Report on Manam (Papua New Guinea) — March 1986
Scientific Event Alert Network Bulletin, vol. 11, no. 3 (March 1986)
Managing Editor: Lindsay McClelland..
Manam (Papua New Guinea) Ash plumes; B-type events; weak tremor
Please cite this report as:
Global Volcanism Program, 1986. Report on Manam (Papua New Guinea). In: McClelland, L. (ed.), Scientific Event Alert Network Bulletin, 11:3. Smithsonian Institution. https://doi.org/10.5479/si.GVP.SEAN198603-251020.
Papua New Guinea
4.08°S, 145.037°E; summit elev. 1807 m
All times are local (unless otherwise noted)
"Activity continued at a low level until mid-February, with Main and Southern Craters releasing a thin white vapour plume. Heavy rainfall after the 14th (up to 80 mm/day) produced a grey to brown ash-laden plume that was forcefully but silently released from Southern Crater (14-20 and 24 February). These emissions often followed a regular pattern, lasting 20-30 minutes with repose periods of 3-5 minutes. Thick plumes rose as much as 900 m above the crater before being carried away by NW winds. Light ashfalls were reported on the downwind side of the island until the end of the month.
"The activity produced no explosion shocks but did generate some weak harmonic tremor. There was otherwise no noticeable change in the seismicity, which remained at a non-eruptive level (1,200-1,700 low-amplitude B-type events daily) throughout February. The Tabele water tube tiltmeters . . . showed 5 µrad of radial inflation during the month.
"A very weak level of activity prevailed throughout March. Main and Southern Craters released weak to moderate grey and brown emissions. Low roaring sounds were occasionally heard (13, 18, and 19 March). Occasional very light ashfalls were reported on the downwind side of the island.
"The seismicity remained at an inter-eruptive level (100-1,800 small B-type events/day) throughout March. No changes were recorded by the Tabele water tube tiltmeter."
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: P. Lowenstein, RVO.