The Theory of Plate Tectonics
Plate tectonics is one of the most important theories that account for the distribution of various geological events across the planet. It refers to the activity of the lithosphere. In particular, the theory allows identifying how formation, movement, collision, and destruction of tectonic plates trigger such geological phenomena as earthquakes, volcanic eruptions, rock building, and others (Marshak, 2011).
According to the theory, there exist seven major plates and 18 regional smaller ones forming a complex pattern of the crust. These plates can converge, diverge, and overlap. However, even micro-plate boundaries reveal geological activity that can result in various events (Marshak, 2011).
Plates can be both continental and oceanic. The former consists mostly of granite whereas the latter are composed of basalt, which makes them considerably heavier (it accounts for the fact that continents float higher than the oceanic crust). Plates continue to form, and the excessive material melts into magma (Condie, 2013).
Grand Canyon: Earthquakes and Volcanoes
Grand Canyon, located in Arizona, is characterized by a moderate risk of earthquakes (10 cases have been registered since 1931). The possibility of an earthquake within 50 km is lower than 20%. The most severe of the recent ones happened in 1994 and was 3.6 magnitude. The intensity of an earthquake is predetermined by its location, distance from the most populated areas, population density, etc. It refers to the effects that it has on people and landscapes.
The most destructive earthquakes in Grand Canyon happened in a narrow land corridor: the seismic activity was caused by two neighboring fracture systems – the Mesa Butte and West Kaibab. The reason is that a part of the crust moves eastward past the Canyon, which predetermines the location and intensity of earthquakes (Crow et al., 2014).
As for volcanoes, their activity is explained by the presence of the Uinkaret volcanic field in northwestern Arizona to the north of the Canyon. The field is over 3 million years old and has already produced more than 150 eruptions of basaltic lava, which resulted in the appearance of dams along with the flow of the Colorado River. The intensity of the eruptions is largely predetermined by three main factors: magma composition, temperature, and dissolved gases that it contains. The most significant and destructive one is temperature (King, 2015).
The Main Movement that Shaped the Region
The formation started in Precambrian time when the tectonic plate movement led to the thinning of continental crust, which created several rift basins. The region of Laurentia was flooded with a seaway coming from the Lake Superior. As a result, the Grand Canyon Supergroup of sedimentary units was formed. It consists of nine geological units (the oldest section is the Bass Formation) (Marshak, 2011).
However, geologists still argue what forces contributed most to the appearance of rocks: erosion, climate, volcanic activity, or plate movement. The North American plate was located further to the south and had different climatic conditions. When the Pacific plate moved beneath it, the mountain range was formed (causing light minerals to melt, which accounts for the composition of the rock). As the granite rocks have been eroded for millions of years, they are fully covered with sedimentary deposits (limestone, sandstone, and shale) (Wernicke, 2011).
As far as water bodies are concerned, the opening of the Gulf of California that occurred more than 6 million years ago changed the direction of the river to the northeast. It later took the existing drainage and formed the Colorado River that had a great impact on the process of shaping the Canyon.
Geological Events that Occurred in the Region and the Rocks they Formed
A whole number of geological events led to the formation of the mountains in the region. There was previously a chain of rocks that were later eroded to create a plan. Climatic changes caused oceanic movement that deposited a new layer of rocks each time it occurred (Marshak, 2011). The Colorado River, which changed its course, is responsible for the formation of younger rocks to the west of the Canyon. As it has been mentioned above, water erosion explains the composition of the rocks formed: they are all covered with deposits (Wernicke, 2011).
The peculiar shape of the Canyon was created by different tock layers – each of them reacted differently to water, and some eroded more slowly than others. Minerals that they contain (mostly iron) give the Canyon rocks their bright colors ranging from yellow and red to green and dark brown. Besides, a lot of mountain groups that had been formed in earlier periods were later washed away. They were reduced to hills and formed the basement for younger rocks composed of limestone (King, 015).
Due to the uniqueness of the sight, the Canyon has millions of visits each year. Thus, the mountains, being a popular touristic destination, are also important from the economic point of view. They have already contributed over $500 million to the state (which puts the Canyon in the third place among all the American parks) (Barkley & Stewart, 2008).
References
Barkley, J., & Stewart, W. (2008). When a landscape is bigger than itself: A stakeholder analysis at Grand Canyon National Park. National Park Service, 19 (2), 12-49.
Condie, K. C. (2013). Plate tectonics & crustal evolution. New York, NY: Elsevier.
Crow, R., Karlstrom, K., Darling, A., Crossey, L., Polyak, V., Granger, D.,… & Schmandt, B. (2014). Steady incision of Grand Canyon at the million year timeframe: A case for mantle-driven differential uplift. Earth and Planetary Science Letters, 397, 159-173.
King, P. B. (2015). Evolution of North America. Princeton, NJ: Princeton University Press.
Marshak, S. (2011). Earth: Portrait of a planet: Fourth International Student Edition. New York, NY: WW Norton & Company.
Wernicke, B. (2011). The California River and its role in carving Grand Canyon. Geological Society of America Bulletin, 123(7-8), 1288-1316.