An often overlooked factor in glacial ablation is the influence of supraglacial debris deposits, which can have both positive and negative effects. A critical thickness exists at which sub-debris ablation is equal to that of bare ice; debris will hinder ablation if it exceeds this thickness, and enhance it if its thickness is lower. The value of the critical thickness depends on various factors, including the physical properties of the debris. While the effects of such deposits have long been recognised, investigations into their contribution to ablation have mostly been limited to site-specific field studies, with the majority conducted in the northern hemisphere using non-volcanic deposits. Volcanic debris has differing physical properties and temporal and spatial distribution patterns to non-volcanic debris which should be considered when assessing their effects. There is a lack of information about the potential scale and distribution of supraglacial volcanic material. The influence of physical properties of such material on sub-debris ablation have not been systematically investigated in a laboratory setting, and the hazards and risks associated with cold volcanic supraglacial deposition have not been thoroughly assessed.
This thesis aims to address these knowledge gaps and provide an overview of the role of cold supraglacial deposits in glacial ablation. The potential extent and significance of cold supraglacial volcanic deposits is assessed, and a grading system applied to all known active volcanoes in order to indicate their ability to generate such deposits. Field experiments are carried out with results adding to the existing body of site-specific sub-debris ablation data, and contributing information for volcanic material, located in the southern hemisphere, in particular. The influences of individual debris properties are investigated in a laboratory environment, and the effects of volcanic material on ablation are related to hazardous scenarios which may arise due to such volcano-glacier interactions.