Sketch of the lava fountain cycle at Fagradalsfjall. Credit: Natural communications (2023). DOI: 10.1038/s41467-023-42569-9
A multi-institutional team of Earth scientists, meteorologists, geologists and volcanologists has developed a new theory to explain the nature of volcanic fountains. In their project, reported in the journal Natural communicationsThe group studied the 2021 eruption of the Fagradalsfjall volcano in Iceland, which produced what some described as spectacular examples of volcanic fountains.
Volcanic fountaining occurs when a volcano erupts, as shown in cartoons, with hot lava gushing straight into the sky before falling back to Earth and cascading down the sides of a caldera. It remains unclear how and why they form and what drives their energy, although some experts in the field suggest it is due to the rapid rise of magma. In this new effort, the research team took advantage of the unique features of the Fagradalsfjall eruption to learn more about the fountains.
The 2021 eruption of Fagradalsfjall did not happen all at once as a large explosion. Instead, it was a series of fountains of different heights. The fountains were also reasonably well contained, allowing researchers to get closer to the action to learn more about what was driving the fountain’s formation.
To study the eruptions, the research team used a device that allowed them to perform Fourier transform infrared spectroscopy (OP-FTIR) on gases emitted by the volcano over four cycles of eruption and pauses. Then, by studying the chemical composition of the gases, they found attributes suggesting an explanation for the formation of a volcano rather than a simple explosion from its summit. And that led them to a theory.
The new theory suggests that volcanoes like Fagradalsfjall have a shallow cavity beneath their magma-filled caldera. As the magma rises in the cavity, the gases lead to a layer of foam on top of the magma inside the cavity. The researchers suggest that the collapse of the foam layer is what causes the pressure that pushes the magma into the air, creating a fountain effect, like that of soda from a shaken can. The cyclical nature of such a fountain is due to the gases repeatedly creating a layer of foam inside the cavity.
Further studies of volcanic fountains are needed, but the research team suggests their theory could help explain fountaining in a variety of volcanoes around the world.
More information:
Samuel Scott et al, Instability of near-surface magma flows results in cyclical lava fountains at Fagradalsfjall, Iceland, Natural communications (2023). DOI: 10.1038/s41467-023-42569-9
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