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Gangotri proglacier streams; sediments texture; streams hydrochemistry; weathering processes.

Proglacial streams play an important role in water–rock interaction due to different climatic conditions at different altitudes. The main objective of the present study is to analyze the variation of glacier hydrochemistry and sedimentation processes at different altitudes. The results show that the bed sediments in higher altitude streams are fine sand, poorly sorted, leptokurtic in nature and dominated with high proportion of feldspar and biotite. At lower altitude, the bed sediment is coarse sand, moderately sorted and platykurtic in nature with relatively high proportion of quartz. The high concentration of biotite and feldspar in silt/lay size fraction are responsible for high proportion of magnesium in Gangotri proglacier meltwater than others. Meltwater is slightly acidic and hydrochemical facies shows Ca$^{+2}$–Mg$^{+2}$–HCO$_3^{-}$ type. The concentration of Ca$^{+2}$, Mg$^{+2}$, Na$^{+}$, and K$^{+}$ decreases with altitude due to dilution produced by augmentation of freshly monsoonal recharged groundwater from meadow and forest in downstream. The cation exchange, carbonate/silicate weathering and groundwater, subglacial water sources control the hydrochemistry of proglacial streams at lower altitude.

SARFARAZ AHMAD¹ ZABIULLAH ANSARI¹

1. Department of Geology, Aligargh Muslim University, Aligarh, India.

Published

22 August 2020

Manuscript received

18 March 2019

Manuscript revised

9 March 2020

Accepted

23 April 2020

Final version published online

18 August 2020