Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Is it possible to have tidal currents in the Earth's molten mantle?

  1. Oct 23, 2011 #1
    Since the tectonic plates ride on the convection currents in the molten mantle, I was wondering if tidal effects could create currents in the molten mantle.

    The reason I am asking I found this http://bowie.gsfc.nasa.gov/ggfc/tides/intro.html" [Broken]
    where it states:
    This made me wonder if there tidal currents in the molten mantle that the tidal friction with tectonic plates would be significantly greater than the tidal friction created by the oceans.
    Last edited by a moderator: May 5, 2017
  2. jcsd
  3. Oct 24, 2011 #2
    The scientists at NASA are very qualified people and I am certain that they considered all possible sources of tidal friction. Therefore, since they said "tidal braking in the earth's rotation is actually caused primarily by friction in the oceans" that this must be the case otherwise how embarrassing would it be if someone on some forum discovered something that they missed.
  4. Oct 25, 2011 #3
    Thanks for replying. I would hope your statement is true and not just "...the light is better here."

    Since the tidal potential deforms the entire earth. It seems to me qualitatively that more of tidal potential would be dissipated in the solid earth than in the ocean. However, the main stream believes

    from http://www.geo.ucalgary.ca/~wu/Goph681/EarthRotation.pdf"
    Last edited by a moderator: Apr 26, 2017
  5. Oct 25, 2011 #4
    This is not something I claim to know very much about.

    With that caveat, it seems to me that the viscosity of the mantle is too high to permit dissipation by currents. However, I believe that some tidal energy is dissipated by heating the mantle.
    Last edited by a moderator: May 5, 2017
  6. Oct 25, 2011 #5

    D H

    User Avatar
    Staff Emeritus
    Science Advisor

    First things first: What molten mantle? The Earth's mantle is a solid (it supports shear waves) that is capable of plastic flow over geological time spans.

    You missed the key word "primarily". They did not say "exclusively".

    The key problem in your reasoning is your use of the term "molten mantle". Over very long time spans (geological time) the mantle appears to be plastic. Over very short time spans such as those resulting from tidal interactions, the mantle is better modeled as an elasto-rigid body with a small degree of anelasticity.

    Just as the oceans are subject to tides from the Moon and the Sun (and to a lesser extent the other planets), so is the Earth itself. The same tidal forces that result in the ocean tides also affect the Earth as a whole. Google the terms "Earth tides" and "solid body tides" for more. The Earth tides are for the most part loss-free because the Earth as a whole is mostly elastic on the time scales of the tides (hours to decades). The small amount of anelasticity in the mantle will lead to some losses, but these are small compared to those resulting from the ocean tides.
    Last edited by a moderator: May 5, 2017
  7. Oct 25, 2011 #6
    Thank you Billiards & D H for your comments

    From Billiards
    The post-glacial bounce in 11,000 years indicates to me though highly viscous that flow does exist. Also, tidal heating to me indicate friction which indicate that there is an opposing force to movement. Maybe the solid earth tidal bulging is inducing that movement.

    From D H
    I know it is not exclusively, I was challengining the word "primarily" which in my terminology means the #1 contributor. I have not found any paper yet that substantiate that claim.
    Last edited: Oct 25, 2011
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook