Lava Dome

A lava dome is a circular, mound-shaped protrusion formed by the slow extrusion of viscous lava from a volcano, common in convergent plate boundary settings and responsible for around six percent of Earth's eruptions. The characteristic dome shape results from the lava's high viscosity, which prevents it from flowing far, produced either by high silica content in the magma or by degassing of fluid magma. Because low-silica domes weather quickly and break apart when more fluid lava is added, most preserved lava domes have high silica content and consist of rhyolite or dacite.