Seamount
Encyclopedia
A seamount is a mountain
rising from the ocean
seafloor that does not reach to the water's surface (sea level
), 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 1000 – depth. They are defined by oceanographers
as independent features that rise to at least 1000 metres (3,281 ft) above the seafloor. The peaks are often found hundreds to thousands of metres below the surface, and are therefore considered to be within the deep sea
. There are an estimated 100,000 seamounts across the globe, with only a few having been studied. Seamounts come in all shapes and sizes, and follow a distinctive pattern of growth, activity, and death. In recent years, several active seamounts have been observed, for example Loihi in the Hawaiian Islands
.
Because of their abundance, seamounts are one of the most common oceanic ecosystems in the world. Interactions between seamounts and underwater currents, as well as their elevated position in the water, attract plankton
, coral
s, fish
, and marine mammal
s 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 literally 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, extrusion
s seeping in the seamounts put pressure on their sides, causing landslides that have the potential to generate massive tsunami
s.
Most seamounts are volcanic in origin, and thus tend to be found on oceanic crust
near mid-ocean ridge
s, mantle plume
s, and island arc
s. Nearly half of the world's seamounts are found in the Pacific Ocean
, and the rest are distributed mostly across the Atlantic
and Indian
oceans. Overall there is also a significant bias in distribution towards the southern hemisphere.
Seamounts are often found in groupings or submerged archipelago
s, a classic example being the 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
. Isolated seamounts and those without clear volcanic
origins are less common; examples include Bollons Seamount
, Eratosthenes Seamount
, Axial Seamount
and Gorringe Ridge
. If all known seamounts were collected into one area, they would make a landform the size of Europe
. Their overall abundance makes them one of the most common, and least understood, marine structures and biome
s on Earth, a sort of exploratory frontier.
Most seamounts are built by one of two volcanic processes. Volcanoes near plate boundaries
and mid-ocean ridge
s are built by decompression melting of rock in the mantle that then floats up to the surface, while volcanoes formed near subducting zones
are created because the subducting plate
adds volatiles
to the rising plate that raise its melting point
. Which process formed the seamount has a profound effect on its eruptive materials. Lava flows from mid-ocean ridge and plate boundary seamounts are mostly basalt
ic (both tholeiitic and alkalic), whereas flows from subducting ridge volcanoes are mostly calc-alkaline
lavas. Compared to mid-ocean ridge seamounts, subduction zone seamounts generally have more sodium
, alkali
, and volatile abundances, and less magnesium
, resulting in more explosive, viscous eruptions.
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 oceanic island (for example, the 2009 eruption
of Hunga Tonga
). After a period of explosive activity near the ocean surface
, the eruptions slowly die away. With eruptions becoming infrequent and the seamount losing its ability to maintain itself, the volcano starts to erode. After finally becoming extinct (possibly after a brief rejuvenated period), they are ground back down by the waves. Seamounts are built in a far more dynamic oceanic setting then their land counterparts, resulting in horizontal subsidation as the seamount moves on the grinding plate
towards a 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.
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 xenolith
s.
In recent years, geologists have confirmed that a number of seamounts are active undersea volcanoes; two examples are Lo‘ihi in the Hawaiian Islands
and Vailulu'u
in the Manu'a Group
(Samoa
).
The most apparent lava flows at a seamount are the eruptive flows which 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 unusual 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.
and Detroit Seamount
; others are built more steeply, such as Loihi Seamount
and Bowie Seamount
. Some seamounts also have a carbonate
or sediment
cap
.
Many seamounts show signs of intrusive activity
, which is likely to lead to inflation, steepening of volcanic slopes, and ultimately, flank collapse. There are also several sub-classes of seamounts. The first are guyot
s, seamount 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). Knolls are isolated elevation spikes measuring less than 1000 metres (3,281 ft). Lastly, pinnacles are small pillar-like seamounts.
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.
Seamounts provide habitats and spawning grounds for these larger animals, including numerous fish. Some species, including black oreo
(Allocyttus niger) and blackstripe cardinalfish (Apogon nigrofasciatus), have been shown to occur more often on seamounts then anywhere else on the ocean floor. Marine mammal
s, shark
s, tuna
, and cephalopod
s all congregate over seamounts to feed, as well as some species of seabird
s when the features are particularly shallow.
Seamounts often project upwards into shallower zones more hospitable to sea life, providing habitats
for marine species that are not found on or around the surrounding deeper ocean bottom. Because seamounts are isolated from each other they form "undersea islands" creating the same biogeographical interest. As they are formed from volcanic rock
, the substrate is much harder than the surrounding sediment
ary 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. 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 difficulty surviving elsewhere.
The volcanic rocks on the slopes of seamounts are heavily populated by suspension feeders, particularly coral
s, which capitalize on the strong currents around the seamount to supply them with food. This is in sharp contrast with the typical deep-sea habitat, where deposit-feeding animals rely on food they get off the ground. In tropical zones extensive coral growth results in the formation of coral atoll
s late in the seamount's life.
In addition soft sediments tend to accumulate on seamounts, which are typically populated by polychaete
s (annelid
marine worm
s) oligochaetes (microdrile worms), and gastropod mollusks
(sea slug
s). Xenophyophore
s 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. Many seamounts also have hydrothermal vent
communities, for example Suiyo
and Loihi
seamounts. This is helped by geochemical exchange between the seamounts and the ocean water.
Seamounts may thus be vital stopping points for some migratory animal
s, specifically whale
s. Some recent research indicates whales may use such features as navigational aids throughout their migration. For a long time it has been surmised that many pelagic animal
s visit seamounts as well, to gather food, but proof of this aggregating effect has been lacking. The first demonstration of this conjecture has been published.
. 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.
Nearly 80 species of fish and shellfish are commercially harvested from seamounts, including spiny lobster
(Palinuridae), mackerel
(Scombridae and others), red king crab
(Paralithodes camtschaticus), red snapper (Lutjanus campechanus), tuna
(Scombridae), Orange roughy
(Hoplostethus atlanticus), and perch
(Percidae).
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. Much of this lack of information can be attributed to a lack of technology, 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.
Overfishing is a serious threat to seamount ecological welfare. There are several well-documented cases of fishery exploitation, for example the orange roughy
(Hoplostethus atlanticus) off the coasts of Australia and New Zealand and the pelagic armorhead
(Pseudopentaceros richardsoni) near Japan and Russia. 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. Bottom trawling
in particular is extremely devastating to seamount ecology, and is responsible for as much as 95% of ecological damage to seamounts.
Coral
s 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.
Individual nations are beginning to note the effect of fishing on seamounts, and the European Commission
has agreed to fund the OASIS project, a detailed study of the effects of fishing on seamount communities in the North Atlantic. Another project working towards conservation is 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.
Possibly the best ecologically studied seamount in the world is Davidson Seamount
, with six major expeditions recording over 60,000 species observations. The contrast between the seamount and the surrounding area was well-marked. One of the primary ecological havens on the seamount is its deep sea coral
garden, and many of the specimens noted were over a century old. Following the expansion of knowledge on the seamount there was extensive support to make it a marine sanctuary
, a motion that was granted in 2008 as part of the Monterey Bay National Marine Sanctuary
. Much of what is known about seamounts ecologically is based on observations from Davidson. Another such seamount is Bowie Seamount
, which has also been declared a marine protected area by Canada for its ecological richness.
The study of seamounts has been stymied 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, only a scant 1% of the total number have been explored, and sampling and information remains biased towards the top 500 m (1,640 ft). New species are observed or collected and valuable information is obtained on almost every submersible
dive at seamounts.
Before seamounts and their oceanographic impact can be fully understood, they must be mapped, a daunting task due to their sheer number. 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 1500 m (4,921 ft) or larger. In the future, technological advances could allow for a larger and more detailed catalogue.
Seamounts are abundant, and all have metal resource potential because of various enrichment processes during the seamount's life. Hydrogenic Iron
-manganese
, hydrothermal
iron oxide
, sulfide
, sulfate
, sulfur
, hydrothermal manganese oxide
, and phosphorite
are all mineral resources that are founded by various processes and deposited upon seamounts. However, only the first two have any potential of being targeted by mining in the next few decades.
is named after the ship that hit it in 1973. More recently, the submarine USS San Francisco
ran into an uncharted seamount in 2005 at a speed of 35 kn (42.6 mph; 68.6 km/h), sustaining serious damage and killing one seaman.
One major seamount risk is that often, in the late of stages of their life, extrusion
s begin to seep in the seamount. This activity leads to inflation, over-extension of the volcano's flanks, and ultimetly flank collapse, leading to submarine landslides with the potential to start major tsunami
s. This is one of the largest natural disasters in the world. In an illustration of the potent power of flank collapses, a summit collapse on the northern edge of Vlinder Seamount resulted in a pronounced headwall
scarp
and a field of debris up to 6 km (4 mi) away. A catastrophic collapse at Detroit Seamount
flattened its whole structure extensively. Lastly, in 2004, scientists found marine fossil
s 61 m (200 ft) up the flank of Kohala mountain
in Hawaii (island)
. 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, 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.
Ecology
Mountain
Image:Himalaya_annotated.jpg|thumb|right|The Himalayan mountain range with Mount Everestrect 58 14 160 49 Chomo Lonzorect 200 28 335 52 Makalurect 378 24 566 45 Mount Everestrect 188 581 920 656 Tibetan Plateaurect 250 406 340 427 Rong River...
rising from the ocean
Ocean
An ocean is a major body of saline water, and a principal component of the hydrosphere. Approximately 71% of the Earth's surface is covered by ocean, a continuous body of water that is customarily divided into several principal oceans and smaller seas.More than half of this area is over 3,000...
seafloor that does not reach to the water's surface (sea level
Sea level
Mean sea level is a measure of the average height of the ocean's surface ; used as a standard in reckoning land elevation...
), and thus is not an 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...
. These are typically formed from extinct volcanoes, that rise abruptly and are usually found rising from a seafloor of 1000 – depth. They are defined by oceanographers
Oceanography
Oceanography , also called oceanology or marine science, is the branch of Earth science that studies the ocean...
as independent features that rise to at least 1000 metres (3,281 ft) above the seafloor. The peaks are often found hundreds to thousands of metres below the surface, and are therefore considered to be within 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...
. There are an estimated 100,000 seamounts across the globe, with only a few having been studied. Seamounts come in all shapes and sizes, and follow a distinctive pattern of growth, activity, and death. In recent years, several active seamounts have been observed, for example Loihi in the Hawaiian Islands
Hawaiian Islands
The Hawaiian Islands are an archipelago of eight major islands, several atolls, numerous smaller islets, and undersea seamounts in the North Pacific Ocean, extending some 1,500 miles from the island of Hawaii in the south to northernmost Kure Atoll...
.
Because of their abundance, seamounts are one of the most common oceanic ecosystems in the world. Interactions between seamounts and underwater currents, as well as their elevated position in the water, attract plankton
Plankton
Plankton are any drifting organisms that inhabit the pelagic zone of oceans, seas, or bodies of fresh water. That is, plankton are defined by their ecological niche rather than phylogenetic or taxonomic classification...
, coral
Coral
Corals are marine animals in class Anthozoa of phylum Cnidaria typically living in compact colonies of many identical individual "polyps". The group includes the important reef builders that inhabit tropical oceans and secrete calcium carbonate to form a hard skeleton.A coral "head" is a colony of...
s, fish
Fish
Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...
, and marine mammal
Marine mammal
Marine mammals, which include seals, whales, dolphins, and walruses, form a diverse group of 128 species that rely on the ocean for their existence. They do not represent a distinct biological grouping, but rather are unified by their reliance on the marine environment for feeding. The level of...
s alike. Their aggregational effect has been noted by the commercial fishing industry
Commercial fishing
Commercial fishing is the activity of catching fish and other seafood for commercial profit, mostly from wild fisheries. It provides a large quantity of food to many countries around the world, but those who practice it as an industry must often pursue fish far into the ocean under adverse conditions...
, 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
Orange roughy
The orange roughy, red roughy, or deep sea perch, Hoplostethus atlanticus, is a relatively large deep-sea fish belonging to the slimehead family . The Marine Conservation Society has categorized orange roughy as vulnerable to exploitation...
(Hoplostethus atlanticus). 95% of ecological damage is done by bottom trawling
Bottom trawling
Bottom trawling is trawling along the sea floor. It is also often referred to as "dragging".The scientific community divides bottom trawling into benthic trawling and demersal trawling...
, which literally scrapes whole ecosystems off seamounts.
Because of their large numbers, many seamounts remain to be properly studied, and even mapped. Bathymetry
Bathymetry
Bathymetry is the study of underwater depth of lake or ocean floors. In other words, bathymetry is the underwater equivalent to hypsometry. The name comes from Greek βαθύς , "deep", and μέτρον , "measure"...
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
Muirfield Seamount
The Muirfield Seamount is a submarine mountain located in the Indian Ocean approximately 130 kilometres southwest of the Cocos Islands. The Cocos Islands are an Australian territory, and therefore the Muirfield Seamount is within in Australia's Exclusive Economic Zone...
is named after the ship that struck it in 1973. However, the greatest danger from seamounts are flank collapses; as they get older, extrusion
Extrusion
Extrusion is a process used to create objects of a fixed cross-sectional profile. A material is pushed or drawn through a die of the desired cross-section...
s seeping in the seamounts put pressure on their sides, causing landslides that have the potential to generate massive tsunami
Tsunami
A tsunami is a series of water waves caused by the displacement of a large volume of a body of water, typically an ocean or a large lake...
s.
Geography
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 elevational rising of 1000 m (3,281 ft) or more from the surrounding seafloor, and with a limited summit area, a definition drafted in 1964. This definition is no longer strictly adhered to however, and some scientists recognize features as short as 100 m (328 ft) as seamounts. Under the strictest definition there are up to 100,000 seamounts in the oceans, and under the loosest there may be as many as 2 million; however, there are many very small and very deep seamounts that are difficult to analyze, so the true number may never be known.Most seamounts are volcanic in origin, and thus tend to be found on oceanic crust
Oceanic crust
Oceanic crust is the part of Earth's lithosphere that surfaces in the ocean basins. Oceanic crust is primarily composed of mafic rocks, or sima, which is rich in iron and magnesium...
near mid-ocean ridge
Mid-ocean ridge
A mid-ocean ridge is a general term for an underwater mountain system that consists of various mountain ranges , typically having a valley known as a rift running along its spine, formed by plate tectonics. This type of oceanic ridge is characteristic of what is known as an oceanic spreading...
s, mantle plume
Mantle plume
A mantle plume is a hypothetical thermal diapir of abnormally hot rock that nucleates at the core-mantle boundary and rises through the Earth's mantle. Such plumes were invoked in 1971 to explain volcanic regions that were not thought to be explicable by the then-new theory of plate tectonics. Some...
s, and island arc
Island arc
An island arc is a type of archipelago composed of a chain of volcanoes which alignment is arc-shaped, and which are situated parallel and close to a boundary between two converging tectonic plates....
s. Nearly half of the world's seamounts are found in the Pacific Ocean
Pacific Ocean
The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...
, and the rest are distributed mostly across the Atlantic
Atlantic Ocean
The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...
and Indian
Indian Ocean
The Indian Ocean is the third largest of the world's oceanic divisions, covering approximately 20% of the water on the Earth's surface. It is bounded on the north by the Indian Subcontinent and Arabian Peninsula ; on the west by eastern Africa; on the east by Indochina, the Sunda Islands, and...
oceans. Overall there is also a significant bias in distribution towards the southern hemisphere.
Seamounts are often found in groupings or submerged archipelago
Archipelago
An archipelago , sometimes called an island group, is a chain or cluster of islands. The word archipelago is derived from the Greek ἄρχι- – arkhi- and πέλαγος – pélagos through the Italian arcipelago...
s, a classic example being the Emperor Seamounts, an extension of the Hawaiian Islands
Hawaiian Islands
The Hawaiian Islands are an archipelago of eight major islands, several atolls, numerous smaller islets, and undersea seamounts in the North Pacific Ocean, extending some 1,500 miles from the island of Hawaii in the south to northernmost Kure Atoll...
. Formed millions of years ago by volcanism
Volcanism
Volcanism is the phenomenon connected with volcanoes and volcanic activity. It includes all phenomena resulting from and causing magma within the crust or mantle of a planet to rise through the crust and form volcanic rocks on the surface....
, 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
Hawaii (island)
The Island of Hawaii, also called the Big Island or Hawaii Island , is a volcanic island in the North Pacific Ocean...
. Isolated seamounts and those without clear 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...
origins are less common; examples include Bollons Seamount
Bollons Seamount
Bollons Seamount is a seamount just east of the international date line, a few hundred miles off the coast of New Zealand....
, Eratosthenes Seamount
Eratosthenes Seamount
The Eratosthenes Seamount is a seamount in the Eastern Mediterranean about 100 km south of western Cyprus. It is a large, submerged massif, about 120 km long and 80 km wide. Its peak lies at the depth of 690 m and it rises 2000 m above the surrounding seafloor, which is located at...
, Axial Seamount
Axial Seamount
Axial Seamount is a seamount and submarine volcano located on the Juan de Fuca Ridge approximately west of Cannon Beach, Oregon. The seamount, high, stands above the average height of the Juan de Fuca Ridge...
and Gorringe Ridge
Gorringe Ridge
The Gorringe Ridge is a seamount in the Atlantic Ocean. It is located about 130 miles west of Portugal, between the Azores and the Strait of Gibraltar along the Azores-Gibraltar fault zone...
. If all known seamounts were collected into one area, they would make a landform the size of Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
. Their overall abundance makes them one of the most common, and least understood, marine structures and biome
Biome
Biomes are climatically and geographically defined as similar climatic conditions on the Earth, such as communities of plants, animals, and soil organisms, and are often referred to as ecosystems. Some parts of the earth have more or less the same kind of abiotic and biotic factors spread over a...
s on Earth, a sort of exploratory frontier.
Geochemistry and evolution
Divergent boundary
In plate tectonics, a divergent boundary or divergent plate boundary is a linear feature that exists between two tectonic plates that are moving away from each other. Divergent boundaries within continents initially produce rifts which produce rift valleys...
and mid-ocean ridge
Mid-ocean ridge
A mid-ocean ridge is a general term for an underwater mountain system that consists of various mountain ranges , typically having a valley known as a rift running along its spine, formed by plate tectonics. This type of oceanic ridge is characteristic of what is known as an oceanic spreading...
s are built by decompression melting of rock in the mantle that then floats up to the surface, while volcanoes formed near subducting zones
Subduction
In geology, subduction is the process that takes place at convergent boundaries by which one tectonic plate moves under another tectonic plate, sinking into the Earth's mantle, as the plates converge. These 3D regions of mantle downwellings are known as "Subduction Zones"...
are created because the subducting plate
Plate tectonics
Plate tectonics is a scientific theory that describes the large scale motions of Earth's lithosphere...
adds volatiles
Volatiles
In planetary science, volatiles are that group of chemical elements and chemical compounds with low boiling points that are associated with a planet's or moon's crust and/or atmosphere. Examples include nitrogen, water, carbon dioxide, ammonia, hydrogen, and methane, all compounds of C, H, O...
to the rising plate that raise its melting point
Melting point
The melting point of a solid is the temperature at which it changes state from solid to liquid. At the melting point the solid and liquid phase exist in equilibrium. The melting point of a substance depends on pressure and is usually specified at standard atmospheric pressure...
. Which process formed the seamount has a profound effect on its eruptive materials. Lava flows from mid-ocean ridge and plate boundary seamounts are mostly basalt
Basalt
Basalt is a common extrusive volcanic rock. It is usually grey to black and fine-grained due to rapid cooling of lava at the surface of a planet. It may be porphyritic containing larger crystals in a fine matrix, or vesicular, or frothy scoria. Unweathered basalt is black or grey...
ic (both tholeiitic and alkalic), whereas flows from subducting ridge volcanoes are mostly calc-alkaline
Calc-alkaline
The calc-alkaline magma series is one of two main magma series in igneous rocks, the other magma series being the tholeiitic. A magma series is a series of compositions that describes the evolution of a mafic magma, which is high in magnesium and iron and produces basalt or gabbro, as it...
lavas. Compared to mid-ocean ridge seamounts, subduction zone seamounts generally have more sodium
Sodium
Sodium is a chemical element with the symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals; its only stable isotope is 23Na. It is an abundant element that exists in numerous minerals, most commonly as sodium chloride...
, alkali
Alkali
In chemistry, an alkali is a basic, ionic salt of an alkali metal or alkaline earth metal element. Some authors also define an alkali as a base that dissolves in water. A solution of a soluble base has a pH greater than 7. The adjective alkaline is commonly used in English as a synonym for base,...
, and volatile abundances, and less magnesium
Magnesium
Magnesium is a chemical element with the symbol Mg, atomic number 12, and common oxidation number +2. It is an alkaline earth metal and the eighth most abundant element in the Earth's crust and ninth in the known universe as a whole...
, resulting in more explosive, viscous eruptions.
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 oceanic island (for example, the 2009 eruption
2009 Tonga undersea volcanic eruption
The 2009 Tonga undersea volcanic eruption refers to ongoing volcanic activity that began on March 16, 2009, near the island of Hunga Tonga, approximately from the Tongan capital of Tongatapu. The volcano is in a highly active volcanic region that represents a portion of the Pacific Ring of Fire...
of Hunga Tonga
Hunga Tonga
Hunga Tonga-Hunga Haapai is a volcano located about 30 km south-southeast of Fonuafoou , part of Tonga.The volcano is part of the highly active Tonga-Kermadec Islands volcanic arc, a subduction zone extending from New Zealand north-northeast to Fiji. The volcano lies about above a very active...
). After a period of explosive activity near the ocean surface
Sea level
Mean sea level is a measure of the average height of the ocean's surface ; used as a standard in reckoning land elevation...
, the eruptions slowly die away. With eruptions becoming infrequent and the seamount losing its ability to maintain itself, the volcano starts to erode. After finally becoming extinct (possibly after a brief rejuvenated period), they are ground back down by the waves. Seamounts are built in a far more dynamic oceanic setting then their land counterparts, resulting in horizontal subsidation as the seamount moves on the grinding plate
Plate tectonics
Plate tectonics is a scientific theory that describes the large scale motions of Earth's lithosphere...
towards a subduction zone
Subduction
In geology, subduction is the process that takes place at convergent boundaries by which one tectonic plate moves under another tectonic plate, sinking into the Earth's mantle, as the plates converge. These 3D regions of mantle downwellings are known as "Subduction Zones"...
. 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.
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 xenolith
Xenolith
A xenolith is a rock fragment which becomes enveloped in a larger rock during the latter's development and hardening. In geology, the term xenolith is almost exclusively used to describe inclusions in igneous rock during magma emplacement and eruption...
s.
In recent years, geologists have confirmed that a number of seamounts are active undersea volcanoes; two examples are Lo‘ihi in the Hawaiian Islands
Hawaiian Islands
The Hawaiian Islands are an archipelago of eight major islands, several atolls, numerous smaller islets, and undersea seamounts in the North Pacific Ocean, extending some 1,500 miles from the island of Hawaii in the south to northernmost Kure Atoll...
and Vailulu'u
Vailulu'u
Vailulu'u is a volcanic seamount discovered by geophysicist Rockne Johnson in the Samoa Islands on October 18, 1975. The finding of an active, undersea, hotspot volcano is significant for scientists studying the Earth's fundamental processess...
in the Manu'a Group
Manua
Manua, or the Manua Islands Group , in the Samoan Islands, consists of three main islands: Tau, Ofu and Olosega...
(Samoa
Samoa
Samoa , officially the Independent State of Samoa, formerly known as Western Samoa is a country encompassing the western part of the Samoan Islands in the South Pacific Ocean. It became independent from New Zealand in 1962. The two main islands of Samoa are Upolu and one of the biggest islands in...
).
Lava types
Dike (geology)
A dike or dyke in geology is a type of sheet intrusion referring to any geologic body that cuts discordantly across* planar wall rock structures, such as bedding or foliation...
and sills
Sill (geology)
In geology, a sill is a tabular sheet intrusion that has intruded between older layers of sedimentary rock, beds of volcanic lava or tuff, or even along the direction of foliation in metamorphic rock. The term sill is synonymous with concordant intrusive sheet...
, are also an important part of seamount growth. The most common type of flow is pillow lava
Pillow lava
Pillow lavas are lavas that contain characteristic pillow-shaped structures that are attributed to the extrusion of the lava under water, or subaqueous extrusion. Pillow lavas in volcanic rock are characterized by thick sequences of discontinuous pillow-shaped masses, commonly up to one metre in...
, named so after its unusual shape. Less common are sheet flows, which are glassy
Volcanic glass
Volcanic glass is the amorphous product of rapidly cooling magma. Like all types of glass, it is a state of matter intermediate between the close-packed, highly ordered array of a crystal and the highly disordered array of gas...
and marginal, and indicative of larger-scale flows. Volcaniclastic
Pyroclastic rock
Pyroclastic rocks or pyroclastics are clastic rocks composed solely or primarily of volcanic materials. Where the volcanic material has been transported and reworked through mechanical action, such as by wind or water, these rocks are termed volcaniclastic...
sedimentary
Sedimentary rock
Sedimentary rock are types of rock that are formed by the deposition of material at the Earth's surface and within bodies of water. Sedimentation is the collective name for processes that cause mineral and/or organic particles to settle and accumulate or minerals to precipitate from a solution....
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.
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. Some are built very large and very low, such as Koko GuyotKoko Guyot
Koko Guyot is a 48.1 million year old guyot, a type of underwater volcano with a flat top, which lies near the southern end of the Emperor seamounts, about north of the "bend" in the volcanic Hawaiian-Emperor seamount chain...
and Detroit Seamount
Detroit Seamount
Detroit Seamount, which was formed around 76 million years ago, is one of the oldest seamounts of the Hawaiian-Emperor seamount chain...
; others are built more steeply, such as Loihi Seamount
Loihi Seamount
Lōihi Seamount is an active undersea volcano located around off the southeast coast of the island of Hawaii about below sea level. It lies on the flank of Mauna Loa, the largest shield volcano on Earth...
and Bowie Seamount
Bowie Seamount
Bowie Seamount is a large submarine volcano in the northeastern Pacific Ocean, located west of Haida Gwaii, British Columbia, Canada.The seamount is named after William Bowie of the Coast & Geodetic Survey....
. Some seamounts also have a carbonate
Carbonate rock
Carbonate rocks are a class of sedimentary rocks composed primarily of carbonate minerals. The two major types are limestone, which is composed of calcite or aragonite and dolostone, which is composed of the mineral dolomite .Calcite can be either dissolved by groundwater or precipitated by...
or sediment
Sediment
Sediment is naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of fluids such as wind, water, or ice, and/or by the force of gravity acting on the particle itself....
cap
Caprock
The Caprock is a region in the Panhandle of Texas . It is the land to the west of the Caprock Escarpment, which separates it from plains stretching to the east at a much lower elevation....
.
Many seamounts show signs of intrusive activity
Intrusion
An intrusion is liquid rock that forms under Earth's surface. Magma from under the surface is slowly pushed up from deep within the earth into any cracks or spaces it can find, sometimes pushing existing country rock out of the way, a process that can take millions of years. As the rock slowly...
, which is likely to lead to inflation, steepening of volcanic slopes, and ultimately, flank collapse. There are also several sub-classes of seamounts. The first are guyot
Guyot
A guyot , also known as a tablemount, is an isolated underwater volcanic mountain , with a flat top over 200 meters below the surface of the sea. The diameters of these flat summits can exceed ....
s, seamount 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). Knolls are isolated elevation spikes measuring less than 1000 metres (3,281 ft). Lastly, pinnacles are small pillar-like seamounts.
Ecological role of seamounts
Seamounts are exceptionally important to their biome ecologically, but their role in their environment is little understood. Because they project out above the surrounding sea floor, they disturb standard water flow, causing eddiesEddy (fluid dynamics)
In fluid dynamics, an eddy is the swirling of a fluid and the reverse current created when the fluid flows past an obstacle. The moving fluid creates a space devoid of downstream-flowing fluid on the downstream side of the object...
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
Plankton
Plankton are any drifting organisms that inhabit the pelagic zone of oceans, seas, or bodies of fresh water. That is, plankton are defined by their ecological niche rather than phylogenetic or taxonomic classification...
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.
Seamounts provide habitats and spawning grounds for these larger animals, including numerous fish. Some species, including black oreo
Black oreo
The black oreo, Allocyttus niger, is an oreo of the family Oreosomatidae, found around Australia and New Zealand between latitudes of between 43°S and 55°S at depths of between 560 and 1,300 m. Its length is up to 47 cm....
(Allocyttus niger) and blackstripe cardinalfish (Apogon nigrofasciatus), have been shown to occur more often on seamounts then anywhere else on the ocean floor. Marine mammal
Marine mammal
Marine mammals, which include seals, whales, dolphins, and walruses, form a diverse group of 128 species that rely on the ocean for their existence. They do not represent a distinct biological grouping, but rather are unified by their reliance on the marine environment for feeding. The level of...
s, shark
Shark
Sharks are a type of fish with a full cartilaginous skeleton and a highly streamlined body. The earliest known sharks date from more than 420 million years ago....
s, tuna
Tuna
Tuna is a salt water fish from the family Scombridae, mostly in the genus Thunnus. Tuna are fast swimmers, and some species are capable of speeds of . Unlike most fish, which have white flesh, the muscle tissue of tuna ranges from pink to dark red. The red coloration derives from myoglobin, an...
, and cephalopod
Cephalopod
A cephalopod is any member of the molluscan class Cephalopoda . These exclusively marine animals are characterized by bilateral body symmetry, a prominent head, and a set of arms or tentacles modified from the primitive molluscan foot...
s all congregate over seamounts to feed, as well as some species of seabird
Seabird
Seabirds are birds that have adapted to life within the marine environment. While seabirds vary greatly in lifestyle, behaviour and physiology, they often exhibit striking convergent evolution, as the same environmental problems and feeding niches have resulted in similar adaptations...
s when the features are particularly shallow.
Seamounts often project upwards into shallower zones more hospitable to sea life, providing habitats
Habitat (ecology)
A habitat is an ecological or environmental area that is inhabited by a particular species of animal, plant or other type of organism...
for marine species that are not found on or around the surrounding deeper ocean bottom. Because seamounts are isolated from each other they form "undersea islands" creating the same biogeographical interest. As they are formed from volcanic rock
Volcanic rock
Volcanic rock is a rock formed from magma erupted from a volcano. In other words, it is an igneous rock of volcanic origin...
, the substrate is much harder than the surrounding sediment
Sediment
Sediment is naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of fluids such as wind, water, or ice, and/or by the force of gravity acting on the particle itself....
ary 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. However, recent research especially centered at Davidson Seamount
Davidson Seamount
Davidson Seamount is a seamount located off the coast of Central California, southwest of Monterey and west of San Simeon. At long and wide, it is one of the largest known seamounts in the world. From base to crest, the seamount is tall, yet its summit is still below the sea surface...
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 difficulty surviving elsewhere.
The volcanic rocks on the slopes of seamounts are heavily populated by suspension feeders, particularly coral
Coral
Corals are marine animals in class Anthozoa of phylum Cnidaria typically living in compact colonies of many identical individual "polyps". The group includes the important reef builders that inhabit tropical oceans and secrete calcium carbonate to form a hard skeleton.A coral "head" is a colony of...
s, which capitalize on the strong currents around the seamount to supply them with food. This is in sharp contrast with the typical deep-sea habitat, where deposit-feeding animals rely on food they get off the ground. In tropical zones extensive coral growth results in the formation of coral 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 late in the seamount's life.
In addition soft sediments tend to accumulate on seamounts, which are typically populated by polychaete
Polychaete
The Polychaeta or polychaetes are a class of annelid worms, generally marine. Each body segment has a pair of fleshy protrusions called parapodia that bear many bristles, called chaetae, which are made of chitin. Indeed, polychaetes are sometimes referred to as bristle worms. More than 10,000...
s (annelid
Annelid
The annelids , formally called Annelida , are a large phylum of segmented worms, with over 17,000 modern species including ragworms, earthworms and leeches...
marine worm
Marine worm
Any worm that lives in a marine environment is considered a marine worm. Marine worms are found in several different phyla, including the Platyhelminthes, Nematoda, Annelida , Chaetognatha, Hemichordata, and Phoronida....
s) oligochaetes (microdrile worms), and gastropod mollusks
Gastropoda
The Gastropoda or gastropods, more commonly known as snails and slugs, are a large taxonomic class within the phylum Mollusca. The class Gastropoda includes snails and slugs of all kinds and all sizes from microscopic to quite large...
(sea slug
Sea slug
Sea slug is a common name used for several different groups of saltwater snails that either lack a shell or have only an internal shell, in other words this name is used for various lineages of marine gastropod mollusks that are either not conchiferous or appear not to be.The phrase "sea slug" is...
s). Xenophyophore
Xenophyophore
Xenophyophores are marine protozoa, giant single-celled organisms found throughout the world's oceans, at depths of up to 10,641 meters . Xenophyophores are found in the greatest numbers on the abyssal plains of the deep ocean. They were first described as sponges in 1889, then as testate...
s 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. Many seamounts also have hydrothermal vent
Hydrothermal vent
A hydrothermal vent is a fissure in a planet's surface from which geothermally heated water issues. Hydrothermal vents are commonly found near volcanically active places, areas where tectonic plates are moving apart, ocean basins, and hotspots. Hydrothermal vents exist because the earth is both...
communities, for example Suiyo
Suiyo Seamount
Suiyo Seamount is a seamount off the eastern coast of Japan, directly south of Torishima and Sofugan volcano at the southern tip of the Izu Islands...
and Loihi
Loihi Seamount
Lōihi Seamount is an active undersea volcano located around off the southeast coast of the island of Hawaii about below sea level. It lies on the flank of Mauna Loa, the largest shield volcano on Earth...
seamounts. This is helped by geochemical exchange between the seamounts and the ocean water.
Seamounts may thus be vital stopping points for some migratory animal
Animal migration
Animal migration is the relatively long-distance movement of individuals, usually on a seasonal basis. It is a ubiquitous phenomenon, found in all major animal groups, including birds, mammals, fish, reptiles, amphibians, insects, and crustaceans. The trigger for the migration may be local...
s, specifically whale
Whale
Whale is the common name for various marine mammals of the order Cetacea. The term whale sometimes refers to all cetaceans, but more often it excludes dolphins and porpoises, which belong to suborder Odontoceti . This suborder also includes the sperm whale, killer whale, pilot whale, and beluga...
s. Some recent research indicates whales may use such features as navigational aids throughout their migration. For a long time it has been surmised that many pelagic animal
Pelagic zone
Any water in a sea or lake that is not close to the bottom or near to the shore can be said to be in the pelagic zone. The word pelagic comes from the Greek πέλαγος or pélagos, which means "open sea". The pelagic zone can be thought of in terms of an imaginary cylinder or water column that goes...
s visit seamounts as well, to gather food, but proof of this aggregating effect has been lacking. The first demonstration of this conjecture has been published.
Fishing
The effect that seamounts have on fish populations has not gone unnoticed by the commercial fishing industryCommercial fishing
Commercial fishing is the activity of catching fish and other seafood for commercial profit, mostly from wild fisheries. It provides a large quantity of food to many countries around the world, but those who practice it as an industry must often pursue fish far into the ocean under adverse conditions...
. 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
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,...
. Seamounts have been the site of targeted fishing since that time.
Nearly 80 species of fish and shellfish are commercially harvested from seamounts, including spiny lobster
Spiny lobster
Spiny lobsters, also known as langouste or rock lobsters, are a family of about 45 species of achelate crustaceans, in the Decapoda Reptantia...
(Palinuridae), mackerel
Mackerel
Mackerel is a common name applied to a number of different species of fish, mostly, but not exclusively, from the family Scombridae. They may be found in all tropical and temperate seas. Most live offshore in the oceanic environment but a few, like the Spanish mackerel , enter bays and can be...
(Scombridae and others), red king crab
Paralithodes camtschaticus
The red king crab, Paralithodes camtschaticus, is a species of king crab native to the Bering Sea. It grows to a leg span of , and is heavily targeted by fisheries.-Description:...
(Paralithodes camtschaticus), red snapper (Lutjanus campechanus), tuna
Tuna
Tuna is a salt water fish from the family Scombridae, mostly in the genus Thunnus. Tuna are fast swimmers, and some species are capable of speeds of . Unlike most fish, which have white flesh, the muscle tissue of tuna ranges from pink to dark red. The red coloration derives from myoglobin, an...
(Scombridae), Orange roughy
Orange roughy
The orange roughy, red roughy, or deep sea perch, Hoplostethus atlanticus, is a relatively large deep-sea fish belonging to the slimehead family . The Marine Conservation Society has categorized orange roughy as vulnerable to exploitation...
(Hoplostethus atlanticus), and perch
Perch
Perch is a common name for fish of the genus Perca, freshwater gamefish belonging to the family Percidae. The perch, of which there are three species in different geographical areas, lend their name to a large order of vertebrates: the Perciformes, from the Greek perke meaning spotted, and the...
(Percidae).
Conservation
Bathymetry
Bathymetry is the study of underwater depth of lake or ocean floors. In other words, bathymetry is the underwater equivalent to hypsometry. The name comes from Greek βαθύς , "deep", and μέτρον , "measure"...
, a task that is still in progress.
Overfishing is a serious threat to seamount ecological welfare. There are several well-documented cases of fishery exploitation, for example the orange roughy
Orange roughy
The orange roughy, red roughy, or deep sea perch, Hoplostethus atlanticus, is a relatively large deep-sea fish belonging to the slimehead family . The Marine Conservation Society has categorized orange roughy as vulnerable to exploitation...
(Hoplostethus atlanticus) off the coasts of Australia and New Zealand and the pelagic armorhead
Pelagic armorhead
The pelagic armorhead, pelagic armourhead, Richardson's boarfish, or southern boarfish, Pseudopentaceros richardsoni, is an armorhead of the genus Pseudopentaceros, found in the north and south Pacific Ocean, South Africa, South America, and the South Island of New Zealand, from the surface to...
(Pseudopentaceros richardsoni) near Japan and Russia. 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
Trawling
Trawling is a method of fishing that involves pulling a fishing net through the water behind one or more boats. The net that is used for trawling is called a trawl....
, which damages seamount surface communities, and the fact that many seamounts are located in international waters, making proper monitoring difficult. Bottom trawling
Bottom trawling
Bottom trawling is trawling along the sea floor. It is also often referred to as "dragging".The scientific community divides bottom trawling into benthic trawling and demersal trawling...
in particular is extremely devastating to seamount ecology, and is responsible for as much as 95% of ecological damage to seamounts.
Coral
Corals are marine animals in class Anthozoa of phylum Cnidaria typically living in compact colonies of many identical individual "polyps". The group includes the important reef builders that inhabit tropical oceans and secrete calcium carbonate to form a hard skeleton.A coral "head" is a colony of...
s 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.
Individual nations are beginning to note the effect of fishing on seamounts, and the European Commission
European Commission
The European Commission is the executive body of the European Union. The body is responsible for proposing legislation, implementing decisions, upholding the Union's treaties and the general day-to-day running of the Union....
has agreed to fund the OASIS project, a detailed study of the effects of fishing on seamount communities in the North Atlantic. Another project working towards conservation is CenSeam, a Census of Marine Life
Census of Marine Life
The Census of Marine Life was a global network of researchers in more than 80 nations engaged in a 10-year scientific initiative to assess and explain the diversity, distribution, and abundance of life in the oceans...
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
Biogeography
Biogeography is the study of the distribution of species , organisms, and ecosystems in space and through geological time. Organisms and biological communities vary in a highly regular fashion along geographic gradients of latitude, elevation, isolation and habitat area...
, biodiversity
Biodiversity
Biodiversity is the degree of variation of life forms within a given ecosystem, biome, or an entire planet. Biodiversity is a measure of the health of ecosystems. Biodiversity is in part a function of climate. In terrestrial habitats, tropical regions are typically rich whereas polar regions...
, productivity
Productivity (ecology)
In ecology, productivity or production refers to the rate of generation of biomass in an ecosystem. It is usually expressed in units of mass per unit surface per unit time, for instance grams per square metre per day. The mass unit may relate to dry matter or to the mass of carbon generated...
and evolution
Evolution
Evolution is any change across successive generations in the heritable characteristics of biological populations. Evolutionary processes give rise to diversity at every level of biological organisation, including species, individual organisms and molecules such as DNA and proteins.Life on Earth...
of marine organisms.
Possibly the best ecologically studied seamount in the world is Davidson Seamount
Davidson Seamount
Davidson Seamount is a seamount located off the coast of Central California, southwest of Monterey and west of San Simeon. At long and wide, it is one of the largest known seamounts in the world. From base to crest, the seamount is tall, yet its summit is still below the sea surface...
, with six major expeditions recording over 60,000 species observations. The contrast between the seamount and the surrounding area was well-marked. One of the primary ecological havens on the seamount is its deep sea coral
Deep water coral
The habitat of deep water corals, also known as cold water corals, extends to deeper, darker parts of the oceans than tropical corals, ranging from near the surface to the abyss, beyond where water temperatures may be as cold as 4°C...
garden, and many of the specimens noted were over a century old. Following the expansion of knowledge on the seamount there was extensive support to make it a marine sanctuary
Marine Protected Area
Marine Protected Areas, like any protected area, are regions in which human activity has been placed under some restrictions in the interest of conserving the natural environment, it's surrounding waters and the occupant ecosystems, and any cultural or historical resources that may require...
, a motion that was granted in 2008 as part of the Monterey Bay National Marine Sanctuary
Monterey Bay National Marine Sanctuary
The Monterey Bay National Marine Sanctuary is a US Federally protected marine area offshore of California's central coast around Monterey Bay....
. Much of what is known about seamounts ecologically is based on observations from Davidson. Another such seamount is Bowie Seamount
Bowie Seamount
Bowie Seamount is a large submarine volcano in the northeastern Pacific Ocean, located west of Haida Gwaii, British Columbia, Canada.The seamount is named after William Bowie of the Coast & Geodetic Survey....
, which has also been declared a marine protected area by Canada for its ecological richness.
Exploration
Submersible
A submersible is a small vehicle designed to operate underwater. The term submersible is often used to differentiate from other underwater vehicles known as submarines, in that a submarine is a fully autonomous craft, capable of renewing its own power and breathing air, whereas a submersible is...
dive at seamounts.
Before seamounts and their oceanographic impact can be fully understood, they must be mapped, a daunting task due to their sheer number. The most detailed seamount mappings are provided by multibeam echosounding (sonar
Sonar
Sonar is a technique that uses sound propagation to navigate, communicate with or detect other vessels...
), 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 1500 m (4,921 ft) or larger. In the future, technological advances could allow for a larger and more detailed catalogue.
Deep-sea mining
Seamounts are a possible future source of heavy metals. The growth of the human population and, with it, heavy industry, has pressed demands for Earth's finite resources. Even though the ocean makes up 70% of the world, technological challenges with deep-sea mineral mining have severely limited its extent. But with the constantly decreasing supply on land, many see oceanic mining as the destined future, and seamounts stand out as candidates.Seamounts are abundant, and all have metal resource potential because of various enrichment processes during the seamount's life. Hydrogenic Iron
Iron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...
-manganese
Manganese
Manganese is a chemical element, designated by the symbol Mn. It has the atomic number 25. It is found as a free element in nature , and in many minerals...
, hydrothermal
Hydrothermal vent
A hydrothermal vent is a fissure in a planet's surface from which geothermally heated water issues. Hydrothermal vents are commonly found near volcanically active places, areas where tectonic plates are moving apart, ocean basins, and hotspots. Hydrothermal vents exist because the earth is both...
iron oxide
Iron oxide
Iron oxides are chemical compounds composed of iron and oxygen. All together, there are sixteen known iron oxides and oxyhydroxides.Iron oxides and oxide-hydroxides are widespread in nature, play an important role in many geological and biological processes, and are widely utilized by humans, e.g.,...
, sulfide
Sulfide
A sulfide is an anion of sulfur in its lowest oxidation state of 2-. Sulfide is also a slightly archaic term for thioethers, a common type of organosulfur compound that are well known for their bad odors.- Properties :...
, sulfate
Sulfate
In inorganic chemistry, a sulfate is a salt of sulfuric acid.-Chemical properties:...
, sulfur
Sulfur
Sulfur or sulphur is the chemical element with atomic number 16. In the periodic table it is represented by the symbol S. It is an abundant, multivalent non-metal. Under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a bright yellow...
, hydrothermal manganese oxide
Manganese oxide
Manganese oxide is a generic term used to describe a variety of manganese oxides and hydroxides. It may refer to:* Manganese oxide, MnO* Manganese oxide, Mn3O4* Manganese oxide, Mn2O3* Manganese dioxide, , MnO2...
, and phosphorite
Phosphorite
Phosphorite, phosphate rock or rock phosphate is a non-detrital sedimentary rock which contains high amounts of phosphate bearing minerals. The phosphate content of phosphorite is at least 15 to 20% which is a large enrichment over the typical sedimentary rock content of less than 0.2%...
are all mineral resources that are founded by various processes and deposited upon seamounts. However, only the first two have any potential of being targeted by mining in the next few decades.
Dangers
Some seamounts have not been mapped and thus pose a navigational danger. For instance, Muirfield SeamountMuirfield Seamount
The Muirfield Seamount is a submarine mountain located in the Indian Ocean approximately 130 kilometres southwest of the Cocos Islands. The Cocos Islands are an Australian territory, and therefore the Muirfield Seamount is within in Australia's Exclusive Economic Zone...
is named after the ship that hit it in 1973. More recently, the submarine USS San Francisco
USS San Francisco (SSN-711)
USS San Francisco , a Los Angeles-class nuclear submarine, is the third ship or boat of the United States Navy to be named for San Francisco, California.-History:...
ran into an uncharted seamount in 2005 at a speed of 35 kn (42.6 mph; 68.6 km/h), sustaining serious damage and killing one seaman.
One major seamount risk is that often, in the late of stages of their life, extrusion
Extrusion
Extrusion is a process used to create objects of a fixed cross-sectional profile. A material is pushed or drawn through a die of the desired cross-section...
s begin to seep in the seamount. This activity leads to inflation, over-extension of the volcano's flanks, and ultimetly flank collapse, leading to submarine landslides with the potential to start major tsunami
Tsunami
A tsunami is a series of water waves caused by the displacement of a large volume of a body of water, typically an ocean or a large lake...
s. This is one of the largest natural disasters in the world. In an illustration of the potent power of flank collapses, a summit collapse on the northern edge of Vlinder Seamount resulted in a pronounced headwall
Headwall
In physical geography and geology the headwall of a glacial cirque is its highest cliff.In civil engineering, a headwall is a small retaining wall placed at the outlet of a stormwater pipe or culvert....
scarp
Scarp
-Landforms and geology:* Cliff, a significant vertical, or near vertical, rock exposure* Escarpment, a steep slope or long cliff that occurs from erosion or faulting and separates two relatively level areas of differing elevations...
and a field of debris up to 6 km (4 mi) away. A catastrophic collapse at Detroit Seamount
Detroit Seamount
Detroit Seamount, which was formed around 76 million years ago, is one of the oldest seamounts of the Hawaiian-Emperor seamount chain...
flattened its whole structure extensively. Lastly, in 2004, scientists found marine fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
s 61 m (200 ft) up the flank of Kohala mountain
Kohala (mountain)
Kohala is the oldest of five volcanoes that make up the island of Hawaii. Kohala is an estimated one million years old—so old that it experienced, and recorded, a reversal of magnetic field 780,000 years ago. It is believed to have breached sea level more than 500,000 years ago and to...
in Hawaii (island)
Hawaii
Hawaii is the newest of the 50 U.S. states , and is the only U.S. state made up entirely of islands. It is the northernmost island group in Polynesia, occupying most of an archipelago in the central Pacific Ocean, southwest of the continental United States, southeast of Japan, and northeast of...
. 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, far too high for a normal wave to reach. The date corresponded with a massive flank collapse at the nearby Mauna Loa
Mauna Loa
Mauna Loa is one of five volcanoes that form the Island of Hawaii in the U.S. state of Hawaii in the Pacific Ocean, and the largest on Earth in terms of volume and area covered. It is an active shield volcano, with a volume estimated at approximately , although its peak is about lower than that...
, and it was theorized that it was a massive tsunami, generated by the landslide, that deposited the fossils.
See also
- Asphalt volcanoAsphalt volcanoAn asphalt volcano is a rare type of submarine volcano first discovered in 2003. Several examples have been found: first, along the coasts of America and Mexico, and, recently, all over the world; a few are still active...
- Dry topographic prominence
- Evolution of Hawaiian volcanoesEvolution of Hawaiian volcanoesThe fifteen volcanoes that make up the eight principal islands of Hawaii are the youngest in a chain of more than 129 volcanoes that stretch across the North Pacific Ocean, called the Hawaiian-Emperor seamount chain....
- Marine Protected AreaMarine Protected AreaMarine Protected Areas, like any protected area, are regions in which human activity has been placed under some restrictions in the interest of conserving the natural environment, it's surrounding waters and the occupant ecosystems, and any cultural or historical resources that may require...
- Mud volcanoMud volcanoThe term mud volcano or mud dome are used to refer to formations created by geo-excreted liquids and gases, although there are several different processes which may cause such activity. Hot water mixes with mud and surface deposits. Mud volcanoes are associated with subduction zones and about 700...
- List of submarine volcanoes
- Submarine eruption
- BathymetryBathymetryBathymetry is the study of underwater depth of lake or ocean floors. In other words, bathymetry is the underwater equivalent to hypsometry. The name comes from Greek βαθύς , "deep", and μέτρον , "measure"...
External links
Geography and geology- Earthref Seamount Catalogue. A database of seamount maps and catalogue listings.
- Volcanic History of Seamounts in the Gulf of Alaska.
- The giant Ruatoria debris avalanche on the northern Hikurangi margin, New Zealand. Aftermath of a seamount carving into the far side of a subduction trench.
- Evolution of Hawaiian volcanoes. The life cycle of seamounts was originally observed off of the Hawaiian arc.
- How Volcanoes Work: Lava and Water. An explanation of the different types of lava-water interactions.
Ecology
- A review of the effects of seamounts on biological processes. NOAA paper.
- Mountains in the Sea, a volume on the biological and geological effects of seamounts, available fully online.
- SeamountsOnline, seamount biology database.
- Vulnerability of deep sea corals to fishing on seamounts beyond areas of national jurisdiction, United Nations Environment Program.
- A collection of seamount videos