Isostasy is a concept in the Geology invoked to explain why the gravity of the Earth's structures do not behave according to the standard gravitational theory which states that greater mass should have greater attraction. It is expected that there should be a greater gravitational pull from mountains than from hills, plateaus, and oceans, since mountains are more massive; yet 'gravity' readings do not reflect this. The concept of isostasy suggests that below sea level there is a mass deficit beneath the mountains, and is used to explain the disagreement between theory and data.
Louis Hessnik is a retired geologist who maintains a science blog called Louis Hissink's Crazy World.
“ Louis Hissink (MSc, Macquarie University) was a consulting diamond geologist, formerly of John Taylors, Western Mining Corporation Ltd and De Beers. He has worked for other smaller companies in Western Australia and the Northern Territory. ”
On the topic of isostasy, Louis Hessnik tells us:
Gravity and Isostasy
by Louis Hissink
“ Gravitational theory is firmly entrenched as dogma and is unchallengeable and punishable by excommunication and if the heresy great enough, by permanent expulsion from polite society. It is thus similar to religion in that as a basic premise it cannot be challenged.
So what about isostasy, a theory developed from the observation that surveying plumb-bobs were not attracted by an adjacent mountain? Or that they were not deflected as much as expected. This observation is similar to the laboratory Cavendish experiment to determine big G, the gravitational constant, where bodies have the attractive force measured in the horizontal plane. Herein lies the problem and the manner of thinking adopted when anomalous results are observed.
The reaction to the lack off deflection of the plumb-bob from vertical was to assume that the adjacent mountain had a mass shortfall, rather than question the theory that matter attracts matter. Clearly the lack of attraction observed would lead to one questioning the principle, and not the data, but no, it is the data which are erroneous, and not the principle of gravitation.
This manner of thinking is simply the religious mind at work, for religious minds cannot contradict received authority, here the belief that come what may, matter always attracts matter. This attitude was driven home when I presented the anomalous downhole survey data to the consulting geophysicists, who opined that if the readings are true, then there had to be a gravitating mass above the drill hole and since this is not observed, which is correct, then the data have to be in error, and an instrument malfunction the cause of the anomalous data preented in Gravity Update previously. It never occurred to them that maybe the theory is the problem.
Most scientists hold one or other religious beliefs, and the manner in which they think thus determines how they interpret scientific observations, especially observations that cannot be easily tested in a laboratory. Minds dominated by a belief system inculcated by education, will tend to only see what the believe system asserts, here that matter attracts matter, and hence if the data do not confirm the theory, or belief, then the data have to be in error. This led to the idea of mountain ranges, or some of them, having deep low density roots into the upper mantle, and the development of Plate Tectonics theory. Except that plates with mountains on them with interpreted under-slab keels should not be able to move, but this inconsistency in the theory seems never a problem, and readily explained as a collision effect between two converging tectonic plates.
Because of this manner of thinking, which leads to the illogical scenario of low density rocks floating in a more dense substrate, ice caps are believed to depress the crust underneath them, and when the ice melts, the crust re-adjusts by expanding upwards. Proof of this is the crustal emergence around the Baltic sea due to the melting of the earlier Pleistocene ice age when an ice cap is postulated to have existed in this part of Europe, and also in Canada where crustal uplift is also observed. But just how a rock of density 1 Kg/M^3 can sink into crust of density 2.7Kg/M^3 is explained by the principle of isostasy. This assertion is simply crazy – logical but crazy and came about from misinterpeting the earlier surveying data where the plumbline did not deflect as expected from calculations compensating for the mass of the adjacent mountain.
In both cases, the non-deflecting plumb-line and the anomlous downhole survey data, the mainstream reaction to the discordant data was to reject the data and confirm the supremacy of the belief in gravitation. But if the theory of gravity is wrong, then a great lot of theory and assumptions become, if not moot, just plain wrong. Retrocalculation of planetary orbits becomes problematical, gravitational accretion becomes a nonsense leading to a rather drastic paradigm shift in the physical sciences. It is tantamount to questioning our cultural world-view, that of the Abrahamic Religions, and that could be a most dangerous entreprise.
One challenge to this world view is being mounted by Tim Cullen at the Malaga Bay Blog, and of course this one has been politically incorrect for a long time. It is an intellectual battle between the Oriental and Occidental world-views, that of a cyclical orientalism and a linear occidentalism.
Update: I now wonder if Gravity has replaced God as the prime mover of the Universe. Both are words starting with a capital G. ”
“ I think you will find that we may not understand gravity very well. There are many things we don’t understand, it seems. ”
On discrepancies, one writer says:
“ On the basis of newtonian gravity, it might be expected that gravitational attraction over continents, and especially mountains, would be higher than over oceans. In reality, the gravity on top of large mountains is less than expected on the basis of their visible mass while over ocean surfaces it is unexpectedly high. To explain this, the concept of isostasy was developed: it was postulated that lowdensity rock exists 30 to 100 km beneath mountains, which buoys them up, while denser rock exists 30 to 100 km beneath the ocean bottom. However, this hypothesis is far from proven. Physicist Maurice Allais commented: "There is an excess of gravity over the ocean and a deficiency above the continents. The theory of isostasis provided only a pseudoexplanation of this."15
The standard, simplistic theory of isostasy is contradicted by the fact that in regions of tectonic activity vertical movements often intensify gravity anomalies rather than acting to restore isostatic equilibrium. For example, the Greater Caucasus shows a positive gravity anomaly (usually interpreted to mean it is overloaded with excess mass), yet it is rising rather than subsiding. ”
Journal of the Geological Society of India
Bouguer Anomalies Over The Continents and Oceans (Archive) in the Journal of the Geological Society of India tells us that the anomalies are often greater over the ocean than over the land, which is contrary to gravity theory:
“ Why, in general, the Bouguer gravity anomalies are negative in continental areas and positive in oceanic areas? Extending the question further, why do the predominant negative and positive anomalies respectively correspond to the mountain peaks and ocean depths? Although the Bouguer gravity data are not brought on to an even datum, there is fairly a good inverse correlation of Bouguer anomalies with height/depth as well as seismic data. This obviously indicates the excess mass reflected as gravity lows and the deficit mass as gravity highs with respect to the geoid/ellipsoid surface. This is in contrast to the theory of the gravity field which is proportional to the excess or deficit mass. Mathematically speaking, the observed anomalies are proportional to the vertical gradient of gravity, indicating excess mass above the geoid as gravity lows and deficit mass below the geoid as gravity highs. If this were true, far reaching implications arise in the understanding of the theory and interpretation of Bouguer anomalies. ”