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Roger Weller, geology instructor                     

Colossal Cave,
Tuscon, Arizona
Rose Phillips
Physical Geology
Fall 2006

The Beauty of Caves

            A cave is a natural hole or passageway in the earth’s crust.  There are several types of caves, including lave tube caves, sea caves, sandstone caves, and limestone caves.  Caves can be found in various areas, but they are commonly found in areas where there is a high amount of limestone.

            Colossal Cave is a limestone cave, although you will also find the minerals calcite and gypsum throughout the cave.  Limestone caves are formed when rain water seeps through the earth and passes through the soil.  When the rain water picks up carbon dioxide given off by decomposing plants in the soil, the rain is changed into carbonic acid.  Carbonic acid is a weak acid of carbon dioxide and water.  The carbonic acid seeps into small cracks in the limestone and some of the rock is gradually dissolved.  Over many thousands of years, the crack becomes larger and eventually underground passageways and rooms are formed.  The cave stops growing when water stops dripping or flowing into the limestone. 


Small cavern-Photo courtesy of William Phillips


Caves can remain filled with water for many years.  Eventually though, the water must recede in order for the rooms and passageways to become seen and accessible.  A couple of things may cause this recession of water within the cave.  First, a river may carve a deeper channel which results in the level of water underground to drop.  Another possibility is the earth may push upward as a result of rising magma in the earth’s crust, causing the water in the cave to drain.



Large cavern divided by a column-Photo courtesy of William Phillips


            As water seeps into the limestone, it carries dissolved calcite.  As time passes, the calcite builds up forming speleothems or cave decorations.

            Stalactites are formed when there is a build-up of calcite that hangs from the ceiling.  You can remember that the word stalactite has the letter “c” in it, thus it is the formation hanging from the ceiling.

Stalactite in Colossal Cave-Photo courtesy of William Phillips


            Stalagmites are formed when water drips off of a stalactite and falls to the ground.  Over many years, the build-up of calcite makes the formation that grows upward from the ground.  You can remember the word stalagmite has the letter “g” in it, thus it is the formation growing upward from the ground. 


Stalagmites-Photo courtesy of Dave Bunnell


            When stalactites and stalagmites both grow to the point where they meet each other, a column is formed.

Stalagmite at Colossal Cave-Photo courtesy of William Phillips


            Artifacts have been formed in Colossal Cave indicating that it was inhabited by the Hohokam Indians approximately 1100 years ago.  It was rediscovered by Soloman Lick in 1879.  It delves 600 feet into the mountainside, with 40 feet being below the main entrance to the cave.

            Within Colossal Cave, there are some magnificent sights!  My two favorite “rooms” of the cave are the Drapery Room and the room with the silent waterfall.  The Drapery Room was formed by flowstone when water flowed heavily and formed what now has the appearance of drapes. 

Drapery Room-Photo courtesy of Y. Yeats


The Silent Waterfall was also formed by flowstone as the water freely flowed down a wall.  According to our tour guide Katie, the legend is that stolen stagecoach silver was hidden behind this structure.  This flowstone looks as though it is a waterfall frozen in time.

Silent Waterfall-Photo courtesy of Marija Potkonjak


Silent Waterfall-Photo courtesy of William Phillips


            The lowest point in the cave is the Living Room, which is 70 feet below the parking lot.  This massive room is said to have been the hideout of the stagecoach robbers.

            Colossal cave is a great place to visit if you are ever near Tucson, Arizona.  The cave itself has been slightly improved with flagstone floors laid by the Civilian Conservation Corps in the 1930’s.  Fiberglass lights have also been installed to make the pathway lit for safer touring.  Although only approximately two miles have been mapped, it is a wonderful adventure and a great opportunity to see the beauty that only natural forces can provide.  The cave itself has been dry for about 2,000 to 10,000 years.  This means that water has not flowed or dripped into the cave during this time, and the formations have quit growing.  The cave remains a constant 70 degrees because there is a great deal of air exchange between the cave and the outside atmosphere.  But, do not let this fool you!!! You can still see and smell bat guano inside the cave. 

            If you are feeling adventurous, you can take a more extreme tour of the cave where you will have to wear actual caving gear and explore narrow tunnels. There is even an evening tour offered by reservation only, where participants can go through the cave exploring only by candlelight. 

            Colossal Cave is a currently a dry cave, but with nature being what it is, the tides could turn at any time. Maybe one day, water will again enter Colossal Cave and form more beautiful sights for us all to enjoy!


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