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101-500: Sangay (also known as Macas , Sanagay , or Sangai ) is an active stratovolcano in central Ecuador . It exhibits mostly strombolian activity. Geologically, Sangay marks the southern boundary of the Northern Volcanic Zone , and its position straddling two major pieces of crust accounts for its high level of activity. Sangay's approximately 500,000-year-old history is one of instability; two previous versions of

202-541: A ghost town ) and Fourpeaked Mountain in Alaska, which, before its September 2006 eruption, had not erupted since before 8000 BCE. Equator In spatial (3D) geometry , as applied in astronomy , the equator of a rotating spheroid (such as a planet ) is the parallel (circle of latitude) at which latitude is defined to be 0°. It is an imaginary line on the spheroid, equidistant from its poles , dividing it into northern and southern hemispheres. In other words, it

303-488: A meridian (a great circle passing through the two poles). The IUGG standard meridian is, to the nearest millimetre, 40,007.862917 kilometres (24,859.733480 mi), one arc-minute of which is 1,852.216 metres (6,076.82 ft), explaining the SI standardization of the nautical mile as 1,852 metres (6,076 ft), more than 3 metres (9.8 ft) less than the geographical mile . The sea-level surface of Earth (the geoid )

404-886: A mid-ocean 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 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

505-407: A brief pause, it erupted again on August 8, 1934, and has not completely quelled ever since, with heavy eruptive periods occurring in 1934–1937 and 1941–1942. Eruptions at Sangay exhibit strombolian activity, producing ashfall , lava flows , pyroclastic flows , and lahars . All known eruptions at the volcano have had a Volcanic Explosivity Index (VEI) of 3 or less. Despite its activity, Sangay

606-423: A catastrophic collapse that created a debris avalanche 5 km (3 mi) wide and up to 20 km (12 mi) in length. It was likely less voluminous than the volcano's first version, and its summit lay near Sangay's current summit. Sangay currently forms an almost perfect glacier -capped cone 5,286 m (17,343 ft) high, with a 35° slope and a slight northeast-southwest tilt. Its eastern flank marks

707-437: 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,

808-486: A large part of its southern caldera wall to slide off the mountain, forming an embayment lower on its slopes. This 400 m (1,312 ft) thick block, the best-preserved specimen of Sangay's early construction, consists of sequentially layered breccias , pyroclastic flows , and lahar deposits . Acidic andesites with just under 60% silicon dioxide dominate these flows, but more basic andesites can be found as well. Sangay's second edifice began to form anew after

909-443: 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

1010-452: A pristine ecology relatively untouched by human interaction, and the park hosts a biome ranging from alpine glaciers on the volcanoes' peaks to tropical forest on their flanks. Altitude and rainfall are the most significant local factors affecting fauna, and therefore the lushest ecosystems are found on the wetter parts of the volcano's eastern slope. The highest level below the snowline is dominated by lichen and bryophytes . Below this lies

1111-501: A significant distance. Mainly andesitic in composition, Sangay is highly active . The earliest report of a historical eruption was in 1628; ash fell as far away as Riobamba , located 50 km (31 mi) northwest of Sangay, and was severe enough to cover pastures and starve local livestock. The volcano erupted again in 1728, remaining essentially continuously active through 1916, with particularly heavy activity in 1738–1744, 1842–1843, 1849, 1854–1859, 1867–1874, 1872, and 1903. After

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1212-632: 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

1313-555: 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

1414-465: 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

1515-584: A year. Geological samples show that the Equator significantly changed positions between 48 and 12 million years ago, as sediment deposited by ocean thermal currents at the Equator shifted. The deposits by thermal currents are determined by the axis of Earth, which determines solar coverage of Earth's surface . Changes in Earth's axis can also be observed in the geographical layout of volcanic island chains, which are created by shifting hot spots under Earth's crust as

1616-512: A zone of small trees and shrubs which develops into montane forest , principally in western valleys and on well-irrigated eastern slopes, which occurs below 3,750 m (12,303 ft). Tree heights develop from 5 m (16 ft) near the top to up to 12 m (39 ft) below 3,000 m (9,843 ft); below 2,000 m (6,562 ft), subtropical rainforest is present, with temperatures between 18 and 24 °C (64 and 75 °F) and up to 500 cm (196.9 in) of rainfall. Fauna

1717-739: 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

1818-445: 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 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,

1919-401: Is a standard for use in cartography, geodesy, and satellite navigation including GPS , also has an equatorial radius of 6,378.137 km (3,963.191 mi). For both GRS 80 and WGS 84, this results in a length for the Equator of 40,075.0167 km (24,901.4609 mi). The geographical mile is defined as one arc-minute of the Equator, so it has different values depending on which radius

2020-552: Is also the equatorial radius used for the IERS 2003 ellipsoid. If it were really circular, the length of the equator would then be exactly 2π times the radius, namely 40,075.0142 km (24,901.4594 mi). The GRS 80 (Geodetic Reference System 1980) as approved and adopted by the IUGG at its Canberra, Australia meeting of 1979 has an equatorial radius of 6,378.137 km (3,963.191 mi). The WGS 84 (World Geodetic System 1984) which

2121-406: Is assumed. For example, by WSG-84, the distance is 1,855.3248 metres (6,087.024 ft), while by IAU-2000, it is 1,855.3257 metres (6,087.027 ft). This is a difference of less than one millimetre (0.039 in) over the total distance (approximately 1.86 kilometres or 1.16 miles). Earth is commonly modeled as a sphere flattened 0.336% along its axis. This makes the Equator 0.16% longer than

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2222-412: 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

2323-565: 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

2424-584: 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

2525-464: Is irregular, so the actual length of the Equator is not so easy to determine. Aviation Week and Space Technology on 9 October 1961 reported that measurements using the Transit IV-A satellite had shown the equatorial diameter from longitude 11° West to 169° East to be 1,000 feet (305 m) greater than its diameter ninety degrees away. Download coordinates as: The Equator passes through

2626-402: Is located in a remote, uninhabited region; only a large Plinian eruption could threaten occupied areas 30–100 km (19–62 mi) to its west. Nonetheless, a flank collapse on its eastern side, possible given the volcano's construction and history, could displace nearby forest and possibly affect settlements. Access to the volcano is difficult, as its current eruptive state constantly peppers

2727-462: Is more thermally stable than the northern rock, and to this is attributed the long break in volcanic activity in the Andes; Sangay occupies a position at the boundary between these two bodies, accounting for its high level of activity. Sangay developed in three distinct phases. Its oldest edifice, formed between 500,000 and 250,000 years ago, is evidenced today by a wide scattering of material opening to

2828-585: Is on the eastern edge of the Andes Mountains in central Ecuador about 160 km (99 mi) south of Quito and 20 km (12 mi) east of Riobamba . It lies within Sangay National Park. Two nearby volcanoes, Tungurahua and El Altar , are also located within the national park. The three volcanoes reach exceed 5,000 m (16,000 ft) above sea level with El Altar being the tallest. The principal rivers draining Sangay are

2929-537: 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

3030-606: Is similarly distributed, with distinct altitudinal zonation present. The highest altitudes support the endangered mountain tapir , cougar , guinea pig , and Andean fox . Lower down, the spectacled bear , jaguar , ocelot , margay , white-tailed deer , brocket deers , northern pudú , and endangered giant otter can all be found. Bird species common in the area include the Andean condor , Andean cock-of-the-rock , giant hummingbird , torrent duck , king vulture , and swallow-tailed kite . Sangay can be and has been climbed . It

3131-620: Is sourced from the Amazon rainforest. Observed rainfall averages from 4,827 mm (190.0 in) per year at Pastaza to the northeast of the volcano to 423 mm (16.7 in) at Riobamba just 20 km (12 mi) west of the summit in the rain shadow . Orographic lift and the Intertropical Convergence Zone are major factors in precipitation values. Annual temperatures see little variability but diurnal changes in temperature can be wide in more arid portions of

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3232-444: Is the intersection of the spheroid with the plane perpendicular to its axis of rotation and midway between its geographical poles . On and near the Equator (on Earth), noontime sunlight appears almost directly overhead (no more than about 23° from the zenith ) every day, year-round. Consequently, the Equator has a rather stable daytime temperature throughout the year. On the equinoxes (approximately March 20 and September 23)

3333-429: Is tilted towards or away from the sun, resulting in either summer or winter in both hemispheres. This also results in a corresponding movement of the equator away from the subsolar point, which is then situated over or near the relevant tropic circle . Nevertheless, temperatures are high year-round due to the Earth's axial tilt of 23.5° not being enough to create a low minimum midday declination to sufficiently weaken

3434-471: 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

3535-617: 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

3636-469: The Equator . It is disputed whether or not the volcano has a glacier though ice and snowfields are present. The snow line in this part of South America lies approximately 4,800 m (15,700 ft) above sea level. The mountain environment leads to significant changes in precipitation across short distances. Prevailing winds are out of the east, causing rainfall to be greatest to the east where moisture

3737-732: The Northern Volcanic Zone , a subgroup of Andean volcanoes whose northern limit is Nevado del Ruiz in Colombia . The next active volcano in the chain, Sabancaya , is in Peru , 1,600 km (990 mi) to the south. Sangay is above a seismogenic tectonic slab about 130 km (80 mi) beneath Sabancaya, reflecting a sharp difference in the thermal character of the subducted oceanic crust , between older rock beneath southern Ecuador and Peru (dated more than 32 million years old), and younger rock under northern Ecuador and Colombia (dated less than 22 million years old). The older southern rock

3838-752: The core–mantle boundary , 3,000 kilometres (1,900 mi) deep within Earth. This results in hotspot volcanism , of which 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,

3939-834: 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

4040-468: The subsolar point crosses Earth's equator at a shallow angle, sunlight shines perpendicular to Earth's axis of rotation, and all latitudes have nearly a 12-hour day and 12-hour night. The name is derived from medieval Latin word aequator , in the phrase circulus aequator diei et noctis , meaning 'circle equalizing day and night', from the Latin word aequare 'make equal'. The latitude of

4141-610: The Earth's equator is, by definition, 0° (zero degrees ) of arc. The equator is one of the five notable circles of latitude on Earth; the other four are the two polar circles (the Arctic Circle and the Antarctic Circle ) and the two tropical circles (the Tropic of Cancer and the Tropic of Capricorn ). The equator is the only line of latitude which is also a great circle —meaning, one whose plane passes through

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4242-565: The Equator. However, its island of Annobón is 155 km (96 mi) south of the Equator, and the rest of the country lies to the north. France , Norway ( Bouvet Island ), and the United Kingdom are the other three Northern Hemisphere -based countries which have territories in the Southern Hemisphere . Seasons result from the tilt of Earth's axis away from a line perpendicular to the plane of its revolution around

4343-661: The Llushin, Palora , and the Upano , each of which have numerous smaller tributaries on the middle and upper slopes. Flash flooding from significant rainfall is frequent and erosion is a problem despite thick forests. Rivers drain east into the Amazon Basin . Topography is dominated by volcanic and glacial features. Hanging valleys from prior glaciation feature numerous waterfalls and lakes. Sangay reaches high enough to enjoy snow cover on its upper slopes despite its location near

4444-622: 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

4545-597: The Sun's disk contacts the horizon. Earth bulges slightly at the Equator; its average diameter is 12,742 km (7,918 mi), but the diameter at the equator is about 43 km (27 mi) greater than at the poles. Sites near the Equator, such as the Guiana Space Centre in Kourou , French Guiana , are good locations for spaceports as they have the fastest rotational speed of any latitude, 460 m (1,509 ft)/sec. The added velocity reduces

4646-513: The Sun's rays even during the solstices. High year-round temperatures extend to about 25° north or south of the equator, although the moderate seasonal temperature difference is defined by the opposing solstices (as it is at higher latitudes) near the poleward limits of this range. Near the equator, there is little temperature change throughout the year, though there may be dramatic differences in rainfall and humidity. The terms summer, autumn, winter and spring do not generally apply. Lowlands around

4747-545: The Sun. Throughout the year, the Northern and Southern hemispheres are alternately turned either toward or away from the Sun, depending on Earth's position in its orbit. The hemisphere turned toward the Sun receives more sunlight and is in summer, while the other hemisphere receives less sun and is in winter (see solstice ). At the equinoxes , Earth's axis is perpendicular to the Sun rather than tilted toward or away, meaning that day and night are both about 12 hours long across

4848-613: 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

4949-534: The United States' National Weather Service issued an ashfall advisory as the volcano went into a state of unrest, producing a plume of volcanic ash. Mariners traveling in the vicinity were cautioned about the possibility of debris. Sangay is one of two active volcanoes in the Sangay National Park, the other being Tungurahua to the north. As such it has been listed as a UNESCO World Heritage Site since 1983. The area's isolation has allowed it to maintain

5050-477: The afternoon and 23 °C (73 °F) around sunrise. Rainfall is very high away from cold ocean current upwelling zones, from 2,500 to 3,500 mm (100 to 140 in) per year. There are about 200 rainy days per year and average annual sunshine hours are around 2,000. Despite high year-round sea level temperatures, some higher altitudes such as the Andes and Mount Kilimanjaro have glaciers. The highest point on

5151-737: The axis and crust move. This is consistent with the Indian tectonic plate colliding with the Eurasian tectonic plate , which is causing the Himalayan uplift. The International Association of Geodesy (IAG) and the International Astronomical Union (IAU) use an equatorial radius of 6,378.1366 km (3,963.1903 mi) (codified as the IAU 2009 value). This equatorial radius is also in the 2003 and 2010 IERS Conventions. It

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5252-510: 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

5353-402: 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

5454-464: The center of the globe. The plane of Earth's equator, when projected outwards to the celestial sphere , defines the celestial equator . In the cycle of Earth's seasons , the equatorial plane runs through the Sun twice a year : on the equinoxes in March and September . To a person on Earth, the Sun appears to travel along the equator (or along the celestial equator) at these times. Locations on

5555-495: The cities may have reached a population between 15,000 and 100,000 people. They were surrounded by agricultural fields that archaeologist Stéphen Rostain speculates may have been particularly productive because their proximity to Sangay. Seventeen additional archaeological sites had been located prior to the 2024 announcement including potential monuments. An estimated 30,000 people lived in the region before Spanish occupation began in 1534. The Spanish prospected for gold on and around

5656-418: The east, defined by a crest about 4,000 m (13,120 ft) high, pockmarked by secondary ridges; it is thought to have been 15–16 km (9–10 mi) in diameter, with a summit 2 to 3 km (1 to 2 mi) southeast of the present summit. The curved shape of the remnants of this first structure shows that it suffered a massive flank collapse, scattering the nearby forest lowlands with debris and causing

5757-619: The edge of the Amazon Rainforest , and its western flank is a flat plain of volcanic ash , sculpted into steep gorges up to 600 m (1,970 ft) deep by heavy rainfall. It has a west-east trending summit ridge , capped by three active craters and a lava dome . Sangay has been active in its current form for at least 14,000 years, and is still filling out the area left bare by its earlier incarnations, being smaller than either of them. Uniquely, in its 500,000 years of activity, its magma plume has never changed composition or moved

5858-799: 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

5959-404: The equator experience the shortest sunrises and sunsets because the Sun's daily path is nearly perpendicular to the horizon for most of the year. The length of daylight (sunrise to sunset) is almost constant throughout the year; it is about 14 minutes longer than nighttime due to atmospheric refraction and the fact that sunrise begins (or sunset ends) as the upper limb, not the center, of

6060-632: The equator generally have a tropical rainforest climate , also known as an equatorial climate, though cold ocean currents cause some regions to have tropical monsoon climates with a dry season in the middle of the year, and the Somali Current generated by the Asian monsoon due to continental heating via the high Tibetan Plateau causes Greater Somalia to have an arid climate despite its equatorial location. Average annual temperatures in equatorial lowlands are around 31 °C (88 °F) during

6161-473: The equator is at the elevation of 4,690 metres (15,387 ft), at 0°0′0″N 77°59′31″W  /  0.00000°N 77.99194°W  / 0.00000; -77.99194  ( highest point on the equator ) , found on the southern slopes of Volcán Cayambe [summit 5,790 metres (18,996 ft)] in Ecuador . This is slightly above the snow line and is the only place on the equator where snow lies on

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6262-431: 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

6363-610: 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

6464-512: The fuel needed to launch spacecraft eastward (in the direction of Earth's rotation) to orbit, while simultaneously avoiding costly maneuvers to flatten inclination during missions such as the Apollo Moon landings . The precise location of the Equator is not truly fixed; the true equatorial plane is perpendicular to the Earth's rotation axis , which drifts about 9 metres (30 ft) during

6565-585: 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

6666-466: 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

6767-492: 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

6868-625: The land of eleven sovereign states . Indonesia is the country straddling the greatest length of the equatorial line across both land and sea. Starting at the Prime Meridian and heading eastwards, the Equator passes through: The Equator also passes through the territorial seas of three countries: Maldives (south of Gaafu Dhaalu Atoll ), Kiribati (south of Buariki Island ), and the United States (south of Baker Island ). Despite its name, no part of Equatorial Guinea lies on

6969-457: The massif with molten rock and other ejecta . For these reasons it is not nearly as well-studied as other, similarly active volcanoes in the Andes and elsewhere; the first detailed study of the volcano was not published until 1999. The current phase of the ongoing eruption began on 26 March 2019, and it has remained in continuing eruption status (intermittent eruptive events without a break of 3 months or more) as of January 2024. On 15 June 2022,

7070-418: The massive sector collapse that damaged the first, being constructed between 100,000 and 50,000 years ago. Remnants of its second structure are within the southern and eastern parts of the debris from its first collapse; some remnants of the volcano lie to the west and north as well. Sangay's second structure is believed to have had an east-to-west elongated summit, and like its first summit structure, it suffered

7171-419: 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

7272-551: 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

7373-415: 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

7474-446: The mountain is hampered by its remoteness, poor weather conditions, river flooding, and the danger of falling ejecta , the volcano is regularly climbed, a feat first achieved by Robert T. Moore in 1929. Folklore sourced from native people in the region compared Sangay to a lighthouse surrounded by a sea, which represented the dense jungle. The density of the jungle caused people to lose their way, but seeing ash and steam emissions from

7575-525: The mountain routes impassable. Nonetheless, the Instituto Ecuatoriano Forestal y de Areas Naturales, which maintains an office near the mountain, facilitate such activities by providing local guides and rooms for rent to visitors. Ascension takes between 7 and 10 days from Quito . Conditions on the volcano are usually very wet and foggy, which may impair visibility significantly during the ascent. Volcano#Active A volcano

7676-471: The mountain were destroyed in massive flank collapses, evidence of which still litters its surroundings today. Due to its remoteness, Sangay hosts a significant biological community with fauna such as the mountain tapir , giant otter , Andean cock-of-the-rock and king vulture . Since 1979, its ecological community has been protected as part of the Sangay National Park . Although climbing

7777-592: The mountain's slopes. Higher elevations never rise above 0 °C (32 °F). Climate change threatens the snowpack and the high altitude grasslands. Lying at the eastern edge of the Andean cordillera , Sangay was formed by volcanic processes associated with the subduction of the Nazca Plate under the South American Plate at the Peru–Chile Trench . It is the southernmost volcano in

7878-438: 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

7979-452: 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

8080-876: 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

8181-549: 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

8282-420: 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

8383-471: 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

8484-468: 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

8585-425: 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

8686-619: 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

8787-435: 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

8888-492: 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

8989-622: 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

9090-406: 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

9191-434: 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

9292-444: 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

9393-431: 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

9494-458: The volcano through the 16th and 17th Centuries and settled the area but expeditions undertaken in the 19th Century noted no inhabitants nearby. Modern development of the eastern side of the volcano began in the early 20th Century. The volcano and lands surrounding it were placed in a National Wildlife Reserve by the Ecuadorian government in 1975. This became Sangay National Park in 1979, which

9595-522: The volcano would help orient travelers along their way. Scientists have interpreted folklore like this as evidence of frequent and long-lasting eruptive activity at Sangay. In January 2024, archaeologists announced the discovery of archaeological sites on the east side of the volcano known as the Upano Valley sites . It is estimated that this cluster of urban settlements were inhabited between about 500 BCE to sometime between 300 and 600 CE. Altogether

9696-492: 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

9797-424: 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

9898-445: The whole of Earth. Near the equator, this means the variation in the strength of solar radiation is different relative to the time of year than it is at higher latitudes: maximum solar radiation is received during the equinoxes, when a place at the equator is under the subsolar point at high noon, and the intermediate seasons of spring and autumn occur at higher latitudes; and the minimum occurs during both solstices, when either pole

9999-421: 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

10100-521: Was expanded in 1992. The United Nations added it to their list of World Heritage Sites in 1983. From 1992 to 2005, poaching and human development led the UN to consider the site as being endangered but removed this status in 2005. The modern native inhabitants of the region primarily consist of Quechua people . The name Sangay comes from the Quechuan languages and is translated as "the frightener." Sangay

10201-482: Was first ascended in 1929 by Robert T. Moore , prior to its current eruption beginning in 1934. However, the volcano's current active state presents dangers to mountaineers in the form of falling ejecta ; in 1976, two members of an expedition on the volcano were struck and killed by falling debris. In addition, the volcano is located in a remote region with poor roads and is difficult to access, and periods of heavy rainfall can flood rivers and cause landslides , rendering

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