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46-686: A major three phase eruption of the Aira Caldera formed in the first phase the Osumi pumice fall, had a second phase Tsumaya pyroclastic flow and in the third Ito eruption phase produced the widely distributed Aira-Tn tephra that has been dated at 29,428 to 30,148 years calibrated before present. The Aira-Tn tephra falls from this eruption were up to 0.800 m (2 ft 7.5 in) thick extending to significant depth that would have affected plant life in south eastern South Korea and Honshu. This and Ito Ignimbrite up to 160 m (520 ft) thick, are

92-482: A Volcanic Explosivity Index of 7, so making it one of the most explosive in the last 10,000 years, ranking alongside the eruptions of Santorini , Paektu , Crater Lake , Kurile Lake , Samalas and Tambora . The eruption had a major impact on the Jōmon culture in southern Kyūshū although the impact was not as great as some commentary had suggested with Nishinozono sub-type pottery tradition, that had started prior to

138-686: A caldera that was 17 km (11 mi) by 23 km (14 mi). The Aira Caldera is one of a series of volcanic complexs in the Kagoshima Graben which has been postulated to extend northward from the undersea Kikai Caldera to the Ata South Caldera, Ata North Caldera (see Ata Caldera ), the Aira Caldera associated with Kagoshima Bay and through past to the Kirishima Volcano Group . This alignment

184-471: A common reservoir. However, not all the volcanic systems are connected all the time as magma pathways open and close. The connection between Aira and Kirishima represents the clearest example of volcano interconnectivity revealed by geodetic monitoring. The inflation of one volcano can enhance the eruption probability of a neighbouring volcano. The subduction of the Philippine Sea Plate beneath

230-566: A disaster prevention system with the world's best high-tech volcanic monitory system was put in place. The Caldera is now closely monitored by the Sakurajima Volcano Research Centre which is a part of the University of Kyoto and Disaster Prevention Research Institute. This ensures the safety of the residents and provides a peaceful coexistence with the people of Kagoshima and the active caldera. Aira Caldera

276-658: A faster rate than the Sakurajima volcano erupts. The reservoir is expanding each year as a volume of 14 million m is supplied to the system. Dr Haruhisa Nakamichi, Associate Professor at the Disaster Prevention Research Institute, Kyoto University, and co-author, said: "It is already passed by 100 years since the 1914 eruption, less than 30 years is left until a next expected big eruption, Kagoshima city office has prepared new evacuation plans from Sakurajima, after experiences of evacuation of

322-456: A few hundred meters from the eruption’s center, causing the formation of a pyroclastic flow. Since the center of the volcano was under water, the Akahoya eruption had the character of a steam explosion (or a series of explosions) due to the instantaneous release of steam upon contact of hot magma with water. As a result, a double caldera was formed. Scientists had conducted a detailed study of

368-421: A final stage, which partially spread along the seabed and released into the atmosphere in the form of an eruptive column (ash, fragments of pumice, small crystals and tephra). The tephra cloud covered an area of more than 2.8 million km2. The volume of ash material amounted to more than 370 km3 in terms of hard rock. The Plinian phase ended with the destruction of the eruptive column. A huge column of hot tephra fell

414-465: A large-scale volcanic event and identified three directions of flow of eruption products: in the atmosphere, along the seabed and along the water's edge. Details of the marine expedition include conducting seismological studies and collecting sediment samples around the Kikai caldera. Scientists have confirmed that volcanic formations on the ocean floor and nearby islands have a common position. Analysis of

460-434: A series of disasters such as the eruption in 1914 which killed 58 people and sank the magma chamber by 60 cm. Aira caldera is located at Kyushu, the southernmost island of Japan. The supervolcano peaks at 1117 m. The eruption forming the Aira Caldera, occurred approximately 30,000 years ago, and resulted in tephra and ignimbrite from a vast amount of magma affecting the nearby land. The eruption also aided in

506-475: A suspended stream, which can cover long distances even up the slope, as it turned out. Having built a model of the Kikai-Akahoya eruption, researchers have found that in addition to the underwater pyroclastic flow and the powerful release of the tephra cloud into the atmosphere, there was also a third stream of thin volcanic material that spread along the surface of the water to the nearest islands. Kikai

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552-473: Is a stub . You can help Misplaced Pages by expanding it . Aira Caldera Aira Caldera is a gigantic volcanic caldera located on the southern end of Kyushu , Japan. It is believed to have been formed about 30,000 years ago with a succession of pyroclastic surges . It is currently the place of residence to over 900,000 people. The shores of Aira Caldera are home to rare flora and fauna, including Japanese bay tree and Japanese black pine . The caldera

598-590: Is a massive, mostly submerged caldera up to 19 kilometres (12 mi) in diameter in the Ōsumi Islands of Kagoshima Prefecture , Japan. The Kikai Caldera Complex has twin ovoid caldera 20 km (12 mi) by 17 km (11 mi) in diameter. Yahazu-dake (north west part of Satsuma Io-jima ) and Takeshima , located on the caldera rim, are pre-caldera volcanoes. The pre-caldera stage of volcanic activity involved rhyolite , basalt , and andesite phases. The earliest definitive caldera formation has been dated back to at least 140,000 years ago, resulting from

644-474: Is almost rectangular in shape related to local faulting and was created in a series of large scale of pyroclastic surges that contributed to the Shirasu-Daichi pyroclastic plateau with the last now dated to 29,428 to 30,148 years calibrated before present although earlier work had the date at ~22,000 years ago with wide possible range from 34,500 to 16,500 years before present. The eruption formed

690-538: Is home to Mount Sakurajima , and the Mount Kirishima group of stratovolcanoes lies to the north of the caldera. The most famous and active of this group is Shinmoedake . Aira Caldera has an underlying magmatic chamber that connects with the Kirishima magmatic system. This has enabled magma from the caldera to feed into Sakurajima stratovolcano, causing it to expand over time. Thus, Sakurajima has caused

736-522: Is likely subsequent eruptions in this series were at vents in what has been termed the Wakamiko caldera to the north west. Basement rock fragments and pumiceous materials from a massive explosion formed the Ito pyroclastic flow which deposited more than 800 km (190 cu mi) of Ito Ignimbrite (known as “Shirasu” locally) and 300 km (72 cu mi) of Aira-Tn Tephra in volume. Within

782-542: Is located between MIS 5.2 and 5.3, providing a loosely constrained preliminary eruption age of approximately 95,000 years before present. More reliable age constraints were imposed by the high-resolution chronology derived from the Lake Suigetsu sediment sequence, which yielded an age of 94,500 ± 4,800 years before present for this eruption. The caldera was the source of the Kikai-Akahoya eruption , one of

828-542: Is still an active volcano. Io-dake (Mount Iō) , Inamura-dake (south coast of Satsuma-Io-jima ), Tokara-Iwo-Jima (north east coast of Satsuma-Io-jima) and Shōwa Iōjima (Shin-Io-jima) are post-caldera volcanoes within it. Minor eruptions occur frequently on Mount Iō, one of the post-caldera subaerial volcanic peaks on Iōjima. Iōjima is one of three volcanic islands, two of which lie on the caldera rim. On June 4, 2013, weak tremors were recorded. Shortly after, eruptions began and continued off-and-on for several hours. Io-dake

874-601: The Eurasian Plate is the reason for the active volcanism. Aira Caldera and Kirishima's magma storage is linked through tunnels that extend horizontally over tens of kilometers which is able to be explained through the presence of hotspots. However, the volcanic systems are not always connected since the magma pathways open and close. For example, the Shinmoedake vertical connection was closed for approximately 300 years until reactivation. The changes in volume for

920-530: The Aira and Kirishima systems suggest they had different inflation and deflation periods. Between 2009 and 2013, there was evidence of inflation in the Aira system. However, after the 2011 eruption at Kirishima, the Aira system experienced a deflation. This was Aira caldera's only deflation between 2009 and 2013. The magma storage underlying Aira Caldera has been feeding into the stratovolcano Sakurajima, expanding over time. However, there have been points in time where

966-533: The K-Kob pyroclastic flows has been dated using K-Ar dating to be 140,000 ± 20,000 years before present. While no distal tephra from this eruption has been reported, a tephra layer with potential geochemical and age correlation has been discovered in Lake Suigetsu . Kikai-Tozurahara (K-Tz) tephra is a widespread rhyolitic tephra layer of Late Pleistocene age, attributed to a large VEI -7 eruption from

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1012-731: The Kikai caldera. This layer is confirmed to have a wide distribution, extending from south Kyushu to eastern Honshu and reaching the Pacific Ocean , and possibly including the Shandong Peninsula . The proximal equivalents of K-Tz are the Nagase pyroclastic flow and the Nishinoomote pyroclastic surges . The combined bulk volume of both distal and proximal deposits is estimated to exceed 150 km (36 cu mi). In marine isotope stratigraphy (MIS), K-Tz

1058-480: The Osumi pumice fall and the Tsumaya pyroclastic flow occurred from the same vent. There was only a very short period between the Tsumaya pyroclastic flow and the formation of the present caldera in the Ito eruption. In contrast the Ito pyroclastic flow extends outside the basin as well as occupying inside the basin. The Aira-Tn tephra falls from this eruption were up to 0.800 m (2 ft 7.5 in) thick in

1104-424: The centre of the caldera and 40 mm (1.6 in) in the south urban area of Kokubu. The plants near Sakurajima regrow after eruptions. The Japanese bay trees and Japanese black pines are two species which grow furthest away. These plants are able to repopulate; however they cannot withstand the debris and pumice after an eruption. Eurya japonica and Alnus firma can be found in the middle ground away from

1150-410: The chamber has deflated as a result of eruptions releasing the pressure built which cannot be explained by stress changes. Thus, it has been described as a consequence of magma withdrawing from the Aira system when Kirishima was replenishing. A prime example is the Sakurajima eruption in 1914 (approximately 1.5 km in volume), which caused the magma chamber to sink 60 cm. 58 people were killed in

1196-404: The constraints that much of the caldera is under the sea, the reason for the large vent area is because the caldera erupted well over earlier estimates of 140 km (34 cu mi) of magma in a short amount of time. The caldera is known for its gravitational anomalies which is associated with a funnel-like shape in the strata. The structure of the caldera seemed unique in early work as it

1242-583: The crisis in August 2015." A group of scientists led by Dr Dominique Remy used Synthetique Aperture Radar (SAR) to detect levels of inflation of Aira Caldera over the Kokubu urban district. They observed a change in the pattern of Kokubu's surface. Through a model of the deformation field of the caldera, it is predicted there is "a maximum volume increase of 20–30×10  m between 1995 and 1998." They deduced an inflation of approximately 70 mm (2.8 in) at

1288-531: The different eruptions in different eras. Kagoshima Bay (Kinko Bay) is home to much wildlife; including 1000 different species of fish, a population of dolphins , as well as rare creatures such as the Satsumahaorimushi tube worm. Rare minerals exist on the sea bottom with hydrothermal vents including volcanic chimneys. Kikai Caldera Kikai Caldera ( 鬼界カルデラ , Kikai karudera ) (alternatively Kikaiga-shima , Kikai Caldera Complex )

1334-482: The distribution of these deposits around the eruption site helps to understand how the pyroclastic flow and water interacted. The eruption occurred with a strong ejection of debris and ash, which corresponds to the usual phase of the Plinian type, during which there was a series of prolonged emissions under high pressure of fragmented lava and pumice in the form of a gas-ash mixture. It was a volumetric pyroclastic flow as

1380-477: The eruption of Koabiyama pyroclastic flows . The formation of caldera has been associated with at least three catastrophic ignimbrite eruptions. Additionally, there are two older deposits (Koseda pyroclastic flows and Anbo tephra) of large caldera-forming eruptions in the vicinity, although their attribution to the Kikai caldera remains controversial. The Kikai-Koabiyama (K-Kob) pyroclastic flows are rhyolitic and are distributed across most of Takeshima and

1426-448: The eruption, maintained in Kyūshū. Japanese scientists conducted an extensive study of the volcanic activity of the Kikai underwater caldera. They had estimated the volumes of ejected volcanic material, which range from 332 to 457 cubic kilometers, and proved that it was the largest eruption in the last 11,700 years that occurred here 7,300 years ago. They were able to recreate the sequence of

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1472-458: The eruption. For this amount of magma to erupt, it would take approximately 130 years for the chamber to refill as according to Dr James Hickey and his co-authors. Dr Hickey stated "These results were made possible by combining data from various monitoring methods and applying them to new numerical modelling techniques, moving away from older modelling methods that have been in use since the 1950s." Nevertheless, there are continuous measurements of

1518-420: The formation of present-day Aira Caldera. The first phase of activity resulted from injection of mafic magmas that destabilized the stored rhyolite magma and was the mainly homogeneous Osumi Pumice Fall (named because the pumice fall extended across the Ōsumi Peninsula to the south east). Above the Osumi pumice fall deposit, is the second phase Tsumaya pyroclastic flow deposit which is wholly confined within

1564-424: The formation of the 200 m (660 ft) deep Kinko Bay which formed after sea water entered the area. Aira caldera is surrounded by the major city of Kagoshima which has a population of more than 900,000. Residents do not mind small eruptions because they have measures in place for protection. For example, school students are required to wear hard helmets for protection against falling debris. Additionally,

1610-403: The ground movement that indicate the area is now inflating. Recent GPS deformation measurements, amalgamated with geophysical data and computer modelling enable the reconstruction of the magma system beneath the caldera. Through this, Dr James Hickey and his co-authors were able to create a depiction of the tunnels beneath the caldera. They discovered that magma is filling the magma chamber at

1656-516: The largest eruptions during the Holocene (10,000 years ago to present) that produced the Kikai-Akahoya (K-Ah) tephra . Between 7,200 and 7,300 years ago, pyroclastic flows producing Koya ignimbrite from that eruption reached the coast of southern Kyūshū up to 100 km (62 mi) away, and ash fell as far as Hokkaidō . The eruption produced about 133–183 km (32–44 cu mi)  DRE , most of it tephra. giving it

1702-539: The most significant pyroclastic deposits of the plateau. However an eruption about 11,000 years before present did result in the Satsuma pumice fall and there have been multiple relatively minor ash falls since from the local active volcanoes. This Japanese location article is a stub . You can help Misplaced Pages by expanding it . This Miyazaki Prefecture location article is a stub . You can help Misplaced Pages by expanding it . This Kagoshima Prefecture location article

1748-518: The north end of Aira caldera. One of these volcanoes, Shinmoedake , has produced two strong magmato-phreatic eruptions, separated by almost 300 years. Starting in December 2009, active diving and inflation before the outbreak were noticed. A series of sub-plinian events then occurred from January 19 to the 31st. The first phase (eruption climax) was accompanied by a strong co-eruptive deflation. Aira Caldera may respond to small eruptions that come from

1794-416: The peak. They are able to grow back from an eruption and withstand its destruction more than the vegetation furthest away. Japanese Pampas grass and knotweed are located closest to the volcano. They respond quickly after an eruption and form a meadow of mosses and lichens during regrowth. Nevertheless, It takes many years for the forest to regrow. This enables people to observe the changes of vegetation from

1840-466: The plateau-like area on the northwest side of the caldera rim of Satsuma Iwo-Jima. They consist of numerous thin flow units and fill the basins in the basement, exhibiting significant variation in thickness. In Takeshima, the pyroclastic flows are thick, ranging from 20–100 m (66–328 ft), whereas in Iwo Jima, they are relatively thin, measuring a few to 30 m (98 ft). The eruption of

1886-445: The pre-Aira basin. The Tsumaya pyroclastic flow buried the pre-Aira topography such as box canyons (formed by older pyroclastic flow deposits). The maximum thickness in the caldera is 130 m (430 ft) in the Kokubu area with the average thickness being 30 m (98 ft) or less. The Tsumaya pyroclastic flow consists of a "pale pinkish brown glass matrix containing a small amount of pumice and lithic fragments" consistent with

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1932-426: The south east and this and Ito Ignimbrite up to 160 m (520 ft) thick, are the most significant pyroclastic deposits. The depth of the ash fall over the whole island of Kyūshū was over 32 cm (13 in) and more than 4 cm (1.6 in) for much of Japan Aira caldera is one of the most active and hazardous calderas in the world. It is home to the Kirishima volcanoes, a group of active volcanoes at

1978-409: The spread of volcanic material over an area of about 4,500 square kilometers around the center of the eruption and mapped the thickness of the underwater pyroclastic sediment. In their opinion, 133 to 183 cubic kilometers of pumice and ash settled on the studied area. After analyzing the textures and nature of the fragments of the underwater volcanic strata, the authors concluded that it was formed from

2024-419: Was a wide and shallow basin of nearly the same size as the present Aira Caldera occupying the northern end of Kagoshima Bay with an east–west orientation. The basin is separated from the rest of the bay by a ridge with heights 300 m (980 ft) to 500 m (1,600 ft) above sea level. The topography encompasses the outline of an older caldera so suggesting there were pyroclastic flows that pre-dated

2070-524: Was different from the then typical Valles-type Caldera whose defining characteristics include a Valles-type ring fracture which acts as a channel for such large-scale pyroclastic flows. Such diffuse non directional pyroclastic flows, overwhelming the local landscape, have now also been described in New Zealand , for example in the Hatepe eruption . Before the initial eruption of 25,000 years ago there

2116-593: Was first noted in the 1940s. The tectonic processes are rather complex in this region where the Okinawa Plate is colliding with the Amur Plate and the Pacific Plate is subducting under both. The formation of Aira Caldera started with a Plinian pumice eruption of the Osumi pumice fall from a vent near where Sakurajima is now and was quickly followed by an oxidised Tsumaya pyroclastic flow. It

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