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Report on Suwanosejima (Japan) — 31 March-6 April 2021


Suwanosejima

Smithsonian Institution / US Geological Survey
Weekly Volcanic Activity Report, 31 March-6 April 2021
Managing Editor: Sally Sennert.

Please cite this report as:

Global Volcanism Program, 2021. Report on Suwanosejima (Japan) (Sennert, S, ed.). Weekly Volcanic Activity Report, 31 March-6 April 2021. Smithsonian Institution and US Geological Survey.

Weekly Report (31 March-6 April 2021)

Suwanosejima

Japan

29.638°N, 129.714°E; summit elev. 796 m

All times are local (unless otherwise noted)


JMA reported that during 30-31 March large volcanic bombs were ejected at least 41 times from Suwanosejima's Ontake Crater as high as 800 m above the crater rim and to distances as far as 1 km. The Alert Level was raised to 3 (on a 5-level scale) at 0330 on 31 March and the public was warned to stay outside a 2 km radius of the crater. The increased activity prompted an overflight that same day where scientists confirmed several hundred high-temperature bomb deposits with a thermal camera within a 1 km radius. Explosions at 2205 on 30 March and 0257 on 31 March ejected bombs onto the S and SE flanks, respectively. Grayish-white emissions rose from the crater. After 1500 eruption plumes rose as high as 1.4 km above the crater rim. The number of explosions decreased; two per day were recorded during 1-2 April and one was recorded on 3 April. The Alert Level was lowered to 2 on 5 April and the public was warned to stay 1 km away from the crater.

Geological Summary. The 8-km-long island of Suwanosejima in the northern Ryukyu Islands consists of an andesitic stratovolcano with two active summit craters. The summit is truncated by a large breached crater extending to the sea on the E flank that was formed by edifice collapse. One of Japan's most frequently active volcanoes, it was in a state of intermittent Strombolian activity from Otake, the NE summit crater, between 1949 and 1996, after which periods of inactivity lengthened. The largest recorded eruption took place in 1813-14, when thick scoria deposits covered residential areas, and the SW crater produced two lava flows that reached the western coast. At the end of the eruption the summit of Otake collapsed, forming a large debris avalanche and creating an open collapse scarp extending to the eastern coast. The island remained uninhabited for about 70 years after the 1813-1814 eruption. Lava flows reached the eastern coast of the island in 1884. Only about 50 people live on the island.

Source: Japan Meteorological Agency (JMA)