School of Earth Sciences - Theses
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ItemFire weather in two regions of the Southern HemispherePazmiño, Daniel ( 2017)This thesis investigated fire weather in Victoria, Australia and the Ecuadorian Andes. The selection of these areas considered several criteria. First of all, bushfires cause significant impacts in these two regions. Victoria has endured some of the most catastrophic bushfire events in Australian history (e.g. “Black Friday” (1939), “Ash Wednesday” (1983), “Black Saturday” (2009)). On the other hand, bushfires in Ecuador destroy every year large areas of national parks in one of the most biodiverse countries in the world. Secondly, the El Niño- Southern Oscillation (ENSO) is a strong climate driver in the two study areas. Finally, Victoria and Ecuador share the Eucalyptus as the dominant bushfire-prone species. The aim of this thesis is to better understand the drivers and evolution of fire weather in these two regions of the Southern Hemisphere. Specifically, it examined three aspects. First of all, it investigated fire weather spatial patterns in Victoria and their relationship with associated events like heatwaves. Subsequently, the study explored long-term fire weather variability and changes. Finally, the investigation evaluated the influence of ENSO and other climate drivers over fire weather. The analyses used three groups of data: bushfire records, meteorological and climate indices data. Consistent bushfire records were available only for Victoria during the period 1961-2010. Additionally, the investigation required observations from weather stations in Victoria and the Ecuadorian Andes. This research also analysed reanalysis data from the Twentieth Century Reanalysis Project (20CR) and the European Reanalysis of Global Climate Observations ERA-Clim project (ERA-20C). The study had a stronger emphasis on ENSO since it affects both regions. This research used two indices to represent fire weather. The first index was the McArthur Forest Fire Danger Index (FFDI). This Australian metric was designed for an Eucalyptus environment. Therefore, this investigation applied the FFDI for Victoria and Ecuador. Additionally, this thesis proposes an alternative fire weather index for Victoria: the “Victorian Seasonal Bushfire Index” (VSBI). The VSBI combines local meteorological variables and sea surface temperature in ENSO regions to represent—and predict—extreme fire weather. The investigation of fire weather in Victoria and the Ecuadorian Andes yielded several findings. First of all, bushfire and heatwave weather patterns display differences from one another in Victoria. These comparisons used synoptic climatologies with reanalysis data during the period 1961-2010. Additionally, the investigation showed that Victoria experienced an increase in fire danger during the period 1974-2010. There is also weaker evidence suggesting an increasing trend since 1920. “El Niño” events are the leading remote driver of fire activity in Victoria. In fact, the incorporation of ENSO indicators in a simple index (VSBI) shows skill to forecast extreme fire weather in this region. For the Ecuadorian Andes, this research indicates that its fire danger season (July-September) is longer than reported. October and November also display “high” fire danger during the period 1997-2012. Finally, “El Niño” events increase fire risk in the Ecuadorian Andes.
ItemMeasurement and modelling of heat flow in the Gippsland Basin, VictoriaHARRISON, BENJAMIN ( 2015)Geothermal energy has the potential to provide significant quantities of highly available power with little environmental impact. Enhanced geothermal system (EGS) technologies have the potential to become major contributors to global energy production, with a much wider geographic scope than the more established conventional geothermal systems. Certain favourable geological conditions have been recognised as providing improved prospectivity for EGS resources, primarily elevated heat flow rates and thermally insulating cover sequences. Most attention has been given to the location of regions having anomalously high heat flow, typically due to increased heat production in basement rocks such as granites rich in radiogenic isotopes. Little attention has been paid to extremes in thermal insulation, which offer an alternative but equally effective mechanism for increasing geothermal gradients and thus reducing the depth to a geothermal resource. Large and thick deposits of highly insulating coal present a unique thermal environment, where the commonly assumed one-dimensional relationship between surface heat flow and temperature at depth described by Fourier's Law is not maintained due to heat refraction -- a three-dimensional process. Understanding the effects of heat refraction due to thermal insulation and its effect on surface heat flow is a crucial element of exploration strategies in coal-bearing sedimentary basins. The onshore Gippsland Basin, and in particular the Latrobe Valley, is an ideal setting to study the effects of buried confined insulators on surface heat flow and thermal structure. This thesis combines the results of observational insights from empirical field data collection with mathematically driven insights of theoretical models, and simulation-driven insights of numerical finite-element modelling. Additionally, it explores the relatively modern paradigm of data-driven statistical science to generate predictions of rock properties from related intrinsic variables. Measured surface heat flow is moderately variable, with the ten most reliable calculations from borehole data having an interquartile range of 61--78 mW/m², with a mean and standard deviation of 72±14 mW/m², slightly higher than previous estimates. Groundwater advection identified in previous studies appears to affect the thermal structure of only the Cainozoic stratigraphy. Losses of up to 37 mW/m² in the vertical heat flow in the sandy Balook Formation of borehole Rosedale-301 represents a local maximum of heat transfer associated with groundwater advection. Only minor thermal effects are observed in the uppermost Mesozoic section, indicating a return to a dominantly conductive thermal regime there. The self-organising map technique was applied to the prediction of lithostratigraphy and thermal conductivity from well-log data. It successfully identified 91.3% of lithostratigraphy samples from a supervised mapping of well-log data. Mapping of thermal conductivity with corresponding well-log data produced more variable results compared with a petrophysical log interpretation technique over a large cohort of boreholes. However, the SOM analysis returned predicted values with a better correlation with measured values at sampled depths, required less pre-processing of log data, and was able to perform with non-standard log data and legacy tools. With further refinements of the technique, potential improvements may be made with its prediction performance of thermal conductivity and other rock properties. Heat flow theory applied to an idealised simulation of the Latrobe Valley coal seams showed that temperature increases of 35°C beneath the coal are possible over a reference model having no such insulation. Finite-element forward models of cross-sections and 3D volumes through the onshore Gippsland Basin identified highly variable surface heat flow, having up to ±30 mW/m² variance from the basal flux input. Complex patterns resulting from heat refraction were produced, with two common features indicative of confined insulators: 1. the greatest increase in subsurface temperature is correlated with the greatest decrease in surface heat flow, however, 2. surface heat flow tends to be slightly increased above the margins of buried insulators. The main implication from these results is the identification of an end-member insulation-dominated geothermal resource style, requiring new strategies for exploration and resource targeting.
ItemLeachate chemistry of two modern municipal waste landfills in Melbourne, VictoriaStrudwick, Darryl Grant ( 1999-11)This study investigates the occurrence and chemical composition of leachate at Clayton South and Brooklyn Municipal waste landfills in Melbourne, Victoria. Both are ‘modern’ municipal waste landfills, being engineered and managed consistent with current regulatory requirements. These landfills accept only putrescible and solid inert waste, but not soluble chemical, hazardous, liquid or prescribed industrial waste. (For complete abstract open document) Analyses of an extensive range of chemical parameters reveals a complex mixture of inorganic and organic compounds, similar to those of international authors researching leachate chemistry. Dominant ions in these leachates are NH4+, Na+, HC03- and Cl-. Except for Fe, heavy metals are not present in significant concentrations (mostly
ItemThe hydrogeology of the Gippsland Basin, and its role in the genesis and accumulation of petroleumNahm, Gi Young ( 2002)The Gippsland Basin of southeastern Australia is the most energy-rich basin of Australia producing petroleum, gas and brown coal. Three-quarters of the Basin lies offshore and the rest onshore. The basin was initiated as a rift valley, caused by the separation of the Australian continent from the Antarctic followed by a number of tectonic events throughout the basin history. Early Cretaceous sedimentary rocks form the basement, which is in turn covered with Late Cretaceous to Recent sediment of sand, clay, limestone, and brown coal seams. The total thickness of the in-filling sediments offshore attains up to 6000 m, but onshore is up to 1200 m. There are three main acquifer systems, the Hydrostratigraphic Units 2, 4, and 7, all of which are confined. The two lower aquifer systems, Units 4 and 7, contain high temperature groundwater. It is generally agreed that the hydrocarbons offshore have been derived from terrestrial matters including brown coal and ligneous clay offshore. In the present study, the author has developed a case that hydrocarbons offshore being derived not only from the offshore source but also from onshore brown coals and coaly matter and in this hydrocarbon forming processes, groundwater has played a significant role. The Central Deep, in particular, provides favourable conditions for hydrocarbon maturation. Throughout the basin history, the Central Deep has experienced the oil window temperatures. In supporting this hypothesis, geochemical studies on groundwater, brown coal, and hydrocarbons as well as hydrodynamics are presented.
ItemTectonic geomorphology of the Bogong and Dargo High Plains region, east Victorian highlands, AustraliaOrr, Meredith Lee ( 1999)The Australian Alps, a sub-region of the Australian Eastern Highlands, have enigmatically high elevations of relief for a highland belt renowned for its ancient origins and landscapes. In debates over the Eastern Highlands history, the development and significance of the Alps have been under-represented. This study defines the morphological extent of the Australian Alps and investigates their tectonic and erosional development. The focus of investigation is the Bogong and Dargo High Plains area and the broader surrounding highlands region. The Cainozoic history of this area has not been investigated in detail since last century. The geological record of the region has substantial gaps, and the erosional history is the main indicator of tectonic change. A methodological structure different to traditional approaches is devised for this study. Cause and response are compared on a process geomorphology basis. Causes investigated are (1) intra-highland tectonics and (2) basin tectonics and sea level change. Denudational relief change is the main response investigated. Spinal and temporal comparison of quantitative results enables relationships to be determined. Peak height distribution and relief observations are used to define the morphological context of the Australian Alps. Within the Alps, the high plains area is used as a case study. Tectonic constructional morphology is investigated using peak height distributions, lineament analysis, tectonic landforms and lava offsets. A Cainozoic fault block is identified, and reactivated fault displacements are determined for bounding and intra-block faults. The erosional development of the area is determined and compared with the constructional morphology results. The sub-volcanic relief of the Bogong Volcanic Province is mapped and compared with post-volcanic stream incision. Guidelines are established for interpreting strath terraces and strath terrace long profiles are used to reconstruct the post-volcanic stream erosion development. Sources and magnitudes of oversteepened stream reaches in the present rivers are identified. Spatial and temporal relationships between fault reactivation and stream incision are determined, and the relative roles of active and passive tectonics are assessed. The tectonic and erosional development of the fault block is reconstructed in cross-sectional form. Finally, the proportion and nature of highland margin-derived stream incision is identified. This study finds that the Australian Alps were substantially affected by fault block uplift during Oligocene, with more minor phases in the Miocene and Pliocene. Broader highland margin warping accompanied fault block uplift. Uplift amounts varied between 150m and over 1000m according to proximity to major faults. Stream incision was upstream-increasing and periodic, with three incision phases during the Oligocene and Pliocene. The later phases include a possible isostatic rebound component. An additional incision phase unrelated to uplift occurred in the Gippsland Basin catchment during the Quaternary. The Australian Alps is delineated here as a separate entity within the Eastern Highlands, with its own tectonic history. Cainozoic uplift created the higher elevations and greater relief of the Alps. This history is not representative of the Eastern Highlands generally, and it should not be used as a guide to a ‘united’ Eastern Highlands uplift. The highlands consist of a ‘patchwork’ of landscape evolution scenarios, rather than a single tectonic province. More definable tectonic histories can be derived from erosional regions of geologically unrecorded time using a process geomorphology perspective. This study provides a suggested step towards redressing interpretation problems recognised in landscape evolution studies generally.
ItemPhysical and chemical hydrogeology of the Otway Basin, southeast AustraliaBush, Angela L. ( 2009)The Otway Basin of southeast Australia is the subject of this thesis, which incorporates pre-existing geological, hydraulic and major element hydrogeological data with new isotope hydrogeochemical investigations. The region is an Upper Cretaceous–Tertiary basin, filled with siliciclastic and calcareous aquifers and aquitards and characterised by late volcanic activity, pervasive faulting and karstification. (For complete abstract open document.) As part of this study, an hydrogeological database is compiled for the Otway Basin region from existing distinct datasets from the states of Victoria and South Australia. Utilising this new resource, the data are reinterpreted into a 3D model of the hydrostratigraphy for the basin in GoCAD, and interpolated surfaces of hydraulic head and electrical conductivity are created for 5 aquifers/aquitards. The Victorian hydraulic head data is analysed for long term declining or inclining trends and hydrograph trend maps are created for different aquifer systems. The data are also compiled into representative cross sections of flow and chemical composition, with one section located in each of the three major sub-basins. The records of groundwater chemistry from the Victorian section of the Otway Basin are used to plot the relative concentration of major cations and anions for the main aquifers. More than 120 groundwater samples were taken for analysis of major and minor ion concentration and/or oxygen, hydrogen, carbon, strontium and chlorine isotope composition. These data are used to characterise the hydrogeochemical evolution of the groundwater and to identify the processes that the groundwater drives or experiences in the system. The potentiometric maps and cross sections reveal the interconnected nature of the flow in all aquifers and the relationship between local and regional flow systems. Regional flow paths originate inland near basement highs or the basin margins. In the shallower aquifers they terminate at the coastline where the groundwater mixes with ocean water at a diffuse interface and density differences induce groundwater discharge at the land surface or the ocean floor. In the deeper confined aquifers, discharge is submarine via several possible mechanisms, which include: diffuse intergranular leakage to overlying units; flow along faults or volcanic conduits; and/or seepage directly to the ocean from exposed sections of the aquifer, e.g. in submarine canyons. These mechanisms may be operating up to 50 km offshore but the interface is currently migrating landward, which will result in a shortening of that estimated distance. Local-scale flow lines are complex and may be oriented against the direction of regional coastward flow. Local hydraulic divides are often associated with volcanic eruption centres, which have elevated topography and relatively high hydraulic head, making them important recharge zones. These zones contain low salinity groundwater because infiltration is relatively rapid. Conversely, basalt flows that have developed clay horizons through weathering reduce drainage and allow significant evapotranspiration which concentrates the cyclic salts in solution. Many local flow systems discharge mainly via evapotranspiration, which acts again to concentrate the cyclic salts in solution. Other local discharge zones are rivers, creeks and lakes or lagoons that receive baseflow and seeps and springs associated with geological contacts or boundaries and faults. Evaporitic concentration of solutes in surface water bodies and shallow groundwater affects the quality of water recharging the underlying aquifers and aquitards. This quality has changed over the last 50,000 years or so due to fluctuations in climate and hence variation of the precipitation/evaporation ratio. Stresses on the aquifers are climate fluctuations, sea level change, land use change and groundwater extraction. These stresses have resulted in the system being out of hydraulic equilibrium in many cases. Lags in response to these changes in boundary conditions are identified and/or hypothesised. In particular, the confined aquifer’s response to sea level change could be subject to a lag in the order of millennia. The stress on an aquifer is often transferred to its adjacent units, in some cases inducing cross-formational leakage, which is possibly supported by radiocarbon dating evidence. The area of the Otway Ranges appears to have escaped the effects of stress to date because of its stable microclimate, its distance from the ocean and from groundwater extraction. Increase in demand on groundwater resources, development of geothermal, sequestration and hydrocarbon industries and future climate change may yet have a detrimental effect on the groundwater of the Otway Basin. Isotopic composition of the groundwater confirms its meteoric origin and chlorine isotopes from several samples of the deep groundwater indicate that accumulation of solutes along the flow path is not due to diffusion or dissolution of connate salt. Thus, the salinity of the water is sourced from cyclic salts and solutes from water-rock interaction, both of which may be concentrated by evapotranspiration. Water-rock interaction is dominated by dissolution of carbonates and weathering of silicates as a result of the surficial geology being dominated by calcarenite or limestone and young basalt. The volcanic activity has produced gas that has interacted with the groundwater, and continues to do so, fractionating oxygen, hydrogen and carbon isotopes and contributing fluorine, boron and sulphur to solution. The addition of volcanic CO2 creates an uncommon situation for water-rock interaction, where continued dissolution of carbonate and silicate minerals along the deeper flow paths is demonstrated by the silicon/chloride ratios and strontium isotopic composition of the groundwater. These water-rock interaction processes, with the addition of cation exchange, are responsible for the development of a relatively fresh Na+HCO− 3 type water that is characteristic in parts of the deep aquifer. The study confirms the existing hydrogeological understanding of the Otway Basin and forms new conclusions regarding the history of the groundwater and the processes of flow and chemical evolution by integrating numerous lines of evidence. Significant contributions of this work which improve current scientific knowledge include these findings: the maps and cross sections of hydraulic head and electrical conductivity reveal the connected nature of flow systems within all the aquifers and aquitards; geological features can induce discharge, e.g. at contacts or faults, and recharge, e.g. volcanic eruption centres; the changes to the surface drainage system as a result of the eruption of basalt flows have affected the water chemistry and flow systems in all the underlying units; there is a lag in aquifers’ responses to sea level change and therefore future migration of the interface is expected regardless of further boundary changes; climate change has influenced surface water quality by changing the regional water balance, and therefore has affected groundwater quality; the discharge from the confined aquifer is submarine via various pathways, interaction between the groundwater and volcanic gas has occurred in the past and is ongoing, and consequently mineral dissolution persists at deep levels; the origin of high salinity of brackish groundwater in all Tertiary aquifers and aquitards is concentrated solutes from water rock interaction and cyclic deposition.