A complex volcano, also called a compound volcano, is a volcano with more than one feature. They form because of changes in their eruptive characteristics or the location of multiple vents in an area. Stratovolcanoes may form complex volcanoes, because they may overlap another from repeated explosive eruptions, lava flows, and pyroclastic flows to make multiple summits and vents. Stratovolcanoes can also form a large caldera that gets filled in by multiple small cinder cones, lava domes and craters may also develop on the caldera's rim.