Geomorphometric delineation and subdivision of the Altai mountains using DEM-based analysis

Abstract

This study redefines the borders, extent, and internal subdivisions of the Altai Mountains - one of the principal mountain systems in western Mongolia - by addressing longstanding inconsistencies in previous geographical and geological interpretations. A two-stage geomorphometric approach was applied to delineate the boundaries of the range. First, geomorphon classification was used to identify key terrain features, followed by the application of the Topographic Position Index (TPI) to refine boundary transitions based on relative elevation gradients. This combined methodology enabled the accurate differentiation of mountain extents from surrounding depressions, plains, and low-relief areas. Results indicate that the Altai Mountains extend approximately 2,400 km in a straight line from the Tigirig Range at the Russia–Kazakhstan border to the Khuut Mountain Range in Mongolia, with a cumulative watershed length of about 3,820 km. The total area covered by the range is estimated at 485,000 km2. Additionally, the study suggests that the low-relief mountain ridges in southwestern Mongolia likely represent the easternmost extension of the Tian Shan mountain system. By integrating recent neotectonic evidence with quantitative geomorphometric techniques, this research provides new insights into the structural geography of Central Asia and contributes to the refinement of regional mountain classification schemes.