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Anatahan Volcano Update, June 21-23
June 25, 2003
08:00 A.M. Pacific/Saipan (GMT+10 hours)
On June 20, USGS and CSIRO personnel took an overflight of Anatahan
and landed at the village briefly, just long enough to collect a sample.
The ash emissions were light and the plume small. The eruption cloud
was light colored. and steam seemed to dominate the column. The column
was tilted westward by the ambient winds and eventually attained heights
of about 2,500 m (8,000 ft).
Clouds covered the east crater and obscured views of the crater floor.
The relocated seismic station in eastern Anatahan continues to be operational.
However, high-frequency interference continues to plague about 15 percent
of the recorded data. A team from the Volcano Disaster Assistance Program
(VDAP) arrived early Monday to troubleshoot the interference from the
telemetered Anatahan station and install a new seismic analysis computer
system.
Since June 17, tremor amplitudes have remained low, with virtually no
long-period events recorded. Occasional banding has been observed, with
amplitudes up to about twice the ambient tremor background. Previous
periods of high-amplitude banding of long-period events and tremor correlated
with increased phreatic activity and vertical ash columns to about 2,500
m (8,000 ft), but seismic amplitudes were much higher during those observations.
A regional earthquake was recorded by the Anatahan station on June 22
at 10:31 pm local time. The USGS National Earthquake Information Center
located the M 5.0 event about 10 miles (15 km) northwest of Farallon
de Pajaros at a depth of 132 km. The Anatahan station recorded the S-arrival
at 10:33:37 with a peak-to-peak maximum amplitude of about 40 mm.
Contact persons:
Juan Takai Camacho, Geophysical Seismic Technician, EMO Saipan; tel:
(670) 322-9528, fax: (670) 322-7743, email: juantcamacho@hotmail.com
Ramon Chong, Geophysical Instrument Specialist, EMO Saipan; tel: (670)
322-9528, fax: (670) 322-7743, email: rcchongemo@hotmail.com
Frank Trusdell, Geologist, USGS; tel: (808) 967-8812, fax: (808) 967-8890,
email: trusdell@usgs.gov
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