The volcanic landform formed when the more resistant pipe remains after most of the cone has been eroded is called a volcanic neck or plug.

Here's why:

* Volcanic Pipe: This is the vertical conduit that carries magma from the Earth's interior to the surface.

* Volcanic Cone: The cone is built up over time by eruptions, primarily composed of ash, lava, and other ejected material.

* Erosion: Over long periods, weathering and erosion can wear down the cone, exposing the more resistant pipe.

* Volcanic Neck/Plug: The hardened, solidified magma within the pipe is more resistant to erosion than the surrounding rock. This results in a tall, often columnar, structure that stands out from the surrounding landscape.

Examples of volcanic necks include:

* Shiprock, New Mexico (USA)

* Devil's Tower, Wyoming (USA)

* The Giant's Causeway, Northern Ireland