Yellowstone supervolcano: Expert on ‘danger’ of Caldera in 2015
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Beneath the surface of the picturesque Yellowstone National Park, filled with an abundance of geysers and hot springs, lies an enormous magma chamber. According to an analysis of earthquake data eight years ago, the magma chamber is 80km (50 miles) long and 20km (12 miles) wide. Three previous eruptions have formed a caldera, a large volcanic crater formed after the emptying of a magma chamber. This measures some 70km (43 miles) by 45km (28 miles).
The three supereruptions occurred 2.1 million, 1.3 million and approximately 640,000 years ago.
Though Yellowstone is ‘due’ an eruption, based on the timeline of previous eruptions, scientists believe the proportion of molten rock in the magma chamber is far too low to allow for another supereruption — the last of which dwarfs anything seen in the modern day.
The eruption 640,000 years ago was believed to have been 1,000 times bigger than the devastating eruption of Mount St Helens in 1980.
The Mount St Helens eruption in Washington state killed about 57 people and reduced hundreds of square miles to wasteland, causing over $1billion (£737million) in damage (equivalent to $3.5billion or £2.5billion in today’s money).
Supervolcanoes are defined by eruptions of a Volcanic Explosivity Index (VEI) of 8, the largest recorded value on the index. Mount St Helens had a VEI of 5.
Eruptions occur when magma in the mantle rises, but is unable to break through it. Pressure continues to build in a large and constantly growing magma pool until the crust is no longer able to contain the pressure.
These eruptions can occur at hotspots, such as Yellowstone, or at subduction zones, notably Toba in Indonesia.
The 2004 Naked Science documentary ‘Super Volcanoes’ explored how a Yellowstone eruption would affect the world, and the impact it would have on the United States in particular.
The blast itself would be enormous, but nothing compared to what would follow.
The documentary’s narrator said: “Spreading out from Yellowstone would come one of nature’s most deadly forces — violent, deadly clouds of rock, ash and gas called pyroclastic flows.”
Professor Bill McGuire, one of Britain’s leading volcanologists, told the documentary: “Pyroclastic flows are the nastiest of all volcanic phenomena. They are blasts of fragmented magma, hot ash and incandescent gases that travel at hurricane velocities.
“They blast out across the ground surface in all directions from the eruption.”
Hidden beneath the cloud of ash is a mass of tumbling rocks.
The flow travels at high speeds, at temperatures of up to 1,500℃, destroying everything it touches.
Prof McGuire continued: “Death comes pretty quickly, not from the actual burning of the skin outside, but from inhaling these very, very hot gases.
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“They really wreck the lungs and the throat almost instantaneously.
“After that, the water in the human tissue is boiled off, and there are cases in some past eruptions where people’s skulls have been popped apart as the brain has essentially exploded.”
When the Taupō Volcano in New Zealand, another supervolcano, last erupted, it produced one of the most violent eruptions in geologically recent times.
Around 1,800 years ago, Taupō erupted in what is known as the Hatepe eruption.
It remains the most violent eruption in the world in the last 5,000 years.
The main pyroclastic flow climbed some 1,500m, and covered the land within 80km (50 miles) with igneous rock ignimbrite.
Another eruption at Taupō, the Oruanui eruption, approximately 26,500 years ago, caused even greater disruption.
Tephra covered much of New Zealand’s central North Island up to 200 metres deep, with the Chatham Islands some 1,000km away coated in an 18cm layer of ash.
In Yellowstone’s case, an eruption is not considered anything like being imminent.
Scientific analysis in 2013 suggested around 6-8 percent of the magma chamber, with an underground volume of 4,000km3, is filled with molten rock.
Though the magma chamber is about 2.5 times bigger than previously thought, the proportion of molten rock is far too low to allow for another eruption.
Further research in 2017 indicated that the magma chamber underwent a substantial increase in temperature and change in composition prior to the eruption.
The analysis suggested that these changes could occur within decades, although volcanologists had once thought this might take centuries.
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