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See Inside January 2008

Hot Spots Unplugged

Long considered fixed founts of molten material from deep within the planet, hot spots now join the list of moving parts



RENE FREDERICK Getty Images

Where was the cone? We had just pulled up our drill pipe, replaced its worn drill bit, and lowered it back down to the seafloor, a mile under our ship. Crowding into the control room, we watched images from a camera attached to the end of the pipe, looking for a cone we had left as a marker to guide the pipe back to the hole we were drilling. The team had gone through this exercise many times before. Usually we would see a fish swim by or a squid momentarily grab the pipe, and then the cone would appear. This time we saw only fish and squid. What had gone wrong?

We had come to the northwestern Pacific Ocean to extract core samples from the submerged extinct volcanoes, known as the Emperor seamounts, that form the northernmost leg of the Hawaiian-Emperor volcanic chain. The neat pattern formed by the chain is apparent on any world map and, along with the jigsaw-puzzle shape of South America and Africa, has long stood as a testament to plate tectonics—the principle that our planet’s surface is an ever shifting mosaic of rocky puzzle pieces. Not only do the islands and seamounts form an uncannily straight line for 3,500 kilometers across the Pacific, their rocks get steadily older as you move northwest up the chain: from the Big Island (which is still growing) through Maui, Oahu, Kauai and on up to the Midway atoll, whose long-extinct volcano has subsided so much that it barely sticks up above the sea surface. Past Midway, the line makes a sharp bend, continuing northward along the Emperor seamounts and stretching nearly as far as the tip of the Aleutian Islands.

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