In many locations the hot molten magma from deep within the Earth rises up through the crust to reach the surface. This sometimes happens in the middle of plates. When a hot spot forms in the middle of a plate, it remains constant, as the plate continues to move over it. The result is that a trail of volcanoes is left behind, with older volcanoes moving away from the hot spot, and newer ones forming over top of the hot spot.
One of the most famous hot spots on Earth are the Hawaiian Islands. The oldest islands found in the Hawaiian Island chain consist of mostly dead volcanoes. These volcanoes were active millions of years ago, but the moving crust of the ocean floor has carried them away the hot spot that feed the volcanoes. The newest island is the big island, which today has two active volcanoes. These volcanoes are feed by the same hot spot that used to feed the dead volcanoes on older islands. Millions of years from now, it is likely that additional islands will form over the same hot spot, as the Earth’s crust carries the big island away from the hot spot it know sits on.