Lava Dome Formation

Lava dome formation occurs when magma too viscous to flow far, typically silica-rich dacite or rhyolite, is extruded at a vent and piles up over and around it rather than spreading into a lava flow, building a steep-sided mound directly above the conduit. A growing dome is unstable and prone to collapse, which can trigger fast-moving pyroclastic flows and block-and-ash flows down the volcano flank, the mechanism behind some of the deadliest eruptions in recorded history, including Mont Pelee in 1902.