Morphology and Formation of Glassy Volcanic Ash from the August 12-15, 1991 Eruption of Hudson Volcano, Chile

The 1991 explosive eruption of Hudson volcano in Chile ejected about 2.7 km3 (DRE) of basalt and trachyandesite magma as tephra fall. A majority of the fallout occurred from an eruption during the period August 12-15, 1991, producing an extensive deposit to the east of the volcano in Chile and Argentina. Dacitic, glassy tephra from this phase of the eruption exhibit a remarkable variety in particle morphology and color, ranging from dark, poorly-vesicular shards to light-colored, pipe-vesicular micropumice. Fractal analysis of glassy particle outlines shows that at least four distinct types can be discriminated: blocky, poorly-vesicular, highly vesicular with spherical vesicles, and pipe vesicular. A quantitative comparison of particle morphologies using principal component analysis of fractal spectrums of the Hudson tephra with other tephra produced by eruptions with known fragmentation mechanisms, together with SEM imaging of particle surfaces, indicates that production of the Hudson tephra involved both interaction with external water and exsolution of dissolved volatiles. Blocky particles likely represent magma that was fragmented by magma-water interactions before exsolution of all dissolved volatiles could occur. The great diversity of particle types in the August 12-15, 1991 Hudson tephra fall can be attributed to eruption of volatile-rich trachyandesite magma through an ice-filled caldera where subglacial melting led to a supply of external water that interacted intermittently with the discharge of magma driven primarily by volatile exsolution.La erupción explosiva de 1991 del Volcán Hudson en Chile expulsó cerca de 2,7 km3 (DRE) de magma traquiandesítico y basáltico en forma de caída de tefra. La mayoría de la caída se produjo durante el período del 12 al 15 de agosto de 1991, a partir de una erupción que produjo un extenso depósito hacia el este del volcán, en Chile y en Argentina. Para esta fase de la erupción, la fracción vítrea correspondiente a la tefra traquiandesítica muestra composición dacítica, con fragmentos de forma y color muy variados, que fluctúan desde trizas oscuras y poco vesiculadas hasta fragmentos pumíceos de color claro e intensa vesiculación de canalículos. El análisis fractal del contorno de las partículas vítreas permite la separación en por lo menos cuatro tipos distintos: blocosas, poco vesiculadas, altamente vesiculadas con vesículas esféricas y canalículo-vesiculadas. El análisis cuantitativo de las formas de las partículas, mediante el análisis de componentes principales de los espectros fractales de las partículas de la tefra del Hudson, y su comparación con los de otras tefras producidas por erupciones cuyos mecanismos de fragmentación son conocidos, junto con las imágenes de microscopio electrónico de barrido de la superficies de las partículas, indica que la producción de tefra del Hudson es resultado de un proceso mixto que comprende la interacción del magma con agua externa y la exsolución de los volátiles disueltos en el magma. Las partículas blocosas probablemente representan magma fragmentado por interacción con agua antes de que tuviera lugar la exsolución de todos los volátiles disueltos. La gran variedad de partículas en la caída de cenizas de la erupción del 12 al 15 de agosto de 1991 del volcán Hudson puede atribuirse a la erupción de un magma traquiandesítico rico en volátiles a través de una caldera rellena de hielo, en la cual la fusión de la base del relleno de hielo aportó agua externa al sistema magmático, que interactuó intermitentemente con la descarga de magma impulsada por la exsolución de volátiles.Fil: Scasso, Roberto Adrian. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires; ArgentinaFil: Carey, Steven. University of Rhode Island; Estados Unido

An Evaluation of the Teacher Advancement Program (TAP) in Chicago: Year One Impact Report

Based on test scores, teacher records, surveys, and interviews, examines the first-year impact of the TAP program, in which teachers delivering added value to student achievement and quality classroom performance earn extra pay and become mentors

Exploring Submarine Arc Volcanoes

Three quarters of Earth’s volcanic activity occurs beneath the sea, predominantly along the extensive mid-ocean ridge system that winds its way through the major ocean basins. The style of eruptive activity along mid-ocean ridges has been extensively studied and well characterized. Submarine eruptions at mid-ocean ridges are dominated by effusive production of pillow and sheet-flow lavas at water depths of several thousands meters. The other major style of submarine eruptions occurs along island arcs where subduction of oceanic crust triggers melting of mantle rocks by the release of volatile components, such as water and carbon dioxide. Submarine volcanism constitutes an important component of active island arc systems, although a significant part of arc volcanism can also occur subaerially

Measurements of thermal properties of icy Mars regolith analogs

In a series of laboratory experiments, we measure thermal diffusivity, thermal conductivity, and heat capacity of icy regolith created by vapor deposition of water below its triple point and in a low pressure atmosphere. We find that an ice-regolith mixture prepared in this manner, which may be common on Mars, and potentially also present on the Moon, Mercury, comets and other bodies, has a thermal conductivity that increases approximately linearly with ice content. This trend differs substantially from thermal property models based of preferential formation of ice at grain contacts previously applied to both terrestrial and non-terrestrial subsurface ice. We describe the observed microphysical structure of ice responsible for these thermal properties, which displaces interstitial gases, traps bubbles, exhibits anisotropic growth, and bridges non-neighboring grains. We also consider the applicability of these measurements to subsurface ice on Mars and other solar system bodies

Dixmier Traces as Singular Symmetric Functionals and Applications to Measurable Operators

This paper introduces a new approach to the non-normal Dixmier and Connes-Dixmier traces (introduced by Dixmier and adapted to non-commutative geometry by Connes) on a general Marcinkiewicz space associated with an arbitrary semifinite von Neumann algebra. By unifying various constructions, and translating the situation of Dixmier traces into the theory of singular symmetric functionals on Marcinkiewicz function/operator spaces, we obtain the results (i) and (ii) below. The results are stated here, for the reader, in terms of the ideal $L^{(1,\infty)}$ of compact operators whose partial sums of singular values are of logarithmic divergence. (i) a positive compact operator $x$ in $L^{(1,\infty)}$ yields the same value for an arbitrary Connes-Dixmier trace (ie. $x$ is measurable in the sense of Connes) if and only if $\lim_{N\to\infty} \frac{1}{Log N}\sum_{n=1}^N s_n(x)$ exists, where $s_n(x)$ are the singular values of the compact operator $x$; (ii) the set of Dixmier traces and the set of Connes-Dixmier traces are norming sets (up to equivalence) for the space $L^{(1,\infty)}/L^{(1,\infty)}_0$, where the space $L^{(1,\infty)}_0$ is the closure of all finite rank operators in the norm $||.||_{(1,\infty)}$.Comment: 31 pages, LaTex source, to appear in J. Funct. Ana

Influence of Volatile Degassing on Initial Flow Structure and Entrainment During Undersea Volcanic Fire Fountaining Eruptions

Release of dissolved volatiles during submarine fire fountaining eruptions can profoundly influence the buoyancy flux at the vent. Theoretical considerations indicate that in some cases buoyant magma can be erupted prior to fragmentation (~75% vesicle volume threshold). Laboratory simulations using immiscible fluids of contrasting density indicate that the structure of the source flow at the vent depends critically on the relative magnitudes of buoyancy and momentum fluxes as reflected in the Richardson number (Ri). Analogue laboratory experiments of buoyant discharges demonstrate a variety of complex flow structures with the potential for greatly enhanced entrainment of surrounding seawater. Such conditions are likely to favor a positive feedback between phreatomagmatic explosions and volatile degassing that will contribute to explosive volcanism. The value of the Richardson number for any set of eruption parameters (magma discharge rate and volatile content) will depend on water depth as a result of the extent to which the exsolved volatile components can expand

Hydrothermal oxide and nontronite deposits at Seamount 3, Wolf-Darwin lineament, Galapagos Archipelago, Ecuador

An unusual deposit of Fe-rich hydrothermal nontronite was recovered by remotely operated vehicle (ROV) from Seamount 3 of the Wolf-Darwin lineament, Galapagos Marine Reserve. X-ray diffraction, ICP-MS/ICP-AES, and SEM-EDS analyses show that this deposit is chemically and mineralogically similar to other deep-sea hydrothermal nontronites, indicating a formation temperature of about 30o to 50o Celsius. These Fe-Si-oxides and Fe-rich Al-poor nontronite deposits contain about 38-51 weight % SiO2 and 40-50 weight % Fe2O3. Although hydrothermal nontronite has been sampled at a number of sites by coring and dredging, this is the first in situ documentation of its sinuous, tubular structure on the sea floor. Image-analysis of ROV imagery suggests that this unusual pattern might be controlled by fluid pathways in the underlying pillow lavas