Back here on Earth, we’re once again held captive and fascinated by the power and awesomeness of volcanoes. I don’t think we can overstate the love that our team has for these powerful structures, no matter the type: cinder cones like in La Palma and Iceland, shield volcanoes like Kīlauea, or stratovolcanoes like those in the Andes and Japan. And we even love a type of volcano that seems a bit misunderstood, in my opinion – the caldera. Of course, most of us are familiar with the huge caldera under Yellowstone, but that’s one of many here on Earth.

New research published in Nature Communications and led by Dr. Simona Petrosino has found a novel way to understand just how liquids, in this case magma, flow underground when it comes to caldera. Specifically, the team used ambient noise from the sea and the wind to map processes deep beneath the earth in a region known as the Phlegraen Fields, or Campi Felgrei, in Italy.

Dr. Petrosino explains: Sea and wind constantly interact with the caldera and produce waves that scan its depths. Ambient noise waves enter the caldera with their direction changing above faults and magma feeding systems. Our work shows that, while the change of direction is essential to detect structures, the loss of any directionality is a signal of activation. The energy release is followed by migrations of fluids that produce additional noise sources, hindering our ability to reconstruct directionality. Thus, the loss of directionality gives us a tool to track the migration of deep fluids before they reach the surface.

When scientists analyzed noise data that was collected over the last decade, they found just such a loss of directionality in 2018, which corresponds to a time when some of those deep magmatic fluids migrated up into more shallow hydrothermal systems. That migration likely caused the earthquakes felt in the region in 2019.

Co-author De Siena goes on to further explain: The volcano releases its stress through migrations of fluids following paths opened during its intense activity in 1983/1984. These deep fluids combine with those from rainfalls, which make the shallow part of the volcano more permeable. This produces strong earthquakes, like those recorded at the volcano in 2019/2020. By observing directionality changes through time, we can now detect the progressive migration of fluids towards the eastern caldera, whose structure suffers the largest stress and which acts as a barrier for further migration toward the East.

This is an interesting new method to model the movement of deep magmatic fluids, and while it doesn’t help precisely predict either earthquakes or eruptions as a result, it is definitely a step in the direction of understanding when activity levels are increasing for a caldera. That understanding could give us a bit of a heads up that something may happen relatively soon.

More Information

Johannes Gutenberg University Mainz press release

“Fluid migrations and volcanic earthquakes from depolarized ambient noise,” S. Petrosino and L. De Siena, 2021 November 17, Nature Communications