The volcano of Ischia, a resort island famed for its thermal waters off the coast of Naples, could potentially erupt, Italian disaster experts said.
Guido Bertolaso, the head of Italy's civil protection agency, said that while Vesuvius was more commonly considered the nation's most worrisome volcano, Ischia, which last erupted 700 years ago, was experiencing a build-up of magma.
No eruption is imminent, but "if I had to say which is the volcano with the most loaded gun barrel, I'd say it's not Vesuvius but the island of Ischia", Mr Bertolaso said in Rome last night.
Ischia, a short hydrofoil trip from the port of Naples and the chic vacation island of Capri, is often overrun with Italian and foreign visitors seeking to ease their aches and pains in pools filled with thermal waters pumped in from the sea.
Ischia's "magma chamber is loading up", said Mr Bertolaso, whose agency's mandate includes both disaster relief and prevention. An eruption on Ischia "could be worse than a hypothetical Vesuvius eruption", he said.
While scientists detect no sign of an eruption in the offing, Ischia's volcanic potential is being monitored along with that of Vesuvius, the mountain that looms over Naples and destroyed Pompeii when it blew in 79 AD.
Vesuvius is a disaster planner's nightmare, since its slopes are officially inhabited by some 500,000 people, although perhaps as many as 150,000 more live in illegal, unregistered housing in the 18 hamlets clinging to its side, Mr Bertolaso said.
Considering that parts of crowded, chaotic Naples could be in the path of Vesuvius' fury, more than a million people might ultimately be ordered to evacuate in case of eruption, he estimated.
Vesuvius last exploded in 1944.
Seismologists have detected no signs of the quakes that are expected to rattle Vesuvius before any major eruption and could serve as a warning to evacuate, said Mr Bertolaso, whose agency includes vulcanologists as well as quake experts.
Italian volcano and earthquake experts are about to launch a project over several years to monitor and explore 13 largely unstudied undersea volcanoes in the Mediterranean, near Sicily and the south-west Italian coast, Mr Bertolaso announced.
The scientists "want to take their pulse, check them and understand their behaviour to see if their fellow above-sea volcanoes behave like them", he said. Experts particularly want to fathom the submerged volcanoes' potential for triggering tsunamis.
Clustered in the Tyrrhenian waters off southern Italy are a handful of lively volcanoes, including Etna, with Catania, Sicily, at its base, as well as Europe's most monitored volcano, the tiny island of Stromboli, where a few hundred residents live on upper part of what is a mountain mostly submerged in the sea.
Stromboli, studded with TV cameras which monitor the rumbling mountain, experiences mild explosions lets it let off steam without heavy outpouring of lava. But in 2002, so much lava crashed into the sea that it triggered a small tsunami of sorts that flooded a beach and caused minor injuries as residents fled to higher ground.
Etna's last major eruption was in 1992, but it tends to spring to life every few months, sometimes forcing closure of roads that lead to hamlet on its slopes when flaming lava advances.
Air travel risks disruption, as in 2006 when clouds of billowing ash from an eruption prompted officials to close Catania airport for several nights as a precaution. The airport was only closed at night since pilots during the day were able to avoid the thick column of smoke and ash.
Catania was destroyed by a huge eruption in 1669.