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75-569: The Ōkāreka Embayment extends from the western margin of Lake Tarawera to include to its north Lake Ōkāreka and in the west Lake Tikitapu and the eastern half of Lake Rotokakahi . Both the Ōkāreka Embayment and the Tarawera volcanic complex are inside the old Ōkataina Caldera , often termed the Ōkataina volcanic centre . The caldera forming its eastern boundary has been called the Haroharo Caldera , but as no major single event formed it, this

150-842: 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

225-465: A German explorer Dr Ernst Dieffenbach described near Rotoroa the first recorded description of layered tephras from ash fall in New Zealand. However correlation between eruption years and what has been coined as tephrostratigraphy is not straightforward where there is no historical written record. Radiocarbon dating was later used in the vicinity, to date recent eruptions, as deposition of each tephra

300-437: 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,

375-405: A hut and on returning the following season found that both his spears and hut had been turned to ashes. Lake Tarawera is 298 m (978 ft) above sea level, and has a surface area of 41 km (16 sq mi). To the north-west is Lake Ōkataina , to the west as you go south, lakes Ōkāreka , Tikitapu and Rotokākahi and to the south-east Lake Rotomahana . Lake Tarawera township

450-405: A lesser-known Black Terrace spring). As of 2023 no sample of any terrace has been recovered, so any claim of survival of any of the terrace formations is unproven. Lake Tarawera is classified as mesotrophic, with a trophic level index of 3.0 in 2014 which was a decline. The native bush has regenerated since the 1886 eruption. Lake Tarawera is home to eels and rainbow trout . During

525-426: A level just before the 1314 Kaharoa eruption of 17 m (56 ft) above present lake levels. The 1314 eruption blocked the outlet in a temporary dam to a temporary lake height of 32 m (105 ft) above present lake levels, which was subsequently eroded with a great flood at one stage, to reach by the time of European settlement first surveys 8 m (26 ft) below present lake level. The lake outlet

600-638: A linear trend in height decrease since then. Also assumed destroyed were the nearly famed Pink and White Terraces which were located to the south of the lake and accessed via boat across the lake and the old Lake Rotomahana. However, in February 2011 a team mapping the lake floor discovered what appeared to be part of the Pink Terraces. The lowest two tiers of the terraces were reportedly found in their original place at 60 metres (200 ft) deep (too deep for scuba diving without special gas gear). Subsequently,

675-443: 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

750-603: A portion of the White Terraces was reportedly rediscovered in June 2011. The announcement of the rediscovery of the White Terraces coincided with the 125th anniversary of the eruption of Mt. Tarawera in 1886. It was thought that the rest of the terraces may be buried in sediment rather than having been destroyed. More recent research question these earlier findings and reports the Pink and White terrace spring sites instead lie on land (along with

825-435: A rural settlement, and covers 4.50 km (1.74 sq mi). It had an estimated population of 280 as of June 2024, with a population density of 62 people per km . Lake Tarawere township is part of the larger Kaingaroa-Whakarewarewa statistical area . The township had a population of 267 at the 2018 New Zealand census , an increase of 60 people (29.0%) since the 2013 census , and a decrease of 3 people (−1.1%) since

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900-632: 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

975-555: 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

1050-465: 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

1125-727: Is a volcanic field of over 60 cinder cones. Based on satellite images, it has been suggested that cinder cones might occur on other terrestrial bodies in the Solar system too; on the surface of Mars and the Moon. Stratovolcanoes (composite volcanoes) are tall conical mountains composed of lava flows and tephra in alternate layers, the strata that gives rise to the name. They are also known as composite volcanoes because they are created from multiple structures during different kinds of eruptions. Classic examples include Mount Fuji in Japan, Mayon Volcano in

1200-445: 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,

1275-412: 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

1350-486: Is deposited from the Rotorua event. The soils between the tephra layers in the Ōkāreka Embayment have been analysed and are consistent with a cold dry climate between 25.2 ka to 14 ka and a more wet and warm climate since. Okareka Tephra was produced from vents in an eruption of Mount Tarawera 23,535 ± 300 years BP, so does not have an origin in the embayment. A repeat of the Rotorua eruption with its ash distribution against

1425-554: Is derived from the name of Vulcano , a volcanic island in the Aeolian Islands of Italy whose name in turn comes from Vulcan , the god of fire in Roman mythology . The study of volcanoes is called volcanology , sometimes spelled vulcanology . According to the theory of plate tectonics, Earth's lithosphere , its rigid outer shell, is broken into sixteen larger and several smaller plates. These are in slow motion, due to convection in

1500-567: Is expressed using the volcanic explosivity index (VEI), which ranges from 0 for Hawaiian-type eruptions to 8 for supervolcanic eruptions. As of December 2022 , the Smithsonian Institution 's Global Volcanism Program database of volcanic eruptions in the Holocene Epoch (the last 11,700 years) lists 9,901 confirmed eruptions from 859 volcanoes. The database also lists 1,113 uncertain eruptions and 168 discredited eruptions for

1575-422: Is less than the 2,358 L/s (83.3 cu ft/s) rainfall on the lake surface itself and much less than either the estimated total outflow from the lake approaching 10,000 L/s (350 cu ft/s). Therefore there is a fair subsurface inflow into the lake. An estimate has been made of total inflows both surface and subsurface from the surrounding lake catchments The main hot water sources are in

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1650-429: Is on the western shore, between Lake Tarawera and Lake Ōkāreka. The main road access is from Rotorua to the west. The lake was substantially affected by the eruption of Mount Tarawera on 10 June 1886 to the lake's east. There were changes in lake level and sediment carriage. The lake has a large catchment. This includes Lake Tarawera's immediate catchment, being 143.8 km (55.5 sq mi) in area, and

1725-524: Is one of the several tuyas in the area of the Tuya River and Tuya Range in northern British Columbia. Tuya Butte was the first such landform analysed and so its name has entered the geological literature for this kind of volcanic formation. The Tuya Mountains Provincial Park was recently established to protect this unusual landscape, which lies north of Tuya Lake and south of the Jennings River near

1800-561: Is perhaps better regarded as a general categorisation term, explaining why some maps of the Horahora Caldera include the embayment. It is now regarded as a subsidiary volcanic part of the Ōkataina Caldera related to a mechanism of collapse and subsidence at the edges of a major event caldera due to lateral movement of magma . The Ōkataina Caldera has in the last 21,000 years contributed a total magma eruptive volume greater than about 80 km (19 cu mi). The Northern Dome, just to

1875-523: Is the largest of a series of lakes which surround the volcano Mount Tarawera in the North Island of New Zealand . Like the mountain, it lies within the Ōkataina Caldera . It is located 18 kilometres (11 mi) to the east of Rotorua , and beneath the peaks of the Tarawera massif i.e. Wahanga, Ruawahia, Tarawera and Koa. Tarawera means "Burnt Spear", named by a visiting hunter who left his bird spears in

1950-466: Is typically low in silica, shield volcanoes are more common in oceanic than continental settings. The Hawaiian volcanic chain is a series of shield cones, and they are common in Iceland , as well. Lava domes are built by slow eruptions of highly viscous lava. They are sometimes formed within the crater of a previous volcanic eruption, as in the case of Mount St. Helens , but can also form independently, as in

2025-563: Is where Tapahoro lava flows created by the 5526 ± 145 BP Whakatane eruption run into a 14,009 ± 155 BP Pokohu lava flow which the Tarawera River flows across in a 10 m (33 ft) wide channel. Before the Whakatane eruption it is thought the lake had a lower level than at present. Immediately after the Whakatane eruption its level increased by at least 100 m (330 ft) with gradual cutting down and Taupō Rift subsidence to

2100-476: The 2006 census . There were 132 households, comprising 132 males and 135 females, giving a sex ratio of 0.98 males per female, with 30 people (11.2%) aged under 15 years, 33 (12.4%) aged 15 to 29, 126 (47.2%) aged 30 to 64, and 78 (29.2%) aged 65 or older. Ethnicities were 91.0% European/ Pākehā , 11.2% Māori , 2.2% Pacific peoples , 4.5% Asian , and 2.2% other ethnicities. People may identify with more than one ethnicity. Although some people chose not to answer

2175-600: The Cascade Volcanoes or the Japanese Archipelago , or the eastern islands of Indonesia . Hotspots are volcanic areas thought to be formed by mantle plumes , which are hypothesized to be columns of hot material rising from the core-mantle boundary. As with mid-ocean ridges, the rising mantle rock experiences decompression melting which generates large volumes of magma. Because tectonic plates move across mantle plumes, each volcano becomes inactive as it drifts off

2250-792: 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,

2325-770: 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

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2400-612: The Philippines, and Mount Vesuvius and Stromboli in Italy. Ash produced by the explosive eruption of stratovolcanoes has historically posed the greatest volcanic hazard to civilizations. The lavas of stratovolcanoes are higher in silica, and therefore much more viscous, than lavas from shield volcanoes. High-silica lavas also tend to contain more dissolved gas. The combination is deadly, promoting explosive eruptions that produce great quantities of ash, as well as pyroclastic surges like

2475-622: The Te Rere eruptions totals about 11.5 km (2.8 cu mi). All the vents in the Ōkareka Embayment lie on the Haroharo linear vent zone's western end. The Rotorua eruption now dated at 15,635 ± 412 cal.yr BP , was a two phase eruption commencing with a plinian eruption that deposited 2.6 cubic kilometres (0.62 cu mi) of material to the north-west from a vent now under the Trig 7693 dome and that lasted no more than 4 days. Significant ash cover

2550-609: The USGS defines a volcano as active whenever subterranean indicators, such as earthquake swarms , ground inflation, or unusually high levels of carbon dioxide or sulfur dioxide are present. The USGS defines a dormant volcano as any volcano that is not showing any signs of unrest such as earthquake swarms, ground swelling, or excessive noxious gas emissions, but which shows signs that it could yet become active again. Many dormant volcanoes have not erupted for thousands of years, but have still shown signs that they may be likely to erupt again in

2625-503: 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

2700-402: 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

2775-477: The catchment of the nearby higher lakes, being a total of 380.9 km (147.1 sq mi), with an estimated mean annual precipitation of 20,001 L/s (706.3 cu ft/s). Lake Tarawera is filled primarily by water flowing through the volcanic rocks and ashes, only about 42% being from water flowing in streams, etc. The mean surface inflows are estimated to be: Thus surface water inflows contribute 1,649.5 L/s (58.25 cu ft/s) which

2850-520: The census's question about religious affiliation, 59.6% had no religion, 32.6% were Christian and 1.1% had other religions. Of those at least 15 years old, 69 (29.1%) people had a bachelor's or higher degree, and 27 (11.4%) people had no formal qualifications. 66 people (27.8%) earned over $ 70,000 compared to 17.2% nationally. The employment status of those at least 15 was that 114 (48.1%) people were employed full-time, 42 (17.7%) were part-time, and 3 (1.3%) were unemployed. Volcano A volcano

2925-525: The east of Lake Tikitapu formed 25,171 ± 964 years ago in the Te Rere rhyolite eruption which also had other vents in the Ōkataina Volcanic Complex. Such domes typically form over a vent that have an initial pyroclastic eruption and the vent(s) for this eruption lies under the Northern and Eastern domes. The Te Rere tephra deposits from the initial pyroclastic eruption had a volume of 5 km (1.2 cu mi) and are widely distributed. The DRE volume of all

3000-772: 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

3075-431: 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

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3150-592: 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

3225-568: 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

3300-461: 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

3375-492: 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

3450-419: 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

3525-545: The modelling of the factors that produce eruptions, have helped the understanding of why volcanoes may remain dormant for a long time, and then become unexpectedly active again. The potential for eruptions, and their style, depend mainly upon the state of the magma storage system under the volcano, the eruption trigger mechanism and its timescale. For example, the Yellowstone volcano has a repose/recharge period of around 700,000 years, and Toba of around 380,000 years. Vesuvius

3600-415: 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

3675-438: 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

3750-452: 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

3825-867: The north side of the mountain. Cinder cones result from eruptions of mostly small pieces of scoria and pyroclastics (both resemble cinders, hence the name of this volcano type) that build up around the vent. These can be relatively short-lived eruptions that produce a cone-shaped hill perhaps 30 to 400 metres (100 to 1,300 ft) high. Most cinder cones erupt only once and some may be found in monogenetic volcanic fields that may include other features that form when magma comes into contact with water such as maar explosion craters and tuff rings . Cinder cones may form as flank vents on larger volcanoes, or occur on their own. Parícutin in Mexico and Sunset Crater in Arizona are examples of cinder cones. In New Mexico , Caja del Rio

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3900-541: The ocean surface as new islands or floating pumice rafts . In May and June 2018, a multitude of seismic signals were detected by earthquake monitoring agencies all over the world. They took the form of unusual humming sounds, and some of the signals detected in November of that year had a duration of up to 20 minutes. An oceanographic research campaign in May 2019 showed that the previously mysterious humming noises were caused by

3975-420: 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

4050-471: 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

4125-462: The one that destroyed the city of Saint-Pierre in Martinique in 1902. They are also steeper than shield volcanoes, with slopes of 30–35° compared to slopes of generally 5–10°, and their loose tephra are material for dangerous lahars . Large pieces of tephra are called volcanic bombs . Big bombs can measure more than 1.2 metres (4 ft) across and weigh several tons. A supervolcano is defined as

4200-425: 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

4275-595: The plume, and new volcanoes are created where the plate advances over the plume. The Hawaiian Islands are thought to have been formed in such a manner, as has the Snake River Plain , with the Yellowstone Caldera being part of the North American plate currently above the Yellowstone hotspot . However, the mantle plume hypothesis has been questioned. Sustained upwelling of hot mantle rock can develop under

4350-460: The prevailing winds but towards the major population centres of Rotoroa , Hamilton and Auckland would be very destructive and disruptive. The town of Rotorua would be made uninhabitable by a 0.5 metres (1 ft 8 in) ash fall, as happened in the Rotorua eruption. This would collapse all normally built homes and 60 square kilometres (23 sq mi) of land would be denuded of all vegetation. Lake Tarawera Lake Tarawera

4425-435: 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

4500-485: The same way; they are often described as "caldera volcanoes". Submarine volcanoes are common features of the ocean floor. Volcanic activity during the Holocene Epoch has been documented at only 119 submarine volcanoes, but there may be more than one million geologically young submarine volcanoes on the ocean floor. In shallow water, active volcanoes disclose their presence by blasting steam and rocky debris high above

4575-622: 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

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4650-487: The southern section of the lake at the Wairua Stream, Hot Water Beach and Te Puha and Tarawera fumaroles. There is also a small geothermal area at Humphrey's Bay, to the south of Lake Ōkataina. Water varies between 37 °C (99 °F) and 90 °C (194 °F). Lake Tarawera's outflow at its north east end, has been heavily influenced by the local geology, with a mean 7 m /s (250 cu ft/s) discharged on

4725-511: The summer it is popular for both fishing and water sports, and also camping as there a number of hot water beaches. Much of the more inaccessible lake shore is part of the Lake Tarawera Scenic Reserve with hunting permits possible. There are multiple popular walking trails with access to thermal features and rock paintings, often without a permit. The township on the shores of Lake Tarawera is described by Statistics New Zealand as

4800-546: The surface into the Tarawera River , which flows north-east into the Bay of Plenty . An estimate of subsurface outflow has been made by measuring flow below Tarawera Falls where total river flow has increased to 9.9 m /s (350 cu ft/s). Lake Tarawera has been modified by eruptions within the Ōkataina Caldera , most recently the 1314 ± 12 CE Kaharoa eruption and the 10 June 1886 eruption. Its current outlet control

4875-406: 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

4950-434: 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

5025-444: 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

5100-431: 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

5175-492: 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

5250-424: 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

5325-491: Was assessed at a peak flow of 700 m /s (25,000 cu ft/s). After 1906 it is now known that the main change in lake level relative to reference sea level would have been due to the slow subsidence of this area of the Taupō Rift. This rate can be estimated to have been about 1.5 m (4 ft 11 in) in 100 years from the nearest NZ Geonet station RGTA data which has been operative since November 2007 and shows

5400-523: Was blocked for two decades after the 1886 eruption and the lake level increased to a maximum of 12.8 m (42 ft) above its present level. The eruption killed over 120 people, and buried the Māori village of Te Wairoa on the southwest shore of the lake. The last major decrease in lake level occurred in a flood of 1904 down the Tarawera River valley after the new volcanic material dam first broke on 1 November 1904. The main flood surge on 3 November 1904

5475-421: 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

5550-475: Was followed by a period of quiescence and soil formation. Such a series as published in 1990 (so the dates may have been modified by scientific discourse since) reads (with some translation from original jargon) : The impact on the Waikato region must have been marked as lake sediment from near Hamilton, New Zealand shows evidence of very active plant turnover just before almost 5 cm (2.0 in) of tephra

5625-482: Was towards the Rotorua area (hence the name) but ash fall was as far away as Auckland with a total ash volume of 6 km (1.4 cu mi) including later minor ash deposits. The largely degassed magma body then in a dominantly effusive rhyolite dome forming process built up Trig 7693 and Middle Dome to the south east of the Ōkāreka Embayment over several years, but no more than 6, to a total volume of 0.62 cubic kilometres (0.15 cu mi). As far back as 1839

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