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St. Helens

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.

Type/Process: Lava Dome
Volcanic Status: Historical
Image Number: 029-033
Photographer: Bob Symonds, 1983 (U.S. Geological Survey)
Summit Elevation: 2549 meters
Latitude/Longitude: 46.20 N / 122.18 W
Timeframe: Last known eruption 1964 or later
Region: Canada and Western USA

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