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Water Erosion

  1. Dec 20, 2003 #1
    How plastic is the Earth? I don't mean like literal plastic, but I mean "how moldable is it?". How long would it take water to erode away ground? Does the amount of water make a difference?

    Obviously I'm lost, as far as geology goes, so any help is appreciated :smile:.
  2. jcsd
  3. Dec 21, 2003 #2
    Well eh yes what is the point?

    Earth as a big huge body is remarkable plactic, yes. It is assuming that the land uplift in Canada and Scandinavia is caused by a elastic (Isostatic) rebound after being depressed during the ice age.

    But what has eroding water to do with it?
  4. Dec 22, 2003 #3
    Well, like under the oceans or other bodies of water...how dramatic an effect does the water pressure have on the bottom surface?
  5. Dec 31, 2003 #4


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    sorry to point out anything obvious...

    The "ground" is made of many different materials...there are rocks and soils of many different types. Otherwise, geology would not be much of a subject to study would it? Physical geology has all kinds of factors to consider...faulting, fracturing, folding, and probably some other f words. (No, not that one.) Some rocks are tough for water to erode, other types are easier. "Dirt" can be sand, rock, gravel, silt, clay, till, etc. each of which has different characteristics to consider (not to mention packing, porosity, and other p words...no, not that one...please get your mind out of the gutter).

    In short, there is no short answer. But what the heck, here's a short answer. I seem to recall Sagan saying in his book Pale Blue Dot that it takes something like 10 million years to erode a mountain...or did he say 100 million? Aw, crud. I forget.

    In human terms (say, a lifetime) the Earth is, overall, very resilient. Mountains don't seem to change and river banks don't alter that much. Sherpas don't notice that India is smashing into Asia and driving up the Himalyas. Well, perhaps things look static until you see your first mudslide or volcano, then you may wonder what the heck is holding everything together the rest of the time! The mudslide bit is probably a good visual answer to your "amount of water" question.

    But in geologic time frames, the Earth is very "plastic". Things are constantly shifting around. Rock flows and crumbles. Dirt is pushed around. New rock forms. Continents drift (what is it, I forget...like an inch per year?) and collide and dive back into the Earth's mantle or are thrust upwards into new mountain ranges.

    I'd have to sneak a peak at a geology textbook for specific plasticities/strengths of specific rocks.
  6. Dec 31, 2003 #5


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    Why are rocky planets round, due to gravity or due to erosion?
  7. Dec 31, 2003 #6
    Well, sum of all the forces causes the Earth to be oblate sheroid shaped.

    Gravity is the most important, centrifugal forces due to the rotation are next.

    http://www.colorado.edu/geography/courses/geog_5003_s03/lecnotes/Datums%20projections% [Broken]
    Last edited by a moderator: May 1, 2017
  8. Jan 2, 2004 #7


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    Mostly gravity, but an honorable mention for erosion. Planets formed when tiny bits o' material from the original nebula stuck together. As the accreting material got bigger and bigger, the impacts became more energetic. Smashing asteroids/planetoids together creates lots of debris and heat...heat which can liquify some or all of a planet's surface. Gravity keeps pulling stuff "down" toward the center of mass. Debris rolls downhill. Liquids flow to low points. Materials are compressed/crushed from the weight of overlying materials. The early formational period of the solar system had a whole lot of smashing going on. The planets formed to be round and then erosion would wear down any land mass that got thrust up due to geologic processes. Let's not forget that the Earth's rocky surface is but a thin crust atop a the liquid-like mantle.
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