Mount Etna, the rambunctious volcano on the Italian island of Sicily, grumbled back to life on Monday, spewing hot ash and lava in a pyroclastic flow, the nation's volcano monitoring body said.

Pyroclastic density current (PDC): A turbulent, high-density flow composed of volcanic ash, lapilli and gases that descends rapidly along a volcano’s slope following an eruption.

Italy's Mount Etna, Europe's tallest volcano, erupted on June 2, causing tourists to seek safety. Several videos online have shown people fleeing as smoke and ash billowed from the side of the ...