Yosemite National Park

Justin Doll
GEOL C105
October 24, 2014
National Park Essay
Yosemite National Park first became a national park in 1890 with the help of Yosemite’s most famous advocate, John Muir. (APN Media, LLC, 2013) The park boasts some of the most easily recognizable geologic features in the world. Many of the most recognizable features are glacier cut granite walls and domes, and the waterfalls that fall off of them. The views of and from features like El Capitan, Half Dome, Glacier Point, Clouds Rest compared to the valley floors and meadows like Yosemite Valley, and Tuolumne Meadows are what make Yosemite a special place. For this paper we will discuss just two of the geological features listed above; Half Dome and Yosemite Valley. We will also
(Scenic Wonders, 2014) The peak of Half Dome is over 4,700 feet above the valley floor. The Granite rock that makes up Half Dome was formed over 93 million years ago during the Cretaceous period. The granite was formed from magma that solidified underground. Through erosion of the sediment on top of the rock, the granite of Half Dome was exposed. Erosion is defined as “the process in which wind, water, or glaciers remove weathered particles from the environment.” (Renton, 2011) Half Dome got its shape from the geological process called sheeting. Sheeting is when an exposed rock fractures along is joints and breaks off. The granite of Half Dome is susceptible to this type of weathering and in 2009 a large section of granite actually fell off of the dome. Like most of Yosemite’s geological feature Half Dome is a product of glaciations. (Huber, 2014) Glaciation is “the process by which ice covers large amounts of the earth’s landmass.” (Renton,
(Nation Park Service U.S. Department of the Interior, 2014) The Merced and Tuolumne Rivers are two of the major factors of erosion that carved out the valley. Then through the process of at least three different glaciations the valley was carved into the granite and became much wider. The most prominent of the three glaciations was the Sherwin glaciation. The Sherwin glaciation is believed to have lasted over 300 thousand years and ended over a million years ago. The valley floor was eventually made from the deposit of sedimentary material from the effects of the glaciations and erosion. Yosemite Valley was actually once a lake. (Nation Park Service U.S. Department of the Interior, 2014) The lake eventually vanished and the sediment became the meadows that now make up Yosemite Valley.
As discussed above in 2009 Half Dome lost a large amount of granite. (Scenic Wonders, 2014) This is an example of the geological concerns that Yosemite faces. Granite holds up relatively well against most forms of weathering but do to the joints in the rock it is susceptible to sheeting. Water fills these joints and then freezes and expands. This causes the granite to exfoliate. This is why half dome is considered to be an exfoliation dome. This process can be dangerous but thankfully the 2009 event on Half Dome did not harm anyone. Although a large amount of trees where