ScienceShot: Massive Ancient Flood Traveled From China to India

23 July 2013 5:45 pm

NASA/GSFC/METI/ERSDAC/JAROS; (inset) K. Huntington

Talk about a deluge. A massive flood that struck northeastern India sometime in the past 2 million years may have originated hundreds of kilometers away in Tibet, a new study suggests. Tiny crystals known as zircons taken from the meters-thick flood deposits sport distinctive proportions of trace elements found only in zircons eroded from a peak in China dubbed Namche Barwa (arrow) and from rocks even farther up the Yarlung Tsangpo River (from an area located off the upper left of the satellite image), the team will report in a forthcoming issue of Geology. Previous studies suggested that there, on the Tibetan Plateau, a lake holding 800 cubic kilometers of glacial meltwater broke through a natural dam—either an arm of an ice sheet or a landslide deposit—sending floods carrying as much as 1 million cubic meters of water per second down the 200-kilometer-long, less-than-200-meter-wide Tsangpo Gorge. But the flood deposits in India—at least four of them sitting between 30 and 150 meters above river level—are the first downstream evidence of such megafloods. It's not clear whether the four flood deposits are associated with separate events or with different stages of one event; the researchers are now trying analyzing the sediments to determine when those materials were laid down. Regardless, the researchers say, the flow rate during the height of the largest flood would have been enough to move house-sized boulders and to carry 1-meter-wide stones as easily as smaller streams transport sand and silt.

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