Report on Manam (Papua New Guinea) — 29 July-4 August 2015
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 29 July-4 August 2015
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2015. Report on Manam (Papua New Guinea). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 29 July-4 August 2015. Smithsonian Institution and US Geological Survey.
Papua New Guinea
4.08°S, 145.037°E; summit elev. 1807 m
All times are local (unless otherwise noted)
RVO reported that an eruption at Manam's Southern Crater began at about 1130 on 31 July with low roaring noises. Soon after, variously-sized scoria were ejected; fist-sized scoria fell in Warisi village on the E side of the island, and clasts 10-20 cm in diameter fell on the N side of the island in Baliau. Two people were knocked unconscious after being hit with scoria. According to a news article residents started evacuating around midday. Residents in Bogia (25-30 km SSW of Manam on the N coast of the mainland) reported ashfall at around 1245, and by 1300 the sky was darker. Ashfall was also reported in Potsdam (on the coast, NW of Bogia). RVO stated that at around 1330, immediately after scoria fall ceased, dark gray ash emissions rose from the crater. Based on satellite images and ground observations, the Darwin VAAC reported that the ash plume rose to an altitude of 19.8 km (65,000 ft) a.s.l., spread out in multiple directions, and then drifted 370 km SW. By 1740 RVO noted that activity had declined and emission turned to light gray, and by the next morning only dense white emission were observed.
Geologic Background. 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 1807-m-high basaltic-andesitic stratovolcano to its lower flanks. These "avalanche 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 historical eruptions have originated from the southern crater, concentrating eruptive products during much of the past century into the SE valley. Frequent historical 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.