RVO reported that ash emissions increased at Rabaul on 3 March and were mainly brownish. Emissions again increased the next day, occurring almost every minute. Billowing brown ash clouds slowly rose from the crater then quickly dispersed to the SE. The emissions decreased to about every hour on 7 March.

Seismicity was very high during 4-6 March and then declined in the evening of 7 March. Three regional earthquakes felt during this period ranged in magnitude from 5.1-5.5, and occurred SSE from Rabaul offshore outside the Wide Bay area at depths ranging between 50 and 60 km. They were felt in Rabaul town with intensities of III-IV. Emissions were absent during 8-11 March.

Activity resumed on 12 March at 1108. An explosion ejected tephra and a gray-to-black billowing ash plume rose 300 m and drifted SE. The forcefulness and color lessened over at least the next 40 minutes; ash plumes rose 100 m, but were carried to 1 km with the wind. Seismicity remained low.

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.

Source: Rabaul Volcano Observatory (RVO)