Abstract This study examines the morphometric and sedimentological characteristics of tributary-junction alluvial fans in the Upper Ganga catchment to better understand the roles of tectonics, climate, and geomorphic processes in fan development. Unlike classical fans formed in arid or tectonically stable settings, Himalayan fans in this region are typically small, steep, and debris flow dominated, sourced from high-relief, short, and steep catchments. High values of morphometric indices such as the Melton ruggedness number and stream gradient suggest a strong predisposition to debris flow activity, especially in catchments underlain by weak, tectonically disrupted lithologies. Regression and principal component analyses (PCA) show that catchment relief, shape, and apex elevation are more significant controls on fan geometry than catchment area alone. The weak correlation between catchment area and fan area reflects the influence of valley confinement, trunk river incision, and episodic sediment supply in shaping fan morphology. Stratigraphic records reveal evidence of high-energy, episodic debris flow deposition followed by fluvial incision, producing abandoned and reworked fan surfaces that now host human settlements. The region's high rainfall, active tectonics, and presence of paraglacial sediments in the upper reaches contribute to sediment saturation during extreme events, triggering debris flows and flash floods. These processes lead to complex, composite fan morphologies and increase the hazard potential, particularly where settlements are located on perched or inactive fan surfaces. Overall, the study highlights the critical influence of active tectonics, lithological variability, and extreme climatic conditions on alluvial fan development in the Himalayan hinterland. The findings underscore the need for region-specific hazard assessments and land-use planning strategies that account for geomorphic instability and the potential for high-magnitude events in the Upper Ganga catchment. Highlights <UnorderedList Mark="Bullet"> <ItemContent> Fans in the Upper Ganga catchment are small, steep, and debris flow dominated, sourced from high-relief, short, and steep catchments. </ItemContent> <ItemContent> High values of morphometric indices such as the Melton ruggedness number and stream gradient suggest a strong predisposition to debris flow activity. </ItemContent> <ItemContent> Weak correlation between catchment and fan parameters reflects the influence of valley confinement, trunk river incision, and episodic sediment supply in shaping fan morphology. </ItemContent> <ItemContent> Stratigraphic records reveal evidence of high-energy, episodic debris flow deposition followed by fluvial incision, producing abandoned and reworked fan surfaces that now host human settlements. </ItemContent> <ItemContent> Urgent need for region specific hazard assessments and land-use planning strategies where settlements are located on perched or inactive fan surfaces. </ItemContent> </UnorderedList>

Investigating geomorphic characteristics of alluvial fans in the Upper Ganga catchment, NW Himalaya

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发表日期：

2026年1月28日

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Neha Chauhan,
Yaspal Sundriyal,
Sameeksha Kaushik,
Anil D Shukla,
M P S Bisht

摘要

Abstract

This study examines the morphometric and sedimentological characteristics of tributary-junction alluvial fans in the Upper Ganga catchment to better understand the roles of tectonics, climate, and geomorphic processes in fan development. Unlike classical fans formed in arid or tectonically stable settings, Himalayan fans in this region are typically small, steep, and debris flow dominated, sourced from high-relief, short, and steep catchments. High values of morphometric indices such as the Melton ruggedness number and stream gradient suggest a strong predisposition to debris flow activity, especially in catchments underlain by weak, tectonically disrupted lithologies. Regression and principal component analyses (PCA) show that catchment relief, shape, and apex elevation are more significant controls on fan geometry than catchment area alone. The weak correlation between catchment area and fan area reflects the influence of valley confinement, trunk river incision, and episodic sediment supply in shaping fan morphology. Stratigraphic records reveal evidence of high-energy, episodic debris flow deposition followed by fluvial incision, producing abandoned and reworked fan surfaces that now host human settlements. The region's high rainfall, active tectonics, and presence of paraglacial sediments in the upper reaches contribute to sediment saturation during extreme events, triggering debris flows and flash floods. These processes lead to complex, composite fan morphologies and increase the hazard potential, particularly where settlements are located on perched or inactive fan surfaces. Overall, the study highlights the critical influence of active tectonics, lithological variability, and extreme climatic conditions on alluvial fan development in the Himalayan hinterland. The findings underscore the need for region-specific hazard assessments and land-use planning strategies that account for geomorphic instability and the potential for high-magnitude events in the Upper Ganga catchment.

Highlights

Fans in the Upper Ganga catchment are small, steep, and debris flow dominated, sourced from high-relief, short, and steep catchments.

High values of morphometric indices such as the Melton ruggedness number and stream gradient suggest a strong predisposition to debris flow activity.

Weak correlation between catchment and fan parameters reflects the influence of valley confinement, trunk river incision, and episodic sediment supply in shaping fan morphology.

Stratigraphic records reveal evidence of high-energy, episodic debris flow deposition followed by fluvial incision, producing abandoned and reworked fan surfaces that now host human settlements.

Urgent need for region specific hazard assessments and land-use planning strategies where settlements are located on perched or inactive fan surfaces.