Lava domes are rounded, steep-sided mounds built by magma that is highly
resistant to flow, usually either dacite or rhyolite. Such magmas are
typically too viscous to move far from the vent before cooling and
crystallizing. Domes may consist of one or more individual lava flows.
Left: An aerial view of the 600-foot lava dome in the
crater of Washington's Mt. St. Helens, as seen between the May and July
eruptions in 1980.