Geologic Background:
Anatahan is located about 120 km north of
Saipan. Prehistoric volcanic activity at Anatahan has
built an island about 9.5 km long and 4 km wide,
consisting of two large cones linked at their summits by
an elongate, roughly E-W trending depression (compound
caldera of both collapse and explosive origin). The
elongated, 9-km-long island of Anatahan consists of two
coalescing volcanoes with a 2.5 x 5 km, E-W-trending
summit depression formed by overlapping summit craters.
The floor of the steep-walled crater of the younger
eastern cone is only 68 m above sea level. The spareness
of vegetation on the most recent lava flows on Anatahan
indicate that they are of Holocene age.
Historic Activity:
- No historic eruption are known, but solfataric
activity occurs in the summit area. Boiling hot springs
on the eastern crater floor and solfataras at the base of
the nearby crater wall
Recent Activity:
- Series of earthquakes March 30-April 27, 1990,
magnitude 3 to 5. Large shallow lake in east part of main
caldera disappeared, but had reappeared by October.
Ground surveys showed no significant deformation since
Sept. 1990.
- An earthquake swarm beneath Anatahan on May 29, 1993
resulted in the islands of Anatahan, Farallon de
Medinilla, and Sariguan being declared off-limits until
further notice. Seismicity continued into mid August and
then declined. The island was evacuated in 1990 following
a shallow earthquake swarm and has remained
uninhabited.
Data Sources:
- Global Volcanism Network (V. 15, No. 3 to V. 18, No.
8)
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