Smithsonian Institution Global Volcanism Network Bulletin v. 20, no. 2, February 1995 Rabaul New Britain Island, Papua New Guinea 4.27S, 152.20E; summit elev. 688 m All times are local (= GMT + 10 hours) "Eruptive activity resumed at Tavurvur on 13 February after one and a half months of quiescence; no precursory activity was detected. Following the end of the 1994 eruption on 23 December (Bulletin v. 19, no. 12), Tavurvur had exhibited only fumarolic activity. The amount of vapour released declined during January and emissions became intermittent in the first half of February. Seismicity was low, although some volcanic earthquakes continued to be recorded. The deflation rate of the caldera was also extremely low. In consequence, the alert level for Rabaul was reduced from Stage IV to Stage I on 5 January. "After about 0100 on 13 February, small explosions started from Tavurvur's 1994 crater. Activity increased during the early hours of the morning, and large explosions occurred at 0328, 0857, 0919, 0937, 1012, 1100, and 1230. Each of these lasted 2-3 minutes and generated ash clouds that rose 1,500-3,000 m above the crater. Some of the ash clouds were laced with lightning. Ballistic blocks were seen falling onto the flanks of the cone and into the sea around Tavurvur. Between the larger explosions, emissions were less energetic or in "puffs" over periods of 5 minutes or more. After the first day, the emissions generally rose 500-1,000 m above the crater and were blown SE, producing a 10-km-long discontinuous, diffuse, pale-grey plume. "Each of the explosions was accompanied by a distinctive explosive or low-frequency earthquake whose amplitude corresponded to the size of the explosion. Changes in the eruptive activity could therefore be tracked using RSAM data from station KPTH on Matupit Island (figure 4). An analysis of RSAM 1-minute data produced the event counts and mean amplitudes shown in figure 4. These showed that after a few hours of large events, at an average rate of ~10/hour, the activity was dominated by smaller explosions that peaked after about a day and a half on 14 February, at an average rate of 15/hour. The number of explosions and their amplitude then declined over the next 2-3 days. On 17 and 18 February, however, the activity increased again, perhaps associated with heavy rain on the 16th and 17th. The event count stayed fairly constant until the end of the month, although event amplitudes exhibited a slowly increasing trend. "Apart from the low-frequency explosive events associated with the Tavurvur eruption, earthquake activity at Rabaul was very low in February. There were only four small high-frequency earthquakes recorded, compared to 28 in January. Two were located at shallow depths near Vulcan and the other two were outside the seismic network to the NE. "Throughout the first part of February, ground deformation data continued to show the slowing deflationary trend seen since September 1994, with the deflation centered S of Matupit Island. Electronic tilt data from station MPT on Matupit Island showed deflation of ~0.5 śrad/day during this period (figure 4). Seashore survey measurements around Greet Harbour were in good agreement, with subsidence of <1 cm/month. Following the renewal of activity at Tavurvur, ground deformation rates seem to have decreased, with only 3 śrad of tilt at MPT in 3 weeks, and no measurable changes in seashore levelling data. The gap in the tilt data on figure 4 was because the battery at MPT was stolen the day before the explosive activity began. "There were three aerial inspections of Tavurvur during this period. On the morning of 13 February, before the large explosions took place, there was no marked change in the configuration of the bowl-shaped crater compared to the previous inspection in January. There also was no open vent, although the explosive emissions rose through the central part of the crater floor, which was covered with ash and rubble. On 20 February, emissions were seen rising from an obstructed vent in the SE part of the crater, while a strong fumarole was active on the W side of the crater (at the head of the 1994 lava flow). A small mound of lava seen on the 27th at the base of the crater was 20-30 m wide, only a few meters high, and was partly mantled with ash. Emissions were released through cracks in the lava or from between blocks near the edges. "Throughout February, Vulcan continued to exhibit only very weak fumarolic activity from diffuse sources around the edge of the floors of both the 1937 and 1994 craters. At some time in late January or February, hot steaming springs appeared along the N shore of the Vulcan headland. Measured temperatures were consistently around 100 deg C. "The Gazelle Peninsula has remained under a State of Emergency, with access to Rabaul controlled because of the risk from mudflows and flooding. Although the rainy season has been unusually mild so far, mudflows and flash floods are causing much damage to the roads into Rabaul and are flooding the remaining buildings in the town and in nearby villages." Information Contacts: same as for Manam. Figure 4. Rabaul tilt and seismicity measured at stations MPT and KPTH on Matupit Island, 1 February-10 March. Positive N and W tilts indicate deflation of the caldera. Note that times are GMT (= local time - 10 hours). Courtesy of Rabaul Volcano Observatory.