The Ouachita Folds EarthCache
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In the state of Arkansas, there are two mountain ranges: The Ouachita (pronounces “Wah-shi-tah”) Mountains and the Ozark Mountains. These two mountain ranges create the United States Interior Highlands. They are the only major mountainous region between the Rocky Mountains and the Appalachian Mountains. They also represent two diverse types of mountains. In this Earthcache, you will be learning about how Fold Mountains are formed and how this applies to the Ouachita Mountains.
When learning about the rock layers of the Ouachita Mountains, one needs to start about 300 million years ago. It is believed that Arkansas was on the shore of a deep ocean, scientist called the Ouachita Basin. As time went on, sediment washed down from the erosion of the North American continent causing deep layers of sediment on the ocean floor. These layers eventually turned into sedimentary rocks. As the South American plate drifted northward, its crust was forced underneath the North American continental plate. The sedimentary rock layers were strained, compressed, and folded.
The mountain building process, called orogeny creates folds, faults, and overturned layers of rock causing them to bulge or crack. Geologists call the clash from the South American plate and the North American plate the Ouachita orogeny. Think of the Earth’s crust as a piece of thin paper. Hold one end of the paper down on a table with your hand. Use your other hand to push the other end of the paper toward your hand that is on the table. The paper will fold, buckle, or wrinkle. The forces in the nature act like that.
The Earth’s crust is continually being stretch out and squeezed together. Forces push on the land, forcing it upward and sometimes ‘buckling’ the Earth’s surface. Folds predominantly go up and down. Anticlines are folds that are going up and synclines are ones that go down. These anticlines and synclines can be large as in hills and valleys, or small as the wavy lines found in rocks.
Other mountain ranges that are Fold Mountains include the Appalachians and Rocky Mountains in North American, the Andes in South American, and the Alps in Europe. At one time the Ouachita Mountains were much like the Rocky Mountains of the western United States; with very similar heights of the current Mountain elevations. Because the Ouachita Mountains are very old, much of the rocks that built up the mountain range have been eroded away in time from water and wind. After millions of years of weathering the rough mountain tops have been whittled away, and what now is the surface was once buried under many kilometers of younger rocks.
In the Ouachita Mountains of Arkansas,
the layers of rocks are so twisting and complex that understanding what caused these deformations has brought about extensive research among geologists. When studying the Ouachita Mountains scientist have found that it is mostly composed of sedimentary rocks. Some rocks, like slate, shale, and schist, have more give and will fold without cracking at times. Sandstone, however, is not as yielding and will crack, with cracks running parallel to the folding. The physical properties, rock structures, and Arkansas; varying temperatures played a role in the forming of the mountain’s folds.
There are other unique features of the Ouachita Mountains. Unlike most other mountain ranges in the United States, the Ouachita Mountains run east and west rather than north and south. The Ouachita Mountains are noted for quartz crystal deposits and for novaculite whetstones. The quartz most likely was formed during the Ouachita orogeny, as the folded rocks cracked many times, allowing fluids from deep in the Earth to fill the cracks. In fact the quartz crystals are very old, and their formation has nothing to so with the presence of the hot water springs. There’s no unusual heat source at the base of the mountains, as the presence of hot wells in Hot Springs National Park would suggest. This water has been heated because the arrangement of cracks in the rock layers allows for a circulation of waters through deeper layers of rocks.
This earth cache will have you drive through a cut away of the mountain. You will need to observe what the rock layers look like and the direction they are going.
Location 1: N 34º 28.149 W 093º 05.248
(The traffic can be busy so at times stopping might be difficult. PLEASE NO PHOTOS of this location in the online log.)
Then you will drive to another location to observe the rock layers.
Location 2: N 34º 28.332 W 093º 05.474
(The business owner has asked us not to chip away at the rock wall. Also please use the entrance just past
the business. I have placed the cords on that end of the
building/rock wall so that should help. It is at this, the SECOND location, which you will need to take your photo with your GPS.)
Requirements: (Email me the following information.)
Compare the two locations in the following ways:
a) Describe the color of the rock layers at each location.
b) Identify the kinds of rocks you observe at each location.
c) Explain the direction of which the rock layers are going at each location.
If it is not too much trouble it would be great if you would post a photo of yourself at location 2.
I will delete any logs not completing the requirements in a timely manner. As always, the more effort put into your log, the more you are appreciated and the more you are remembered.
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