Re: Was the moon ever close enough to pull on the mantle?

"Stuart" <bigdakine@xxxxxxx> wrote in message news:8c628b17-018d-49f1-9e5f-7db9fe212889@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
On Dec 25, 3:01 pm, "Perplexed in Peoria" <jimmene...@xxxxxxxxxxxxx>
wrote:
"Stuart" <bigdak...@xxxxxxx> wrote in messagenews:3f38d2d1-ba50-4a2d-9abf-41d70da7c5fc@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

On Dec 24, 6:11 am, rnorman <rnor...@xxxxxxxxx> wrote:



On Dec 24, 8:25 am, nos...@xxxxxxxxxx (Paul Ciszek) wrote:

In article <MPG.23bad2998667725098a...@xxxxxxxxxxxxxxxxxxxxxxxx>,

WangoTango <asgar...@xxxxxxxxxxxxxx> wrote:
In article <228ddbb9-4f52-4bc0-9e4b-
f89a376b8...@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>, miasc...@xxxxxxxxxxx says...

I was looking at this map of the former areas where the Yellowstone
hot spot has been and noticed that they are evenly spaced:

You don't think it pulls on the mantle NOW?
How is rock suddenly immune to gravity and water is not.....

The Earth bulges toward the moon.

Does anyone have any handy data on this--how much does the Earth's
mantle and crust flex due to tides raised by the moon?

I assume that the ocean tides are higher than this due to resonance
effects and momentum. How much out-of-round would the Earth be if
it were not rotating relative to the moon (i.e., tides were stationary)
and "totally relaxed"?

"Earth tide" is about 300 mm in vertical amplitude. See, for example,
http://en.wikipedia.org/wiki/Earth_tide

Although resonance explains the magnitude of enormous tidal swells
like the Bay of Fundy, I don't think it is responsible for the fact
that the ocean tide averages a higher swing than that of the
relatively inflexible earth.

Not by as much as one might typically guess.

Google "Love Numbers"

---------
The ocean rises more than the rock because water is
lighter than rock. Thats all. If there were a layer of
salad oil lying on top of the water, the oil layer would
get thicker at high tide.

Sorry, but the more I read this, the more I don't like it. You make it
sound like tides
are purely some sort of buoyancy phenomena. In actuality tides are the
response of the oceans and solid earth to the deforming effects of the
tidal potential. And the nature of that response is determined by the
rheology of the materials as well as density. If the earth was
perfectly rigid, there would be no tide regardless of whatever density
structure it had.

By the same token if the oceans had the density of mercury the tides
would be much less since it requires much more energy to deform the
free surface in this case.

Please read up on Love numbers.

Well, as frequently happens to me, I seem to have run up against someone
who knows more about a subject than me. Thanks for the corrections.
And for the reference to Love numbers, of which I had never heard.
Unfortunately, I was unable to find a tutorial-level web page - too bad
PlanetMath is not math about planets.

I'll take your word for it that Bay of Fundy is a resonance thing. And,
now that you point it out, it is clear that both potential energy of
deformation (stress and strain) and gravitational potential energy
have to be involved. I guess I was saying that the latter is much
more important than the former.

But your hypothetical of an ocean of mercury is interesting. If
such a thing could be geologically stable (a solid planet supporting
a denser-than-rock ocean) my intuition says that the ocean tide would
be negative with respect to the solid coastline. I.e., the mercury
would be deepest with the moon on the horizon rather than with
the moon at the zenith as with a water ocean. Is my intuition
wrong about this? Also, the only reason I can see why a 50
meter deep water ocean would yield smaller tides than a 5 km
deep ocean is friction (the resonance thing). A significant factor
if we were talking about a 5 cm deep ocean with a 24 hr rotation
period. But not a significant factor if the ocean is deeper or the
period is longer. Again, am I wrong about this?

.

Relevant Pages

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  • Re: Was the moon ever close enough to pull on the mantle?
    ... How is rock suddenly immune to gravity and water is not..... ... it were not rotating relative to the moon (i.e., tides were stationary) ... The ocean rises more than the rock because water is ...
    (talk.origins)