Mystery of the Megavolcano, and: Monster of the Milky Way, and: Mystery of the Megaflood (review)

Popular culture, along with high school science classes, leads us to expect that “real science” happens in the laboratory, where experiments can repeated time and again under the watchful eyes of scientists. Much of biology, chemistry, and physics does work that way, but large swaths of astronomy and geology do not. Astronomers and geologists routinely study phenomena and that, by nature – too big, too slow, too distant, too powerful – cannot brought to (or replicated in) a laboratory. They deal, as a matter of course, with events and processes to which no human observer can bear direct witness, and which no laboratory, however well equipped, can possibly duplicate. Just how geologists and astronomers do that is the subject of the trip of films reviewed here. Produced by PBS for its long-running science documentary series Nova they allow viewers to look over the shoulders of scientists working to make sense of phenomena whose power, scope, and intensity are – even for those used to thinking beyond normal human frames of reference – nearly unimaginable.

Mystery of the Megavolcano begins with the biggest volcanic event in recorded history: the 1815 eruption of Mount Tambora, which generated 12 cubic miles of magma and spewed so much ash into the atmosphere that 1816 became known as “The Year Without a Summer.” Awesome as it is, however, Tambora is simply there for scale. The film’s real subject is Toba, an Indonesian “supervolcano” that poured out 672 cubic miles of magma in a two-week-long eruption 74,000 years ago. It filled the air with pumice-rich ash and clouds of sulfur dioxide, producing climate change on a scale usually associated with asteroid impacts, and generating copious amounts of acid rain. Tambora altered the climate of Europe and North America for a year; Toba may have helped to precipitate the beginning of the last Ice Age.

A topic like this offers ample opportunity for breathless, lurid sensationalism: gruesome descriptions of victims suffocating as their lungs fill with ash and fluid, nightmarish visions of ash clouds smothering plants and blotting out the sun, and grim reminders (based on the existence of a supervolcano beneath Yellowstone National Park) that It Could Happen Here. Mystery of the Megavolcano touches on such subjects but does not dwell on them. Consistent with Nova’s long tradition of emphasizing science rather than sensation, it focuses on a more mundane but more important question: “How, in the absence of eyewitness accounts, do we know that a catalcysmic eruption took place at Toba 74,000 years ago?”

The answer involves the work of three different scientists: climatologist Greg Zielinski, who found high concentrations of sulfuric acid in cores from the Greenland ice sheet; geologist Mike Rampino, who found evidence of a sharp temperature drop in ocean-floor sediments; and volcanologist John Westgate, who found a distinctive chemical signature in volcanic ash deposits from throughout Southeast Asia. The film is—again, in the Nova tradition—scrupulous in its depictions of the science. Its scenes of the scientists gathering and interpreting data are shot on location at field sites and in laboratories but they are never encumbered with the too familiar, never-convincing pretense that discoveries were being made (rather than simply explained) as the cameras rolled. Interspersed with these scenes are concise explanations of essential background knowledge. One particularly effective example describes how the oxygen atoms in tiny marine fossils known as foraminifera record temperature fluctuations in the deep ocean. The “fit” between the different lines of evidence is explained clearly and economically in the linking narration.

The film’s only significant limitation has more to do with the subject matter than with the filmmakers’ shortcomings. The scope of geological time is notoriously difficult to convey to non-geologists, and Mystery...