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Daniel SolomonGeography 5 Professor Patrich 15 January 2018The Grandeur of the Geological Phenomenon Half DomeYosemite National Park has some of the most iconic landscapes in the United States of America. The park was established in 1890, and continues to draw millions of visitors each year to see its magnificent features that include unique rock formations such as the Half Dome, and several hills, valleys, waterfalls, meadows, and mountains. The incredible features found in Yosemite National Park have led many scientists to question how the park developed over time. Perhaps the most famous rock formation in the park is Half Dome. Half Dome is a granite exposure that has existed since the Cretaceous period 65 million years ago, and is unique in its appearance. (How Half Dome Formed). The formation of smooth granite cliff faces are the result of magma solidifying underground combined with overriding tectonic plates. Scientists and geologists claim that the park was formed underground by intrusions of magma during the Cretaceous period and was gradually pushed up to the earth’s crust (Geology). Additionally, according to the National Park Service, Half Dome was never full, as it is a geological wonder that is the result of glaciers, rivers, and erosion effects upon natural fissures and joints. The geological development and glacier formation of Half Dome at Yosemite is astounding. This paper demonstrates the geologic formations of Yosemite National Park and more specifically, the formation of Half Dome, along with theories about its inception, weather patterns, and underground activity.  There are two central theories about the formation of Yosemite Valley’s Half Dome. The first theory was initiated by Harvard University’s geologist Josiah Whitney; he believed that Yosemite Valley was formed as a result of the valley being positioned between two major faults. Whitney’s theory was valid at the time of its conception due to very little information being available about the earth’s crust and layers of the earth. The second theory was initiated by John Muir. As we learned throughout our Geography class, Muir was the founder of Sierra Club, father of the national parks system, and helped preserve Yosemite Valley. He believed that Yosemite was originally formed by glaciers. Ironically, Muir, who was not a geologist, lived in the park for years and observed Yosemite National Park throughout different seasons and weather. Eventually, after much study by geologists and the United States Geological Survey, Muir was proven correct. The freezing and thawing of rock surfaces in the National Park eventually led to exfoliation and erosion of Yosemite Valley and its granite features. Scientists have noted that layers of rock were exfoliated to reveal the granite surfaces that visitors to the park witness today. Many formations consist of quartz monzonite and as a result, they seem to glimmer in the sun (Geology). Half Dome has been known throughout history as an anomaly in granite development and weathering which warrants further investigation.  Yosemite Valley’s granitic rocks all look the same from the outside, but in reality, each mountain is an individual rock body that is established well beneath the earth’s surface. As previously mentioned, the granite mountains were initially formed underground by solidified magma. Half Dome is a granite feature that exists well below the earth’s surface and weathers uniquely. According to the National Park Service, this granite dome is over 8,000 feet in elevation (How Half Dome Formed). Although the mountains were formed underground, each mountain and rock in Yosemite National Park has different characteristics and compositions. It is important to note the different characteristics, mineral compositions, and textures of each rock body in order to understand how intricate Yosemite National Park’s ecosystem is and how valuable the national park is to humanity and nature. Variations of the characteristics of the mountains and rocks include the coarseness of their crystals, while uniformity or variation in grain size play crucial roles in a rock’s resistance to abrasion, fracturing, and weathering joints. In Yosemite Valley, bedrock structures have the greatest effects on the park’s landform development. According to the United States Geological Survey for the National Parks Service, bedrock structures are rooted in different types of soil from erosion from the granitic rocks. Most of the granitic rock found in Yosemite, such as Half Dome, is unbroken on a small scale. However, “on a larger scale, the rock is broken by joints, which are more or less planar cracks commonly found as sets of parallel fractures in the rock… regional-scale joints commonly determine the orientation of major features of the landscape, such as the planar face of Half Dome” (How Half Dome Formed).  Half Dome was cut in half at these joints and fissures by erosion, exfoliation, and pressure over time. Many of the rocks in Yosemite have joints that determine how the rocks will be oriented and carved by water, ice, and sediment (Gunther). For example, the river erosion along these joints throughout the Merced River carved the first rock formations in the park (Gunther). Later, the river turned into ice and expanded, thus causing further weathering of the rock.  Glaciers, water, and ice have played a large role in the carving of the rock features and other natural features in Yosemite National Park such as Half Dome. Since the Cretaceous period, water and ice along with cold weather led to glacier formations. Millions of years ago, an enormous amount of ice moved from Canada and froze within Yosemite Valley and throughout the North. These glaciers did not affect Half Dome directly because it transcended the glacier, however, the base of the mammoth granite fixture was still affected. In fact, there was major glacial action in Yosemite that may have affected Half Dome at three different points in time.  These glaciers were originally studied by the scientists Joseph LeConte, John Muir, and Francois Matthes. According to the United States National Parks, these scientists and many others “have explored and studied the Lyell and Maclure glaciers for nearly 150 years. (They) mapped the glaciers’ extent, measured their movement, and observed changes throughout time” (Geology).  These glaciers continue to be monitored by geologists and scientists today. Yosemite glaciers essentially polish the granite in by “literally grinding, tooling and polishing their beds with the rock debris that is frozen in the bottom layers” (Matthes). Also, landforms that are the result of glaciation include U-shaped canyons, jagged peaks, rounded domes, waterfalls, and moraines” (“Geology”). All of these features and landforms can be found in Yosemite National Park today. The United States National Park Service states that “more than once, Pleistocene glaciers spilled down the west-side Sierra river drainages from the range’s crest, with their relentless scraping turning sharp, stream-cut canyons into broad, U-shaped valleys” (“Geology”). Perhaps the greatest example of glaciation was the valley formation in Yosemite and was completed by the Sherwin glacier which almost completely filled the Yosemite Valley. Gunther explains that as the water that forms the glaciers expand, the river valley deepened and widened resulting in Yosemite Valley and Half Dome (Gunther). A second major example of glaciation that occurred in Yosemite happened over 10,000 years ago and carved the face of Half Dome (How Half Dome Formed). Half Dome is a unique granite dome since it has three sloped sides with one straight face with a clear drop to the ground. Essentially, glaciers account for the widening of rock, the polishing of surfaces, and also account for some slope movement. While glaciers account for some slope movement, further weathering to Yosemite Valley also occurs from other sources.Flowing water is another major cause of weathering to the rocks of Yosemite National Park. However, flowing water is also responsible for the transportation of minerals and rocks and also progressively cuts rock/deepens canyons. In addition, erosion from flowing water precipitates erosion and landslides, which can lead to the additional carving of rock surfaces.  For example, the original river called the Merced River caused a canyon shaped in a V throughout Yosemite Valley (Huber). Rivers such as the Merced River are important to the formation of valleys and cliffs. On the other hand, rivers are also “considered evidence of a glacial origin for the valley”‘ according to the National Park Service (“Geology”). Part of the geologic story of Yosemite National Park and Half Dome includes the formations of new rivers when other rivers became clogged by glaciers and ice. These new river formations caused waterfalls, lakes, rivers, and other streams which had an impact on rock formations in Yosemite Valley. In fact, in areas where streams and rivers flow faster due to gravity and other steep rock formations, water cut through the rock even faster (Huber). Francois E. Matthes, a scientist and naturalist, originally proposed that valleys are first formed by water erosion and then are further formed by glaciers (Matthes). The National Park Service, scientists, and geologists believe in Matthes’ theory and have adopted it today after watching the park transform since the 1800’s (Huber). In sum, moving water combined with glaciers caused the smooth granite rock formations such as Half Dome and other features that can be viewed throughout Yosemite National Park today. While water, glaciers, and ice are major reasons for the features seen today in Yosemite Valley, other weathering such as rockslides, erosion, and exfoliation are also responsible for major park features such as Half Dome and El Capitan (Matthes).Further weathering to Yosemite Valley and Half Dome has occurred over time as a result of rockslides and from pressure releasing within the rocks. Weathering is defined as the breaking down or dissolving of rocks and minerals on Earth’s surface, into small grains and soil. In essence, as the rocks and minerals are broken down, the particles are used by weather elements to break down rock. Weathering occurs naturally in the fissures, or joints, where rocks are most vulnerable and are easily worn down by erosion. Water, ice, acids, salt, plants, animals, and changes in temperature are agents of weathering that can significantly impact the erosion and exfoliation of rock. After a rock has been broken down, a process called erosion transports the bits of rock and minerals away to nearby water sources such as a river or lake. A prime example of erosion is when the solidified chamber was exposed at Half Dome. When the solidified chamber was exposed at Half Dome as a result of weathering, the pressure from within the rock’s chamber was released due to erosion (How Half Dome Formed). This erosion caused the rock to become smooth and weather in a unique way. A second weathering element for rock formations in Yosemite National Park is exfoliation. Exfoliation–the peeling and breaking off of layers of rock over time–is considered to be an onion-like process whereby the rock peels back layer after layer due to pressure inside the rock. In fact, some rock features in the Sierra Nevada have been cut in half by exfoliation and pressure from within the rocks. The National Park Service explains that “the rounded crown of Half Dome probably stems from whole sheets of rock peeling off,” or exfoliation (Geology). Although erosion and exfoliation have caused a lot of landscape and geological transformation in Yosemite Valley, rockslides, rock falls, earthquakes and snowmelt can also trigger slope movements and changes in the valley, and more specifically, Half Dome (Wieczorek). Earthquakes, snow melts, rockslides, and rockfalls have transformed Yosemite throughout history. The current Yosemite National Park is very different from the Yosemite Valley first encountered in the 1800s. Fault lines are present throughout Yosemite Valley and as a result, earthquakes do occur (Wieczorek). These earthquakes can cause the landscape of the park to change drastically, and very quickly as well. According to the National Park Service, “the rock along these faults becomes so strained that eventually it slips or breaks” (Geology). Half Dome came into being because the granite cracked open, become laterally displaced, vertically displaced, and the ground began to roll (Geology). Although earthquakes can cause quick changes in the features of a park, snow melting can cause erosion and rockslides which can also quickly change natural features. When snow turns into water and begins to move, rocks begin to move and erosion happens in new areas of the park. Often, snow melting can cause granite to become unstable and unpredictable. Snowmelts have a history of causing rockslides and rockfalls in Yosemite Valley, especially Half Dome. Due to instability, Half Dome can only be climbed several months out of the year (Geology). In conclusion, Yosemite National Park is full of magnificent rock formations such as Half Dome, which are deeply rooted in the history of national parks. Colossal granite bodies such as Half Dome began beneath the earth’s surface as magma solidified underground and eventually came to fruition above ground. The geologic history of Yosemite Valley in the Sierra Nevadas is a perfect example of how many weathering and natural processes can occur within a brief period of time with colossal results. Weathering, erosion, rock slides, glaciers, waterfalls, flowing water, and exfoliation all play a role in the process of changing landscape. Curved slopes, expanding rocks, and expansion bring about Yosemite’s landform development and leave all visitors in awe of their beauty. Rock formations such as Half Dome and El Capitan are constantly changing as a result of the movement of overriding tectonic plates, freezing, thawing, exfoliation, erosion, earthquakes, and glaciers. In the future, generations will continue to see a different Yosemite National Park and Half Dome structure each time they visit this geological phenomenon. Bibliography “Geology.” National Parks Service, U.S. Department of the Interior, www.nps.gov/yose/learn/nature/geology.htm.Gunther, Richard L. “Yosemite Valley: A Glacier-Carved Jewel.” Yosemite, 25 Nov. 2004, academic.emporia.edu/aberjame/student/gunther2/yosemite.html.”How Half Dome Formed” | Scenic Wonders Yosemite” Yosemite’s Scenic Wonders, https://www.scenicwonders.com/blog/how-half-dome-formedMatthes, Franc?ois E. Geologic history of the Yosemite Valley. S.n., 1930.Huber, N. King. “The Geologic Story of Yosemite Valley.” National Parks Service, U.S. Department of the Interior, 1938, www.nature.nps.gov/geology/usgsnps/yos/topobk.html.Wieczorek, Gerald F., and Stefan Jäger. “Triggering mechanisms and depositional rates of postglacial slope-Movement processes in the Yosemite Valley, California.” Geomorphology, vol. 15, no. 1, 1996, pp. 17–31., doi:10.1016/0169-555x(95)00112-i.

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