Rabaul Volcano Observatory (RVO) reported that variable amounts of white steam emissions rose from Ulawun’s summit crater during 1-28 October and drifted SE; small volumes of blue vapor were visible on 18 October. Low-level seismicity, characterized by small continuous volcanic tremors recorded during the last week of September, continued through the first week of October. Small, discrete, low-frequency volcanic earthquakes and short-duration sub-continuous volcanic tremors emerged on 8 October and fluctuated at low-to-moderate levels through 28 October. The pattern of seismicity again changed on 28 October when both low-frequency and high-frequency earthquakes were detected. Though activity was forecasted to remain low, RVO noted that some of the seismic patterns were similar to those observed before the 14 and 25 September eruptions; RVO recommended that the Alert Level be raised to Stage 2 (on the four-level scale).

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)