Rabaul Volcano Observatory (RVO) reported a small eruption at Ulawun during 14-15 September. Minor incandescence at the summit crater was first visible at around 2107 on 14 September from Ulamona Observatory. The incandescence intensified, and eruption plumes reflecting the glow were visible in webcam images drifting NE. Starting at about 0004 and lasting to about 0800 on 15 September there were brief periods when the plumes appeared darker, likely due to denser and more intense emissions. The plumes drifted W and WSW. Rumbling noises were reported, though they became less frequent by 0800. The Alert Level was raised to Stage 2 (the second level on the four-level scale).

Staff from the West New Britain Provincial Disaster Office conducted a field inspection on 15 September and found only minor ashfall around the volcano. During 0800 on 15 September to 1430 on 19 September the volcano was quiet; small volumes of diffuse white emissions sometimes rose from the summit and drifted W and WSW. On 19 September RVO recommended that the Alert Level should be lowered to Stage 1.

Increased seismicity coincided with the eruption. During most of 14 September RSAM values were 200-300, though they began to increase at about 1955 and reached a value of around 800 by midnight. RSAM continued to increase; values reached 1,600 by 0100 on 15 September, rapidly increased during 0100-0200, and reached a value of 4,060 almost two hours later at 0300. Seismicity was dominated by continuous low-frequency volcanic tremors. Seismicity began to decline at 0700, reached background levels by 0900, and remained low with values of 200-450. During 16-19 September seismicity was characterized by low level volcanic tremors with sporadic occurrences of discrete, small, low-frequency volcanic events. RSAM values were around 200.

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)