[Tom Bishop]

Look at the Complete Bougeur Anomaly and the cross section illustration of the low density root beneath the Rocky Mountains at the bottom of the diagram. Are we supposed to believe that inverse low-density root mirror images of the mountain form which correspond with the all of the mountain peaks of the Rocky Mountains?

https://www.researchgate.net/figure/Gravity-anomaly-profiles-on-a-West-East-transect-across-the-Rocky-Mountains-in-the-State_fig1_258829035



"Gravity anomaly profiles on a West/East transect across the Rocky Mountains in the State of Colorado. Note the change in vertical scales for the anomalies and the vertical exaggeration of the surface topography. The geological cross-section shows the sources of the modeled isostatic gravity anomaly."



http://earthsci.org/education/teacher/basicgeol/earthq/earthq.html

"Negative anomalies exist beneath mountain ranges, and mirror the topography and crustal thickness as determined by seismic studies. Thus, the low density continents appear to be floating on higher density mantle."



Amazing.

[Iceman]

I'm starting to worry that the flaws you perceive related only to your lack of understanding gravity, mass, and density... you seem to be implying that it's not plausible that something less dense can push down something more dense.  Ice is less dense than water. We know this because ice floats ...if you have a glass of water and place an ice cube into it, the ice cube doesnt sit on top of the water, it deforms it, displacing it around it.

That's obviously an oversimplification, but it still holds: for mountains, less dense rocks are thrust together and accumulate to greater thicknesses, thus adding more mass, which deforms the underlying mantle boundary downward. During glaciation, several kilometers of ice accumulates on top of the crust deforming/compressing it over thousands of years. As the ice melts and retreats, that mass is removed and the crust rebounds back to equilibrium.

[Tom Bishop]

Pretty weird. All mountains don't form the same way. If the upper mantle/lower crust had this low density rock material I would expect that it builds up somewhere in the middle of fold mountains, or off to one side, not outlining the profile of the fold mountains.

https://www.quora.com/What-are-the-characteristics-of-famous-fold-mountains



It outlines the profiles of the mountains every time? Come on.

There is another correlation too. The previous quote says that the inverse correlation also applies to crustal thickness:

"Negative anomalies exist beneath mountain ranges, and mirror the topography and crustal thickness as determined by seismic studies. Thus, the low density continents appear to be floating on higher density mantle."



So below the crust there is a mirror image of low density roots which masks and counters its thickness in regards to how thick it is too?

It's just one coincidence after another.

[Iceman]

You're right, not all mountain chains form in the same way.
This site is the only place I've seen the term 'fold mountains'
The upper mantle has high (not low) density material.
You "would expect..." what are you basing your expectations on? Logic? Common sense? Willful optimism?
That quote from quora(?) Mixes up continent-continent orogenic belts with subduction belt orogenies.
Those negative anomalies exist because when you pile up a bunch of low-density material, it pushes down the underlying high-density material, making the dense stuff relatively further away from the measuring device, creating a weaker observed pull.
It's not coincidence - its correlation.

[Veritatisferebat09]

The gravity vs. Upward acceleration/ equivalency principle arguments are an interesting set of discussions. They commonly quote the constant value of 9.8 m/s² for g. This is true enough for our every day lives.

The problem is that Earth's gravity is nowhere near that uniform once to start using more sensitive instruments in different areas - i.e. the significant digits after 9.8 become significant to the discussion. Gravitational strength varies based on a number of regional factors, like your latitude (because of the earth's rotation, you weigh very slightly less at the equator than you do at the poles, even though you're at a greater distance to the center of the earth).

Ignoring large regional effects, local variations in earth's gravity occur over as little as tens of meters! And in mapping out these changes, weve been able to discover geologic features like buried mineral deposits, oil and gas reservoirs, and buried bedrock valleys that may host large aquifers capable of supplying groundwater for large municipalities. (e.g. Greenhouse and Williams, 1986. A gravity survey of the Dundas buried valley west of Copetown, Ontario. Canadian Journal of Earth Sciences, v.23: 110-114 available free online)

Aside from the multi-billion dollar applications of gravity for exploration, understanding temporal variations in earth's gravity is becoming increasingly effective. The GRACE satellite system can now detect tiny changes in gravitational strength that relate to changes in water and ice storage on land on seasonal and multi-year timescales. These help measure climate change impacts and long-term over use of major aquifer systems that are causing subsidence problems in many cities (examples in California and Arizona are widespread in google searches https://lmgtfy.com/?q=land+subsidence+aquifers )

How do these measured changes in local acceleration due to gravity fit within a FE framework? The UA would induce an apparent acceleration of 9.8 m/s2 uniformly across earth's plane, and the equivalency principle is really only valid for local reference frames and cannot account for these local variations.

Without an oversimplification, God Created the heaven(firmament) and the earth(circle/compass). To that end, the fact that you go up and come back down is simply so you do not float to the top of the firmament dome.....

[Tom Bishop]

Those negative anomalies exist because when you pile up a bunch of low-density material, it pushes down the underlying high-density material, making the dense stuff relatively further away from the measuring device, creating a weaker observed pull.
It's not coincidence - its correlation.

You are talking about the buildup of the mounain pushing down the higher density layers (circled in purple). You are saying that this mass buildup pushes down the higher density layers away from the gravimeter.

But there is also mass buildup pushing the mantle downwards elsewhere (circled in light blue).



So why should this cause a negative gravity profile which matches the topside profile of the mountain peaks?

In this next one, why should the mass pushing down the mantle at the orange circle be distributed like the masses at the peaks?

[Iceman]

We might be getting closer here, cause yeah that's exactly what isostacy says. And it's not nonsense at all... put enough mass of something and it will start to do work to something beneath it, regardless of their relative densities.

Think snowflakes slowly compressing underlying snow into denser glacier ice, sediments slowly compacting and lithifying underlying layers into rock, and ice cube in a glass of water, or a bunch of colliding low density continental crust deforming the contact with the underlying denser mantle (pictured above and circles in purple in your post)

I would just caution that the diagram is a 3D conceptual model and is no way drawn to scale, so in this case your blue circle isnt really meaningful.

[Tom Bishop]

I would just caution that the diagram is a 3D conceptual model and is no way drawn to scale, so in this case your blue circle isnt really meaningful.

What? Many diagrams of mountain formation have continental plates stacked on top of each other, more so or differently on one side of the mountain range than the other.

If you won't trust the University of Bristol, why not show us how mountains really form.

[Iceman]

I never said it was wrong, I said there was no scale. I have no issue with Bristol  - tons people there smarter than I am!

The conceptual drawings demonstrate plate tectonic theory accurately enough ( the second one you added later is probably better than the first one you had originally, but that's just my opinion). The maximum amount of downward deformation of the mantle contact will occur beneath the area that has the thickest accumulation of continental crust (your purple oval in the first and orange circle in the second).

I feel like this would be easier if, instead of pulling out individual slides from things, you read the whole documents. You could then include some references on the mountains and volcanoes page which currently has none.

[Tom Bishop]

All of the diagrams I've seen of mountain formation show unique mass distributions beneath the mountains to one side, so I don't really know where you are suggesting I look for these more accurate diagrams or information for mountain formation.

You like to use floating things as an example of isostasy, but how it is logical that the mass distribution beneath the surface would necessarily conform to the profile above the surface considering the multiple ways mountains can form?

From Dr. Narendranath Guria - https://www.researchgate.net/publication/336639287_Isostasy_Theory



Are you claiming that this iceberg would eventually morph to a form where the roots form a mirror image of the surface? Maybe we just need to throw around the word "eons" or something?

Why can't the topside and root profile have their own unique shapes so long as the ratio of floating material stays above the surface, per Archimedes' principle? If the top side or roots were flat, would the opposite side become flat?

If you are going to dismiss it because of its size, just imagine that it's the size of a mountain or two.

[DuncanDoenitz]

Are we missing the elephant in the room here? 

This thread has moved on ("gravitated", if you will) to discussion of hypotheses for the documented stable variations in gravity in different parts of the Earth under a RE model.  There is no sign of agreement, but there is at least one hypethesis. 

What is the FE/UA hypothesis, if the whole Earth is accelerating at the same rate?  Are some parts being left behind?   

[Iceman]

I'm not saying anything specific about the mass distributions beneath mountains.... but you seem to be claiming it would be a mirror image of the surface profile, but also has a unique mass distribution to one side.

I don't like using examples of floating things, but the do demonstrate clearly that the weight of non-dense things can induce deformation of underlying denser material, which seems the be the main issue you disagree with here ( I hope that doesnt over simplify your stance). In the case of that ice Berg, if the surface or subsurface morphology changes enough, the uneven mass distribution will cause the ice very to roll over, to find a new equilibrium.

Duncan's right though Tom, all this recent stuff should be on a different board, and we should go back to the examples of local-scale changes in measured pull over buried valleys, the references I provided, and whether UA can address those spatial variations.

[Longtitube]

Are we missing the elephant in the room here? 

This thread has moved on ("gravitated", if you will) to discussion of hypotheses for the documented stable variations in gravity in different parts of the Earth under a RE model.  There is no sign of agreement, but there is at least one hypethesis. 

What is the FE/UA hypothesis, if the whole Earth is accelerating at the same rate?  Are some parts being left behind?

What has happened here is what has happened so often in the past: someone asks a difficult question which the FAQ and wiki don't answer and someone, by muddying the water, avoids answering the question. Several pages of irrelevant discussion ensue and the original question is forgotten.

Variations in the strength of gravity are documented from many locations, so how does FE thinking account for these? Several answers are possible, including "We don't know" - or - "No idea, but this person (link supplied) should be able to answer your question" - or - "There are no variations, there's no such thing as gravity. Read up about Universal Acceleration, duh."

Instead, we have in order:–

(1) references to not measuring in a vacuum chamber. which is meaningless without context, and vague references to underground density variations affecting gravity (which the OP asked for an FE explanation of)

(2) attempt to dismiss gravity variations as seismic noise in the gravimetric signal, ignoring the great difference in the period of low-frequency gravity variations compared to much higher frequency seismic noise and quite ignoring the vast difference in gravity signal size compared to the noise level in the signal (signal to noise ratio exceeding 1000:1). Additional attempt to make out the gravimeter is only a seismometer by producing graphs from a scientific paper which the poster does not understand, confusing signal noise at  the nano scale with the main signal variations at a minimum of micro scale, again at least 1000:1 difference, often much more.

(3) challenged on grounds of evidence introduced by the FE responder, attempt to dismiss this evidence as crude experimentation, alleging weights are piled indiscriminately directly on to expensive, sensitive gravimetric equipment and affecting instrument's sensitivity. Simple arithmetic refuting this claim, using figures from that evidence and manufacturer's data, ignored.

(4) FE responder introduces another scientific paper on gravimetry to dismiss mathematical methods used in processing results in the paper as mere guesswork and deception. Note to responder: the complete lack of mathematical understanding demonstrated here is not just laughable, it's embarassing. Please, for your own sake, don't do that; you're only inviting ridicule.

(5) repeated misunderstanding of effect of changes in nearby masses or height on gravimeters.

(6) introducing Bouguer anomalies into response without any understanding of what these are, despite earlier quoting an article from the Aligarh Muslim University which explains them

(7) dismissing gravimeter as a crude tool whose results can be interpreted any way, ignoring the necessary field work which follows a gravimetric survey.

(8/) attempt to make theories of mountain building part of dismissal of gravimetry, using case of fold mountains – an archaic term not used in geology since the 19th century

(9) irrelevant squabble about symmetry in geological and iceberg formations, concluding with challenge to show how mountains form

That is how the original question is avoided, as the regulars here know all too well. By now we're at the end of three pages of increasingly muddy waters, none of which gives an FE explanation for the well-documented variations in gravity in many parts of the world.

Just what explanation does FE theory have for this variation? If there's currently none, just say so.