The expulsion of magma, ash, gas or rock fragments from a volcano onto Earth's surface, ranging from the slow, effusive outpouring of fluid lava to the sudden, violent explosion of gas-charged, viscous magma into a towering ash column. An eruption's character depends heavily on the magma's chemistry and gas content, and the largest explosive eruptions can inject enough ash and sulfur aerosols into the stratosphere to measurably cool global climate for a year or more.
Facts
PeriodicityVolcanoes are classed as active, dormant or extinct by their eruption history: a dormant volcano has not erupted since roughly the start of the Holocene, about 12,000 years ago, but may erupt again, while an extinct volcano has no remaining magma source and is not expected to erupt at all. 1 ScaleExplosive intensity is measured on the Volcanic Explosivity Index (VEI), which runs from 0 for gentle Hawaiian-type eruptions to 8 for supervolcanic eruptions; only about 60 VEI 8 eruptions are known from the geologic record over millions of years. 1 First DescribedThe first proposed natural, rather than supernatural, explanations for volcanic eruptions came from the Greek philosopher Anaxagoras in the fifth century BC, who attributed eruptions to a great wind, and from Seneca the Younger around 65 CE, who proposed combustion as the cause. 1 Identification
Distinguishing AppearanceA vent or fissure through which hot lava, volcanic ash and gases escape from a magma chamber below the surface, most often at diverging or converging tectonic plate boundaries. 1 Connections
Associated With
Volcanic eruptions are typically preceded and accompanied by volcano-tectonic earthquakes and seismic swarms caused by magma movement through the crust, a mechanistic link volcanologists use to forecast eruptions.
Lahar, Natural Phenomena Lahars are volcanic mudflows commonly triggered directly by an eruption, when hot pyroclastic material rapidly melts snow and ice or mixes with a volcano's crater lake and heavy rainfall on its flanks.
Pyroclastic flows are a direct, fast-moving product of certain explosive volcanic eruptions, formed when an eruption column collapses or a lava dome fragments, sending superheated gas and volcanic matter down the slope.
Volcanic lightning is generated within the ash-rich eruption plume itself, produced by charge separation among colliding ash particles and ice during an explosive eruption.
Sources
1. Volcano (Wikipedia)
WikipediaIntroduction
"Dormant" volcanoes have not erupted in a long time - generally accepted as since the start of the Holocene, about 12,000 years ago - but may erupt again.
Wikipedia 'Volcano', Eruption styles section
The intensity of explosive volcanism is expressed using the volcanic explosivity index (VEI), which ranges from 0 for Hawaiian-type eruptions to 8 for supervolcanic eruptions
Wikipedia 'Volcano', History of volcano understanding section
In the fifth century BC, Anaxagoras proposed eruptions were caused by a great wind. By 65 CE, Seneca the Younger proposed combustion as the cause
Wikipedia 'Volcano', lead section
A volcano is a vent or fissure in the crust of a planetary-mass object that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface.
View the Source Reader Challenges (0)
No disputes yet. Spotted an error or a better source? Open the first one.
Sign in to dispute this or suggest a correction.