Surface facies analysis of the Gangotri and neighbouring glaciers, central Himalaya

Abstract

Glaciers are primarily monitored using medium-to-high resolution satellite data, undermining the potential of coarse-resolution data. In pursuance of this, high resolution 10 m super-resolved glacier maps derived from 56 m coarse-resolution AWiFS data are applied here to assess the facies, firn-line altitude, and frontal variations of the Gangotri and neighbouring glaciers, central Himalaya between 2005 and 2017. The wet and warming trends estimated over the study area appear to have caused excess firn (56.53 ± 6.22%) and ice (27.50 ± 3.03%) melting, contributing to the significant progression in fresh and slightly metamorphosed snow (12.09 ± 1.33%), wet-snow (21.79 ± 2.40%), ice-mixed debris (9.24 ± 1.02%) and supraglacial debris (2.49 ± 0.27%) during 2005–2016. Mean firn-line of the study glaciers has ascended from 5327 ± 23 m to 5376 ± 24 m at an average rate of 3.44 ± 0.45 m a⁻¹ during 2005–2016. Mean firn-line altitude ascent is the highest for the sparsely debris-covered (<10% debris) Arwa glacier followed by the extensively debris-covered (≥35% debris) Gangotri, Bhagirathi-Kharak and Satopanth glaciers. Contrastively, the moderately debris-covered (17–29% debris) Raktvarn and Chaturangi glaciers show slight variations in their mean firn-line altitudes. These firn-line variations are governed by the rising average annual temperature, glacier size and predominant glacier facie. All the glaciers show an overall tendency of termini retreat at variable rates during 2005–2017. The highest retreat rate is estimated for the Gangotri glacier (12.01 ± standard deviation: 8.16 m a⁻¹) followed by Chaturangi (7.97 ± 5.79 m a⁻¹), Bhagirathi-Kharak (5.99 ± 9.26 m a⁻¹), Raktvarn (3.28 ± 2.28 m a⁻¹), Satopanth (1.89 ± 2.87 m a⁻¹), and Arwa (0.85 ± 1.90 m a⁻¹) glaciers. These retreat rates vary significantly with the exclusion of static points in the retreat estimation, revealing its subjective nature. The temporal facies maps obtained here have the potential for the hydrological modelling of meltwater production of the study glaciers.