On 21 March a strong (M 6.9) earthquake occurred near Urakawa, off the S coast of Hokkaido and 182 km SW of Akan. Local seismicity at Me-Akan increased after the earthquake, but the JMA has reported that there is no evidence of a causative relationship. The total number of seismic events recorded in March was 411 (table 1). The numbers of recorded seismic events at Me-Akan for 1977-81 are 97, 45, 491, 254, and 194.

Table 1. Number of seismic events recorded at Me-Akan during 19-31 March 1982. Courtesy of JMA.

Geological Summary. Akan is a 13 x 24 km caldera located immediately SW of Kussharo caldera. The elongated, irregular outline of the caldera rim reflects its incremental formation during major explosive eruptions from the early to mid-Pleistocene. Growth of four post-caldera stratovolcanoes, three at the SW end of the caldera and the other at the NE side, has restricted the size of the caldera lake. 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. Within the Akan volcanic complex, only the Meakandake group, east of Lake Akan, has been historically active, producing mild phreatic eruptions since the beginning of the 19th century. Meakandake is composed of nine overlapping cones. The main cone of Meakandake proper has a triple crater at its summit. Historical eruptions at Meakandake have consisted of minor phreatic explosions, but four major magmatic eruptions including pyroclastic flows have occurred during the Holocene.

Information Contacts: JMA, Tokyo.