The Japan Meteorological Agency (JMA) reported increasing unrest at Me-Akan (also known as Meakan-dake, which means Meakan Peak) of the Akan volcanic complex during 11-15 September. The number of small-amplitude volcanic earthquakes with epicenters near Ponmachineshiri Crater began to increase at around 1500 on 11 September and remained elevated during the week with daily counts of 19-50 events. A large tilt change in the direction of the crater was detected at 1440 on 12 September, followed by a period of volcanic tremor during approximately 1440-1447. Tilt continued at a lower rate through 15 September. At around 1800 on 12 September, the typical white steam-and-gas plumes at 96-1 Crater within Ponmachineshiri became more voluminous and taller, rising to 100 m above the crater rim and drifting N, NE, and E. The plumes remained voluminous on 12, 13, and 15 September; weather conditions obscured views on 14 September. Increased thermal activity at the crater was confirmed based on field observations on 15 September. At 1520 on 15 September the Alert Level was raised to 2 (the second lowest level on a 5-level scale) and the public was warned to exercise caution within 500 m of Ponmachineshiri Crater. During an overflight on 16 September scientists confirmed that the vigorous steam-and-gas plumes were rising 200 m above 96-1 Crater and there were proximal ash deposits, mainly to the N. No significant changes were detected in the ground surface temperatures around 96-1 Crater.

Geological Summary. Akan is a 13 x 24 km caldera located immediately SW of Kussharo caldera in eastern Hokkaido. The elongated, irregular outline of the caldera rim reflects its incremental formation during major explosive eruptions from the early to mid-Pleistocene. There are four post-caldera stratovolcanoes, three at the SW end of the caldera and the other on the NE side. Conical Oakandake was frequently active during the Holocene. The 1-km-wide Nakamachineshiri crater of Meakandake was formed during a major pumice-and-scoria eruption about 13,500 years ago. The Meakandake group, composed of nine overlapping cones E of Lake Akan, has produced mild phreatic eruptions since the beginning of the 19th century. The main cone of Meakandake proper has a triple crater at its summit. Although recorded eruptions at Meakandake have consisted of minor phreatic explosions, four major magmatic eruptions with pyroclastic flows have also occurred during the Holocene.

Source: Japan Meteorological Agency (JMA)