"Further intensification of activity in May was shown by increased seismicity, stronger ash emissions, and more frequent sightings of nighttime incandescence.

"Both craters continued to emit pale grey ash clouds, but the emissions from Southern crater were frequently reported to be strong and thick. The emission column from Southern crater usually rose several hundred meters above the summit, and a plume several tens of kilometers in length was reported on a few days. Intervals between discrete explosion and rumbling sounds varied from about 3 to 35 minutes. Glow and incandescent lava ejections were observed on most nights. Ballistic trajectories of incandescent tephra reached heights of up to 600 m above the crater rim.

"A brief period of intensified Main crater activity took place 12-19 May. Stronger ash emissions were accompanied by explosion and rumbling sounds, and crater glow and incandescent lava ejections were reported 12-16 May. Incandescent tephra fragments reached a maximum height of about 500 m.

"Volcano-seismic amplitudes continued to increase from the elevated April levels and reached a peak of about 5 times normal 22-24 May. A slight reduction was evident during the last week of May. At the month's end, amplitudes were still about 3 times normal. The number of volcano-seismic events declined from the peak of about 3500 per day reached in late April, and stabilized at about 2500 per day in May.

"A small but distinct tilt change was evident in May on the E-W component of the water tube tiltmeters at Tabele Observatory, about 4 km SW of the summit. The amplitude of the change was about 1 µrad, and its orientation was consistent with inflation of the volcano. No corresponding changes were shown by the N-S component."

Geological Summary. The 10-km-wide island of Manam, lying 13 km off the northern coast of mainland Papua New Guinea, is one of the country's most active volcanoes. Four large radial valleys extend from the unvegetated summit of the conical basaltic-andesitic stratovolcano to its lower flanks. These valleys channel lava flows and pyroclastic avalanches that have sometimes reached the coast. Five small satellitic centers are located near the island's shoreline on the northern, southern, and western sides. Two summit craters are present; both are active, although most observed eruptions have originated from the southern crater, concentrating eruptive products during much of the past century into the SE valley. Frequent eruptions, typically of mild-to-moderate scale, have been recorded since 1616. Occasional larger eruptions have produced pyroclastic flows and lava flows that reached flat-lying coastal areas and entered the sea, sometimes impacting populated areas.

Information Contacts: C. McKee, RVO.