Hawaiian Volcano Update: Build-up to Kīlauea Summit Eruption’s Episode 33 - September 18, 2025

Last night around 10:45 pm, after 16 days of pause following episode 32, a series of lava overflows from the north vent began to advance a short distance on the northwest part of Halemaʻumaʻu crater floor. Earlier on September 17, the first lava spilled out of the north vent at 8:38 am, marking the start of precursory activity to episode 33. Sustained, vigorous fountaining is expected later today or “tomorrow at the latest” according to the USGS Hawaiian Volcano Observatory. The last 4 episodes have lasted about 12 or 13 hours once fountaining ramps up, which has followed lava overflows by up to 19 hours (in episode 30).

As with every summit eruption in the last 5 years, vog and tephra are currently the most common hazards for island residents and visitors. The usual precautions and preparations apply, especially for those with respiratory sensitivities – more information at https://vog.ivhhn.org/. These hazards are worse at the start of each episode, and much reduced between episodes. 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.

Maunaloa continues to inflate its established post-eruption pattern, with localized adjustments evident on monitoring instruments in recent weeks, perhaps coincident with pressure changes at Kīlauea. 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. 

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