New studies of molten rock 20 kilometers below the Earth’s surface could help improve predictions of volcanic activity, scientists say in a new study published May 10 in the journal Science Advances.
Currently, volcanic eruptions are predicted based on the activity of the volcano itself and the several kilometers of Earth’s crust beneath it, which contains molten rock potentially ready to erupt. However, the new study highlights the importance of looking for clues much deeper in the Earth’s crust, where rocks first melt into magma and then rise to chambers closer to the surface.
To understand the internal nature of our planet’s most explosive events, researchers from Imperial College London and the University of Bristol carried out in-depth studies to shed light on the frequency, composition and magnitude of volcanic eruptions around the world.
Their results show that the size and frequency of eruptions are closely related to the time it takes for extremely hot molten rock known as magma to form in these deposits deep beneath the Earth’s crust (up to 20 kilometers deep), as well as the size of these reservoirs.
The study analyzed data from 60 of the most powerful volcanic eruptions spanning nine countries: the United States, New Zealand, Japan, Russia, Argentina, Chile, Nicaragua, El Salvador and Indonesia.
“Contrary to previous beliefs, our study suggests that the eruptions are caused by the buoyancy of magma, rather than the ratio of solid to molten rock.said Dr Catherine Booth of Imperial College London. — The buoyancy of magma is determined by its temperature and chemical composition compared to the surrounding rock: as magma builds up, its composition changes, making it less dense, making it more “buoyant” and allowing it to rise.”.
He added that once magma becomes mobile enough to float, it rises and creates cracks in the overlying solid rock, and then moves through those cracks very quickly, causing an eruption.
In addition to identifying magma buoyancy as an important factor in triggering eruptions, the researchers also studied how magma behaves when it reaches smaller underground chambers just before an eruption. They found that the length of time magma is stored in these smaller chambers can also influence volcanic eruptions: longer storage periods lead to smaller eruptions.
While larger reservoirs might be expected to cause larger, more explosive eruptions, the results also showed that very large reservoirs dissipate heat, slowing the process of converting solid rock into magma. This led the researchers to conclude that the size of reservoirs is another key factor in accurately predicting the size of eruptions, and that there is an optimal size for the most explosive eruptions.
The findings also suggest that eruptions are rarely isolated and are instead part of a repeating cycle. Additionally, the magma emitted by the volcanoes they studied was rich in silica, a natural compound known to play a role in determining the viscosity and explosiveness of magma; Magma with high silica content tends to be more viscous and cause more explosive eruptions.
Co-author Professor Matt Jackson said the study “is a fundamental step towards better monitoring and forecasting of these powerful geological events”.
Source: Rossa Primavera
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