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Ancient Mexican Carvings Being Erased by Acid Rain, Experts Say

Stefan Lovgren
for National Geographic News
January 26, 2007
 
Pollution is threatening to erase thousand-year-old stone carvings at one of Mexico's most important archaeological sites, a new study shows.

The pre-Aztec city of El Tajin, located on Mexico's Gulf coast, is famous for its temple pyramids and intricately carved reliefs.

But acidic air pollutants pumped out by oil-drilling platforms and power stations along the coast are slowly eroding these carvings, according to Humberto Bravo, an air pollution specialist.

"The deterioration is alarming … and could cause irreparable damage to monuments that are an important part of our cultural heritage," said Bravo, of the University of Mexico's Center for Atmospheric Sciences.

God of Thunder

El Tajin was built in what is now the state of Veracruz by the Totonac, a civilization that reached its peak from the early 9th to the early 13th century A.D. (See Mexico map.)

Much of El Tajin—the city name refers to one of the names for the Totonac god of thunder—remains unexcavated.

The site's most famous building is an elaborate niche-studded pyramid.

The ceremonial center also has a number of other temple pyramids, palaces, and courts for playing a ritual Mesoamerican ball game sometimes compared to basketball.

No other site has as many depictions of ball players and their equipment as the sculptures and carvings at El Tajin, whose inhabitants were apparently great fans of the game.

It is unclear how exactly the game was played, but it may have served as a training exercise for young warriors. Losers of the game may have been sentenced to death.

Now the carvings depicting the game are beginning to erode at an alarming rate, according to Bravo.

"Within 10, 20, or 100 years, these hieroglyphics will disappear if we don't do anything about it," Bravo said.

Acid Rain

Bravo and his colleagues spent several years simulating the effects of polluted air and acid rain on El Tajin's soft limestone buildings.

He blamed the erosion on contaminants like chlorine, sulfates, and nitrates in the air from power stations and oil refineries.

Acid rain causes erosion on ancient monuments because the sulfuric and nitric acid chemically reacts with the calcium carbonate in the stones to create gypsum, which then flakes off.

Acid rain forms when pollutants in the air become trapped inside water droplets in a cloud. The pollution is then carried down to earth with the rain.

"The Veracruz region has some of the highest acid levels in the air in Mexico," Bravo said.

Widespread Problem

Other scholars expressed similar alarm at the detrimental effects of pollution on El Tajin.

"The art of El Tajin is crucial to our understanding of the ancient history of the Gulf coast," said John Machado, a pre-Columbian art historian at Chaffey College in Rancho Cucamonga, California.

"It gives evidence of a powerful and complex civilization that had broad interaction with Mesoamerican cultures in both central Mexico and Maya-controlled regions but still cultivated its own unique Veracruz style and iconography."

"The loss of these images would be devastating to the cultural heritage of the area," said Machado, who has done extensive research at El Tajin.

But the problem of pollution affects archaeological sites throughout Mexico.

The sources of degradation vary, said Maria Lourdes Gallardo, chief conservator at the main Aztec temple, Templo Mayor, in Mexico City.

"The pollutants … in the archaeological zone of Templo Mayor … range from the smog to water filtrations underground," Gallardo said.

"We found that there had been a significant change in the rate of pollutants derived from sulfur, which had diminished considerably, compared to an increase in the quantity of chloride and heavy metal pollutants."

(Read related story: "Aztec Temple Found in Mexico City 'Exceptional,' Experts Say" [October 5, 2006].)

David Grove, a professor emeritus of anthropology at the University of Illinois at Urbana-Champaign, has worked extensively at the site of Chalcatzingo in Morelos, 60 miles (97 kilometers) south of Mexico City.

The site is noted for its Olmec-style bas-relief carvings dating back to 700 B.C. in granodiorite, a rock much harder than limestone.

"I can document with 30 years of photographs just how acid rain is destroying those magnificent works of art," he said. "The details are slowly disappearing."

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