Report on Manam (Papua New Guinea) — August 1991
Bulletin of the Global Volcanism Network, vol. 16, no. 8 (August 1991)
Managing Editor: Lindsay McClelland.
Manam (Papua New Guinea) Occasional ash emission; lava dome
Please cite this report as:
Global Volcanism Program, 1991. Report on Manam (Papua New Guinea). In: McClelland, L. (ed.), Bulletin of the Global Volcanism Network, 16:8. Smithsonian Institution. https://doi.org/10.5479/si.GVP.BGVN199108-251020.
Papua New Guinea
4.08°S, 145.037°E; summit elev. 1807 m
All times are local (unless otherwise noted)
"Main Crater produced weak emissions of white vapour with low ash content on 1, 2, and 3 August. Blue vapour was visible on 8, 11, and 12 August and only white vapour during the last week of the month. There were no audible noises and no night glow was seen.
"The emissions from Southern Crater consisted of tenuous white vapour with occasional grey-brown ash clouds resulting in fine ashfalls on parts of the island. Occasional weak deep roaring and rumbling noises were heard 2-14 August and a weak red glow was observed around the crater mouth on the night of 7 August. An aerial inspection was carried out on 13 August. Southern Crater was partly filled with vapour but Main Crater was clear. The floor of Main Crater was occupied by a solid plug or mound of lava, at a level ~20 m below the lower (NE) part of the crater rim. White mofettes were released by numerous fumaroles around the base and lower walls of the crater. The crater floor was mostly covered by debris from the crater walls, but in the central area, the lava plug was visible over an area ~5 m in diameter, and consisted of steaming lava surrounded by small blocks and scoriae ejected during a stronger degassing phase. During the aerial inspection, emissions from Southern Crater were low-energy, thermally buoyant clouds, released fairly regularly at ~15-minute intervals.
"Seismicity was at a moderate level and tilt measurements showed a deflation of ~1.5 µrad since mid-August."
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.
Information Contacts: B. Talai, C. McKee, and P. de Saint-Ours, RVO.