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Cambridge University Science Magazine
The conventional image of a volcanic eruption is one of sudden, explosive destruction, with molten rock hurtling through the air and great plumes of smoke darkening the sky. This is not always the case, however – some eruptions consist of slow-moving lava flows, which work their way down the flank of the volcano and pose much less threat to human life.

Volcanoes tend to produce the same types of eruptions over millions of years. This means that some reliably erupt these less hazardous lava flows, while others, such as Vesuvius or Mt. St. Helens, can produce much larger explosive eruptions. Armed with the knowledge of what kind of eruption a volcano consistently produces, local authorities are able to plan better for the risks involved in living near the volcano.

A research team of scientists from the US, UK and Ecuador, including several from the Department of Earth Sciences at the University of Cambridge, studied two Galápagos volcanoes which have so far only produced small basaltic lava eruptions. By analysing the physical and chemical composition of microscopic crystals in the lavas, the researchers were able to reconstruct the characteristics of magmas stored beneath the surface of the volcanoes, offering an indication of the types of eruptions they could produce.

Surprisingly, the team found that the underground plumbing systems of these volcanoes contained chemically diverse magmas, in contrast to the monotonous basaltic lavas released at the Earth’s surface. These diverse magmas include compositions similar to those erupted at Mt. St. Helens, indicating the potential to generate explosive activity of a kind never seen before from the Galápagos volcanoes being studied.

Lead author Dr Michael Stock said: “This was really unexpected. We started the study wanting to know why these volcanoes were so boring and what process caused the erupted lava compositions to remain constant over long timescales. Instead we found that they aren’t boring at all – they just hide these secret magmas under the ground.”

Though the Galápagos volcanoes themselves are unlikely to change their eruptive behaviour in the near future, the study points towards an explanation for why certain other volcanoes might have done so in the past. Uniformity of eruptions seems to be a result of high amounts of magma flushing through the ground beneath volcanoes, effectively “overprinting” any chemical diversity. It is possible, however, for chemically diverse magmas – such as those discovered by the researchers – to become mobile and ascend to the surface, leading to unexpected changes in eruption pattern and even explosive activity from the volcano.

Dr Stock explained: “The study will also help us to better understand the risks posed by volcanoes in other parts of the world – just because they’ve always erupted a particular way in the past doesn’t mean you can rely on them to continue doing the same thing indefinitely into the future.” These insights have the potential to play a valuable role in volcano monitoring and hazard assessment.

Publication: M. J. Stock, D. Geist, D. A. Neave, et al. Cryptic evolved melts beneath monotonous basaltic shield volcanoes in the Galápagos Archipelago. Nat Commun 11, 3767 (2020).

Zak Lakota-Baldwin is a 4th year History and Philosophy of Science undergraduate, and news editor at BlueSci