How Erosion Builds Mountains

Mountains have evoked awe and inspired artists and adventurers throughout human existence. Recent research has led to important new insights into how these most magnificent of Earths formations came to be. Mountains are created and shaped, it appears, not only by the movements of the vast tectonic plates that make up Earths exterior but also by climate and erosion. In particular, the interactions between tectonic, climatic and erosional processes exert strong control over the shape and maximum height of mountains as well as the amount of time necessary to build — or destroy — a mountain range.

Paradoxically, the shaping of mountains seems to depend as much on the destructive forces of erosion as on the constructive power of tectonics. In fact, after 100 years of viewing erosion as the weak sibling of tectonics, many geologists now believe erosion actually may be the strong one in the family. In the words of one research group, “Savor the irony should mountains owe their [muscles] to the drumbeat of tiny raindrops.”

Because of the importance of mountain building in the evolution of Earth, these findings have significant implications for earth science. To a geologist, Earth’s plains, canyons and, especially, mountains reveal the outline of the planets development over hundreds of millions of years. In this sprawling history, mountains indicate where events in or just below Earth’s crust, such as the collisions of the tectonic plates, have thrust this surface layer skyward. Thus, mountains are the most visible manifestation of the powerful tectonic forces at work and the vast time spans over which those forces have operated.

The role of tectonics

Mountain building is still explained as the addition of mass, heat or some combination of the two to an area of Earths crust (the crust is the upper part of the lithosphere). Thicker or hotter crust rises upward, forming mountains, because the crust is essentially floating on the mantle under it, and crust that is either thicker or hotter (less dense) floats higher. Plate tectonics contributes to the thickening of the crust by either lateral convergence between adjacent plates or through the upward flow of heat and magma (molten rock).