GEOLOGIC HISTORY
The Azuma volcanic group consists of a cluster
of stratovolcanoes, shield volcanoes, lava domes, and
pyroclastic cones. The complex was constructed in two E-W
rows above a relatively high basement of Tertiary
sedimentary rocks and granodiorites. Volcanic activity
has migrated to the east, with the Higashi-Azuma volcano
group being the youngest.
Historic Activity:
- Historical eruptions, mostly small phreatic
explosions, have been restricted to Issaikyo volcano at
the northern end of the Higashi-yama group.
- The last eruption occurred in December 1977.
Earthquakes began in Sept. 1977, followed by mud and sand
spattering and ejection of small blocks in October, and
active fuming in Novermber. The small eruption on Dec. 7,
1977 sent ash 500-1,000 m above the crater and produced
minor ashfall. Similar ash ejections occurred through
January 1978.
Recent Activity:
- Small-amplitude volcanic tremor was detected on April
26, May 26, June 10, 17, and 30, and July 27, 1996.
- Increase in seismic activity during April-May
2001
Data Sources
- Smithsonian's SEAN Bulletin (V. 3, No. 1 and 2)
- Global Volcanism Network (V. 21, No. 5 to V. 26, No.
10).
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