for National Geographic News
A recent discovery that the so-called "fixed" hot spot, which created the Hawaiian Islands, actually drifted southward between 81 and 47 million years ago is causing geologists to revise their descriptions of the interior workings of the Earth.
The findings stem from analysis of ancient lava flows found on four seamounts, or undersea mountains, in the Pacific Ocean. Rock samples from the seamounts were gathered during a two-month expedition to the Pacific Ocean in 2001. The project was co-led by John Tarduno, a researcher at the University of Rochester in New York.
Hot spots have long been defined as stationary plumes of molten material that sit beneath tectonic plates. As these plates pass by, molten material periodically spews through the crust to create a chain of volcanic mountains.
Since hot spots are easiest to locate where the crust is thinnest, they are commonly found on seafloors. There they create strings of seamounts and volcanic islands that are believed to tell the story of how the overlying plates moved over time.
A well-known example of this phenomenon is the Hawaii-Emperor Seamount chain that stretches some 3,000 miles (5,800 kilometers) along the floor of the Pacific Ocean from the Big Island of Hawaii to Alaska's Aleutian Trench.
William Siesser, a geologist at Vanderbilt University in Nashville, Tennessee, who is familiar with the work by Tarduno and colleagues, said the evidence clearly indicates the Hawaii hot spot moved between 81 and 47 million years ago.
"Recognition that the Hawaii hot spot has moved suggests the possibility that other hot spots may have moved as well," he said. "If so, this means that all estimates of global plate motion based on hot spot trails would have to be recalculated for the movement of the hot spots themselves."
Hawaii Hot Spot
The prevailing theory among geophysicists is that the Hawaii-Emperor Seamounts formed as the Pacific Plate moved over a fixed hot spot that today is located beneath the island of Hawaii and is responsible for the world's most active volcano, Kilauea.
The segment known as the Hawaiian Ridge, which includes the main Hawaiian Islands and a chain of islands, atolls, and seamounts known collectively as the Northwestern Hawaiian Islands, extends some 1,800 miles (3,000 kilometers) northwest across the Pacific.
At the end of the Northwestern Hawaiian Islands, the chain turns sharply northward and becomes the Emperor Seamounts, which stretch to their intersection with the Aleutian Trench at the Kamchatka Peninsula in Siberia.
According to most researchers, this sharp bend represents a rapid change in direction of the Pacific Plate as it passed over the fixed hot spot 47 million years ago.
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