1. Mount Vesuvius, Italy
Located near densely populated Naples, Mount Vesuvius is one of the most dangerous volcanoes in the world. Famous for burying Pompeii in 79 AD, it’s still active with signs of unrest. The volcano’s proximity to 3 million people makes any potential eruption catastrophic. Experts continue monitoring seismic activity, knowing that another sudden explosion could disrupt life in southern Italy with little warning.