A thorough examination of tiny crystals of zircon, a mineral found in rhyolites, an igneous rock, from the Snake River Plain has solidified evidence for a new way of looking at the life cycle of super-volcanic eruptions in the long track of the Yellowstone hotspot, say University of Oregon scientists.
Many people do not realize that the US is riding over one of the major hotspots in the world, a place where the mantle directly exits into the world we live in.
The land mass essentially plugs up the hotspot, like a cork in a champagne bottle. The pressure builds up and the magma spreads out under the Earth, melting more of the crust, until the cork pops and the huge pressure built up pushes out huge amounts of magma.
This is the Yellowstone supervolcano. The caldera where the lava comes out can be 20 miles or more in diameter. They produce a huge amount of material – some of the basalts in the Snake River Plain are thousands of feet thick. They are not explosive but ash fall can reach 1000 miles away and be over a foot deep.
It is a nightmare to think about. So, figuring out when the next major eruption occurs is a nice thing to understand. And this new report suggests we have a lot of time.
What they did was look at the isotope distribution found in certain minerals found in the basalts. In particular they looked at an isotope of oxygen. They were able to examine the ratio of the O18 (8 protons and 10 neutrons) isotope with the most common form, O16 (8 protons and 8 neutrons). This would give them an idea of how long the magma was parked in underground reservoirs before finding itself on the surface. Mixture with rainwater would change the ratio, so they could get an idea of how rapid volcanic calderas and basalt deposition were.
If it was rapid, the ratio would be relatively homogenous throughout the basalt, as there was little time to react with ground water. Essentially they could get a detailed look at the timing of multiple eruptons.
By getting a detailed look, they could recreate the eruption cycle of the hotspot when that part of Idaho was on top of it.
From that data, and a lot more from other areas of the Snake Rive Plain, it appears that Yellowstone is unlikely to erupt in a major explosion anytime in the next million years or so.