RVO reported that during 22-28 May Ulawun emitted thick white vapor plumes that rose 800 m high. Some areas of the plumes were gray on 22 and 25 May. People on the S and SE sides of the island heard "low jetting" noises during 24-25 May. Weak and fluctuating incandescence was seen at night during 28-29 May by people on the S part of the island. The emissions changed color to gray on 29 May and continued similarly the next two days. On 30 May very fine ashfall was reported in areas to the SSW, S, and SSE. On 1 and 2 June only white vapor emissions were noted. RVO recommended to the WNB Provincial Disaster Committee to declare a Stage 1 Alert to reflect an increasing trend of seismic energy, and a recent presence of occasional gray plumes, incandescence, and audible noises from Ulawun.

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)