The role of glacier structures in the degradation of debris-covered glaciers.

Crynodeb

Glaciers in High Mountain Asia (HMA) are in a state of rapid decline, attributed to climatic changes at an intra-regional scale. Mass loss from glaciers in the region occurs in the form of the thinning and recession of glacier tongues, formation and coalescence of supraglacial ponds, and a growth in the size and number of glacial lakes, leading to a stagnation in glacier flow speed. Despite the stagnation and surface lowering of many HMA glaciers, glacier structures are thought to persist both in the current glacier and in ice masses separated from the glacier. As of yet, the role of these structures in the degradation of these landform is largely unexplored. This can be examined in two key areas. First, at current lake-terminating glaciers, in which there have been numerous efforts to quantify the size and rate of expansion of the associated glacial lakes. However, the role glacier structures plays in influencing the rate and pattern of recession at the icefront has yet to be investigated. Here, detailed analysis of the pattern of icefront recession and the locations of glacier structures reveals the influence of transverse structures on dictating icefront morphology and of flow unit boundaries as zones of mechanically weaker ice, more readily exploited during calving processes. Second, the role of glacier structures can be considered in the development of glacial lake dams, suspected to contain dead ice. These lake dams are highly researched, with a focus on the hazard they pose from Glacial Lake Outburst Floods (GLOFs). The relative importance of the susceptibility of a glacial lake dam to a GLOF is commonly misunderstood, with a focus primarily on lake size, often failing to consider glaciological influences on the dam. Many of these dams, suspected to contain dead ice were previous glacier termini and thus may contain relict glacier structures that will affect dam morphological development. From analysis of remotely sensed data, there is a clear pattern from comparison of current and historical imagery showing a concurrence in the positions of hydrological pathways and prior glacier structure positions, inferring that these areas are more readily exploited for erosion and are key in the morphological development of the dam. Structures within debriscovered ice masses are investigated further via the use of Ground Penetrating Radar to develop a robust framework for investigation of ice volume and glacier structures within debris-covered ice masses in a high mountain environment. First, via a detailed study on an Alpine debris-covered glacier in which debris thickness, ice thickness and internal structures were imaged. This study led to further development of the methods with considerations as to the effects of complex topography and debris cover on radio
wave transmission. Second, via the investigation and quantification of units of buried ice within a rock glacier, situated in HMA, yielding the first geophysical data from a rock glacier in this region. The integration and comparison of these remotely sensed and geophysical datasets within this thesis points to a clear pattern of glacier structures being exploited for erosion in both current glaciers and dead ice contained within glacial lake dams.

Dyddiad Dyfarnu	2023
Iaith wreiddiol	Saesneg
Sefydliad Dyfarnu	Prifysgol Aberystwyth
Goruchwyliwr	Neil Glasser (Goruchwylydd) & Tom Holt (Goruchwylydd)