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Paterae (volcano-tectonic depressions) are among the most prominent topographic features on Io. They are unique, yet in some aspects they resemble calderas known and studied on Earth, Mars, and Venus. They have steep walls, flat floors, and arcuate margins, typical of terrestrial and Martian basalt shield calderas. However, they are much larger (2 km - 202 km diameter, mean 42 km 3 km) and typically lack obvious shields. They are often angular in shape or are found adjacent to mountains, suggesting tectonic influences on their formation. A preferential clustering of paterae at the equatorial sub- and anti-jovian regions is likely a surface expression of tidal massaging and convection in the asthenosphere. Paterae adjacent to mountains have a mean diameter 14 km 9 km larger than that for all paterae, which may indicate paterae grow larger in the fractured crust near mountains. Nightside and eclipse observations of Pele Patera by the Cassini and Galileo spacecraft reveal that much of Pele’s visible thermal emission comes from lava fountains within a topographically confined lava body, most likely a lava lake. Multiple filter images provided color temperatures of 1500 80 K from Cassini ISS data, and 1420 100 K from Galileo SSI data. Hotspots found within paterae (79% of all hotspots) exhibit a wide range of thermal behaviors in global eclipse images. Some hotspots are similar to Pele, consistently bright and confined; others, such as Loki, brighten or dim between observations and move to different locations within their patera. A model for patera formation begins with heating and convection within a high-temperature, low-viscosity asthenosphere. Magma rises through the cold, dense lithosphere either as diapirs [for thermal softening of the lithosphere and sufficiently large diapirs (20 km - 40 km diameter, >5 km thickness)] or through dikes. Magma reaches zones of neutral buoyancy and forms magma chambers that feed eruptions. Collapse over high-level chambers results in patera formation, filling of the patera with lava to create a lava lake, or lateral spreading of the magma chamber and subsequent enlargement of the patera by consuming crustal materials.

Instrumental and observational records of climate in West Africa suggest that this region may be susceptible to abrupt, decades-long drought events, with potentially catastrophic impacts for the people living in this region. However, because of the dearth of long, continuous and high quality climate records from sub-Saharan Africa, little is known about the long-term frequency and persistence of drought events in this region. It is also unclear whether observed 20th century droughts are natural or due to human impacts. In the present study, we use several complementary approaches to develop a high-resolution record of paleoclimatic changes in West Africa from the geological record preserved at Lake Bosumtwi, Ghana.Our results suggest that West Africa has undergone significant hydrologic variations over the last ca. 10,000 years. The dominant influence on hydrologic changes over this interval was changes in northern hemisphere summer insolation and the associated feedback processes acting in the oceans and on land. This led to a more northerly position of the Intertropical Convergence Zone (ITCZ) and increased precipitation during the early to mid-Holocene. In the late Holocene, a second increase in precipitation occurred along the Guinea coast as a result of the southward migration of the ITCZ from its northern position. This maximum was followed by an abrupt decrease in precipitation at ca. 2.5-3 kyr.The West African monsoon also varies on timescales from millennia to decades. Millennial and century-scale variations appear to be partly paced by changes in solar irradiance, either directly or indirectly. On decadal timescales, variability appears to be dominated by changes in Atlantic sea surface temperatures. The dominant mode is a ca. 40 year oscillation, which in strongly coherent and in phase with the Atlantic Multidecadal Oscillation (AMO). It is unclear from this study, however, if drought conditions over the last century are related to this multidecadal oscillation, or if they are forced by anthropogenic changes.

In order to explore the dynamic between history and place, I consider four methodological issues within the historical space of Sumas Lake, B.C., a large lake that was drained in the 1920’s. The first “Opening” reflects on the connection between historical and technological frontiers, while critiquing my creation of the attached HyperCard stack “Disappearing A Lake: A Meditation on Method and Mosquitos.” The stack documents the creative process of history-making, allowing the “reader” to review and record comments, to see examples of cartography and photography, to hear oral interviews and to read selections of narrative tradition either inside or outside the logic and context of an essay format. The written document flows from the stack. “Listening For Pleasure” discusses the process of oral history as it relates to the negotiated and contested space of the Sumas Lake commons. Diving into archives from Victoria to Ottawa, “Margins and Mosquitos” recycles written records to explore federal, provincial and local involvements with a flood lake. “Memory Device” moves into the archive of land and waterscapes, looking for connections between place and history, mindful of both Native oral tradition and written historical accounts of the lake. Interactive history is located not only in the interface between people and computers, but also in the process of making oral history and in the creative transformation of archival documents. Most importantly, interactive history is alive in the links people forge between stories and the actual places around them.

The general goal of this thesis was to examine and quantify the role of rooted submerged aquatic macrophytes in the cycling of metals in the littoral zone. An empirical study using data from an extensive literature survey showed that aquatic plants do not differ markedly in element composition from the sediments in which they grow, and that during uptake the plant's roots do not discriminate between elements essential and not essential for growth. The organic content, pH and redox potential of the sediments were shown to affect the bioavailability of metals to the plants. Biomass density was used to categorize species to assess broad patterns in plant-sediment metal relationships. It was found that the presence/absence of an understory contributed variation to the plant-sediment metal relationships. The role of rooted macrophytes as vectors for various elements between the sediments and attached epiphyte was quantified by growing Myriophyllum spicatum in radio-labelled sediments. This species was found to be a link between the sediments and attached epiphytes for the 4 elements studied (Co, Cs, Eu and Mn). Finally, the export of dissolved metals from weedbeds during plant senescence was quantified using a mass balance approach. It was found that approximately 15% to 30% (depending on the metal) of the metal inventory of the plants at maximum seasonal biomass was lost as dissolved compounds during senescence. During the growing season the macrophyte beds were net sources of metals to the lake, but were net sinks annually.

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Organic and inorganic carbon can enter inland waters in different ways, and often a considerable amount of this carbon is coming from terrestrial input. Once this terrestrial carbon enters a lake, the carbon may be degraded, mineralized or eventually buried in the sediment. Below the oxic zone of the sediment carbon may be used by archaea to produce methane (CH4). The CH4 can then diffuse up in the sediment and escape to the bottom waters, or the CH4 can be oxidized by bacteria using oxygen as an oxidant. There is also an anoxic process to oxidize CH4 (anaerobic oxidation of methane: AOM), using sulfate (SO4) and by recent findings also ferric iron (Fe(III)) as electron acceptors. In this study the main questions of interest were if CH4 is produced in deep (i.e. old) lake sediments and if CH4 is oxidized anaerobically using Fe(III). Two Swedish boreal forest lakes were studied, sediment profiles of CH4 were conducted in the field (down to 60 cm). Collected sediments were sliced anoxically at different depths and then analyzed for ferrous iron (Fe(II)), Fe(III) and SO4. Sediment from different depths was also incubated anoxic in order to test if CH4 production depends on sediment age. The results show that methanogenic activity occurs by degrading old carbon in deep boreal forest lake sediments, and that a certain part of this might then be oxidized anaerobically. However, all cores exposed a general trend of increasing CH4 concentrations with sediment depth, indicating that CH4 production in old sediment layers is greater than AOM. AOM could therefore only act as a partial sink for CH4 in anoxic deep sediments.

The discipline of hydrology encompasses all studies of the occurrence, origins, properties, and distribution of the earth's waters. It is a branch of physical geography, but forms indistinct boundaries with other earth sciences. [...]

Since the 'discovery' of the high abundance of viruses in aquatic environments, it has been generally assumed that viruses in lakes are similar to those in oceans. I directly compared these two systems using a large, robust data set. Viral abundance was significantly different among the surveyed environments. The relationship between viral and bacterial abundance indicated a fundamental difference between lakes and oceans, and suggested that viruses infecting phytoplankton may be more important in lakes. Molecular techniques (PCR & DGGE) were used to document spatial and temporal variations in the richness of viruses that infect eukaryotic phytoplankton (Phycodnaviridae) in lakes at the Experimental Lakes Area (ELA). Phycodnavirus richness was highest in the eutrophic lake, and during the spring/early summer in all the lakes. Viral richness was closely associated with phytoplankton abundance and composition. As a result, richness was influenced by trophic status, while patterns of richness were affected by regional climatic conditions. Phylogenetic analysis of environmental Phycodnavirus DNA polymerase (pol) sequences indicated that freshwater Phycodnaviruses are genetically different from cultured isolates and marine environmental sequences. A genetic distance analysis indicated that pol sequences > 7 % different infected different host species. Therefore, the 20 different freshwater sequences likely infected nine different hosts. Multivariate statistics identified seven possible phytoplankton hosts, including chlorophytes, chrysophytes, diatoms and dinoflagellates. Finally, the modified dilution experiment was evaluated as an approach for estimating viral-mediated phytoplankton mortality in two lakes at the ELA. Experiments resulted in non-significant apparent growth rate regressions. While a model analysis, indicated that the method was sensitive to poorly constrained parameters such as burst size and length of the lytic cycle, making it unsuitable for estimating mortality rates in these lakes. These studies indicate that Phycodnaviridae are a genetically rich and dynamic component of lakes. Their richness is influenced by both the chemical and physical components of their environment. Although the presence of these viruses indicates that they are a source of phytoplankton mortality, the magnitude of their impact on structuring phytoplankton communities awaits methodological advances. Nonetheless, these findings support the view that viruses infecting phytoplankton are ecologically important components of lake ecosystems.

Advancements in technology in mining have allowed previously unfeasible ore bodies to be developed. Paste backfill is one technological advancement that has allowed for the development of high-grade, low tonne production when employing the cut and fill mining method. Goldcorp Inc.'s Red Lake Mine currently utilizes this method and is the site for the study of this thesis. Paste backfill (paste) is defined as a mine backfill material that consists of eighty-five percent solids by weight and does not bleed water when placed often consisting of between two and fifteen percent Portland cement by weight. A paste barricade or paste fill fence is a constructed barricade whose purpose is to retain backfill within a mined out stope. The construction of the barricade varies with different operations, for Red Lake Mine the barricade consists of an anchored rebar skeleton covered with an adequate thickness of shotcrete. The majority of the applicable barricade research focuses on hydraulic fill barricades in open stope mining. The barricade pressures in these instances are much larger than those experienced in paste backfill barricades. As such, the current paste loading theory is based on material with a different loading mechanism. Although some research is currently underway, the majority of the barricade research is based on brick barricades and not the shotcrete, rebar skeleton as used at Red Lake. Catastrophic failures of barricades can occur without an understanding of the loading mechanisms. Based on the catastrophic risk, this thesis provides an investigation into the behaviour of the paste backfill and paste barricades at Red Lake Mine in order to provide a safe, cost effective design of paste barricades. This thesis develops an understanding of paste loading mechanisms and barricade capacity derived from a field study of nine instrumented fill fences at Red Lake Mine. Eight of thefences were instrumented to monitor the reaction strain in the fence and the applied pressures during standard production paste pours, the ninth fence was a controlled destructive test that determined the ultimate capacity of the fence. The data for these tests were gathered in real time and was subsequently reduced to assist in analysis. Yield Line Theory, Rankine Theory, strain induced stress, stress vs. strain analysis and numerical modeling were used to develop an understanding of the paste loading mechanisms and the capacity of the paste fill barricades. The analysis determined that the paste backfill behaves as a Rankine-like soil in the initial stages of loading with an average coefficient of lateral earth pressure, Ka, of 0.56. The destructive test determined that the yielding stress of a paste barricade is approximately 100 kPa. Further findings from the research determined that the rate of placement of paste does effect the loads applied to the fence and that the largest pressures exerted on the fill fence occur when paste lines were flushed with water at the end of the pour. This thesis provides an understanding of the paste loading and fill fence interaction with respect to failure. Based on this research the Red Lake Mine should be able to increase production without increasing risk to mine personnel by quantifying the overall loading and strengths of the fill barricade.