Geologic Background:
The 8-km-wide island lying 202 km S of Tokyo
forms a stratovolcano with a 3.5- and 1.5-km-wide double
caldera summit containing the scoria cone called Oyama.
Parasitic craters and vents, including maars near the
coast and radially oriented fissure vents, dot the
volcano.
Historic Activity:
- Historical eruptions have occurred between 21- 69
year quiescence periods and indicate a pattern of a
sudden increase in seismic activity hours prior to an
eruption.
- In the 13 recorded eruptions since 1085, the village
of Ako was destroyed or badly damaged in 1643, 1712,
1763, and 1835.
- Miyakejima's erupted Aug. 24-27, 1962, when
explosions and lava flows originated from fissures on the
NE flank.
Recent Activity:
- Miyakejima erupted on Oct. 3, 1983 after 21 years of
quiescence. Two hours of increasing seismicity preceded
the eruption onset. A column of tephra and vapor rose to
10 km, and lava flowed down the southwest flank. The
eruption began in the summit crater, and downslope along
a 3 km-long fissure from the summit to the SW coast. Lava
advanced in 5 flows resulting in heavy damage to two
villages (Ako and Usuki). The eruption forced evacuation
of the island.
- Seismic activity began on June 26, 2000 and minor
offshore volcanic activity was reported on June 27. On
July 7 an eruption occurred from the summit crater. The
period from July 8 to Aug. 31 was marked by strong
outbursts, large plumes, pyroclastic flows, ashfalls, and
a series of concentric crater collapses.
- Activity continued into 2001. March 19 eruption
produced a significant ash cloud.
Data Sources:
- Smithsonian's SEAN Bulletin (V. 8, No. 9 to V. 8, No.
10)
- Global Volcanism Network (V. 21, No. 2 to V. 26, No.
2).
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