Earth Sciences - Theses, Dissertations, and other Required Graduate Degree Essays

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Assessing the Risk of Saltwater Intrusion on the Gulf Islands, BC

Date created: 
2015-09-30
Abstract: 

In coastal regions, the quality of groundwater can be compromised due to saltwater intrusion (SWI) caused by various natural (sea level rise and storm surge) and anthropogenic (pumping) hazards. The goal of this research was to distinguish groundwaters impacted by SWI in the bedrock aquifers of the Gulf Islands, BC and identify thresholds for select chemical parameters that can be used for monitoring purposes, as well as to develop and test an approach for assessing risk to groundwater quality in coastal aquifers. The most reliable indicators were Cl/(HCO3 + CO3), BEX (base exchange index), Cl vs. EC, depth vs TDS, and a quantile analysis, resulting in 138 well samples (out of 795) that appear to be impacted by SWI. Based the 95th percentiles, for which 100% of the samples graphically showed strong evidence of SWI, the recommended threshold for Cl is 480 mg/L, 2,090 µS/cm for EC, and 970 mg/L for TDS. These samples were collected from wells that predominantly fall along the coastline. The vulnerability of the bedrock aquifers to SWI was assessed spatially by mapping hazards in combination with the aquifer susceptibility. Hazards due to pumping have the greatest influence on the vulnerability. Risk was evaluated spatially using an economic valuation of loss – here replacement of a water supply. The combination of chemical indicators and risk assessment maps are useful tools for identifying areas vulnerable to SWI, and these tools can be used to improve decision-making related to monitoring and community development for coastal areas.

Document type: 
Thesis
File(s): 
Senior supervisor: 
Diana Allen
Department: 
Science: Department of Earth Sciences
Thesis type: 
(Thesis) M.Sc.

Characterization of Brittle Damage in Rock from the Micro to Macro Scale

Author: 
Date created: 
2015-08-10
Abstract: 

An Increasing need for mining and constructing underground facilities at a greater depth and under high in-situ stresses have introduced new challenges in the form of brittle rock fracture. Brittle fracture is a complex mechanism comprising different stages of failure including initiation, propagation and coalescence. Brittle fracture studies in rock can be undertaken at a wide range of scales from the micro scale i.e. microcrack/grain scale in laboratory samples through the meso scale (underground excavations) to the macro scale such as in-situ engineered/natural rock slopes or block cave mines. At all these scales the rock/rock mass is subjected to “damage” which influences the engineering performance. Improved understanding of brittle damage at various scales requires development of damage intensity measures to quantify brittle fracture for both pre-existing and stress-induced fractures and the use of advanced numerical modelling approach. In this study, a state-of-the-art numerical modelling approach based on the combined finite/discrete element method (FDEM) is integrated with discrete fracture network engineering, DFNE, in order to evaluate brittle damage at varied scales. The influence of micro-heterogeneity is studied at the laboratory scale by incorporating a micro discrete fracture network (µDFN). A wide range of laboratory testing including Brazilian, uniaxial, biaxial and triaxial compression tests are modeled to investigated the complete 3D fracture process. At the meso scale, mechanisms leading to strain bursting and spalling damage around underground openings are studied focusing on the influence of pre-existing cracks in a massive rock mass. Finally at the macro scale, a finite/discrete element modelling approach coupled with a discrete fracture network (FDEM-DFN) is utilized to analyze the hanging wall surface subsidence associated with sub-level caving. A suite of model data interpretation methods including time-displacement hanging wall deformation characterization, numerical inverse velocity analysis and virtual hanging wall inclinometers is adopted to improve our understanding of the extent and mechanism of hanging wall failure with mine advance.

Document type: 
Thesis
File(s): 
Senior supervisor: 
Doug Stead
Department: 
Science: Department of Earth Sciences
Thesis type: 
(Thesis) Ph.D.

Characterization and Analysis of the Mitchell Creek Landslide: A Large-scale Rock Slope Instability in northwestern British Columbia

Date created: 
2014-08-13
Abstract: 

The Mitchell Creek Landslide (MCL) is a large, 74 Mm3, complex, active landslide located in the Coast Mountains of B.C. The slope is composed of foliated and hydrothermally altered volcanic-sedimentary rocks. The Mitchell Thrust and Brucejack faults constrain landslide geometry. Visible deformation initiated mid-20th century, coincident with rapid glacial retreat. This thesis presents results of a detailed characterization study which combines the results of geomorphological analysis, deformation feature mapping, and photogrammetric analysis of historic aerial photography from 1956, 1972, 1992, and 2010; geological and geomechanical borehole data; and geotechnical monitoring of landslide motion and groundwater conditions. Rates of movement vary spatially by geomorphological zone between 0.80 m/yr in the toe to 0.19 m/yr at the backscarp. Numerical modelling simulations were undertaken using continuum and discontinuum methods to evaluate failure mechanisms and landslide evolution. Glacier retreat, regional geology and rupture surface configuration were identified as the primary controls on landslide behaviour.

Document type: 
Thesis
File(s): 
Senior supervisor: 
Doug Stead
Department: 
Science: Department of Earth Sciences
Thesis type: 
(Thesis) M.Sc.

Geostatistical modeling and upscaling permeability for reservoir scale modeling in bioturbated, heterogeneous tight reservoir rock: Viking Fm, Provost Field, Alberta

Author: 
Date created: 
2015-08-13
Abstract: 

While burrow-affected permeability must be considered for characterizing reservoir flow, the marked variability generated at the bed/bedset scale makes bioturbated media difficult to model. Study of 28 cored wells of the Lower Cretaceous Viking Formation in the Provost Field, Alberta, Canada integrated sedimentologic and ichnologic features to define recurring hydrofacies possessing distinct permeability grades. Transition probability analysis was employed to model spatial variations in biogenically enhanced permeability at the bed/bedset scale. Results suggest that variations in permeability are strongly related to variations in hydrofacies rather than grain size. The variability in permeability at the bed/bedset scale was simplified by calculating an equivalent permeability that represents the thickness-weighted sum of permeability at the bed/bedset scale using expressions for layered media. Numerical block models were then generated for both the bed/bedset hydrofacies and the upscaled hydrofacies. Vertical and horizontal flows were simulated at both scales, and the volumetric flows in each direction were compared to verify the representativeness of the equivalent permeability. Vertical and horizontal flows simulated for bed/bedset scale and composite hydrofacies differ by less than +/-5%, suggesting that permeabilities at the bed/bedset scale can be simplified through upscaling. Reservoir-scale groundwater flow was simulated along a hydrogeological cross section comprised of the composite hydrofacies. The resulting flow regime was consistent with those simulated using permeability estimates from tight reservoir units of the Viking Formation. This approach may lead to improved reserve calculations, estimates of resource deliverability, and understanding of reservoir responses during recovery.

Document type: 
Thesis
Senior supervisor: 
James MacEachern
Diana Allen
Department: 
Science: Department of Earth Sciences
Thesis type: 
(Thesis) M.Sc.

Constraining accretion rates in a tide-dominated, freshwater river (Pitt River, Canada) and implications for lateral accretion of channels in the tidal-fluvial transition

Date created: 
2015-08-20
Abstract: 

A vibracore-based investigation of channel and floodplain deposits in the Pitt River Valley (PRV) was conducted to spatially and temporally confine the evolution of the PRV floodplain and the tide-dominated Pitt River. Sedimentological and ichnological assessment of cores is supplemented by geochronological and palynological analyses. The lateral migration rate of a Pitt River meander is quantified using Carbon-14 age dates of organic detritus at the base of a channel-margin core and the position of the core relative to the present-day channel profile. The Pitt River meander bar is shown to laterally migrate between 0.16 and 0.28 metres per year. A comparison of this rate to previous studies reveals that channels modulated by tides are capable of migrating at a rate equivalent to slowly meandering purely fluvial systems, and tidally affected channels migrate at less than 1.5% of the channel’s width each year.

Document type: 
Thesis
Senior supervisor: 
Shahin Dashtgard
Department: 
Science: Department of Earth Sciences
Thesis type: 
(Thesis) M.Sc.

Characterisation of High Rock Slopes using an Integrated Numerical Modelling - Remote Sensing Approach

Author: 
Date created: 
2015-08-18
Abstract: 

During the last decade significant advances have been made in geomechanical modelling and remote sensing data acquisition techniques. These developments have allowed for improved rock slope stability analysis through consideration of the role of brittle fracture, kinematics and spatial variability in discontinuities within numerical models. This thesis investigates the role of several key parameters including damage, failure surface geometry and kinematics in rock slope failure using both conceptual slope geometries and natural and engineered rock slopes. Investigation of bi-planar and ploughing failure mechanisms in footwall slopes using the hybrid FDEM code, ELFEN, highlights the role of both brittle fracture in the development of secondary release surfaces and rock mass dilation in facilitating the slope failure. The bi-planar models show development of a highly damaged transition zone between the active and passive blocks. This failure mechanism is also observed in pseudo-two-dimensional bi-planar simulations using Slope Model. Three-dimensional simulation of non-daylighting wedges using Slope Model shows that this type of wedge, although apparently kinematically stable may in practice fail through stress concentration at the slope toe leading to failure of rock bridges, toe-breakout and slope collapse. Long-range terrestrial photogrammetry was conducted of the north-east slope of the Delabole Quarry, Cornwall, UK. The photogrammetry model was used to characterize rock discontinuities and to develop a realistic 3D geometry for subsequent distinct element analysis using 3DEC. The effect of selected input parameters (discontinuity friction angle, spacing and persistence) on the stability of the quarry slope was investigated using a deterministic approach. A stochastic approach using discrete fracture networks (DFN) was also employed to investigate the role of discontinuity uncertainty and spatial variability on the failure mechanism of the quarry slope. The deterministic and stochastic 3DEC-DFN models highlighted the role of kinematics and spatial variability of discontinuity characteristics on the slope failure mechanism, size and shape of the failed blocks.Lattice spring 3D simulations (using Slope Model) of the 1963 Vajont Slide, a catastrophic landslide that resulted in the loss of 1910 lives, clearly emphasized the role of brittle fracture, kinematics, block size and raised groundwater level on the failure mechanism. The Slope Model simulations conducted represent the first 3D brittle fracture simulation of the landslide considering the effect of groundwater on the failure.Innovative data post processing techniques are introduced throughout the thesis and used to gain a better understanding of the failure mechanisms of the modeled rock slopes. Damage extent parameters (ellipse of damage in 2D and ellipsoid of damage in 3D) are introduced and used to characterize the extent of the damaged zone within the numerical simulations. Inverse numerical velocity is also adopted within this dissertation to determine the numerical onset-of-failure and to better understand the regressive and progressive failure stages within the model simulations.

Document type: 
Thesis
File(s): 
Senior supervisor: 
Doug Stead
Department: 
Science: Department of Earth Sciences
Thesis type: 
(Thesis) Ph.D.

Quaternary geology and drift prospecting in the Mount Polley region (NTS 093A)

Author: 
Date created: 
2015-03-25
Abstract: 

Drift prospecting studies were conducted in the Mount Polley Mine region, integrating surficial mapping, paleoflow measurements and Quaternary stratigraphy to infer glacial history. Eighty seven till samples were taken with the objective of determining the geochemical and mineralogical dispersal in till down-ice from Mount Polley. Surficial mapping identified till as the most abundant surficial material. Colluvium was mapped at high elevations and on steep slopes, and glaciofluvial and alluvial sediments are widespread in the river valleys. The stratigraphic record documents till associated with Fraser Glaciation followed by retreat phase glaciolacustrine and glaciofluvial sediments. Two distinct ice-flow movements have been identified; an initial west, southwestward flow during glacial advance, followed by a northwestward flow. The till sampling survey identified mineralized glacial dispersal up to 10 km to the northwest, Hg and Zn as pathfinder elements and apatite, andradite, chalcopyrite, epidote, gold grains and jarosite as porphyry indicator minerals (PIMs).

Document type: 
Thesis
Senior supervisor: 
Brent Ward
Department: 
Science:
Thesis type: 
(Thesis) M.Sc.

The evolution of the late Paleoproterozoic Wernecke Supergroup, Wernecke Mountains, Yukon, from sedimentation to deformation

Date created: 
2015-04-02
Abstract: 

The Wernecke Supergroup of Yukon is a metasedimentary succession deposited between ca. 1.66 and 1.60 Ga on the northwestern margin of ancestral North America (Laurentia). U-Pb detrital zircon geochronology, major and trace element geochemistry, and Nd isotope geochemistry reveal that the clastic sediments were derived mostly from collisional orogens that resulted from the amalgamation of Laurentia during Paleoproterozoic. Some detritus may have originated from non-North-American terranes such as eastern Australia or exotic arc terranes. Deposition of the Wernecke Supergroup occurred in a passive margin which resulted from the initial breakup of the supercontinent Columbia, and involved separation of northwestern Laurentia from adjacent continents, probably eastern Australia and the Yangtze craton of South China. This reconstruction is similar to the SWEAT configuration proposed for the Neoproterozoic supercontinent Rodinia. The Wernecke Supergroup was deformed at ca. 1.60 Ga by the Racklan orogeny which was accompanied by greenschist facies metamorphism, exhumation and erosion of the Wernecke Supergroup, and obduction of an exotic terrane, named Bonnetia, which was previously located offshore from the northwestern margin of Laurentia. The final stage of the Racklan orogeny was the result of the collision between eastern Australia and western Laurentia in another SWEAT-like configuration. The Racklan orogeny is regarded as part of a long orogenic belt which flanked the supercontinent Columbia at 1.65-1.60 Ga. This belt was developed on Amazonia, Baltica, eastern and southern Laurentia, East Antarctica, East Australia, and northwestern Laurentia. Following Racklan orogeny, a set of hydrothermal fluids intruded and brecciated the Wernecke Supergroup and caused collapse of fragments of the tectonically overlying Bonnetia. This hydrothermal event was responsible for the emplacement of iron oxide-copper-gold (IOCG) mineralization in the area, and is similar in age, and is possibly related to, IOCG deposits located in east Australia and South China.

Document type: 
Thesis
File(s): 
Senior supervisor: 
Derek Thorkelson
Department: 
Science:
Thesis type: 
(Thesis) Ph.D.

Pleistocene stratigraphy, glacial limits and paleoenvironments of White River and Silver Creek, southwest Yukon

Author: 
Date created: 
2014-09-26
Abstract: 

Quaternary glacial and non-glacial sediment exposed at White River and Silver Creek provide a record of environmental change in southwest Yukon for much of the late-Middle to Late Pleistocene. Eighteen sites at White River, located beyond the marine oxygen isotope stage (MIS) 2 glacial limit, contain thick accumulations of till, loess, peat, gravel and glaciolacustrine silt and clay, with tephras, paleosols, plant and insect macrofossils and large mammal fossils. Radiocarbon ages and eleven tephra beds constrain two tills to MIS 4 and 6. These tills correlate to the Gladstone and Reid glaciations and represent the penultimate and maximum all-time limits of the St. Elias lobe of the northern Cordilleran Ice Sheet. Two peat beds located between these tills indicate that interglacial conditions existed in the area during MIS 5e and 5a. Pond sediment deposited during mid-MIS 5 suggests that the sites were covered by an open birch tundra at this time. The MIS 3/2 transition was marked by a treeless, dry steppe-tundra populated by mammoth, horse and bison.The eleven Silver Creek sites, located ~200 km up-ice, contain a similar record of glacial and non-glacial sediment. Infrared-stimulated luminescence (IRSL) and radiocarbon dating constrain the glacial deposits at these sites to MIS 2, 4, either MIS 7 or 6, and to two Early to Middle Pleistocene, Pre-Reid glaciations. Tilting of glaciolacustrine beds of up to 1.9 mm/yr may be from uplift along the Denali fault since MIS 7. Pollen and macrofossils analyses from overlying MIS 3-aged sediment suggest that the environment was dominated by herbs and forbs, with few shrubs and almost no tree pollen at this time. Combined, the White River and Silver Creek sites contain a record of glacial and non-glacial conditions in southwest Yukon since the Middle Pleistocene.The glacial limits in southwest Yukon are markedly different from those in central Yukon. In southwest Yukon, the glacial limits are closely-spaced and were more extensive in the Middle to Late Pleistocene than in the Late Pliocene and Early Pleistocene. In central Yukon, glacial limits are separated by up to 300 km and were most extensive in the latest Pliocene and Early Pleistocene. This suggests that different forcing mechanisms controlled the extents of the St. Elias and Selwyn lobes during successive glaciations. Boundary conditions such as varying substrates, topography, moisture pathways and atmospheric circulation likely had a greater affect than tectonics and sea level on these glacial limits throughout the Plio-Pleistocene.

Document type: 
Thesis
Senior supervisor: 
Brent Ward
Department: 
Science:
Thesis type: 
(Thesis) Ph.D.

Earthquake Loss Estimates, Greater Victoria, British Columbia

Date created: 
2014-08-05
Abstract: 

I compare loss estimates for a range of earthquake scenarios and built environment models for municipalities in Greater Victoria, British Columbia, Canada, using Hazards United States Multi-Hazard version 2.1 (HAZUS) software. Best-estimate losses use region-specific site-condition maps and built-environment inventories updated with municipal assessment information for five scenarios representing subduction-interface, shallow-crustal, and in-slab earthquake types. Losses are higher for a major, near-source, shallow-crustal event than for larger magnitude, great subduction-interface earthquakes. Loss estimates differ by two to three orders of magnitude depending on the source scenario. Site-condition mapping and built-environment updates also significantly affect loss estimates (differences of up to 600% and 450%, respectively), depending on the scenario and loss metric under consideration.

Document type: 
Thesis
File(s): 
Senior supervisor: 
John Clague
Department: 
Science: Department of Earth Sciences
Thesis type: 
(Thesis) M.Sc.