12m 15s: Lenght

自衛隊が御嶽山の捜索活動の動画公開 YouTube 53. Ontakesan Continuously Monitored by Japan Meteorological Agency Latitude: 35°53'34" N, Longitude: 137°28'49" E, Elevation: 3,067 m (Kengamine) (GSI Measuring Point) Summary The Ontake volcano is a stratovolcano located at the southern tip of the Norikura volcano range. The volcanic edifice was built up during an early and late stage of activity, separated by a period of erosion. During the start of the late stage Ontake, a caldera was formed, but later activity filled in the caldera and the radiated valley, forming the roughly conical shape that exists today. During the most recent stage of activity, several small andesitic stratovolcanoes were formed at the summit, extending from north to south. Several of the craters are now crater lakes. Ontake consists of basalt, andesite, and dacite. A steam plume has been observed since the eruption of 1979, and in March, 2007 (Heisei 19), a small phreatic eruption occurred. Fumarolic areas exist on both the west side of the Otaki summit and in Jigokudani. The late stage Ontake volcano was made up of the Mamahahadake and Marishiten volcano groups. Approximately 90,000 to 110,000 years ago it became active with a large pumice eruption of rhyolite which began at the Pm-I air-fall pumice layer, tephra covering a wide area, and the formation of a caldera. Approximately 80,000 to 90,000 years ago activity began at the rhyolite-dacite Mamahahadake volcano group, filling in the caldera and forming a volcanic edifice composed of lava domes and pyroclastic flows. This was followed by the activity at the andesitic Marishiten volcano group approximately 80,000 years ago. The activity encompassed 8 volcanoes, with the locations of craters shifting within the caldera. The caldera was almost completely filled in, and the current summit group, which stretches north-south, was formed. The Kiso River lahar deposits came from a large debris avalanche and debris flow which occurred approximately 50,000 years ago, during this stage. This flow extended along the Kiso River approximately 150 km. During the last 20,000 years, activity consists mainly of phreatic explosions. At the southeastern foot of the volcano earthquakes have been frequent since 1978. On September 14, 1984 (Showa 59) an M6.8 earthquake, the Western Nagano Earthquake of 1984, struck, which caused 4 major landslides and flank failures at and around Ontakesan, killing 29. A particularly large flank failure, which occurred upstream in the Denjo River, involved 34 million cubic meters of soil. The collapsed soil flowed 12 km down the Denjo, Nigori, and Otaki rivers, depositing soil several dozen meters deep. Almost all of the sand was washed into the Denjo River, downstream. The SiO2 content is between 50.3 and 72.6 wt %. Ontakesan is also known as Kiso-Ontakesan. http://www.data.jma.go.jp/svd/vois/data/tokyo/STOCK/souran_eng/volcanoes/053_ontakesan.pdf NATIONAL CATALOGUE OF THE ACTIVE VOLCANOES IN JAPAN (THE FOURTH EDITION, ENGLISH VERSION) http://www.data.jma.go.jp/svd/vois/data/tokyo/STOCK/souran_eng/menu.htm