Magazine article Science News

Gone with the Flow: Ancient Andes Canals Irrigated Farmland

Magazine article Science News

Gone with the Flow: Ancient Andes Canals Irrigated Farmland

Article excerpt

Archaeologists working in a valley on the western slopes of Peru's Andes mountains have discovered the earliest known irrigation canals in South America, a find that illuminates the origins of large-scale agriculture in the New World.

Tom D. Dillehay of Vanderbilt University in Nashville and his colleagues came across three buried canals, stacked one on top of the next, on the southern side of a river running through the Zana Valley. Radiocarbon measurements of carbon fragments date the bottom canal to about 5,380 years ago, the researchers report in an upcoming Proceedings of the National Academy of Sciences. They estimate the ages of the middle and top canals at around 4,390 years and 1,190 years, respectively.

The researchers also found traces of a fourth canal, about 6,700 years old, beneath the others.

Remnants of at least 51 sites once inhabited by people dot the countryside around the canals, Dillehay says. A majority of the sites, ranging from 4,500 to 6,000 years old, include remains of domesticated cotton, beans, squash, and coca. Preserved bits of both wild and cultivated plants have turned up at earlier sites.

The Zana Valley canals were designed to pipe water from a nearby river into adjoining agricultural fields, Dillehay says. The earliest canal was 2 feet wide and ran for slightly more than 1 mile. Each succeeding canal was built wider, longer, and with a flatter gradient. The top channel was 4 feet wide and stretched about 2.5 miles.

The two older canals were dirt ditches with pebbles and rocks along the bottom. In the third canal, rough stone and burned clay line the channel. …

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