Like earthquakes,most volcanoes are located along the 'Ring of Fire' a 40000-kilometers stretch that encircles the Pacific Ocean. However,there many other regions with active volcanoes scattered around the globe.
A volcano is usually a mountain topped by a crater. It erupts when lava and gases come out of a vent from a chamber of magma deep in the ground. Far below the surface, the magma and gases are always under pressure. When the pressure become very great,it forces the magma and gases violently out of a crack or vent ,shooting them high into the air together with pieces of rock,ash and soil from around the vent and the surface. This creates a crater from which more lava flows down the mountain slopes as red-hot 'river'. The material in the air then rain down,sometimes covering more than 30 kilometers around the mountain!
A volcanic eruption can be very destructive. The lava flow,for one thing not only destroys everything in its path,it can also alter the entire ecosystem of the area,wiping out both plants and animals.