Hawaiian Volcano Update: Post-Episode 37 Subsidence, 1975 M7.7 Earthquake Anniversary - December 4, 2025

The week following episode 37 of Kīlauea’s ongoing summit eruption was uneventful until the past couple of days, when a small area of the crater floor where lava typically ponds subsided, as it has done before. Presumably some volume of buried lava or magma is being shifted, draining through an underground network back into the vent, which at the same time caused a small deflation signal and slowed the onset of episode 38. According to USGS-HVO, the most likely window for the next lava fountains is between December 6 and 9, based on ground deformation models with data showing continued magma recharge.

Inter-episode background emissions of volcanic gas continue, affecting nearby communities through typical releases of 1,200 to 1,500 tonnes of SO2 per day, sometimes rising to 3,000 to 4,000 tonnes as in the days ahead of episode 37. Vog and tephra remain the most common hazards for island residents, and the usual precautions and preparations apply, especially for those with respiratory sensitivities – more information at https://vog.ivhhn.org/. All eruptive activity has been confined to Kīlauea’s summit caldera within Hawaiʻi Volcanoes National Park, with no increased lava threat to people. There continue to be no significant changes on either of Kīlauea’s rift zones. 

Just ahead of its 3-year eruption anniversary last week, Maunaloa appears to have taken a pause in its long-term post-eruption filling pattern, instead showing small-scale contraction and subsidence across its summit ever since its recent slight peak in earthquakes. Such variations have been common in the past, and don’t affect the long-term prognosis of the volcano slowly continuing to recharge its magma, eventually leading to future activity.. As usual, we summarize the monitoring signals, imagery, and reports available courtesy of the USGS Hawaiian Volcano Observatory, annotating the presentation on screen as we go and discussing live viewer questions. 

In a bonus segment this week, we review the 1975 Kalapana earthquake, a magnitude 7.7 which caused an eruption of Kīlauea as well as a fatal tsunami. We consider both research as well as survivor accounts to inform island residents of the continued hazard of cascading disasters as well as preparedness for locally-generated tsunamis.

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