Key Concepts

• Volcanic hotspots, such as the one creating the Hawaiian Islands today, have long been considered fixed points in the scheme of slowly moving tectonic plates that form the earth’s outer surface.
• New evidence that hotspots can instead be mobile comes from study of Hawaii’s chain of islands and submerged defunct volcanoes. The chain’s elbowlike geometry has traditionally been attributed only to a change in the motion of the Pacific plate. Now it is in part credited to hotspot migration, itself an expression of movement in the earth’s mantle deep below the surface.
• Implications include textbook rewrites, as well as new views on paleo­climate records and the stability of the entire earth on its spin axis.

 —The Editors

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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