281 research outputs found
The Role of New Magma Recharges and Crystal-Mush Interaction in the Campanian Ignimbrite Activity
Equilibrium Cross Section of River Channels With Cohesive Erodible Banks
Predicting the equilibrium cross section of natural rivers has been widely investigated in fluvial morphology. Several approaches have been developed to meet this aim, starting from regime equations to the empirical formulations of Parker et al. (2007) and Wilkerson and Parker (2011), who proposed quasi-universal relations for describing bankfull conditions in sand and gravel bed rivers. Nevertheless, a general physics-based framework is still missing, and it remains an open issue to better clarify the basic mechanisms whereby a river selects its width. In this contribution we focus our attention on lowland rivers with cohesive banks, whose resistance to erosion is crucial to control the river width. In particular, we formulate a theoretical model that evaluates the equilibrium width of river cross sections modeling the interaction between the core flow in the central part of the section and the boundary layer that forms in the vicinity of the cohesive banks. The model computes the cross-section equilibrium configuration by which the shear stresses on the banks equal a critical threshold value. These stresses are computed by partitioning the total shear stress into an effective grain roughness component and a form component (Kean and Smith, 2006a). The model is applied to a large data set, concerning both sand and gravel bed rivers, and it is used to determine the relations expressing the channel width and the bankfull flow depth to the bankfull discharge, which appear to provide a unitary description of bankfull hydraulic geometry
Poesia concreta : Indirizzi concreti, visuali e fonetici. | Concrete poetry: concrete addresses, visual and phonetic.
155 p. ill. 23 cm. Esposizione a cura di Dietrich Mahlow e Arrigo Lora-Totino. Ca\u27 Giustinian, Sala delle Colonne, 25 settembre-10 ottobre 1969. (Exhibition curated by Dietrich Mahlow and Arrigo Lora-Totino. Ca \u27Giustinian, Sala delle Colonne, 25 September-10 October 1969.) On cover: Mostra di poesia concreta. (Exhibition of concrete poetry.) At head of title: La Biennale di Venezia. (The Venice Biennale.) Catalog by Carlo Belloli, Ernesto L. Francalanci.https://digitalcommons.risd.edu/specialcollections_books_graphicdesign/1004/thumbnail.jp
Magma dynamics during the 2007 Stromboli eruption (Aeolian Islands. Italy): mineralogical, geochemical and isotopic data
After the 6 month-long effusive event of 2002-2003, a new lava effusion occurred at Stromboli between 27
February and 2 April 2007. Despite the different durations, approximately the same volume of magma was
emitted in both eruptions, in the order of 107
m3
. A paroxysmal eruption occurred at the summit craters in
both the 2002–2003 and 2007 episodes, during which a significant amount of low porphyritic (LP), volatile-
rich magma was erupted. In both cases, the paroxysm did not interrupt the lava emission. Here, we present
compositional data, including texture, mineralogy, chemistry and Sr and Nd isotope ratios of bulk-rock,
groundmass and separated minerals of lavas erupted in 2007, together with chemistry and Sr and Nd isotope
composition of the pumices emitted during the 15 March paroxysm. As a whole, the lavas have the same
texture and chemistry that characterize the highly porphyritic (HP) products usually erupted at Stromboli
during normal Strombolian activity and effusive events. Compared to the previous HP products, the 2007
lavas show minor but systematic mineralogical and isotopic variations which are consistent with a modest
increase of the magma supply rate of the volcano. Compositional variations during the entire duration of the
event are very modest. Glass chemistry changes in lavas erupted in the second half of March can be explained
by theminormixing between the volatile-rich LPmagma rising through the shallowmagmatic systemduring the
15 March paroxysm and the degassed residing HP magma. A first conclusion of this study is that there is no
compositional evidence supporting major changes in the magma dynamics of the volcano accompanying the
effusive activity, as also suggested for the 2002–2003 event. The activity of Stromboli is controlled by a steady
state feeding system in which refilling, mixing, degassing and crystallization at shallow level continuously
operate,withmodest oscillations in themagma supply rate. Switching between normal Strombolian and effusive
activity is related to periods of relatively more vigorous refilling of the shallow system, leading to progressive
pressure increase in the upper conduits associated with only minor compositional variations in the erupted
products
Crystal-mush reactivation by magma recharge: Evidence from the Campanian Ignimbrite activity, Campi Flegrei volcanic field, Italy
International audienceProcesses of crystal-mush remobilization by mafic magma recharges are often related to the outpouring of largevolumes of silicic melt during caldera-forming eruptions. This occurred for the Campanian Ignimbrite (CI) erup-tion (Campi Flegrei, Italy), which produced a voluminous trachy-phonolitic ignimbrite in southern-central Italyabout 40 ka ago. We focussed on the proximal-CI deposits at San Martino that are composed of a main sequenceof early-erupted, crystal-poor units and a late-erupted (post-caldera collapse) crystal-rich Upper Pumice FlowUnit (UPFU). Detailed micro-analytical geochemical data were performed on glasses and crystals of pyroclastsfrom these deposits and coupled with Sr-Nd isotopic measurements on glasses. Results show that the CI eruptionwas fed by two distinct melts for the early-erupted units and the late UPFU, respectively. The glasses of the early-erupted units have negative Eu anomalies and show more evolved compositions and higher Nd isotope ratiosthan those of the UPFU, which have positive Eu/Eu*. The magmas of the early units formed the main volume oferuptible meltof the CI reservoir, and are interpretedashaving beenextractedfrom cumulate crystal-mushwith-out a vertical geochemical gradient within the magma reservoir. The data indicate that the generation of thedistinctive UPFU melts involved the injection of a new batch of mafic magma into the base of the CI reservoir.The mafic magma allowed heating and reactivation of the CI crystal-mush by melting of low-Or sanidines(+/−low-An plagioclases), leaving high-An plagioclases and high-Mg# clinopyroxenes as residual phases anda crystal-mush melt, made of 20% of the initial mush interstitial melt (with a composition similar to the early-erupted units) and 80% of sanidine melt. When the mush crystallinity was sufficiently reduced, the maficmagma was able to penetrate into the reactivated crystal-mush, mixing with variable proportions of crystal-mush melt and generating cooler hybrid melts, which underwent further crystallization of high-Or sanidine atvariable degrees (10–25%). Finally, possibly a short time before the eruption, the UPFU magmas were able tomix and mingle with the crystal-poor eruptible melts still persisting in the CI reservoir at the time of UPFU emis-sion. We suggest that the complex mechanisms described for the magma evolution feeding the CI eruption mayoccur whenever a crystal-mush is reactivated by new mafic magma input
The onset of an eruption: selective assimilation of hydrothermal minerals during pre-eruptive magma ascent of the 2010 summit eruption of Eyjafjallajokull volcano, Iceland
The complex processes occurring in the initial phases of an eruption are often recorded in the products of its opening stage, which are usually characterized by small volume and limited dispersal, and thus generally poorly studied. The 2010 eruption of Eyjafjallajökull (Iceland) represents a unique opportunity for these investigations thanks to the good preservation of tephra deposits within the ice/snow pack. A detailed geochemical investiga- tion on the glassy groundmass of single ash clasts disclosed a population of fragments with unusual high 87Sr/86Sr (up to 0.70668) for Icelandic magmatism, and anomalous elemental composition with respect to most of the ju- venile material of the eruption. This suggests that during its rise, before intruding into the ice cover, magma at a dyke tip selectively assimilated hydrothermal minerals with seawater-related, high-Sr isotopic ratios (zeolites, silica phases, anhydrite) hosted in altered volcanic/epiclastic rocks. According to the observed precursory seismic- ity, only restricted to few hours before the onset of the eruption, this process could have accompanied subcritical aseismic fracture opening during the days before the eruption, possibly related to stress corrosion-cracking pro- cesses, which enhanced the partial dissolution/melting and subsequent selective assimilation of the host rocks
Unveiling the occurrence of transient, multi-contaminated mafic magmas inside a rhyolitic reservoir feeding an explosive eruption (Nisyros, Greece)
Data on unveiling the occurrence of transient, multi-contaminated mafic magmas inside a rhyolitic reservoir feeding an explosive eruption (Nisyros, Greece)
This data article includes the description and the geochemical and mineralogical dataset of 67 pyroclastic rock samples from the Upper Pumice (UP) explosive activity of Nisyros volcano (eastern South Aegean Active Volcanic Arc). A detailed field and petrographic description of the studied outcrops and samples are reported, including representative photomicrographs and SEM images, whole-rock major and trace elements compositions of 31 representative samples and Sr-Nd isotope ratios on 22 selected samples. Analytical methods and conditions used for data acquisition are also reported. The UP eruption produced a stratigraphic sequence constituted by a basal fallout deposit, gradually substituted by pyroclastic density current (PDC) deposits; these are overlaid by a lag-breccia unit, and the sequence is closed by a grey ash flow level. The juvenile is mainly constituted by white-yellow, moderately crystalline pumice with rhyolitic composition and homogenous Sr-Nd isotope values. Variable amounts of dense, grey, crystalline juvenile lapilli clasts (CRC, Crystal-Rich Clast), with rounded shape and less evolved composition (andesite to dacite) are also present in the deposit. These mafic CRCs are peculiar due to their large variability in textures (from distinctive diktytaxitic to strongly fragmented structure without a defined fabric) and in the geochemical and isotopic composition. The data acquired were fundamental to reconstruct the complex and peculiar history of ascent, storage and differentiation/assimilation processes of these mafic melts before their intrusion into the shallow, rhyolitic magma chamber, with important implication on the possible eruption trigger during the more recent explosive phase of activity at Nisyros volcano. Moreover, the geochemical and isotopic analyses provide new original data to the general knowledge of the Aegean volcanics. All the data reported in this paper are related to the research article Braschi et al. (2022
New Onset Cardiac Murmur and Exertional Dyspnea in an Apparently Healthy Child: A Rare Localization of Obstructive Myxoma in the Right Ventricle Outflow Tract without Pulmonary Embolization-A Case Report and Literature Review
Myxomas are slowly growing benign neoplasms which are rare in children. Up to 80% can be located in the left atrium and generate symptoms such as embolism, cardiac failure, fever and weight loss. Rarely, myxomas can be detected in the right ventricle outflow tract, causing arrhythmias, pulmonary emboli and sudden death. We report the case of a 13-year-old healthy child brought to the Emergency Department (ED) of the Children's Hospital Bambino Gesu, Rome, for recent dyspnea, chest pain on exertion and new onset cardiac murmur. Patient underwent medical examination and echocardiogram with the finding of a rounded and lobulated voluminous mass in the right ventricle outflow tract (RVOT) which caused severe obstruction. The contrast computed tomography (CT) scan confirmed the presence of a heterogeneously enhancing soft-tissue mass occupying the RVOT with no evidence of pulmonary embolization. The mass was surgically excised, and the pathologic examination confirmed our suspicion of myxoma. Our experience suggests that myxoma can have mild clinical symptoms, the presentation may be non-specific, and diagnosis can be a challenge Careful examination and a diagnostic imaging workup, primarily with the transthoracic echocardiogram, are needful to make a rapid differential diagnosis and to better manage surgical treatment and follow-up
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