Search

The interaction between volcanic activity and flank instability during the Christmas Eve eruption at Mount Etna in 2018 is explored, using a mechanically consistent inverse model fitting high spatial resolution SAR data. Inversions search for fractures that may be curved and can accommodate co‐eval pressure and shear stress changes. Displacements associated with the eruption result from the interaction between two intrusion sources: a buried dyke and a curved sheared intrusion that fed the eruption. Moreover, we identify that the sheared magmatic intrusion induced the observed eastward slip on the Pernicana fault, while the Fiandaca fault was undergoing stress accumulation, which was suddenly released during a M5.0 seismic event. The Fiandaca fault is determined to be listric, rooting beneath the mobile eastern flank of the volcano. This study highlights the role of curved fractures, acting as sheared intrusions or as faults, in volcanoes exhibiting flank instabilities. Plain Language Summary: In this study, we thoroughly examine how volcanic activity and flank dynamics interacted during the 2018 eruption of Mount Etna. We use high‐resolution satellite SAR data and a model considering complex mechanical aspects of the volcano's behavior. Formal inversions reveal that the eruption is triggered by the interplay between two intrusion sources: a buried dyke and a curved sheared intrusion, consistent with the earthquake pattern. This study emphasizes the significant role of curved sheared intrusions and faults at volcanoes prone to flank instabilities. Furthermore, we quantify how summit magmatic intrusions promote fault slip in the eastern flank of Etna. These findings differ from previous research that used simpler approaches. In summary, our study provides a new insight into how volcanoes like Etna can erupt and trigger flank slip, shedding light on the complex interactions between magma and tectonics. Key Points: Modeling shows that the magma intrusion feeding the 2018 eruption accommodated coeval opening and shear displacementsBoth the summit intrusions and the Fiandaca fault are curved, probably connected to the detachment at the base of the mobile eastern sectorThe Fiandaca fault was previously locked. It released accumulated stress, while the Pernicana fault passively responded to the intrusion [ABSTRACT FROM AUTHOR]

On 22 December 2018, parts of the Anak Krakatau edifice collapsed, triggering a deadly tsunami. To investigate pre‐collapse surface displacements, we analyzed Interferometric Synthetic Aperture Radar satellite geodetic data from 2006 to 2018, acquired from ALOS‐1 (2006–2011), COSMO‐SkyMED (2012–2018), and Sentinel‐1 (2014–2018). We identified line‐of‐sight displacements on the southwestern flank throughout the study period. Inversion of COSMO‐SkyMED data revealed a rectangular dislocation with a cumulative slip of 12 m from April 2012 to December 2018. Fixing the fault geometry, we found the optimal slip for time periods corresponding to slip rate changes, ranging from 1.2 to 3.1 m/yr. The slip estimates for ALOS‐1 and Sentinel‐1 data were 0.88 m/yr and 1.1 m/yr, respectively, over their individual time periods. Overall, the detachment fault experienced approximately 15 m of slip from 2006 to 2018 with acceleration and deceleration periods, and a notable acceleration prior to the 2018 collapse. Plain Language Summary: In this study, we investigated the changes that occurred on Anak Krakatau volcano before its collapse on 22 December 2018. We used satellite data from three different sources; ALOS‐1, COSMO‐SkyMED, and Sentinel‐1, covering the period from 2006 to 2018. Our analysis revealed that the southwestern side of the volcano was moving over time from 2006 to before the collapse in 2018. By examining data from COSMO‐SkyMED, we found that there was a rectangular area where the ground shifted by about 12 m. We investigated detailed movement and calculated that the ground slipped at different rates over time, ranging from 1.2 to 3.1 m per year. Data from ALOS‐1 and Sentinel‐1 gave us slightly different slip estimates and rates. Overall, our findings show that the deeper part of the ground moved around 15 m in total from 2006 to 2018 with varying speed and a significant acceleration before the 2018 collapse occurred. Key Points: InSAR time series show ground motion away from the satellite on the southwest flank of Anak Krakatau for the period 2006–2018The signal is likely induced by long‐term normal slip on a preexisting detachment fault which slipped rapidly in 2018 causing a collapseThe surface displacements and slip rate involve accelerations and decelerations, with a major acceleration right before the collapse [ABSTRACT FROM AUTHOR]

We report the first detection of unrest at Socompa volcano during our recent survey of Central Andean volcanos in Northern Chile using Interferometric Synthetic Aperture Radar measurements spanning January 2018 to October 2021. We find that Socompa volcano, whilst initially undeforming and no recorded eruptions for 7.2 kyr, shows a steady uplift (17.5 mm/yr) from November 2019, independently recorded by near‐field continuous Global Positioning System data. The deformation pattern can be fitted with pressure increase in an ellipsoidal source region stretching from 2.1 to 10.5 km, with a volume change rate of ∼6.2 × 106 m3/yr. Our observations of the onset of uplift suggest it is unlikely that a nearby Mw 6.8 deep intraslab earthquake on 3 June 2020 triggered the unrest. The deformation signal we detect indicates the initiation of unrest at Socompa, after at least two decades without measurable deformation, and many thousands of years without volcanic activity. Plain Language Summary: Here we report the first observation of unrest of the Socompa volcano, Northern Chile, which is thought to have last erupted thousands of years ago. Using radar interferometry technique and differencing radar images from two dates, it is possible to retrieve millimeter‐level surface displacements during this period. Here, we use a time series of multiple images spanning January 2018 to January 2023, over the Central Andean volcanoes in Northern Chile, to estimate the change in ground movement through time. Combined with Global Positioning System data, we find Socompa volcano started to uplift in November 2019 at a relatively stable speed (of 17.5 mm/yr) without any trace of slowing down up to December 2021. Our analysis suggests that this volcanic deformation is unlikely to have been triggered by a nearby 112 km depth, Mw 6.8 earthquake, which occurred in June 2020, and was thus after the onset time. Deformation at Socompa has similarities with other volcanoes in the Central Andes, where low rates of magmatic uplift have been detected at other apparently quiescent volcanoes. Such large‐scale monitoring efforts using remote sensing data are important, as we can better understand the deformation style of these volcanoes in areas that are poorly instrumented. Key Points: We combine Interferometric Synthetic Aperture Radar and Global Positioning System data to survey the Central Andean volcanoes, some of which have been updated for the first time in over 10 yearsWe show the first detection of unrest at Socompa volcano with steady uplift up to 17.5 mm/yr since November 2019Deformation patterns are consistent with an ellipsoidal source, stretching from 2.1 to 10.5 km and with a volume change of ∼6.2 × 106 m3/yr [ABSTRACT FROM AUTHOR]

Eruptions at shield volcanoes often occur from radially aligned linear fissures fed by blade‐like magma‐filled cracks (dykes). The fissures of the 2018 Sierra Negra eruption were scattered on the flank of the volcano. Space‐borne radar interferometric data (interferometric synthetic aperture radar) revealed that, unexpectedly, part of the eruption was fed by a 15 km long, tortuous and flat‐lying crack (sill). Here we develop a framework that captures the full three‐dimensional (3D) kinematics of non‐planar intrusions. This includes both an analytical and comprehensive numerical scheme. We constrain the models such that they match the observed ground deformation at Sierra Negra. We show that the peculiar sill trajectory is due to the competing stress gradient magnitudes being close to one another throughout its propagation. By accounting for the interaction of all these factors, these 3D models open the possibility to understand and simulate the geometry of magma transport at volcanic systems. Plain Language Summary: Here, we show in unprecedented detail using space‐borne radar interferometric data, a large volume eruption at Sierra Negra volcano, Galápagos Islands fed by a flat‐lying crack (sill). The observations are particularly intriguing as this sill's trajectory was over 15‐km‐long and while it remained flat it was highly curved, which, cannot be explained by existing models. We employ simple fracture mechanics models to show that the sill grew away from the summit due to the stresses induced by the slope of the volcano. Further from the summit, forces caused by the magma/rock weight contrast began to compete with the slope stresses causing the sill's growth direction to turn as observed. We show how parameters such as: magma volume, weight contrast, sill depth and the tectonic stresses, play a role in defining if/where the flank eruption occurs. To summarize, we show a well constrained example of a curved sill‐fed eruption, which has never been observed in such detail before. These observations warranted the use of new three‐dimensional (3D) models to help explain the process. This work shows how to analyze the paths of cracks feeding volcanic flank eruptions efficiently in 3D, and can be used to understand the potential hazard of a particular batch of magma. Key Points: The 2018 eruption at Sierra Negra volcano, Galápagos Islands, was fed by a highly curved sillThe curvature of the sill's trajectory was due to competing stresses: topographic loading, weight contrasts, and free surface effectsShallow flat‐lying intrusions are unstable and as such are extremely likely to turn at a given distance from the edifice's center [ABSTRACT FROM AUTHOR]

On January 12, 2020, Taal volcano, Philippines, erupted after 43 years of repose, affecting more than 500,000 people. Using interferometric synthetic aperture radar (InSAR) data, we present the pre‐ to post‐eruption analyses of the deformation of Taal. We find that: (1) prior to eruption, the volcano experienced long‐term deflation followed by short‐term inflation, reflecting the depressurization‐pressurization of its ∼5 km depth magma reservoir; (2) during the eruption, the magma reservoir lost a volume of 0.531 ± 0.004 km3 while a 0.643 ± 0.001 km3 lateral dike was emplaced; and (3) post‐eruption analyses reveal that the magma reservoir started recovery approximately 3 weeks after the main eruptive phase. We propose a conceptual analysis explaining the eruption and address why, despite the large volume of magma emplaced, the dike remained at depth. We also report the unique and significant contribution of InSAR data during the peak of the crisis. Plain Language Summary: Taal volcano in the Philippines erupted on January 12, 2020. Here, we present the pre‐, co‐, and post‐eruption data, model, and analyses using interferometric synthetic aperture radar (InSAR) data acquired by various satellite systems. We find that: (1) prior to the eruption, the volcano experiences a sequence of long‐term (>1 year) deflation followed by short‐term (≤1 year) inflation as a result of the depressurization‐pressurization of its ∼5 km depth magma reservoir; (2) during the eruption, the magma reservoir lost a volume of 0.531 ± 0.004 km3 while a 0.643 ± 0.001 km3 lateral dike was emplaced; and (3) post‐eruption analyses reveal that the magma reservoir is in recovery starting ∼3 weeks after the main eruptive phase. We propose a conceptual analysis to explain the 2020 Taal eruption and the dike emplacement. We also report the unique and significant contribution of remote sensing data, particularly InSAR during the peak of the crisis. Key Points: We present a comprehensive interferometric synthetic aperture radar (InSAR)‐based data, analyses, and models of Taal's pre‐ to post‐eruptive stateDuring the eruptive crisis, Taal's magma reservoir lost 0.531 ± 0.004 km3 of volume while a 0.643 ± 0.001 km3 lateral dike was emplacedLow‐latency InSAR‐derived products provided crucial and significant information to PHIVOLCS during the January 2020 eruptive event [ABSTRACT FROM AUTHOR]

The Sanriku ocean‐bottom seismometer system uses an optical fiber cable to guarantee real‐time observations at the seafloor. A dark fiber connected to a Distributed Acoustic Sensing (DAS) interrogator converted the cable in an array of 19,000 seismic sensors. We use these measurements to constrain the velocity structure under a section of the cable. Our analysis relies on 24 hr of ambient seismic field recordings. We obtain a high‐resolution 2‐D shear‐wave velocity profile by inverting multimode dispersion curves extracted from frequency‐wave number analysis. We also produce a reflection image from autocorrelations of ambient seismic field, highlighting strong impedance contrasts at the interface between the sedimentary layers and the basement. In addition, earthquake wavefield analysis and modeling help to further constrain the sediment properties under the cable. Our results show for the first time that ocean‐bottom DAS can produce detailed images of the subsurface, opening new opportunities for cost‐effective ocean‐bottom imaging in the future. Plain Language Summary: Distributed Acoustic Sensing (DAS) is a relatively new measurement method that has the potential to convert existing fiber optic communication infrastructure into arrays of thousands of seismic sensors. In this research, we connected a DAS to a cable that was originally installed at the bottom of the ocean to sustain a seismic and tsunami observatory in the Sanriku Region. We show that this new type of measurement can provide reliable information to image and explore the shallow subsurface under this fiber cable. This is the first time such analysis is performed in an oceanic environment, and our methods could be readily exportable to other fiber‐optic cables that are the backbones of our modern telecommunication. Key Points: Ocean‐bottom Distributed Acoustic Sensing is used to image shallow VS structureRayleigh wave phase velocity dispersion curves are extracted from frequency‐wave number analysisReflection image is obtained from autocorrelations of ambient seismic field [ABSTRACT FROM AUTHOR]

Hydrofracturing is a routine industrial technique whose safety depends on fractures remaining confined within the target rock volume. Both observations and theoretical models show that, if the fluid volume is larger than a critical value, pockets of fluid can propagate large distances in the Earth's crust in a self‐sustained, uncontrolled manner. Existing models for such critical volumes are unsatisfactory; most are two‐dimensional and depend on poorly constrained parameters (typically the fracture length). Here we derive both analytically and numerically in three‐dimensional scale‐independent critical volumes as a function of only rock and fluid properties. We apply our model to gas, water, and magma injections in laboratory, industrial, and natural settings, showing that our critical volumes are consistent with observations and can be used as conservative estimates. We discuss competing mechanisms promoting fracture arrest, whose quantitative study could help to assess more comprehensively the safety of hydrofracturing operations. Plain Language Summary: Fractures in rocks can act as channels for fluids. Fracking, or hydrofracturing, involves injection of fluids at high pressure in order to grow fractures within the rock and increase its permeability. Fluid volumes need to be kept below a threshold value: If the fluid volume is larger, then the stresses at the tips of the fluid pocket will be large enough for the fluids to force their way around by fracturing the rock ahead of them. Previous theoretical models for the critical volumes are unsatisfactory as they are two‐dimensional and based on poorly constrained parameters. We derive and test a new three‐dimensional equation that uses only rock and fluid parameters. We find that typical volumes injected in hydrofracturing operations are over the limit we define. We argue they are still mostly safe as additional processes often hinder fracture growth. Further work is needed to comprehensively quantify mechanisms that hinder hydrofracture arrest. Key Points: We define critical volumes for fractures under the influence of a stress gradients that cause self‐sustaining propagationWe define such critical volumes analytically such that they are independent of scale. These are verified numericallyThe equation predicts the correct scale in natural and analog examples but for hydro‐fracturing its too low [ABSTRACT FROM AUTHOR]

Automated systems for detecting deformation in satellite interferometric synthetic aperture radar (InSAR) imagery could be used to develop a global monitoring system for volcanic and urban environments. Here, we explore the limits of a convolutional neural networks for detecting slow, sustained deformations in wrapped interferograms. Using synthetic data, we estimate a detection threshold of 3.9 cm for deformation signals alone and 6.3 cm when atmospheric artifacts are considered. Overwrapping reduces this to 1.8 and 5.2 cm, respectively, as more fringes are generated without altering signal to noise ratio. We test the approach on time series of cumulative deformation from Campi Flegrei and Dallol, where overwrapping improves classification performance by up to 15%. We propose a mean‐filtering method for combining results of different wrap parameters to flag deformation. At Campi Flegrei, deformation of 8.5 cm/year was detected after 60 days and at Dallol, deformation of 3.5 cm/year was detected after 310 days. This corresponds to cumulative displacements of 3 and 4 cm consistent with estimates based on synthetic data. Key Points: We adapt a pretrained convolutional neural networks for detecting slow, steady deformation in InSAR imagesSynthetic tests show the detection threshold is 6.3 cm in volcanic environments but is reduced to 5.0 cm by decreasing wrapping intervalWe demonstrate the method on cumulative time series of interferograms from Campi Flegrei, Italy (8.5 cm/yearr) and Dallol, Ethopia (3.5 cm/year) [ABSTRACT FROM AUTHOR]

The present study assesses the added value of high‐resolution maps of precipitable water vapor, computed from synthetic aperture radar interferograms , in short‐range atmospheric predictability. A large set of images, in different weather conditions, produced by Sentinel‐1A in a very well monitored region near the Appalachian Mountains, are assimilated by the Weather Research and Forecast (WRF) model. Results covering more than 2 years of operation indicate a consistent improvement of the water vapor predictability up to a range comparable with the transit time of the air mass in the synthetic aperture radar interferograms footprint, an overall improvement in the forecast of different precipitation events, and better representation of the spatial distribution of precipitation. This result highlights the significant potential for increasing short‐range atmospheric predictability from improved high‐resolution precipitable water vapor initial data, which can be obtained from new high‐resolution all‐weather microwave sensors. Plain Language Summary: Weather forecasts will never be perfect because our models are simplified representations of nature and our observations of the atmosphere are inaccurate. In this study we show, nevertheless, that it is possible to improve such forecasts by interpreting the atmospheric signals in spaceborne radar observations of the Earth surface, indicative of the distribution of water vapor. Better and more detailed maps of water vapor are found to lead to better forecasts not just of water vapor but also of precipitation. A two and a half years assessment covering a wide range of weather conditions in a very well monitored region near the Appalachian Mountains, USA, suggests that the proposed methodology has a significant impact in the quality of the forecasts and could easily be implemented. Key Points: Assimilation of synthetic aperture radar interferograms consistently extends the skill of hindcasts of water vapor and precipitationA large fraction of forecast rain errors is due to errors in the distribution of water vaporThe near‐range forecast of heavy precipitation events may be substantially improved with better initial states of water vapor [ABSTRACT FROM AUTHOR]

Volcano‐tectonic seismicity has been recorded for decades on various volcanoes and is linked with the magma transport and reservoir pressurization. Yet earthquakes often appear broadly distributed such that magma movement is difficult to infer from its analysis. We explore the seismicity that occurred before eruptions at Piton de la Fournaise in the last 5 years. Using template matching and relocation techniques, we produce a refined image of the summit seismicity, demonstrating that most earthquakes are located on a ring structure. However, only a portion of this structure is activated before each eruption, which provides an indication as to the direction of the future eruptive site. Furthermore, we show that the delay between the pre‐eruptive swarm and the eruption onset is proportional to the distance of the eruptive fissures relative to the summit cone. This reveals that the beginning of the intrusion already bears information regarding the future eruption location. Plain Language Summary: Earthquakes on volcanoes are usually related to the ascent of magma in the edifice and can therefore provide information concerning an impending eruption. Yet on many occasions, it is not easy to relate the recorded seismicity to the propagation of magma in the volcano. In this study, we detect and locate earthquakes that occurred before 13 eruptions at Piton de la Fournaise, a hawaiian‐type volcano located on La Réunion island in the Indian Ocean. We demonstrate that a detailed analysis of the seismicity occurring when the magma starts its ascent can bring important information regarding the future eruption location. Key Points: We use a template matching technique to detect and relocate earthquakes during the 13 last eruptive unrests at Piton de la Fournaise volcanoAlmost all detected events are located on a ring‐shaped structure, corresponding to an area of weakness in the upper edifice of the volcanoThe location and timing of pre‐eruptive seismic swarms on this ring‐shaped structure bring information on the future eruptive site [ABSTRACT FROM AUTHOR]