Here's why:

* Mantle plumes: These are upwellings of hot, buoyant rock from deep within the Earth's mantle.

* Volcanic hotspots: These are areas of volcanic activity that are not associated with plate boundaries. They are thought to be caused by mantle plumes.

When a mantle plume reaches the Earth's surface, the hot, molten rock (magma) erupts through the crust, forming volcanoes. These volcanoes can form chains of islands, like the Hawaiian Islands, or large volcanic fields, like the Yellowstone Caldera.