Fold mountains

The Mystery of the Forces Hidden Behind Earth’s Tallest Mountains May Finally Be Solved

It’s a process that can take billions of years, but mountains do grow – and exactly what factors control this growth have been the subject of ongoing debate among scientists. Now, it looks like we may finally have a definitive answer.

According to a new study, tectonic forces beneath mountains — rather than weathering and erosion at the top — control their height. Thus, for mountains close to tectonic plate collision zones, the maximum mountain height is primarily determined by a balance of forces deep within the earth’s crust.

As tectonic plates shift and move toward each other, one of the plates is forced down into the Earth’s mantle; as the plates bend and fold, mountain ranges then appear on the surface. The big question has been whether this is the primary driver of mountain height, or whether weather-related wear plays a more important role.

There is a third factor at play, called isostasis – a process that keeps the mountains “floating” above the warm, soft mantle – but this is thought to be less important and partly driven by the other two factors.

Scientists analyzed the strength of particular plate boundaries and modeled the various forces that would act on tectonic plates, using in part measurements of near-surface heat flux as an indicator of the underlying frictional energy at play. .

By comparing these models with the actual heights of mountain ranges in the Himalayas, Andes, Sumatra and Japan, the team concluded that in mountains that continue to actively grow, height and weight remain in balance with the enormous underground forces below. If the friction and the stress underneath change, the height of the mountain also changes.

“Erosional processes can modulate mountain topography and trigger active faulting, as suggested by conceptual and numerical models of climate-tectonic interactions,” the researchers write in their new published article.

“However, our findings suggest that erosion is not able to overcome the tectonic and isostatic processes that keep the convergent margins close to force balance, because the upper plate is effectively weak.”

Researchers liken it to putting your hands under a tablecloth and then bringing them together – the folds of fabric that stick up in the middle are mountains, and the friction of fabric that slowly comes back over your hands is tectonic activity.

It remains to be seen whether the same is true for mountains that are not close to subduction zones, where one tectonic plate slides under another – in these cases it is always possible that the height of the mountain is limited by climatic conditions, such as the position of the snow line.

Additionally, to make sense of the new findings, geologists will need to re-evaluate their ideas about the strength of the Earth’s crust in mountainous areas.

Further research should lead to more answers and a better idea of ​​how the height of mountain ranges is controlled around the world. For now, the new study gives geologists a new way to think about the forces below the crust that affect the majestic mountain ranges we see spanning our planet’s surface.

“We conclude that temporal variations in mountain height reflect long-term changes in the balance of forces but are not indicative of direct climatic control over mountain elevation,” the researchers write in their to study.

The research has been published in Nature.