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NOVA: Mystery Of The Megavolcano

Airs Tuesday, May 25, 2010 at 8 p.m. on KPBS TV

Above: Visualization of Toba eruption. The Toba eruption may have helped kick the climate into an unprecedented freeze and perhaps even pushed ancestral human populations to the brink of extinction.

NOVA joins four scientists in their global pursuit of clues to a massive volcanic eruption that appears to have had a devastating impact on the Earth 75,000 years ago. And if they're right, the ancient supervolcano—and others like it—may someday reawaken, with catastrophic consequences for our modern world. Now, an array of clues—scattered ashes and ice cores, tiny ocean creatures and steaming lakeside rocks—are brought together to solve the "Mystery Of The Megavolcano."

A Supersized Volcano

As this interactive shows, Toba's upheaval dwarfs all eruptions of recorded history.

The destructive power unleashed by supervolcanoes goes far beyond that of any eruption in recorded human history. Picture an eruption blasting 10 miles into the stratosphere, raining down ash and rock over an entire continent. Picture a worldwide fog of sulfuric acid droplets released high into the atmosphere, dimming the sun and plunging the Earth into a global "volcanic winter." These monsters lurking within Earth's crust dwarf the likes of Vesuvius, Pinatubo, and Mount St. Helens. And they are hiding all around us, in Italy, New Zealand, Japan, even the United States (see Blasts From the Past).

Why Toba Matters

NASA's Drew Shindell reflects in this interview on the lessons we can learn.

To qualify as a supervolcano, a volcano must produce at least 240 cubic miles of magma, or partly molten rock, in a single eruption—about the same volume of water the Mississippi River dumps into the Gulf of Mexico during a single year. In fact, the supervolcano with the world's largest magma chamber sits directly below Yellowstone National Park. If it erupts, as it has twice in the ancient past, the magma would be enough to fill more than 200 Grand Canyons.

The Next Big One by Peter Tyson

What could we expect if a supereruption were to occur today?

NOVA heads into the field and the laboratory as a team of scientists struggles to make sense of the clues that all point to an unprecedented catastrophe, one of the biggest supervolcanic eruptions of all time—an event thought to have unleashed fire, famine, and death upon a quarter of the globe. Evidence of this natural Armageddon first emerges in a most unlikely place: the Greenland ice cap. Here, the mile-thick ice sheet, built up from hundreds of thousands of years of snowfall, captures an annual record of the chemical composition of Earth's atmosphere. Drilling into the ice and back in time, climatologist Greg Zielinski stumbles upon the chemical signature of billions of tons of sulfuric acid in the atmosphere about 75,000 years ago.

Thousands of miles away, drilling in the deep ocean floor, geologist Mike Rampino also unearths clues to a cataclysmic shift in Earth's environment 75,000 years ago—a point in time when usually stable ocean temperatures plummeted. To Rampino, the evidence looks like the sudden onset of a mini-ice age. And when Zielinski and Rampino put their data together, the profile of a suspect emerges.

Video

Preview: NOVA: Mystery Of The Megavolcano

Above: The Toba eruption may have helped kick the climate into an unprecedented freeze and perhaps even pushed ancestral human populations to the brink of extinction. In a classic science detective story, NOVA pieces together the clues about this great catastrophe and probes questions about human evolution and Earth's fragile ecosystems.