What Limits a Mountain’s Height: A New Theory

Alex Camerino | | BrainsBrains
Mountains, height
Two continental plates converge to form the Himalayas. Photo by Rohan Reddy on Unsplash

A new study published earlier this month suggests convergent plate boundaries are the sole contributor to a mountain’s height. It was previously believed that these convergent plate boundaries pushed up the crust as one plate was subducted beneath the other (this is still true). After the mountain was formed it then started to weather and erode becoming shorter as it succumbs to the forces of nature.

Below are the three types of convergent plate boundaries. For all three types, earthquakes occur when the two plates move against each other. Volcanoes also occur near plate boundaries due to the subducted plate melting and the magma rising to the surface.

Converging plates with subduction zone
Ocean-Ocean Convergence. ThoughtCo.
Two continental plates converging
Continental-Continental Convergence. ThoughtCo.
Ocean converging with Continent, creating mountains
Ocean-Continental Convergence. ThoughtCo.

In the early 20th century many scientists believed that the continents “drifted” around over time, but it was not until the mid-1960s that the theory of plate tectonics was able to be fully explained. Since Earth’s tectonic plates shift at different velocities and directions some boundaries between them are on a collision course. This convergence is like two cars smashing into each other and the hoods of the cars are the crust. As the cars collide the hoods crumple and “mountains” are formed.

Researchers, from the GFZ German Research Centre for Geoscience and the University of Münster in Germany, believe forces in the crust determine a mountain’s maximum height, not erosion and weathering. They collected data on friction in the subsurface of mountain ranges of varying heights (Himalayas, Andes, Sumatra, Japan). The stress and therefore force could then be calculated to determine uplift. Once the uplift could be determined they were able to show the forces from the height and weight of the mountains were in balance with the force on the plate boundaries.

Even though mountains are located in many different climates with differing rates of erosion the balance of forces in mountains always exists. The study concludes that “mountain ranges are able to react to processes on the Earth’s surface and to grow with rapid erosion in such a way that the balance of forces and the height of the mountain range are maintained.” With these new findings on orographic creation, it is expected that the long-term growth and development of mountains will be studied in the future.

Mountain shear force vs height
This graph shows the average mountain height on the vertical axis and the shear force on the horizontal axis. This shows that the height of mountain ranges is tectonically controlled and that global differences in mountain height result from differences in the shear force. GFZ

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