Report on Rabaul (Papua New Guinea) — January 1984
Scientific Event Alert Network Bulletin, vol. 9, no. 1 (January 1984)
Managing Editor: Lindsay McClelland.
Rabaul (Papua New Guinea) Earthquakes, tilt indicate magma intrusion; eruption more likely within next few months
Please cite this report as:
Global Volcanism Program, 1984. Report on Rabaul (Papua New Guinea) (McClelland, L., ed.). Scientific Event Alert Network Bulletin, 9:1. Smithsonian Institution. https://doi.org/10.5479/si.GVP.SEAN198401-252140
Rabaul
Papua New Guinea
4.2459°S, 152.1937°E; summit elev. 688 m
All times are local (unless otherwise noted)
"There was a marked increase in the amount of unrest in Rabaul Caldera during January, with a total of 8,372 volcanic earthquakes recorded, an increase of 1,255 over the December total.
"A major seismic crisis took place on 15 January when 942 earthquakes occurred, including several strongly felt events. The maximum magnitude earthquake (ML 4.9) was accompanied by underground rumbling sounds. This crisis was accompanied by a maximum tilt change of 32.5 µrad at [a station immediately N of Greet Harbour] . . . .
"The overall distribution of earthquakes in January was similar to that in December, with high concentrations on the NE (Greet Harbour) and W (Karavia Bay) sides of the harbour. . . . Steady inflation of the Karavia Bay and Greet Harbour magma reservoirs continued throughout the month. . . .
"As a result of the increased activity in January, a warning was issued to the authorities to the effect that the eruption, which was previously thought to be only a possibility when the Stage-2 volcanic alert was declared on 29 October, was now much more likely to occur within the next few months."
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. Lowenstein, RVO.
