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UV camera measurement at a dormant volcano
No full textThe UV camera is now becoming a new important tool in the armory of volcano geochemists for high rate SO2 flux measurements. The high spatial resolution of the camera is particularly useful for exploring multiple-source SO2 gas emissions, as the large composite fumarolic systems topping most quiescent volcanoes. We report here on the first SO2 flux measurements from individual fumaroles of the fumarolic field of La Fossa crater (Vulcano island, Aeolian island), which we performed using a UV camera in two field campaigns on November 12, 2009 and February 4, 2010. Making advantage of the high temporal and spatial resolution of the UV camera, we derived ~0.5 Hz SO2 flux time-series for the main fumarolic areas, deriving fluxes from individual fumaroles ranging from 1.4 to 5.2 tons/day; and a total cumulative flux from the whole system of ~ 13 tons/day. The data of each campaign were implemented by determining, for each fumarolic vent, the molar SO2/H2S and CO2/SO2 ratios (which we derived using a portable multi-gas analyzer). Using the SO2 flux data in tandem with the molar ratios, we also calculated the flux of volcanic species CO2 (355 tons/day) and H2S (5.6 tons/day) from Vulcano island
Spectroscopic capture of 1 Hz volcanic SO2 fluxes and integration with volcano geophysical data
No full textPassive vs. active degassing modes at an open-vent volcano (Stromboli, Italy)
Full text linkWe report here on a UV-camera based field experiment performed on Stromboli volcano during 7 days in 2010 and 2011, aimed at obtaining the very first simultaneous assessment of all the different forms (passive and active) of SO2 release from an open-vent volcano. Using the unprecedented spatial and temporal resolution of the UV camera, we obtained a 0.8 Hz record of the total SO2 flux from Stromboli over a timeframe of 14 h, which ranged between 0.4 and 1.9 kg s 1 around a mean value of 0.7 kg s 1 and we concurrently derived SO2 masses for more than 130 Strombolian explosions and 50 gas puffs. From this, we show erupted SO2 masses have a variability of up to one order of magnitude, and range between 2 and 55 kg (average 20 kg), corresponding to a time integrated flux of 0.0570.01 kg s 1. Our experimental constraints on individual gas puff mass (0.03–0.42 kg of SO2, averaging 0.19 kg) are the first of their kind, equating to an emission rate ranging from 0.02 to 0.27 kg s 1. On this basis, we
conclude that puffing is two times more efficient than Strombolian explosions in the magmatic degassing process, and that active degassing (explosionsþpuffing) accounts for 23% (ranging from 10% to 45%) of the volcano’s total SO2 flux, e.g., passive degassing between the explosions contributes the majority ( 77%) of the released gas. We furthermore integrate our UV camera gas data for the explosions and puffs, with independent geophysical data (infrared radiometer data and very long period seismicity), to offer key and novel insights into the degassing dynamics within the shallow conduit systems of this open-vent volcano
Non-stationary nature of SO2 degassing at Etna’s North-east crater (Italy).
No full textInvestigating Etna’s long-term SO2 flux behaviour has led to important conclusions on the structure of the volcano’s magma feeding system, magma production (and degassing) rates, and causes for the excess degassing behaviour. Nonetheless, our knowledge of the short-term (timescales of seconds to a few hours) behaviour of magmatic volatiles (e.g., bubble coalescence, separate ascent and surface bursting of gas-rich bubbles) in the volcano’s upper feeding conduit system is still fragmentary, and based on indirect evidences (petrologic-textural data, observation of geophysical signals , physical modelling and laboratory experiments). In the past, direct gas flux measurements at Etna have been taken with insufficient temporal resolution for fast conduit processes to be investigated. UV cameras now allow imaging of gas flux emissions, and exploration of underlying volcanic degassing processes, with an improved temporal resolution. In this work we show that UV cameras can valuably assist in capturing the rapid (timescale of seconds) SO2 flux variations occurring during the quiescent activity of a basaltic volcano. We have, in particular, investigated the non-stationary nature of degassing activity at Etna’s North-east crater, which is shown here to exhibit a somewhat periodic degassing behaviour (characteristic periods ranging 40-250 s). A similar degassing behaviour has recently been observed at other volcanoes (Stromboli, Erebus, San Cristobal, Gorely), and probably represents a common feature of all basaltic volcanoes. We finally present a preliminary model, which results suggest that the periodic degassing pattern may reflect inhomogeneous distribution of gas bubbles in a magmatic conduit, and their clustering to form trains of variably spaced gas bubble layers
Ozone depletion in tropospheric volcanic plumes
Full text linkWe measured ozone (O3) concentrations in the atmospheric plumes of the volcanoes St. Augustine (1976), Mt. Etna (2004, 2009) and Eyjafjallajkull (2010) and found O3 to be strongly depleted compared to the background at each volcano. At Mt. Etna O3 was depleted within tens of seconds from the crater, the age of the St. Augustine plumes was on the order of hours, whereas the O3 destruction in the plume of Eyjafjallajkull was maintained in 1-9 day old plumes. The most likely cause for this O 3 destruction are catalytic bromine reactions as suggested by a model that manages to reproduce the very early destruction of O3 but also shows that O3 destruction is ongoing for several days. Given the observed rapid and sustained destruction of O3, heterogeneous loss of O3 on ash is unlikely to be important
Protocols for UV camera volcanic SO2 measurements
Full text linkUltraviolet camera technology offers considerable promise for enabling 1 Hz timescale acquisitions of
volcanic degassing phenomena, providing two orders of magnitude improvements on sampling frequencies
from conventionally applied scanning spectrometer systems. This could, for instance enable unprecedented
insights into rapid processes, such as strombolian explosions, and non-aliased corroboration with volcano
geophysical data. The uptake of this technology has involved disparate methodological approaches, hitherto.
As a means of expediting the further proliferation of such systems, we here study these diverse protocols,
with the aim of suggesting those we consider optimal. In particular we cover: choice and set up of hardware,
calibration for vignetting and for absolute concentrations using quartz SO2 cells, the retrieval algorithm and
whether one or two filters, or indeed cameras, are necessary. This work also involves direct intercomparisons
with narrowband observations obtained with a scanning spectrometer system, employing a differential
optical absorption spectroscopic evaluation routine, as a means of methodological validation
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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