Document Type : Research Article
Author
Department of Geography, Faculty of Literature and Humanities, University of Yasouj, Yasouj, Iran
Abstract
The Zagros Mountains represent one of the most tectonically active orogenic belts worldwide, exhibiting pronounced morphological asymmetry between their southwestern and northeastern flanks. This study presents a quantitative analysis of topographic relief across both flanks using a high-resolution (12.5 m) digital elevation model (DEM). Over 200 longitudinal profiles and transverse cross-sections were extracted and fitted with linear and polynomial regression models. Key morphometric indices—including effective slope, coefficient of determination (R²), and curvature trend (convex vs. concave)—were systematically analyzed. Results show the southwestern flank has a steeper effective slope (0.46–0.51), deeply incised concave upper profiles shaped by glacial erosion amplified by structural steepness, and morphological instability in lower segments due to intense fluvial and mass-wasting processes. In contrast, the northeastern flank displays gentler slopes (0.27–0.46), predominantly linear or convex profiles, and greater morphological stability. Although Quaternary glaciation influenced elevations above 3700 m on both flanks, the final morphology of cirques and glacial benches is structurally controlled: gentle convex platforms dominate the structurally concordant northeastern flank, whereas steep, U-shaped valleys characterize the discordant southwestern flank. These findings confirm that subsurface structures—particularly the Main Zagros Thrust and bedrock dip orientation—primarily govern surface topography, with surface processes operating within a tectonically defined framework. This study provides a robust quantitative methodology for analyzing tectonics–erosion interactions in young orogens, transferable to other active mountain belts globally.
Introduction
The Zagros Mountains, formed by the ongoing collision between the Arabian and Eurasian plates, constitute one of the most tectonically active orogenic belts on Earth. A striking morphological asymmetry characterizes this range: the southwestern flank—adjacent to the Main Zagros Thrust—exhibits steep, dynamic topography, whereas the northeastern flank—dipping in harmony with sedimentary strata—displays gentler, more extended slopes. Although numerous studies have addressed the tectonics and geomorphology of the Zagros, a critical research gap persists in the systematic, quantitative analysis of morphometric differences between these two flanks at elevations above 3,000 m, where Quaternary glacial processes and active tectonics interact simultaneously. This study aims to address this gap by testing the hypothesis that the observed topographic asymmetry directly reflects the geometry and activity of subsurface structures.
Material and Methods
The study area is located in the central-southern part of the Zagros heights and spans the provinces of Isfahan, Chaharmahal and Bakhtiari, and Kohgiluyeh and Boyer-Ahmad. This region includes part of the Dena Mountains, one of the most significant and prominent morphological structures in the southern fold belt of the Zagros. The geographical coordinates of the area are precisely: latitude from 30° 40' to 31° 10' north and longitude from 51° 20' to 51° 40' east.
We employed a high-resolution (12.5 m) digital elevation model (DEM), processed in Global Mapper, to extract and analyze topographic profiles across the Dena Mountains in the Central Zagros. Over 200 longitudinal profiles were categorized into three groups: (1) northeastern flank profiles (facing the Iranian Plateau), (2) southwestern flank profiles (adjacent to the Main Zagros Thrust), and (3) valley-aligned profiles on both flanks. Additionally, transverse cross-sections perpendicular to the mountain trend were generated. For each profile, elevation data were exported as numerical series and statistically analyzed in Microsoft Excel. Linear regressions were first fitted to each profile, and the coefficient of determination (R²) was calculated. Where R² fell below 0.95, polynomial models (degrees 2–6) were applied to improve fit quality. Key morphometric parameters—including effective slope, horizontal length, relative relief, and curvature behavior (convex vs. concave)—were systematically compared between flanks.
Results and Discussion
All profiles consistently reveal a pronounced morphological asymmetry: the southwestern flank displays steeper effective slopes (0.46–0.51), while the northeastern flank exhibits gentler gradients (0.27–0.46) and longer horizontal extents. Above 3,700 m, glacial landforms—such as cirques and glacial benches are present on both flanks. However, their final morphology is structurally controlled: on the structurally concordant northeastern flank, cirques manifest as broad, convex platforms; in contrast, the structurally discordant southwestern flank hosts deep, U-shaped valleys with steep, glacially sculpted walls. The coefficient of determination (R²) is consistently higher on the northeastern flank (0.970–0.998) than on the southwestern flank (0.900–0.990), indicating greater morphological stability and homogeneity. Conversely, the southwestern flank shows greater R² dispersion and curvature oscillations, reflecting high geomorphic dynamism and rapid response to tectonic forcing.
These findings align with established structural models of the Zagros. According to the thick-skinned wedge model (Mouthereau et al., 2006) and the blind thrust framework (Berberian, 1995), focused crustal shortening along the Main Zagros Thrust generates steep, unstable topography on the southwestern flank, while the northeastern flank—acting as the upper surface of the tectonic wedge—retains relatively stable, gently sloping forms. Thus, even under similar surface processes (e.g., glacial erosion), structural geometry dictates the expression of topography.
Conclusion
This study provides robust quantitative evidence for deep‑seated structural control over surface topography in the Zagros Mountains. The morphometric asymmetry between the two flanks is not merely a surface geomorphological feature but a direct expression of contrasting tectonic settings: the active collisional front along the southwestern side versus the relatively stable hinterland domain in the northeast. These findings reinforce the theoretical framework of structural control on surface morphology in young orogenic belts and demonstrate that geomorphic analyses cannot fully explain landscape evolution without considering underlying structural geology. Methodologically, the quantitative approach employed in this study—based on fitting mathematical relationships to longitudinal profiles and analyzing morphometric indices such as effective slope, coefficient of determination (R²), and curvature trends—provides a transferable framework for systematic comparison of tectonically active mountain belts worldwide. In addition, the results have practical implications for geomorphological hazard assessment and environmental planning in the Zagros Mountains, particularly with respect to rockfall susceptibility and slope instability along the steep southwestern slopes. Overall, the contrasting morphometric characteristics of the two flanks illustrate two distinct states of tectonic–surface interaction in a young mountain system, offering insight into the long‑term evolution of collisional mountain belts.
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