The story of Diamond Caverns is one of water, living things, and a vast amount of time. There are three major time periods in the story. First was when the limestone was laid down, second was when the cave passages were carved out by underground streams, and third was when all the beautiful calcite stalactites and stalagmites you see in Diamond Caverns formed, which is still happening today.

Bedrock Formed in an Ancient Sea
Most of the rock you see in the cave 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, similar to the Great Barrier Reef of Australia today.

How can this be you might ask? Well, all the continents slowly move. For example, Europe and North America move 1-2 inches farther apart every year, making the Atlantic Ocean just a little wider. Perhaps you have heard of the supercontinent Pangea, back during the Age of Dinosaurs? When Pangea began to break up around 200 million years ago, the Atlantic Ocean was “born” in a sense, and of course it is still growing. These things take time.

The rocks we see in Diamond Caverns are even older than Pangea! So old that dinosaurs did not yet exist.

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 seafloor. Calcium carbonate that forms directly from the seawater also winds up on the seafloor, 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 Diamond Caverns. Slowly, the ooze gets compressed into limestone.

Slow. Let’s talk about slow. 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 Diamond Caverns, 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 cave we see on the tour is developed in about 100 feet of limestone, and at 40,000 years per foot, that means we are looking at about 4 million years of earth’s history during the Mississippian period in the walls of Diamond Caverns!

A Stream Creates the Cave
Let’s fast forward to a time roughly 10 million years ago. With our limestone firmly in place, North America actually in the northern hemisphere, and above sea level, the stage is set for the cave to develop. In most parts of the world, runoff from rain flows mostly on the surface all the way to the ocean. In places 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. They, like us, take in oxygen and give off carbon dioxide. 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. When you walk into the tall, roomy canyon passages of Diamond Caverns, try to imagine how many crawlway-sized passages it would take to equal the size of Diamond Caverns, and you will get a rough idea of how long it took to make this cave passage!

Imagine also how much water could flow through Diamond Caverns. 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 the Diamond Caverns 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 Diamond Caverns, and the shape of the tall canyon passage we travel through on the tour route was altered even while it was filled. How can we know this you might wonder? Look carefully at the limestone walls of the cave and 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 gravel fill (obviously, or else we would not be able to walk through today!).

Where did the cave stream go? It is still flowing and dissolving away limestone, but it is at a much lower level today. This stream, known as Hawkins River, flows just to the North and about 150 feet below the level of Diamond Caverns. All the water we see in Diamond Caverns goes to Hawkins River, which flows into Mammoth Cave. So we have a water connection with Mammoth Cave even though nobody has found a passage yet that explorers can travel through between the two caves. Exploration is ongoing, and the caves may one day connect.

click here for the next page...