By Hawaiian Volcano Observatory
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The episodic summit eruption of Kilauea in Halema‘uma‘u crater has been going on for over three months now, with sixteen eruptive episodes displaying lava fountains and lava flows within Kaluapele (the summit caldera). What clues can observations of sparse episodic eruptions in Kilauea’s past tell us about the ongoing episodic eruption at Kilauea summit?

Similar episodic eruptions at Kilauea took place in 1959 (Kilauea Iki), 1969 (Maunaulu), and from 1983–1986 (first three years at Pu‘u‘o‘o). An understanding ofwhat happened before and after these similar eruptions on Kilauea, as well as how the eruptions themselves progressed, can inform our understanding of the ongoing summit eruption.

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An important consideration is how pressurized the magma chambers beneath Kilauea summit are. One tool that scientists at the USGS Hawaiian Volcano Observatory use to measure pressurization in magma chambers is tiltmeters. Tiltmeters can detect very small changes in how the ground is tilting around Kilauea summit. While tiltmeter technology has changed over time, the measurements haven’t. As pressure accumulates in the magma chambers (inflation) beneath the ground surface, the ground surface bulges outwards and tiltmeters track these subtle changes in ground tilting over time.

Leading to the 1959 summit eruption of Kilauea Iki, the magma chambers beneath Kilauea summit region had been refilling and repressurizing for years following the 1955 lower East Rift Zone eruption. Following the 1959 eruption, which consisted of seventeen high fountains every couple of days over about a month, pressure within Kilauea’s summit magma chambers had only increased.

The twelve episodic lava fountains at Maunaulu, on the upper East Rift Zone of Kilauea in 1969 followed several brief summit and East Rift Zone eruptions which were preceded by rapid inflation of the magma chambers beneath Kilauea summit. Before those events, Kilauea summit had been in a prolonged lava lake eruption from 1967–1968 that was accompanied by little ground deformation.

Similar to during the 2025 eruption, the summit magma chambers deflated during Maunaulu lava fountaining episodes, which happened days to weeks apart, and inflated during pauses. After the episodic lava fountaining phase of Maunaulu ended, it entered a multi-year phase of lava flows building a shield and traveling downslope towards the ocean.

Prior to the Pu‘u‘o‘o eruption on the middle East Rift Zone of Kilauea, there had been several years of summit eruptions and rift zone intrusions on Kilauea and overall inflation of Kilauea’s summit. Like the Maunaulu eruption, the phase of 44 lava fountains (occurring about once a month over about three years) was followed by lava flows building a shield and traveling downslope towards the ocean. Kilauea summit deflated with the onset of the Pu‘u‘o‘o eruption, and that deflation continued for the next two decades as the Pu‘u‘o‘o eruption continued.

During the ongoing eruption, tiltmeters have shown inflationary tilt prior to a lava fountaining episode, as pressure builds beneath the surface, and a switch to deflationary tilt when a lava fountain episode begins, indicative of the pressure within the magma chambers being released.

This pattern of inflation and deflation with every recent lava fountain episode creates a saw-tooth pattern in ground tilt records over the past several months; however, Kilauea summit has shown little net change in pressurization since the eruption began on Dec. 23, 2024. This indicates that Kilauea summit has been in some level of equilibrium since the eruption began. The north and south eruptive vents in Halema‘uma‘u are able to incrementally release the pressure that accumulates within Kilauea summit magma chambers with each eruptive episode.

As long as that equilibrium is maintained, the episodic eruption at the summit of Kilauea is likely to continue. The ongoing eruption patterns have also allowed HVO staff to publish windows of probability for when future eruptive episodes could begin. Changes such as a decrease in the rate of inflation or a severe blockage of the vents could alter the current pattern of fountaining episodes, including bringing them to an end. HVO will continue to closely monitor the activity, especially the amount of pressurization of Kilauea’s summit magma chambers, for any changes that could herald a potential change in eruptive activity.

Volcano activity updates

Kilauea has been erupting episodically within the summit caldera since Dec. 23, 2024. Its USGS Volcano Alert level is WATCH.

The summit eruption at Kilauea volcano that began in Halema‘uma‘u crater on Dec. 23 continued over the past week. Episode 16 began the evening of March 31 and ended the afternoon of April 2. North-northwestern winds resulted in tephra and Pele’s Hair being deposited on parts of Highway 11 in Ka‘u. Since the end of Episode 16, the summit region has showed inflation suggesting another episode is possible. Sulfur dioxide emission rates are elevated in the summit region during active eruption episodes. No unusual activity has been noted along Kilauea’s East Rift Zone or Southwest Rift Zone.

Mauna Loa is not erupting. Its USGS Volcano Alert Level is at NORMAL.

Two earthquakes were reported felt in the Hawaiian Islands during the past week: a M3.3 earthquake 20 km (12 mi) SSE of Honaunau-Napo‘opo‘o at 8 km (5 mi) depth on March 30 at 4:25 a.m. and a M3.0 earthquake 21 km (13 mi) SSE of Fern Forest at 42 km (26 mi) depth on March 28 at 11:45 p.m.

Please visit HVO’s website for past Volcano Watch articles, Kilauea and Mauna Loa updates, volcano photos, maps, recent earthquake information, and more. Email questions to askHVO@usgs.gov.