Report on Manam (Papua New Guinea) — 17 August-23 August 2011
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 17 August-23 August 2011
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2011. Report on Manam (Papua New Guinea). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 17 August-23 August 2011. 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 the summit area of Manam was obscured by atmospheric clouds on most days during 1-19 August. When the summit was clear to viewers on the mainland, 15-20 km away from Manam, both vents were emitting white vapor plumes. Main Crater produced light-gray ash clouds during 13 and 17-18 August, and bright, steady incandescence was visible on most clear nights. Weak incandescence was visible from Southern Crater on some nights. People living on the island reported occasional noises from both craters on 3 and 11 August. Seismicity during the reporting period was dominated by volcanic tremors. Discrete high-frequency volcano-tectonic earthquakes were also recorded. RVO noted that high-frequency volcano-tectonic earthquakes are not very common for Manam. An electronic tiltmeter located about 4 km SW from the summit craters continued to show inflation towards the summit area.
Based on analysis of satellite imagery, the Darwin VAAC reported that during 18-21 August ash plumes rose to altitudes of 1.8-2.1 km (6,000-7,000 ft) a.s.l. and drifted 45-90 km NW and W.
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.
Sources: Darwin Volcanic Ash Advisory Centre (VAAC), Rabaul Volcano Observatory (RVO)