Mitt Romney's sister-in-law found dead in Southern California: What we know Woman cut down Israeli hostage ribbons because ...

Pyroclastic density currents (PDCs) represent some of the most formidable and complex volcanic phenomena, characterised by a turbulent mixture of solid particles and gases that surge down slopes at ...

A plume of ash and gas rises from Mount Etna on the Italian island of Sicily on Monday. The eruption also featured lava fountains and a pyroclastic flow. Salvatore Allegra / Anadolu via Getty Images ...