Barton Creek Honeycombed Edwards Limestone
This is an earth cache and there is no physical container placed at this location. You will be making observations and answering questions based on those observations. As with most roadside swimming holes like this one, there is limited to no parking right at the cache. There is a pull off/gate not far where you can safely pull into while you make your observations.
Most times we stop to enjoy the view and/or feel of the water and the peace and quiet areas like this provide. We may even notice the rock and bed formations and admire them. Now we will make you wonder how the rocks at this location were formed and you will be able to answer the questions at the end.
Take a look at the rock formations at this location. It may make you feel like you have landed on the planet Mercury. Have you ever seen so many holes on a creek-side rock bed? Let's start out by understanding what types of rocks these are.
The rocks at this location are limestone. The process/development of the holes in this limestone is called porosity. The reservoirs in these rocks are created over time by deposits of solutions created by acids. This results in the breakdown of the rock by bacteria. This process is continuous. Limestone has three types of porosity. These are equi-solution, channel, and cellular. Most rocks have porosity. It just comes down to whether the porosity for each specific type of rock is high or low.
So now that we know that there is a porosity process, we need to also understand what element(s) come in contact with these rocks that help shape them. Water flow is what creates the holes in the limestone at GZ. The placement of the rock also has a lot to do with the formation. The rocks along this creek are subjected to constant and a decent rate of water current which are the cause of the holes the rocks at this location have.
As ridiculous as it sounds, you can compare these rocks and their holes to a sponge. Much like a sponge, these rocks store water that passes through them. This stored water is also easily released at a very fast pace. This is the reason why these areas littered with these types of rocks flood very easily. Not far from you is a flood gauge. Depending on the season or recent rainfall the water level could rise substantially and flood this entire area.
Questions and Tasks
1. Research the types of porosity for limestone and let us know what type of porosity is here and why you believe that to be the case.
2. Does this limestone have high or low porosity?
3. Take a look at your surroundings. Has this rock bed you are standing on/near been subjected to a decent current of water from the time it was formed until present day?
4. Do you see any sign of erosion or shaping here at GZ based on water flow?
5. As proof that you were at the location of this earthcache, please post a picture of yourself and/or your group or a picture of your GPS or phone at this location.