Just west of Naples, Italy, the ground swells and strains around the Campi Flegrei caldera, mythical home of the Roman fire god Vulcan. The volcanic region’s most recent rise came between 1982 and 1984 when the ground rose around 2 meters. Officials evacuated nearly 40,000 people from the nearby town of Pozzuoli in fear of an eruption. It never came.
At the time, Tiziana Vanorio was a teenager in Pozzuoli. Now a geophysicist at Stanford University, Vanorio says she has figured out how the rocks beneath the caldera bulge without breaking.
Examining a rock core drilled from the caldera, Vanorio and Waruntorn Kanitpanyacharoen of Chulalongkorn University in Bangkok discovered a layer of stiff, fibrous rock similar to concrete around 1.3 to 1.7 kilometers deep. This layer probably formed over time as rising hydrated lime, one of the main ingredients in manufactured concrete, mixed with volcanic ash. Together, they formed an impenetrable lid that resists fracturing even as the underlying pressure mounts.
This natural engineering could have inspired the ancient Romans to mix their own concrete, the researchers propose online July 9 in Science.
Editor’s Note: This article was updated July 16, 2015. It incorrectly said that manufactured concrete has two main ingredients.