Endogenous growth of persistently active volcanoes

Intense overpressurization at basaltic open-conduit volcanoes as inferred by geochemical signals: The case of the Mt. Etna December 2018 eruption

The balance between the amount of gas coexisting with mantle-derived magmas at depth and that emitted during intereruptive phases may play a key role in the eruptive potential of volcanoes. Taking the December 2018 eruption at Mt. Etna volcano as a case study, we discuss the geochemical data streams observed. The signals indicate a long-lasting prelude stage to eruption, starting in 2017 and involving magma-fluid accumulation in the deep (>7 km bsl) reservoir, followed by pressure buildup in the system at intermediate depth (5 to 2 km bsl), 6 to 7 months before the eruption. A brief preeruptive phase marks the pressurization at 2 to 3 km below the craters. By comparing the magma and fluid recharge at depth to the measured volcanic degassing from the plume, we provide evidence that Mt. Etna was in a state of extreme overpressurization in the weeks before the onset of the eruption.

Crystal aggregates record the pre-eruptive flow field in the volcanic conduit at Kīlauea, Hawaii

Developing reliable, quantitative conduit models that capture the physical processes governing eruptions is hindered by our inability to observe conduit flow directly. The closest we get to direct evidence is testimony imprinted on individual crystals or bubbles in the conduit and preserved by quenching during the eruption. For example, small crystal aggregates in products of the 1959 eruption of Kīlauea Iki, Hawaii contain overgrown olivines separated by large, hydrodynamically unfavorable angles. The common occurrence of these aggregates calls for a flow mechanism that creates this crystal misorientation. Here, we show that the observed aggregates are the result of exposure to a steady wave field in the conduit through a customized, process-based model at the scale of individual crystals. We use this model to infer quantitative attributes of the flow at the time of aggregate formation; notably, the formation of misoriented aggregates is only reproduced in bidirectional, not unidirectional, conduit flow.

Volcanic Hot-Spot Detection Using SENTINEL-2: A Comparison with MODIS–MIROVA Thermal Data Series

In the satellite thermal remote sensing, the new generation of sensors with high-spatial resolution SWIR data open the door to an improved constraining of thermal phenomena related to volcanic processes, with strong implications for monitoring applications. In this paper, we describe a new hot-spot detection algorithm developed for SENTINEL-2/MSI data that combines spectral indices on the SWIR bands 8a-11-12 (with a 20-meter resolution) with a spatial and statistical analysis on clusters of alerted pixels. The algorithm is able to detect hot-spot-contaminated pixels (S2Pix) in a wide range of environments and for several types of volcanic activities, showing high accuracy performances of about 1% and 94% in averaged omission and commission rates, respectively, underlining a strong reliability on a global scale. The S2-derived thermal trends, retrieved at eight key-case volcanoes, are then compared with the Volcanic Radiative Power (VRP) derived from MODIS (Moderate Resolution Imaging Spectroradiometer) and processed by the MIROVA (Middle InfraRed Observation of Volcanic Activity) system during an almost four-year-long period, January 2016 to October 2019. The presented data indicate an overall excellent correlation between the two thermal signals, enhancing the higher sensitivity of SENTINEL-2 to detect subtle, low-temperature thermal signals. Moreover, for each case we explore the specific relationship between S2Pix and VRP showing how different volcanic processes (i.e., lava flows, domes, lakes and open-vent activity) produce a distinct pattern in terms of size and intensity of the thermal anomaly. These promising results indicate how the algorithm here presented could be applicable for volcanic monitoring purposes and integrated into operational systems. Moreover, the combination of high-resolution (S2/MSI) and moderate-resolution (MODIS) thermal timeseries constitutes a breakthrough for future multi-sensor hot-spot detection systems, with increased monitoring capabilities that are useful for communities which interact with active volcanoes.

Monitoring endogenous growth of open-vent volcanoes by balancing thermal and SO2 emissions data derived from space

Measuring the amount of magma intruding in a volcano represents one of the main challenges of modern volcanology. While in closed-vent volcanoes this parameter is generally assessed by the inversion of deformation data, in open-vent volcanoes its measurement is more complicated and results from the balance between the magma entering and leaving the storage system. In this work we used thermal and SO₂ flux data, derived from satellite measurements, to calculate the magma input and output rates of Mt. Etna between 2004 and 2010. We found that during the analysed period more magma was supplied than erupted, resulting into an endogenous growth rate equal to 22.9 ± 13.7 × 10⁶ m³ y^-1. Notably, this unbalance was not constant in time, but showed phases of major magma accumulation and drainage acting within a compressible magma chamber. The excellent correlation with the inflation/deflation cycles measured by ground-based GPS network suggests the thermal, SO₂ flux and deformation data, can be combined to provide a quantitative analysis of magma transport inside the shallow plumbing system of Mt Etna. Given the global coverage of satellite data and the continuous improvement of sensors in orbit, we anticipate that this approach will have sufficient detail to monitor, in real time, the endogenous growth associated to other world-wide open-vent volcanoes.

Space- and Ground-Based Geophysical Data Tracking of Magma Migration in Shallow Feeding System of Mount Etna Volcano

After a month-long increase in activity at the summit craters, on 24 December 2018, the Etna volcano experienced a short-lived lateral effusive event followed by a rapid resumption of low-level explosive and degassing activity at the summit vents. By combining space (Moderate Resolution Imaging Spectroradiometer; MODIS and SENTINEL-2 images) and ground-based geophysical data, we track, in near real-time, the thermal, seismic and infrasonic changes associated with Etna’s activity during the September–December 2018 period. Satellite thermal data reveal that the fissural eruption was preceded by a persistent increase of summit activity, as reflected by overflow episodes in New SouthEast Crater (NSE) sector. This behavior is supported by infrasonic data, which recorded a constant increase both in the occurrence and in the energy of the strombolian activity at the same crater sectors mapped by satellite. The explosive activity trend is poorly constrained by the seismic tremor, which shows instead a sudden increase only since the 08:24 GMT on the 24 December 2018, almost concurrently with the end of the infrasonic detections occurred at 06:00 GMT. The arrays detected the resumption of infrasonic activity at 11:13 GMT of 24 December, when tremors almost reached the maximum amplitude. Infrasound indicates that the explosive activity was shifting from the summit crater along the flank of the Etna volcano, reflecting, with the seismic tremor, the intrusion of a gas-rich magma batch along a ~2.0 km long dyke, which reached the surface generating an intense explosive phase. The dyke propagation lasted for almost 3 h, during which magma migrated from the central conduit system to the lateral vent, at a mean speed of 0.15–0.20 m s−1. Based on MODIS and SENTINEL 2 images, we estimated that the summit outflows erupted a volume of lava of 1.4 Mm3 (±0.5 Mm3), and that the lateral effusive episode erupted a minimum volume of 0.85 Mm3 (±0.3 Mm3). The results presented here outline the support of satellite data on tracking the evolution of volcanic activity and the importance to integrate satellite with ground-based geophysical data in improving assessments of volcanic hazard during eruptive crises.

Risk evaluation, detection and simulation during effusive eruption disasters

Lava ingress into a vulnerable population will be difficult to control, so that evacuation will be necessary for communities in the path of the active lava, followed by post-event population, infrastructural, societal and community replacement and/or relocation. There is a pressing need to set up a response chain that bridges scientists and responders during an effusive crisis to allow near-real-time delivery of globally standard ‘products’ for a timely and adequate humanitarian response. In this chain, the scientific research groups investigating lava remote-sensing and modelling need to provide products that are both useful to, and trusted by, the crisis response community. Requirements for these products include (a) formats that can be immediately integrated into a crisis management procedure, and (b) in an agreed and stable standard. A review of current capability reveals that we are at a point where the community can provide such a response, as is the aim of the RED SEED (Risk Evaluation, Detection and Simulation during Effusive Eruption Disasters) working group. This book is the first production of this group and is intended not only as a directory of current capabilities and operational service providers, but also as a statement of intent and need, while providing a simulation designed to demonstrate how a truly pan-disciplinary response to an effusive crisis could work.

Chapter 14 Stromboli volcano, Aeolian Islands (Italy): present eruptive activity and hazards

Stromboli, the northernmost island of the Aeolian archipelago, is known for its persistent volcanic activity over the last several centuries and for its cone which, on clear days, is surmounted by a gas plume rising from its summit. The island hosts two settled areas: the village of Stromboli (c. 500 inhabitants) to the NE and that of Ginostra (c. 40 inhabitants) to the SW, both situated along the coast. In summer the number of residents grows considerably, reaching c. 5000 people. This paper provides a description of the present activity and reassesses volcanic hazards on the basis of data from a new monitoring system and from studies on the 2002–2003 and 2007 crises. The normal activity, that of mild Strombolian explosions, is occasionally interrupted by violent eruptions of variable scale (paroxysmal events) and lava flows. Volcanic hazards directly generated by eruptive activity consist of ballistic and tephra fallout, pyroclastic flows, lava flows, wildfires and minor lahars, presenting serious problems to the settled areas only occasionally. In addition to hazards directly related to eruptive phenomena, the Sciara del Fuoco depression has been the site of landslides at various scales, sometimes accompanied by the formation of tsunamis.

FTIR remote sensing of fractional magma degassing at Mount Etna, Sicily

The chemical composition of volcanic gas emissions from each of the four summit craters of Mount Etna was measured remotely in May 2001, using a Fourier transform infrared (FTIR) spectrometer operated on the upper flanks of the volcano. The results reveal constant HCl/HF ratio but distinct SO2/HCl and SO2/HF ratios in the emitted gases, which, in the light of melt inclusion data for Etna basalts, can be interpreted in terms of escape of gases from partially, and variably, degassed magma at different depths beneath the summit. Gases released from the three main summit craters (Bocca Nuova, Voragine, and Northeast) had an identical composition, controlled by bulk degassing of a single magma body that had previously lost c. 25% of its original sulphur. The similar gas composition at all three main craters suggests that these are connected to a central conduit system that branches at relatively shallow depth. Measurements of the bulk volcanic plume on the same day, c. 7 km downwind, show that degassing from these craters dominated the total gas output of the volcano, and that no significant chemical evolution occurred within the plume over a time-scale of c. 12 min. Weaker gas emissions from the Southeast crater were comparatively depleted in SO2 (SO2/HCl and SO2/HF ratios a factor of two lower), implying that this crater is fed either by a separate conduit or by a branch of the central conduit whose geometry favours solubility-controlled volatile fractionation. Still lower SO2/HCl and SO2/HF ratios measured for residual degassing of a lava flow erupted from the Southeast crater verify the lower solubility and earlier escape of sulphur compared to halogens at Etna. Fractional magma degassing is also implied by strong chemical contrasts between the bulk volcanic plume and fissure gas emissions measured during the July-August 2001 flank eruption. These results highlight the ability of FTIR spectrometry to detect fine spatial and temporal variations in magma degassing processes, and thereby constrain models of shallow plumbing systems.