800-Mile-Wide Hot Anomaly Found Under Seafloor off Hawaii

Photograph by Patrick McFeeley, National Geographic

Dave Mosher

for National Geographic News

Hawaii‘s traditional birth story—that the volcanic islands were, and are, fueled by a hot-rock plume running directly to Earth’s scorching core—could be toast, a new study hints.

(See pictures of a recent eruption Hawaii’s Kilauea volcano.)

Scientists say they’ve found solid evidence of a giant mass of hot rock under the seafloor in the region. But it’s not a plume running straight from the core to the surface—and it’s hundreds of miles west of the nearest Hawaiian island.

Until now, the researchers say, good seismic data on the region has been scarce, so it was tough to question the traditional explanation: that a stream of hot rock directly from around Earth’s core formed the 3,100-mile-long (5,000-kilometer-long) chain of islands and undersea mountains in the Pacific Ocean.

As Earth’s crust slid over the plume, as if on a conveyor belt, the erupting seafloor built mounts, mountains, and islands out of layers of cooled lava over tens of millions of years—or so the conventional wisdom goes.

But after analyzing 20 years’ worth of earthquake data, geophysicists say they’ve found an 800-mile-wide (1,300-kilometer-wide) region of hot rock in the Hawaiian region—but nothing beneath the Big Island of Hawaii. The island, the youngest in the chain, is traditionally thought to be above the purported plume.

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