A volcanic neck, also called a lava neck or volcanic plug, is a cylindrical-shaped volcanic landform created when magma hardens inside the vent of a volcano, according to the University of Wisconsin. Examples of volcanic necks include Devil's Tower in Wyoming, Lizard Head in Colorado and Morro Rock in California.
A volcanic neck is referred to as a plug because unless the neck or plug is preserved, an active volcano can build up much pressure from trapped magma, which can trigger an explosive eruption. Once preserved, the volcanic neck or "plug" becomes erosion resistant, even as the surrounding rock erodes, exposing the volcanic neck. A popular tourist destination in Sri Lanka, Sigiriya or "Lion's Rock," is a volcanic neck with ancient castle ruins sitting atop on the flat surface.