The two vents inside Kilauea’s Halema’uma’u crater are glowing but quiet, and the silence is making people nervous. The Hawaiian Volcano Observatory says lava fountains could erupt from the summit at any point between now and Wednesday, with the most likely window falling on Tuesday, May 26, or Wednesday, May 27. Visitors at Hawaii Volcanoes National Park, Big Island residents downwind of the summit, and pilots flying Hawaiian airspace are all watching the same USGS feeds for the signal that Episode 48 has begun.
Episode 47 set the baseline
The prior fountaining event is officially over. HVO closed out Episode 47 in a HANS status report that documented fountain heights, estimated lava volume, effusion rates, plume altitude, and tephra impacts including Pele’s hair deposits at specific downwind locations. The report also recorded the deflation signal on the Uekahuna (UWD) tiltmeter that marked the episode’s end. That deflation curve is the starting point scientists are using to forecast when pressure will rebuild enough to drive the next round of fountaining.
Kilauea’s current eruption sequence has now produced 47 discrete fountaining episodes, each separated by pauses that typically last a few days. During those pauses, magma continues rising into the shallow reservoir beneath the summit, inflating the ground surface by fractions of a degree that tiltmeters can detect. When enough pressure accumulates, the magma forces its way to the surface and fountains erupt from the vents. The cycle has been remarkably consistent, which is why HVO can issue forecast windows at all.
Why the forecast window shifted
HVO’s daily volcano update initially pointed to a likely Episode 48 start on Monday, May 25, or Tuesday, May 26, based on steady summit inflation observed after Episode 47 ended. But a wrinkle appeared later in the day. A separate posting on HVO’s observatory messages feed reported that a sharp deflation began after 4 p.m. HST, producing a 1-microradian drop on the UWD tiltmeter.
That deflation did not produce visible lava. Instead, it appears the summit vented a small amount of pressure internally, possibly through a minor magma intrusion into surrounding rock or a subtle shift in the geometry of the shallow reservoir. The effect was to reset the inflation clock: the summit now has to re-inflate past the level it had already reached before magma pressure will be high enough to trigger fountaining. HVO’s revised estimate pushed the window to May 26 or May 27, roughly one day later.
HVO has published a Volcano Watch explainer describing how these forecasts are built. Analysts track the rate of tilt recovery during each pause, compare the curve against patterns observed before prior episodes, and use the relationship between pause length, tilt change, and episode volume to generate a predicted start window. The method works well on average but is vulnerable to exactly the kind of mid-pause deflation recorded on Sunday. One unexpected pressure release, and the timeline slides.
What the monitoring network shows right now
As of the most recent HVO postings, no precursory activity has been detected. That means no increase in seismic tremor beneath the summit, no rapid acceleration in tilt, and no visible changes at the vents beyond the persistent glow that has been present since Episode 47 ended. The eruption remains paused.
The 1-microradian deflation figure is the only hard deformation number HVO has published for the current pause. Real-time tilt and seismic data are referenced in the updates but not quoted with additional specific values. Summit webcams continue to show glow from both vents, which confirms that molten lava remains at shallow depth even though it is not actively fountaining.
No fresh Washington Volcanic Ash Advisory Center (VAAC) notice has been issued for the current window, which is expected: VAAC advisories are triggered by active ash emission, not by pauses. When Episode 48 begins and produces a plume, the VAAC will issue an advisory documenting ash cloud extent, altitude, and movement using GOES satellite imagery and forecast models. Until then, the aviation hazard level remains tied to HVO’s alert status.
What to expect when fountaining starts
Based on the pattern across dozens of prior episodes, Episode 48 will likely begin with a rapid increase in seismic tremor followed within minutes by lava breaking the surface at one or both Halema’uma’u vents. Fountain heights have varied across the sequence, with some episodes producing jets tens of meters tall and others sending lava considerably higher. Each episode has also varied in duration, from hours to more than a day.
HVO typically posts updates within hours of a new episode’s onset, describing fountain height, lava flow direction, and any ash or gas hazards. Sulfur dioxide emissions spike during active fountaining, and vog (volcanic smog) can degrade air quality across broad sections of the Big Island, particularly in communities downwind of the summit like Pahala and Ocean View. The National Park Service adjusts access to viewing areas and closes roads when conditions warrant.
For residents and visitors, the practical guidance is straightforward: check the HVO daily update page before making plans. That page reflects the most current official assessment of eruption status, hazard level, and air quality. People with respiratory conditions should monitor SO2 levels through the Hawaii Department of Health’s air quality index and limit outdoor exposure when vog is elevated.
A forecast, not a schedule
The gap between the two published windows illustrates how tight the margins are in short-term eruption forecasting. The same inflation trend that initially suggested enough pressure might build by late Monday became less convincing once the tiltmeter recorded that mid-afternoon deflation. Tiltmeters and seismometers are extraordinarily sensitive instruments, but they measure the volcano’s response to magma movement, not the magma itself. A small subsurface shift can produce a measurable signal without leading to surface activity, and forecasters have to account for that ambiguity.
None of that means the models are broken. Across the 47 prior episodes, HVO’s forecast windows have generally captured the onset of fountaining within the predicted range. The system works because Kilauea’s current behavior is repetitive enough to be modeled, even if individual pauses throw curveballs.
For now, the volcano sits in its familiar holding pattern: vents glowing, magma shallow, pressure rebuilding. The most reliable information will always be the newest posting on HVO’s feeds. When Episode 48 finally breaks through, the first confirmation for most people will not come from a tiltmeter trace but from a fresh line on the daily update page announcing that lava fountains have returned to Halema’uma’u.
More from Morning Overview
*This article was researched with the help of AI, with human editors creating the final content.
