Study says 'hotspot' that created Island chain drifted

By Kevin Dayton
Advertiser Staff Writer

A new study suggests the subterranean "hotspot" that fed the volcanoes and formed the Hawaiian island chain isn't stationary, a finding that could help unravel longstanding puzzles in earth science.

The 3,800-mile Hawaiian Ridge-Emperor Seamounts chain of volcanoes that includes the Hawaiian Islands was formed by a plume of magma surging up from hundreds of miles below the Pacific Plate. Scientists believe as the tectonic plate moved, it transported each new volcano away from the hotspot that created it.

Now a new study co-authored by 11 scientists from the United States, Japan and Canada has concluded that not only has the Pacific Plate been moving, but the underlying well of magma that fed the volcanoes drifted as well.

The study, which appeared in yesterday's online version of the journal Science, concludes that the hotspot probably moved southward at a rate of 44 millimeters a year between 47 million and 81 million years ago.

Peter Cervelli, research geophysicist at Hawaiian Volcano Observatory, said the findings don't change the basic concept of how the Hawaiian Islands formed, but they are startling because the hotspot that created the Islands was believed to be nearly fixed.

Previous studies had suggested there might be some movement in the hotspot, but the movement was believed to be much slower.

"Nobody ever thought that the hotspot would be moving at 44 millimeters a year," Cervelli said.

Geophysicist John A. Tarduno of the University of Rochester was lead author of the study, which tested a mineral called magnetite taken from four submerged Seamounts volcanoes to determine where the volcanoes were formed.

Magnetite residues in hot magma align with the Earth's magnetic pole and become locked in place as the lava cools, which allowed scientists to calculate the latitudes where the volcanoes were created.

From that information, scientists calculated how far the hotspot had moved.

If the study findings prove to be correct, Cervelli said it might help explain the curious bend in the Hawaiian Ridge-Emperor Seamounts that stretches from the Big Island to Alaska's Aleutian Trench.

The Hawaiian Ridge, which includes the Hawaiian and Midway islands, extends for about 1,800 miles northwest before meeting the Emperor Seamounts, an older chain that veers off in a more northerly direction for more than 1,000 miles.

If the volcano chain were formed exclusively by movement of the Pacific Plate, that raises the question of what caused the bend in the chain, Cervelli said.

"It has always been a big puzzle to people how you take something the size of the Pacific Plate and just turn it on a dime," Cervelli said. "To think about the forces that would be required to do that, it really is astonishing."

The new study may have part of the answer: Perhaps the bend in the Island chain can be attributed to the movement of the hotspot, rather than movement of the Pacific Plate, he said.

Reach Kevin Dayton at kdayton@honoluluadvertiser.com or (808) 935-3916.

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