Report on Manam (Papua New Guinea) — April 1984
Scientific Event Alert Network Bulletin, vol. 9, no. 4 (April 1984)
Managing Editor: Lindsay McClelland.
Manam (Papua New Guinea) Strong strombolian activity; debris avalanches
Please cite this report as:
Global Volcanism Program, 1984. Report on Manam (Papua New Guinea). In: McClelland, L. (ed.), Scientific Event Alert Network Bulletin, 9:4. Smithsonian Institution. https://doi.org/10.5479/si.GVP.SEAN198404-251020.
Papua New Guinea
4.08°S, 145.037°E; summit elev. 1807 m
All times are local (unless otherwise noted)
"The intensity of the eruption remained at a moderate-high level throughout April. Moderate-strong Strombolian explosions from two vents in Southern crater produced an eruption column about 0.5 km high until 18 April. Incandescent lava ejections took place at relatively steady rates of up to about 4 per minute throughout the month, but an increase in average height of ejections from about 190 m to about 260 m was noted beginning 15 April. This tended to correlate with a change in eruption sound effects from roaring and rumbling in the first half of the month to sharp detonations beginning 15 April. Ashfalls in coastal areas were reportedly light throughout the month.
"Several cycles of waxing and waning seismicity were noted, with an overall peak (about 15 times normal amplitude) at the beginning of the month. Succeeding seismic peaks (18-19 April and early May) were less intense. Daily earthquake totals correlated with trends in seismic amplitudes. Up to 2500 events per day were recorded when amplitudes were high, and about 1300 per day in the intervening lulls. Cyclicity of the seismicity has been noted since January, with a period ranging from 2.5 to 3.5 weeks. The highest seismic peak in 1984 was at the start of April.
"The sustained high rate of explosions in April resulted in constant feeding of the cinder apron around Southern crater. These deposits were highly unstable, and frequent avalanches of debris flowed down the upper parts of the SE and SW valleys, usually coming to rest at elevations greater than 1,000 m. A breach developed in the S side of Southern crater about 27 March. This appeared to channel flowing lava to the precipitous headwall of the SW valley until early April when the crater rim was reconstructed. The lava flow fragmented completely in its descent into the SW valley.
"Main crater produced pale grey-brown, lightly ash-laden emissions in low-moderate volumes through April. These emissions were usually silent. No crater incandescence was noted.
"Fairly steady deformation of the volcano since late March has resulted in an accumulation of about 2 µm of radial inflation up to the end of April."
Further Reference. Scott, B.J., 1985, Manam volcano, Papua New Guinea: eruptive activity 26 March-17 April 1984: New Zealand Geological Survey Report G88.
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, RVO.