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Clear out junk files and repair common Windows errorsFree Scan →Fix the driver behind crashes, sound loss and screen glitchesFind Drivers →Kīlauea’s recent summit lava fountains are driven by pressure building beneath the volcano as new magma arrives, then by gas bubbles expanding as magma rises. The eruption releases pressure; as magma supply continues, pressure can build again. The continuous 2018 Fissure 8 fountain had a different principal driver: a pressure gradient moving magma from summit storage toward a low-elevation flank vent.
How pressure and gas produce a fountain
- New magma builds pressure. As magma accumulates beneath Kīlauea’s summit, pressure rises. Hawaiian Volcano Observatory geologist Katie Mulliken describes the cycle: “As new magma accumulates, the amount of pressure builds. Eventually, lava erupts and de-pressurizes the system.” (USGS Hawaiian Volcano Observatory)
- Gas expands during ascent. As magma rises and pressure falls, dissolved magmatic gas comes out of solution and forms bubbles. The expanding bubbles help propel lava upward. Ejected lava is vesicular—full of bubbles—and can resemble stiff foam.
- The eruption releases pressure. Once lava erupts, pressure drops. In the recent episodic summit activity, this release is followed by renewed pressure buildup as magma continues to accumulate.
Why the 2018 Fissure 8 fountain was different
Not every Hawaiian lava fountain has the same immediate cause. The recent summit fountains are episodic, with pressure buildup and expanding gas playing central roles. By contrast, the 2018 lower East Rift Zone Fissure 8 fountain was continuous and primarily driven by a pressure gradient: magma moved from storage beneath the summit toward a vent at lower elevation. Treating both as the same kind of gas-driven burst would miss the difference in setting and mechanism. (USGS Hawaiian Volcano Observatory)
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What gas pistoning can—and cannot—tell us
Before Kīlauea’s Episode 15, more than 100 cycles of lava rising and falling, vent overflows, and spattering were observed at the north vent. In a March 26, 2025 notice, HVO called this activity “gas pistoning” and noted that it has occurred in other Kīlauea eruptions. It is a documented precursor to that episode, not evidence that the same behavior reliably predicts every future episode. A single observation, gas-pistoning cycle, or fountain height does not by itself establish when another episode will begin or how high a fountain will rise. (USGS HVO, March 26, 2025)
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Outbyte Driver Updater FREEScan for outdated or missing drivers - takes under a minuteDriver Scan →Outbyte PC Repair FREEClear out junk files and repair common Windows errorsFree Scan →Fountains also create hazards beyond the lava jet
Fountaining releases volcanic gases and throws out tephra, including fine fragments that wind can carry beyond the vent. HVO identifies water vapor, carbon dioxide, and sulfur dioxide among gases released during summit fountaining. The USGS Kīlauea Eruption Information page reports sulfur dioxide emissions of up to 75,000 tonnes per day during episodes; that is a reported maximum, not a constant rate or a live measurement. Lava-flow locations and other conditions can change, so consult the latest USGS update for current hazards. (USGS Kīlauea Eruption Information)
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USGS’s historical examples show that fountains have recurred in different Kīlauea eruptions: its HVO explainer counts 44 fountaining episodes in the first three years of the Puʻuʻōʻō eruption and 17 during the November 14–December 20, 1959 Kīlauea Iki eruption. The highest fountain measured at Kīlauea, 1,900 feet (580 meters), occurred during episode 15 of the 1959 eruption. Those examples put the phenomenon in context; they do not provide a simple rule for predicting the height or timing of a future fountain. (USGS Hawaiian Volcano Observatory)
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