Renowned cave explorer Dr. Chris Groves goes deep into Mammoth Cave to see how torrential rainfall above affects underground rivers and ancient passages.
Photo © J. Carl Ganter / Circle of Blue
Dr. Chris Groves, director of the Hoffman Environmental Research Institute at Western Kentucky University, explores Mammoth Cave, the longest known cave system in the world, in early May as two-day floods damage nearby Nashville, Tennessee.
Welcome to Circle of Blue Radio’s Series 5 in 15, where we’re asking global thought leaders five questions in 15 minutes, more or less. These are experts working in journalism, science, communication design, and water. I’m J. Carl Ganter. Today’s program is underwritten by Traverse Internet Law: tech savvy lawyers, representing internet and technology companies. In early May 2010, Nashville, Tennessee, was drowning. The Grand Ole Opry and the entire downtown was under water following torrential rains. But not far away–near Bowling Green, Kentucky–researchers were going underground into caverns carved through solid limestone by eons of water flow. They wanted to get a sense of how an ancient cave system was behaving as the rains fell above. So, deep down, in Mammoth Cave, I joined Dr. Chris Groves, a world renowned cave and limestone karst expert who directs the Hoffman Institute at Western Kentucky University. I follow him on a tour of tunnels, water, and a bit of history.
How far underground are we?
Chris Groves: Right here, roughly probably 250 feet–something like a 20 or 25 story building of more or less solid rock above us.
So, we’re underground in Mammoth Cave. While it’s raining up above in water events, we’re deep down in the karst system in Kentucky.
Chris Groves: Actually, this is the only bathroom we’ll pass. Anybody need to use the restroom: either of you?
No, I’m good.
We’re coming up here to a …. most of the cave’s been very dry, and one of the issues here that surprises people in Mammoth Cave is that you expect to see a lot of stalactites and stalagmites and such, and you just don’t see them here, for the most part. And that’s because the geology is such that there’s a waterproof sandstone layer over top that prevents water from coming down, but we’ll come up to a hole in that pretty soon. It’s more of waterfalls coming up. What’s a little different than normal is that we have gotten quite a bit of rain in the last few days here, and–I think somewhere exceeding ten inches, but I’m not really sure of the exact amount–but this is probably the most rain we’ve had here over a similar period of time since, probably for 25 years.
Just as we’re coming down here in River Hall at Mammoth Cave is the lowest level that are on the public tours, and you can see how the floor’s kind of dark. There’s actually kind of a bathtub ring right here, so this is the highest that the water’s got just in the last couple days and now apparently is receding. This level here that you can see, this is about 45 feet higher than the normal “low” water condition. You see some of the water’s still pooled up. In fact, those benches are usually lined up along the side. They’ve apparently been floating in a lake, and that’s their position as the lake receded. You can see also these–what look like giant rulers, that are essentially giant rulers–those are kind of an old fashioned version of the methods that they used to look at the water levels during the floods. Now, actually, there’s computers that are measuring with probes back there, but just from looking at those, they saw that it was up to 45 feet.
The last time it got up here was up to right about here. . . was in 1984, so we’re real close to it. I have some data from a study in a river in another part of the cave, where it flooded in 1997, where it rained a little bit less than this one, and we have data from there that the river rose about 94 feet in 12 hours–including rising about 24 feet per hour at one point. And 1997 was here. That tape up there was from 1984. Then on the point of that rock up, there there’s actually some tags up there from 1937. So it’s definitely a very dynamic system in here.
So up above, we have a very dynamic water system and we forget about what’s happening down below, often times.
Chris Groves: Well, water drains downhill, just like in a bathtub. And here, what’s a little different is that downhill is not necessarily down the side of a mountain or in a river, but here–because the ground is so dissolved out–it’s literally going straight down into the ground. So the nice thing here in Mammoth Cave, and other caves in south central Kentucky and other areas, is that we can actually go into the aquifer and just see for ourselves what it looks like and sample water and really kind of learn about it first-hand.
What are some of the things you learn when you’re down here?
Chris Groves: Well, the big issue here is that we’re in a National Park–which is pretty much the most highly protected land that the Government has in terms of land use–so you’d think that the water would be pristine, just because it’s mostly forest above the surface here. And the cave is, as we know now, so remarkably vast that the passages extend far beyond the boundaries of the National Park. In some cases, these are the upstream ends of some of the underground rivers that are drained in agricultural land. So there’s septic tanks, animal waste, fertilizers, and what have you.
Photo © J. Carl Ganter / Circle of Blue
Jason Polk, professor of karst, climate change and environmental policy at Western Kentucky University and Chris Groves discuss the quality of the water that flows inside the cave. A steady stream of scientists from around the world also come each year to visit the famous site, according to Groves.
So tell me about the water quality: we’ve got a whole flow, we have a whole other world up above us–what’s flowing below us?
Well, we can see actually two different sources of water here. There’s the river below us–actually where it’s back flooded–and that’s actually from the Green River outside that’s back flooding into the Cave. Then this waterfall that’s in front of us is draining just the local area above us. And it’s very likely that the water that we’re seeing in this waterfall is probably, really, pretty good quality. That’s because it’s drained in a forested area in the National Park. There may be some impact from the visitors and the roads and such, but it’s pretty minimal here. Unfortunately, the water that we can see at the bottom of this shaft here–because that’s actually coming from a combination of water back flooding from the Green River and also the cave streams that are coming into it, and in some cases areas that are draining outside the National Park and agricultural land–that water at the bottom is probably pretty poor quality with various agricultural chemicals, primarily fecal bacteria from human and animal waste, and that water down there may exceed drinking water standards by tens of thousands of times for fecal bacteria. This time of year, we have an issue with an herbicide, Atrizine, which is widely used for corn production here. That has very, very, very low levels allowable in drinking water. There’s quite a bit of controversy regarding the use of Atrizine, these days. During the spring is when they apply it in the fields here, and so we typically get a pretty big slug of it coming through the ground water here, and in some cases, does exceed the drinking water standards.
We’ll take a little side trip up here that’s pretty cool. So what happens here is that this is the place where the sandstone over top has been removed by erosion–so this waterproof cover has been removed so that you can hear all the water coming down through waterfalls, especially with the rainfall. Now if you look here, this is a bottomless pit–obviously not quite bottomless, since that’s about 90 feet–in fact, it doesn’t look as deep as it usually is because the water’s so high; it’s actually flooded back. I’m not sure, that water may be 20 feet deep? You can make the trip now; you can dive in there just like in Acapulco? I’ll hold your camera if you want, Carl–if you want to try it.
Any of these side passages we’re seeing pretty frequently. . . some of these just extend for miles and miles and miles. One thing about this is that the Cave here is not a pretty dangerous or difficult cave to explore.–I mean, it is because it’s so vast; there’s definitely very remote sections of it–but of all the hazards, this idea of flooding is really the most potentially hazardous issue.
One of the most famous cave explorers was a guy named Stephen Bishop in the 1830’s and 1840’s. He really got very interested in the Cave and made really very significant discoveries. Everything that we’ve just seen from the lower levels that we’ve just been in–Green River Hall and Mammoth Dome–he discovered. One of the stories is that right across here, what we’re seeing is a bottomless pit, he had come to this point from the main entrance up to here in the 1830’s sometime and had gone across the pit to the unexplored passage to our right and apparently had come with either a cedar pole or some kind of ladder, depending on which story you hear, and set it right across here where we are and made the first trip. During the subsequent trip, he discovered Mammoth Dome, where we came down the steps, and River Hall, the actual river that we didn’t get to see because it’s flooded. In fact, there, when he discovered the underground rivers down there, he was the first person to see the eyeless fish that are quite well known for Mammoth Cave. This was a place of great adventure, apparently.
This waterfall runs continuously, but a lot of times–during drier conditions–it’s just a little drip, drip, drip. Here it’s flowing pretty well because of the rainfall we’ve had.
So, Mammoth Cave holds a pretty important position in karst research–tell me a little bit about that.
Chris Groves: Yeah, very much. One thing that’s distinctive is that, by far, it’s the longest known, most extensive known, cave in the world. The length of somewhere close to 370 miles, all of which has been measured foot by foot with measuring tapes and compasses. Here’s some more shafts, just like the big ones we saw. These are little ones that are bringing in water. Those, in fact, form independently of the main cave; this was actually an underground river, forming in these big passages that we’re in. Now that river is down by River Hall, where we were before; it’s down several hundred feet lower than where we are. These shafts are just formed from drips that are coming down through the rock from the surface where some little streams are sinking.
So when we look at karst regions around the world, this is what they look like down deep.
Chris Groves: Yeah, this is an example of one. There’s so many different kinds, it really depends on the details of the geology and climate and such. This is certainly one of the quintessential examples. In fact, because it’s the longest cave in the world, there’s a huge amount of interest in it among cave explorers and scientists. I think really since I’ve been working at the University, I’ve probably been in the Cave with people from at least 30 countries. The way I look at it, there’s a list of iconic karst areas–Slovenia, the home of the word “karst,” places in south China–there’s a certain set of really iconic karst places for people that are really into it, that are just on your checklist of must see places. Absolutely, this is one of them. And so we’re really lucky at the University that, because of that, there’s a relatively constant stream of major cave scientists from around the world that are just continually coming through here. It’s really a great resource for us and our students.
Photo © J. Carl Ganter / Circle of Blue
Mammoth cave is sometimes referred to as a limestone labyrinth because of its numerous passageways and shafts, like this 90-feet-deep pit pictured above. It is a “quintessential” karst region that has helped inform people from similar regions, such as in China, according to Groves.
So, globally, how does the research here affect how we manage freshwater resources in other parts of the world?
Chris Groves: We’re obviously studying local phenomenon and collecting our data at this place or that place, but what we’re really trying to achieve is to learn about the way these landscapes and aquifers function in a way that transcends just the local details so that we can learn about things and ideas and ways of thinking that we can apply to karst landscapes more widely. Through the 20th century, and even continuing, there’s a good bit of work that’s been done here by various people that has really helped people understand how karst aquifers and landscapes function–not just here in Mammoth Cave, but how they function generally. There’s a lot of lessons that have been learned here that have really informed people around the world. We’ve done a lot of exchange, where my colleagues and I spend a good amount of China, and Chinese colleagues are coming over here. It’s not just a technology transfer through professional publications and such, but through a lot of just personal interactions. I think there’s a lot of information about methods and understanding about karst that really is informed by work that’s taken place here, relationships that have been established.
Great. Well, Chris, thank you.
Chris Groves: My pleasure, Carl.
We’ve been speaking with Dr. Chris Groves, who is Director of the Hoffman Institute Research Center for Environmental Studies and karst around the world. He’s also Professor of Geography at Western Kentucky University. Thanks for joining us for another broadcast of 5 in 15 at Circle of Blue. I’m J. Carl Ganter.
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