Report on Manam (Papua New Guinea) — October 1983
Scientific Event Alert Network Bulletin, vol. 8, no. 10 (October 1983)
Managing Editor: Lindsay McClelland.
Manam (Papua New Guinea) Tephra clouds; glow; rumbling; increased seismicity
Please cite this report as:
Global Volcanism Program, 1983. Report on Manam (Papua New Guinea) (McClelland, L., ed.). Scientific Event Alert Network Bulletin, 8:10. Smithsonian Institution.
Papua New Guinea
4.08°S, 145.037°E; summit elev. 1807 m
All times are local (unless otherwise noted)
"Activity intensified somewhat at Manam's Main crater in October, while Southern crater activity was generally mild with forceful ejections of tephra on 2 days. The intensified Main crater activity took place in several brief periods. Explosive eruption sounds (rumbling, roaring, and booming) were heard about 4-5 km away on 14-15, 23-25, and 29-31 October, and crater glow was seen on 14, 23-24, and 29-30 October. Moderate, pale grey-brown emissions were observed during these periods, but at other times only small to moderate amounts of tephra-poor vapour were emitted.
"For most of the month, Southern crater emissions consisted of pale grey-brown ash clouds, but on 16 and 31 October impulsive, dense ejections of tephra and vapour to 200-250 m above the crater occurred. On 20, 22, and 31 October the emissions from both craters combined to form a plume several tens of kilometers long.
"Amplitudes of volcanic earthquakes were mainly steady at about 2-3 times normal levels, but increased 15-25 October. Daily earthquake totals remained around 2,700 for the first half of the month, decreased to about 1,900 at mid-month, and approached 2,600 on 31 October. A small down-tilt of about 1 µrad to the N (deflation) accumulated steadily during the month."
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 basaltic-andesitic stratovolcano to its lower flanks. These 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 observed eruptions have originated from the southern crater, concentrating eruptive products during much of the past century into the SE valley. Frequent 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.