Campi Flegrei makes its own concrete caprock

In the 1980s, Tiziana Vanorio was a teenager living in the Italian port city of Pozzuoli west of Naples when the  Campi Flegrei volcanic complex that underlies the town and its harbor began to stir. Between 1982 and 1984, the caldera swelled more than 2 meters — the most rapid volcanic uplift ever measured anywhere. The rising seafloor shallowed Pozzuoli’s harbor so that ships could no longer enter. The uplift was followed by a magnitude-4 earthquake and thousands of microquakes that prompted the evacuation of 40,000 residents. Thereafter, the seismicity waned and the residents returned home, but geologists were left with a puzzle: How did the caldera withstand such extreme strain and deformation for so long without rupturing?