Lava Dome - John Seach

Landforms of this sort consist of steep domal mounds of lava so viscous that the lava piles up over its vent without flowing away. The rock types that form lava domes are generally andesites, dacites, or rhyolites. Somehow these viscous lavas have lost much of their gas content in prior eruptions or by slow rise to the surface. Even so, it is not unusual for an actively growing lava dome to have an explosive eruption that disrupts all or part of the dome. Many lava domes grow by internal intrusion of lava that causes swelling and oversteepening of the dome. Rockslides build up an apron of talus blocks around the lower sides of the dome. Lava domes can form mounds several hundred metres high and from several hundred to more than 1,000 metres in diameter. Thick lava flows sometimes move short distances from the dome and distort its generally circular or oval shape. Currently domes are forming at Merapi, Mt St Helens, and Montserrat as well as others.