| Just south of Mt. Rushmore is the world’s fourth longest known cave; the Wind Cave. Over 125 miles of passages have been mapped out in this cave. Actually, this could be the world’s longest cave, but it’s not known for sure. As opposed to having just one or two main passage ways with some smaller tributary routes like many other caves, this cave is a three-dimensional matrix of crisscrossing tunnels. There are so many of these passages that within a five minute spelunking trek off the well-beaten path, you could be exploring cave that has never been seen by man. To give you a perspective, all of the 125+ miles of passages are beneath a 1.1 by 1.3 mile rectangle of surface land above. Present expeditions involved in mapping out the larger undiscovered parts of the cave require about a two-day journey just to begin. And how do they measure cave length in this modern, digital age? Tape measures. Flat Stanley was on the case to figure out why this cave was called Wind Cave. It turns out that the cave is so large and deep that it spans a significant amount of elevation, so significant that the barometric pressure difference between inside and outside the cave can often result in a strong wind at the cave entrance; up to 75 miles per hour! It was the sound of this howling wind that lead to the cave discovery. Wind Cave is home to over 95% of the word’s known boxwork. Boxwork is a curious cave formation that requires some fairly special circumstances to occur. The base rock of the cave is limestone. Through plate earthquakes and other natural phenomenon, small cracks developed in the limestone. Then as the rain fell on the ground above, the mineral gypsum was leached into the cracks. As the gypsum crystallized, it expanded, in the same way that water expands when it is frozen. This expansion acted to enlarge existing cracks in the sandstone, and to create new cracks as well. Gypsum again was leached into the cracks, and the process was repeated. Calcite also leaked into these cracks over the base gypsum, providing an enhanced strength. At some point, the cave became flooded for a very long time; long enough that the limestone actually dissolved in a mix of water, hydrogen sulfide, and sulfuric acid. The gypsum and calcite, resistant to the acid bath, were left behind in delicate and intricate patterns. Today we see them as fossilized cracks, which is pretty amazing! |
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