Folding and Faulting in United States National Parks
Folding and faulting is a major feature in geomorphology, the study of the physical features of the surface of the earth and their relation to its geological structures. They are the most common deformation processes. Folding and faulting happen when two pieces of a plate come together and push against each other. To start, folding occurs under compression when forces act towards each other, such as when plates collide. It is a bend in the rock layers, a type of earth movement resulting from the horizontal compression of rock layers by internal forces of the earth plate boundaries. The amount of folding depends on the force used by the movement of the plates. Folds are sometimes, but not always, the cause of features such as hills or valleys. On the other hand, faulting occurs when the Earth’s crust cracks, under tension, causing layers of rocks to stretch and crack. Earthquakes can happen when there is sudden movement along faults; when rocks break and move suddenly, the energy released creates an earthquake. Faults can occur at the Earth’s surface, or perhaps deep into the crust. There are many different types of folding and faulting in different areas of the world.
The three main types of folds are monoclines, anticlines, and synclines. A monocline is “a simple bend in the rock layers so they are no longer horizontal but are inclined”. In this type of fold, the older rocks are at the bottom and the youngest are at the top. In the Grand Canyon, there are examples of monoclines. On the other hand, an anticline is a fold that arches upward. Compared to a monocline, the oldest rocks are found at the center of an anticline, and the youngest ones are hung over the older rocks at the top of the formation. The last main type of fold is a syncline, which is a fold that bends downward. Compared to the monoclines and anticlines, the youngest rocks are at the center, and the oldest is on the outside.
The three main types of faults are normal faults, reverse faults, and strike-slip faults. Normal faults “are caused by tensional stress that pulls the crust apart, causing the hanging wall to slide down relative to the footwall”. The hanging wall is the rock overlying the fault; the footwall is beneath the fault. Normal faults can cause the uplifting of mountain ranges in areas experiencing tensional stress. However, when compression squeezes the crust into a smaller space, the hanging wall pushes up in relation to the footwall. This is called a reverse fault. A subcategory of a reverse fault is a thrust fault, which is when the fault plane angle is almost horizontal. Lastly, a strike-slip fault is where the dip of the fault plane is vertical. This kind of fault results from shear stresses; the most famous strike-slip fault is the San Andreas fault. Folding and faulting are found in many national parks in the United States and in Canada.
This brings us to the first placemark, Zion National Park in Utah. Even though this national park is not near any major plate boundaries, the plate tectonic movement in this area plays a role in the formation of the area. Most of the folds and faults in Zion National Park “are associated with two different orogenic events or processes in which a section of the Earth’s crust is folded and deformed by lateral compression to form a mountain range: The Sevier Orogeny and the Laramide Orogeny”. These events occurred millions of years ago for both periods, and are both a result of lithospheric plate impacts, ultimately forming the base of Zion Canyon, The Grand Canyon, and Bryce Canyon are all within: The Grand Staircase. The Grand Staircase is a group of rock layers that have been folded and altered by plate tectonics. The folding created a steeper gradient and made the top areas of the Grand Staircase capable of being eroded or weathered. In addition to the staircase, the Colorado Plateau affected the uplift of the region. The steeper gradient also resulted in severe downcutting into the underlying sandstone, as you can see in figures Zion National Park 1a and 1b. In addition, the main faults in the park are the Taylor Creek fault zone, Hurricane fault, Sevier fault, and the Paunsaugunt fault.
The next placemark is Grand Canyon National Park in Arizona. In the walls of the Grand Canyon are numerous faults that document the region’s tectonic history. Since faults in the Grand Canyon are not only shown on horizontal surfaces, but also on the walls of the canyon, “geologists are provided with a rare opportunity to study what faults look like thousands of feet down into the Earth’s crust”. Shown in Grand Canyon 1a and 1b, faults can be seen cutting through every geologic layer in the canyon. Monoclines seen in the Grand Canyon is another example of the area’s faults. As mentioned before, monoclines are folds, or bends, in the rock’s layers so are they are not horizontal anymore but at an incline. The most visible example of a fold in the canyon is from Desert View Watchtower, where a monocline is passes through the canyon and has folded the rock layers.
The next stop brings us to Canyonlands National Park in Utah. In this park, the strata there, which is a layer of sedimentary rock or soil, or igneous rock that was formed at the Earth’s surface, are virtually flat-lying or very gentle dips. Along the Colorado river you can see in Canyonlands National Park 1a, “the slightly dipping strata are disturbed by gentle anticlinal and synclinal folds, and by at least one fault”. On the other hand, faulting that occurred in Canyonlands developed in jointed sandstones, and the valleys are developed at the Earth’s surface. The valleys formed by undercutting of the Colorado and Green rivers resulted in erosion. Canyonlands National Park 1b shows a closer look at the fault lines and the different rock formations.
Capitol Reef National Park, also in Utah, is the next stop. The park got its name for its “reef, or ‘barrier-like’, appearance and its tall, white, rounded Navajo Sandstone cliffs reminded onlookers of the U.S. Capitol building in Washington D.C”. The geology is well shown due to weathering and erosion. In Capitol Reef National Park 1b, you can see a broad view of monoclines present. In Capitol Reef National Park 1a, the interaction of tilted bedding with the erosional surface results in a teeth-like appearance. In addition, some parts of the park show a change from a fluvial environment to a possible lake environment due to a change in a deposition.
Arches National Park is placemark five; this national park is known for its various arches made of sandstone. The park covers over 70,000 acres of land and has over 2,000 arches. The arches were formed due to salt diapirs, a domed rock formation where a core of rock has moved upward to penetrate the covering strata. You can see in Arches National Park 1a, the meandering river, as well as normal faulting. The fault zone is a result of the flow of salt beneath the more capable sediments, which then caused salt diapirs to lift the covering layers. As you can see in both Arches National Park 1a and 1b, normal faulting indicates extension in the rock layers.
Placemark six is Bryce Canyon National Park also in Utah. The Sevier Orogeny resulted in folding and faulting across the state of Utah, which is why there are so many national parks in Utah with folding and faulting features. Some of the most notable geological features found in Bryce Canyon are the “hoodoos”. Hoodoos are “pillars of rock that have been created through frost wedging of water in vertical fractures”. You can see these unique formations in Bryce Canyon National Park 1a and 1b. There are many conjugate fractures found in the area surrounding the hoodoos. These fractures are used to interpret the direction of maximum compression.
The Great Smoky Mountains, the next placemark, located in North Carolina and Tennessee, includes 16 mountains over 6,000 feet high, making this one of the highest mountain ranges in North America. The mountains are a part of the Appalachian mountain chain that expands along the coast of North America, and then finally into Oklahoma. A unique feature of the mountains is that the older rocks sit on top of the younger rocks: “The very high peaks are composed of hard, resistant, old metamorphic rocks, of the sort that one finds deep in a mountain range. Beneath them are younger, sedimentary rocks that were deposited in shallow seaways”. Between these is a surface called a thrust-fault, or push-together fault. As explained earlier, a thrust fault shows evidence of sliding, and when the fault plane angle is almost horizontal. In addition to the thrust faults, many folds occur; in such collisions called obduction, layers of rock are either bent into folds or broken into thrust faults.
The next placemark is Death Valley, located in California. It is in “the Southwestern portion of the Basin and Range geomorphic province. The Basin and Range province has a long and active geologic history, including faulting and regional tectonic movement”. Similar to the Great Smoky Mountains, faulting is one of the main reasons Death Valley exists. Most faulting, as you can see in mostly Death Valley 1a, but also in Death Valley 1b, is strike-slip along with normal movement. Strike-slip faults occur where the dip of the fault plane is vertical. The most famous fault in Death Valley is the San Andreas fault, which is the next placemark. With faulting comes the possibility for earthquakes to happen, and while most earthquakes cause little to no damage, the fault systems, such as the San Andreas itself, are possible to create catastrophic events.
Placemark nine is the San Andreas fault located in California. The fault is the sliding boundary between the Pacific Plate and the North American Plate. Communities like “Desert Hot Springs, San Bernardino, Wrightwood, Palmdale, Gorman, Frazier Park, Daly City, Point Reyes Station, and Bodega Bay lie squarely on the fault and are like sitting ducks”. The type of fault that San Andreas is a transform fault or a strike-slip fault; the plates are slowly moving past one another at a couple of inches a year, but not at a constant rate. However, suddenly the built-up strain breaks the rock along the fault, and the plates slip a few feet suddenly. The breaking rock then sends waves out, signaling an earthquake. As you can see in San Andreas 1a and San Andreas 1b, the fault is easy to see as a string of ridges and scarps. In other places, it is not as easy to see since the fault is covered with alluvium, and overrun with bushes. Many roads in California along the fault cut through mountains of the gouge, which is powdery, crumbled rock that has been destroyed by the moving plates. The San Andreas fault is more approachable than any other fault in the world. With California’s climate, many roads and pathways are located along the fault.
The Rocky Mountains, located in Colorado, is placemark ten. The structural form of the Rocky Mountains is formed by faulting and faulting. The faults can be anywhere from normal faults to low-angle reverse faults. In this location, the faults and rotations are best explained by a movement system dominated by vertical motions. Sedimentary layers, as shown in Rocky Mountains 1a and the Rocky Mountains 1b, are usually deformed by forced folding. Measurements on “natural folds demand that the section either thinned or detached”. From this information, it can be determined the organizational style in the Rocky Mountains is not unique, but rather a great illustration of a more comprehensive class of deformation; in other words, force folding.
Placemark 11 is the Appalachian Mountains; this enormous mountain range extends over 14 American states, such of them named West Virginia, Virginia, Maryland, Tennessee, Pennsylvania, Kentucky, North Carolina, South Carolina, Alabama, and Georgia. Looking back at rocks uncovered today in the Appalachians, the geology reveals extended belts of folded and thrust faulted sedimentary rocks, volcanic rocks, and flakes of the ancient ocean floor, thus showing strong evidence rocks were formed by plate collisions. As you can see in Appalachian Mountains 1a, some meandering streams are flowing along weaker layers showing the folds and faults created many years ago. Other streams around the area downcut so fast that they cut across the resilient folded rocks of the mountain core. This is what carves canyons across rock layers and geologic formations. Thrust faulting, also known as reverse faulting, “uplifted and warped older sedimentary rock laid down on the passive margin. As mountains rose, erosion began to wear them down. Streams carried rock debris downslope to be deposited in nearby lowlands”.
The second to last stop is Yellowstone National Park, located in Wyoming. There is much evidence of eroding away of rock, as shown in Yellowstone National Park 1a and Yellowstone National Park 1b. From Yellowstone National Park Overview, although the park covers a widespread area, parts of it are near an oxbow lake, a stream that has been cut off but still has water in it. Sporadic mountain peaks around the park show an immediate observation of folding and faulting. In fact, “one of the most exciting discoveries of the past year is the realization that post-glacial faulting has occurred in many places in the park”. Displacements throughout the park conclude Yellowstone must have been one of the most active places for earthquakes many years ago.
The last stop is Ash Cave in Hocking Hills State Park, located in Southern Ohio. Ash Cave is one of the most spectacular locations to visit. The topography, such as the sandstone and the rock formations, is unique in themselves. The wildlife is vast, like the flora and fauna, as well as the vegetation, which made it a great site to research.
Overall, folding and faulting are found in many national parks throughout the United States and create various landforms that are unique in their own ways.