Description and Logging Requirements
Read the description below, visit Flat Rock Park, answer the following questions and send them to me by e-mail:
1. In your own words, how does a pothole form?
2. At the listed coordinates, is the streambed generally smooth or is it uneven?
3. At the listed coordinates, there are multiple potholes to examine.
3a. Are the potholes typically wide and shallow or are they narrow and deep?
3b. Are there any stones or pebbles at the bottom of any of the potholes? If so, how many and what is their general size?
3c. How is the stream “interacting” with the potholes? Are any currently under water or filled with water? Or are there any that are just simply dry?
4. Why is it necessary for the stones or pebbles to be harder then the streambed to form a pothole?
5. With your "found it" log, include a photo of you or your group somewhere within the park. Optionally, you can take a photo of a personal item such as a geocoin or a piece of paper with your geocaching name.
If your answers are profoundly off, I’ll contact you. Otherwise, please log your find after you send an e-mail. In the e-mail, please indicate your geocaching name and include the names of other geocachers with you. Logs without accompanying answers sent will be deleted without notice. Sending the answers is a requirement, not a request.
Please be careful if walking along the stream bed to GZ, the rocks can be exceptionally slick. Better to walk in the grass. Depending on the time of year, at GZ you may find that some of the potholes are under the water or are filled with water, but the surrounding rock is dry. Unless there has been heavy rain recently there should be several examples for you to discover and analyze.
At the end of they day, use your best judgement based on the conditions.
Potholes
Geologic “potholes” are also known by a variety of other names including, “pot, (stream) kettle, giant's kettle, evorsion, hollow, rock mill, churn hole, eddy mill, and kolk.” They are also known as gnamma in Australia and opferkessel in Germany. Despite their various names, a pothole is a circular or cylindrical hole in the riverbed which is produced by force of water and abrasion. They are a testament to how, in geology, small things to lead to relatively larger changes over time. They can range in size from just a few inches (or centimeters) to several feet (meters) in both diameter and depth.
How does a pothole form?
Potholes start out as an uneven surface area in a turbulent river or streambed. When flowing water encounters bedload, it is forced over it and downcuts behind the bedload in swirling eddie currents. These currents erode the river’s bed and create small depressions in it. These actions are typically circular in motion which is what causes the potholes to be circular.
Once that depression takes shape, additional pebbles or stones then can become trapped within the pothole and, powered by the eddies, continue to erode the bedrock. Over time, the potholes become larger in both width and depth.
Key to this abrasion is that the pebbles or stones must be harder than the bedrock. If they are not, the opposite occurs, and the pebbles will erode over time. Two potholes can even merge over time if they are close enough.
Flat Rock Park
Park is open from 5am to 9pm. It has about 5.2 miles of trails, biking trails, geocaches, a lake for fishing, access to the Fall Line Trace trail, and 18 holes of frisbee golf. There are bathrooms on site (located a little bit past the entrance) as well as multiple picnic tables and covered areas. Pets are welcome but must remain on a leash.
If you intend to enjoy the stream that runs through the park, please use caution as the rocks can be quite slick.
Sources
www.parks.columbusga.gov
www.geo.mtu.edu/KeweenawGeoheritage/The_Fault/Potholes.html
https://geographyas.info/rivers/river-landforms/
For a visual description: https://www.youtube.com/watch?v=p5rXGQk_N8M