Scientists have developed a new classification system for mountain ranges that uses a single number to describe whether the elevation of the mountain range is controlled primarily by weathering and erosion or by the properties of the earth’s crust, that is to say the lithospheric force: the “Beaumont number” (Bm). It is named after Chris Beaumont, a scientist who, with his team, developed coupled models of surface processes and tectonic forces. Scientists report their findings in the current issue of Nature.
A Beaumont number between 0.4 and 0.5 means that the mountains are in a so-called steady state of flux in which the growth controlling factors of mountains are tectonic forces and the lithospheric strength, balanced by weathering processes as, for example, in Taiwan. With a Bm value of less than 0.4, the mountains are also in a steady state of flux but with erosion as a controlling factor like the Southern Alps of New Zealand. A Beaumont number greater than 0.5 means that the mountains continue to grow (non-steady state) with the lithospheric force controlling the process. Examples of this type are the Himalaya-Tibet mountains and the central Andes.
This classification resolves a long-standing question of whether tectonic forces and the resistance of the earth’s crust are the controlling factors of mountain elevation or whether weathering processes are under control. The new study says it could be either, depending geographical positionclimate and subsoil properties.
The team of scientists led by Sebastian G. Wolf from the University of Bergen in Norway used a novel coupled surface process and mantle-scale tectonic model for their study by combining the thermomechanical tectonic model FANTOM with the model evolution of the FastScape landscape. Thus, they were able to reconcile high erosion rates in some active orogens with the long-term survival of mountain ranges for hundreds of millions of years.
Jean Braun of the German GFZ Research Center for Geosciences, co-author of the paper, says that “with our Beaumont number we can determine to what extent tectonics, climate and crustal strength control the height mountain ranges. And, for most mountain belts, this can be done without complex measurements or assumptions, just knowing the rate of convergence obtained from current plate velocities or plate reconstructions, the height of the mountain obtained from a topographical map and the enlargement rate obtained from the geological records. In a nutshell: whether a mountain is short or high is the product of a slow or rapid convergence, of a climate wet or dry, or with a strong or weak crust.” The Beaumont number indicates which of these three factors dominates.
Sebastian G. Wolf et al, Topography of mountain ranges controlled by rheology and surface processes, Nature (2022). DOI: 10.1038/s41586-022-04700-6
Helmholtz Association of German Research Centers
Quote: What forces control the elevation of mountains? (2022, June 2) retrieved June 2, 2022 from https://phys.org/news/2022-06-elevation-mountains.html
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