Rates and magnitudes of paraglacial fan formation in the Garhwal Himalaya: implications for landscape evolution

The development of paraglacial fans, studied in the upper Bhagirathi valley, Garhwal Himalaya, northern India, relates to the retreat of the Gangotri Glacier over the last 200 years. These fans demonstrate the speed by which mass movement and fluvial processes may lead to the modification and readjustment of the Himalayan landscapes during deglaciation. The paraglacial fans in this region grew within approximately 100 years of deglaciation, and there after were modified by small debris flows and entrenched by fluvial incision. On the basis of the preservation of moraines which were deposited during the Last Glacial, total resedimentation of glacial sediments by mass movement and fluvial processes is estimated to occur over approximately 100,000 years in this region. A knowledge of the magnitude and frequency of development of paraglacial fans is essential for hazard mitigation and management in Himalayan environments where glaciers are presently retreating and are likely to retreat in the near future if global warming occurs.