Eruptive activity continued through March, apparently accompanied by increased seismicity. The summit vent emitted mostly moderate to strong white to brown-gray vapor and ash clouds. Blue vapour emissions were observed 17-19 March. Weak summit glows were reported on most nights and incandescent lava fragments were ejected to ~50 m above the summit on 31 March. Rumbling sounds accompanied the eruption. Rockslides from the edges of the lava flow on the N and NW flanks indicated that effusion was continuing.

Although seismic recordings were intermittent, seismicity appeared to have begun increasing on 11 March [see also 12:4]. The highest daily total of volcanic earthquakes was 110. A total of 333 earthquakes were recorded for the month (the highest total since September 1986) but the actual number of earthquakes could have been significantly higher.

Geological Summary. Bagana volcano, in a remote portion of central Bougainville Island, is frequently active. This massive symmetrical cone was largely constructed by an accumulation of viscous andesitic lava flows. The entire edifice could have been constructed in about 300 years at its present rate of lava production. Eruptive activity is characterized by non-explosive effusion of viscous lava that maintains a small lava dome in the summit crater, although occasional explosive activity produces pyroclastic flows. Lava flows with tongue-shaped lobes up to 50 m thick and prominent levees descend the flanks on all sides.

Information Contacts: B. Talai and P. Lowenstein, RVO.