Answer Key

Lesson 3 "How Plates Move"

1. What causes mountain building?
   Mountains are formed from the Earth's plates movements. As plates crash into each other they push the crust up high into mountains.
   
   
2. What is the difference between how folded mountains and block-fault mountains are formed.
   Folded mountains form into rollercoaster like formations. The layers are bent but not broken. When block-fault mountains are formed the layers are pushed up and broken into high sharp peaks and valleys.
   
   
3. How do dome mountains form?
   Dome mountains form when the layers of the Earth don't break or fold but are pushed up into a rounded dome shape.
   
   
   
4. In your own words explain what happens at a subduction zone.
   Two plates come together, one overriding the other at a subduction zone. The oceanic plate, which is thinner and denser, is driven under the continetal plate and into the mantle. A deep ocean trench is produced at the subduction zone.
   
   
5. In your own words explain what happens at a mid-ocean ridge.
   Two plates are separating with magma welling up and filling the void with newly produced crust. These spreading plates are making the oceans wider and wider while the subduction zones are making the oceans smaller and destroying old crust.
   
6. At a subduction zone what causes magma to rise?
   The oceanic crust and the upper layer of the mantle melts as it is driven into the mantle. The oceanic crust is not as dense as the mantle is. Because this material is less dense it will rise.

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