Mount St. Helens is an active strato-volcano in Skamania County, Washington, in the Pacific Northwest region of the United States. It is well known for its ash explosions and pyroclastic flows.Mt. Vesuvius is a somma-stratovolcano located in Naples, Italy. It is universally acknowledged to be an extremely dangerous volcano.Mount Krakatoa is a Caldera in the Sunda Strait between the islands of Java and Sumatra in the Indonesian province of Lampung.