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June 15, 2003 The eruption of Anatahan Volcano continues today. On June 12, USGS and EMO personnel took an overflight of Anatahan’s east crater and performed maintenance and adjustment on the east-side seismic station. The observers heard no sound from the eruption while at the seismic station. During the overflight, the floor of the east crater seemed deeper than it was during the previous aerial observations on June 6. The observers spotted spines on the crater floor closest to the septum that divides the east crater from the main crater. More ash had been evacuated from the crater floor, making viewing of the new lava dome or flow easier. One of the sources for the convecting ash cloud is apparently on the east side of the floor of the east crater; other regions emitting ash were obscured from view. The observers saw no ballistic ejection of material.Examination of the seismic records shows that the period of time from the first record, midday on June 5, until late on June 14 (local time) was entirely given to banded volcanic tremor. No specific events could be seen on the records until the evening of June 12, when three long-period earthquakes were recorded, the largest with a magnitude of about 2. Other earthquakes followed on the late afternoon and early evening of June 13. Two explosion signals were recorded during the next day. The largest, at 0010 June 14, removed much of the small new dome, as determined by an overflight later in the day. Just before noon on June 14, long-period earthquakes began to occur at intervals of 1-2 minutes. Similar “hybrid” earthquakes at Montserrat volcano indicated pressurization within the magma column and immediately preceded dome growth. However, the overflight on June 12, just after the pulse of hybrid earthquakes, saw no new dome. In general, the overflight found that the east crater and portions of the main crater were dusted with a light tan or gray ash. The crater floor was deeper than it was on June 12. The spines and pinnacles were gone. 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 |
U.S. Department of the Interior, U.S. Geological Survey, Reston, Virginia, USA
