Seismic activity . . . remained at relatively high levels through November. The monthly total of [319] shocks was down from 546 in October (figure 5); none were felt. Surface activity remained unchanged, with white steam rising to a few hundred meters.

Figure 5. Number of recorded earthquakes during 10-day periods at Akan, 1985-92. Arrows mark phreatic eruptions in 1988. Courtesy of JMA.

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.

Information Contacts: JMA.