JMA lowered the Alert Level for Suwanosejima to 2 (on a 5-level scale) on 11 July, reflecting declining activity and a reduced likelihood that tephra would be ejected farther than 1 km. The number and intensity of explosions had been variable since early April but decreased overall, and material had not been ejected beyond a 1-km radius. Eruption plume heights had occasionally exceeded 3 km above the crater rim since July 2021 but none that high had been observed since mid-April. The number of volcanic earthquakes had temporality increased on 17 May but were generally low. 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)