A volcanic neck is solidified rock from a volcano’s conduit, exposed after erosion removes much of the surrounding structure. Beacon Rock illustrates how a former passage for magma can remain as a prominent landmark.
Compare its resistant core with the idea of a cone built from loose fragments. The surviving rock is an intrusive feature because it hardened underground, despite its connection to an eruption system. It belongs here because today’s silhouette may preserve the inside of a volcano rather than its original exterior.
Source / photo: NPS · Public domain. Resized. No claim to original U.S. Government works.