Geology Theses and Dissertations
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Item GEOMORPHIC AND HYDROLOGIC CHARACTERISTICS OF SMALL URBANIZED TRIBUTARIES TO A FALL ZONE STREAM(2024) Harris, John Allen; Prestegaard, Karen; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Many rivers along the Atlantic Coast contain major knickpoints, which define the Fall Zone. These often-urbanized rivers straddle multiple physiographic regions with spatial variations in lithology, topography, and hydrology. This research evaluates the effects of mainstem channel incision and urbanization on channel and catchment morphology, bed substrate mobility, catchment water storage dynamics, and hydrologic response in tributaries of the Northwest Branch of the Anacostia River above and below the Fall Zone knickpoint. Topographic analyses show that differential incision below the mainstem knickpoint has initiated steep secondary channels incised into bedrock. Measurements at representative reaches show that bankfull shear stress exceeds critical shear stress in these newly initiated tributaries, resulting in erosive channels outside of threshold conditions. Increased urban runoff introduced at storm drain outfalls maintains these non-steady state conditions. Geophysical surveys reveal that regolith depth for water storage capacity is primarily below the flatter ridgetops of the tributary catchments, where development is concentrated. The secondary tributaries cannot access these upland storage zones, and thus have limited infiltration and recharge capacity. I installed streamgages in the tributaries and constructed catchment water balances to study storage dynamics and hydrologic response. Hydrologic consequences of urbanizing the steep secondary tributaries include flashy, elevated stormflows, greater total runoff, and reduced baseflows that are not maintained during drought periods. The combination of steep channels, thin regolith, and urban overprint limits infiltration to moderate storm responses and recharge storage. These effects were not seen in non-urbanized secondary tributaries, urbanized tributaries above the knickpoint, or the forested reference streams above the Fall Zone. These findings define the geomorphic adjustment of tributaries to differential mainstem incision and explore the hydrologic impacts of urbanizing small steep catchments with limited effective storage capacity. Supplementary files:S1: Table with the location, drainage area, stream gradient, bankfull hydraulic values, and grain size values at each Northwest Branch tributary and reference reach used in the study. S2: Spreadsheet with the water level logger gage height values collected at 5-minute intervals from April 2023-March 2024 and calculated discharge from the Northwest Branch tributary streamgages. S3: Spreadsheet with the monthly water balance values for the Northwest Branch tributary catchments and reference watersheds from April 2023-March 2024. S4: Table with the depth to bedrock values and corresponding slope angles measured from the seismic profiles and LiDAR-derived digital elevation models.Item USING BAYESIAN ELECTRICAL RESISTIVITY INVERSION TO REVEAL HILLSLOPE DRY-UP PROCESS IN A MEDITERRANEAN CLIMATE(2024) Shahid, Saffat; Huang, Mong-Han; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Hydrologic dynamics in hillslopes is essential for comprehending the processes that shape landscape evolution and sustain the Earth’s critical zone. Electrical resistivity (ER) is considered as one of the best geophysical methods to observe these dynamics due to its sensitivity to subsurface water content. To understand hillslope water dynamics and mitigating the risks of slope instability caused by extreme weather events, we studied how subsurface hydrological processes are being influenced by variations in vegetation type across different aspects of hillslopes. Thus, how accurately ER can quantify the dry-up process during the growing season on hillslopes becomes critical, particularly in regions with distinct dry summers and wet winters (i.e. Mediterranean climates). The Blue Oaks Ranch Reserve (BORR) in Central California provides an ideal location for this study due to its consistent ridge-valley systems, which well represents the regional climatic and topographic conditions. Previous work at BORR used active source seismic refraction (SR) to constrain subsurface structure. To additionally investigate moisture content in regolith, we conduct ER surveys with Schlumberger and Dipole-Dipole configurations to invert for resistivity using Transdimensional Hierarchical Bayesian (THB) inversion framework with reversible-jump Markov Chain Monte Carlo (THB rj-MCMC). We also performed 2D synthetic tests to evaluate how well THB can recover a synthetic model with imposed data uncertainty. The results indicate that Schlumberger outperforms Dipole-Dipole in the THB rj-MCMC inversion. However, these results also reveal limited depth resolution to ~10 m depth using current ERT configurations. Finally, we adopt the THB approach for a series of ER surveys at BORR between June and September 2023. The findings suggest a distinct increase in resistivity on the North-facing slope during growing seasons, indicating reduced moisture content particularly in areas with presences of oak trees as they draw water from deep regolith. On the South-facing slope, resistivity remained stable due to the dominance of grass that lacks deep roots for consuming deep moisture. Our resistivity results show that vegetation type particularly trees play a critical role in regolith moisture distribution. To compare and correlate changes in resistivity over dry periods, we analyzed soil probe data previously collected at the site. The correlation suggested that increases in resistivity are related to decreases in volumetric moisture content. Additionally, we compared ERT data with seismic survey data to better understand changes in subsurface properties like porosity and saturation along depth, as ERT and seismic velocity is sensitive to moisture content and material porosity.Item QUANTIFICATION OF MELT DISTRIBUTION, MELT CONNECTIVITY, AND ANISOTROPIC PERMEABILITY OF DEFORMED PARTIALLY MOLTEN ROCKS USING X-RAY MICROTOMOGRAPHY(2024) Bader, James Alexander; Zhu, Wenlu; Montesi, Laurent G.J.; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Volcanic activity plays a dominant role in shaping the surface of Earth and other planets. For example, Earth’s ocean floor is created by volcanic activity at mid-ocean ridges. There, magma is sourced from a ~60 km deep, ~100 km wide region of the mantle, from which partial rock ascends and erupts along narrow ridges that run along the middle of Earth’s oceans. Volcanic activity at mid-ocean ridges, the strength of Earth’s mantle, and the geochemical composition of volcanic rocks and ocean water are all influenced by how the melt is distributed in partially molten rocks, and how easily it can flow through the partially molten mantle beneath these ridges. In particular, it is often assumed that most of the melt ascends through isolated channels that direct it towards the mid-ocean ridges, making melt transport localized and anisotropic. A possible origin of these channels is the differential stress induced by upwelling mantle material beneath the ridge, which has been shown in laboratory experiments to localize melt into planar regions named “melt-rich bands.” To date, the development and characteristics of melt-rich bands have been studied principally using theoretical models and two-dimensional (2D) images of sheared partially molten rocks. There has been little experimental research using 3D techniques until now. This thesis uses 3D images of sheared partially molten rocks created in the laboratory, obtained using high-resolution x-ray microtomography (X-ray µCT), to investigate how the distribution of melt, its orientation, its connectivity, and its ability to flow through the rocks changes when stress is applied. This study shows how melt connectivity and, therefore, rock permeability changes as melt changes from being dispersed through a partially molten rock to being localized on well-developed melt-rich bands. This work shows that melt forms melt volumes that are preferentially elongated within the plane of melt-rich bands even before these bands form. This discovery emphasizes the importance of permeability anisotropy at all stages of melt-rich band development. We also measured permeability and melt connectivity at all scales, both inside and outside melt-rich bands. Our results show that melt can hardly flow perpendicular to melt-rich bands over distances larger than a few grains. Additionally, the permeability along the melt-rich bands is also reduced by half compared to that in a partially molten rock that is not subjected to differential stress. This research quantifies the uneven distribution of permeability in a sheared, partially molten rock. It also proposes a scheme to average local permeability estimates, helping us understand and quantify how melt travels along melt-rich bands at various scales. These findings provide valuable insights into how magma flows in the Earth’s mantle, especially at active plate boundaries like mid-ocean ridges. Overall, this research provides the first experimental constraints, based on 3D microtomography images, on the melt network and how melt flows in the presence of stress in partially molten rocks.Item GEOCHEMICAL INDICATORS OF REDOX AND WEATHERING ACROSS THE EDIACARAN-CAMBRIAN TRANSITION IN SIBERIA(2024) Doerrler, Andrew; Kaufman, Alan Jay; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The transition between the Ediacaran and Cambrian periods witnessed the fall of the enigmatic Ediacara biota. The cause of their extinction is poorly understood, but the timing broadly coincides with a significant negative ẟ13C anomaly, the BAsal Cambrian Carbon isotope Excursion (BACE). These macroscopic organisms were likely tolerant of anoxic conditions, so oceanic oxidation may have been a kill mechanism. This study utilizes uranium isotopes, sulfur isotopes, and cerium anomalies to understand oceanic redox conditions from two BACE sections in Siberia, as well as lithium isotopes to constrain weathering intensity. Reconstruction of seawater ẟ238U values from equivalent evaporite and carbonate-dominated successions indicate a notable increase in oxygen during the event supporting the oxidation hypothesis. Global sea level fall and evaporite formation suggest that seawater salinity increased dramatically along continental margins, which may provide an alternative osmotic kill mechanism for the softbodied Ediacaran biota. Support for the salinity hypothesis comes from profound ẟ7Li and ẟ34S compositions of carbonate and pyrite, respectively, which arguably resulted from the distillation of lithium and sulfate from seawater into evaporite-rich lithologies.Item Integrated Geochemical Studies of the Shuram Excursion in Siberia and South China(2024) Pedersen, Matthew; Kaufman, Alan J; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The Ediacaran Period Shuram Excursion (SE) is a globally-distributed and highly controversial phenomenon where over millions of years, sedimentary carbonates record δ13C values of -10‰ and lower. This carbon cycle anomaly may reflect disequilibrium in the world’s oceans, driven by the oxidation of a large pool of dissolved organic carbon (DOC), with the oxidants sourced from the intense weathering of the continents, forcing major changes to ocean chemistry through the ventilation of the deep ocean, evidenced by a positive shift in carbonate uranium isotope values, and invoking the onset of early animal biomineralization. This study utilizes high-resolution carbonate Li isotopes from two SE-successions, U isotopes, REE abundances and Ce anomalies which reveal the dynamic interplay between intensified continental weathering associated with tectonic reconfiguration and the subsequent environmental and ecological response that may have been amplified by the ecosystem-engineering abilities of a newly discovered sponge-grade animal.Item PREDICTING THE SEISMIC SIGNATURE OF LAVA TUBES FOR THE EARTH, THE MOON, AND MARS(2024) Wike, Linden; Schmerr, Nicholas; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Lava tubes are a type of volcanically-generated subsurface void structure found on Earth, the Moon, and Mars and hold the potential to serve as shelters for crew members, preservation sites of pristine geological samples, and locations of in situ resources. A key question for lava tube science is how to locate them through geophysical methods. Here, we create a workflow that locates and characterizes the geometry of subsurface voids. We build a suite of subsurface synthetic seismic wavefield models that contain lava tube structures and investigate which seismic method best images them. Our models show that the more readily detectable lava tube simulations have a geophone spacing of 0.5 m, variable diameter, and shallow ceiling depth; and reverse-time migration and phase-shift-plus-interpolation migration techniques produce more accurate lava tube reconstructions than the Kirchhoff method. The synthetic modeling serves as a benchmark for understanding seismic wave propagation around lava tubes and helps answer how voids on the Moon and Mars would be imaged through seismology.Item Safer Grounds: A Study of Landmine Detection using UAV- and Ground-Based Multi-Modal Geophysics(2024) Myers, Heidi Patricia; Lekic, Vedran; Lathrop, Daniel; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This dissertation addresses the urgent global crisis of landmines, unexploded ordnance (UXO), and explosive remnants of war (ERW) through the lens of multimodal geophysics. Chapter 1 sets the stage by highlighting the humanitarian imperative while underscoring the broader applicability of the developed methods and instruments for shallow critical zone exploration. Unlike conventional engineering-centric approaches, our geoscience-centered methodology offers promising avenues for effectively detecting and characterizing buried hazards. Chapter 2 meticulously examines various geophysical sensors, identifying limitations and proposing innovative solutions. Notably, TetraMag, a novel triaxial magnetic gradiometer, overcomes the deficiencies of single-sensor systems, demonstrating superior sensitivity to small-scale variations in the magnetic field. Chapter 3 delves into the intricate symmetries and invariants of the finite-difference magnetic gradient tensor (FDMGT), elucidating its pivotal role in precise target localization and parameter estimation within the shallow critical zone. The methodology outlined streamlines data processing and interpretation, laying a robust foundation for UAV-based detection systems. Chapter 4 introduces machine learning techniques, particularly convolutional neural networks (CNNs), as robust target detection and parameter estimation tools. By synergizing multiple geophysical modalities, these methods enhance our ability to discern subtle anomalies with high accuracy. Chapter 5 proposes a method to mitigate magnetic self-noise in UAV-mounted gradiometers, enhancing data fidelity and spatial coherence. This approach, applicable to various vehicle platforms, further extends the reach of our detection capabilities. In Chapter 6, we integrate and apply these methodologies to a real-world minefield scenario, successfully detecting and localizing buried targets. While acknowledging limitations such as payload constraints and computational demands, our findings underscore the versatility and robustness of the developed techniques. This dissertation addresses the pressing humanitarian challenge of landmine detection and advances the broader field of shallow critical zone geophysics. The methodologies and technologies presented here hold promise for diverse applications beyond military contexts, ranging from infrastructure mapping to hydrogeological studies.Item THE CONCENTRATION OF HYDROGEN IN INCOMPLETELY AND WHOLLY MELTED TERRESTRIAL BUILDING BLOCKS(2024) Peterson, Liam Donald; Newcombe, Megan E; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Hydrogen (H) is the most abundant element in our solar system and exerts a primary control on the habitability, and geochemical and geodynamic evolution of rocky bodies. Therefore, constraining the source(s), timing of accretion, and abundance of H in the Earth and other bodies is of fundamental importance for understanding how planets evolve. Direct constraints on the source(s) of H and other highly volatile elements (HVEs; e.g., H, C, F, Cl, and S) to the bulk Earth can be provided by analyzing meteorites, which are the remnants of early-formed rocky bodies that were present during the accretion of the terrestrial planets. Such samples either directly sample or provide analogs for terrestrial precursor materials.Rocky solar system materials can be subdivided based upon their nucleosynthetic isotopic compositions (“genetic” tracers; e.g., 50Ti, 54Cr) into two groups, which are thought to correspond to the inner- and outer- solar system. Materials may be further subdivided by their extent of thermal processing (i.e., unmelted, incompletely melted, and wholly melted). Earths H budget is commonly accounted for by addition of unmelted (i.e., chondritic) materials, namely carbonaceous chondrite-like (CC-like) materials, thought to be derived from the outer solar system, which have high H concentrations (up to ~14 wt. % H2O; total H as H2O equivalents) and similar H isotopic compositions to the bulk Earth. Furthermore, chondrites derived from the inner solar system (e.g., ordinary and enstatite chondrites) are H-poor relative to carbonaceous chondrites. Similarly, all melted planetesimals are commonly assumed to be anhydrous. However, recent analyses of enstatite chondrites (ECs), which are formed in the inner solar system and are the closest match to the nucleosynthetic isotopic composition of the bulk Earth, suggest that ECs have a similar H isotopic composition to the bulk Earth and can account for its entire H budget. Furthermore, recent analyses suggest that melted (i.e., achondritic) bodies may retain considerable amounts of H, potentially enough to account for Earth’s H budget in the case of the enstatite achondrites (i.e., aubrites). However, achondritic materials are predominantly highly H-poor relative to chondritic materials, and it is unclear if the aubrites are an anomaly, and at which stage of planetesimal evolution H and other HVEs are lost. In chapter 2, I re-examine prior bulk analyses of H in aubrites, and by extension ECs, using in situ methods and suggest that nearly all H measured in aubrites by bulk methods reflects pervasive terrestrial contamination and alteration, a result which may extend to concurrent bulk H analyses of ECs. In chapters 3 and 4, I examine the H content of incompletely melted (i.e., primitive achondritic) planetesimals to constrain at what stage of planetesimal evolution H is lost. Chapter 3 characterizes the H contents of the ureilites, a group of C-rich primitive achondrites, and chapter 4 characterizes the H contents of the acapulcoite-lodranite clan which represents the “prototypical” primitive achondritic parent body. I find that primitive achondritic parent bodies are highly H-depleted relative to chondrites, requiring that H is efficiently lost prior to or at the onset of planetesimal melting, and that Earth’s H budget is accounted for by accretion of thermally primitive materials (e.g., chondrites). Within my primitive achondrite data sets, I observe apparent disequilibrium with respect to H between olivine, pyroxene, and feldspar. In chapter 5, I explore whether this apparent disequilibrium is the result of extrapolating high pressure experimental data to low pressures. I conduct olivine–melt H partitioning experiments at low pressures (10 – 200 MPa) and find that the olivine-melt H partition coefficient increases at low pressures, contrary to extrapolation from high pressure data. This observation is best explained by a control of H speciation in the melt on the partitioning of H between olivine and melt.Item EXPERIMENTAL CONSTRAINTS ON PHYSICAL PROPERTIES OF VOLCANIC ROCKS WITH IMPLICATIONS FOR LUNAR EXPLORATION(2023) Braccia, Casey Marie; Zhu, Wenlu; Schmerr, Nicholas; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The lunar subsurface is a primary science target for future missions to the Moon and serves as a potential host location for resources such as water ice, void spaces for astronaut shelter, and important ore bodies for in-situ manufacturing and building materials (Horz, 1985; Coombs and Hawke, 1992; Wendell, 2017). Here we conducted laboratory experiments to investigate how the seismic signature obtained at or near the lunar surface is related to subsurface material properties and structures. A range of analog basaltic samples collected from the San Francisco Volcanic Field (SFVF) in Arizona, Kilbourne Hole (KH) in Southern New Mexico, and Lava Beds National Monument (LBNM) in Northern California are collected and their geophysical properties are measured. The relationships between the seismic wave velocity and porosity of basaltic rocks from different locales are obtained and the measured velocities are compared to local seismic surveys of the sample locale. Using laboratory techniques, the SFVF basalts P-wave and S-wave velocities range from ~5 km/s to ~6 km/s +/- 0.1 km/s and ~2.1 km/s to ~3 km/s +/- 0.1 km/s, respectively. For the KH basalts P-wave and S-wave velocities range from ~3.5 km/s to ~4.4 km/s +/- 0.1 km/s and ~1.8 km/s to ~2.3 km/s +/- 0.1 km/s, respectively. For LBNM basalts P-wave and S-wave velocities range from ~3.1 km/s to ~6 km/s +/- 0.1 km/s and ~1.2 km/s to ~2.4 km/s +/- 0.1 km/s, respectively. A relationship between the porosity and velocity of basalts from these three locations was determined. Using the field seismic data for each study site and the relationship derived from the laboratory seismic data and porosity, the amount of possible large-scale fracturing is derived. Based on these experimental measurements, we estimate the large-scale fractures and voids are ~84 vol% at the SFVF, ~42 vol% at the KH, and ~39 vol% at the LBNM. These results provide quantitative constraints for subsurface exploration in future lunar surface missions.Item LONGITUDINAL STREAM SYNOPTIC (LSS) MONITORING TO EVALUATE WATER QUALITY IN RESTORED STREAMS(2023) Malin, Joseph Thomas; Kaushal, Sujay S; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Many kilometers of streams are being restored in the Chesapeake Bay watershed and elsewhere in efforts to stabilize streambanks, protect infrastructure, and improve water quality. Urban development and impervious surface cover increase peak flows, which degrade streams. Restoration strategies often employ engineering approaches to enhance stream-floodplain reconnection, dissipate erosive forces from urban runoff, and enhance contaminant retention. In this study, longitudinal stream synoptic (LSS) monitoring (sampling multiple points along flowpaths across both space and time) was conducted to assess the effectiveness of different forms of stream restoration in attenuating pollutants downstream. Spatial and temporal monitoring of carbon, nutrients, salt ions, and metals were conducted across five watersheds experiencing varying levels of stream-floodplain reconnection and stormwater management within the Chesapeake Bay region. Study sites included Sligo Creek (minimal floodplain reconnection), Paint Branch (streambank stabilization without significant reconnection), Scotts Level Branch (engineered stream-floodplain reconnection), Little Paint Branch (natural floodplain reconnection from sedimentation), and Campus Creek (regenerative stormwater conveyance with engineered floodplain reconnection). We investigated: (1) whether changes in water chemistry can be detected along longitudinal flowpaths in response to stream-floodplain reconnection, and (2) which monitoring scales across space and time can provide useful information regarding the effectiveness of restoration. Results from this work suggest that longitudinal synoptic monitoring can track the fate and transport of multiple contaminants and evaluate restoration strategies across high spatial-resolution scales. Along all five watersheds, stream water chemistry varied substantially across finer spatial scales (sometimes within hundreds of meters) in response to changes in landscapes, restoration features, or local hydrology. There were significant declining concentrations (p<0.05) or stable concentrations of nutrients, salts, and metals as streams flowed through restoration features. There were significant increasing trends in chemical concentrations (e.g. Na+, Ca2+, K+) in unrestored stream reaches with increasing impervious surface cover. Principal component analysis (PCA) also indicated that there were changes in the chemical compositions of mixtures of salts, metals, and nutrients in response to restoration projects, storm events, and seasons. Interestingly, dissolved Fe and Mn concentrations showed significant increasing trends along some stream reaches with hydrologically connected floodplains. Fe and Mn also showed significant decreasing trends along some unrestored stream reaches surrounded by increasing impervious surfaces. Increased concentrations of dissolved Fe and Mn may have been an indicator of increased hydrologic connectivity between groundwater and surface water and decreased redox potentials. Overall, longitudinal water quality changes over meters and kilometers can be useful in detecting effects of stream restoration on water quality at the watershed scale. Results suggest that water quality in urban streams can change locally in response to restoration projects for multiple chemicals, but the incremental changes associated with different forms of stream restoration and riparian conservation can also be overwhelmed across broader watershed spatial scales and during storm events.