Isostasy

n. balance between the gravity which tends to depress and the buoyancy which tends to raise a given segment of the earth's crust (Geology)

Isostasy is a term used in Geology to refer to the state of gravitational equilibrium between the Earth's lithosphere and asthenosphere such that the tectonic plates "float" at an elevation which depends on their thickness and density. It is invoked to explain how different topographic heights can exist at the Earth's surface. When a certain area of lithosphere reaches the state of isostasy, it is said to be in isostatic equilibrium. It is important to note that isostasy is not a process that upsets equilibrium, but rather one which restores it. It is generally accepted that the earth is a dynamic system that responds to loads in many different ways, however isostasy provides an important 'view' of the processes that are actually happening. Nevertheless, certain areas (such as the Himalayas) are not in isostatic equilibrium, which has forced researchers to identify other reasons to explain their topographic heights (in the case of the Himalayas, by proposing that their elevation is being "propped-up" by the force of the impacting Indian plate).
See more at Wikipedia.org...

The equilibrium maintained between the gravity tending to depress and the buoyancy tending to raise a given segment of the lithosphere as it floats above the asthenosphere.

isostasy /ai'sɔstəsi/
danh từ sự đẳng tĩnh; tính đẳng tĩnh
(C) 2007 www.TừĐiểnTiếngViệt.net

ISOSTASIA. ISOSTASI