Insights into eruption dynamics from textural analysis: the case of the May, 2008, Chaitén eruption

The May, 2008, Chaitén (southern Chile) eruption was characterized by several explosive events, each associated with plumes which reached up to about 19km above sea level on May 6. A study of the textural and physical features of the juvenile clasts erupted during the climactic phase of the 2008 eruption of Chaitén is presented. Pumice clasts show unimodal density distribution (main mode at 600kg/m3), average vesicularity of about 69%, a glassy groundmass with no microcrystals, and vesicles with dimension between ∼1μm and ∼2mm. They also show a unimodal vesicle size distribution with most frequent vesicle size in the range 0.05-0.08mm and an estimated vesicle number density of 1.3 ± 0.5 × 105 mm−3 related to a rapid nucleation event produced during the late phases of magma rise. This is confirmed by the absence of microcrystals that could otherwise have delayed vesicle formation and allowed the magma to maintain a low viscosity and a supersaturation in volatiles. Vesiculation and fragmentation were triggered by a sudden decompression of the melt associated with the opening of the volcanic conduit (∼10MPa s−1

Fatigue analysis of adhesive joints with laser treated substrates

Abstract Recent literature works focused on the analysis of laser irradiation on the strength of adhesive joints under quasi-static loading conditions. It has been demonstrated that laser surface preparation allows to remove impurity and weak boundary layers from the mating substrates and, depending on the energy density, it is also able to modify surface morphology promoting mechanical interlocking. In previous works, the authors assessed the effect of Yb-fiber laser ablation over the quasi-static strength and toughness, of aluminum and stainless steel adhesively bonded joints. The experimental results demonstrated the ability of laser irradiation to improve the mechanical properties of the joints. The aim of this work is to extend the scope of previous investigations to fatigue loading. Double Cantilever Beam (DCB) samples with laser treated aluminum substrates have been bonded with a two component epoxy adhesive. For comparison standard degreasing and grit blasting have been also deployed for samples preparation. The results have been compared in terms of cycles to failure and the fracture surfaces have been analyzed by means of Scanning Electron Microscopy (SEM) in order to investigate the mechanism of failure

Tephra stratigraphy and eruptive volume of the May, 2008, Chaitén eruption, Chile

On May 1st 2008 Mount Chaitén (southern Chile) interrupted a long period of quiescence, generating a sequence of explosive eruptions and causing the evacuation of Chaitén town located a few kilometers south of the volcano. The activity was characterized by several explosive events each associated with plumes which reached up to about 19km above sea level. The products were dispersed across a wide area, with the finest ash reaching the Atlantic coast of Argentina. Our field observations in the proximal-medial area (3-25km from the vent) indicate that the May 2008 tephra deposit consists of numerous layers, most of which can be correlated with individual eruptive events. These layers vary from extremely fine-grained ash to layers of lapilli and blocks, composed of both juvenile and lithic material. Here we describe the stratigraphy and physical characteristics of the May 2008 deposits, and propose a reconstruction of the timing of the May 2008 events. The deposits are mainly associated with the three main explosive phases which occurred on 1st-2nd May, 3rd-5th May and 6th May, with an estimated bulk tephra volume of 0.5-1.0km3 (integration of both exponential and power-law fitting). For the 6th May event, represented by a layer composed mainly of lithic lapilli and blocks (>2mm), an isopleth map was compiled from which a 19km plume height was determined, which is in good agreement with satellite observation

fracture toughness of structural adhesives for the automotive industry

Abstract Adhesive bonding is currently employed by automotive manufacturers to complement (or replace) welding in joining dissimilar materials. In order to reduce the impact on the existing manufacturing infrastructures, structural adhesives are deployed in the body shop but hardening is accomplished in the paint cure oven. Various adhesive formulations have been specifically developed for the implementation in the automotive manufacturing chain. However, it is very important to assess the mechanical behaviour of the joints which results from the peculiar curing strategy. In the present work, automotive grade single component epoxy and two component epoxy modified acrylic adhesives were evaluated. T-joints were fabricated using a cold rolled galvanized steel (FeP04) employed in the production of car body parts. The fracture toughness of the joints was determined using the test protocol proposed by the European Structural Integrity Society (ESIS). Optical microscopy was employed to ascertain the mechanisms of failure. The results indicated that both adhesives were able to provide a fairly good mechanical response with minimum preparation of the mating substrates. Moreover, the obtained values of fracture toughness were shown to be essentially independent of the adhesive layer thickness

Self-Healing and reprocessable oleic acid-based elastomer with dynamic S-S bonds as solvent-free reusable adhesive on copper surface

In the last decade, the application of dynamic covalent chemistry in the field of polymeric materials has become the subject of an increasing number of studies, gaining applicative relevance. This is due to the fact that polymers containing dynamic functions possess a structure that affords reprocessability, recyclability and peculiar self-healing properties inconceivable for “classic” polymer networks. Consequently, the synthesis of a dynamic covalent chemistry-based polymer and its chemical, thermal, and mechanical characterizations are reported in the present research. In particular, oleic acid has been used as starting material to follow the founding principles of the circular economy system and, thanks to the aromatic disulfide component, which is the foundation of the material dynamic characteristics, the obtained polymer resulted as being reprocessable and self-healable. Moreover, the polymer can strongly interact with copper surfaces through the formation of stable Cu-S bonds. Then, the application of the polymer as a solvent-free reusable adhesive for copper was investigated by lap joint shear tests and comparisons with the properties of an analogous material, devoid of the disulfide bonds, were conducted

Fluidal pyroclasts reveal the intensity of peralkaline rhyolite pumice cone eruptions

This work is a contribution to the Natural Environment Research Council (NERC) funded RiftVolc project (NE/L013932/1, Rift volcanism: past, present and future) through which several of the authors are supported. In addition, Clarke was funded by a NERC doctoral training partnership grant (NE/L002558/1).Peralkaline rhyolites are medium to low viscosity, volatile-rich magmas typically associated with rift zones and extensional settings. The dynamics of peralkaline rhyolite eruptions remain elusive with no direct observations recorded, significantly hindering the assessment of hazard and risk. Here we describe uniquely-preserved, fluidal-shaped pyroclasts found within pumice cone deposits at Aluto, a peralkaline rhyolite caldera in the Main Ethiopian Rift. We use a combination of field-observations, geochemistry, X-ray computed microtomography (XCT) and thermal-modelling to investigate how these pyroclasts are formed. We find that they deform during flight and, depending on size, quench prior to deposition or continue to inflate then quench in-situ. These findings reveal important characteristics of the eruptions that gave rise to them: that despite the relatively low viscosity of these magmas, and similarities to basaltic scoria-cone deposits, moderate to intense, unstable, eruption columns are developed; meaning that such eruptions can generate extensive tephra-fall and pyroclastic density currents.Publisher PDFPeer reviewe

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di Calogero Piro. Convertire la realtà che ci circonda in immagini, è stata fin dai primordi dell’essere umano un’atavica necessità. Ancora oggi nella nostra cultura visiva è tutto basato sull’utilizzo dell’immagine per conoscere la realtà che ci circonda. Con la scoperta della fotografia, la riflessione intorno alla natura si fa sempre più interessante. Il ruolo della macchina fotografica in questo progetto per raccontare l’ambiente, la struttura, gli oggetti, i segni, i colori e le atmosfere che caratterizzano il centro del CNR di capo Granitola ha trovato prepotentemente in questi giovani allievi della cattedra di fotografia dell’Accademia di Belle Arti di Palermo, diretta dal Professore Sandro Scalia, momenti di grande professionalità, realizzando un grande reportage con tutti gli aspetti essenziali della struttura e delle articolazioni primarie del linguaggio fotografico. Questa esperienza extradidattica difficile ed impegnativa non soltanto per la necessità del confronto col “nuovo” in termini organizzativi, ma anche per la necessità di descrivere attraverso la fotografia il tema della Biodiversità, è stato affrontato brillantemente. Mettendo in primo piano, siti naturali, siti storici come: Mozia e Selinunte, i laboratori del centro di ricerche, la Flora e la Fauna, sono riusciti a raggiungere con acuta osservazione ottimi risultati visibili in questo catalogo, e con la tangibile riprova di cosa possa e debba essere una educazione estetica assolutamente “libera” da condizionamenti, viatico ineludibile perché l’espressione artistica, sotto qualunque forma, sia artefice dei grandi processi di vera maturazione culturale, si avverte in questi giovani artisti la purezza e la consapevolezza dei propri messaggi ancora privi, e speriamo sempre, di qualunque tipo di inquinamento tendenzioso

IN "POLPO ... SITION" E ALTRI BREVI RACCONTI

Assalito dalla felicità corsi al mare, guardai l’acqua e fui preso da una forza, non mia, non umana che mi trascinò in acqua. Lì venni rapito da fantastiche sensazioni, l’adrenalina salì a mille, vidi un enorme creatura che suscitò in me delle emozioni mai provate prima, si era avvicinata talmente tanto che stava per toccarmi e, appena lo fece, il mio corpo si illuminò magicamente, le mie mani iniziarono pian piano ad assottigliarsi, il mio petto diventava sempre più piccolo e tondo e da lì a poco, ero diventato un polpo

Morphology and microtextures of tephra particles

The purpose of this PhD thesis is to give insights into the dynamics of highly explosive eruptions and on both tephra dispersal and sedimentation, based on the characterization of the erupted material. A systematic and detailed morphological characterization of tephra particles from different eruptions and the calculation of their terminal fall velocity is carried out in order to give new insights in understanding the influence of the morphology of volcanic particles on the settling process. The May 2008 Chaitén eruption has been taken as a case study. The eruption has been studied based on the data collected in the field on January 2009 in order to describe its stratigraphy and to determine the main eruptive parameters (i.e., volume, column height, mass eruption rate). On May 6th the eruption reached its climax producing a tephra layer composed mainly of lithic lapilli and blocks (> 2 mm) and a 19 km high subplinian column. Textural analysis have been carried out on pumice samples produced in this phase and a fractal analysis of the associated ash have also been conducted in order to study the influence of the vescicularity on particle morphology and to get information about the dynamic processes that characterized the eruption