Valley evolution by meandering rivers

Fluvial systems form landscapes and sedimentary deposits with a rich hierarchy of structures that extend from grain- to valley scale. Large-scale pattern formation in fluvial systems is commonly attributed to forcing by external factors, including climate change, tectonic uplift, and sea-level change. Yet over geologic timescales, rivers may also develop large-scale erosional and depositional patterns that do not bear on environmental history. This dissertation uses a combination of numerical modeling and topographic analysis to identify and quantify patterns in river valleys that form as a consequence of river meandering alone, under constant external forcing. Chapter 2 identifies a numerical artifact in existing, grid-based models that represent the co-evolution of river channel migration and bank strength over geologic timescales. A new, vector-based technique for bank-material tracking is shown to improve predictions for the evolution of meander belts, floodplains, sedimentary deposits formed by aggrading channels, and bedrock river valleys, particularly when spatial contrasts in bank strength are strong. Chapters 3 and 4 apply this numerical technique to establishing valley topography formed by a vertically incising, meandering river subject to constant external forcing—which should serve as the null hypothesis for valley evolution. In Chapter 3, this scenario is shown to explain a variety of common bedrock river valley types and smaller-scale features within them—including entrenched channels, long-wavelength, arcuate scars in valley walls, and bedrock-cored river terraces. Chapter 4 describes the age and geometric statistics of river terraces formed by meandering with constant external forcing, and compares them to terraces in natural river valleys. The frequency of intrinsic terrace formation by meandering is shown to reflect a characteristic relief-generation timescale, and terrace length is identified as a key criterion for distinguishing these terraces from terraces formed by externally forced pulses of vertical incision. In a separate study, Chapter 5 utilizes image and topographic data from the Mars Reconnaissance Orbiter to quantitatively identify spatial structures in the polar layered deposits of Mars, and identifies sequences of beds, consistently 1-2 meters thick, that have accumulated hundreds of kilometers apart in the north polar layered deposits.

Oxygen relationships in intermittent sand filtration of wastewaters

A model for some of the many physical-chemical and biological processes in intermittent sand filtration of wastewaters is described and an expression for oxygen transfer is formulated.

The model assumes that aerobic bacterial activity within the sand or soil matrix is limited, mostly by oxygen deficiency, while the surface is ponded with wastewater. Atmospheric oxygen reenters into the soil after infiltration ends. Aerobic activity is resumed, but the extent of penetration of oxygen is limited and some depths may be always anaerobic. These assumptions lead to the conclusion that the percolate shows large variations with respect to the concentration of certain contaminants, with some portions showing little change in a specific contaminant. Analyses of soil moisture in field studies and of effluent from laboratory sand columns substantiated the model.

The oxygen content of the system at sufficiently long times after addition of wastes can be described by a quasi-steady-state diffusion equation including a term for an oxygen sink. Measurements of oxygen content during laboratory and field studies show that the oxygen profile changes only slightly up to two days after the quasi-steady state is attained.

Results of these hypotheses and experimental verification can be applied in the operation of existing facilities and in the interpretation of data from pilot plant-studies.

The structure and petrology of the Johnny Lyon Hills area, Cochise County, Arizona

The Johnny Lyon Hills area is located in Cochise County in southeastern Arizona. The rocks of the area include a central core of Lower pre-Cambrian igneous and metamorphic rocks surrounded by a complexly faulted and tilted section of Upper pre-Cambrian and Paleozoic strata. Limited exposures of Mesozoic and Tertiary sedimentary and volcanic rocks are present at the north end of the map area. Late Tertiary and Quaternary alluvium almost completely surrounds and overlaps upon the older rocks.

The older pre-Cambrian rocks include a section of more than 9000 feet of generally moderately metamorphosed graywackes, slates and conglomerates of the Pinal schist injected in zones by somewhat younger rnyolite sheets. The original sediments were deposited in a geosyncline whose extent probably included large parts of Arizona, New Mexico and west Texas. During the Mazatzal Revolution the Pinal schist was deformed into northeast-trending, steeply dipping and plunging structures and the entire local section was overturned steeply toward the northwest. The pre-Cambrian Johnny Lyon granodiorite was emplaced as a large epi-tectonic pluton which modified the metamorphic character of part of the Pinal schist. Larsen method determinations indicate an age of about 715 million years for this rock, which is about the minimum age compatible with the geologic relations.

The Laramide orogeny produced numerous major thrust faults in the area involving all rocks older than and including the Lower Cretaceous Bisbee group. Major compression from the southwest and subsequent superimposed thrusting from the southeast and east are indicated. Minimum thrust displacements of more than a mile are clear and the probable displacements are of much greater magnitude. The crystalline core behaved as a single structural unit and probably caused important local divergences from the regional pattern of northeast-trending compressive forces. The massif was rotated as a unit 40 degrees or more about a northwest-trending axis overturning the pre-Cambrian fold axes in the Pinal schist.

Swarms of Late Cretaceous(?) or Early Tertiary(?) lamprophyric dikes cross the Laramide structures and are probably related to the large Texas Canyon stock several miles southeast of the map area. Intermittent high angle faulting, both older and younger than the dikes, has continued since the Laramide orogeny and has been superimposed on the older structures. This steep faulting combined with the fundamental northwesterly Laramide structural grain to produce the northwesterly trends characteristic of the mountain ridges and valleys of the area.

Dendrites Inhibition in Rechargeable Lithium Metal Batteries

The specific high energy and power capacities of rechargeable lithium metal (Li⁰) batteries are ideally suited to portable devices and are valuable as storage units for intermittent renewable energy sources. Lithium, the lightest and most electropositive metal, would be the optimal anode material for rechargeable batteries if it were not for the fact that such devices fail unexpectedly by short-circuiting via the dendrites that grow across electrodes upon recharging. This phenomenon poses a major safety issue because it triggers a series of adverse events that start with overheating, potentially followed by the thermal decomposition and ultimately the ignition of the organic solvents used in such devices.

In this thesis, we developed experimental platform for monitoring and quantifying the dendrite populations grown in a Li battery prototype upon charging under various conditions. We explored the effects of pulse charging in the kHz range and temperature on dendrite growth, and also on loss capacity into detached “dead” lithium particles.

Simultaneously, we developed a computational framework for understanding the dynamics of dendrite propagation. The coarse-grained Monte Carlo model assisted us in the interpretation of pulsing experiments, whereas MD calculations provided insights into the mechanism of dendrites thermal relaxation. We also developed a computational framework for measuring the dead lithium crystals from the experimental images.