The Cave Breathes and the Numbers Prove It
Near Custer, South Dakota
Wind Cave National Park takes its name from a phenomenon that park rangers still demonstrate to visitors on tours: at the natural entrance to the cave, air is either flowing in or flowing out at speeds that can be measured with an anemometer and felt by anyone standing within a few feet of the opening.
The mechanism is straightforward atmospheric physics. The cave system, with its hundreds of miles of connected passages and chambers, acts like a large pressure vessel. When barometric pressure outside the cave is lower than the average pressure inside the system, air flows outward. When outside pressure is higher, air flows inward. The differential is enough, on days of strong barometric change, to produce air speeds of several miles per hour at the natural entrance. Rapid weather changes, particularly the approach of storm systems, produce the strongest flows.
The cave's boxwork formations, thin calcite blades projecting from the walls and ceilings in honeycomb patterns, cover roughly ninety-five percent of the known boxwork in the entire world. They formed when calcite filled cracks in the cave walls and then the surrounding limestone dissolved away, leaving the harder calcite fins standing. Wind Cave is not the largest cave in the world. It is not the longest. It contains, however, a geological feature that exists almost nowhere else, in an abundance that makes it one of the most distinctive cave environments on the continent.
The breathing continues regardless of who names it or what system measures it. The cave does not require an audience.
