THE THEORY OF ISOSTACY. Isostacy derived from two Greek words and it means equal standing. The theory suggests that "the continent and their major features are maintained in a sort of equilibrium or moving towards equilibrium" It further explain that a large portions of the earth's crust are floating on a dancer underlying layer called the "MANTLE" . Thus where the areas of less dancer rocks rise topographically as a mountains and the areas with heavier rocks goes down. In short the lithosphere has highland and lowland due to the variation in density of the materials and gravity, so lowlands have dancer materials than highlands.
Due to variations the earth tends to maintain its balance, such that any disturbance on the earth's crust causes the movement of the molten materials "Asthenosphere" in mantle to different directions for the sake of bringing back equilibrium. There two types of movement of molten materials, "Vertical and Lateral movement". Vertical movement include upward and downward movement and this cause either uplift or sagging of the earth's crust. Highland are centre of denudation while the lowlands are the centres of deposition. So when the highland worn down there occur land uplift as a result of upward movement of mantle material caused by reduction in weight on the earth's surface.
The same balancing brought the formation of ice, when ice formed led to subsidence because of its weight and when ice melt there occur land uplift because of the reduction of weight after melting. THE EFFECTS OF ISOSTATIC MOVEMENT. faulting leading to formation of rift valley and block mountains. Folding leading to formation of fold mountains. Volcanic eruptions forming different volcanic features. Displacement of the lithosphere leading to plate tectonic movements and continental drifting.
EVIDENCES OF ISOSTATIC MOVEMENTS. the depression of the crust in northern part of America and Europe was due to weight of ice sheet of vast thickness during the ice age. The continental shelf around Antarctica is covered with water to a depth of about 750m compared with 180m around continents. Presence of Ria's and estuaries between cost lands of Gambia and Sierra Leone. Submergence of forests on the shores of Britain.
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