How does a volcano work? A scientific discovery upends our understanding of the process


Taking samples of magma in full eruption is not an easy task: between the impossibility of predicting the event, the inaccessibility of the site, the risk of suffocation with toxic gases and the risk of being trapped by a lava flow, even I might say it’s an impossible mission, and yet. In March 2021, from the time a fault opened and erupted near the Fagradalsfjall volcano in the Geldingadalur region on the Reykjanes peninsula in southwest Iceland, a series of 50,000 earthquakes – some of magnitude 4 and more – will shake the Icelandic ground for several weeks.⋙ In Iceland, the first images of the eruption of lava from a dormant volcano for 800 years Matthew Jackson, professor of volcanology at the University of California at Santa Barbara (UC Santa Barbara), Sæmundur Halldórsson from the University of Iceland and his colleagues immediately went to the scene. Without knowing what unprecedented circumstances were going to converge and make their work much easier. Ideal conditions to study an erupting volcano. In fact, thanks to the winds that chased the noxious gases from the bowels of the Earth, as well as the slow flow of lava, these scientists were able to get close enough to continuously taste the magma, and this, Three questions plagued the researchers: How deep in the Earth’s mantle did the magma originate, originally? How deep below the surface was it stored just before the eruption? And finally, what was happening in the magma chamber before and during the eruption?⋙ Impressive: an expedition sinks into the heart of the underwater volcanoes of the Mediterranean SeaPublished in the prestigious journal Nature (14/9/2022), the result of this study of the analysis of samples collected in Iceland reveals a much more dynamic process than might have been assumed during the last two centuries. More magma variability in a single month than in 10,000 years! According to the best-supported hypothesis before the publication of this new study, it was common to consider “that a magma chamber fills slowly over time, and that the magma is perfectly mixed” before. being “drained (to the surface) during the eruption,” explains Matthew Jackson, the study’s lead author, quoted in a press release. In such a way that the chemical composition of the magma does not vary – or only slightly – between the beginning and the end of the eruption “This is what we observe, for example, at Mount Kilauea, in Hawaii”, explains the researcher. “Eruptions last for several years, with minor changes (of the magma) over time.” ⋙ 4 surprising things you need to know about volcanoes A hypothesis inconsistent with the recent eruption witnessed by the authors of the study. “In Iceland, the rates of change of the main chemical indicators have multiplied by more than 1000”, says the volcanologist. “In one month, the eruption of Fagradalsfjall showed a greater variability in the composition (of the magma) than the eruptions of Kilauea in several decades,” compares Professor Jackson. “The total range of chemical compositions (of magma) taken from this eruption in the first month covers the full range of all eruptions that have occurred in southwest Iceland in the last few months. The last 10,000 years” , he says a volcano job? Imagine… a lava lamp!, but why so much chemical variability in magma, and above all, what can we conclude about how a volcano works? According to the authors of the study published in Nature, these measurements show that magma from deep in the Earth’s mantle came to flow into the magma chamber in successive “batches”, and not as a well-made mixture. To understand this, the main author evokes a design object, very fashionable between the 60s and 70s: the “lava lamp”. Who hasn’t been mesmerized by this glass globe stretched aloft, filled with a transparent liquid and in which balls of molten wax evolve? Picture a lava lamp in your mind, suggests Matthew Jackson. “You have a hot bulb at the bottom, which heats a ball (of wax). This ball rises up, cools and then sinks. We can imagine that the Earth’s mantle – from the top of the core to the bottom of the tectonic plates – It works a bit like a lava lamp.”⋙ You’ll know all about Iceland’s volcanoes. So when heat causes certain regions of the Earth’s mantle to rise, plumes of molten rock form and rise to the surface, then accumulate. in the magma chambers. But the comparison with the light fixture of the disco years ends there: when the molten rock crystallizes, the gas escapes through the earth’s crust, so much so that the pressure increases, until the magma finally finds its way to to escape A finding applicable to all volcanoes on Earth? In their study, the researchers were able to break down the eruption in the Fagradalsfjall volcano area into several stages. During the first few weeks, the lava coming to the surface came directly from a magma chamber located about 16 km below the surface, where the magma had been depleted of chemical elements. Then, in April 2021, the composition of the magma became enriched in magnesium and carbon dioxide, indicating that the magma chamber had been “recharged” with molten rock from another plume circulating through the Earth’s mantle, like another ball of wax rising in a lamp. Whether these rapid changes in magma composition had “never been observed before.” in near real time”, according to the authors, this would be because it is generally difficult – if not impossible – to collect samples at such an early stage of an eruption cycle, which can last for centuries. And it must be said that the opportunity is not presents so often: on the Reykjanes peninsula where the researchers were, the previous eruption was … 800 years ago!, although the authors are not able to state to what extent this process is representative. of functioning of all the volcanoes on our planet, its discovery, however, sheds new light on phenomena that until now were impossible to verify.⋙ The risk of a massive volcanic eruption over the course of the century is greatly underestimated, according to a study. Does it prove that the Earth still has secrets to reveal to humanity? Anyway, this is what Professor Jackson thinks: “From now on, when I go to taste an ancient lava flow, or when I read or write articles in the future, I will always take it into account: it may be that t is not the full story of the eruption,” he smiles. Also read: What are the different types of volcanoes? Volcanic eruptions that have marked the world during the last ten years What is the difference between lava and magma?
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