A
volcanic plug, also called a
volcanic neck or
lava neck, is a
volcanic object created when
magma hardens within a
vent on an active volcano. When present, a plug can cause an extreme build-up of
pressure if rising volatile-charged
magma is trapped beneath it, and this can sometimes lead to an explosive eruption.
Glacial erosion can lead to exposure of the plug on one side, while a long slope of material remains on the opposite side. Such landforms are called
crag and tail. If a plug is preserved,
erosion may remove the surrounding rock while the erosion-resistant plug remains, producing a distinctive upstanding landform.