Lavadome

Lavadome, more commonly referred to as a lava dome, is a geological feature formed by the extrusion of highly viscous magma at a volcano. The lava’s high silica content makes it too thick to flow far, so it piles up around the vent to create a bulbous, often steep-sided mound. Lavadomes can vary widely in size, from small features to large, complex domes.

Domes grow through episodic or persistent extrusion of viscous lava. A rough outer rind may form as the interior crystallizes, while continued activity adds to the dome’s volume. Some domes remain confined within a crater, whereas others develop adjacent to or beyond the vent, sometimes forming a chain or field of domes in a volcanic system.

Most lava domes are silicic or intermediate, typically composed of rhyolitic to andesitic magma. The high viscosity traps gases, which can lead to explosive activity if pressure builds. Dome growth is often associated with ground deformation and seismic signals, and domes can produce pyroclastic flows or tephra during collapse events.

Lava domes occur in subduction-related settings and other regions with silicic magmatism. Notable examples include Lassen Peak (United States), the lava-dome complexes at Mount St. Helens crater, Unzen (Japan), Soufrière Hills on Montserrat, and Chaitén (Chile). Dome activity is closely monitored at active volcanoes due to the potential for rapid changes and hazardous collapses.

Monitoring typically involves seismic watching, geodetic measurements, gas flux analysis, and crater observations to assess stability and eruption risk.