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Report on Aira (Japan) — 20 July-26 July 2022


Smithsonian Institution / US Geological Survey
Weekly Volcanic Activity Report, 20 July-26 July 2022
Managing Editor: Sally Sennert.

Please cite this report as:

Global Volcanism Program, 2022. Report on Aira (Japan) (Sennert, S, ed.). Weekly Volcanic Activity Report, 20 July-26 July 2022. Smithsonian Institution and US Geological Survey.

Weekly Report (20 July-26 July 2022)



31.5772°N, 130.6589°E; summit elev. 1117 m

All times are local (unless otherwise noted)

A notable eruption at Minamidake Crater (at Aira Caldera’s Sakurajima volcano) occurred on 24 July. The event was preceded by inflation first detected at around 0900 on 18 July. JMA warned residents that the inflation represented an intrusion of magma that could result in a large explosion. Sulfur dioxide emissions were at 1,900 tons per day, measured during a field visit on 22 July. Four eruptive events recorded between 23 July and 1500 on 24 July produced plumes that rose 1.2 km above the crater rim; the events did not change the rate of inflation. A larger eruptive event occurred at 2005 on 24 July that ejected bombs more than 2.4 km E, the first time material fell beyond 2 km from the crater since 4 June 2020. The event produced minor plumes that rose 300 m before mingling with weather clouds. The Alert Level was raised to 5 (the highest level on a 5-level scale) at 2050, signaling that residents should evacuate. According to a news article 51 people in 33 households living within a 3-km radius of both Minamidake and Showa craters left their homes. Ashfall was reported in Kagoshima City (about 10 km W). JMA noted that inflation ceased after the event. On 25 July JMA scientists conducted a field visit and confirmed that bombs were deposited more than 2.4 km from the vent and observed ashfall in an area from Shirahamacho to Kurokamicho. During 25-26 July a few small explosions and eruptive events generated plumes that rose as high as 2.2 km above the crater rim and disappeared into the weather clouds. Deformation had stagnated.

Geological Summary. The Aira caldera in the northern half of Kagoshima Bay contains the post-caldera Sakurajima volcano, one of Japan's most active. Eruption of the voluminous Ito pyroclastic flow accompanied formation of the 17 x 23 km caldera about 22,000 years ago. The smaller Wakamiko caldera was formed during the early Holocene in the NE corner of the caldera, along with several post-caldera cones. The construction of Sakurajima began about 13,000 years ago on the southern rim and built an island that was joined to the Osumi Peninsula during the major explosive and effusive eruption of 1914. Activity at the Kitadake summit cone ended about 4,850 years ago, after which eruptions took place at Minamidake. Frequent eruptions since the 8th century have deposited ash on the city of Kagoshima, located across Kagoshima Bay only 8 km from the summit. The largest recorded eruption took place during 1471-76.

Sources: Japan Meteorological Agency (JMA), The Japan Times