There are four main types of volcanoes: shield volcanoes form from layers of slow-erupting lava and are the largest; cinder-cone volcanoes eject ash and form small cones; composite-cone volcanoes alternate layers of lava and ash making them larger than cinder-cones; and volcanoes are commonly found at plate boundaries but can also form at hot spots from upwellings in the earth's mantle.

1. Main Idea: Types of Volcanoes