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Subduction termination leads to complex tectonic and geological activity, with the observational record often including clear evidence for exhumation, anomalous magmatism and topographic subsidence, followed by rapid uplift. However, the mechanism(s) driving these responses remain enigmatic and cannot be reconciled with our current understanding of post-subduction tectonics. A prime example of recent subduction termination can be found in northern Borneo (Malaysia), where subduction ceased in the late Miocene (at ~9 Ma). Here we use recently acquired passive seismic data to image, at unprecedented resolution (~35 km), a sub-vertical lithospheric drip, inferred to have developed as a Rayleigh–Taylor gravitational instability from the root of a volcanic arc. We use thermo-mechanical simulations to reconcile these images with time-dependent dynamical processes within the crust and underlying mantle following subduction termination. Our model predictions illustrate how substantial extension from a lithospheric drip can thin the crust in an adjacent orogenic belt, facilitating lower-crustal melting and possible exhumation of sub-continental material, as is observed. These discoveries provide evidence for extension-driven melting of the lower crust, exhumation, core-complex formation and orogeny that also may occur in other areas of recent subduction termination.Post-subduction downwelling of lithosphere—or drips—can lead to extension and crustal thinning, influencing the tectonic evolution of continental crust after subduction termination, according to thermo-mechanical simulations.

The profile of tephra concentration along a volcanic plume (i.e., the tephra segregation profile) is an important source parameter for the simulation of tephra transport and deposition and thus for the tephra sedimentation load. The most commonly-used approach is to treat an eruption as a single event (i.e., with a time-averaged mass eruption rate; MER). In this case, it is common to use pre-determined profiles that feature most of the tephra segregate at the top of the plume. However, case studies based on observations have revealed that large concentration maxima also appear at the lower part of the plume. To investigate this discrepancy, the impact of plume height on the temporal variations in the MER is examined. To this end, we use the tephra transport and dispersion model Tephra4D with MER estimates obtained from geophysical monitoring and maximum plume height observations to calculate the spatial distribution of the tephra deposit load for 39 eruptive events that consisted of explosions and quasi-steady particle emission from the Sakurajima volcano, Japan. A comparison of the model results with observations from a disdrometer network revealed that for both kinds of activity, maxima in tephra segregation can occur at heights below the reported plume height. The tephra segregation profiles of Vulcanian eruptions at Sakurajima volcano are consistent with most of the modeling studies giving profiles that feature most of the tephra segregating at the top of the plume if the temporal variation of the MER is taken into consideration to properly represent the total series of eruptive events in a sequence. This highlights that even though the activity at Sakurajima volcano is commonly characterized simply as Vulcanian eruptions, in addition to the primary plume developed due to the initial instantaneous release caused by the explosion, the subsequent continuous plume that can accompany the eruption plays an important role in particle emission. Calculations could not reproduce the simultaneous deposition of particles with a wide range of settling velocities in observations, suggesting the importance of volcanic ash fingers caused by gravitational instability in tephra transport simulations. Graphical Abstract

This investigation aims to study the effect of dust pressure anisotropy, self-gravitational forces, and magnetic forces on the gravitational instabilities and associated low-frequency rogue wave (RW) profile as well as oblique interaction characteristics of low-frequency dust-acoustic (DA) solitary waves (DASWs) in an electron-depleted dusty plasma. The current plasma model comprises inertial warm, positively and negatively charged massive dust grains and non-extensive ions. Following the quasi-linear theory, the extended Poincaré–Lighthill–Kuo (PLK) perturbation technique, and Jean’s criterion, the two-sided Korteweg-de Vries (KdV) equations and corresponding analytical phase shifts due to collision are derived and analyzed. The critical configuration of the current plasma model that renders the KdV compressive or rarefactive DASWs invalid and leads to the formation of the modified KdV (mKdV)-type solitons is determined. The findings from computational simulations unequivocally demonstrate that parallel and perpendicular dust pressures do not exhibit the same behavior rigorously. Furthermore, the presence of the magnetic field and dust pressure anisotropy has been found to inhibit gravitational instabilities and significantly modify DA RW triplets, which can evolve into super rogue waves through the superposition of triplets. The collision scenarios involving solitons of both similar and opposite polarities traveling toward each other, as well as the influential roles played by the crossing angle, magnetic field, gravitational field, ion entropic index, and dust pressure along and across magnetic field lines on phase shifts and DA RWs, are extensively discussed in detail. The possible applications of the present work for various space plasma scenarios, including dense molecular clouds and interstellar medium, are anticipated. This study will contribute to understanding the dynamics of the generation and propagation of both RWs and the collision of solitons. Once the mechanics of their generation and propagation are understood, these waves can be devoted to many industrial and medical applications.

In this paper, using the hydrodynamic model, the Jeans gravitational instability in a dusty plasma with q-nonextensive velocity distributions is investigated. The change in the Jeans instability criterion and growth rate due to the effects of the dust-ion collision, polarization force, and nonextensivity parameters are analyzed in the dust acoustic frequency range. It is shown that by increasing the nonextensivity and polarization parameters, the threshold condition and growth rate of the instability enhance. Furthermore, it is represented that the dust-ion collisions have a stabilizing influence on the growth rate of the instability and drive the system toward thermal equilibrium. These results can be applied to astrophysical phenomena such as the collapse of interstellar gas clouds and subsequent star formation, and also, in the laboratory dusty plasmas.

The canonical theory for planet formation in circumstellar disks proposes that planets are grown from initially much smaller seeds 1 – 5 . The long-considered alternative theory proposes that giant protoplanets can be formed directly from collapsing fragments of vast spiral arms 6 – 11 induced by gravitational instability 12 – 14 —if the disk is gravitationally unstable. For this to be possible, the disk must be massive compared with the central star: a disk-to-star mass ratio of 1:10 is widely held as the rough threshold for triggering gravitational instability, inciting substantial non-Keplerian dynamics and generating prominent spiral arms 15 – 18 . Although estimating disk masses has historically been challenging 19 – 21 , the motion of the gas can reveal the presence of gravitational instability through its effect on the disk-velocity structure 22 – 24 . Here we present kinematic evidence of gravitational instability in the disk around AB Aurigae, using deep observations of 13 CO and C 18 O line emission with the Atacama Large Millimeter/submillimeter Array (ALMA). The observed kinematic signals strongly resemble predictions from simulations and analytic modelling. From quantitative comparisons, we infer a disk mass of up to a third of the stellar mass enclosed within 1″ to 5″ on the sky. Observations of gravitational instability in the disk around AB Aurigae using deep observations of 13 CO and C 18 O line emission provide evidence that giant protoplanets can be formed from collapsing fragments of vast spiral arms.

The importance of submesoscale instabilities, particularly mixed layer baroclinic instability and symmetric instability, on upper-ocean mixing and energetics is well documented in regions of strong, persistent fronts such as the Kuroshio and the Gulf Stream. Less attention has been devoted to studying submesoscale flows in the open ocean, far from long-term, mean geostrophic fronts, characteristic of a large proportion of the global ocean. This study presents a year-long, submesoscale-resolving time series of near-surface buoyancy gradients, potential vorticity, and instability characteristics, collected by ocean gliders, that provides insight into open-ocean submesoscale dynamics over a full annual cycle. The gliders continuously sampled a 225 km 2 region in the subtropical northeast Atlantic, measuring temperature, salinity, and pressure along 292 short (~20 km) hydrographic sections. Glider observations show a seasonal cycle in near-surface stratification. Throughout the fall (September–November), the mixed layer deepens, predominantly through gravitational instability, indicating that surface cooling dominates submesoscale restratification processes. During winter (December–March), mixed layer depths are more variable, and estimates of the balanced Richardson number, which measures the relative importance of lateral and vertical buoyancy gradients, depict conditions favorable to symmetric instability. The importance of mixed layer instabilities on the restratification of the mixed layer, as compared with surface heating and cooling, shows that submesoscale processes can reverse the sign of an equivalent heat flux up to 25% of the time during winter. These results demonstrate that the open-ocean mixed layer hosts various forced and unforced instabilities, which become more prevalent during winter, and emphasize that accurate parameterizations of submesoscale processes are needed throughout the ocean.

Galaxies in the early Universe that are bright at submillimetre wavelengths (submillimetre-bright galaxies) are forming stars at a rate roughly 1,000 times higher than the Milky Way. A large fraction of the new stars form in the central kiloparsec of the galaxy 1 – 3 , a region that is comparable in size to the massive, quiescent galaxies found at the peak of cosmic star-formation history 4 and the cores of present-day giant elliptical galaxies. The physical and kinematic properties inside these compact starburst cores are poorly understood because probing them at relevant spatial scales requires extremely high angular resolution. Here we report observations with a linear resolution of 550 parsecs of gas and dust in an unlensed, submillimetre-bright galaxy at a redshift of z  = 4.3, when the Universe was less than two billion years old. We resolve the spatial and kinematic structure of the molecular gas inside the heavily dust-obscured core and show that the underlying gas disk is clumpy and rotationally supported (that is, its rotation velocity is larger than the velocity dispersion). Our analysis of the molecular gas mass per unit area suggests that the starburst disk is gravitationally unstable, which implies that the self-gravity of the gas is stronger than the differential rotation of the disk and the internal pressure due to stellar-radiation feedback. As a result of the gravitational instability in the disk, the molecular gas would be consumed by star formation on a timescale of 100 million years, which is comparable to gas depletion times in merging starburst galaxies 5 . The molecular gas in the inner kiloparsec of a submillimetre-bright galaxy is clumpy and gravitationally unstable, collapsing to form stars at a rate that will deplete the gas in about 100 million years.

The deep structure of the continental collision between India and Asia and whether India’s lower crust is underplated beneath Tibet or subducted into the mantle remain controversial. It is also unknown whether the active normal faults that facilitate orogen-parallel extension of Tibetan upper crust continue into the lower crust and upper mantle. Our receiver-function images collected parallel to the India–Tibet collision zone show the 20-km-thick Indian lower crust that underplates Tibet at 88.5–92°E beneath the Yarlung-Zangbo suture is essentially absent in the vicinity of the Cona-Sangri and Pumqu-Xainza grabens, demonstrating a clear link between upper-crustal and lower-crustal thinning. Satellite gravity data that covary with the thickness of Indian lower crust are consistent with the lower crust being only ∼30% eclogitized so gravitationally stable. Deep earthquakes coincide with Moho offsets and with lateral thinning of the Indian lower crust near the bottom of the partially eclogitized Indian lower crust, suggesting the Indian lower crust is locally foundering or stoping into the mantle. Loss of Indian lower crust by these means implies gravitational instability that can result from localized rapid eclogitization enabled by dehydration reactions in weakly hydrous mafic granulites or by volatile-rich asthenospheric upwelling directly beneath the two grabens. We propose that two competing processes, plateau formation by underplating and continental loss by foundering or stoping, are simultaneously operating beneath the collision zone.

Planet formation occurs around a wide range of stellar masses and stellar system architectures 1 . An improved understanding of the formation process can be achieved by studying it across the full parameter space, particularly towards the extremes. Earlier studies of planets in close-in orbits around high-mass stars have revealed an increase in giant planet frequency with increasing stellar mass 2 until a turnover point at 1.9 solar masses ( M ⊙ ), above which the frequency rapidly decreases 3 . This could potentially imply that planet formation is impeded around more massive stars, and that giant planets around stars exceeding 3  M ⊙ may be rare or non-existent. However, the methods used to detect planets in small orbits are insensitive to planets in wide orbits. Here we demonstrate the existence of a planet at 560 times the Sun–Earth distance from the 6- to 10- M ⊙ binary b Centauri through direct imaging. The planet-to-star mass ratio of 0.10–0.17% is similar to the Jupiter–Sun ratio, but the separation of the detected planet is about 100 times wider than that of Jupiter. Our results show that planets can reside in much more massive stellar systems than what would be expected from extrapolation of previous results. The planet is unlikely to have formed in situ through the conventional core accretion mechanism 4 , but might have formed elsewhere and arrived to its present location through dynamical interactions, or might have formed via gravitational instability. A direct imaging study demonstrates the existence of a giant planet in a wide orbit around the high-mass b Centauri binary system, and uses measurements of the orbital properties to discuss its formation mechanism.

The spatial distribution of mare basalts, titanium and KREEP (potassium, rare earth elements and phosphorus) on the Moon is asymmetrical between the nearside and farside. These asymmetries cannot be readily explained by solidification of a global magma ocean and subsequent mantle overturn, which should result in a layered and spherically symmetric lunar interior. Alternative scenarios have been proposed to explain the observed compositional asymmetry, but its origin remains enigmatic. Here, we present hydro- and mantle convection numerical simulations of the giant impact event that formed the South Pole–Aitken basin—the largest impact basin on the Moon—and the subsequent impact-induced convection with the assistance of gravitational instability. We find that the impact induces thermochemical instabilities that drive the dense KREEP-rich ilmenite-bearing cumulate to migrate towards the nearside following lunar magma ocean solidification. This results in the formation of a chemical reservoir under the nearside crust that could explain the observed geochemical asymmetries. We suggest that enrichments of ilmenite and KREEP in the nearside hemisphere following the South Pole–Aitken impact event provide a viable explanation for the wide composition range of mare basalts observed on the lunar surface. The compositional asymmetry between the Moon’s near- and farsides can be explained as the result of impact-induced mantle convection and gravitational instability, according to numerical modelling of the South Pole–Aitken impact and the ensuing mantle evolution.