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Earth Science
Rock Deformation, Part 1

Earth Science
Earth Science


Rock Deformation, Part 1
Print Rock Deformation, Part 1 Reading Comprehension


Reading Level
     edHelper's suggested reading level:   grades 7 to 8
     Flesch-Kincaid grade level:   7.17

Vocabulary
     challenging words:    isostasy, subsidence, ductile, divergent, isostatic, equilibrium, tremendous, compression, currently, deform, regain, retreat, deals, collide, tension, fracture
     content words:    Mississippi River, United States, In Rock Deformation


Rock Deformation, Part 1
By Trista L. Pollard
  

1     We may not see it everyday, but our planet's crust is constantly bending, tilting, and breaking. It's this deformation of the Earth's crust that produces some of our most beautiful landforms. Our mountains, plateaus, and volcanic islands are formed through deformation.
 
2     There are many ways deformation occurs. Scientists, like geologists, try to understand how our rocks respond to stress. Through this understanding scientists hope to find out why and how our planet's crust changes. First on the deformation trail is isostasy.
 
3     There are two opposing forces that affect the lithosphere as it moves vertically. Gravity or weight causes the lithosphere to push down on the asthenosphere. As parts of the lithosphere become thicker, it becomes heavier and sinks farther into the asthenosphere. Likewise, thinner lithosphere is lighter and rises higher in the asthenosphere. As the lithosphere is pushing down, the asthenosphere is pushing up. This opposing force is buoyancy. The lithosphere and asthenosphere are in a state of isostasy or equilibrium when both gravity and buoyancy are balanced. Of course, the state of isostasy does not always occur without a little help.
 
4     Isostatic adjustment occurs when the lithosphere moves to reach isostasy. For example, erosion on the surface wears away the crust. As this happens, the lithosphere becomes lighter and rises due to the asthenosphere's buoyant force. Therefore, the crust bends up or down as the adjustment is taking place. This is when rocks in this area begin to deform and change. The process will continue as erosion of the crust continues.
 
5     There are three types of isostatic adjustments that occur. Where there are mountains, there are also isostatic adjustments. This process is constant in mountainous areas because mountains are exposed to a tremendous amount of erosion. These majestic landforms are worn away over millions of years by wind, water, and ice. This means that our mountains shrink in height and weight. The erosion causes the mountains to become smaller and the crust that surrounds it to become lighter. The crust goes through the isostatic adjustment called uplift.

Paragraphs 6 to 12:
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