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Roger Weller, geology instructor
Crystal Cave, Wisconsin
by Steven Hessil
Crystal Cave, Wisconsin
Crystal Cave is the largest cave in the state of Wisconsin and is enjoyed by
40,000 guests from around the world every year. A local farm boy named William
Vanasse stumbled upon this cavity in 1881 while out exploring. In its original
state it was filled with much debris and the immense size was not suspected.
After many decades of excavation the cave was opened to the public in 1942. The
cave itself stretches for nearly a mile underground, though only a portion of
this expanse is open to the public, and newfound openings show a possibility of
another large portion yet unexcavated.
When exploring the cave a newly christened spelunker will be 70 feet below the
surface at most points. The sedimentary rocks forming the cave are known as the
Prairie du Chein formation, and there are also small amounts of flint and “bog
iron” present. This formation is found throughout the Midwest in the states of
Illinois, Wisconsin, Michigan and Indiana. Three separate distinct layers are
evident within Crystal Cave and each has its own specific texture. These layers
are composed of limestone and dolostone created in a deepwater environment,
sandstone composed in a shallow water environment, and a thick layer of dolomite
respectively. The estimated age of the Prairie du Chein formation is 485
million years old.
Within Crystal Cave there are different formations. It is full of your basic
stalactite and stalagmites. The most widespread and interesting formations
within the cave are that of soda straws. These stalactites are formed when
calcium bicarbonate reaches the cavern and is exposed to air and becomes calcium
carbonate forming calcite. Soda straws are interesting because they have a hole
in the center of the formation resembling a straw. Flowstone is
also present within the cave.
Stalactites and Stalagmites
Stalactites are formed by rainwater seeping its way through soil. As the water seeps through the soil it picks up small amounts of limestone and carries it downward. Upon reaching the roof of a cave the water evaporates leaving behind the small amount of limestone on the cavern ceiling. On the other hand, if the water does not have time to evaporate then it will drop off of a formed stalactite and impact the floor of the cavern. Soon enough it will evaporate and leave behind the same trace amount of limestone, thus forming a stalagmite. This is also the reason why stalagmites generally grown directly underneath a stalactite.
Flowstone is created in much the same way as stalactites and stalagmites except it is produced while water is flowing down the walls of a cave. This gives the formation a very distinct pattern. Also, often there are other minerals within the water along with the limestone and they can produce different colored formations, including; red from rust, green from copper, grey from aluminum oxide, and white from pure calcite.
How are caves formed?
Caves are formed when water mixed carbon dioxide and forms carbonic acid. The
carbonic acid then runs through a fracture in a jointed rock and begins to erode
it. When the carbonic acid dissolves limestone it then produces a calcium
bicarbonate solution. Moving water is needed throughout the process to move the
carbonic acid and continue erosion. This process is very slow, in reference to
human time, and often takes tens of thousands of years to produce a cave of any
size at all.
Bats populate Crystal Cave during the winter months. They often enter the cave during October or November to hibernate and leave again during April or May. Bats are extremely active during the summer months and can eat up to three thousand insects in a single night. There are three separate species that inhabit the cave, including; The Little Brown, the Northern Myotis, and the Eastern Pipistrelle.