Explosive eruption of Mount Aso spews ash 11 km (36 000 feet) a.s.l., Japan

Japanese Asosan volcano (Mount Aso; the largest active volcano in Japan) erupted at 16:46 UTC on October 7, 2016, sending a column of ash up to 11 km (36 000 feet) above sea level. JMA issued its third-highest alert (of 5), warning people not to approach the volcano.

The agency said this was the first 'explosive eruption' at the peak since January 1989.

Japanese media said volcanic ash had accumulated on cars, houses and roads in the city of Aso. Ash, however, was reported as far as 320 km (200 miles) from the crater.

According to Reuters, farmers have reported that some vinyl greenhouses where tomatoes and asparagus were being grown 6 – 8 km (4 – 5 miles) away from the crater had been broken by ash and small rocks. A window was cracked by a falling rock at an Aso youth center about 5 km (3 miles) away from the crater.

Some 29 000 households lost power shortly after the eruption, but the problem was fixed in less than two hours, Kyushu Electric spokesman said and added the eruption had no impact on its Sendai nuclear plant, located about 160 km (100 miles) south of the volcano.

“Mount Aso is in an unstable condition and could erupt again on the same scale,” JMA official told reporters, warning residents of volcanic ash, rocks and gas.

It is unclear whether the eruption was related to powerful earthquakes that hit Kumamoto and neighboring Oita Prefecture in April, killing 49 people, he said.

This is the first eruption since a minor one took place in May.

Japanese broadcaster NHK captured the moment on video when Asosan erupted:

Video courtesy AP

Geological summary

The 24-km-wide Asosan caldera was formed during four major explosive eruptions from 300,000 to 90,000 years ago. These produced voluminous pyroclastic flows that covered much of Kyushu. The last of these, the Aso-4 eruption, produced more than 600 cu km of airfall tephra and pyroclastic-flow deposits. A group of 17 central cones was constructed in the middle of the caldera, one of which, Nakadake, is one of Japan's most active volcanoes. It was the location of Japan's first documented historical eruption in 553 AD.

The Nakadake complex has remained active throughout the Holocene. Several other cones have been active during the Holocene, including the Kometsuka scoria cone as recently as about 210 CE. Historical eruptions have largely consisted of basaltic to basaltic-andesite ash emission with periodic strombolian and phreatomagmatic activity. The summit crater of Nakadake is accessible by toll road and cable car, and is one of Kyushu's most popular tourist destinations. (GVP)

Featured image: Explosive eruption at Asosan volcano, Kumamoto Prefecture, Kyushu, Japan on October 7, 2016. Credit: NHK (via AP)