Report on Manam (Papua New Guinea) — December 1998
Bulletin of the Global Volcanism Network, vol. 23, no. 12 (December 1998)
Managing Editor: Richard Wunderman.
Manam (Papua New Guinea) Pyroclastic flows and lava flows in November
Please cite this report as:
Global Volcanism Program, 1998. Report on Manam (Papua New Guinea) (Wunderman, R., ed.). Bulletin of the Global Volcanism Network, 23:12. Smithsonian Institution.
Papua New Guinea
4.08°S, 145.037°E; summit elev. 1807 m
All times are local (unless otherwise noted)
Volcanologists observed pyroclastic flows and lava flows at Manam in mid-November and mild Strombolian eruptions during the last week of December.
November activity. In early November, Main Crater emitted pale gray ash clouds at irregular intervals, accompanied by roaring and rumbling, while South Crater released both white vapor and ash clouds that rose 500-800 m. On 6 November, following deep roaring and rumbling sounds, both craters emitted thick, dark, convoluting clouds that rose 600 m above the summit. Beginning at 0047 on 7 November, very loud explosions blasted out of South Crater at 5-20 minute intervals. The explosions led to ash columns that sent pyroclastic flows ~1 km down the SW valley. Later emissions produced a steadier and more forceful dark gray cloud accompanied by large explosions 20-60 minutes apart. At 1938 a large explosion sent pyroclastic flows ~2 km down the SW valley. Similar explosions were heard during the next few hours and incandescent projections were seen. A strong explosion at 2334 produced pyroclastic flows that ran ~2 km down SW Valley and 1 km down the SE valley. Similar activity continued until 10 November.
During the morning of 13 November frequent explosions led to small pyroclastic flows; later activity was irregular and accompanied by roaring noises. Activity increased at 1637 and sometime before 1900 lava began fountaining 180-350 m above the crater rim. Lava then spilled over the rim and flowed ~1-2 km down the SE and SW valleys. Ash emissions and loud noise were continuous while the lava was flowing. At 2100 the ash column abated, sending pyroclastic flows into the NW valley.
At 0221 on 14 November a voluminous ash column was produced and lava fragments ejected ~400-500 m above the summit. The incandescent projections within this column lit the mountain spectacularly. Later a very thick, dark gray ash cloud rose ~2 km above the summit and lava flowed ~2 km down the SE and SW valleys. Most ashfall was toward the SE, but a shower of ash with grain size of 1.5-2.0 mm fell at Tabele Observatory 4 km to the SW. Activity ended at about 2100 and afterward there were no noises heard or glows seen. From then until the end of the month activity at South Crater was restricted to mostly thin, white vapor emissions.
December activity. Emission from South Crater from 30 November to 20 December consisted mostly of white vapor with an occasional ash cloud rising 500 m above the summit. The ash clouds drifted SE and left a fine ashfall. Weak roaring noises were heard during 1-2 December and weak but steady glow was visible on the 1st.
A brief episode of Strombolian activity occurred on 24 December. At 1217 deep, weak explosions were followed by discontinuous, forceful emissions of dark-gray, convoluting clouds that rose 1,000-1,200 m above the summit. The emissions occurred at 1-2 minute intervals accompanied by roaring sounds. The activity continued until 1330 before declining to occasional emissions of thin, gray ash clouds. At night projections of incandescent lava fragments reached 200 m above the summit. Fine scoria and ashfall were reported on the SE of the island. During the next two days, moderate emissions were sometimes accompanied by forceful ejections of thick, dark gray ash clouds rising 800 m above the summit. A fluctuating glow and weak projections of glowing lava fragments were visible. From the 28th until the month's end South Crater released only white vapor while Main Crater released white vapor with occasional pale gray ash.
Geophysics. A steady accumulation of tilt took place before mid-November; it measured ~2 µrad at the radial water-tube tiltmeter of Tabele Observatory heralding renewed eruptive activity. Although during the mid-November eruption tilt appeared unaffected, seismicity reflected the changes in eruptive intensity; after 20 November a deflation of ~1.5 µrad was recorded. During 1-21 December, the tiltmeter recorded an inflation of ~1 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: Herman Patia, RVO.