Particle size characteristics of suspended sediment transported in meltwater from the Gangotri Glacier, central Himalaya — An indicator of subglacial sediment evacuation

Proglacial meltwater streams draining out of the Himalayan glaciers carry considerable amounts of suspended sediment, with a variety of particle sizes, because of the supraglacial, englacial, and subglacial debris, as well as formation of sediments from erosion by the movement of the ice. This paper examines particle size transported in the proglacial meltwater stream of Gangotri Glacier for seven consecutive melt seasons (May–October, 2000–2006) in order to provide information on (i) temporal variations in the particle size distribution, (ii) texture and mineralogy of the sediments, and (iii) origin and evacuation pattern of the sediments. Our results indicate dominance of silt size (0.002–0.06 mm) particles (71%) followed by sand size (0.06–0.6 mm) particles (24%) and clay size (< 0.002 mm) particles (5%) during the melt season, with increased variation as melt season progresses. The sediment contains quartz, feldspar, mica, illite, and kaolinite minerals, which represent a poor to poorly sorted fraction with a coarse to fine skewed textural distribution. Overall, this study indicates a subglacial evacuation pattern of the suspended sediment based on (i) size classification, (ii) higher percentage of coarser particles toward the end of the melting season, (iii) symmetrical to positively skewed with a kurtosis of mesokurtic to platykurtic texture, and (iv) a less-rounded shape of particle size. Our result on the evolution of meltwater pathways indicates a progressively better interconnected drainage system with advancing melt season. The evolution of meltwater pathways also demonstrates complex behavior of the glacial system and the need for a better understanding of sediment availability and contribution.