Report on Manam (Papua New Guinea) — December 1981
Scientific Event Alert Network Bulletin, vol. 6, no. 12 (December 1981)
Managing Editor: Lindsay McClelland.
Manam (Papua New Guinea) Explosions and seismicity intensify
Please cite this report as:
Global Volcanism Program, 1981. Report on Manam (Papua New Guinea) (McClelland, L., ed.). Scientific Event Alert Network Bulletin, 6:12. Smithsonian Institution.
Papua New Guinea
4.08°S, 145.037°E; summit elev. 1807 m
All times are local (unless otherwise noted)
"Activity further intensified in December. Southern crater emissions became darker after 9 December when spearheaded projections of tephra were first reported. Rumbling, thudding, and roaring sounds also intensified after the 9th. Larger tephra was visible beginning 13 December. Incandescent tephra ejections were seen throughout the month. Daytime incandescence, visible from Tabele Observatory (4 km from the summit), was reported occasionally, but became more common at the end of the month. These ejections rose to a maximum height of about 0.7 km. Spearheaded tephra projections became common at the end of the month. Light ashfalls in coastal areas 4-5 km from the summit were reported on several days in the second half of the month.
"Main crater was less active than Southern crater. Weak to moderate volumes of brown to grey emissions were reported occasionally in the first 10 days of December. However, activity intensified later in the month, and tephra emissions were reported every day 21-30 December. Weak glow from Main crater was seen on 29 December. Seismicity strengthened throughout December, reaching August and September levels by the end of the month. Distinct inflation was evident from tiltmeter measurements."
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.