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volcanoes … standard theory awry?

15 September 2014

In this instance, mainstream theory is being revised in a mainstream kind of way – the story is at http://phys.org/print329398219.html

According to researchers in a paper in PNAS (Sept 8th 2014) the consensus model is upside down. Volcanoes erupt when magma gushes out via narrow jets from deep inside the Earth – mantle plumes. Seismology data seems to show these jets do not exist. Heat from deep inside the Earth is thought to generate jets of hot magma that gush up to the surface. The jets are regarded as a sought of pipe structure which transfer heat from the core and lower mantle upwards. When the pipes reach the surface they are said to create hot spots. It is assumed the upper mantle is a sort of liquid sludge on which the rocky crust floats. The crust itself is divided up into plates which move around and grind against each other. As the plates drift across hot spots a chain of volcanoes is thought to form – such as the Hawaii Islands and Samoa. It is the magma creeping through the rocky crust that creates volcanoes.

Seismic stations have become more common in recent years, all around the world. No evidence of mantle plumes have been found. Instead, large slow upward moving chunks of mantle up to a 1000km wide have been detected – not exactly pipes.

In the consensus model the heat is forced upwards via jets of magma – but is counter balanced by a slower decreased motion of cooled chunks of mantle from near the surface. The new theory is that it is the surface cooling that is responsible – from than the heat from the core. It turns the theory upside down – but basically keeps the consensus intact. Sinking material from near the surface, known in the literature as slabs, causes broad upwellings from deep inside the Earth – a convection model first proposed over a 100 years ago by Lord Kelvin. Material near the crust sinks as it cools and displaces material depper in the mantle, forcing it upwards. The researchers still have faith in Plate Tectonics it would appear – so this is not as revolutionary as it could be. The upwelling magma reaches the bottom of the plaes or fissures that run through them and is squeezed out dur to pressure from one plate against another, or simply by the fact they are moving. In other words, magam has gushed out by volcanoes, has an origin in the upper mantle rather than deep inside the Earth. See www.pnas.org/cgi/doi/10.1073/pnas.1410229111

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