Lava dome
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In volcanology, a lava dome is mound-shaped growth resulting from the eruption of high-silica lava (usually rhyolite and/or dacite) from a volcano. It is also known as a plug dome, although that term is rarely used. The high silica content makes the lava very viscous, so that it cannot flow very far from its vent before solidifying. Lava domes are one of the principal structural features of many stratovolcanoes worldwide. Domes may reach heights of several hundred metres, and can grow slowly and steadily for months or years. 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. Ultimately, many volcanic domes are destroyed by large explosive eruptions.
Some of the world's most famous active lava domes include those at Mount Merapi in central Java of Indonesia, Soufriere Hills volcano in Montserrat, and Mt. St. Helens in the U.S. state of Washington. Lassen Peak in the northern part of the U.S. state of California is the largest single lava dome in the world and has the distinction of being the only other Cascade volcano besides Mount St. Helens to have erupted (1914-1921) in the 20th Century.
