Moderate Erosion relative to Shortening Maximizes Mountain Heights in Active Orogenic Belts: Insight from tectonic-geomorphology analogue modelling

The interplay between tectonic shortening and surface erosion critically influences mountain building, yet their combined effects on vertical orogenic growth remain unclear. Here we present a suite of tectonic-geomorphology analogue experiments that combine brittle deformation with controlled rainfall-driven erosion. Under a certain shortening rate, we find that wedge height does not monotonically decrease with increasing erosion. Instead, the maximum orogenic wedge height occurs at a moderate rainfall/erosion rate, rather than under no or low erosion. To quantify this relationship, we introduce a dimensionless parameter, the rainfall-to-shortening ratio (R2S), and show that wedge height peaks at R2S ≈ 1. Compilation of data from 28 natural orogenic belts shows a similar bell-shaped trend, with maximum average elevations occurring at R2S ≈ 100, supporting the experimental results. The R2S difference between modeled and natural results likely represents the scaling difference of rainfall rate relative to shortening rate. We suggest that moderate erosion promotes vertical growth by reducing internal wedge strength and allowing the development of steeper critical surface slopes. These findings underscore the dynamic coupling between tectonics and surface processes and offer a scalable, physically grounded framework for understanding and predicting variations in mountain height across both experimental and natural systems.