Thesis (M.A.)--University of Virginia, 1998. / Description based on content as of June 1999. Title from title screen.

Thesis (MS)--Montana State University--Bozeman, 2009. / Typescript. Chairperson, Graduate Committee: Rick L. Lawrence. Includes bibliographical references (leaves 93-106).

Thesis (D. Min.)--Mid-America Baptist Theological Seminary, 2002. / Includes bibliographical references (leaves 124-130).

Thesis (D. Min.)--Mid-America Baptist Theological Seminary, 2002. / Includes bibliographical references (leaves 124-130).

xix, 189 p. : ill. (some col.), maps (some col.) / Caldera-forming eruptions are dramatic and destructive natural phenomena, causing severe and sustained consequences to society. This dissertation presents new geochemical and geochronologic data for caldera-forming tuffs and pre- and post-caldera rhyolites of the two youngest caldera complexes in the Snake River Plain (SRP) in the western USA: Heise (6.6-4.5 Ma) and Yellowstone (2.1-0.6 Ma). Caldera complex evolution at Heise and Yellowstone can be described by formation of 3-4 spatially overlapping "nested" calderas, successive collapse of intracaldera fill, and development of a large hydrothermal system. Comparison between Heise and Yellowstone reveals that late-stage rhyolite eruptions have drastic depletions in 18 O that require remelting of large volumes (1,000's of km 3 ) of hydrothermally altered rock. Archean xenoliths and Phanerozoic rocks of the crustal basement beneath the SRP province are not depleted in 18 O and therefore cannot be a source of these rhyolites. Isotopic mixing models indicate that early large-volume rhyolites are produced by melting and hybridization of the crust by mantle-derived basalt, and late-stage rhyolites tap hydrothermally altered portions of intracaldera rocks from previous eruptions. Caldera-forming eruptions at Heise culminated 4.45 Ma with eruption of the 1,800 km 3 Kilgore Tuff, the most voluminous 18 O-depleted rhyolite in the SRP and worldwide. O, Sr, and Nd isotope geochemistry, zircon ages, mineral and whole-rock geochemistry, and liquidus temperatures for Kilgore Tuff samples erupted >100 km apart are similar and/or overlapping within error, indicating derivation from a remarkably homogeneous low-δ 18 O magma reservoir (δ 18 O=3.4[per thousand]). Caldera-wide batch assembly and homogenization of variably 18 O-depleted melt pockets with diverse zircon populations can explain the Kilgore Tuff's genesis. Central Plateau Member (CPM) rhyolites at Yellowstone have the same timing (∼2 million years after the initiation of volcanism), magnitude of δ 18 O depletion (∼3[per thousand] depleted relative to normal rhyolites), and cumulative eruptive volume (∼4,000-4,500 km 3 ) as the Kilgore Tuff of the Heise volcanic field. Isotopic, age, and geochemical data for CPM rhyolites show that they become progressively more homogeneous and evolved from 260 ka to 75 ka. Whereas the Kilgore Tuff erupted climactically as an explosive caldera-forming tuff, CPM rhyolite eruptions record sequential, predominantly effusive, "snapshots" of magma assembly, homogenization, and differentiation. This dissertation includes co-authored materials both previously published and submitted for publication. / Committee in charge: Ilya Bindeman, Chairperson; Gregory Retallack, Member; Mark Reed, Member; W. Andrew Marcus, Outside Member

The purpose of this study is to present both the educational and the geographical opportunities of Yellowstone National Park which is a region that provides inspiring areas of observation and experiences for American children.

abstract: I present for the first time a broad-scale assessment of dissolved organic matter in the continental hot springs of Yellowstone National Park. The concentration of dissolved organic carbon in hot springs is highly variable, but demonstrates distinct trends with the geochemical composition of springs. The dissolved organic carbon concentrations are lowest in the hottest, most deeply sourced hot springs. Mixing of hydrothermal fluids with surface waters or reaction with buried sedimentary organic matter is typically indicated by increased dissolved organic carbon concentrations. I assessed the bulk composition of organic matter through fluorescence analysis that demonstrated different fluorescent components associated with terrestrial organic matter, microbial organic matter, and several novel fluorescent signatures unique to hot springs. One novel fluorescence signature is observed exclusively in acidic hot springs, and it is likely an end product of thermally-altered sedimentary organic matter. This acid-spring component precipitates out of solution under neutral or alkaline conditions and characterization of the precipitate revealed evidence for a highly condensed aromatic structure. This acid-spring component serves as a reliable tracer of acidic, hot water that has cycled through the subsurface. Overall, dissolved organic carbon concentrations and fluorescent features correlate with the inorganic indicators traditionally used to infer spring fluid mixing in the subsurface. Further, the fluorescence information reveals subtle differences in mixing between fluid phases that are not distinguishable through classic inorganic indicator species. My work assessing dissolved organic carbon in the Yellowstone National Park hot springs reveals that the organic matter in hydrothermal systems is different from that found in surface waters, and that the concentration and composition of hot spring dissolved organic matter reflects the subsurface geochemical and hydrological environment. / Dissertation/Thesis / Doctoral Dissertation Chemistry 2020

The 7.7 Ma Kimberly Member of the Cassia Formation is part of a succession of A-type rhyolites associated with the Yellowstone hotspot track. It was sampled by the Kimberly core that was drilled on the Snake River Plain as part of Project HOTSPOT (Shervais, et al., 2013). The Kimberly Member is a 170 m thick high-silica rhyolite lava flow containing quartz, plagioclase, anorthoclase, sanidine, augite, pigeonite, magnetite, ilmenite, zircon, and apatite. δ 18O of zircon ranges from 0 to 4.9‰ (Colón et al., 2018), typical low values for the Snake River Plain. Quartz is intensely embayed. Exsolved and resorbed pigeonite cores are mantled by augite. REE-poor apatite cores are resorbed and oscillatory zones truncated by rims with SiO2 as high as 12.8 wt% and LREEtot up to 4.7%. There are three chemically distinct feldspars. Rounded and pitted anorthoclase (Or21 Ab64 An15) mantles plagioclase (An20 to An40) cores. Sanidine (Or47 Ab48 An05) forms thin, subhedral drapes on the outer edges of anorthoclase. Sanidine also fills some of the sieved holes in plagioclase and anorthoclase. There are two chemically distinct glasses, a light glass (~95%) and a dark glass (~5%). Relative to the light glass, the dark is enriched in Al2O3 , CaO, and Na2O and depleted in Fe2O3 and K2O. The dark glass is depleted in Rb and enriched in Sr and Ba, but they have similar concentrations of the high field strength elements (Y, Zr, Nb, Hf, and Ta). LREE are slightly more enriched in the dark glass than in the light glass. Temperatures of 926°C (magnetite-ilmenite thermometry with QUILF), 894°C (pigeonite-augite pairs with QUILF), and 889°C (zircon-saturation) are calculated for the magma. Although Fe-Ti oxides appear to have equilibrated with melt before eruption, most of the other phases preserve strong evidence of disequilibrium. These complex mineral textures also indicate assimilation and mixing processes. We propose a pigeonite-bearing, dry, metasomatized, A-type granite was fragmented and assimilated by the Kimberly member, mantling exsolved pigeonite with augite. Also incorporated into the Kimberly member were volcanic xenocrysts indicative of rhyolite assimilation or magma mixing. These components are embayed volcanic quartz, and composite plagioclase-anorthoclase grains (mantled by sanidine upon assimilation). Complex zircon grains could be sourced from metasomatized rhyolite or intrusion, and complex apatite grains could be due to mixing or assimilation. We propose the distinct glass types are caused by mingling of the Kimberly magma with the melted metasomatized assimilant. This scenario demonstrates the complexity of open system processes involved in some Snake River Plain magmas.

Prior to 1968, the National Park Service contended that an unnaturally large population of elk had severely damaged Yellowstone Park's northern winter range, including aspen and willow communities. However, under "natural regulation" management adopted in the earl y 1970s the agency now believes that vegetation changes in the park are due to normal plant succession, climatic change, or fire suppression, not ungulates. The agency also believes that large numbers of elk (12, 000 - 15, 000) have wintered on the park's northern range for the last several thousand years. This study tested several of the major assumptions or predictions of the Park Service's "natural regulation" paradigm by collecting vegetational data, reviewing historical source materials, and analyzing archaeological reports. The available evidence suggests that observed changes in Yellowstone's tall willow and aspen communities are due primarily to ungulate browsing, not other factors. The future of sexually reproducing willow and aspen communities on the park's northern range appears to be in jeopardy. Under current management, their extinction is only a matter of time. Moreover, entire plant and animal communities have been affected, not just aspen and willows. Historical accounts and archaeological data indicate that few elk inhabited Yellowstone prior to creation of that national park in 1872. These results do not support the "natural regulation" paradigm. Prior to European influence, predation by Native Americans and carnivores limited elk, as well as other ungulate numbers throughout the Greater Yellowstone area.

Although the impacts of livestock and human activities on riparian zones and associated wildlife have been well documented, little is known about the impacts that browsing by large native ungulates such as elk and moose may have. In the northern Yellowstone area, some willow stands experience intense browsing by elk and moose whereas others experience medium or very low amounts of browsing. The objectives of this study were (1) to compare the species and densities of birds among willow stands that have experienced different intensities of browsing by native ungulates, (2) to measure the relationship between five species of birds and aspects of habitat structure, and (3) to develop and evaluate predictive models that relate presence or absence of the five species to habitat characteristics. In 1989 and 1990, I measured densities of nesting songbirds and aspects of habitat structure in eight large willow stands that have experienced different intensities of browsing. The densities of five focal species (Common Yellowthroat, Lincoln's Sparrow, Warbling Vireo, Wilson's Warbler, and Yellow Warbler) varied considerably among sites. Only two sites had all five species and only one species--the Lincoln's Sparrow'was found in all eight sites. The proportion of severely browsed willows in the eight sites ranged from 3.5% to 100%. The nonlinear relationship between total bird densities and frequency of severe browsing suggests that birds have a threshhold of tolerance for browsing, beyond which bird numbers and total numbers of species drop. Principal Components Analysis of 14 habitat variables indicates that the study sites varied in terms of distances between shrubs, shrub heights, height heterogeneity, foliage density at various height intervals, and frequency of severely browsed willows. Browsing does appear to affect the assemblages of breeding birds in these sites, but site- and landscape-level factors such as food abundance, willow species composition, hydrology, type and gradient of adjacent community, and riparian zone width and elevation also play important roles. such variables should be incorporated into future predictive models to improve model performance. (82 pages)