Are Climate-Related Calamities Erasing Illinois’ Cultural History? An Archaeologist Explains

Jan Bartek - AncientPages.com -  A recent report by scientists from the Illinois State Archaeological Survey highlights the impact of increased flooding, erosion, and other consequences of human-induced climate change on many cultural sites across the state. Andrew White, a research archaeologist with ISAS and co-author of the report, discussed the extent of this issue with Diana Yates, life sciences editor at News Bureau.

Artist’s visualization of Cahokia. Credit: Cahokia Mounds State Historic Site, painting by William R. Iseminger

In "An Assessment of the Impacts of Climate Change on Cultural Heritage in Illinois," you and your colleagues describe climate-related harms to cultural sites across the state.

What are the worst climate-related forces endangering Illinois cultural sites?

Our report focuses on what we think are three major threats to cultural sites in Illinois: flooding, erosion and development. All three have been damaging or destroying cultural sites in our state for more than a century. Climate change will likely amplify the effects of all of them, perhaps significantly.

Our climate scientists tell us to expect more intensive rainfall events and more extreme heat in the coming century. Intense rainfall events will likely overwhelm natural and artificial drainage systems, damaging cultural sites by generating more surface runoff, eroding riverbanks and flooding rural and urban areas.

Extreme heat will lead to drought and crop failures, increasing the vulnerability of agricultural fields to erosion that can damage the fragile archaeological sites that lie just below the surface.

Development will also have a major impact. Despite an increase in climate-related events that we expect here, Illinois will likely remain more hospitable than many other parts of the country. After all, our risk from things like wildfires, sea level rise and hurricanes is low to zero.

Climate-related migration will likely lead to population increases in our towns and cities. Even moderate population growth will cause developed areas to expand by perhaps 1–2 million acres, destroying thousands of archaeological sites that exist now in agricultural fields and natural areas. Increasing population will also encourage the redevelopment of the core areas of cities, potentially threatening historic structures and neighborhoods.

What is the value of these cultural sites?

Cultural sites are valuable to different people for different reasons. For archaeologists, cultural sites preserve material evidence that teaches us about the past. These sites and the materials that we find there help us tell the stories of people, events and cultures that are not written down anywhere.

To others, cultural sites are places integral to their identity, connecting them to past generations in personal and profound ways. Destruction of a cultural site, whether by a sudden flood, the planned construction of a strip mall, or a gradual process like erosion, erases both what we can learn and what we can feel from that place.

How much is known about what the extent of the damage will be?

We can't say exactly what will happen in any given site or region, but we can make some reasonable predictions about how things are likely to play out over the long term.

To do that, we've combined what we know about the cultural sites that exist in Illinois with both climate projections and information about flooding, erosion and development. We project that increasingly severe flooding will damage thousands of historic buildings and historic districts and intensify erosion along streams and rivers, which were prime locations for people to live in the past just as they are today.

Illinois is an agricultural state, and soil erosion threatens most of the 70,000 cultural sites that we know about, as well as many more we have yet to discover. And we project that even a modest population increase of 1% per year will affect more than 50,000 sites. In many cases, the sites will be completely lost.

Which Illinois sites are most affected so far?

It's easy to see the damage to sites that are the most visible. Earthen mounds, like Monks Mound at Cahokia, are extremely vulnerable to erosion associated with intense rainfall. Flooding damage is also highly visible. Many historic structures and historic districts are in areas that are inundated more frequently.

The Farnsworth House in Plano, for example, is a well-known historic house that was purposely built along the Fox River. Frequent floods are making the structure more difficult to maintain and insure. Saving this historic landmark is likely to be costly.

Although the visible damage is significant, the damage that we can't see is likely much worse. The erosion of agricultural fields is a slow process that erases archaeological sites gradually —each year a bit more topsoil is washed away, and the plow cuts a little bit deeper. Development gobbles up farmland before we have a chance to even recognize the sites that are there, let alone learn anything about them.

You mention changes to Monks Mound at the historic site of Cahokia. What does it look like today? What is being lost or is in danger of being lost?

Monks Mound is a great example of how even known, protected sites may be vulnerable to climate change. The mound is the largest earthwork in the Western Hemisphere and is a focal point of the ancient city we call Cahokia, located across the Mississippi River from what is now St. Louis.

Monk's Mound, a Pre-Columbian Mississippian culture earthwork, located at the Cahokia site near Collinsville, Illinois. Credit: Skubasteve834 - CC BY-SA 3.0

Although the mound is protected within a state historic site, it is vulnerable to slumping and erosion caused by excessive rainfall. Built more than 900 years ago, the shape of the mound has changed significantly over the last few decades as portions of the original surface have slumped after heavy rains. This sort of damage is likely to continue and worsen if episodes of intense rainfall increase.

Cahokia is a National Historic Landmark and UNESCO World Heritage Site. It is important to both Indigenous communities and scientists for its connection to the Mississippian peoples that built it and lived there a thousand years ago. Losing Monks Mound to climate change would be a major tragedy.

Do you expect these trends to continue or worsen?

Climate change is likely to intensify the negative effects of flooding, erosion and development—and things are likely to get worse. The amount of destructive change we expect to see also largely depends on the amount of global warming we experience in the coming decades. A warmer planet means stronger storms, more flooding, more intense heat and more displacement of people living in some parts of the country.

We estimate that there were perhaps a million or more cultural sites in Illinois in the early 1800s. A good percentage of those, maybe 12%, has already been lost to development and other factors. It's possible we could lose another 10–12% over the next 100 years, which would nearly double the rate of site destruction. Many of the sites that are not destroyed will be seriously degraded.

That's a tremendous amount of information and cultural value that is in danger of being lost. Most cultural sites are fragile and unprotected, and those that we have not discovered far outnumber those we have. Once a site or historic structure is destroyed, it is gone forever.

Are there interventions that can help mitigate these problems?

Identifying the issues and the scope of the problem is just a first step. Having some working hypothesis about the impacts that we can expect makes it possible to start planning. And while this is a pressing issue, the gradual "slow onset" nature of many of the threats means that we do have some time to plan and act to lessen the effects.

To plan effectively, we'll need to know more about how the three main threats will unfold and affect particular areas or sites. That means we will need more information about erosion rates, flooding potential and areas likely to be targeted for new development.

We also will need to know more about the cultural sites that are in harm's way in areas of the highest potential impact. We can't save a site if we don't know it exists, so we should prioritize survey and site-identification activities in areas most likely to have cultural sites that are also at most risk of climate-related damage.

Even our best efforts will not save every cultural site. Effective collaboration among archaeologists, Indigenous communities, city and state agencies, preservation organizations and interested members of the public could go a long way toward slowing the destruction of our cultural heritage and leaving meaningful places for future generations to manage, enjoy, learn from and be inspired by. That is a worthwhile goal.

Written by Jan Bartek - AncientPages.com Staff Writer