A stratovolcano (also composite cone or composite volcano) is a tall, conical mountain (volcano) composed of both hardened lava and volcanic ash. The shape of these volcanoes is characteristically steep in profile because lava flows that formed them were highly viscous, and so cooled and hardened before spreading very far. Such lava tends to be high in silica. At the other end of the spectrum are shield volcanoes (such as Mauna Loa in Hawai'i), which are formed from less viscous lavas, giving them a wide base and more gently sloping profile. Many exceed a height of 2500m. Stratovolcanoes are often created by subduction of tectonic plates.
Because all volcanoes of any size have a stratified (layered) structure—that is, are built up from sequential outpourings of eruptive materials—volcanologists prefer to use the term stratovolcano for these mountains.
Mount St. Helens-a stratovolcano-the day before the
May 18,
1980, eruption that removed much of the top of the mountain
Examples of stratovolcanoes are: