Some volcanoes erupt explosively, like opening a shaken soda bottle, because their magma is full of gases. Other volcanoes erupt gently, like boiling milk spilling over the sides of a pot, because their magma has fewer gases. An "active" volcano erupted recently or might erupt soon. A "dormant" or sleeping volcano has been quiet for a long time, but may erupt again someday. An "extinct" volcano has not erupted for over 10,000 years.

Image credits: main image, courtesy of USGS; Jim Webster, courtesy of AMNH.