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Thread: Viscosity of the mantle

  1. #1 Viscosity of the mantle 
    New Member
    Join Date
    Mar 2006
    Im 16 and writing a project for school about glacial rebound and isostacy. I was wondering if anyone could explain to me how the viscosity of the upper and lower mantle effect the rates of uplift of the crust after an ice sheet has melted.
    I thought that if the viscosity of the mantle is low then rebound should be faster than if the mantle had a higher viscosity, but i've read that sometimes this is not the case. I dont understand why.How do rates of uplift change over time? Please help. :?

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  3. #2  
    Forum Senior silkworm's Avatar
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    Nov 2005
    The uplift of the crust after ice has left has nothing to do with the mantle, it's all about the crust. The weight of the ice simply compresses the land and when the ice leaves the land that weight is gone so the land decompresses.

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  4. #3  
    Universal Mind John Galt's Avatar
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    Jul 2005
    That effect extends into the mantle. It is not compression, it is displacement of the mantle, which flows away from the depressed continental mass.

    Hales, I am not familiar with examples of the type you describe. I agree with you that low viscosity should respond more rapidly.
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  5. #4  
    Forum Senior
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    Sep 2006
    You're 16, jeezus that's a toughy. Actually you're right, a higher viscosity means a greater resistance to flow, thus slower uplift. Rates of uplift get slower with time as the buoyancy force gradually gets weaker, in fact the fastest uplift rates in scandinavia today correspond to where they think the thickest ice would have been in the ice age (also where the buoyancy force would have been/still is strongest).
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  6. #5  
    There is a little island rising out of the water at about 7? cm per year?
    whilst London is sinking....
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