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102-565: Paramushir is roughly rectangular and is the second largest of the Kuril Islands with an area of 2,053 square kilometres (793 sq mi). Geologically, Paramushir is a continuous chain of 23 volcanoes . At least five of them are active, and exceed 1,000 m (3,281 ft): Paramushir has a sub-arctic climate strongly modulated by the cooling effects of the North Pacific Oyashio Current . The arboreal flora of Paramushir

204-496: A ghost town ) and Fourpeaked Mountain in Alaska, which, before its September 2006 eruption, had not erupted since before 8000 BCE. 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 the Aleuts "; possibly from

306-476: A magma chamber below the surface. The process that forms volcanoes is called volcanism . On Earth, volcanoes are most often found where tectonic plates are diverging or converging , and because most of Earth's plate boundaries are underwater, most volcanoes are found underwater. For example, a mid-ocean ridge , such as the Mid-Atlantic Ridge , has volcanoes caused by divergent tectonic plates whereas

408-575: 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

510-658: 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

612-437: A graduated spectrum, with much overlap between categories, and does not always fit neatly into only one of these three separate categories. The USGS defines a volcano as "erupting" whenever the ejection of magma from any point on the volcano is visible, including visible magma still contained within the walls of the summit crater. While there is no international consensus among volcanologists on how to define an active volcano,

714-450: 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

816-443: A paper was published suggesting a new definition for the word 'volcano' that includes processes such as cryovolcanism . It suggested that a volcano be defined as 'an opening on a planet or moon's surface from which magma , as defined for that body, and/or magmatic gas is erupted.' This article mainly covers volcanoes on Earth. See § Volcanoes on other celestial bodies and cryovolcano for more information. The word volcano

918-632: A volcano is largely determined by the composition of the lava it erupts. The viscosity (how fluid the lava is) and the amount of dissolved gas are the most important characteristics of magma, and both are largely determined by the amount of silica in the magma. Magma rich in silica is much more viscous than silica-poor magma, and silica-rich magma also tends to contain more dissolved gases. Lava can be broadly classified into four different compositions: Mafic lava flows show two varieties of surface texture: ʻAʻa (pronounced [ˈʔaʔa] ) and pāhoehoe ( [paːˈho.eˈho.e] ), both Hawaiian words. ʻAʻa

1020-555: A volcano is of a conical mountain, spewing lava and poisonous gases from a crater at its summit; however, this describes just one of the many types of volcano. The features of volcanoes are varied. The structure and behaviour of volcanoes depend on several 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 (including lava and ash ) and gases (mainly steam and magmatic gases) can develop anywhere on

1122-465: A volcano that has experienced one or more eruptions that produced over 1,000 cubic kilometres (240 cu mi) of volcanic deposits in a single explosive event. Such eruptions occur when a very large magma chamber full of gas-rich, silicic magma is emptied in a catastrophic caldera -forming eruption. Ash flow tuffs emplaced by such eruptions are the only volcanic product with volumes rivalling those of flood basalts . Supervolcano eruptions, while

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1224-594: 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

1326-727: Is a volcanic field of over 60 cinder cones. Based on satellite images, it has been suggested that cinder cones might occur on other terrestrial bodies in the Solar system too; on the surface of Mars and the Moon. Stratovolcanoes (composite volcanoes) are tall conical mountains composed of lava flows and tephra in alternate layers, the strata that gives rise to the name. They are also known as composite volcanoes because they are created from multiple structures during different kinds of eruptions. Classic examples include Mount Fuji in Japan, Mayon Volcano in

1428-472: 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

1530-412: Is characterized by a rough, clinkery surface and is the typical texture of cooler basalt lava flows. Pāhoehoe is characterized by its smooth and often ropey or wrinkly surface and is generally formed from more fluid lava flows. Pāhoehoe flows are sometimes observed to transition to ʻaʻa flows as they move away from the vent, but never the reverse. More silicic lava flows take the form of block lava, where

1632-424: Is consequently limited to dense, stunted copses of Siberian dwarf pine and shrubby alder . The alpine tundra which dominates the landscape produces plentiful edible mushrooms and berries , especially lingonberry , Arctic raspberry , whortleberry and crowberry . Red fox , Arctic hare and ermine are notably abundant and hunted by the inhabitants. The island also supports a population of brown bears . In

1734-554: 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 called volcanology , sometimes spelled vulcanology . According to the theory of plate tectonics, Earth's lithosphere , its rigid outer shell, is broken into sixteen larger and several smaller plates. These are in slow motion, due to convection in

1836-668: Is due in part to the crash of the formerly lucrative herring fishery, to the extremely destructive tsunami of 1952, and general economic hardships in the more remote reaches of Russia since the fall of the Soviet Union. The island is now administered as part of the Sakhalin Oblast of the Russian Federation . Volcanoes A volcano is a rupture in the crust of a planetary-mass object , such as Earth , that allows hot lava , volcanic ash , and gases to escape from

1938-567: Is expressed using the volcanic explosivity index (VEI), which ranges from 0 for Hawaiian-type eruptions to 8 for supervolcanic eruptions. As of December 2022 , the Smithsonian Institution 's Global Volcanism Program database of volcanic eruptions in the Holocene Epoch (the last 11,700 years) lists 9,901 confirmed eruptions from 859 volcanoes. The database also lists 1,113 uncertain eruptions and 168 discredited eruptions for

2040-559: 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

2142-458: 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,

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2244-524: Is one of the several tuyas in the area of the Tuya River and Tuya Range in northern British Columbia. Tuya Butte was the first such landform analysed and so its name has entered the geological literature for this kind of volcanic formation. The Tuya Mountains Provincial Park was recently established to protect this unusual landscape, which lies north of Tuya Lake and south of the Jennings River near

2346-622: 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

2448-515: Is the longest river on the island. Paramushir was inhabited by the Ainu at the time of European contact. The island appears on an official map showing the territories of Matsumae Domain , a feudal domain of Edo period Japan dated 1644. Russian fur traders are known to have visited the island in 1711 and 1713, and Russian Orthodox missionaries established a church in 1747 to convert the local inhabitants. Imperial Russia 's claim of sovereignty over

2550-466: Is typically low in silica, shield volcanoes are more common in oceanic than continental settings. The Hawaiian volcanic chain is a series of shield cones, and they are common in Iceland , as well. Lava domes are built by slow eruptions of highly viscous lava. They are sometimes formed within the crater of a previous volcanic eruption, as in the case of Mount St. Helens , but can also form independently, as in

2652-592: 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

2754-584: 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

2856-732: 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

2958-490: 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

3060-547: 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

3162-600: The Cascade Volcanoes or the Japanese Archipelago , or the eastern islands of Indonesia . Hotspots are volcanic areas thought to be formed by mantle plumes , which are hypothesized to be columns of hot material rising from the core-mantle boundary. As with mid-ocean ridges, the rising mantle rock experiences decompression melting which generates large volumes of magma. Because tectonic plates move across mantle plumes, each volcano becomes inactive as it drifts off

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3264-722: 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

3366-618: The Hawaiian hotspot is an example. Volcanoes are usually not created where two tectonic plates slide past one another. Large eruptions can affect atmospheric temperature as ash and droplets of sulfuric acid obscure the Sun and cool Earth's troposphere . Historically, large volcanic eruptions have been followed by volcanic winters which have caused catastrophic famines. Other planets besides Earth have volcanoes. For example, volcanoes are very numerous on Venus. Mars has significant volcanoes. In 2009,

3468-630: 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

3570-522: The Invasion of the Kuril Islands , and combat operations continued through August 23, ending with the surrender of the surviving members of the Japanese garrison. The Soviets forcibly deported the remaining Japanese civilian inhabitants and sent the prisoners of war to labor camps . Kashiwabara was renamed Severo-Kurilsk and the island annexed by the Soviet Union in 1946. Japan formally gave up sovereignty over

3672-555: 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

3774-603: 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

3876-494: 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

3978-824: The landform and may give rise to smaller cones such as Puʻu ʻŌʻō on a flank of Kīlauea in Hawaii. Volcanic craters are not always at the top of a mountain or hill and may be filled with lakes such as with Lake Taupō in New Zealand. Some volcanoes can be low-relief landform features, with the potential to be hard to recognize as such and be obscured by geological processes. Other types of volcano include cryovolcanoes (or ice volcanoes), particularly on some moons of Jupiter , Saturn , and Neptune ; and mud volcanoes , which are structures often not associated with known magmatic activity. Active mud volcanoes tend to involve temperatures much lower than those of igneous volcanoes except when

4080-450: 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

4182-520: 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

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4284-524: 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

4386-476: 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

4488-691: 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

4590-554: 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

4692-610: 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

4794-629: 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

4896-458: 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,

4998-673: 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

5100-787: The Pacific Ring of Fire has volcanoes caused by convergent tectonic plates. Volcanoes can also form where there is stretching and thinning of the crust's plates, such as in the East African Rift , the Wells Gray-Clearwater volcanic field , and the Rio Grande rift in North America. Volcanism away from plate boundaries has been postulated to arise from upwelling diapirs from the core–mantle boundary , 3,000 kilometres (1,900 mi) deep within Earth. This results in hotspot volcanism , of which

5202-612: The Philippines, and Mount Vesuvius and Stromboli in Italy. Ash produced by the explosive eruption of stratovolcanoes has historically posed the greatest volcanic hazard to civilizations. The lavas of stratovolcanoes are higher in silica, and therefore much more viscous, than lavas from shield volcanoes. High-silica lavas also tend to contain more dissolved gas. The combination is deadly, promoting explosive eruptions that produce great quantities of ash, as well as pyroclastic surges like

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5304-503: 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

5406-503: 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

5508-609: The USGS defines a volcano as active whenever subterranean indicators, such as earthquake swarms , ground inflation, or unusually high levels of carbon dioxide or sulfur dioxide are present. The USGS defines a dormant volcano as any volcano that is not showing any signs of unrest such as earthquake swarms, ground swelling, or excessive noxious gas emissions, but which shows signs that it could yet become active again. Many dormant volcanoes have not erupted for thousands of years, but have still shown signs that they may be likely to erupt again in

5610-421: 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

5712-446: The boundary with the Yukon Territory . Mud volcanoes (mud domes) are formations created by geo-excreted liquids and gases, although several processes may cause such activity. The largest structures are 10 kilometres in diameter and reach 700 meters high. The material that is expelled in a volcanic eruption can be classified into three types: The concentrations of different volcanic gases can vary considerably from one volcano to

5814-402: The case of Lassen Peak . Like stratovolcanoes, they can produce violent, explosive eruptions, but the lava generally does not flow far from the originating vent. Cryptodomes are formed when viscous lava is forced upward causing the surface to bulge. The 1980 eruption of Mount St. Helens was an example; lava beneath the surface of the mountain created an upward bulge, which later collapsed down

5916-428: 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

6018-601: 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

6120-553: The enormous area they cover, and subsequent concealment under vegetation and glacial deposits, supervolcanoes can be difficult to identify in the geologic record without careful geologic mapping . Known examples include Yellowstone Caldera in Yellowstone National Park and Valles Caldera in New Mexico (both western United States); Lake Taupō in New Zealand; Lake Toba in Sumatra , Indonesia; and Ngorongoro Crater in Tanzania. Volcanoes that, though large, are not large enough to be called supervolcanoes, may also form calderas in

6222-469: 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

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6324-431: The flow is covered with angular, vesicle-poor blocks. Rhyolitic flows typically consist largely of obsidian . Tephra is made when magma inside the volcano is blown apart by the rapid expansion of hot volcanic gases. Magma commonly explodes as the gas dissolved in it comes out of solution as the pressure decreases when it flows to the surface . These violent explosions produce particles of material that can then fly from

6426-434: The formation of a submarine volcano off the coast of Mayotte . Subglacial volcanoes develop underneath ice caps . They are made up of lava plateaus capping extensive pillow lavas and palagonite . These volcanoes are also called table mountains, tuyas , or (in Iceland) mobergs. Very good examples of this type of volcano can be seen in Iceland and in British Columbia . The origin of the term comes from Tuya Butte , which

6528-445: The future. In an article justifying the re-classification of Alaska's Mount Edgecumbe volcano from "dormant" to "active", volcanologists at the Alaska Volcano Observatory pointed out that the term "dormant" in reference to volcanoes has been deprecated over the past few decades and that "[t]he term "dormant volcano" is so little used and undefined in modern volcanology that the Encyclopedia of Volcanoes (2000) does not contain it in

6630-412: The glossaries or index", however the USGS still widely employs the term. Previously a volcano was often considered to be extinct if there were no written records of its activity. Such a generalization is inconsistent with observation and deeper study, as has occurred recently with the unexpected eruption of the Chaitén volcano in 2008. Modern volcanic activity monitoring techniques, and improvements in

6732-448: 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

6834-492: The interior of a continent and lead to rifting. Early stages of rifting are characterized by flood basalts and may progress to the point where a tectonic plate is completely split. A divergent plate boundary then develops between the two halves of the split plate. However, rifting often fails to completely split the continental lithosphere (such as in an aulacogen ), and failed rifts are characterized by volcanoes that erupt unusual alkali lava or carbonatites . Examples include

6936-407: The island under the terms of the San Francisco Peace Treaty of 1951. In November 1952, Severo-Kurilsk was destroyed by the 1952 Severo-Kurilsk tsunami and was rebuilt in another location. Following the dissolution of the Soviet Union in 1990, the population of the island has decreased (2592 in 2002 census, 5180 in the 1989 census), and villages that once lined the coast are now ghost towns. This

7038-417: The island was initially confirmed under the terms of the Treaty of Shimoda in 1855, but was transferred to the Empire of Japan per the 1875 Treaty of Saint Petersburg , along with the rest of the Kuril Islands . The Japanese established a settlement, Kashiwabara, on the site of the largest Ainu village, which became the major port on the island, and a center for the commercial fishing industry. The island

7140-474: The island. In addition, the Imperial Japanese Army constructed four airfields: Kashiwabara Airfield in the northeast with Ki-43 Oscars , Kakumabestu Airfield on the southwest coast with a 3,800 ft (1,158 m) runway and Ki-44 Tojos , Kitanodai Airfield on the northeast coast with a 4,000 ft (1,219 m) runway, and Suribachi Airfield, an auxiliary base in the center of the south coast with two runways. The Imperial Japanese Navy had Musashi Airfield on

7242-421: 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

7344-469: 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,

7446-419: The mid-oceanic ridge is above sea level, volcanic islands are formed, such as Iceland . Subduction zones are places where two plates, usually an oceanic plate and a continental plate, collide. The oceanic plate subducts (dives beneath 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

7548-545: The modelling of the factors that produce eruptions, have helped the understanding of why volcanoes may remain dormant for a long time, and then become unexpectedly active again. The potential for eruptions, and their style, depend mainly upon the state of the magma storage system under the volcano, the eruption trigger mechanism and its timescale. For example, the Yellowstone volcano has a repose/recharge period of around 700,000 years, and Toba of around 380,000 years. Vesuvius

7650-415: The most dangerous type, are very rare; four are known from the last million years , and about 60 historical VEI 8 eruptions have been identified in the geologic record over millions of years. A supervolcano can produce devastation on a continental scale, and severely cool global temperatures for many years after the eruption due to the huge volumes of sulfur and ash released into the atmosphere. Because of

7752-438: The mud volcano is actually a vent of an igneous volcano. Volcanic fissure vents are flat, 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 generally do not explode catastrophically but are characterized by relatively gentle effusive eruptions . Since low-viscosity magma

7854-452: The next. Water vapour is typically the most abundant volcanic gas, followed by carbon dioxide and sulfur dioxide . Other principal volcanic gases include hydrogen sulfide , hydrogen chloride , and hydrogen fluoride . A large number of minor and trace gases are also found in volcanic emissions, for example hydrogen , carbon monoxide , halocarbons , organic compounds, and volatile metal chlorides. The form and style of an eruption of

7956-867: The north side of the mountain. Cinder cones result from eruptions of mostly small pieces of scoria and pyroclastics (both resemble cinders, hence the name of this volcano type) that build up around the vent. These can be relatively short-lived eruptions that produce a cone-shaped hill perhaps 30 to 400 metres (100 to 1,300 ft) high. Most cinder cones erupt only once and some may be found in monogenetic volcanic fields that may include other features that form when magma comes into contact with water such as maar explosion craters and tuff rings . Cinder cones may form as flank vents on larger volcanoes, or occur on their own. Parícutin in Mexico and Sunset Crater in Arizona are examples of cinder cones. In New Mexico , Caja del Rio

8058-475: 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;

8160-541: The ocean surface as new islands or floating pumice rafts . In May and June 2018, a multitude of seismic signals were detected by earthquake monitoring agencies all over the world. They took the form of unusual humming sounds, and some of the signals detected in November of that year had a duration of up to 20 minutes. An oceanographic research campaign in May 2019 showed that the previously mysterious humming noises were caused by

8262-420: The ocean surface, due to the rapid cooling effect and increased buoyancy in water (as compared to air), which often causes volcanic vents to form steep pillars on the ocean floor. Hydrothermal vents are common near these volcanoes, and some support peculiar ecosystems based on chemotrophs feeding on dissolved minerals. Over time, the formations created by submarine volcanoes may become so large that they break

8364-471: The ocean's surface. In the deep ocean basins, the tremendous weight of the water prevents the explosive release of steam and gases; however, submarine eruptions can be detected by hydrophones and by the discoloration of water because of volcanic gases . Pillow lava is a common eruptive product of submarine volcanoes and is characterized by thick sequences of discontinuous pillow-shaped masses which form underwater. Even large submarine eruptions may not disturb

8466-462: The one that destroyed the city of Saint-Pierre in Martinique in 1902. They are also steeper than shield volcanoes, with slopes of 30–35° compared to slopes of generally 5–10°, and their loose tephra are material for dangerous lahars . Large pieces of tephra are called volcanic bombs . Big bombs can measure more than 1.2 metres (4 ft) across and weigh several tons. A supervolcano is defined as

8568-425: The overlying mantle wedge, thus creating magma . This magma tends to be extremely viscous because of its high silica content, so it often does not reach the surface but cools and solidifies at depth . When it does reach the surface, however, a volcano is formed. Thus subduction zones are bordered by chains of volcanoes called volcanic arcs . Typical examples are the volcanoes in the Pacific Ring of Fire , such as

8670-595: The plume, and new volcanoes are created where the plate advances over the plume. The Hawaiian Islands are thought to have been formed in such a manner, as has the Snake River Plain , with the Yellowstone Caldera being part of the North American plate currently above the Yellowstone hotspot . However, the mantle plume hypothesis has been questioned. Sustained upwelling of hot mantle rock can develop under

8772-625: 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

8874-435: The same time interval. Volcanoes vary greatly in their level of activity, with individual volcanic systems having an eruption recurrence ranging from several times a year to once in tens of thousands of years. Volcanoes are informally described as erupting , active , dormant , or extinct , but the definitions of these terms are not entirely uniform among volcanologists. The level of activity of most volcanoes falls upon

8976-485: The same way; they are often described as "caldera volcanoes". Submarine volcanoes are common features of the ocean floor. Volcanic activity during the Holocene Epoch has been documented at only 119 submarine volcanoes, but there may be more than one million geologically young submarine volcanoes on the ocean floor. In shallow water, active volcanoes disclose their presence by blasting steam and rocky debris high above

9078-622: The solidified erupted material that makes up the mantle of a volcano may be stripped away that its inner anatomy becomes apparent. Using the metaphor of biological anatomy , such a process is called "dissection". Cinder Hill , a feature of Mount Bird on Ross Island , Antarctica , is a prominent example of a dissected volcano. Volcanoes that were, on a geological timescale, recently active, such as for example Mount Kaimon in southern Kyūshū , Japan , tend to be undissected. Eruption styles are broadly divided into magmatic, phreatomagmatic, and phreatic eruptions. The intensity of explosive volcanism

9180-503: The south-western tip of the island with two 4,000 ft (1,219 m) runways, one 4,300 ft (1,311 m) and another 4,200 ft (1,280 m), operating a variety of aircraft as well as a radar site. These bases were subject to sporadic air raids from the US Army Air Forces and US Navy based in the Aleutian Islands from 1943 until the end of the war . Soviet troops landed on Paramushir on August 18, 1945, during

9282-500: The spring crested auklet nest on the island. The straits between Paramushir and Shumshu island support a notably dense population of sea otters ; harbor seals are also common. North Pacific right whales , one of the rarest and the most endangered whale species are known to appear in the surrounding waters. Several species of charr and Pacific salmon spawn in its rivers, notably in the Tukharka river, which at 20 km (12 mi)

9384-406: The surrounding areas, and initially not seismically monitored before its unanticipated and catastrophic eruption of 1991. Two other examples of volcanoes that were once thought to be extinct, before springing back into eruptive activity were the long-dormant Soufrière Hills volcano on the island of Montserrat , thought to be extinct until activity resumed in 1995 (turning its capital Plymouth into

9486-434: The theory of plate tectonics. For example, some volcanoes are polygenetic with more than one period of activity during their history; other volcanoes that become extinct after erupting exactly once are monogenetic (meaning "one life") and such volcanoes are often grouped together in a geographical region. At the mid-ocean ridges , two tectonic plates diverge from one another as hot mantle rock creeps upwards beneath

9588-444: The thinned oceanic crust . The decrease of pressure in the rising mantle rock leads to adiabatic expansion and the partial melting of the rock, causing volcanism and creating new oceanic crust. Most divergent plate boundaries are at the bottom of the oceans, and so most volcanic activity on Earth is submarine, forming new seafloor . Black smokers (also known as deep sea vents) are evidence of this kind of volcanic activity. Where

9690-431: The underlying ductile mantle , and most volcanic activity on Earth takes place along plate boundaries, where plates are converging (and lithosphere is being destroyed) or are diverging (and new lithosphere is being created). During the development of geological theory, certain concepts that allowed the grouping of volcanoes in time, place, structure and composition have developed that ultimately have had to be explained in

9792-492: The volcano. Solid particles smaller than 2 mm in diameter ( sand-sized or smaller) are called volcanic ash. Tephra and other volcaniclastics (shattered volcanic material) make up more of the volume of many volcanoes than do lava flows. Volcaniclastics may have contributed as much as a third of all sedimentation in the geologic record. The production of large volumes of tephra is characteristic of explosive volcanism. Through natural processes, mainly erosion , so much of

9894-424: The volcanoes of the East African Rift . A volcano needs a reservoir of molten magma (e.g. a magma chamber), a conduit to allow magma to rise through the crust, and a vent to allow the magma to escape above the surface as lava. The erupted volcanic material (lava and tephra) that is deposited around the vent is known as a volcanic edifice , typically a volcanic cone or mountain. The most common perception of

9996-637: 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

10098-733: 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

10200-564: Was administered as part of Shimushu District of Nemuro Subprefecture of Hokkaidō . During World War II the island was strongly garrisoned by both the Imperial Japanese Army and Imperial Japanese Navy . The headquarters of the IJA 91st Infantry Division, responsible for defense of the northern Kurils, was established at Kashiwabara, and numerous coastal artillery positions and fortified bunkers were constructed in various locations around

10302-497: 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,

10404-421: Was described by Roman writers as having been covered with gardens and vineyards before its unexpected eruption of 79 CE , which destroyed the towns of Herculaneum and Pompeii . Accordingly, it can sometimes be difficult to distinguish between an extinct volcano and a dormant (inactive) one. Long volcano dormancy is known to decrease awareness. Pinatubo was an inconspicuous volcano, unknown to most people in

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