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St Helens Volcano, USA
Lava domes are formed by the extrusion of viscous, silica-rich lava that accumulates above the volcanic vent.
This steaming lava dome partially fills the crater of Mount St. Helens in April 1983.
Dome extrusion often follows explosive eruptions, which decrease the gas content of the remaining magma.
Dome growth, however, is commonly accompanied by explosive activity and pyroclastic flows.
Lava domes can form within the summit craters of volcanoes or on their flanks.
They may build solitary, domical masses, or a complex of overlapping domes.
PHOTO SOURCE: Bob Symonds 1983, US Geological Survey, courtesy of the Global Volcanism Program, Smithsonian National Museum of Natural History, used with permission.
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