Lava dome
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In volcanology, a lava dome is mound-shaped growth resulting from the eruption of high-silica lava (such as rhyolite) from a volcano. The high silica content makes the lava very viscous, so that it cannot flow very far from its vent before solidifying. Lava domes are the principle building materials of stratovolcanoes. Because high-silica lava can build more highly and steeply than low-silica lava (such as basalt), lava domes can be unstable and prone to collapse. When part of a lava dome collapses while it still contains molten rock and gases, it produces a pyroclastic flow, one of the most lethal forms of volcanic event.
Some of the world's most famous active lava domes include those at Merapi volcano in Java, at Soufriere Hills volcano in Montserrat, and at Mt. St. Helens in the U.S. state of Washington.