Ablation Patterns of the Debris Covered Tongue of Halong Glacier Revealed by Short Term Unmanned Aerial Vehicle Surveys

Wanqin Guo,Liqun Chen,Donghui Shangguan,Xiaojun Guo,Yushuo Liu,Jin Ga,Jing Li

doi:10.3389/feart.2021.740160

Abstract

Debris-covered glaciers are an important glacier type and have attracted more and more attention. This study presents the results of ablation patterns of debris-covered tongue of the Halong Glacier in the northeastern Tibetan Plateau, by using two repeated unmanned aerial vehicle (UAV) surveys performed on August 11 and September 15, 2019. The results show that the tongue of Halong Glacier has experienced strong ablation during the surveyed period, with an overall ice loss amount to 4.17 × 105 metric tons. Among all the briefly classified surface types, supraglacial debris has the largest area (80.9%) and also mass losses (58.6%) comparing to others. However, ice cliffs show the strongest and the most significant ablation rates (averagely 1.36 and 1.22 m w.e. for supraglacial and lateral ice cliffs, respectively), followed by clean ice regions (1.01 m w.e.). The backwastes of ice cliffs also resulted in up to 7.8 m horizontal back-off at different parts of Halong Glacier, lead to fast terminal retreat and narrowing down of the glacier tongue, and may result in the break off of Halong Glacier tongue into separated parts in the future. The surface ablation rates show a clear negative exponential relationship with the measured debris thicknesses, well in accordance with previous studies. Regions in cutting and flushing by supraglacial and lateral rivers have the largest surface elevation decreases but are not significant due to their limited area and the relatively lower quality of UAV digital surface models (DSMs) in those covered regions.

Highlights

Debris-covered glaciers are one of the major types of glaciers worldwide, which are covered by varying extents and thicknesses of debris formed by different sources of sediments with diverse grain sizes (Bozhinskiy et al, 1986)
It clearly illustrated the strong ablation of Halong Glacier between August 11 and September 15, 2019
Our study shows that the overall mass loss between August 11 and September 15 in 2019 among the surveyed region of Halong Glacier is 417,158 tons w. e., in which 58.6%, 21.9%, 16.3% happened on regions covered by debris, clean ice, and ice cliffs, respectively

Summary

Introduction

Debris-covered glaciers are one of the major types of glaciers worldwide, which are covered by varying extents and thicknesses of debris formed by different sources of sediments with diverse grain sizes (Bozhinskiy et al, 1986). Like clean-ice glaciers, it was proved that debris-covered glaciers experienced dramatic mass losses in response to the warming climate (e.g., Glasser et al, 2016; Pratibha and Kulkarni, 2018). Some studies have further illustrated that the debris-covered glaciers have a similar magnitude of mass loss with adjacent clean-ice glaciers, leading to a so-called “debris-cover anomaly” (Pellicciotti et al, 2015; Vincent et al, 2016; Salerno et al, 2017). Large discrepancies still exist in the knowledge acquired on the evolutions of debris-covered glaciers and their disparities with clean-ice glaciers, in which the limited accuracies and large inconsistencies of the data (in-situ observations versus remote sensing techniques) used in those studies is one major reason

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