The Wind of Wind Cave
The winds at the entrance of Wind Cave have drawn the attention of people for eons. American Indian oral history dating back centuries speaks of a "hole that breathes cool air" near the Buffalo Gap. Regarded as the origin site for the Lakota people, there are many stories about the role the cave played in their culture and they consider the place sacred.
One of the stories tell of a beautiful woman, known as the buffalo woman, who came out of the cave and gave the bison to the Lakota people. Sitting Bull's nephew is quoted as saying that "Wind Cave in the Black Hills was the cave from which Wakan Tanka, the Great Mystery, sent the buffalo out to the Sioux hunting grounds".
Cowboys, Jesse and Tom Bingham, found the cave in 1881 when they were in the area hunting deer. As the story goes, one of them, probably Jesse, was following a wounded deer up a ravine when he heard a loud whistling sound and noticed grass caught in a strong breeze on what otherwise was a calm day. Upon investigation he found a small hole. When he looked into the hole, the wind at the entrance of the cave was blowing with such force that it blew his hat right off his head!. A few days later when they returned to show this phenomenon to some friends, one of them put a hat in front of the hole and, suprisingly, it was sucked into the cave! The the wind had switched directions.
Today, we understand that the direction of the wind is related to the difference in atmospheric pressure between the cave and the surface. To understand this phenomenon we must know what barometric pressure, also called air or atmospheric pressure, is.
Barometric pressure is the pressure exerted by the weight of air over a given area of Earth's surface. While it is uncommon for us to think of gas as weighing anything, as matter it does have mass. That mass is related to how many molecules of air there are in a specific area; how fast they are moving; and how often they collide. Because the air has mass, gravity has an effect on it causing the air above us and around us to weigh down on us and on the surface of the earth. This force is called barometric, atmospheric or air pressure. This pressure is measured by an instrument called a barometer.
At sea level (the level of the ocean's surface) gravity is strongest and air pressure is greatest. Because gravity weakens as you go up, air pressure is lower at higher altitudes. However, the barometric pressure at any given location on the earth is constantly changing. On the surface, weather is driven by the sun, which heats some areas of the earth more than others. Temperature differences lead to pressure differences.Those changes produce winds, bring in clouds, or clear the way for sunny skies. Understanding barometric pressure readings help forecast the weather. A rising barometric pressure often suggests clearing skies and fair weather where falling pressure indicates that wet or stormy weather may be on the way. Areas of very low pressure are associated with severe storms, such as tornadoes or hurricanes.
Because Wind Cave is so large and has a lot of space, it also has an air pressure system. That air pressure system is always working to be equal to the air pressure system on the surface. So if a high pressure system is on the surface air will be forced into the cave to create a high pressure system in the cave. When there is a low pressure system on the surface the high pressure in the cave forces air out so the cave will have a low pressure system also. This is referred to as cave breathing.
Barometric airflow through the natural entrance of Wind Cave not only gave the cave its name, but also provides an opportunity for determining the approximate volume or size of the cave passages. Monitoring and recording the barometric airflow through the cave natural entrances help us understand the volume of air in the cave and that can be used to calculate the total volume of cave passage. By using the amount of air that comes from the cave we can determine the volume of space in the cave. At this time we have determined that we have found less than 10% of the cave. However, that does not mean we can determine the mileage of the cave. We could have many very small passages or one great huge one. But it does give us an idea of how big the cave could be.
Many caves are big enough to have barometric winds. However the wind at Wind Cave is very noticeable because of its very small natural entrance. Wind Cave, one of the longest caves in thw world, is also one of the most complex. Currently almost all of the cave lies beneath about a 1 mile square area of land. Click here to view a map of the cave. Besides its length and complexity, the cave is well known for its unusual formation call boxwork. Click here for information about this unique feature of the cave.
Video of the Wind at the Entrance of Wind Cave - See how the winds at the entrance of the cave can be blowing in or out of the cave depending upon changes in the barometric pressure.
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