What is Volcanic plug?
[[File:Rocher St Michel à Aiguilhe.JPG|thumb|180px|right|[[Saint Michel d'Aiguilhe]] chapel, on top of a volcanic plug in [[Le Puy-en-Velay]], France.]] [[File:Sigiriya AS1.jpg|thumb|180px|[[Sigiriya]] Rock Fortress, [[Sri Lanka]]]] A '''volcanic plug''' is a [[landform]] created when [[volcano|volcanic]] [[magma]] hardens inside a [[Volcanic vent|vent]] on an [[active volcano]]. They are sometimes called volcanic necks or ''puys''. The plug is revealed when the surrounding land is [[erosion|eroded]].<ref>Francis, Peter 1993. ''Volcanoes: a planetary perspective''. Oxford University Press. p358. {{ISBN|0-19-854033-7}}</ref> As it forms, a plug may cause an extreme build-up of [[pressure]] if [[gas]]-charged [[magma]] is trapped beneath it. This sometimes leads to an explosive eruption. But if the explosion does not occur, then the volcano becomes a solid block made of hard material. The plug is usually harder than the surrounding rock. [[Glaciation|Glacial]] erosion can lead to exposure of the plug on one side, while a long slope of material remains on the lee side. Such landforms are called [[:en:Crag_and_tail|crag and tail]]. If a plug is preserved, [[erosion]] may remove the surrounding rock while the erosion-resistant plug remains. This is what produces the distinctive upstanding landform. == Related pages == *[[Intrusion]] == References == {{reflist}} [[File:Edinburgh Castle From Princes Street Garden 001.jpg |thumb|250px|left|[[Edinburgh Castle]] in [[Scotland]] is built on an ancient volcanic plug.]] [[Category:Volcanoes]] [[Category:Volcanic landforms|*]]