The Darwin VAAC reported that a thermal anomaly over Manam was identified in satellite images on 15 December, prior to an ash emission that rose to 6.1 km (20,000 ft) a.s.l. and drifted SW. An ash plume rising to the same altitude was visible in satellite images on 16 December but had dissipated by mid-morning. Later that day diffuse ash plumes rising to 2.4 km (8,000 ft) a.s.l. were visible in satellite images and reported by ground observers, according to RVO. An eruptive event was recorded by the seismic network at 0600 on 17 December; ground observations indicated that an ash plume likely rose to 3 km (10,000 ft) a.s.l. and drifted SE. At 0840 ash emissions identified in satellite images and by observers rose to 3 km, drifted SE, and dissipated within about five hours. At 0220 on 18 December an ash plume rose to 3 km, drifted SE, and again dissipated within about five hours; a thermal anomaly over the summit was visible in the satellite data. At 1600 on 21 December an ash plume rose to 1.5 km (5,000 ft) a.s.l., drifted NE, and dissipated within about three hours. The thermal anomaly persisted.

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.

Source: Darwin Volcanic Ash Advisory Centre (VAAC)