1029/jb093ib09p10408
    .
  7. ^ Kitchingman, A., Lai, S., 2004. Inferences on Potential Seamount Locations from Mid-Resolution Bathymetric Data. in: Morato, T., Pauly, D. (Eds.), FCRR Seamounts: Biodiversity and Fisheries. Fisheries Centre Research Reports. University of British Columbia, Vanvouver, BC, pages 7–12.
  8. ^
    ISBN 9781118664209
  9. ^ a b "Seamount Scientists Offer New Comprehensive View of Deep-Sea Mountains". ScienceDaily. 23 February 2010. Retrieved 25 July 2010.
  10. ^ a b "Seamounts Identified as Significant, Unexplored Territory". ScienceDirect. 30 April 2010. Retrieved 25 July 2010.
  11. ^ a b c d e f g h i j Hubert Straudigal & David A Clauge. "The Geological History of Deep-Sea Volcanoes: Biosphere, Hydrosphere, and Lithosphere Interactions" (PDF). Oceanography. Seamounts Special Issue. 32 (1). Archived from the original (PDF) on 13 June 2010. Retrieved 25 July 2010.
  12. doi:10.1038/ngeo1331
    .
  13. NOAA
    . Retrieved 25 July 2010.
  14. ^ "SITE 1206". Ocean Drilling Program Database-Results of Site 1206. Ocean Drilling Program. Retrieved 26 July 2010.
  15. ^ a b Kerr, B. C.; D. W. Scholl; S. L. Klemperer (July 12, 2005). "Seismic stratigraphy of Detroit Seamount, Hawaiian–Emperor Seamount chain" (PDF). Stanford University. Retrieved 15 July 2010.
  16. School of Ocean and Earth Science and Technology
    . Retrieved 26 July 2010.
  17. ^ "The Bowie Seamount Area" (PDF). John F. Dower and Frances J. Fee. February 1999. Retrieved 26 July 2010.
  18. ^ "Guyots". Encyclopædia Britannica. Retrieved 24 July 2010.
  19. ^
    PhysOrg
    . February 11, 2009. Retrieved December 7, 2009.
  20. NOAA, Monterey Bay National Marine Sanctuary
    . 2006. Retrieved 2 December 2009.
  21. ^
    PMID 19127302
    .
  22. ^
    doi:10.3354/meps07745
    .
  23. ^ "NOAA Ocean Explorer: Mountains in the Sea 2004".
  24. ^
    ISSN 1042-8275. Archived from the original
    (PDF) on 13 June 2010. Retrieved 25 June 2010.
  25. PMID 19712321
    .
  26. ^ "Introduction to the Biology and Geology of Lōʻihi Seamount". Lōʻihi Seamount. Fe-Oxidizing Microbial Observatory (FeMO). 2009-02-01. Retrieved 2009-03-02.
  27. ^ Kennedy, Jennifer. "Seamount: What is a Seamount?". ask.com. Archived from the original on 7 August 2010. Retrieved 25 July 2010.
  28. ^ a b Morato, T., Varkey, D.A., Damaso, C., Machete, M., Santos, M., Prieto, R., Santos, R.S. and Pitcher, T.J. (2008). "Evidence of a seamount effect on aggregating visitors". Marine Ecology Progress Series 357: pages 23–32.
  29. ^ a b c d "Seamounts – hotspots of marine life". International Council for the Exploration of the Sea. Archived from the original on 13 April 2010. Retrieved 24 July 2010.
  30. ^ a b "CenSeam Mission". CenSeam. Archived from the original on 24 May 2010. Retrieved 22 July 2010.
  31. ^ Report of the Secretary-General (2006) The Impacts of Fishing on Vulnerable Marine Ecosystems United Nations. 14 July 2006. Retrieved on 26 July 2010.
  32. ^ "CenSeam Science". CenSeam. Retrieved 22 July 2010.
  33. NOAA. November 20, 2008. Retrieved 2 December 2009.[permanent dead link
    ]
  34. ^ "Bowie Seamount Marine Protected Area". Fisheries and Oceans Canada. 1 October 2011. Retrieved 31 December 2011.
  35. ^ Amos, Jonathan. "Satellites detect 'thousands' of new ocean-bottom mountains" BBC News, 2 October 2014.
  36. ^ "New Map Exposes Previously Unseen Details of Seafloor"
  37. S2CID 31851740
    .
  38. DTU Space
  39. ^
    ISSN 1042-8275. Archived from the original
    (PDF) on 13 June 2010. Retrieved 26 July 2010.
  40. S2CID 129643758
    .
  41. ^ C.Michael Hogan. 2011. Phosphate. Encyclopedia of Earth. Topic ed. Andy Jorgensen. Ed.-in-Chief C.J.Cleveland. National Council for Science and the Environment. Washington DC
  42. ^ a b "USS San Francisco (SSN 711)". Archived from the original on 25 September 2009. Retrieved 25 July 2010.
  43. ^ Nigel Calder (2002). How to Read a Navigational Chart: A Complete Guide to the Symbols, Abbreviations, and Data Displayed on Nautical Charts. International Marine/Ragged Mountain Press.
  44. ^ Seach, John. "Kohala Volcano". Volcanism reference base. John Seach, vulcanologist. Retrieved 25 July 2010.
  45. ^ "Hawaiian tsunami left a gift at foot of volcano". New Scientist (2464): 14. 2004-09-11. Retrieved 25 July 2010.


Bibliography

Geology

Ecology

External links

Geography and geology

Ecology

Retrieved from "https://en.wikipedia.org/w/index.php?title=Seamount&oldid=1211857795"