NOTE: This EarthCache is about Diamond Caverns... NOT Mammoth Cave.
How it all started
The story of this cavern starts over 200 million years ago when the limestone was first laid down. Most of the rock you see in the cavern is limestone, which formed in a warm, shallow sea. This happened so long ago that what is now Kentucky was not only under water, it was located south of the equator. The water was clear and harbored many living things much like the Great Barrier Reef of Australia today.
There was once a super-continent called Pangea. Pangea began to beak up around 200 million years ago forming the continents we have today. These continents slowly move apart. For example, Europe and North America move 1-2 inches farther apart every year, making the Atlantic Ocean just a little wider.
Some things about shallow tropical seas then and now are very similar: for instance, this is where limestone comes from. Corals, shellfish, and smaller sea creatures take dissolved calcium carbonate from the seawater to build protective shells. As these creatures die, their remains accumulate on the sea floor. Calcium carbonate that forms directly from the seawater also winds up on the sea floor, and geologists call it “ooze” since it is soft like slimy mud. Only the hard shells of animals like clams or corals are big enough to see, and we can still see them today in the walls of the cavern. Slowly, the ooze gets compressed into limestone.
Based upon study of local limestone layers, geologists estimate that, on average, every foot of thickness we see today represents about 40,000 years. When you go into the cavern, look at how much limestone thickness you see. As you go down the entrance stairs, you are traveling back in time roughly 23,000 years for every step you take. The part of the cavern seen on the tour is developed in about 100 feet of limestone, and at 40,000 years per foot, that means about 4 million years of earth’s history during the Mississippian period in the walls of the cavern.
Water cut through it
Moving ahead to about 10 million years ago. The limestone is in place. North America is now in the northern hemisphere, and above sea level.
In most parts of the world, runoff from rain flows mostly on the surface all the way to the ocean. In places like this, with limestone bedrock, the water can take a shortcut through tiny cracks in the rock and emerge as a seep of water someplace lower down, often near a river. As the water slowly moves through the limestone, it dissolves a tiny amount of the rock, which makes the cracks a little bit bigger.
The water can dissolve the limestone because raindrops pick up carbon dioxide as they fall from the sky, and even more as they soak into the soil. Soil contains a lot of carbon dioxide because of all the small animals, bacteria, and fungi that live in it. Water and carbon dioxide combine to make carbonic acid (as in carbonated soft drinks), which can dissolve the limestone. As the cracks carrying water gradually get dissolved out, they can carry more water, which means that they can be enlarged faster. Even so, geologists who study caves in the area estimate that it might take 50,000 years to dissolve away enough limestone to make a passage big enough to crawl into.
What began as a trickle perhaps 10 million years ago became a major underground river by about 2-3 million years ago, and then a strange thing happened. The entire cave was filled with sediment. The filling of the cave was linked to the advance of continental glaciers that affected all the major rivers in North America directly or indirectly. Glaciers never reached this area, and so Green River was indirectly affected. In brief, higher water levels in the Mississippi River made it so that the Green River and its cave stream tributaries could not move sediment, and so it piled up. You can still see some of the gravels stuck high up in the ceiling of the cavern.
The shape of the tall canyon passage in the cavern was altered even while it was filled. If you look carefully at the limestone walls of the cavern, you will find networks of interconnected channels that were dissolved out by water flowing between the sediment and the cave wall. We normally see these kinds of networks, called anatomoses, between bedding planes of limestone, but they can also form between sediment and walls. With another change in the cycle of advance and retreat of glaciers, the cave stream eventually washed out most of the sediment.
Time to make the formations
Once the cavern was open again, rainwater started seeping back into it. The rainwater gets carbon dioxide from that atmosphere and also from the soil as it soaks into the ground making carbonic acid. Now here’s the fun part: if the water stays in contact with the limestone long enough, then it will reach a point where it can dissolve no more limestone. When this water seeps into the cave, it can lose some of its carbon dioxide to the air in the Cavern. This is much like what happens when your soft drink goes flat after losing its fizz. Less carbon dioxide in the water means less carbonic acid, and so the water cannot keep as much dissolved limestone as before. So, some of the dissolved limestone crystallizes out as calcite on the ceiling, floor, and walls of the cavern. This can happen as a purely chemical reaction, but microbiologists who study caves have shown that bacteria are present on cave formations and may be involved in helping the calcite to crystallize.
If the calcite deposits on the ceiling at a spot with an active drip, then a stalactite may form. Water dripping from the ceiling may form a stalagmite on the floor, and if water runs down an overhanging wall, then if may form a thin ribbon called a “drapery”. If the drapery is thin enough for light to shine through, and it is banded from changes in water chemistry as it grew, then it is called a “bacon formation” because that’s what it looks like. If water seeps into the cave and evaporates at about the same rate as it seeps in, then “popcorn” can form.
Until recently we thought that it takes a century for a cubic inch of a formation to form. In a few cases this might accidentally be right, but usually it is wrong. Fact is the growth rate varies a lot, but in human terms it is slow. One stalagmite from this cavern has been studied by scientists who can actually date the calcite layers. This stalagmite is only about 9 inches tall, and yet the youngest part of it at the top is approximately 170,000 years old, and the bottom is roughly 306,000 years old. Based upon these dates, this stalagmite took 136,000 years to grow, and then it sat in the dark for 170,000 years until cave explorers first saw it. If we do the math on this, we find out that it took 1430 years for one cubic inch to form.
Logging Requirements
In order to log this EarthCache, send me your answers to the following questions either through email from my profile page or through messages on my profile page.
1. List at least 3 different formations that can be found in the cavern.
2. How many levels are there in the cavern?
3. How long is the cavern?
4. There are several Stalagmites that are cut off. Describe the colors and rings in any one of them.
5. List two ways that humans have damaged the cavern.
Pictures are not required, but they are appreciated. Please post a picture of you, your GPS or anything you found interesting anywhere around the mine.
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