Scientists have discovered a vast magma reservoir beneath Tuscany, containing approximately 6,000 cubic kilometres of molten rock, comparable in volume to the magma systems beneath supervolcanoes such as Yellowstone in the United States and Lake Taupo in New Zealand.
The finding, published in the journal Nature, came as a surprise because the region shows almost none of the typical surface signs of large magma bodies, such as major craters, significant eruptions in hundreds of thousands of years, or dramatic ground deformation. The last volcanic eruption in the area, from Mount Amiata, occurred around 300,000 years ago and was relatively minor.
The reservoir was identified by an international team using ambient noise tomography, which records natural vibrations from ocean waves, wind and human activity. Around 60 high-resolution seismic sensors deployed across the region detected unusually slow vibrations, indicating molten material. The team built a three-dimensional image of the crust down to 15 kilometres depth.
“We knew that this region is geothermally active, but we did not realise it contained such a large volume of magma, comparable to that of supervolcanic systems such as Yellowstone,” said Matteo Lupi, associate professor at the University of Geneva, who led the study.
The magma sits between 8 and 15 kilometres below the surface, with a core of liquid melt surrounded by a shell of crystal-rich partially molten rock. Despite its scale, the researchers say the magma poses no immediate volcanic threat due to its high viscosity, which makes it less likely to erupt. The discovery explains the region's extreme geothermal activity, powering one of the world's most productive geothermal energy systems at Larderello.
Lupi said the study demonstrated the potential of ambient noise tomography as a rapid and relatively cheap tool for locating geothermal reservoirs or deposits of lithium and rare earth elements.
