Long before Europeans arrived to settle St. Louis, an impressive human construction stood on the eastern side of the Mississippi River. It was the Native American city of Cahokia. At its height, tens of thousands lived in and around Cahokia, leaving behind great earthen mounds as testament. The largest still stands about a hundred feet tall today, minus what was likely a temple that once adorned its crest.
Like all societies that disappear, we naturally wonder what brought this one to an end around 1350 AD, after a run of hundreds of years. Several familiar scenarios have been proposed: drought, over-exploitation of natural resources, and conflict. However, rather than the onset of a drought, it may have been the end of a dry period that did in Cahokia.
Cahokia was built near the Mississippi River and within its floodplain, and it wasn't protected by any of the levees and flood control structures that exist today. Samuel Munoz of the University of Wisconsin-Madison and a group of collaborators set out to find a record of floods on the Mighty Mississippi that might have impacted the denizens of Cahokia. Some previous work with a sediment core from a nearby lake contained what appeared to be a flood-deposited layer from around 1200 AD—the start of Cahokia’s precipitous decline. To find out more, they collected a second core from another floodplain lake about 200 kilometers downstream and focused on reconstructing the flood history in detail.
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