Arkansas provides many great opportunities to explore nature, as the "Natural State" you will not want to forget your camera, a walking stick, and a buddy or two to go out and enjoy nature.
When exploring this particular area, I felt like I was in a special place, I sat and just breathed in nature I also discovered the local blue heron just below. Looking at me for a moment, assessing I was no threat to him, he allowed me to watch his expert fishing skills and I took shelter in the limestone overhang. Resting in this sanctuary I realized I was witness to something very special and want to share with you this place of peace.
In this Earth Cache lesson to lean about the formation of caves.
If you have been working on the Earth Caches on these trails you may have learned what erosion is and the different forms of erosion. On this Earth Cache Adventure we are going to how caves are born.
After completing this Earth Cache you will have a better understanding of:
- How caves are formed
- the time frame in which caves are born
- what the key elements is needed for limestone caves to develop
- what meandering is and its long term effects on the environment
- Cut banks
In the ashes rises new beginnings
In other lessons you have learned that the area was all underwater millions of years ago, and that limestone is primarily made out of dead marine life organisms. One possible theory to this formation is this nothing more that the remains of a cut bank from meandering. But with the continuing process the ending is only the beginning of something new. Before we get to that we must understand where we are at in the process today.
A meander, in general, is a bend in a sinuous watercourse or river. A meander forms when moving water in a stream erodes the outer banks and widens its valley, and the inner part of the river has less energy and deposits silt. A stream of any volume may assume a meandering course, alternately eroding sediments from the outside of a bend and depositing them on the inside. The result is a snaking pattern as the stream meanders back and forth across its down-valley axis.
A cut bank, also known as a river cliff or river-cut cliff, is the outside bank of a water channel (stream), which is continually undergoing erosion. Cut banks are found in abundance along mature or meandering streams, they are located on the outside of a stream bend, known as a meander, opposite the slip-off slope on the inside of the bend. They are shaped much like a small cliff, and are formed by the erosion of soil as the stream collides with the river bank. As opposed to a point bar which is an area of deposition, a cut bank is an area of erosion.
Typically, cut banks are nearly vertical and often expose the roots of nearby plant life. Often, particularly during periods of high rainfall and higher-than average water levels, trees and poorly placed buildings can fall into the stream due to mass wasting events. Given enough time, the combination of erosion along cut banks and deposition along point bars can lead to the formation of an oxbow lake. Material eroded here is deposited downstream in point bars.
Not only are cut banks steep and unstable, they are also the area of a stream where the water is flowing the fastest at a higher pressure and often deeper, making them rather dangerous. Geologically speaking, this is known as an area of high-energy.
HOW LIMESTONE CAVES ARE FORMED
A cave is a natural opening or cavity within the earth, generally extending from the earth's surface to beyond the zone of light. Three generic classes of caves can be recognized according to the major sculpturing process:
- (1) caves formed by pressure or flow
- (2) caves carved by erosion
- (3) caves dissolved by solution
Pressure-Those structures formed by mechanical pressure or flow include lava tunnels associated with volcanoes (e.g., Catacombs Cave in Lava Beds National Monument, California) and "badland caves" excavated from poorly consolidated rock by hydraulic pressure (e.g., small caves of the arid Badlands of South Dakota).
Erosion-The caves carved by erosion include shoreline grottos created by the mechanical action of waves (e.g., La Jolla sea caves near San Diego, California) and rock shelters cut by river meanders (e.g., like the one at ground zero).
Solution-The caves dissolved by solution include ice caves associated with glaciers and the familiar limestone caverns or caves. Limestone caves are, by far, the most common type of caves.
A limestone cave or cavern is a natural cavity that is formed underneath the Earth’s surface that can range from a few meters to many kilometers in length and depth.
Most of the world’s caves are formed in porous limestone. Over millions of years, acidic groundwater or underground rivers dissolve away the limestone, leaving cavities which grow over time.
Early life forms appeared in the oceans about 3.8-billion years ago. These were single-celled, blue-green algae, called cyanobacteria, which made their own food through photosynthesis, releasing oxygen into the atmosphere in the process.
Dolomitic limestone, a sedimentary rock, was formed over millions of years through chemical reactions generated by these early organisms.
With movements within the Earth’s crust, the sedimentary dolomitic limestone eventually became exposed on dry land.
As time passed the limestone, which is permeable and soluble, was eroded by water. Weak carbonic acid in rainwater, reacting with the chemicals in the rock, dissolved and eroded away the limestone as the water filtered into the underlying depths of sediments. Large hollow solution cavities were formed in the limestone in this way.
Recently, it has been discovered that the well-known caves of Carlsbad Caverns and Lechuguilla Cave were not formed from carbonic acid but from sulfuric acid. It was discovered that oil-eating microorganisms deep within the earth produce hydrogen sulfide that rose up and mixed with ground water producing sulfuric acid. It was this sulfuric acid that dissolved the limestone forming the caves.
Either way, because the soluble limestone is partially dissolved and carried away, these are a type of solutional cave.
Many cavities occur at various depths in a cave system due to the continual seepage and flow of the mildly acidic water through the deposits, while underground rivers may eventually carve their way through a mountainside, creating openings and entrances to the outside.
Other cave entrances include pit and depression areas that are located at the tops of caves.
Many beautiful structures – including stalagmites and stalactites – form inside caves as carbonic acid, carrying limestone, drips through cave roofs and onto their floors. Structures inside a cave may require millions of years to develop.
Did you Know?
The great size and beauty of limestone caves have made them features of public amazement and wonder. More than 130 caves in the United States are open commercially, and at least 13 national parks and monuments contain caves. The world's longest cave appears to be Kentucky's Mammoth Cave which has more than 240 kilometers (150 miles) of accessible passages. The largest subterranean chamber yet discovered is the Big Room of New Mexico's Carlsbad Caverns. The Big Room is about 400 meters (1,312 feet) long, 200 meters (656 feet) wide, 90 meters (295 feet) high, and contains the Great Dome, a stalagmite 19 meters (62 feet) tall. Gouffre Berger Cave near Grenoble, France, descends at least 1,100 meters (3,680 feet) below the surface and is the deepest cave yet explored by man. Records of the National Speleological Society of America indicate more than 11,000 caves in the United States, and it appears likely that 100,000 caves exist in the whole earth.
Requirements: (please do not put your answers in the log)
Now that we learned a little bit about erosion and the effects it has on limestone, take a moment to study ground zero. With the information above, and information at GZ you should be able to answer the following questions. You have 24 hours to send me an email (found in my geocaching profile) with the correct answers. Failure to do so will result in the removal of your "Found it log". Please add the GC code and title in the subject line. If you are sending answers for multiple people in your group, please add all the names in your email to ensure they don't have their log deleted :) Photos with you/group of the area would be greatly appreciated.
1 In your own words define how a cut bank is formed.
2 How many Meanders do you see directly in front of ground zero
3 What are the three sculpting techniques for cave
4 Of the three sculpturing techniques which two are most likely the cause of ground zero?
5 Is ground zero undergoing a solution type of erosion?