This thesis presents the development of various methods for measuring rainfall rates using horizontally-pointing millimetre-wave radars. This work builds from the combination of a T-matrix scattering model that allows the scattering from almost arbitrarily pro led rotationally symmetric particles to be calculated, and drop shape models that allow the effects of temperature and pressure on the shape to be taken into account. Many hours of rain data have been collected with 38 and 94 GHz FMCW radars, as well as with a disdrometer and weather station. These have been used to develop single- and dual-frequency techniques for measuring rainfall rate. A temperature, polarisation and attenuation corrected application of simple power-law relationships between reflectivity and rainfall rate has been successfully demonstrated at 38 GHz. However, at 94 GHz it has been found that more detailed functions relating reflectivity, attenuation and rainfall rate are beneficial. A reflectivity-based determination of attenuation has been adapted from the literature and successfully applied to the 94 GHz data, improving the estimate of rainfall rate at longer ranges. The same method for estimating attenuation has also been used in a dualfrequency technique based on the ratio of the extinction coefficients at 38 and 94 GHz, but with less success. However, a dual-frequency reflectivity ratio based approach has been successfully developed and applied, producing good estimates of rainfall rate, as well as reasonable estimates of two drop-size distribution parameters. Simulations of radar measurements of airborne volcanic ash have also been carried out, demonstrating that for most reasonable measurement configurations the optimal frequencies would typically be 35 GHz or 94 GHz, not the more commonly used 3-10 GHz. It has also been shown that various existing millimetre-wave radars could be used to detect ash. Finally, there is a discussion of the optimal frequencies for dual-frequency measurement of volcanic ash.

The Black Rock volcanic cluster consists of 30 small volume monogenetic volcanoes. The volcanoes of this cluster have exhibited bimodal volcanism for > 9 Ma. The most recent eruption of Ice Springs volcano ~600 yrs. ago along with ongoing geothermal activity attests to the usefulness of a hazard assessment for this area. The likelihood of a future eruption in this area is estimated to be between a 0.16 and 24% chance over the next 1 Ka (95% confidence). The explosivity and nature of many of these eruptions is not well known. In particular, the physical volcanology of Tabernacle Hill suggests a complicated episodic eruption. Initial phreatomagmatic eruptions at Tabernacle Hill are reported to have begun no later than ~14 Ka. The initial eruptive phase produced a tuff cone approximately 150 m high and 1.5 km in diameter with distinct bedding layers. Recent mapping and sampling of Tabernacle Hill's lava and tuff cone deposits was aimed at better constraining the sequence of events, physical volcanology, and energy associated with this eruption. Blocks located on the rim of the tuff cone of were mapped and analyzed to yield preliminary minimum muzzle velocities of 60-70 m s-1. After the initial phreatomagmatic explosions, the eruption style transitioned to a more effusive phase that partially filled the tuff cone with a semi-steady state lava lake 200 m wide and 15 m deep. Eventually, the tuff cone was breached by the impinging lava resulting in large portions of the cone rafting on top of the lava flows away from the vent. Eruption onto the Lake Bonneville lake bed allowed the Tabernacle Hill lava flows to flow radially from the tuff cone and cover an area of 19.35 km², producing a very uniform high aspect ratio (100:1) flow field. Subsequent eruptive phases cycled several times between effusive and explosive, producing scoria cones and more lava flows, culminating in an almost complete drainage of the lava lake through large lava tubes and drain back.

Large-volume silicic eruptions are often evacuated from magma reservoirs which display gradients in composition, temperature, crystallinity, and volatile content. The 9.7 Ma Devine Canyon Tuff (DCT) of eastern Oregon represents such an eruption, with >300 km³ of compositionally zoned pyroclastic material deposited as a variably-welded ignimbrite. The ignimbrite displays homogenous bulk tuff major element compositions with a wide range of trace element compositions, allowing for the investigation of how these magmas were generated, stored, and modified in the magma reservoir by studying pumices which represent the primary magmas composing the DCT. Five pumices ranging from dacite to rhyolite bulk compositions were selected across the range of trace element compositions and were crushed and sieved to measure how crystallinity and mineral abundances change within each pumice at different particle size fractions. Single alkali feldspar and clinopyroxene crystals were analyzed using EMP and LA ICP-MS from each pumice. Physical results yielded a systematic decrease in crystallinity from 22% to 3% going from the dacite to the most evolved rhyolite composition, with the highest crystallinity occurring between <991-425 microns for all pumices analyzed. The dacite pumices displayed a glomerocrystic texture not observed in rhyolite pumices. Two populations of crystals were distinguished using single crystal chemical data, one belonging to the rhyolitic magmas and another belonging to the dacitic magma. Acquired mineral data have relevance for how strongly zoned with regard to trace elements the rhyolitic magmas of the DCT were, how these magmas were generated, and how they were stored within the magma reservoir. Applying melt extraction models to explain observed patterns in trace element compositions between pumices is problematic. In this model, the observed range of trace elements in rhyolite pumices would be attributed to two separate melt extraction events from an intermediate crystal mush where the first expulsion of melt from the mush produced the most evolved rhyolite composition and a second expulsion coupled with partial melting produced a second rhyolite with an indistinguishable major element composition but less evolved trace element composition. Mixing of these two rhyolite end members would then be needed for generating the range of intermediate rhyolite compositions. Magma mixing modeled using a mixing equation produced a poor fit for trace elements, suggesting the range of observed trace element compositions cannot be solely generated through the mixing of the extracted rhyolite melts but require processes that subsequently modify the mixed rhyolite compositions. The occurrence of crystal aggregates in the dacite may represent fragments of the crystal mush. However, the dacite was unlikely produced by partial remelting of the crystal mush, generating a less evolved, more intermediate bulk composition. In summary, mush extraction combined with partial melting of the crystal mush and mixing of compositional end members cannot fully explain the trace element patterns observed in the DCT pumices thus warranting further study.

The Dinner Creek Tuff erupted during a period of rhyolitic volcanism coeval to the flood volcanism associated with the Columbia River Basalt Group. The High Rock Caldera Complex, Lake Owyhee and McDermitt volcanic fields account for ~90% of the rhyolites erupted between 16.7-15.0 Ma. Situated at the northern end of the Lake Owyhee volcanic field, the Dinner Creek Tuff was originally mapped as a ~2,000 km2 single ignimbrite confined to the Malheur Gorge. Streck et al. (2015) correlated tuff outcrops previously mapped as generic Miocene welded tuff as well as local units such as the "Mascall" or "Pleasant Valley" tuff of eastern Oregon to individual cooling units that comprise the newly redefined Dinner Creek Tuff, enclosing an area of ~25,000 km2. Areal extents defined in this study show that all outcrops now determined to be Dinner Creek Tuff enclose an area of ~31,800 km2 not including any fallout deposits that likely extended beyond the defined area. Although Dinner Creek Tuff rhyolites have nearly identical compositions, different ages and subtle geochemical and mineralogical differences exist and were used to divide the Dinner Creek Tuff into four discrete cooling units. Except for unit 4, the units are lithologically very similar. Unit 1 is the Dinner Creek Tuff unit associated with the Malheur Gorge type section. The four cooling units have ages of 16.15-16 Ma (unit 1), 15.6-15.5 Ma (unit 2), 15.46 Ma (unit 3) and 15.0 Ma (unit 4). Areal extents were established for all four cooling units based on feldspar compositions along with lithological and bulk rock geochemical data. Minimal extents of individual units are as follows: ~22,590 km2 (unit 1), ~17,920 km2 (unit 2), ~14,170 km2 (unit 3) and ~8,370 km2 (unit 4). Using conservative thicknesses, determined erupted tuff volumes are ~170 km3 (unit 1), ~125 km3 (unit 2), ~99 km3 (unit 3) and ~46 km3 (unit 4), totaling ~440 km3 and dense rock equivalents are ~152 km3 (unit 1), ~96 km3 (unit 2), ~76 km3 (unit 3) and ~31 km3 (unit 4), totaling ~356 km3. These extents and volumes are the absolute minimum based solely on the locations of exposed tuff sections and the inclusion of the source. Centering eruptive units on source areas where they are known, expands the tuff extents into a more radial pattern as would be expected for low-aspect ratio, high energy ash-flow tuff eruptions. These probable extents increase the areal extents of the individual units to: ~36,900 km2 (unit 1), ~31,660 km2 (unit 2), ~17,290 km2 (unit 3) and ~10,150 km2 (unit 4) distributed over a ~43,490 km2 area. Likewise, erupted tuff volume and dense rock equivalents also increase: volume-- ~277 km3 (unit 1), ~222 km3 (unit 2), ~121 km3 (unit 3) and ~56 km3 (unit 4); DRE-- ~248 km3 (unit 1), ~170 km3 (unit 2), ~93 km3 (unit 3) and ~38 km3 (unit 4). New mapping confirms previous hypotheses that the Castle Rock caldera erupted unit 1 and identified the new Ironside Mountain caldera as the source for unit 2 while precise source areas for unit 3 and 4 are not yet known but are thought to lie within the Dinner Creek Eruptive Center. Minimal calculated caldera volumes for units 1 and 2 are ~98.5 km3 (unit 1) and ~31.1 km3 (unit 2). Adding the thick ponded intra caldera tuff volume to the determined and probable erupted tuff volumes determined in this study, increases the erupted volumes to ~268 km3 (determined) and ~375 km3 (probable) for unit 1 along with ~157 km3 (determined) and ~253 km3 (probable) for unit 2. DREs increase to ~251 km3 (determined) and ~347 km3 (probable) for unit 1 along with ~128 km3 (determined) and ~202 km3 (probable) for unit 2.

The Wildcat Creek Tuff is a thin (~3-12 m), rhyolite to andesitic ash-flow tuff with a minimal extent of 1500 km2 in Malheur county, eastern Oregon. The previously undated tuff yielded a single crystal, anorthoclase 40Ar/39Ar age of 15.49±0.02 Ma and thus is closely related to mafic and silicic volcanism of the Columbia River Province. The tuff texturally stands out by its high proportion of co-mingled mafic inclusions appearing as dark, scoriaceous, and phenocryst-poor fragments, and their proportion dictate bulk tuff compositions ranging from rhyolite (74% SiO2) to andesite (59% SiO2). Glass analyses confirm rhyolite end member at 74-75 wt.% SiO2 and two mafic members, one at 59-60 wt.% SiO2 and the other at 56-57 wt.% SiO2. Rare plagioclase and even rarer pyroxene phenocrysts with compositions clustering at An60-74 and An35-45, and Mg17-19 and Mg80-84, respectively, similarly suggest two andesitic magmas with the 60% member being the dominant mafic composition. It has distinctly lower TiO2 and CaO, slightly lower FeO, and comparable Al2O3, MgO, and alkalis. Eruption of crystal-poor dacitic to basaltic-andesitic cognate components is also observed in other Miocene ash-flow tuffs from eastern Oregon, like the Rattlesnake, Dinner Creek, and the Devine Canyon Tuffs, as well as other less voluminous tuffs. However, the high proportion of mafic components in the Wildcat Creek tuff seems currently unrivaled. The co-eruption of intermediate magmas with rhyolite implies that mafic magmas were tapped from a common reservoir, and these magmas increased in proportion during the course of the eruption(s). This continued up to the point where nearly all deposited tuff material consisted of andesite. This is consistent with progressively deeper magma withdrawal, in turn implying that mafic magmas resided below the rhyolites as a discrete magma batch. Dacitic components of voluminous rhyolitic tuffs have been recently interpreted as remelted samples of a crystal mush after crystal-poor rhyolites where extracted. Dacitic Wildcat Creek Tuff samples do not bear any evidence of this. To the contrary, small negative Eu anomalies, normal Ba and Sr concentrations, and nearly aphyric nature are consistent with a large portion of mixing between Wildcat Creek Tuff rhyolites and regional mid Miocene, Fe-rich, and crystal poor basaltic andesite magmas that occur ubiquitously as lava flows.

At Zwartbas, about 10 km west of Vioolsdrif, southern Namibia, the Dwyka succession is composed of tillites and distal fossiliferous dropstone-bearing glacio-marine shales. The completely exposed Dwyka succession is interbedded with thin bentonites, altered distal pyroclastic deposits, which were derived from the magmatic arc at the southern rim of Gondwana. Dropstone-bearing and dropstonefree sequences intercalate with four diamictites, of which the two lowest were certainly recognised as tillites. Four events of deglaciation were proven at Zwartbas and thus consist with correlative deposits in southern Africa. Numerous fossilised fishes, trace fossils, and plant fragments appear frequently within the lower half of the Dwyka succession whereas trace fossils were principally found in the complete succession. Although the environmental determination is quite problematic, the fossil assemblage rather implies proximal, shallow water conditions with temporary restricted oxygenation. The hinterland was covered with considerable vegetation, which points to a moderate climate. Water salinity determinations based on shale geochemistry rectify contrary palaeontological results and point to rather brackish or non-marine conditions in comparison to present-day salinites. Geochemical analyses of the bentonites relate the pyroclastic deposits with acid to intermediate source magmas, as they are known from the magmatic arc in present-day Patagonia. Tectono-magmatic comparisons furthermore emphasise a syn-collision or volcanic-arc situation of the magma source. However, significant cyclicity in the production of the pyroclastic deposits was not observed. Radiometric age determinations of two tuff beds clearly date the onset of glacial activity into the Late Carboniferous.

Graduation date: 2002 / Best scan available for black and white figures.

About 7,000 years ago two major tephra-falls blanketed the Pacific Northwest in volcanic ash. These two tephra-falls, identified as the Llao and climatic tephra-falls, were a part of the eruptive events that led up to the collapse of Mount Mazama to form Crater Lake in the southern Oregon Cascades. The tephra-falls occurred about 200 years apart at around 7,000 years B.P. and 6,800 years B.P. for the Llao and climatic eruptions respectively. The effects of the tephra-falls on the flora, fauna, and people of the period have been characterized by different researchers as ranging from minimal to catastrophic. In an attempt to better understand the affects of these two events on the flora, fauna, and people, a model is presented to help organize the various lines of research into a coherent whole and to suggest profitable areas of research which have not yet been completed. The model is based on ecological and anthropological theory with a strong reliance on analogy with modern ecosystems and volcanic hazards research. The model makes use of the ecosystem concept as the framework for the interaction of the abiotic, or nonliving habitat, with the biotic, or living system. The biotic organisms are adapted to the characteristics of the abiotic habitat and in many respects the composition, frequencies, and distributions of biotic organisms are determined by their tolorance levels to these characteristics. Tephra-falls act as environmental disturbances which change the abiotic habitat of the ecosystem. Therefore, any changes caused by such a disturbance in the abiotic characteristics that are not optimal or are outside of the tolorance limits of the biotic (flora and fauna) components should cause changes in the composition, distribution, and frequency of organisms within the ecosystem. The changes brought about by the tephra-falls may be described by successional and evolutionary processes through analysis of pollen and faunal remains, population demography as described by mortality profiles, and research into the reaction of specific flora and fauna within adaptational types to the properties of tephra-falls and the tephra as a soil body. The state factors used to describe the abiotic component of the ecosystem are: time, distribution, material properties, climate, and geomorphology. The state factor of time involves the determination of the occurrence in time of the event(s), the duration of the event(s), the season of occurrence of the event(s), and the residence time of tephra in the ecosystem. This state factor is used to define the specific point in time and duration of the effects of the tephra-fall(s) for individual ecosystems. The state factor of distribution describes the aerial extent and thickness of the air-fall deposits. This state factor determines the extent of the initial disturbance. The state factor of climate describes the specific components of rainfall, wind, and temperature which control ecosystem composition and development, and the changes to the climate which may have occurred due to volcanic aerosols associated with the eruption. The state factor of geomorphology describes the location of tephra and nontephra bodies across the landscape and through time as the tephra is reworked by wind, water, and gravity from the initial air-fall positions. The determination of the long term distribution of the tephra is important in determining post-event influences on ecosystems as described by the material properties of the tephra. It is argued that most people were not greatly harmed by the Mazama tephra-fall events themselves, but instead may have been greatly affected by a loss of food resources during and after the events. Changes in food resource availability and exploitation locations due to the tephra-falls may have resulted in changes in both settlement and subsistence activities. Changes in settlement and subsistence activities may be seen in a corresponding change in differential frequencies of functional tool types across space and time. The kind and amount of expected changes in settlement and subsistence systems are linked to distance from the source of the tephra, the stability and compostion of pre-disturbance ecosystems, the types and intensity of resource exploitation, and the amount of variability in subsistence and settlement traits which were available to the sociocultural system. / Graduation date: 1988

This thesis attempts to detect the ignimbrite units in which the underground cities were carved and the relationship between the joints in these ignimbrites and the walls of underground cities. Orientation of rooms, directions of walls and joints are input data used in the study. Two sites in Cappadocia (Derinkuyu and Kaymakli) are selected to investigate the relationship. Measurements taken from 46 rooms of Derinkuyu and 64 rooms of Kaymakli are analyzed for the room and joint directions, joint locations in the room and joint densities. The density analyses are also performed in the field for Kizilkaya and G&ouml / rdeles ignimbrites. Conclusions derived from the analysis are: 1) Derinkuyu is carved within Kizilkaya and Kaymakli is carved within G&ouml / rdeles ignimbrite, 2) The thickness of Kizilkaya and G&ouml / rdeles ignimbrites observed 13.5 and 34 m, respectively, in the field. The probable thickness of Derinkuyu and Kaymakli underground cities are 40 and 25 m, respectively, 3) The rooms and the joints are oriented arbitrarily, 4) Forming the room walls that are perpendicular to joints were not preferred, 5) The joint densities in Derinkuyu show ascending tendency, while the joint densities in Kaymakli have descending tendency from top to ground floors, 6) The joint density of Kizilkaya in the field is higher than the joint density in Derinkuyu underground city. Similarly, the joint density of G&ouml / rdeles in the field is higher than the density of Kaymakli underground city, 7) The joint density of Kizilkaya ignimbrite is higher than G&ouml / rdeles ignimbrite in both field and underground measurements.

The purpose of this study is to understand the geological, petrographical, mineralogical and geochemical characteristics of analcime-bearing tuffs in the Biga Peninsula and to determine formation process of these tuffs. The study area lies between Ayvacik and K&uuml / &ccedil / &uuml / kkuyu. The rock units are pre-Eocene basement rocks, Miocene Behram Volcanics (Arikli Tuff, andesite, andesitic agglomerate), Pliocene volcanics, Miocene lacustrine sediments (K&uuml / &ccedil / &uuml / kkuyu Formation) and Quaternary alluvium. Analcimes which are found in Arikli Tuff are the main objective of this study. Detailed petrographical, mineralogical and geochemical studies were caried out on the Arikli Tuff samples by using petrographical microscope, X-ray diffractometry, scanning electron microscopy, diffrential thermal analyses inductively coupled plasma &amp / #8211 / mass spectrometry and optical emission spectrometry. Fine-grained and coarse-grained analcime crystals in Arikli Tuff were determined by their colorless, isotropic, trapezohedral and low relief. In addition to petrographic study, SEM and XRD methods also confirmed the presence of analcime. Two modes of occurrences were determined by the petrographical and mineralogical studies / coarse-grained euhedral or anhedral crystals in cavities and pumice fragments and single crystals or clusters of fine-grained analcimes embedded in the matrix. It was stated that there are two types of formation of analcime / alteration of volcanic glass and precipitation from alkaline solution based on petrographical and SEM studies. Geochemical methods, moreover, support the formation types.