"Activity remained at the low, non-erupting level displayed since January 1990, gently releasing a white vapour plume and generating an average of ~200 very small low-frequency earthquakes/day.

"An aerial inspection and ground deformation survey was carried out 14-16 May. The plume emitted by the crater, although of moderate volume, seemed rich in SO₂ and could distinctly be seen stretching horizontally >40 km downwind. No significant changes were noted in summit crater morphology since the last inspection in May 1990, apart from a series of cracks on the terminal cone's upper W flank, suggesting a slight inward sagging of this side of the crater rim.

"EDM and dry tilt measurements suggest that no significant deformation has occurred over the last 12 months."

Information Contacts: D. Lolok and P. de Saint-Ours, RVO.

Geological Summary. 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. The volcano, also known as the Father, rises above the N coast of the island of New Britain across a low saddle NE of Bamus volcano, the South Son. The upper 1,000 m is unvegetated. A prominent E-W escarpment on the south may be the result of large-scale slumping. Satellitic cones occupy the NW and E flanks. A steep-walled valley cuts the NW side, 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.