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Report on Rabaul (Papua New Guinea) — 13 October-19 October 2021


Smithsonian / US Geological Survey Weekly Volcanic Activity Report,
13 October-19 October 2021
Managing Editor: Sally Kuhn Sennert

Please cite this report as:

Global Volcanism Program, 2021. Report on Rabaul (Papua New Guinea). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 13 October-19 October 2021. Smithsonian Institution and US Geological Survey.

Weekly Report (13 October-19 October 2021)


Papua New Guinea

4.271°S, 152.203°E; summit elev. 688 m

All times are local (unless otherwise noted)

On 6 October RVO raised the Alert Level for Rabaul to Stage 1 (the lowest level on a four-stage scale) due to ongoing deformation and recent increases in seismicity. During the month of September, the seismic network detected a total of 22 high-frequency volcano-tectonic earthquakes, which was more than the 12 recorded in August. The earthquakes were distributed in the Beehives, Vulcan, Greet Harbour, and Namanula areas. Deformation data from a GPS station located at the S part of Matupit Island showed a continuing trend of uplift, with 39 mm/month in August and 35-39 mm/month in September. Diffuse white fumarolic plumes rose from the crater floor and inner walls.

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 688-m-high asymmetrical pyroclastic 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 1400 years ago. An earlier caldera-forming eruption about 7100 years ago is now considered to have originated from Tavui caldera, offshore to the north. Three small stratovolcanoes lie outside the northern and NE caldera rims. Post-caldera eruptions built basaltic-to-dacitic pyroclastic cones on the caldera floor near the NE and western 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.

Source: Rabaul Volcano Observatory (RVO)