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
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