80-878: The Waitahaia River is a river in the Waiapu Valley of the Gisborne Region of New Zealand 's North Island . It flows northeast from the southern end of the Raukumara Range to reach the Mata River 20 kilometres (12 mi) west of Te Puia Springs . Brown trout , a European species of fish, was introduced into New Zealand for fishing in the late 1860s. "Place name detail: Waitahaia River" . New Zealand Gazetteer . New Zealand Geographic Board . Retrieved 12 July 2009 . 38°01′S 178°04′E / 38.017°S 178.067°E / -38.017; 178.067 This article about
160-561: A NZ$ 110 million financial redress, and the return of sites culturally significant to the iwi totally approximately 5,898 hectares (14,570 acres). Ngāti Porou have a number of whakataukī or pēpeha (sayings or proverbs) relating to Waiapu Valley. These include: NB: This section is based on text from Mackay, Joseph Angus (1949). Historic Poverty Bay and the East Coast, N.I., N.Z , available here at The New Zealand Electronic Text Centre . There were several “ gold rushes ” in
240-598: A Ngāpuhi war party, and been made their slave in the Bay of Islands . He escaped several years later, and was protected by the missionaries , who introduced him to Christianity , and taught him to read and write. When he returned to the Waiapu Valley in 1834, he introduced his people to the religion. Richard Taylor's drawing of the church, done after visiting in April 1839, can be viewed here . Whakawhitirā Pā , in which
320-484: A magma chamber below the surface. The process that forms volcanoes is called volcanism . On Earth, volcanoes are most often found where tectonic plates are diverging or converging , and because most of Earth's plate boundaries are underwater, most volcanoes are found underwater. For example, a mid-ocean ridge , such as the Mid-Atlantic Ridge , has volcanoes caused by divergent tectonic plates whereas
400-440: A bridge was built from Tikitiki to Waiomatatini , to the protest of local Māori who were concerned that it would disturb the taniwha. The night before the bridge was completed, a storm came washing the bridge away — the weather till then had been calm. From then, one person would drown in the river nearly every year. If it did not happen one year, two would drown the next. A local tohunga , George Gage (Hori Te Kou-o-rehua Keeti)
480-437: 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,
560-406: A number of bridges in the valley have had to be raised to accommodate their rising riverbeds. As the riverbed rises, so does the river, which is causing extensive riverbank erosion. The banks eroded at a rate of 8 metres (26 ft) per year between 1988 and 1997. By the 2003 to 2008 period this rate had doubled, with 22 metres (72 ft) per year eroding in 2005 and 2006. This erosion threatens
640-443: 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
720-718: A river in the Gisborne District is a stub . You can help Misplaced Pages by expanding it . Waiapu Valley Waiapu Valley , also known as the Waiapu catchment , Waiapu River valley or simply Waiapu , is a valley in the north of the Gisborne Region on the East Coast of the North Island of New Zealand. It is the catchment area for the Waiapu River and its tributaries , and covers 1,734 square kilometres (670 sq mi). The Raukumara Range forms
800-476: A safe place. When it turned out that the metal was only mundic, Reupane became an object of ridicule, and, afterwards, was known as “Tommy Poorfellow.” The area was home to politician Sir Āpirana Ngata , and Te Moananui-a-Kiwa Ngārimu — the second of three Māori to receive a Victoria Cross . Volcanic 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
880-632: 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
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#1732786685469960-555: 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
1040-465: 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
1120-739: 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
1200-412: 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
1280-565: 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
1360-584: 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
1440-587: Is extracted at approximately 12 different sites, predominantly for use on nearby rural and forestry roads. The water quality of the river's tributaries is often much higher, as they are closer to the native vegetation cover of the Raukumura Range. In lower areas, much of the eroded gravel from the catchment area settles on the riverbed of the Waiapu River, making it rise rapidly. The riverbed rose 1 metre (3.3 ft) between 1986 and 2007, and
1520-537: 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
1600-514: Is the iwi's most important icon, and in Māori mythology , was the first part of the North Island to emerge when Māui , an ancestor of Ngāti Porou, pulled it as a giant fish from the ocean. According to these beliefs, his waka , Nukutaimemeha , became stranded on the mountain, and lies petrified near the mountain's summit. Nine whakairo (carvings) depicting Māui and his whānau were erected on
1680-471: 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
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#17327866854691760-617: 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
1840-626: 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,
1920-490: The New Zealand state highway network . The western border of the valley is the Raukumara Range , and has a relief ranging from 500 to 1,500 m (1,600 to 4,900 ft). Moving east, the middle and lower parts of the valley are hilly, with a relief of 100–500 m (330–1,640 ft), and the eastern side is made of lower sets of terraces and floodplains just above sea level. There are many large mountains in
2000-492: The Opotiki District Council in the Bay of Plenty Region . The area is of immense cultural, spiritual, economic, and traditional significance to the local iwi , Ngāti Porou , and in 2002 approximately 90% of its 2,000 inhabitants were Māori . Waiapu Valley is sparsely inhabited, with a population density in 2002 of approximately 1.15/km (3.0/sq mi) — less than 8% of the national average at
2080-834: 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
2160-485: The Encyclopedia of New Zealand calls an "awe-inspiring vista". The valley receives a high level of rainfall — from 1,600 mm (63 in) per year at the coast, to more than 4,000 mm (160 in) per year in the Raukumura Range. This water drains into a large number of streams and rivers, which flow to Waiapu River , the main stem in the north-east of the valley. The Waiapu River flows north-east from
2240-883: The Pacific Ring of Fire has volcanoes caused by convergent tectonic plates. Volcanoes can also form where there is stretching and thinning of the crust's plates, such as in the East African Rift , the Wells Gray-Clearwater volcanic field , and the Rio Grande rift in North America. Volcanism away from plate boundaries has been postulated to arise from upwelling diapirs from the core–mantle boundary , 3,000 kilometres (1,900 mi) deep within Earth. This results in hotspot volcanism , of which
2320-622: 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
2400-578: The Raukumara Range on the west of the valley, the most prominent of which is Mount Hikurangi , on a spur of the Raukumura Range inland from Ruatoria. At 1,752 m (5,748 ft) above sea level, it is the highest non- volcanic peak in the North Island . Other summits in the area include Whanokao (1,428 m or 4,685 ft), Aorangi (1,272 m or 4,173 ft), Wharekia (1,106 m or 3,629 ft) and Taitai (678 m or 2,224 ft). Together, these mountains provide what Te Ara -
2480-613: 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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2560-421: The Waiapu River, which continues to be one of the most sediment laden rivers in the world. The annual suspended sediment load is 36 million tonnes, and 90.47 m (3,195 cu ft) of sediment flows into the sea every second. Anecdotal evidence suggests that this sediment may have adversely affected nearby coastal and marine environments. Gravel deposited by the river onto shingle beaches near its mouth
2640-478: The Waiapu Valley in the early days of European settlement. In 1874 about 100 Māori went prospecting on and around Mount Hikurangi. Sir James Hector , who examined the locality, found no signs of gold . In 1875 “Scotty” Siddons, mate of the Beautiful Star , claimed to have met, on the East Coast, a Māori who had a few ounces of gold. He and a mate named Hill found a lot of mundic on the north-west side of
2720-452: The area, and this, combined with the development, resulted in widespread erosion and large amounts of sediment being deposited in the Waiapu River and its tributaries. This has changed the landscape significantly. Since the late 1960s, much work has been done to repair the area by planting exotic forests in eroding areas, and encouraging the return of native scrub. However, by 2002 the catchment area had few natural habitats remaining. It
2800-419: The area. In 1840, Ngāti Porou extensively cultivated the area around the river. The valley was a place where they could live, offering safe refuge during periods of war, and supplies of fresh water and various species of fish. The first Māori church in New Zealand was built on the banks of Waiapu River sometime between 1834 and 1839. The previous decade, Taumata-a-Kura of Ngāti Porou had been captured by
2880-510: 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
2960-402: 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
3040-431: The church was located, was described to Taylor as the largest in the region. Just prior to 1840, the pā had approximately 3,000 inhabitants. Many Ngāti Porou hapū still live in the valley, which has a large number of marae . In 2002, the valley's population was approximately 90% Māori, and traditional culture is still practised in the area — though it has changed significantly in the last 150 years. Since they arrived,
3120-799: 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
3200-431: 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
3280-610: The formation of a submarine volcano off the coast of Mayotte . Subglacial volcanoes develop underneath ice caps . They are made up of lava plateaus capping extensive pillow lavas and palagonite . These volcanoes are also called table mountains, tuyas , or (in Iceland) mobergs. Very good examples of this type of volcano can be seen in Iceland and in British Columbia . The origin of the term comes from Tuya Butte , which
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3360-524: 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
3440-466: 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
3520-465: The highest sediment yields in the world (20,520 t /km /year in 2000), more than two and a half times that of the adjacent catchment area of the Waipaoa River . The high level of sediment in Waiapu River means it is undesirable as a source of drinking water, and very little of the river's water is used. Approximately one sixth of the annual sediment flow in all New Zealand river systems is in
3600-492: 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
3680-776: The joining of the Mata River and the Tapuaeroa River near Ruatoria, and reaches the Pacific Ocean near Rangitukia . Other tributaries in the valley include the Mangaoporo , Poroporo , Wairoa , Maraehara rivers , and the Paoaruku stream . A tributary of the Mata River, the Waitahaia River , is renowned for its brown trout — a European species of fish introduced into New Zealand for fishing in
3760-406: The late 1860s. In 1840, approximately 80% of the Waiapu Valley was native forest, with a rich array of native flora and fauna . There was a small area to the east of the river covered in coastal forest and scrub due to partial clearance and burning. Between 1890 and 1930 there was large-scale clearing, felling and burning of native forests for pastoralism . Floods and heavy rainfall are common to
3840-479: The many hapū that live alongside the Waiapu River have been responsible for preserving the mauri (life principle or special nature) of the river, and the hapū of the valley act as kaitiakitanga (guardians) of the river and its tributaries. The techniques the iwi use to catch Kahawai at the mouth of the river are unique to that river, and are considered sacred. According to an affidavit of Hapukuniha Te Huakore Karaka, two taniwha were placed in strategic locations in
3920-419: 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
4000-551: 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
4080-415: 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
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#17327866854694160-469: The mountain to commemorate the millennium in 2000 ( photo ). Another of Ngāti Porou's mythological ancestors, Paikea , is also associated with the mountain. According to myth, Paikea's younger half-brother, Ruatapu, attempted to kill about 70 of his older kin ("brothers") at sea in Hawaiki to exact revenge on his father for belittling him as a low-born son of a slave. The massacre, called Te Huripūreiata ,
4240-419: The mountain, but only outcrops of limestone on the higher slopes. In 1886 Reupane te Ana, of Makarika , discovered what he fondly imagined was an enormous deposit of gold. With what Joseph Angus Mackay called “noble unselfishness”, he let all his friends into the secret. Drays , wheelbarrows and receptacles of all kinds were rushed to the scene, and large quantities of the “precious metal” were removed to
4320-438: 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
4400-452: 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
4480-876: 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
4560-549: 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
4640-420: 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
4720-471: 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
4800-468: 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
4880-425: 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
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#17327866854694960-619: 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
5040-499: The river since the time of Māui, which serves to unite those who live on either side of it. Ngāti Porou believe that taniwha dwell in and protect the river, in turn protecting the valley and its hapū . Taniwha believed to be in Waiapu River include Kotuwainuku, Kotuwairangi, Ohinewaiapu, and Ngungurutehorowhatu. Māori settlement of Waiapu Valley was widespread until the 1880s, while in March 1874 there were only 20 Pākehā living in
5120-468: The river to protect the hapū from invading tribes — one near Paoaruku (a locality at 37°49′38″S 178°20′21″E / 37.82716138°S 178.3390364°E / -37.82716138; 178.3390364 ) and one at the Wairoa River (a small creek at 37°50′13″S 178°24′00″E / 37.83695267°S 178.3998781°E / -37.83695267; 178.3998781 ). Karaka said that
5200-435: 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
5280-492: 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
5360-622: 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
5440-406: 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
5520-434: 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
5600-444: 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
5680-472: The time (approximately 14.71/km or 38.09/sq mi). The population of the valley is centred in Ruatoria , though the area contains a large number of small settlements. In the 2006 census , Ruatoria had a population of 756 — down 9.7% since 2001, and 94.8% of its population were Māori , with 46% of the population able to speak te reo Māori . The second largest town, Tikitiki , is the easternmost point on
5760-458: The town of Ruatoria , and groynes have been installed in an attempt to divert the river away from the town. The Waiapu Valley, called Te Riu o Waiapu in te reo Māori, lies within the rohe of Ngāti Porou , the largest iwi on the East Coast, and second largest in New Zealand. Mount Hikurangi, Waiapu River, and the Waiapu Valley itself are of immense cultural, spiritual, economic, and traditional value to Ngāti Porou. Mount Hikurangi
5840-431: 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
5920-492: 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
6000-424: 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
6080-644: The western side of the valley, with Mount Hikurangi in the central west. The towns of Ruatoria and Tikitiki are in the north-east of the valley. The vast majority of the catchment area lies within the Waiapu and Matakaoa wards of the Gisborne District Council , with the southernmost area in the Waikohu and Uawa wards . Some of the most Western points fall within the Coast Ward of
6160-400: Was 37% pasture, 26% exotic Pinus radiata forest, 21% native forest, and about 12% kānuka and mānuka scrub. It was highly degraded and modified, and had extensive and serious erosion problems. About half of the pasture area could be considered erosion-prone and unsustainable. Many of the catchment's rivers were full of sediment, and classed as highly degraded. The Waiapu River had one of
6240-490: Was approached to help the situation, and after that there were no similar drownings. The deforestation and land development of the area, largely planned and managed by non-Maori groups, have had a huge negative impact on Māori. In December 2010, Ngāti Porou signed a settlement deal with the New Zealand Government for various grievances, some of which relate to the Waiapu Valley. The settlement included
6320-421: 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
6400-450: Was survived only by Paikea, who called on the sea gods and ancestors to save him. Paikea travelled to New Zealand on the back of a whale, but Ruatapu sent a great flood to kill the survivors in New Zealand, called Te Tai a Ruatapu . Mt. Hikurangi became a refuge for the people from this deluge. The Waiapu River is also of great significance to Ngāti Porou. According to traditional beliefs, they have had an undisturbed relationship with
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