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The experience of 85 days of volcanic eruption lived in La Palma in 2021 has taught us that the detailed mineralogical and chemical analysis -using new laser techniques- of the composition of the magma throughout the days of the eruption would allow us to predict when it will be its end.
This is the conclusion of a study published in Science Advances in which the Complutense University of Madrid (UCM) participates together with the Rey Juan Carlos University, the Geological and Mining Institute of Spain (IGME-CSIC), the Telesforo Bravo Foundation and two Australian universities.
According to the study, the deep magmatic system that feeds this type of eruptions (monogenetic eruptions in which a new volcano is formed with each eruption) is highly complex, involving different sources (areas of the Earth's mantle where magmas are formed). and evolves throughout the eruption.
"For this reason, the systematic and detailed sampling in real time of the different flows that are emitted during an eruption is key to understanding its evolution," highlights Álvaro Márquez, a researcher in the UCM's Petrology and Geochemistry Area.
Calcium and chrome, some clues from the end in November
The study was carried out during the eruption of the La Palma volcano (September 19 – December 13, 2021). There, the field work was carried out by a mixed research group from the UCM, URJC and the Fundación Canaria Telesforo Bravo – Juan Coello, who continuously took samples of the different lava flows emitted.
Meanwhile, a detailed analysis of a significant and representative set of the more than 80 samples collected was carried out. The mineralogy of these samples was studied using an electron microscope and microprobe at the UCM, while the chemical and isotopic composition of the rock matrix -performed with laser techniques- was determined at the University of Queensland (Australia).
With this analysis, the researchers were able to verify how at the end of November (when the eruption had already been going on for more than 2 months) there were changes in the trends of the calcium content in plagioclase and chromium in pyroxene, as well as in various chemical elements. of the parent company, which went from gradually increasing until that date to beginning to decrease. These changes would indicate that the magmatic system at depth was ceasing to be fed by magma inputs. The eruption ended just a couple of weeks after that change.
"The application of novel, highly precise chemical analytical techniques based on the use of lasers," says Márquez, "allows us to obtain key information that is not detected with conventional analysis methods that focus on analyzing the whole of the rock."
“The key to the success of this work is having combined the previous experience of the team in the study of Canary Islands eruptions and conventional study techniques, with advanced analytical techniques of greater precision. Without geological control and exhaustive sampling, the possibilities of the laser technique would not have been fully exploited”, underlines Raquel Herrera, a researcher in the Geology Department of the URJC.
The next step for the researchers is to apply the methodology developed in rock collections from other eruptions on La Palma (1949 and 1971) to confirm these key aspects that can be used in forecasting and monitoring future eruptions of this type in the Canary Islands and other similar environments.
UCC+I-URJC/ UCC-UCM