| Mount Unzen | |
|---|---|
 Mt. Unzen, showing extensive pyroclastic flow and lahar deposits |
|
| Elevation | 1,500 m (4,921 ft) |
| Location | Kyūshū, Japan |
| Coordinates | |
| Type | Complex stratovolcano |
| Age of rock | Oldest 500 Kyr[1] |
| Last eruption | 1996 |
Mount Unzen (jp: 雲仙岳 Unzendake) is an active volcanic complex of several overlapping stratovolcanoes, also known as a composite volcano, near the city of Shimabara, Nagasaki Prefecture, on the island of Kyūshū, Japan’s southernmost main island. is a language spoken by over 130 million people in Japan and in Japanese emigrant communities Plate tectonics and hotspots Divergent plate boundaries At the A stratovolcano, also called a composite volcano is a tall conical Volcano composed of many layers of hardened Lava, Tephra, and Volcanic A stratovolcano, also called a composite volcano is a tall conical Volcano composed of many layers of hardened Lava, Tephra, and Volcanic is a city located on the north-eastern tip of the Shimabara Peninsula,facing Ariake Bay in the east and Mt WikipediaWikiProject Japanese prefectures for guidelines --> is a prefecture of Japan located on the island of Kyūshū. or Kyushu is the third-largest Island of Japan and most southwesterly of its four main islands. For a topic outline on this subject see List of basic Japan topics.
In 1792, the collapse of one of its several lava domes triggered a tsunami that killed about 15,000 people in Japan’s worst-ever volcanic disaster. In Volcanology, a lava dome or plug dome is a roughly circular Mound -shaped protrusion resulting from the slow eruption of Felsic Lava A tsunami ((tsuːˈnɑːmi is a series of waves created when A disaster is the impact of a natural or human-made hazard that negatively affects society or environment. The volcano was most recently active from 1990 to 1995, and a large eruption in 1991 generated a pyroclastic flow that killed 43 people, including three volcanologists. Year 1991 ( MCMXCI) was a Common year starting on Tuesday (link will display full calendar of the Gregorian Calendar. A pyroclastic flow (also known as a pyroclastic density current) is a common and devastating result of some volcanic eruptions. Volcanology (also spelled vulcanology) is the study of Volcanoes, Lava, Magma, and related geological and Geophysical phenomena
Currently its highest peaks are Fugendake (普賢岳) at 1,359 meters and Heisei Shinzan (平成新山) at 1,486 meters. The latter emerged during the eruptions of the early, eponymous Heisei era (1989–). is the current era name in Japan. The Heisei era started on January 8, 1989, just one day after the death of the reigning Emperor Hirohito
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Eruptive history
To 1989
Mount Unzen forms part of the Shimabara Peninsula, which has seen extensive volcanism over thousands of years. Shimabara Peninsula (島原半島 is east of Nagasaki City, Nagasaki Prefecture, Kyūshū, Japan. The oldest volcanic deposits in the region date from over 6 million years ago, and extensive eruptions occurred over the whole peninsula between 2. 5 and 0. 5 million years ago.
The origins of the Unzen complex are traced to the formation of a graben through crustal faulting. A graben is a depressed block of land bordered by parallel faults Graben is German for ditch. This caused parts of the peninsula to subside by up to 1,000 m below sea level and may have caused eruptive activity to localize at one site inside the graben. Eruptions of dacitic lava began from a site slightly to the south of today’s Mount Unzen and migrated north over time. Dacite ( deɪsaɪt) is an igneous, volcanic rock with a high iron content
The volcano grew rapidly during its first 200,000 years, forming a large cone. Later eruptions over the following 150,000 years filled in much of the graben. Initially, activity was dominated by blocky andesitic lava and ash flows, changing to dacitic pumice flows and airfall deposits from 500,000 to 400,000 years ago. For the extinct cephalopod genus see Andesites. Andesite (ˈændəsaɪt is an igneous, Volcanic rock, of intermediate Dacite ( deɪsaɪt) is an igneous, volcanic rock with a high iron content Pumice is a textural term for a volcanic rock that is a solidified frothy lava composed of highly microvesicular glass Pyroclastic with very thin translucent The period from 400,000 to 300,000 years ago saw the emplacement of large areas of pyroclastic flow and lahar deposits; these form the major part of the volcanic fan surrounding the volcano. A pyroclastic flow (also known as a pyroclastic density current) is a common and devastating result of some volcanic eruptions. Beginning 300,000 to 150,000 years ago, thick phreatomagmatic deposits were laid down, suggesting the subsidence of the volcano into its graben was rapid during this period. A Phreatic eruption, also called an ultravulcanian eruption, occurs when rising Magma makes contact with ground or surface water
Activity from 150,000 years ago to the present has occurred at a number of sites around the volcanic complex, building four main domes at different times: the Nodake (70-150,000 years old), Myokendake (25-40,000 years old), Fugendake (younger than 25,000 years old) and Mayuyama (4,000 years old) volcanic peaks. Fugendake has been the site of most eruptions during the past 20,000 years and lies about 6 km of the centre of Shimabara.
Unzen’s deadliest eruption occurred in 1792, with a large dacitic lava flow coming from Fugendake. The east flank of the Mayuyama dome collapsed unexpectedly following a post-eruption earthquake, creating an avalanche and tsunami that killed an estimated 15,000 people. A tsunami ((tsuːˈnɑːmi is a series of waves created when This remains Japan’s worst-ever volcanic disaster.
In the 17th Century, the Japanese government used Fumie to reveal practicing Catholics and sympathizers. A fumie (踏み絵 'step-on picture' was a likeness of Jesus or Mary upon which the religious authorities of the Tokugawa shogunate of Fumie were pictures of the Virgin Mary and Christ. Christ is the English term for the Greek ( Khristós) meaning "the anointed " Government officials made everybody trample on these pictures. People reluctant to step on the pictures were identified as Catholics and then sent to Nagasaki. The policy of the Japanese government (Edo) was to turn them from their faith, Catholicism. However, if the Catholics refused to change their religion, they were tortured. Torture, according to the United Nations Convention Against Torture, is "any act by which severe pain or suffering, whether physical or mental is intentionally But since many of them still refused to abandon their faith, they were killed by the government. Execution took place at Nagasaki's Mount Unzen, where many were dumped into the volcano
1990–1995
After 1792, the volcano remained dormant until an earthquake swarm began about 20 km underneath and 10 km west of Fugendake in November 1989. ( is the Capital and the largest city of Nagasaki Prefecture in Japan. Plate tectonics and hotspots Divergent plate boundaries At the Over the following year, earthquakes continued, their hypocentres gradually migrating towards the summit. The hypocenter or hypocentre (literally 'below the center' from the Greek υπόκεντρον) refers to the site of an earthquake or to that of a nuclear The first phreatic eruptions began in November 1990, and after inflation of the summit area, fresh lava began to emerge on May 20, 1991. A Phreatic eruption, also called an ultravulcanian eruption, occurs when rising Magma makes contact with ground or surface water Events 325 - The First Council of Nicaea &ndash the first Ecumenical Council of the Christian Church is held Year 1991 ( MCMXCI) was a Common year starting on Tuesday (link will display full calendar of the Gregorian Calendar. [2]
The threat of further, disastrous events prompted authorities to evacuate 12,000 local residents from their homes. Emergency evacuation is the movement of people from a dangerous place due to the threat or occurrence of a disastrous event On June 3, 1991, the volcano erupted violently, possibly as a result of depressurization of the magma column after a landslide in the crater. Events 350 - Roman usurper Nepotianus, of the Constantinian dynasty, proclaims himself Roman Emperor, entering Year 1991 ( MCMXCI) was a Common year starting on Tuesday (link will display full calendar of the Gregorian Calendar. Magma (Plurals magmas and magmata) is molten rock that sometimes forms beneath the surface of the Earth (or any other Terrestrial planet A landslide is a geological phenomenon which includes a wide range of ground movement such as rock falls deep failure of slopes and shallow debris flows which can occur A pyroclastic flow reached 4. A pyroclastic flow (also known as a pyroclastic density current) is a common and devastating result of some volcanic eruptions. 5 km from the crater and claimed the lives of 43 scientists and journalists, including volcanologists Katia and Maurice Krafft and Harry Glicken. A scientist, in the broadest sense refers to any person that engages in a systematic activity to acquire Knowledge or an individual that engages in such practices A journalist (also called a newspaperman) is a person who practices Journalism, the gathering and dissemination of information about current events trends Volcanology (also spelled vulcanology) is the study of Volcanoes, Lava, Magma, and related geological and Geophysical phenomena Katia Krafft ( Mulhouse, 17 April 1942 – 3 June 1991) and her husband Maurice Krafft ( Guebwiller, 25 Harry Glicken (1958 &ndash 1991 nickname The Glick) was a Volcanologist who was killed on 3 June 1991 by a Pyroclastic flow
Between 1991 and 1994 the volcano generated at least 10,000 small pyroclastic flows, destroying about 2,000 houses. From 1993 onward, the rate of lava effusion gradually decreased, and eruptions came to an end in 1995. Since then heavy rains have frequently remobilised pyroclastic material, generating lahars. A lahar is a type of Mudflow / Landslide composed of Pyroclastic material and Water that flows down from a Volcano, typically Dikes have been constructed in several river valleys to channel lahar flows away from vulnerable areas, and warning systems and evacuation plans have been developed and deployed. LeveeEmbankmentDitch A dike (or dyke) levee, levée, embankment, floodbank or stopbank is a natural or artificial "Riverine" redirects here For the use of that term in Maritime geography, see there In Geology, a valley (also called a vale, dale, glen or strath and near or in Appalachia, a draw) is
Mount Unzen was designated a Decade Volcano in 1991 as part of the United Nations’ International Decade for Natural Disaster Reduction, due to its history of violent activity and location in a densely populated area. The Decade Volcanoes are 16 Volcanoes identified by the International Association of Volcanology and Chemistry of the Earth's Interior (IAVCEI as being worthy The United Nations ( UN) is an International organization whose stated aims are to facilitate cooperation in International law, International security Population density (in agriculture standing stock and Standing crop) is a measurement of Population per unit area or unit volume
Unzen Scientific Drilling Project (USDP)
In 1999, an ambitious project began at Mount Unzen to drill deep inside the volcano and sample magma in the 1990–1995 eruption conduit. The project hoped to shed light on some fundamental questions in volcanology, such as why magma repeatedly travels in the same conduits despite the solidification of magma in them at the end of each eruption, and how it can lose enough gas on its ascent to erupt effusively rather than explosively.
Drilling began with test bores to assess the viability of a deep borehole. Two holes were bored, 750 m and 1,500 m deep, and cores taken from these holes were used to better determine Unzen’s eruptive history. One further 350 m-deep borehole was drilled to test the methods to be used in the final drilling project.
The main drill began in 2003, starting from the northern flank of the volcano with a 17. 5 inch wide hole at an angle of 25 degrees from vertical. At greater depths, the direction of boring was tilted towards the conduit, reaching an angle of 75 degrees from vertical at a depth of 800 m. Drilling reached 1,800 m, the original target depth, without reaching the conduit, but in July 2004 at a depth of 1,995 m, the conduit was finally reached. The vertical depth below the summit was 1,500 m.
The temperature at the conduit was about 155°C, much lower than pre-drill estimations of 500°C and over. This was attributed to hydrothermal circulation accelerating the cooling of the magma over the nine years since the end of the eruption.
References
- Hoshizumi H. , Uto K. , Matsumoto A. (2001), Core stratigraphy of the Unzen Scientific Drilling: Volcanic History of the Unzen Volcano, Kyūshū, SW Japan, American Geophysical Union, Fall Meeting 2001
- Hoshizumi H. , Uto K. , Matsumoto A. , Kurihara A. (2004), Growth History Of Unzen Volcano, Kyūshū, Japan, American Geophysical Union, Fall Meeting 2004
- Sakuma S. , Nakada S. , Uto K. (2004), Unzen Scientific Drilling Project: Challenging drilling operation into the magmatic conduit shortly after eruption, American Geophysical Union, Fall Meeting 2004
- Uto K. , Hoshizumi H. , Matsumoto A. , Oguri K. , Nguyen H. (2001), Volcanotectonic history of Shimabara Peninsula and the evolution of Unzen volcano in Southwest Japan, American Geophysical Union, Fall Meeting 2001
- Uto K. , Nakada S. , Shimizu H. , Sakuma S. , Hoshizumi H. (2004), Overview and the achievement of the Unzen Scientific Drilling Project, American Geophysical Union, Fall Meeting 2004
See also
External links
- Unzen Decade Volcano home page
- Smithsonian Institution Global Volcanism Program: Mount Unzen
- USGS description page
- Unzen Videos (GSJ)
- Article about the USDP
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