"This maritime farming community had been successful for over 2,000 years, they had no incentive to change, and then all of a sudden, boom, they just got the props knocked out from under them," anthropologist Mike Moseley of the University of Florida said in a statement.
Moseley and colleagues were studying civilization of the Supe Valley along the Peruvian coast, which was established up to 5,800 years ago.
The people thrived on land adjacent to productive bays and estuaries, the researchers report in Tuesday's edition of Proceedings of the National Academy of Sciences.
The Supe fished with nets, irrigated fruit orchards and grew cotton and a variety of vegetables, according to evidence found by research co-author Ruth Shady, a Peruvian archaeologist. They also built stone pyramids thousands of years before the better known Mayans.
But the Supe disappeared about 3,600 years ago and, after studying the region, the researchers think they know what happened.
They found that a massive earthquake, or series of quakes, struck the seismically active region, collapsing walls and floors and launching landslides from barren mountain ranges surrounding the valley.
In addition, layers of silt indicate massive flooding followed.
Then came El Nino, a periodic change in the winds and currents in the Pacific Ocean, which brought heavy rains that damaged irrigation systems and washed debris into the streams and down to the ocean, where the sand and silt settled into a large ridge, sealing off the previously rich coastal bays.
In the end, land where the Supe had lived for centuries became uninhabitable and their society collapsed, the researchers concluded.
The study was funded by the University of Florida and the Heyerdahl Exploration Fund, University of Maine.