New research suggests that supervolcanos do not need an external trigger to erupt. Bouyancy effects and the magma volume could be sufficient for spontaneous eruption.
Wim J. Malfait, Rita Seifert, Sylvain Petitgirard, Jean-Philippe Perrillat, Mohamed Mezouar, Tsutomu Ota, Eizo Nakamura, Philippe Lerch, Carmen Sanchez-Valle. Supervolcano eruptions driven by melt buoyancy in large silicic magma chambers. Nature Geoscience, 2014; DOI:10.1038/ngeo2042
From the Press Release:
Scientists have reproduced the conditions inside the magma chamber of a supervolcano to understand what it takes to trigger its explosion. These rare events represent the biggest natural catastrophes on Earth except for the impact of giant meteorites. Using synchrotron X-rays, the scientists established that supervolcano eruptions may occur spontaneously, driven only by magma pressure without the need for an external trigger. The results are published in Nature Geosciences.
A well-known supervolcano eruption occurred 600,000 years ago in Wyoming in the United States, creating a huge crater called a caldera, in the centre of what today is Yellowstone National Park. When the volcano exploded, it ejected more than 1000 km3 of ash and lava into the atmosphere, 100 times more than Mt Pinatubo in the Philippines did in 1992. Big volcanic eruptions have a major impact on the global climate. The Mt Pinatubo eruption decreased the global temperature by 0.4 degrees C for a few months. The predictions for a super volcano are a fall in temperatures by 10 degrees C for 10 years.
Abstract: Super-eruptions that dwarf all historical volcanic episodes in erupted volume and environmental impact are abundant in the geological record. Such eruptions of silica-rich magmas form large calderas. The mechanisms that trigger these super-eruptions are elusive because the processes occurring in conventional volcanic systems cannot simply be scaled up to the much larger magma chambers beneath supervolcanoes. Over-pressurization of the magma reservoir, caused by magma recharge, is a common trigger for smaller eruptions, but is insufficient to generate eruptions from large supervolcano magma chambers. Magma buoyancy can potentially create sufficient overpressure, but the efficiency of this trigger mechanism has not been tested. Here we use synchrotron measurements of X-ray absorption to determine the density of silica-rich magmas at pressures and temperatures of up to 3.6 GPa and 1,950 K, respectively. We combine our results with existing measurements of silica-rich magma density at ambient pressures to show that magma buoyancy can generate an overpressure on the roof of a large supervolcano magma chamber that exceeds the critical overpressure of 10–40 MPa required to induce dyke propagation, even when the magma is undersaturated in volatiles. We conclude that magma buoyancy alone is a viable mechanism to trigger a super-eruption, although magma recharge and mush rejuvenation, volatile saturation or tectonic stress may have been important during specific eruptions.
Supervolcanos do not occur all that often – perhaps one every 50,000 to 100,000 years. When they do occur they devastate a large geographical area and affect the climate for a decade or so. How much destruction of organic life occurs depends on the geographical area affected and the life that is extant there.
New Zealand’s Taupo Volcano was the most recent and erupted about 26,500 years ago. With a VEI of 8, just over 1,000 km3 of ash were ejected. Though modern man had reached Australia by then, the effects of this eruption do not seem to have significantly delayed the march of humans. The Toba eruption 74,000 years ago occurred when the total population of all human species (Modern Humans, Neanderthals, Denisovans …..) was between 1 and 10 million. This eruption is also classified as a VEI of 8 and 2,800 km³ of material was ejected. Life was virtually extinguished from India to South East Asia. The effects were devastating not only in the fall out-zone but also – it seems – in hampering the expansion of modern humans out of Africarabia. This eruption may thus have caused one of the critical bottlenecks which has determined the subsequent evolution and expansion of humans.
Toba Fallout (Smithsonian Institute)
While a supervolcano could erupt at any time, it is much more probable to occur than a major asteroid collision with the earth (one in 100,000 years as opposed to once in tens of millions of years). But the volume of magma involved suggests that some early detection (perhaps 5 -10 years) may be possible. For the pressure to build up sufficiently in such a volume a significant bulging of the earth’s crust is likely and should be detectable. But while science fiction can imagine a battery of nuclear warheads to divert an oncoming asteroid in its trajectory, it is difficult to conceive of any way to prevent a supervolcano from erupting. Geo-engineering on a scale massive enough to relieve some of the pressure in the magma is just conceivable at the edge of fantasy but even that could not prevent the eruption.
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