Report on Ulawun (Papua New Guinea) — June 1988

Scientific Event Alert Network Bulletin, vol. 13, no. 6 (June 1988)
Managing Editor: Lindsay McClelland.

Ulawun (Papua New Guinea) Seismicity declines; vapor emission; deflation

Please cite this report as:

Global Volcanism Program, 1988. Report on Ulawun (Papua New Guinea). In: McClelland, L (ed.), Scientific Event Alert Network Bulletin, 13:6. 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)

"Low-level activity persisted. Weak to moderate amounts of white vapour continued to be released from the summit crater. The recorded seismicity fluctuated between 1,500 and 300 small B-type events/day (relatively less numerous than during the last two months). The average amplitude of these events built up considerably (up to 8 times the norm) from early May to mid-June before decreasing again to regular non-eruptive levels. Apparent tremors were also recorded for long periods from 6-10, 15-16, and 19-29 June. It is not certain to what extent that signal was caused by the strong seasonal wind.

"An aerial and field inspection was carried out on 6 and 7 June. The interior of the summit crater was mostly obscured by abundant white and blue vapours. Little morphological change was noted compared to the last inspection, in July 1987, apart from the erosion. However, a series of fissures enhanced by fumarolic encrustations were observed to run horizontally, ~100 m below the rim of the internal S wall.

"Dry tilt measurements indicated summit area deflation of up to 55 µrad since the last eruption in November 1985. EDM measurements showed minor contractions of three lines radial to the flanks of the volcano since previously measured in November."

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: P. de Saint-Ours and P. Lowenstein, RVO.