éruption

Éruption, from the Latin erumpere via French, denotes the act of bursting forth, appearing suddenly, or breaking out. In English usage, eruption most often refers to natural or medical phenomena in which material or activity surges to the surface or outward from a concealed source.

Volcanic eruption is the best-known sense: the rapid expulsion of magma, volcanic ash, pumice, and gases from a vent. Eruptions can be effusive, producing lava flows that spread across the landscape, or explosive, ejecting ash clouds and pumice high into the atmosphere. Eruptive activity is driven by pressure from rising magma, gas buildup, and rock fracturing. Hazards include lava flows, ashfall, pyroclastic surges, and tsunamis when nearby bodies are displaced by eruption or landslides. Monitoring uses seismic data, ground deformation measurements, and gas emissions to forecast eruptive phases and assess risk to populations and aviation.

In medicine, an eruption refers to a skin or mucous membrane rash or lesion that appears suddenly. Eruptions can be vesicular, maculopapular, or pustular and have numerous causes, including infections, allergies, medications, and autoimmune conditions. Evaluation considers morphology, distribution, accompanying symptoms, and patient history; treatment targets the underlying cause and may include topical or systemic therapies to relieve symptoms.

The term also appears in metaphorical uses, describing sudden, widespread emergence of events, emotions, or phenomena. Across disciplines, éruption is a versatile descriptor for rapid outward manifestation from an inner source.