New research has found that the hotspots that create volcanic islands like those of Hawaii, Iceland, or the Galapagos are surprisingly cool, and may not originate from active lava plumes in the earth's deep mantle.
The research has been published in the 'Science Journal'.
The findings challenged the classical plume theory of the origin of hotspots. There are two types of volcanism observed on the Earth's surface. The dominant type occurs where tectonic plates meet and is driven by the large-scale circulation of the planet's mantle.
The other type occurs as isolated intraplate "hotspot" volcanoes, which are thought to be fed by hot, active upwelling plumes rising up from the deep mantle, with excess temperatures (Tex) roughly 100-300 degrees Celsius higher than those located along mid-ocean ridges.
However, Tex estimates for volcanic hotspots are limited in geographical coverage and are often inconsistent for individual hotspots. To determine whether oceanic hotspots are indeed hotter than ridges, Xiyuan Bao and colleagues converted seismic velocity measurements from oceanic ridges and hotspots into temperature.
Contrary to previous assumptions, Bao found that some hotspots are surprisingly cool. According to the authors, while 45 percent of plume-fed hotspots are hot (Tex being 155 °C or higher), roughly 40 percent are not hot enough to act up well from the deep mantle.
What's more, 15 percent are cold (Tex 36 °C or lower.) Bao suggested that cooler hotspots may instead originate at upper mantle depths or are fed by deep plumes that are entrained and cooled by small-scale convection dynamics.
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