This article was published in Scientific American’s former blog network and reflects the views of the author, not necessarily those of Scientific American
For decades, Louisiana’s coast has been sinking into the Gulf of Mexico. The rate at which it has been disappearing has only been amplified by modern industrial channelization, the effects of saltwater intrusion, and, in what may prove to be its greatest accelerant, the rising of the sea itself. Already, Louisiana’s coastal land loss has caused immense changes to the physical geography and environment in a relatively short amount of time. As we rush to understand, monitor, and, if possible, remediate some of the effects of coastal land loss to Louisiana’s renewable and non-renewable resources, it’s worth mentioning the loss to a resource less apparent, but just as real: the archaeological record.
The archaeological record can help us refine the age and geographic extent of a culture, understand which groups that culture interacted with, and understand trends in ancient economies and trade networks. In a lot of cases, the archaeological record is the only evidence of these peoples and cultures. This is especially true for peoples without a written record, either because they pre-dated written language, didn't use it, or weren’t represented in the record during that time. But what’s particularly useful about archaeology is that it can anchor a place within the broader antiquity of a region where we live. It’s hard to imagine what thousands of years of human occupation on a landscape looked like through time. Often it is only within the archaeological site that we have evidence of any of it.
As the Louisiana coast subsides, sites that were once situated on land become inundated and then fully submerged as the shorelines and marsh islands they sit on slowly sink down into the bayous and bays. The sinking land allows these bayous and bays to expand, becoming less distinct and eventually give way to undifferentiated open water. Achaeological artifacts and features (such as trash middens) can be ripped from their primary contexts and scattered into the waters. Some archaeological sites get capped by wave-carried sediments as they become submerged, allowing some deposits to remain intact, but there is no doubt that sites are eroded and destroyed more than they are preserved. Evidence of damaged or fully destroyed archaeological sites, in the form of loose, wave-washed artifacts, are readily apparent along miles of the nook-and-cranny shorelines in the bayous and back bays of the coast. Artifacts dating from different times and affiliated with different groups and cultures are intermixed with decayed shells and get kicked-up by wave action onto shorelines, where they’re redeposited. As we continue to investigate the Louisiana coast for evidence of the past peoples that lived on it, these mixed assemblages of artifacts will increasingly be the only evidence left.
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A wave-washed prehistoric ceramic sherd, found along the shoreline of a marsh island. Photo courtesy of Brian Ostahowski
Along the coast in Plaquemines Parish, located at the terminus of the Mississippi River (it makes that distinctive “crow’s foot” at the end), some of the most dramatic land loss on record has occurred and, as a consequence, the highest rates of terrestrial archaeological site loss has occurred. Some recent data suggest that archaeological sites located along the marsh islands have been inundated at a rate somewhere just under 2 sites per year. Sites once documented as located within the protective boundaries of marsh islands, are, only decades later, today located 50 feet off-shore. This is disturbingly common; some examples include prehistoric mound sites, prehistoric villages and historic shrimping and oyster camps, to name just a few. Some of these sites are 500-800 years old, having been occupied for maybe as much as 100 years during their creation, and have been now completely erased from the landscape in as little as 20 years.
We interpret and characterize patterns of the past, such as diversity or similarity between peoples, by looking at the range of variability within and between groups; as we lose archaeological sites, larger patterns of prehistory and history begin to soften, limiting our ability to ask deeper questions about our past. These kinds of concerns are relevant, not just to Louisiana, but to any coastal areas with barrier islands, beaches, estuaries, and coastal forests threatened by sea level rise.
With that threat increasing, so must our vigilance of the possible adverse effects. The ability to monitor the environmental impacts to these threatened archaeological sites is of paramount importance. Hopefully, with the proper resources, we can try to investigate and record these sites before they’re gone.
