HOT SPOTS of volcanic activity don鈥檛 turn up just anywhere. Geologists have
discovered that the hottest hot spots are concentrated in two narrow bands
encircling the globe at mid-latitudes, and now they are struggling to explain
why.
Hot spots lurk under the Earth鈥檚 surface like candle flames, heating up small
areas of the mantle and causing volcanic activity. Geologist Douglas Oliver from
the Southern Methodist University in Dallas looked at the distribution of the 47
biggest hot spots on the planet, such as the one under the Hawaiian islands.
Weighting them by the amount of heat they produce, he found that more than half
of the activity occurs at latitudes between 10 and 30 degrees in both the
northern and southern hemispheres. 鈥淭hat鈥檚 quite a narrow band,鈥� says Norman
Sleep, a geophysicist at Stanford University. Oliver presented the results last
week at a meeting of the Geological Society of America in Reno, Nevada.
Geologists believe that hot spots form when hot material from deep inside the
Earth makes its way to the surface through channels left behind in the mantle by
larger plumes of molten rock. 鈥淚f heat is the only thing generating hot spots
and mantle plumes, then they should be random and uniformly distributed,鈥� Oliver
says. 鈥淏ut they鈥檙e not.鈥�
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Oliver thinks the distribution might be a sign of circulation in the liquid
outer core. But Thorne Lay, a geophysicist from the University of California at
Santa Cruz, says it鈥檚 a 鈥渞eal leap鈥� to relate what鈥檚 going on in the core to
patterns on the surface.
