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Increased activity at Sakurajima’s Minamidake crater, Japan

increased-activity-at-sakurajima-minamidake-crater-japan

After several relatively calm weeks, eruptions have picked up again at Japan's Sakurajima volcano. This time, the center of increased activity is Minamidake crater, Sakurajima's old summit vent, instead of the usual Showa crater.

After a gradual increase of activity at Minamidake during February, the explosive activity has picked up on March 24. Some explosions since then, like the one on March 26, were relatively large. Ash plumes were observed rising to 3 and 3.6 km (10 000 and 12 000 feet).

Sakurajima eruption on March 26, 2016. Video courtesy Yozhi Hayato.

Browsing Global Volcanism Program's (GVP / Smithsonian/USGS) Weekly Volcanic Activity Reports from July 2002 onwards, we can see that eruption at Minamidake crater was first mentioned on May 8, 2014. It was a very small eruption that produced an ash plume rising some 400 meters (1 313 feet) above the crater rim. Small explosions at Minamidake were again observed on August 30 and between September 14 and 21, 2015.

After that, Minamidake was calm until February 20, 2016, when activity at the crater started picking up, leading to the first noticeable explosion on March 4. Ash plume generated by that eruption rose to 1.6 km (5 250 feet). On March 8, explosion at Minamidake generated an ash plume that rose to 1.9 km (6 233 feet).

Sakurajima erupting on March 26, 2016. Image copyright: Luz Oracle Films – Naoto Yoshidome

Sakurajima erupting on March 24, 2016. Video courtesy Genki Sakurajima.

Sakurajima erupting on March 26, 2016. Video courtesy SkyeGoesWhaaaaaat?

Sakurajima erupting on March 26, 2016. Video courtesy Genki Sakurajima.

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 Aira caldera, along with several post-caldera cones. The construction of Sakurajima began about 13,000 years ago on the southern rim of Aira caldera and built an island that was finally joined to the Osumi Peninsula during the major explosive and effusive eruption of 1914. Activity at the Kitadake summit cone ended about 4850 years ago, after which eruptions took place at Minamidake.

Frequent historical eruptions, recorded since the 8th century, have deposited ash on Kagoshima, one of Kyushu's largest cities, located across Kagoshima Bay only 8 km from the summit. The largest historical eruption took place during 1471-76.

Featured image: Sakurajima eruption on March 26, 2016. Credit: SkyeGoesWhaaaaaat?

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