Hawaii's volcanic hotspot appears badly off-center

[n2doc]

By Scott Johnson | Published 22 minutes ago

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 results so far have been a bit confusing, challenging researchers to come up with some fresh ideas. It’s true that the most important discoveries often come from the least satisfying results, but sometimes they’re confusing simply because they’re wrong. Figuring out which category a study will end up in is a tricky business.

Back in April, Ars reported on some fantastic imaging of the mantle structure below Yellowstone, which produced a slightly different picture of the hotspot than had been seen previously. Last week in Science, a group reported using another innovative technique (adapted from the petroleum industry) to study the Hawaiian hotspot, and they also report a surprising departure from earlier results.

Analysis of seismic waves produced by earthquakes is the primary tool that geophysicists use to probe the Earth’s interior. Using data from the vast network of seismographs around the world, subtle changes in the direction or speed of seismic waves can be detected. After a great many earthquakes, differences in material properties (like temperature and density) can be spatially resolved. The whole process works somewhat analogously to a CT scanner in a hospital.
more

http://arstechnica.com/science/news/2011/06/hawaiis-volcanic-hotspot-appears-badly-off-center.ars