Lavadomes

Lava domes, or lavadomes, are rounded, mound-like accumulations that form when highly viscous magma erupts slowly onto the surface or intrudes into existing crater or vent areas. The lava’s high silica content makes it reluctant to flow, so it piles up around the vent rather than spreading into widespread lava flows. Domes are typically composed of dacitic to rhyolitic magma and can grow by the extrusion of successive lava lobes that crust over and push outward.

Domes vary in size and shape, from compact, steep-sided mounds to irregular, blocky accumulations. The surface crust often forms a rough, glassy or rubbly rind while the interior remains partially molten. Dome growth can inflate the structure as gas pressure and magma supply continue, and interior crystallization and cooling can create cracks, spines, or lobate protrusions. Because the interior can remain partially molten, domes may be unstable and prone to rapid collapse, which can generate pyroclastic flows, ash clouds, and ballistic ejecta.

Hazards associated with lava domes include sudden dome collapse, gas emissions, and explosive fragmentation, all of which can threaten nearby populations and air traffic. Monitoring of dome dynamics incorporates seismic data, ground deformation measurements, gas monitoring, and remote sensing to detect rapid changes in growth or instability.

Lava domes occur worldwide, especially in subduction-related volcanic arcs. Notable examples include domes associated with Mount St. Helens in the United States, Soufrière Hills in Montserrat, Merapi in Indonesia, and Unzen in Japan, where prolonged eruptive activity produced significant dome growth and related hazards.