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isostasy|aɪˈsɒstəsɪ|
Also isostacy (rare).
[f. Gr. ἰσο- iso- + στάσις setting, weighing, standing, station; cf. Gr. ἰσοστάσι-ος in equipoise, equivalent.]
Equilibrium or stability due to equality of pressure; the condition thought to exist within the earth's crust of approximate hydrostatic equilibrium between portions of different density, the land masses being supported by underlying denser material that yields or flows under their weight and those parts of them that reach to a greater height also extending to a greater depth, any (large) part slowly rising (or falling) if matter is removed from (or added to) its surface.
1889C. E. Dutton in Bull. Philos. Soc. Washington XI. 53 For this condition of equilibrium of figure, to which gravitation tends to reduce a planetary body, irrespective of whether it is homogeneous or not, I propose the name isostasy... We may also use the corresponding adjective isostatic. 1893Ann. Rep. U.S. Geol. Survey 1891–2 ii. 280 The condition of isostasy prevailing in the earth's mass demanded that compensation should be made to the continental area for the load taken from it. 1896Pop. Sci. Monthly L. 243 The general problems of isostasy. 1900Ibid. LVI. 443 Now, so sensitive is the earth to changes of gravity that, given time enough, it responds to increase or decrease of pressure over large areas by corresponding subsidence or elevation...This principle of isostasy is undoubtedly a valuable one, which must be borne in mind in all our reasonings on crust movements. 1914[see asthenosphere]. 1923Discovery Dec. 315/2 The suggestion which has gained most favour, and seems to fit in with many observations, is the theory of Isostacy, which contends that all visible land is composed of the lighter parts of the Earth's crust and is floating upon the components of greater density. 1944A. Holmes Princ. Physical Geol. iii. 34 It must..be clearly realized that isostasy is only a state of balance; it is not a force or a geological agent. It is the disturbance of isostasy by denudation and deposition, earth movements and igneous activity, that brings into play the gravitational forces that restore isostasy. 1950Antiquity XXIV. 43 The dating of these sites involves the post-Algonquin changes in Great Lakes water-levels through isostasy and drainage. 1960New Scientist 19 May 1278/2 The gravity variations are generally consistent with the theory of isostasy, according to which mountains ‘float’ in hydrostatic equilibrium in the dense mantle as do icebergs in the sea. |