"Seismicity continued to show interesting variations in May. Very low levels of seismicity were recorded at the beginning and end of the month, but somewhat stronger seismicity took place 5-23 May. On 19 May a new seismic crisis was recorded. Commencing at about 1000, the crisis consisted first of continuous tremor which lasted for about 7 hours. The strongest part of the crisis was in the first few hours. The tremor became discontinuous from about 1700, gradually giving way over the following few hours to frequent discrete shocks.

"Throughout the month, emissions from the summit crater were reported to be strong white vapours. During an aerial inspection 24 May a white emission column rose several hundred meters above the summit, but the vapours were not being emitted with any force. A plume 5-10 km long was formed by the emissions."

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.