The Rabaul Volcano Observatory reported that activity at Rabaul Caldera remained at background levels during 1-31 October. Fumarolic activity produced thin, white emissions from small fumaroles on the crater floor and inner walls. Seismicity included 11 high-frequency volcano-tectonic (VT) earthquakes, with nine located at depths of 1-9 km, primarily near the Vulcan and Tavurvur vents. Deformation monitoring revealed ongoing inflation since January 2024, with a cumulative vertical displacement of about 7 cm. Temperature measurements of two hotspots within the crater remained below 50 degrees Celsius, which is consistent with background levels. The Alert Level remained at Stage 1 (the first level on a four-level scale).

Source: Rabaul Volcano Observatory (RVO)

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.