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Tuesday, December 16, 2008

Lava dome

In volcanology, a lava dome or plug dome is a roughly circular mound-shaped projection resulting from the slow eruption of felsic lava (typically rhyolite or dacite) from a volcano, or from multiple lava episodes of dissimilar magma types. The characteristic dome shape is credited to high levels of silica in the magma, causing the magma to be quite viscous and broad. The viscosity of the lava prevents it from graceful far from the vent that it extrudes from, causing it to solidify rapidly and build on preceding volcanic extrusions, creating a dome-like shape. Domes may reach heights of several hundred meters, and can produce slowly and steadily for months or years. The sides of these structures are composed of unbalanced rock debris. Due to the option of the building up of gas pressure, the dome can experience more volatile eruptions over time. When part of a lava dome collapses while it still contains molten rock and gases, it can create a pyroclastic flow, one of the most fatal forms of a volcanic event. Other hazards linked with lava domes are the destruction of property, forest fires, and lahars triggered by pyroclastic flows close to snow and ice. Lava domes are one of the principal structural features of many stratovolcanoes universal.

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