Volcano
A vent in a planet's crust that erupts magma.
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A volcano is an opening in the crust of a planet or similar body where molten rock, ash, and gases from an underground magma chamber reach the surface. On Earth, these openings are most common where tectonic plates either move apart or collide. Since most plate boundaries lie under the ocean, the majority of volcanoes are underwater. They can also appear where the crust is being stretched and thinned, or far from plate edges due to mantle plumes—hot columns rising from deep within the planet—which create hotspot volcanism.
Extinct
Volcanoes are classified by how often they erupt. Active ones have a history of activity and are expected to erupt again. Extinct volcanoes have lost their magma supply and cannot erupt.
Dormant volcanoes have not erupted for a long time—generally since the start of the Holocene, about 11,700 years ago—but could still erupt. These categories are not strict and can overlap. Large eruptions can cool the atmosphere by releasing ash and sulfuric acid droplets that block sunlight, sometimes leading to volcanic winters and famines. Other planets also have volcanoes.
Etymology and terminology
Venus has many, and Mars has notable ones. In 2009, a paper proposed a broader definition of "volcano" to include processes like cryovolcanism, defining it as any opening on a planet or moon from which magma or magmatic gas erupts. The word "volcano" comes from the early 17th century, from the Italian name Vulcano, a volcanic island in the Aeolian Islands, which itself comes from the Latin Volcānus, the Roman god of fire. The study of volcanic activity is called volcanism, and the scientific field is volcanology.
Plate tectonics
Plate tectonics explains most volcanic activity. Earth’s outer shell is broken into sixteen larger and several smaller plates that move slowly due to mantle convection. Volcanoes form mainly at plate boundaries where plates converge or diverge.
Divergent plate boundaries
Some volcanoes are polygenetic, with multiple eruption periods, while others are monogenetic, erupting only once before becoming extinct. At divergent boundaries, plates move apart, allowing hot mantle rock to rise and melt, creating new oceanic crust. Most of this activity is submarine, forming seafloor and black smokers. Where ridges rise above sea level, volcanic islands like Iceland appear.
Quick Facts
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- Geology, Volcanology
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Lore & Background
The word volcano originates from the early 17th century, derived from the Italian name Vulcano, a volcanic island in the Aeolian Islands of Italy, which in turn comes from the Latin name Volcānus or Vulcānus, referring to Vulcan, the god of fire in Roman mythology. The set of processes and phenomena involved in volcanic activity is called volcanism, and the study of volcanism is volcanology. Cryovolcanoes (or ice volcanoes), particularly on some moons of Jupiter, Saturn, and Neptune.
Reader's Guide
Volcanoes are significant because they are primary agents of planetary change, shaping landscapes, creating new crust, and influencing climate. On Earth, most volcanic activity occurs underwater along mid-ocean ridges, where divergent plates create new seafloor. Convergent plate boundaries produce violent eruptions that form volcanic arcs, such as those in the Pacific Ring of Fire.
Hotspot volcanism, like that of the Hawaiian Islands, creates volcanic island chains as tectonic plates move over mantle plumes. The study of volcanoes, volcanology, helps scientists understand Earth's interior processes, plate tectonics, and planetary evolution. Volcanoes also pose hazards: large eruptions can inject ash and sulfuric acid into the atmosphere, causing volcanic winters and famines.
The classification of volcanoes as active, dormant, or extinct aids in risk assessment, though these categories can overlap. Beyond Earth, volcanoes are numerous on Venus and significant on Mars, and the definition of volcano has been proposed to include cryovolcanism on other planetary bodies. The term itself derives from Roman mythology, reflecting humanity's long fascination with these powerful natural features.
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Sources
Compiled from Wikipedia and the sources listed below. Text from Wikipedia is available under CC BY-SA 4.0; this entry is adapted from it.
- Wikipedia: Volcano (CC BY-SA 4.0).
- Word definitions: the Codexery glossary, each quoted from its Wikipedia article.
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