A dark plume leapt into the sky over southern Mexico. Below, waves of hot gas and rock screamed down volcanic slopes, stripping the mountain and surrounding area of vegetation, killing any living thing in their path. It mixed with rivers to create torrents of water, mud and other material as thick as wet concrete. For days afterward the air was choked with ash—microscopic shards of glass—that sickened survivors who inhaled it. It fell like snow onto the surrounding landscape, jamming rivers to create massive floods that wreaked havoc on agriculture. It was A.D. 540, and El Chichón—a small and previously unremarkable volcano—had plunged Maya civilization into darkness and chaos.

At least that is the story according to a new paper published in the February Geology, jumping into the long-running archaeological debate about what drove Maya civilization—one of the most sophisticated of its time—into a century-long “dark age.”

The Maya, who thrived from A.D. 250 to 900, are widely considered the most advanced civilization in the pre-Columbian Americas. They developed a writing system, precise calendars, new mathematics and magnificent cities with pyramids that still cast their shadows today. But a major mystery remains. In 1938 an archaeologist noticed a strange gap in dated Maya monuments. For more than 100 years the Maya inexplicably halted construction projects, seemingly deserted some areas and engaged in warfare. And in the 75 years since the discovery archaeologists have failed to find an explanation—although they have come up with a lot of hypotheses. Some have speculated an earthquake or hurricane struck the area. Others think trade routes might have collapsed.

An early hint that an ancient volcanic eruption might be the culprit came far from the Maya lowlands, in Greenland and Antarctica. A volcano can send a large amount of sulfur particles rocketing into the stratosphere, where they can easily spread across the globe. Once they reach the area over the poles they fasten to snow crystals and eventually become trapped in the ice sheets below, leaving a precise record for scientists to uncover centuries later. That is how Michael Sigl, a chemist from the Paul Scherrer Institute in Switzerland, deduced that a massive eruption must have happened somewhere in the world in A.D. 540—right at the start of the mysterious Maya “dark age.” Tree ring records indicate that sunlight-reflecting sulfur particles high in the atmosphere caused the global temperature to plummet by 1.5 to 2 degrees Celsius at the same time. A volcanic eruption had clearly rocked the world. But could scientists pinpoint its location?

8m thick deposits along the Platanar river from the 1982 eruption. Credit: Kees Nooren

The answer came at a chance meeting. Sigl encountered Kees Nooren, a PhD student from Utrecht University in the Netherlands, when the two were presenting side-by-side research posters at a conference. Nooren had been studying lake sediments in a delta just west of the Términos Lagoon along the Gulf of Mexico near the Yucatan Peninsula, when he unearthed a few shiny layers of volcanic ash. He analyzed individual shards of volcanic glass in the sediment and traced them back to El Chichón, then used carbon dating to pin the layers to A.D. 540, give or take 16 years. So when Nooren saw the sulfur spike at 540 on Sigl’s poster, he turned to him and said: “Hey, I might have a candidate for that.”

The resulting study clearly shows El Chichón erupted around the same time that sulfur particles got into the ice sheets, and that the Maya “dark age” began. Still, scientists disagree on what the eruption’s exact effect on the Maya might have been. If this eruption was the major event that lofted sulfur particles halfway across the world, it would not have only caused harsher winters (as seen from tree ring records), but also regional droughts. This is what Payson Sheets, an archaeologist at the University of Colorado Boulder who was not involved in the study, thinks interrupted Maya civilization. When Tikal—a powerful Maya city that dominated much of the region—was especially devastated by the ensuing drought, it was attacked by other Maya cities that fared better, causing a temporary collapse, Sheets believes. He also thinks drought affected other civilizations across the world, from the Wei Dynasty in northern China to the pre-Columbian city of Teotihuacán in the Mexican highlands (both civilizations are believed to have revolted against their rulers after poor harvests in the mid-6th century A.D.).

But it is also possible that El Chichón did not cause these global changes and that the true culprit has yet to be detected. “The equatorial Pacific is really a hotspot for these big eruptions,” says Matthew Toohey, a climate scientist from the Helmholtz Center for Ocean Research Kiel in Germany, who was not involved in the latest study. “But it’s also a blind spot, and there could be a different eruption there that we just don’t have any records of at the moment.” A number of studies have tried to link other tropical volcanoes to the sulfur spike, albeit with dates that are less certain. Discovering ash in the ice cores (along with the previously detected sulfur) would give scientists a smoking gun, allowing them to trace that ash to a specific volcano. But none has been discovered yet.

Nor can researchers be sure El Chichón’s A.D. 540 eruption was massive enough for its effects to span the entire globe. Nooren’s team assumes it was as large as the devastating event that occurred in 1982, when the mountain released huge amounts of sulfur dioxide gas, buried nine villages and killed 2,000 people. Juan Espindola, a volcanologist at the National Autonomous University of Mexico who was not involved in the study, agrees with this assessment given the large distance between the deposited ash that Nooren’s team studied in the Mexican Delta and El Chichón itself. Only a massive eruption would blow ash more than 100 kilometers, he thinks. Volcanologists will have to search for other ash deposits in order to really measure the event’s magnitude.

Kees coring sediment from a swale. Credit: Wim Hoek

However, even if the eruption was too small to have global effects, its proximity could have helped it play a role in the Maya “dark age.” Nooren and his colleagues think ash and pyroclastic flows from El Chichón could have easily thrown nearby cities into chaos.

Other archaeologists who were not part of this research agree the Maya hiatus was likely caused by the volcano—but they think it is because the eruption was beneficial, not disastrous. “Human societies are amazingly resilient and adaptable to natural disasters,” says Robin Torrence, an archaeologist from the Australian Museum. “People can often pick themselves up, dust themselves off and in many cases take advantage of new opportunities.” Those opportunities could have included the volcanic ash itself; in small amounts it can be a great fertilizer. Kenneth Tankersley, an archaeologist from the University of Cincinnati, thinks the Maya might have deserted some areas after the eruption to move closer to the beneficial ash. He goes so far as to suggest they depended on the fertilizing ash so much that a dearth of major volcanism at the end of the eighth century might have led to their civilization’s ultimate collapse—another mystery waiting to be solved.

Large or small, El Chichón likely played a role in the Maya’s mysterious dark age. It is no wonder that Sheets thinks this era could easily be turned into a screenplay. “This is great drama,” he says, “and it’s based in reality.”