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Mount Unzen
is an active volcanic group of several overlapping stratovolcanoes, near the city of Shimabara, Nagasaki on the island of Kyushu, Japan's southernmost main island. In 1792, the collapse of one of its several lava domes triggered a megatsunami that killed 14,524 people in Japan's worst volcanic-related disaster. 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. Its highest peaks are at and at . The latter emerged during the eruptions of the early, eponymous Heisei era (1989–2019). Overview Mount Unzen (or ) rises in the central part of the Shimabara Peninsula, Nagasaki Prefecture. It is located on the outer ring of the Chijiwa Caldera centering on Tachibana Bay in the west of the peninsula. It consists of a total of more than 20 mountains, however, the complexity in the shape of was expressed by various numbers (such as Mitake Goho/Mimine Godake as " ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pyroclastic Flow
A pyroclastic flow (also known as a pyroclastic density current or a pyroclastic cloud) is a fast-moving current of hot gas and volcanic matter (collectively known as tephra) that flows along the ground away from a volcano at average speeds of but is capable of reaching speeds up to . The gases and tephra can reach temperatures of about . Pyroclastic flows are the most deadly of all volcanic hazards and are produced as a result of certain explosive eruptions; they normally touch the ground and hurtle downhill, or spread laterally under gravity. Their speed depends upon the density of the current, the volcanic output rate, and the gradient of the slope. Origin of term The word ''pyroclast'' is derived from the Greek (''pýr''), meaning "fire", and (''klastós''), meaning "broken in pieces". A name for pyroclastic flows which glow red in the dark is (French, "burning cloud"); this was notably used to describe the disastrous 1902 eruption of Mount Pelée on Martinique, a Fr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Shimabara Peninsula
is a peninsula located in Nagasaki Prefecture on the island of Kyushu, Japan. The peninsula incorporates the cities of Shimabara, Minamishimabara, Unzen. It was also the site of the Shimabara Rebellion, a 1637-1638 peasant and rōnin revolt, led by Christians. This further reinforced distrust of Christians and foreigners by Shōgun Iemitsu and contributed to the 1639 decision to isolate Japan from the outside world. From then on, the Dutch and the Chinese were the only ones permitted to enter Japan through Nagasaki in a very limited fashion until Japan was reopened again.Hane, Modern Japan: A Historical Survey, p. 24 Administrative region *Eastern section of Isahaya * Shimabara *Minamishimabara *Unzen is an active volcanic group of several overlapping stratovolcanoes, near the city of Shimabara, Nagasaki on the island of Kyushu, Japan's southernmost main island. In 1792, the collapse of one of its several lava domes triggered a megatsunami ... References La ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Deformation (volcanology)
In volcanology, deformation is any change in the shape of a volcano or the land surrounding it. This can be in the form of inflation, which is a response to pressurization, or deflation, which is a response to depressurization. Inflation is represented by swelling of the ground surface, a volcanic edifice, or a subsurface magma body. It can be caused by magma accumulation, exsolution of volatiles, geothermal processes, heating, and tectonic compression. Deflation is represented by shrinking of the ground surface, a volcanic edifice, or a subsurface magma body. It can be caused by magma withdrawal (related to intrusion or eruption), volatile escape, thermal contraction, phase changes during crystallization, and tectonic extension. Deformation is a key indicator of pre-eruptive unrest at many active volcanoes. The term bradyseism is used in the volcanological literature to mean the vertical ground movements associated with the Phlegraean Fields volcanic area west of Napl ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Debris Flow
Debris flows are geological phenomena in which water-laden masses of soil and fragmented rock rush down mountainsides, funnel into stream channels, entrain objects in their paths, and form thick, muddy deposits on valley floors. They generally have bulk densities comparable to those of rock avalanches and other types of landslides (roughly 2000 kilograms per cubic meter), but owing to widespread sediment liquefaction caused by high pore-fluid pressures, they can flow almost as fluidly as water. Debris flows descending steep channels commonly attain speeds that surpass 10 m/s (36 km/h), although some large flows can reach speeds that are much greater. Debris flows with volumes ranging up to about 100,000 cubic meters occur frequently in mountainous regions worldwide. The largest prehistoric flows have had volumes exceeding 1 billion cubic meters (i.e., 1 cubic kilometer). As a result of their high sediment concentrations and mobility, debris flows can be very de ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hypocentre
In seismology, a hypocenter or hypocentre () is the point of origin of an earthquake or a subsurface nuclear explosion. A synonym is the focus of an earthquake. Earthquakes An earthquake's hypocenter is the position where the strain energy stored in the rock is first released, marking the point where the fault begins to rupture.''The hypocenter is the point within the earth where an earthquake rupture starts. The epicenter is the point directly above it at the surface of the Earth. Also commonly termed the focus.'' This occurs directly beneath the epicenter, at a distance known as the ''hypocentral depth'' or ''focal depth''. The focal depth can be calculated from measurements based on seismic wave phenomena. As with all wave phenomena in physics, there is uncertainty in such measurements that grows with the wavelength so the focal depth of the source of these long-wavelength (low frequency) waves is difficult to determine exactly. Very strong earthquakes radiate a large fr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Unzen Volcano
is an active volcanic group of several overlapping stratovolcanoes, near the city of Shimabara, Nagasaki on the island of Kyushu, Japan's southernmost main island. In 1792, the collapse of one of its several lava domes triggered a megatsunami that killed 14,524 people in Japan's worst volcanic-related disaster. 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. Its highest peaks are at and at . The latter emerged during the eruptions of the early, eponymous Heisei era (1989–2019). Overview Mount Unzen (or ) rises in the central part of the Shimabara Peninsula, Nagasaki Prefecture. It is located on the outer ring of the Chijiwa Caldera centering on Tachibana Bay in the west of the peninsula. It consists of a total of more than 20 mountains, however, the complexity in the shape of was expressed by various numbers (such as Mitake Goho/Mimine Godake as ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Japan Times
''The Japan Times'' is Japan's largest and oldest English-language daily newspaper. It is published by , a subsidiary of News2u Holdings, Inc.. It is headquartered in the in Kioicho, Chiyoda, Tokyo. History ''The Japan Times'' was launched by Motosada Zumoto on 22 March 1897, with the goal of giving Japanese people an opportunity to read and discuss news and current events in English to help Japan to participate in the international community. The newspaper was independent of government control, but from 1931 onward, the paper's editors experienced mounting pressure from the Japanese government to submit to its policies. In 1933, the Japanese Ministry of Foreign Affairs appointed Hitoshi Ashida, former ministry official, as chief editor. During World War II, the newspaper served as an outlet for Imperial Japanese government communication and editorial opinion. It was successively renamed ''The Japan Times and Mail'' (1918–1940) following its merger with ''The Japa ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Megatsunami
A megatsunami is a very large wave created by a large, sudden displacement of material into a body of water. Megatsunamis have quite different features from ordinary tsunamis. Ordinary tsunamis are caused by underwater tectonic activity (movement of the earth's plates) and therefore occur along plate boundaries and as a result of earthquakes and the subsequent rise or fall in the sea floor that displaces a volume of water. Ordinary tsunamis exhibit shallow waves in the deep waters of the open ocean that increase dramatically in height upon approaching land to a maximum run-up height of around in the cases of the most powerful earthquakes. By contrast, megatsunamis occur when a large amount of material suddenly falls into water or anywhere near water (such as via a meteor impact or volcanic activity). They can have extremely large initial wave heights ranging from hundreds and possibly up to thousands of metres, far beyond the height of any ordinary tsunami. These giant wave hei ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ariake Bay
The is a body of salt water surrounded by Fukuoka, Saga, Nagasaki, and Kumamoto Prefectures, all of which lie on the island of Kyūshū in Japan. It is the largest bay in Kyūshū. Its deepest point is only about 50 meters (165 ft) deep, and extreme tides exceed , covering roughly . Isahaya Bay is a branch of the Ariake Sea. Across the Amakusa Islands lies the Yatsushiro Sea. Many harbors are located on the coast of the Ariake Sea. Among them are Misumi (in the city of Uki, Kumamoto Prefecture), Shimabara (Shimabara, Nagasaki), Taira (Unzen, Nagasaki), Nagasu (Nagasu, Kumamoto), Kumamoto (Kumamoto, Kumamoto), Miike ( Omuta, Fukuoka), Kuchinotsu (Minamishimabara, Nagasaki), and Oniike (Amakusa, Kumamoto). Five ferry routes cross the Ariake Sea. Various species of fauna, including mudskippers, pen shells (''Atrina pectinata''), and fiddler crabs, live in the Ariake Sea. In autumn, the ''Suaeda'' halophyte ''shichimenso'' ('' Suaeda japonica'') grows along the shore. The A ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Phreatic Eruption
A phreatic eruption, also called a phreatic explosion, ultravulcanian eruption or steam-blast eruption, occurs when magma heats ground water or surface water. The extreme temperature of the magma (anywhere from ) causes near-instantaneous evaporation of water to steam, resulting in an explosion of steam, water, ash, rock, and volcanic bombs. At Mount St. Helens in Washington state, hundreds of steam explosions preceded the 1980 Plinian eruption of the volcano. A less intense geothermal event may result in a mud volcano. Phreatic eruptions typically include steam and rock fragments; the inclusion of liquid lava is unusual. The temperature of the fragments can range from cold to incandescent. If molten magma is included, volcanologists classify the event as a phreatomagmatic eruption. These eruptions occasionally create broad, low-relief craters called ''maars''. Phreatic explosions can be accompanied by carbon dioxide or hydrogen sulfide gas-emissions. Carbon dioxid ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pumice
Pumice (), called pumicite in its powdered or dust form, is a volcanic rock that consists of highly vesicular rough-textured volcanic glass, which may or may not contain crystals. It is typically light-colored. Scoria is another vesicular volcanic rock that differs from pumice in having larger vesicles, thicker vesicle walls, and being dark colored and denser.Jackson, J.A., J. Mehl, and K. Neuendorf (2005) ''Glossary of Geology'' American Geological Institute, Alexandria, Virginia. 800 pp. McPhie, J., M. Doyle, and R. Allen (1993) ''Volcanic Textures A guide to the interpretation of textures in volcanic rocks'' Centre for Ore Deposit and Exploration Studies, University of Tasmania, Hobart, Tasmania..198 pp. Pumice is created when super-heated, highly pressurized rock is violently ejected from a volcano. The unusual foamy configuration of pumice happens because of simultaneous rapid cooling and rapid depressurization. The depressurization creates bubbles by lowering the solu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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