National Treasure Underground Delights EarthCache
National Treasure Underground Delights
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Jewel Cave National Monument located near Custer South Dakota. To log this cache you will be required to gather information from one of the tours offered at the cave. The Visitor Center is open daily year-round, except Thanksgiving Day, Christmas Day and News Years Day. Hours are: 8:00 AM - 4:30 PM Sept. thru May; 8:00 AM - 6:00 PM June, July & August. Call 1-605-673-2288 for daily tour schedules. You can take any of the tours (Scenic, Discovery, Lantern, or Spelunking) to answer the questions. The cost ranges from $4.00 to $8.00 for adults.
Required Information for Logging this Cache:
What is the current length of the cave?
What is the depth at which you entered the cave?
How tall is the main cavern you entered?
How was the cave formed?
How were the Calcite Crystals formed?
What is the chemical makeup of Calcite?
What are the two types of Spar you saw on your tour?
An optional picture with you and your GPSr any where on the tour.
During the Mississippian time period a shallow sea covered the area. The sea advanced and receded several times. Sediment and calcium carbonate shells accumulated at the bottom of the sea, and over time, were compressed to form the Pahasapa Limestone. The shells that formed the limestone came from ancient marine animals such as brachiopods. Fossils from Mississippian time are visible in the cave today.
Jewel cave was formed by slowly circulating, acid-rich groundwater. Its unique story begins with the geologic history of the Black Hills. The oldest rocks in South Dakota’s Black Hills are Precambrian-era igneous and metamorphic rocks, which formed under heat and pressure. As the limestone was forming, bodies of gypsum (calcium sulfate) crystallized from the seawater during periods of high evaporation. The gypsum formed irregular masses within the limestone. Shortly after the limestone was deposited, thin gypsum beds in the upper part of the Pahasapa were dissolved away and the overlying limestone collapsed into the resulting voids. This marked the first stage of cave development at Jewel Cave.
The sea advanced and receded across the area several times. As the sea receded, the limestone was exposed to the open air. It was also exposed to fresh water from rainfall, which began to dissolve the limestone, creating sinkholes and caves. This was the second phase of cave development at Jewel Cave. During the Pennsylvanian period, the Minnelusa Formation was deposited as freshwater streams carried sediments into the sea. The Minnelusa consists primarily of sandstone, with a few thin beds of limestone and dolomite. The Minnelusa covered the Pahasapa Limestone and filled the Mississippian sinkholes, cave entrances, and many passages. This reddish "paleofill" is visible in the upper passages of present-day Jewel Cave.
Long after the sea receded for the last time, the Black Hills began to form. At the center of this new mountain range, the Precambrian rocks were thrust upward several thousand feet. The younger sedimentary rocks (the Minnelusa and Pahasapa) were eroded from the highest areas, exposing the Precambrain rocks to the surface. The remaining sedimentary rocks now surround the central Black Hills and tilt away from the center of the uplift. Jewel Cave is located in the southwestern Black Hills, where the sedimentary rocks tilt (or "dip") at an angle of approximately 4 degrees from the northeast to the southwest.
The climate changed and rainfall increased. Much of this freshwater made its way slowly underground. It first passed through the overlying soil, which was rich in carbon dioxide from decaying plants. The carbon dioxide transformed the water into carbonic acid. This weak acid traveled through fractures in the rock until it reached the water table, which rose and filled cracks in the limestone. This standing or slow-moving acid-rich water formed the majority of Jewel Cave. The water slowly drained from the cave as surface erosion created exits for the water in the form of springs.
*Information was gathered from Jewel Cave National Monument Web Site
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