Date of Award

Spring 5-13-2017

Level of Access Assigned by Author

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Earth Sciences

Advisor

Karl Kreutz

Second Committee Member

Seth Campbell

Third Committee Member

Ellyn Enderlin

Abstract

Climatic warming causes different magnitudes of glacier retreat depending on

glacier size, location and time scales. Individually, a small mountain glacier like the

Cathedral Glacier in Northern British Columbia (BC) contains less than a millionth

of one percent of glacial ice in the world, but collectively the world’s small glaciers

contribute 10% of global glacial mass. Therefore, it is important to look at small

glaciers to better predict the contribution of glaciers to sea level rise. The demise of

small glaciers will reduce water resources in their vicinity. These glaciers will

disappear sooner than polar glaciers because they are found at generally lower

latitudes leading to higher ice temperatures, smaller thermal masses, smaller

accumulation area ratios and higher surface area to volume ratios. These factors

make them particularly sensitive to a changing climate. One major problem in

accurately assessing changes of small glaciers is that few have long-term

observations.

This project attempts to reconstruct volume change of Cathedral Glacier, a

small, north-facing cirque glacier in Northern British Columbia, Canada, using GPS

surveys and Structure from Motion (SfM) models made from photographs collected

between 1971 and 2015. The SfM technique uses offset, overlapping, unordered

images to construct a three dimensional model. From archive photographs, I

reconstructed three annual glacier surface models. I compared these models to a

topographic map from 1975, GPS surveys from 1999 and 2015, and a SfM model

from 2015. Digital elevation models made from the 1975 topographic map and the

2015 GPS survey indicate that the glacier surface lowered by an average of -23.5 m

over the 40 year period. The surface lowering was not uniform with the current

terminus being over 50 m lower than in 1975 but the upper reaches is within the

observational uncertainty and may have stayed the same or even thickened. The

area of Cathedral Glacier decreased from 1.67 km2 in 1975 to 1.20 km2 in 2015

(-28%) and lost an estimated 56.9 million cubic meters of ice. Glaciers melting in

the Yukon River watershed account for 40% of the summer discharge and 10% of

the annual discharge of the upper Yukon River.

Even though Cathedral Glacier has a more complete observational record than

the majority of small glaciers in the Yukon River watershed, the available data were

insufficient to develop an accurate time series for calculating area and volume loss.

Based on my analysis, the 2015 SfM model and 2015 GPS survey could be made

more useful with more GPS points as ground controls collected both on and off the

glacier. Numerous round control points (GCP) make SfM models more accurate. In

the area deglaciated since 1975, GCP would make the SfM model more accurate and

provide a comparison between 1975 and 2015. Although the SfM models did not

construct the detailed time series needed for high-resolution study, I gained better

understanding of the capabilities and limitations of SfM as well as its great

potential for future study of small glaciers and how their disappearance will effect

local water supplies and sea level rise.

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