Land Feature Paper Essay Example
Land Feature Paper
The Pacific Northwest is the most volcanically active regions in the United States. It consists of several volcanic peaks which stretch all the way from Canada to northern California. Falling in this region is the southwester territory of Washington State, which has witnessed some of the most spectacular volcanic activities in recent times. Mount St. Helens, which erupted in 1980, is located in this region (Harris, 2005). The volcanic eruptions in this region result from plate tectonic movements.
The plate tectonic theory is based on the postulation that the Earth’s outer layer, lithosphere, is composed of several plates. The plates are in constant motion sliding over and against each other. The movement of the tectonic plates is a complex process that originates from the rocks deep beneath the Earth’s surface. The interior of the Earth, asthenosphere, contains convectional cells that transmit heat energy to the surface plates at the surface of the earth. When the convectional cells reach the lithosphere, they release the heat which escapes to the atmosphere through the spaces in the plate boundaries. The movement of heat to the surface is a very slow process. The plastic rocks containing convectional cells, having lost their heat, cool and move underneath the earth’s surface then descends to the subduction zones where they are heated again. It is this movement that causes tectonic plate movements. Sometimes, large amounts of heat escape from the convectional cells when they reach the lithosphere leading to volcanic eruptions.
The main reason why the Northwest region experiences frequent volcanic eruptions and earthquakes is its location. The region is located along the convergent continental boundary, the Cascadia Subduction Zone. The Cascadia Subduction Zone is characterized by two colliding plates and runs from British Columbia, Canada to California. Here, the Juan de Fuca plate pushes northeast into the North American plate leading to accumulation of stress at the point of their collision. It is estimated that the plates are moving at the rate of two inches a year as they converge. It is the stress accumulated at their point of convergence that causes the earthquakes and volcanic eruptions frequently witnessed in the area.
Over the past decades, several geological events have taken place in the Pacific Northwest, ranging from earthquakes to volcanic eruptions, leading to formation of various types of rocks. The events took place in the Cenozoic, Mesozoic, Paleozoic and Precambrian eras (Lasmanis, 1991). The Cenozoic era witnessed the Holocene period whose hallmark was the deposition of various materials along the coastal areas. These were majorly deltaic and alluvial deposits in the southwest and Colombian Basin. It led to formation of basalt, tephra and other volcanistic deposits. The Pleistocene period saw major glaciation activities filling Puget lowlands with clay, sand, silt and gravel. The Pliocene and Miocene periods were marked by massive depositions along the coastlines. Other events in the Cenozoic era include Oligocene, Eocene and Paleocene periods, all of which were characterized by the formation of various rocks found in the region today.
In the Mesozoic era, the Cretaceous, Jurassic, and Triassic periods were critical in the formation of marble, ultrabasic intrusive, carbonate rocks and marine sediments. During the Paleozoic era, the Permian period was characterized by the formation of sedimentary rocks in the northern cascade. The Pennsylvanian period is associated with the formation of carbonate rocks, basalt flaws and metavolcanic rocks. Other periods in this era over which important developments in rock formation took place are the Mississippian, Devonian, Silurian, Ordovician and Cambrian periods. In the Precambrian era, siltstone, intrusive rocks and different metamorphic rocks were formed.
The Washington Cascades are rich in various types of rocks formed as a result of the volcanic activities that have taken place in the region over the years. The northern cascade is composed of metamorphic and Mesozoic crystalline rocks while the South cascades mostly consist of tertiary volcanic rocks. The Methow Valley contains the richest variety of sedimentary rocks. It consists of conglomerate, arkose and sandstones which have accumulated for centuries as a result of various geological activities in the region. The upper section of the valley contains Jurassic rocks as well as basalt, gabbro and limestone. The region also spots scattered intrusives some of which are massive and cut across large swathes of land extending over several townships.
Volcanic activities in the Cascadia subduction zone are of great economic importance the local communities living in the area and the governments of the states the zone traverses.As a result of the rich rock deposits in the cascades, mining has become a major economic activity in the region. Mining industries have been set up in the region to explore minerals such as gold, silver, copper, and other metals. In the mines, copper is obtained from Breccia pipes (Miler, 1989). The pipes are also known to contain tungsten and molybdenum both of which are highly valuable and have been critical to the economy of Washington State. Batholiths in the region also contain large deposits of copper that have attracted various investors in the mining industry.
Harris, S. L., (2005). Fire Mountains of the West: The Cascade and Mono Lake Volcanoes, Mountain Press Publishing Company.
Lasmanis, R., (1991). The geology of Washington: Rocks and Minerals, v. 66, no. 4, p. 262-277
Miller, C.D., (1989). Potential Hazards from Future Volcanic Eruptions in California, USGS Bulletin.
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