A hot plume of mantle material which may extend to the core boundary produces a hotspot.

Here's why:

* Mantle Plumes: These are rising columns of abnormally hot rock from deep within the Earth's mantle.

* Core Boundary: The boundary between the Earth's mantle and its core.

* Hotspot: A region of volcanic activity that is not associated with a plate boundary. Hotspots are thought to be caused by mantle plumes.

When these plumes reach the Earth's surface, they can cause volcanic activity, forming islands (like Hawaii) or large volcanic fields (like Yellowstone).