Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2000. / Includes bibliographical references (p. 225-248). / Near-infrared spectra (~0.90 to ~1.65 microns) were obtained for 196 main-belt and near-Earth asteroids to determine plausible meteorite parent bodies. These spectra, when coupled with previously obtained visible data, allow for a better determination of asteroid mineralogies. Over half of the observed objects have estimated diameters less than 20 k-m. Many important results were obtained concerning the compositional structure of the asteroid belt. A number of small objects near asteroid 4 Vesta were found to have near-infrared spectra similar to the eucrite and howardite meteorites, which are believed to be derived from Vesta. These asteroids appear almost certainly to be fragments of Vesta. Spectral variations between these objects are consistent with being primarily due to differences in particle size. These asteroids also tend to have stronger band depths with increasing ejection velocity from Vesta. Objects with distinctive olivine bands appear to provide definitive evidence that spectral alteration is occurring in the asteroid belt. These objects have similar band depths but appear significantly reddened relative to measured olivine samples due to their significantly higher reflectance values with increasing wavelength. The only laboratory-simulated "weathering" process that reddens the spectra but does not significantly suppress the bands is alteration by laser irradiation, which is hoped to duplicate the effects of micrometeorite bombardment. A number of plausible main-belt parent bodies were identified. These include 19 Fortuna and the CM chondrites, Eos family members with the CO chondrites and 599 Luisa with the CV chondrites. A significant fraction of S asteroids have spectral properties that range from similar to ordinary chondrites to much redder with weaker absorption bands. These objects tend to have spectra consistent with a mixture of ordinary chondrite material and metallic iron. However, other alteration processes cannot be ruled out. Asteroids with distinctive olivine bands are relatively rare. The available evidence is consistent with a scenario where, with the exception of Vesta, all differentiated bodies were either disrupted or had their mantles stripped very early in the age of the solar system. Olivine-rich metal-free fragments were then continually broken down until they almost all now fall below our current astronomical measurement limits. / by Thomas H. Burbine, Jr. / Ph.D.

Thesis: S.B., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2013. / "June 2013." Cataloged from PDF version of thesis. / Includes bibliographical references (pages 23-24). / This thesis was designed to make spectroscopic measurements of Ceres within the visible spectrum, specifically within the wavelength range of 6000 and 7000 Angstroms. The asteroid was observed for 6 nights, for lengths of time varying from 3 to 7.5 hours. The main goal was to support/refute the previous findings about absorption features within the wavelength range being observed. Additionally, this thesis was designed to determine the rotational variability of minerals on Ceres. In order to determine the asteroid's variablity, the rotational period of Ceres was divided into eight phases, and average spectra were determined for each phase. The results show that there is a weak rotational variability of the feature between 6200 and 6400 Angstroms. The feature varies over the surface of Ceres by 2.5% with a mean error of 1.6%. There have been previous reports of absorption features on asteroids between 6000 and 6500 Angstroms, which have been associated with ferric Fe absorptions in Fe alteration minerals. Examples of such minerals include goethite and iron oxide hematite. / by Phoebe J. Henderson. / S.B.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2004. / Some pages folded. / Includes bibliographical references. / (cont.) Xianshuihe-Xiaojiang fault system during growth of the southeast plateau margin. Cosmogenic ²⁶A1 and ¹⁰Be basin-wide erosion rate and burial ages indicate a background incision rate of [approximately] 0.05 to 0.10 mm/a, lower than the long-term incision rate minimum of [approximately] 0.26 mm/a. Cosmogenically-determined incision rate approximately doubles to [approximately] 0.20 mm/a in the region of maximum dip-slip displacement on the Red River fault. This thesis also develops a new cosmogenic tool for quantitative landscape analysis: using depth dependence data for multiple cosmogenic nuclides from a single site to constrain an erosion history. This method is applied in the Dry Valleys region of Antarctica. / This thesis outlines the Cenozoic development of the Red River region, exploring regional landscape evolution and tectonic accommodation of the India-Eurasia collision, focusing on the Oligo-Miocene, left-lateral Ailao Shan shear zone and the active, right-lateral Red River fault on the northeast margin of the shear zone, along which the Red River has incised a deep valley. Oligo-Miocene fluvial and alluvial conglomerates in the valley record shear zone unroofing: pervasive, syn-depositional shortening indicates transpressional exhumation. A low-relief landscape, developed in Late Miocene time, was probably uplifted in Pliocene time, triggering the incision of the Red River and isolating the low-relief landscape from modem base level. On the basis of stratigraphic data, river incision began in Pliocene time or later. Tributary longitudinal profiles indicate two-phase incision, the result of pulsed plateau growth or trunk channel adjustments to changing climate conditions. Paleo-Red River reconstruction indicates [approximately] 1400 m river incision, 1400-1500 m surface uplift and 750 m vertical displacement across the northern part of the Red River fault. Minimum right-lateral displacement on the fault is 40 km, 15-16 km of which predates river incision, plateau growth and development of other regional fault systems. Long term average slip-rate is a minimum of [approximately] 5 mm/yr. Rotation of a crustal fragment around the eastern Himalayan syntaxis, bounded on the east by the Xianshuihe-Xiaojiang fault system, causes deflection of the Red River fault, accommodated by distributed shear along strike of the Xianshuihe-Xiaojiang fault system. The Red River fault has decreased in regional importance since the initiation of the / by Lindsay M. Schoenbohm. / Ph.D.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1987. / Microfiche copy available in Archives and Science. / Bibliography: leaves 71-75. / by Marc H. Larrère. / M.S.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2006. / Includes bibliographical references (p. 205-214). / Studies of the response of ice sheets to climate change require data sets with high accuracy and uniform ice-sheet coverage. The most common technique used in analyzing satellite altimetry data to study height change in the ice sheets is the dH/dt technique based on the cross-over geometry. In this thesis two alternative techniques to cross-overs are studied and applied to all ERS radar and ICESat laser altimetry data to study height change in Antarctica. The first technique, block kriging, uses all available data to build a statistical model of the elevation field. Results of height rate of changes dh/dt ill Antarctica for the years 1995-2001 produced using block kriging and cross-over analysis are compared. In the Amery Ice Shelf and in the West Antarctic coastal area and near latitude -81°N, the difference in dh/dt between the two methods are statistically significant. A second technique combines kriging and Kalman filtering to allow for time evolutions of the height change rate and other parameters used in the description of the surface elevation field. An application of the technique to laser altimetry data from the current NASA's ICESat mission shows the potential of the technique in detecting height change. / (cont.) In addition, the method can potentially characterize surface elevation in Antarctica at small horizontal scales of the order of the laser footprint size. The quality of laser altimetry data at the present is not sufficient for height change detection at the accuracy level of 2cm/yr required for studying mass balance in Antarctica. / by An Thanh-Thuy Nguyen. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2003. / Includes bibliographical references (p. 132-144). / This work provides a statistical description of the near-Earth asteroids (NEAs) in terms of number, orbital parameters, reflectance spectra, albedos, diameters, and terrestrial and lunar collision rates. I estimate the size and shape of the NEA population using survey data from the Lincoln Near-Earth Asteroid Research project including more than 1300 NEA detections. The NEA population is more highly inclined than previously estimated and the total number of NEAs with absolute magnitudes (H) brighter than 18 is 1227 +170/-90. The absolute magnitude and orbital parameter distributions for the NEAs are combined with reflectance spectra and albedo measurements. I obtain a debiased estimate of the fraction of NEAs in each of 10 taxonomic complexes, and a debiased average albedo for each. The number of NEAs larger than 1 km is 1090 +/- 180. Next, I determine the impact frequency, collision velocity distribution and collision energy distribution for impacts of NEAs into the Earth and Moon. Globally destructive collisions ([approx.] 1021 J) of asteroids 1 km or larger strike the Earth once every 0.60 +/- 0.1 Myr on average. Regionally destructive collisions with impact energy greater than 4x1018 J ([approx.] 200 m diameter) strike the Earth every 47,000 +/- 6,000 years. The rate of formation of craters expected from the NEAs is found to be in close agreement with the observed number of craters on the Earth and Moon. / (cont.) These results combine the largest set of NEA discovery statistics from a single survey, the largest set of physical data on NEAs, and corrections for observational bias. The result is a comprehensive estimate of the total NEA population in terms of orbital parameters, absolute magnitudes, albedos, and sizes. This improved description of the NEAs will help us to plan surveys to find and study the remaining undiscovered NEAs, to connect the NEAs to their origins in the main-belt, to connect the NEAs to meteorite samples, to compare the lunar and terrestrial cratering record to the current population of potential impactors, and to understand the magnitude of the NEA impact hazard to the Earth's biosphere. / by Joseph Scott Stuart. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1987. / Microfiche copy available in Archives and Science. / Bibliography: leaves 197-204. / by Wesley Nobuo Ebisuzaki. / Ph.D.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2000. / Includes bibliographical references. / The study of Streaming potentials has applications in the earth sciences, ranging from fluid flow monitoring, to permeability determination, to studying the surface chemistry of rocks and minerals. In this thesis study of frequency-dependent electrokinetics is presented with both theoretical development and experimental verification. The complex (real and imaginary) streaming potential coupling coefficient is explained. This is followed by the first experiments to measure the real and imaginary part of frequency-dependent streaming potential coupling coefficients. As part of this study an experimental apparatus and data acquisition system were constructed to measure the streaming potential coupling coefficients as a function of frequency. The purpose of the experiments was to measure, for the first time, the real and imaginary part of streaming potentials. In addition, the measured frequency range was extended beyond any previous measurements. Frequency-dependent streaming potential experiments were conducted on one glass capillary, two porous glass filters, and one rock. The sample pore diameters ranged from 34 micrometers to 1 millimeter. Without these experiments, the validity of modeling of the frequency dependence of the seismoelectric effect using existing models streaming potential models would be in question. Two frequency- dependent models (Packard and Pride) were compared to the data. Both Pride's and Packard's models have a good fit to the experimental data in the low and intermediate frequency regime where viscous terms dominate in the fluid. In the high frequency regime, where inertial terms start to dominate, the data fits the theory after being corrected for capacitance effects of the experimental setup. Pride's generalized model appears to have the ability to more accurately estimate pore sizes in the porous medium samples. Packard's model has one unknown model parameter whereas Pride's model has four unknown model parameters, two of which can be independently determined experimentally. Pride's additional parameters may allow for a determination of permeability. As part of the study of frequency-dependent electrokinetics, this thesis presents the theory for frequency-dependent electro- osmosis. It is shown that the electro- osmosis frequency-dependent coupling coefficient is constant with increasing frequency until the critical frequency is reached, at which point the coupling coefficient starts to decrease with increasing frequency. The frequency response- electro- osmosiso- osmosis coupling coefficient is dependent on the capillary radius. The smaller the capillary radius the higher the critical frequency. Data is presented for a 0.127 mm capillary. In addition to studying frequency-dependent electrokinetics, this thesis examines the temperature-dependent behavior of streaming potential coupling coefficients. As part of this examination a review is made of the previous literature that discusses the temperature dependence of streaming potentials. The streaming potential coupling coefficient is determined using the permittivity, the conductivity, and the viscosity of the fluid. It has been determined that the temperature-dependent behavior of the permittivity, conductivity, and viscosity are well documented and do not alone account for temperature dependence of streaming potentials. The other quantity used in calculating the streaming potential coupling coefficient is the zeta potential. The temperature dependence of the zeta potential is not well understood at the present time. By examining the theory, it appears that the zeta potential temperature dependence is controlled by the fluid concentration and the adsorption properties of the surface. After examining the theory, streaming potential experiments at elevated temperature and pressure were conducted on Fontainebleau Sandstone, Berea Sandstone, and Westerly Granite. The experiments were conducted in a pressure vessel with temperatures ranging from 23° C to 200° C at pore pressure ranging from 20 bar to 50 bar and confining pressures ranging from 200 bar to 250 bar. The zeta potential was found to increase with increasing temperature, and the coupling coefficient can increase or decrease depending on how the conductivity of the sample varies. This implies that in geothermal regions, streaming potentials can have large magnitudes depending on the conductivity of the geothermal fluid. / by Philip M. Reppert. / Ph.D.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric and Planetary Sciences, 1984. / Microfiche copy available in Archives and Science. / Bibliography: leaves 378-403. / by Eric Allen Bergman. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2010. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 171-184). / Increased industrialization and human activity modified the atmospheric aerosol composition and size-distribution during the last several decades. This has affected the structure and evolution of clouds, and precipitation from them. The processes and mechanisms by which clouds and precipitation are modified by changes in aerosol composition and size-distribution are very intricate. The objective of this thesis is to improve the understanding of the processes and mechanisms through which the changes in aerosol concentrations impact the evolution of deep convective clouds and precipitation formation. We develop a new coupled model in which a very detailed model of aerosol activation is coupled to a three-dimensional cloud resolving model. This coupled model can accurately represent different kinds of aerosol populations. This coupled model is used to investigate the impact of changing aerosol concentrations on the dynamics, microphysical evolution and precipitation formation in deep convective clouds. We examine the theories of aerosol activation, and the representation of aerosol activation in cloud models. The limitations of the extant methods of representation of aerosol activation in cloud models are evaluated. Then we descibe the components of the coupled model - Modified Eulerian and Lagrangian Aerosol Model (MELAM) and the Cloud Resolving Model (CRM). The features of these two component models with respect to aersol activation and cloud formation are discussed. The evaluation of the coupled model by simulation of a deep convertive event observed during the INDian Ocean EXperiment (INDOEX) by statistcal comparison of observed and simulated cloud fields shows that the coupled model can simulate deep convective events reasonably well. We present a study of the senstivity of the model to initial thermodynamic conditions (CAPE). Different initial thermodynamic conditons sampled during the INDOEX are used to initialize the coupled model and, the structure and evolution of the deep convective event are discussed. The study sheds new light on the respone of deep convection to CAPE. It is found that when the atmosphere has moderate CAPE, the precipitation forming processes are very active and when the CAPE is (cont.) low or high, they are comparatively less efficient. / As the most important part of our study, we examine the response of deep convection to changing initial aerosol concentration. Different aerosol concentrations from those representing pristine to polluted atmospheres are considered. We look at the buoyancy of the cloud and the microphysical evolution. It is found that the dynamics and microphysics are tightly coupled and we infer that to understand aerosol-cloud interactions in deep convective clouds, both - dynamics and microphysics - and their interaction have to be taken into consideration. Our results show that the response of a deep convective cloud to changing aerosol concentration is very different from the much well understood reponse of shallow clouds or small cumulus clouds. In general, increase in aerosol concentratin is seen to invigorate convection and lead to greater condensate. Although the cloud droplet size decreases, collision-coalescence is not completely inefficient. The precipitation in high aerosol regime is seen to occure in short spells of intense rain. A very interesting anomalous response of deep convection to initial aerosol concentration is observed at intermediate aerosol concentrations. The cloud lifetime, and precipitation are seen to increase in this regime. A possible mechanism to explain this anomalous behavior is proposed and the available circumstantial support for the mechanism from extant observations is presented. It is proposed that the efficient collection of rain and cloud droplets by ice and graupel particles in the middle troposphere is primarily responsible for this increased cloud lifetime and precipitation. / by Udaya Bhaskar Gunturu. / Ph.D.