Mount Unzen
Mount Unzen, showing extensive pyroclastic flow and lahar deposits
Elevation:	4,921 ft (1,500 m)
Coordinates:	32° 45′24″N, 130° 17′40″E
Location:	Kyushu, Japan
Range:
Last eruption:	1996
Type:	Complex stratovolcano

Mount Unzen (雲仙岳) is an active volcano near the city of Shimabara in Nagasaki Prefecture on the island of Kyushu in Japan. It is a volcanic complex consisting of several overlapping peaks. Image File history File links Unzen_pyroclastic_and_lahar_deposits. ... A topographical summit is a point on a surface which is higher in elevation than all points immediately adjacent to it. ... This article is about longitude and latitude; see also UTM coordinate system Map of Earth showing lines of latitude (vertically) and longitude (horizontally); large version (pdf) The geographic (earth-mapping) coordinate system expresses every horizontal position on Earth by two of the three coordinates of a spherical coordinate system which... Kyushu region, Japan Kyushu (九州) is the third largest island of Japan and most southerly and westerly of the four main islands. ... The most general definition of a mountain range is a group of mountains bordered by lowlands. ... Last eruption refers to the last volcanic event of a volcano. ... 1996 (MCMXCVI) is a leap year starting on Monday of the Gregorian calendar, and was designated the International Year for the Eradication of Poverty. ... Mountains can be characterized in several ways. ... View of Mount Rainier, a stratovolcano. ... Eruption redirects here. ... Shimabara Castle Feeding carp (nishikigoi) along the streets of Shimabara Shimabara (島原市; -shi) is a city located in Nagasaki, Japan. ... Nagasaki Prefecture (長崎県; Nagasaki-ken) is located on Kyushu island, Japan. ... Kyushu region, Japan Kyushu (九州) is the third largest island of Japan and most southerly and westerly of the four main islands. ...

In 1792, the collapse of one of its several lava domes triggered a tsunami which killed about 15,000 people in Japan's worst ever volcanic disaster. The volcano was most recently active from 1990 to 1995, and a large eruption in 1991 generated a pyroclastic flow which killed 43 people, including three volcanologists. In volcanology, a lava dome is mound-shaped growth resulting from the eruption of high-silica lava (such as rhyolite) from a volcano. ... The tsunami that struck Malé in the Maldives on December 26, 2004. ... This article is about the year. ... 1995 (MCMXCV) was a common year starting on Sunday of the Gregorian calendar. ... 1991 (MCMXCI) is a common year starting on Tuesday of the Gregorian calendar. ... Pyroclastic flows sweep down the flanks of Mayon Volcano, Philippines, in 1984 Pyroclastic flows are a common and devastating result of some volcanic eruptions. ... Volcanology (also spelled vulcanology) is the study of volcanoes, lava, magma and related geological phenomena. ...

Geological history

The Shimabara peninsula on which Unzen lies has seen extensive volcanism over millions of years. The oldest volcanic deposits in the region are about 6 million years old, and extensive eruptions occurred over the whole peninsula between 2.5 and 0.5 million years ago.

At this time, a graben formed through crustal faulting, and parts of the peninsula dropped to up to 1000 m below sea level. The formation of the graben may have caused the eruptive activity to become concentrated at one site, and the Unzen complex began to form within this graben. Eruptions of dacitic lava began from a site slightly to the south of today's Mount Unzen, and migrated north over time. USGS image A graben is a depressed block of land bordered by parallel faults. ... Gray, red, black, altered white/tan, flow-banded pumice dacite Dacite is a high-silica igneous, volcanic rock. ...

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 andesitic blocky lava and ash flows, changing to dacitic pumice flows and airfall deposits from 500,000 to 400,000 years ago. The period from 400,000 to 300,000 years ago saw the emplacement of large areas of pyroclastic flow and lahar deposits, which form the major part of the volcanic fan surrounding the volcano. From 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 time. A sample of andesite (dark groundmass) with amygdaloidal vesicules filled with zeolite. ... Gray, red, black, altered white/tan, flow-banded pumice dacite Dacite is a high-silica igneous, volcanic rock. ... Specimen of highly porous pumice from Teide volcano on Tenerife, Canary Islands. ... Pyroclastic flows sweep down the flanks of Mayon Volcano, Philippines, in 1984 Pyroclastic flows are a common and devastating result of some volcanic eruptions. ... Phreatic eruption at the summit of Mount St. ...

Activity from 150,000 years ago to the present day has occurred at a number of sites around the volcanic complex, building four main domes at different times: Nodake (70-150,000 years old), Myokendake (25-40,000 years old), Fugen-dake (younger than 25,000 years old) and Mayuyama (4,000 years old) volcanoes. Fugen-dake has been the site of most eruptions in the past 20,000 years, and lies about 6km from the centre of Shimabara city.

Unzen's most serious eruption came in 1792, with a large dacitic lave flow coming from Fugen-dake. The east flank of the Mayuyama dome collapsed unexpectedly following an earthquake after the end of the eruption, creating an avalanche and tsunami which killed an estimated 15,000 people. This remains Japan's worst ever volcanic disaster. The tsunami that struck Malé in the Maldives on December 26, 2004. ...

1990-1995 eruptions

Space radar image of Unzen

After 1792, the volcano remained dormant until November 1989, when an earthquake swarm began about 20km down and 10km west of Fugen-dake. Over the next year, earthquakes continued, with their hypocentres gradually migrating towards the summit. The first phreatic eruptions began in November 1990, and after inflation of the summit area, fresh lava began to emerge on June 20 1990. Image File history File links Download high resolution version (512x649, 77 KB)Space radar image of Unzen Volcano, Japan image description here larger version here Image courtesy: NASA/JPL-Caltech File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Image File history File links Download high resolution version (512x649, 77 KB)Space radar image of Unzen Volcano, Japan image description here larger version here Image courtesy: NASA/JPL-Caltech File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... The hypocenter or hypocentre (literally: below the center from the Greek υπόκεντρον), also known as the focus, is the point inside the Earth where an earthquake originates. ... Phreatic eruption at the summit of Mount St. ... This article is about the year. ... June 20 is the 171st day of the year (172nd in leap years) in the Gregorian Calendar, with 194 days remaining. ...

Due to the volcanic threat, 12,000 local residents were evacuated from their homes. On June 3, 1991, the volcano erupted violently, possibly as a result of depressurization of the magma column after a landslide in the crater. A pyroclastic flow reached 4.5km from the crater, and claimed the lives of 43 scientists and journalists, including well-known vulcanologists Katia and Maurice Krafft and Harry Glicken. Evacuation can have several meanings: In wilderness first aid, evacuation is the transport of a seriously injured person out of the wilderness to the nearest point an ambulance can reach to take them to the hospital, or to the nearest emergency room. ... June 3 is the 154th day of the year in the Gregorian calendar (155th in leap years), with 211 days remaining. ... 1991 (MCMXCI) is a common year starting on Tuesday of the Gregorian calendar. ... Magma is molten rock often located inside a magma chamber beneath the surface of the Earth. ... It has been suggested that Mudslide be merged into this article or section. ... Pyroclastic flows sweep down the flanks of Mayon Volcano, Philippines, in 1984 Pyroclastic flows are a common and devastating result of some volcanic eruptions. ... A scientist is a person who is an expert in at least one area of science and who uses the scientific method to research that area. ... A journalist is a person who practices journalism, the gathering and dissemination of information about current events, trends, issues and people. ... Volcanology (also spelled vulcanology) is the study of volcanoes, lava, magma and related geological phenomena. ... Katia Krafft (17 April 1942 – 3 June 1991) and her husband, Maurice Krafft ( 25 March 1946 – 3 June 1991) were French vulcanologists who died in a pyroclastic flow on Mt Unzen, in Japan, on June 3, 1991. ... Harry Glicken was a 33-year old volcanologist who was killed on 3 June 1991 by a pyroclastic flow on Mount Unzen in Japan, along with 42 other scientists and journalists, including well-known vulcanologists Katia and Maurice Krafft. ...

From 1991 to 1994 the volcano generated at least 10,000 small pyroclastic flows. In total, about 2,000 houses were destroyed. From 1993 onwards, the rate of lava effusion gradually decreased, and eruptions came to an end in 1995. Since eruptions ended, heavy rains have frequently remobilised pyroclastic material, generating lahars. 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. A lahar is a mixture of rock, mud, water and usually debris that flows down from a volcano (or occasionally other mountains), typically along a river valley. ... A dike (or dyke) is an earthen wall, constructed as a defence or as a boundary. ... The Murray River in Australia. ... Fljótsdalur in East-Iceland A valley is a landform, which can range from a few square miles (square kilometers) to hundreds or even thousands of square miles (square kilometers) in area. ...

The volcano 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. A map showing locations of the 16 Decade Volcanoes The Decade Volcanoes are 16 volcanoes identified by the International Association of Volcanology and Chemistry of the Earths Interior (IAVCEI) as being worthy of particular study in light of their history of large, destructive eruptions and proximity to populated areas. ... This law-related article does not cite its references or sources. ... Population density is a measurement of population per unit area or unit volume. ...

Unzen Scientific Drilling Project (USDP)

Devastation from Mt. Unzen's 1991 eruption

In 1999, an ambitious project began at Mt. 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. Devastation resulting from eruption of Mt. ... Devastation resulting from eruption of Mt. ...

Drilling began with test bores to assess the viability of a deep borehole. Two holes were bored, 750m and 1500m deep, and cores taken from these holes were used to better determine Unzen's eruptive history. One further 350m-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 800m. Drilling reached 1800m, the original target depth, without reaching the conduit, but in July 2004 at a depth of 1995m, the conduit was finally reached. The vertical depth below the summit was 1500m. July is the seventh month of the year in the Gregorian Calendar and one of seven Gregorian months with the length of 31 days. ... 2004 (MMIV) was a leap year starting on Thursday of the Gregorian calendar. ...

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

1. Hoshizumi H., Uto K., Matsumoto A. (2001), Core stratigraphy of the Unzen Scientific Drilling: Volcanic History of the Unzen Volcano, Kyushu, SW Japan, American Geophysical Union, Fall Meeting 2001
2. Hoshizumi H., Uto K., Matsumoto A., Kurihara A. (2004), Growth History Of Unzen Volcano, Kyushu, Japan, American Geophysical Union, Fall Meeting 2004
3. 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
4. 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
5. 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

External links

• Unzen Decade Volcano home page
• Global Volcanism Program page
• USGS description page
• Article about the USDP