A recent discovery is shaking up our understanding of dormant volcanoes. Researchers have identified significant magma reservoirs beneath volcanoes that have been inactive for millennia, challenging established theories about their functioning.
This study, conducted by a team from Cornell University, reveals that magma chambers persist long after eruptions, even beneath volcanoes considered long dormant. These findings could transform how scientists monitor and predict eruptions, offering new insights into the internal dynamics of volcanoes.
Magma reservoirs beneath dormant volcanoes
The researchers used seismic waves to study six volcanoes in the Cascade Range in the United States. Among them, Crater Lake volcano, inactive for thousands of years, still harbors a vast magma reservoir. This discovery contradicts the idea that magma chambers dissipate after a period of inactivity.
The results show that these reservoirs persist throughout a volcano's life, whether active or not. According to Guanning Pang, lead author of the study, these magma bodies are a constant feature, not an imminent sign of eruption.
This persistence suggests that eruptions do not entirely empty magma chambers. Instead, they release part of the magma, while the reservoir slowly replenishes through the gradual melting of the Earth's crust.
Implications for volcanic monitoring
This discovery changes how scientists interpret the warning signs of an eruption. Previously, the presence of a large volume of magma was considered an indicator of increased risk. Now, it seems to be a normal situation for many volcanoes.
Seismic monitoring networks, such as those deployed by the U.S. Geological Survey, could be optimized with this new data. A better understanding of magma location would allow for more effective targeting of at-risk areas.
Geoffrey Abers, co-author of the study, points out that many volcanoes worldwide are still poorly monitored. This method, based on a limited number of seismic stations, could be applied to other regions, such as Alaska, to improve volcanic risk prevention.
Going further: Why do some volcanoes remain dormant for so long?
Dormant volcanoes, like those in the Cascade Range, can remain inactive for millennia while retaining significant magma reservoirs. This prolonged dormancy is explained by a balance between pressure, temperature, and magma composition. As long as these conditions remain stable, the magma does not rise to the surface, thus avoiding an eruption.
The partial melting of the Earth's crust plays a key role in maintaining these reservoirs. This slow and continuous process feeds magma chambers with fresh magma, compensating for losses from past eruptions. For example, Crater Lake volcano, inactive for millennia, still retains a vast magma reservoir beneath its surface.
Finally, magma viscosity also influences this dormancy. Silica-rich magma is more viscous and flows less easily, which can prevent an eruption even in the presence of a large reservoir. These combined factors explain why some volcanoes remain "dormant" for thousands of years, while still being potentially active deep down.
What is a magma chamber?
A magma chamber is a vast underground pocket located several kilometers beneath the surface of a volcano, where magma accumulates before an eruption. It forms when heat and pressure cause partial melting of the Earth's crust or upper mantle rocks. These reservoirs can extend over several cubic kilometers and evolve over time.
The magma stored in these chambers is a mixture of molten rocks, gases, and crystals. Its composition varies depending on the type of volcano and its geological environment. For example, in Cascade Range volcanoes, the magma is often rich in silica, making it more viscous and influencing the type of eruptions.
Magma chambers are not static. They gradually fill through the melting of surrounding rocks and partially empty during eruptions. However, as the recent study revealed, these reservoirs can persist for millennia, even beneath volcanoes considered dormant, playing a central role in the life cycle of volcanoes.
Article author: Cédric DEPOND