Volcanic Hot Spots.

The article discusses research on volcanic hot spots. The apparent chronology of the Hawaiian archipelago of volcanoes and seamounts, along with evidence culled from the chemistry of their respective lavas, led some scientists decades ago to speculate that the islands were formed as the ocean crust supporting them inched northwest over an abnormally hot spot in Earth's mantle. As these geologists saw it, that hot spot, now under Kilauea, is generated by an upwelling zone of hot rock, called a mantle plume, that intermittently pierces Earth's crust blowtorch style. Because hot spots lie deep within Earth, researchers who developed the mantle-plume hypothesis had a tough time convincing skeptical colleagues. To be sure, plumes may not explain every volcanic island and seamount. Now, however, researchers are performing sophisticated analyses of seismic waves that have traveled deep within the mantle beneath Hawaii as well as within some other volcanically active regions. The result is strong evidence that plumes are major actors in sculpting Earth's volcanoes. By analyzing patterns of seismic waves that travel through rock as pressure pulses, which seismologists call P-waves, researchers identified 32 broad regions in the mantle worldwide where seismic waves travel more slowly than average. Six of those regions-those that lie beneath Ascension Island in the South Atlantic, the Azores and Canary Islands in the North Atlantic, and Easter Island, Tahiti, and Samoa in the Pacific-clearly extend all the way to the core-mantle boundary.