"Activity was at a very low level in June. Only 90 caldera earthquakes were recorded, and during one 6-day period there were no recorded caldera events. Located events originated from the N part of the annular caldera seismic zone.

"Levelling radial to the center of the caldera showed only minor uplift (<=4 mm) since last month's measurement, and there were no significant changes in tilt and EDM measurements.

"A release of CO₂ in a pit crater on Tavurvur caused the death of six persons. The accident occurred in a crater 25 m deep with lateral dimensions of 130x90 m, at an elevation of 40 m on the S flank of Tavurvur (Fisher, 1976, Fig. 2). The crater is a nesting place for Megapode birds (Johnson, 1985).

"Three people who ventured into the crater on 24 June to collect Megapode eggs were overcome by CO₂. Early on 25 June, 3 other people unsuspecting of the danger also died when trying to rescue them. The release of CO₂ responsible for the casualties would have started only a couple of days earlier as the same people were unaffected when collecting eggs at the same place a week earlier.

"Recovery of the bodies and subsequent explorations of the crater were carried out with the aid of SCUBA equipment. An emission vent was found at the foot of the NW crater wall with a temperature of 48°C. The thickness of the CO₂ layer at the bottom of the pit crater was found to fluctuate between 1.7 and 4.8 m in the following days, although on windy days the crater was either free of gas or the CO₂ was mixed with air in a non-lethal concentration. It is uncertain whether other gases were released with the CO₂. Gas samples await laboratory analysis for the identification of all species present. It is also hoped that laboratory work will determine whether the CO₂ is of volcanic origin or has a biogenic source in the thermal decomposition of coral reefs buried under the products erupted by Tavurvur in the last few centuries (Fisher, 1939, p. 37).

"The occurrence of CO₂ in this crater has been identified once previously, in October 1981, after villagers had reported finding dead animals there. There is no evidence of CO₂ being released in Tavurvur's summit craters."

References. Fisher, N.H., 1939, Geology and vulcanology of Blanche Bay, and the surrounding area, New Britain: Territory of New Guinea Geol. Bull. 1, 68 p.

Fisher, N.H., 1976, 1941-1942 Eruption of Tavurvur volcano, Rabaul, Papua New Guinea: in Johnson, R.W., ed., Volcanism in Australasia, Elsevier, Amsterdam, p. 201-210.

Johnson, R.W., 1985, Megapodes, feathered volcano monitors?: Volcano News, no. 19-20, p. 6.

Geological Summary. The low-lying Rabaul caldera on the tip of the Gazelle Peninsula at the NE end of New Britain forms a broad sheltered harbor utilized by what was the island's largest city prior to a major eruption in 1994. The outer flanks of the asymmetrical shield volcano are formed by thick pyroclastic-flow deposits. The 8 x 14 km caldera is widely breached on the east, where its floor is flooded by Blanche Bay and was formed about 1,400 years ago. An earlier caldera-forming eruption about 7,100 years ago is thought to have originated from Tavui caldera, offshore to the north. Three small stratovolcanoes lie outside the N and NE caldera rims. Post-caldera eruptions built basaltic-to-dacitic pyroclastic cones on the caldera floor near the NE and W caldera walls. Several of these, including Vulcan cone, which was formed during a large eruption in 1878, have produced major explosive activity during historical time. A powerful explosive eruption in 1994 occurred simultaneously from Vulcan and Tavurvur volcanoes and forced the temporary abandonment of Rabaul city.

Information Contacts: P. de Saint-Ours and C. McKee, RVO.