Report on Manam (Papua New Guinea) — July 1983
Scientific Event Alert Network Bulletin, vol. 8, no. 7 (July 1983)
Managing Editor: Lindsay McClelland..
Manam (Papua New Guinea) Moderate ash, vapor emissions; B-type events continue
Please cite this report as:
Global Volcanism Program, 1983. Report on Manam (Papua New Guinea). In: McClelland, L. (ed.), Scientific Event Alert Network Bulletin, 8:7. Smithsonian Institution. https://doi.org/10.5479/si.GVP.SEAN198307-251020.
Papua New Guinea
4.08°S, 145.037°E; summit elev. 1807 m
All times are local (unless otherwise noted)
"Most observed parameters showed little or no change in July. Visible activity at Southern crater was unchanged from that of June: pale grey ash-laden emissions in moderate volumes ejected to no more than about 100 m above the crater rim. Occasional weak rumbling and booming sounds accompanied these emissions. Blue vapour emissions also continued at the same rate. On several days a bluish emission plume stretched several tens of kilometers downwind. The crater was often obscured at night, and incandescence was seen only on the nights of 2, 4, 12, and 13 July, as weak fluctuating glow. On 2 July ejections of incandescent tephra to heights of about 250 m were also seen.
"Main crater activity was weaker in July than in June. Usually, pale grey ash-laden clouds were emitted in small to moderate volumes. Blue vapour emissions were seen on 12 and 14 July, and 26-31 July. No eruption sounds could be detected from Main crater, and no instances of nighttime incandescence were reported.
"A helicopter inspection on 26 July revealed that Main crater was a deep funnel-shaped structure having a central vent from which weakly ash-laden, blue-tinged clouds were being released. Abundant fumaroles were noted on the crater walls. Views of Southern crater were obscured by steady emission of ash-laden clouds that filled the entire crater.
"Amplitudes of B-type volcanic earthquakes were remarkably steady throughout July at about double non-eruptive levels, but representing a distinct decline from the high levels of mid-June. Daily totals of seismic events were about 2,000 at the beginning and end of the month, but varied up to about 3,000 in mid-month. Tilt measurements showed a continuation of the flat trend evident in June."
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: C. McKee and P. de Saint Ours, RVO.