三宅島火山 1983 年噴火と噴出物 : とくに溶岩流について

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On October 3, 1983, the Miyakejima Volcano, a volcanic island in the Izu Seven Islands, suddenly started a fissure eruption. Eruptive fissures were about 4.5 km in length and ran from the southwest flank of the volcano, about 2 km away from the Oyama Central Cone, to southwest coast of the island during the first 2 hours. The eruption lasted only 15 hours from 15 : 15-15 : 20 and basaltic magma poured out accompaning lava fountaining along the fissures located on the flank higher than 50 meters above sea level and formed several flow lobes of aa lava. Phreato-magmatic eruptions occurred along the fissures near and on the coastal region to form large craters and a tuff ring more than 100 meters in diameter. Lavas poured out from craters A to E flowed down to the west on the slope of the volcano. The largest flow covered the most part of the Ako Village located on the west coast of the island. Lava issued out of craters H to K flowed down to the south and entered the sea near the Abe district. Many surface features on lava flow were identified such as lava wrinkles, lava levees, lava streaks and lava crevasses in vertical aerophotographs. Lava wrinkles appeared near the distal end of lavas. Lava levees are not remarkable except caldera floor areas, but lava streakes are observed characteristically throughout lava flows and commonly two streaks form a pair which represents faster flow inside them. There are many lava crevasses on relatively steep slope. They are thought to have been made by gravitational tension forces after lava supply from fissures stopped. From the eyewitnesses of the opening of fissures and estimation of effusion rate, lava and pyroclastics were fed from 2 or 3 dike systems which intruded laterally from the central conduit beneath the Oyama Central Cone.
特定非営利活動法人日本火山学会の論文
1984-12-28

三宅島火山 1983 年噴火と噴出物 : とくに溶岩流について

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