Here's why:
* Isostasy: The Earth's crust "floats" on the denser mantle below. This is the principle of isostasy. Imagine a block of wood floating in water – it sinks until the buoyant force of the water balances the weight of the wood.
* Mountain Formation: When mountains form, the crust thickens. This added weight pushes down on the mantle.
* Root Formation: The mantle, being a fluid, flows outwards, creating a depression beneath the mountain range. This depression is known as the mountain root.
* Compensation: This root helps to balance the weight of the mountain range, ensuring that the crust remains in equilibrium.
Think of it like this: Imagine placing a heavy object on a piece of elastic. The elastic will stretch and sag downwards to accommodate the weight. Similarly, the Earth's crust bends downwards to accommodate the weight of mountains.
