Volcanoes

Abstract

There are hundreds of active volcanoes on earth, most of them in the Circum-Pacific “ring-of-fire” at tectonic plate boundaries where a sea plate moves under a land plate at what is called a subduction zone. A volcano is considered active if it has erupted at least once in the past 10,000 years. Japan has 110 active volcanoes, Indonesia has 127 while Chile lays claim to 123, and Central America has 45. Volcanoes also occur where plates pull away from each other such as at the mid-Atlantic Ocean ridge or slide past one another (e.g., Hawaii). Geologists study volcanoes and the materials they deposit (ash, lava) in order to determine when a volcano erupted in the past and from these data how often. In many cases, where delicate monitoring equipment is in place, the onset of volcanic activity is often predictable.