La Palma volcano: the composition of the magma determines the tremor

Jan. 10 () –

A new study based on the analysis of ashes from the Cumbre Vieja volcanoon the island of La Palma, suggests that the composition of the magma could drive tremors during volcanic eruptions.

The findings, which are detailed in the journal Nature Geoscience In an article led by scientists from the American Museum of Natural History (AMNH) and the City University of New York (CUNY), they highlight the potential of volcanic ash analysis as a monitoring and forecasting tool.

“The volcano research community has gotten much better in recent years at predicting the onset of a volcanic eruption, but it is still difficult to predict the style and duration of the eruption,” said study co-author Samantha Tramontano, a postdoctoral fellow at the AMNH. “If our findings hold for other volcanoes, we might be able to monitor the properties of interior magma from the surface of an eruption, and that could be very important for risk assessment.”

ERUPTION IN THE PALM OF 2021

In September 2021, after remaining dormant for 50 years, the Cumbre Vieja volcano eruptedcausing the evacuation of thousands of residents. Over the next 85 days, it destroyed more than 3,000 buildings and hundreds of acres of farmland. Tramontano and his advisor at the time, Marc-Antoine Longpré of CUNY, established a system to collect almost daily samples of ash fall during the three-month eruption with the help of colleagues at the Canary Islands Volcanological Institute and the National Geographic Institute. .

The samples, which captured 94 percent of the eruption chronology, were sent to the AMNH for analysis. chemical analysis of glass within ashwhich originated from rapidly cooled magma that was expelled from the volcano, using an electron microprobe. The resulting data set was a daily time series of the composition of the liquid part of the magma, the first of its kind.

The study revealed changes in the amount of silica in the samples, a compound that makes magma more viscous. More viscous magma is usually associated with more explosive eruptions. The researchers found that the silica content was high in the first week of the eruption, and then gradually decreased until a sharp reversal two weeks before the end of the eruption, which probably marks the cut-off of the mantle’s magma supply.

The researchers then compared this chemical record to physical observations being made at the same time and found a correlation between the silica content and the strength of the volcano’s tremor, a seismic “rattle” associated with the movement of liquid and gas beneath of the surface. Based on additional modeling and analysis, the research team proposes that the presence of more viscous magma with high silica content causes greater amplitude of volcanic tremor, although more research is needed to confirm this mechanism.

In addition to offering new clues about the cause of volcanic shaking, which is a key parameter for eruption monitoring, the study shows the benefit of combining the collection of petrological data (such as ash fall) with geophysical data to improve eruption forecasting, risk assessment and decision making during volcanic crises.

“A major challenge for petrological monitoring is the coordination of field work and sample transfer during eruptive crises to allow rapid analysis,” Longpré said. “Careful advance planning and technological advances should make efficient analysis of samples in the vicinity possible in the future, facilitating better timely interpretation of geophysical data.”