Introduction — Cinder cone
A cinder cone, or scoria cone, is a small, steep-sided volcanic hill formed by the accumulation of loose pyroclastic fragments around a single vent. These cones result from relatively explosive, gas-rich eruptions that fragment ascending lava into ash, lapilli and scoria; the fragments cool in flight and fall back ballistically to build a largely concentric deposit surrounding the vent.
Morphologically, cinder cones tend toward radial symmetry with near-circular planforms and steep flank angles commonly between 30° and 40°, reflecting the angle of repose of the coarse, vesicular fragments. A bowl-shaped summit crater typically caps the cone directly above the vent. The cones are therefore distinct in external form from broader shield volcanoes or stratovolcanoes, recording a localized and often short-lived eruptive episode.
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Internally, the structure comprises a central, roughly cylindrical conduit encircled by outward-dipping beds of pyroclastic fallout. Coarser, blockier material accumulates closer to the vent, grading outward into finer ash and lapilli; the resulting deposits are porous and largely unconsolidated. This architecture governs the cone’s permeability, susceptibility to erosion, and subsequent morphological change.
Because cinder cones are constructed from discrete fallout episodes sourced at a single locus, their preserved stratigraphy and summit crater provide a direct record of the eruption locus and style. Their unconsolidated nature and steep slopes explain both the rapid construction during eruption and the comparatively rapid modification by post-eruptive processes.
Mechanics of eruption
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Cinder (scoria) cones are small pyroclastic edifices, typically tens to hundreds of metres high, built predominantly of loose fragments rather than coherent lava; this fragmental construction contrasts with spatter cones, which are formed from agglutinated volcanic bombs. The constituent pyroclasts are commonly basaltic to andesitic, glassy and highly vesicular, reflecting explosive fragmentation and rapid quenching of gas-rich magma. Discrete ballistic fragments or volcanic bombs (≥64 mm) are frequently produced and contribute both to the cone’s accumulation and to proximal fall deposits.
Cone growth proceeds through a characteristic sequence. Initial accumulation around the vent produces a low scoria ring; continued fallout builds the rim and an external talus slope of fallen scoria. Subsequent episodes of collapse and explosivity can modify or partially destroy the rim, and later deposition may extend talus beyond the immediate ballistic zone—the region near the vent where clasts follow ballistic trajectories and fall directly to ground. In the final eruptive phase the residual melt is largely degassed and no longer sustains energetic fountains; instead it extrudes effusively.
Summit effusion is uncommon because the unconsolidated, weak scoria walls cannot support sustained upward magma pressure, so late-stage, gas-poor lava typically migrates along or beneath the cone base. Owing to its lower vesicularity and higher density relative to the surrounding cinders, this lava tends to enslide or undercut the scoria, sometimes buoying lighter fragments and forming an outward lava apron. The typical end-product is a relatively symmetric scoria cone centered on a surrounding lava pad or flow; if late effusion or collapse breaches the rim, the remnant may assume an amphitheatre- or horseshoe-shaped morphology around the vent.
Occurrence
Basaltic cinder cones are widespread products of intraplate mafic volcanism, frequently associated with alkali-rich basalts whose elevated Na2O and K2O contents reflect alkaline magmatism. They often form as small, monogenetic edifices that mark localized eruptive vents rather than long-lived central systems.
Cinder cones commonly occur as parasitic or satellite vents on the flanks of larger volcanoes—including shield volcanoes, stratovolcanoes and calderas—and may represent late-stage, mafic activity of a volcanic complex. For example, nearly one hundred cones have been mapped on the flanks of Mauna Kea, illustrating how flank volcanism can produce numerous scoria cones around a major shield. Where erupted basalt is extremely fluid, however (Hawaiian-style eruptions), ejected clasts are prone to welding on landing and typically form spatter cones or welded ramparts rather than loose, scoria-rich cinder cones.
Well-documented historical eruptions demonstrate the variety of cinder-cone behaviour and settings. The Parícutin eruption that began in a Mexican cornfield in 1943 produced a classical monogenetic cinder cone that grew to about 424 m in height over nine years and emplaced lava flows that covered roughly 25 km2. Cerro Negro in Nicaragua, part of a cluster of young cones northwest of Las Pilas, is among the most persistently active cinder cones on Earth: first noted in 1850, it has erupted on the order of twenty times, with episodes as recent as 1995 and 1999.
Cinder cones also form in continental volcanic provinces; for instance, cinder deposits in the San Bernardino Valley record local basaltic eruptions within the southwestern United States. Beyond Earth, volcano-like cones with morphological characteristics comparable to terrestrial cinder cones have been identified from orbit: candidate cones occur on the flanks of Pavonis Mons and within chaotic terrains such as Hydraotes Chaos on Mars, in the Ulysses Colles field, and domical constructs in the Marius Hills on the Moon. These analogues help constrain eruptive styles and volatile content in planetary basaltic volcanism.
SP Crater in Arizona exemplifies the morphology and eruptive behavior of scoria‑producing cinder cones and illustrates how environmental parameters shape cone form. Gravity and atmospheric pressure critically influence the trajectories and settling distances of ejected pyroclasts, so that the same eruptive dynamics produce different cone geometries under different planetary conditions. On Mars, lower atmospheric density and reduced gravity allow scoria to travel substantially farther, producing cones with basal diameters more than twice those of analogous terrestrial cones; because erupted volumes commonly remain too small for flank slopes to reach the local angle of repose, Martian cones are largely molded by ballistic deposition from the vent rather than by extensive post‑depositional redistribution. By contrast, Earthly cinder cones frequently undergo flank processes — rolling, avalanching and settling of tephra — that rework deposits until slopes approach the angle of repose, yielding the characteristically steep, narrow profiles when particle supply is sufficient. Strong prevailing winds during eruption can impose systematic asymmetry on otherwise symmetric cones by concentrating thicker tephra accumulations on the downwind (lee) side, producing a consistent bias in plan and profile.
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Monogenetic cones
Monogenetic cinder cones are volcanic edifices formed by a single, short-lived eruptive episode that typically produces only a modest volume of lava. Eruptive activity that constructs these cones commonly endures for weeks to months, though on rare occasions it can continue for a decade or more; Sunset Crater in Arizona, which began forming around 1075 CE, exemplifies such a single-event construct. Because each eruption is essentially standalone, monogenetic cones tend to be small, spatially discrete features with limited eruptive output.
These cones occur across a range of volcanic settings, as illustrated by well-known examples such as Parícutin (Mexico), Diamond Head, Koko Head, Punchbowl Crater, Mt Le Brun (Coalstoun Lakes field) and various cones on Mauna Kea. However, not all cinder cones are monogenetic: some older cones preserve intercalated soil horizons between lava flows, indicating repeated eruptions separated by millennial timescales and thus a polygenetic history.
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The dominant explanation for monogenetic behavior invokes a low regional magma supply combined with eruptions that are widely dispersed in space and time. Under these conditions no persistent subsurface conduit or plumbing system becomes established, so each eruption must independently find and ascend its own pathway to the surface. The absence of long-lived feeders therefore produces numerous isolated vents, each with a limited eruptive lifespan and small erupted volume.