The Hawaiian Islands are in the Pacific Ocean, and Yellowstone National Park is near the center of North America. Other than millions of tourists, what could they possibly have in common? They're both above hot spots — places where a plume of hot solid rock rises through Earth's mantle, partially melts, and generates magma. As an overlying plate travels across a hot spot, a chain of volcanoes forms. The ages and orientation of the volcanoes record the plate's past motion.

• Hawaiian Islands
• Yellowstone National Park