The influence of bedrock geology on glacier dynamics in the St. Elias Mountains, Yukon, Canada

• Main Author: Crompton, Jeffrey
• Format: Thesis
• Language: unknown
• Published: 2019
• Subjects: Yukon; Canada; glacier*
• Online Access: http://summit.sfu.ca/item/19478

Glacier surges are characterized by order-of-magnitude increases in flow that can be sustained for months to years, facilitated by a dramatic increase in basal water pressure that permits rapid sliding. An explanation for the non-random geographical distribution of surge-type glaciers and the underlying causes of surges remain the source of speculation. Glacier surges are dynamic end-members of glacier behaviour that showcase fundamental processes operating under all warm-based glaciers. Providing an explanation for the distribution and mechanisms of surging will allow us to better predict the role and responses of glaciers in a warming climate. The primary objective of this research is to understand the relationship between geological substrates and surge-type glaciers. A second objective is to understand the more general relationships between bedrock properties and the physical and chemical processes of glacial erosion. Using data from 11 surge-type and 9 non-surge-type glaciers in the St. Elias Mountains of Yukon, Canada, I investigate geological variables that represent system inputs, such as bedrock mineralogy and fracture characteristics, and system outputs such as meltwater chemistry and the grain size and mineralogy of proglacial river suspended sediments. I find that glacier surging is correlated with bedrock fracture spacing and the grain size of suspended sediments. I propose that bedrock fracture spacing controls the rate of clast production, and therefore the distribution of a clast-rich till-transition zone, which provides the excess friction necessary for the development of an ice reservoir prior to surging. Within a given climate envelope and mass-balance regime, this conceptual model can help to explain the geographical distribution of surge-type glaciers. Through a mineralogical analysis of electrically fragmented bedrock samples and proglacial suspended sediment samples, I observe that primary minerals are comminuted to sub-micron sizes, and grain rounding appears to be shaping medium-silt size grains and smaller. Finally, I find that chemical alteration of sediment and clay mineral precipitation could be mechanisms to explain the characteristically low silica in glacier meltwaters. Through this work, I have highlighted some of the ways in which the geological substrate can drive subglacial physical and chemical erosion and thus, glacier dynamics.