Mammoth Cave formations, formation.
This article is not to be confused with Cave formation Identification.
There are lots of different cave formations. You know the ones: cave popcorn, cave bacon, soda straws. (Anyone getting the idea that people were hungry when they were naming different features found in caves?) I will do an article in the future about how to identify them. But I’m saving that for a different park, and a different cave.
Today, I want to focus on the two most prominent formations.
If you’ve ever been in any ‘living’ cave with a guide, you will probably have been told their names, and maybe even a nice pneumonic about how to identify them. Stalactites which hold on tight to the ceiling, and stalagmites which push up mightily from the floor. That was the version I remember, there are other, similar phrases to help people remember which is which.
But how are they made?
Well, in an effort to “save myself time” and go “word-lite” for an episode. I created two fancy infographic.
It all starts with water.
To make cave formations you need water, and minerals which can dissolve in it. (aka: Soluble Minerals.) You also need a cave. To remember how those are formed, guess, or find a past blog!
Water doesn’t always make caves. If there are too many soluble minerals, the rocks are too easily weathered, or the water is too acidic, too fast moving, or too comically violent, then an entirely different process occurs and other features appear. Those are cool too. But we already have conditions for a cave (again, see previous blog) and this things are set up for cave formation.
(and last week I wrote about how I wasn’t an artist. Yet, its even more obvious why I chose not to find a job as a scientific illustrator)
If you wind up reading about Sloan’s Pond in Mammoth Cave. It talks about how most of the water in the region is absorbed by the limestone. Where it slowly, makes it’s way down to the water table. Sloan’s pond is the rare exception where the water is contained on the surface.
Once the water begins to filter through rock, many things can happen, but if they happen in the right order, then we get cave formations. First it has to find soluable minerals, and pick them up. Then it has to find a cave. Water usually moves through the path of least resistance, and despite a certain chaotician’s explaination of water flow aside, once water has found the best path, all of its friends tend to follow. Thus water begins to filter through the rock following along the same general path and ending up in the same general place.
So water filters down into the cave. If it ends up on the cave ceiling, then it does that thing water does, where it pools against gravity. Stuck to the ceiling and collecting until, eventually gravity wins— a drop at a time.
As each drop leaves the ceiling and falls to the floor, it leaves a teeny-tiny, small amount minerals behind. These minerals slowly build up on the ceiling, becoming stalactites. The rest of the mineralized water falls to the floor where it leaves behind more minerals. These minerals slowly build up and become stalagmites. Given enough time, these two cave formations often grow, in opposite directions, to reach each other forming pillars.
There are other trends. More minerals usually end up on the ground, thus stalagmites are typically bigger than their gravity defying counterparts. The time it takes for the minerals to deposit can vary rapidly, based upon a ton of conditions, leaving some cave formations to grow for thousands of years to the size others grow in tens of years. The minerals in the rocks effect the minerals in the water, and thus the minerals in the stalactites and stalagmites. Thus small amounts of iron, magnesium, or other chemicals can change the the formations colors over time.
But yeah. It’s that simple. Water flows through the rocks, picks up minerals along the way, then when it reaches the cave ceiling it leaves some minerals there before falling to the floor to drop more minerals off before flowing to lower ground. (If there is no lower ground you might get a cave pool beneath stalactites, instead of stalagmites.)
Or to put it even more simply, here is another drawing.
Yes there is a typo. No i am not fixing it. I made this in photoshop and am lazy. Once the Mammoth cave book sells 10,000 copies, I will commission an artist to go back and fix both of these drawings.
So, that drawing should explain everything. There you go. That’s how cave formations form.
Fun bonus fact: Cave formations have another name: speleothems.
We’re done!
Except, I mentioned “living cave” what does that mean? Well, a living cave, or a wet cave is a cave which still has water flowing through the rocks, and passages. Speleothems are still being deposited, and cave passages are still being carved (sometimes on a geologic time-scale so we don’t get to see it happening.)
Many parts of Mammoth Cave are dry. There is not a steady flow of water seeping through the rocks to deliver minerals to the ceilings and floors of many passages. Thus many parts of Mammoth Cave lack Cave formations. But not all. There are some beautiful cave formations throughout the cave, but you need to know where to find them. To do that: consult my upcoming book. Or even better: Ask a ranger!
Another noteworthy fact. You can find a similar process taking place outside of caves. Limestone, and it’s manufactured descendants: Concrete, mortar, and coral sand fill, are used in construction. These also absorb water, and can be mineralized. A consequence is that you can see speleotherms in man-made structures, given the right conditions.
Here is an example from Fort Jefferson in the Dry Tortugas.
And I’ll leave you with several warnings.
It used to be common practice at Mammoth Cave, and other caves, to break off speleothems as soverniers. Some people in cave country even made a business selling them. (rumors also have it that during the cave wars: waring cave guide factions—each representing their own cave tour— would break off formations in rival caves to ruin their tours.) This is sad on 2 accounts. A: outside of their natural environment, most speleotherms look like what they are: Rocks. B: Some of these formations take thousands of years to form and seconds to break. When they are ruined, they do not come back.
Minerals collect because they can stick together. The oils we secrete make things not stick. Touching speleotherms can stop their growth. And if you have the power of acidic sweat, your secretions can ruin them or change thier colors forever.
It is said that if you get hit by a drop of falling water in a cave, it’s good luck. But if you stand there for a couple hundred years, you might become a speleothem yourself.
This has been your lesson in how to explain a simple things
water->water+minerals->into cave->deposited mierals->speleotherms
in 500 words or more.
*Authors note: I made the illustrations to save the need and time for long written explanations. Editing these illustrations took 4x as long as writing all of this, but was much more fun. However, this is why I did not choose a job as a scientific illustrator. (well, that + lack of innate talent.)
My favorite cave formation is soda straws.
What’s yours?