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Tsunami
Submarine Earthquakes, Part I



Submarine Earthquakes, Part I
Reading Level
     edHelper's suggested reading level:   grades 5 to 7
     Flesch-Kincaid grade level:   9.33

Vocabulary
     challenging words:    aftershocks, magnitude, mid-ocean, oceanic, smooth-surfaced, extension, margin, saying, especially, surrounding, coastal, bridges, stress, people, extend, western
     content words:    Pacific Ocean, Pacific Northwest, Fuca Plate, United States, North American, Cascadia Subduction Zone, Continental Plate, Subduction Zone, In Submarine Earthquakes, Part II


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Submarine Earthquakes, Part I
By Trista L. Pollard
  

1     When people hear the word earthquake, they visualize shaking buildings, cracked road surfaces, and collapsed bridges. What about submarine earthquakes? A submarine earthquake is an earthquake that occurs under the ocean floor. You are probably saying, "I thought the ocean floor was only made of sand, so how can an earthquake happen?" Let's explore the bottom of the ocean to find out!
 
2     If we were to drain the water from the world's oceans and take a ride along the bottom, we would see that the land under the sea has similar landforms to the earth's surface that is above water. The ocean bottom begins at the continental shelf. The continental shelf is a gentle sloping underwater plain that surrounds all of the earth's continents. This is also an extension to the coastal plain that exists above the water. As we travel from the continental shelf, we would reach the continental slope and the smooth-surfaced continental rise. All three sections make up the continental margin.
 
3     Once we pass the continental margin we get into some of the deepest parts of the world's oceans. In this area, the ocean floor has trenches. These trenches can be thousands of kilometers long, hundreds of kilometers wide, and extend three to four kilometers below the surrounding ocean floor. In the Pacific Ocean, there are long V-shaped trenches that border the edges of volcanic islands. In fact, the Pacific basin is encircled or surrounded by these trenches. Beyond the trenches we would see the mid-ocean mountains and mid-ocean ridges. This is the area, especially in the Pacific Ocean, where a large number of underwater volcanoes exist. It is these volcanoes and the areas near the trenches that produce submarine earthquakes.

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