The Ilgachuz Range is a name given to an extinct shield volcano in British Columbia, Canada. It is not a mountain range in the normal sense, because it was formed as a single volcano, eroded for the past 5 million years, it lies on the Chilcotin Plateau, located some 350 kilometres north-northwest of Vancouver and 30 km north of Anahim Lake. The highest peak of the range is Far Mountain; the range supports a unique grassland ecosystem. This type of grassland has not been seen anywhere else in southern British Columbia; the climate is dry. The 280 kilometres long West Road River rises in the Ilgachuz Range and flows east to its confluence with the Fraser River between Prince George and Quesnel, it drains an area of 12,000 km2, dropping over 900 m before joining with the Fraser. The Ilgachuz Range began erupting 6.1 million years ago and has grown since then. Like all of the Anahim volcanoes, the Ilgachuz Range has its origins in the Anahim hotspot—a plume of magma rising from the Earth's mantle in central British Columbia.
The hotspot remains in a fixed position, while the North American Plate drifts over it at a rate of 2 to 3.3 centimetres per year. The upwelling of the hot magma creates volcanoes, each individual volcano erupts for a few million years before the movement of the plate carries it away from the rising magma. However, where hotspots occur under continental crust, basaltic magma is trapped in the less dense continental crust, heated and melts to form rhyolites. Due to their high content of crystals and gasses, rhyolites initiate violent eruptions, though their water content is low and they have a low temperature; the hotspot has existed for at least 13 million years, the Anahim Volcanic Belt stretches 600 kilometres away from the hotspot. More the hotspot has formed the Itcha Range and Nazko Cone, a cinder cone east of the Ilgachuz Range and the youngest Anahim volcano; the Ilgachuz Range is the largest of these, although the Rainbow Range is the largest of all volcanoes in the Anahim Volcanic Belt.
The first recorded ascent of the Ilgachuz Range was by Chilcotin tribes. They have lived in the area for hundreds of years, travelling when necessary to hunt and trap animals such as beaver, moose, to gather plants and roots. Fishing camps were established in the area; the Ilgachuz Range is, or was, an important source of obsidian for the South Carrier and Chilcotin tribes. Obsidian was desired because sharp arrowheads and cutting knives could be made from it. Like all glass and some other types of occurring rocks, obsidian breaks with a characteristic conchoidal fracture, creating razorlike edges, it was used for jewelry. Anahim obsidian was traded extensively throughout the BC Interior and up and down the Coast from Bella Coola. Red ochre used in paint and decoration was obtained from this area; the Ilgachuz Range is the second largest shield volcano in the Anahim Volcanic Belt which includes other nearby ranges, the Rainbow Range and Itcha Range. It stands at 2,410 metres above sea level - shorter than its neighbor, Rainbow Range.
It has a diameter of 25 km. The Ilgachuz Range was created by two chemically separate magmatic periods. Evacuation of the volcano's magma chamber resulted in the failure of one or more centrally located calderas, it is divided into Dome Forming, Intra Caldera and Shield Forming assemblages. The Precaldera Assemblage is best exposed on the east side of Pipe Organ Mountain where it contains a bedded pile over 300 m thick of weakly consolidated, moderately to different, pyroclastics and deposits of uncertain origin. Colours range from mottled green to grey, ochre and white. A green tuffbreccia composed of pumice fragments, feldspar crystals and minor debris is recognizable in several areas; the Dome Forming Assemblages include most of the rhyolite domes, related flows and the Ilgachuz Comendite. The northerly domes are subcircular talus mounds of plate sized pieces of light to dark grey porphyritic, flowbanded rhyolite with minor obsidian. Massive to banded chalcedony blobs and veinlets are related with these domes.
The southern domes are somewhat different in nature, comprising intrusive and extrusive phases of cream colored porphyries. The Sax Dome contains an upper portion of cream coloured, aphanitic to fine quartz porphyry felsite with abnormal green glass filled fractures, a lower unit of microsyenite with red and green glassy zenocrysts; the Intra Caldera Assemblage is best exposed on the north edge of the caldera. The lower unit, indicative of caldera formation, is an epiclastic boulder-landslide deposit bedded and dipping into the caldera. Similar material, grading up into finer debris flows and lahars, has been uncertainly known in the gap between Phacelia Peak and Calliope Mountain suggesting this area is the southern edge of the caldera. Alternatively unsorted breccia and debris deposits exist on the ridge north of Saxifraga Peak indicating the main, or a subsidiary, caldera edge; the Shield Forming Assemblage contains a series of basalt and minor comendite eruptions, is best exposed on Far Mountain and Mount Scot.
The basalts issued from fissure vents located peripheral to the calderas. Brick red cinder deposits are considered to be a late phase of this assemblage. Surrounding and including the range is Itcha Ilgachuz Provincial Park, a 112
John Tuzo Wilson
John Tuzo Wilson, CC, OBE, FRS, FRSC, FRSE was a Canadian geophysicist and geologist who achieved worldwide acclaim for his contributions to the theory of plate tectonics. Plate tectonics is the idea that the rigid outer layers of the Earth, the lithosphere, are broken up into numerous pieces or "plates" that move independently over the weaker asthenosphere. Wilson maintained that the Hawaiian Islands were created as a tectonic plate shifted to the northwest over a fixed hotspot, spawning a long series of volcanoes, he conceived of the transform fault, a major plate boundary where two plates move past each other horizontally. His name was given to two young Canadian submarine volcanoes called the Tuzo Wilson Seamounts; the Wilson cycle of seabed expansion and contraction bears his name. Wilson's father was of Scottish descent and his mother was a third-generation Canadian of French descent, he was born in Ontario. He became one of the first people in Canada to receive a degree in geophysics, graduating from Trinity College at the University of Toronto in 1930.
He obtained various other related degrees from Cambridge. His academic years culminated in his obtaining a doctorate in geology in 1936 from Princeton University. After completing his studies, Wilson enlisted in the Canadian Army and served in World War II, he retired from the army with the rank of Colonel. John Tuzo Wilson was President of the International Union of Geophysics. In 1969, he was made an Officer of the Order of Canada and was promoted to the rank of Companion of that order in 1974. Wilson was awarded the John J. Carty Award from the National Academy of Sciences in 1975. In 1978, he was awarded the Wollaston Medal of the Geological Society of London and a Gold Medal by the Royal Canadian Geographical Society, he served as honorary vice president of the RCGS. He was a Fellow of the Royal Society, the Royal Society of Canada, of the Royal Society of Edinburgh, he was the Principal of Erindale College at the University of Toronto and was the host of the television series The Planet of Man.
He was elected President of the American Geophysical Union. He served as the Director General of the Ontario Science Centre from 1974 to 1985, he and his plate tectonic theory are commemorated on the grounds outside by the Centre by a giant "immovable" spike indicating the amount of continental drift since Wilson's birth. The John Tuzo Wilson Medal of the Canadian Geophysical Union recognizes achievements in geophysics, he is commemorated by a named memorial professorship and an eponymous annual public lecture delivered at the University of Toronto. He is one of the 2016 inductees into Legends Row: Mississauga Walk of Fame. Wilson was an avid traveller and took a large number of photographs during his travels to many destinations, including European countries, parts of the USSR, the southern Pacific, to both polar regions. Although many of his photos are geological—details of rocks and their structures or panoramas of large formations—the bulk of his photos are of the places and people that he saw on his travels: landscapes, city views, sites, vehicles and fauna, occupations and people.
Wilson, Tuzo. "Cabot Fault, An Appalachian Equivalent of the San Andreas and Great Glen Faults and some Implications for Continental Displacement". Nature. 195: 135–138. Bibcode:1962Natur.195..135W. Doi:10.1038/195135a0. Wilson, J. Tuzo. "Evidence from Islands on the Spreading of Ocean Floors". Nature. 197: 536–538. Bibcode:1963Natur.197..536W. Doi:10.1038/197536a0. Wilson, J. Tuzo. "A Possible Origin of the Hawaiian Islands". Canadian Journal of Physics. 41: 863–870. Bibcode:1963CaJPh..41..863W. Doi:10.1139/p63-094. Wilson, J. Tuzo. "A new Class of Faults and their Bearing on Continental Drift". Nature. 207: 343–347. Bibcode:1965Natur.207..343W. Doi:10.1038/207343a0. Vine, F. J.. "Magnetic Anomalies over a Young Oceanic Ridge off Vancouver Island". Science. 150: 485–9. Bibcode:1965Sci...150..485V. CiteSeerX 10.1.1.473.7395. Doi:10.1126/science.150.3695.485. PMID 17842754. Wilson, J. Tuzo. "Did the Atlantic close and re-open?". Nature. 211: 676–681. Bibcode:1966Natur.211..676W. Doi:10.1038/211676a0. Wilson, J. Tuzo. "Are the structures of the Caribbean and Scotia arc regions analogous to ice rafting?".
Earth and Planetary Science Letters. 1: 335–338. Bibcode:1966E&PSL...1..335T. Doi:10.1016/0012-821X90019-7. Wilson, J. Tuzo. "A Revolution in Earth Science". Geotimes. Washington DC. 13: 10–16. Wilson, J. Tuzo. "Du Toit, Alexander Logie". Dictionary of Scientific Biography. 4. Pp. 261–263. List of geophysicists Science and technology in Canada Supercontinent cycle "J. Tuzo Wilson". GSA Today, Rock Stars. September 2001. Retrieved October 14, 2013. West, Gordon F.. "John Tuzo Wilson: a man who moved mountains". Canadian Journal of Earth Sciences. 51: xvii–xxxi. Bibcode:2014CaJES..51D..17W. Doi:10.1139/cjes-2013-0175. The life of John Tuzo Wilson, history pages, Department of Physics, University of Toronto; the Tuzo Wilson Lecture, an annual public lecture given at the University of Toronto. The J. Tuzo Wilson Professorship, a named memorial professorship at the University of Toronto. Travel Photographs of J. Tuzo Wilson
Alaska is a U. S. state in the northwest extremity of North America, just across the Bering Strait from Asia. The Canadian province of British Columbia and territory of Yukon border the state to the east and southeast, its most extreme western part is Attu Island, it has a maritime border with Russia to the west across the Bering Strait. To the north are the Chukchi and Beaufort seas—southern parts of the Arctic Ocean; the Pacific Ocean lies to southwest. It is the largest U. S. state by the seventh largest subnational division in the world. In addition, it is the most sparsely populated of the 50 United States. Half of Alaska's residents live within the Anchorage metropolitan area. Alaska's economy is dominated by the fishing, natural gas, oil industries, resources which it has in abundance. Military bases and tourism are a significant part of the economy; the United States purchased Alaska from the Russian Empire on March 30, 1867, for 7.2 million U. S. dollars at two cents per acre. The area went through several administrative changes before becoming organized as a territory on May 11, 1912.
It was admitted as the 49th state of the U. S. on January 3, 1959. The name "Alaska" was introduced in the Russian colonial period when it was used to refer to the Alaska Peninsula, it was derived from an Aleut-language idiom. It means object to which the action of the sea is directed. Alaska is the northernmost and westernmost state in the United States and has the most easterly longitude in the United States because the Aleutian Islands extend into the Eastern Hemisphere. Alaska is the only non-contiguous U. S. state on continental North America. It is technically part of the continental U. S. but is sometimes not included in colloquial use. S. called "the Lower 48". The capital city, Juneau, is situated on the mainland of the North American continent but is not connected by road to the rest of the North American highway system; the state is bordered by Yukon and British Columbia in Canada, to the east, the Gulf of Alaska and the Pacific Ocean to the south and southwest, the Bering Sea, Bering Strait, Chukchi Sea to the west and the Arctic Ocean to the north.
Alaska's territorial waters touch Russia's territorial waters in the Bering Strait, as the Russian Big Diomede Island and Alaskan Little Diomede Island are only 3 miles apart. Alaska has a longer coastline than all the other U. S. states combined. Alaska is the largest state in the United States by total area at 663,268 square miles, over twice the size of Texas, the next largest state. Alaska is larger than all but 18 sovereign countries. Counting territorial waters, Alaska is larger than the combined area of the next three largest states: Texas and Montana, it is larger than the combined area of the 22 smallest U. S. states. There are no defined borders demarcating the various regions of Alaska, but there are six accepted regions: The most populous region of Alaska, containing Anchorage, the Matanuska-Susitna Valley and the Kenai Peninsula. Rural unpopulated areas south of the Alaska Range and west of the Wrangell Mountains fall within the definition of South Central, as do the Prince William Sound area and the communities of Cordova and Valdez.
Referred to as the Panhandle or Inside Passage, this is the region of Alaska closest to the rest of the United States. As such, this was where most of the initial non-indigenous settlement occurred in the years following the Alaska Purchase; the region is dominated by the Alexander Archipelago as well as the Tongass National Forest, the largest national forest in the United States. It contains the state capital Juneau, the former capital Sitka, Ketchikan, at one time Alaska's largest city; the Alaska Marine Highway provides a vital surface transportation link throughout the area, as only three communities enjoy direct connections to the contiguous North American road system. Designated in 1963; the Interior is the largest region of Alaska. Fairbanks is the only large city in the region. Denali National Park and Preserve is located here. Denali is the highest mountain in North America. Southwest Alaska is a sparsely inhabited region stretching some 500 miles inland from the Bering Sea. Most of the population lives along the coast.
Kodiak Island is located in Southwest. The massive Yukon–Kuskokwim Delta, one of the largest river deltas in the world, is here. Portions of the Alaska Peninsula are considered part of Southwest, with the remaining portions included with the Aleutian Islands; the North Slope is tundra peppered with small villages. The area is known for its massive reserves of crude oil, contains both the National Petroleum Reserve–Alaska and the Prudhoe Bay Oil Field; the city of Utqiagvik known as Barrow, is the northernmost city in the United States and is located here. The Northwest Arctic area, anchored by Kotzebue and containing the Kobuk River valley, is regarded as being part of this region. However, the respective Inupiat of the No
A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, gases to escape from a magma chamber below the surface. Earth's volcanoes occur because its crust is broken into 17 major, rigid tectonic plates that float on a hotter, softer layer in its mantle. Therefore, on Earth, volcanoes are found where tectonic plates are diverging or converging, most are found underwater. For example, a mid-oceanic ridge, such as the Mid-Atlantic Ridge, has volcanoes caused by divergent tectonic plates whereas the Pacific Ring of Fire has volcanoes caused by convergent tectonic plates. Volcanoes can form where there is stretching and thinning of the crust's plates, e.g. in the East African Rift and the Wells Gray-Clearwater volcanic field and Rio Grande Rift in North America. This type of volcanism falls under the umbrella of "plate hypothesis" volcanism. Volcanism away from plate boundaries has been explained as mantle plumes; these so-called "hotspots", for example Hawaii, are postulated to arise from upwelling diapirs with magma from the core–mantle boundary, 3,000 km deep in the Earth.
Volcanoes are not created where two tectonic plates slide past one another. Erupting volcanoes can pose many hazards, not only in the immediate vicinity of the eruption. One such hazard is that volcanic ash can be a threat to aircraft, in particular those with jet engines where ash particles can be melted by the high operating temperature. Large eruptions can affect temperature as ash and droplets of sulfuric acid obscure the sun and cool the Earth's lower atmosphere. Volcanic winters have caused catastrophic famines; the word volcano is derived from the name of Vulcano, a volcanic island in the Aeolian Islands of Italy whose name in turn comes from Vulcan, the god of fire in Roman mythology. The study of volcanoes is sometimes spelled vulcanology. At the mid-oceanic ridges, two tectonic plates diverge from one another as new oceanic crust is formed by the cooling and solidifying of hot molten rock; because the crust is thin at these ridges due to the pull of the tectonic plates, the release of pressure leads to adiabatic expansion and the partial melting of the mantle, causing volcanism and creating new oceanic crust.
Most divergent plate boundaries are at the bottom of the oceans. Black smokers are evidence of this kind of volcanic activity. Where the mid-oceanic ridge is above sea-level, volcanic islands are formed. Subduction zones are places where two plates an oceanic plate and a continental plate, collide. In this case, the oceanic plate subducts, or submerges, under the continental plate, forming a deep ocean trench just offshore. In a process called flux melting, water released from the subducting plate lowers the melting temperature of the overlying mantle wedge, thus creating magma; this magma tends to be viscous because of its high silica content, so it does not attain the surface but cools and solidifies at depth. When it does reach the surface, however, a volcano is formed. Typical examples are the volcanoes in the Pacific Ring of Fire. Hotspots are volcanic areas believed to be formed by mantle plumes, which are hypothesized to be columns of hot material rising from the core-mantle boundary in a fixed space that causes large-volume melting.
Because tectonic plates move across them, each volcano becomes dormant and is re-formed as the plate advances over the postulated plume. The Hawaiian Islands are said to have been formed in such a manner; this theory, has been doubted. The most common perception of a volcano is of a conical mountain, spewing lava and poisonous gases from a crater at its summit; the features of volcanoes are much more complicated and their structure and behavior depends on a number of factors. Some volcanoes have rugged peaks formed by lava domes rather than a summit crater while others have landscape features such as massive plateaus. Vents that issue volcanic material and gases can develop anywhere on the landform and may give rise to smaller cones such as Puʻu ʻŌʻō on a flank of Hawaii's Kīlauea. Other types of volcano include cryovolcanoes on some moons of Jupiter and Neptune. Active mud volcanoes tend to involve temperatures much lower than those of igneous volcanoes except when the mud volcano is a vent of an igneous volcano.
Volcanic fissure vents are linear fractures through which lava emerges. Shield volcanoes, so named for their broad, shield-like profiles, are formed by the eruption of low-viscosity lava that can flow a great distance from a vent, they do not explode catastrophically. Since low-viscosity magma is low in silica, shield volcanoes are more common in oceanic than continental settings; the Hawaiian volcanic chain is a series of shield cones, they are common in Iceland, as well. Lava domes are built by slow eruptions of viscous lava, they are sometimes formed within the crater of a previous volcanic eruption, as in the case of Mount Saint Helen
Magma is the molten or semi-molten natural material from which all igneous rocks are formed. Magma is found beneath the surface of the Earth, evidence of magmatism has been discovered on other terrestrial planets and some natural satellites. Besides molten rock, magma may contain suspended crystals and gas bubbles. Magma is produced by melting of the mantle and/or the crust at various tectonic settings, including subduction zones, continental rift zones, mid-ocean ridges and hotspots. Mantle and crustal melts migrate upwards through the crust where they are thought to be stored in magma chambers or trans-crustal crystal-rich mush zones. During their storage in the crust, magma compositions may be modified by fractional crystallization, contamination with crustal melts, magma mixing, degassing. Following their ascent through the crust, magmas may feed a volcano or solidify underground to form an intrusion. While the study of magma has relied on observing magma in the form of lava flows, magma has been encountered in situ three times during geothermal drilling projects—twice in Iceland, once in Hawaii.
Most magmatic liquids are rich in silica. Silicate melts are composed of silicon, aluminium, magnesium, calcium and potassium; the physical behaviours of melts depend upon their atomic structures as well as upon temperature and pressure and composition. Viscosity is a key melt property in understanding the behaviour of magmas. More silica-rich melts are more polymerized, with more linkage of silica tetrahedra, so are more viscous. Dissolution of water drastically reduces melt viscosity. Higher-temperature melts are less viscous. Speaking, more mafic magmas, such as those that form basalt, are hotter and less viscous than more silica-rich magmas, such as those that form rhyolite. Low viscosity leads to less explosive eruptions. Characteristics of several different magma types are as follows: Ultramafic SiO2 < 45% Fe–Mg > 8% up to 32%MgO Temperature: up to 1500°C Viscosity: Very Low Eruptive behavior: gentle or explosive Distribution: divergent plate boundaries, hot spots, convergent plate boundaries.
At any given pressure and for any given composition of rock, a rise in temperature past the solidus will cause melting. Within the solid earth, the temperature of a rock is controlled by the geothermal gradient and the radioactive decay within the rock; the geothermal gradient averages about 25 °C/km with a wide range from a low of 5–10 °C/km within oceanic trenches and subduction zones to 30–80 °C/km under mid-ocean ridges and volcanic arc environments. It is very difficult to change the bulk composition of a large mass of rock, so composition is the basic control on whether a rock will melt at any given temperature and pressure; the composition of a rock may be considered to include volatile phases such as water and carbon dioxide. The presence of volatile phases in a rock under pressure can stabilize a melt fraction; the presence of 0.8% water may reduce the temperature of melting by as much as 100 °C. Conversely, the loss of water and volatiles from a magma may cause it to freeze or solidify.
A major portion of all magma is silica, a compound of silicon and oxygen. Magma contains gases, which expand as the magma rises. Magma, high in silica resists flowing, so expanding gases are trapped in it. Pressure builds up until the gases blast out in a dangerous explosion. Magma, poor in silica flows so gas bubbles move up through it and escape gently. Melting of solid rocks to form magma is controlled by three physical parameters: temperature and composition; the most common mechanisms of magma generation in the mantle are decompression melting and lowering of the solidus. Mechanisms are discussed further in the entry for igneous rock; when rocks melt, they do so and because most rocks are made of several minerals, which all have different melting points. As a rock melts, for example, its volume changes; when enough rock is melted, the small globules of melt soften the rock. Under pressure within the earth, as little as a fraction of a percent of partial melting may be sufficient to cause melt to be squeezed from its source.
Melts can stay in place long enough to melt to 20% or 35%, but rocks are melted in excess of 50%, because the melted rock mass becomes a crystal-and-melt mush tha
Hawaiian–Emperor seamount chain
The Hawaiian–Emperor seamount chain is a 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, the Emperor Seamounts: together they form a vast underwater mountain region of islands and intervening seamounts, shallows and reefs along a line trending southeast to northwest beneath the northern Pacific Ocean; the seamount chain, containing over 80 identified undersea volcanoes, stretches over 5,800 kilometres from the Aleutian Trench in the far northwest Pacific to the Loʻihi seamount, the youngest volcano in the chain, which lies about 35 kilometres southeast of the Island of Hawaiʻi. The chain can be divided into three subsections; the first, the Hawaiian archipelago, consists of the islands comprising the U. S. state of Hawaii. As it is the closest to the hotspot, this volcanically active region is the youngest part of the chain, with ages ranging from 400,000 years to 5.1 million years.
The island of Hawaiʻi is composed of five volcanoes. Haleakalā on the island of Maui is dormant. Lōʻihi Seamount continues to grow offshore of Hawaiʻi island, is the only known volcano in the chain in the submarine pre-shield stage; the second part of the chain is composed of the Northwestern Hawaiian Islands, collectively referred to as the Leeward isles, the constituents of which are between 7.2 and 27.7 million years in age. Erosion has long since overtaken volcanic activity at these islands, most of them are atolls, atoll islands, extinct islands, they contain many of the most northerly atolls in the world. On June 15, 2006, U. S. President George W. Bush issued a proclamation creating Papahānaumokuākea Marine National Monument under the Antiquities Act of 1906; the national monument, meant to protect the biodiversity of the Hawaiian isles, encompasses all of the northern isles, is one of the largest such protected areas in the world. The proclamation limits tourism to the area, called for a phase-out of fishing by 2011.
The oldest and most eroded part of the chain are the Emperor seamounts, which are 39 to 85 million years in age. The Emperor and Hawaiian chains form an angle of about 120°; this bend was long attributed to a sudden change of 60° in the direction of plate motion, but research conducted in 2003 suggests that it was the movement of the hotspot itself that caused the bend. The issue is still under academic debate. All of the volcanoes in this part of the chain have long since subsided below sea level, becoming seamounts and guyots. Many of the volcanoes are named after former emperors of Japan; the seamount chain extends to the West Pacific, terminates at the Kuril–Kamchatka Trench, a subduction zone at the border of Russia. The oldest age for the Emperor Seamounts is 81 million years, comes from Detroit Seamount. However, Meiji Guyot, located to the north of Detroit Seamount, is somewhat older. In 1963, geologist John Tuzo Wilson hypothesized the origins of the Hawaiian–Emperor seamount chain, explaining that they were created by a hotspot of volcanic activity, stationary as the Pacific tectonic plate drifted in a northwesterly direction, leaving a trail of eroded volcanic islands and seamounts in its wake.
An otherwise inexplicable kink in the chain marks a shift in the movement of the Pacific plate some 47 million years ago, from a northward to a more northwesterly direction, the kink has been presented in geology texts as an example of how a tectonic plate can shift direction comparatively suddenly. A look at the USGS map on the origin of the Hawaiian Islands shows this "spearpoint". In a more recent study and Clague interpret the bend as starting at about 50 million years ago, they conclude that the bend formed from a "traditional" cause—a change in the direction of motion of the Pacific plate. However, recent research shows; some evidence comes from analysis of the orientation of the ancient magnetic field preserved by magnetite in ancient lava flows sampled at four seamounts: this evidence from paleomagnetism shows a more complex history than the accepted view of a stationary hotspot. If the hotspot had remained above a fixed mantle plume during the past 80 million years, the latitude as recorded by the orientation of the ancient magnetic field preserved by magnetite should be constant for each sample.
Instead of remaining constant, the paleolatitudes of the Emperor Seamounts show a change from north to south, with decreasing age. The paleomagnetic data from the seamounts of the Emperor chain suggest motion of the Hawaiian hotspot in Earth's mantle. Tarduno et al. have summarized evidence that the bend in the seamount chain may be caused by circulation patterns in the flowing solid mantle rather than a change in plate motion. The chain has been produced by the movement of the ocean crust over the Hawaiʻi hotspot, an upwelling of hot rock from the Earth's mantle; as the oceanic crust moves the volcanoes farther away from their source of magma, their eruptions become less frequent and less powerful until they cease to erupt altogether. At that point erosion of the volcano and subsidence of the seafloor cause the volcano to diminish; as the volcano sinks and erodes, it first becomes an atoll island and
The Hawaii hotspot is a volcanic hotspot located near the namesake Hawaiian Islands, in the northern Pacific Ocean. One of the most well-known and studied hotspots in the world, the Hawaii plume is responsible for the creation of the Hawaiian – Emperor seamount chain, a chain of volcanoes over 5,800 kilometres long. Four of these volcanoes are active, two are dormant, more than 123 are extinct, many having since been ground beneath the waves by erosion as seamounts and atolls; the chain extends from south of the island of Hawaiʻi to the edge of the Aleutian Trench, near the eastern edge of Russia. While most volcanoes are created by geological activity at tectonic plate boundaries, the Hawaii hotspot is located far from plate boundaries; the classic hotspot theory, first proposed in 1963 by John Tuzo Wilson, proposes that a single, fixed mantle plume builds volcanoes that cut off from their source by the movement of the Pacific Plate, become inactive and erode below sea level over millions of years.
According to this theory, the nearly 60° bend where the Emperor and Hawaiian segments of the chain meet was caused by a sudden shift in the movement of the Pacific Plate. In 2003, fresh investigations of this irregularity led to the proposal of a mobile hotspot theory, suggesting that hotspots are mobile, not fixed, that the 47-million-year-old bend was caused by a shift in the hotspot's motion rather than the plate's. Ancient Hawaiians were the first to recognize the increasing age and weathered state of the volcanoes to the north as they progressed on fishing expeditions along the islands; the volatile state of the Hawaiian volcanoes and their constant battle with the sea was a major element in Hawaiian mythology, embodied in Pele, the deity of volcanoes. After the arrival of Europeans on the island, in 1880–1881 James Dwight Dana directed the first formal geological study of the hotspot's volcanics, confirming the relationship long observed by the natives; the Hawaiian Volcano Observatory was founded in 1912 by volcanologist Thomas Jaggar, initiating continuous scientific observation of the islands.
In the 1970s, a mapping project was initiated to gain more information about the complex geology of Hawaii's seafloor. The hotspot has since been tomographically imaged, showing it to be 500 to 600 km wide and up to 2,000 km deep, olivine and garnet-based studies have shown its magma chamber is 1,500 °C. In its at least 85 million years of activity the hotspot has produced an estimated 750,000 km3 of rock; the chain's rate of drift has increased over time, causing the amount of time each individual volcano is active to decrease, from 18 million years for the 76-million-year-old Detroit Seamount, to just under 900,000 for the one-million-year-old Kohala. Overall, this has caused a trend towards more active but quickly-silenced spaced volcanoes—whereas volcanoes on the near side of the hotspot overlap each other, the oldest of the Emperor seamounts are spaced as far as 200 km apart. Tectonic plates focus deformation and volcanism at plate boundaries. However, the Hawaii hotspot is more than 3,200 kilometers from the nearest plate boundary.
Wilson proposed that mantle convection produces small, hot buoyant upwellings under the Earth's surface. This "mid-plate" volcanism builds peaks that rise from featureless sea floor as seamounts and as fully-fledged volcanic islands; the local tectonic plate slides over the hotspot, carrying its volcanoes with it without affecting the plume. Over hundreds of thousands of years, the magma supply for the volcano is cut off going extinct. No longer active enough to overpower erosion, the volcano sinks beneath the waves, becoming a seamount once again; as the cycle continues, a new volcanic center manifests, a volcanic island arises anew. The process continues until the mantle plume; this cycle of growth and dormancy strings together volcanoes over millions of years, leaving a trail of volcanic islands and seamounts across the ocean floor. According to Wilson's theory, the Hawaiian volcanoes should be progressively older and eroded the further they are from the hotspot, this is observable. Another consequence of his theory is that the chain's length and orientation serves to record the direction and speed of the Pacific Plate's movement.
A major feature of the Hawaiian trail is a sudden 60° bend at a 40- to 50-million-year-old section of its length, according to Wilson's theory, this is evidence of a major change in plate direction, one that would have initiated subduction along much of the Pacific Plate's western boundary. This part of the theory has been challenged, the bend might be attributed to the movement of the hotspot itself. Geophysicists believe that hotspots originate at one of two major boundaries deep in the Earth, either a shallow i