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Articles 151 - 180 of 29967
Full-Text Articles in Entire DC Network
Do National Parks Significantly Improve Air Quality?, Xinyi Liu
Do National Parks Significantly Improve Air Quality?, Xinyi Liu
Honors Capstones
Healthy living has long been a goal pursued by individuals. In an era where PM2.5 concentrations and greenhouse gas levels are steadily increasing, many people prefer to live in areas with relatively lower levels of air pollution. National parks, as well-known protected areas, typically contain more vegetation and water resources, along with lower levels of human activity. This suggests two potential mechanisms: first, pollutant emissions are expected to be lower; second, vegetation, water bodies, and non-urban land may contribute to the removal or deposition of airborne pollutants, including particulate matter. In everyday experience, people often perceive the air to be …
Sedimentary Provenance Of The Pliocene – Pleistocene Giant Foresets Formation, Offshore Taranaki Basin, Aotearoa New Zealand, Anurag Kulkarrni
Sedimentary Provenance Of The Pliocene – Pleistocene Giant Foresets Formation, Offshore Taranaki Basin, Aotearoa New Zealand, Anurag Kulkarrni
Graduate Theses and Dissertations
Sediment input and dispersal in the Taranaki Basin, offshore New Zealand’s North Island, was influenced by a complex interplay of ocean currents and sea level fluctuations over the late Neogene. This period of time was recorded in the Pliocene-Pleistocene Giant Foresets Formation (GFF) that represents a rapid progradation of the western continental shelf into the basin. High sedimentation rates during this time were likely a major contributing factor to the emplacement of multiple, large-scale (up to ~3,500 km3) mass-transport deposits (MTD) that were caused by shelf and slope collapse within the GFF of similar scale to that of the well-studied …
Active And Passive Seismic Studies Across Glacial And Geothermal Environments, Lucia Fernanda Gonzalez
Active And Passive Seismic Studies Across Glacial And Geothermal Environments, Lucia Fernanda Gonzalez
Open Access Theses & Dissertations
The collection of passive and active-source seismic data remains central to the detailed investigation and understanding of complex Earth processes across diverse and often inaccessible environments. Of equal importance is the selection of methodologies that must be tailored to the geological setting and dataset resolution to accurately depict the subsurface. In this dissertation, we apply a range of classic and/or "newly" developed algorithms, unique to each chapter, on seismic datasets from distinct glaciological and geothermal settings to evaluate their performance and enhance subsurface interpretation. In Chapter 1, we analyze active-source seismic data from Lemon Creek Glacier in Juneau, Alaska, using …
Leveraging The Iron Oxide Archive Of Mineralization, Deformation, And Exhumation Across Geologic Time, Jordan L. Jensen
Leveraging The Iron Oxide Archive Of Mineralization, Deformation, And Exhumation Across Geologic Time, Jordan L. Jensen
All Graduate Theses and Dissertations, Fall 2023 to Present
The iron oxide mineral hematite commonly forms from groundwater near Earth’s surface and can preserve a history of fluid flow, fault slip, and landscape evolution. This record can be decoded using (U-Th)/He thermochronology, a dating method based on the temperature-sensitive ingrowth of helium from uranium and thorium decay. Because later heating and natural variation in hematite crystals can produce ambiguous (U-Th)/He results, I integrate dating with tools that reveal differences in hematite chemistry and textures. I apply these techniques to two distinct settings: ancient granitic rocks in Colorado and an active fault zone in the southern San Andreas fault (SSAF) …
Crossing Boundaries: Brachinites And Their Diverse Asteroidal Origins, B. G. Rider-Stokes, F. A. Davies, T. H. Burbine, E. Maclennan, R. C. Greenwood, S. L. Jackson, M. Anand, Daniel Sheikh, M. M. Grady
Crossing Boundaries: Brachinites And Their Diverse Asteroidal Origins, B. G. Rider-Stokes, F. A. Davies, T. H. Burbine, E. Maclennan, R. C. Greenwood, S. L. Jackson, M. Anand, Daniel Sheikh, M. M. Grady
Geology Faculty Publications and Presentations
Brachinite meteorites are typically linked to the olivine-rich A-type asteroids. In this study, however, they appear to exhibit unexpected spectral diversity. Spectroscopic analysis of seven meteorites from the brachinite clan reveals two distinct populations in band parameters, overlapping with both the A-type and S-complex asteroids. This dual association shows that a single meteorite group can originate from multiple asteroid taxonomies. Notably, one S-complex-like specimen, Northwest Africa (NWA) 14,635, displays band parameters similar to those of asteroid (65803) Didymos, the target of the European Space Agency's (ESA) ongoing Hera mission. These results underscore the value of spectroscopic characterization of poorly understood …
Phase Equilibria Modeling Constraints On Seismic Velocity And Density For Mafic Granulites In The Athabasca Granulite Terrane, Western Canadian Shield, Olivia Wyllie
Geosciences Undergraduate Honors Theses
Samples of mafic granulite and eclogite from the Athabasca granulite terrane, thought to be representative of the lower continental crust, were analyzed via bulk geochemistry analysis and seismically modelled with Perple_X v.7.1.6. Modeled P-wave speeds, S-wave speeds, and densities for the samples were graphed by region and calculated for wet (1.00 wt.% H2O) versus dry (0.01 wt.% H2O) conditions at 460 °C and 648 °C. The samples were found to have higher median P-wave values than those determined by Rudnick and Fountain (1995; 7.4 km/s to 7.8 km/s, as compared to 6.9 km/s to 7.2 km/s). This indicates both a …
Morphological Evolution And Sediment Budget Of A Flood-Tidal Delta On The Rio Grande Delta Plain: Bahia Grande, Texas, Usa, Aleen Pertuz Paz
Morphological Evolution And Sediment Budget Of A Flood-Tidal Delta On The Rio Grande Delta Plain: Bahia Grande, Texas, Usa, Aleen Pertuz Paz
Theses and Dissertations
The Isabel Delta is a recently formed flood-tidal delta within the restored Bahia Grande system on the Rio Grande Delta Plain, Texas, USA, where renewed tidal connectivity has created conditions for rapid sediment buildup and landform evolution. This study quantified morphological changes from 2008 to 2025 using satellite imagery. It assessed sediment retention by comparing the effective sediment discharge required to reproduce observed delta growth with field-based estimates of sediment supply derived from channel hydrodynamics, cross-sectional area, and suspended sediment concentration. The delta expanded steadily throughout the study period, with increases in bar, channel, and total surface area, and an …
On The Paleontology Of Belize, Alson Ovando
On The Paleontology Of Belize, Alson Ovando
Electronic Theses and Dissertations
Paleontology can be considered an underrepresented and emerging area of science in Belize. A primary aim of this thesis is to provide a background of paleontology in Belize and present the first comprehensive study of Quaternary vertebrate fossils known from the country. Quaternary fossil sites across Belize include caves, rivers, and sinkholes. In addition to reviewing and assessing material from known sites, this thesis presents new information and discoveries that were made while investigating Belize’s Quaternary fossil record. This thesis also includes a geospatial model depicting ecoregions in Belize during the last glacial maximum. Overall, the results presented here demonstrate …
Machine-Learning Landslide Susceptibility And Runout Modeling In The Nolichucky River Gorge After Hurricane Helene, Grace Braver
Machine-Learning Landslide Susceptibility And Runout Modeling In The Nolichucky River Gorge After Hurricane Helene, Grace Braver
Electronic Theses and Dissertations
Extreme rainfall from Hurricane Helene (September 2024) triggered widespread landslides across the southern Appalachian region, highlighting the need for rapid landslide susceptibility assessments that capture both landslide initiation and downstream runout. Traditional susceptibility models often focus solely on initiation zones, limiting their ability to identify which slopes will generate destructive landslides or where material will travel. This study addresses that gap by (1) integrating Geographic Information System (GIS)-based machine learning susceptibility modeling using ArcGIS Pro: Maximum Entropy (MaxEnt) and Random Forest-Based and Boosted Classification and Regression (FBBC) and (2) the U.S. Geological Survey (USGS) Grfin (Growth, Flow, and Inundation) runout …
Hvsr-Based Resonance Analysis And Fault Zone Characterization In The El Paso Region, Alexandro Dominguez
Hvsr-Based Resonance Analysis And Fault Zone Characterization In The El Paso Region, Alexandro Dominguez
Open Access Theses & Dissertations
Horizontal to Vertical Spectral Ratio (HVSR) analysis offers an efficient method for characterizing near-surface structure, resolving sediment thickness, and identifying fault-controlled basin geometry in regions with strong impedance contrasts. This study applies HVSR techniques to continuous ambient-noise recordings collected across the El Paso region, a tectonically active segment of the southern Rio Grande Rift where accurate subsurface mapping is essential for seismic hazard assessment. Ambient-noise windows were processed, spectrally smoothed, and stacked to obtain stable HVSR curves, from which fundamental resonance frequencies and corresponding sediment-thickness estimates were derived. Spatial patterns in these resonance frequencies reveal pronounced basin asymmetry, abrupt lateral …
Characterization Of The Synhalokinetic Megaflap Lithofacies And Stratigraphy At Sinbad Valley, Paradox Basin, Western Colorado, Michael David Laase
Characterization Of The Synhalokinetic Megaflap Lithofacies And Stratigraphy At Sinbad Valley, Paradox Basin, Western Colorado, Michael David Laase
Open Access Theses & Dissertations
This study documents the halokinetic evolution of the Sinbad Valley salt wall and flanking megaflap through the characterization of its lithofacies, stratigraphy, and major structures. Sinbad Valley salt wall is in the northern Paradox Basin, in western Colorado, and is the most proximal salt diapir to the Uncompahgre Uplift, the clastic sediment source for the basin. Megaflaps are recently defined structures involving early minibasin strata that are folded up to form steeply dipping "stratal panels" along the sides of steep diapirs. The Sinbad Valley megaflap crops out as a ~7.5km long and 400m wide panel of folded and deformed Pennsylvanian- …
Hinterland To Foreland Regional Transition From Basement-Involved To Thin-Skinned Deformation In The Southern U.S. Cordillera: Sierra Rica, New Mexico, Sarafina Middaugh
Hinterland To Foreland Regional Transition From Basement-Involved To Thin-Skinned Deformation In The Southern U.S. Cordillera: Sierra Rica, New Mexico, Sarafina Middaugh
Open Access Theses & Dissertations
Late Cretaceous to Paleogene age contractional deformation in the southern Basin and Range province is obscured by widespread, Cenozoic extensional faulting and volcanism. As a result, debate continues about the structural style and tectonic evolution of the region. There are two end-member structural models that have been proposed for deformation: 1) high-angle reverse faulting and basement uplift and 2) thin-skinned faulting and development of a thrust belt. We undertook new geologic mapping, cross-section construction, and structural analysis in Sierra Rica, in the bootheel region of southern New Mexico, to help evaluate these hypotheses. A major thrust system, the Sierra Rica …
Eocene To Oligocene Continental Arc Migration In Ecuador And The Origin Of Spatiotemporal Trends In Zircon Lu-Hf Radiogenic Isotopes, Muriel M. Sandoval Vazquez
Eocene To Oligocene Continental Arc Migration In Ecuador And The Origin Of Spatiotemporal Trends In Zircon Lu-Hf Radiogenic Isotopes, Muriel M. Sandoval Vazquez
Open Access Theses & Dissertations
The modern continental arc system in Ecuador is well understood but less is known about arc systems in the past, hindering our understanding of the tectonic evolution of the northern Andes. The Macuchi arc, located in the Western Cordillera of Ecuador, was thought to be the main continental arc system during the Eocene, but new zircon U-Pb LA-ICPMS dates from intrusive arc rocks in central Ecuador indicate a more complex history. During the mid-Eocene, the footprint of arc magmatism broadened and expanded into the Inter-Andean Valley and Eastern Cordillera. During the late Eocene to Oligocene, the arc migrated back toward …
Exhumation Of The Pelona-Orocopia-Rand Schist And Fault Kinematic Constraints On Evolution Of The Eastern California Shear Zone, James Boyette Barker
Exhumation Of The Pelona-Orocopia-Rand Schist And Fault Kinematic Constraints On Evolution Of The Eastern California Shear Zone, James Boyette Barker
Open Access Theses & Dissertations
Southeastern California has experienced a complex recent geologic history as it continues to evolve from a convergent boundary to a period of NE-directed extension and evolution of the Eastern California Shear Zone (ECSZ). This transition is recorded in exhumed bodies of Pelona-Orocopia-Rand (POR) schist and in changing styles of fault deformation. This thesis has two interrelated goals. First, I aim to refine the timing of transition from NE extension to NS contraction in the ECSZ of southeastern California by integrating (U-Th)/He thermochronology with field-based structural analysis. The second prong of this study is to constrain broader patterns of POR schist …
Exploring Connectivity And Element Distribution In The Critical Zone Using Deep Cores Below Agricultural And Natural Drylands In The American Southwest, Angie Lynette Cano
Exploring Connectivity And Element Distribution In The Critical Zone Using Deep Cores Below Agricultural And Natural Drylands In The American Southwest, Angie Lynette Cano
Open Access Theses & Dissertations
Water movement controls how solutes are transported and stored in arid Critical Zone (CZ) systems. In natural drylands, low precipitation and high evapotranspiration lead to long term salt accumulation in the CZ, whereas irrigation increases water input and increases downward solute transport. This study investigates how agricultural practices alter subsurface hydrology and geochemistry by comparing two deep CZ cores from the southwestern United States: a 50 m deep core beneath a flood irrigated pecan farm named 5R farm, in the Rio Grande Valley in Tornillo, Texas, and a 97.5 m deep core from the Red Lake Playa in the Jornada …
Geothermal Gradient And Lithium Co-Generation Power Potential In Lafayette County, Arkansas, Juan Agustin Falquez
Geothermal Gradient And Lithium Co-Generation Power Potential In Lafayette County, Arkansas, Juan Agustin Falquez
Graduate Theses and Dissertations
The Smackover formation in south Arkansas is a known reservoir for brines with high temperature and salinity. Recently, Smackover formation brines in Lafayette County, Arkansas are a target for lithium extraction. A county-wide dataset of Bottomhole Temperatures (BHT) is used to estimate a lower bound geothermal gradient of 36 C/km and a reservoir temperature of 116 C at an approximate depth of 2725 m. The high temperatures make the brines a candidate for geothermal power co-generation. Geothermal power co-generation can be achieved by implementing an Organic Rankine Cycle (ORC) power plant. The Southwest Arkansas Lithium project anticipates a total of …
Quantifying The Short-Term Hydrogeologic Responses Of Highway Construction In Hot Springs, Arkansas, Billy Jack Summerford
Quantifying The Short-Term Hydrogeologic Responses Of Highway Construction In Hot Springs, Arkansas, Billy Jack Summerford
Graduate Theses and Dissertations
In late 2020, excavation for the Highway 5 Bypass in Hot Springs, Arkansas exposed seepage faces along roadcut walls. Groundwater levels at nearby wells decreased by up to 20.9 ft and have remained ~20 ft below pre-construction values on average. This study quantifies changes in storage in the unconfined aquifer within the Hot Springs thermal recharge zone associated with the seepage faces using a numerical groundwater model calibrated to pre-construction head at well ARb4. Model scenarios are used to evaluate whether construction-induced seepage or drought best explains the decrease from late 2020 to early 2021. The numerical groundwater simulation represented …
Groundwater Responses To Tidal Restoration At Pelican Marsh And Sea-Level Rise In Elkhorn Slough, California, Julie E. Nelson
Groundwater Responses To Tidal Restoration At Pelican Marsh And Sea-Level Rise In Elkhorn Slough, California, Julie E. Nelson
Graduate Theses and Dissertations
Coastal wetlands represent a dynamic but vulnerable terrestrial-aquatic interface with future resilience controlled by historic hydrologic alterations, sea-level rise, and groundwater extraction. In diked coastal settings, poor tidal connectivity can degrade habitat from the impoundment of freshwater or hypersaline surface waters. Restoring tidal connectivity could foster marsh revitalization, but altering the surface hydrologic system could lead to unwanted salinity intrusion in shallow aquifers. Saline groundwater intrusion degrades freshwater quality and, while inevitable with sea-level rise, could be accelerated with tidal marsh restoration. To investigate this, I developed a steady-state groundwater flow model of Pelican Marsh, a diked, muted tidal marsh …
Integrated Geophysical, Geotechnical, And Mineralogical Characterization Of Expansive Weches Formation Soils In East Texas: Implications For Infrastructure Design, Samuel Annobil
Electronic Theses and Dissertations
This study investigates the geotechnical, geophysical, and mineralogical characteristics of soils derived from the Weches Formation in Nacogdoches County, East Texas, with emphasis on the relationships among electrical resistivity, moisture condition, compaction state, and mineralogical composition. The Weches Formation is well known for producing clay-rich, moisture-sensitive soils that pose challenges to subgrade performance because of their plasticity and swelling behavior. Representative soil samples were collected and subjected to laboratory testing, including particle size analysis, Atterberg limits, Standard Proctor compaction, free swell tests, electrical resistivity measurements, and X-ray diffraction (XRD) mineralogical analysis. The soils are predominantly fine-grained and clay-rich, with USCS …
Mgrre_Thinsections_Mgrre-150_10, Mgrre
Mgrre_Thinsections_Mgrre-95_15, Mgrre
Mgrre_Thinsections_Mgrre-150_3, Mgrre
Mgrre_Thinsections_Mgrre-150_5, Mgrre
Mgrre_Thinsections_Mgrre-150_7, Mgrre
Mgrre_Thinsections_Mgrre-150_9, Mgrre
Mgrre_Thinsections_Mgrre-150_18, Mgrre
Mgrre_Thinsections_Mgrre-150_25, Mgrre
Mgrre_Thinsections_Mgrre-151_1, Mgrre