Scientists think massive volcanism triggers magnetic reversals. I think they have it backward.
Scientists at the University of Liverpool have discovered that variations in the long-term reversal rate of the Earth’s magnetic field may be caused by changes in heat flow from the Earth’s core.
The scientists focused on the time interval between around 200 and 80 million years ago, when magnetic polarity started reversing very frequently – up to 10 times every million years. However 50 million years later, it stopped reversing altogether for nearly 40 million years. (The Liverpool scientists appear to be ignoring the 11,500-year cycle of magnetic excursions altogether.)
“We suspect that this process … changed the pattern of heat flowing out of the core in such a manner as to cause the magnetic field to first become less stable, with lots of reversals, and then become much more stable – and stop reversing,” said Dr Andrew Biggin, from the University’s School of Environmental Sciences.
The team conjectures that this big drop in the frequency of reversals may also be related to a similar decrease in the number of ‘large igneous provinces’ (LIPs)* or concentrated outpourings of magma from the Earth’s core, 50 million years later.
The last LIP happened around 16 million years ago and produced the Columbia Plateau in the North West US.
I think they have it backward. I think the magnetic reversals triggered the volcanic activity, not the other way around.
See entire article:
http://www.terradaily.com/reports/Scientists_probe_link_between_magnetic_polarity_reversal_and_mantle_processes_999.htm
Thanks to Wanda for this link
* According to Nature.com, large igneous provinces (LIPs) are known for their rapid production of enormous volumes of magma (up to several million cubic kilometres in less than a million years), for marked thinning of the lithosphere, often ending with a continental break-up, and for their links to global environmental catastrophes.
The Siberian Traps and Deccan Traps, where huge amounts of magma poured out of the earth, were both synchronous with large mass-extinction events – the Great Permian extinction and the dinosaur extinction.
http://www.nature.com/nature/journal/v477/n7364/full/nature10385.html
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This got me to looking and I found this interesting hypothesis:
http://www.newgeology.us/presentation25.html
It seems that what scientists have measured – the bookmatched magnetic stripes on the seafloor – may not be exactly what they assume it to be, that is, corresponding stripes of opposite magnetic polarities. Differences in depth(of magmatic deposition), changes in spread rates, and rotation of plates all serve to confuse the findings! Yet there is no doubt that changes in magnetic polarity do occur, whether wholesale flips, or prolonged excursions with eventual return to ‘normalcy’, the evidence is there.
It reminds me of the Chicken and the Egg. Whether changes in Magnetic Field Strength/Orientation cause Volcanism, or whether Volcanism causes changes in MFS/O. These forces obviously affect each other, and are ultimately inseparable. I tend to agree with your view however, that magnetic field strength is the likely driver of volcanism, and that volcanism-while having a slight affect upon magnetic distribution within Earth’s cores(solid,liquid) is perhaps less likely to have an effect upon the planet’s overall magnetic orientation.