Conor Watkins' Ozark Mountain Experience
Article 2
Caves And Karst In And Around Rolla
By Conor Watkins

Caves And Karst In And Around Rolla

"Flying like a bat out of hell!"
This poor bat in Lone Hill Onyx Cave happened to be flying right in front of
the camera when the flash fired.  Notice the four foot shadow of the wingspan.
Bats are a beneficial inhabitant of Missouri caves.

The bedrock in the Rolla area consists mainly of dolomite, which is made up of calcium magnesium carbonate (CaMg(CO3)2). Natural and man-made acids in the water dissolve many carbonates, which lead to karst processes and features.  Carbonic acid is the largest player in the dissolution of bedrock.  This weak acid is formed when raindrops combine with carbon dioxide in the atmosphere.  Acids are also created in the soil as organic material decomposes.  As this acidic water seeps into the ground, it slowly dissolves the rock.

This process leads to the creation of sinkholes, caves, springs, losing streams, and other karst features.  Missouri has some excellent examples of karst.  As for sinkholes, the area has both recent and ancient examples.  Some of the best and easiest to see examples of recently formed sinkholes are Conical and Slaughter Sink which are just 15 miles west of Rolla off of I-44.  These are along a county road and on National Forest land so angry landowners with shotguns are not a worry.  After viewing these sinks, visit Onyx Mountain Caverns (http://www.missouricaves.com/onyxmtn.htm), a commercial cave very close to the sinks.  It was created by the same karst processes that made the sinks.  To get to these two sinks, take I-44 west to exit 169. Turn right at this exit and follow the signs as though you are going towards Onyx Mountain Caverns.  After turning left onto the first gravel road, look for a barbed wire fence on the left side of the road with a drop-off on the other side.  Park here and observe.

This is Conical Sink, the smaller of the two sinks.  Its close proximity to the road has made it an illegal dumping ground for years so expect to see tires, refrigerators, and other discards.  Dumping in a sinkhole is a particularly bad idea since these features serve as natural drains for rainwater.  That garbage you see ends up in the groundwater and eventually drinking water.  This isn’t a huge concern with an old washing machine but used motor oil and car batteries are toxic.

Next, turn exactly 180 degrees and start following the small trail into the woods.  Keep following until the large overlook is reached.  This is Slaughter Sink, one of the largest sinkholes in the state.  It is hard to imagine that this feature was formed when the roof of a cavern collapsed thousands of years ago.  The bottom of this sink can be reached by following the trail down through a small natural bridge.  A more gradual hike is available if you walk farther down the road.  Excellent exposures of Roubidoux Sandstone are visible at the bottom.  Satellite and King Sink are a similar example of two sinkholes in the area.  These two sinks are not as impressive, harder to get to and find, and are partly on private property (owner loading shotgun as he reads this).

While in the vicinity of Conical and Slaughter Sink, one should visit Boiling Spring.  At 42 million gallons per day, this spring has the 9th largest average flow in the state.  Take I-44 west to the Dixon exit (exit 163).  Turn right on Hwy 28 and follow it to Hwy PP.  Follow this road until you reach Boiling Spring Campground on the right side of the road.  Turn right and park near the Gasconade River.  The spring is actually in the far bank of the river and appears as a boil at the side of the river.  This spring has been relatively unimpressive lately due to the dry weather, but is worth seeing.  Direct access to this spring is only available through privately owned land.  This spring is actually very close to Onyx Mountain Caverns and is associated with the two sinks and and cave.  Please do not drive down the private road as the landowners have many “No Trespassing” signs and no not want un-announced sightseers.

Recent research by Jim Kaufmann of the UMR Geology and Geophysics Department and the MSM Spelunkers indicates that 84 million gallons per day is a much better estimate of the long term flow of Boiling Spring which historically has been measured only during extreme drought.  This concurs with the estimated recharge area of about 250 square miles which has been determined through dye tracing.  With a flow of 84 million gallons per day, Boiling Spring is the seventh largest in the Ozarks, just behind Blue Spring in Shannon County.

Photo mosaic of the Boiling Spring area by Gary Johnson using photos by
Conor Watking and Gary Johnson.  Boiling Spring is at a low flow in photo.

During the mid 1930's, four large dams were proposed along the Gasconade River near the towns of Richland, Arlington, Vienna, and Rich Fountain.  During the preliminary studies before building the dams, there was concern that the spring might reverse flow under the water pressure head induced by the reservoir impounded at Arlington, serving as a major leakage path from the reservoir.  Later studies indicated that  the spring would not reverse flow but would exit the bluff at pre-existing cave passages located in the bluff just above the spring.  These caves are likely prehistoric spring outlets for Boiling Spring that were developed before the Gasconade River had downcut to its current elevation. 

The laws dictating fluid flow are very similar to those controlling the flow of electrical current.  In fact, the laws are so similar that electrical models can be used to simulate fluid flow.  Don't worry, we won't get into any complex equations here.  The similarity were are interested in here is the fact that both electrical and fluid flows prefer to take the path of least resistance when moving between two points.  The increased pressure head in the reservoir would serve to drive some water flow away from the lower outlet to the older upper outlets.

Ancient examples of sinkholes are also common in the Rolla area.  These are referred to as paleosinks, fossil sinks, and filled sinks.  Excellent examples of these are viewable in roadcuts on I-44 and Hwy 63 north of Rolla.  One of the best exposures in the world is in Rolla.  This sink is known as the Vichy Road Filled Sink and is viewable in the I-44 roadcut from the highway or the Vichy Road overpass.  The Thomas Jefferson Towers and my rental house are located on nearby filled sinks.  These sinkholes formed mostly during the Mississippian and Pennsylvanian Periods, which took place between around 360 and 286 million years ago.  The rock they formed in is mainly dolomite from the Ordovician Period, which took place between 505 and 440 million years ago.  For reference, the dinosaurs died out around 65 million years ago.  These sinks are generally filled with a lighter colored and softer rock than the surrounding bedrock in areas north of I-44.  Some of these sinks contain high-quality clays used in dishes and pottery.  Sinkholes to the south of I-44 tend to be filled with iron ores and other valuable mineral deposits.  These have been mined in the past.  Filled sinks tend to appear as breaks in the natural layering of the rock and are usually a different color.  There are multiple theories on how these sinks were formed and not all of them are related to standard karst processes. Although these sinks are very old and filled with material, they can still pose problems for Geological Engineers and others.

Onondaga and Cathedral Cave are two commercial caves located in Ononaga Cave State Park (http://www.mostateparks.com/onondaga.htm), which is operated by the Missouri DNR Divison of State Parks.  These are located 30 miles east of Rolla at exit 214, which is labeled Leasburg.  The park closes these two caves in the winter to perform maintenance.  Both have large rooms and excellent formations.

For more information on all these features, please see “Geological Wonders And Curiosities of Missouri” and “Springs of Missouri” which are available at the Missouri Division of Geology and Land Survey at 111 Fairgrounds Road in Rolla.  Also see The Missouri Caves Website at http://www.umsl.edu/~joellaws/ozark_caving/springs/boiling.htm.

For an interesting dining experience in a real cave, the Caveman BBQ in Richland, MO is worth a visit.  From Rolla, take I-44 west to Hwy 7 (exit 150).  Turn right at this exit and take another immediate right on Hwy W.  Follow this for a few miles until it dead ends at a T intersection.  Take a left turn at the T and you will be on Rochester Rd.  Go less than a mile until you see the signs for the BBQ on the left at 26880 Rochester Rd.