Super Volcano: The Ticking Time Bomb Beneath Yellowstone National Park

Voyageur Press, 2007
© 2007 by Greg Breining  

The Big Blast
Yellowstone had been trembling and thundering for months, years, even centuries. The quakes came in swarms. There were hundreds each day, many too faint to feel. But often the earth shuddered. Faults broke through the surface, destroying trees, throwing clods of earth. 

For years the ground had been heaving upward. A region the size of Delaware, some forty miles by sixty miles centered on the southwestern corner of Yellowstone, had not only been shaking and splitting. It had also been rising and falling as though a giant deep below the ground were breathing, turning, heaving, sighing. And recently all this commotion had intensified. The ground was mostly rising now, as though something below, fierce and monstrous, were about to break loose. 

As the ground shuddered, swelled, and stretched, fissures spread across the surface. Red-hot lava issued from deep within the earth. The heat and smoke were intense. At first the lava oozed and spread, setting the ground ablaze as it advanced. Then along the perimeter of this huge area, fissures spread and lava began to explode, heaving great slabs of molten rock. 

Then something unimaginable happened. Something on a scale that has rarely occurred before or since. As magma jetted to the surface, the release of pressure reached a tipping point. Gas contained in the pressurize magma boiled away violently. As magma escaped to the surface, the pressure dropped even more, and ever more vigorously the gas escaped. It didn't fizz. Or roar. Or even merely blow up. It propagated exponentially with the speed and power of a nuclear explosion. 

Earth-shaking eruptions issued from three primary sites—what are now Island Park, Lewis Lake, and Old Faithful. In term of energy, imagine a machine gun burst issuing from Yellowstone, each blast the equivalent of a nuclear bomb. The magma chamber beneath the vast area of Yellowstone emptied with the force of hundreds of thousands of bombs the size of the explosions that leveled Hiroshima, Japan. 

Until this moment, the Gallatin Range ran continuously into the Red Mountains, forming a spine through Yellowstone, clear south to the Tetons. In moments, or hours, or at the most, days—thirty miles of the Gallatins were obliterated. The continual explosions blew major portions of the mountains into the upper atmosphere and ejected six hundred cubic miles of magma. Imagine a block of rock more than eight miles by eight miles at the base, and more than eight miles high—a mountain far more massive than Everest—ejected from the earth, rocketed more than twenty miles into the stratosphere, blasted down the mountainsides, pulverized, melted, and reformed as rock. Water released from erupting magma billowed high into the atmosphere. Lightning storms thundered in the plumes of smoke, vapor, and ash.

Glowing ash shot upward from each of the vents and blasted outward. These pyroclastic surges of hot gases and nearly vaporized particles of rock and volcanic glass, raced down slopes and across the landscape as fast as several hundreds of miles an hour. Following close behind were pyroclastic flows, glowing rushing rivers of heavier material, exceeding 1,000 degrees F. The hot flows uprooted, leveled, and burned whole forests, and killed all animals from insects to bison.

Pyroclastic flows radiated outward from the volcano vents, running northward through the valleys of the Madison, Gallatin, and Yellowstone rivers, southward through the valley of the Snake, and broadly, as a sheet, southwest through the Snake River Plain. These cascades of glowing ash traveled as far as eighty miles before settling and welding to the ash beneath to form solid rock. This welded tuff ranged from five hundred to twenty-five hundred feet thick and covered six thousand square miles, an area the size of Connecticut.

For hours, or days, explosions from the three vents continued to hurl gas, water vapor, and rock. Eventually, the magma chamber beneath Yellowstone emptied enough that the ground collapsed. The surface—what hadn't been vaporized and blown to bits—broke along the ring fissures at the edge of the immense chamber and dropped like a piston hundreds of yards into the vacated chamber below. Even massive Mount Washburn, a much older and now extinct volcano, was sheered in half, the southern portion of the 10,000-foot mountain, plunging into the evacuated magma chamber. This falling piston expelled more magma, which exploded from the fractures at the edges. The surrounding land, covered by ash and welded tuff, cascaded as avalanches into this newly formed caldera, more than fifty miles across. Much of the Gallatin Range fell into the fiery earth. For miles and miles all around, not a living thing remained. There was only a lunar landscape of hot rock, mud, and ash.

Dark clouds of ash and volcanic glass, blown throughout the stratosphere, drifted on the westerlies. The coarsest particles fell out first, as a light gray ash fall in perpetual darkness, burying areas near Yellowstone twenty feet deep. Finer bits of rock and glass remained aloft for hours or days, traveling hundreds of miles in the jet stream and lower-altitude winds. As the cloud blew eastward the ash fell in decreasing depths and increasing fineness. Within days, snowlike ash fall blanketed the western United States from the Pacific to the present course of the Mississippi. Prairie winds blew the ash into drifts that filled swales to thirty feet deep. The finest particles of ash remained aloft for weeks.

Clouds of water vapor, carbon dioxide, hydrogen chloride, and hydrogen fluoride, ejected high into the atmosphere by the eruption, remained aloft for much longer. Sulfur dioxide converted to sulfuric acid, which condensed to form sulfate aerosols. A vast cloud of these aerosols in the middle and lower stratosphere of encircled the globe within weeks. Within a year, these aerosols completely covered the globe, reflecting the sun's radiation, causing the Earth's lower atmosphere to cool. For years the climate dropped several degrees, as the Earth plunged into a long volcanic winter. 

America's oldest and most famous national park sits atop one of the largest, most explosive volcanoes ever to exist. 

We can only imagine the explosion at what we now call Yellowstone National Park. No one witnessed it. It happened 2.1 million years ago. We are left estimate its power by mapping exposures of welded tuff and studying strata of ash beds in far flung reaches of the West.

But scientists have concluded the eruption was immense, the energy released unfathomable—twenty-five hundred times greater than the explosion that would rip Mount St. Helens in 1980, blowing off 1,300 feet of mountain, killing fifty-seven, and destroying forests for miles around eastern Washington. The Yellowstone eruption ejected more than a hundred times as much magma and ash as did Krakatau in Indonesia in 1883, when more than 36,000 died in one of the most famous volcanic eruptions ever. Yellowstone—and other few other known volcanic eruptions—are known as "super volcanoes." That means they have expelled at least 1,000 cubic kilometers (about 240 cubic miles) of magma more of less all at once. No volcano in historic times, when literate humans were around to witness it, even comes close. 

But we may get a chance to see Yellowstone blow first-hand. Because Yellowstone is not only the site of one of the largest volcanic eruptions ever known. It is also the largest, potentially most explosive, most violent, most deadly active volcano on the planet. Scientists say the chances of another catastrophic explosion someday are almost inevitable. 

Since the cataclysmic explosion of 2.1 million years ago, two other large eruptions have rocked Yellowstone, buried it in volcanic rock, and left behind huge calderas. Though smaller than the first eruption, both subsequent explosions dwarfed better-known volcanoes, such as Mount St. Helens and Vesuvius. An explosion 1.3 million years ago blew sixty-seven cubic miles of rock and ash across nearly 1,000 square miles, leaving behind at caldera ten miles across at Island Park. An even bigger eruption 640,000 years ago spewed 240 cubic miles of lava and ash across 1,700 square miles, an area larger than Rhode Island. The caldera created by this most recent super explosion measures fifty miles by thirty miles and sits nearly in the center of Yellowstone National Park. Nearly a third of the park's 2.2 million acres either blew sky high or collapsed into the earth. The caldera is so filled with lava from subsequent smaller eruptions, that most visitors would never recognize they are standing on the remnants of an eruption so powerful it covered much of the continent with volcanic ash and transformed the Earth's climate for years, or perhaps decades.

But the Yellowstone volcano didn't stop then. During the last 640,000 years, the caldera and surrounding areas have filled with lava from about eighty smaller eruptions. Some of the lava fields would have buried a thirty-story skyscraper. The most recent eruption occurred 70,000 years ago, but there's no reason to believe that the Yellowstone volcano is tapped out—and plenty of reason to believe it will reawaken. 

Robert Christiansen, recently retired from the U.S. Geological Survey, is the geologist perhaps most responsible for piecing together the volcanic history of Yellowstone. He recently told the BBC: "Millions of people come to Yellowstone every year to see the marvelous scenery and the wildlife and all and yet it's clear that very few of them really understand that they're here on a sleeping giant." 

And the giant sleeps fitfully, at that. What are the signs? 

For one, the ground beneath Yellowstone is restless. About 2,000 earthquakes shake the park each year—an average of more than five a day. Most are too small to feel, but some are significant. The Hebgen Lake quake of 1959, a 7.5 magnitude temblor centered just west of the park, opened a crack in the earth and triggered a landslide. Altogether, twenty-eight people died. The Borah Peak earthquake of 1983, centered 15 miles west of Mackay, Idaho, registered nearly as strong—magnitude 7.3. A quake of 6.5 magnitude shook the Norris Geyser Basin in 1975. Ten years later, in October 1985, an earthquake swarm began to rock the park. For the next several months, more than 3,000 quakes occurred, as many as 200 shot through the ground each day. Ten years later, another swarm rattled the park, like a nest of mad hornets. 

For another, heat from magma near the surface drives the gushing geysers, blurping mud pots, and steaming fumaroles that distinguish the national park. The heat flow from the Firehole area, location of Old Faithful, is seven hundred times the global average. Beneath the entire Yellowstone caldera (from the most recent explosion), the average heat flow is thirty to forty times greater than the average worldwide, suggesting that new magma continues to heat the ground, perhaps maintaining another partially melted magma chamber. In fact, Christiansen believes the reservoir of magma is as much as ten times greater than what has already been expelled, as if the volcano is already primed and ready. This reservoir of heat sustains the greatest concentration of geysers in the world. Steam and hot water have at times found violent and spectacular release, blowing out craters hundred of yards across during the last several thousand years. 

Even today the thin, heated crust of Yellowstone is heaving like the chest of a gasping man. The ground beneath Yellowstone is literally rising and falling. From 1923, when road surveyors determined the exact altitude of specific Yellowstone landmarks, until 1984, the ground beneath the central portion of the park bulged upward more than a yard. The breathing paused for a year or two. Then it began to drop. The land began rising again in 1996. As the ground north of Yellowstone Lake has bulged upward, the lake has inundated trees at the southern shore. In recent years, a global positioning system station at Steamboat, in the Norris Geyser Basin, has risen six inches a year. What causes the land to heave? Scientists say it may be superheated water and steam, or it may be magma. Either way, the movement is powered by the same molten rock that could cause another eruption 

So, hell, yes, Yellowstone is still active. It's the lair of a fire-breathing dragon. Writes Robert Smith, another giant of Yellowstone geologic research, "Yellowstone really is a living, breathing thing." 

Says Christiansen in the pages of a comprehensive geologic report on the park—the kind of thing you'd think would be written cautiously: "Volcanism almost certainly will recur in the Yellowstone National Park region." 

When such an explosion occurs, it will be a disaster. Christiansen calls it a "major human disaster"—not just for the park, but for the entire region. The park itself would be destroyed, the forest leveled, and every living thing vaporized, incinerated, blown to bits, buried in welded ash and mud, or asphyxiated by carbon dioxide. People in the surrounding towns of West Yellowstone, Gardiner, and Cooke City will face the same fate. Towns and cities throughout the West will have to dig out from deep volcanic ash. Cars, buses, planes will all be grounded till the ash clears. Respiratory illness will soon take a toll. Domestic livestock and wildlife west of the Mississippi will be stuck, and probably doomed. Great Plains wheat fields, the global breadbasket, will miss a season—or several—leading to widespread famine. The global volcanic winter will last years and influence the climate for decades or centuries. The worldwide death toll, says Michael Rampino, New York University associate professor of earth and environmental sciences, could reach a billion. "How do you get food, how do you get suplies, how do you get in and out, even after the eruption?" says Rampino, who has studied the climatic effects of huge volcanos. "It depends on what you mean by killled—killed right away, starved to death?" 

So we have something to look forward to—a probable disaster of global proportions. The question is when. 

What is tantalizing—and a bit alarming—to consider is the timing of Yellowstone's super eruptions: 2.1 million years, 1.3 million years, 640,000 years ago. The intervals are 800,000 and 660,000 years. That suggests another explosion is due—and, in geologic time, soon! 

Meanwhile, the geysers vent, the hot springs bubble, fumaroles hiss, powered by the magma beneath the ground, by the same magma that has charged the largest active volcano on earth and one of the largest volcanic eruptions ever to rock the planet. They remind us the monster still stirs. How does it work? What are the chances it will reawaken? And what can we do when it does? 

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