Soda Straws: The Young Stalactites
Soda straws, otherwise known as straws, are hollow, young, delicate stalactites. These took shape when crystals gather around a droplet of carbonic acid.
Simply put, Tim Martin summarized it this way [1]:
"As water slowly drips from the ceiling of a cave, dissolved calcium carbonate will crystallize around the edges of a drop of water producing a long narrow tube. This will continue until calcite deposits block the water flow through the center of the tube. If water continues to flow over the external surface of the formation, a larger tapered stalactite will form."
Water flow and Fracture Network Flow
In one study, it was mentioned that, stalactite shape and chemistry appear to be governed by the two main water flow processes in limestone [2]. First, the porosity water flow, which tends to homogenize the growth, shape and chemistry of stalactites. Second, the fracture network water flow causes variations in stalactite growth rate, shape and chemistry.
Of Carbon Dioxide, Calcium Carbonate and Minerals
Limestone caves are commonly laden with stalactites and stalagmites. This is because they are mainly composed of calcite, a common mineral found in sedimentary rocks. Calcite molecules are made of calcium and carbonate ions, and are referred to as calcium carbonate. When rainwater falls over a cave and trickles through rocks, it picks up carbon dioxide and minerals from the limestone. Then water comes into contact with the air inside the cave.
This process causes some of the calcium bicarbonate to be transformed back into calcium carbonate. Calcite then starts to form around the crack. As water continues to drip, the length and thickness of the calcite grows, and eventually a stalactite forms on the ceiling [3].
Then You Can See It
Slowly, the crystals build to make a small, hollow tube suspended from the ceiling. The carbonic acid continues to run through the inside of the tube. Calcite continues to be deposited on the outside at the same time. This creates formation of longer straw.
To be a true soda straw, the stalactite must be hollow and only one drop wide. Soda straws grow relatively slowly and have a fairly short lifespan. These tubes often get plugged and calcite will start depositing on the outside of the straw giving it a wider diameter. The straws also often collapse under their own weight [4].
In conclusion, soda straws are a delicate mineral formation which is crucial in the formation of many other types of speleothems. Soda straw formation involves a droplet of carbonic acid and minerals. It takes decades before a small portion becomes visible because the process is painstakingly slow .
The growth, preservation and prevention of disruption of speleothem growth is easily done if the leave-no-trace principles is be adhered to. Like any other stone formations and flora and fauna inside the the subterranean ecosystem, t
References:
[1] Martin, T., 2002. Soda Straws And Helictites. [online] Epod.usra.edu. Available at: <https://epod.usra.edu/blog/2002/03/soda-straws-and-helictites-1.html> [Accessed 24 June 2020].
[2] Perrette, Y. and Jaillet, S., 2010. Spatial distribution of soda straws growth rates of the Coufin Cave (Vercors, France). International Journal of Speleology, [online] 39(2), pp.61-70. Available at: <https://scholarcommons.usf.edu/cgi/viewcontent.cgi?article=1132&context=ijs> [Accessed 25 June 2020].
[3] Fuller, J., n.d. What’s The Difference Between Stalactites And Stalagmites?: The Formation Of Stalactites And Stalagmites. [online] HowStuffWorks. Available at: <https://science.howstuffworks.com/environmental/earth/geology/stalactite-stalagmite1.htm> [Accessed 24 June 2020].
[4] Wichlacz, A., 2007. Soda Straws. [online] People.uwec.edu. Available at: <https://people.uwec.edu/jolhm/Cave2007/TeamB/soda_straws.html> [Accessed 24 June 2020].
