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The Lhasa‐Qiangtang collision closed the Meso‐Tethys Ocean, but the exact timing of this event remains hotly debated. Here, we present geochronological and paleomagnetic analyses conducted on Cretaceous volcanics from western Qiangtang to constrain the Lhasa‐Qiangtang collision in western Tibet. Our investigations yield a paleolatitude of ∼30.5 ± 5.0°N for western Qiangtang during ca. 110–100 Ma. A reanalysis of previously acquired Mesozoic‐Cenozoic paleomagnetic data from western Qiangtang suggests a stationary position during ca. 136–34 Ma. Examination of paleomagnetic data from western Lhasa reveals a significant reduction in northward paleolatitudinal motion during the Early Cretaceous, dropping from ∼12.3 cm/yr to nearly zero. Integration of our paleomagnetic findings with available geological records has led to conclude that the Lhasa‐Qiangtang collision in western Tibet occurred at ca. 132 Ma. Additionally, we infer that crustal shortening on the order of ∼1,000 km happened between Lhasa and Qiangtang during the Early Cenozoic. Plain Language Summary: The Tibetan Plateau comprises multiple different blocks, which originated from the Gondwana in the southern hemisphere. Their convergence histories toward Euraisa have changed the global land‐sea distributions since the Late Paleozoic. The time at which the Lhasa block, one of the Tibetan blocks, accreted to the Qiangtang block to the north remains poorly constrained. In this work, we provide robust data suggesting a latitude of ∼30.5 ± 5.0°N for western Qiangtang during the Early Cretaceous (ca. 110–100 Ma). We also compiled the available latitudinal data from western Tibet in combination with geological observations. We suggest Lhasa collided with Qiangtang during 132 million years ago in western Tibet. Significant shortening of the continental crust by ∼1,000 km between the Lhasa and Qiangtang blocks occurred after their collision. Key Points: Western Qiangtang had a paleolatitude of ∼30.5 ± 5.0°N at ca. 110–100 MaA substantial decrease in the paleolatitudinal motion of western Lhasa occurred in the Early CretaceousThe Lhasa‐Qiangtang collision in western Tibet occurred at ca. 132 Ma [ABSTRACT FROM AUTHOR]

Over the last 7 years, geodetic data have detected periods of uplift and subsidence of the active volcano Ol Doinyo Lengai in Tanzania. Although numerous eruptions of the volcano have occurred historically, a systematic investigation of transient deformation using continuous Global Navigation Satellite System (GNSS) data has not been undertaken. We use the Targeted Projection Operator (TPO) to assess 7 years of continuous GNSS data from the TZVOLCANO network for transient signals and find rapid uplift spanning March 2022–December 2022 and then steady‐state uplift through August 2023. We conduct a nonlinear inversion of the GNSS velocities associated with the transient signal using dMODELS and find consistency with an inflating spheroidal source located 2.3 ± 0.6 km beneath the crater. Prior to March 2022, geodetic data indicated quiescence just below Ol Doinyo Lengai, thus detecting transient deformation with TPO allows for tracking changes in the magmatic system over time in the Natron Rift. Plain Language Summary: Ol Doinyo Lengai is an active stratovolcano in the youthful Natron Rift characterized by alternating periods of calm lava flows and explosive eruptions. Volcanic hazards and risk are major issues in the Natron Rift largely because of nearby communities, tourism, and air traffic. Volcanic eruptions are often preceded by magma intruding into a shallow reservoir that causes observable surface uplift. The uplift phase normally occurs before an eruption and is regarded as a key precursor for eruptive processes. These precursory uplift signals can be quite small. In this study we use high precision terrestrial data to monitor surface motions and use numerical approaches to detect potential volcanic signals due to magma reservoir changes. We detect rapid uplift from March 2022 to December 2022 and continued steady uplift through August 2023. Modeling suggests the uplift is from an active shallow magmatic source. This work demonstrates the ability to detect temporal changes in surface uplift at an active volcano. Key Points: Continuous Global Navigation Satellite System (GNSS) data systematically detect transient deformation for the first time at Ol Doinyo LengaiNo transient motion is detected before March 2022, then a period of rapid uplift until December 2022, and afterward steady‐state upliftTransient signal detection with the Targeted Projection Operator (TPO) allows for tracking temporal changes in the magmatic system [ABSTRACT FROM AUTHOR]

It was recognized that two magmatic belts in the Lhasa‐Tengchong terrane formed due to the Mesozoic‐Cenozoic Tethyan evolution. Still, their spatiotemporal variations of magmatic flare‐ups/lulls are rarely discussed. Here we use the new U‐Pb and Lu‐Hf isotopic data of captured zircons and a comprehensive data set to show that the flare‐up of northern magmatic belt has peak ages of 110 Ma in central and northern Lhasa and 120 Ma in eastern Tengchong, possibly related to the tectonic transition from Meso‐ and Neo‐Tethyan double subduction to Neo‐Tethyan single subduction. For the southern magmatic belt, the flare‐ups at 100–85 Ma and 65–45 Ma in eastern southern Lhasa indicate obvious juvenile crustal growth, while flare‐ups at 75–45 Ma in western southern Lhasa and Tengchong record ancient crustal reworking. Such flare‐up variations in the southern magmatic belt possibly resulted from asynchronous changes in the Neo‐Tethyan slab dip. Plain Language Summary: The Tethyan slab subduction and following collision of India and Asia produced two magmatic belts in the Lhasa‐Tengchong terrane. How did the magmatic flare‐ups or high‐flux episodes and sources spatiotemporally vary? We combine the new U‐Pb and Lu‐Hf isotopic data of captured zircons (xenocrystic zircons caught by volcanics from country rocks) and a comprehensive data set to show that the peak ages of early Cretaceous flare‐up of the northern magmatic belt are ca.10 Ma younger in central and northern Lhasa than in eastern Tengchong, possibly related to the diachronous closure of the Meso‐Tethys and flat subduction of the Neo‐Tethys. The southern magmatic belt in Tengchong and western southern Lhasa exhibit 75–45 Ma flare‐ups featured by the reworking of ancient crust, different from the eastern southern Lhasa with the flare‐ups at 100–85 Ma and 65–45 Ma which are dominated by the juvenile crustal growth. Such flare‐up variations may be related to changes of the Neo‐Tethyan slab dip. Key Points: The Neo‐Tethyan arc has asynchronous magmatic flare‐ups and diverse magmatic sourcesThe spatiotemporal changes of slab dip triggered the asynchronous flare‐ups of the Neo‐Tethyan arc [ABSTRACT FROM AUTHOR]

Abstract Over the last 7 years, geodetic data have detected periods of uplift and subsidence of the active volcano Ol Doinyo Lengai in Tanzania. Although numerous eruptions of the volcano have occurred historically, a systematic investigation of transient deformation using continuous Global Navigation Satellite System (GNSS) data has not been undertaken. We use the Targeted Projection Operator (TPO) to assess 7 years of continuous GNSS data from the TZVOLCANO network for transient signals and find rapid uplift spanning March 2022–December 2022 and then steady‐state uplift through August 2023. We conduct a nonlinear inversion of the GNSS velocities associated with the transient signal using dMODELS and find consistency with an inflating spheroidal source located 2.3 ± 0.6 km beneath the crater. Prior to March 2022, geodetic data indicated quiescence just below Ol Doinyo Lengai, thus detecting transient deformation with TPO allows for tracking changes in the magmatic system over time in the Natron Rift.

Arc volcanism, crustal deformation, and their interplay are poorly understood in northwestern Sumatra. Traditional receiver function H‐κ stacking studies constrain the variations in crustal thickness and Vp/Vs ratio in volcanic zones but rarely estimate the melt fractions. Here, we propose a H‐Φ stacking method, a variant of the H‐κ stacking method, and apply it to the dense nodal array data from Aceh, northern Sumatra, to estimate crustal thickness, Vp/Vs ratio, and melt fraction. Most results show considerably high Vp/Vs ratios (∼1.98) and melt fractions (up to 19%), indicating pervasive crustal magmatic mush. The northwestern edge of the Aceh crust is much thinner (∼22 km) than extended crust globally, reflecting a highly stretched crust due to tectonic processes governing the opening of the Andaman Sea. This thin crust and high melt fractions explain the Bouguer gravity anomaly, and partly explain the northward migration of Quaternary volcanics. Plain Language Summary: Crustal thickness and melt fraction are important indicators of crustal magmatism and deformation. Situated between the Sumatran and Andaman subduction zones, Aceh, in northwestern Sumatra, is distinguished by strong crustal deformation, resulting in active crustal seismicity, and Quaternary volcanics that have migrated northward over time. However, the abnormal arc volcanism, crustal deformation, and their interplay, remain unclear because of poor understanding of the crustal structure. To fill this knowledge gap, we deployed 155 nodal seismic stations in Aceh for 18 months. In this work, we develop a new receiver function method that takes advantage of converted seismic energy from the base of the crust to constrain the crustal thickness and melt fraction beneath the stations in Aceh. We find that: (a) the average crustal melt fraction is as high as 19%, indicating a considerable volume of partially molten rock in the crust and (b) the crust in northern Aceh is as thin as ∼22 km, suggesting high stretching of the crust associated with the opening of the Andaman Sea. The stretched crust with a high melt fraction partly explains the northward migration of Quaternary volcanics and active seismicity/crustal deformation, but the migration mechanism of other volcanics requires further investigation. Key Points: A new receiver function method is developed to constrain crustal thickness and melt fractionApplications to dense nodal array data in northwestern Sumatra show a thin (∼22 km) crust and high crustal melt fraction (up to 19%)The new constraints partly explain abnormal volcanic migration and crustal stretching [ABSTRACT FROM AUTHOR]

Timely estimations of magma volumes emitted during an eruption or a sequence of explosive events are vital for investigating the eruptive activity and evaluating the associated hazard. A reliable method for estimating erupted volumes is based on the analysis of digital surface models that nowadays can be obtained subsequently using stereo or tri‐stereo optical satellite imagery. However, the real‐time estimation of the erupted volumes is still an open challenge. Here, we explore the capacity of extracting volume estimates from continuous measurements of volumetric strain changes recorded by borehole dilatometers. We compare the volumes derived from numerous high spatial resolution satellite images with high precision strain records at Etna during 2020–2022, when more than 60 lava fountains occurred. The good correlation between the two data sets shows that strain changes can be used as a proxy to estimate the emitted volumes both over time and in real‐time. Plain Language Summary: Quantifying erupted volumes is fundamental in volcanology to provide a robust characterization of eruptions. To date, estimates of erupted volumes have been calculated after the eruptions have ended and the real‐time estimation of the erupted volumes is still an on‐going challenge. In recent decades, the sequences of lava fountain‐type eruptions at Etna, with dozens of episodes close in time and more than 100 episodes occurring since 2011, has made the task of estimating the volumes in real‐time during each single eruption ever more essential. This would enable providing precise information to Civil Protection authorities and contribute toward hazard evaluation. In this study, we took on this new challenge by exploring the potential to extract erupted volume estimates from continuous measurements of strain changes, recorded by high‐precision borehole instruments installed on the volcano's flanks. We compared and validated the volumes deriving from numerous high spatial resolution satellite images with high‐precision strain records at Etna during 2020–2022, when more than 60 lava fountains occurred. The good correlation between the two data sets shows that strain changes can be used effectively as a proxy to estimate the emitted volumes, both over time and, more importantly, in real‐time. Key Points: Detection of strain changes during sequences of lava fountain eruptions from continuous recording high‐precision borehole instrumentsQuantifying erupted volumes from strain changes, comparison and validation with the volumes calculated from high spatial resolution satellite measurementsNew method to estimate the erupted volumes in real‐time by using the continuous strain recording [ABSTRACT FROM AUTHOR]

A pyroclastic density current (PDC) is characterized by its strong stratification of particle concentration; it consists of upper dilute and lower dense currents, which generally control the dynamics and deposits of PDCs, respectively. To explain the relationship between the dynamics and deposits for magmatic and phreatomagmatic eruptions in a unified way, we developed a two‐layer PDC model considering thermal energy conservation for mixing of pyroclasts, external water, and air. The results show that the run‐out distance of dilute currents increases with the mass fraction of external water at the source (wmw) owing to the suppression of thermal expansion of entrained air. For wmw ∼ 0.07–0.38, the particle concentration in the dilute current becomes too low to generate the dense current so that the deposits directly form at the bottom of the dilute current in the entire area. These results capture the diverse features of natural PDCs in magmatic and phreatomagmatic eruptions. Plain Language Summary: Explosive volcanic eruptions eject mixtures of hot fragmented magma and gas from the volcanic vent and form eruption columns, which can collapse and propagate along the ground surface as pyroclastic density currents (PDCs). The dynamics and deposits of PDCs are extremely diverse depending on the amount of external water (e.g., groundwater, lakes, and oceans) that mixes with magma. To explain the diverse features of the dynamics and deposits of PDCs for various amounts of external water, we developed a two‐layer model for PDCs considering thermal energy conservation for mixing of magma and external water. The two‐layer model successfully reproduces the dynamics and deposits of PDCs with strong stratification of particle concentrations in a unified way. The results show that the run‐out distance of upper dilute currents increases with the increasing amount of external water. For a relatively small proportion of external water, the lower dense current tends to be absent, resulting in the direct formation of the deposits from the dilute current in the entire area. These model predictions are useful to mitigate the diverse hazards caused by natural PDCs under various geological conditions. Key Points: A two‐layer pyroclastic density current model with heat conservation for mixing of pyroclasts, external water, and air is developedIn phreatomagmatic eruptions, the upper dilute current flows over longer distances and the lower dense current tends to be absentOur results explain the diverse features of the dynamics and deposits of natural pyroclastic density currents in a unified way [ABSTRACT FROM AUTHOR]

Most basaltic lavas begin flowing as pāhoehoe but sometimes transition into 'a'ā. Field observations and previous models have demonstrated that the rheology of smooth, liquid‐like pāhoehoe is distinct from rough, pasty 'a'ā, but the cause of this dramatic and rapidly occurring change in rheology has remained unclear. Here, we propose that the pāhoehoe to 'a'ā transition could be initiated by the Yih instability, an internal shear instability, in layered pāhoehoe flow. We show that the conditions under which instability arises depend on both extrinsic and intrinsic factors and derive a non‐dimensional regime diagram. We test the model's prediction of stable flow configurations against field observations of solidified lava flows. Plain Language Summary: Most lavas begin to flow as a ropy lava called pāhoehoe that can suddenly transition into 'a'ā, a clinkery and crystal‐rich lava. These fundamental differences in flow characteristics have made understanding the transition a classic question in volcanology. We propose a model to explain the mechanism that triggers the transition. Field observations of cooled pāhoehoe lava suggest that pāhoehoe lava may have internal layers. The differences in flow speeds between the layers may trigger rapid mixing. This rapid mixing would lead to cooling, thus crystal formation of the lava flow. We suggest that this process may explain the pāhoehoe‐to‐'a'ā transition and the higher density of crystals in 'a'ā. Key Points: Layering within pāhoehoe lava flows make them subject to the Yih instabilityWe compile a regime diagram that summarizes when extrinsic and intrinsic factors create flow instabilityThe Yih instability may initiate the onset of the pāhoehoe to 'a'ā transition [ABSTRACT FROM AUTHOR]

Abstract A pyroclastic density current (PDC) is characterized by its strong stratification of particle concentration; it consists of upper dilute and lower dense currents, which generally control the dynamics and deposits of PDCs, respectively. To explain the relationship between the dynamics and deposits for magmatic and phreatomagmatic eruptions in a unified way, we developed a two‐layer PDC model considering thermal energy conservation for mixing of pyroclasts, external water, and air. The results show that the run‐out distance of dilute currents increases with the mass fraction of external water at the source (wmw) owing to the suppression of thermal expansion of entrained air. For wmw ∼ 0.07–0.38, the particle concentration in the dilute current becomes too low to generate the dense current so that the deposits directly form at the bottom of the dilute current in the entire area. These results capture the diverse features of natural PDCs in magmatic and phreatomagmatic eruptions.

Estimates of intruded magma volume are critical for forecasting volcanic unrest. Geodetic modeling can provide such estimates but is of limited use in submarine and highly vegetated settings. A complementary approach could be to use estimates of seismic moment release. In this study, we examine the moment‐volume scaling of several proximal volcanic earthquake sequences and compare it to that of injection‐induced seismicity. We find a notable similarity in scaling between the volcanic sequences, which contrasts with the broad range of responses exhibited by anthropogenic injection‐induced sequences. This may imply an underlying similarity in the geologic conditions for volcanoes that is distinct from induced seismicity settings. It could also allow for estimates of intruded volume to be made without geodetic information. This provides further insight into the factors controlling seismogenesis in these different settings and has implications for volcano seismology and injection‐induced seismicity hazard estimation. Plain Language Summary: Knowing how much magma is beneath a volcano before or during an eruption can help forecast its behavior and aid evacuation or relief efforts. Currently, satellite images or sensitive measurements of the ground inflation are used to model the amount of magma, but this isn't always possible if the volcano is underwater or shrouded by tree cover. A proposed alternative to this is to use the size and number of earthquakes as a gauge on the amount of volume change occurring underground. The relationship between the total amount of energy released by earthquakes and volume change has been a key research area of earthquakes triggered in the injection of fluids by industries like geothermal energy or hydraulic fracturing (i.e., fracking). We study several well‐recorded volcanoes and see that there is a similarity in the observed volume change and the amount of energy released from associated earthquakes. This is very different from the many examples of anthropogenic injection‐induced seismicity, which show a very broad spread. This implies that the similar conditions under volcanoes lead to similar responses to volume changes. This helps us better understand and thus potentially mitigate the hazards of both volcanoes and industrial fluid injection. Key Points: We observe a similar moment‐volume scaling for volcano seismicity, contrasting with the range exhibited by injection‐induced examplesThe results show that scaling between moment release and volume change can be used to estimate intruded volumesThis also provides insights into the geologic factors which control the crust's response to volume changes [ABSTRACT FROM AUTHOR]

The kinematics of the Paleoproterozoic assembly of Earth's first supercontinent, Nuna, are still debated. We present new paleomagnetic results from two Paleoproterozoic rock formations in the North Australia Craton (NAC) that exemplify cratonic assembly processes in the leadup to Nuna formation. Our new paleomagnetic data for the 1,825 Ma Plum Tree Creek Volcanics of the proto‐NAC and the layered mafic‐ultramafic 1,855 Ma Toby intrusion of the Kimberley Craton suggest their amalgamation just prior to ca. 1.8 Ga through a scissor‐like ocean closure to form the NAC, in accord with geological records. Comparing these new results with extant poles from Australia and other major cratons suggests similarly minor relative plate motions between ca. 1.9 and 1.65 Ga during craton and supercontinent formation. A global reconstruction suggests that these events could be related to a major slab‐suction event leading to Nuna formation. Plain Language Summary: Earth's evolution is characterized by the recurring assembly of most tectonic plates into one single supercontinent. There is mounting evidence that at least three supercontinents existed throughout Earth history. This cycle of supercontinents potentially played an important role for the evolution of life and is inextricably connected to plate tectonics. However, we still don't understand how and when exactly the supercontinent cycle initiated. We present here new paleomagnetic data allowing us the most precise paleogeographic reconstruction for the time interval before the first of the three known supercontinents formed. Our data reveals a small‐scale collisional assembly of the Australian cratons in the vicinity of the formation of other major cratons at that time. Our global reconstruction using the most up to date paleomagnetic data set can be interpreted as evidence for a model where all cratons formed over a mantle downwelling structure that ultimately lead to the initiation of the supercontinent cycle. Key Points: Two new high‐quality Paleoproterozoic paleopoles for the North Australian Craton are presentedThe new paleomagnetic data suggest a scissor‐like assembly of the North Australian CratonOur new kinematic model proposes a situation prior to the formation of the first supercontinent related to a major slab‐suction event [ABSTRACT FROM AUTHOR]

In April 2022, a seismic swarm near Mt. Edgecumbe in southeast Alaska suggested renewed activity at this transform fault volcano, which was last active ≈800 years ago. Previously, thin rhyolitic tephras were deposited 5 and 4 ka. Satellite radar data from 2014 to 2022 resolves line‐of‐sight rapid inflation up to 7.1 cm/yr beginning in August 2018. Bayesian modeling suggests a transcrustal system of a deflating (−0.528 km3) dipping sill at 20 km depth recharging a magma chamber at 10 km (0.222 km3). A near‐vertical conduit could capture the volume difference without noticeable surface deformation. Reanalyzed seismicity, recorded 25 km away, shows increases since July 2019. Magma ascent through ductile material and brittle strain release in a stressed overburden could explain the time delay. Cloud‐native open data and workflows enabled discovery and analysis of this signal within days after going unnoticed for >3 years. Plain Language Summary: In April 2022, a cluster of earthquakes, detected near Mt. Edgecumbe in Southeast Alaska, suggested magmatic activity. As the volcano is near the major Queen‐Charlotte Fairweather fault that separates the Pacific and North American plates, similar earthquakes were previously assumed to be tectonic. Since magmatic activity at volcanoes is often accompanied by ground deformation, we analyzed available satellite radar data going back to fall of 2014. This reveals ongoing crustal motion toward the satellite of up to 7.1 cm/yr starting in August 2018. Modeling of the deformation suggests that magma sourced from gently dipping tabular body at 20 km depth is pooling at about 10 km depth. Since the nearest seismograph is 25 km away, we record only large seismicity, which increases in July 2019, but we perhaps missed some lower energy seismicity due to this distance. We believe that we are observing magma rising through malleable crust into an existing magmatic system and that the observed earthquakes are created as the overlying rock adjusts to the increased magmatic pressure. The observed activity is rare, especially in similar tectonic settings, and presents an opportunity to better understand the reactivation of dormant volcanoes. Key Points: InSAR reveals up to 7.1 cm/yr of constant line‐of‐sight inflation since August 2018 at Mt. Edgecumbe with microseismicity since July 2019Bayesian modeling suggests a deflating sill at 20 km and an inflating magma chamber at 10 km depth; a narrow conduit likely connects themWe expect continued deformation with future rate changes due to supply or visco‐elastic dynamics as observed at similar systems [ABSTRACT FROM AUTHOR]

Deception Island is one of the most active and best‐documented volcanoes in Antarctica. Since its last eruption in 1970, several geophysical surveys have targeted reconstructing its magmatic systems. However, geophysics fails to reconstruct the pathways magma and fluids follow from depth to erupt at the surface. Here, novel data selection strategies and multi‐frequency absorption inversions have been framed in a Geographical Information System, using all available geological (vents and faults distribution), geochemical and geophysical knowledge of the volcano. The result is the detection of these eruptive pathways. The model offers the first image of the magma and associated fluids pathways feed the 1967, 1969, and 1970 eruptions. Results suggest that future ascending paths might lead to active research bases and zones of planned helicopter rescue. The connection between seismic absorption, temperature, and fluid content makes it a promising attribute for detecting and monitoring eruptions at active calderas. Plain Language Summary: Deception Island is the gateway for tourists to Antarctica and a laboratory to understand ice‐capped volcanoes and their eruptions. While the Island has been the target of many geophysical studies, no clear tomographic model shows how deep eruptive pathways of its last eruptions have reached the surface in the 1960s and 1970s. This is a recurrent topic in volcano geophysics: dikes and fluid migrations develop across structures considered too small to be detected by tomographic techniques. This paper demonstrates that seismic absorption has sufficient sensitivity to temperature and fluid content to detect these pathways. Once integrated within a Geographical Information System with all the information we have on the volcano, the models resolve the feeding systems of these eruptions, from a tectonically deformed deep magma chamber to shallow cold dyke intrusions and fluid migrations still feeding the volcano today. The correlation between seismic absorption, temperature, and fluid content offers a new tool for detecting and monitoring shallow volcanic hazards. Key Points: High absorption detects deep eruptive pathways from the caldera center to its rimAbsorption imaging reconstructs shallow pathways of hazardous materialsSeismic absorption is sensitive to thermal anomalies at depth [ABSTRACT FROM AUTHOR]

Monitoring of active volcanic systems is a challenging task due in part to the trade‐offs between collection of high‐quality data from multiple techniques and the high costs of acquiring such data. Here we show that magnetic data can be used to monitor volcanoes by producing similar data to gravimetric techniques at significantly lower cost. The premise of this technique is that magma and wall rock above the Curie temperature are magnetically "transparent," but not stationary within the crust. Subsurface movements of magma can affect the crustal magnetic field measured at the surface. We construct highly simplified magnetic models of four volcanic systems: Mount Saint Helens (1980), Axial Seamount (2015–2020), Kīlauea (2018), and Bárðarbunga (2014). In all cases, observed or inferred changes to the magmatic system would have been detectable by modern magnetometers. Magnetic monitoring could become common practice at many volcanoes, particularly in developing nations with high volcanic risk. Plain Language Summary: Scientists monitor volcanoes and try to predict volcanic eruptions using a variety of techniques. In this study, we show how a relatively inexpensive magnetometer can be used to monitor volcanoes by tracking magma movement below the surface. Rocks produce a magnetic signal that can be measured using a magnetometer, but magma produces no magnetic signal. We construct magnetic models showing that when magma migrates below the surface, it affects the magnetic field because it is displacing or melting the rocks. The volcanoes that we model are Mount St. Helens (pre‐1980 eruption), Axial Seamount (from 2015 to 2020), Kīlauea, Hawaii (pre‐2018 eruption), and Bárðarbunga (pre‐2014 eruption). Magnetic volcano monitoring may become standard practice at many volcanoes, particularly in developing nations with low monitoring budgets but high volcanic risk. Key Points: Magnetic models of four volcanic systems are presented, showing that movement of magma produces measurable magnetic signalsMagnetic data can be used for low‐cost volcano monitoring in a wide variety of settings and environmental conditionsThis monitoring technique has several advantages over existing methods, but consistent workflows and best‐practices need to be developed [ABSTRACT FROM AUTHOR]

Axial Seamount in the northeast Pacific erupted in 2015, 2011, and 1998. Although monitored by the Regional Cabled Array of the Ocean Observatory Initiative, few magnetic surveys have been conducted over the region. This study uses high‐resolution magnetic data over the seamount collected by autonomous underwater vehicle Sentry during three years (2015, 2017, and 2020). The goal is to investigate whether there are temporal changes in the near‐surface magnetic field observable over the time scale of one volcanic cycle. We compare magnetic maps from repeated tracklines from each year. We find maps of the yearly difference in magnetization show coherent patterns that are not random. The central region of the caldera has become more magnetic during recent years, suggesting cooling of the surficial lava flows since 2015. Sentry data are more sensitive to shallow crustal structure compared to sea surface data which show longer wavelength anomalies extending deeper into the crust. Plain Language Summary: Axial Seamount is an active underwater volcano located off the coast of Oregon that has recently erupted in 2015, 2011, and 1998. Though Axial is monitored by many seafloor instruments, the magnetism of the region and how it changes with time has not been studied. However, we believe studying the magnetics of Axial can provide powerful insights into the internal structure of the volcano. Specifically, volcanic rocks contain magnetic minerals called magnetite. Above a certain temperature, called the Curie temperature, these minerals become non‐magnetic. Thus, magnetism may be able to detect changes in the high temperature areas of the volcano between eruptions, such as the magma chamber or young lava flows. Here, we perform the first study analyzing three separate years of high‐resolution magnetic data collected using an autonomous underwater vehicle over Axial seamount. We create magnetic maps using repeated vehicle tracklines to highlight differences between each year and compare our findings with broader surveys of the region. Our results indicate the central region of Axial has become more magnetic during recent years, suggesting cooling of the lavas erupted in 2015 and their associated subsurface feeder zones. Key Points: Repeat magnetic surveys at active submarine volcanos image temporal change in thermal structure related to geologic and volcanic processesHigh resolution magnetic data can be used for low‐cost volcano monitoring in the marine environment over relevant timescales [ABSTRACT FROM AUTHOR]

Abstract Monitoring of active volcanic systems is a challenging task due in part to the trade‐offs between collection of high‐quality data from multiple techniques and the high costs of acquiring such data. Here we show that magnetic data can be used to monitor volcanoes by producing similar data to gravimetric techniques at significantly lower cost. The premise of this technique is that magma and wall rock above the Curie temperature are magnetically “transparent,” but not stationary within the crust. Subsurface movements of magma can affect the crustal magnetic field measured at the surface. We construct highly simplified magnetic models of four volcanic systems: Mount Saint Helens (1980), Axial Seamount (2015–2020), Kīlauea (2018), and Bárðarbunga (2014). In all cases, observed or inferred changes to the magmatic system would have been detectable by modern magnetometers. Magnetic monitoring could become common practice at many volcanoes, particularly in developing nations with high volcanic risk.

Abstract Axial Seamount in the northeast Pacific erupted in 2015, 2011, and 1998. Although monitored by the Regional Cabled Array of the Ocean Observatory Initiative, few magnetic surveys have been conducted over the region. This study uses high‐resolution magnetic data over the seamount collected by autonomous underwater vehicle Sentry during three years (2015, 2017, and 2020). The goal is to investigate whether there are temporal changes in the near‐surface magnetic field observable over the time scale of one volcanic cycle. We compare magnetic maps from repeated tracklines from each year. We find maps of the yearly difference in magnetization show coherent patterns that are not random. The central region of the caldera has become more magnetic during recent years, suggesting cooling of the surficial lava flows since 2015. Sentry data are more sensitive to shallow crustal structure compared to sea surface data which show longer wavelength anomalies extending deeper into the crust.

Crustal‐stored magma reservoirs contain exsolved volatiles which accumulate in the reservoir roof, exerting a buoyancy force on the crust. This produces surface uplift and sudden loss of volatiles through eruption results in syn‐eruptive subsidence. Here, we present three‐dimensional, visco‐elasto‐plastic, numerical modeling results which quantify the ground deformation arising from the growth and release of a volatile reservoir. Deformation is mostly independent of crustal thermal distribution and volatile reservoir shape, but is a function of volatile volume, density and depth and crustal rigidity. We present a scaling law for the volatiles' contribution to syn‐eruptive subsidence and show this contributes ∼20% of the observed subsidence associated with the 2015 Calbuco eruption. Our results highlight the key role that volatile‐driven buoyancy can have in volcano deformation, show a new link between syn‐eruptive degassing and deflation, and highlight that shallow volatile accumulation and release may have a significant impact on ground deformation of volcanoes. Plain Language Summary: Magma contains a lot of gases which separate from it when it approaches the surface. These gases can collect right above the magma storage region a few kilometers below the surface. They have a much lower density than the rocks surrounding them and push upwards like a balloon filled with air that is pressed under water. In this study, we use computer models to understand how much a volcano would grow from the push of the gases below and how much it would shrink when the gases escape because of an eruption. We find that the gases can cause the volcano to grow and shrink up to a few centimeters during accumulation and release, respectively. The amount of surface movement depends on the volume, density and depth of the gas reservoir as well as on the toughness of the rocks above it. We derive a simple equation which allows us to compute the surface movement using the aforementioned parameters. With this equation and estimates about the amount of accumulated gas at the 2015 Calbuco eruption, we can assume that about 20% of the observed surface movement was caused by the release of the magmatic gases. Key Points: Exsolving volatiles accumulate at the roof of a magma storage zone and contribute to surface deformation through buoyancy forces3D numerical models show that surface deformation is a function of the volatiles' volume, density and depth as well as crustal rigidityVolatile release during eruption can cause syn‐eruptive subsidence of a few cm, which is 20% of the observed signal at Calbuco in 2015 [ABSTRACT FROM AUTHOR]

Most of the largest volcanic activity in the world occurs in remote places such as deep oceans or poorly monitored oceanic island arcs. Thus, our capacity of monitoring volcanoes is limited to remote sensing and global geophysical observations. However, the rapid estimation of volcanic eruption parameters is needed for scientific understanding of the eruptive process and rapid hazard estimation. We present a method to rapidly identify large volcanic explosions, based on analysis of seismic data. With this methodology, we promptly detect the 15 January 2022 Hunga Tonga Ha'apai eruption. We then analyze the seismic waves generated by the volcanic explosion and estimate its important first‐order parameters. We further relate the parameters with the volcanic explosivity index (VEI). Our estimate of VEI ∼ 6 indicates that how the Hunga Tonga eruption is among the largest volcanic activity ever recorded with modern geophysical instrumentation and can provide new insights into the physics of large eruptions. Plain Language Summary: The Hunga Tonga Ha'apai volcanic eruption that occurred on 15 January 2022 had a global impact by ejecting a huge volume of ashes and volcanic gases in the atmosphere and with generating a tsunami that affected many Pacific countries. This volcanic event has been also well recorded by modern satellite and land‐based geophysical instruments. Despite the unprecedented wealth of high quality and rapidly available scientific data, main quantitative parameters of the Hunga Tonga volcanic eruption such as its size in comparison with previous major eruptions could not be estimated rapidly with "standard" monitoring algorithms. This emphasizes the need to develop new approaches for analysis of instrumental observations. We show how the data recorded by seismographic stations operating all around the World, which are available in real time, can be analyzed to determine main eruption parameters including its location and size within less than 2 hr after its occurrence. Key Points: Hunga Tonga volcanic explosion has been automatically detected with surface waves recorded by global seismological networksAnalysis of global surface waves resulted in measurement of the explosion impulse and led to estimating its Volcanic Explosivity Index as 6With near‐real‐time implementation of our methods, major volcanic explosions can be detected and characterized within less than 2 hr [ABSTRACT FROM AUTHOR]

Habitable ocean environments on Europa require an influx of reactants to maintain chemical disequilibrium. One possible source of reactants is seafloor volcanism. Modeling has shown that dissipation of tidal energy in Europa's asthenosphere can generate melt, but melt formation cannot be equated with volcanism. Melt must also be transported through Europa's cold lithosphere to erupt at the seafloor. Here, we use two models of dike propagation to show that dikes can only traverse the lithosphere if either the fracture toughness of the lithosphere or the flux into the dike is large (>500 MPa m1/2 or ∼1 m2 s−1, respectively). We conclude that cyclic volcanic episodes might provide reactants to Europa's ocean if magma accumulates at the base of the lithosphere for several thousand years. However, if dikes form too frequently, or are too numerous, the magma flux into each will be insufficient, and volcanism cannot support a habitable ocean environment. Plain Language Summary: Beneath the icy crust of Jupiter's moon Europa lies a deep, liquid‐water ocean that might provide an environment suitable for life. In the absence of sunlight, organisms must extract energy from chemical reactions within the ocean. Over time, organisms would use up all the chemical ingredients needed for these reactions, leading to extinction unless new ingredients were added to the environment. Because the ocean is closed‐off from Europa's surface by the thick ice crust, seafloor volcanism has been proposed as a source of chemical ingredients. Europa's deep rock interior can get hot enough to form small amounts of magma that will rise upward; however, the magma must also travel across the outer cold portion of the rock interior, which requires the formation and growth of magmatic dikes. Here we determine that dikes long enough to supply magma to Europa's seafloor only form if the rock is either very strong, or the amount of magma entering the dike is very large. In those cases, volcanism could occur on Europa's seafloor every few thousand years, supplying the necessary life‐sustaining chemical ingredients. NASA's upcoming Europa Clipper mission will provide new data that helps clarify whether the conditions needed for seafloor volcanism are met. Key Points: For volcanism to provide life‐sustaining reactants to Europa's ocean, asthenospheric‐formed melt must traverse the cold thick lithosphereDikes can propagate across the entire lithosphere if either the fracture toughness or the flux into the dike is largeVolcanism plausibly provides reactants to Europa's ocean every several thousand years, but seafloor volcanism is far from assured [ABSTRACT FROM AUTHOR]

Long‐period (LP), hybrid, and volcano‐tectonic (VT) seismicity are important indicators for tracking the evolution of volcanic processes. Here, we propose an unsupervised learning method to classify 5,949 seismic events in Kilauea volcano, Hawai'i, during a 4‐month period before the collapse of Pu'u' O'o on April 30, 2018. The LPs and hybrids exhibit three major episodes, which progressively intensified and had increasing shallow events toward the eruption. The most intense episode starting 3 weeks before eruption coincides with changes in near‐caldera deformation and lava lake elevation in Halema'uma'u, serving as possible immediate precursors. However, the first two episodes imply magma migration was already active months prior to the eruption. The spatiotemporal patterns of abundant hybrids reveal that they are associated with magma movement but mixed with shear‐failure or near‐surface resonance. Our results provide useful constraints on the magmatic processes in the preparation phase of the Kilauea eruption in 2018. Plain Language Summary: Many volcanoes around the world have been known to produce different types of seismic events, which can be used to infer volcanic processes underneath. However, classification of these events remains a challenging task. We propose a new classification method and apply it to numerous seismic events in Kilauea volcano, Hawai'i, before the collapse of Pu'u' O'o in 2018. We successfully separate different types of events and observe interesting spatiotemporal patterns. The results show that, before the eruption, the long‐period and hybrid events have three episodes. Together with surface observations, the latest episode in April 9–27 shows an unusually high rate and more shallow origins, indicative of the impending eruption. In addition, the spatiotemporal patterns of hybrid events shed light on their physical mechanisms. These results provide useful constraints on the magma migration processes in the preparation phase of the Kilauea eruption in 2018. Key Points: We classify long‐period, volcano‐tectonic, and hybrid events by spectral dissimilarity and hierarchical clusteringThe unusual high seismicity rate and more shallow origins in the last episode in April 9–27 may be indicative of the impending eruptionThe spatiotemporal patterns of hybrid events shed light on their physical mechanisms [ABSTRACT FROM AUTHOR]

Paleocene lavas of the Dianzhong Formation preserved in the Linzhou Basin of South Tibet provide a unique opportunity to constrain the initial geometry of the India‐Asia collision; however, earlier studies argued a complex magnetic signature resulting from thermal and/or chemical remagnetizations. To better characterize the remanences obtained from the Dianzhong lavas, we carried out an intraformational conglomerate test on a previously‐studied section in the Linzhou Basin. The positive conglomerate test suggests that the characteristic remanences reported from the Dianzhong Formation are primary. The updated Paleocene pole confirms a paleolatitude of 6.7° ± 4.4°N for the Lhasa terrane and positions the southern margin of Asia in the equatorial humid belt. An initial collision, between India, Asia and an intra‐oceanic arc in the equatorial humid belt, may have intensified silicate weathering and resulted in an extra consummation of carbon dioxide, which contributes to a long‐term cooling of the Earth during the Cenozoic. Plain Language Summary: The locus of the initial India‐Asia collision can be constrained using paleomagnetic studies on the Paleocene volcanics from the Linzhou Basin, South Tibet. However, the primary nature of the magnetic signature previously reported from the Dianzhong Formation was questioned. This study carries out an intraformational conglomerate test collected from the middle part of the Dianzhong Formation. The stable remanences isolated from a layer of intercalated lava cobbles yield a random distribution in contrast to the well‐grouped directions obtained from the over‐ and underlying lava layers resulting in a positive conglomerate test. We therefore argue for a primary nature for the characteristic remanence recorded by the Dianzhong lavas from the Linzhou Basin. Our study confirms a low latitude of ∼7°N, that is, within the equatorial humid belt, for the southern margin of Asia during ∼64–60 Ma. An initial low‐latitude collision between India and Asia is critical for understanding the tectonic and climatic significance of the India‐Asia collision. Key Points: Characteristic remanences reported from the Dianzhong lavas in the Linzhou Basin are primary in originThe updated Paleocene pole confirms a low latitude of ∼7°N for the Lhasa terraneAn initial collision between India, Asia and an oceanic arc in the equatorial humid belt may contribute to the Cenozoic cooling of the Earth [ABSTRACT FROM AUTHOR]

Identification of internal structures in an active volcano is mandatory to quantify the physical processes preceding eruptions. We propose a fully unsupervised Bayesian inversion method that uses the point compound dislocation model as a complex source of deformation, to dynamically identify the substructures activated during magma migration. We applied this method at Piton de la Fournaise. Using 7‐day moving trends of Global Navigation Satellite System (GNSS) data preceding the June 2014 eruption, we compute a total of 15 inversion models of 2.5 million forward problems each, without a priori information. Obtained source shapes (dikes, prolate ellipsoids, or pipes) show magma migration from 7–8 km depth to the surface, drawing a mechanical "tomography" of the magma pathway. Our results also suggest source geometries compatible with observed eruptive fissures and seismicity distribution. In case of finite magma volume involved in final dike injection, source volume estimates from this method allow forecasting volumes of erupted lava. Plain Language Summary: Imaging the interior of an active volcano and estimating volumes of magma present at depth are major challenges of eruption anticipation. In this work we propose an effective method of data processing that combines a mathematical model of the potential source at depth and standard ground deformation measurements at the surface in a fully automated process that has been implemented as a real‐time monitoring tool to anticipate eruptions at Piton de la Fournaise volcano. The method is sensitive to magma migration, highlighting the magma pathway, like a scanner that displays a 3‐D image of the volcano plumbing system. In specific circumstances, this method can be used also to forecast volumes of erupted lava. Key Points: Unsupervised GNSS modeling offers fast detection and volume estimate of migrating magmaDeformation source modeling draws a mechanical tomography of the volcano internal substructuresFull model space Bayesian inversion serves as a robust real‐time monitoring tool [ABSTRACT FROM AUTHOR]

Using ~25 years of GPS and InSAR observations and the time‐dependent inversion filter, we invert for the volume change history of three active volcanoes in the east central Alaska Aleutian arc and the secular velocity of the region. The inferred time‐dependent volume change shows (1) two exponentially decaying pulses followed by a nearly linear inflation period at Westdahl volcano, (2) multiple episodic inflation events at Akutan volcano, and (3) transient volcanic inflation and long‐term deflation signals at Makushin volcano. Comparing our regional velocity estimates with recently published block models, we find a small signal that can be explained by slip deficit on the megathrust, either from a shallow (<20 km depth) almost fully locked zone or a weakly locked zone confined to 25–50 km depth. Plain Language Summary: In the east central Alaska Aleutian arc, the surface is deforming due to magma supply beneath the active volcanoes, tectonic plate motion, and slip deficit on the plate interface (at some places where two tectonic plates cannot freely slide relative to each other). In this study, we separate and model those geophysical processes using measurements of surface deformation during the past 25 years and interpret the long‐term variations in magma supply at each volcano. Key Points: Inflation at Westdahl volcano shows two distinct exponentially decaying pulses followed by a long linear inflation periodAkutan volcano has experienced multiple episodic inflation events, and we observe long‐term transient volcanic signals at Makushin volcanoBlock motion and a small elastic strain signal from the subduction interface beneath the region can explain the steady nonvolcanic signal [ABSTRACT FROM AUTHOR]

Conceptual models of magma storage and transport under calderas favor a connected system of sills and dikes. These features are individually below the resolution of standard seismic tomography, but radial seismic anisotropy can reveal where they exist in aggregate. We model radial anisotropy at Okmok caldera, Alaska, to demonstrate the presence of a caldera‐centered stacked sill complex and surrounding dike system. We show that ascending magma, inferred from seismicity, either intersects the sill complex, resulting in a larger volume eruption of evolved magma, or bypasses the overlying sill complex via dikes, resulting in a low‐volume mafic eruption. Our results exemplify how the locations of magma storage and paths of transport impact eruption size and composition. As this type of crustal storage is likely common to many calderas, this analysis offers a potential new framework for volcano observatories to forecast the size of impending eruptions. Plain Language Summary: Okmok caldera, in the central Aleutian Arc, has erupted approximately every decade for the last century and represents a notable hazard to the trans‐Pacific air traffic routes that overlie it. We deployed a temporary array of seismic instruments to supplement Okmok's existing seismic network. Modeling these seismic data, we identify a central region of magma storage at the volcano arranged in horizontal sheets (sills) surrounded by an adjacent ring of vertical sheets of cooled magma (dikes). Using the spatial patterns of earthquakes, we infer paths of magma transport in relation to these structures. For the 2008 Okmok eruption, we show that deeper, silica‐poor magma moved through and mobilized more silica‐rich magma stored in the shallow central sill region. This resulted in the 2008 eruption being larger and more explosive relative to the last century. In a typical historic eruption, by contrast, we conclude that the deeper magma source ascended through the dike system and bypassed the sill region, leading to smaller, silica‐poor eruptions. We suggest that the analysis presented in this study is a potential new framework for forecasting volcanic eruption size and may be of use to volcano observatories worldwide. Key Points: Okmok caldera is underlain by radially anisotropic velocity structures indicating a central sill complex and a surrounding ring of dikesThe path of magma through or around the central stacked sill complex can control the volume and composition of erupted magmas [ABSTRACT FROM AUTHOR]

Determining the spatial relations between volcanic edifices and their underlying magma storage zones is fundamental for characterizing long‐term evolution and short‐term unrest. We compile centroid locations of upper crustal magma reservoirs at 56 arc volcanoes inferred from seismic, magnetotelluric, and geodetic studies. We show that magma reservoirs are often horizontally offset from their associated volcanic edifices by multiple kilometers, and the degree of offset broadly scales with reservoir depth. Approximately 20% of inferred magma reservoir centroids occur outside of the overlying volcano's mean radius. Furthermore, reservoir offset is inversely correlated with edifice size. Taking edifice volume as a proxy for long‐term magmatic flux, we suggest that high flux or prolonged magmatism leads to more centralized magma storage beneath arc volcanoes by overprinting upper crustal heterogeneities that would otherwise affect magma ascent. Edifice volumes therefore reflect the spatial distribution of underlying magma storage, which could help guide monitoring strategies at volcanoes. Plain Language Summary: Magma reservoirs are commonly assumed to be located directly beneath their associated volcanic edifices. This "central reservoir" paradigm dominates volcano modeling and monitoring. However, the actual spatial relations between volcanoes and underlying magma reservoirs are poorly known. We compile a database of geophysical studies at subduction zone volcanoes where magma reservoirs were detected through subsurface modeling of seismic waves, electrical conductivity, and ground deformation. We then systematically map volcano shapes and compare their center locations with associated magma reservoirs. We find that while the majority of volcanoes are located directly above their source reservoirs, a substantial number of magma reservoirs are laterally offset multiple kilometers from their volcano's centers. Approximately 20% of magma reservoirs are located beyond the "footprints" of their volcanoes. Additionally, magma reservoirs are more laterally offset at small volcanoes, but more centrally aligned at large volcanoes. We propose that increased magma flux at large volcanoes thermally overprints crustal faults and heterogeneities, leading to progressively more centrally focused magmatic systems. Our work suggests that the central reservoir view of volcanic systems should be revised to account for magma focusing as volcanoes grow. Recognizing the global prevalence of laterally offset magmatic systems may better help design volcano monitoring networks. Key Points: Geophysical imaging suggests that magma reservoirs are often significantly laterally offset from overlying arc volcanoesOffset magma reservoirs are more prevalent at small volcanoes, whereas larger volcanoes have more centrally aligned magma storageCharacterizing edifice topography may help predict subsurface magma storage geometries and guide volcano monitoring networks [ABSTRACT FROM AUTHOR]

We present three‐dimensional numerical simulations of eruption clouds from circular to linear fissure vents to investigate the control of vent shape on the height and stability of volcanic plumes during large explosive eruptions. Our results show that clouds ejected from circular or low‐aspect‐ratio (nearly square‐like) fissure vents can be associated with radially suspended flow (RSF) at the top of the jet region, whereas those emitted from narrow‐fissure vents are not. Non‐RSF plumes are more stable than those associated with RSF because the highly concentrated parts of the ejected mixture are easily dissipated and mixed with air near the vent. Plume height in the RSF regime decreases while that in the non‐RSF regime increases with increasing aspect ratio, even for a fixed magma flow rate. These observations suggest that the efficiency of air entrainment is influenced by the vent shape, which in turn controls the dynamics of eruption plumes. Plain Language Summary: Explosive volcanic eruptions eject hot mixtures of gas and ash, forming eruption clouds. Eruption clouds can either become buoyant and rise upward as kilometer‐scale volcanic plumes, from which they release ash and gas into the atmosphere, or flow downward along the ground, resulting in devastating pyroclastic flows. Understanding the dynamics of eruption clouds and the critical conditions for generating pyroclastic flows versus volcanic plumes is an important focus of modern volcanology research. We present numerical simulations of eruption clouds using a three‐dimensional numerical model to investigate the effects of volcanic vent geometry on plume stability and height. Our simulation results indicate that plume height depends on the shape of the volcanic vent and can have different dynamics even for the same eruption intensity. These effects of vent shape are caused by the complex mechanism of mixing between the eruption cloud and the ambient air. The efficiency of such mixing inside the cloud largely controls the critical conditions for the generation of pyroclastic flows; above a critical mass flow rate, clouds ejected from circular vents can generate pyroclastic flows, whereas those ejected from thin fissure vents develop stable volcanic plumes. Key Points: Three‐dimensional numerical simulations reveal the effects of volcanic vent shape on plume stability and plume heightPlumes from narrow fissures are more stable than those from circular vents owing to more efficient dissipation mechanisms near the ventPlume height has complex dependency on vent aspect ratio because of changes in the efficiency of air entrainment [ABSTRACT FROM AUTHOR]

The 2018 Kīlauea eruption and caldera collapse generated intense cycles of seismicity tied to repeated large seismic (Mw ~ 5) collapse events associated with magma withdrawal from beneath the summit. To gain insight into the underlying dynamics and aid eruption response, we applied waveform‐based earthquake detection and double‐difference location as the eruption unfolded. Here, we augment these rapid results by grouping events based on patterns of correlation‐derived phase polarities across the network. From April 29 to August 6, bracketing the eruption, we used ~2,800 events cataloged by the Hawaiian Volcano Observatory to detect and precisely locate 44,000+ earthquakes. Resulting hypocentroids resolve complex, yet coherent structures, concentrated at shallow depths east of Halema'uma'u crater, beneath the eventual eastern perimeter of surface collapse. Based on a preponderance of dilatational P wave first motions and similarities with previously inferred dike structures, we hypothesize that failure was dominated by coupled shear and crack closure. Plain Language Summary: We used high‐resolution methods to examine seismicity associated with the 2018 Kīlauea eruption and summit collapse, as magma drained underground from the summit region and eventually erupted toward the east. In total, we detected and precisely located more than 44,000 earthquakes from late April to early August 2018. The location patterns of these earthquakes reveal numerous seismically active structures, both on the boundary and within the collapsing zone. Based on the characteristics of these earthquakes, we hypothesize that most events were generated by a combination of fault slip and crack closure as the surface rocks collapsed into the underground region previously occupied by magma. Key Points: We apply high‐precision earthquake detection, location, and phase polarity analysis to illuminate the 2018 Kīlauea summit collapse sequenceSeismicity was most active near the eventual eastern perimeter of surface collapse but also occurred in the interior of the collapse areaA preponderance of dilatational P wave first motions suggests that seismicity was largely generated by coupled shear and crack closure [ABSTRACT FROM AUTHOR]

Wind abrasion is important for planetary landscape evolution, and wind‐abraded bedrock landscapes contain many landforms that are difficult to interpret. Here we exploit a natural experiment in Chile where topographic shielding by an upwind lava flow yields diverse erosional landforms in a downwind ignimbrite. Using a 3‐D topographic wind model, we find that low velocities in the wake of a lava lobe coincide with a transition from landforms reflecting fracture‐parallel erosion to flow‐parallel erosion. Erosion rates across these landforms vary with shear velocity and abrasion susceptibility of the windward escarpment. We hypothesize that this morphologic threshold is controlled by whether particles can be lofted in suspension and overcome topographic steering imposed by fractured bedrock blocks. Within a phase space set by Rouse and Stokes numbers, our data illustrate that wind‐abraded landforms reflect a competition between the material skeleton of the landscape and the strength of the flow that shapes it. Key Points: In wind‐eroded bedrock landscapes, particle abrasion can focus along fracture networks or cross‐cut them, yielding unique landform patternsThese erosion patterns emerge from a competition between flow strength, particle inertia, and topographic steering by fractured bedrockUnderstanding aerodynamic and structural thresholds can help with interpretations of abrasion processes across planetary landscapes [ABSTRACT FROM AUTHOR]

During the 2018 Kīlauea eruption the caldera floor dropped 500 m in 62 nearly periodic events of up to 8 m. Caldera collapse maintains pressure in the magma reservoir necessary to sustain high‐rate eruptions. The 2018 collapses were accompanied by inflationary tilts and displacements, similar to observations at other basaltic calderas. Collapse is modeled in 2‐D by uniform slip dislocations intersecting a magma chamber. Collapses occurred rapidly, such that mass within the chamber was constant. For vertical faults surface deformation outside the collapse results only from chamber pressurization with displacements antiparallel to precollapse deflation, similar to observations. For inward dipping faults the predicted ratio of horizontal to vertical displacements during collapse is greater than for the precollapse deflation, as observed. For outward dipping faults the horizontal displacements are inward, contrary to data. The average deformation trends during the eruption depend on fault dip and whether stress required to trigger collapses was constant or changed with time. Plain Language Summary: When large volumes of magma are erupted from a volcano the roof of the evacuated magma chamber can founder leading to caldera formation. The weight of the roof block maintains pressure on the magma chamber providing a driving force to sustain the eruption. During the 2018 Kīlauea Volcano Hawaii eruption the caldera collapse occurred in discrete, nearly periodic events. Understanding the mechanics of these events is important for predicting how caldera collapse initiates and evolves with time. We use simple elastic models of collapse into a magma chamber, together with measurements of surface deformation during collapse events, to elucidate the geometry of the chamber‐roof system at Kīlauea. Key Points: Two‐dimensional elastic model predicts deformation due to collapse on caldera faults that bottom in a magma chamberFor vertical faults deformation external to caldera is solely due to collapse‐induced pressurization of chamberOutward dipping faults predict horizontal displacements opposite in sign to observations [ABSTRACT FROM AUTHOR]

Volcanic eruptions are energetic events driven by the imbalance of magmatic forces. The magnitudes of these forces remain poorly constrained because they operate in regions that are inaccessible, either underground or dangerous to approach. New techniques are needed to quantify the processes that drive eruptions and to probe magma storage conditions. Here we present X‐ray microdiffraction measurements of volcanic stress imparted as lattice distortions to the crystal cargo of magma from Yellowstone and Long Valley eruptions. Elevated residual stresses between 100 and 300 MPa are preserved in erupted quartz. Multiple volcanic forces could be culpable for the deformation so we analyzed crystals from pyroclastic falls, pyroclastic density currents, and effusive lavas. Stresses are preserved in all quartz but cannot be attributed to differences in eruption style. Instead, lattice deformation likely preserves an in situ measurement of the deviatoric stresses required for the brittle failure of viscous, crystal‐bearing glass during ascent. Plain Language Summary: Because of inherent danger, volcano scientists have little direct understanding of the stresses active during volcanic eruptions. We propose that the crystal cargo carried by a volcanic eruption may preserve a record of those stresses. We used synchrotron X‐ray microdiffraction to measure crystal deformation in quartz from explosive and effusive eruptions from Yellowstone and Long Valley calderas. All the crystals were strained by stresses ranging from 100 to 300 MPa. These values are large but are not related to eruption style. The stresses may have been caused by crystal‐crystal impingements in the crystal‐rich magma chambers. More likely, we propose that the residual stresses record those required for brittle failure of the crystal‐bearing melt in the conduit during eruptive ascent. Key Points: Explosive and effusive eruptions from volcanoes contain deformed quartz crystals with the same residual stressesResidual stresses are proposed to originate from the stresses required to fragment magmaResidual stress may also originate from crystal‐crystal contacts in crystal‐rich magmatic mushes [ABSTRACT FROM AUTHOR]

An episode of unrest began at Kīlauea in April 2018 that produced both significant volcanic output and high rates of seismicity, including a Mw 6.9 earthquake on 4 May 2018. In this study, we image the rupture process of this earthquake using a genetic algorithm‐based back‐projection technique. The dominant feature of the earthquake is a slowly propagating western rupture, which shares similar characteristics with the region's largest recorded event in 1975 (Mw 7.7). The location of this western segment suggests that small asperities on this section of the décollement that frequently fail as slow slip events may achieve seismic slip rates when rupture is initiated on adjacent sections of the fault. Given the interaction between volcanic and seismic activity in this region, imaging the rupture properties of these events can improve our understanding of future geologic hazards in this region. Plain Language Summary: Voluminous lava flows and explosive eruptions at Kīlauea Volcano in Hawaiʻi have captured the attention of the media and general public during the past year. In the early stages of this volcanic activity, a magnitude 6.9 earthquake occurred beneath the south flank of Kīlauea, which was the second largest earthquake recorded by modern instrumentation in this region. The research presented in the manuscript uses a novel source imaging technique to study the fine‐scale spatiotemporal evolution of the rupture that produced this event. The details of this rupture provide new insight into the relationship between fault properties, background seismicity, slow slip events, and major earthquakes in volcanic settings. Key Points: The complex rupture process of the 2018 Mw 6.9 Hawaiʻi earthquake is imaged using a genetic algorithm‐based back‐projection techniqueThe dominant high‐frequency feature of this earthquake is a slow western propagating rupture that overlaps with previous slow slip eventsThese rupture properties can be explained by slip on a décollement composed of soft sediments with small velocity‐weakening asperities [ABSTRACT FROM AUTHOR]

Identification of unambiguous signals of volcanic unrest is crucial in hazard assessment. Processes leading to phreatic and phreatomagmatic eruptions remain poorly understood, inhibiting effective eruption forecasting. Our 5‐year gas record from Poás volcano, combined with geophysical data, reveals systematic behavior associated with hydrothermal‐magmatic eruptions. Three eruptive episodes are covered, each with distinct geochemical and geophysical characteristics. Periods with larger eruptions tend to be associated with stronger excursions in monitoring data, particularly in SO2/CO2 and SO2 flux. The explosive 2017 phreatomagmatic eruption was the largest eruption at Poás since 1953 and was preceded by dramatic changes in gas and geophysical parameters. The use of drones played a crucial role in gas monitoring during this eruptive period. Hydrothermal sealing and volatile accumulation, followed by top‐down reactivation of a shallow previously emplaced magma body upon seal failure, are proposed as important processes leading to and contributing to the explosivity of the 2017 eruption. Plain Language Summary: High‐frequency monitoring of phreatic eruptions shows that clear precursory signals often exist to these dangerous explosive events. We interrogate the processes that lead to phreatic eruptions and investigate the intricate connections between magma intrusions and the hydrothermal systems that they feed. Key Points: Three eruptive phases are characterized in detail through five years of high‐frequency monitoringWe identify and discuss precursors to phreatic and phreatomagmatic eruptionsEnhanced hydrothermal sealing can lead to larger eruptions and top‐down remobilization of magma [ABSTRACT FROM AUTHOR]