Earth Sciences and Ecology Question #1284

Brian, a 9 year old male from Jersey City asks on February 23, 2003,

How are mountains created?

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The answer

(Barb Cloutier) Earth Sciences Information Centre answered on March 13, 2003

Below the relatively thin crust on the surface of the Earth where we live, our planet is mostly hot molten liquid rock called magma. The Earth's crust is made up of giant floating plates that drift very slowly upon the surface of this liquid magma. Mountains are created when two of these surface plates collide. This process is called plate tectonics or continental drift. The formation of mountains is very slow and takes millions of years to occur. To learn more about this process, visit Enchanted Learning, or This Dynamic Earth, U.S. Geological Survey.

Derek Thorkelson answered on November 13, 2003

The answer by B. Cloutier is partly right and partly wrong. Mountains are built in two main ways. In one, they are generated by volcanic activity, in which magma from the mantle moves upward through the crust toward the surface of the Earth. The Andes of South America are an example. Magma is localized, however, and the crust sits mainly on solid rock of the mantle, which can flow slowly over time. The other type of mountain building involves collision of continents or volcanic islands. The continents are buoyant parts of tectonic plates which move slowly relative to one another above the underlying, convecting (slowly flowing) mantle. Some plates dive down below others, or "subduct". Continents are too buoyant to subduct and when they encounter a subduction zone or another continent they become compressed and their margins are uplifted and deformed. The Himalayas are an example. Usually, volcanic activlty occurs before and at about the same time as this deformation. Thus, many mountain belts are produced by both volcanic and tectonic activity.

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