The Yellowstone Caldera is essentially a giant, lidded steam boiler, and it's so huge that it can only be seen from Earth orbit. Its crater reaches 72 kilometers in size, and its caldera contains tens of thousands of cubic kilometers of magmatic material. It would take Niagara Falls 624 years to fill a caldera of this size.
What happens if this monster explodes, shaking the world with a terrifying volcanic eruption?
Who will live, who will die - and will the United States of America survive? We spoke to one of the country's most respected volcanologists for the latest information on the future of the world's most famous supervolcano.
The two-stage magma chamber is now dormant. According to a scientist at the Yellowstone Volcano Observatory, Dr. Michael Poland, currently the volcano may not have enough energy to produce a super-eruption.
"Right now, most of the Yellowstone magma body is partially solidified, and you need a lot of magma to feed the big eruption."
For most of its life, the region has been characterized by extensive lava flows and much more often hydrothermal explosions, suggesting that any future eruption will be much less frequent.
The odds of superculan paroxysm are currently around 730,000, making it less likely than a catastrophic asteroid impact.
However, a sudden injection of new magma from below or a sudden weakening of the geological layers covering it may be enough to cause a sudden depressurization event, as a result of which everything that has accumulated in the depths of the volcano will be ejected in the form of a powerful explosion.
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What happens next is somewhat hypothetical, but Yellowstone's chilling story gives us a clue to the implications. We're thinking of a worst-case scenario, so let's assume that his entire magma cauldron is emptied in a colossal supervolcanic explosion.
This happened in Yellowstone three times already in a cycle of 660,000-800,000 years: 2.1 million years ago, 1.3 million years ago and 640,000 years ago.
The most explosive eruption was its first, which produced 2.5 times the amount of volcanic material than the 1980 Mount St. Helens eruption. Even the most recent explosion created an eruption ash column so colossal that it covered about 60 percent of the United States in a thick layer of ash.
So let's just say that such a powerful explosion will be repeated today: what will happen to the United States and the world?
It is unclear how warning organizations such as the United States Geological Survey (USGS) will act, but shortly before the eruption occurs, the ground around Yellowstone National Park will heave and the ground level will rise.
The hydrothermal system, including geysers and geothermal pools, will quickly heat up to above boiling point and are likely to become extremely acidic - more than usual.
An earthquake swarm will be detected heading towards the central point, indicating that magma is rapidly advancing through the crust. Then the cover of the magma chamber covering the caldera will collapse and a powerful volcanic eruption will occur, which the world has not yet seen.
A huge column of ash and lava will rise to a height of about 25 kilometers. Ash clouds will cover the sky, and lava bombs will fly around for many kilometers, destroying everything around. This will continue for several days and the ash will gradually spread across the stratosphere.
Huge pyroclastic flows will sweep through Yellowstone Park, destroying all life in its path.
This mixture of ash, lava and superheated gas exceeds a temperature of 1000 ° C (1832 ° F) and these streams can travel at speeds up to 482 kilometers per hour (about 300 miles per hour). If they catch someone on their way, these people or animals will die within a few seconds, they will simply be burned as the air heats up to about 300 ° C (570 ° F).
Pyroclastic currents travel up to 15 kilometers (9.3 miles) from their source, but theoretically they could spread up to 100 kilometers (62 miles) if a supervolcano explodes.
This is, in fact, the length of Yellowstone National Park, so if the mouth of a new eruption appeared right in the center, and the pyroclastic flows were especially vigorous, many in the park would die either from pyroclastic flows or because of the collapsing caldera roof.
On average, there are about 11,000 visitors to the park every day, based on an annual visit of 3.8 million. There are many more visitors during the summer months, so the summer eruption will be much more deadly.
When pyroclastic flows and ash sediments settle and cool down, they may appear harmless, but they are not. They accumulate on hills and slopes, can mix with mud, streams of water after rain and turn into fast moving cement slurries called lahars. Everyone who falls into such a lahar will die.
However, the most dangerous aspect of the eruption is the fallout of ash both locally and globally.
Breathe it in and it will tear your lungs apart and form a vitreous cement. This ash is also about six times denser than water, which means that most of the buildings will collapse under their own weight as the ash accumulates on the rooftops. Our interlocutor Poland says that "even a few tens of centimeters of wet ash can lead to the collapse of weak buildings."
Roads and sewer systems will clog and collapse, water supplies will be polluted, and electrical grids will fail. Millions of homes could become uninhabited.
In this sense, those who take refuge in Montana, Idaho and Wyoming are most at risk of harm. The eruption could last for months and people in these states will have to survive in incredibly harsh conditions.
An area of about 80 km (50 mi) around the volcano's vent will be covered in 3 meters (about 10 feet) of ash in just a few days. Simulations have also shown that superelementation can bury Salt Lake City and its surroundings under a layer of ash more than a meter high.
If there are no strong winds, Denver will receive about 30 centimeters of ash cover, while Calgary will receive about 10 centimeters. The Federal Emergency Management Agency (FEMA) will help clean up and move this ash for months or even years.
Elsewhere - say San Francisco, Los Angeles, Seattle, Minneapolis and Chicago - about 3 centimeters of ash will fall out. Within a few days, a thin layer of ash could reach Miami, New York and Toronto, and it would be enough to cause cars to break down and turn drinking water sources into poisoned swamps.
Flights will be stopped over the entire United States for at least a few weeks, and the National Guard and possibly the military will almost certainly be mobilized to help evacuate the many tens of millions of people from the affected region.
The death toll is extremely difficult to predict, but Poland suggests that "if people were present in the immediate vicinity of the eruption, say, for several tens to several hundred kilometers, they would be in danger."
But there is another threat - air pollution.
The release of ash into the stratosphere will darken the sky and cool the planetary temperature. If the eruption is especially rich in sulfur - an effective blocker of sunlight - then the temperature will drop several degrees and there will be no summer in the next few years.
“There will probably be significant cooling over the years,” explains Poland. “But how long it will continue, and how much cooling will be, I cannot say. I'm not sure if anyone can."
If the much smaller but very sulfur-rich eruption of Mount Tambora occurred in 1815, then the Yellowstone explosion will be much stronger for many years to "change global weather patterns and have a huge impact on human activity," according to the USGS.
The paths and duration of the monsoons would change. The formation of the tropical cycle will become much more unpredictable over time, and the spread of waterborne diseases can be very widespread.
Agriculture will also be affected, which could severely disrupt food supplies. This would result in overall economic damage that would be severe: A recent FEMA estimate of the impact of the Yellowstone explosion suggests total US damage of $ 3 trillion, which is about 16 percent of the country's total GDP. To put this in perspective, that's $ 400 million more than was lost during the recent global recession.
The USGS reports in the report that "scientists today do not have the predictive ability to determine the specific consequences or duration of possible global impacts of such large eruptions."
Poland is confident that this will not lead to the destruction of civilization. “This does not mean the end of life on Earth,” says Poland. "In fact, this experiment has already been launched, but few people understand it."
He points to the eruption of Toba that occurred 74,000 years ago, and humanity survived it, and "then they did not have the advantage of technology!"
However, the professor himself agrees that it is impossible to accurately predict all the consequences of the Yellowstone eruption, since it will be such a global and grandiose event that its consequences for our world can be very unpredictable and catastrophic, and we can only hope that our modern technology will help humanity cope with these consequences and survive in the world after the eruption of the Yellowstone supervolcano.