Kilauea stays on watch with no way left to forecast when episode 55 begins

The U.S. Geological Survey’s Hawaiian Volcano Observatory still lists Kīlauea at alert level WATCH with an aviation color code of ORANGE, and it has stopped giving a time window for the next lava fountain. The observatory’s latest daily update, issued at 9:25 a.m. Hawaii time on Wednesday, September 30, says forecast windows for a potential episode 55 can no longer be modeled because of irregular changes in inflation and deflation at the summit.

Episode 54 ended on August 25, which leaves the summit more than five weeks past its last fountain, with the volcano visibly active the whole time.

The September 30 notice from HVO

The observatory’s notice is unsigned and issued in the name of HVO, and it is the newest HVO update listed in the USGS notification system at the start of October 1. It reports intermittent overflows and spatter from both the north and south vents in Halemaʻumaʻu crater over the past day, occasional glow from the west vent overnight, and no anomalous activity outside the summit. Continuous tremor is described as the dominant seismic signal across the summit, and about twenty small, shallow earthquakes were recorded in the past 24 hours.

The observatory says episode 55 fountaining remains a possibility during the ongoing summit eruption, and that the alert levels were left at ORANGE and WATCH because the volcano continues to show heightened unrest with an increased potential for eruption.

The tiltmeter method and its limits

For most of the eruption, HVO could say when the next fountain was likely. The method leaned on summit tilt, a measure of how the ground swells as magma refills the chamber, which gave the observatory a gauge to compare against an eruption threshold between episodes. The notice puts the current tilt at roughly 0.8 microradians of minor inflation in the last day and about 17.4 microradians in total since episode 54 ended. A Tech Times report from September 23 cited a tiltmeter threshold of about 16 microradians, with a reading of 15.8 at that point, and said the observatory was warning that fountaining could begin within about a day. It did not.

Another warning signal went quiet as well. According to Tech Times, continuous tremor from glowing vents has drowned out the escalating earthquake swarms that used to precede an episode, and HVO stated that none of the likely events would produce a strong seismic precursor. That leaves webcams as the main real-time alert, and it is the stated reason the alert level stays at WATCH rather than dropping between episodes.

Five weeks of missed forecasts

The forecasts have missed repeatedly. HVO’s notice of September 7 raised the alert level from ADVISORY to WATCH and said fountaining episode 55 was forecast to start between September 7 and 10, adding that precursory activity can continue for hours to days before a fountain begins. Hoodline’s report on that escalation notes that the eruption cycle has already passed every earlier record, with episode 48 on June 1 exceeding the 47 episodes of the 1983 to 1986 Puʻuʻōʻō eruption, and that magma supply has run about 25 percent above Kīlauea’s long-term average since December 2024.

Instead of an episode, new vents opened. Big Island Now reported that five fissures opened along the crater’s northwest wall on September 14 and 15 and stagnated by September 17, with no active lava on the ground, and that observatory scientists saw two most likely outcomes for the new vents. By the September 30 notice, overflows had resumed at the north vent on September 22 and begun at the south vent on September 27, where more than 100 rapid overflow cycles had been counted through September 29.

The historical gap between episodes had a median near ten days, according to Hoodline. The last fountain, episode 54, lasted about nine hours on August 25, with the north vent reaching a maximum height of roughly 500 feet, or 150 meters, per the observatory’s description.

Watching without a clock

The cumulative figures matter because they show the system is still pressurizing without a fountain to release it. The notice lists 17.4 microradians of inflation since episode 54 ended, and the observatory describes the system as active and pressurized, which is its stated reason for keeping the higher alert level.

HVO research geophysicist Ingrid Johanson explained in May how the observatory reads tilt to track pressure in the magma chamber, according to Tech Times, and that method is exactly what the irregular inflation and deflation now undermines. With the clock gone, the observatory’s own notice is the reference: ORANGE and WATCH, episode 55 possible, and no forecast window it is willing to publish.

The September 30 notice is the last word the observatory has published: ORANGE and WATCH, episode 55 still possible, and no forecast window it is willing to give. HVO issues these updates daily, so a change in alert level or a new window would appear in the next one.

This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.

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