Master of Science / Department of Geology / Matthew E. Brueseke / Low-[delta][superscript]1[superscript]8O silicic magmas are found in many volcanic provinces throughout the world, including the Snake River Plain-Yellowstone volcanic province (SRPY). The origin of SRPY low-[delta][superscript]1[superscript]8O silicic magmas is controversial, and centers on two disputed models: [1] a caldera collapse model that proposes reworking of the hydrothermally altered intra-caldera fill into the underlying silicic magma body, where each successive eruption lowers the [delta][superscript]1[superscript]8O of the magma eventually producing a low-[delta][superscript]1[superscript]8O magma and [2] melting previously hydrothermally altered mid-upper crust to form low-[delta][superscript]1[superscript]8O magmas. The mid-Miocene Santa Rosa-Calico volcanic field (SC) lies in northern Nevada. Brueseke and Hart (2008) described the geology and petrology of the SC, but did not deal with the [superscript]1[superscript]8O compositions of any locally sourced silicic magma. In the existing geological framework of the SC, this project aims to evaluate the two disputed models for low-[delta][superscript]1[superscript]8O silicic magma generation by analyzing the [delta][superscript]1[superscript]8O values of SC silicic eruptive products. Fifteen representative samples of locally erupted silicic units (e.g. ash-flow tuffs and lavas) were chosen for [superscript]1[superscript]8O analyses based on Sr-Nd-Pb isotope compositions, whole rock geochemistry, and field/temporal relationships. Each sample was crushed, sieved, and quartz and feldspar crystals were handpicked, described, and analyzed for their [superscript]1[superscript]8O compositions. Our results show that low-[delta][superscript]1[superscript]8O values exist in the SC and are limited to the youngest erupted silicic unit, the 15.8 to 15.4 Ma Cold Springs tuff, which was also the only unit erupted from a caldera. Cold Springs tuff [delta][superscript]1[superscript]8O feldspar values range from 2.36 to 4.05[per mil]; the unit is not quartz-bearing. Older silicic lavas that are not petrogenetically related to the Cold Springs tuff are characterized by normal [delta][superscript]1[superscript]8O feldspar values that range from 7.19 to 10.04[per mil]. Magma mixing models indicate that the source of the Cold Springs is a mixture of hydrothermally altered Granite Peak-Sawtooth granitoid and local mid-Miocene basalt, with an approximate range of [delta][superscript]1[superscript]8O values of 2-4[per mil], by fluids (with [delta][superscript]1[superscript]8O values ranging from -12[per mil] to + 7[per mil]) from the nearby hydrothermal system at Buckskin Mountain. This result follows the model by Boroughs et al. (2005) of prior alteration and melting, forming low-[delta][superscript]1[superscript]8O silicic magmas.

Meadows in the Sierra Nevada Mountains are an important ecological resource that have degraded in quality and distribution due to several environmental and anthropogenic stressors. The encroachment of conifers beyond forest meadow ecotones is largely responsible for the decline of meadow habitat throughout the past century. Currently, there is little research that quantifies the hydrologic response to removal of conifers encroaching meadows in terms of implicating successful meadow restoration. This study has implemented a before after control intervention (BACI) study design to determine the hydrologic response associated with the removal of conifers from a historic meadow encroached by conifers. The primary goals of this research were to: (1) establish a method to evaluate the weekly water balance of an encroached meadow before and after conifer removal (restoration) (2) characterize the hydrology of an encroached meadow and a nearby control meadow prior to restoration (3) assess the effectiveness of electrical resistivity tomography in improving the spatial interpretation of subsurface hydrology on our study site. A water budget approach was developed to quantify the hydrology of a control and study meadow (Marian Meadow) before and after restoration. In order to determine weekly changes in groundwater depth, 14 Odyssey water level capacitance instruments were installed to a 1.5 meter depth in PVC wells. In order to quantify changes in soil moisture storage, 14 soil moisture probes were installed to a ~1 ft (30 cm) depth. Both sets of instruments were installed using a spatially balanced random sampling approach. Electrical resistivity tomography was conducted on both meadows on three separate dates during: September 9-10 2013, May 5 2014 and September 6-7 2014. A method to quantify runoff from a stream that drains Marian Meadow (Marian Creek) was also established. The Priestley Taylor model was used to estimate daily evapotranspiration from both meadows. Electrical resistivity tomography improved the spatial interpretation of groundwater recharge and facilitated the use of a recession curve analysis to model groundwater recharge when the water table receded beyond instrument detection depths. Electrical resistivity also demonstrated a change in hydrologic characteristics across a forest –meadow ecotone. Analysis of the pre-removal hydrologic characteristics from September 2013 to December 2014 indicates that Marian Meadow may be a favorable candidate for restoration (in terms of hydrology). On Marian Meadow, volumetric soil moisture was higher than the Control Meadow from May-November 2014. Sufficient soil moisture in the summer months is thought to be critical to the maintenance of endemic meadow flora. The water table depth on Marian Meadow and the Control Meadow was similar throughout the analysis period, but Marian Meadow had a shallower water table during the summer months. The Control Meadow had near surface groundwater during short periods from February-April 2014 and December 2014. If conifer removal from Marian Meadow causes an increase in seasonal volumetric soil moisture and a decrease in seasonal groundwater depth, an augmented version of the stable hydrologic system already present on Marian Meadow may result in hydrologic conditions more favorable to meadow restoration.

The recent mass shooting on October 1, 2017 in Las Vegas, Nevada has been marked in history as the worst mass shooting in the United States to this point. The details of the shooting beg the question, is it coincidence that it happened in Nevada, a state with some of the least restrictive gun control laws? Mass shootings have become an unfortunate part of reality in the United States, but these are fairly uncommon occurrences. While they are horrific and deserve attention, daily gun violence cannot be forgotten. In the face of such a multitude of gun violence, what can be done to prevent future violence from occurring? This paper compares Nevada and California, two states that are geographically similar, but could not be more different when it comes to gun control. The paper draws connections between state gun control laws and gun violence trends in an attempt to determine what the best course of action is for addressing the problem.

The Sierra Nevada snowpack is vital to the water supply of California, the world’s sixth largest economy. Though tree ring and instrumental records show the dramatic influence of environmental change on California’s hydroclimate over the last millennium, few proxy archives assess winter precipitation variability farther back in time. Here, we use diatoms from a ~3,200 yr. old sediment core to reconstruct the paleolimnology of June Lake, a hydrologically closed glacial lake in the eastern Sierra Nevada. We test the hypothesis that limnologic and climatic changes control diatom assemblages at June Lake. Fossil diatom assemblages from June Lake sediments chiefly consist of the planktic genera Stephanodiscus and Lindavia; their relative abundances in sediments are controlled by lake response to changes in the length of the winter season. We establish a Lindavia:Stephanodiscus index to infer winter length; our results indicate three periods where winter seasons are longer than average: ~3.2-2.9 ka, ~2.2-1.7 ka, and ~0.6 ka-0.05 ka. Over the last ~100 yrs., June Lake has experienced stronger water column stratification and an expansion of the available benthic diatom habitat, indicating significantly warmer winters and lower lake levels. It is possible that this change is the result of anthropogenic climate warming.

Structural and geochemical analyses of the Top and Casino deposits, Bald Mountain-Alligator Ridge district, Nevada, were conducted to determine how structures affected gold deposition in Carlin-type deposit s. We also examined how permeability changed over time in a fault that cuts siltstone-dominated sedimentary rocks. The association of gold and related arsenic with faults at the margins of a Jurassic pluton and sedimentary rocks suggests that ore fluids migrated along faults and fracture s. Permeability of the faults changed over time within the Casino deposit, where the ore-controlling fault was a distributed conduit in the early stages of mineralization but a barrier and a localized conduit a t opposite ends of the deposit during later stages. Results indicate that faults may significantly influence patterns of ore deposition and change character over deposit-scale distances, and continued slip along faults may create clay-rich low-permeability faults that are mineralized during early stages of development.

Although water is considered a renewable resource, there is only a fixed amount of water available. No additional water can be made, and we cannot easily control how fast water is recycled or in what form it will appear and where. With expected growth in the world’s population and economy, the same amount of water must supply more needs. Taking into account climate change projections and water-related environmental stresses, even less water might be available for human uses. People will need to decide how to serve a multitude of water needs. This dissertation uses the Southern Nevada Water Authority’s (SNWA) Groundwater Development Project to investigate how water policy designs handle the challenges of meeting urban and rural as well as human and ecological water needs when allocating scarce water supplies. The Southern Nevada Water Authority (SNWA) plans to build a pipeline to transfer groundwater from five rural basins in northeastern Nevada 300 miles south to the Las Vegas metropolitan area in Southern Nevada. SNWA has asked the Nevada State Engineer to approve its water right applications to develop and use groundwater from these rural basins. One of the basins, Snake Valley, straddles the border between Nevada and Utah. An interstate agreement allocating the groundwater between the two states is required before the State Engineer can approve water rights that would be diverted from Snake Valley. We found that policy debates and people’s rationales for how water should be allocated revolved around disagreements over beneficial use. In addition, water agreements need to be designed so that the risks from hydrologic uncertainties and impacts from other users are also apportioned clearly and equitably. Policy designs are purposefully crafted and have enormous impact, yet analysis of the actual contents of policies and their societal impacts has not received adequate attention within the policy sciences. The significance of this research is that it focuses on the foundational principles and rules for the allocation of scarce water resources that must necessarily balance urban and rural interests as well as human and environmental needs.

Graduation date: 1994

Estimates of average annual precipitation (AAP) are-needed for hydrologic modeling at Yucca Mtn., Nevada, site of a proposed, high-level nuclear waste repository. Historical precipitation data and station elevation were obtained for stations in southern Nevada and southeastern California. Elevations for 1,531 additional locations were obtained from topographic maps. The sample direct-variogram for the transformed variable TAAP = ln(AAP) * 1000 was fit with an isotropic, spherical model with a small nugget and a range of 190,000 ft. The sample direct-variogram for elevation was fit with an isotropic model with four nested structures (nugget, Gaussian, spherical, and linear) with ranges between 0 and 270,000 ft. There was a significant (p = 0.05, r = 0.75) linear correlation between TAAP and station elevation. The sample cross-variogram for TAAP and elevation was fit with two nested structures (Gaussian, spherical) with ranges from 55,000 to 355,000 ft. Alternate model structures and parameters were compared using cross-validation. Isohyetal maps for average annual precipitation (AAP) were prepared from estimates obtained by kriging and cokriging using the selected models. Isohyets based on the kriging estimates were very smooth, increasing gradually from the southwest to the northeast. Isohyets based on the cokriging estimates and the spatial correlation between AAP and elevation were more irregular and displayed known orographic effects. Indirect confirmation of the cokriging estimates were obtained by comparing isohyets prepared with the cokriging estimates to the boundaries of more densely vegetated and/or forested zones. Estimates for AAP at the repository site were 145 and 165 mm for kriging and cokriging, respectively. Cokriging reduced estimation variances at the repository site by 55% relative to kriging. The effectiveness of an existing network of stations for measuring AAP is evaluated and recommendations are made for optimal locations for additional stations. / Graduation date: 1991

Ash-flow tuff (ignimbrite) is a general term indicating consolidated deposits of volcanic ash flow; a flow of a mixture of gas and pyroclastic materials as products of explosive volcano eruptions (Smith, 1960). Two different ash-flow tuffs are studied in this research: 1. Topopah Spring Tuff at Yucca Mountain, Nevada and 2. the Bandelier Tuff at Pajarito Plateau, New Mexico. Various dynamic test parameters (e.g. confining pressure, shearing strain, etc) were studied with two existing devices: (1) the combined resonant column and torsional shear (RCTS) device, and (2) the free-free, unconfined, resonant column (URC) device. The effects of these parameters are evaluated for two different types of ash-flow tuffs. In addition, a Large Resonant Column (LgRC) device was developed and used to test the some tuffs from Yucca Mountain at larger strain amplitudes than possible with the RCTS and URC devices. Relationships between the linear and nonlinear dynamic properties and lithostratigraphic features were further investigated. Finally, potential problems related to sample disturbance and specimen size are considered based on comparisons of small-strain shear wave velocity (VS) values measured in the laboratory and in the field. / text

Tectonic signatures such as growth strata, clastic progradation, detrital composition, thickness trends, paleoflow shifts, lithofacies distribution, and vertical stratigraphic stacking patterns provide the basis for a range of tectonic/structural interpretations. Complete understanding of the application and limitations of tectonic signatures is important to maintain consistency and reduce uncertainty of interpretations that use them. This study provides insight into the external controls on two frequently used tectonic signatures in foreland basins: (1) growth strata, and (2) clastic wedge progradation. First, two syntectonic unconformity types are recognized in non-marine, Cenomanian growth strata adjacent to the Sevier thrust-belt in southeastern Nevada, USA. Unconformities with larger angular discordance (>10°, “Traditional Type”) developed when uplift outpaced sediment accumulation. More subtle unconformities with less discordance (2-10°, “Subtle Type”) developed when sediment accumulation nearly kept pace with uplift. Increasing sediment supply with positive net accommodation, allows syntectonic deposits to aggrade above a growing structure, with no change in uplift rate. Hence, sediment supply and regional accommodation impart an important control over growth strata geometries that are often interpreted on the basis of tectonics alone. Identification of unconformity types in growth strata can therefore document additional phases of uplift, particularly for intervals where sediments aggraded above an active structure due to higher sediment supply during regional subsidence, or sea level rise. Second, an anomalous, Campanian clastic wedge is identified in Cordilleran Foreland basin fill, Utah and Colorado. The complex internal architecture, tide-dominated facies and characteristic flat-to-falling shoreline stacking patterns of the wedge reflect rapid progradation of wide (60-80 km), embayed, tide-influenced shorelines; these characteristics distinguish the anomalous wedge from the underlying and overlying clastic wedges in the basin. A high-resolution regional correlation and isopach maps for the anomalous wedge provide evidence that extensive clastic progradation was coeval with both Sevier- and Laramide-style deformation. Stratigraphic relations suggest that development of the anomalous character of Wedge B was due to uplift of a Laramide structure within the foredeep, and possibly enhanced by reduced dynamic subsidence. / text