The Rabaul Volcano Observatory (RVO) reported that activity at Ulawun remained quiet during February 2004. The main vent emitted white vapor at weak to moderate rates. No emissions were reported from the two north valley vents. No noise or night time glow was reported, and seismicity was at a low level. RVO reported in similar terms for the period 15 March-1 April, noting also that tiltmeter measurements recorded a long-term inflationary trend. According to Darwin VAAC, on 12 and 13 April thin ash plumes from Ulawun were visible on satellite imagery at a height of -~ 700 m above the volcano extending ~ 75 E and NE. On 14 April the ash plume rose ~ 3 km altitude and extended ~ 37 km NE. No HIGP-MODIS thermal alerts were recorded at Ulawun over the year to 11 May 2004.

Note that a 16 January 2001 VAAC report of Ulawun emitting a cloud, ashes, and 'flames' ~ 10.6 km altitude, which was not confirmed by satellite imagery or RVO, has not previously been mentioned in the Bulletin.

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 and Herman Patia, Rabaul Volcano Observatory, Papua New Guinea; Darwin Volcanic Ash Advisory Centre (VAAC), Commonwealth Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, NT, 0811, Australia (URL: http://www.bom.gov.au/info/vacc/).