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.
Grouping
Seamount
Seamount | Grouping
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. They are typically formed from extinct volcanoes that rise abruptly and are usually found rising from the seafloor to in height Volcanoes near plate boundaries and mid-ocean ridges are built by decompression melting of rock in the upper mantle. They are typically formed from extinct volcanoes that rise abruptly and are usually found rising from the seafloor to in height.
what is a chain of underwater mountains called
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Seamount
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what can you tell about its geographic features?
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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 or more from the surrounding seafloor, and with a limited summit area, of conical form.
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how are these chain of mountains formed?
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The chain-like arrangement of summits and the formation of long, jagged mountain crests – known in Spanish as sierras ("saws") – is a consequence of their collective formation by mountain building forces. The often linear structure is linked to the direction of these thrust forces and the resulting mountain folding which in turn relates to the fault lines in the upper part of the earth's crust, that run between the individual mountain chains. In these fault zones, the rock, which has sometimes been pulverised, is easily eroded, so that large river valleys are carved out. These, so called longitudinal valleys reinforce the trend, during the early mountain building phase, towards the formation of parallel chains of mountains.
Mountain chain | Formation of parallel mountain chains
The overthrust folds of a nappe belt (e.g. the Central Alps) are formed in a similar way. Although the fold mountains, chain mountains and nappe belts around the world were formed at different times in the earth's history, all during their initial mountain building phases, they are nevertheless morphologically similar. Harder rock forms continuous arêtes or ridges that follow the strike of the beds and folds. The mountain chains or ridges therefore run approximately parallel to one another. They are only interrupted by short, usually narrow, transverse valleys, which often form water gaps. During the course of earth history, erosion by water, ice and wind carried away the highest points of the mountain crests and carved out individual summits or summit chains.
Mountain chain | Formation of parallel mountain chains
Between them, notches were formed that, depending on altitude and rock-type, form knife-edged cols or gentler mountain passes and saddles.
Mountain chain | Formation of parallel mountain chains
They appear to have been formed under the influence both of fracture zones and of a melt anomaly that also formed a topographic anomaly west of the Lamont seamount chain along with elongated volcanic structures; a bathymetric swell is also noted around the seamounts as well as a deep depression that may be an isostatic moat. The volcanism may be ultimately the consequence of hotspot activity.
Lamont seamount chain | Geology
All the seamounts in the group are complex northeast-southwest trending structures, consisting of parallel ridges separated by sediment-filled troughs. The ridges constructed run parallel to an ancient spreading center which has since been replaced in its role by the San Andreas Fault system. They are unique in this origin, as they are formed from the remnants of an old ocean-ridge spreading center. A series of "knobs" are aligned with the ridges; however the distinctive summit crater, evident in many oceanic volcanoes, is absent. This lack of a collapse crater suggests that magma was never stored in a chamber within the structure, as with most other volcanoes.
Davidson Seamount | Geology
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.
Seamount | Grouping
The Foundation chain eventually becomes a set of three ridges close to the Pacific-Antarctic Ridge, the northern two of which are the more voluminous ones. These northern ridges are probably the main ones; the southern one may have formed through cracks in the crust induced by the northern ridge, but it might also be a "paired" expression of a hotspot similar to the Kea and Loa trends in Hawaii. The seamounts reach depths of beneath sea level (the highest seamount is located at ), and contain typical volcanic features such as smaller volcanic cones, calderas and individual rift zones. Some of the seamounts close to the ridge have flat tops and show evidence of having formed islands above sea level in the past.
Foundation Seamounts | Geography
Mountain chains are typically formed by the process of plate tectonics. Tectonic plates slide very slowly over the Earth's mantle, a lower place of rock that is heated from the Earth's interior. Several huge sections of the earth's crust are impelled by heat currents in the mantle, producing tremendous forces that can buckle the material at the edges of the plates to form mountains. Usually one plate is forced underneath the other, and the lower plate is slowly absorbed by the mantle. Where the two plates pass one another, heated rock from the mantle can burst through the crust to form volcanoes.
List of longest mountain chains on Earth | Formation
Other types of range such as horst ranges, fault block mountain or truncated uplands rarely form parallel mountain chains. However, if a truncated upland is eroded into a high table land, the incision of valleys can lead to the formations of mountain or hill chains.
Mountain chain | Introduction
A mountain chain is a row of high mountain summits, a linear sequence of interconnected or related mountains, or a contiguous ridge of mountains within a larger mountain range. The term is also used for elongated fold mountains with several parallel chains ("chain mountains"). While in mountain ranges, the term mountain chain is common, in hill ranges a sequence of hills tends to be referred to a ridge or hill chain. Elongated mountain chains occur most frequently in the orogeny of fold mountains, (that are folded by lateral pressure), and nappe belts (where a sheetlike body of rock has been pushed over another rock mass).
Mountain chain | Introduction
In the middle of the chain lies Mount Steere with a summit elevation of and a rectangular summit caldera. Lie Cliff is a volcanic outcrop on the northeastern flank. Mount Steere is heavily dissected, bears evidence of former glaciation in the form of moraines and cirques have been eroded into its northern and northeastern flanks. As with Mount Rees, volcanic rocks alternate between these that formed subglacially and these formed subaerially. Outcrops feature breccias and lava with numerous intruded dikes.
Crary Mountains | Geography and geomorphology
The Cobb-Eickelberg seamount chain is a range of undersea mountains formed by volcanic activity of the Cobb hotspot located in the Pacific Ocean. The seamount chain extends to the southeast on the Pacific Plate, beginning at the Aleutian Trench and terminating at Axial Seamount, located on the Juan de Fuca Ridge.The seamount chain is spread over a vast length of approximately 1800 km. The location of the Cobb hotspot that gives rise to these seamounts is 46° N -130° W. The Pacific plate is moving to the northwest over the hotspot, causing the seamounts in the chain to decrease in age to the southeast.
Cobb–Eickelberg Seamount chain | Introduction
A further sampling cruise by the United States Geological Survey (USGS) recovered pillow lava and hyaloclastite from 4 of the 8 volcanoes. The samples seemed to be of more primitive origin then those erupted elsewhere on the ridge. In 1998, the Monterey Bay Aquarium Research Institute conducted two dives on a cone cluster located southeast of the main structure. The chain consists of eight volcanoes. Of these, four are self-dependent, whereas the other four form twin fused, morphalogically complex, flat-topped structures. The volcanoes form a linear chain, and are relatively small, measuring less than in diameter, and are nearly circular in shape.
President Jackson Seamounts | Introduction
As with all the prealpine massifs, the Aravis chain is primarily formed of limestone and its derivatives.
Bornes Massif | Geology
The tendency, especially of fold mountains (e. g. the Cordilleras) to produce roughly parallel chains is due to their rock structure and the propulsive forces of plate tectonics. The uplifted rock masses are either magmatic plutonic rocks, easily shaped because of their higher temperature, or sediments or metamorphic rocks, which have a less robust structure, that are deposited in the synclines. As a result of orogenic movements, strata of folded rock are formed that are crumpled out of their original horizontal plane and thrust against one another. The longitudinal stretching of the folds takes place at right angles to the direction of the lateral thrusting.
Mountain chain | Formation of parallel mountain chains
A number of flat-topped seamounts rise from the floor of the western Pacific Ocean to depths of below sea level. They are called guyots and are clustered in an elongated region with and between the Marshall Islands and the Tuamotus. It is presumed that hotspots generated most of these seamounts. The Marshall Islands are grouped in two chains and three groups, the Ratak Chain including Limalok Guyot, the Ralik Chain including Wōdejebato Guyot and an isolated cluster farther west including Eniwetok Island.
Ruwitūn̄tūn̄ | Geological context
The Lamont seamount chain is a group of five seamounts in the Pacific Ocean; from southeast to northwest they are known as "Sasha", "MIB", "MOK", "DTD" and "NEW" and there is an additional unnamed seamount southwest from "NEW". The seamounts were discovered in 1983 and named later. The seamounts reach heights of and have summit craters/calderas, that on "DTD", "MOK" and "NEW" form nested, complex calderas. Horseshoe-shaped volcanic ridges accompany the calderas and lava effusion appears to have preferentially occurred on the margins of the calderas, along with mass wasting. The Lamont seamount chain forms a long chain and the individual seamounts surrounded by lava cones high.
Lamont seamount chain | Geography and geomorphology
In addition there are long gullies formed either by erosional or volcanic processes, as well as parasitic vents and volcanic ridges.
Tropic Seamount | Local
Seamounts are often found in groupings or submerged archipelagos, 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. 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. Seamount chains occur in all three major ocean basins, with the Pacific having the most number and most extensive seamount chains.
Seamount | Grouping
The Foundation Seamounts form a long and wide band of seamounts that extend northwestward away from the Pacific-Antarctic Ridge towards the Resolution () and Del Cano () fracture zones. A small ridge continues from there to the Macdonald seamount, but the relation of this ridge to the Foundation Seamounts appears to be questionable at best, and there are no other clear bathymetric features in between Foundation and Macdonald. Close to the western end of the Foundation Seamounts lie the "Old Pacific Seamounts", which may have the same origin. On the other end of the chain, the seamounts become short ridges decorated by volcanic cones; the Pacific-Antarctic Ridge is migrating northwestward and approaching the hotspot, and the younger crust close to the ridge results in the morphology of developing volcanoes being altered.
Foundation Seamounts | Geography
The rocks here were formed by much the same process that the rest of the peninsula was formed; the Pacific plate sliding under the Antarctic Peninsula in an ocean/continent subduction-type tectonic event. This process, called orogenesis, is one of the most common ways for a mountain chain to form. The Andres and the coast ranges of North America are other classic examples of this type of tectonism. The mountain building has nearly stopped though; it is only at the very tip of the peninsula and in the South Shetland Islands that the process continues. For the rest of the peninsula, it erosion and gravity's turn to shape the landscape.
Yalour Islands | Introduction
Most seamounts form at mid-ocean ridges, but hotspots and transform faults can also produce seamounts. These mechanisms cannot really explain the origin of Shimada Seamount, however; it may be part of a hotspot trace. Evidence from core samples around the seamount, the appearance of the summit area, and the presence of thin manganese crusts imply an age of about 10,000 years for some volcanic rocks at Shimada; the rocks are too young to be dated by potassium-argon dating, and all the evidence indicates that volcanic activity at Shimada is of late Quaternary-Holocene age. Possibly alive "Lithothamnium" corals have been dredged from a depth of at Shimada.
Shimada Seamount | Introduction
It might have formed either through erosion of surrounding sediments by ocean currents or through isostatic subsidence.
Anton Dohrn Seamount | Geography and geomorphology
MIT Guyot formed during the Cretaceous about 123 million years ago. Based on paleomagnetic data, the seamount formed at a latitude of 11.5 ± 2.3 degrees south and is at least 118 million years old. A paleolatitude of 32.8 degrees south may also be possible and would be consistent with that of the Macdonald hotspot.
MIT Guyot | Geologic history
The volcano is of Barremian age, the limestones are of Aptian to Albian age. Magnetic traits in the seamount suggest that it formed 140 - 120 million years ago close to a spreading center, which is older than the age of 100 million years inferred from fossils but comparable to ages inferred from radiometric dating. Radiometric dating has yielded ages of 120.4 ± 2.7 million years ago for the eastern and of 117.8 ± 8.4 million years ago for the western side of the seamount. The seamount is thus considered to be 120 - 100 million years old, while the underlying crust is about 20 million years older.
Daiichi-Kashima Seamount | Geological history
The Pacific Ocean contains several long seamount chains, formed by hotspot volcanism. These include the Hawaiian–Emperor seamount chain, the Tasmantid Seamount Chain, the Lord Howe Seamount Chain and the Louisville Ridge.
Geology of the Pacific Ocean | Seamount chains and hotspots
The New England Seamounts were once at or above sea level. As time passed, however, and the chain moved farther away from the New England hotspot, the crust cooled and contracted, and the chain sank into the ocean. All the peaks are now a kilometer or more below the surface.
New England Seamounts | Formation
The Bear Seamount is the first guyot in a chain of about 30 extinct volcanoes extending in a straight line south-eastwards from the edge of the continental shelf near Woods Hole, Massachusetts to north-east of Bermuda. These seamounts resulted from the movement of a mantle plume hotspot. This hotspot is now under the Great Meteor Seamount. The chain rises about above the surrounding Sohm Abyssal Plain. Over time they have been eroded and have developed flat table-like summits surrounded by slopes with an inclination of about 20°. The currents in the vicinity of the Bear Seamount include the warm water Gulf Stream flowing towards the north east, the deep boundary current flowing along the continental shelf towards the south west, and the deep, icy cold Arctic bottom water that flows past the lower flanks of the chain.
Bear Seamount | Formation
The chain formed out of sea sediments in the middle Triassic period, somewhat earlier than the rest of the Apennines, and on a rather different geological structure. Over time, these sediments hardened into limestone, dolomite, sandstone, and shale. Harsh pressure approximately 25 million years ago transformed the limestone in many places into the Carrara marble (named for the nearby city of Carrara) for which the range is renowned. Erosion carved much of the remaining sedimentary rocks into a jagged karst topography. The highest peak is the Monte Pisanino, at .
Apuan Alps | Geology and geography
The New England Seamounts is a chain of over twenty underwater extinct volcanic mountains known as seamounts. This chain is located off the coast of Massachusetts in the Atlantic Ocean and extends over 1,000 km from the edge of Georges Bank. Many of the peaks of these mountains rise over 4,000 m from the seabed. The New England Seamounts chain is the longest such chain in the North Atlantic and is home to a diverse range of deep sea fauna. Scientists have visited the chain on various occasions to survey the geologic makeup and biota of the region. The chain is part of the Great Meteor hotspot track and was formed by the movement of the North American Plate over the New England hotspot.
New England Seamounts | Introduction
Another hypothesized origin of some or all seamounts in the Kodiak-Bowie Seamount chain is that they formed on top of the Explorer Ridge, a divergent tectonic plate boundary west of Vancouver Island, and have been displaced from it by seafloor spreading.
Bowie Seamount | Origins
The mountains are not particularly ancient, despite their old-looking appearance. They are considered middle-aged in geologic terms. They were created when the Falkland Plateau collided with Southern Africa, when Pangaea, the supercontinent formed during the Cambrian-Ordovician periods (from 510 to about 330–350 million years ago). Their stature, with heights varying from 1000m to 2300m, is mostly due to the weather-resistant rocks of quartzitic sandstone of the Peninsula Group (see above). They occur in long parallel ranges each not much more than 10 km wide, separated by equally long valleys with a maximum width of about 50 km (mostly only 15–30 km wide).
Cape Fold Belt | Appearance
This is a 100-to-150-km-wide morphological swell presumably of thickened hotspot generated crust, although there are no seismic refraction data across the swell to define crustal thickness. The crest of one such peak, Patton Seamount originally formed off Washington state as a submerged volcano 33 million years ago. Over time, as the Pacific Plate moved steadily northwest, Patton Seamount has carried off the Bowie hotspot and into the Gulf of Alaska. New volcanoes were formed one after another over the hotspot, creating the Kodiak–Bowie Seamount chain. Explorations of the Kodiak–Bowie Seamount chain have shown that despite the fact that most of the seamounts were created by the Bowie hotspot, all are unique in their size, shape, and volcanic features.
Kodiak–Bowie Seamount chain | Introduction
For hard rock massifs, rugged rock faces (e.g. in the Dolomites) and mighty scree slopes are typical. By contrast, flysch or slate forms gentler mountain shapes and "kuppen" or domed mountaintops, because the rock is not porous, but easily shaped.
Mountain chain | Dominant rocks and mountain forms
The chain-like arrangement of hills in a chain is a consequence of their collective formation by mountain building forces or ice age earth movements. Hill chains generally have a uniform geological age, but may comprise several types of rock or sediment. Hill chains normally form a watershed. They are crossed by roads that often use a natural saddle in the terrain.
Hill chain | Introduction
Guyots show evidence of having once been above the surface, with gradual subsidence through stages from fringed reefed mountain, coral atoll, and finally a flat-topped submerged mountain. Seamounts are made by extrusion of lavas piped upward in stages from sources within the Earth's mantle, usually hotspots, to vents on the seafloor. The volcanism invariably ceases after a time, and other processes dominate. When an undersea volcano grows high enough to be near or breach the ocean surface, wave action and/or coral reef growth tend to create a flat-topped edifice. However, all ocean crust and guyots form from hot magma and/or rock, which cools over time.
Guyot | Formation
The New England hotspot formed the White Mountains 124 to 100 million years ago when the North American continent was directly overhead. As the continent drifted to the west, the hotspot gradually moved offshore. On a southeasterly course, the hotspot formed Bear Seamount, the oldest in the chain, about 100 to 103 million years ago. Over the course of millions of years, it continued creating the rest of the seamounts, eventually culminating in the Nashville Seamount about 83 million years ago. As the Atlantic Ocean continued to spread, the hotspot eventually traveled further east, forming the Great Meteor Seamount where it is found today.
Great Meteor Seamount | Formation
The chain began to form approximately 95,000 years ago, and the volcanic activity that formed the range stopped about 10,000 years ago. The majority of the cones were formed by Strombolian eruptions, and these cones usually have well-defined summit craters. Some have nested craters, and others show broken rims where lava poured through. In contrast, Puy de Dôme was created by a Peléan eruption; this type of eruption is characterized by long dormant periods periodically interrupted by sudden, extremely violent eruptions.
Chaîne des Puys | Formation
This geological lineament may extend all the way to Tonga. Crough seamount was probably formed by the Easter hotspot that also generated Easter Island albeit with the participation of a nearby fracture zone that modified the trend of the hotspot path. In this case the Easter Island-Sala y Gomez ridge and the Crough Seamount would be conjugate volcanic ridges paired across the East Pacific Rise. although it is possible that two separate hotspots were active on the eastern and western side of the East Pacific Rise. Another theory postulates that Crough was formed by its own hotspot, the Crough hotspot.
Crough Seamount | Regional
A conspicuous feature of the chain, as of the adjacent tableland, is the number of its parameras, isolated plateaus shut in by lofty mountains or even by precipitous walls of rock.
Cantabrian Mountains | Geography
Compositionally, the seamount is formed by alkali basalts and hydrothermally altered basalts containing palagonite and plagioclase with additional clay, hyaloclastite and palygorskite; additionally it features biogenic limestone, carbonate sands, carbonate sandstone, corals, foraminifera sands, iron-manganese crusts, muddy sands, sands, shelly debris and volcanic breccia. The volcanic rocks display some geochemical differences between the western ridge and the eastern summit. These iron-manganese crusts can be as much as thick. Vernadite is among the most important components of the iron-manganese crusts, followed by manganese-containing feroxyhyte; additional components are apatite, asbolane, birnessite, buserite, goethite, mica smectite, smectite, palygorskite, quartz, todorokite and zeolites. The formation of the iron-manganese crusts was influenced by hydrothermal activity, when Krylov Seamount was close to the Mid-Atlantic Ridge about 97 million years ago (Cenomanian).
Krylov Seamount | Composition
Undersea mountain ranges are mountain ranges that are mostly or entirely underwater, and specifically under the surface of an ocean. If originated from current tectonic forces, they are often referred to as a "mid-ocean ridge". In contrast, if formed by past above-water volcanism, they are known as a "seamount chain". The largest and best known undersea mountain range is a mid-ocean ridge, the Mid-Atlantic Ridge. It has been observed that, "similar to those on land, the undersea mountain ranges are the loci of frequent volcanic and earthquake activity".
Undersea mountain range | Introduction
The Pacific Ocean is characterized by long island chains, which typically extend from the southeast to the northwest in direction of the motion of the Pacific Plate. Often, such chains begin in the southeast with volcanoes such as Hawaii that become progressively more eroded northwestward and eventually end as series of atolls. This has led to the suggestion that they are formed by deep sources over which the Pacific Plate drifts and eventually carries the volcano away from its magma source. These sources are known as "hotspots", and their total number has been estimated to be between 42 and 117.
Macdonald seamount | Regional setting
Hotspot volcanism results in the formation of isolated mountains and mountain chains that look as if they are not necessarily on present tectonic-plate boundaries, but they are essentially the product of plate tectonism.
Orogeny | Relationship to mountain building
Fold mountains form when two tectonic plates move towards each other at convergent plate boundary. When plates and the continents riding on them collide, the accumulated layers of rock may crumple and fold like a tablecloth that is pushed across a table, particularly if there is a mechanically weak layer such as salt. The mountains such formed are usually more in length instead of breadth.
Fold mountains | Formation
The rim of the summit plateau is formed by volcanic rocks on the eastern part of the seamount and by reefal limestones on the western; the reef deposits form a long ring around the summit platform of Ioah Guyot and cover an area of over . The lower slopes are gentle but steepen between depth. Only the lower slopes are covered with thick sediment layers; the upper slopes have sediment accumulations only in sheltered areas and also feature step-like structures. A number of volcanic cones grew on Ioah and form morphostructures, with a density of about 11.1 vents per .
Ioah Guyot | Geography and geomorphology
The Fogo Seamounts, also called the Fogo Seamount chain, are a group of seamounts located about offshore of Newfoundland and southwest of the Grand Banks of Newfoundland. They consist of basaltic submarine volcanoes that formed during the Early Cretaceous period. The volcanic activity that formed the Fogo Seamounts could have originated in two ways. They may have formed as a result of magma rising along a linear fault zone or from the North American Plate passing over the Canary or Azores hotspots.
Fogo Seamounts | Introduction
The Ōu Mountains began to form in the Pliocene. They sit over the middle of the inner arc of the Northeastern Japan Arc. This is the result of the Pacific Plate subducting under the Okhotsk Plate. A chain of Quaternary volcanoes along the range forms the volcanic front.
Ōu Mountains | Geology
They average ± in volume, but range from to . In addition to the eight main seamounts, there is a scattered disk of minor volcanic cones and flows about southeast of the chain.
President Jackson Seamounts | Introduction
Lava flows or landslide deposits appear to surround a number of the seamounts. A number of processes has been proposed to explain the formation of seamounts close to spreading ridges. In the case of Rano Rahi, both line-like sources and point-like sources of magma may be involved, with a common source of magma that results in a tradeoff between the sizes of neighbouring seamount chains. Seismic tomography has identified low-velocity material beneath the seamounts which may be flows in the mantle. The neighbouring Pukapuka ridge appears to be related to the Rano Rahi seamounts, which are located east of its eastern end and form a wedge-shaped extension thereof.
Rano Rahi seamounts | Geology
Ngatemato seamounts (Name derived from a ruling family in Rapa) are a series of seamounts in the southern Pacific Ocean. These seamounts have the shape of ridges and display calderas. The Aureka () and Make () seamounts are part of the Ngatemato track. Dredged rocks are weakly tholeiitic basalts of Oligocene age. They are about high and wide at their base. Despite being smaller in size than the Macdonald seamounts however the Ngatemato seamounts have larger volumes which is masked by stronger plate deformation; the magma output that created the Ngatemato and Taukina chains when summed up is about .
Ngatemato seamounts | Introduction
Lamont seamount chain is a chain of submarine mountains in the eastern Pacific Ocean which are named "Sasha", "MIB", "MOK", "DTD" and "NEW". They are located close to the East Pacific Rise and reach a minimum depth of . These seamounts are submarine volcanoes of Pleistocene to Holocene age that are usually capped off by summit calderas and craters. They have erupted lava flows of tholeiitic composition; the last eruption may have occurred less than 8,000 years ago.
Lamont seamount chain | Introduction
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 or more from the surrounding seafloor, and with a limited summit area, of conical form. There are more than 14,500 seamounts. 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. Most seamounts are volcanic in origin, and thus tend to be found on oceanic crust near mid-ocean ridges, mantle plumes, and island arcs.
Seamount | Geography
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 Guyot 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 guyots, seamounts with a flat top.
Seamount | Structure
They are formed from mud volcanism. The composition for the seamounts differ in the Izu-Ogasawara Trench and Mariana systems which indicates regional changes in geology.
Mariana Plate | Defining Features
A seamount is a large geologic landform that rises from the ocean floor but that does not reach to the water's 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 in height. They are defined by oceanographers as independent features that rise to at least above the seafloor, characteristically of conical form. The peaks are often found hundreds to thousands of meters below the surface, and are therefore considered to be within the deep sea. During their evolution over geologic time, the largest seamounts may reach the sea surface where wave action erodes the summit to form a flat surface.
Seamount | Introduction
There are thought to be up to an estimated 50,000 seamounts in the Pacific basin. The Hawaiian–Emperor seamount chain is an excellent example of an entire volcanic chain undergoing this process, from active volcanism, to coral reef growth, to atoll formation, to subsidence of the islands and becoming guyots.
Guyot | Formation
The seamount was probably formed by a mantle diapir with eruptions occurring along fissures and in association with the Mid-Atlantic Ridge. It probably began to form no less than 70-75 million years ago, as reefs of that age containing coccoliths, corals and foraminifers have been found on the seamount; they also indicate that the seamount was emergent at that time. The seamount may have risen between above sea level before thermal subsidence lowered it to its current depth. Corals, golden corals, sea stars and sponges have been found at Krylov Seamount.
Krylov Seamount | Geology and geochronology
Nappe or fold mountains, with their roughly parallel mountain chains, generally have a common geological age, but may consist of various types of rock. For example, in the Central Alps, granitic rocks, gneisses and metamorphic slate are found, while to the north and south, are the Limestone Alps. The Northern Limestone Alps are, in turn, followed by soft flysch mountains and the molasse zone. The type of rock influences the appearance of the mountain ranges very markedly, because erosion leads to very different topography depending on the hardness of the rock and its petrological structure. In addition to height and climate, other factors are the layering of the rock, its gradient and aspect, the types of waterbody and the lines of dislocation.
Mountain chain | Dominant rocks and mountain forms
Not all of these hotspots are necessarily fed by a deep continuous mantle plume; some may be nourished by discrete batches of melting material that rise through the mantle. Other chains may be controlled by mantle flow towards a spreading ridge, which has been proposed for the Musicians chain.
Musicians Seamounts | Geologic context
The Pacific Ocean contains several long seamount chains, formed by hotspot volcanism. These include the Hawaiian–Emperor seamount chain and the Louisville Ridge.
Pacific Ocean | Seamount chains
The Southern Atlantic Ocean contains a number of volcanic systems such as the Discovery Seamounts, the Rio Grande Rise, the Shona Ridge and the Walvis Ridge which are commonly attributed to hotspots, although this interpretation has been challenged. The hotspot origin of Discovery and the Walvis-Tristan da Cunha seamount chains was first proposed in 1972. In the case of the Shona Ridge and the Discovery Seamounts, the theory postulates that they formed as the African Plate moved over the Shona hotspot and the Discovery hotspot. It is not clear if a Discovery Hotspot exists, nor whether it is linked in any way to Gough Island or to the Tristan hotspot.
Discovery Seamounts | Geology
The Cobb hotspot has created an underwater mountain range that extends to the northwest and ends at the Aleutian Trench. The oldest mount in the chain is the Marchland Seamount, at 30 to 43 Ma (million years old). The old, northwestern end of the chain collides with a subduction zone; therefore, the true age of the hotspot is difficult to determine as the oceanic crust is being consumed. Axial Seamount is the hotspot's most recent eruptive center, which last erupted in 2015, 2011 and 1998. The central ridge of the hotspot is thicker than the surrounding crust by a few kilometers and may be accumulated buildup from the magma released at the hotspot, which is essentially a submarine volcano with a root in diameter, reaching a depth of beneath the volcano.
Cobb hotspot | Cobb Seamount chain
Patton Seamount was created by the Cobb hotspot, and it lies in the Cobb–Eickelberg Seamount chain. The Cobb chain is unusual in that it is not one individual volcanic chain, but a mosaic of many, created by several hotspots that now lie along the western coast of North America. Patton Seamount lies near the northwestern edge of the chain, in the Gulf of Alaska, and is 33 million years of age, among the oldest in the group. The part of the chain that Patton Seamount lies in is known variably as either the "Gulf of Alaska Seamounts" or the "Patton Seamounts." The Gulf seamounts are the best-known and most heavily studied features in the chain.
Patton Seamount | Geology
Foreland basins form because as the mountain belt grows, it exerts a significant mass on the Earth's crust, which causes it to bend, or flex, downwards. This occurs so that the weight of the mountain belt can be compensated by isostasy at the upflex of the forebulge. The plate tectonic evolution of a peripheral foreland basin involves three general stages. First, the passive margin stage with orogenic loading of previously stretched continental margin during the early stages of convergence. Second, the "early convergence stage defined by deep water conditions", and lastly a "later convergent stage during which a subaerial wedge is flanked with terrestrial or shallow marine foreland basins" (Allen & Allen 2005).
Foreland basin | Formation of basins
While the Clipperton Fracture Zone is located just north, the East Pacific Rise lies east of the seamounts; Sasha Seamount lies just from the Rise. It appears to contain a magma chamber at that latitude and seems to have produced voluminous volcanism that generated a topopgraphic elevation that is now associated with the Lamont seamounts. The volcanism is quite young and accompanied by hydrothermal activity; seafloor spreading here proceeds at a rate of and a volcanic eruption in 2003-2006. The seamounts have produced hyaloclastites, sheet- and lobe-like lava flows as well as pillow lavas and talus. The total volume of each seamount ranges between and the volume increases away from the East Pacific Rise, which along with other patterns indicates a progressive development of the seamount as they move away from the East Pacific Rise.
Lamont seamount chain | Geology
Seamounts are created at hot spots. These are isolated areas within tectonic plates where plumes of magma rise through the crust and erupt at the surface. This creates a chain of submarine volcanoes and seamounts. The Cobb hot spot is located at the Juan de Fuca Ridge in the Pacific Ocean. The Pacific Plate is moving north-westward direction at a speed of ~5.5 cm per year. Periodic volcanic events have led to magma eruption onto the seafloor, forming seamounts. The last known volcanic activity was at Axial Seamount, which is currently directly overlying the hot spot. The total magmatic flux from the Cobb Hot Spot is about 0.3 cubic m/yr.
Cobb–Eickelberg Seamount chain | Formation
The New England hotspot, also referred to as the Great Meteor hotspot, formed the White Mountains 124 to 100 million years ago when the North American continent was directly over the zone. As the continent drifted to the west, the hotspot gradually moved offshore. On a southeasterly course, the hotspot formed Bear Seamount, the oldest seamount in the chain, about 100 to 103 million years ago. Over the course of millions of years, the hotspot continued to create the other seamounts in the chain, culminating about 83 million years ago with the creation of the Nashville Seamount. As the Atlantic Ocean continued to spread, the hotspot eventually "travelled" further east, forming the Great Meteor Seamount south of the Azores, where it is located today.
New England Seamounts | Formation
This fault, which appears to be split in two or three subsidiary faults separated by grabens, extends past the Daiichi-Kashima seamount and covers a length of ; evidently Daiichi-Kashima has been split in half by the fault, which is much younger than the ocean floor and moved at a rate of but does not appear to be presently active in light of the sediment cover on the scarp. Aside from a normal motion, the western half of the seamount has also been moved away from the eastern half and is tilted west. The seamount appears to be part of a seamount chain called Joban Seamount Chain or Kashima-Ryofu No.1 that formed during the Cretaceous in the Equatorial Pacific and about 30° south of their present-day position.
Daiichi-Kashima Seamount | Local
The Hawaiian–Emperor seamount chain is a mostly undersea mountain range in the Pacific Ocean that reaches above sea level in Hawaii. It is composed of the Hawaiian ridge, consisting of the islands of the Hawaiian chain northwest to Kure Atoll, and the Emperor Seamounts: together they form a vast underwater mountain region of islands and intervening seamounts, atolls, shallows, banks and reefs along a line trending southeast to northwest beneath the northern Pacific Ocean. The seamount chain, containing over 80 identified undersea volcanoes, stretches about from the Aleutian Trench in the far northwest Pacific to the Loʻihi seamount, the youngest volcano in the chain, which lies about southeast of the Island of Hawaiʻi.
Hawaiian–Emperor seamount chain | Introduction
Most seamounts are built by one of two volcanic processes, although some, such as the Christmas Island Seamount Province near Australia, are more enigmatic. Volcanoes near plate boundaries and mid-ocean ridges are built by decompression melting of rock in the upper mantle. The lower density magma rises through the crust to the surface. Volcanoes formed near or above subducting zones are created because the subducting tectonic plate adds volatiles to the overriding plate that lowers its melting point. Which of these two process involved in the formation of a seamount has a profound effect on its eruptive materials. Lava flows from mid-ocean ridge and plate boundary seamounts are mostly basaltic (both tholeiitic and alkalic), whereas flows from subducting ridge volcanoes are mostly calc-alkaline lavas.
Seamount | Geochemistry and evolution
The Appalachian Mountain chain was formed starting around 420 million years ago with the collision of the North American craton and the Iapetus Ocean and culminating with the collision of the modern-day eastern seaboard of the then Euramerican continent with Africa, then Gondwana, about 290 million years ago forming the supercontinent Pangea. Since the collision event the mountains have been eroding from the break-up of Pangea and through sedimentation formed the coastal plains to the east and limestone plateaus to the west. The footprints of the mountains formed the ridge and valley geological region in which Penns Valley was formed through glacial and other activity.
Penns Valley | History
The mountain range contains a series of cirques formed by glaciers. Many cirques developed in the Pleistocene Epoch from isolated glaciers that existed separedly from ice sheets further west. The rocks of Sierra Baguales belong to various formations of Magallanes Basin. These rocks contain fossils of plants, mammals and marine invertebrates.
Sierra Baguales | Geology
Between 200,000 and 700,000 years ago, the hotspot was encroached by the tectonic spreading center, displacing it by as much as and building up the long Juan de Fuca Ridge. At least 7 spreading centers have been recognized, and plate measurements near Axial show that the ridge is separating at a rate of per year, producing a complex system of oceanic basins and ridges. However some scientists have questioned this theory, pointing out that the high density of the chain's overlapping seamounts is incompatible with such an origin, as a hotspot would form a well organized, widely spaced chain. Although the exact nature of Axial Seamount remains unknown, its complex origins makes it one of the most geologically interesting features in the North Pacific.
Axial Seamount | Tectonic setting
Daiichi-Kashima Seamount is a guyot in the Pacific Ocean off Japan. It is about high and reaches a depth of . Daiichi-Kashima formed during the Barremian as a result of volcanic activity; during the Albian reefs formed on the seamount and generated a limestone cap. The seamount later. The seamount has been approaching the Japan Trench and a noticeable vertical offset of about between the eastern and western halves of Daiichi-Kashima appears to be the result of normal faulting as the seamount enters the trench, with the western half dropping down; it may also reflect a past sector collapse when the volcano was still active.
Daiichi-Kashima Seamount | Introduction
Volcanic belts are similar to a mountain range, but the mountains within the mountain range are volcanoes, not mountains that are formed by faulting and folding by the collision of tectonic plates.
Volcanic belt | Introduction
The region is in the Ridge and Valley Province of the Appalachian Mountains. The province consists of a thick layer of sedimentary rock that has undergone folding and/or faulting to create a series of ridges and valleys. During the sedimentation process fossils were formed leaving evidence of life existing millions of years ago. The fossils can be seen in rock exposures throughout the mountains.
Mountain Lake Wilderness Cluster | Geologic history
Today, the remains of this chain can be seen in the Fall Line region in the Eastern United States. Some remnants can also be found in the later formed Appalachians in North America.
Atlas Mountains | Geology
Bear Seamount rises approximately above the surrounding seabed and the roughly flat summit is about below the surface of the sea. The top is covered by a deep layer of sediment through which basaltic rocks and erratic boulders protrude. Much of this material has fallen from above, probably from icebergs that drifted southwards during the Pleistocene.
Bear Seamount | Formation
Geologically the Fichtel massif consists mainly of granite. The history of its orogeny begins in the Precambrian Eon about 750–800 million years ago. From that time only the truncated uplands of the once-towering mountain chain are left. Subsequently, the area was covered by sea, and rivers transported sediments from the old eroding mountains on the coast. These sediments were deposited as layers of clay, sand and limestone. At the beginning of the Cambrian Period, about 570 million years ago, these beds were folded and raised up to form new mountains. High temperatures and pressure during this mountain folding process, which lasted into the Upper Carboniferous Period, created metamorphic rock.
Fichtel Mountains | Early mountain building
The crust underneath these seamounts tends to subside as it cools, and thus the islands and seamounts sink. Continued subsidence balanced by upward growth of the reefs led to the formation of thick carbonate platforms. Sometimes volcanic activity continued even after the formation of the atoll or atoll-like structure, and during episodes where the platforms rose above sea level erosional features such as channels and blue holes developed. The formation of many seamounts has been explained by the hotspot theory, which suggests that the chains of volcanoes become progressively older along the length of the chain, with an erupting volcano only at one end of the system.
Resolution Guyot | Regional setting
Foundation Seamounts are a series of seamounts in the southern Pacific Ocean. Discovered in 1992, these seamounts form a long chain which starts from the Pacific-Antarctic Ridge. Some of these seamounts may have once emerged from the ocean. The Foundation Seamounts were probably formed by a now-weakening mantle plume called the Foundation hotspot that is located close to the Pacific-Antarctic Ridge. It is possible that this hotspot generated additional volcanoes, such as the Ngatemato and Taukina seamounts farther west. The oldest volcanism on the Foundation Seamounts occurred 21 million years ago, while the youngest volcanism appears to be hydrothermal venting and the eruption of a lava flow between 1997-2001 where the Foundation Seamounts intersect the Pacific-Antarctic Ridge.
Foundation Seamounts | Introduction
The mountain completely surrounds Burkes Garden, an unusual geologic formation. From above Burke's Garden looks like the remnant of a volcano or a large lake. It is about 10 miles long and 5 miles wide (16 × 8 km). Called the Great Swamp by native Americans, it was probably too wet for crops. There are several proposals about its creation. One claims the valley was a lake drained by a creek, Burke's Garden Creek, flowing through the gap on the western edge. Another claims it was a dome formed by a sandstone cap. Eroded by water, the cap cracked forming a flat valley below.
Garden Mountain Cluster | Geologic history
Movements of tectonic plates create volcanoes along the plate boundaries, which erupt and form mountains. A "volcanic arc system" is a series of volcanoes that form near a subduction zone where the crust of a sinking oceanic plate melts and drags water down with the subducting crust. Most volcanoes occur in a band encircling the Pacific Ocean (the Pacific Ring of Fire), and in another that extends from the Mediterranean across Asia to join the Pacific band in the Indonesian Archipelago. The most important types of volcanic mountain are "composite cones" or "stratovolcanoes" (Vesuvius, Kilimanjaro and Mount Fuji are examples) and "shield volcanoes" (such as Mauna Loa on Hawaii, a hotspot volcano).
Mountain formation | Volcanic mountains
He and other Swiss geologists now started mapping the nappes of Switzerland in more detail. From that moment on, geologists began recognizing large thrusts in many mountain chains around the world. However, it was still not understood where the huge forces that moved the nappes came from. Only with the arrival of plate tectonic theory in the 1950s an explanation was found. In plate tectonics, the horizontal movement of tectonic plates over the Earth's soft asthenosphere causes horizontal forces within the crust. Presently, geologists believe most mountain chains are formed by convergent movements between tectonic plates.
Glarus thrust | History
The Lord Howe Seamount Chain is defined by coral-capped guyots stretching to the north of the island for and including the Middleton ( away) and Elizabeth ( away) reefs of the Elizabeth and Middleton Reefs Marine National Park Reserve. This chain of nine volcanic peaks was probably produced by the northward movement of the Indo-Australian Plate over a stationary hotspot, so the oldest guyots were the first formed and most northerly as the plate moved northward at a rate of per year (see plate tectonics).
Lord Howe Island | Geological origins
and Henry D. Rogers showed, in 1847, that the ridge and valley system in the western part of the Appalachians was caused by erosion of large anticlines and synclines. Similar folds exist in almost all mountain chains, but nowhere as pronounced as in this area of the Appalachians. A system of parallel anticlines and synclines has become known as an “Appalachian Structure”. Brushy Mountain and Hogback Mountain are principal ridges in the cluster. Brushy Mountain, one of the broad ridges composing the Ridge and Valley formation, is capped by Mississippian Price sandstone. Hogback Mountain is another ridge running parallel to Brushy Mountain on the west.
Kimberling Creek Cluster | Geologic history
This deep depression may be a volcanic crater but the more likely explanation is that the rim was formed by living organisms. The whole summit plateau covers an area of and the total volume of the seamount is about . Dredging has yielded no volcanic material, but chert, limestones (in the form of grainstone, packstone and wackestone) encrusted with ferromanganese as well as living animals were pulled up. The seafloor underneath the guyot lies at a depth of and has an age of 157 million years.
Darwin Guyot | Geography and geomorphology
The Lamont seamounts probably formed within the last 400,000 years. While the ages of the seamounts are not known, they are by necessity younger than the underlying 740,000 - 100,000 years old seafloor; the lack of sediment cover and thick ferromanganese deposits as well as the youthful appearance of lava flows also speaks for a young age although there is no evidence of hydrothermal activity, past or present. The reflectance of the seafloorm has been used to infer increasing ages from 33,000 years at Sasha to 230,000 at "MOK". Radiocarbon dating of foraminifera encased in lava flows of "NEW" seamount has yielded an age of 18,540 ± 216 radiocarbon years ago, indicating recent activity; additionally, a sample from Sasha seamount may be less than 8,000 years old on the basis of a radium-thorium isotope disequilibrium.
Lamont seamount chain | Geochronology
This is a list of Seamounts in the Southern Ocean. 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, islet or Cliff-rock. Seamounts are typically formed from extinct volcanoes that rise abruptly and are usually found rising from the seafloor to in height. They are defined by oceanographers as independent features that rise to at least above the seafloor, characteristically of conical form.
List of seamounts in the Southern Ocean | Introduction
Hotspots may also be formed by cracks propagating in the crust, and such hotspots would not necessarily show an age progression.
Macdonald seamount | Regional setting
Hebrides Terrace Seamount is a seamount in the Atlantic Ocean, west-southwest from the Hebrides, Scotland. It formed through volcanism during the early Cenozoic in the Rockall Trough 60 million to 67 million years ago and afterwards sank below sea level. Presently, it is a flat-topped underwater mountain that rises to about 980 metres (3,220 ft) depth. "Coral gardens" that host a number of animals are found on its slopes.
Hebrides Terrace Seamount | Introduction
Many longitudinal valleys follow the strike of the rock strata or significant geological fault lines. These are formed in conjunction with the tectonic movements during mountain building, which in turn are due to plate tectonic processes. The faults are structures that reach deep into the lower part of the Earth's crust, which is already in place before the actual mountain building phase and is later reactivated. The Periadriatic Seam in the Alps is a good example of this. In the formation of longitudinal valleys, however, nappe overthrusts also play a major, if not the most important, role. The nappes that are present in many young fold mountain ranges are responsible to a large extent for the morphological division of a mountain belt into parallel chains.
Longitudinal valley | Description
When plates collide or undergo subduction (that is – ride one over another), the plates tend to buckle and fold, forming mountains. Most of the major continental mountain ranges are associated with thrusting and folding or orogenesis. Examples are the Balkan Mountains, the Jura and the Zagros mountains.
Mountain formation | Fold mountains
The seamount splits an old peridotite block, the remains of which project on either side of the ridge, and fills the rift valley in between, resulting in a double-peaked volcano sitting on the SWIR. East of the seamount (11°30'-10°24'E) there is a 180 km-long and 4,200 m-deep amagmatic segment. Reaching a maximum depth of 4,700 m, its deepest part has a rough floor void of signs of recent volcanism but filled with irregular horst blocks partially made of serpentinised peridotite.
Southwest Indian Ridge | Bouvet TJ–Andrew Bain TF
These tops must be or more below the surface of the sea; the diameters of these flat summits can be over . Knolls are isolated elevation spikes measuring less than . Lastly, pinnacles are small pillar-like seamounts.
Seamount | Structure
The Western Pacific Ocean features many seamounts with flat tops at depths of below sea level which are known as guyots. They were considered to be remnants of eroded islands before Cretaceous carbonate platforms were discovered on them which resemble present-day atolls although they do not have exactly the same properties. Later similar submarine mountains were identified elsewhere in the Pacific Ocean as well. Menard 1958 suggested that the Western Pacific guyots once were part of an elevated region known as the Darwin Rise, later compared to present day French Polynesia. Many of these seamounts originally formed in the South Pacific, such as in French Polynesia, where a number of recent volcanoes and volcanic chains can be found.
Takuyo-Daisan | Regional
Sometimes volcanic activity occurred even after the formation of the atoll or atoll-like landforms, and during episodes where the carbonate platforms were lifted above sea level erosional features such as channels and blue holes developed. The crust underneath these seamounts tends to subside as it cools and thus the islands and seamounts sink. The formation of many such seamounts including Limalok has been explained with the hotspot theory, which discusses the formation of chains of volcanoes which get progressively older along the length of the chain, with an active volcano only at one end of the system. Seamounts and islands in the Marshall Islands do not appear to have originated from such simple age-progressive hotspot volcanism as the age progressions in the individual island and seamount chains are often inconsistent with a hotspot origin.
Lo-En | Regional setting
They are formed by a volcanic field, containing Pleistocene-to-Holocene lava domes and cinder cones. The highland reaches a height of 1800–2000m up to 3000m in the dividing ridge.
Gegham mountains | Introduction
Discovery Seamounts are a chain of seamounts in the Southern Atlantic Ocean, which include the Discovery Seamount. The seamounts lie east of Gough Island and once rose above sea level. Various volcanic rocks as well as glacial dropstones and sediments have been dredged from the seamounts. The Discovery Seamounts appear to be a volcanic seamount chain controlled by the Discovery hotspot, which had its starting point either in the ocean, Cretaceous kimberlite fields in southern Namibia or the Karoo-Ferrar large igneous province. The seamounts formed between 41 and 35 million years ago; presently the hotspot is thought to lie southwest of the seamounts, where there are geological anomalies in the Mid-Atlantic Ridge that may reflect the presence of a neighbouring hotspot.
Discovery Seamounts | Introduction