Complex volcanoes, also known as compound volcanoes, are volcanoes that consist of more than one cone. Some of Earth's largest mountains are inactive complex volcanoes.
The four basic types of volcanoes are composite, cinder, shield and lava domes. These four types are additionally classified depending on whether they occur separately or in geographic groups. Volcanoes that occur in groups are known as compound or complex volcanoes.
Formation determines volcano type. Composite volcanoes become larger as layers of lava and ash build up over time. Cinder volcanoes are formed as cinders from explosive events layer around the volcano's core. Shield volcanoes are formed from liquid lava flow. If the lava flow is thick and mounds up, a lava dome volcano is created.
Complex volcanoes contain a central vent running to a crater or cone at the peak of the volcano. This central vent splits off underground into side fissures that rise to the flanks of the central cone. This creates a clustered group of vents at the surface. Each of these vents gives rise to its own individual volcano.
Famous mountains that began as complex volcanoes include Mount Fuji in Japan, Mount Cotopaxi in Ecuador, Mount Shasta in California, Mount Hood in Oregon, and Mount Saint Helens and Mount Rainier in Washington.