Near Naples, Italy, the Campi Flegrei supervolcano is showing troubling signs of activity. Earthquakes, gas emissions, and ground swelling suggest this “sleeping giant may be stirring.” With a violent history, including one of Earth’s largest eruptions 40,000 years ago, scientists are watching it closely.

Campi Flegrei, or the Phlegraean Fields, is “one of the most dangerous on Earth.” In May, a 4.4-magnitude quake—“the strongest in 40 years”—shook the area. Over 3,000 smaller quakes have followed in just six months. These tremors likely signal magma moving beneath the surface.

Gas emissions have also surged, with “4,000 to 5,000 metric tons of carbon dioxide” released daily—unusual for a long-quiet volcano. Rising magma is “cracking the crust,” creating pathways for an eruption. Since 2005, the ground near Pozzuoli has lifted nearly five feet, another warning sign.

This volcano threatens millions in Naples and nearby towns. An eruption could release ash, lava, and toxic gases, with effects spreading far beyond Italy. “An eruption could lower temperatures worldwide,” disrupting food supplies and economies.

Though no one knows when it will erupt, scientists are monitoring closely. For now, “watching and waiting remain the only options” as the world eyes Campi Flegrei’s uncertain future.