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Report on Rabaul (Papua New Guinea) — March 1991


Rabaul

Bulletin of the Global Volcanism Network, vol. 16, no. 3 (March 1991)
Managing Editor: Lindsay McClelland.

Rabaul (Papua New Guinea) Low-level seismicity; brief deformation episode

Please cite this report as:

Global Volcanism Program, 1991. Report on Rabaul (Papua New Guinea) (McClelland, L., ed.). Bulletin of the Global Volcanism Network, 16:3. Smithsonian Institution. https://doi.org/10.5479/si.GVP.BGVN199103-252140



Rabaul

Papua New Guinea

4.2459°S, 152.1937°E; summit elev. 688 m

All times are local (unless otherwise noted)


"Seismicity remained at a low level in March. The total number of caldera earthquakes for the month was 140. Daily totals ranged between 0 and 9. All events were of small magnitude (ML <1.0). None were large enough to be computer-located, but the patterns of station registration indicated that most of the events were from the NE part of the caldera seismic zone, with a few from the E and NW parts.

"Tide gauge measurements indicated there was little or no net elevation change in March in the central part of the caldera (Matupit Island area). There was, however, a progressive rise of ~10 mm from the beginning of the month until the 17th, followed by rapid subsidence of about the same magnitude until the 24th."

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: C. McKee, RVO.