Report on Ulawun (Papua New Guinea) — December 1984

Scientific Event Alert Network Bulletin, vol. 9, no. 12 (December 1984)
Managing Editor: Lindsay McClelland

Ulawun (Papua New Guinea) Incandescent tephra from lava mound; seismicity builds

Please cite this report as:

Global Volcanism Program, 1984. Report on Ulawun (Papua New Guinea). In: McClelland, L (ed.), Scientific Event Alert Network Bulletin, 9:12. Smithsonian Institution.

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Papua New Guinea

5.05°S, 151.33°E; summit elev. 2334 m

All times are local (unless otherwise noted)

"Seismicity, which had intensified in November, decreased to a normal level by early December. A re-intensification began on 17 December and reached a peak near the end of the month, when seismic amplitudes were about 10 times normal.

"Weak summit crater glow was observed on 30 December, indicating that an eruption was probably in progress. Fluctuating glow was observed on 3 January at about 0400, and occasional small dark tephra emissions from the summit crater were noted between 0800 and 0900. Seismic amplitudes began to increase at about 2300 on 3 January and steadily climbed to a peak of about 20 times normal on 8 January.

"Aerial inspections by volcanologists on 4 and 5 January revealed that the eruptive activity consisted of weak ejections of incandescent tephra from several vents in a mound of fresh lava within the summit crater. The ejections occurred at a rate of 1-2 per minute, and the largest rose about 100 m. The ash content of the emissions was low, and the plume was only a few kilometers long.

"A change in visible activity was evident from 9 January when the emissions became rich in white vapour, and ash ejections were less frequent. Crater glow, which had been observed consistently from 3 January, was absent from 9 January. Despite the weaker visible activity, seismicity persisted at about the same level as that of 8 January."

Geologic Background. The symmetrical basaltic-to-andesitic Ulawun stratovolcano is the highest volcano of the Bismarck arc, and one of Papua New Guinea's most frequently active. Ulawun volcano, also known as the Father, rises above the north coast of the island of New Britain across a low saddle NE of Bamus volcano, the South Son. The upper 1000 m of the 2334-m-high Ulawun volcano is unvegetated. A prominent E-W-trending escarpment on the south may be the result of large-scale slumping. Satellitic cones occupy the NW and eastern flanks. A steep-walled valley cuts the NW side of Ulawun volcano, and a flank lava-flow complex lies to the south of this valley. Historical eruptions date back to the beginning of the 18th century. Twentieth-century eruptions were mildly explosive until 1967, but after 1970 several larger eruptions produced lava flows and basaltic pyroclastic flows, greatly modifying the summit crater.

Information Contacts: C. McKee, RVO.