In 1982 the ground beneath the Italian port town of Pozzuoli, near Naples, began to swell. In the next two years, the town rose more than six feet. Rocks underground cracked under the strain, sparking tiny earthquakes. And some 40,000 residents were forced to evacuate. Tiziana Vanorio was one of them.

"We were scared, not because of the earthquakes but because of the fear that an eruption was about to come."

But that eruption never came. And Vanorio, who's now a geophysicist at Stanford University, wanted to find out how the rock endured the strain. So she and a postdoctoral student obtained rock cores from the Campi Flegrei Caldera, the volcanic area underlying Pozzuoli, taken just before the swelling in 1982. They discovered a layer of what’s called caprock, almost like a lid, that sealed off the caldera below. And the caprock's microstructure was an intricate network of mineral fibers—the key, she says, to its strength, and ability to flex under pressure. The findings are in the journal Science. [Tiziana Vanorio and Waruntorn Kanitpanyacharoen, Rock physics of fibrous rocks akin to Roman concrete explains uplifts at Campi Flegrei Caldera]

And that fibrous rock structure? Vanorio says it looked familiar—very similar to the famous ancient Roman concrete, used to build aqueducts and the Colosseum. And, similarly to concrete production, the caprock probably formed when lime-rich geothermal fluids percolated upward, mixing with the volcanic ash.

It's probably no accident the Romans ended up with that same chemical recipe. "They were keen observers, they knew very well that the volcanic ash from that region was very special. And they also shipped the volcanic ash throughout the Mediterranean."

And now that we're discovering these secrets, she says, we might do as the Romans, and emulate nature once again—to pave the way toward more durable, self-healing concrete.

—Christopher Intagliata

[The above text is a transcript of this podcast.]