How Volcanoes Work

Image Described in Caption
 Mount St. Helens Lava dome -- The current lava dome occupying the amphitheater region of Mt. St. Helens, is shown here in its early stage of formation. The photo was taken in June, 1981. Note the rifted "flower structure" along the axis of the dome, which is produced by the viscous flow of dacitic lava from beneath. Courtsey of Daniel Dzurisin, USGS.