Kilauea's run of 54 lava fountains points to a gas-driven piston in its vents

Kilauea has been erupting almost continuously for nearly 200 years ^[1]. Even so, researchers have known relatively little about what starts, sustains and ends episodic fountains, according to Ashton Flinders and his colleagues ^[6]. Flinders is a research geophysicist at the U.S. Geological Survey's Hawaiian Volcano Observatory in Hilo ^[6]. The reason they give is rarity ^[6].

The current run gives them dozens of events to work with. It began at dawn on December 23, 2024, with an eruption inside Halema'uma'u, the summit crater ^[2]. From then to September 2026 is about 20 to 21 months, so 54 fountains comes to roughly one every 12 days on average ^[14]. That average flattens real variation. Repeated fountains are distinct bursts separated by anything from minutes to weeks ^[4]. The 457-meter figure is the top of the range, reached by some fountains ^[3].

Kilauea is also heavily instrumented. It has been monitored for decades, with continuous records of seismic activity, temperature, low-frequency acoustics, ground swelling and deflation, and escaping gas ^[8]. The gas record matters because the two prevailing explanations predict different things. In one, water dissolved in rising magma escapes suddenly as the pressure changes ^[7]. In the other, a carbon dioxide-rich foam sitting on trapped magma expands violently, like the froth in a shaken soda bottle ^[7]. A foam-driven burst should leave carbon dioxide in the gas measurements.

It did not leave much. The volcano released some sulfur dioxide and relatively little carbon dioxide, and the team concluded that the foam hypothesis was not at work ^[12]. I think this is the firmest part of the result, because it is the one measurement where the two ideas disagreed before anyone looked.

The piston picture rests more on interpretation. The team links repeating bursts of seismic energy and low-frequency sound to trapped gas building up and releasing, making magma rise and fall through narrow vents like a piston in a car ^[11]. Those bursts were detected just before fountains ^[10]. Their timing is the observation. Reading them as gas pressure is the team's explanation of that timing.

The pattern also took time to appear. It emerged as the eruption matured and was first detected just before the fourteenth fountain ^[10]. Flinders and his colleagues describe the work as a preliminary glimpse of the phenomenon, with a lot of questions remaining ^[13].