Lava Flows and Domes

Additional scientific description

A lava flow may comprise smaller masses of lava known as 'lava flow units', or 'lava flow lobes'; a lava flow comprising multiple lava flow units is known as a 'lava flow field'. Individual flows may branch around obstacles to create multiple flow fingers and may inflate or thicken from the original thicknesses. There are many types of lava flows. Pillow lavas are lava flows formed under water. Fluid, subaerial lava flows may be channelized ʻaʻā, lobate pāhoehoe, or blocky lavas. Lava domes may be described by their geometry. Domes are typically blocky and steep-sided and can contain uplifted solid plugs of lava (lava spines) which typically have a higher aspect ratio formed from stiffer more crystalline material. Lava coulées are a hybrid between lava domes and flows that form short, thick, viscous lava flows on a slope.

Most volcanoes erupt lava flows and/or domes during their lifetimes. Effusions of lava commonly continue from days to months, but occasionally last decades. Lava flows damage and destroy land and property but usually (not always) advance slowly enough for populations to escape. Understanding where future lava may be erupted from (the vent or vents), how far a lava flow may advance, the velocity of the flow front and the area that may be covered are critical for hazard assessments (Diettrich et al., 2025). Viscous lava domes are often crater-confined, so their flow runout typically does not destroy infrastructure. However, domes often collapse to generate very hazardous and fast-moving pyroclastic density currents (Charbonnier et al. 2025. See GH0203). The main factors controlling how a lava flow or dome develops are the rheological properties of the lava, effusion (or extrusion) rate and underlying topography.

The rheological properties of lava are influenced by chemical composition and factors such as pre- and syn-eruptive crystallization. Fluid and mobile lava flows tend to be low in silica (e.g., mafic compositions such as basalt); lava with moderate silica content is more viscous and tends to form short blocky lava flows or lava domes (e.g., intermediate compositions such as andesite); the most silica-rich lava is most likely to form a lava dome (e.g., felsic compositions such as rhyolite). The Cordón Caulle eruption in 2011-2012, shows that rhyolitic and basaltic compound lava flows may have much in common in terms of physical processes, despite very different rheologies (Tuffen et al., 2013).

Lava flows and domes typically have a molten core, with a solid crystallized outer shell, which crystallizes with increased degassing and cooling through time. Parts of lava flows and lava domes can therefore remain molten after an eruption has ended (Dietterich et al., 2025; Harnett et al., 2025). Lava flow advance of lava dome spreading can therefore occur outside of an active eruption

Lava flow characteristics: Surface morphology of subaerial basaltic lava flows may be described as pāhoehoe (Hawaiian meaning 'smooth, unbroken') or a'ā (Hawaiian meaning 'stony, rough lava'), whereas intermediate or silica-rich lava is more likely to have a blocky surface morphology.

Models: The simplest empirical models are volcano-specific and link effusion rate to runout length, but more complex models account for cooling-induced changes in rheology as lava flows downslope. Outputs are highly sensitive to topography, as well as effusion rate and flow dynamics (Dietterich et al., 2025). High resolution Digital Elevation Models are necessary but in urban and man-made environments Digital Surface Models may be more appropriate to account for the built environment.

Probabilistic hazard assessments for lava flows can anticipate inundation so are useful for long-term planning (e.g., hazard maps) and short-term forecasting (e.g., Vicari et al., 2011). However, more study is required at many volcanoes that lack important metrics such as recurrence interval, or volume of previous lava flows. New methodologies are constantly developing and generally have a two-step process: statistical analysis to establish known vent distributions and identify most likely future vent sites, followed by an estimation of the areas of inundation by lavas flowing from those vents using lava flow models (e.g., Gallant et al. 2018).

Lava flow and dome collapses: Viscous lava flows and domes may exhibit various collapse styles from persistent rock falls to partial or total collapse of a lava dome. Lava flow or dome collapse may generate pyroclastic density currents called block-and-ash flows and associated hazards such as tephra and gas emissions (Harnett et al., 2025). Lava dome collapse hazard assessments are rarely in place but are needed (Harnett et al., 2025).

Metrics and numeric limits

Basaltic pāhoehoe flows commonly have the highest eruption temperatures of 1050 to 1200°C, whereas rhyolitic lavas are typically 700-900°C (Diettrich et al., 2025). The unique 'natrocarbonatite' lava flows at Ol Doinyo Lengai volcano in Tanzania are dominated by carbonates rather than silicates and form very fluid, relatively low temperature lavas (500-600°C) (Pinkerton et al., 1995).

At the start of an eruption, basaltic lavas may advance at several kilometres per hour, but flow velocity decreases with distance to walking pace or less within a few hours (Diettrich et al., 2025). However, flow velocity decreases less dramatically with time for long-lived eruptions. On steep slopes some lavas may reach higher velocities of tens of kilometres per hour. Exceptionally, in 1977, lava flowed down the slopes of Nyiragongo with a maximum velocity of up to 100 km/h (Balagizi et al., 2018). Viscous lavas typically advance at rates of 0.1 km/day or less.

Basaltic lava flows typically reach lengths of 1-30 km, but occasionally more than 50 km (e.g., Mauna Loa 1859 eruption, Hawaii) (Diettrich et al., 2025). Basaltic lava flows may be 3-30 m thick and typical volumes of historical lava flows on land are between 0.01 and 1 km3 (flow fields can exceptionally exceed 10 km3). Intermediate and silicic lavas are usually shorter in length, typically up to 5 km but some are up to 15 km. They may be 20-300 m thick and volumes are typically 0.01 and 0.1 km3 but can be up to 10-20 km3 (Diettrich et al., 2025). If lava flows into a body of water, the interaction can form littoral explosions that deposit tephra locally, or the interaction may be passive and generate steam and formation of a lava delta.

Lava domes most commonly form in andesitic-dacitic composition but have also been observed at rhyolite volcanoes. Lava domes can grow at a range of extrusion rates (~0.01-100 m3/s) and vary in maximum volume from small lobes and spines (<0.0001 km3) to large summit domes (~0.5 km3) to enormous coulées (>5 km3), with most domes growing to ~0.001-0.2 km (Harnett et al., 2025).