Stratovolcano

A stratovolcano, also known as a composite volcano, is a conical volcano built up by many alternating layers (strata) of hardened lava and tephra.^[1] Unlike shield volcanoes, stratovolcanoes are characterized by a steep profile with a summit crater and explosive eruptions.^[2] Some have collapsed summit craters called calderas.^[3] The lava flowing from stratovolcanoes typically cools and solidifies 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.^[4] Extensive felsic lava flows are uncommon, but can travel as far as 8 km (5 mi).^[5]

The term composite volcano is used because the strata are usually mixed and uneven instead of neat layers.^[6] They are among the most common types of volcanoes;^[7] more than 700 stratovolcanoes have erupted lava during the Holocene Epoch (the last 11,700 years),^[8] and many older, now extinct, stratovolcanoes erupted lava as far back as Archean times.^[9][10] Stratovolcanoes are typically found in subduction zones but they also occur in other geological settings. Two examples of stratovolcanoes famous for catastrophic eruptions are Krakatoa in Indonesia (which erupted in 1883 claiming 36,000 lives)^[11] and Mount Vesuvius in Italy (which erupted in 79 A.D killing an estimated 2,000 people).^[12] In modern times, Mount St. Helens (1980) in Washington State, US, and Mount Pinatubo (1991) in the Philippines have erupted catastrophically, but with fewer deaths.^[7]