Mississippi Megafloods May Have Wiped Out the Ancient American Civilization of Cahokia

Mega floods from the Mississippi River may have helped wiped out an entire civilization. Scientists have discovered that at Cahokia, the largest prehistoric settlement of the Americas north of Mexico, major flood events caused its sharp decline.

Cahokia saw frequent flood events before AD 600 and after AD 1200. However, it rose to prominence during a relatively arid and flood-free period; it flourished during the years before a major flood in 1200. After the major flood, though, there was a time of political instability and population decline that led to its abandonment just 200 years later.

Traditionally, drought has been implicated as one of several factors leading to the decline of many early agricultural societies in North America and around the world. However, the findings of this study present new ideas and avenues for archaeologists and anthropologists to explore.

The researchers first made the discovery by collecting cores of lake mud to look for pollen and other fossils that document environmental change. In the end, they found evidence of major floods within the region. By around 1200, coinciding with a major flood fingerprint in the sediments, the population of the settlement began to decline along with other shifts in the archaeological record.

"We see some important changes in the archaeology of the site at this time, including a wooden wall that is built around the central precinct of Cahokia," said Sissel Schroeder, one of the researchers, in a news release. "There are shifts in craft production, house size and shape, and other signals in material production that indicate political, social and economic changes that may be associated with social unrest."

The findings reveal a bit more about this region and show that floods may be behind the decline of this settlement. This tells researchers a bit more about the past and about Mississippi flooding in general.

The findings are published in the journal Proceedings of the National Academy of Sciences.

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