Modelling melt beneath supraglacial debris : implications for the climatic response of debris-covered glaciers

Glaciers--Environmental aspects;Thawing--Mathematical models;Mass budget (Geophysics);Meltwater

Nicholson, Lindsey ; Benn, Douglas I. ; Benn, Douglas I.

University:University of St Andrews

Department:Earth & Environmental Sciences and Geography & Sustainable Development (Schools of)

关键词: Glaciers--Environmental aspects;    Thawing--Mathematical models;    Mass budget (Geophysics);    Meltwater;   

Others  :  https://research-repository.st-andrews.ac.uk/bitstream/handle/10023/10264/LindseyNicholsonPhDThesis.pdf?sequence=2&isAllowed=y

来源: DR-NTU

【 摘 要 】

Understanding how debris-covered glaciers respond to climate is necessary in order toevaluate future water resources and glacier flood hazard potential, and to make sense of theglacier chronology in mountain regions, In order achieve this, it is necessary to improve thecurrent understanding of how surface debris affects glacier ablation rate, and to developmethods by which the ablation of debris-covered glaciers can be predicted under variousclimatic scenarios.This thesis develops a numerical surface energy balance model that uses simplemeteorological data to calculate melt beneath a debris layer of given thickness and thermalcharacteristics. Field data from three contrasting sites demonstrate that the assumptionsmade within the model concerning the thermal properties of supraglacial debris are validduring most ablation conditions and that model performance is considerably better thanprevious models.Model results indicate that the effect of debris on melt rate is highly dependent onmeteorological conditions. Under colder climates, thin debris can accelerate ice melt byextending the ablation period at both diurnal and seasonal scales. However, in milder mid-summer conditions, even a very thin debris cover inhibits melt rate compared to that ofexposed ice.The new melt model is applied to produce the first quantified ablation gradients for debris-covered glaciers, and to model the evolution of ice surfaces under a debris layer of variablethickness. Modelled ablation gradients are qualitatively similar to hypothetical ones outlinedpreviously, and quantitatively similar to those measured in the field. The ablation gradientsare used to explore the factors affecting the response of debris-covered glaciers to climatechange. Beneath a debris layer of variable thickness, the melt model produced ablationtopography, as observed in the field, which underwent topographic inversion over time inresponse to debris redistribution. Debris thickness variability was found to cause calculatedablation rate to increase compared to that calculated using a mean debris thickness by one totwo orders of magnitude, suggesting that melt calculations made on the basis of spatiallyaveraged debris thickness may be inaccurate.