Dangerous Volcanoes Which Caused Number Of Casualties - A volcano is an opening, or rupture, in a planet's surface or crust, which allows hot magma, ash and gases to escape from below the surface. Volcanoes are generally found where tectonic plates are diverging or converging. There are many active volcanoes around the world. In this article 5 world's most dangerous volcanoes have been introduced which caused many casualties.