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Unformatted text preview: Plate Tectonics:1 Plate Tectonics Orders of Relief Continental Drift Plate Tectonics Plate Boundaries We have covered the creation of the universe, our solar system and our planet. Now lets look at how the major physical features of Earths surface and how the crust moves around. Orders of Relief Relief refers to the shape of the land, especially the elevation difference between the highest and lowest parts of an area (Lubbock is in an area of low relief, Denver has higher relief). If the continents and oceans are considered the first order of relief , then the second order of relief is the major features of continents and oceans. The third order of relief is the individual landforms, such as hills, valleys, beaches, etc. We will spend most of the semester on third order relief forms. For now let's look at second order relief forms- Oceans : Oceans frequently have a mountain range near their center. This mid-ocean ridge is flanked by flat areas known as abyssal plains . Near the continents, the floor of the oceans begin to slope gently upward. This is the continental rise and this merges into the continental slope , which is steeper. The continental slope then meets the continental shelf , which is an underwater extension of the continent. These features are not all present in all oceans. shelf rise slope abyssal plain mid-ocean ridge abyssal plain trench Continents : Continents frequently have mountain chains , like the Rocky Mountains (and other mountain chains in Western North America), Himalayas and Andes, which indicate active regions of either volcanism or tectonic activity (land forced up from Plate Tectonics:2 below or moved sideways to fold it into new shapes). They frequently have quiet areas, too, known as shields . Shields are generally very old and relatively flat. They can be covered shields if they have a cover of sediment (like the Great Plains) or exposed shields if the base rock is present at the surface. Mountain roots are the remains of old mountain chains in areas which are no longer active in mountain building. The Appalachian Mountains are a good example. Here, too, these features are not all present on all continents....
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- Fall '08