A volcanic conduit that has solidified and been exposed by erosion is called a volcanic neck.

Here's a breakdown:

* Volcanic conduit: The pathway through which magma travels from a magma chamber to the surface.

* Solidification: After an eruption, the magma within the conduit cools and solidifies.

* Erosion: Over time, the surrounding rock is eroded away, exposing the solidified conduit.

Volcanic necks are often more resistant to erosion than the surrounding rock, which is why they stand out as prominent features. Examples of volcanic necks include Shiprock in New Mexico, Devil's Tower in Wyoming, and the volcanic plug at the center of Crater Lake in Oregon.