1,720,983 research outputs found
Watery Relations: Assessing Complex Hydrological Systems and Pastoralism in the High Puna of the Bolivian Apolobamba
Get PDFThe author has granted permission for their work to be available to the general public.This thesis examines how pastoralist societies develop, construct, and manage the flow of water and, in turn, what a study of complex hydrological systems can reveal about a community's social and economic entanglements. The Apolobamba region of Bolivia boasts several hydrological features like qochas, bofedales, and tajanas that are sometimes engineered to work together or in singularity to produce such complex hydrological systems. Specifically, qocha water reservoirs have facilitated pastoral lifeways in the high-altitude puna grasslands, but the deep relational connectivity between water, humans, animals, and mobility in the Andes needs exploring with significance placed upon a hydrological understanding of qocha formation and management. To explore these relationships, the study conducted a pedestrian survey and ArcGIS-based landscape analysis of a 307.7 km2 area in southwestern Apolobamba, which revealed how pastoralists have modified and transformed the qocha complex hydrological system from the Tiwanaku Period, and perhaps earlier, to contemporary times to better manage its waters. This evidence for qocha management implies embedded symbiotic relationships between the landscape, water, and human-animal mobility practices through localized, small community involvement and responsibility.Anthropolog
Characterization of Large Hailstone Growth Using Stable Isotopes
No full textThe author has granted permission for their work to be available to the general public.The stable isotope composition of a hailstone is related to the source and transport of moisture, atmospheric temperature, cloud droplet, and vapor conditions that occur at crystallization into ice. The isotope content of cloud water is preserved as it transitions from the liquid to solid phase on a hailstone. Water isotope fractionation therefore is an indicator for assessing flow path and accretion mechanisms of hail as it forms in supercell thunderstorms. The stable isotope values such as δD can be used as indicator of cloud temperature and therefore altitude of hailstone formation. δD values obtained from the layers across a hailstone section therefore aid in defining the origin and trajectory of the hailstone through the storm event. Two separate hail events at Burkburnett and Del Rio, Texas in the spring of 2020, both provided greater than 5 cm (2 inch) diameter hailstone samples in this study. Sixteen hailstones from these two events have been dissected at nominal 0.5 cm intervals, providing 254 subsamples of melt water for isotopic analysis together with thin sections for ice structure analysis. Hailstone isotopic analysis with the ice structure microphotographs were used as proxies to determine the deposition of cloud water as a glaze layer was added. Results were compared to radar soundings of the two storms and made possible ground truthing of hail size and location estimates. The goal of this research is to provide better information on hail formation and growth within clouds that will contribute to storm prediction, warning and risk mitigation of hailstorms.Earth and Planetary Science
A Probabilistic Analysis of Lahar Bulking and Debulking in Channelized Proximal Volcanic Settings
No full textThis item is available only to currently enrolled UTSA students, faculty or staff. To download, navigate to Log In in the top right-hand corner of this screen, then select Log in with my UTSA ID.Lahars are gravitationally driven mudflows that occur on volcanic slopes and pose a significant threat to communities located downslope. The initial stages of their evolution, particularly bulking and debulking, within the proximal hazard zone are understudied and poorly understood. The goal of this study is to investigate the relationship between certain geometric channel characteristics and field observations of bulking and debulking from a 2012 lahar along a section of the Jamapa watershed, located within the proximal zone of the Pico de Orizaba. Drone acquired Digital Elevation Models (DEMs) were used to extract the geometric channel characteristics. The relationships were then investigated by developing logistic regression models with bulking and debulking as dependent variables and the 14 independent variables. When used in a multivariate model, these models show that lithology, channel width, and channel shapes are significantly related to observations of bulking and debulking, whereas slope, sinuosity, average catchment slope, and watershed contributing area are not. Although the models developed here are based on variables related to channel geometry and a single lahar event, this author recommends additional variables related to the physical characteristics of lahar flow itself be incorporated into future models. This could help improve its predictive capability and resolve issues related to abnormally small parameter estimates. Even though the models' results are far from perfect, they provide a foundation for developing more complex models that could advance our understanding of lahar evolution during the early stages that could be used to improve lahar flow models in the future.Geoscience
Stable carbon isotope analysis in a South Texas cave: Investigating sources of CO2 production
No full textThis item is available only to currently enrolled UTSA students, faculty or staff. To download, navigate to Log In in the top right-hand corner of this screen, then select Log in with my UTSA ID.Studies of interactions between modern local climate, cave atmosphere, and ?13C ratios are needed to determine sources of CO2 in caves, and the cycles of seasonal variations that alter karst geochemistry. A seasonal study, focusing on the analysis of stable isotopes collected from a modern cave system, was conducted in Robber Baron Cave (RBC) in order to identify sources of CO2 in its atmosphere. Determining what conditions affect cave morphology and the transfer path of carbon through a cave system is necessary in order to assess the role of caves in the carbon cycle and correctly interpret past ecological changes. This study investigates the extent that stable isotopic values of carbon in CO2 are affected by CO2 sourced from soils, bedrock, atmospheric air, and vegetation, and how ?13C signals are transmitted in a modern cave system. This study also measures how ventilation affects CO2 concentration and ?13C on seasonal scales. In-cave air grab samples were collected monthly at various transects located in RBC in order to measure CO2 composition in addition to factors such as temperature, and barometric pressure. Soil gas and limestone bedrock were also collected and tested for ?13C composition. Air samples were analyzed using an Ambient Air-Model G2101-I Picarro Cavity Ring-Down Spectroscopy Analyzer for both the concentration and ?13C isotopic value of CO2. These values were then compared to isotopic values of known sources of CO2 in order to determine possible sources of CO2 that result in high CO2 concentrations found in RBC. The background stable isotopic value of carbon from CO2 measured in RBC is -19.1‰ VPDB.Geoscience
Examining NDVI at Low Vegetation Percentages: Is NDVI a Good Indicator of Vegetation Presence?
No full textThis item is available only to currently enrolled UTSA students, faculty or staff. To download, navigate to Log In in the top right-hand corner of this screen, then select Log in with my UTSA ID.Vegetation research in arid and semi-arid environments tends to not only be costly but time consuming because they are either found in isolated areas and/or tend to cover large areas. Remote sensing has been a more cost efficient method in monitoring vegetation in these areas. Accurate data is needed for these areas not only for current research of the state of the land but also for simulation models that illustrate the interactions between land surfaces and the atmosphere.
A lab experiment was conducted using a vegetation component along with an ASD FieldSpec Pro Spectroradiometer to acquire reflectance values to calculate the NDVI values, which was followed up by performing a computer simulated experiment of the lab experiment.
The study was to explore NDVI values at low vegetation percentages, with two objectives: (1) if NDVI values at low vegetation percentages are good indicators of the presence of vegetation and (2) if a simulation experiment will provide similar results. Our conclusion is that NDVI is not a good indicator of vegetation presence in low vegetation cover areas and computer-based simulation does not produce the same results from the laboratory experiments.Geoscience
Summer Melt of McMurdo Ice Shelf from Satellite Data: 2013-2019
No full textThis item is available only to currently enrolled UTSA students, faculty or staff. To download, navigate to Log In in the top right-hand corner of this screen, then select Log in with my UTSA ID.Using Landsat 8 imagery, a six-year tendency (2013-2019) of the melt percentage of the McMurdo Ice Shelf is developed based on Normalized Difference Water Index Ice. The water pixels are mapped using an index value of 0.12 and above. The summer melt season is defined as the period of October 1st – February 28th, when liquid surface melt water presents. The retrieved melt water percentages are then compared with the daily mean and daily maximum of air temperature and solar irradiance, to determine if a possible correlation existed. The air temperature data are from automated weather stations recorded at ice runways located directly on the McMurdo Ice Shelf. Solar irradiance data (280-600 nm) are from National Oceanic and Atmospheric Administration’s Antarctic UV Monitoring Network.
It is found that four of the six years when analyzed individually showed no correlation between melt water percentage with either daily averaged temperature or daily averaged solar irradiance, except for two years with good correlations: R2 of 0.80 (2013-2014 season) and 0.72 (2015-2016 season), at 99% significant level. The results are similar when daily maximum temperature or daily maximum solar irradiance are used for the analysis. A multiple regression for all six years combined produces a low correlation of 0.16 for both averaged and maximum daily temperatures and solar irradiance, but at 99% significant level.
Additionally an overall slight decrease tendency for each of the three variables (temperature, solar irradiance, and melt water percentage) during the cloudless days of the study period is found. A slight increasing tendency for solar irradiance, with a slight decreasing tendency for temperature is found when the entire season data is taken into account for both daily averaged and daily maximum variables.Geoscience
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Geology and Structure of the University of Texas at San Antonio Campus Within the Balcones Fault Zone and Edwards Aquifer Recharge Zone in Bexar County, Texas
Get PDFThis item is available only to currently enrolled UTSA students, faculty or staff. To download, navigate to Log In in the top right-hand corner of this screen, then select Log in with my UTSA ID.This project is a study of the University of Texas at San Antonio (UTSA) campus, which lies within the Balcones Fault Zone and the Edwards Aquifer. It used integrated methods to gather data using geographic information systems (GIS), geological mapping, well information, and geophysical methods to characterize the structural geology that governs the water flow into the aquifer. This case study provides information on recharge pathways into the aquifer, as well as showing how integrated methods can more effectively describe a study area's hydrogeology using combined geoscientific tools and methods. This study used electrical resistivity, electromagnetic, and ground penetrating radar near surface geophysical methods plus field mapping and GIS to determine the structural framework and stratigraphy of the UTSA campus. It was found that the study area contains four fault blocks separated by three faults, with a central fault block tilting to the southwest that constitutes a relay ramp. Karst features are present in outcropped area of the Person Formation of the Edwards Group. They also act as point recharge features on the northern portion of the campus and play an important role in groundwater flow. Fractures are present throughout the Person Formation with orientations consistent with Balcones faulting and provide avenues for water infiltration. Groundwater recharges through the Edwards rocks in the recharge zone in the northern campus, with a large amount of recharge occurring through fractured streambeds. Groundwater travels from the surface to the aquifer through solution features and fractures, along faults, or along the relay ramp between faults. In the southeastern portion of campus, in the contributing zone where the upper confining zone outcrops, water travels overland into streams contributing to Leon Creek.Earth and Planetary Science
Geophysical and Hydrological Characteristics of the Leona Formation (Pleistocene): East Bexar County, Texas
No full textThis item is available only to currently enrolled UTSA students, faculty or staff. To download, navigate to Log In in the top right-hand corner of this screen, then select Log in with my UTSA ID.The Leona Formation in east Bexar County, Texas consists primarily of shallow subsurface fluvial gravels which are Pleistocene in age. Situated along the Balcones Escarpment these gravel deposits are the result erosion of into the Cretaceous carbonates causing debris from the Texas Hill Country to move basin ward off the escarpment into isolated braided stream-like systems. Because of the high permeability and porosity, the Leona Formation is both a local water resource for farmers in the east Bexar County area, and a gravel resource. Using a combination of electromagnetic (conductivity) and resistivity surveys, a 250 acre area on the border of Guadalupe County and Bexar County was mapped to determine both the lateral and vertical extent of the gravel as well as the potential for new water and gravel resources. The electromagnetic survey was used over the entire study area using the instrument's ability to map relatively quickly. Resistivity surveys and excavations of the gravel were used to confirm the electromagnetic data. Gravel, and non-gravel areas were determined from the electromagnetic data and confirmed with resistivity data, while the physical lithological data was used to correlate the geophysical data. With the combination of these three sources of data an accurate map was produced to determine where possible gravel resources are located, as well as the feasibility of using such resources. From the suite of data collected it was determined that the Leona Formation is likely a gravel dominated braided river. The Leona Formation may be part of a larger fluvial fan system.Geoscience
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