Most people haven't thought about earth science since high school geography class; that is, until the world's volcanoes began closing the skies and wreaking havoc on our global world. Suddenly, everyone's on alert to see which volcano will erupt next and how it might affect us.

Geologists classify volcanoes into three distinct groups: dormant, extinct, and active. Active volcanoes have erupted recently and are expected to continue to erupt again soon. The Smithsonian Global Volcanism Program defines an active volcano as having erupted within the last 10,000 years. A volcano finally goes extinct when there's no lava supply in the magma chamber beneath the volcano. There are approximately 1,500 active volcanoes in the world today and 75 percent of them are located in the Pacific Ring of Fire. On average, 50-70 volcanoes erupt every year.

Click Start to view the ten most active volcanoes on Earth.