Define the concept of isostasy in geology.

The concept of isostasy in geology refers specifically to the equilibrium state of the Earth's crust. It explains how the lithosphere (the rigid outer part of the Earth) floats on the more fluid asthenosphere beneath it. This balance is achieved due to differences in density and thickness among the Earth's materials.

When geological processes such as erosion, sediment deposition, or glacial melting occur, the crust can either sink or rise in response, striving to maintain this equilibrium. For instance, when heavy ice sheets melt, the previously compressed crust begins to rebound upwards, while in areas of significant sediment deposition, the crust may gradually sink due to the added weight.

Understanding isostasy is essential for various geological phenomena, including mountain ranges' formation, the stability of coastal areas, and how tectonic forces are balanced over geological timescales. This key principle illustrates the dynamic nature of the Earth's surface in response to internal and external forces.