About 20,000 years ago, where I am sitting in Chicago was covered by about a kilometer of ice. This was the height of the most recent advance of ice sheets in the Northern Hemisphere, which had begun some 80,000 years earlier. About 15,000 years ago the ice sheets began to retreat and within the next 5000 years they had totally disappeared. These great ice sheets left an indelible mark on the landscape, the most notable being Lake Michigan and the other Great Lakes, carved by the glaciers in the underlying bedrock. Paralleling the current shore of Lake Michigan to the south and west are linear hills, moraines, up to a hundred feet high, deposited by the glacier as it temporarily slowed in its retreat. And as the ice melted it produced an ancestor to Lake Michigan, Lake Chicago, whose northeastern shore was the retreating glacier and whose southwestern shores were the morainal hills. In one spot, to the southwest, a mile-wide river cut a channel in the moraine, through which flowed water not only from Lake Chicago but from the entire newborn Great Lakes.
Eventually Lake Michigan reached its current shorelines and the great river channel was abandoned, although the gap in the morainal hills remained. The area that had been covered by the lake became a low-lying and flat region of marshes, lakes, low-gradient rivers, tall grass prairies, and small wooded areas. To the east of the morainal hills, water drained via the Chicago River into Lake Michigan, whereas to the west of the hills it drained towards rivers that eventually connected with the Mississippi. This was the situation when humans first entered the area.
For the Native Americans, the numerous lakes and rivers throughout the region provided ready avenues for trade. Especially appealing was the low area across the hills, which provided an easy portage between the Great Lakes and the Mississippi. This did not go unnoticed by the first Europeans to visit the area, the French explorers Louis Jolliet and Jacques Marquette; Jolliet noted that it would take only a short canal to create an inland water route through the region North America. And as European settlement occurred, it became obvious that this location would be of great economic and strategic importance. The first permanent settlement was built near the Chicago River in 1779, a fort was constructed in 1808, and in 1833 the city of Chicago first incorporated.
Until the arrival of Europeans, the geography of the area was unchanged since the retreat of the ice sheets. The first change was small, the soldiers at the fort cut a short channel between a bend in the river and the lake. But in the period from 1836–1848, Jolliet’s vision was realized — the Illinois and Michigan Canal was built through the old portage. The safe and easy inland transportation route was the crucial catalyst for the growth of Chicago; one could now go from New York City to New Orleans without once venturing into the open seas. The city boomed; the development of railroads was an even greater shot in the arm.
But the growth of the city ran into the legacy of Lake Chicago, with the twin issues of water supply and sewerage. Water was obtained from offshore inlets in the lake, while wastewater flowed into the river. The low and flat area provided very little gradient for sewage to flow, so in the late 1850’s sidewalks were raised to facilitate drainage. However, waste still ran into the lake, leading to periodic contamination of the drinking water and epidemics of cholera.
So, in the late nineteenth century a radical engineering fix was carried out, once again taking advantage of the ancient river channel. A new and much larger canal was constructed, completed in 1900, which reversed the flow of Chicago River so that it now longer flowed into the lake, but towards the west and the Mississippi (to the chagrin of St. Louis).
Problem fixed? Not really. Heavy storms could overwhelm the sewer system, which carried both rainwater and sewerage, and pollute area lakes, rivers, and homes. So, beginning in 1975 and continuing until the present day, at a cost of more than $3.5 billion dollars, the Tunnels and Reservoir Plan, aka Deep Tunnel, was constructed. More than a hundred miles of tunnels, some up to 33 feet in diameter, were put in place some 300 feet below the surface and connect to large quarries and the existing sewer system. The Deep Tunnel system acts as storage until the sewerage can be safely treated and released.
The canals, the quarries, the Deep Tunnel, are just some of the many ways in which the humans have produced huge transformations of the natural environment which will be long-lasting. For example, since the river was reversed, some 80% of the marshes in the region have disappeared and the remaining are small and isolated. The lake shore has been built out. We must look hard to see the signal of natural processes; they have become overwhelmed by the physical, chemical, and biological impacts of humans.
For the past several decades, it has been proposed that we call the age of human domination of natural processes the Anthropocene. Those of us in Chicago, and in fact nearly everyone on Earth, are clearly living in that era. Humans effectively control the entire planet; whatever happens next is up to us.
(Note: whether the Anthropocene should become an official part of the geological time and when we should designate its beginning are fiercely debated scientific questions. I strongly support the informal use of the term for modern times).