Aactivity at Ulawun since early 2007 has consisted primarily of low-frequency earthquakes and white vapor emissions, with ash reported on 1 May and 25 December 2007 (BGVN 33:03). No additional activity was reported by the Rabaul Volcano Observatory (RVO) until a seismic swarm preceded observations of glow on 13-14 June 2008. Incandescence was seen again in mid-May 2009.

RVO reported that increased seismic activity at Ulawun consisting of high-frequency volcano-tectonic (VT) earthquakes began on 7 June 2008. After peaking at 22 events on 12 June, the daily totals dropped and fluctuated between one and seven events per day, although totals of 14-15 events occurred on 14, 29, and 30 June. Some of the VT earthquakes were felt, including three on 30 June. Low-frequency earthquakes continued to occur as well, but remained within background levels; daily totals were between 257 and 775.

Summit activity was very low and consisted of variable amounts of white vapor. Bluish vapor was observed on some days during 16-21 June. Other reported activity included low roaring noises on 1, 2, 12, and 14 June, and summit glow on the 13th and 14th. On 22 June noises heard in villages to the NE accompanied some of the earthquakes. On 28 June an earthquake accompanied by a booming noise was felt in nearby areas. White vapor plumes were emitted during 2-6 July, and occasional roaring noises were reported during 1-3 July.

Additional reports by RVO in February and April 2009 noted that the volcano remained quiet, only releasing white vapor, with no reports of glow at night. Seismicity was moderate to low in February until power problems disabled the instrument. The number of seismic events that month fluctuated between 400 and 950 before declining to a range of 250-300 during 20-24 February. Low-frequency events dominated the record, although some high-frequency activity was recorded at a daily rate of 1-6 events.

Ulawun remained quiet throughout September and October 2009. Summit activity was dominated by weak to moderate volumes of white vapor, and seismicity was generally low. During September, daily totals for high-frequency volcano-tectonic events ranged between 0 and 7, and low-frequency earthquakes were registered at a rate of 167-547. For the month of October, daily totals for high-frequency volcano-tectonic events were as high as 11, and the number of low-frequency earthquakes ranged between 74 and 404.

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.

Information Contacts: Ima Itikarai, Rabaul Volcano Observatory (RVO), P.O. Box 386, Rabaul, Papua New Guinea.