EXAMPLES OF THESE PHENOMENA IN GEOLOGY These are some of the more commonly known geological occurrences and how they are explained by understanding plate tectonics: •
Mid-oceanic earthquakes and tsunamis – these happen along the mid-oceanic ridges as the magma and crust are shaken in the process. These are deep ocean earthquakes that can disrupt the ocean enough to create giant tsunamis.
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Continental arcs – these are lines of volcanoes on the edges of continents made by the combination of convergence and subduction. There are often both earthquakes and volcanoes here. The Juan de Fuca plate in the Pacific Northwest is a tiny underwater plate subducting under the North American plate. This has led to the formation of Mount Shasta, the Medicine Lake Volcano, Mount St. Helens, and the Lassen Peak volcanoes in the Cascade Mountains.
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Island Arcs and Ocean trenches – these happen where an oceanic plate subducts underneath another oceanic plate. You will get the upper plate pushing up to make an arc of islands. The Aleutian Islands were made this way. Figure 19 shows this type of situation:
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