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Volcanoes

Types of volcanic eruption

A Hawaiian eruptionA Hawaiian eruptionWhen volcanoes erupt, lava, pumice, ash and gas are all expelled from a volcanic vent—an opening in the Earth’s crust. Eruptions range from gentle lava flows to violent explosions, and can be classified according to patterns of behaviour. The weakest type of eruptions are Hawaiian, followed by Strombolian, Vulcanian and Surtseyan. The strongest eruptions are Pelean, followed by Plinian. The most violent, supervolcanic eruptions, are called Ultra-Plinian—although none has occurred in historical times. A measure of eruptive strength is the Volcanic Explosivity Index (VEI), which ranges from 0 to 8. These eruption types are mostly named after famous volcanoes where that type of eruption has occurred.

Types of volcanic eruptionTypes of volcanic eruption
Lava fountains in a Hawaiian eruptionLava fountains in a Hawaiian eruption

Hawaiian

Hawaiian eruptions are named after the volcanoes on the Hawaiian Islands in the Pacific. These are the calmest types of eruption in which highly liquid lavas with low gas content steadily spew out of the ground. The lava cools to form the rock basalt, building up into broad shield volcanoes. Eruptions do not always occur at the main summit, as with other volcanic types, but often ooze out of vents or fissures in the gentle slopes instead. 

Pillow lava is typically formed when lava emerges from an underwater volcano or where lava flows into the ocean. The tongue of lava quickly gains a thin, solid crust as it hits the water and breaks up into pillow-shaped mounds of rock.

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