Report on Manam (Papua New Guinea) — July 1987
Scientific Event Alert Network Bulletin, vol. 12, no. 7 (July 1987)
Managing Editor: Lindsay McClelland.
Manam (Papua New Guinea) Tephra eruption; seismicity decreases
Please cite this report as:
Global Volcanism Program, 1987. Report on Manam (Papua New Guinea). In: McClelland, L (ed.), Scientific Event Alert Network Bulletin, 12:7. Smithsonian Institution. https://doi.org/10.5479/si.GVP.SEAN198707-251020.
Papua New Guinea
4.08°S, 145.037°E; summit elev. 1807 m
All times are local (unless otherwise noted)
After the short-lived phase of violent Strombolian activity at Southern Crater on 30 June activity declined rapidly to a low level that persisted through July.
From early 1 July, a dense column of light to dark-gray ash was ejected to ~2 km above the summit. For ~5 hours, convoluting dense tephra clouds were fed in frequent pulses into the vertical eruption column. The ash emission was accompanied by continuous very weak roaring sounds. Continuous fallout of ejecta from the eruption column produced small pyroclastic avalanches that descended into the SW and SE valleys. Fine ash fell over the W part of the island. By 1330 the rate of ash production had decreased to a very low level. Seismic activity declined sharply after the 30 June eruption and in the first week of July. From 8 July until the end of the month, seismic activity was at a low level, similar to that recorded in January (SEAN 12:01).
Glow from Southern Crater disappeared after 4 July, and beginning about 9 July emissions became mostly white vapour and decreased steadily in volume. Very weak roaring sounds were heard throughout the month. Measurements from the water-tube tiltmeter at Tabele Observatory indicated that inflation peaked in mid-June, and ~2 µrad of deflation had taken place by the end of July.
Activity from Main Crater was confined to emission of moderately thick white and blue vapour during the second half of the month. Weak dull glow around the mouth of the crater was observed on most nights until 27 July.
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: B. Talai and P. Lowenstein, RVO.