Report on Manam (Papua New Guinea) — April 1991
Bulletin of the Global Volcanism Network, vol. 16, no. 4 (April 1991)
Managing Editor: Lindsay McClelland.
Manam (Papua New Guinea) Tephra emission from two craters
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, 16:4. Smithsonian Institution. https://doi.org/10.5479/si.GVP.BGVN199104-251020.
Papua New Guinea
4.08°S, 145.037°E; summit elev. 1807 m
All times are local (unless otherwise noted)
"The increased activity at Main Crater in late March continued until mid-April, then declined. However, Southern Crater then became more active.
"Main Crater emissions consisted of weak to moderate white-grey ash and vapour with occasional thin blue vapour from 1 to 14 April. Emission clouds reached heights of 180-1,000 m above the crater rim. Light ashfall was noted 5 km downwind on 4 April. Deep roaring noises were heard on most days during this period. Weak red glow was seen above the crater 1-11 April, with some incandescent lava ejections on the 4th.
"Southern Crater activity increased for the first time since August 1990. From about mid-April, emissions consisted of weak to moderate white-grey vapour and ash. Light ashfalls were reported 23 and 25 April on the E side of the volcano, ~5 km from the summit. Low rumbling noises associated with the vapour and ash emissions were heard on 16 and 23-25 April.
"The seismograph at Manam became inoperable from 8 April. Before this time, seismic amplitudes remained at about the same level as at the end of March (~3x normal levels), although the daily totals of recorded volcanic shocks dropped from ~550 to 100. Tiltmeter measurements showed a slight radial deflation of ~1.5 µrad."
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.