Mystery of the Megaflood

Boasting stunning cinematography and fascinating computer animation, this episode from the acclaimed PBS-aired NOVA series features breathtaking fly-over helicopter footage of the 16,000-square-mile region of Washington state known as the “Channeled Scablands," so named because it resembles a variety of unusual "wounds" to the Earth's surface—including a waterless waterfall, gorges nearly 1,000 feet deep, strange layers of silt and ash, inexplicable giant "potholes," and huge granite boulders (called "erratics") that seem to have appeared from out of nowhere. These perplexing geological mysteries eluded scientific explanation until one maverick geologist, J. Harlen Bretz, proposed the controversial and largely dismissed theory (in 1927) that the unusual features of the Scablands were formed almost literally overnight (and not, as widely accepted, over millions of years) by a giant flood—although the source of the high-volume water remained a mystery. Combining scale-model testing, computer animation, and examination of present-day evidence, expert geologists proceed to demonstrate why Bretz was right—positing that glacial erosion, and the eventual high-pressure explosion of a gigantic glacial ice-dam near what is now Missoula, Montana were the causes behind the sudden megaflood. DVD extras include printable materials for educators. Highly recommended. Aud: H, C, P. (J. Shannon)