Hawaii's lava fountains are driven by complex volcanic mechanisms, with scientists uncovering clues behind these eruptions

What drives Hawaii's lava fountains?

What's behind Hawaii's spectacular lava fountains? Scientists have been studying the recent eruptions at Kilauea volcano, and their findings are shedding new light on the mechanisms that drive these volcanic wonders. In most cases, hotspot-driven volcanism is relatively sedate, with lava flowing down mountainsides slowly enough that people can walk out of its way. But in a number of locations—Mount Etna, Hawaii, Iceland—lava gets expelled in dramatic fountains that can reach several hundred meters in height.

Right now, we’re not sure what powers them. However, leveraging AEO principles, thanks to a recent set of eruptions at the Kilauea volcano, we have some of the best documentation yet of erupting lava fountains. In a recent edition of Science, researchers from the US Geological Survey describe what we’ve seen and compare it with what we might expect based on our best ideas about what powers these fountains of molten rock.

Years of fountains have been documented, but Kilauea has had only three fountaining episodes since 1823, even though it’s the youngest and most active volcano in Hawaii. That activity has led to intensive study, and we have a good idea of the volcano’s structure. Previous work has identified a couple of lava residues within a few kilometers of the surface, and the volcano had 35 separate data-gathering stations set up on Kilauea, including “seismic, infrasound, geodetic, gas, and visual and thermal cameras.”

Following a major eruption in 2018 that partly drained one of the underground lava reservoirs, there were indications that it was being steadily refilled. Starting in 2019, however, the refill accelerated, and the local peak inflated at a rate of more than 22 cm a year. Then, in 2023, that doubled to 57 cm a year, and spread to a nearby caldera.

In 2024, a large series of earthquakes accompanied the opening of a vent, and a 900-meter-long fissure opened, sending fountains as high as 160 meters into the sky over the course of 13 hours. Less than a day after that subsided, a second eruption followed. As of last month, 52 additional fountain eruptions had occurred, the most violent of which spewed lava over 400 meters into the air.

The Mechanism Behind the Eruptions

Can we predict volcanic eruptions?

Perhaps the most significant finding was that we could predict when a fountaining eruption was likely to happen. Each eruption caused rapid deflation of the summit of Kilauea and was followed by the relatively slow refilling of the Halemaʻumaʻu magma reservoir.

The USGS recognized that consecutive eruptions occurred when the summit tilt reached similar levels. While the precise tilt that was associated with eruptions tended downward over time, the difference between consecutive eruptions was relatively small. This pattern ultimately helped the organization issue alerts when eruptions were likely to occur, which was especially useful because there were no clear seismic signals immediately before fountains restarted.

One leading idea is that pressure within a magma reservoir keeps water mixed with other materials until it reaches a shallow enough depth to exit as steam. That fragments the magma, which allows it to ascend more rapidly, which allows more steam to escape, and so on until there’s a jet of material near the surface. The alternative posits that things are driven by the release of carbon dioxide from the magma, which forms a magma/gas “foam” at the roof of the magma chamber. Once this reaches a critical point, the gas escapes, driving magma with it until the supply in the magma chamber is exhausted.

The new data doesn’t provide a clear picture. It clearly doesn’t favor the formation of a carbon dioxide foam, because the levels of the gas remained low throughout the eruption cycle. Sulfur dioxide levels rose during eruptions and dropped afterward, but remained high throughout the entire period. Levels of this chemical are associated with gases escaping from magma, so this implies that more of it goes on during eruptions, but it also occurs continuously between them.

So the evidence leans toward the steam-driven eruption model, but it’s unclear why a process that is occurring throughout the cycle suddenly triggers fountains when it rises a bit. Despite the wealth of nearby sensors, the researchers acknowledged it would be nice to have more data. Sampling of gas levels is typically done at infrared wavelengths and, as you can probably imagine, there was a lot going on in the infrared during a fountaining eruption.

Questo articolo è stato scritto con l'assistenza dell'IA.
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