Wind+Cave

~Wind Cave~​ Caroline Kelley and Julia Wang

​​**Introduction:**

Wind Cave is a 28,295 acre park located six miles North of Hot Springs, South Dakota 2. It is near the border of Wyoming and South Dakota; its specific coordinates are 43° 34' 0"N 103° 29' 0" W 2. This extremely complex cave system is surrounded by a variety of prairie and forest lands with many animal species. The Karst topography of this area includes this cave, Wind Cave and a nearby cavern Jewel Cave, part of the Black Hills system 2. The caves contain many interesting geological features, including many intricate speleothems such as boxwork. It is the third longest cave in the USA at over 134.16 miles long (in passages), and the fourth longest cave in the world 2. It is named due to the wind that rushes out of the cave entrance due to the variations between high and low pressure at the cave mouth and outside 2. It was first discovered //and// entered in 1881 by Tom and Jesse Bingham. Some notable places inside Wind Cave are Calcite Lake, which includes calcite rafts, the Club Room, the Garden of Eden, the Dungeon, and the Half Mile Hall. Cave features are not the only thing to do at Wind Cave. Many hikers enjoy the three nature trails, the Elk Mountain, Prairie Vista and Rankin Trails, which are each a mile long and a way to enjoy the wildlife and prairie found around Wind Cave 2. Don't forget to stop by the service center to pick up a guide!



**Geologic Features:**

The features of Wind Cave are mainly formed from agents of erosion and weathering. The oldest bedrock of the cave is in the Northwest part of the park; it is made of schists and other types of metamorphic rock that metamorphosed due to plate tectonics 1 - the building of mountains, or the movement of convergent collision plates. There are also sloping layers of sedimentary rock that date back 600 million years, when there was abundant amounts of sea life, determined from fossils found in the layers. There are also signs of erosion due to unconformities also seen in the layers of sedimentary rock. Another old rock type found were pegmatites, which are a type of igneous rock 1. They are younger than the schist rock however, because they intruded into the schists, probably forced in due to mountain building once again 1 and the principle of original horizontality.

The cavern formed in Pahasapa limestone, which formed during a period of of shallow sea 1. It is made up of the calcium carbonate in sea shells 1 Within the limestone, there are bodies of crystallized gypsum. This was crucial for many features to be formed such as boxwork. The gypsum is able to expand and recede due to the absorption and the evaporation of water 1. This caused cracks in the surrounding limestone, which eventually the gypsum filtered in and crystallized 1. 300 million years ago, layers of clay, sand stone, and limestone layered on top of the body of limestone, causing the ability of a cavern to form underground 1. The water levels over the years also rose and fell, so development of the cave was slow; a more recent rise, the Bad Hills, caused water to seep in 1 and cause cracks in the limestone due to the carbonic acid in the water from dissolved carbon in the air. These gradually created cracks are the reason for the extensive, intricate and maze-like features around the caverns.

Some of the well known speleothems of the cave are the boxwork, calcite rafts, frostwork, and more! The rare, unique boxwork is found in only a select amount of caves and Wind Cave is one of them 2. Boxwork is formed from the gypsum that were able to intrude in the cracks of limestone that was mentioned above; as groundwater erodes the limestone away, the gypsum that were crystallized in the limestone is left behind 1. The resulting formation is an awesome box pattern left on the ceiling of the caverns. Other speleothems such as calcite rafts form from precipitating calcite - happening right now. They are also evidence that there were higher water levels as they are also found on the ground surrounding Calcite Lake where the calcite rafts float on 2. Another famous example would be the frostwork that precipitates on top of boxwork and cave popcorn. These needle-like growths are formed out of calcite or a similar mineral aragonorite, but the cause of formation is still debated 2. Most people believe that evaporation has a important role, where there are passages with above average windflow in Wind Cave 2. Helictite bushes are look like miniature trees with branches extending out of the body of the speleothem 2. The branches form from miniature capilliary movement where water seeps through and is so small that it is not controlled by gravity, which allows it to deposit minerals upwards 2. They may have formed underwater where there is a different chemical composition 2. The more common cave popcorn forms from water leaking evenly from the limestone walls and precipitate calcite, or from water dripping from the ceiling and splashing on the ground causing the loss of carbon dioxide which also helps the precipitation of calcite 2. Finally, the the dripstone features, such as stalactites which form from the ceiling, stalagmites, which form from the ground, and soda straws are some of the more common features in Wind Cave. The curious thing is that Wind Cave does not hold many dripstone features, many scientists think this is due to the lack of water 2. While most dripstone features like stalagmites, stalactites, and soda straws form from the gradual dripping of water when it seeps through the cracks of the limestone cavern, with the gradual deposit of calcite. The soda straw forms from the edge of the water drop and each drop of water leaves a trace of calcite that grows down into a hollow tube 4. When the tube is plugged or water flow increases to deposit calcite around the outside of the sodastraw which creates a cone like shape, called a stalactite 4. When the water drops onto the ground, it will also leave traces of calcite, which causes and upward growth called a stalagmite, which does not have a central tube, because of the random splattering of water on the ground 4. The difference between this normal formation and the formation in Wind Cave is that the water comes out of small pores from the walls of limestone, not cracks 2. Consequently, there is more of a layer of calcite along the walls instead of formations at cracks 2.

**Agents of Erosion:**

Wind Cave's most obvious agent of erosion is groundwater. It infiltrates in through cracks in limestone caused by weathering mechanisms, such as frost wedging. Frost wedging is where water filters into the cracks, freezes, and expands. Once the water melts again, it leaves a larger gap, as liquid water takes up less space than ice. Once the cracks from mechanical weathering appear, chemical weathering is made a lot easier. Dissolved gases from the air such as carbon is rained down upon limestone, which has a fairly violent reaction with acid. The carbonic acid also has a reaction with the calcite in limestone which forms calcium bicarbonate which is carried by groundwater in solution to form the speleothems 4. That groundwater also erodes to form caverns, usually at or below the water table, the plane that separates the zone of saturation, which is below the water table and the zone of aeration, which is the above the water table. For the erosion outside of the cavern, there are ridges and valleys as well. Rocks like sandstone and pegmatites are hardy against weathering and erosion, form ridges, while schists and shale which are weaker against weathering form valleys 2. There are some examples are along State Route 87, in Red Canyon, and in Wind Cave Canyon 2. Weathering and erosion in the prairie occurs from biological activity, where this is a wide variety of plants and animals living off the prairie, burrowing, and other natural activities. The plants roots are able to grow into cracks and wedge the rocks apart.

The climate in the park is semi-arid [1], or a dry mid-latitude climate zone [4] in the Koppen classification system. It is a sunny area[2], and during the spring and summer, it experiences about 15 hours of daylight[3]. Average daytime temperatures in June range from 51 degrees Celsius to 81 degrees Celsius[2], while day and night temperatures can differ by up to 60 degrees[1]. Wind Cave usually has windy springs, warm summers with thunderstorms, cool autumns, and cool but relatively mild winters[2]. It is part of a warmer and drier area called the banana belt[2], due to two main processes. One is when warm, moist Pacific Ocean air is orographically lifted by the Rocky Mountains[2], allowing it to cool and expand in to clouds. The water vapor condenses into clouds and precipitates, while the air continues moving down the other side of the mountain and heating[2]. The other process is when arctic air comes down from Canada over the Northern black hills and is then blocked from the other slopes, including where Wind Cave is located[2]. These two features give the prairie very warm, dry air, which thus dries out the soil and only allows for plants that need little water to grow there[2].
 * Climate:**

interior of the cave, however, is not heated by surface temperatures because it is difficult for convection to occur from the limestone and sandstone that is heated by the sun’s rays and the air in the cave[1]. Within Wind Cave, there is a high geothermal gradient (increase in temperature with depth)[1]. This means that the temperature inside the cave is influenced by the surface temperature[1] as well as Earth’s internal heat[1]. The atmospheric conditions of Wind Cave, however, are driven by wind. Since 1,000,000 cubic feet of air enter or exit the cave per hour[1], it takes a long time for that much air to heat or cool to a certain temperature, and there are temperature variations deep within the cave[1].

Climate change is becoming more evident within the park. Temperatures are increasing up to 2 degrees Fahrenheit in the Great Plains, but up to 5.5 degrees Celsius specifically in the Dakotas, which is faster than in most of the U.S[2]. Also, precipitation in the Black Hills is down 10%[2]. Both of these can lead to much drier soil and drought conditions, which can increase the fire hazard[2]. Also, the increased amount of water vapor in the air is expected to cause more frequent summer downpours and thunderstorms, and therefore more flooding and erosion from the running water[2]. In the winter, lower temperatures would make rain the more likely form of precipitation, which would decrease the amount of snow and change drainage patterns[2]. On the other hand, the colder night time temperatures have led to the decline of blue grama grass, the most common short species[2]. Higher temperatures in the grasslands may lead to a 50% increase in water use, as well as less fertile soil due to a faster decomposition process[2]. Climate change can affect animal life cycles, including breeding and migration patterns[2].


 * Biomes of Wind Cave:**

The park is in both a grasslands biome and a taiga biome. The grasslands biome is marked by the hardy prairie grasses, and the burrowing or grazing animals that characterize such areas. The taiga biome is marked by large ponerosa pine trees, large predators, and small herbivores who are their prey. Grassland plant species include tall grass species from the eastern tall grass prairies and short grass species from the western high plains. The tall species, such as big bluestem, need more water to survive, and are usually found in the valleys of the park[2]. The short species, such as needle-an-thread grass, are usually found on the dryer Southern slopes of the mountains[2]. Animal species there include bison, elk, and pronghorns. After being hunted nearly to extinction, the bison at Wind Cave are part of efforts to release them back in the wild. Part of these efforts included killing most of the bisons' natural predators starting in the 1800's, such as brown bears, grizzly bears, and wolves[1]. There are also many prairie dogs, which burrow underground and live in large groups[2], and several types of rabbits[2]. In the taiga biome, there are frogs, toads, ducks, geese, turkeys, songbirds, black-footed ferrets (a natural predator of the prairie dog that was recently reintroduced into the park), coyotes, squirrels, and chipmunks, as well as the elk and mule deer also found on the prairie[2]. There is evidence of adaptation of various species to the climate. The plant species in this area aren't very lush and don't use large amounts of water, although some species need more than others. Also, over half of the plant/root matter of prairie grass is underground to protect it from harsh winters and from grazing animals, thus allowing the actual plant to survive if the top section is eaten or frozen[2]. There are many burrowing animals, who are thus well protected from the winds, and they are often brownish to blend in well with their surroundings, such as the mule deer, which has spots to blend in with the prairie[2]. There are many grazing animals, who depend heavily on the abundant prairie grasses[1]. On a side note, there is also a unique eco-system within the cave, including various bats, such as the Little Brown Myotis[2], and a variety of micro-organisms and other small animals that depend heavily on the moist cave environment[1].


 * Human Impact:**

Human impact has affected several aspects of Wind Cave. The cave's man-made openings have allowed for the cave's internal climate to be altered[2]. The increased airflow eventually caused a rock fall at the main entrance due to cooling and thawing, so camp authorities added airlocks to the artificial entrances[2]. More evaporation in winter can decrease the amount of dripping water in the cave, which can severely hinder the growth of stalactites[1]. The amount of evaporation can also affect the dripstone material that forms there, as aragonite tends to form in high-evaporation areas, while calcite does not[1]. Also, the old electric lights from the 1930's to 1980's heat the cave, thus allowing more green plants, such as algae, to grow[2]. There is a three-year project going on to make the lighting system safer and more efficient, and will help conserve more energy. Another key consequence is the production of lint. All people produce dead skin cells/clothing lint/hair, and it gets deposited in the cave by its thousands of visitors[2]. Volunteers then have to pain-stakingly remove the carpets of lint to prevent bacteria from growing in the cave[2]. Also, due to buildings and vehicles on the surface near the cave, harmful chemicals can contaminate the groundwater and the cave[2]. This can affect cave life and crystal formation, so a filtration system was built under the parking lot[2]. Also, there are over 100 foreign plant species spread in part by humans and vehicles, and the eco-system has never fully recovered since the overhunting of large mammals during the 1800's[2]. This has led to the need for bio-control, or importing bugs that eat certain plants[2], and the re-introduction of different animal species, such as the black-footed ferret, back in to the environment[2]. However, humans have a positive effect on the environment regarding fire. Fire controls many aspects of the eco-system, by burning any trees that stray on to the prairie, decrease the bisons' habitat, and absorb water that would have gone to the cave's delicate eco-system[2]. It also removes the dead grass tops from the prairie to allow for new growth[1]. Since uncontrolled, lightning-based fires are a threat to the park, man-made, carefully supervised fires are used instead to maintain balance in the environment[2].

Bibliography

1. “Animal & Plant Guide, Cave Climate, Cave Meteorology, Geology, Location.” __Wind Cave National Park Information.__ 1995-2007. 4 June 2010. []

2. “Animals, Climate Change, Environmental Concerns, Natural Features and Ecosystems, Plants, Vanishing Prairie, Weather, Wind Cave Exploration.” __Wind Cave.__ 2008. 4 June 2010. []

3. “Sun or Moon Rise/Set Table for One Year: U.S. Cities and Towns.” __Naval Oceanography Portal.__ 2010. 8 June 2010. [] >

4. Tarbuck, Edward and Lutgens, Frederick. __Earth Science.__ Pearson Prentice Hall, 2009.