Between 542 and 66 million years ago—long before the “supervolcano” became part of Yellowstone’s geologic story—the area was covered by inland seas. 
NPS/Jim Peaco

A Long, Long Time Ago: Geologic History of Yellowstone

Most of Earth’s history (from the formation of the earth 4.6 billion years ago to approximately 541 million years ago) is known as the Precambrian time. Rocks of this age are found in northern Yellowstone and in the hearts of the Teton, Beartooth, Wind River, and Gros Ventre ranges. During the Precambrian and the subsequent Paleozoic and Mesozoic eras (541 to 66 million years ago), the western United States was covered at times by oceans, sand dunes, tidal flats, and vast plains. From the end of the Mesozoic through the early Cenozoic, mountain-building processes formed the Rocky Mountains.
During the Cenozoic era (approximately the last 66 million years of Earth’s history), widespread mountain-building, volcanism, faulting, and glaciation sculpted the Yellowstone area.

Magma (molten rock from Earth’s mantle) has been close to the surface in Yellowstone for more than 2 million years. Its heat melted rocks in the crust, creating a magma chamber of partially molten, partially solid rock. Heat from this shallow magma caused an area of the upper crust to expand and rise. The Yellowstone Plateau became a geomorphic landform shaped by episodes of volcanic activity. Stress also caused rocks overlying the magma to break, forming faults and causing earthquakes. Eventually, these faults reached the deep magma chamber. Magma oozed through these cracks, releasing pressure within the chamber and allowing trapped gases to expand rapidly. A massive volcanic eruption then occurred along vents, spewing volcanic ash and gas into the atmosphere and causing fast super-hot debris (pyroclastic) flows on the ground. As the underground magma chamber emptied, the ground above it sunk, creating the first of Yellowstone’s three calderas.

This diagram shows the general ideas behind two theories of how magma rises to the surface.   Adapted with permission from Windows into the Earth by Robert Smith and Lee J. Siegel, 2000.

Based on minerals from the last major eruption, the researchers found that the changes leading up to an eruption may happen in a matter of decades rather than thousands of years in advance as previously thought.

Supervolcanoes are characterized as volcanic centers that have had eruptions that covered more than 240 cubic miles. The US has two: one in Yellowstone and another in California’s Long Valley.  An eruption could emit ash that would expand over 500 miles.  The eruption would likely cover the ground with as much as 4 inches of gray ash, which could be detrimental to crops growing in the Midwest.  Another less worrisome concern is the 1,000 degree F molten lava that could ooze out.  Gases, including sulfur dioxide, which contributes to acid rain would be spewed from the supervolcano and the global cooling issues associated with reflecting sunlight away from the Earth are also concerns.

But there are other supervolcanos in the world with sooner predictions than Yellowstone’s.  Campi Flegri, a name that aptly translates as “burning fields, is in a “critical state,” according to researchers in Italy.  It consists of a vast and complex network of underground chambers that formed hundreds of thousands of years ago, stretching from the outskirts of Naples to underneath the Mediterranean Sea.  Though its last eruption was in 1538, it’s due for an eruption soon.  It would be a minor event compared to the 72 cubic miles of molten rock it spewed in its most notorious eruption 39,000 years ago, called Campanian Ignimbrite, that likely contributed to the extinction of the Neanderthals.

Fortune website article reported that if the Yellowstone supervolcano erupts, it could shoot out more than 1,000 cubic kilometers of rock and ash into the air.  That’s 250 cubic miles. That’s more than three times as large as the Campanian Ignimbrite eruption in Italy, which created a sulfurous cloud that floated more than 1,200 miles away to hang over Russia. That’s 2,500 times more material than Mount St. Helens expelled in 1980, killing 57 people.  An eruption at Yellowstone would result in a cloud of ash more than 500 miles wide, stretching across nearly the entire western United States.

NASA has a plan to neutralize supervolcano threats however.  They believe the most viable solution could be to drill up to 6 miles down into the supervolcano, and pump down water at high pressure. The circulating water would return at a temperature of around 662F, thus slowly day by day extracting heat from the volcano. And while such a project would come at an estimated cost of around $3.46 billion, it comes with an enticing catch which could convince politicians to make the investment.  It would become a source of geothermal energy. But there are considerable risks, too. It could trigger the eruption it’s meant to save us from.

Historically, four types of volcanic events have taken place in Yellowstone (you may click on each one to learn more):
1.  Caldera Forming Eruptions — 2.1 and 1.3 million years ago
2.  Lava Flows — about 30 between 640,000 and 70,000 years ago
3.  Earthquakes — 1000 to 3000 yearly; last notable quake was in 1959
4.  Hydrothermal (Steam) Explosions — small explosions in the 20th century; a
dozen or so major explosions between 14,000 and 3,000 years ago

The likelihood of an eruption in the near future is still low.  However those who instigate such a project will never see it to completion, or even have an idea whether it might be successful within their lifetime. Cooling Yellowstone in this manner would happen at a rate of 3.2808399 feet a year, taking of the order of tens of thousands of years until just cold rock was left.

Featured Image:  Yellowstone harbours a giant magma chamber that will blow one day if we don’t act (Credit: iStock)

Contributing Sources:

NPS,  Yellowstone, BusinessInsider, BBC, NationalGeographics, Fortune, BBC