By Will Dunham
WASHINGTON (Reuters) - A wall of debris stretching about 30 miles (50 km) may be the remnants of a natural disaster that struck Mexico's Caribbean coast more than 1,000 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 caused a large body count 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 AD and 900 AD, 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 in the Journal of Coastal Research.
The researchers said other evidence suggests the wave may have extended along about 150 miles (250 km) of Yucatan coastline.
Some later Mayan structures, dating from between 900 AD and 1200 AD, were built atop the berm, they said.
The berm's boulders are made up of coral and limestone, and an impressive amount of force was needed to tear this reef material from the seabed, the researchers said.
The researchers added they do not know what unleashed the tsunami, whether it was an earthquake or something else.
Benson said that while this tsunami was powerful, it likely was not as potent as the 2004 Indian Ocean tsunami that was triggered by a 9.15-magnitude earthquake and killed about 226,000 people.
"Tsunamis can be very destructive when they strike densely populated areas, so an historical example should be a wake-up call against complacency," Benson said.
(Reporting by Will Dunham; Editing by Sandra Maler)