A wall of debris stretching about 30 miles (50 km) may be the remnants of a natural disaster that struck Mexico's Caribbean coast between 1,500 and 900 years ago in an area where tourists now flock to beach resorts and ancient Maya ruins. A huge tsunami is the likely culprit, propelling debris including boulders made of reef material ripped from the seafloor far inland, scientists said on Thursday. The tsunami appears to have struck during the height of the ancient Maya civilization, but may not have killed many people because the area was not densely populated, they said. The debris tracks the shape of the coast near the seaside tourist resorts of Playa del Carmen and Cancun and the ancient Maya ruins of Tulum. "Were it to occur today, there are about 1.4 million people who live along the Yucatan coast, which would be in its path," said Larry Benson, an anthropology curator at the University of Colorado Museum of Natural History and a former U.S. Geological Survey scientist.

The researchers said the tsunami waves reached at least 15 feet (4.5 meters) and maybe higher. Benson estimated the tsunami hit between about 450 A.D. and 900 A.D., erecting the 16-foot (5-meter) tall berm formed from debris thrust about 1,200 feet (365 meters) inland by the force of the waves. "Its 30-mile extent along the shore is impressive," said geologist Charles Shaw, the former director of the Centro Ecológico Akumal ecological organization in Mexico who worked with Benson in the research published online this week in the Journal of Coastal Research.

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— Reuters and NBC News staff