Volcano Watch: Ups and downs of lava fountaning episode forecasting with tilt data

“Volcano Watch” is a weekly article and activity update written by U.S. Geological Survey Hawaiian Volcano Observatory scientists and affiliates. Today’s article is by Hawaiian Volcano Observatory geophysicist Ingrid Johanson.

Beginning with Episode 5 of lava fountaining in January 2025 during the ongoing episodic summit eruption of Kīlauea volcano on the Big Island, Hawaiian Volcano Observatory has issued forecast windows for when the next fountains will occur in Halemaʻumaʻu Crater.

So what do recent changes at the eruption site mean for the future of fountain forecasting?

Forecasts are based on observing re-inflation of the summit magma chamber using tiltmeter data. As detailed in past “Volcano Watch” articles, episodes typically begin when ground tilt recovered as much tilt as was lost during the previous fountaining episode.

The regularity of this process is what allowed the forecasts to be made.

Recently, re-inflation became more unsteady. Now, following the opening of new vents in Halemaʻumaʻu on Sept. 14-16, it appears the behavior of the volcano might have changed.

Tiltmeters would sometimes indicate the magma chamber was going through a period of deflation during recent pauses between episode, which would alter the forecast. The deflation periods usually lasted 1 to 2 days and had a variety of amplitudes, meaning the amount of deflation in each period is not consistent.

Once inflation started again, sometimes it came back with the same rate as before — which would mean the fountaining was delayed — and sometimes inflation would come back at a faster rate, such that there wasn’t much noticeable delay at all.

Episode 53 was an example of this second pattern.

Summit tiltmeters showed deflationary tilt as the forecast window got closer. Once the deflation period was finished, summit inflation came roaring back at a faster rate and the episode started in just more than a day.

This variability was also on display during recent activity.

Tilt variations during pauses became more common with time. Prior to Episode 42, deflation periods were rarer and usually associated with overflows from the vents during the precursory period.

Pauses more recently were accompanied by several of these deflations. In hindsight, the increasing variability of re-inflation seems like a possible sign of changes to come.

Re-inflation of the magma chamber after Episode 54 fountaining was quickly interrupted by a period of deflation. Two more deflation periods were observed until overflows from the north vent began Sept. 7, after which summit tiltmeters recorded little change in tilt.

However, inflationary tilt began again Sept. 10 and continued through the most significant change to the eruption site so far.

Three new vents opened Sept. 14 north of the existing vent complex followed by another two nearby Sept. 15 and a sixth Sept. 16.

The reason for the deflation periods is unknown.

Tiltmeters show that deflationary tilt is in line with inflationary tilt, meaning the same source (Halemaʻumaʻu magma chamber) is likely responsible for both signals. They are reminiscent of a phenomenon called deflation-inflation events commonly observed at Kīlauea.

These events have a unique shape that is not as evident in more recent tilt data, making it unclear whether these newer periods should be classified as such. Still, a shared underlying mechanism cannot be ruled out.

The origin of deflation-inflation events is also somewhat mysterious. However, while before 2018 the active vent was at Puʻuʻōʻō on the East Rift Zone of Kīlauea, it was noted that Puʻuʻōʻō would also experience a deflation-inflation event after a short delay following a similar event at the summit.

This means deflation during a deflation-inflation event wasn’t because more magma was leaving the magma chamber (which would have caused rift zone inflation), but because less magma was entering it, meaning there is reason to think that the variability in re-inflation during recent pauses is because of variability in supply of magma into the magma chamber.

It is too soon to know for sure whether fountaining ended at the summit, and too soon to know if the new vents that opened will persist.

Earthquake activity increased slightly around Kīlauea’s summit, but we see no anomalous deformation or seismic activity in the East Rift Zone or Southwest Rift Zone that would indicate activity is moving out of the summit region.

Scientists are keeping a close eye on Kīlauea, tracking monitoring data to see if recent changes develop further at the summit.

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VOLCANO ACTIVITY UPDATES

KĪLAUEA volcano

VOLCANO ALERT LEVEL: Watch

Kīlauea has erupting episodically since Dec. 23, 2024, within the summit caldera. Irregular summit region inflation along with earthquakes in and around the caldera signaled that Kīlauea’s summit region is at a high level of pressurization.

Six new vents that erupted from Sept. 14-16 in Halemaʻumaʻu are no longer active. No unusual activity has been noted along Kīlauea’s East Rift Zone or Southwest Rift Zone.

WHAT’S NEXT: Fountaining forecast windows can no longer be modeled because of the irregular changes in ground deformation. Current conditions remain favorable for another fountaining episode or change in eruptive activity if inflation returns.

MAUNA LOCA volcano

VOLCANO ALERT LEVEL: Normal

Mauna Loa is not erupting. Read the most recent monthly Mauna Loa activity update online.

Hawaiian Volcano Observatory continues to closely monitor Kīlauea and Mauna Loa.

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EARTHQUAKE ACTIVITY UPDATE

Three earthquakes were reported felt during the past week in the Hawaiian Islands:

• MAGNITUDE-2.6 earthquake at 8:20 p.m. Sept. 13 located 1 mile south-southwest of Pāhala at a depth of 7 miles.
• MAGNITUDE-4.0 earthquake at 8 a.m. Sept. 13 located 2 miles south of Pāhala at a depth of 7 miles.
• MAGNITUDE-2.2 earthquake at 12:28 p.m. Sept. 10 located 2 miles west-southwest of Volcano at a depth of 0 miles.

Visit the Hawaiian Volcano Observatory website for past “Volcano Watch” articles, Kīlauea and Mauna Loa updates, volcano photos, maps, recent earthquake information and more. Email questions to askHVO@usgs.gov.