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Vulcanian eruption An explosive type of volcanic eruption that occurs when the pressure of entrapped gases in a relatively viscous magma becomes sufficient to blow off the overlying crust of solidified lava. A characteristic feature of Vulcanian eruptions is that the material ejected comes from the older rocks in the volcanic edifice and new magma is not erupted. The activity is often long lasting, with the formation of volcanic gas and ash clouds and the violent ejection of solid angular fragments of all sizes. See VOLCANO. Compare HAWAIIAN ERUPTION; PELÉEAN ERUPTION; STROMBOLIAN ERUPTION; SURTSEYAN ERUPTION; and VESUVIAN ERUPTION.