[music playing] Kentucky is known around the world as the Bluegrass State, but it can also be known as cave country.

Beneath our feet stretches a vast network of limestone passages, carved by water over millions of years.

Let's explore the hidden world of Kentucky's caves and karst landscapes and why protecting them matters to us all.

[music playing] [music playing] Kentucky is cave country.

It is one of the most famous cave regions in the world.

It hosts Mammoth Cave, for example, the longest cave in the world.

[music playing] There's roughly about 5,000 named and documented caves throughout the state of Kentucky.

I'm actually expecting there to be about 10,000 caves throughout the state that aren't known about.

[music playing] And I think coming into these caves really puts in perspective, “Oh, this is what's underneath most of Kentucky.

This is what I'm living on top of, and I'm not aware of it.” It's invisible to most people.

The cave country is known as karst to geologists because it has certain characteristics that distinguish it from other types of landscapes.

These would be the presence, for example, of sinkholes, sinking streams, natural springs bursting out of the ground, and, of course, the caves that people love to explore.

This is built up limestone from roughly the Mississippian era, so about 300 to 360 million years ago.

And what happened was there was a very warm, shallow ocean that was throughout this part of Kentucky.

And with those warm temperatures and the shallow marine conditions, this was a perfect environment for the precipitation of calcium carbonate out of the seawater and deposition as limestone bedrock.

And this is the material that the caves of Kentucky have formed in.

[music playing] Karstification is whenever rainwater outside mixes with carbon dioxide (CO2) and makes something called carbonic acid.

It goes through the limestone that's underneath us, and limestone's pretty unique because it has little pores in it.

So, that carbonic acid travels through the limestone, goes down underneath us, and expands upon these caves that we have.

And so these crevices over time get wider and wider, creating a network of groundwater flow pathways that take water from the surface, move it through the bedrock, and discharge at springs later.

[birds chirping] When you go to McConnell Springs, you have the Blue Hole, which is this gorgeous blue pond.

And what you don't know about it, you can't tell just looking at it, but underneath it, there's a hidden passage, a sinking spring, that goes into it.

And that's why it has that unique blue color to it.

You walk a little further up the trails on McConnell Springs, you'll actually see a karst window.

So there's a little opening in the limestone that kind of gives you an example of what it looks like normally underground.

You'll see the water going through it, and then it goes back underground and comes up at the boils, where you'll see boiling water in this creek bed.

McConnell Springs educates people really wonderfully on these karst systems, especially in the bluegrass.

[music playing] Now, the presence of karst across Kentucky is really dependent upon the geology, and Kentucky has a rather interesting geologic pattern.

Right in the center, which is the inner Bluegrass region, we have the oldest bedrock in the state.

And if we move outward from that and into what's called the Mississippian Plateau or the Pennyroyal region, that is a limestone that is much younger, as much as 150 million years younger than the Ordovician-era limestones of the Bluegrass.

The bedrock tends to be rather thinly bedded.

And so the caves that form here don't get as large as they do out in the Mississippian Plateau region, where the limestones are very massive, very thickly bedded, and have very extensive sequences.

So that's where we find gigantic caves like Mammoth Cave forming in limestones of that type in the Mississippi area.

Slack's Cave, which is located in Scott County, is one of the longest caves in the inner Bluegrass region.

Since the limestones are thinner here, caves don't tend to get as big as they do elsewhere in the state, but this is one of the biggest caves, and it's certainly one of the ones that's been known the longest.

[music playing] The Bluegrass Grotto is a chapter of the National Speleological Society that was founded back in the early 1960s by a group of biologists at the University of Kentucky.

So, among the priorities in the grotto has always been the study of the organisms, and in particular, to find ways to minimize the ecological impact upon these very fragile systems.

In some of the larger cave systems, you're going to find a lot of organisms that are very specialized to live in a cave environment.

So I always love to talk about bats.

They're my favorite.

There are 16 native bats to the state of Kentucky, and they rely on these cave systems for their hibernation or their torpor periods, which is similar to hibernation.

But they're going into these caves and utilizing them to sleep for several months in the wintertime and protect them from these harsh winter conditions.

You have crayfish, or what some people call crawdads.

They have no pigmentation to them and no eyes whatsoever because caves are total natural darkness.

You don't need these adaptations over time.

They develop their other senses more acutely.

They may have long antennae that are sensitive to vibrations.

So we find many, many unique and fascinating organisms that live in caves and are able to survive in this relatively harsh environment.

Now, one of the reasons that we map caves, such as we did with Slack's Cave, is to understand how the passages relate to the surface.

And we do this for a number of reasons.

One is that it may help us discover other caves that might be hydrologically connected.

We also use groundwater tracing using nontoxic dyes to help determine those same patterns.

And all those are actions that are beneficial in a karst area to protect the quality of the water in a system.

[water flowing] The water supplies in karst are extremely vulnerable because there's no filtration, there's no purification of the water between the surface and what comes out of the spring somewhere.

Water goes into a sinkhole, and it carries anything that happens to be with it, goes right into the ground, follows the conduits underground, and discharges from a spring.

[birds chirping] [water flowing] You're going to find chemicals, pesticides, metals of various kinds; all of these can get into groundwater, whether we're talking about water flow in karst or in some other type of aquifer.

And all this does is put that material in somebody's water supply elsewhere.

[water dripping] Probably the best thing that casual visitors to any cave can do is to follow the basic mantra for cavers, which is to take nothing but pictures, leave nothing but footprints, and kill nothing but time.

It's such a unique experience.

You're walking through, and you're seeing millions of years of history built up in front of you.

And you don't get to see that all the time, but we're lucky enough to be in Kentucky, where you're probably within a two-hour drive of a commercial cave toward any point.

It really is one of the last frontiers of human endeavor.

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