Reseachers have finally discovered the causes for volcanic 'super-eruptions' — one of the most catastrophic natural events on Earth.
The violent explosions, which occur about every 100,000 years, are now thought to be caused by a combination of temperature and the shape of the magma chamber inside certain volcanoes.
Scientists at Oregon State University presented the finding at the annual meeting of the Geological Society of America in Minneapolis.
Patricia Gregg, lead author on the modelling study, said the creation of a 'halo' of rock around the magma chamber allows the pressure to build over tens of thousands of years, resulting in extensive uplifting in the roof above the magma chamber.
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| Catastrophic: The Huckleberry Ridge eruption of present-day Yellowstone Park about two million years ago was more than 2,000 times larger than the 1980 eruption of Mount St. Helens in Washington |
Eventually, faults from above trigger a collapse — and then eruption. She said: 'You can compare it to cracks forming on the top of baking bread as it expands.'
'As the magma chamber pressurises at depth, cracks form at the surface to accommodate the doming and expansion.'
She added: 'Eventually, the cracks grow in size and propagate downward toward the magma chamber. 'In the case of very large volcanoes, when the cracks penetrate deep enough, they can rupture the magma chamber wall and trigger roof collapse and eruption.' The eruption of super-volcanoes dwarfs the eruptions of recent volcanoes and can trigger planetary climate change by inducing Ice Ages and other impacts.
One such event was the Huckleberry Ridge eruption of present-day Yellowstone Park about two million years ago, which was more than 2,000 times larger than the 1980 eruption of Mount St. Helens in Washington.
'Short of a meteor impact, these super-eruptions are the worst environmental hazards our planet can face,' Gregg said.
'Huge amounts of material are expelled, devastating the environment and creating a gas cloud that covers the globe for years.'
Previous modelling efforts have focused on an eruption trigger from within the magma chamber, which scientists thought would leave a visible trace in the form of a precursor eruption deposits, according to Shanaka 'Shan' de Silva, an OSU geologist and co-author of the study.
Yet there has been a distinct lack of physical evidence for a pre-cursor eruption at the site of these super-volcanoes.
The model suggests the reason there may be no precursor eruption is that the trigger comes from above, not from within, de Silva pointed out.
'Instead of taking the evidence in these eruptions at face value, most models have simply taken small historic eruptions and tried to scale the process up to super-volcanic proportions,' de Silva said.
'Those of us who actually study these phenomena have known for a long time that these eruptions are not simply scaled-up Mt. Mazamas or Krakataus - the scaling is non-linear. The evidence is clear.'
It takes a 'perfect storm' of conditions to grow an eruptible magma chamber of this size which is one reason super-volcano eruptions have occurred infrequently throughout history.
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| Shanaka 'Shan' de Silva: Co-author of the study |
The magma reservoirs feeding the eruptions could be as large as 10,000- to 15,000-square cubic kilometers, and the chamber requires repeated intrusions of magma from below to heat the surrounding rock and make it malleable.
It is that increase in ductility that allows the chamber to grow without magma evacuation in a more conventional manner. When magma chambers are smaller, they may expel magma before maximum pressure is reached through frequent small eruptions. The Yellowstone eruption is one of the largest super-volcano events in history and it has happened several times. Other super-volcano sites include Lake Toba in Sumatra, the central Andes Mountains, New Zealand and Japan.
Gregg said that despite its explosive history, it doesn't appear that Yellowstone is primed for another super-eruption anytime soon, though the slow process of volcanic uplift is taking place every day.
'The uplift of the surface at Yellowstone right now is on the order of millimeters,' she explained.
'When the Huckleberry Ridge eruption took place, the uplift of the whole Yellowstone region would have been hundreds of meters high, and perhaps as much as a kilometer.'
© Daily Mail, London |
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