How and where do mountains form?
What will be an ideal response?
Answer: Most mountain belts form near convergent plate boundaries where crust thickens by compressional shortening and by intrusion and crystallization of magma. The high elevations in the western United States do not have a thick crustal root but are held up, instead, by unusually low-density mantle. Even as crustal thickening causes uplift of mountains, thrust faults weigh down adjacent lowlands to form deep basins. These basins fill with sediment eroded from the mountains and contain rich resources of oil, natural gas, and coal. Mountains rise vertically at rates of 3-10 millimeters per year, or only about one-tenth the speed of horizontal plate motion.
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