Report on Ulawun (Papua New Guinea) — January 1985

Scientific Event Alert Network Bulletin, vol. 10, no. 1 (January 1985)
Managing Editor: Lindsay McClelland

Ulawun (Papua New Guinea) Mild strombolian activity concludes eruptive phase

Please cite this report as:

Global Volcanism Program, 1985. Report on Ulawun (Papua New Guinea). In: McClelland, L (ed.), Scientific Event Alert Network Bulletin, 10:1. 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)

"The eruption, characterized by generally low-intensity Strombolian activity, terminated on 27 January. At the peak of seismicity (about 20 times normal levels, on 8 January), weak ejections of incandescent tephra occurred at a rate of 1-2/minute from one or two vents in a mound of fresh lava in the summit crater. From 9 January, seismicity declined steadily, and nighttime incandescence from the crater was absent.

"Seismicity stabilized on about 17 January at about ten times normal levels. Despite the reduced seismicity, summit crater incandescence returned on 16 January and persisted until the 25th. Ejections of incandescent tephra were more frequent than earlier in the month, occurring at rates of up to about 10 per minute, and rising to about 130 m above the crater rim. The ash content of ejections was insignificant, and the eruption plume was only 1-2 km long. Seismicity started to decline on 25 January and dropped sharply to normal levels on the 27th, marking the end of the eruption.

"An aerial inspection on 30 January revealed complex topographic changes in the summit crater. The lava dome formed early in the eruption was surmounted by a small cinder cone, and the flanks of the dome were draped with a mantle of scoria and ash. Lava flows formed an almost continuous moat around the base of the dome. There was no overflow of lava onto Ulawun's flanks, but the lava had almost reached the lowest point in the crater rim, at the head of the NW valley. A small pit crater was present near the SW edge of the summit crater. The volume of new lava and tephra in the summit crater is provisionally estimated to be 105-106 m3."

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.