Wind Cave National Park

The next morning after our aborted trip to the Badlands (arrived at noon to way too many people so we decided to return on another day), we made our way to Wind Cave National Park. We had heard that the cave parks were also heavily visited, so we made sure to arrive when they opened at 8am. You can only view the cave on a tour and there are several to choose from. The park is free, but the tours are not. With Bev’s Access Pass, we paid $18 for the two of us. We were lucky to get the Natural Entrance tour at 8:40. The route stays in the middle cave area and descends for a half mile. The tour lasts one hour twenty minutes.

Once on the tour, we learned that the cave was found in 1881 by two brothers, Jesse and Tom Bingham. They heard a loud whistling sound and found the opening to the cave. There was a wind coming out of the opening strong enough to blow Jesse’s hat off.  The wind is what gives the cave its name. It is caused by the difference in atmospheric pressure between the inside and outside. This type of cave is called a barometric cave. Even today, the wind blows in and out, like it is breathing. The opening is so small that one can’t help but think of it being more like an oversize rabbit hole!

The first settler to squeeze down this rabbit hole and explore Wind Cave, was an 18 year old boy named Alvin McDonald. Alvin was very systematic in his explorations. He kept a journal and made detailed notes and maps of what he had traversed and saw. He used a candle to explore. I sure can’t imagine using just a candle for light. During the tour, there was a stop where the lights in the cave were turned off for a few minutes. Yup, absolute darkness is pretty dark…as in pitch black.

In addition, to using candlelight to find his way, Alvin used string to mark his trail through the cave passageways. The cave is very extensive. To date, about 143 miles of corridors have been mapped in a one square mile area! By studying the barometric wind patterns, it is estimated only 5% of the cave has been mapped. Recently, someone found 2 lakes, about 500 – 600 feet below the middle cave section that has new life forms (algae or some such thing).

Okay, now to the formation of the cave (You didn’t think I wouldn’t give you a lesson in geology did you?).

The cave is part of the Madison Formation which was deposited in a warm shallow sea about 350 million years ago. It is composed of calcium carbonate seashells.  At the same time the limestone was being deposited, irregular shaped masses of gypsum were being added as a result of crystallization from evaporating seawater (during drought periods). The gypsum was unstable and caused fracturing to occur in the limestone similar to cracks in pavement caused by multiple freeze\thaw cycles. The gypsum was squeezed into the cracks and later was changed to calcite.

About 320 million years ago, the sea water was replaced by fresh water. The water interacted with the gypsum to create sulfuric acid. This ate away at the limestone and opened up passageways. The seas came back and deposited more layers – limestone, red clay and sandstone. Some of these sediments filled the new passageways. The seas kept inundating and receding, depositing and dissolving the rock in the cave over the next 240 million years.

The Black Hills, where the Wind Cave is located, finally come into the picture 60 million years ago. They were formed by a big “push up” of the earth’s core from below, opening more fractures. Now the water just sat on the cave’s limestone, but it was still dissolving it.  Once again, while dissolving the limestone, the calcite from the crystalized gypsum was being left behind. This formation is called Boxwork and is all over the Wind Cave. In fact 90% of the world’s Boxwork formations are in this cave. So it is rather unique.

Some of the other types of formations are Cave Popcorn, Dogtooth Spar, and Frostwork. We saw examples of these on our tour. There are no stalactites or stalagmites because those are formed from water dripping into a cavern. The other types of formations (besides the Boxwork) do come from seeping or dripping water, but there isn’t enough water to form the stalactites or stalagmites.

OK, the geology lecture is now over.

There are other things to do here. They have 8 hiking trails ranging from 1.4 to 8.6 miles in length. Pets are not allowed on those trails, though. There are two nature trails you can walk the dogs on. We didn’t hike any of the trails since we had to leave the dogs at home and that would have made for a very long day away. We did get to see some bison on the way into the park in the morning.

All in all it was another educational day filled with awesome sights. Even though we would never go spelunking on our own, joining the ranger led tour was an easy way to see the wonders underground.