|MadSci Network: Earth Sciences|
Mountains form primarily in two different ways. Mountain ranges typically form where two lithospheric plates collide. These are the plates that form the Earth's surface. For instance, most of North America is a single continental plate; other plates are mostly seafloor (the Atlantic Ocean is mostly underlain by two plates that grow outward from the mid-Atlantic Ridge). Anyway, where two plates come together typically one is pushed up on top of the other. This is how the Appalachian Mountains formed a couple of hundred million years ago. This is how the Rocky Mountains formed around 50 million years ago. This is how the Himalayas formed even more recently. Volcanoes can result indirectly from plate movements. For instance, many of the mountains in California are volcanoes. As the eastern part of the Pacific ocean seafloor is pushed down under the western part of North America it gets hotter. The earth is hotter and hotter at greater depths. Rock doesn't melt easily, but once the temperature reaches about 1000°C the former seafloor starts to melt. Then, because it is less dense, it tends to rise up. Weak places in the overlying material allow the magma to reach the surface. Liquid rock at the surface is called lava. Other volcanoes form where the seafloor moves across a place where the rock underneath is unusually hot. These volcanoes start out underwater, but if they get big enough, they can become islands. The Hawaiian islands formed in this way. More information is available from government and university websites and geology textbooks. Here are a couple of helpful links. http://pubs.usgs.gov/gip/volc/ http://pubs.usgs.gov/gip/dynamic/dynamic.html http://en.wikipedia.org/wiki/Orogeny http://www.physicalgeography.net/fundamentals/10k.html
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