"There was an increase in the level of activity in April. At the beginning of the month, emissions consisted of moderate white vapour. However, these emissions changed through the month to strong thick white vapour and there were occasional reports of grey and blue emissions. On 19 April, very strong, thick, dark grey emissions were reported. Very fine ashfall was reported on the NW side of the volcano on 28 April, and steady weak red glow was seen on the 30th.

"Seismic monitoring was affected by telemetry problems from mid-March until 12 April. When the system was restored, daily earthquake totals were ~400-500. On 18 April there was a sharp increase to ~540 earthquakes/day. The daily totals then increased steadily through the remainder of the month to ~630 at month's end. Earthquake amplitudes showed a progressive increase after 12 April."

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: I. Itikarai and C. McKee, RVO.