Volcanic plumes are common and far-reaching manifestations of volcanic activity during and between eruptions. Observations of the rate of emission and composition of volcanic plumes are essential to recognize and, in some cases, predict the state of volcanic activity. Measurements of the size and location of the plumes are important to assess the impact of the emission from sporadic or localized events to persistent or widespread processes of climatic and environmental importance. These observations provide information on volatile budgets on Earth, chemical evolution of magmas, and atmospheric circulation and dynamics. Space-based observations during the last decades have given us a global view of Earth's volcanic emission, particularly of sulfur dioxide (SO₂). Although none of the satellite missions were intended to be used for measurement of volcanic gas emission, specially adapted algorithms have produced time-averaged global emission budgets. These have confirmed that tropospheric plumes, produced from persistent degassing of weak sources, dominate the total emission of volcanic SO₂. Although space-based observations have provided this global insight into some aspects of Earth's volcanism, it still has important limitations. The magnitude and short-term variability of lower-atmosphere emissions, historically less accessible from space, remain largely uncertain. Operational monitoring of volcanic plumes, at scales relevant for adequate surveillance, has been facilitated through the use of ground-based scanning differential optical absorption spectrometer (ScanDOAS) instruments since the beginning of this century, largely due to the coordinated effort of the Network for Observation of Volcanic and Atmospheric Change (NOVAC). In this study, we present a compilation of results of homogenized post-analysis of measurements of SO₂ flux and plume parameters obtained during the period March 2005 to January 2017 of 32 volcanoes in NOVAC. This inventory opens a window into the short-term emission patterns of a diverse set of volcanoes in terms of magma composition, geographical location, magnitude of emission, and style of eruptive activity. We find that passive volcanic degassing is by no means a stationary process in time and that large sub-daily variability is observed in the flux of volcanic gases, which has implications for emission budgets produced using short-term, sporadic observations. The use of a standard evaluation method allows for intercomparison between different volcanoes and between ground- and space-based measurements of the same volcanoes. The emission of several weakly degassing volcanoes, undetected by satellites, is presented for the first time. We also compare our results with those reported in the literature, providing ranges of variability in emission not accessible in the past. The open-access data repository introduced in this article will enable further exploitation of this unique dataset, with a focus on volcanological research, risk assessment, satellite-sensor validation, and improved quantification of the prevalent tropospheric component of global volcanic emission. Datasets for each volcano are made available at https://novac.chalmers.se (last access: 1 October 2020) under the CC-BY 4 license or through the DOI (digital object identifier) links provided in Table 1.

The monitoring of the frequency, intensity/magnitude and dynamics of explosive events at volcanoes in a state of unrest is key to surveying and forecasting their activity. Thermal and visual video observations of eruptive phenomena, and their correlation with data from deformation and seismic networks, are often limited by technical constraints including lack of time synchronisation, data volumes and power consumption. Several solutions are currently available and here we present an instrument designed for the permanent and real-time observation of volcanic explosive events in the visible and thermal infrared wavelengths, the output of which can be fully synchronised with ancillary monitoring data. Our system (VIGIA: visual and infrared ground-based imagery analyser) follows an edge computing approach whereby information is processed on-site, and periodic reports are sent to the local observatory and the system “decides” when to acquire high-temporal resolution data so as to capture key explosive events. As a permanent installation, VIGIA enables the continuous, long-term and time-synchronised observation of volcanic activity while reducing power consumption and data volumes. We suggest that VIGIA-style instruments could provide useful scientific and monitoring information, and provide here the key details of the components, assembly, and code so that observatories can replicate the system and build their own VIGIA at minimal cost. We use the Reventador volcano, in Ecuador, as a case study to present the capabilities of the instrument.

Continuous monitoring of volcanoes is essential for advancing scientific understanding and issuing alerts to at-risk populations. Many volcanoes are equipped with ground-based RGB cameras, whose recordings are analyzed by experts or semi-automatic models. Automatically distinguishing clouds from volcanic columns and other emissions remains a major challenge. To date, no open-source labeled database of volcanic images exists, and no study has attempted to localize multiple emissions beyond ash columns. We introduce VIGIA-PlumeNet, capable of operating across diverse environments a,nd sky conditions. It performs multi-class segmentation, identifying the volcano and distinguishing plumes, gases, and lava, with 88 % accuracy on the 58 test images when excluding the background class. This is achieved by using the versatile DINO-v2 AI model as a general visual processor, paired with a specialized component that we specifically trained to pinpoint and outline volcanic features; and constructing VIGIA-PlumeData, a dataset of 250 manually annotated images from over 60 volcanoes worldwide, collected through community effort. VIGIA-PlumeData and VIGIA-PlumeNet are released publicly, establishing the first benchmark dataset for volcanic image segmentation.

El Reventador is a highly active stratovolcano located ≈90 km east of Quito (Ecuador). Since a paroxysmal eruption (VEI 4) in 2002, it has exhibited persistent open-vent degassing accompanied by frequent vulcanian-/strombolian-style explosions, as well as lava flows and small pyroclastic density currents. The relatively remote nature of this volcano, requiring 4-5 hours of arduous uphill hiking through thick jungle, hinders extensive research on this system. Furthermore, with changeable and often wet weather conditions in the region, reliable remote spectroscopic measurements of gas emissions can be particularly difficult to achieve. These complications highlight the importance of permanent instrument installations that can work autonomously, thus reducing the need for field campaigns and improving the chances of capturing high-quality data and/or interesting volcanic phenomena. Here, we present the first measurements from a permanent SO2 camera installation on El Reventador, focussed on a window of good measurement conditions lasting a few hours on 24th April 2022. During this period, explosions typically occurred at a sub-hourly rate, with varying sizes and repose periods. Prior to a number of the explosions we find a decrease in SO2 emissions suggestive of gas accumulating under a reduced-permeability magma seal in the upper conduit. Sealing appears to occur on the order of 10-20 minutes prior to explosions, although establishing a baseline emission rate for the freely degassing system is often precluded by the frequency of explosions. Indeed, we find periods where permeability in the upper conduit appears to begin reducing immediately after the previous explosion.

Volcanic plumes are common and far-reaching manifestations of volcanic activity during and between eruptions. Observations of the rate of emission and composition of volcanic plumes are essential to recognize, and in some cases predict, the state of volcanic activity. Measurements of the size and location of the plumes are important to assess the impact of the emission from sporadic or localized events to persistent or widespread processes of climatic and environmental importance. These observations provide information on volatile budgets on Earth, chemical evolution of magmas and atmospheric circulation and dynamics. Space-based observations during the last decades have given us a global view of Earth’s volcanic emission, particularly of sulphur dioxide (SO₂). Although none of the satellite missions were intended to be used for measurement of volcanic gas emission, specially adapted algorithms have produced time-averaged global emission budgets. These have confirmed that tropospheric plumes, produced from persistent degassing of weak sources, dominate the total emission of volcanic SO₂. Although space-based observations have provided this global insight into some aspects of Earth's volcanism, it still has important limitations. The magnitude and short-term variability of lower-atmosphere emissions, historically less accessible from space, remain largely uncertain. Operational monitoring of volcanic plumes, at scales relevant for adequate surveillance, has been facilitated through the use of ground-based scanning-differential optical absorption spectrometers (ScanDOAS) since the beginning of this century, largely due to the coordinated effort of the Network for Observation of Volcanic and Atmospheric Change (NOVAC). In this study, we present a compilation of results of homogenized post-analysis of measurements of SO₂ flux and plume parameters obtained during the period March 2005 to January 2017 on 32 volcanoes in NOVAC. This inventory opens a window into the short-term emission patterns of a diverse set of volcanoes in terms of magma composition, geographical location, magnitude of emission, and style of eruptive activity. We find that passive volcanic degassing is by no means a stationary process in time and that large sub-daily variability is observed in the flux of volcanic gases, which has implications for emission budgets produced using short-term, sporadic observations. The use of a standard evaluation method allows intercomparison between different volcanoes and between ground- and space-based measurements of the same volcanoes. The emission of several weakly degassing volcanoes, undetected by satellites, is presented for the first time. We also compare our results with those reported in the literature, providing ranges of variability in emission, not accessible in the past. The open-access data repository, introduced in this article, will enable further exploitation of this unique dataset, with a focus on volcanological research, risk assessment, satellite-sensors validation, and improved quantification of the prevalent tropospheric component of global volcanic emission. Data sets for each volcano are made available at https://novac.chalmers.se, under license CC-BY 4, or through the DOI-links provided in Table 1.