Wednesday, October 22, 2008

Caves in the United States

Caves are found in every state in the United States, with over 44,000 recorded caves in the 48 contiguous states (Culver et al. 1999). Where are these caves?
The map above shows the karst areas of the U.S. in green. Karst is a type of terrain that includes limestones, dolomites, and gypsum. These rocks are soluble, and caves, sinkholes, and underground drainages are common features. Nearly one-quarter of the U.S. is comprised of karst. Looking at the map above, you might guess that Florida has the most caves because it has the most karst. But just because karst is present does not mean that a cave is present. In many cases, the rock is soluble, but the water table is so high that the caves are flooded and can only be entered by highly trained cave divers, or the caves are still forming and are not large enough for humans to enter. 

This second map, made by Culver et al., shows a dot for every cave by county. So if a county has ten caves, there will be ten dots randomly placed in that county. These caves may be found in karst, but also could be lava tube caves, talus caves, or other types of caves. What is obvious in this map is that there are some sections of the country that are just filled with caves, like the middle part of Texas, Missouri, Kentucky, Tennessee, and others. The desert southwest doesn't have as many caves, but it still has quite a few black dots.

When I headed to Kentucky last week, it was with the knowledge I was heading towards cave central. Kentucky is home to the longest cave in the world, Mammoth Cave, which stretches over 360 miles with more passageways still being found. My brother offered to take us to one of the smaller caves in the state, and I couldn't resist.

The trip to a cave almost always includes a hike to the entrance. Sometimes this hike can be grueling, involving many miles, rough terrain, poisonous plants, unpleasant weather, and obnoxious mosquitoes. Fortunately, on this fine fall day, the weather was great and we followed a trail most of the way.

The entrance was huge, with large boulders providing good perches as we looked off into the Kentucky woods. We put on our helmets and headlamps and got ready to enter the large, dark void.

This cave, called Wind Cave, is about 1.3 miles in length. It was formed by water dissolving the limestone rock. Water still flows through parts of the cave, but because Kentucky has had a drought this last year, my brother didn't think we would get too wet. I was skeptical. In my experience, I nearly always get wet and muddy in Midwest caves.

One of the first passages we went into was a canyon-like passage. The walls were fairly smooth and dry. I enjoyed the walking passage, because many of the caves in the area where I live are small and require lots of crawling.

Eventually the canyon passage got smaller and it was time to squeeze through a little hole. You can see some graffiti to the right of the hole. Unfortunately some people don't respect caves and leave trash or paint stupid things on the cave walls. They don't think about the cave being a home.

Caves are home to a variety of cave biota. Squeezing provides the opportunity to be very close to the cave surfaces, and then it's easier to see some of the creatures that make the cave their home, like this cave cricket. Notice the extremely long back legs and antennae, which help the cricket find its way around the totally dark cave. We saw lots of crickets--some cracks had about 15 together. 

In addition to crickets, we also saw this neat looking spider, along  with flies, moths, and millipedes. Water flowing into the cave provides nutrients for these cave creatures.

Back in the main passageway, we can see that the water has been flowing through the cave for a long time to dissolve away this much rock. 

Eventually the ceiling got lower and we had to stoop walk. We also came to mounds of sand, places where the water has slowed and deposited the finer sediments.

And then we got into another crawling passage. We found many side passages going off from the main trunk passage. Basically smaller drainages are emptying into a larger drainage, but instead of happening in rivulets and gullies up on the surface, it's occurring underground.

Some passages got even tighter, requiring some nearly contortionist moves to get past the ninety-degree turns. (Can you see the foot and leg in the photo?) To make things more complicated, water was flowing and bubbling up on the bottom of the passage. I was right about getting wet!

It was a fun trip, and it felt great to be underground again. I always enjoy the silence and mysterious nature of caves. Are there still more passageways to be found? How much bigger will the cave get over time as the water keeps dissolving away more rock? How is it connected to the surface, and will it be impacted by surface activities? What else lives in the cave? I always leave a cave with more questions than I went in with!

If you'd like to learn more about caves, a good place to start is the National Speleological Society website.

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