RVO reported that activity at Manam increased slightly during 15-31 July, except from 18 to 20 July when there were fewer ash emissions. During most of the reporting period, when visibility was clear, gray-to-sometimes-black ash plumes were observed rising 300-700 m above the crater from two vents and drifting NW. Rumbling was often heard on the island; rumbling on 25 July was heard on the mainland 25 km SW. Bright glow visible at night was attributed to ejected incandescent tephra. Sub-Plinian activity occurred on most nights during 21-31 July. Small lava flows descended the SW flank. Four pyroclastic flows traveled down the SE flank on 30 July at 0638, 0640, during 1200-1300, and at 1428. The first event was the largest, and generated an ash plume that rose 1.8 km above the crater and drifted NW. Emissions from Main Crater were milder and mostly characterized by white and bluish plumes, and occasional gray ash plumes.

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: Rabaul Volcano Observatory (RVO)