Archived Update

Anatahan Volcano Update, June 15-20
June 21, 2003
08:00 A.M. Pacific/Saipan (GMT+10 hours)
 

The eruption of Anatahan Volcano continues. On June 16 USGS, EMO and CSIRO personnel took an overflight of Anatahan. The ash emissions and plume were small, the eruption cloud light colored, and steam dominated the column. The column was tilted westward by the ambient wind.

At 1613 during the flight, the eruption column became darker and was propelled vertically despite the wind. Where a few minutes before it took a pulse an average of 2-3 minutes to attain a full height of about 2,500 m (8,000 ft), now the column rose to full height in 20- 40 seconds. The activity was much more energetic, and the ash cloud much darker and ash laden. Accompanying this increased vigor, the seismic amplitude of tremor went from small to large by a factor of 5-10.

Since the explosions around midnight on June 13-14 and the 1-1/2 hour-long periods of banded tremor and long-period earthquakes at intervals of about 12, 12, 12, 12, and 4 hours through late June 16, there has been nothing but very low-amplitude tremor, and even that low level is gradually shrinking. The periods of banded tremor correlate with increased steam-explosion activity and vertical ash columns to about 2,500 m (8,000 ft), whereas the quieter periods of low-amplitude tremor correlate with feeble (wind-tilted) columns of steam. One interpretation of this change is that the hydrothermal system at depth within the volcano seems to have nearly boiled off.

Contact persons:

Juan Takai Camacho, Geophysical Seismic Technician, EMO Saipan; tel: (670) 322-9528, fax: (670) 322-7743, email: juantcamacho@hotmail.com

Frank Trusdell, Geologist, USGS; tel: (808) 967-8812, fax: (808) 967-8890, email: trusdell@usgs.gov