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No description available.

The composition of volcanic gas plumes depends largely on the chemistry of the degassing magma, the depth of volatile exsolution, and the level of volcanic activity. The ratios between the most common volcanic gases: C02, H2O, SO2, HCl and HF, as measured at the surface, can be used to provide information on the evolution of the magma body. My research on volcanic gases has centred on the use of open-path Fourier transform IR spectroscopy (Op_FTTR) and correlation spectroscopy (COSPEC). I have also used data collected using other direct and remote-sensing techniques. Remote-sensing techniques rely on the characteristic IR or UV absorbances of natural and/or artificial radiation by different gases. The longer range of these techniques enables the analysis of gases in inaccessible plumes; thus reducing the need for operators to enter hazardous areas. As the instruments do not interact with the analysed gases there is no contamination, condensation or secondary reactions. However, the instruments tend to be heavy, expensive, and complex. Environmental factors can complicate analyses; clouds can dissolve and remove analyte rapidly, and variations in wind speed can result in gas fluxes having high errors. It is also much more difficult to analyse specific gas sources remotely as mixing of gases from different sources can occur. Direct-sampling techniques rely on gases being trapped, dissolved or adsorbed before being analysed by traditional methods, e. g. wet-chemistry, colourimetry, and gas chromatography. The capture of gases is best achieved as close to the source as possible, thus increasing the risk to the operator, and may only be possible during periods of low activity. The physical interaction of gases with instrument and collection vessels can lead to contamination and initiation of secondary reactions. Direct-sampling techniques are labour intensive and thus are capable of only generating a relatively small amount of data compared to the more automated remote-sensing techniques. The suitability of an individual technique therefore depends greatly on: the type of gas to be measured; the location of vent or fumamle; the level of volcanic activity; and the environment in which data are collected. I used OP-FrIR on La Fossa di Vulcano to measure the S02: HCI mass ratios of gases emitted from the rim and central crater fumaroles, -4.3 - 6.1 and 0.9 - 2.6 respectively. I attributed the higher crater rim gas ratios to the interaction of the gases with shallow hydrothermal reservoirs, causing scrubbing of the more soluble HCl- At Mt. Etna, my OP-FTIR analysis of gases emitted from the central craters showed that, in 1994, S02: HC1 mass ratios were -4.9 - 5.8. These values lie between those reported for eruptive degassing, >10, and background degassing, < I, and probably relate to refilling of the magma system prior to the 1997 eruption. A comparative study of lava effusion rates and COSPEC-derived SO2 fluxes for the 1991 - 1993 Etna eruption showed that variations were generally synchronous; small scale differences relating to the drainage of degassed magma from beneath the summit craters into the eruptive fissure. I also conducted OP-FT'IR and COSPEC analyses on Montserrat in June 1996 to show the gas plume to be relatively S02 poor, with S02: HC1 mass ratios of < 0.5. The OP-FTIR technique enabled the first remote measurements of SiF4 in volcanic plumes to be made. I have also used HF-SiF4 ratios to estimate gas equilibrium temperatures at La Fossa and Mt. Etna to be --200°C and -250 - 290°C respectively. I have also investigated the structural evolution of the Masaya Volcanic Complex. The visible complex has formed over -1000 years; with average rates of effusion of -0.2 x 106 m3/y, much lower than those required to provide the estimated volume of caldera infill, -2 x 106 m3/y. Historic activity has centred on the twin massifs of Volcän Masaya and Volcän Santiago and is dominated by pit-crater collapses. I propose that the degassing episodes, which occur with no increase in eruptive activity, are related to the convective overturn of magma beneath the craters.

The dynamics of different classes of turbulent and miscible fountains are stud- ied: from classic axisymmetric fountains issuing from round sources, to confined fountains propagating in a quasi-two-dimensional environment, to line fountains which form when release conditions are approximately two-dimensional at the source. Each class is characterised by distinct dynamical behaviour, which this the- sis analyses both through theoretical arguments and experimental measurements. A model for the entrainment of ambient fluid into a fluctuating fountain top is developed and implemented into a first complete description for round fountains. The solutions of the resulting 'three-region-model' lie in improved agreement with available data and, uniquely, do not diverge near the top of the fountain. Next, con- fined fountains (unexplored to date) are classified into four flow regimes and their behaviour collapsed according to a single governing parameter that captures the severity of confinement. Finally, new experiments on line foutains shed light on the quasi-steady structure of these flows, revealing (and motivating) a strong con- nection between their motion in the vertical and lateral planes. Round, confined and line fountains are then contrasted in the conclusions, where we reflect on what is required to progress towards a unified theory of turbulent fountains.

In plume theory it is generally assumed that a plume issuing from a round source maintains a round cross section throughout. The consequences of this hypothesis are significant; this fact should motivate research into its validity. This paper investigates conditions and analyzes mechanisms that cause fluid plumes to undergo systematic deformation in their cross section. The process of deformation is referred to as differential growth. In search of support for these ideas some available plume experiments are investigated and some supporting evidence is found and presented. It is argued that ambient wind and variations in vertical buoyancy cause these effects. A rudimentary examination of plume physics tends to support these ideas. Approximations for these mechanisms are developed. For simplicity an important approximation is made in characterizing the plume cross section with an ellipse. By way of illustrating the effect of such cross sections on plume dynamics the computer plume model of Winiarski and Frick is adapted for differential growth. Based on the results of these modifications of the model compared with round plume results and compared with some plume data it is found that the modified model is able to predict behavior the conventional theory does not predict. / Graduation date: 1977

This dissertation presents the turbulence of multiphase plumes and tidal vortices by studying and quantifying coherent structures that affect the dynamics of the flow. The measurements presented in this dissertation were taken using particle image velocimetry (PIV). After preprocessing the images and conducting the PIV analysis to get the final velocity fields, the local swirl strength was used to identify coherent structures (vortices) in the flow. This dissertation used the identified vortices to quantify the turbulent properties of the flows. The mean and turbulent properties of bubble plumes are found to be self-similar within the measured air flow rates when appropriately nondimensionalized. The timeaveraged velocity profile was shown to have a Gaussian distribution when nondimensionalized by the centerline velocity and plume radius. The bubble plumes were found to have the most energetic vortices along the plume edge and a modulated turbulent energy spectrum with a slope in the inertial subrange from -7/6 instead of the classical -5/3. The mean and turbulent properties of an inertial particle plume are presented, revealing the time-averaged velocity and vorticity profiles to be self-similar for all cases when nondimesionalized by the centerline velocity and plume radius. The average vortex properties were not self-similar for all flow cases with the largest two particles sizes being self-similar and the smallest particle vortex properties being similar to bubble plume data. Despite the difference in vortex properties, the turbulent energy spectra in inertial particle plumes followed the same modulation as the bubble plumes. PIV experiments from the tidal starting-jet vortices detail the influence of a finite channel length using identified vortice. The results show the trajectory and development of the tidal starting-jet vortices to be changed by a region of vorticity that develops inside the channel and is expelled as a vortex during the ebb tide. This expelled lateral boundary layer vortex is shown to move the starting-jet vortex away from the tidal jet shear layer thus reducing the input vorticity. When the expelled boundary layer vortex strength is 1/5 the starting-jet vortex the system dynamics change resulting in a deviation in the starting-jet vortices' trajectory. This dissertation successfully uses the local swirl strength to quantify the turbulence of multiphase plumes and tidal starting-jet vortices. Using these results, engineers will be able to better predict the efficiency of CO2 ocean sequestration and tidal flushing. Furthermore, the techniques of quantifying coherent structures developed in this dissertation can be applied to a multitude of turbulent flows.

No description available.

No description available.

No description available.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Meteorology, 1973. / Microfiche copy available in Archives and Science / Includes bibliographical references. / by John S. Lague. / M.S.