Monday, January 22, 2007

Mantle plumes

Here's a "hot" controversy (in more ways than one) that you don't hear about often, unless you're a geophysicist. Geophysics doesn't get as much attention as many other topics in science, such as black holes, evolution, etc. But there are nevertheless very interesting open – or at least, controversial – questions in the field. One of these has to do with "mantle plumes".

A mantle plume, according to Wikipedia, is "an upwelling of abnormally hot rock within the Earth's mantle". For many years, the conventional wisdom has been that such plumes, when breaking through the Earth's crust where it is thinnest, on an ocean floor, are responsible for the formation of island chains, such as the Hawaiian islands. However, some skeptics have questioned whether plumes are really necessary to explain volcanic islands. Now there appears to be more evidence that the traditional idea is correct:

Hotspots or Not? Isotopes Score One for Traditional Theory
A running battle has evolved over the last 30 years concerning hotspots: One camp claims it is not necessary to invoke mantle plumes to explain such volcanic islands, and the other camp - a sizeable portion of the geological community - supports mantle plumes as the most internally consistent explanation for a wide variety of data.

A study published this week in the journal Nature raises the bar for plume opponents by finding a close correlation between modeled and observed ratios of uranium-series isotopes across eight island locations. The study strongly supports upwelling of mantle material as the source of these islands. Moreover, the detailed data allow researchers to estimate the change in temperature, speed and size of mantle plumes at the locations studied.

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