September 27, 2014 Eruption of Ontakesan

24 September-30 September 2014

According to the Japan Meteorological Agency, an unexpected phreatic eruption at Ontakesan occurred at 1152 on 27 September after an 11-minute period of tremor and uplift detected just minutes beforehand. The eruption produced a pyroclastic flow that traveled more than 3 km down the S flank and an ash plume that rose 7-10 km and drifted E. Ashfall was extensive in the area and up to 50 cm thick near the craters. The Alert Level was raised to 3.

Earthquakes near the summit had temporarily increased during 10-11 September, and low-frequency signals were detected on 14 September.

News articles on 1 October noted that 47 people had died, most of them found at the summit area while others were at a slightly lower elevation. Almost 70 more people were injured. Survivors described falling ash and boulders, and being in total darkness for several minutes as they made their way down the flanks. The volcano is popular to climb and nearly 300 people were hiking on the mountain that day.

Seismicity fluctuated but remained elevated during 28 September-1 October. Ash-and-gas plumes rose 300-400 m above the craters and drifted E and SE.

1 October-7 October 2014

JMA reported that ash emissions from Ontakesan likely continued during 1-7 October. The plume height could not be determined due to poor visibility although on 7 October observers noted that the plume rose 300 m above the crater rim and drifted E. Seismic levels fluctuated; tremor continued to be detected. A news article from 8 October noted that the number of people killed in the 27 September eruption had reached 55; nine were still missing. The Alert Level remained at 3 (on a scale of 1-5).

(above from reference #2432)