Volcano remote sensing with ground-based spectroscopy

The chemical compositions and emission rates of volcanic gases carry important information about underground magmatic and hydrothermal conditions, with application in eruption forecasting. Volcanic plumes are also studied because of their impacts upon the atmosphere, climate and human health. Remote sensing techniques are being increasingly used in this field because they provide real-time data and can be applied at safe distances from the target, even throughout violent eruptive episodes. However, notwithstanding the many scientific insights into volcanic behaviour already achieved with these approaches, technological limitations have placed firm restrictions upon the utility of the acquired data. For instance, volcanic SO2 emission rate measurements are typically inaccurate (errors can be greater than 100%) and have poor time resolution (ca once per week). Volcanic gas geochemistry is currently being revolutionized by the recent implementation of a new generation of remote sensing tools, which are overcoming the above limitations and are providing degassing data of unprecedented quality. In this article, I review this field at this exciting point of transition, covering the techniques used and the insights thereby obtained, and I speculate upon the breakthroughs that are now tantalizingly close

Great challenges in volcanology: how does the volcano factory work?

INTRODUCTION Scientists are asked to describe and understand the complex behavior of natural processes. This is often done in difficult conditions, with instruments detecting specific indicators and providing limited datasets to satisfy knowledge and imagination. Despite these limitations, many studies have been able to provide unprecedented understanding of different processes in nature, albeit often under specific (i.e., simplified) conditions. A progressively more quantitative approach has been often obtained exploiting the latest technological improvements available. The study of volcanic, or more generally, magmatic processes well exemplifies these conditions and progression (Figure 1). Qualitative reports of how volcanoes erupt date back to thousands of years, as the description of the 79 AD Vesuvio eruption from Pliny the Younger; however, most of our qualitative and quantitative understanding of the volcano factory and its various indicators has been definitely achieved in the frame of the technological boost of the last decades. Certainly, the tremendous improvement of the monitoring system of active and erupting volcanoes has allowed detecting many changes in the geophysical, geodetic and geochemical behavior before, during and after eruptions (e.g., Lowenstern et al., 2006; Sigmundsson et al., 2010; Chiodini et al., 2012). As a result, a significant amount of data has been collected on a reasonable amount of active volcanoes worldwide, and it is in general possible to assign some physical or chemical meaning to many detected changes. This knowledge is also crucial to define when a volcano enters a phase of deviation from its baseline, or unrest, which may culminate in an eruption and to forecast any impending eruption. The understanding of the processes occurring within volcanoes, ultimately leading to the geophysical, geodetic and geochemical changes detected at the surface, is supported by analytical, numerical, and experimental models (e.g., Cayol et al., 2000; Gudmundsson, 2006; Caricchi et al., 2007; Ruch et al., 2012). Modeling has reached a relatively sophisticated stage, allowing understanding otherwise inaccessible and/or long-lasting 2D and, to a lesser extent, 3D processes. Similarly crucial to understand the mean to longerterm behavior of volcanoes are many field and petrological-geochemical studies, supported by dating techniques (e.g., Gravley et al., 2007; Thordarson and Larsen, 2007; Collins et al., 2009; Wilson and Charlier, 2009; Corsaro et al., 2013). In particular, field studies prove fundamental in reconstructing the eruptive history of a volcano, including the eruption location, type, size and frequency; petrological and geochemical studies provide an invaluable amount of information on the processes and times characterizing the formation of the magma, its rise and emplacement within the crust, including mixing, mingling, crustal assimilation, and fractionation. These approaches have allowed reaching a dramatic advancement in our understanding of volcanoes. An overview of the major improvements in volcanology in the last decades is beyond the scope of this contribution. For facts, one can refer to the comprehensive, detailed and essential overview of Cashman and Sparks (2013). This includes many of the important studies on the emplacement (formation of magma chambers), rise (eruption triggers, dike propagation), and eruption of magma (conduit construction and evolution, magma rheology and fragmentation, eruptive styles). The described amount of research underlines the impressive efforts made by the volcanological community in considering and analyzing the several complex evolutionary stages of a magma within the volcano factory, from its generation to its eruption. Even though the reached level of knowledge may not unravel the many questions behind the volcano factory, it certainly provides a robust platform to test hypotheses and plan more advanced and sophisticated studies. Indeed, despite the important achievements, modern volcanology still has to fully define and understand several major processes, involving different topics and approaches, and resulting in likewise challenges for the future. Here the first-order processes, or challenges for volcanology, are summarized in an ideal journey from the deepest to the shallowest portions of the volcano factory (Figure 2). Many of these processes may be unraveled not only by observations on volcanoes on Earth, but also on extraterrestrial volcanoes, including those on Venus, Mars and Io. While studies on terrestrial volcanism provide the key to understand also extraterrestrial volcanism, it is likewise expectable that observations on adequately imaged volcanic edifices from Mars and Venus allow to better define volcanic processes on Earth

Ground based ultraviolet remote sensing of volcanic gas plumes

Ultraviolet spectroscopy has been implemented for over thirty years to monitor volcanic SO2 emissions. These data have provided valuable information concerning underground magmatic conditions, which have been of utility in eruption forecasting efforts. During the last decade the traditionally used correlation spectrometers have been upgraded with miniature USB coupled UV spectrometers, opening a series of exciting new empirical possibilities for understanding volcanoes and their impacts upon the atmosphere. Here we review these technological developments, in addition to the scientific insights they have precipitated, covering the strengths and current limitations of this approach

Heat and SO2 Emission Rates at Active Volcanoes - The Case Study of Masaya, Nicaragua

No abstract included in the book chapte

Heat and SO2 Emission Rates at Active Volcanoes – The Case Study of Masaya, Nicaragua

The necessity of understanding volcanic phenomena, so as to assist hazard assessment and risk management, has led to development of a number of techniques for the tracking of volcanic events so as to support forecasting efforts. Since 1980s scientific community has progressively drifted research and surveillance at active volcanoes by integrated approach. Nowadays, volcano observatories over the world record and integrate real or near-real time data for monitoring and understanding volcano behaviour. Among the geophysical, geochemical, and volcanological parameters, the tracking of temperature changes at several volcanic features (e.g., open-vent systems, eruptive vents, fumaroles) and variations in sulphur dioxide flux and concentration at volcanic plumes are key factors for studying and monitoring active volcanoes. Temperature is one of the first parameters that have been considered in understanding the nature of volcanoes and their eruptions. Thermal anomalies have proved to be precursors of a number of eruptive events, and once an eruption begins, temperature plays a major role in lava flow emplacement and lava field development. At active volcanoes, temperature has been measured by direct and indirect methodologies. Direct measurements represent the traditional thermal monitoring carried out at fumaroles, hot springs, molten lava bodies, and crater lakes, using thermocouples. Indirect measurements, also known as thermal remote sensing, can be performed by satellite, ground, and airborne surveys. Owing to the danger of most kinds of eruption, and the need of monitoring inaccessible areas on volcanoes, indirect measurements are especially attractive. Among them, thermal imagery is the most widespread and results from the capability to detect the infrared radiation emitted from the surface of hot bodies, and to provide the radiometric map of heat distribution of the body’s surface. This has been of primary importance for capturing the evolution of thermal anomalies, which shed light on magma movements at shallow depths. While magma is rising, hot gases separate from the melt and escape either directly from the main conduits, or indirectly by leaking through fumaroles, fractures, and faults, or by dissolving within crater lakes and hot spring waters, resulting in variations in their temperature and chemical composition. At the surface, these phenomena are also associated with radiative heat fluxes, which can be detected by infrared thermal detectors. The application of thermal imaging to volcanology was largely performed using satellite surveys, but in the last decade there has been increasing application of compact (hand-held or tripod-mounted) thermal imagers used from the air or ground. Volcanic degassing plays a key role in magma transport and style, and timing of volcanic eruptions observed at the Earth’s surface. The assessment of volcanic gas composition and flux has become a standard procedure for volcanic monitoring and forecasting since degassing regimes are fundamentally linked to volcanic processes. Magma contains dissolved gases that are released into the atmosphere during both quiescent and eruptive stages. At high pressures, deep beneath the Earth’s surface, gases are dissolved in magma; however as soon as magma rises toward the surface, where pressures are lower, gases start to exsolve according to the solubility-pressure relationship of each species, as well as compositional and diffusional constraints. The abundance and final gas phase composition of the emitted plume depends on magma composition(s), volatile fugacities, crystallisation and on the dynamics of magma degassing, including kinetic effects. However, at the surface, the composition and flux of volcanic gases may change with time, reflecting variations in the magmatic feeding system of the volcano. Hence by studying and tracking this variability a number of parameters, such as magma residing depths and the amount of degassing magma bodies can be determined. Among the volcanic gas species, sulphur dioxide (SO2) is one of the most-well investigated in remote sensing. As for temperature, SO2 concentration and emission rates can be measured using both direct sampling and non-contact, remote sensing measurements. The latter carried out during air- and ground-based surveys and satellite platforms, are based on optical spectroscopy. Since the 1970s, SO2 flux has been remotely measured using the COrrelation SPECtrometer (COSPEC) at several volcanoes worldwide. Over the last 10 years the advent of small, commercial and low cost spectrometers offered a valuable replacement to the outdated COSPEC. In particular, the combination of UV spectrometers with the Differential Optical Absorption Spectroscopy (DOAS) analytical method improved significantly data collection offering a number of advantages such as the possibility of obtaining measurements in the challenging environments typical of volcanic areas and detection of other plume species. Our intent here is to discuss findings and implications arising from the integration of thermal imaging-derived temperature and SO2 emission rates. Calibrated temperatures from thermal imagery can provide qualitative as well as quantitative information, fundamental insights and parameters contributing to understanding and modelling of several eruptive features. Anomalies in SO2 emission rates have been often documented at several volcanoes prior to eruptive crisis. In syn-eruptive stages, anomalies in the SO2 flux pattern might indicate variations in the eruptive style and regime associated with changes in the volcano shallow feeder system. At open-vent systems, in non-eruptive phases, changes in SO2 flux emission have provided information on increases or decreases of magma supply in the shallow plumbing system suggesting likely volcanic unrests or magma migration towards peripheral areas of the volcano edifice, respectively. There is still much to explore about volcano behaviour and eruptive mechanisms, however, the combination of different types of monitoring techniques is crucial for constraining baselines for predicting phases of volcano unrests and for gaining useful insights for volcano hazard assessment

Carbon Dioxide Emissions from Subaerial Volcanic Regions

Volcanism and metamorphism are the principal geologic processes that drive carbon transfer from the interior of Earth to the surface reservoir.1–4 Input of carbon to the surface reservoir through volcanic degassing is balanced by removal through silicate weathering and the subduction of carbon-bearing marine deposits over million-year timescales. The magnitude of the volcanic carbon flux is thus of fundamental importance for stabilization of atmospheric CO2 and for long-term climate. It is likely that the “deep” carbon reservoir far exceeds the size of the surface reservoir in terms of mass;5,6 more than 99%of Earth’s carbon may reside in the core, mantle, and crust. The relatively high flux of volcanic carbon to the surface reservoir, combined with the reservoir’s small size, results in a short residence time for carbon in the ocean–atmosphere–biosphere system (~200 ka).7 The implication is that changes in the flux of volcanic carbon can affect the climate and ultimately the habitability of the planet on geologic timescales. In order to understand this delicate balance, we must first quantify the current volcanic flux of carbon to the atmosphere and understand the factors that control this flux.Published188-2363V. Proprietà chimico-fisiche dei magmi e dei prodotti vulcanic

Sulfur Degassing From Volcanoes: Source Conditions, Surveillance, Plume Chemistry and Earth System Impacts

International audienceDespite its relatively minor abundance in magmas (compared with H2O and CO2), sulfur degassing from volcanoes is of tremendous significance. It can exert substantial influence on magmatic evolution (potentially capable of triggering eruptions); represents one of the most convenient opportunities for volcano monitoring and hazard assessment; and can result in major impacts on the atmosphere, climate and terrestrial ecosystems at a range of spatial and temporal scales. The complex behavior of sulfur in magmas owes much to its multiple valence states (-II, 0, IV, VI), speciation (e.g., S2, H2S, SO2, OCS and SO3 in the gas phase; S2-, SO42- and SO32- in the melt; and non-volatile solid phases such as pyrrhotite and anhydrite), and variation in stable isotopic composition (32S, 33S, 34S and 36S; e.g., Métrich and Mandeville 2010). Sulfur chemistry in the atmosphere is similarly rich involving gaseous and condensed phases and invoking complex homogeneous and heterogeneous chemical reactions. Sulfur degassing from volcanoes and geothermal areas is also important since a variety of microorganisms thrive based on the redox chemistry of sulfur: by reducing sulfur, thiosulfate, sulfite and sulfate to H2S, or oxidizing sulfur and H2S to sulfate (e.g., Takano et al. 1997; Amend and Shock 2001; Shock et al. 2010). Understanding volcanic sulfur degassing thus provides vital insights into magmatic, volcanic and hydrothermal processes; the impacts of volcanism on the Earth system; and biogeochemical cycles. Here, we review the causes of variability in sulfur abundance and speciation in different geodynamic contexts; the measurement of sulfur emissions from volcanoes; links between subsurface processes and surface observations; sulfur chemistry in volcanic plumes; and the consequences of sulfur degassing for climate and the environment

Multi-Decadal Space-Based Observations of Basaltic Effusive Eruptions from MODIS Infrared Data.

Ph.D. Thesis. University of Hawaiʻi at Mānoa 2018

Exploiting ground-based optical sensing technologies for volcanic gas surveillance

Measurements of volcanic gas composition and flux are crucial to probing and understanding a range of magmatic, hydrothermal and atmospheric interactions. The value of optical remote sensing methods has been recognised in this field for more than thirty years but several recent developments promise a new era of volcanic gas surveillance. This could see much higher time- and space-resolved data-sets, sustained at individual volcanoes even during eruptive episodes. We provide here an overview of these optical methods and their application to ground-based volcano monitoring, covering passive and active measurements in the ultraviolet and infrared spectral regions. We hope thereby to promote the use of such devices, and to stimulate development of new optical techniques for volcanological research and monitoring

Open vent volcanoes fuelled by depth-integrated magma degassing

Open-vent, persistently degassing volcanoes—such as Stromboli and Etna (Italy), Villarrica (Chile), Bagana and Manam (Papua New Guinea), Fuego and Pacaya (Guatemala) volcanoes—produce high gas fluxes and infrequent violent strombolian or ‘paroxysmal’ eruptions that erupt very little magma. Here we draw on examples of open-vent volcanic systems to highlight the principal characteristics of their degassing regimes and develop a generic model to explain open-vent degassing in both high and low viscosity magmas and across a range of tectonic settings. Importantly, gas fluxes from open-vent volcanoes are far higher than can be supplied by erupting magma and independent migration of exsolved volatiles is integral to the dynamics of such systems. The composition of volcanic gases emitted from open-vent volcanoes is consistent with its derivation from magma stored over a range of crustal depths that in general requires contributions from both magma decompression (magma ascent and/or convection) and iso- and polybaric second boiling processes. Prolonged crystallisation of water-rich basalts in crustal reservoirs produces a segregated exsolved hydrous volatile phase that may flux through overlying shallow magma reservoirs, modulating heat flux and generating overpressure in the shallow conduit. Small fraction water-rich melts generated in the lower and mid-crust may play an important role in advecting volatiles to subvolcanic reservoirs. Excessive gas fluxes at the surface are linked to extensive intrusive magmatic activity and endogenous crustal growth, aided in many cases by extensional tectonics in the crust, which may control the longevity and activity of open-vent volcanoes. There is emerging abundant geophysical evidence for the existence of a segregated exsolved magmatic volatile phase in magma storage regions in the crust. Here we provide a conceptual picture of gas-dominated volcanoes driven by magmatic intrusion and degassing throughout the crust