by Gregory Vogel

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2008 July 9
Floods, Archeology, and the Future Above our Heads

            Visitors to archeological excavations sometimes ask if people used to live underground.  This is a fair question, of course: why do we need to dig, sometimes quite deeply, in order to uncover artifacts from times past?  The answer is that prehistoric people didn't actually live underground, but the landscapes they inhabited were sometimes covered by sediment before archeologists discovered them.  From our perspective the past is under our feet, and from their perspective the future was above their heads. 

            And how do archeological sites become covered by this sediment?  Take a close look as the waters of the recent flooding recede, and you'll notice clay, silt, sand, and even large rocks and other debris left behind.  As powerful as water is over the course of a few weeks or months of flooding, its work over the course of centuries or millennia can be awesome.  As part of their natural cycles, rivers remove sediment from some places and deposit it in others.  Where they remove sediment archeological sites are destroyed, and where they deposit sediment archeological sites become buried and preserved over time.

            The archeology and geology of western Illinois show ample evidence of floods throughout the ages.  Fine-grained sediments like silt and clay indicate low-energy water environments: marshy back-waters, slow currents at the edges of floods, and other places where rivers were quiet but muddy.  Coarse deposits indicate fast-moving water with the ability to move heavy objects: swift flood currents, waterfalls, or white-water river rapids.  Where archeological sites are found above, below, or within a particular sediment event, we can date the archeology and determine how long ago the sediment was deposited.  

            The largest flood the Illinois River experienced is named the Kankakee Torrent, dating to about 17,000 years ago.  Enormous glaciers from the last ice age, centering around the Great Lakes region, had begun to melt.  The meltwater was trapped behind long hills made up of bedrock and soil that had been pushed south by the glaciers.  Geologically, hills formed in this way are called end moraines.  When the waters became high enough they broke through the end moraines and roared down the Illinois valley, filling it nearly up to the bluff-line with sediment-laden water.  High sand deposits, rocks, and enormous boulders attest to the power of this flood. 
 
            There's not much chance we'll experience another Kankakee Torrent in the next few thousand years, but more floods, even larger than those within living memory, are inevitable sooner or later.  High floods are hard on everyone in the valley, forcing people to leave their homes, travelers to navigate long detours, and delaying planting and destroying standing crops.  This has been the case for thousands of years, as long as people have lived in this area.  

            It doesn't appear that people in prehistoric times sandbagged against rising waters, but they did experience floods and deal with them somehow.  An archeological site on the east side of the Mississippi River near the city of Hannibal shows evidence of a major flood about 1,000 years ago.  The flooding was so severe it re-routed tributaries of the Mississippi, and dumped several feet of coarse sand right on top of an occupied village, burying or destroying nearly everything the people had.  The villagers re-built on top of the sands that covered their old homes.  Because of the village's location in the floodplain of the Mississippi, it has certainly flooded again and again since then.  The archeology of the region shows that people have re-built again and again too. 

            It's difficult to know what to make of re-building in flood-prone areas.  Persistent determination in the face of adversity?  Stubborn folly in a losing fight?  Perhaps, in some cases, it's simply a practical solution in light of wider circumstances – rivers, after all, have always attracted settlements.  From ten thousand years ago to today, large numbers of people have lived and worked on the banks of rivers.  I suspect that, like the ancient villagers east of Hannibal, we won't change that pattern anytime soon. 

            Take a look again at the sediments left behind by the recent flooding, and imagine how this landscape will look one thousand years from now after countless future floods.  Many of our homes, farms, roads, and entire villages will be buried and preserved by then.  I certainly hope the archeologists of the time look as sympathetically on us as I try to look on the villagers of the past. 

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