The Impact of the Mount Polley Tailings Pond Failure on the Sedimentary Record of Quesnel Lake, British Columbia By Ayana Aden A thesis submitted in conformity with the requirements for the degree of Master of Science Department of Geography and Planning University of Toronto © Copyright by Ayana Aden, 2018 The Impact of the Mount Polley Tailings Pond Failure on the Sedimentary Record of Quesnel Lake, British Columbia Ayana Aden Master of Science Department of Geography and Planning University of Toronto 2018 Abstract The Mount Polley tailings pond failure that occurred on August 4, 2014 provided an opportunity to understand the effects of point-source sedimentation events in the sedimentary record. Six sediment cores that were taken at both distal and proximal locations in Quesnel Lake (B.C.) were used to identify if turbidity currents or subaqueous debris flows were generated. Geotechnical (grain size and LOI), mineralogical and copper metal concentrations confirmed the presence of turbidite deposits in four cores. All of these turbidites contained a coarser-grained base and an uppermost fine-grained cap. Two out of the four turbidite deposits that were most proximal to the spill mouth contained mixed basal layers that may signify the energy of the current at that depth. Sediment is focused in the deepest part of the basin. The spill sediments will compress over time but will represent sedimentation rates at 4-5 orders of magnitude larger than Holocene natural rates. ii Acknowledgments I would first like to thank Dr. Joseph R. Desloges for giving me the opportunity to complete my M.Sc research under his supervision. The compassion and patience he has shown me throughout this trying process has given me the courage to complete this thesis with as much diligence as I could muster. The following people have provided me with support on analysis, field work, and other resources: Dr. Ellen Petticrew and Dr. Phil Owens of the Quesnel River Research Centre, Mr. Sam Albers, Mr. Laszlo Enyedy and Ms. Kristy Rasmus while field work was conducted, Dr. Eduard Reinhart at McMaster for allowing me to use the ITRAX core scanner, Dr. Sarah Finkelstein for accommodations in using her lab space, George Kretschmann and Yanan Liu in the Earth Sciences department for microprobe analysis and Yining Wang for her assistance with laboratory analysis. I also want to thank Dr. Mathew Wells and Dr. Danny Harvey for serving on my committee and for their insightful comments. To my family: my mother, father and brothers, who have listened to my woes, assisted me both financially and mentally, and believed in me during times of hardship, the thought of you encouraged me to push through and I thank you for believing in me. To my friends who have listened to my endless complaining, who gave me a shoulder to cry on, and for encouraging me when I felt frustrated, thank you for your support. iii Table of Contents Acknowledgments ....................................................................................................................................................... iiii Table of Contents ......................................................................................................................................................... iv List of Tables ................................................................................................................................................................. vi List of Figures ............................................................................................................................................................... vii Chapter 1 ......................................................................................................................................................................1 1.1 Introduction ............................................................................................................................................................1 1.2 The problem: Mount Polley tailings pond failure .................................................................................................... 2 Chapter 2 ....................................................................................................................................................................... 4 2.1 Introduction ............................................................................................................................................................. 4 2.2 Lake classifications................................................................................................................................................... 4 2.2.1 Thermal stratification and sediment distribution ......................................................................................... 5 2.2.2 Turbidity currents and subaqueous debris flows – differences and similarities ........................................ 13 2.2.3 Geostrophic forces ...................................................................................................................................... 16 2.3 Sedimentary environments and records of lakes .................................................................................................. 17 2.3.1 Sediment focusing ...................................................................................................................................... 17 2.3.2 Flocculation, diagenesis .............................................................................................................................. 18 2.4 Research objectives ............................................................................................................................................... 20 Chapter 3 ..................................................................................................................................................................... 21 3.1 Introduction ........................................................................................................................................................... 21 3.2 Cariboo Region ...................................................................................................................................................... 21 3.2.1 Climate ........................................................................................................................................................ 21 3.2.2 Regional Geology ........................................................................................................................................ 21 3.3 Quesnel Lake – Physical description and hydrology .............................................................................................. 22 3.4 The Mount Polley tailings spill: failure of the tailings pond .................................................................................. 25 Chapter 4 ..................................................................................................................................................................... 27 4.1 Introduction ........................................................................................................................................................... 27 4.2 Field Methods ........................................................................................................................................................ 27 4.2.1 Sediment cores ........................................................................................................................................... 27 4.3 Laboratory methods .............................................................................................................................................. 28 4.4 Laboratory Analysis ............................................................................................................................................... 28 4.4.1 Subsample protocol .................................................................................................................................... 28 4.4.2 Loss on ignition ........................................................................................................................................... 29 4.4.3 Grain size analysis ....................................................................................................................................... 30 4.4.4 ITRAX scanner – XRF, magnetic susceptibility ............................................................................................ 31 4.4.5 Microprobe analysis ................................................................................................................................... 32 4.4.6 Metals analysis ........................................................................................................................................... 33 iv Chapte r 5 ..................................................................................................................................................................... 34 5.1 Introduction ........................................................................................................................................................... 34 5.2 Pre-spill sedimentation processes observed in Quesnel Lake ............................................................................... 37 5.2.1 The sedimentary environment and pre-spill state of the water column, in the west arm of Quesnel Lake ............................................................................................................................................................................