Activity on Ulawun occurs frequently and is monitored and reported from several sources including the Rabaul Volcano Observatory (RVO), the Darwin Volcanic Ash Advisory Center (VAAC), the U.S. Air Force Weather Agency (AFWA), and imagery from several satellites including NOAA GMS (daylight) and MODIS (infrared). The continuing activity after an eruption on 28 September 2000 (see BGVN 25:08) resulted in BGVN reports every few months since that event (BGVN reports on Ulawun have appeared in nine subsequent issues through the end of 2003).

This issue supplements the Bulletin reports with those from the Darwin VAAC archives (table 2), which included information provided from ground, airborne, and space-based sensing. RVO reports that Ulawun remained quiet during February 2004. Emissions from the main vent consisted of white vapor being released at weak to moderate rates. No noise or night-time glow were reported during the month. No emission was reported from the two N-valley vents. Seismicity was at a low level.

Table 2. Dates of issue and the principal comments in Darwin VAAC reports concerning Ulawun, September 2000-July 2003. Similar or duplicate messages are not shown. In many cases ash cloud trajectory information has been omitted. On this table, the distance unit Nautical Miles (NM) has not been converted to kilometers (1 NM = 1.852 km (exactly)). Courtesy of the Darwin VAAC.

The VAAC reports contain numerous abbreviations; however, a few of the terms here are in widespread use referring to satellites, meteorology, and various related agencies (NOAA, AFWA, GOES9, MODIS, and KGWC . . . DMSP Imagery, etc.) or AIREP (atmospheric conditions reported from aircraft). "RVO" stands for Rabaul Volcano Observatory. Other terms may be less familiar: "AIR NIUGINI, ANK." refers to a commuter plane in the fleet of the national airline based in Papua New Guinea. The stated dates and times are not local ones, but instead refer to those at the zero (prime) meridian. For example, 04/2240Z means the fourth day of the stated month at 2240 UTC (i.e. "Z," spoken as Zulu, is shorthand for Coordinated Universal Time (UTC).

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: Rabaul Volcano Observatory (RVO), P.O. Box 386, Rabaul, Papua New Guinea; Darwin Volcanic Ash Advisory Center (VAAC), Commonwealth Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, NT 0811, Australia (URL: http://www.bom.gov.au/info/vaac/).