Exploring Karst: Blanchard Springs Caverns
From GeoClasses
by Franklin, Safa and Gilman from ESCI 1020 Summer 2007.
Contents |
Abstract
Karst is a term defining the landforms that occur due to the dissolution of underlying bedrock. The region in north-central Arkansas where the Ozarks lie is one such region heavily influenced by these processes. Blanchard Springs Caverns is owned and administered by the United States Forest Service, and has a cave and spring both formed via karstification. Supported by discoveries we made during our visit to the park, this project will discuss the various aspects of caves, and the formations found within them.
The Ozarks
How Caves are Formed
Blanchard Springs Caverns is mostly sculpted by carbonic acid, which comes from carbon dioxide in the atmosphere. Rainwater trickles down through piles of leaves and into the soil, picking up acids along the way and eventually reaching the limestone bedrock. This acidic water eats away at the limestone, dissolving it and creating cracks downwards and sideways. Over time water travels further down along these crevices weathering out caverns.
The multiple levels of cave systems form due to fluctuations in the level of the water table over many thousands of years. Cave passages first start to develop where acidic groundwater dissolves limestone at or near the water table level. The movement of the water table level depends largely on the amount of rainfall in the area over a period of time. As the climate becomes drier and the level of the water table lowers, the cavities that previously were filled with water become filled with air. Speleothems then form as the carbonic acid in the water releases carbon dioxide into the air, leaving calcite precipitates behind.
In the case of Blanchard Springs, the flowing water formed a stream that burst out of the side of the mountain in the form of a spring. Were it not for this spring, we would not be able to see inside the cave today.
The Cave
Named for Confederate soldier John Blanchard, who owned a grist mill just below the springs, Blanchard Springs Caverns is a large and beautiful cavern, described by local songwriter Jimmy Driftwood as, "a castle underground."
Blanchard Spring's interior temperature is usually 58 degrees, which is also the annual mean temperature for the area. It is also a live cave, indicated by the presence of water. This means that the caverns are constantly growing and changing as water dissolves limestone and deposits calcite. After a heavy rain, water will seep into the Coral room, the highest level of the cave, within 45 minutes.
The cave reaches its maximum depth of 292 feet below the surface inside the Christmas Tree Room along the lower cave level.
The natural entrance to the cave is a ninety foot sinkhole positioned between two valleys. The natural air flow in the cave rushes toward this opening, reaching maximum speeds of sixty to seventy miles per hour inside the wind tunnel.
Water in Blanchard Springs flows through air filled passages at a rate of 10 feet per minute. It takes 18 and a half hours however, for the water to pass through 1,000 feet of submerged passages, or almost a foot per minute. Therefore the water in these air-filled passages is around 10 times more turbulent than the water underground (see the Reynolds number).
Speleothems
Don't touch anything in the cave!!
Sometimes speleothems appear multi-colored due to stains from the impurities deposited with the calcite. When made of calcite crystals in their purest form, speleothems are white in appearance, but the presence of iron oxides often adds shades of red or brown.
A large concentration of dripstone speleothems can be found in the upper level of Blanchard Springs. Due to its position close to the surface, the upper cave level receives more acidic water and thus greater numbers of calcite deposits than the lower level. Water becomes less acidic the deeper it moves below the surface since it has already deposited out all or most of the calcite, so there are far fewer calcite speleothems. The upper level of the cave also formed before the lower level, giving its calcite speleothems more time to develop.
It is very important not to touch these pretty formations, as the oils on your hand will adversely effect their growth.
Rimstone Dams
 | Rimstone dams (also known as travertine terraces) are calcite barriers that surround pools of water. A rim forms in a shallow cave stream or on a cave ledge where water flows over an irregularity. Carbon dioxide is lost as a result and a layer of calcite is left behind. As water repeatedly spills over the top of the rim, the calcite barrier thickens and increases in height. Blanchard Spring's "Salamander Pool" is one such example. The dam bounding the Salamander Pool currently stands three feet high but has stopped growing due to a leak that prevents water from flowing over the top of the rimstone.
In 1982 a devastating flood caused severe damage to much of North-Eastern Arkansas. Flooding caused the water level in the cave's stream to rise 12 feet, filling lower passages with water, mud, rocks, and sticks. The added weight and the washing away of clays created sinkholes within the cave, and may have damaged the salamander pool and its rimstone dam. |
Basic Dripstone Formations
 | Soda straws are young formations that begin to form off the cave ceiling when water dripping down into the cave deposits little crystals of calcite. Water drips through the inside of these hollow tubes, growing downward around its rim. Eventually, if the soda straw becomes clogged, the water will flow on the exterior of the formation, widening it and creating a stalactite. |
| Stalagmites form from the bottom of the cave when dripping water hits the cave floor, depositing calcite that builds up into a formation. When these spires connect with a stalactite, a column is formed. In Blanchard Spring's Cathedral Room, one such column spans 70 feet in height. The photo to the right shows a stalactite and a stalagmite are almost forming a column. |  |
Stalactiflats
 | Stalactiflats, or clastic canopies, are shelves of flowstone that hang from cave walls. Each stalactiflat began developing thousands of years ago when terra rosa clay, or “peanut butter mud” as some cavers call it, nearly filled Blanchard Springs. As acidic water flowed down into the cave, a calcite flowstone formed atop the high banks of clay. Streams later eroded away the clay, leaving the flowstone suspended in the air with a relatively flat surface where its foundation had been originally. |
Flowstones
 | A Flowstone forms when water flows down a cave wall and deposits thin sheets of calcite in a sloping shape. As the layers accumulate, the formation tends to grow rounder as well as thicker. The multicolored, waterfall-shaped Great Flowstone at Blanchard Springs is one of the largest flowstone speleothems in the world.
Sometimes the sheets of deposited calcite plug up the flowstone’s water source. These large flowstone plugs can potentially interfere with cave exploration by sealing off entire passageways. |
Draperies and Cave Bacon
 | Cave curtains (aka. draperies, "cave bacon") are formed where walls are not completely vertical or horizontal. As water runs down the wall, it leaves a track of calcite. Future water droplets will run along this track and form long sheets. These formations turn and twist due to the natural air flow in the cave. Right now all that air is rushing toward the natural entrance which is a 90 foot sinkhole in the middle of two valleys. This picture was taken at our half-way point of the tour. Some draperies are multi-colored due to minerals and organic compounds that may have been in the water that formed them. |  |
Cave Coral and Popcorn
 | Cave coral or cave popcorn have knobby features resembling cauliflower, and of course popcorn and coral. This globular shaped speleothen forms in a variety of ways. In Blanchard Springs it is sometimes a result of water flowing off flowstones and splashing against the wall, depositing calcite. Many other examples of popcorn, especially in the Ozarks are formed by seeping water. |
Other Architectural Features
Erosional and solutional features known as speleogens decorate the ceiling in Blanchard Springs Cavern in a dramatic way. One such feature is called a cave pendant, appearing along the lower cave level as a group of weathered bedrock remnants that are suspended from the ceiling. The pendants in the photo to the left began developing when the height of the terra rosa clay that once filled the cave forced the stream to flow up against the ceiling rock. Whenever flooding occurred, the increased amount of sediment suspended in the stream abraded, dissolved, and eroded the ceiling bedrock. The resulting ceiling channels and hanging pendants that are visible to us today were revealed once the clay and other sediment filling the cave had finally eroded away.
The process of breakdown affects ceilings with less sculptural results. Breakdown begins during the stage of cave formation in which newly formed passages are still filled with water. Blocks of weak rock tumble down from ceilings and walls, collecting on the floor below to be dissolved by water. The breakdown rocks that do not weather away remain in a heaps on the cave floor. This process gives many of the ceilings along the lower cave level a "stair-step" appearance.
The Springs
Rainwater travels from the sky, through the soil and limestone, into the cave, and exits through Blanchard Springs at an average of 7,000 gallons per minute (FAST!). During the spring's formation, the caverns retained the rainwater that formed them. It was not until surface erosion began to form valley that the spring was created and water began to be released. As the valley cut deeper and deeper, lower levels of the cave were drained. It is believed that this water flowed from holes higher up on the bluff when the stream bed was 20-30 feet higher than it is today.
The water flowing through the caverns of Blanchard Springs passes under many bat nests, collecting bat wastes and the decaying remains of dead bats. It is unwise, therefore, to drink this water despite its crystal clarity.
Comparisons with Other Caves
Hidden River Cave
Hidden River Cave (formerly known as Horse Cave) is located in the town of Horse Cave in south-central Kentucky. The landscape in this hilly part of the country looks very similar to that of the Ozarks. Seas covered most of Kentucky over 300 million years ago, leading to the creation of limestone in the area which accounts for why almost 40% of Kentucky is made up of karst. Much younger than Blanchard Springs, Hidden River's formation began only a few million years ago. Despite its age, Hidden River has miles of passages and some of the largest rooms in the United States. The water flowing through the cave also exits through the largest spring in Kentucky before flowing into the Greene River. A century ago local residents used the cave as a dump, leading to severe pollution. Contaminated water halted the growth of formations in the cave. Many of the cave passages are low compared to those at Blanchard Springs and flood easily. This flooding prevents formations from growing and also leaves the cave muddy and slick. The ecology of the cave is now closely monitored and scientists hope it is on its way to recovery.
Diamond Caverns
Also located in south-central Kentucky, Diamond Caverns, along with other caves in the area, were formed in limestone capped by a layer of sandstone. These caves are quite stable as a result. Diamond Caverns is also quite old. By studying the geology of the area scientists have concluded that each foot of limestone represents an about 40,000 years. It is estimated that Diamond Caverns began to form over 10 million years ago. A stream began to flow beneath the forming cave, which is today called the Hawkins River. At present the Hawkins flows at a level 150 feet below what is considered Diamond Caverns, flowing into Mammoth Cave. The two caverns may someday connect to each other.
The formations in Diamond Caverns are similar to those found in Blanchard Springs. It has ceilings covered in stalactites, walls draped in cave bacon, and is covered in crystalline calcite deposits making the cavern walls appear (in certain light) to be covered with diamonds. Diamond Caverns also has cave popcorn formed by water seeping into the cave and evaporating at the same rate.
Cave Conservation Efforts
There are serious environmental concerns about the anthropogenic activity surrounding Blanchard Springs, and the surrounding Ozark Region. In this rural area, people frequently have used sinkholes as landfills, dumping their garbage which reacts with the rainwater that slowly seeps into the cave systems. When this contaminated water makes its way through the cave, it can drastically upset the biochemical equilibrium necessary to sustain the animal life underground. Many of these creatures are rare, but not all. The most common are bats. One may consider conservationist efforts insignificant to our everyday lives, but these bats do humans a great service by controlling the mosquito population. Save the bats!!!
Furthermore, contaminated water can easily seep into the water supply in karstified regions such as this. Environmental scientists have been working with farmers in the region to use their fertilizers and pesticides responsibly so that they do not poison the water. This is not just to protect natural wildlife, but to protect the population that drinks the water as well.
There are many foundations that work to conserve and study caves such as the National Speleological Society and the Cave Conservancy.
Photo Gallery
 Drapery forming over limestone breakdown in Blanchard Springs |
 Drapery and column in Blanchard Springs |
 Flowstone, stalagmite, stalactites in Blanchard Springs |
 Large flowstone. Blanchard Springs |
 Stream flowing through Blanchard Springs |
 Flowstone, stalactites, stalagmites. Rimstone dam in lower right. Blanchard Springs |
 Cave popcorn and limestone layers. Blanchard Springs |
 "Great Flowstone" Blanchard Springs |
 Flowstone forming over limestone layers. Blanchard Springs |
 Stalactites in Diamond Caverns, KY |
 Having fun at Blanchard Springs exhibit |
 "Don't break stalactites!" |
 Muddy after a 5 hour trip through muddy Hidden River Cave, KY |
Sources
American Cave Museum. Hidden River Cave. Retrieved June 22,2007, from http://cavern.org.
Bewley, D., & Bunnell, D. (2007). The Virtual Cave. Retrieved June 25, 2007, from http://www.goodearthgraphics.com/virtcave/.
Motion Picture Service of the US Department of Agriculture (Producer). Amazing World Below [Motion Picture]. United States: Ozark National Forest.
Olson, Rick (2006). Geology of Diamond Caverns. Retrieved June 22, 2007, from http://diamondcaverns.com/2006/geology.htm.
US Department of Agriculture. Blanchard Springs. Viewed exhibition June 23, 2007. Ozark-St. Francis National Forests.
US Geological Survey Western Earth Surface Processes Team (2000). Geology of Caves. Retrieved June 25, 2007, from http://www2.nature.nps.gov/geology/USGSNPS/cave/cave.html.
Wallace, Kyle: Park Ranger, personal communication, June 23, 2007.
Weaver, H.D. (1992). THE WILDERNESS UNDERGROUND: Caves of the Ozark Plateau. Columbia, Missouri: University of Missouri Press.
Wikipedia (2007). Mammoth Cave National Park. Retrieved June 22, 2007, from http://en.wikipedia.org/wiki/Mammoth_Cave_National_Park.
Wines, A. (2002). Geology of Lehman Caves. Retrieved June 25, 2007, from http://www.nps.gov/archive/grba/cavegeologydet.htm.
