Southern and Main Craters emitted small to moderate amounts of white vapour throughout December. Main Crater also emitted blue vapour on several days. Weak roaring and rumbling from Southern Crater were heard on a few days early in the month. Glow above Main Crater was observed on 8 and 27 December and was accompanied on the 27th by weak rumbling. Seismic amplitudes were stable at about twice non-eruptive levels and daily totals of volcanic earthquakes were ~1,400. Tilts were steady until 21 December when a mild deflationary phase began. About 2 µrad of deflationary tilt had accumulated by month's end.

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 and P. Lowenstein, RVO.