The changes of Hailuogou Glacier in the Southeastern Tibetan Plateau and the impacts on glacier dynamics from the mechanical ablation

Abstract

Glaciers in the Tibetan Plateau are melting at an unprecedented rate in the context of global warming. As the critical resources of fresh water, the recession and continuous negative mass balance of glaciers have induced local, regional, or even global issues (e.g., water shortages, glacial lake outbursts, mudslides, and sea level rise).
Hailuogou (HLG) Glacier, a typical partly debris-covered temperate valley glacier in the southeastern margin of the Tibetan Plateau, has been experiencing rapid receding in recent two decades. The terminus of HLG Glacier has been becoming highly crevassed and fractured, which can be described as the glacier losing mass through frontal mechanical ablation induced by the intensive interaction between glacier ice and water (e.g., collapsing and calving). The frontal mechanical ablations partly control the dynamics of the glacier terminus and even might have negative impacts on the entire glacier, for which the quantification of these is critical for improving the understanding of future projections of HLG Glacier.
This thesis presents three major components: 1) the outcomes of nine field trips to HLG Glacier terminus/tongue, including aerial images, ground control points from Real-time kinematic positioning (RTK) and field surveying. Based on the datasets captured from field trips, orthophoto mosaics and digital surface models are generated by using Uncrewed Aerial Vehicle (UAV) images and the algorithm of Structure from Motion with Multiple View Stereo (SfM-MVS). Then, quantitively investigation on mechanical ablations at the glacier terminus was conducted through geomorphological mapping, Digital Eelevation Model (DEM) of Difference (DoD), and digital image correlation (DIC) to derive the landform changes in the glacier terminus area, the ice volume changes of glacier terminus and the glacier surface displacements, respectively. 2) This thesis also provides four comprehensive time-sequenced landform maps for the entire/partly HLG Glacier tongue from 2018 to 2021 showing the detailed evolution of glacier changes as the ice recedes, including geomorphological, hydrological, and glaciological features. 3) Photogrammetrically satellite-based stereopsis (ASTER-based stereophotogrammetry) and daily updated high-resolution images (PlanetScope imagery) are used to derive the multiple-year DEMs and glacier extents from 2002 to 2021, respectively. Thus, the ice volume changes and corresponding mass balance changes are then estimated, quantitively illustrating the dynamic evolution s of HLG Glacier for the recent two decades. Combined with the rough estimation of ice volume change attributed to the mechanical ablation, the contribution of mechanical ablation to the overall mass balance change is then calculated.
The main findings are that 1) the dynamics of the glacier have changed by interpreting the mapped features from 2018 to 2021. The glacier is in the process of rapid recession, and even possible disintegration. 2) By analysing the UAV-derived datasets between 2017 to 2020, the HLG Glacier experienced a severe recession as evident by the reduction of the terminal area, the retreat of the terminus position, and reduce of ice volume at the glacier terminus. The margin of the glacier terminus retreated - 132.12 m and in the area affected by the ice collapse events retreated – 236.42 m. The overall ice loss is - 184.61 ± 10.32 × 10⁴ m³, within which the volume change induced by the ice collapse events comprises roughly 28%. 3) Comparisons between multitemporal DEMs derived from ASTER-based stereophotogrammetry indicate that the mass balance of the entire HLG Glacier is - 12.60 ± 0.89 metre water equivalent (m w.e.) with 19 years from 2002 to 2021 and the annual mean ice mass change is - 0.66 ± 0.05 m w.e.. The annual average is 1.5 times higher than the period of 1968 to 2000 (i.e., 32 years). HLG Glacier has undergone negative mass balance for several decades and the mass loss has been accelerating in the most recent 20 years. 4) The contribution to the mass balance change of the entire glacier that is attributed to frontal ice collapse is limited (i.e., ranges from 0.48% to 1.12% from 2017 to 2021). However, the mechanical ablation (e.g., frontal ice collapse and subglacial/englacial conduit’s roof collapse) has changed the glacier dynamics and the way of losing ice mass to some extent.
The processes of thinning-retreating with extensive mechanical ablation (i.e., frontal ice collapsing-ablation) in HLG Glacier terminus are important to improve the understanding of this form of ice loss from mechanical ablating margins at valley glaciers. Investigations into this with UAVs, optical satellite images, stereophotogrammetry, and alternatively supportive meteorological data provide insights into the glacier changes and impacts of frontal mechanical ablation events via different scales. The results of this thesis not only contribute to the recent changes of HLG Glacier and its projected dynamics, but also the mechanical ablation of the valley glacier and the forecasting of changes in regional glacierized areas.

Date of Award	Jul 2023
Original language	English
Awarding Institution	University of Nottingham
Supervisor	Ping Fu (Supervisor), Meili Feng (Supervisor), Stuart Marsh (Supervisor) & Duncan Quincey (Supervisor)