How a pyramid rose from the ashes of a colossal volcanic eruption

Fifteen hundred years ago, Ilopango, a caldera volcano in what is now El Salvador, erupted in one of the largest events of its kind in recorded history. Known as the Tierra Blanca Joven eruption, it shot 10.5 cubic miles’ worth of tephra—pumice and ash—into the air, more than 100 times the amount produced by the Mount St. Helens eruption of 1980. The solids that resettled blanketed the valley below; those that didn’t are thought to have contributed to a cooler climate throughout the Northern Hemisphere.

The eruption has long been credited with hastening the end of the ancient Maya civilisation that flourished throughout Mexico and Central America. But a new study in the journal Antiquity suggests that the eruption didn’t portend doom—at least not for an area only about 25 miles from the caldera. Instead, it enabled the swift construction of a massive Maya pyramid, a monumental structure that signalled the resilience of those who built it.

“Events like eruptions and drought have often been considered a main factor in ancient collapse, abandonment, or decline,” says study author Akira Ichikawa, a postdoctoral associate at the University of Colorado, Boulder. “My research suggests ancient people were more resilient, flexible, and innovative.”

Ichikawa conducted excavations in San Andrés, a Maya settlement in the Zapotitán Valley near what is now San Salvador, the capital of El Salvador. There lie the ruins of the Campana structure, a towering pyramid that at the time would have dwarfed everything else in the valley.

As the team dug several excavation trenches, they uncovered eight layers of building materials. Eventually they hit some 16 feet of pure white tephra that contained only a few shards of ceramics and other materials, suggesting the builders had carefully sifted through the ash and pumice before using it to build.

Construction began remarkably soon after the explosion decimated the valley. Radiocarbon dating indicate building may have begun as few as five years after the eruption. (Though estimates of the date of the disaster vary, Ichikawa says later generations didn’t use the tephra, suggesting the builders began construction while the eruption still loomed large in local memory.)

The builders may have chosen to use the tephra because of its white colour, says Kathryn Reese-Taylor, an archaeologist and professor at the University of Calgary who has studied community formation in Maya culture. “[The colour] likely had some significance,” says Reese-Taylor, who was not involved in the study.

Venerating volcanoes

Mesoamerican cultures saw volcanoes as sacred, Ichikawa says. “They may have believed that dedicating a monumental structure to the volcano was a logical and rational way to resolve the problem of possible future eruptions.” 

The Maya were not alone in venerating volcanoes, says Mark Elson, an associate professor of anthropology at the University of Arizona who studies humans’ response to volcanic reactions. He points to corncob impressions found in black basalt near Arizona’s Sunset Crater Volcano, which erupted around 1085.

“We think the corn was left as an offering in the lava flow by the Hopi in an attempt to control the volcano as best they could,” says Elson, who didn’t participate in the Maya study.

But the Maya’s use of tephra “was not only religious or symbolic, but practical and functional,” Ichikawa says. As he learned from one of his coworkers, tephra from the explosion is still used as a construction material because of its excellent compaction.

Religious or not, the structures would have helped local people—either the valley’s survivors, people who migrated to the area after the blast, or a combination of the two—come together for a common purpose. That resonates with Ichikawa, whose native Japan has faced down disaster after disaster during his lifetime.

“Monumental construction projects were collective work. That’s an effective way to get back to a normal life,” he says. By emphasising social ties, integration, and unity, people can work their way out of even the most catastrophic disasters.

It’s still unclear how many people did the construction. Ichikawa estimates that it would have taken a minimum of 13 years for a workforce of 100 labouring four months a year, and as little as 11 months for 1,500 workers. He says more study is needed to determine how the workers procured food, and whether they built at the behest of local rulers or as a religious tribute.

Why look back at an eruption that happened so long ago? “Disaster studies help us cope with upcoming disasters,” Elson says. “Things aren’t going to get better.”

Reese-Taylor says the Maya study is an important addition to the scant body of research about a little-studied region. “Volcanic eruptions happened regularly in this area,” she says. “The resilience it takes to come back and rebuild bigger and even better astounds me.”