In-situ and modelled debris thickness distribution on Panchi Nala Glacier (western Himalaya, India) and its impact on glacier state

This study presents extensive in-situ debris thickness measurements over the Panchi Nala Glacier (western Himalaya, India) and models its spatial distribution using remote sensing and ERA-5 reanalysis data. A rigorous comparison of in-situ and modelled debris thickness and a systematic assessment of its influence on glacier state (2000–2019) are also made. In-situ measurements reveal debris thickness ranging from 0 to 70 ± 0.25 cm. Modelled debris thickness ranges from 0 to 64 ± 1.75 cm. Debris thickness pattern is such that it increases from centre to margins and snout to upglacier. In-situ and modelled debris thickness show a good positive correlation (r = 0.73; p < 0.05). Further, the glacier-wide mass balance is −0.51 ± 0.09 m w.e./y. Modelled debris thickness showed a moderate positive correlation (r = 0.66; p < 0.05) with surface lowering, indicating reduced melt under thick debris. These moderate-to-good correlations in both cases can be ascribed to the inability of coarse resolution data to capture small supraglacial feature variations. Also, thicker debris over margins probably protected it, manifested through limited area loss (0.13 ± 0.2%/y) and snout retreat (5.9 ± 1.6 m/y). Results show higher thinning over the upper ablation zone (4725–4925 m asl) compared to the lower ablation zone (4546–4725 m asl), likely induced by typical debris distribution, has reduced the glacier-tongue's slope (6.7°). Gentle glacier-tongue in a negative mass balance regime with growing debris (0.3 ± 0.2%/y) has become conducive to supraglacial ponds and ice cliffs development, which now dominate ablation processes. Overall, the study presents crucial data on debris thickness and provides vital insights into glacier evolution.