Pikes Peak Pebble Pups and Earth Science Scholars: Badlands Erosion Study Trip Report

By Jack Shimon, age 8
Member: Colorado Springs Mineralogical Society Pebble Pups

Introduction: My family went on a road trip this summer to South Dakota and ended up at Badlands National Park. We camped at the Cedar Pass Campground, hiked the Saddle Pass Trail and had two days to explore, which wasn’t enough but was still very fun. One day we did the GPS Adventure Tour. On this tour we counted cliff swallow nests on the Notch Trail, learned about the “slump” on the Cliff Shelf Nature Trail (a slump occurs when a layer is squished down due to the force from a rock fall), visited the Saber Site and Fossil Lab where we saw our friend Matt’s picture on their fossil finds board, and finally we completed the erosion study which was the most difficult and interesting task.

Badlands Overview. Photo by Jeff Shimon

This is a scenic overview of Badlands National Park from the North entrance. This was our first impression of the park when we drove in and I couldn’t wait to explore. I have learned from Edward Welsh, a Geologist in Resource Education at Badlands that this is the Brule Formation and the colored bands are very interesting. The red bands are formed by paleosol which is a fossil soil. The color formed when the soil was oxidized by vegetation. The gray/white layers formed when water, oxygen and nutrients leeched from the soil. All of the beds also have a lot of volcanic ash, about 80%, and are dated from the middle of the Cenozoic to the end of the Eocene, or 36-28 million years old. This was the Age of Mammals which explains why they found a saber cat skull and other related fossils in the park.

One of the things scientists in the park are studying is the rate of erosion. Erosion occurs when soil and rock are pushed off the surface by wind or water. I thought people climbing on the buttes would also cause erosion but according to the Ranger at the night program I attended at the amphitheater human impact is minimal. That was great news for me because I was allowed to climb all over. I still think the buttes most people climb are probably shrinking fastest but my guess is most of the park remains untouched.

For the Erosion Study we had to locate three markers by GPS near the Visitor Center and do some measuring, calculations, and guessing. I found all the markers and measured from the base of the rod where it went into the butte, to the very top of the rod curve. My mom recorded the numbers for me and helped with the calculations so the Data Table is a clean copy of my results. It turns out we visited the park almost two years after the markers were placed, which made our calculations easier since we cut the erosion rate in half to determine erosion in inches/year.

Before we did the calculations we made a hypothesis on what we thought would erode faster. I guessed the marker on the bottom of the butte, erosion marker 1, would have the highest rate of erosion because the rain would rush down and push more of it away. My mom thought erosion marker 2, on the top of a mound, would erode the fastest because it had greater exposure to wind and rain.

Art by Jack Shimon

As it turns out, I guessed correctly but not entirely for the right reasons. When I submitted my work to Julie Johndreau, Education Specialist at Badlands National Park, I was rewarded with an interesting discussion. She first confirmed that my calculated rates were correct and then brought up the point that different rock layers erode at different rates due to their composition. The red layer, which is a fossilized soil layer called paleosol, erodes slower. According to Johndreau limestone lenses and sandstone channels resist erosion more than the clay and siltstones that are present in much of the Badlands. We have a lot of sandstone near my home I have studied and I can visualize how they erode differently and at different rates. Monument Rock, only a few miles away, is a large sandstone formation with all sorts of holes and rounded shapes from weathering. It appears to erode along the sides rather than from the top resulting in intricate patterns and channels on all the faces but the top is as wide as the base. Until I got this information from Johndreau to think about I never realized that. I also learned one other important variable I hadn’t considered. As sediment washes down the buttes it can accumulate at the markers so some of them temporarily appear to have very slow erosion. This could explain the disparity in the rate at erosion marker 3 which was the same composition as erosion marker 1, just placed in a white later in the flat area at the base of the butte.

My conclusion is that the white layer is softer and consequently erodes faster than the red fossilized paleosol. It would be very interesting to return in one or two years and see if my calculated erosions rates still apply. In the questions to discuss at the bottom of the data form it asks how long would it take for the butte with erosion marker 1 to disappear if it was 30 feet tall? My mom helped me convert that to inches and then we calculated it would take 600 years! That seems like a really long time until I thought about question 2. If the park starts to get more rain it will erode faster. Rain is a good thing, but maybe not for the park. I definitely want to go back to Badlands National Park to learn more about the geology.