MadSci Network: Earth Sciences
Query:

Re: What creates a mountain, why do they grow so tall, whre are most?

Date: Thu Oct 15 07:34:13 2009
Posted By: David Kopaska-Merkel, Staff Economic Geology Division
Area of science: Earth Sciences
ID: 1255304414.Es
Message:

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 1000C 
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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