Report on Suwanosejima (Japan) — 22 July-28 July 2020
Smithsonian / US Geological Survey Weekly Volcanic Activity Report,
22 July-28 July 2020
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2020. Report on Suwanosejima (Japan). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 22 July-28 July 2020. Smithsonian Institution and US Geological Survey.
29.638°N, 129.714°E; summit elev. 796 m
All times are local (unless otherwise noted)
JMA reported that nighttime incandescence at Suwanosejima’s Ontake Crater was occasionally visible during 17-24 July. An explosion at 2247 on 22 July generated a gray plume that rose as high as 1.2 km above the crater rim and ejected large rocks as far as 300 m from the crater. The Tokyo VAAC reported that during 25-27 July ash plumes rose to 1.8-2.7 km (6,000-9,000 ft) a.s.l. (1-1.9 km above the crater rim) and drifted NW, N, NE. 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 historically active summit craters. The summit is truncated by a large breached crater extending to the sea on the east 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 blanketed 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 the open Sakuchi caldera, which extends 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.