RVO reported that variable amounts of white steam plumes were visible rising from Ulawun during 1-18 July. Seismicity was low during 1-16 July and consisted of small, discrete, low-frequency earthquakes and occasional small high-frequency volcano-tectonic events. RSAM values generally fluctuated around 50, but during 1800-2300 on 16 July the values increased to 500. The values continued to climb at a slow irregular rate to 610 through 0500 on 18 July, but then dropped to 400-500 during the next two hours (0500-0700), though peaks as high as 1,600 were recorded. By 0700 the values had decreased to 300 and remained steady afterwards. Minor ash emissions began on 18 July and during the morning of 19 July brown-to-gray emissions with low ash content were rising a few hundred meters above the crater rim and drifting SE.

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.

Source: Rabaul Volcano Observatory (RVO)