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Mystery of the Megavolcano

TV Program Description
Original PBS Broadcast Date: September 26, 2006

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."

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).

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.

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.

Only an asteroid impact could have had a similar cooling effect on Earth's climate, but such an impact can't explain the release of sulfuric acid into the atmosphere—leaving a supervolcano eruption as the only logical explanation. But to have substantially cooled the atmosphere worldwide the eruption had to have been thousands of times more powerful than any in recorded history.

Enter John Westgate, a volcano detective, who has developed techniques to identify specific eruptions from the distinctive chemical signature of their volcanic ash. Westgate is intrigued by samples of "mystery ash" that he receives from many locations spread across southern Asia, which all prove to be of matching chemistry and age. Westgate's findings now pose a challenge to his geologist colleagues: Can they track down the exact source of the ash, the unidentified fire-breathing mountain that exploded with such incredible violence 75,000 years ago?

So begins a geological detective hunt that ultimately leads to the shores of an enigmatic lake in Southeast Asia. NOVA reveals the final telltale clues that enable geologists to nail down Lake Toba as the site of a gigantic, collapsed volcanic crater, or caldera (see A Supersized Volcano). Vivid computer-generated imagery then brings to life the epic scale of the ancient eruption. But even as the mystery is solved, is the case really closed? Could such a disaster happen again? Lake Toba's megavolcano is showing signs of stirring once again, while the supervolcano under Yellowstone will certainly host a supereruption again. It is just a matter of time.


Program Transcript
Program Credits

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Eruption

The scale of Toba's supereruption 74,000 years ago is almost beyond imagining, since no eruption even remotely approaching its magnitude has ever occurred in recorded history. But another one of its size will happen again.

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