The inhabitants of the island of La Palma in the Canary Islands began to be evacuated, preventively, on the same day that the eruption of the Cumbre Vieja Volcano last September 19th. These hours of break prevented injuries, but were insufficient to save personal belongings, among others. The main reason is that these geological events cannot yet be predicted with greater reliability and accuracy.
Today, however, between 40 and 50 volcanoes are erupting or in turmoil around the world, and 800 million people living nearby are at risk to their health and lives, especially those that are potentially heritage sites. In addition, they also pose a threat to global air traffic.
“The field of eruption prediction is in its infancy and we still have a long way to go before we anticipate eruptions as we predict the weather,” he tells SINC. Daniel J Rasmussenresearcher of Smithsonian National Museum of Natural History and lead author of a paper, the results of which bring scientists closer to reliable predictions.
Until now, these predictions have been complex, largely because volcanologists don’t fully understand the dynamics and natural processes of magma beneath a volcano before it rises to the surface. In fact, most of these predictions are made by comparing the current activity of a volcano, such as earthquakes or the ground movementswith previous activity patterns.
But, Rasmussen had a question on his mind since 2015: Why is the depth Does magma storage vary from volcano to volcano and what controls that depth? In search of the answer, the work, published in the journal Sciencemanaged to identify what scientists expect to be the most important factor in controlling the depth at which magma is stored: the water content in this fluid material.
“Understanding magma storage conditions, including its water content, is important to help us develop the next generation of volcanic prediction models,” emphasizes Rasmussen.
View of Cleveland volcano from the research vessel in 2016. / Daniel Rasmussen
Water, the ‘fuel’ that drives eruptions
The results reveal that, in the most common type of volcano in the world – the volcanic arcs–, magma with higher water content tends to be stored in greater depth in the earth’s crust. In this way, the water content of magma would be responsible for controlling its depth, rather than simply being correlated with it.
“This study relates the depth at which magma is stored with water, which is significant because water initiates and largely fuels eruptions,” says the volcanologist, who compared the imposition of water in eruptions to carbon dioxide. . of carbon that can explode a shaken soda bottle.
“With water dissolved in the magma that is stored under a volcano, if there is a sudden decrease in Pressurelike when the cap of a shaken soda bottle is suddenly opened, gas bubbles that make the magma rise and leave the volcano, similar to when a soft drink comes out of a bottle”, exemplifies Rasmussen. “More water content in the magma means more gas bubbles and potentially a more violent eruption,” he continues.
The researcher explains to SINC that if these bubbles remain with the magma upon reaching the surface, it is likely that a explosive eruption. If the gas bubbles escape from the magma [desgasificación]it will come out of the volcano smoothly in what we call effusive eruption“, add. In both cases, the water content of the magma is an important eruption factor.
“Our results tell us where these gas bubbles form in relation to the depth of magma storage,” says the expert. Contrary to what was previously thought, scientists show that most magma is buoyant in its storage depth, which provides a driving force for magma to rise from its accumulation region.
“However, it doesn’t tell us anything about the beginning of this ascent, which is a process called triggering eruptions,” says Rasmussen, who notes that a lot of effort has gone into understanding these processes that have yet to be understood. the prevalence.
Geophysicist Diana Roman of Carnegie Institution for Science on the flank of Cleveland volcano in 2016. / Anna Barth, University of California, Berkeley
To study the ashes of Alaska’s volcanoes
To reach these conclusions, the team detected the presence of chemical markers associated with the formation of magmas that contain water in the Earth’s mantle. To do this, Rasmussen set out to collect volcanic material from eight volcanoes located in the rugged and remote region. Aleutian Islands from Alaskain the USA, along with geophysics Diana Romanfrom the Carnegie Institution for Science. The researchers focused on the so-called volcanic arcsthat occur at the intersection of two converging tectonic plates.
“These types of volcanoes are the most common on Earth’s land surface and are the ones that pose the greatest danger,” says the researcher, who hopes to analyze other systems, such as those in Hawaii and Iceland, to see if the findings apply as well. to these volcanoes.
Using boats and helicopters, the team collected, amid the rough seas and the threat of grizzly bears, chunks of volcanic ash, which may contain green olivine crystals – which underground can trap small pieces of magma that cool when they form. and turn into glass. Each of these crystals is about a millimeter in diameter, about the thickness of a plastic ID card.
By analyzing the chemical composition of these tiny pieces of cooled magma Coming from inside a volcano, scientists were able to estimate the water content of magma in six of the Aleutians’ eight volcanoes. In addition, they combined this data with other estimates of magmatic water content taken from the scientific literature of 56 other volcanoes around the world. The final list of magmatic water content estimates included 3,856 individual samples from 62 volcanoes.
To examine the relationship between the estimated water content of these magma reservoirs and their respective storage depths, the researchers consulted the scientific literature and created a watch list of 331 depth estimates for 112 volcanoes.
After years of fieldwork, geochemical analysis, and literature review, the team was able to plot the estimated magma storage depths for 28 volcanoes worldwide in relation to their respective estimated magma water contents.
We still have work to do before our results impact physics-based eruption prediction models similar to weather prediction models.
“We still have work to do before our results have an impact. forecast models of eruptions, based on physics, and similar to weather prediction models. Its ultimate goal is to have more accurate predictions about the timing, type and duration of volcanic eruptions,” attests Rasmussen.
For this, the volcanologist points out that it is necessary to know the conditions of the magma storage region before the eruption, in a similar way to knowing the temperature and humidity of the atmosphere to make a weather forecast. “The results help us to understand the storage conditions and, above all, the state of the water contained in the magma. This is a small step forward.”
Daniel Rasmussen et al. “Magmatic water content controls the pre-eruptive depth of arc magmas” Science