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70-637: The Luzon Volcanic Arc is a chain of volcanoes in a north–south line across the Luzon Strait from Taiwan to Luzon . The name "Luzon Volcanic Arc" was first proposed by Carl Bowin et al. to describe a series of Miocene to recent volcanoes due to eastward subduction along the Manila Trench for approximately 1,200 km from the Coastal Range in Taiwan south to southern Mindoro in

140-595: A border between the Bering Sea to the north and the Pacific Ocean to the south. Crossing longitude 180° , at which point east and west longitude end, the archipelago contains both the westernmost and easternmost parts of the United States, by longitude ( Amatignak Island and Semisopochnoi Island , respectively). The westernmost U.S. island, in real terms, however, is Attu Island , west of which runs

210-613: A circle whose radius is θ/2. This means that arcs where the subducting slab descends at a shallower angle will be more tightly curved. Prominent arcs whose slabs subduct at about 45 degrees, such as the Kuril Islands , the Aleutian Islands , and the Sunda Arc , have a radius of about 20 to 22 degrees. Volcanic arcs are divided into those in which the overriding plate is continental (Andean-type arcs) and those in which

280-496: A depth of roughly 120 kilometres (75 mi) and is a zone of volcanic activity between 50 and 200 kilometers (31 and 124 mi) in width. The shape of a volcanic arc is typically convex towards the subducting plate. This is a consequence of the spherical geometry of the Earth. The subducting plate behaves like a flexible thin spherical shell, and such a shell be bent downwards by an angle of θ, without tearing or wrinkling, only on

350-675: A generation, the day-to-day administration of the Russian-American colonies was largely in the hands of native-born Alaskans. Reversing the usual trend in colonization where indigenous technologies are replaced, the Russians adopted the Aleut kayak, or baidarka , sea otter hunting techniques, and the working of native copper deposits. The Russians instituted public education, preservation of the Aleut language through transliteration of religious and other texts into Aleut via an adaptation of

420-469: A given time. Active fronts may move over time (millions of years), changing their distance from the oceanic trench as well as their width. A volcanic arc is part of an arc-trench complex , which is the part of a subduction zone that is visible at the Earth's surface. A subduction zone is where a tectonic plate composed of relatively thin, dense oceanic lithosphere sinks into the Earth's mantle beneath

490-407: A less dense overriding plate. The overriding plate may be either another oceanic plate or a continental plate. The subducting plate, or slab , sinks into the mantle at an angle, so that there is a wedge of mantle between the slab and the overriding plate. The boundary between the subducting plate and the overriding plate coincides with a deep and narrow oceanic trench . This trench is created by

560-440: A narrow arc some distance from the trench. The distance from the trench to the volcanic arc is greater for slabs subducting at a shallower angle, and this suggests that magma generation takes place when the slab reached a critical depth for the breakdown of an abundant hydrous mineral. This would produce an ascending "hydrous curtain" that accounts for focused volcanism along the volcanic arc. However, some models suggest that water

630-450: A new volcanic cone rose between the islets of Bogoslof and Grewingk, near Unalaska, followed by another in 1907. These cones were nearly demolished by an explosive eruption on September 1, 1907. In 2017, the volcanic cone erupted sending ash and ice particles 30,000 feet (9000 m) into the air. Alfred Russel Wallace 's 1879 book Australasia , Ian Todd's 1974 book Island Realm: A Pacific Panorama and Dean Kohlhoff's 2002 book Amchitka and

700-401: A number of volcanoes along the arc have been measured. There are five distinct geochemical domains within the arc (Mindoro, Bataan, Northern Luzon, Babuyan, and Taiwan). The geochemistry of the segments verified that the volcanoes are all subduction related (e.g., strong niobium anomalies and calc-alkaline characteristics). Isotopes and trace elements show unique geochemical characteristics in

770-415: A simple age-pattern. There are two types of volcanic arcs: In some situations, a single subduction zone may show both aspects along its length, as part of a plate subducts beneath a continent and part beneath adjacent oceanic crust. The Aleutian Islands and adjoining Alaskan Peninsula are an example of such a subduction zone. The active front of a volcanic arc is the belt where volcanism develops at

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840-616: A voyage of discovery in the Northern Pacific. After the ships were separated by a storm; Chirikov discovered several eastern islands of the Aleutian group, and Bering discovered several of the western islands. Bering was shipwrecked and died in the Komandorski Islands ( Commander Islands ); one of which now bears his name ( Bering Island ), along with the surrounding Bering Sea. The survivors of Bering's party reached

910-477: Is because the islands, much like the Falklands and other islands of similar latitudes , experience such strong winds that taller trees are vulnerable to snapping off. Instead of trees, the islands are covered with a luxuriant, dense growth of herbage and shrubs, including crowberry , bluejoint , grasses , sedges , and many flowering plants. There are areas of peat bog near the coasts. Endemic plants include

980-408: Is continuously released from the slab from shallow depths down to 70 to 300 kilometers (43 to 186 mi), and much of the water released at shallow depths produces serpentinization of the overlying mantle wedge. According to one model, only about 18 to 37 percent of the water content is released at sufficient depth to produce arc magmatism. The volcanic arc is then interpreted as the depth at which

1050-431: Is formed. Arc volcanism takes place where the slab descends out from under the cool shallow corner, allowing magma to be generated and rise through warmer, less stiff mantle rock. Magma may be generated over a broad area but become focused into a narrow volcanic arc by a permeability barrier at the base of the overriding plate. Numerical simulations suggest that crystallization of rising magma creates this barrier, causing

1120-415: Is lost from the subducted plate when the temperature and pressure become sufficient to break down these minerals and release their water content. The water rises into the wedge of mantle overlying the slab and lowers the melting point of mantle rock to the point where magma is generated. While there is wide agreement on the general mechanism, research continues on the explanation for focused volcanism along

1190-553: Is low in volcanic arc rocks. Because volcanic rock is easily weathered and eroded , older volcanic arcs are seen as plutonic rocks , the rocks that formed underneath the arc (e.g. the Sierra Nevada batholith ), or in the sedimentary record as lithic sandstones . Paired metamorphic belts , in which a belt of high-temperature, low-pressure metamorphism is located parallel to a belt of low-temperature, high-pressure metamorphism, preserve an ancient arc-trench complex in which

1260-571: Is much cooler than Southeast Alaska (around Sitka ), but the winter temperature of the islands and of the Alaska Panhandle is nearly the same. According to the Köppen climate classification system, the area southwest of 53°30′N 167°00′W  /  53.5°N 167.0°W  / 53.5; -167.0 , on Unalaska Island , has a "Subpolar Oceanic Climate" (type "Cfc", as does Reykjavík , Tórshavn , Punta Arenas , Ushuaia and

1330-458: Is not quite visible from within the town of Unalaska , though the steam rising from its cone is visible on a (rare) clear day. Residents of Unalaska need only to climb one of the smaller hills in the area, such as Pyramid Peak or Mt. Newhall, to get a good look at the snow-covered cone. The volcanic Bogoslof and Fire Islands , which rose from the sea in 1796 and 1883 respectively, lie about 30 miles (50 km) west of Unalaska Bay . In 1906,

1400-615: Is particularly characteristic of volcanic arcs, though it sometimes also occurs in regions of crustal extension. In the rock record, volcanic arcs can be recognized from their thick sequences of volcaniclastic rock (formed by explosive volcanism) interbedded with greywackes and mudstones and by their calc-alkaline composition. In more ancient rocks that have experienced metamorphism and alteration of their composition ( metasomatism ), calc-alkaline rocks can be distinguished by their content of trace elements that are little affected by alteration, such as chromium or titanium , whose content

1470-637: Is similar albeit colder, with the coldest month averaging below 0 °C (32 °F). During the winter, the islands become the center of a semi-permanent low-pressure area called the Aleutian Low . The mean annual temperature for Unalaska, the most populated island of the group, is about 38 ° F (3 ° C ), being about 30 °F (−1 °C) in January and about 52 °F (11 °C) in August. The highest and lowest temperatures recorded on

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1540-596: The Aleut . The Aleut language is one of the two main branches of the Eskimo–Aleut language family. This family is not known to be related to any others. The 2020 U.S. Census recorded a population of 7,152 on the islands, of whom 4,254 were living in the main settlement of Unalaska . On the less mountainous islands, the raising of sheep and reindeer was once believed to be practicable. There are bison on islands near Sand Point. Sheep raising seems to have died off with

1610-603: The Aleutian Islands Wilderness . Observations have identified sea otters as a keystone species along the coasts of many of the Aleutian Islands. Their presence encourages the growth of kelp forests , as the otters control sea urchin populations (as large populations of sea urchins can create urchin barrens by clearing away kelp stands). The native people refer to themselves as Unangan, and are now generally known by most non-natives as

1680-706: The Aleutian Islands campaign of World War II . The Japanese landing and occupations of Kiska and Attu , in June of 1942 , were one of only two invasions of the United States in North America during WWII; the Philippines , Guam and Wake Atoll , Pacific territories of the United States , were also invaded. Motion between the Kula Plate and the North American Plate along the margin of

1750-845: The Aleuts "; possibly from the Chukchi aliat , or "island")—also called the Aleut Islands , Aleutic Islands , or, before 1867 , the Catherine Archipelago —are a chain of 14 main, larger volcanic islands and 55 smaller ones. Most of the Aleutian Islands belong to the U.S. state of Alaska , with the archipelago encompassing the Aleutians West Census Area and the Aleutians East Borough . The Commander Islands , located further to

1820-498: The Auckland Islands ), characterized by the coldest month averaging above 0 °C (32 °F), one to three months averaging above 10 °C (50 °F), and no significant precipitation differences between seasons. To the northeast of that point, the climate becomes "Subarctic With Cool Summers And Year Around Rainfall" (type "Dfc", like Petropavlovsk-Kamchatsky , Murmansk , St. Moritz , and Labrador City ), where it

1890-562: The Cannikin , was the largest underground nuclear explosion by the U.S. The Alaska Native Claims Settlement Act became law in 1971. In 1977, the Ounalashka Corporation (from Unalaska) declared a dividend . This was the first village corporation to declare and pay a dividend to its shareholders. The Aleutian Islands were designated a UNESCO biosphere reserve in 1976. The Aleutians were one of 17 biosphere reserves in

1960-650: The International Date Line . The Aleutian Islands, with their 57 volcanoes, form the northernmost part of the Pacific Ring of Fire . Physiographically , they are a distinct section of the larger Pacific Border province, which, in turn, is part of the larger Pacific Mountain System physiographic division. The islands are considered to be among the most geographically-isolated areas of the Northern Pacific. Battles and skirmishes took place during

2030-565: The Japanese naval codes , proceeded as if this was just a diversion, and it did not expend large amounts of effort in defending the islands. More than 90 Americans were taken to Japan as prisoners of war. Most of the civilian population (over 800) of the Aleutians and Pribilovians were detained by the United States in camps in the Alaska Panhandle . During the Aleutian Islands campaign , American forces invaded Japanese-held Attu and defeated

2100-620: The Kamchatka Peninsula in a boat constructed from the wreckage of their ship, and reported the islands were rich in fur-bearing animals. Siberian fur hunters flocked to the Commander Islands and gradually moved eastward across the Aleutian Islands to the mainland. In this manner, Russia gained a foothold on the northwestern coast of North America. The Aleutian Islands consequently belonged to Russia, until that country transferred all its possessions in North America to

2170-510: The common rosefinch , Siberian rubythroat , bluethroat , lanceolated warbler , and the first North American record of the intermediate egret . The habitats of the Aleutians are largely unspoiled, but wildlife is affected by competition from introduced species such as cattle, caribou , and foxes . Nearly all of the Aleutians are protected as part of the Alaska Maritime National Wildlife Refuge and

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2240-450: The Aleutian archipelago, accurately determined the position of some of the more important islands, and corrected many errors of former navigators. Among the first Christian missionaries to arrive in the Aleutian Islands was a party of ten Russian Orthodox monks and priests, who arrived in 1793. Within two years, a monk named Herman was the only survivor of that party. He settled on Spruce Island , near Kodiak Island , and often defended

2310-526: The Aleutians are Attu (the farthest from the mainland), and Unalaska , Umnak , and Unimak in the Fox Islands. The largest of those is Unimak Island, with an area of 1,571.41 mi (4,069.9 km ), followed by Unalaska Island, the only other Aleutian Island with an area over 1,000 square miles (2,600 km ). The axis of the archipelago near the mainland of Alaska has a southwest trend, but at Tanaga Island (about 178° W) its direction changes to

2380-536: The Aleutians lie between the Pacific and North American tectonic plates . The general elevation is greatest in the eastern islands and least in the western. The island chain is a western continuation of the Aleutian Range on the mainland. The great majority of the islands bear evident marks of volcanic origin, and there are numerous volcanic cones on the north side of the chain, some of them active; many of

2450-481: The Americans suffered significant casualties during their “invasion” – 313 men died as a result of accidents, with many dying due to accidental fire. President Roosevelt visited Adak in 1944, meeting with commanders and eating with soldiers of the garrison. This was his first and only trip to the Aleutian Islands and Alaska as a whole. A rumor spread that FDR had accidentally left his Scottish Terrier "Fala" on one of

2520-722: The Bering Shelf (in the Bering Sea north of the Aleutian arc) ended in the early Eocene . The Aleutian Basin, the ocean floor north of the Aleutian arc, is the remainder of the Kula Plate that was trapped when volcanism and subduction jumped south to its current location at c. 56 Ma. The Aleutian island arc formed in the Early Eocene (55–50  Ma ) when the subduction of the Pacific Plate under

2590-621: The Bomb: Nuclear Testing in Alaska all associate the Aleutian Islands with the Oceania region due to their status as remote islands in the Pacific. The islands, having biogeographical and ethnocultural affinities to North America , are not ordinarily considered a part of the region. The climate of the islands is oceanic, with moderate and fairly uniform temperatures and heavy rainfall. Fogs are almost constant. Summer weather

2660-630: The Cyrillic alphabet, vaccination of the native population against smallpox , and science-based sea mammal conservation policies that were ahead of their time. By 1760 the Russian merchant Andrian Tolstykh had made a detailed census in the vicinity of Adak and extended Russian citizenship to the Aleuts. During his third and last voyage in 1778, Captain James Cook surveyed the eastern portion of

2730-653: The Islands and had to send a destroyer to retrieve the dog, costing taxpayers several million dollars. The President made fun of these rumors during a talk with the Teamsters Union in Washington DC, now known as the "Fala Speech". At this speech the President joked with the crowd saying, "Well, of course, I don't resent attacks, and my family doesn't resent attacks, but Fala does resent them!" June 3, 2002

2800-518: The Japanese. American and Canadian troops later launched an invasion of Kiska , in which 34,426 men composed of both Americans and Canadian participated; however, Japanese forces had already withdrawn, ending the campaign in the islands. The invasion was an embarrassment for the Allied forces as the entire Japanese force of 5,183 men had left the island on July 28 without the Americans noticing; however,

2870-691: The North American Plate began. The arc is made of separate blocks that have been rotated clockwise. The basement underlying the islands is made of three stratigraphic units: an Eocene layer of volcanic rock, an Oligocene – Miocene layer of marine sedimentary rock, and a Pliocene – Quaternary layer of sedimentary and igneous rock. The islands, known before 1867 as the Catherine Archipelago, include six groups (east to west) All six are located between 51° and 55° N latitude and 172° E and 163° W longitude. The largest islands in

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2940-728: The North Pacific, with the Aleutian Arc consisting of the Aleutian Islands and their extension the Aleutian Range on the Alaska Peninsula , and the Kuril–Kamchatka Arc comprising the Kuril Islands and southern Kamchatka Peninsula . Aleutian Islands The Aleutian Islands ( / ə ˈ l uː ʃ ən / ə- LOO -shən ; Russian : Алеутские острова , romanized :  Aleutskiye ostrova ; Aleut : Unangam Tanangin , "land of

3010-482: The North Palawan-Mindoro crustal block and perhaps sediment contamination was derived from this region. This substantiates preliminary early isotope and trace element studies on the central Luzon arc Further work was done on the northern Luzon arc by McDermott et al. who found systematic variations in an assortment of isotopes with latitude not only in the lavas analyzed over the 500 km section of

3080-550: The Philippines. Islands that form part of the arc are the Eastern Coastal Range of Taiwan , Green Island, Taiwan , Orchid Island , Kaotai Rock , Mavudis or Y'ami Island , Mabudis , Siayan Island , Itbayat Island , Diogo Island , Batan Island , Unnamed volcano Ibuhos , Sabtang Island , Babuyan , Didicas , and Camiguin de Babuyanes . At the south end it terminates on Luzon . The geochemistry of

3150-513: The U.S. in 1867. During the consolidation of the Russian-American Company there was sporadic conflict with the native population (frequently disastrous to the poorly armed and vastly outnumbered Russians). The colonies soon entered a relatively stable state based on cooperation, intermarriage, and official policies that provided social status, education, and professional training to children of mixed Aleut-Russian birth. Within

3220-508: The U.S. islands. Because the islands stretch like a broken bridge from the continent Asia to the continent North America, many anthropologists hypothesize they were a route of the first human occupants of the Americas . However, the earliest known evidence in public recorded history of human occupation in the Americas is found much farther south. The early human sites in the Bering Sea were probably submerged by rising waters and sand during

3290-493: The advent of synthetic fibers, which lowered the value of wool. During the 1980s, there were some llama being raised on Unalaska. The current economy is primarily based on fishing , and the presence of U.S. military. The only crop is potato . Chickens are raised in barns under protection from the cold. In addition to a partial air service and a ferry service, the Alaska Marine Highway passes through many of

3360-587: The arc but also in sediments along the trench. The only way to explain the latitudinal variations was through the addition of an increasing input of terrigenous sediments toward the continental regions in the north China and Taiwan During the Middle Miocene , 16-15 Ma , activity started in Taiwan. Batan Island volcanics are dated at 9.36 Ma, while north of Luzon, the volcanic islands are younger than 6.5 Ma. Volcanic arc Volcanic arcs are distinct from volcanic chains formed over hotspots in

3430-628: The crust. Volcanic arcs are characterized by explosive eruption of calc-alkaline magma, though young arcs sometimes erupt tholeiitic magma and a few arcs erupt alkaline magma. Calc-alkaline magma can be distinguished from tholeiitic magma, typical of mid-ocean ridges , by its higher aluminium and lower iron content and by its high content of large-ion lithophile elements, such as potassium , rubidium , caesium , strontium , or barium , relative to high-field-strength elements, such as zirconium , niobium , hafnium , rare-earth elements (REE), thorium , uranium , or tantalum . Andesite

3500-482: The current interglacial period. People living in or on the Aleutian Islands developed skills in hunting, fishing, and basketry. The baskets were woven with shredded stalks of beach rye. Explorers, traders and missionaries arrived from Russia beginning in 1741. In 1741 the Russian government sent Vitus Bering , a Danish-born Russian, and Aleksei Chirikov , a Russian, in the ships Saint Peter and Saint Paul on

3570-402: The degree of melting becomes great enough to allow the magma to separate from its source rock. It is now known that the subducting slab may be located anywhere from 60 to 173 kilometers (37 to 107 mi) below the volcanic arc, rather than a single characteristic depth of around 120 kilometers (75 mi), which requires more elaborate models of arc magmatism. For example, water released from

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3640-730: The endangered Aleutian shield fern . There is currently almost no naturally occurring forest in the Aleutian Islands, except with the help of human intervention. For example, the Adak Forest on Adak Island is a man-made tree group consisting of 33 trees. The Aleutians are home to many large colonies of seabirds. Buldir Island has 21 breeding seabird species, including the Bering Sea-endemic red-legged kittiwake . Large seabird colonies are also present at Kiska , Gareloi , Semisopochnoi , Bogoslof , and others. The islands are also frequented by vagrant Asiatic birds, including

3710-469: The exception of some stunted willows , the vast majority of the chain is devoid of native trees. On some of the islands, such as Adak and Amaknak , there are a few coniferous trees growing, remnants of the Russian period . While tall trees grow in many cold climates, Aleutian conifers — some estimated to be two hundred years old — rarely reach a height of even 10 feet (3 m), and many of them are still less than 5 feet (1.5 m) tall. This

3780-455: The gravitational pull of the relatively dense subducting plate pulling the leading edge of the plate downward. Multiple earthquakes occur within the subducting slab with the seismic hypocenters located at increasing depth under the island arc: these quakes define the Wadati–Benioff zones . The volcanic arc forms on the overriding plate over the point where the subducting plate reaches

3850-497: The high-temperature, low-pressure belt corresponds to the volcanic arc. In a subduction zone , loss of water from the subducted slab induces partial melting of the overriding mantle and generates low-density, calc-alkaline magma that buoyantly rises to intrude and be extruded through the lithosphere of the overriding plate. Most of the water carried downwards by the slab is contained in hydrous (water-bearing) minerals, such as mica , amphibole , or serpentinite minerals. Water

3920-504: The indigenous peoples of Alaska) in 1924. A hospital was built in Unalaska in 1933 by the U.S. Bureau of Indian Affairs . During World War II , in what were the only two invasions of the United States during the war, small parts of the Aleutian islands were occupied by Japanese forces, when Attu and Kiska were invaded possibly to divert American forces away from the main Japanese attack at Midway Atoll . The U.S. Navy, having broken

3990-527: The islands were 78 °F (26 °C) and 5 °F (−15 °C), respectively. The average amount of annual rainfall is about 80 inches (2,000 mm); Unalaska, with about 250 rainy days per year, is said to be one of the rainiest places within the U.S. The growing season lasts approximately 135 days, from early in May until late in September, but agriculture is limited to the raising of few vegetables. With

4060-474: The islands, however, are not wholly volcanic, but contain crystalline or sedimentary rocks, and also amber and beds of lignite . The coasts are rocky and surf-worn, and the approaches are exceedingly dangerous, the land rising immediately from the coasts to steep, bold mountains. These volcanic islands reach heights of 6,200 feet (1,900 m). Makushin Volcano (5,691 feet (1,735 m)) on Unalaska Island,

4130-432: The middle of a tectonic plate. Volcanoes often form one after another as the plate moves over the hotspot, and so the volcanoes progress in age from one end of the chain to the other. The Hawaiian Islands form a typical hotspot chain, with the older islands to the northwest and Hawaii Island itself, which is just 400,000 years old, at the southeast end of the chain over the hotspot. Volcanic arcs do not generally exhibit such

4200-524: The north were approached (China and Taiwan). The sediment thicknesses increased toward the north along the trench. The geochemistry and tectonic setting of the southern Luzon arc has been studied in detail. The geochemistry suggested that continental crust (probably from sediments) played an important role in the Macolod corridor and the Mindoro segments. Crustal collision had occurred in the south between

4270-408: The north. Geochemical variations northward (Babuyan segment) were due to the subduction of sediments derived from the erosion of continental crust from China and Taiwan. There is a distinct increase in strontium isotopic ratios with latitude northward. This supports the conjecture that the variations were due to an increasing "crustal" component in subducted sediments as the continental blocks in

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4340-420: The northwest. This change of direction corresponds to a curve in the line of volcanic fissures that have contributed their products to the building of the islands. Such curved chains are repeated about the Pacific Ocean in the Kuril Islands , the Japanese chain, and in the Philippines . All these island arcs are at the edge of the Pacific Plate and experience much seismic activity, but are still habitable;

4410-408: The overriding plate is oceanic (intraoceanic or primitive arcs). The crust beneath the arc is up to twice as thick as average continental or oceanic crust: The crust under Andean-type arcs is up to 80 kilometers (50 mi) thick, while the crust under intraoceanic arcs is 20 to 35 kilometers (12 to 22 mi) thick. Both shortening of the crust and magmatic underplating contribute to thickening of

4480-410: The released water lowers the melting point of the overlying mantle wedge enough for melting. The location of the volcanic arc may be determined by the presence of a cool shallow corner at the tip of the mantle wedge, where the mantle rock is cooled by both the overlying plate and the slab. Not only does the cool shallow corner suppress melting, but its high stiffness hinders the ascent of any magma that

4550-698: The remaining magma to pool in a narrow band at the apex of the barrier. This narrow band corresponds to the overlying volcanic arc. Two classic examples of oceanic island arcs are the Mariana Islands in the western Pacific Ocean and the Lesser Antilles in the western Atlantic Ocean. The Cascade Volcanic Arc in western North America and the Andes along the western edge of South America are examples of continental volcanic arcs. The best examples of volcanic arcs with both sets of characteristics are in

4620-647: The rights of the Aleuts against the Russian trading companies. He is now known in the Orthodox Church as Saint Herman of Alaska . Another early Christian missionary of the Russian Orthodox Church was Father Veniaminov who arrived in Unalaska in 1824. He was named Bishop Innokentii in 1840 and moved to Sitka . He is now known in the Orthodox Church as Saint Innocent of Alaska . The principal settlements were on Unalaska Island. The oldest

4690-412: The slab at moderate depths might react with amphibole minerals in the lower part of the mantle wedge to produce water-rich chlorite . This chlorite-rich mantle rock is then dragged downwards by the subducting slab, and eventually breaks down to become the source of arc magmatism. The location of the arc depends on the angle and rate of subduction, which determine where hydrous minerals break down and where

4760-401: The west, belong to the Russian federal subject of Kamchatka Krai , of the Russian Far East . The islands form part of the Aleutian Arc of the Northern Pacific Ocean , and occupy a land area of 6,821 sq mi (17,666 km ) that extends westward roughly 1,200 mi (1,900 km) from the Alaskan Peninsula mainland, in the direction of the Kamchatka Peninsula ; the archipelago acts as

4830-573: Was Iliuliuk (also called Unalaska), settled in 1760–1775, with a customs house and an Orthodox church. After the American purchase of Alaska from Russia in 1867, further development took place. New buildings included a Methodist mission and orphanage, and the headquarters for a considerable fleet of United States revenue cutters , which patrolled the sealing grounds of the Pribilof Islands . The first public school in Unalaska opened in 1883. The U.S. Congress extended American citizenship to all Native Americans (and this law has been held to include

4900-443: Was celebrated as Dutch Harbor Remembrance Day. The governor of Alaska ordered state flags lowered to half-staff to honor the 43 Americans who died during the two-day Japanese air attack in 1942. The Aleutian World War II National Historic Area Visitors Center opened that month. The U.S. conducted underground tests of nuclear weapons on Amchitka Island from 1965 to 1971 as part of the Vela Uniform program. The final detonation,

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