Activity remained at a low level during March. Weak to moderate [emissions of white] vapor from both Southern and Main Craters were observed throughout the month. Deep rumbling sounds from Southern Crater were heard on 5, 6, and 7 March (followed by a short-term rise in microseismicity), and muffled explosion sounds accompanied forceful emissions of brown ash and vapor clouds on the 28th and 31st. The heavier, more dense fragments from those emissions fell back on the sides of the summit cone. Amplitudes of low-frequency earthquakes remained at about the same level as in the previous 4 months. No significant tilt changes were observed.

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: P. de Saint-Ours and C. McKee, RVO.