Report on Suwanosejima (Japan) — 31 July-6 August 2019
Smithsonian Institution / US Geological Survey
Weekly Volcanic Activity Report, 31 July-6 August 2019
Managing Editor: Sally Sennert.
Please cite this report as:
Global Volcanism Program, 2019. Report on Suwanosejima (Japan) (Sennert, S, ed.). Weekly Volcanic Activity Report, 31 July-6 August 2019. Smithsonian Institution and US Geological Survey.
Suwanosejima
Japan
29.638°N, 129.714°E; summit elev. 796 m
All times are local (unless otherwise noted)
JMA reported that at 2331 on 1 August an explosion at Suwanosejima’s Ontake Crater ejected blocks 400 m from the crater. Weather clouds prevented visual confirmation of an ash plume. Crater incandescence was sometimes visible at night. The number of volcanic earthquakes increased on 4 August and four explosions were recorded on 5 August. The Alert Level remained at 2 (on a 5-level scale).
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.