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Investigating 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.

Ultraviolet 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 SO 2 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.

We 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 SO 2 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 SO 2 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 SO 2 masses for more than 130 Strombolian explosions and 50 gas puffs. From this, we show erupted SO 2 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 0.05±0.01 kg s −1 . Our experimental constraints on individual gas puff mass (0.03–0.42 kg of SO 2 , 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 (explosions+puffing) accounts for ∼23% (ranging from 10% to 45%) of the volcano's total SO 2 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.

[1] Here we present a novel spectroscopic approach to capturing, with unprecedented time resolution and accuracy, volcanic SO2 fluxes. This is based on two USB2000 spectrometers, coupled to cylindrical lens telescopes, each collecting light which has transited horizontal sections of the rising plume. We report on field data from Stromboli volcano, in which the entire emission rate from the volcano was measured, as well as flux signatures associated with individual crater explosions. The latter were integrated with seismic and thermal data, demonstrating correlations in both cases, and representing the first such geophysical-geochemical data corroboration on this timescale. Such a holistic empirical capability could significantly expedite our understanding of explosive volcanic processes.