Geologic Background:
Iwo-jima lies within a 9-km-wide submarine
caldera. The triangular, 8-km-long island narrows toward
its SW tip. Iwo-jima has undergone dramatic uplift for at
least the past 700 years accompanying resurgent doming of
the caldera. The Moto-yama plateau consists of submarine
tuffs overlain by coral deposits; a shoreline landed upon
by Captain Cook's surveying crew in 1779 is now 40 m
above sea level. Many fumaroles are located on the
island, and temperature gradients are high.
Historic Activity:
- Numerous historical phreatic eruptions, many from
vents on the west and NW sides of the island, have
accompanied the remarkable uplift of Iwo-jima.
Recent Activity:
- Iwo-Jima last erupted March 9-10, 1982, when 5 small
phreatic explosions occurred from a new crater, north of
Asodai Crater. An earthquake swarm and 2 weak steam
explosions occurred Nov. 25-30, 1982. The explosions were
from Asodai Crater.
- A submarine eruption occurred offshore (SE of island)
on Sept 21, 2001. On Oct 19 a small phreatic eruption
occurred on a beach on the NW coast of the island.
Data Sources:
- Smithsonian's SEAN Bulletin (V. 7, No. 9 and V. 8,
No. 4).
- Global Volcanism Network (V. 26, No. 10).
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