At roughly 4 p.m. HST on Sunday, May 25, Kilauea’s summit did something scientists were not expecting: it stopped inflating and started to sag. The Hawaiian Volcano Observatory had spent the previous day watching tiltmeter readings climb toward the threshold that typically precedes a new fountaining episode, and forecasters had told the public that Episode 48 could begin within hours. Then the ground tilted the other way, and the clock reset.
HVO’s observatory message issued that evening confirmed the reversal: inflation had switched to deflation without producing an eruption. The agency pushed its forecast window for Episode 48 to May 26 or 27, extending a wait that has kept park visitors, downwind communities, and volcanologists on edge since Kilauea’s current eruptive sequence began on December 23, 2024.
What the tiltmeter is telling scientists
The instrument at the center of every Episode 48 forecast is the UWD tiltmeter, a sensor near Kilauea’s summit that measures changes in ground slope in microradians. Since late December, it has traced a repeating sawtooth pattern: the summit inflates over days to weeks as magma pools in a shallow reservoir, then drops sharply when a fountaining episode drains that reservoir through vents in Halemaumau crater.
HVO uses the inflation rate between episodes as its primary forecasting tool. When tilt climbs past a certain level and the rate of rise accelerates, scientists know the reservoir is nearing the pressure needed to crack open a pathway to the surface. On May 25, the tilt was approaching that zone before it abruptly reversed. The magma supply appears to have stalled or redistributed beneath the caldera floor without breaking through, effectively requiring the system to re-pressurize before fountaining can resume.
Sulfur dioxide measurements add a second line of evidence. Between episodes, Kilauea has been releasing roughly 1,000 to 5,000 tons of SO₂ per day, according to routine USGS volcano updates. That ongoing degassing confirms fresh magma is still feeding the system from depth, even when the surface is quiet. The combination of active gas output and a deflation reversal tells HVO that the plumbing remains charged but has not yet built enough force to trigger the next eruption.
Why the timing is so hard to pin down
HVO has not published the exact microradian values at which deflation began on May 25 or the precise inflation target it is watching for Episode 48. Without those numbers, outside analysts cannot independently calculate how many hours the delay will last. The observatory has acknowledged in previous Volcano Watch explainers that mid-pause deflation events can push episodes back, but it has also cautioned that eruption behavior can shift without warning. A January 2026 information statement specifically addressed the possibility that the volcano’s patterns could change as the eruption matures.
No detailed seismic or gas-flux data from the hours immediately surrounding the 4 p.m. reversal have appeared in the timestamped observatory notes. That gap matters: a sudden swarm of small earthquakes or a spike in SO₂ could reveal whether the deflation is a brief hiccup or a meaningful reset. If re-inflation resumes quickly, the Episode 48 window could tighten again within hours, making May 26 to 27 a floor rather than a firm prediction.
The most recent completed episode offers some context but not a direct template. Episode 47 ended at 12:27 a.m. HST on May 15, roughly 10 days before the current pause. Fountain heights, effusion rates, and erupted volume were documented in the official HANS status report for that event, but those figures describe what happened during active fountaining, not what governs the timing of the next one. Each of the 47 episodes so far has shown slightly different behavior, and the intervals between them have not been perfectly regular.
There is also a longer-term question scientists are watching. The repeating sawtooth pattern suggests a relatively stable magma supply from depth, yet subtle shifts in the rate of inflation, the peak tilt reached before each eruption, or the length of pauses could signal that the reservoir’s geometry or pressure conditions are gradually evolving. Kilauea’s Volcano Alert Level remains at WATCH, reflecting ongoing eruption hazards, and HVO continues to treat every forecast as provisional.
What this means for park visitors and downwind residents
For anyone heading to Hawaii Volcanoes National Park in the coming days, the practical reality is that conditions can flip fast. Tephra from earlier episodes has forced temporary closures of roads and viewing areas inside the park, according to a National Park Service update issued in May 2026. Park managers adjust access based on ashfall, vog (volcanic smog), and the location of active vents, sometimes with only minutes of lead time.
Visitors hoping to witness Episode 48 should prepare for both outcomes. If the summit stays in a deflationary or neutral state, there may be nothing to see at the surface, even as instruments show magma moving underground. Once inflation resumes and crosses HVO’s internal threshold, however, fountains can ignite with little advance notice, turning a quiet caldera into a towering display of molten rock and gas.
Communities downwind face a different calculus. Even modest fountaining episodes loft ash and sulfur dioxide high enough to degrade air quality tens of kilometers from the summit. And because SO₂ emissions persist between episodes, vog can hang over leeward neighborhoods regardless of whether lava is visible. For residents with asthma or other respiratory conditions, the cumulative exposure over days and weeks matters more than the exact start time of any single episode.
HVO and partner agencies urge both residents and visitors to rely on official channels rather than social media speculation. The USGS notification system, the latest Kilauea updates, and the most recent HVO observatory messages synthesize tiltmeter trends, seismic data, gas measurements, and visual observations into concise hazard assessments updated multiple times a day.
A delay, not a stand-down
Nothing about Sunday’s deflation suggests Kilauea is winding down. The magma supply from depth appears intact, SO₂ output remains elevated, and the tiltmeter will almost certainly resume its upward march once the current pause runs its course. When it does, the same instruments that flagged the reversal will signal when the summit is pressurized enough for Episode 48 to break through.
Until then, the volcano is doing what volcanoes do: operating on its own schedule, indifferent to forecasts. The tools HVO has built over decades of monitoring Kilauea are remarkably good at narrowing the window, but they cannot eliminate the wait. For now, the island watches the tiltmeter and keeps one eye on the sky above Halemaumau.
More from Morning Overview
*This article was researched with the help of AI, with human editors creating the final content.
