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Alert level raised Azumayama volcano, last eruption was in 1977, Japan

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The Japan Meteorological Agency raised the alert level for Azumayama volcano from level 1 to level 2 on September 15, 2018. The alert was raised to 1 on September 9, 2018. The last eruption of this volcano took place in 1977 (VEI 1).

The alert level was raised at 04:00 UTC (13:00 JST) today after a sharp increase in seismicity detected since 00:13 UTC (09:13 JST) today and continuous deformation, JMA said.

There is a possibility that a small scall eruption will take place in Ayumayama, the agency said, adding that vigilance is required in the range of approximately 1.5 km (0.93 miles) from the large crater.

Local authorities are urging population and tourists not to approach dangerous area.

The last time seismicity increased under Azuma was in May 2001. The Coordinating Committee for the Prediction of Volcanic Eruptions' seismic network detected 51 small-magnitude volcanic earthquakes during May 21 and 22 and 39 on May 21 (the most recorded in one day since November 1998). During March four low-frequency tremor events were recorded, while 40 were detected in April.

The last known eruption of this volcano took place on December 7, 2018. It had Volcanic Explosivity Index of 1. Its previous known eruption took place in 1950 (VEI 1).

Geological summary

The Azumayama volcanic group consists of a cluster of stratovolcanoes, shield volcanoes, lava domes, and pyroclastic cones. The andesitic and basaltic complex was constructed in two E-W rows above a relatively high basement of Tertiary sedimentary rocks and granodiorites west of Fukushima city. Volcanic activity has migrated to the east, with the Higashi-Azuma volcano group being the youngest.

The symmetrical Azuma-Kofuji crater and a nearby fumarolic area on the flank of Issaikyo volcano are popular tourist destinations. The Azumayama complex contains several crater lakes, including Goshikinuma and Okenuma. Historical eruptions, mostly small phreatic explosions, have been restricted to Issaikyo volcano at the northern end of the Higashiyama group.

Featured image: The symmetrical cone of Azuma Ko-Fuji, truncated by a 300-m-wide crater, is one of many volcanic features of the Azuma volcanic complex. The Azuma volcano group consists of a cluster of stratovolcanoes, shield volcanoes, lava domes, and pyroclastic cones. Volcanic activity has migrated to the east, with the Higashi-Azuma volcano group being the youngest. This photo was taken from the NW on the flanks of Issaikyo-yama, which has been the site of all historical eruptions (mostly small phreatic explosions) from the Azuma complex. Photo by Lee Siebert, 1988 (Smithsonian Institution).

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