The Yellowstone volcano

Deep beneath Yellowstone National Park lies one of the world’s largest supervolcanoes, a force of nature responsible for the park’s famous geysers and hot springs. However, this geological marvel also conceals a massive magma chamber, a reservoir far larger than previously imagined. In 2015, researchers from the University of Utah made a startling discovery: not only was the magma chamber significantly more extensive than expected, but there was also a second, even larger reservoir beneath it. Together, these two chambers hold enough magma to fill the Grand Canyon 11 times over.

The implications of such a colossal magma reserve are unsettling. As the magma builds up, it exerts pressure on the ground above, causing the land in Yellowstone to rise by one to two inches each year. Compounding this concern is Yellowstone’s status as an active volcano, with a Volcanic Explosivity Index (VEI) of 8 out of 8, the highest possible rating. This means that if Yellowstone were to erupt, the event would be nothing short of apocalyptic. To put it in perspective, the 1991 eruption of Mount Pinatubo in the Philippines, one of the most powerful eruptions in living memory, only rated a 6 on the VEI scale.

Despite these daunting facts, the likelihood of an imminent eruption is low. In March 2023, the University of Utah’s seismograph stations recorded 354 earthquakes in the Yellowstone region. While this might sound alarming, the largest of these quakes was a modest magnitude 3.7, part of a swarm of 106 earthquakes that began on March 29 and continued through the month. Although Yellowstone’s seismic activity is higher than usual, experts like Michael Poland, a geophysicist at the Yellowstone Volcano Observatory, assure us that the volcano is stable. For a supereruption to occur, there would need to be sufficient magma beneath the surface and enough pressure to force it upward, conditions that do not currently exist.

Nonetheless, Poland and his team closely monitor Yellowstone’s underground activity for any warning signs. They pay particular attention to the frequency of earthquakes and ground deformation, as well as changes in the park’s thermal features, such as geysers and gas emissions. While some media outlets claim that Yellowstone is overdue for an eruption because its last major eruption occurred 70,000 years ago, experts explain that volcanoes don’t operate on predictable timelines.

If a supereruption were to happen, the most devastating consequence would not be the lava flows or the accompanying earthquakes. Instead, the biggest threat would be the ashfall. To understand this, we can look back at Yellowstone’s past. The park has experienced at least three supereruptions, with the most powerful of them being 2,500 times more devastating than the 1980 eruption of Mount St. Helens in Washington state. The most recent supereruption, known as the Lava Creek eruption, formed the Yellowstone Caldera and spewed an enormous amount of volcanic ash, dust, and rock into the atmosphere.

Scientists recently uncovered evidence of two other previously unknown supereruptions that occurred around 9 and 8.7 million years ago. The younger of these is now considered the largest recorded event in the entire Snake River-Yellowstone volcanic province. Millions of years ago, these eruptions were preceded by subtle signs of impending disaster. For thousands of years, heat had been rising from deep within the Earth, melting rock beneath the planet’s crust and forming vast chambers of pressurized magma, water vapor, and gases.

As the magma continued to accumulate, the land above the volcanic system began to rise, almost imperceptibly at first. A year before the supereruption, Yellowstone might have given a warning—a slight "burp" of activity. However, since there were no humans around to interpret these signals, the warning went unnoticed. Decompression underground caused gas bubbles to form, which powered particular kinds of eruptions. In the months leading up to the catastrophe, small-scale earthquakes became more frequent, and the ground grew hotter. Lakes and groundwater also warmed, and unusual steam began to fog the area.

In the days before the eruption, the pressure beneath the surface became too great. The ground around Yellowstone began to lift, creating a dome-shaped uplift. Cracks formed along the edges of this dome, releasing pressure in a way similar to opening a shaken soda bottle. Finally, the rock roof of the magma chamber could no longer hold, and the eruption began. Small tremors escalated, and within minutes, a deafening roar signaled the start of a massive eruption. A column of lava and ash shot into the sky, followed by a pyroclastic flow—a deadly mix of lava, ash, and gases—rushing across the landscape at hurricane speeds.

This flow, with temperatures reaching 1,300 degrees Fahrenheit, incinerated everything in its path. The eruption continued for days, spewing volcanic ash that quickly covered the surrounding area. Inhaling this ash turned it into a glassy cement, lethal to all living creatures. Even the sturdiest trees collapsed under the weight of the dense ashfall. As the ash entered the stratosphere, global temperatures began to drop, leading to years without a summer. Animals struggled to find food and clean water, and the land was left barren.

The Graze Landing supereruption, as it is now known, was a colossal event that sterilized the land and left it covered in scorching hot volcanic glass. If such an eruption were to occur today, it would blanket Colorado, Utah, and Wyoming in nearly three feet of toxic ash. The resulting ash cloud would darken the skies across much of the United States, disrupting life even on the coasts. Crops would be destroyed, power lines ruined, and entire regions plunged into darkness.

Thankfully, experts agree that such a disaster is not expected to occur anytime soon. While Yellowstone remains an active volcano, it’s stable for now, and we have plenty of other challenges to face in the meantime.