Scientists Tackle the Mystery of Earth’s Mountain Growth

Nature

Scientists are still debating the hidden factors that govern mountain growth, but now, researchers may have finally solved this mystery.

Mountains are “alive” and grow. The process could take billions of Earth years. According to a study recently published in the journal Nature, the tectonic forces beneath Earth’s mountains are the ones controlling their growth instead of erosion and weathering. Therefore, for those mountains that are near the collision zones of tectonic plates, their maximum height will largely be determined by the equilibrium of the forces moving in our planet’s crust.

Tectonic plates shift and move towards one other, and as they do, one colliding plate is brought down into the mantle. As these plates buckle and consequently fold, this initiates the process of creating mountain ranges on top of the crust.

The question that scientists are pondering is if this is the primary force that drives the height of a mountain. They contemplate if instead of this, wear and tear caused by climatic forces are a more significant factor.

The third-factor researchers are considering is what is known as isostasy, or the process that “floats” mountains above the soft and hot mantle layer. Scientists argue that this is not so significant. They think the first two factors are more influential.

The authors of the study, composed of Armin Dielforder, Ralf Hetzel, and Onno Oncken,  computed the strength of specific plate boundaries, after which they modeled the forces that act upon these plates. They partly used measurements of heat flow near the crustal surface to account for the energy of friction underlying them.

They compared their models with real mountain ranges, particularly the Andes, the Himalayas, Japan, and Sumatra. They concluded that with actively growing mountains, their weight and height are balanced in relation to the underground forces raging beneath them.  As the stress and friction beneath them shift, their height correspondingly adjusts.

According to the study authors, the processes of erosion may affect mountain topography, which can trigger faulting. These are conclusions made from numerical and conceptual models concerning interactions between tectonic plates and climate.

However, the findings of their new study show that erosion cannot outpace isostatic and tectonic processes which equilibrate convergent margins with force equilibrium, due to the fact that the upper tectonic plate is weak.

As an analogy, the authors compare the process of putting one’s hands beneath a tablecloth and then moving them together. The folds of the tablecloth rise in the middle and represent mountains, while the friction that one feels on the hands represents tectonic activity.

The researchers say that they cannot yet conclude if the same thing happens in the mountains away from subduction zones where tectonic plates slide under one another. In such cases, they say that the conditions of the climate can still limit mountain height.

With these findings, geologists must review old ideas regarding the crust’s strength in areas with mountain ranges. The new study is a way of considering the forces beneath our crust, which affect mountains. The authors say that temporal variations are representative of long-term force balance changes, instead of direct climatic forces.

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