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

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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.

Contemporary subsidence and settlement of the Fraser River delta inferred from SqueeSAR(TM)-type InSAR data

Author: 
Date created: 
2014-12-02
Abstract: 

The Fraser River delta in southwestern British Columbia formed over the past 10 000 years and currently supports a population of about 250 000 people. This research focuses on the urbanized and rapidly expanding Richmond area of the Fraser River delta. Dyking, which began in the early 1900s, has prevented flooding and sediment deposition, with the result that the delta plain is subsiding at an average rate of 1-2 mm/a due to the slow, natural consolidation of thick Holocene sediment. Localized higher rates of subsidence stem from anthropogenic sources, notably the application of loads in construction. InSAR data was used to relate load-induced settlement to geology and the spatial and temporal pattern of urbanization. All displacement rates 10 mm/a or more are associated with industrial or large commercial structures. Similar amounts of total settlement are observed from similar sized loads, yet rates of settlement differ, indicating that while load is important in determining total settlement, lithology is as important as load in determining rates of settlement. Holocene sediments underlying the delta are water-saturated, porous, fine sand, silty sand, silt. They are compressible to considerable depth and can experience significant settlement when subjected to structural loads, dewatering, or seismic shaking. No relationship between subsidence rate and surface geology was observed, although surface settlements are generally removed prior to construction. There is an insufficient amount of subsurface data to disentangle lithology and sediment thickness effects. A weak relationship between Holocene thickness and displacement rate has been observed for commercial sized buildings in eastern Richmond with an increase of 0.95 mm/a in the displacement rate for every 100 m of sediment thickness. A weak logarithmic relationship was also observed for the entire RADARSAT dataset.

Document type: 
Thesis
Senior supervisor: 
John Clague
Department: 
Science:
Thesis type: 
(Thesis) M.Sc.

Applications of Uncertainty Theory to Rock Mechanics and Geotechnical Mine Design

Author: 
Date created: 
2015-01-07
Abstract: 

Uncertainty analysis remains at the forefront of geotechnical design, due to the predictive nature of the applied discipline. Designs must be analysed within a reliability-based framework, such that inherent risks are demonstrated to decision makers. This research explores this paradigm in three important areas of geotechnical design; namely, continuum, Discrete Fracture Network (DFN) and discontinuum modelling. Continuum modelling examined the negative effects of ignoring spatial heterogeneity on model prediction. This was conducted through the stochastic modelling of spatial heterogeneities found within a large open pit mine slope. DFN analysis introduced a novel approach to fracture generation to solve issues associated with the incorporation of traditional DFNs into geomechanical simulation models. Finally, discontinuum modelling explored the inherent mesh dependencies that exist in UDEC grain boundary models (UDEC-GBM). Conclusions suggest that a transition is required from deterministic to uncertainty based design practices within the geotechnical discipline.

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

Characterizing Groundwater - Surface Water Interactions within a Mountain to Ocean Watershed, Lake Cowichan, British Columbia

Author: 
Date created: 
2014-11-19
Abstract: 

Watersheds located within a mountain to coast physiographic setting have been described as having a highly inter-connected surface water and groundwater environment. The quantification of groundwater-surface water interactions at the watershed scale requires upscaling. This study uses MIKE SHE, a coupled numerical model, to explore the seasonally and spatially dynamic nature of these interactions in the Cowichan Watershed on Vancouver Island, British Columbia, Canada. The hydrostratigraphy of the watershed is constructed using several datasets, including electrical resistivity tomography data. The calibrated model simulates a transition of the Cowichan River from mostly gaining within the valley, to losing stream near the coast where groundwater extraction is focused. Losing and gaining sections correlate with geological substrate. Recharge across the watershed accounts for 17% of precipitation. Climate change is projected to lessen snowpack accumulation in the high alpine and alter timing of snowmelt, resulting in higher spring river discharge and lower summer flows.

Document type: 
Thesis
File(s): 
Senior supervisor: 
Diana M. Allen
Dirk Kirste
Department: 
Science:
Thesis type: 
(Thesis) M.Sc.

Risk to water security on small islands: a numerical modeling approach

Date created: 
2014-12-08
Abstract: 

The aim of this research is to characterise risk to water security for small islands. This is achieved by modeling the spatial and temporal impact from major stressors affecting water resources on small islands, and then evaluating the risk to water security through an integrated assessment framework. Numerical density-dependent flow and transport modeling is used to evaluate the response of the freshwater lens on Andros Island in The Bahamas to various climate change and human stressors including: sea level rise, changes in recharge, and increased pumping. SEAWAT models showed a reduction of freshwater lens volume by up to 24% under projected sea level rise and reduced recharge. The response time of the freshwater lens increased with stressor magnitude, resulting in a longer lens adjustment period. In addition, greater upconing was observed for pumping scenarios simulated under projected climate change conditions than under current conditions. The impact of a 2004 storm overwash event on Andros Island was simulated using HydroGeosphere. Results show that potable water is restored one month sooner when timely remedial actions are implemented; however, if delayed by four days or more, there is no improvement in recovery time. To extend the research more broadly, simulations of overwash for various island types observed worldwide were conducted. Dominant factors affecting freshwater lens response include vadose zone thickness and geologic heterogeneity, such as low or high permeability zones, whereas the dominant factor affecting freshwater lens recovery is recharge rate. A framework to characterise risk to water security was developed specific to an island hydrogeological setting. A freshwater lens susceptibility map was generated using the results of the numerical modeling. Hazard threats from climate change and human stressors (derived from numerical modeling and a land-use survey) were overlaid on the susceptibility map to represent vulnerability. Combining vulnerability with loss (or consequence) yielded a risk to water security map. High risk areas are largely concentrated within the developed areas near high chemical hazard activities, as well as along portions of the coastline. These maps were provided to local partners to inform water management policies and raise awareness about factors impacting water security.

Document type: 
Thesis
File(s): 
Senior supervisor: 
Diana Allen
Department: 
Science:
Thesis type: 
(Thesis) Ph.D.