Thursday, September 19, 2013

Giant reservoir of magma under Ethiopia may explain how continents break apart

In the desert of northern Ethiopia, there's a great rift in the ground which has long thought to have been the starting point of a new ocean, but a recent discovery has scientists wondering if they called that right, or if they're instead seeing a whole new kind of feature forming.
The Afar Rift has been called 'an ocean in the making', as this is where the continents of Africa and Asia are slowly spreading apart from one another. Presumably, sometime in the future, the continents would get far enough apart that water from the Red Sea and Gulf of Aden would rush in and we would be witness to the birth of what would someday become a new ocean. Scientists have seen similarities between the Rift and the Mid-Atlantic Ridge, where magma wells up to make the ocean floor spread. However, a research team recently discovered a massive blob of magma, measuring around 500 cubic kilometres in size, lurking deep beneath the region, and that's unlike anything they've seen before.

When magma rises up from deep down under mid-ocean ridges and volcanoes, it tends to form reservoirs just beneath the surface, and these reservoirs act to feed the activity of the ridge or volcano. The magma doesn't stay deeper down in the mantle because it's too buoyant — it gets forced upwards into the crust by the pressures around it.
In the case of the magma under the Afar Rift, though, it's quite far down, roughly 10 kilometres below the surface, and the blob is huge — extending downward to a total depth of around 35 kilometres and it's roughly 30 kilometres wide. Also, this apparently isn't just a recent development, as the researchers say the volume of magma implies that it's been there for tens of thousands of years.
Although this new discovery has sparked a lot of discussion amongst geologists and geophysicists, the researchers have one possible explanation for what they're seeing.
Reservoirs of magma that gather near the surface feed volcanoes and mid-ocean ridges, and these tend to provide these formations with 'fuel' to cause localized or sporadic events. A huge magma reservoir that stays deep down in the mantle, like this one, could be what causes enough strain to build up in the crust to actually split continents apart.