Southern Italy—between the ankle and calf of Italy’s geographical “boot”—is home to one of the most dangerous places on Earth: the Campi Flegrei caldera. A caldera is a vast depression in Earth’s surface created by magma vacating an underground reservoir during an eruption. Regions containing calderas are often volatile, and the Campi Flegrei is especially hazardous because of its proximity to the metropolitan city of Naples. An eruption (which researchers estimate could happen in the next 500 years or so) would be disastrous for the more than 1.5 million people who live there.
The on-land portion of Campi Flegrei has been studied extensively since ancient Roman times, and currently, the area is being monitored by a network of 14 seismic stations, 17 continuous GPS stations, and nine tiltmeters, which measure slight changes in slope across a surface. The part of the caldera that is submerged under the Gulf of Pozzuoli—roughly half the total area—has been studied to a lesser extent, but scientists have been collecting marine data since 2008 through the Cabled Underwater Multidisciplinary Acquisition System (CUMAS) platform. CUMAS uses a suite of instruments on board a buoy and on the seafloor to detect seismic activity, hydroacoustic waves, water pressure, and displacement of the seafloor. In 2016, three more buoys containing even more instruments were added to CUMAS to form the Multiparametric Elastic-beacon Devices and Underwater Sensors Acquisition (MEDUSA) system.
Here Iannaccone et al. used data collected by MEDUSA to generate the first image of seafloor deformation patterns in the Gulf of Pozzuoli portion of the Campi Flegrei caldera. The team found that from April to June 2016, some sections of the seafloor were uplifted by approximately 4.2 centimeters.
The researchers also compared these GPS seafloor data, transmitted from MEDUSA’s four buoys to the Osservatorio Vesuviano monitoring center in Naples, to values projected by a model using only GPS land measurements. Their results matched up, showing that either data collected on land or data from the seafloor can be used to determine the other. They also found that bottom pressure records, or measurements of pressure at the bottom of the ocean, could be used to determine seafloor uplift in shallow water.
Not only did the team provide the first image of seafloor deformation patterns beneath Campi Flegrei, a critical caldera, but their study is also a good example of how GPS buoys can be used to monitor submerged volcanic regions in general. It also shows the potential to use bottom pressure records as a cost-effective, high-resolution mode of monitoring shallow waters. (Journal of Geophysical Research: Solid Earth, http://doi.org/10.1002/2017JB014852, 2018)
—Sarah Witman, Freelance Writer