RVO reported that incandescence from both Manam's Southern Crater and Main Crater fluctuated in intensity during 1-15 April, and incandescent material was occasionally ejected from the craters. RSAM values averaged around 100. On 15 April RSAM values fluctuated, with a peak of 450 at 0600 and other peaks throughout the day, though with RSAM values not as high. RVO interpreted the high RSAM values as changes in seismicity from discrete low-frequency earthquakes, to sub-continuous volcanic tremor, and then to continuous volcanic tremor.

During 0300-0800 on 16 April RSAM values were high (peaking at 400); there were no reports of associated anomalous eruptive activity, though RVO noted communication problems. Based on RSAM data, a small-to-medium eruption began between 1400 and 1600 on 16 April. Seismicity was initially erratic, and peaked at about 0030 and 0100 on 17 April. A Dugulava village resident (S side of island) briefly viewed the eruption and reported that incandescent material was ejected from the crater and fell into the N and SW valleys. Rumbling and roaring was also heard. Activity decreased around 0600 and remained low until the next day. Strong Strombolian activity at Southern Crater was observed at about 1300 on 18 April, and roaring and rumbling was heard. Dense and dark ash clouds rose a few hundred meters above the crater rim and drifted NW. Two small pyroclastic flows descended the SE and SW valleys, terminating at about 1 km a.s.l. At about 1500 Strombolian activity subsided, coinciding with a very loud explosion. Activity fluctuated though was low until 2100, and then afterwards light-gray ash plumes rose above the crater. White-to-gray ash plumes rose above Main Crater during 17-18 April, and small ejections of material occurred about every five minutes.

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)