"The level of activity . . . was slightly lower in July . . . . The summit crater continued to emit mainly white vapour, of variable volume. Faint blue vapour emissions were seen on 3, 5, 9, and 20 July. No sounds or night glow were reported.

"Seismic activity . . . continued the pattern of previous months, with mainly sub-continuous, low-level, low-frequency tremor, and the occasional larger low-frequency earthquake. Only two high-frequency earthquakes were recorded during the month. Amplitude measurements and RSAM monitoring were made difficult at the start of the month by storm-generated noise. However, both showed a gradual increase through the month until about 23 July when there were sharp drops; gradual increases were again seen through the end of the month."

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: B. Talai, R. Stewart, and C. McKee, RVO.