RVO reported that RSAM values at Ulawun steadily increased during 24-25 June, and then sharply increased at around 0330 on 26 June. The RSAM values reflect an increase in seismicity dominated by volcanic tremor. An eruption began in the morning hours of 26 June with emissions of gray ash that over time became darker and more energetic. The plumes rose 1 km and drifted NW, causing minor ashfall in NW and SW areas. Locals heard roaring and rumbling during 0600-0800.

The Darwin VAAC issued several notices about ash plumes visible in satellite data. These stated that during 1130-1155 ash plumes rose to 6.7-8.5 km (22,000-28,000 ft) a.s.l. and drifted W, while ash plumes that rose to 12.8-13.4 km (42,000-44,000 ft) a.s.l. drifted S and SW. A new pulse of activity generated ash plumes that by 1512 rose to 16.8 km (55,000 ft) a.s.l. and drifted S and SE. By 1730 the ash plume had risen to 19.2 km (63,000 ft) a.s.l. and spread over 90 km in all directions. Ash from earlier ejections continued to drift S at 13.4 km a.s.l. and W at 8.5 km a.s.l. RVO stated that RSAM values peaked at about 2,500 units during 1330-1600, and then dropped to 1,600 units as the eruption subsided.

RVO stated that parts of the ash plume at lower altitudes drifted W, causing variable amounts of ashfall in areas to the NW and SW. A pyroclastic flow descended the N flank. Residents evacuated to areas to the NE and W; a news article noted that around 3,000 people had gathered at a local church. According to another news source an observer in a helicopter reported a column of incandescent material rising from the crater, residents noted that the sky had turned black, and a main road in the N part of the island was blocked by volcanic material. Residents also reported a lava flow near Noau village and Eana Valley. RVO reported that the eruption ceased between 1800 and 1900. Incandescence visible on the N flank was either from a lava flow or pyroclastic flow deposits.

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.

Sources: Rabaul Volcano Observatory (RVO), Darwin Volcanic Ash Advisory Centre (VAAC), Agence France-Presse (AFP), Radio New Zealand