Heat plumes rising from the core – mantle boundary cause volcanoes at the Earth's surface. 

We call these regions hot spots. The tracks made by hot spots as they create volcanoes 

on the Earth's surface enable scientists to approximate plate motion relative to the mantle.

 

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Press the green button to see how the Yellowstone Hotspot has moved relative to the lithospheric plate.

 

Because the hot spots move slowly relative to one another at a rate 10 times slower than lithospheric plates move, they can be used to analyze the relative motion of the overlying plates. The length of each arrow indicates the amount of movement over 50 Ma. The numbers indicate plate speed.