Date of Award

Summer 8-22-2019

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Earth Sciences

Advisor

Karl Kreutz

Second Committee Member

Ellyn Enderlin

Third Committee Member

Hester Jiskoot

Additional Committee Members

Luke Copland

Seth Campbell

Abstract

Glacier surges are short periodic episodes of rapid glacier flow that are driven by internal instabilities and bracketed by longer periods of slow flow. These glaciers are important to understand because they are vital to predicting future sea level rise, mitigating glacier hazards, and understanding basal glacial processes. Donjek Glacier, located in the Yukon, Canada has an unusually short and regular surge cycle, with eight surges identified since 1935 from aerial photographs and satellite imagery with a ~12 year repeat interval and ~2 year active phase. Recent surges occurred during a period of long-term negative mass balance and cumulative terminus retreat of 2.5 km since 1874. In contrast to previous work, we find that the constriction where the valley narrows and bedrock lithology changes, 21 km up-glacier of the terminus, represents the upper limit of surging, with negligible surface speed or elevation change up-glacier from this location. This positions the entire surge-type portion of the glacier in the ablation zone. The constriction geometry does not act as the dynamic balance line, which we consistently find at 8 km up-glacier from the glacier terminus. During the 2012–2014 surge, the average lowering rate in the lowest 21 km of the glacier was 9.6 m a-1, while during quiescence it was 1.0 m a-1. Due to reservoir zone refilling, the ablation zone has a positive geodetic balance in years immediately following a surge event. An active surge phase can result in a strong negative geodetic mass balance over the surge-type portion of the glacier. Potential links between climate and glacier surges are not well understood, but are required to enable prediction of glacier surges and mitigation of associated hazards. This thesis investigates the role of snow accumulation and atmospheric temperature on surge periodicity, glacier area changes, and surge initiation since the 1930s for Donjek Glacier. Three ice cores from Eclipse Icefield, at the head of the glacier, indicate that a total accumulation of 13.1 to 17.7 m w.e. of snow occurred in the 10-12 years between each of its last eight surges. This suggests that a threshold must be passed before the initiation of a surge event, although it remains unclear whether the relationship between cumulative snowfall and surging is due to the consistency in repeat surge interval and decadal average precipitation, or if it is indeed related to surging. The 1968 to 2017 climate record from Burwash Landing tests if there is a relationship between surge periodicity and an increase of 2.5°C in mean annual air temperature over this period. No such relationship was found, although each of the past 8 surge events has been less extensive than the previous, with the maximum terminus extent approximately 8 km2 smaller in the most recent 2012-2014 surge event than the ~1947 surge event.

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