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Anatahan Volcano Update
Anatahan Volcano Update for October 26, 2004
Submitted Tuesday, October 26, 2004 at 1130 local Anatahan time
The first long-period seismic events since July were recorded on September
27, though few and quite small. A few other small long-period events
may have occurred occasionally through September 11. Several periods
of small, rather regularly spaced long-period events at
intervals of 4 to 15 seconds have been recorded since October 12. This
seismicity began several hours after the onset of a series of intense
tropical depressions and storms. Very frequent thunder signals have
been recorded from October 12 to the present by the telemetered microphones
on Anatahan Island. During southerly winds on October 18, people on
Saipan reported a H2S smell and very hazy visibility, but
no plume was detected on satellite imagery by the Washington VAAC.
Background: The eruption began this year after the seismicity
began increasing on March 31, 2004. Lava was noted in the crater on
April 15 and may have extruded for a few weeks thereafter. The most
energetic period began on April 24, when a light ash cloud rose to a
few thousand meters. Seismic activity peaked on April 28, then decreased
slowly to about half that peak value during May. That seismicity resulted
from strombolian bursts every one to few minutes that threw solid material
a few hundred meters out of the crater and steam and ash upward of a
few thousand meters. During June, the seismicity level was higher as
a result of more frequent small explosions every few tens of seconds,
and a 100-km-long, light-colored plume of steam and ash was occasionally
visible. An active spatter cone existed since at least June 10, from
which continuous strombolian explosions were throwing material up to
100 meters high every few tens of seconds to minutes. Spatter from these
explosions had filled the inner crater by about July 10. On July 26,
the seismicity level decreased dramatically to very low levels and still
remains very low. The seismic signals and visual reports showed that
the frequent strombolian explosions had ceased and the eruption had
ended.
The Emergency Management Office, Office
of the Governor, CNMI, has placed Anatahan Island off-limits until further
notice and concludes that, although the volcano is not currently dangerous
to most aircraft within the CNMI airspace, conditions may change rapidly,
and aircraft should pass upwind of Anatahan or farther than 30 km downwind
from the island and exercise due caution within 30-50 km of Anatahan.
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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