The Rabaul Volcano Observatory (RVO) reported that activity at Ulawun was low during 7-25 April. Summit emissions were white and had variable densities. On some days there were no emissions. Brief low rumbling sounds were heard during 15-16 and 19 April. In general seismicity was low, though slightly higher that background (RSAM values of 100-200). Data from the seismic station (UULA), 2.8 km from the summit on the lower WSW flank, was characterized by both low- and high-frequency volcanic earthquakes, with low-frequency earthquakes being the dominant signal. Brief surges in seismicity activity occasionally occurred and consisted of changes from discrete low- and high-frequency earthquakes to low-level, continuous volcanic tremors that lasted between several minutes and less than few hours. The Alert Level was at Stage 1 (the lowest level of a four-stage 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)