Environment

Ohachi volcano alert level raised after first activity since 2004


The Japan Meteorological Agency has raised the alert level of Ohachi volcano, a part of Kirishimayama complex in Kyushu, from Level 1 to Level 2 on Friday, February 9, 2018.

Volcanic earthquakes under Ohachi increased around 08:00 local time today, JMA said. At present, no remarkable change is observed using distant observation of the volcano and other observation data but volcanic activity under the volcano is clearly increasing and small eruptions may occur, it added.

The warning affects the area within 1 km (0.62 miles) from the crater and people are warned that this region should not be approached as it is not safe due to the possibility of ashfall and ballistic projectiles. 

Ohachi volcano, Kyushu, Japan. Credit: Hydrographic and Oceanographic Department, Japan Coast Guard (JHOD)

Ohachi volcano, Kyushu, Japan

Ohachi volcano, Kyushu, Japan. Credit: Hydrographic and Oceanographic Department, Japan Coast Guard (JHOD)

Ohachi volcano, Kyushu, Japan. Credit: Hydrographic and Oceanographic Department, Japan Coast Guard (JHOD)

The last time this volcano appeared in the GVP’s Weekly Reports database was in January 2004:

Seismicity increased from ‘normal’ levels at Kirishima on December 13, 2013. On the same day, Dr. Kobayashi of Kagoshima University found new fumarole pits at the volcano’s Ohachi Crater and a video camera at the volcano showed steam rising above the crater rim.

Observers saw two new pits that formed in the middle of the crater’s southern inner wall and steam rising to ~100 m (328 feet). Also, pebbles (that were 2 – 3 cm / 0.8 – 1.2 inches across) and mud were scattered within about 10 m (32.8 feet) of these pits.

JMA issued a volcanic advisory on December 16, as the possibility of a small eruption had increased, judging from the high level of seismic and thermal activity.

On December 17, authorities announced that tourists were not permitted to visit Ohachi Crater. The level of seismicity peaked in mid-December, then declined somewhat, continuing at a relatively high level through at least mid-January 2004.

Geological summary

Kirishimayama is a large group of more than 20 Quaternary volcanoes located north of Kagoshima Bay. The late-Pleistocene to Holocene dominantly andesitic group consists of stratovolcanoes, pyroclastic cones, maars, and underlying shield volcanoes located over an area of 20 x 30 km (12.4 – 18.6 miles). The larger stratovolcanoes are scattered throughout the field, with the centrally located, 1700-m-high (5 577 feet) Karakunidake being the highest.

Onamiike and Miike, the two largest maars, are located SW of Karakunidake and at its far eastern end, respectively. Holocene eruptions have been concentrated along an E-W line of vents from Miike to Ohachi, and at Shinmoedake to the NE. Frequent small-to-moderate explosive eruptions have been recorded since the 8th century. (GVP)

Featured image: Ohachi volcano, Kyushu, Japan. Credit: Hydrographic and Oceanographic Department, Japan Coast Guard (JHOD)



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