Center for Teaching & Learning K. Kopacz - Starved Rock

In January, I wrote about my curiosity and appreciation for Starved Rock State Park, located in north-central Illinois, near Utica. I wrote about the connection that this place allowed me to have both with nature and my past. I asked some questions about the landscape and the geologic processes that formed the massive sandstone canyons scattered around the sandstone bluff that gives the park its name. These questions were primarily focused on the formation of the deep sandstone canyons, and how that much sandstone got there in the first place. I had previously thought that the sandstone was deposited by the Illinois River, a massive tributary to the Mississippi River, located directly next to the state park. Turns out I was wrong. Through my studies in this class I am now able to better understand the origin of the sandstone deposits and how they have been shaped into breathtaking canyons for us to explore.

Initially, I thought that the nearby Illinois River had been depositing sand for so long that it would be able to build up the hundreds of feet of sand that is exposed in the canyons of Starved Rock. However, there were two topics that I learned about that taught me more about processes like this, and I was able to understand the deposition of the sandstone better. The first of these concepts was learning about oceans and beach environments, their depositional footprints, and just how they work in general. The Illinois River just hasn’t been around long enough to deposit the hundreds of feet of sandstone that is laid over the surrounding area of Starved Rock. Additionally, the actual sandstone rock formation of Starved Rock sits high above the river, and from what I can remember (the park is closed so I can’t go and check but I am almost certain) there are no river terraces in the surrounding area, meaning that the river was never at the same height or above the sandstone that was laid to make the Starved Rock formation, and therefore the Illinois River could not possibly be the source of the state park.

In my first journal entry I mentioned that Illinois was once covered by an ocean. After learning about beaches and marine deposits, I am almost certain that this is where the sandstone had come from. Indeed, at the park there are information tables set up that explain some of the history of the land as geologists have come to know it. Upon further investigation, I have found out that the sandstone laid at Starved Rock comes from a very particular and large sandstone deposit called St. Peter Sandstone. This sandstone was said to have been deposited from an ancient ocean that covered the modern Midwest. The formation covers a vast area, spanning from Minnesota to Arkansas in the north-south direction, and from Illinois to Nebraska in the east-west direction. One of the characteristics of the St. Peter Sandstone deposit is that it is very well sorted, with some areas having sandstone that is up to 99.44% silica. This kind of sorting, to my understanding, is very likely to come from a beach environment. Perhaps massive sand dunes could explain the deep sandstone deposits that the canyons cut through. I think this might be the case because the nearby Indiana Dunes State Park has massive sand dunes that are hundreds of feet high, which could explain how the sand could have been piled up in Starved Rock. Additionally, the well sorted and pure sandstone probably was a result of waves hitting the shore of the old ocean, which would weather the quartz sand more and more, over and over until it reached the purity that is found in the area. I think that the combination of these two coastal processes is what led to the large amount of sandstone in the area.

Now that I have a good understanding of where the sandstone likely came from, that doesn’t explain how the canyons in the sandstone were formed. There are streams and small tributaries that pass through the canyons, and they might have been able to carve as deep as we can see today, but I would think that it would take a very long time. Which leads me to the second topic that contributes to the understanding of Starved Rock, which is glaciers and glacial meltwaters. Although the St. Peter Sandstone is many millions of years old, I don’t think that Starved Rock has been around for that long for a couple reasons. First, we know that glaciers covered most of Illinois during the last glacial maximum, which means that the canyons of Starved Rock would probably have been blasted over with ice, and eroded away with the surrounding area. So that must mean that the canyons we see today must have been formed relatively quickly, over the past 20,000 years or so. That must have been a lot of water flowing through the area over that time in order to make canyons so deep. After learning about the Connecticut River and how its formation is the result of glacial meltwater flowing from glacial Lake Hitchcock, it makes me think about how glacial meltwater could have rapidly shaped Starved Rock as well. Most of Illinois was covered with glaciers during the LGM, which means that when those glaciers retreated there was a whole lot of water running through Illinois. I think that the massive amount of meltwater could have shaped the environment at Starved Rock by filling the tributaries and streams with a massive volume of glacial meltwater, which could blast away at the poorly cemented sandstone and form the canyons that are scattered over the area. As expected, the streams in the area all lead to the Illinois River, which could have been like the Connecticut River in that it was the main channel that carried away glacial meltwater after the retreat of the glaciers from Illinois.

Knowing more about the processes that form and shape landscapes has given me more of an appreciation of Starved Rock. When I went there as a kid it was just all about hiking and playing in the canyons and streams. Now I am able to form hypotheses and my own interpretations about how the landscape was formed and I can appreciate all the processes that took place to bring me one of my favorite spots on the planet. With all that I have learned, I look forward to the next time that I can visit Starved Rock and get more information about how the area was formed. I am thankful for the things that I have learned so far because they allow me to piece together the geologic history of places that mean a lot to me.

Kyler Kopacz

5/14/20

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