May 30th, 2012 by James Ayre
Super-volcanos form and erupt much more quickly than previously thought, according to a new study from researchers at Vanderbilt University.
Super-volcanos and super-eruptions are referred to as super because of their massive scale, more than 100 times the size of an eruption like Mount St. Helens. They release tremendous amounts of gas, ash, and lava; enough to blanket entire continents in ash and darken the sun for decades. There is evidence that the Toba super-eruption 74,000 years ago nearly killed off the human species.
Geologists had previously thought that super-eruptions only occurred 100,000-200,000 years after forming. Evidence from the new study suggests that, after a giant magma pool forms, it may erupt after only a couple hundred years.
“Our study suggests that when these exceptionally large magma pools form they are ephemeral and cannot exist very long without erupting,” said Guilherme Gualda, the assistant professor of earth and environmental sciences at Vanderbilt University who directed the study.
The study was performed by examining the remnants of the Bishop Tuff, the Long Valley super-eruption that occurred 760,000 years ago in California. Using the latest methods for dating the process of magma formation, the researchers found several different lines of evidence indicating that the magma pool formed only a couple hundred to a couple thousand years before erupting. The Long Valley super-eruption covered half of North America in thick ash.
The magma pools that supply super-eruptions are generally shaped like pancakes, 10-25 miles in diameter and 1-3 miles deep. As they start to form, the molten rock in them is largely free of crystals and bubbles. As they grow, crystals and bubbles form and gradually change the physical and chemical properties of the magma, and then when the eruption occurs this process stops.
As far as geologists can tell, there aren’t any giant pools of magma capable of producing super-eruptions on the planet right now. The researchers think that this is because they form and erupt so rapidly.
According to the team, the previous 100,000-year estimates were just caused by the method geologists had used, and aren’t accurate. The measurements used previously were zircon crystals which are common in volcanic rocks and contain radioactive elements that decay at a stable rate. They are useful because they can survive most geological processes. However, since they survive the heat and pressure in a magma chamber, they are not good at recording the lifetimes of crystal-poor magma bodies.
So the researchers used the crystallization rates of quartz in the deposits to get information about the lifespans of the magma bodies. They came up with four independent lines of evidence indicating that they definitely took less than 10,000 years and most likely between 500 and 3,000 years to erupt. They suggest that the zircon crystal measurements record the changes that are required to occur in the crust before the magma bodies can form.
The researchers suggest that with the short formation period of these super-eruptions we should monitor the areas where they are likely to occur. Such as Yellowstone, where there has been significant ground swelling in the past couple of years.
Source: PLoS ONE
Image Credits: NASA/JPL, Elements 2008
Keep up to date with all the most interesting green news on the planet by subscribing to our (free) Planetsave newsletter.