On Aug. 24, 2013, visitors arriving at Rome’s Leonardo da Vinci International Airport, located in the Fiumicino municipality, flew over a surprising hazard: a gas emission that suddenly exploded from the ground a few meters outside the airport compound. The expulsion, referred to as the Fiumicino Gas Vent (FGV), occurred about 15 kilometers southwest of Rome and was first noticed by passing motorists. Shortly after the explosion, scientists sought to determine the gas’ makeup and whether it posed a continuing danger.