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
Volcanoes vary quite a bit in their structure - some are cracks in the earth's crust where lava erupts, and some are domes, shields, or mountain-like structures with a crater at the summit.
Rock also comes from volcanoes in other forms, including ash (finely powdered rock that looks like dark smoke coming from the volcano), cinders (bits of fragmented lava), and pumice (light-weight rock that is full of air bubbles and is formed in explosive volcanic eruptions - this type of rock can float on water).
The largest volcano on Earth is Hawaii's Mauna Loa.
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