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Manam is one of the most frequently active volcanoes in Papua New Guinea and is a top contributor to global volcanic volatile emissions due to its persistent open-vent degassing. Here, we present a multi-year time series (2018–2021) of thermal and SO2 emissions for Manam from satellite remote sensing, which we interpret in the context of open-vent feedback between magma supply, reservoir pressure, and outgassing. We classify the time series into four phases based on the varying SO2 flux and observe a transient, yet substantial, increase in time-averaged SO2 flux from background levels of ~ 0.6 to ~ 4.72 kt day−1 between March and July 2019. We also identify a transition from temporally coupled to decoupled gas and thermal emissions during this period which we explain in the context of a magma recharge event that supplied new, volatile-rich magma to the shallow plumbing system beneath Manam. We infer that the arrival of this recharge magma triggered the series of eruptions between August 2018 and March 2019. These explosive events collectively removed 0.18 km3 of degassed residual magma and signalled the onset of a renewed period of unrest that ultimately culminated in a major eruption on 28 June 2019. We quantify the magnitude of "excess" degassing at Manam after the removal of the inferred residual magma. SO2 emissions reveal that ~ 0.18 km3 of magma was supplied, but only ~ 0.08 km3 was erupted between April 2019 and December 2021. We highlight how multi-parameter remote sensing observations over months to years enable the interpretation of open-vent processes that may be missed by short-duration campaign measurements. [ABSTRACT FROM AUTHOR]

We have determined the S contents of 14 different silicate melts equilibrated with Air/SO 2 mixtures at 1 atm pressure and temperatures of 1473–1773 K in 50 K intervals. Under these oxidizing conditions sulfur dissolves in the melts predominantly as sulfate (S6+ or SO 4 2–). The sulfur contents of the quenched products were determined by EPMA (Electron Probe Micro-Analysis) and by SIMS (Secondary Ion-Mass Spectrometry) with the latter being employed for low sulfur contents (i.e., ≤60 ppm). Equilibrium S contents were found to increase strongly with decreasing temperature and with some compositional parameters, especially CaO content. The data were used to calculate the sulfate capacity (log C S6+), for each melt composition at each temperature. Sulfate capacity is related to the equilibrium constant for sulfur dissolution and is defined as follows in terms of SO 4 2– concentration and fugacities of oxygen and sulfur: l o g C S 6 + = l o g SO 4 m e l t 2 - (w t. %) - 1 2 log fS 2 - 3 2 l o g fO 2 By determining log C S6+ at different Air/SO 2 ratios we showed that log C S6+ is independent of sulfur content and hence that Henry's Law is obeyed in the experimental composition and temperature range. We used stepwise linear regression to fit sulfate capacity to an equation incorporating compositional and temperature terms. Parameters which did not pass the F-test at the 95% confidence level were excluded. This approach led to the following fit equation: l o g C S 6 + = - 12.659 + (3692 X CaO - 7592 X SiO 2 - 13736 X TiO 2 + 3762 X Al O 1.5 + 34483) / T The standard error of the fit is 0.154 and R2 is 0.985. The data were used to simulate scenarios for SO 2 -degassing from ascending silicate melts of basaltic and andesitic compositions. The important observations are that SO 2 partitions strongly into an H 2 O-rich fluid phase and that most S is lost at relatively high pressures in the crust. So, for example we estimate that ≥85% of the initial S should be lost before the ascending magma reaches 100 MPa pressure. [ABSTRACT FROM AUTHOR]

On December 22, 2018 the south-western flank of Anak Krakatau collapsed into the sea, removing 93.8 × 106 m3 of subaerial lavas, and generated a tsunami. Synchronously with the collapse, a large volcanic plume of SO2 and ash (14–15 km in height) has formed, marking the onset of a paroxysmal eruption lasting from December 22, 2018 to January 06, 2019. From remote sensing analysis, we show that the eruption can be divided into three main phases. Phase I and II show both tephra and gas emissions while phase III is mostly degassing. The total amount of SO2 injected in the atmosphere is 173±52 kt, while the minimum bulk magma volume emplaced, estimated from a topographic reconstruction, is ∼45 × 106 m3. This value compares well with a petrologic-based estimate of 56.4 × 106 m3, making the existence of external sulphur sources and sinks quite unlikely. The ice-rich ash plume formation shows that a strong sea-water/magma interaction was responsible for the phreatomagmatic activity throughout the eruption. However, we distinguish a first Vulcanian blast-derived eruption (lasting 40 min) just after the collapse having a Mass Eruption Rate (MER) of 9 × 105 kgs−1, followed by a sustained lower-intensity eruption resulting in ash emissions over hours (MER = 5 × 105 kgs−1). From December 23, daytime photos show typical Surtseyan activity.

Abstract Eruption style and dynamics are controlled by various parameters including magma supply rate, magma viscosity, volatile content, and the permeability of the conduit. Rapid changes of these parameters can significantly modify the hazards associated to the eruption processes and understanding their relationship with multiparametric geophysical monitoring data can greatly improve our forecasting capacities. From 2008 to 2016, volcanic activity at Tungurahua was characterized by eruptive phases separated by episodes of quiescence. These phases displayed great variability of eruptive patterns including Vulcanian and Strombolian explosions, low pyroclastic fountaining, continuous or sporadic ash emissions and passive degassing. We use the comparison between geophysical data (seismic, acoustic and SO 2 emission), recorded by permanent monitoring networks, and the characteristics of the emitted ash to track changes in eruption dynamics during an eruptive phase that lasted from late December 2009 to March 2010. We show that the correlation between the analyzed parameters allows imaging and interpretation of the conditions at the vent. At Tungurahua, these conditions can rapidly change at the time scale of a single eruptive phase, corresponding to various degrees of opening, plugging and permeability of the conduit. Two magma intrusions could be identified during a single eruptive phase showing transitions between violent Strombolian and Vulcanian activity. Changes in the componentry of the analyzed ash samples, together with the geophysical data, nicely highlight these evolutions. Studying these parameters simultaneously provides a unique insight into the physical processes controlling superficial volcanic activity and offers a potential tool for better understanding volcanoes and detecting changes in their activity. The joint interpretation of multiparametric data which we propose is potentially applicable to multiple andesitic volcanoes. Highlights • Eruptive dynamics characterized by seismicity, SO 2 degassing and ash componentry. • Conduit conditions explored through multiparametric time series. • Violent Strombolian vs. Vulcanian eruptive dynamics at Tungurahua volcano. • Presence of a two magma waxing-waning cycles during a single eruptive phase. [ABSTRACT FROM AUTHOR]

Abstract Owing to practical limitations less than half of Earth's 1400 subaerial volcanoes have no ground monitoring and few are monitored consistently. Earth-observing satellite missions provide global and frequent measurements of volcanic activity that are closing these gaps in coverage. We compare databases of global, satellite-detections of ground deformation (1992–2016), SO 2 emissions (1978–2016), and thermal features (2000–2016) that together include 306 volcanoes. Each database has limitations in terms of spatial and temporal resolution but each technique contributed 45–86 unique detections of activity that were not detected by other techniques. Integration of these three databases shows that satellites detected ~102 volcanic activities per year before the year 2000 and ~103 activities per year after the year 2000. We find that most of the 54 erupting volcanoes without satellite-detections are associated with low volcano explosivity index eruptions and note that many of these eruptions (71%, 97/135) occurred in the earliest decades of remote sensing (pre-2000) when detection thresholds were high. From 1978 to 2016 we conduct a preliminary analysis of the timing between the onset of satellite-detections of deformation (N = 154 episodes, N = 71 volcanoes), thermal features (N = 16,544 episodes, N = 99 volcanoes), and SO 2 emissions (N = 1495 episodes, N = 116 volcanoes) to eruption start dates. We analyze these data in two ways: first, including all satellite-detected volcanic activities associated with an eruption; and second, by considering only the first satellite-detected activity related to eruption. In both scenarios, we find that deformation is dominantly pre-eruptive (47% and 57%) whereas available databases of thermal features and SO 2 emissions utilizing mainly low-resolution sensors are dominantly co-eruptive (88% and 76% for thermal features, 97% and 96% for SO 2 emissions). Highlights • First global comparison of satellite-detected activity from multiple types of satellite sensors • Of three types of satellite sensors studied, each contributed unique detections which validates the multi-sensor approach. • Most volcanoes that erupted in the past few decades displayed volcanic activity measurable from satellite. • Satellite sensors detect between 100 and 1000 volcanic activities per year. [ABSTRACT FROM AUTHOR]

We present continuous SO 2 measurements performed at Tungurahua volcano with a permanent network of 4 scanning DOAS instruments between 2007 and 2013. The volcano has been erupting since September 1999, but on the contrary to the first years of eruption when the activity was quasi-continuous, the activity transitioned in late 2008 towards the occurrence of distinct eruptive phases separated by periods of quiescence. During our study period we distinguish 11 phases lasting from 17 to 527 days separated by quiescence periods of 26 to 184 days. We propose a new routine to quantify the SO 2 emissions when data from a dense DOAS monitoring network are available. This routine consists in summing all the highest validated SO 2 measurements among all stations during the 10 h of daily working-time to obtain a daily observed SO 2 mass. Since measurement time is constant at Tungurahua the “observed” amounts can be expressed in tons per 10 h and can easily be converted to a daily average flux or mass per day. Our results provide time series having an improved correlation on a long time scale with the eruptive phases and with quiescence periods. A total of 1.25 Mt (1.25 × 10 9 kg) of SO 2 has been released by Tungurahua during the study period, with 95% of these emissions occurring during phases of activity and only 5% during quiescence. This shows a contrast with previous volcanic behaviour when passive degassing dominated the total SO 2 emissions. SO 2 average daily mass emission rates are of 73 ± 56 t/d during quiescent periods, 735 ± 969 t/d during long-lasting phases and 1424 ± 1224 t/d during short-lasting phases. Degassing during the different eruptive phases displays variable patterns. However, two contrasting behaviours can be distinguished for the onset of eruptive phases with both sudden and progressive onsets being observed. The first is characterised by violent opening of the conduit by high energy Vulcanian explosions; and the second by a progressive, in crescendo , development of the activity. The first case is becoming more frequent at Tungurahua making the volcano more dangerous and less predictable. [ABSTRACT FROM AUTHOR]