Glacial Ice and Debris Interactions

Abstract

The work presented within this thesis is focussed upon the interactions between glacial ice and rock debris across the cryosphere; the melt rate of debris-covered ice, the formation of ice sails and the movement of meteorites through Antarctic blue ice have all been investigated. I numerically modelled the melt rate of debris-covered ice and found that the surface temperature of a debris layer can be used to estimate the melt rate of any underlying ice–even when the thermal properties of the debris layer are unknown. This potentially removes the need for the majority of expeditions as it means that it is feasible to predict the melt rate of a debris-covered glacier using data from satellites and weather stations alone. Ice sails are substantial clean ice melt features which can be over 45 m high, last for 50 to 100 years and are distinctively shaped with sloped, flat sides. Due to the rarity of their emergence they had, until now, seldom been studied. By combining a mathematical model, analysis of satellite imagery, a review of historical sightings, and analysis of both pictorial and first-hand evidence, we gained valuable insights into their formation, persistence and decline. We found that, in order for ice sails to emerge, a debris-covered glacier must exist at a high altitude, be only very gently sloped (so that the debris layer remains thin for a long time) and have patchy and uneven debris cover. Two thirds of all meteorite finds have been discovered in Antarctica, concentrated in blue ice areas called meteorite stranding zones. Of these, the vast majority are stony, with only 0.7% being classified as iron–almost eight times less than elsewhere. It was hypothesised by Evatt et al that this deficiency can be explained by a hidden layer of iron meteorites that are trapped roughly 40 cm below the surface of the ice (see Evatt et al, 2016). However, by considering both the three-dimensionality of the problem and by modelling the attenuation of solar radiation through blue ice in a detailed manner, I was able to use numerical modelling techniques to predict that most iron meteorites, as well as some of the larger stony ones, lie less than 10 cm below the surface of the ice. This is a significant difference that will make detection and retrieval far easier during future meteorite recovery missions.

Date of Award	1 Aug 2020
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Ian Abrahams (Supervisor) & Geoffrey Evatt (Supervisor)