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130-670: In 1257, a catastrophic eruption occurred at Samalas, a volcano on the Indonesian island of Lombok . The event had a probable Volcanic Explosivity Index of 7, making it one of the largest volcanic eruptions during the Holocene epoch . It left behind a large caldera that contains Lake Segara Anak . Later volcanic activity created more volcanic centres in the caldera, including the Barujari cone, which remains active. The event created eruption columns reaching tens of kilometres into

260-543: A ghost town ) and Fourpeaked Mountain in Alaska, which, before its September 2006 eruption, had not erupted since before 8000 BCE. Dacitic Dacite is relatively common, occurring in many tectonic settings. It is associated with andesite and rhyolite as part of the subalkaline tholeiitic and calc-alkaline magma series . The word dacite comes from Dacia , a province of the Roman Empire which lay between

390-886: 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

520-457: A phreatic (steam explosion powered) stage that deposited 3 centimetres (1.2 in) of ash over 400 square kilometres (150 sq mi) of northwest Lombok. A magmatic stage followed, and lithic -rich pumice rained down, the fallout reaching a thickness of 8 centimetres (3.1 in) both upwind on East Lombok and on Bali. This was followed by lapilli rock as well as ash fallout, and pyroclastic flows that were partially confined within

650-522: A content of 20% to 60% quartz, with plagioclase making up 65% or more of its feldspar content. However, while the IUGS recommends classifying volcanic rocks on the basis of their mineral composition whenever possible, dacites are often so fine-grained that mineral identification is impractical. The rock must then be classified chemically based on its content of silica and alkali metal oxides ( K 2 O plus Na 2 O ). The TAS classification puts dacite in

780-705: A decade-long thinning of tree rings in Norway and Sweden. Cooling may have lasted for 4–5 years based on simulations and tree ring data. Another effect of the eruption-induced climate change may have been a brief decrease in atmospheric carbon dioxide concentrations. A decrease in the growth rate of atmospheric carbon dioxide concentrations was recorded after the 1992 Pinatubo eruption; several mechanisms for volcanically driven decreases in atmospheric CO 2 concentration have been proposed, including colder oceans absorbing extra CO 2 and releasing less of it, decreased respiration rates leading to carbon accumulation in

910-657: A geoscientist of the Pantheon-Sorbonne University who had already suspected that a volcano on that island may be responsible, to conclude that the Samalas volcano was this volcano. The role of the Samalas eruption in the global climate events was confirmed by comparing the geochemistry of glass shards found in ice cores to that of the eruption deposits on Lombok. Later, geochemical similarities between tephra found in polar ice cores and eruption products of Samalas reinforced this localization. Ice cores in

1040-437: 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,

1170-681: A growth of ice caps and sea ice , and glaciers in the Alps, Bhutan Himalaya , the Pacific Northwest and the Patagonian Andes grew in size. The advances of ice after the Samalas eruption may have strengthened and prolonged the climate effects. Later volcanic activity in 1269, 1278, and 1286 and the effects of sea ice on the North Atlantic would have further contributed to ice expansion. The glacier advances triggered by

1300-443: 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

1430-545: A reference to the aftermath of the eruption. Mount Rinjani avalanched and Mount Samalas collapsed, followed by large flows of debris accompanied by the noise coming from boulders. These flows destroyed Pamatan. All houses were destroyed and swept away, floating on the sea, and many people died. During seven days, big earthquakes shook the Earth, stranded in Leneng, dragged by the boulder flows, People escaped and some of them climbed

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1560-535: A source in a volcano near Greenland had been considered but Icelandic records made no mention of eruptions around 1250 and it was found in 1988 that ice cores in Antarctica —at Byrd Station and the South Pole —also contained sulfate signals. Sulfate spikes were also found in ice cores from Ellesmere Island , Canada, and the Samalas sulfate spikes were used as stratigraphic markers for ice cores even before

1690-579: A temperature of about 1,000 °C (1,830 °F). Its eruption may have been triggered either by the entry of new magma into the magma chamber or the effects of gas bubble buoyancy. The eruption had a Volcanic Explosivity Index of 7, making it one of the largest eruptions of the current epoch, the Holocene. Eruptions of comparable intensity include the Kurile lake eruption (in Kamchatka , Russia) in

1820-518: A tephra layer sampled at Dongdao island in the South China Sea has been tentatively linked to Samalas. Ash and aerosols might have impacted humans and corals at large distances from the eruption. There are several estimates of the volumes expelled during the various stages of the Samalas eruption. The first stage reached a volume of 12.6–13.4 cubic kilometres (3.0–3.2 cu mi). The phreatomagmatic phase has been estimated to have had

1950-401: A thick felsic continental plate. Oceanic crust is hydrothermally altered causing addition of quartz and sodium. As the young, hot oceanic plate is subducted under continental crust, the subducted slab partially melts and interacts with the upper mantle through convection and dehydration reactions. The process of subduction creates metamorphism in the subducting slab. When this slab reaches

2080-514: A time marker in chronostratigraphic studies. Ice cores from Illimani in Bolivia contain thallium and sulfate spikes from the eruption. For comparison, the 1991 eruption of Pinatubo ejected only about a tenth of the amount of sulfur erupted by Samalas. Sulfate deposition from the Samalas eruption has been noted at Svalbard , and the fallout of sulfuric acid from the volcano may have directly affected peatlands in northern Sweden. In addition,

2210-401: A volcanic eruption; one explanation is that climate models tend to assume that aerosol optical depth increases linearly with the quantity of erupted sulfur when in reality self-limiting processes limit its growth. The possible occurrence of an El Niño before the eruption may have further reduced the cooling. The Samalas eruption, together with 14th century cooling, is thought to have set off

2340-446: A volcanic event, the global spread indicating a tropical volcano as the cause. The suggestion that Samalas/Rinjani might be the source volcano was first raised in 2012, since the other candidate volcanoes— El Chichón and Quilotoa —did not match the chemistry of the sulfur spikes. El Chichon, Quilotoa and Okataina were also inconsistent with the timespan and size of the eruption. All houses were destroyed and swept away, floating on

2470-632: 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

2600-555: 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

2730-465: 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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2860-559: A volume of 0.3 cubic kilometres (0.072 cu mi) dense rock equivalent, may have been deposited by an eruption from either Rinjani or Samalas; it is dated to 2,550 ± 50 BP, at the end of the time range during which Rinjani formed. The deposits from this eruption reached thicknesses of 6 centimetres (2.4 in) 28 kilometres (17 mi) away. Additional eruptions by either Rinjani or Samalas are dated 11,980 ± 40, 11,940 ± 40, and 6,250 ± 40 BP. Eruptive activity continued until about 500 years before 1257. Most volcanic activity now occurs at

2990-422: A volume of 0.9–3.5 cubic kilometres (0.22–0.84 cu mi). The total dense rock equivalent volume of the whole eruption was at least 40 cubic kilometres (9.6 cu mi). The magma erupted was trachydacitic and contained amphibole , apatite , clinopyroxene , iron sulfide , orthopyroxene , plagioclase , and titanomagnetite . It formed out of basaltic magma by fractional crystallization and had

3120-401: Is 3 centimetres (1.2 in) thick. Most of the tephra was deposited west-southwest of Samalas. Considering the thickness of Samalas Tephra found at Mount Merapi, the total volume may have reached 32–39 cubic kilometres (7.7–9.4 cu mi). The dispersal index (the surface area covered by an ash or tephra fall) of the eruption reached 7,500 square kilometres (2,900 sq mi) during

3250-739: 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

3380-412: 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

3510-405: Is contentious; Tambora might have produced more sulfur but Samalas may have been more effective at injecting tephra into the stratosphere . After the eruption, it probably took weeks to months for the fallout to reach large distances from the volcano. When large scale volcanic eruptions inject aerosols into the atmosphere, they can form stratospheric veils. These reduce the amount of light reaching

3640-565: 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

3770-584: 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

3900-425: Is often aphanitic microcrystalline , with a web of minute feldspars mixed with interstitial grains of quartz or tridymite; but in many dacites it is largely vitreous, while in others it is felsitic or cryptocrystalline. Dacite usually forms as an intrusive rock such as a dike or sill . Examples of this type of dacite outcrop are found in northwestern Montana and northeastern Bulgaria . Nevertheless, because of

4030-537: 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

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4160-471: 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

4290-617: 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

4420-776: The Danube River and Carpathian Mountains (now modern Romania and Moldova ) where the rock was first described. The term dacite was used for the first time in the scientific literature in the book Geologie Siebenbürgens ( The Geology of Transylvania ) by Austrian geologists Franz Ritter von Hauer and Guido Stache. Dacite was originally defined as a new rock type to separate calc-alkaline rocks with oligoclase phenocrysts (dacites) from rocks with orthoclase phenocrysts (rhyolites). Dacite consists mostly of plagioclase feldspar and quartz with biotite , hornblende , and pyroxene ( augite or enstatite ). The quartz appears as rounded, corroded phenocrysts , or as an element of

4550-654: The Great Famine of 1315–17 . The price for cereal increased in Britain, France, and Italy, augmented by price speculation . Outbreaks of disease occurred during this time in the Middle East, England and Italy, including typhus . During and after the winter of 1258–59, exceptional weather was reported less commonly, but the winter of 1260–61 was very severe in Iceland, Italy, and elsewhere. The disruption caused by

4680-523: The Oligocene – Miocene , with old volcanic units cropping out in southern parts of the island. Samalas was built up by volcanic activity before 12,000 BP . Rinjani formed between 11,940 ± 40 and 2,550 ± 50 BP, with an eruption between 5,990 ± 50 and 2,550 ± 50 BP forming the Propok Pumice with a dense rock equivalent volume of 0.1 cubic kilometres (0.024 cu mi). The Rinjani Pumice, with

4810-436: The biosphere , and increased productivity of the biosphere due to increased scattered sunlight and the fertilization of oceans by volcanic ash. The Samalas signal is only inconsistently reported from tree ring climate information, and the temperature effects were likewise limited, probably because the large sulfate output altered the average size of particles and thus their radiative forcing . Climate modelling indicated that

4940-752: 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,

5070-834: 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

5200-493: The mantle wedge . Before the eruption, Mount Samalas may have been as tall as 4,200 ± 100 metres (13,780 ± 330 ft), based on reconstructions that extrapolate upwards from the surviving lower slopes, and thus taller than Mount Kinabalu which is presently the highest mountain in tropical Asia; Samalas's current height is less than that of the neighbouring Mount Rinjani, which reaches 3,726 metres (12,224 ft). The oldest geological units on Lombok are from

5330-563: The 13th century. The first settlement of New Zealand most likely occurred 1230–1280 AD and the arrival of people there and on other islands in the region may reflect such a climate-induced migration. Contemporary chronicles in Europe mention unusual weather conditions in 1258. Reports from 1258 in France and England indicate a dry fog, giving the impression of a persistent cloud cover to contemporary observers. Medieval chronicles say that in 1258,

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5460-772: The 7th millennium BC , the Mount Mazama (United States, Oregon ) eruption in the 6th millennium BC, the Cerro Blanco ( Argentina ) eruption about 4,200 years ago, the Minoan eruption (in Santorini , Greece) between 1627 and 1600 BC, the Tierra Blanca Joven eruption of Lake Ilopango (El Salvador) in the 6th century, and Mt. Tambora in 1815. Such large volcanic eruptions can result in catastrophic impacts on humans and widespread loss of life both close to

5590-495: The Barujari volcano with eruptions in 1884, 1904, 1906, 1909, 1915, 1966, 1994, 2004, and 2009; Rombongan was active in 1944. Volcanic activity mostly consists of explosive eruptions and ash flows. The rocks of the Samalas volcano are mostly dacitic , with a SiO 2 content of 62–63 percent by weight. Volcanic rocks in the Banda arc are mostly calc-alkaline ranging from basalt over andesite to dacite . The crust beneath

5720-691: The Muntilan Tephra, which was found on the slopes of other volcanoes of Java, but could not be linked to eruptions in these volcanic systems. This tephra is now considered to be a product of the 1257 eruption and is thus also known as the Samalas Tephra. It reaches thicknesses of 2–3 centimetres (0.79–1.18 in) on Mount Merapi , 15 centimetres (5.9 in) on Mount Bromo , 22 centimetres (8.7 in) at Ijen and 12–17 centimetres (4.7–6.7 in) on Bali's Agung volcano. In Lake Logung 340 kilometres (210 mi) away from Samalas on Java it

5850-680: The O3 sector. In hand specimen, many of the hornblende and biotite dacites are grey or pale brown and yellow rocks with white feldspars, and black crystals of biotite and hornblende. Other dacites, especially pyroxene-bearing dacites, are darker colored. In thin section, dacites may have an aphanitic to porphyritic texture. Porphyritic dacites contain blocky highly zoned plagioclase phenocrysts and/or rounded corroded quartz phenocrysts. Subhedral hornblende and elongated biotite grains are present. Sanidine phenocrysts and augite (or enstatite ) are found in some samples. The groundmass of these rocks

5980-497: The P1 and P3 phases is not known individually, but the two phases combined (not including P2) lasted between 12 and 15 hours. The eruption column reached a height of 39–40 kilometres (24–25 mi) during the first stage (P1), and of 38–43 kilometres (24–27 mi) during the third stage (P3); it was high enough that SO 2 in it and its sulfur isotope ratio was influenced by photolysis at high altitudes. The eruption began with

6110-622: 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

6240-454: The Samalas caldera. The eruption that formed the caldera was first recognized in 2003, and in 2004 a volume of 10 cubic kilometres (2.4 cu mi) was attributed to this eruption. Early research considered that the caldera-forming eruption occurred between 1210 and 1300. In 2013, Lavigne suggested that the eruption occurred between May and October 1257, resulting in the climate changes of 1258. Several villages on Lombok are constructed on

6370-517: The Samalas eruption are documented on Baffin Island , where the advancing ice killed and then incorporated vegetation, conserving it. Likewise, a change in Arctic Canada from a warm climate phase to a colder one coincides with the Samalas eruption. According to 2003 reconstructions, summer cooling reached 0.69 °C (1.24 °F) in the southern hemisphere and 0.46 °C (0.83 °F) in

6500-399: The Samalas eruption may have reduced global temperatures by approximately 2 °C (3.6 °F), a value largely not replicated by proxy data. Better modelling with a general circulation model that includes a detailed description of the aerosol indicated that the principal temperature anomaly occurred in 1258 and continued until 1261. Climate models tend to overestimate the climate impact of

6630-613: 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

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6760-505: The atmosphere and pyroclastic flows that buried much of Lombok and crossed the sea to reach the neighbouring island of Sumbawa . The flows destroyed human habitations, including the city of Pamatan , which was the capital of a kingdom on Lombok. Ash from the eruption fell as far as 340 kilometres (210 mi) away in Java ; the volcano deposited more than 10 cubic kilometres (2.4 cu mi) of rocks and ash. The aerosols injected into

6890-464: The atmosphere reduced the solar radiation reaching the Earth's surface, causing a volcanic winter and cooling the atmosphere for several years. This led to famines and crop failures in Europe and elsewhere, although the exact scale of the temperature anomalies and their consequences is still debated. The eruption may have helped trigger the Little Ice Age , a centuries-long cold period during

7020-601: The beginning of the Little Ice Age and the Samalas eruption. Around 1300, settlements in many places of the Pacific relocated, perhaps because of a sea level drop that occurred after 1250, and the 1991 eruption of Pinatubo has been linked to small drops in sea level. Climate change triggered by the Samalas eruption and the beginning of the Little Ice Age may have led to people in Polynesia migrating southwestward in

7150-510: 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

7280-589: The caldera left by the eruption was estimated to be 10–30 kilometres (6.2–18.6 mi), and the location was estimated to be close to the equator and probably north of it. While at first no clear-cut climate anomaly could be correlated to the 1257 sulfate layers, in 2000 climate phenomena were identified in medieval records of the northern hemisphere that are characteristic for volcanic eruptions. Earlier, climate alterations had been reported from studies of tree rings and climate reconstructions. The deposits showed that climate disturbances reported at that time were due to

7410-402: 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

7540-483: The consequences of the Samalas eruption exists. The Babad Lombok describe how villages on Lombok were destroyed during the mid-13th century by ash, gas and lava flows, and two additional documents known as the Babad Sembalun and Babad Suwung may also reference the eruption. They are also—together with other texts—the source of the name "Samalas" while the name "Suwung"—"quiet and without life"—may, in turn, be

7670-410: The early 20th century. The time period 1250–1300 was heavily disturbed by volcanic activity from four eruptions in 1230, 1257, 1276 and 1286, and is recorded by a moraine from a glacial advance on Disko Island , although the moraine may indicate a pre-Samalas cold spell. These volcanic disturbances along with positive feedback effects from increased ice may have started the Little Ice Age even without

7800-645: The early flowering of violets according to reports from the Kingdom of France , European summers were colder after the eruption, and winters were long and cold. The Samalas eruption came after the Medieval Climate Anomaly , a period early in the last millennium with unusually warm temperatures, and at a time when a period of climate stability was ending, with earlier eruptions in 1108, 1171, and 1230 already having upset global climate. Subsequent time periods displayed increased volcanic activity until

7930-799: 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

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8060-403: The eruption although it is possible that the population of Lombok fled before the eruption. In Bali the number of inscriptions dropped off after the eruption, and Bali and Lombok may have been depopulated by it, possibly for generations, allowing King Kertanegara of Singhasari on Java to conquer Bali in 1284 with little resistance. It might have taken about a century for Lombok to recover from

8190-406: The eruption and supplied its phreatomagmatic phase with 0.1–0.3 cubic kilometres (0.024–0.072 cu mi) of water. Alternatively, the water could have been supplied by aquifers . Approximately 2.1–2.9 cubic kilometres (0.50–0.70 cu mi) of rock from Rinjani fell into the caldera, a collapse that was witnessed by humans and left a collapse structure that cuts into Rinjani's slopes facing

8320-446: The eruption column and thus would not have entered the stratosphere, the quantities that have been modelled for the Samalas halogen release (227 ± 18 million tonnes of chlorine and up to 1.3 ± 0.3 million tonnes of bromine) would have reduced stratospheric ozone< although only a small portion of the halogens would have reached the stratosphere. One hypothesis is that the resulting increase in ultraviolet radiation on

8450-566: The eruption may have influenced the onset of the Mudéjar revolt of 1264–1266 in Iberia . Swollen and rotting in groups of five or six, the dead lay abandoned in pigsties, on dunghills, and in the muddy streets. Matthew Paris , chronicler of St. Albans A famine in London has been linked to this event; this food crisis was not extraordinary and there were issues with harvests already before

8580-568: The eruption may have interrupted a prolonged drought period. The climate effect in Alaska may have been moderated by the nearby ocean. In 1259, Western Europe and the west coastal North America had mild weather and there is no evidence for summer precipitation changes in Central Europe . Tree rings do not show much evidence of precipitation changes. The eruption led to global disaster in 1257–1258. Very large volcanic eruptions can cause significant human hardship, including famine, away from

8710-491: The eruption. The famine occurred at a time of political crisis between King Henry III of England and the English magnates . Witnesses reported a death toll of 15,000 to 20,000 in London. A mass burial of famine victims was found in the 1990s in the centre of London. Matthew Paris of St Albans described how until mid-August 1258, the weather alternated between cold and strong rain, causing high mortality. The resulting famine

8840-594: The eruption. The western coast of Sumbawa was depopulated and remains so to this day; presumably the local populace viewed the area devastated by the eruption as "forbidden" and this memory persisted until recent times. Historical events in Oceania are usually poorly dated, making it difficult to assess the timing and role of specific events, but there is evidence that between 1250 and 1300 there were crises in Oceania, for example at Easter Island , which may be linked with

8970-749: The event and recorded it on the Babad Lombok , a document written on palm leaves . Samalas (also known as Rinjani Tua ) was part of what is now the Rinjani volcanic complex, on Lombok, in Indonesia. The remains of the volcano form the Segara Anak caldera, with Mount Rinjani at its eastern edge. Since the destruction of Samalas, two new volcanoes, Rombongan and Barujari, have formed in the caldera. Mount Rinjani has also been volcanically active, forming its own crater, Segara Muncar. Other volcanoes in

9100-422: The first stage and 110,500 square kilometres (42,700 sq mi) during the third stage, implying that these were a Plinian eruption and an Ultraplinian eruption respectively. Pumice falls with a fine graining and creamy colour from the Samalas eruption have been used as a tephrochronological marker on Bali. Tephra from the volcano was found in ice cores as far as 13,500 kilometres (8,400 mi) away, and

9230-431: 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

9360-555: 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

9490-585: 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

9620-409: The geography of Lombok; they and sediments eroded from the Samalas deposits extended the shorelines of the island and buried river valleys ; a new river network developed on the volcanic deposits after the eruption. Volcanic rocks ejected by the eruption covered Bali and Lombok and parts of Sumbawa. Tephra in the form of layers of fine ash from the eruption fell as far away as Java, forming part of

9750-466: 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

9880-468: The ground-mass. The plagioclase in dacite ranges from oligoclase to andesine and labradorite . Sanidine occurs, although in small proportions, in some dacites, and when abundant gives rise to rocks that form transitions to the rhyolites. The relative proportions of feldspars and quartz in dacite, and in many other volcanic rocks, are illustrated in the QAPF diagram . This defines dacite as having

10010-726: The growth season), light tree rings in Canada and northwestern Siberia from 1258 and 1259 respectively, thin tree rings in the Sierra Nevada , California, U.S. cooling in sea surface temperature records off the Korean Peninsula and in lake sediments of northeastern China, a very wet monsoon in Vietnam, droughts in many places in the Northern Hemisphere as well as in southern Thailand cave records, and

10140-502: The hills. The city of Pamatan, capital of a kingdom on Lombok, was destroyed, and both disappeared from the historical record. The royal family survived the disaster according to the Javanese text, which also mentions reconstruction and recovery efforts after the eruption, and there is no clear-cut evidence that the kingdom itself was destroyed by the eruption, as the history there is poorly known in general. Thousands of people died during

10270-457: The history of the magma. The formation of dacite provides a great deal of information about the connection between oceanic crust and continental crust. It provides a model for the generation of felsic, buoyant, perennial rock from a mafic, dense, short-lived one. The process by which dacite forms has been used to explain the generation of continental crust during the Archean eon . At that time,

10400-492: 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

10530-401: The island incinerating the island's vegetation. Interaction between these flows and the air triggered the formation of additional eruption clouds and secondary pyroclastic flows. Where the flows entered the sea north and east of Lombok, steam explosions created pumice cones on the beaches and additional secondary pyroclastic flows. Pyroclastic flows descended the northern slopes of Samalas; on

10660-401: The last thousand years. Before the site of the eruption was known, an examination of ice cores around the world had detected a large spike in sulfate deposition from around 1257 providing strong evidence of a large volcanic eruption occurring at that time. In 2013, scientists linked the historical records about Mount Samalas to these spikes. These records were written by people who witnessed

10790-463: The lava with water, so this eruption phase was probably phreatomagmatic . It was followed by three pumice fallout episodes, with deposits over an area wider than was reached by any of the other eruption phases. These pumices fell up to 61 kilometres (38 mi) to the east, against the prevailing wind, in Sumbawa, where they are up to 7 centimetres (2.8 in) thick. The deposition of these pumices

10920-428: The mantle and initiates the dehydration reactions, minerals such as talc , serpentine , mica and amphiboles break down generating a more sodic melt. The magma then continues to migrate upwards causing differentiation and becomes even more sodic and silicic as it rises. Once at the cold surface, the sodium rich magma crystallizes plagioclase, quartz and hornblende. Accessory minerals like pyroxenes provide insight to

11050-419: 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

11180-551: 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

11310-478: The moderately high silica content, dacitic magma is quite viscous and therefore prone to explosive eruption. A notorious example of this is Mount St. Helens in which dacite domes formed from previous eruptions. Pyroclastic flows may also be of dacitic composition as is the case with the Fish Canyon Tuff of La Garita Caldera . Dacitic magma is formed by the subduction of young oceanic crust under

11440-415: 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

11570-438: 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

11700-494: The need for changes in solar radiation, though this theory is not without disagreement. The Samalas eruption in Europe is sometimes used as a chronological marker for the beginning of the Little Ice Age. Other inferred effects of the eruption are: Other regions such as Alaska were mostly unaffected. There is little evidence that tree growth was influenced by cold in what is now the Western United States , where

11830-452: 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

11960-876: 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

12090-451: The northern and southern hemisphere display sulfate spikes associated with Samalas. The signal is the strongest in the southern hemisphere over the last 1000 years; one reconstruction even considers it the strongest of the last 2500 years. It is about eight times stronger than that of Krakatau . In the northern hemisphere it is only exceeded by the signal of the destructive 1783/1784 Laki eruption. The ice core sulfate spikes have been used as

12220-445: The northern hemisphere. More recent proxy data indicate that a temperature drop of 0.7 °C (1.3 °F) occurred in 1258 and of 1.2 °C (2.2 °F) in 1259, but with differences between various geographical areas. For comparison, the radiative forcing of Pinatubo's 1991 eruption was about a seventh of that of the Samalas eruption. Sea surface temperatures too decreased by 0.3–2.2 °C (0.54–3.96 °F), triggering changes in

12350-451: The ocean circulations. Ocean temperature and salinity changes may have lasted for a decade. Precipitation and evaporation both decreased, evaporation reduced more than precipitation. Volcanic eruptions can also deliver bromine and chlorine into the stratosphere, where they contribute to the breakdown of ozone through their oxides chlorine monoxide and bromine monoxide . While most bromine and chlorine erupted would have been scavenged by

12480-549: 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

12610-420: 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

12740-471: 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

12870-468: 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

13000-425: 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

13130-619: 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

13260-507: The production of dacitic magma was more ubiquitous, due to the availability of young, hot oceanic crust. Today, the colder oceanic crust that subducts under most plates is not able to melt prior to the dehydration reactions, thus inhibiting the process. Dacitic magma was encountered in a drillhole during geothermal exploration on Kīlauea in 2005. At a depth of 2488 m, the magma flowed up the wellbore. This produced several kilograms of clear, colorless vitric (glassy, non-crystalline) cuttings at

13390-480: The pyroclastic flow deposits from the 1257 event. A major volcanic event in 1257–1258 was first discovered from data in ice cores; specifically increased sulfate concentrations were found in 1980 within the Crête ice core ( Greenland , drilled in 1974) associated with a deposit of rhyolitic ash. The eruption was known as the "mystery eruption". The 1257–1258 layer is the third largest sulfate signal at Crête; at first

13520-680: The region include Agung , Batur , and Bratan , on the island of Bali to the west. Lombok is one of the Lesser Sunda Islands in the Sunda Arc of Indonesia, a subduction zone where the Australian Plate subducts beneath the Eurasian Plate at a rate of 7 centimetres per year (2.8 in/year). The magmas feeding Mount Samalas and Mount Rinjani are likely derived from peridotite rocks beneath Lombok, in

13650-435: 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

13780-492: 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

13910-519: The sea, and many people died. Babad Lombok The conclusive link between these events and an eruption of Samalas was made in 2013 on the basis of radiocarbon dating of trees on Lombok and the Babad Lombok , a series of writings in Old Javanese on palm leaves that described a catastrophic volcanic event on Lombok which occurred before 1300. These findings induced Franck Lavigne ,

14040-622: 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

14170-674: The southern slopes they split into two branches that proceeded to the Alas Strait to the east and the Bali Strait to the west. Coral reefs were buried by the pyroclastic flows; some flows crossed the Alas Strait between Sumbawa and Lombok and formed deposits on Sumbawa. These pyroclastic flows reached volumes of 29 cubic kilometres (7.0 cu mi) on Lombok, and thicknesses of 35 metres (115 ft) as far as 25 kilometres (16 mi) from Samalas. The pyroclastic flows altered

14300-405: The sulfate aerosols may have extracted large amounts of the beryllium isotope Be from the stratosphere ; such an extraction event and the subsequent deposition in ice cores may mimic changes in solar activity . The amount of sulfur dioxide released by the eruption has been estimated to be 158 ± 12 million tonnes. Whether the mass release was higher or lower than for Tambora

14430-593: The summer was cold and rainy, causing floods and bad harvests, with cold from February to June. Frost occurred in the summer 1259 according to Russian chronicles. In Europe and the Middle East , changes in atmospheric colours, storms, cold, and severe weather were reported in 1258–1259, with agricultural problems extending to North Africa . In Europe, excess rain, cold and high cloudiness damaged crops and caused famines followed by epidemics , although 1258–1259 did not lead to famines as bad as some other famines such as

14560-617: The surface and cause lower temperatures, which can lead to poor crop yields. Such sulfate aerosols in the case of the Samalas eruption may have remained at high concentrations for about three years according to findings in the Dome C ice core in Antarctica , although a smaller amount may have persisted for an additional time. Other records of the eruption's impact include decreased tree growth in Mongolia between 1258 and 1262 based on tree ring data, frost rings (tree rings damaged by frost during

14690-426: The surface of Earth may have led to widespread immunosuppression in human populations, explaining the onset of epidemics in the years following the eruption. Samalas, along with the 1452/1453 mystery eruption and the 1815 eruption of Mount Tambora , was one of the strongest cooling events in the last millennium, even more so than at the peak of the Little Ice Age. After an early warm winter 1257–1258 resulting in

14820-813: The surface. The dacite magma is a residual melt of the typical basalt magma of Kīlauea. Dacite is relatively common and occurs in various tectonic and magmatic contexts: The type locality of dacite is Gizella quarry near Poieni, Cluj in Romania . Other occurrences of dacite in Europe are Germany ( Weiselberg ), Greece ( Nisyros and Thera ), Italy (in Bozen quartz porphyry, and Sardinia ), Austria (Styrian Volcano Arc), Scotland ( Argyll ), Slovakia , Spain (El Hoyazo near Almería ), France ( Massif de l'Esterel ) and Hungary (Csódi Hill). Sites outside Europe include Iran , Morocco , New Zealand (volcanic region of Taupo ), Turkey , USA and Zambia . Dacite

14950-406: 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

15080-434: 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

15210-444: 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

15340-411: The time it would have taken for its traces to reach the polar ice sheets and be recorded in ice cores and the pattern of tephra deposits. 1257 is the most likely year of the eruption, although a date of 1258 is also possible. The phases of the eruption are also known as P1 (phreatic and magmatic phase), P2 (phreatomagmatic with pyroclastic flows), P3 ( Plinian ) and P4 (pyroclastic flows). The duration of

15470-431: 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

15600-546: The valleys on Samalas's western flank. Some ash deposits were eroded by the pyroclastic flows, which created furrow structures in the ash. Pyroclastic flows crossed 10 kilometres (6.2 mi) of the Bali Sea , reaching the Gili Islands to the northwest of Samalas and Taliwang east of Lombok, while pumice blocks presumably covered the Alas Strait between Lombok and Sumbawa . The deposits show evidence of interaction of

15730-478: The volcano and at greater distances. The eruption created the 6–7 kilometres (3.7–4.3 mi) wide Segara Anak caldera where the Samalas mountain was formerly located; within its 700–2,800 metres (2,300–9,200 ft) high walls, a 200 metres (660 ft) deep crater lake formed called Lake Segara Anak . The Barujari cone rises 320 metres (1,050 ft) above the water of the lake and has erupted 15 times since 1847. A crater lake may have existed on Samalas before

15860-452: The volcano due to their effect on climate. The social effects are often reduced by the resilience of humans; thus there is often uncertainty about causal links between volcano-induced climate variations and societal changes at the same time. Western and central Indonesia at the time were divided into competing kingdoms that often built temple complexes with inscriptions documenting historical events. However, little direct historical evidence of

15990-523: The volcano is about 20 kilometres (12 mi) thick, and the lower extremity of the Wadati–Benioff zone is about 164 kilometres (102 mi) deep. The events of the 1257 eruption have been reconstructed through geological analysis of the deposits it left and by historical records. The eruption probably occurred during the northern summer in September (uncertainty of 2–3 months) that year, in light of

16120-486: The volcano that caused them was known. The ice cores indicated a large sulfate spike, accompanied by tephra deposition, around 1257–1259, the largest in 7,000 years and twice the size of the spike due to the 1815 eruption of Tambora . In 2003, a dense rock equivalent volume of 200–800 cubic kilometres (48–192 cu mi) was estimated for this eruption, but it was also proposed that the eruption might have been somewhat smaller and richer in sulfur. The volcano responsible

16250-492: 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

16380-424: 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

16510-421: 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

16640-435: Was followed by another stage of pyroclastic flow activity, probably caused by the collapse of the eruption column that generated the flows. At this time the eruption changed from an eruption-column-generating stage to a fountain-like stage and the caldera began to form. These pyroclastic flows were deflected by the topography of Lombok, filling valleys and moving around obstacles such as older volcanoes as they expanded across

16770-545: Was severe enough that grain was imported from Germany and Holland. Volcano 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 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,

16900-554: Was thought to be located in the Ring of Fire but could not be identified at first; Tofua volcano in Tonga was proposed at first but dismissed, as the Tofua eruption was too small to generate the 1257 sulfate spikes. A volcanic eruption in 1256 at Harrat al-Rahat near Medina was also too small to trigger these events. Other proposals included several simultaneous eruptions. The diameter of

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