<p>Many surface and dynamical processes affect the evolution of asteroids in our solar system today. The spectral slopes of S and Q-type asteroids are altered by the weathering of their surfaces due to solar wind interactions and micrometeorite impacts, as well as any processes that work to remove that weathered material. These processes of space weathering and asteroid resurfacing compete with each other to determine the spectral slope of each asteroid, with space weathering raising the spectral slope</p> <p>and resurfacing lowering it. By considering the distribution of spectral slopes with respect to orbital location and size, we can determine which potential resurfacing processes are the most dominant. I show that the distribution of spectral slopes with respect to size is present in all populations of S and Q-type asteroids in the inner solar system, regardless of orbit. I also show that the spectral slopes of S and Q-type Near-Earth Asteroids (NEAs) decrease with decreasing perihelion, but only for perihelia q < 0.9 AU.</p> <p>By building Monte Carlo and models N-body simulations of asteroids, I test which resurfacing mechanisms are consistent with these trends in spectral slopes. I find that spin-up and failure from the Yarkovsky-O’Keefe-Radzievskii-Paddack (YORP) effect is an important resurfacing mechanism that creates the observed weathering trends with size. I also show that resurfacing asteroids due to close encounters with the terrestrial planets cannot explain the spectral slope vs. perihelion trend at q .</p> <p>0.9 AU, but that resurfacing asteroids due to thermally induced surface degradation, by assuming a power law relationship between the resurfacing timescale and the solar distance, gives much more consistent results.</p> <p>I also explore the creation rate of asteroid pairs, which are asteroids that have very similar orbits but are not gravitationally bound. The majority of pairs are formed by YORP spin-up and fission, followed by a separation of the two members. Asteroid pairs are then disassociated over time as their orbits become less similar due to chaos, resonances, and the Yarkovsky effect. I simulate both the formation of asteroid pairs in the inner main belt via YORP and their subsequent disassociation. By comparing the distribution of orbital similarity distances from observations and from our model, I estimate that asteroids fission and create an asteroid pair every 8 − 13 YORP cycles, where a YORP cycle is twice the time it takes the YORP effect to change the spin rate of an asteroid from zero to its critical spin rate. I argue that the rate of fissioning via the YORP effect is not substantially limited by any stagnation or stochastic evolution, and that losing mass via rotational fission is much less effective than collisional disruption, even for small asteroids.</p>

Geomorphologic evidence provided by late Holocene glacial advances demonstrates the sensitivity of central Brooks Range to changes in temperature and moisture balance over decadal to centennial timescales. High-resolution climate proxy records covering the middle to late Holocene are sparse from this region. One exception is Blue Lake, a small (<0.5 km2), shallow (4.7 m), glacier-fed lake set on the crest of the Brooks Range (68º05.3 N, 150º27.8 W) in north-central Alaska at an altitude of 1265 m. The 4 km2 watershed contains a small cirque glacier located on the north face of the 1890 m high headwall, on the north side of the continental divide. Field observations and air photos indicate that melt-water from the glacier contributes a substantial quantity of fine-grained sediment to the lake. Sediment cores recovered in August of 1999 contain millimeter-scale laminations comprised of lamina couplets, which exhibit the classic mode of varve formation in a glacial basin consisting of a succession of fine sands to silts deposited during the summer months, followed by a well-defined winter clay cap. In addition to annual variability in varve thickness, long-term trends in thickness were identified and compared with the historical climate record. Blue Lake records the glacial response to late Holocene climate phenomena, such as the Little Ice Age (cooling), Medieval Climatic Anomaly (warming), and the 20th century warming trend.Varve measurements from Blue Lake correlate well with regional cooling and warming trends described for the late Holocene from other proxy records across the Arctic.

Population growth in the Pacific Northwest has led to increased demand for water resources. Current understanding of the natural cycle of moisture availability is limited, however, by the short duration for which instrumental climate data are available. Here, a detailed paleoenvironmental study from Castor Lake in north-central Washington State is presented to examine the frequency, duration, and magnitude of droughts, lake system dynamics, and other climate events during the past ~16,000 years. The combined use of stable isotope measurements of endogenic carbonate and organic sediment with trace element analysis and standard sedimentological methodologies provides a more coherent basis for understanding environmental change through this period than would be possible through the application of a single technique. Results show that the region was significantly affected by the Younger Dryas cold reversal between approximately 12,500 cal yr BP and 11,500 cal yr BP. The period from approximately 8,200 cal yr BP to 5,900 cal yr BP contains evidence for prolonged aridity, as lake-levels declined and water column stratification broke down. The period spanning the last ~6,000 years is characterized by relative climate stability, but the highly resolved sediment proxy data for this interval reveal several drought events larger than anything experienced in the historic record, with some episodes persisting well over a century. Furthermore, the past fifty-years appear to be anomalously wet in the context of the long-term record obtained from Castor Lake. Preparation for large drought events may therefore be inadequate because water resource allocation laws were written during this interval. Future large-scale drought events are inevitable, however, given the frequency with which they are observed to occur in the past, and the increasing influence of anthropogenic warming.

The magnitude and underlying cause of glacial variability in the Venezuelan Andes during the late Quaternary are investigated in order to better understand tropical climate and its forcing mechanisms. Paleo-glaciers were mapped using field observations, aerial photographs, satellite imagery and high-resolution digital topographic data. Paleo-glacier equilibrium-line altitudes (ELAs) were reconstructed using the accumulation-area ratio (AAR) and the accumulation-area balance ratio (AABR) methods. During the local Last Glacial Maximum (LGM) in Venezuela (~20,600 to 17,800 cal yr BP), ELAs were ~870 to 1420 m lower. Paleo-temperature estimates were calculated for the northern Sierra de Santo Domingo region which had a ÄELA of -980 m. Using a combined energy and mass-balance equation (Kuhn, 1989) it appears that temperatures were at least 8.8 ± 2°C cooler than today. This is greater than that estimated by an atmospheric lapse rate calculation, which yields a value of 6.4 ± 1°C cooler. The paleo-ELAs presented here are consistent with other northern tropical sites and the maximum estimates from southern tropical/sub-tropical Andean records. Our paleo-temperature results, based on estimates that take into account the total energy budget across a glaciers surface, are greater than Porters (2001) overall tropical average of 5.4 ± 0.8°C cooler temperatures during the LGM using an atmospheric lapse rate calculaion. The pattern of the LGM gradient in ELA values of Venezuela is consistent with the modern precipitation and cloud cover patterns suggesting similar moisture sources and circulation patterns at both times. The regional deglacial history is characterized using lake sediments and bog deposits. Analyses include AMS radiocarbon dating, sedimentology studies and magnetic susceptibility on a series of cores from 7 lakes and 2 bogs in the Venezuelan Andes. Results show that by 15,950 cal yr BP, glaciers began to retreat. This retreat was interrupted by at least one readvance between 14,000 and 10,000 cal yr BP. Glaciers rapidly retreated after 10,000 cal yr BP in arid areas, whereas ice remained in north facing humid areas until after 6,200 cal yr BP. The deglacial history of the Venezuelan Andes cannot be attributed to insolation forcing alone and must be combined with changes in temperature and moisture availability.

The Precambrian Kalkkloof paleosol, South Africa, developed on an Archean ultramafic complex sometime before &#x223C;2.3 billion years (Ga) ago. This weathering profile is of great interest because it formed during a time when many workers believe atmospheric oxygen levels were rising to near-present day concentrations, and cerium (Ce) anomalies have been measured in Kalkkloof paleosol samples (Watanabe et al., 2003), indicating formation under high-O₂ conditions. In this study, I applied the samarium-neodymium (Sm-Nd) and rubidium-strontium (Rb-Sr) isotope systems to samples of the Kalkkloof paleosol and parent material. The goals of this study are to constrain the age of pedogenesis of the Kalkkloof paleosol, and to determine the extent to which rare earth elements (REE, including Ce) and other elements were mobilized during and after pedogenesis. Titanium-normalized concentration patterns for Sm and Nd are consistent with accumulation of REE in the lower portions of the weathering profile during its formation. Isotopic analysis of eight whole-rock Kalkkloof samples, including the parent ultramafic material, indicates that the Sm-Nd and Rb-Sr systematics have been disturbed by at least two geological events subsequent to formation of the ultramafic parent, and no meaningful ages were obtained. These events are likely to include weathering and formation of the paleosol around 2.5 Ga ago, and later metamorphism associated with intrusion of the Bushveld igneous complex around 2 Ga ago. The four samples with the highest concentrations of Nd (>1 ppm) have ∈Nd(2.5 Ga) values that are consistent with REE fractionation during weathering around 2.5 Ga ago. These four samples also contain significant Ce anomalies. Preservation of REE systematics could result if the REE were concentrated in relatively resistant trace phases such as phosphates. Thus, the data are consistent with a high-O₂ atmosphere (leading to Ce oxidation) when the paleosol formed >2.3 Ga ago. To a first approximation the Rb-Sr data are consistent with the multi-stage history suggested by the Sm-Nd data. The Rb-Sr results further suggest that the Kalkkloof rocks were at least mildly affected by metamorphism and/or weathering events that ended no earlier than about 1.7 Ga ago.

MESO AND MICRO-SCALE ANALYSIS OF FOLIATED ROCKS OF THE SOUTHERN COAST BELT: A TRANSECT FROM WHISTLER TO LILLOOET, BRITISH COLUMBIA Erich Victor Zorn, M.S. University of Pittsburgh, 2005 Between Whistler and Lillooet, British Columbia within the Coast Belt rocks of Gambier Group, Cadwallader Group, Chism Creek Schist, Cayoosh Assemblage, Bridge River Complex/Schist, and the Brew Group, penetrative deformation is commonly recorded. Along this 110 km transect foliation generally dips 30ºNE to vertical and strikes northwest. Down-dip lineation is common in these rocks. Although they are commonly re-crystallized, locally developed microstructures preserve shear-sense indicators in sections cut parallel to dip and perpendicular to foliation. Differences among ductile structures indicate at least five episodes of deformation. 1) Foliation of Oligocene-Miocene (~25-14 Ma) age which strikes northeast and dips steeply is present in Early Cretaceous plutonic rocks east of Whistler. 2) Sub-horizontal penetrative foliation and shear bands in the Brew Group record NW-SE extension that is interpreted to record structural exhumation of the Brew in the footwall of the Cayoosh Creek Fault. 3) Steeply dipping mylonite and L-tectonite with distinct sub-horizontal mineral lineation is present along the dextral, Eocene Marshall Creek Fault. The penetrative deformation overprints microstructures that record left and right lateral shear sense indicators. 4) Pre-85 Ma: Mineral lineations and meso-scale asymmetric folds that give a sense of oblique left-slip and pure shear are recorded in the Chism Creek Schist and Cayoosh Assemblage close to the Bralorne and Downton Creek fault systems. 5) Post-113 Ma: Near Whistler, outcrops of very fine grained volcanic rocks and meta-sediments of the Gambier Group have mylonitic foliation and show strong mineral lineation parallel to the dip direction. Meso-scale kink folds and asymmetric tails in thin section are interpreted to record extension whereas symmetric tails record flattening during pure shear. Late Jurassic intrusive rocks nearby to the west and east of this belt of meta-volcanics are ductily deformed.

Tracing interaction of acid mine drainage and coal combustion byproducts in a grouted coal mine: Application of strontium isotopes Barbara L. Hamel, MS University of Pittsburgh, 2005 The inactive Omega Coal Mine in Morgantown, West Virginia was partially grouted in 1998 by injection of coal combustion by-products (CCB) in order to ameliorate acid discharge; but discharge continued with little measurable change. In this study, discharge chemistry and strontium (Sr) isotope ratios were determined to identify and quantify the extent of interaction between mine waters and the CCB material used to grout the abandoned mine. Eight sampling sites were monitored around the downdip perimeter of the mine. The major and trace element chemistry of the discharges was not generally sufficient to differentiate between discharges that interacted with grout and those that did not. Elements that showed the most separation include potassium and arsenic, both of which were elevated in the waters that interacted with CCB grout. In contrast, the Sr isotope ratios were clearly able to distinguish between discharges from grouted and non-grouted areas. Discharges without exposure to the grout had 87Sr/86Sr ratios ranging from 0.7151 to 0.7159, while two discharges that interacted with grout had ratios in the range of 0.7140 to 0.7146. The Treatment Inlet, which includes both grouted and ungrouted discharges, yielded intermediate isotopic ratios. Leaching experiments on CCB grout, coal, and surrounding rock formations are consistent with the isotopic trends observed in the discharges. Based on these results, waters that interacted with grout received 30-40% of their Sr (and Ca by assumption) from the CCB grout material. This novel application of Sr isotopes illustrates their ability to track fluid flow paths in grouted mine systems.

The objective of this study was to develop data that are broadly applicable to the release of trace metals from fly ash, and to quantify the rate of release as a function of the composition of the ash. Thirty-two samples of Class F fly ash from pulverized coal combustion boilers were leached with seven leaching solutions simulating natural fluids. The leachate was analyzed for 21 cations that were major, minor, or trace constituents of the ash. The rate at which metal ions are released from fly ash is a complex function of the alkalinity of the ash, the distribution of elements in various chemical compounds or minerals, and characteristics of the leachant solution, particularly its pH. In this experiment, the release of cations is defined as a solubility function with respect to the volume of leachant solution. During the first leaching interval, the ashes alkalinity is neutralized, and the release of metal ions, except for Ca, is relatively low. At some point, the release of metal ions increases by one or more orders of magnitude, and remains at that level, until the readily soluble ions are released. Then the elemental release decreases, again by one or more orders of magnitude. The solubility of an element is defined by the three volumetric functions and the median volumes for those functions. The N LF (neutralization leaching function) is describes the release of cations until the sample is neutralized (dMN/dVN, meq/L). The RLF (rapid leaching function) rate is the average slope of cumulative curve between inflection points (dML/dVL, meq/L). The TLF (terminal leaching function) is the average slope of cumulative curve after 2nd inflection point (dMT/dVT, meq/L). In a natural setting, if the infiltration rate is known (L/d), the time dependent release of the elements can be estimated. The results of this study show that most cations in fly ash are only slightly soluble, that elements, other than arsenic, tend to be most soluble in acid solutions, and that non-silicates tend to be more soluble than silicates.

Data from the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) and the Airborne Visible/IR Image Spectrometer (AVIRIS) were used to characterize hot spring deposits in the Lower, Midway, and Upper Geyser Basins of Yellowstone National Park from the visible/near infrared (VNIR) to thermal infrared (TIR) wavelengths. Field observations of these basins provided the critical ground truth for comparison to the remote sensing results. Fourteen study sites were selected based on diversity in size, deposit type, and thermal activity. Field work included detailed site surveys such as land cover analysis, photography, Global Positioning System (GPS) data collection, radiometric analysis, and VNIR spectroscopy. Samples of hot spring deposits, geyser deposits, and soil were also collected. Analysis of ASTER provided broad scale characteristics of the hot springs and their deposits, including the identification of thermal anomalies. AVIRIS high spectral resolution short-wave infrared (SWIR) spectroscopy provided the ability to detect hydrothermally altered minerals as well as a calibration for the multispectral SWIR ASTER data. From the image analysis, differences in these basins were identified including the extent of thermal alteration, the location and abundance of alteration minerals, and a comparison of active, near-extinct, and extinct geysers. The activity level of each region was determined using a combination of the VNIR-SWIR-TIR spectral differences as well as the presence of elevated temperatures, detected by the TIR subsystem of ASTER. The results of this study can be applied to the exploration of extinct mineralized hydrothermal deposits on both Earth and Mars.

This work examines lava emplacement processes by characterizing surface units using field and remote sensing analyses in order to understand the development of lava flow fields. Specific study areas are the 1969-1974 Mauna Ulu compound flow field, (Kilauea Volcano, Hawai'i, USA), and five lava flow fields on Venus: Turgmam Fluctus, Zipaltonal Fluctus, the Tuli Mons/Uilata Fluctus flow complex, the Var Mons flow field, and Mylitta Fluctus. Lava surface units have been examined in the field and with visible-, thermal-, and radar-wavelength remote sensing datasets for Mauna Ulu, and with radar data for the Venusian study areas. For the Mauna Ulu flow field, visible characteristics are related to color, glass abundance, and dm- to m-scale surface irregularities, which reflect the lava flow regime, cooling, and modification due to processes such as coalescence and inflation. Thermal characteristics are primarily affected by the abundance of glass and small-scale roughness elements (such as vesicles), and reflect the history of cooling, vesiculation and degassing, and crystallization of the lava. Radar characteristics are primarily affected by unit topography and fracturing, which are related to flow inflation, remobilization, and collapse, and reflect the local supply of lava during and after unit emplacement. Mauna Ulu surface units are correlated with pre-eruption topography, lack a simple relationship to the main feeder lava tubes, and are distributed with respect to their position within compound flow lobes and with distance from the vent. The Venusian lava flow fields appear to have developed through emplacement of numerous, thin, simple and compound flows, presumably over extended periods of time, and show a wider range of radar roughness than is observed at Mauna Ulu. A potential correlation is suggested between flow rheology and surface roughness. Distributary flow morphologies may result from tube-fed flows, and flow inflation is consistent with observed surface characteristics. Furthermore, the significance of inflation at Mauna Ulu and comparison of radar characteristics indicates that inflation may, in fact, be more prevalent on Venus than at Mauna Ulu. Although the Venusian flow fields display morphologies similar to those observed within terrestrial flow fields, the Venusian flow units are significantly larger.