Increased seismicity has been observed at Ulawun, but surface activity remained limited to release of small to moderate volumes of white vapor until late September. Recorded seismicity since mid-August has consisted of numerous to nearly continuous, very small, low-frequency events. Larger events began to occur in mid-September. Periods of stronger seismic activity were occasionally separated by intervals of little seismicity, producing a banded appearance on seismograms. Similar seismicity has been recorded previously at Ulawun, and at Karkar prior to its 1979 eruption. Gas emission on 29 and 30 September was stronger, and brown plumes were reported.

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: P. de Saint-Ours and C. McKee, RVO.