A volcano is a rupture on the crust of a planetary mass object, such as the Earth, which allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface.Fissure VolcanoFissure volcanoes have no central crater at all. Instead, giant cracks open in the ground and expel vast quantities of lava. This lava spreads far and wide to form huge pools that can cover almost everything around. When these pools of lava cool and solidify, the surface remains mostly flat. Since the source cracks are usually buried, there is often nothing volcano-like" to see - only a flat plain. Composite Volcanoes
The most majestic of the volcanoes are composite volcanoes, also known as strato-volcanoes. Composite volcanoes are tall, symetrically shaped, with steep sides, sometimes rising 10,000 feet high. They are built of alternating layers of lava flows, volcanic ash, and cinders.