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97-684: Mount Ruapehu ( Māori: [ˈɾʉaˌpɛhʉ] ; English / ˈ r uː ə ˌ p eɪ h uː / ) is an active stratovolcano at the southern end of the Taupō Volcanic Zone and North Island volcanic plateau in New Zealand . It is 23 km (14 mi) northeast of Ohakune and 23 km (14 mi) southwest of the southern shore of Lake Taupō , within the Tongariro National Park . The North Island 's major ski resorts and only glaciers are on its slopes. Ruapehu,

194-443: A polar tundra climate ( Köppen : ET ) on the upper slopes, with average temperatures ranging from −4–15 °C in summer and −7–7 °C in winter, depending on elevation and cloudiness. On the lower slopes, Ruapehu has a subpolar oceanic climate (Köppen: Cfc ). The prevalent wind direction in the region is westerly or northwesterly, and gale force conditions (i.e. wind speeds higher than 33 kn (61 km/h)) are common on

291-505: A snow cave and sheltered in it until he was rescued days later. Extreme weather conditions have caused visitors to be trapped on the mountain in the past. In 2003, about 350 visitors to Whakapapa skifield and 70 staff had to stay overnight in various lodges at Iwikau village (small village at the top of mountain road) after a snow storm made the road too dangerous to descend. In 2008 extreme weather resulted in about 2000 visitors being evacuated from Whakapapa skifield, with cars being led down

388-599: A 22-year-old primary school teacher, had a leg pinned and crushed by a boulder as the water subsided. A rescue operation was mounted after his companion, who was unable to free him, went down the mountain for help. The eruption initiated lahars down the Whangaehu valley and the Whakapapa skifield . ERLAWS detected the lahars in the Whangaehu valley. A snow groomer on the Whakapapa skifield narrowly avoided being caught in

485-747: A 4-inch thick ash layer can weigh 120-200 pounds and can get twice as heavy when wet. Wet ash also poses a risk to electronics due to its conductive nature. Dense clouds of hot volcanic ash can be expelled due to the collapse of an eruptive column , or laterally due to the partial collapse of a volcanic edifice or lava dome during explosive eruptions . These clouds are known as pyroclastic surges and in addition to ash , they contain hot lava , pumice , rock , and volcanic gas . Pyroclastic surges flow at speeds over 50 mph and are at temperatures between 200 °C – 700 °C. These surges can cause major damage to property and people in their path. Lava flows from stratovolcanoes are generally not

582-401: A climate where no month has an average temperature of 10 °C (50 °F) or higher, but as this is due to elevation, this climate is referred to as Alpine climate . Alpine climate can mimic either tundra or ice cap climate. On Earth, the only continent where the ice cap polar climate is predominant is Antarctica . All but a few isolated coastal areas on the island of Greenland also have

679-547: A club Tukino field on the east of the mountain. The commercial developments have not been a consistent success, with at least two business failures by 2023. While as of 2001, Mount Ruapehu had the largest total ski area in New Zealand, developments in the South Island may see by 2025 the establishment there of the largest single commercial ski area in New Zealand. A 60-year concession for commercial ski field operation

776-430: A crater wall collapse and alert the relevant authorities. It began operating in 2002. The lake gradually filled with snowmelt and had reached the level of the hard rock rim by January 2005. The lahar finally occurred on 18 March 2007 (see below). Ruapehu erupted at 10:24 p.m. on 4 October 2006. The small eruption was marked by a magnitude 2.9 volcanic earthquake and sent waves 4–5 m (16 ft) tall crashing into

873-479: A fast moving mudflow . Lahars are typically about 60% sediment and 40% water. Depending on the abundance of volcanic debris the lahar can be fluid or thick like concrete. Lahars have the strength and speed to flatten structures and cause great bodily harm, gaining speeds up to dozens of kilometers per hour. In the 1985 eruption of Nevado del Ruiz in Colombia , Pyroclastic surges melted snow and ice atop

970-515: A final intermediate composition . When the magma nears the top surface, it pools in a magma chamber within the crust below the stratovolcano. The processes that trigger the final eruption remain a question for further research. Possible mechanisms include: These internal triggers may be modified by external triggers such as sector collapse , earthquakes , or interactions with groundwater . Some of these triggers operate only under limited conditions. For example, sector collapse (where part of

1067-769: A result of intraplate volcanism on oceanic islands far from plate boundaries. Examples are Teide in the Canary Islands , and Pico do Fogo in Cape Verde . Stratovolcanoes in the East African Rift include Ol Doinyo Lengai in Tanzania, and Longonot in Kenya. Subduction zone volcanoes form when hydrous minerals are pulled down into the mantle on the slab. These hydrous minerals, such as chlorite and serpentine , release their water into

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1164-587: A significant hazard to surrounding river valleys, particularly the Whangaehu River, which is crossed by national highways, the North Island Main Trunk railway line, and electricity transmission lines. Large, destructive lahars have been observed in the Whangaehu River in 1862, 1895, 1953, 1975, and 2007. GNS Science continuously monitors Ruapehu using a network of seismographs, GPS stations, microphones and webcams. Chemical analysis of

1261-461: A significant threat to humans or animals because the highly viscous lava moves slowly enough for everyone to evacuate. Most deaths attributed to lava are due to related causes such as explosions and asphyxiation from toxic gas . Lava flows can bury homes and farms in thick volcanic rock which greatly reduces property value. However, not all stratovolcanoes erupt viscous and sticky lava . Nyiragongo , near Lake Kivu in central Africa ,

1358-552: A steep profile with a summit crater and explosive eruptions. Some have collapsed summit craters called calderas . The lava flowing from stratovolcanoes typically cools and solidifies before spreading far, due to high viscosity . The magma forming this lava is often felsic , having high to intermediate levels of silica (as in rhyolite , dacite , or andesite ), with lesser amounts of less viscous mafic magma . Extensive felsic lava flows are uncommon, but can travel as far as 8 km (5 mi). The term composite volcano

1455-531: Is a passive release of gas during periods of dormancy. As per the above examples, while eruptions like Mount Unzen have caused deaths and local damage, the impact of the June 1991 eruption of Mount Pinatubo was seen globally. The eruptive columns reached heights of 40 km and dumped 17 megatons of SO 2 into the lower stratosphere . The aerosols that formed from the sulfur dioxide (SO 2 ), carbon dioxide (CO 2 ), and other gases dispersed around

1552-486: Is below the fixed threshold of 10 °C (50 °F) cannot support forests. See Köppen climate classification for more information. Otto Nordenskjöld theorized that winter conditions also play a role: His formula is W = 9 − 0.1 C , where W is the average temperature in the warmest month and C the average of the coldest month, both in degrees Celsius. For example, if a particular location had an average temperature of −20 °C (−4 °F) in its coldest month,

1649-460: Is characterized by having at least one month whose average temperature is above 0 °C (32 °F), while an ice cap climate has no months averaging above 0 °C (32 °F). In a tundra climate, even coniferous trees cannot grow, but other specialized plants such as the arctic poppy can grow. In an ice cap climate, no plants can grow, and ice gradually accumulates until it flows or slides elsewhere. Many high altitude locations on Earth have

1746-688: Is located in the centre of the North Island of New Zealand, 23 km (14 mi) northeast of Ohakune , New Zealand and 23 km (14 mi) southwest of the southern shore of Lake Taupō , within Tongariro National Park. Ruapehu is the largest and southernmost volcano in the national park, with an estimated volume of 110 km. The volcano is surrounded by a ring plain of volcanic material, made from lahar deposits, ash fall, and landslide debris. There are three access routes to Ruapehu, and each access route leads to one of

1843-835: Is presently active, a deep crater at the southern end of the summit plateau which is filled with hot, acidic water, dubbed Crater Lake (Te Wai ā-moe). The lake water currently covers separate north and central vents. Ruapehu sits on a basement of Mesozoic greywacke overlain by a thin layer of sediments of the Wanganui Basin , composed of sands, silts, shell beds, and limestone . It has not been clearly established when Ruapehu first began erupting, only that eruptions began at least 250,000 years ago and possibly as early as 340,000 years ago. Ruapehu has been built in four distinct stages of relatively intense eruptive activity followed by periods of relative quiet. Each of these four stages of activity has left behind distinct rock formations, named

1940-451: Is the most famous example of a hazardous stratovolcano eruption. It completely smothered the nearby ancient cities of Pompeii and Herculaneum with thick deposits of pyroclastic surges and pumice ranging from 6–7 meters deep. Pompeii had 10,000-20,000 inhabitants at the time of eruption. Mount Vesuvius is recognized as one of the most dangerous of the world's volcanoes, due to its capacity for powerful explosive eruptions coupled with

2037-450: Is typically between 700 and 1,200 °C (1,300-2,200 °F). Volcanic bombs are masses of unconsolidated rock and lava that are ejected during an eruption. Volcanic bombs are classified as larger than 64mm (2.5 inches). Anything below 64mm is classified as a volcanic block . When erupted Bombs are still molten and partially cool and solidify on their descent. They can form ribbon or oval shapes that can also flatten on impact with

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2134-1014: Is used because the strata are usually mixed and uneven instead of neat layers. They are among the most common types of volcanoes; more than 700 stratovolcanoes have erupted lava during the Holocene Epoch (the last 11,700 years), and many older, now extinct, stratovolcanoes erupted lava as far back as Archean times. Stratovolcanoes are typically found in subduction zones but they also occur in other geological settings. Two examples of stratovolcanoes famous for catastrophic eruptions are Krakatoa in Indonesia (which erupted in 1883 claiming 36,000 lives) and Mount Vesuvius in Italy (which erupted in 79 A.D killing an estimated 2,000 people). In modern times, Mount St. Helens (1980) in Washington State , US, and Mount Pinatubo (1991) in

2231-403: Is very dangerous because its magma has an unusually low silica content , making it much less viscous than other stratovolcanoes. Low viscosity lava can generate massive lava fountains , while lava of thicker viscosity can solidify within the vent, creating a volcanic plug . Volcanic plugs can trap gas and create pressure in the magma chamber, resulting in violent eruptions. Lava

2328-579: The Philippines have erupted catastrophically, but with fewer deaths. Stratovolcanoes are common at subduction zones , forming chains and clusters along plate tectonic boundaries where an oceanic crust plate is drawn under a continental crust plate (continental arc volcanism, e.g. Cascade Range , Andes , Campania ) or another oceanic crust plate ( island arc volcanism, e.g. Japan , Philippines , Aleutian Islands ). Stratovolcanoes also occur in some other geological settings, for example as

2425-954: The Rocky Mountains , Alps , and the Caucasus have tundra climate. Some mountains of the Andes , the Saint Elias Mountains , and most mountains of the Himalayas , the Karakoram , the Hindu Kush Range , Pamir Mountains , the Tian Shan Mountains , and the Alaska Range also have ice cap climates at extremely high elevations, in addition to tundra climates at relatively lower elevations. Only

2522-891: The magma is too viscous to allow easy escape of volcanic gases . As a consequence, the tremendous internal pressures of the trapped volcanic gases remain and intermingle in the pasty magma . Following the breaching of the vent and the opening of the crater, the magma degasses explosively. The magma and gases blast out with high speed and full force. Since 1600 CE , nearly 300,000 people have been killed by volcanic eruptions . Most deaths were caused by pyroclastic flows and lahars , deadly hazards that often accompany explosive eruptions of subduction-zone stratovolcanoes. Pyroclastic flows are swift, avalanche-like, ground-sweeping, incandescent mixtures of hot volcanic debris, fine ash , fragmented lava , and superheated gases that can travel at speeds over 150 km/h (90 mph). Around 30,000 people were killed by pyroclastic flows during

2619-443: The mantle which decreases its melting point by 60 to 100 °C. The release of water from hydrated minerals is termed " dewatering ", and occurs at specific pressures and temperatures for each mineral, as the plate descends to greater depths. This allows the mantle to partially melt and generate magma . This is called flux melting . The magma then rises through the crust , incorporating silica-rich crustal rock, leading to

2716-581: The polar ice pack , keeps the North Pole from being the coldest place in the Northern Hemisphere , and it is also part of the reason that Antarctica is so much colder than the Arctic. In summer, the presence of the nearby water keeps coastal areas from warming as much as they might otherwise, just as it does in temperate regions with maritime climates . The climate of Antarctica is

2813-616: The 1902 eruption of Mount Pelée on the island of Martinique in the Caribbean . During March and April 1982, El Chichón in the State of Chiapas in southeastern Mexico , erupted 3 times, causing the worst volcanic disaster in that country's history and killied more than 2,000 people in pyroclastic flows . Two Decade Volcanoes that erupted in 1991 provide examples of stratovolcano hazards. On 15 June, Mount Pinatubo erupted and caused an ash cloud to shoot 40 km (25 mi) into

2910-643: The 1945 eruptions collapsed on 24 December 1953, sending a lahar down the Whangaehu River and causing the Tangiwai disaster . 151 people died when the lahar swept away the Tangiwai railway bridge just before an express train crossed it. Another dam was deposited by the 1995–1996 eruptions, which collapsed on 18 March 2007. A warning system, the Eastern Ruapehu Lahar Alarm and Warning System (ERLAWS) system began operation on

3007-485: The 1982 eruption of Galunggung in Java , British Airways Flight 9 flew into the ash cloud, causing it to sustain temporary engine failure and structural damage. Although no crashes have happened due to ash, more than 60, mostly commercial aircraft , have been damaged. Some of these incidents resulted in emergency landings. Ashfalls are a threat to health when inhaled and are also a threat to property. A square yard of

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3104-585: The 5,321 m (17,457 ft) high Andean volcano. The ensuing lahar killed 25,000 people and flooded the city of Armero and nearby settlements. As a volcano forms, several different gases mix with magma in the volcanic chamber. During an eruption the gases are then released into the atmosphere which can lead to toxic human exposure. The most abundant of these gases is H 2 O ( water ) followed by CO 2 ( carbon dioxide ), SO 2 ( sulfur dioxide ), H 2 S ( hydrogen sulfide ), and HF ( hydrogen fluoride ). If at concentrations of more than 3% in

3201-521: The Arctic basin. Summits of many mountains of Earth also have polar climates, due to their higher elevations. Some parts of the Arctic are covered by ice ( sea ice , glacial ice , or snow ) year-round, especially at the most poleward parts; and nearly all parts of the Arctic experience long periods with some form of ice or snow on the surface. Average January temperatures range from about −40 to 0 °C (−40 to 32 °F), and winter temperatures can drop below −50 °C (−58 °F) over large parts of

3298-532: The Arctic. Average July temperatures range from about −10 to 10 °C (14 to 50 °F), with some land areas occasionally exceeding 30 °C (86 °F) in summer. The Arctic consists of ocean that is almost surrounded by landmasses like Russia and Canada . As such, the climate of much of the Arctic is moderated by the ocean water, which can never have a temperature below −2 °C (28 °F). In winter, this relatively warm water, even though covered by

3395-809: The Desert Road ( State Highway 1 ) to the Tukino skifield on the eastern slopes. Ruapehu's active crater, dubbed Crater Lake (Te Wai ā-moe), is situated at the southern end of the Summit Plateau, and as the name suggests, is filled with a warm, acidic lake. The lake's outlet is at the head of the Whangaehu Valley, where the Whangaehu River arises. The Whangaehu River is notorious for destructive lahars caused by Ruapehu's eruptions. In historic times, eruptions have built tephra dams across

3492-799: The Taupō Hatepe eruption in 232 CE. Over this period there are 30 assigned tephra units by composition studies to Ruapehu and in the 370 years before 1950 the mean time between these months of eruptive period was 40 years. In recorded history, these eruptions have occurred about 50 years apart, in 1895 ( lahar ), 1945 and 1995–1996. Minor phreatic or hydrothermal eruptions occur every few years on average, with notable minor eruptions occurring in 1969, 1975, and 2007. More than 600 eruptive events of various sizes have been documented since 1830. Ruapehu entered an eruptive phase in March 1945 after several weeks of volcanic tremors. The first indication of an eruption

3589-714: The Te Herenga Formation (erupted 250,000–180,000 years ago), the Wahianoa Formation (erupted 160,000–115,000 years ago), the Mangawhero Formation (erupted 55,000–15,000 years ago), and the Whakapapa Formation (erupted 15,000–2,000 years ago). Each of these rock formations is composed of lava flows and tuff breccias , and studies of these formations has revealed how volcanic activity at Ruapehu has developed over time. During

3686-444: The Te Herenga Formation, and today these formations be seen at Pinnacle Ridge, Te Herenga Ridge, and Whakapapanui Valley, all on the northwestern slopes of Ruapehu. Approximately 160,000 years ago, cone-building eruptions began again, this time from a crater that is thought to have lain northwest of present-day Mitre Peak (Ringatoto)—southeast of the original Te Herenga vent. Eruptions continued until approximately 115,000 years ago, and

3783-488: The Te Herenga stage of activity, magma rose quickly through the crust during eruptions. However, by 160,000 years ago a complex network of magma dikes and sills had formed in the crust under the volcano, and lava erupted since that time shows signs of extensive mixing between different magma chambers prior to eruptions. In modern times, volcanic activity has been centred on Crater Lake. There are two active vents under

3880-421: The active crater: one on the north side of the crater under Paretetaitonga Peak and another one to the south, and these are New Zealand's only crater glaciers. Most of the ice on Ruapehu is contained in only three of its glaciers: the Whangaehu, Summit Plateau, and Mangatoetoenui glaciers. The Summit Plateau glacier is not a glacier in the true sense, but rather an ice field that fills an extinct volcanic crater, and

3977-819: The air, when breathed in CO 2 can cause dizziness and difficulty breathing. At more than 15% concentration CO 2 causes death. CO 2 can settle into depressions in the land, leading to deadly, odorless pockets of gas. SO 2 classified as a respiratory, skin, and eye irritant if come into contact with. It is known for its pungent egg smell and role in ozone depletion and has the potential to cause acid rain downwind of an eruption. H 2 S has an even stronger odor than SO 2 as well as being even more toxic. Exposure for less than an hour at concentrations of over 500 ppm causes death. HF and similar species can coat ash particles and once deposited can poison soil and water. Gases are also emitted during volcanic degassing, which

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4074-748: The air. It produced large pyroclastic surges and lahar floods that caused a lot of damage to the surrounding area. Pinatubo , located in Central Luzon just 90 km (56 mi) west-northwest of Manila , had been dormant for six centuries before the 1991 eruption. This eruption was one of the 2nd largest in the 20th century. It produced a large volcanic ash cloud that affected global temperatures, lowering them in areas as much as .5 °C. The volcanic ash cloud consisted of 22 million tons of SO 2 which combined with water droplets to create sulfuric acid . In 1991 Japan's Unzen Volcano also erupted, after 200 years of inactivity. It's located on

4171-577: The aquatic life downstream. Additionally, the lahars damaged ski installations on the Whakapapa ski field, several bridges and hydroelectric tunnel intakes, but no loss of life occurred. Three days later, on the morning of 27 April, Ruapehu erupted again. A series of five eruptions occurred between 7:10 a.m. and 10:18 a.m., sending surges of mud, rocks, and ash northwards across the summit plateau and producing eruption columns up to 500 m high. The 1975 eruptions deepened Crater Lake from 55 to 60 m to more than 90 m. Earthquake swarms to

4268-494: The coldest on Earth. Antarctica has the lowest naturally occurring temperature ever recorded: −93.3 °C (−135.9 °F) at Vostok Station . It is also extremely dry (technically a desert , or so called polar desert ), averaging 166 millimetres (6.5 in) of precipitation per year, as weather fronts rarely penetrate far into the continent. Summits of most mountains also have polar climates, despite being in lower latitudes, due to their high elevations. All mountains of

4365-420: The crater, sent lahars down three valleys, and generated an eruption column 12 km high. Phreatomagmatic eruptions occurred through the rest of the month and throughout October, with some eruptions continuing for hours at a time. Ash fell up to 250 km downwind. Explosive eruptions on 11 October emptied Crater Lake of water. Following this, activity died off until 15 June 1996 when renewed seismic activity

4462-428: The day, and mountain visitors are advised to be prepared and carry basic survival equipment. Severe weather has claimed several lives over the years, including a party of five NZ Army soldiers and one RNZN naval rating, caught in a week-long storm while undergoing winter survival training in 1990. The same storm also trapped an experienced Japanese mountaineer when the weather unexpectedly closed in on him, but he built

4559-556: The deaths of livestock. Ash in the Tongariro River also damaged the intake turbines at the Rangipo power station, and ash clouds caused airport closures as far away as Auckland and Wellington . The eruptions also caused closures to the three ski fields on the mountain, costing the region an estimated $ 100 million in lost revenue. During the 1995–1996 summer period between the eruptions, Ruapehu Alpine Lifts ran its chairlifts up

4656-771: The early hours of 21 August was heard in Hawkes Bay and the Tararua District , loud enough to awaken people from sleep and cause alarm. Eruptions began declining in December and had ended by January. The eruptions dispersed ash across most of the North Island, and eruption columns could be seen from as far afield as Palmerston North , Whanganui , and Hawkes Bay . Ash caused disruption to several North Island communities, entering houses, causing eye and throat irritation, and damaging paintwork on cars. Crop damage

4753-446: The early hours of 22 June. It was a moderate phreatic eruption, which blasted rocks up to 1 km northwest of the crater and sent lahars down several valleys. The Whakapapa skifield was left covered in mud. This was the largest eruption since 1945. A larger phreatic eruption occurred at 3:59 a.m. on 24 April 1975, blasting rocks up to 1.6 km northwest of the crater, against the wind, and depositing ash more than 100 km to

4850-474: The eroded Wahianoa Formation in two phases: the first occurring 55,000–45,000 years ago and the second 30,000–15,000 years ago. Multiple summit craters were active during this period, all lying between Tahurangi and the northern summit plateau. Parasitic eruptions also occurred at Pukeonake, a scoria cone to the north-west of Ruapehu and at several isolated craters near Ohakune . The Mangawhero Formation can be found over most of modern Ruapehu, and it forms most of

4947-413: The eruption lasted for less than a minute and blasted ash, mud, and rocks northward, reaching to about 2 km from Crater Lake. Two climbers were caught in the eruption at Dome Shelter, an alpine hut approximately 600 m from the crater, when the hut was struck by the surge. The climbers nearly drowned before the hut floor gave way and the water drained into the basement seismometer vault. One of them,

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5044-540: The flank of a volcano collapses in a massive landslide) can only trigger the eruption of a very shallow magma chamber . Magma differentiation and thermal expansion also are ineffective as triggers for eruptions from deep magma chambers . In recorded history , explosive eruptions at subduction zone ( convergent-boundary ) volcanoes have posed the greatest hazard to civilizations. Subduction-zone stratovolcanoes, such as Mount St. Helens , Mount Etna and Mount Pinatubo , typically erupt with explosive force because

5141-478: The ground. Volcanic Bombs are associated with Strombolian and Vulcanian eruptions and basaltic lava . Ejection velocities ranging from 200 to 400 m/s have been recorded causing volcanic bombs to be destructive. Lahars (from a Javanese term for volcanic mudflows) are a mixture of volcanic debris and water. Lahars can result from heavy rainfall during or before the eruption or interaction with ice and snow. Meltwater mixes with volcanic debris causing

5238-458: The high population density of the surrounding Metropolitan Naples area (totaling about 3.6 million inhabitants). In addition to potentially affecting the climate, volcanic ash clouds from explosive eruptions pose a serious hazard to aviation . Volcanic ash clouds consist of ash which is made of silt or sand sized pieces of rock, mineral, volcanic glass . Ash grains are jagged, abrasive, and don't dissolve in water. For example, during

5335-664: The ice cap climate. Summits of many high mountains also have ice cap climate due to their high elevation. Coastal regions of Greenland that do not have permanent ice sheets have the less extreme tundra climates. The northernmost part of the Eurasian land mass, from the extreme northeastern coast of Scandinavia and eastwards to the Bering Strait , large areas of northern Siberia and northern Iceland have tundra climate as well. Large areas in northern Canada and northern Alaska have tundra climate, changing to ice cap climate in

5432-635: The ice there reaches more than 130 m thick. The Whangaehu glacier feeds the Whangaehu River, and the Mangatoetoenui glacier is one of the principal sources of the Waikato River , which arises as a series of streams on Ruapehu's eastern slopes. On the western side of the mountain, many of the streams that arise there, such as the Whakapapa and Manganui o te Ao rivers, feed the Whanganui River . Ruapehu's glaciers are situated at

5529-504: The island of Kyushu about 40 km (25 mi) east of Nagasaki . Beginning in June, a newly formed lava dome repeatedly collapsed. This generated a pyroclastic flow that flowed down the mountain's slopes at speeds as high as 200 km/h (120 mph). The 1991 eruption of Mount Unzen was one of the worst volcanic disasters in Japan's history, once killing more than 15,000 people in 1792. The eruption of Mount Vesuvius in 79 AD

5626-547: The lahar there. Only one eruptive event has been recorded at Ruapehu since the 2007 eruption—a minor event on 13 July 2009 when a small volcanic earthquake beneath Crater Lake caused the lake water level to rise 15 cm and triggered a snow slurry lahar in the upper Whangaehu valley. Since then, Crater Lake has continued its regular cycle of heating and increased gas emissions, although with periods of sustained high temperatures that occurred in 2011, 2016 and 2019. Eruptions at Ruapehu are expected to continue much as they have for

5723-644: The lake, dubbed North Vent and Central Vent. Activity is characterized by cyclic heating and cooling of the lake over periods of 6–12 months. Each heating cycle is marked by increased seismic activity under the crater and is accompanied by increased emission of volcanic gases , indicating that the vents under Crater Lake are open to gas escape. Evidence suggests that an open-vent system such as this has been in place throughout Ruapehu's 250,000 year history. This prevents build-up of pressure and results in relatively small, frequent eruptions (every 20–30 years on average) at Ruapehu compared to other andesitic volcanoes around

5820-474: The largest active volcano in New Zealand, has the highest point in the North Island and has three major peaks: Tahurangi (2,797 m), Te Heuheu (2,755 m) and Paretetaitonga (2,751 m). The deep, active crater is between the peaks and fills with water between major eruptions, being known as Crater Lake ( Māori : Te Wai ā-moe ). The name Ruapehu means "pit of noise" or "exploding pit" in Māori . Ruapehu

5917-413: The lava erupted during this period is known as the Wahianoa Formation. This formation has also been heavily eroded by glacial activity, and it now forms the southeastern flanks of modern Ruapehu. The formation consists of lava flows and tuff breccias . Beginning approximately 55,000 years ago, a third phase of cone-building eruptions began, creating the Mangawhero Formation. This formation was erupted onto

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6014-507: The loss of 151 lives when the Tangiwai railway bridge across the Whangaehu River collapsed while the lahar was in full flood, just before an express train crossed it. Ruapehu saw a period of heightened activity between 1966 and 1982, with multiple small eruptions occurring in Crater Lake and two larger eruptions in 1969 and 1975, which ejected rocks across the summit region and produced significant lahars. The eruption in 1969 occurred in

6111-611: The most northern parts of Canada. Southernmost Argentina ( Tierra del Fuego where it abuts the Drake Passage ) and such subantarctic islands such as the South Shetland Islands and the Falkland Islands have tundra climates of slight temperature range in which no month is as warm as 10 °C (50 °F). These subantarctic lowlands are found closer to the equator than the coastal tundras of

6208-464: The mountain and organised guided tours to within 500 metres of the crater. Hundreds of tourists visited, even though the volcano was still emitting steam and toxic sulphur gas and the Department of Conservation was warning that further eruptions were possible. Both the 1995 and 1996 eruptions were filmed and streamed to the internet via a custom-built 'volcano-cam', possibly the first such camera in

6305-475: The mountain in 2002 to detect such a collapse and alert the relevant authorities. The ERLAWS system detected the 2007 lahar, and roads were closed and railway traffic stopped until the lahar had subsided. The earliest known volcanic activity in Tongariro National Park was approximately 933,000 ± 46,000 years ago at Hauhungatahi , northwest of Ruapehu. Subsequently, andesitic clasts found 100 km southwest of Ruapehu, near Whanganui , demonstrate that volcanism

6402-765: The mountain in groups of five. About 100 cars were left at the skifield overnight. Ruapehu is a composite andesitic stratovolcano located at the southern end of the Taupō Volcanic Zone and forming part of the Tongariro Volcanic Centre. Volcanism at Ruapehu is caused by the subduction of the Pacific Plate under the Australian Plate at the Hikurangi Trough to the east of the North Island . Ruapehu has erupted from multiple craters over its lifetime, however, only one crater

6499-418: The mountain was sacred, and said: "as far as we are concerned if these things [lahars] do happen well we step aside. Let them go past". Other plans considered were building a stop bank on the Desert Road, or creating an early-warning system, which would be much more expensive than digging a trench. In 2001, the Eastern Ruapehu Lahar Alarm and Warning System (ERLAWS) system was installed on the mountain to detect

6596-455: The mountain's high peaks as well as the Turoa skifield . Medium size tephra eruptions of Ruapehu since the 232 CE Taupo eruption Lava flows that have been erupted from Ruapehu since the last glacial maximum are called the Whakapapa Formation. These flows all erupted between 15,000 and 2,000 years ago from a number of different craters on the summit of Ruapehu as well as from craters on

6693-468: The mountain. Rainfall is higher on the western flanks of Ruapehu than the eastern flanks due to the rain shadow effect. Whakapapa Village receives an average of 2,200 mm of rain per year, whereas the Rangipo Desert to the east of Ruapehu receives slightly more than 1,500 mm of rain annually. Snow falls on average as low as 1,500 m elevation. Weather conditions can be changeable over

6790-575: The northern and southern flanks of the mountain. Rangataua on the southern flanks had a large lava flow between 15,000 and 10,000 years ago. Approximately 10,000 years ago, a series of major eruptions occurred, not just on Ruapehu, but also at the Tama Lakes between Ruapehu and Tongariro volcanoes. This period of intense eruptions is called the Pahoka-Mangamate event and is thought to have lasted between 200 and 400 years. On Ruapehu, lava

6887-409: The northern limit for the formation of permanent ice in New Zealand, and thus they are extremely sensitive to changes in climate. Surveys of the glaciers undertaken since 1955 have found that the glaciers have all been thinning and retreating, with the exception of the northern crater glacier, which thickened and lengthened after the 1953 outburst of Crater Lake lowered the lake water level. Ruapehu has

6984-406: The northwestern ring plain that can still be seen today. Since then eruptions have been an order of magnitude lower in intensity and volume. Accordingly, most of the 150 km (36 cu mi) cone and 150 km (36 cu mi) ring-plain is older than 10,000 years. Eruptions between 10,000 and 2,500 years ago generated lava flows that all flowed into the Whakapapa amphitheatre and created

7081-414: The ones in 1995–96 have only occurred within periods of enhanced activity. The main recent volcanic hazard at Ruapehu is from lahars. Two major lahar paths run through the Whakapapa skifield, and in recent times, lahars have travelled through the ski field in 1969, 1975, 1995, and 2007. An eruption warning system operates in the ski field to warn skiers in the event of another eruption. Lahars also represent

7178-444: The outlet on several occasions, most recently in 1945 and 1996. These dams failed in 1953 and 2007 respectively, causing an outburst of Crater Lake each time, which sent destructive lahars down the river. The 1953 lahar was the cause of the Tangiwai disaster , in which 151 people died. Even larger lahars occurred in 1862 and 1895. A total of 18 glaciers have been recognised on Ruapehu, of which six are named. Two glaciers are found in

7275-485: The past 2,000 years, with frequent minor eruptions and more significant events every 20–30 years, although the possibility of larger events like the Pahoka-Mangamate event cannot be ruled out. The previous activity trend until 10,000 years ago was about 7.5 km (1.8 cu mi) erupted each 10,000 years. Minor eruptions, such as the one in 2007, especially if they are hydrothermal, can occur at any time without warning. However, in historic times, major eruptions such as

7372-566: The polar region in Nordenskiöld's system, but part of the island (including Ushuaia , Argentina ) is reckoned as being within the Antarctic under Köppen's. In 1947, Holdridge improved on these schemes , by defining biotemperature : the mean annual temperature, where all temperatures below 0 °C or 32 °F (and above 30 °C or 86 °F) are treated as 0 °C (because it makes no difference to plant life, being dormant). If

7469-464: The size of Mount Pinatubo affected the weather for a few years; with warmer winters and cooler summers observed. A similar phenomenon occurred in the April 1815, the eruption of Mount Tambora on Sumbawa island in Indonesia . The Mount Tambora eruption is recognized as the most powerful eruption in recorded history. Its eruption cloud lowered global temperatures as much as 0.4 to 0.7 °C. In

7566-408: The slopes of the modern skifield. For the past 2,000 years, activity at Ruapehu has been largely focused through a crater lake at the summit. Eruptive activity has typically consisted of relatively small but explosive phreatomagmatic eruptions occurring every few decades and lasting several months each. The eruptive record is only well understood from tephra deposits before 1950 for 1718 years from

7663-431: The southeast. Nine minutes of seismic activity preceded the eruption, but crater dilation had been measured two weeks earlier. Nearly half of the water in Crater Lake was erupted into the air, which subsequently rained down onto the summit, generating lahars down several river valleys. Lahars which travelled down the Whakapapa and Manganui o te Ao rivers entered the Whanganui River and poisoned it, which affected much of

7760-462: The summit of Mount Rainier has an ice cap climate in the Cascade Range . There have been several attempts at quantifying what constitutes a polar climate. Climatologist Wladimir Köppen demonstrated a relationship between the Arctic and Antarctic tree lines and the 10 °C (50 °F) summer isotherm; i.e., places where the average temperature in the warmest calendar month of the year

7857-400: The three skifields that are found on its slopes. State Highway 48 leads to Whakapapa Village at the base of the mountain, and from there an access road leads up the mountain to Iwikau Village at the base of the Whakapapa skifield on the northwestern bumpy hilly slopes. An access road from Ohakune leads to Turoa skifield on the southwestern slopes, and a four-wheel drive track leads from

7954-537: The wall of the crater. No ash was erupted into the atmosphere, and the eruption is presumed to have occurred entirely underwater. At 11:22 a.m. 18 March 2007, the tephra dam which had been holding back Crater Lake burst, sending a lahar down the mountain. An estimated 1.9–3.8 million cubic metres of mud, rock, and water travelled down the Whangaehu river. ERLAWS activated, sending an alarm to pagers at 11:25 a.m. and automatically activating warning lights and barrier arms to close roads and stop trains. There

8051-460: The walls of the crater and damaged some monitoring equipment there. A second eruption on 29 June destroyed the equipment and produced a lahar. Chemical analysis showed that magma was interacting with water under the lake. The first significant eruption took place at 8:05 a.m. on 18 September 1995, raining tephra onto the summit region and sending lahars down the mountain. On 23 September, an even larger eruption blasted rocks up to 1.5 km from

8148-585: The warmest month would need to average 11 °C (52 °F) or higher for trees to be able to survive there as 9 − 0.1(−20) = 11 . Nordenskiöld's line tends to run to the north of Köppen's near the west coasts of the Northern Hemisphere continents, south of it in the interior sections, and at about the same latitude along the east coasts of both Asia and North America. In the Southern Hemisphere, all of Tierra del Fuego lies outside

8245-463: The water in Crater Lake is regularly undertaken along with airborne gas measurements. Live data can be viewed on the GeoNet website . The mountain, as part of Tongariro National Park is host to a wide range of recreational activities. Since the first ski field developments in 1923, Ruapehu has had three ski areas developed, Whakapapa on the north-western side, Tūroa on the south western slopes, and

8342-526: The west of Ruapehu between November 1994 and September 1995 marked the beginning of renewed heightened activity at the volcano. Bursts of earthquake activity immediately preceded rapid rises in the temperature of Crater Lake, with the surface temperature reaching 51.4 °C in January 1995—one of the highest temperatures recorded in 30 years and about 10 °C higher than its usual peak temperature. A minor eruption occurred on 26 April, which sent waves against

8439-474: The world. Crater Lake is emptied by major eruptions, such as the ones in 1945 and 1995–1996, but refills after eruptions subside, fed by melting snow and vented steam. In historic times, major eruptions have deposited a tephra dam across the lake's outlet, preventing lake overflow into the Whangaehu valley. The dam collapses after several years causing a large lahar down the valley. The tephra dam created by

8536-412: The world. The SO 2 in this cloud combined with water (both of volcanic and atmospheric origin) and formed sulfuric acid , blocking a portion of the sunlight from reaching the troposphere . This caused the global temperature to decrease by about 0.4 °C (0.72 °F) from 1992 to 1993. These aerosols caused the ozone layer to reach the lowest concentrations recorded at that time. An eruption

8633-474: The world. The website hosting the feed during the 1996 eruption received up to 4000 hits an hour. After the 1996 eruption it was recognised that a catastrophic lahar could again occur when Crater Lake burst the volcanic ash dam blocking the lake outlet as it did in 1953. In 1997, the government proposed digging a trench through the blockage in the wall of Crater Lake, but this was plan was opposed by conservation groups and Māori. A Ngāti Rangi spokesman noted that

8730-483: The year following the eruption, most of the Northern Hemisphere experienced cooler temperatures during the summer. In the northern hemisphere , 1816 was known as the " Year Without a Summer ". The eruption caused crop failures, food shortages, and floods that killed over 100,000 people across Europe , Asia , and North America . Polar climate#Subtypes There are two types of polar climate: ET , or tundra climate ; and EF , or ice cap climate . A tundra climate

8827-435: Was erupted from Saddle Cone—a flank crater on the northern slopes—and from another crater on the southern slopes. This southern crater erupted three times, and lava flows from this crater travelled nearly 14 km to the south. There is evidence that a sector collapse on the northwestern slopes about 9,400 years ago formed the amphitheatre that now comprises the Whakapapa skifield and left an extensive avalanche deposit on

8924-539: Was granted to the then operator of the Whakapapa ski field, in 2015. After the operator went into receivership in 2023 a new operator has expressed interest in taking over the Whakapapa concession. From April 2024, Tūroa operated by Pure Tūroa Limited has a limited ten year concession. Stratovolcano A stratovolcano , also known as a composite volcano , is a conical volcano built up by many alternating layers ( strata ) of hardened lava and tephra . Unlike shield volcanoes , stratovolcanoes are characterized by

9021-557: Was likely present in the Ruapehu area 340,000 years ago. However, the oldest rocks on Ruapehu itself are approximately 250,000 years old. Eruptions during this period are believed to have built a steep volcanic cone around a central crater, which would have been located somewhere near the present-day upper Pinnacle Ridge. Cone-building eruptions ceased about 180,000 years ago, and the cone began to be eroded away by glacial action. Rock formations that date to this period are collectively named

9118-457: Was no serious damage and no injuries. A toilet block at the Tangiwai memorial was destroyed, but the memorial had already been closed due to the lahar threat. One family was trapped for around 24 hours after the lahar swept away the access route to their home. At 8:16 p.m. on 25 September 2007, volcanic tremor was detected underneath Ruapehu, which was followed at 8:26 p.m. by an explosive surtseyan eruption. The explosive phase of

9215-435: Was recorded. This was followed by eruptions on 17 and 18 June which once again emptied the partially refilled Crater Lake of water. Strombolian eruptions occurred on 27 June and throughout July and August, producing eruption columns more than 10 km high and shooting rocks 1.4 km from the crater. These eruptions produced more than 7 million tonnes of ash, which contaminated water supplies, destroyed crops, and lead to

9312-479: Was reported in Ohakune, and the water supply at Taumarunui was disrupted. After eruptions subsided in late December, Crater Lake slowly began refilling, with a "boiling lake" already filling the bottom of the crater by mid-January. A tephra dam had formed at the lake's normal outlet during the eruptions, which eventually collapsed on 24 December 1953 causing a lahar that led to the Tangiwai disaster with

9409-479: Was reported on 8 March, with ashfall seen on the eastern slopes. A lava dome was observed in Crater Lake on 19 March but was destroyed in a series of explosive eruptions over the following week. A second, larger lava dome appeared in May, which continued to grow over the following months and had emptied Crater Lake of water by July. Eruptions increased from August through November. A particularly powerful eruption in

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