Ancient Roman Tunnels Could Cause Dangerous Sinkholes; Geologists Mapping Rome's Underground Maze

By Ben Wolford on December 3, 2013 4:43 PM EST

Roman Tunnels
Geologists are mapping Rome's underground tunnels to prevent the ground from collapsing. (Photo: Photo: BBC/Screenshot)

Unbeknownst to many of the tourists who pace the ancient streets of Rome, below their feet lies a tangle of quarry tunnels, cut by the first Romans who built the city. But now those tunnels, carefully hewn by the original engineers, have become safety hazards that threaten to undermine modern roads and buildings.

According to a report from LiveScience, the threat isn't just academic. In recent years, dozens of collapses have been documented, and the number is rising. In 2011, 44 streets or portions of buildings fell into the quarries. In 2012, the number rose to 77. And so far in 2013, there have been 83 incidents. Now, scientists are trying to find the areas of weakness and prevent future disasters.

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"What the municipality wants to do is to basically have a map of the risk so at that point they can on their side decide what kind of intervention needs to be done," geologist Giuseppina Kysar Mattietti, of George Mason University, told LiveScience. Together with scientists from the Roman preservationist organization Sotterranei di Roma, Kysar Mattietti is using 3D scanning to map the labyrinth of tunnels.

The quarries exist because of Rome's geology, Kysar Mattietti told LiveScience. The Italian landscape was shaped by volcanos, and still is. Its most active volcano, Mt. Etna in Sicily, has erupted numerous times in recent months. When early masons discovered volcanic rocks underneath the capital of the Roman empire, they found them to be lightweight and sturdy. The rocks were dug up in long narrow lines outside of the city. As Rome stretched into the suburbs, designers were careful to cut narrow enough that the tunnels wouldn't compromise above-ground structures.

But erosion set in, and future builders weren't as careful with the quarries, cutting them wider and less stable than their predecessors, Kysar Mattietti said. "A crack never stops on its own," she told LiveScience. "It always gets bigger." Other research from the Sapienza University of Rome finds that the Roman sinkholes have been caused by other underground cavities built not just as quarries, but for drainage and catacombs over the last 2,000 years. "The presence of these cavities may easily trigger the collapse of the shallow or deeper layers from ground level," Giancarlo Ciatoli writes in the abstract. Ciatoli says additional factors, including runoff caused by rainfall and loose soil, have also led to the sinkholes. He reports there have been at least 1,800 collapses between 1875 and 2011.

Kysar Mattietti and her team have begun with three areas deemed particularly high collapse risks. She says some of the tunnels have caved in but all the way to the surface. The result is a collapsed void between the tunnel and the cityscape above. In some cases, she told LiveScience, the ground between the surface and void is so thin you can stand in the cavity and hear the city above your head. Once the scientists have identified all the worst spots, officials will fill them in with mortar. "Since they weren't serving any use, people tend to forget what can be a problem," Kysar Mattietti said.

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