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Question
#42343. Gimboid
asks:
What were the primary forces that shaped the Grand Canyon?
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robboy
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Wind and water (Colorado River).
Primary force is called erosion. Wind and water movement are ingredients of that force.
Dec 15 03, 10:49 AM
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Gimboid
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Yes, it is erosion, but what kind of erosion? The primary is something other than wind and water.
Dec 15 03, 11:40 AM
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lothruin
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I suppose some would consider God to be the primary force, but aside from that, I'm quite sure that erosion, specifically that of the Colorado River, is the primary force. Unless you're looking for "weathering" or "frost wedging" or "downcut" or some other such thing...
Dec 15 03, 11:57 AM
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potterguy
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Well, there was/is significant uplift in the west/southwest due to plate tectonics. The Pacific Plate is being subducted under the plate in the western US (sorry, been too long since my college geology days, can't remember the name of the upper plate). This has caused the area of which the Grand Canyon is a part to have risen a number of thousand feet (the canyon is about 5000 feet deep, so that is a good approximation), and with that uplift, the drainage system commenced to cut downwards through the higher ground to find it's own level. So, I would say that the answer is uplift/erosion. This is a fairly common phenomenon. The area of southern Ohio where I grew up has a similar story, but with far less significant uplift. In fact, in that case, it is a combination of slight uplift with a rising due to the release of the weight of the glaciers during the last period of glaciation. Not sure what else you're looking for, gimboid.
Dec 15 03, 6:27 PM
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Gimboid
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The Correct Answer! Of course it is erosion! But not wind and water, rather something called "Lahras" - or earth-shaking mud slides.
Dec 16 03, 11:01 AM
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potterguy
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I think you mean "lahars", and as you can see from the below description, they're not what has formed the Grand Canyon...sorry.
 http://www.uccs.edu/~geogenvs/ges199/rainier/lahars.htm
Lahars
What is a lahar?
Lahar (also called debris flow) is an Indonesian word used by geologists to describe a mudflow or a water-saturated debris flow on a volcano. Technically, any flow that is not saturated should be referred to as a debris avalanche; however, lahar is the term most often used to describe any type of debris or mud flow on a volcano. Lahars are powerful forces capable of moving great quantities of debris - house-size boulders, trees, etc. for long distances in a short amount of time. They look and behave like flowing concrete and destroy or incorporate virtually everything in their path. The result of lahars is usually a deposit of sediment that can range anywhere from a few yards to hundreds of yards thick (Hoblitt and others, 1995:4). Topography greatly influences the direction of lahars, so developed regions located at the base of volcano valleys are in extreme danger. In addition, any reservoirs in the path of lahars could add to the threat. The debris carried in the lahars could quickly fill the reservoirs and release the previously contained water (Hoblitt and others, 1995:4).
Lahars develop from volcanic eruptions, glacial melting, and sector collapse but can also develop from earthquakes, steam explosions, and intense rainstorms (Hoblitt and others, 1995:4). All these possibilities exist in profusion on Mount Rainier’s steep slopes. Of all the risks associated with this volcano, the threat of lahars is certainly the greatest. Rainier’s history, as well as current eruptions elsewhere, can prove how destructive these lahars can be.
Dec 16 03, 3:34 PM
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