RVO reported that during 16-17 June white and gray plumes from Ulawun rose 1 km high. Fine ash fell on the SW, W, and NW flanks. Low rumbling noises were heard from the S and SE flanks, and weak fluctuating incandescence was observed for a brief period of time. On 18 and 19 June, white-to-gray plumes rose from the crater, and roaring noises were reported from the NW flank. Seismicity increased to a high level and was dominated by volcanic tremor. During 19-20 June continuing white and gray emissions produced plumes that rose 1 km. Fine ashfall was seen on the NW and SW flanks. Fluctuating incandescence was seen from the S and SE flanks and occasional low roaring noises were noted. Seismicity declined to moderate levels on 20 June.

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)