"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."

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.

Information Contacts: C. McKee, RVO.