Forces of Nature: ThinkQuest 2000 (Team #C003603)
http://library.thinkquest.org/C003603/english/volcanoes/volcanichotspots.shtml
Many volcanoes occur on the plate boundaries, where much geologic activity is going on. However, other volcanoes are found in the main body of a plate, far away from the boundaries. These areas are built above hot spots, or thermal plumes rising through the mantle. Certain thermal plumes have remained in the same place for millions of years. It’s just the crust that has moved over them.