Five major units were mapped in shoreline exposures of the Coast Plutonic Complex adjacent to Douglas, Sue and Loretta Channels: 1) paragneiss and migmatite of the Central Gneiss Complex, 2) quartz-biotite schist, amphibolite, quartzite,and marble of the Metasedimentary Rocks, 3) quartz diorite and quartz monzonite of the Kitkiata pluton, 4) granodiorite of the Quottoon pluton and 5) Agmatite, composed of early xenoliths of banded metamorphic rock, middle stage intrusions of granitic rock, and late pegmatite, aplite and lamprophyre dikes. Pressure estimates of 7 ± 1 kb for this part of the Coast Mountains are arrived at from the stable assemblages in a kyanite-staurolite schist, and by comparison with pressures published for areas along strike to the north. Amphibolites provide a low temperature estimate o f 550°C. Calcsilicate assemblages place the high temperature limit of metamorphism between 560 and 660°C at 5 kb. Elevated pressures would increase temperature somewhat. The area is structurally characterized by a well developed, steeply dipping foliation that strikes northwest, widespread isoclinal folds with axial plane foliation parallel to regional foliation, and a moderate to steeply plunging fold axis lineation. Interference structures show that the abundant isoclinal folds deform earlier approximately northeast-trending folds. Later tight to isoclinal folds deform the regional foliation. Metamorphic recrystallization outlasted deformation. The Kitkiata pluton has an initial ⁸⁷Sr/⁸⁶Sr ratio of 0.7042 to 0.7043, depending on its age. One radiogenic Sr-rich sample gives a model date of 165 ± 11 Ma, but the possibility of anomalous initial ⁸⁷Sr/⁸⁶Sr ratio makes this result highly uncertain. The Quottoon pluton gives a whole-rock isochron of 51 ± 2 Ma with 0.7045 ± 1 initial ratio. The low initial ratios indicate a preponderance of mantle-derived magma of Mesozoic or early Cenozoic age in the plutons studied. Sr isotopic composition of the Central Gneiss Complex is compatible with late Paleozoic-early Mesozoic ages for precursor detrital and volcanic strata and local presence of marine carbonate with moderately enriched ⁸⁷Sr/⁸⁶Sr. The generally low radiogenic Sr content of these core gneisses rules out an origin by remobilization of greatly older rocks. Plutons of the Coast Plutonic Complex may have been generated by partial melting of the Central Gneiss Complex, and emplaced not far from their source of origin during regional metamorphism, as the surrounding rocks cooled from maximum temperature and pressure of metamorphism. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

In the British Columbia Coast Mountains most dendroclimatological and dendroglaciological studies have focused on developing insights from tree‐ring sites located in the southern and central regions. By contrast relatively few studies have been conducted in the northwestern Coast Mountains, where exploratory studies reveal that significant climate‐radial growth relationships exist. The purpose of this study was to develop a proxy record of climate change from tree rings and to reconstruct the late Holocene glacial history of two outlet glaciers spilling eastward from th e Cambria Icefield. Dendroclimate investigations were conducted using mountain hemlock (Tsuga mertensiana) trees growing on three high‐elevation montane slopes. The three stands located along a 35 km transect cross date to form a master chronology for the region spanning 409 years (1596 to 2007 A.D.). Correlation analyses show that the radial growth of the regional tree‐ring chronology corresponds to variations in the mean June‐July‐August (JJA) air temperature. The relationship between the two variables was used to reconstruct mean JJA air temperature from 1680 to 2007 A.D.). The reconstruction illustrates warm and cool intervals that are synchronous ito those derived from other paleoenvironmental research in this region. The proxy record also highlights annual to inter‐decadal climate variability likely resulting from atmospheric‐ocean circulation patterns described by the El Niño‐Southern Oscillat ion and the Pacific Decadal Oscillation. The late Holocene behaviour of White and South Flat glaciers was investigated using radiocarbon dating techniques, dendrochronological cross‐dating techniques and geomorphological analysis of sedimentary units within the White and South Flat glacier forefields. Evidence for a First Millennial Advance (FMA) cumulating around 650 A.D. and early Little Ice Age (LIA) advances at 1200 and 1400 A.D. were documented. These advances are contemporaneous with the late Holocene activity of glaciers throughout the region, suggesting coherent broad‐scale climate forcing mechanisms have influence glacial mass balance regimes over at least the last two millennia. The dendroclimatological and dendroglaciological findings of the study provide the first annually‐resolved climate record for the region and help to enhance our understanding of late‐Holocene glacier behaviour in the Cambria Icefield Area. The thesis documents the complex interactions between climate and the radial growth of mountain hemlock trees in the Pacific Northwest, and describes the role that long‐term climate variability played in glacier dynamics during the FMA and LIA. / Graduate

Fission track dating of zircon and apatite has been used to determine the Cenozoic uplift history of the British Columbia Coast Mountains from 50°-55°N. 115 dates were obtained from rocks of variable geographic location and altitude, and the resulting date pattern constrains the movement and deformation of the fission track retention isotherms (175°C for zircon, 105°C for apatite) within the crust. Because date-altitude correlations (apparent uplift rates) cannot always be used confidently to estimate actual rates of uplift, a finite difference numerical scheme was formulated to construct models of heat flow, uplift, denudation, and cooling that satisfy not only fission track dates, but also present heat flow, other isotopic dates, geologic considerations, and fission track-derived estimates of paleo-geothermal gradient. In most cases, apparent uplift rates derived from apatite date-altitude correlations are very close to modeled rates of uplift. Zircon-derived apparent rates, however, often exceed modeled rates and reflect post-orogenic cooling a,nd relaxation of isotherms. The relationship of the movement of isotherms to rates of uplift and fission track-derived apparent uplift rates is quantified and discussed. Orogenic rapid cooling and uplift occurred from Cretaceous to Eocene time in most of the Coast Mountains. Rates during orogenic uplift were near 1.0 km/Ma, causing setting of K-Ar clocks in biotite and hornblende. Uplift rates during the middle Cenozoic ranged from 0.2 km/Ma in the axial region of the mountains between 52° and 55°N to less than 0.1 km/Ma south of 52°N. The moderate rates north of 52°N were likely the result of gradual erosion of crust thickened during Eocene orogeny. A thermal origin for this northern uplift is not likely. Rates of uplift south of 52°N were low despite arc-related volcanic activity during the Oligocene and Miocene. Accelerated uplift in the Late Miocene near Bella Coola-Ocean Falls was probably the result of passage of the transverse Anahim Volcanic Belt or hotspot beneath the area about 10 Ma ago, after which uplift slowed. Rapid Pliocene-Recent uplift south of 52°N at rates of up to 0.75 km/Ma elevated a broad region creating the present southern Coast Mountains and deforming 7-10 Ma lavas erupted on the mountains' east flank. It is suggested that this uplift resulted from thermal expansion in the mantle related to a westward jump in the locus of late Neogene arc volcanism. The extent of this rapid Pliocene-Recent uplift correlates with the area above the Juan de Fuca-Explorer subducted slab and confirms a relation between continental uplift and plate tectonic setting. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

The focus of this study is the hydrochemical variability of runoff events in two nested alpine/sub-alpine basins. More specifically, the aim is to link hydrograph interpretations to results of hydrochemistry during rain storms in order to understand better short term hydrochemical fluxes and variability in solute sources. Hydrograph separation was undertaken by using four hydrological tracers; electrical conductivity, concentration of silica, and the stable environmental isotopes oxygen-18 and deuterium. The different methods predicted consistent high pre-storm water contribution for the lower station at peak flow (60%-90%) but less consistent results were found at the upper basin outlet (25%-90%). The chemical characteristics of the stream water have been analyzed using three different approaches, namely; statistical, mass balance, and thermodynamic. Linear correlation was used to investigate the statistical association between discharge and the individual chemical species. The mass balance approach was used to correlate stoichiometry of the bedrock mineralogy to dissolved constituents in the stream water. Finally, a thermodynamic technique was used to evaluate to what extent the stream water could be represented as an equilibrium system and how this changed over the course of the storm. The results from these methods showed that the stream water variability was caused almost entirely by dilution from rain water input.

Debris flows in the southern Coast Mountains exhibit different dynamic and sedimentologic characteristics, depending on the lithology of their source areas. Fine-textured debris flows originating in the Quaternary volcanic complexes are much more mobile than those originating in the coarse-textured plutonic rocks which form most of this mountain range. Mobility can be described as the velocity of flow, the distance of travel of debris flows, and the slope required to sustain flow. The objectives of this study are to examine the effect of different sediment composition on the mobility of debris flows, and to determine which rheologic models are most applicable for modeling debris flows in these geologic environments. About 25 debris flow events in or adjacent to the southern Coast Mountains were examined, ranging in volume from 10² m³ to over 10⁷ m³. Field methods included sampling of grain-size distribution, measurement of the deposit and channel dimensions, and observation of the stratigraphy of debris flow fans. Shear strength, permeability, and consolidation tests were performed on samples of reconstituted debris, representative of typical fine-textured and coarsetextured debris flows. These samples were also used to model debris flows in a flume. The coarse-textured, plutonic-source, debris flows typically had a distinct, inverselygraded, clast-supported, surface layer of cobbles and boulders. Their deposits tended to be irregular in thickness, with lobes and levees of coarse material. The fine-textured, volcanicsource, debris flows had no such surface layer, and their deposits were generally uniform in thickness and surface morphology. These observations, and corroborating evidence from the flume results, suggest that fine-textured debris flows behave according to the Bingham flow model, while coarse-textured debris flows can be better described by a granular, or dilatant, flow model. A clay content of about 4% in the matrix (sub-4 mm material) is a useful measure to distinguish the two populations. Several debris flow events of intermediate behaviour and sediment composition were also examined. The permeability of the debris, and hence its rate of consolidation, is an important factor controlling mobility. The volume of debris flow events was found to be the most significant factor controlling runout distance.

Tree-ring records collected from living mountain hemlock trees in the southern British Columbia Coast Mountains have been used to provide insights into the character of historical climatic fluctuations and the behaviour of individual climate forcing mechanisms. The relatively short-duration of these records limits, however, their ability to describe climate variability and atmospheric processes that change gradually or undergo long-term regime shifts. The objectives of this research were to extend the duration and quality of proxy climate information extracted from mountain hemlock tree-ring chronologies. In coastal British Columbia most existing mountain hemlock tree-ring chronologies extend from ca. AD 1600 to present. To extend the duration of these chronologies, coarse woody debris recovered from the bottom of M Gurr Lake, a high-elevation lake in the vicinity of Bella Coola, British Columbia, was cross-dated to nearby living chronologies surrounding M Gurr lake and increment core samples of ancient trees at Mt Cain on northern Vancouver Island. From this, a regional continuous 917-year long record of radial growth was constructed. The resulting regional chronology was used to construct a 785 year-long proxy record of gridded air temperature anomalies displaying periods of cooler and warmer than average regional air temperatures that contained century-long low frequency trends. Cross-dating and tree morphological evidence of snow avalanche activity displayed within living trees surrounding the lake, and within the coarse woody debris, revealed that low-magnitude avalanches occurred in the winter months of AD 1713-1714, 1764-1765, 1792-1793, 1914-1915, 1925-1926, and 1940-1941. High magnitude avalanche events occurred in the winter months of AD 1502-1502 and 1868-1869. A second objective of the thesis was to investigate the radial growth response of mountain hemlock trees to subseasonal climate variables using standardized ring-width and densitometric analyses. Mountain hemlock chronologies from M Gurr Lake, Cyprus Provincial Park, and Mount Arrowsmith were used to describe the inherent climate-growth trends. Maximum annual tree-ring density values provided a robust data series for constructing site-specific proxy records of late-summer temperature. Annual tree-ring width measurements provided independent proxies of spring snowpack trends. Regionally-derived proxy models indicated that intervals of cooler-than-average and higher-than-average air temperatures correspond to years of higher-than-average average and cooler-than-average snowpacks, respectively. Of note were the significant decreases in air temperature and increases in snowpack depths during the early-1700s and early-1800s coinciding with documented glacier advances in the Coast Mountains. Identification of these subseasonal climate signals within the tree-rings of mountain hemlock trees demonstrates the value of incorporating investigations of multiple tree-ring parameters. / Graduate

The focus of this study is the hydrochemical variability of runoff events in two nested alpine/sub-alpine basins. More specifically, the aim is to link hydrograph interpretations to results of hydrochemistry during rain storms in order to understand better short term hydrochemical fluxes and variability in solute sources. Hydrograph separation was undertaken by using four hydrological tracers; electrical conductivity, concentration of silica, and the stable environmental isotopes oxygen-18 and deuterium. The different methods predicted consistent high pre-storm water contribution for the lower station at peak flow (60%-90%) but less consistent results were found at the upper basin outlet (25%-90%). The chemical characteristics of the stream water have been analyzed using three different approaches, namely; statistical, mass balance, and thermodynamic. Linear correlation was used to investigate the statistical association between discharge and the individual chemical species. The mass balance approach was used to correlate stoichiometry of the bedrock mineralogy to dissolved constituents in the stream water. Finally, a thermodynamic technique was used to evaluate to what extent the stream water could be represented as an equilibrium system and how this changed over the course of the storm. The results from these methods showed that the stream water variability was caused almost entirely by dilution from rain water input. / Arts, Faculty of / Geography, Department of / Graduate

Debris flows in the southern Coast Mountains exhibit different dynamic and sedimentologic characteristics, depending on the lithology of their source areas. Fine-textured debris flows originating in the Quaternary volcanic complexes are much more mobile than those originating in the coarse-textured plutonic rocks which form most of this mountain range. Mobility can be described as the velocity of flow, the distance of travel of debris flows, and the slope required to sustain flow. The objectives of this study are to examine the effect of different sediment composition on the mobility of debris flows, and to determine which rheologic models are most applicable for modeling debris flows in these geologic environments. About 25 debris flow events in or adjacent to the southern Coast Mountains were examined, ranging in volume from 10² m³ to over 10⁷ m³. Field methods included sampling of grain-size distribution, measurement of the deposit and channel dimensions, and observation of the stratigraphy of debris flow fans. Shear strength, permeability, and consolidation tests were performed on samples of reconstituted debris, representative of typical fine-textured and coarsetextured debris flows. These samples were also used to model debris flows in a flume. The coarse-textured, plutonic-source, debris flows typically had a distinct, inverselygraded, clast-supported, surface layer of cobbles and boulders. Their deposits tended to be irregular in thickness, with lobes and levees of coarse material. The fine-textured, volcanicsource, debris flows had no such surface layer, and their deposits were generally uniform in thickness and surface morphology. These observations, and corroborating evidence from the flume results, suggest that fine-textured debris flows behave according to the Bingham flow model, while coarse-textured debris flows can be better described by a granular, or dilatant, flow model. A clay content of about 4% in the matrix (sub-4 mm material) is a useful measure to distinguish the two populations. Several debris flow events of intermediate behaviour and sediment composition were also examined. The permeability of the debris, and hence its rate of consolidation, is an important factor controlling mobility. The volume of debris flow events was found to be the most significant factor controlling runout distance. / Arts, Faculty of / Geography, Department of / Graduate

Palaeobotanical records of Holocene climate change in the southern Coast Mountains identify a cooler/wetter Neoglacial period subsequent to 6600 BP. Geomorphic evidence of alpine glacier advance suggests that there were three distinct cooler/wetter periods during the Neoglacial, but this pattern has not been identified in palaeobotanical studies. By careful selection of a sensitive alpine site this thesis has recognised this structure in a palynological record of Neoglacial climate. This continuous record of Neoglacial climate which has the same basis as records of early Holocene climate (i.e. palynological) and hence allows more direct comparisons of the two periods. Pollen spectra, conifer needle macrofossils, organic matter content, and magnetic susceptibility were assessed for a 4800 year continuous sequence of sediment from an alpine lake. Calibration of the Picea/Pinus pollen ratio by using an altitudinal transect of surface pollen samples allowed partial quantification of shifts in treeline. Treeline at the site was at least 85 m above the present level from 4800-3800 BP, suggesting that summer temperatures were at least 0.6°C above the present. High treeline until 3800 BP indicates a relatively late date for the Hypsithermal/Neoglacial transition at this site. Alternatively, the apparent complexity of this transition in the Coast Mountains may be due to difficulties of separating temperature and precipitation signals in many climatic records. Treeline declined to near present levels by 2500 BP and was lower than present from 2500-1500 BP and from 1200 BP until close to the present. Estimates of equilibrium line altitude depression for Coast Mountain glaciers during the Little Ice Age suggest that these periods of lower treeline were due to a cooling of up to 0.8°C. During the last 5000 years the Southern Coast Mountains have experienced fluctuations on the order of 1.5°C.

Palaeobotanical records of Holocene climate change in the southern Coast Mountains identify a cooler/wetter Neoglacial period subsequent to 6600 BP. Geomorphic evidence of alpine glacier advance suggests that there were three distinct cooler/wetter periods during the Neoglacial, but this pattern has not been identified in palaeobotanical studies. By careful selection of a sensitive alpine site this thesis has recognised this structure in a palynological record of Neoglacial climate. This continuous record of Neoglacial climate which has the same basis as records of early Holocene climate (i.e. palynological) and hence allows more direct comparisons of the two periods. Pollen spectra, conifer needle macrofossils, organic matter content, and magnetic susceptibility were assessed for a 4800 year continuous sequence of sediment from an alpine lake. Calibration of the Picea/Pinus pollen ratio by using an altitudinal transect of surface pollen samples allowed partial quantification of shifts in treeline. Treeline at the site was at least 85 m above the present level from 4800-3800 BP, suggesting that summer temperatures were at least 0.6°C above the present. High treeline until 3800 BP indicates a relatively late date for the Hypsithermal/Neoglacial transition at this site. Alternatively, the apparent complexity of this transition in the Coast Mountains may be due to difficulties of separating temperature and precipitation signals in many climatic records. Treeline declined to near present levels by 2500 BP and was lower than present from 2500-1500 BP and from 1200 BP until close to the present. Estimates of equilibrium line altitude depression for Coast Mountain glaciers during the Little Ice Age suggest that these periods of lower treeline were due to a cooling of up to 0.8°C. During the last 5000 years the Southern Coast Mountains have experienced fluctuations on the order of 1.5°C. / Arts, Faculty of / Geography, Department of / Graduate