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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