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Tiny volcanoes spring from underwater cracks

Miniature eruptions leak information about the mantle below.

A cluster of tiny underwater volcanoes off the northeastern coast of Japan has demonstrated that the Earth's inner mantle may not be as solid as was once thought. In a study published online this week by Science1, a team of researchers provides evidence that regions of the mantle contain molten material that can leak out on to the surface through cracks in the plate above.

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Posted by Nicola Jones on July 27, 2006 06:20 PM |

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The crack idea has been around for at least a decade (Sandwell and others). I don't think it is a bad one, but the first thing I do when ever I hear the mechanism proposed is look at their ocean-bottom surveys for any discernible cracks in the seafloor that correlate with the volcanoes. I don't see them here.

If flexing of the plate really is the key, then maybe the upwarp creates room for upwelling into the upwarp, triggering decompression melting. Plate underside topography might be worth taking note in relation to non-hotspot volcanism. E.g., (shameless plug) my 2002 paper in JGR suggests that asthenosphere moving up the underside of the Pacific plate towards the ridge may have triggered melting that created the Puka puka chain.

Posted by: James Conder | August 1, 2006 04:38 PM

The research on the petit spots indicates clearly that the asthenosphere may be molten. The only hindrace to accepting the theory is the expectation that the melts would creep upwards through the cracks and would eventually solidify.

But my question is why should anyone expect that the molten materials would creep up at all? If gravity is pulling all the materials towards its centre, it is expected either to go down or, at best, stay where it is. It would only go up, if it is forced by something else to go up. If we go by this logic, then asthenosphere is never going to be depleted. I have discussed this in detail in the paper that I submitted to Nature for review(on 19-Sept-2006).

Posted by: Promita Chakraborty | September 24, 2006 03:22 AM

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