The Hawaiian Hotspot

Most volcanoes form near the edges of the Earth's tectonic plates, the huge pieces of rock that form the planet's surface. The Hawaiian Islands, however, lie in the middle of the Pacific Plate, thousands of kilometers from the nearest plate boundary. In the 1960s, the geologist J. Tuzo Wilson proposed an explanation: a hotspot, a place where very hot material rises from deep inside the Earth and melts the rock above it.

According to Wilson's idea, the hotspot stays in roughly the same place while the Pacific Plate slowly moves over it, at a rate of several centimeters per year. [A] Each time a part of the plate passes over the hotspot, a new volcano forms. [B] As the plate continues to move, the volcano is carried away from its source of magma, stops erupting, and slowly wears down. [C] The result is a chain of islands that become older the farther they are from the hotspot. [D]

The evidence fits this explanation well. The island of Hawaii, at the southeastern end of the chain, is the youngest and still has active volcanoes. The islands to the northwest, such as Kauai, are millions of years older, and their volcanoes have long been extinct. Southeast of the island of Hawaii, an underwater volcano is already growing on the sea floor. It may one day become the newest Hawaiian island, though probably not for tens of thousands of years.