Introduction
A lava dome is a roughly circular, mound‑shaped volcanic landform produced by the slow extrusion of highly viscous lava that, because of limited lateral mobility, accumulates over the vent to form a prominent protrusion. Dome‑building eruptions are most common where magmas are chemically evolved—notably at convergent plate margins—and account for roughly 6% of volcanic eruptions worldwide. Dome lavas span the compositional range from basalt through andesite/dacite to rhyolite, although most preserved examples are intermediate to high in silica (dacite–rhyolite); instructive cases include the basaltic dome at Semeru (1946), the dacite–andesite domes of Santiaguito, and the rhyolitic dome at Chaitén (2008–2010). The high viscosity that produces dome morphology can result either from intrinsically polymerized, silica‑rich melt or from rapid degassing of initially more fluid magma, both of which impede flow and favor emplacement of steep, coherent carapaces. A preservation bias toward silica‑rich domes exists because less viscous basaltic and andesitic domes are more easily eroded, fragmented, or overrun by subsequent fluid lava, so they survive less well in the geologic record. Dome morphologies and growth dynamics are therefore critical for interpreting eruption style and assessing hazard: slow extrusion commonly builds steep, unstable carapaces whose collapse can generate pyroclastic flows or be associated with explosive activity. Analogous domed volcanic constructs have been proposed for other planets, with candidate examples reported on the Moon, Venus, and Mars (e.g., structures in western Arcadia Planitia and within Terra Sirenum), implying that viscous‑eruption processes operate beyond Earth.
Dome dynamics
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Lava domes are extrusive volcanic constructs whose evolution is governed by inherently non-linear processes within the conduit and shallow system. Progressive crystallization and volatile exsolution in highly viscous, silica-rich magma generate complex feedbacks in pressure, rheology and permeability that produce cycles of emplacement, mechanical failure, cooling and erosion within volcanic craters (e.g., Mount St. Helens). These internal processes make dome behaviour intrinsically unpredictable and capable of abrupt transitions from quiescent growth to violent disruption.
Growth proceeds by two end-member mechanisms that reflect the magma’s high viscosity. Endogenic growth occurs when magma intrudes and inflates the dome interior, whereas exogenic growth involves the emplacement of discrete, short-lived lobes on the dome exterior. The same rheological properties that localize emplacement also favour the formation of steep, hemispherical morphologies, the development of prominent spines or spires, and short, viscous coulées that extend only a small distance from the vent.
Morphologically, domes commonly present flanks covered in unstable rock debris, can reach heights of several hundred metres, and exhibit episodic, cyclic growth patterns punctuated by sudden explosive activity. Timescales of emplacement vary widely: some domes evolve over months (Unzen), others over years (Soufrière Hills) or centuries (Merapi), so domes often represent long-lived volcanic features with sustained hazard potential.
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Seismic monitoring typically records shallow long-period and hybrid events beneath active domes; these signals are interpreted as responses to excess fluid pressures and magmatic–hydrothermal interactions in the immediate conduit–chamber system. While mean dome-growth rate can provide a first-order indication of magma supply, it does not reliably predict the timing or style of explosive episodes because of the system’s non-linearity and internal heterogeneity.
Hazards associated with dome activity are dominated by collapse and decompression-driven explosions. Gravitational failure of unstable dome flanks may uncork pressurized magma and generate pyroclastic flows or block-and-ash flows; intermittent gas build-up within the dome can likewise trigger violent fragmentation. Secondary impacts—short-range lava inundation, ignition of vegetation, and lahars produced by remobilized ash and debris—extend the spatial footprint of danger beyond the immediate collapse zone. Compositional factors amplify risk: rhyolitic, silica-rich domes retain more gas and are therefore more prone to unusually energetic explosions.
Taken together, the combination of viscous rheology, pressurization, cyclic growth and abrupt failure renders dome dynamics complex and challenging to forecast, necessitating integrated monitoring of deformation, seismicity, and eruptive products rather than reliance on a single rate-based metric.
Cryptodomes
A cryptodome is a shallow, dome-shaped intrusive body formed when highly viscous magma accumulates beneath the surface, lifting and warping the overlying rock rather than erupting as an exposed lava dome. The emplacement of this dense, near-surface magma produces a characteristic outward bulge of the volcanic flank and concentrates strain within the edifice, making the morphology of the volcano visibly domed even though the magma remains largely concealed.
Mechanically, cryptodome growth increases internal pressures and progressively deforms the volcano’s slopes. Continued inflation can localize stress to a portion of the edifice, ultimately triggering a sector collapse—a rapid failure and removal of a discrete flank. The sudden loss of confining weight exposes the formerly buried viscous magma to abrupt decompression, permitting rapid volatile exsolution and fragmentation; this process can convert a previously noneruptive intrusion into a highly explosive event.
This causal chain—near-surface intrusion and inflation, flank bulging, sector collapse, and explosive decompression—has been documented in historical eruptions. Notable examples are the 1956 eruption of Bezymianny and the 1980 eruption of Mount St. Helens, where shallow cryptodome growth produced conspicuous bulging prior to catastrophic flank failure. In the case of Mount St. Helens, the pre‑eruption bulge was photographed on 27 April 1980, immediately preceding the sector collapse and ensuing explosive eruption.
From a hazard perspective, the presence of a shallow, inflating cryptodome signifies an elevated risk of sudden flank failure and decompression-driven explosivity. Accordingly, surveillance of surface deformation, shallow intrusions, and edifice stability is essential wherever viscous magma is accumulating beneath a volcano.
Lava spine / Lava spire
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A lava spine, or lava spire, is a steep, often near‑vertical extrusion that rises from the surface of a lava dome when highly viscous magma is forced upward and solidifies into a coherent, tower‑like form. Morphologically it contrasts with the broader, rounded dome by its pronounced height and narrow profile, reflecting the rheological dominance of silicic, highly viscous lavas during extrusion.
Spine growth typically increases the mechanical instability of the dome complex. The slender, brittle spine concentrates stress and is prone to fracturing and collapse; such failure can destabilize the surrounding dome and generate secondary hazards (e.g., rockfalls and pyroclastic density currents) that substantially modify local volcanic risk during an ongoing eruptive phase.
Field observations illustrate these dynamics: for example, a prominent lava spine developed at Soufrière Hills (Montserrat) prior to the 1997 eruption, showing how spine formation may precede or accompany eruptive episodes and alter hazard conditions. More broadly, the recurrent production of spines and dome extrusion is a characteristic feature of prolonged silicic eruptions, as evidenced by sustained dome growth at Mount St. Helens during the 2004–2008 eruptive phase.
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Lava coulées
Coulées (also spelled coulees) are intermediate landforms that form when highly viscous dacitic magma partly extrudes as a dome and then moves laterally, producing deposits that combine the bulbous morphology of lava domes with the elongated, lobate form of lava flows. Their surfaces commonly preserve features diagnostic of viscous emplacement, including pressure ridges and a distinct flow front, reflecting incremental shear and internal deformation during transport.
The Chao dacite complex in northern Chile represents the largest documented example of this style of emplacement. Located between two volcanic edifices, the Chao flow extends for more than 14 km from its source and terminates in a flow front with roughly 400 m of vertical relief; in satellite imagery this margin appears as a dark, scalloped boundary. These dimensions and surface morphologies are readily mapped with remote sensing (for example, Landsat 8), which resolves the flow lobes, ridges and the contact between the coulée and surrounding terrain.
Comparable dacitic coulées occur elsewhere in the central Andes, most notably on the flank of Llullaillaco volcano in Argentina, indicating that viscous dome extrusion with substantial lateral transport is a recurring process in this orogenic volcanic belt. The scale and morphology of the Chao example underscore key emplacement dynamics for high-viscosity magmas: long-distance transport of dacitic material is facilitated by mechanisms such as dome collapse or sustained effusion, producing extensive lobate deposits with pressure‑ridge architecture in volcanic arcs.
Examples of lava domes
Lava domes occur worldwide but are concentrated in tectonically active volcanic arcs and hotspot regions; the listed examples span subduction-related arcs (e.g., the Andes, Cascades, Aleutians, Central America, Lesser Antilles, Sunda and Japan arcs), intracontinental volcanic fields (Chaîne des Puys, Jemez), and hotspot settings (Iceland). This geographic spread illustrates that dome formation is a common manifestation of highly viscous silicic to intermediate magmas in diverse tectonic environments.
Compositional data for these domes are dominated by high-silica end-members: rhyolite and dacite are most frequent (e.g., Chaitén, Novarupta, Valles, Nea Kameni, Mount St. Helens, Lassen), with rhyodacite and trachyte also represented (Wizard Island, Puy de Dôme). Andesite and andesite–dacite compositions occur less commonly (Soufrière Hills, Sollipulli, Tatun), while several domes lack specific compositional reports in the source data.
Regional clustering is evident. Multiple rhyolitic–dacitic domes occur in Chile’s Southern Volcanic Zone (Chaitén, Cordón Caulle, Nevados de Chillán, Sollipulli), reflecting sustained silicic magmatism in that arc. The Cascade Volcanic Arc and its northern extensions host a suite of dacitic to rhyodacitic domes (Lassen Peak, Black Butte, Bridge River Vent, Mount St. Helens, Wizard Island). The Lesser Antilles and Central American arcs produce andesitic to dacitic domes (Soufrière Hills, La Soufrière, Santa María), while Icelandic rhyolitic domes (Katla, Torfajökull) record hotspot-associated silicic activity.
Temporal evidence ranges from Miocene to historical. Some domes are geologically old (Tate-iwa: Miocene; Ciomadul: Pleistocene; Puy de Dôme and Wizard Island: mid-to-late Holocene emplacement ages), whereas others have recorded Holocene or historical growth episodes (e.g., Novarupta 1912, Lassen 1917, Mount St. Helens dome cycles through 1980s–2008, Chaitén 2008–2009, Galeras 2010, La Soufrière 2021). A number of features are dated only approximately (e.g., Bridge River Vent ca. 300 BCE; Sollipulli ~1240 CE; Valles domes 50–60 ka).
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Several of the listed domes are notable for recent activity and associated hazards: dome growth and collapse at Soufrière Hills, Mount St. Helens, Chaitén, and La Soufrière produced pyroclastic flows, ash emissions, and episodic explosivity in the late 20th and early 21st centuries. Other domes (e.g., Nea Kameni, Novarupta) serve as important case studies of post-caldera silicic extrusion.
Collectively, this set of examples illustrates that lava domes are a widespread product of silicic to intermediate magmatism, with compositions, ages, and eruptive behaviors that reflect local tectonic setting, magma supply, and conduit processes; their frequent occurrence in populated volcanic arcs underscores their relevance to volcanic hazard assessment.