A stratovolcano, also known as a composite volcano, is a conical volcano built up by many layers (strata) of hardened lava and tephra. Unlike shield volcanoes, stratovolcanoes are characterized by a steep profile with a summit crater and periodic intervals of explosive eruptions and effusive eruptions, although some have collapsed summit craters called calderas. The lava flowing from stratovolcanoes typically cools and hardens before spreading far, due to high viscosity. The magma forming this lava is often felsic, having high-to-intermediate levels of silica (as in rhyolite, dacite, or andesite), with lesser amounts of less-viscous mafic magma. Extensive felsic lava flows are uncommon, but have travelled as far as 15 km (9 mi).
Stratovolcanoes are sometimes called composite volcanoes because of their composite stratified structure, built up from sequential outpourings of erupted materials. They are among the most common types of volcanoes, in contrast to the less common shield volcanoes. Two famous examples of stratovolcanoes are Krakatoa in Indonesia, known for its catastrophic eruption in 1883, and Vesuvius in Italy, whose catastrophic eruption in AD 79 buried the Roman cities of Pompeii and Herculaneum. Both eruptions claimed thousands of lives. In modern times, Mount St. Helens in Washington State, USA and Mount Pinatubo in the Philippines have erupted catastrophically, but with fewer deaths.
The existence of stratovolcanoes on other bodies of the Solar System has not been conclusively demonstrated. One possible exception is the existence of some isolated massifs on Mars, for example the Zephyria Tholus.