19: Montana Musings D
Glory to Jesus Christ, y'all!
On this warm, humid afternoon, after a much-needed lunchtime thunderstorm, my memory is drawn to all the Caverns and mines that I've visited over the decades.
The overwhelming majority of them are humid, though never warm, this being because their interior temperature reflects the average annual temperature of the air outside, and their mid-latitude locations having a cool annual average from the high forties (Fahrenheit) to the high fifties (roughly nine to fourteen Celsius).
Each cavern has a unique personality as expressed in the orientation of its Flood-caused tunnels as well as in the variety and arrangement of its post-Flood speleothems. The same holds true for underground mines, but the personality of each of these is determined by the uniqueness of its Geology combined with the ingenuity of man through galleries, shafts, and equipment/infrastructure used for extraction of the mineral wealth contained therein.
Mines are for another post. Today's focus is on the production of speleothems. And, as before, examples from Montana's Lewis and Clark Caverns will be used.
As written before, the process of speleothem formation is simple, and, as meditated on before, the results are God's artistry, producing astounding beauty in hidden, thus inspiring of both curiosity and a sense of adventure, places that were the result of a global cataclysm that God had to have happen to both cleanse the world of its rampant, pervasive sin and to give the suddenly-overtaken sinners a chance to repent and save their souls, now that He had their attention through them seeing their world being rapidly (though not instantly) destroyed.
The chemical process involved in making cave formations is simple:
1.) Rain and snowmelt absorb carbon dioxide from the air. The carbon dioxide reacts with the water to form carbonic acid, a weak acid.
2.) As the water seeps into the ground, its acidity is often enhanced by acids released by plant roots and by the acids of decaying plants (and dead critters). The water can even be stained by organic matter dissolved in it or by minerals it has picked up along the way. Formations can then have a growth-ring look inside like tree trunks do, except that the layering just reflects what the water was carrying and depositing, not the number of seasons or years. (This example, like the opening picture, shows the layering. Normally, the layering is invisible, but the final blasting of the Lewis and Clark Caverns access tunnel snapped these stalactites, and exposed their inner layering.)
3.) When that water encounters a layer of limestone, it starts eating away a small portion of it, and ends up carrying dissolved calcium carbonate.
4.) If that water enters an air-filled tunnel left behind by the Great Flood, it drips or trickles in, depending on how much water is coming, and how quickly.
5.) Evaporation can reduce the water's holding capacity, and a bit of calcium carbonate will come out of solution and then stick to the nearest solid surface.
6.) Same if the water is jostled, such as by splashing or by trickling down an irregular surface (Recall Turner Falls in Oklahoma, from a previous post.). The jostling drives out some of the dissolved carbon dioxide, reducing the carbonic acid concentration, and thus reducing the water's ability to keep its dissolved calcium carbonate dissolved.
(All this can occur in mines and in storm sewers. Time for HOMEWORK!!! 😱😱😱 Ya, look up cave formations in mines, and also, specifically, in the older storm sewers of Montréal, a huge city sitting atop limestone.)
Now, cave tunnels generally don't have high winds, so dripping is generally downward, and trickling is also down, down whatever surface the water is clinging to, as water on a solid surface is wont to do. (Note the smooth surface immediately to the left of the tourist's baseball cap.)
A lot of caves don't get flooded, though some levels might be submerged at times, as is the case with Seneca Caverns in Northern Ohio. Florida is honeycombed with caverns, but the overwhelming majority are under the water table, and explorable only by diving; if no formations, either always submerged or insufficient time airfilled. There's only one airfilled cavern open for tours in the state, Florida Caverns, near Marianna, Central Panhandle right under Alabama.
Now for the specific speleothems. This is not an exhaustive list, but simply an overview of the common ones, all found at the Lewis and Clark Caverns:
STALACTITES: StalaCtites…C for ceiling. They are the fang-like things hanging from the ceiling. (If they grow hollow, w calcium carbonate precipitating on the outside of a hanging droplet, they're called SODA STRAWS, but tend to stay small. They're simply hollow calcium carbonate cylinders filled with water.) Because gravity narrows a hanging drop, the stalactite shape generally stays narrow, even when elongating and thickening with time.
STALAGMITES: StalaGmites…G for ground. They're the fanglike things pointing out of the ground…the floor of the cavern. They tend to grow wider than their roof-hanging counterparts because a falling droplet splatters upon landing, depositing calcium carbonate over a wider area, generally resulting in a broader, stubbier formation.
(In the photo above, numerous small stalactites hang from the roof while thick stalagmites rise out of the floor of the cavern. It's from the dripping pattern, and from the difference between hanging elongated up top and splashing widely down below.)
FLOWSTONE: The vertical ridged calcium carbonate deposits that are seen on walls plus, in the case of the Lewis and Clark Caverns, forming the beards on the stalagmites. Just like water running down a windowpane in little rivulets during rain, rivulets of water running down the side of a stalagmite will, by varying speed and having been jostled by splashing, deposit the mineral along their paths, gradually forming a ridge, generally a vertical ridge because of gravity.
COLUMNS: When stalactites and stalagmites grow together.
(Toward the back here.)
(Here, Babe Ruth's Baseball Bat, as mentioned in a previous post, is a long, smooth stalactite joined by growth to the flowstone-bearded stalagmite beneath.)
DRAPERIES: Lined-up stalactites (like those growing from a crack in the ceiling) growing together into a sheet-like slab of stone that often has an undulating shape if the stalactites aren't in a perfect line. (Visible far right above the brim of my friend's cowboy hat.)
Finally,
CAVE POPCORN: Looks like….well…popcorn!! 😉 Forms from seepage out of a surface and/or irregular splashing onto it. (Note the 55-degree-tilted pre-speleothem strata!) Some hanging above and some growing below.
HOMEWORK again!! 😡 Look up HELICTITES and CAVE BACON! And…visit a cave: it's really fun!!! 😇
Until next post,
Our Lady of Guadalupe, guide and protect us!