Mantle hotspots are believed to explain unique geological phenomena—like the formation of the Hawaiian island chain, and the history of volcanism that has culminated in the Yellowstone caldera. At hotspots, stationary plumes of molten rock periodically punch through the crust as tectonic plates slide over, creating a linear chain of eruptions on the surface. It’s an idea taught in introductory geology courses, but the details of the process are actually a source of significant scientific controversy. There’s an excellent reason for that—if you’re standing on the big island of Hawaii, it’s difficult to get a good look at the rocks 100 miles below your feet. But, as always, the scientific process rolls on, and geophysicists have recently brought new tools to bear on the problem.
The researchers used variation in the depths of these mineral horizons to infer temperature—a higher temperature will slightly deepen that transition boundary, and vice versa. This in itself is not new, but the team managed to create a three-dimensional image with much higher resolution than was previously possible. Their method picked up a hot region right below the Hawaiian Islands (so far, so good), but whereas earlier attempts at seismic imaging indicated that this hot region continues more or less straight downward, they saw something very different. They found evidence of a large body of hot material roughly 1,000 km to the west of Hawaii. The structure below this body was beyond the lower limits of their imaging (about 1,000 km depth), leaving the ultimate nature of the feature unsolved.
Personally, this explains quite a bit.