Sunday, October 4, 2015

Wind Cave National Park

South Dakota's Wind Cave National Park is 41 miles from Mt Rushmore, located beneath a remnant island of intact grassland prairie totaling 33,851 acres. The cave, one of the longest and most complex caves in the world, derives its name from the barometric winds at its entrance. In 1881, as the story goes, Jesse and Tom Bingham were attracted to the cave by the whistling noise of air bellowing out of the cave entrance with such force that it blew Tom's hat off his head. A few days later when Jesse returned to show this phenomenon to some friends, he was surprised to find the wind had switched directions and his hat was sucked into the cave. Today, we understand that the movement of the wind is related to the difference in atmospheric pressure between the cave and the surface. The Lakota people who traversed this area were aware of the cave's existence and spoke of this as a sacred place that blew air and was the site where their ancestors first emerged from the underworld.

In the photo below, a park ranger points to the original hole that attracted all the attention.

Wind Cave is explored by experienced cavers who volunteer their time to map, inventory, assist with biologic, geologic, and hydrologic studies, and participate in restoration of areas disturbed by human activities. The photo below shows some cave exporters mapping new sections of the cave.

In the 19th Century, several mining claims were established at Wind Cave, most noteworthy one by the South Dakota Mining Company in 1890. J.D. McDonald was hired to manage the claim. The mining was unsuccessful, but McDonald and his family realized they could make money by giving cave tours and selling formations from the cave. They filed a homestead claim over the opening and worked on improving a manmade entrance and enlarging passageways for tours. One of J.D.'s sons, Alvin, spent much of his time exploring and mapping the cave, faithfully keeping a diary and making a map of his findings. On January 23, 1891, Alvin wrote that he had "given up finding the end of Wind Cave."

Visitors to the national park can take cave tours that are ranger-guided and leave from the visitor center. Tickets are sold on a first-come, first-served basis, and during the summer months long waits may be encountered.

On January 3, 1903, President Theodore Roosevelt signed the bill creating Wind Cave National Park. It was the eighth national park created and the first one created to protect a cave. The park land above the cave at that time was small and there were no bison, elk, or pronghorn, all of which came later as the park boundaries expanded. In 1912, the American Bison Society was looking for a place to re-establish a bison herd. Because of the excellent prairie habitat around the park, a national game preserve was established bordering Wind Cave, managed by the U.S. Biological Survey. In 1913, the animals began to arrive: fourteen bison from the New York Zoological Society, 21 elk from Wyoming, and 13 pronghorn from Alberta, Canada.

Interest in the wildlife attracted more visitors to the park and additional improvements were necessary, first in the 1920's but the major work was accomplished by the Civilian Conservation Corps in the 1930's. In July of 1935, the game preserve became part of Wind Cave National Park. During the early years of the preserve, the animals were kept in small enclosures but eventually it was realized that the bison, elk, and pronghorn needed room to escape from predators. With the help of the CCC, fences within the park were removed, and in 1946, 16,341 additional acres were added, enlarging the park to 28,059 acres. Currently there are 400 to 450 bison in Wind Cave National Park, grazing the grasslands.

Below you can see the walkways that visitors use to safely see the cave's formations...

The mission of Wind Cave National Park is to preserve and protect the natural resources, both the grasslands above the caves and the caves below the ground, because what occurs above the caves influences the caves' health. Because of its relatively small size, park managers must take an active role in helping the ecosystems function as they might have in the past. This requires understanding how everything in the park relates and how the naturally operating system would have functioned. Park rangers work with researchers to replicate that natural system using prescribed fires, bison round-ups, and biological control of exotic plant species. Fire is an important factor in protecting the prairie. Historically, fires burned across the prairie every 4 to 7 years. Fires burn the small trees that would otherwise march across the prairie and turn the grasslands to forest.

Some of the most extensive boxwork deposits in the world are found in Wind Cave.  Boxwork is commonly composed of thin blades of the mineral that project from cave walls or ceilings and intersect one another at various angles, forming a box-like or honeycomb pattern. The boxwork fins once filled cracks in the rock before the host cave formed. As the walls of the cave began to dissolve away, the more resistant vein and crack fillings did not, or at least dissolved at a slower rate than the surrounding rock, leaving the calcite fins projecting from the cave surfaces.

Small, knobby growths of calcite on the cave walls are called cave popcorn. Popcorn commonly forms in one of two ways in the cave: where water seeps uniformly out of the limestone wall and precipitates calcite; or, when water drips from the walls or ceilings of the cave and the water splashes on the floor or on ledges along the walls. This splashing action causes loss of carbon dioxide and the subsequent precipitation of calcite.

Delicate needle-like growths of calcite or a related mineral, aragonite, are called frostwork. In places the frostwork may grow on top of cave popcorn or boxwork, but the origin of frostwork is controversial. In Wind Cave, it seems to concentrate in passages with above average airflow where, it is thought, evaporation plays a role in its formation.

Where the deposition of calcite is concentrated along cracks, calcite is deposited as flowstone or dripstone. Dripstone includes such features as stalactites and stalagmites, speleothems common in many limestone caves but relatively rare at Wind Cave. The comparative scarcity of these features in Wind Cave is another puzzle for geologists. Perhaps a lack of water would explain it. Alternately, the difference may be the way the water passes through the rock. Rather than just flowing along cracks, much of the water which enters Wind Cave today passes more-or-less uniformly through the rock by seeping between pore spaces. Consequently, when the water reaches the cave it coats the cave walls with a frosting-like layer of calcite rather than concentrating the calcite only along cracks.

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