Orders Of Magnitude Variation Research Articles

A performant energy-conserving particle reweighting method for Particle-in-Cell simulations

A new particle-based reweighting method is developed and demonstrated in the Aleph Particle-in-Cell with Direct Simulation Monte Carlo (PIC-DSMC) program. Novel splitting and merging algorithms ensure that modified particles maintain physically consistent positions and velocities. This method allows a single reweighting simulation to efficiently model plasma evolution over orders of magnitude variation in density, while accurately preserving energy distribution functions (EDFs). Demonstrations on electrostatic sheath and collisional rate dynamics show that reweighting simulations achieve accuracy comparable to fixed weight simulations with substantial computational time savings. This highly performant reweighting method is recommended for modeling plasma applications that require accurate resolution of EDFs or exhibit significant density variations in time or space.

Variability of inherent optical properties of seawater in relation to the concentration and composition of suspended particulate matter in the coastal Arctic waters of western Spitsbergen

Inherent optical properties (IOPs) and characteristics of suspended particles in surface seawater samples were measured in summer months of 2021 and 2022 in Arctic fjords and coastal waters of western Spitsbergen in the Svalbard archipelago. The measured IOPs included the spectral backscattering and scattering coefficients of suspended particulate matter, as well as the spectral absorption coefficients of suspended particulate matter and its non-algal particulate and phytoplankton components. The particulate assemblages were characterized by measuring the mass concentrations of suspended particulate matter (SPM), particulate organic matter (POM), particulate inorganic matter (PIM), and phytoplankton pigments including chlorophyll-a (Chla). The investigated coastal waters exhibit high variability of particulate characteristics and associated IOPs. We observed more than two orders of magnitude variation in SPM and particulate IOPs, and Chla varied from below the detection limit to more than 3 mg m−3. The contribution of organic fraction to SPM (POM/SPM ratio) varied from 0.05 to 0.6, and the Chla/SPM ratio spanned more than three orders of magnitude with a maximum value of the order of 10−3. As a result, the mass-specific optical coefficients, especially the mass-specific backscattering and scattering coefficients of particles and mass-specific absorption coefficient of non-algal particulate matter, exhibit large variations. In addition, our study demonstrates the influences of changes in composition of suspended particulate matter parameterized in terms of POM/SPM and Chla/SPM ratios on IOPs. Various variants of spectral parametrizations of optical coefficients in terms of univariate or multivariable relationships with particulate characteristics are provided. These parameterizations are representative of the investigated coastal Arctic waters in Svalbard region and can be used for better interpretation of optical measurements, both in-situ and remote, in this Arctic environment.

Luminosity dependence of the multiple cyclotron lines in 4U 0115+63

Context. The Be X-ray binary 4U 0115+63 underwent a giant outburst in 2023 with the X-ray luminosity of the source reaching 1038 erg s−1. During the outburst, two target of opportunity observations were made with NuSTAR. Aims. The main goal of this work is to model the multiple cyclotron scattering features (CRSFs) present in 4U 0115+63 and study their dependence on the luminosity of the source. Methods. The 3–79 keV broadband X-ray coverage of NuSTAR allowed us to properly model the continuum and investigate the nature of the multiple cyclotron resonance scattering features present in the source spectrum. We used the epoch-folding technique to find the pulsation from the source and also studied the changes in the cyclotron line energy with an order of magnitude variation in the source luminosity. Results. We detected five cyclotron lines during the 2023 outburst near 12, 16, 24, 34, and 47 keV. The ∼16 keV cyclotron line cannot be harmonically related to the other cyclotron lines at ∼12 keV and ∼24 keV. This indicates the presence of two fundamental lines in the spectrum of 4U 0115+63 at 12 keV and 16 keV. Conclusions. With the inclusion of the two latest NuSTAR observations, we have expanded the data set of the CRSF line center to encompass a broad range of luminosity. This enables us to comprehensively investigate the relationship between the centroid energy of the cyclotron lines and luminosity. The CRSF line center shows no anticorrelation with luminosity, unlike previously reported. Instead, a weak positive correlation is found in four out of the five detected cyclotron lines of 4U 0115+63. The luminosity variation of the two fundamental CRSFs could be well explained with the prediction from the collisionless shock model. A tentative negative correlation was observed in the fundamental CRSF at 16 keV and its harmonics beyond a “critical luminosity” of 1038 erg/s. This behavior was not present for the 12 keV fundamental CRSF and its harmonic at 24 keV.

Measuring interfacial thermal resistance across carbon nanotubes with in-situ electron microscopy: Unexpected reduction upon detachment and two orders of magnitude variations across diverse morphologies

The dynamic mechanical processes can notably impact the van der Waals (vdW) interaction at nanoscale contact interface and further interfacial thermal transport, but the experimental study is challenging. Here, by integrating a movable nanoprobe within an electron microscope, we dynamically adjusted the contact and detachment processes of vdW contact between two carbon nanotubes (CNTs), while measuring the thermal contact resistance (TCR) in situ with a nanofabricated thermal sensor. The TCR was found to span approximately two orders of magnitude at the moments when two CNTs just came into contact or detached. Surprisingly, during the initial stage of detachment, we observed that TCR unexpectedly further decreased by 65% instead of increasing. This decrease is attributed to the subtle alteration of exact contact interface in the circumferential direction, induced by the real-time observed rotation during the detachment process. A two-order magnitude difference in TCR for the diverse morphologies in static equilibrium between the same pair of CNTs due to the non-uniformity of the CNT surface structures can also support it. Our work provides valuable insights for dynamically modulating nanoscale interfacial thermal transport in various applications.

Emergence of quantum Griffiths singularity in disordered TiN thin films

The association of quantum Griffiths singularity (QGS) to the magnetic-field-induced superconductor-metal transition predicts the unconventional diverging behaviour of dynamical critical exponent in low disorder crystalline two-dimensional superconductors. But whether this state exists in the superconducting systems exhibiting superconductor-insulator transition remains elusive. Here, we report the emergence of quantum Griffiths singularity in ultrathin disordered TiN thin films with more than two orders of magnitude variation in their normal state resistance. For both superconductor-metal transition and superconductor-insulator transition types, a diverging critical exponent is observed while approaching the quantum phase transition. Further, the magnetoresistance isotherms obey a direct activated scaling governed by an infinite-randomness fixed critical point. Finally, this work establishes the robustness of the QGS phenomenon towards a wide range of temperature and also towards a wide range of disorder strength as correlated with the normal state resistance.

Detection of a cyclotron line in the Be X-ray pulsar IGR J06074+2205

Context. IGR J0607.4+2205 is a transient Be X-ray binary discovered two decades ago. IGR J0607.4+2205 underwent an outburst in 2023 during which it was observed twice with NuSTAR. Aims. The main goal of this work is to model the broadband X-ray spectrum of IGR J0607.4+2205 during the outburst and to study the variations of the spectral and timing features at different intensities. Methods. We extracted the light curve and spectrum of the source from the two NuSTAR observations carried out during the recent outburst in the energy range of 3−78 keV. We used the epoch folding technique to find pulsation from the source and to study the changes in emission characteristics from the source with energy across an order of magnitude variation in source luminosity. Results. IGR J0607.4+2205 shows pulsations with a period of ∼347.6 s during both the observations, with a pulse fraction of ≥50%. The broadband spectrum of the source was modelled using a power-law continuum with a high-energy cutoff. During the first observation, a cyclotron absorption line at ∼51 keV was also present in the source with an optical depth of ∼1.3. However, no cyclotron line feature was detected in the second observation when the source was an order of magnitude fainter. Additionally, soft excess was detected in the second observation, which was modelled with a black body component emerging from close to the neutron star (NS). Conclusions. We report the first ever detection of a cyclotron line in the broadband spectrum of IGR J0607.4+2205 centred at 51 ± 1 keV. The magnetic field strength of the NS is estimated to be ∼4 × 1012 G from the centroid energy of the absorption line. A significant change is observed in the pulse profile with luminosity during the decay of the outburst, indicating an associated change in the beaming pattern.

How can acoustic measurements help us understand severe weather phenomena such as lightning?

Lightning is an indicator for monitoring severe weather events like heavy precipitation, flash floods, hail… It is also a climate variable for monitoring global warming. Lightning emits light, sound and radioelectromagnetic fields, allowing remote detection and analysis. Acoustic measurements can be used to, for instance, track global warming over more than 70 years via the keraunic level (the number of thunderstorm days per year in a specific location), or detect and monitor severe weather events such as cyclones, e.g. the Medicanes, or characterize optical phenomena such as sprites associated with violent thunderstorms, or highlight temporal changes in the upper layers of the atmosphere, such as the semi-annual oscillation of stratospheric winds in tropical zones. At closer ranges, less than 30 km, acoustic network measurements complement electromagnetic observations to reconstruct the 3D structure of cloud-to-ground and intra-cloud discharges. Recently, it has been shown possible to provide the 3D structure of acoustic power within the lightning source. From flash to flash, this power shows four orders of magnitude variations, similarly to electromagnetism or optics. Moreover, it outlines that large variations of power also exist even within a lightning flash, reflecting heterogeneities in conductivity within the discharge.

3D Stresses and Velocities Caused by Continental Plateaus: Scaling Analysis and Numerical Calculations With Application to the Tibetan Plateau

AbstractUnderstanding stresses is crucial for geodynamics since they govern rock deformation and metamorphic reactions. However, the magnitudes and distribution of crustal stresses are still uncertain. Here, we use a 3D numerical model in spherical coordinates to investigate stresses and velocities that result from lateral crustal thickness variations around continental plateaus like those observed for the Tibetan plateau. We do not consider any far‐field deformation so that the plateau deforms by horizontal dilatation and vertical thinning. We assume viscous creep, a simplified plateau geometry, and simplified viscosity and density distributions to couple the numerical results with a scaling analysis. Specifically, we study the impact of the viscosity ratio between crust and lithospheric mantle, a rectangular plateau corner, a stress‐dependent power‐law flow law and Earth's double curvature on the crustal stress field and horizontal velocities. Two orders of magnitude variation in crustal and lithospheric mantle viscosities change the maximum crustal differential stress only by a factor of ≈2. We derive simple analytical estimates for the crustal deviatoric stress and horizontal velocity which agree to first order with 3D numerical calculations. We apply these estimates to calculate the average crustal viscosity in the eastern Tibetan plateau as ≈1022 Pa · s. Furthermore, our results show that a corner strongly affects the stress distribution, particularly the shear stresses, while Earth's curvature has a minor impact on the stresses. We further discuss potential implications of our results to strike‐slip faulting and fast exhumation around the Tibetan plateau's syntaxes.

Devolatilization of extrasolar planetesimals by 60Fe and 26Al heating

ABSTRACT Whilst the formation of Solar system planets is constrained by meteoritic evidence, the geophysical history of low-mass exoplanets is much less clear. The bulk composition and climate states of rocky exoplanets may vary significantly based on the composition and properties of the planetesimals they form. An important factor influenced by planetesimal composition is water content, where the desiccation of accreting planetesimals impacts the final water content of the resultant planets. While the inner planets of the Solar system are comparatively water-poor, recent observational evidence from exoplanet bulk densities and planetary formation models suggests that rocky exoplanets engulfed by substantial layers of high-pressure ices or massive steam atmospheres could be widespread. Here, we quantify variations in planetesimal desiccation due to potential fractionation of the two short-lived radioisotopes 26Al and 60Fe relevant for internal heating on planetary formation time-scales. We focus on how order of magnitude variations in 60Fe can affect the water content of planetesimals, and how this may alter the formation of extrasolar ocean worlds. We find that heating by 26Al is the dominant cause of planetesimal heating in any Solar system analogue scenario, thus validating previous works focussing only on this radioisotope. However, 60Fe can become the primary heating source in the case of high levels of supernova enrichment in massive star-forming regions. These diverging scenarios can affect the formation pathways, bulk volatile budget, and climate diversity of low-mass exoplanets.

The distribution of depth, volume, and basin shape for lakes in the conterminous United States

AbstractDepth regulates many attributes of aquatic ecosystems, but relatively few lakes are measured, and existing datasets are biased toward large lakes. To address this, we used a large dataset of maximum (Zmax; n = 16,831) and mean (Zmean; n = 5,881) depth observations to create new depth models, focusing on lakes < 1,000 ha. We then used the models to characterize patterns in lake basin shape and volume. We included terrain metrics, water temperature and reflectance, polygon attributes, and other predictors in a random forest model. Our final models generally outperformed existing models (Zmax ; root mean square error [RMSE] = 8.0 m and Zmean ; RMSE = 3.0 m). Our models show that lake depth followed a Pareto distribution, with 2.8 orders of magnitude fewer lakes for an order of magnitude increase in depth. In addition, despite orders of magnitude variation in surface area, most size classes had a modal maximum depth of ~ 5 m. Concave (bowl‐shaped) lake basins represented 79% of all lakes, but lakes were more convex (funnel‐shaped) as surface area increased. Across the conterminous United States, 9.8% of all lake water was within the top meter of the water column, and 48% in the top 10 m. Excluding the Laurentian Great Lakes, we estimate the total volume in the conterminous United States is 1,057–1,294 km3, depending on whether Zmax or Zmean was modeled. Lake volume also exhibited substantial geographic variation, with high volumes in the upper Midwest, Northeast, and Florida and low volumes in the southwestern United States.

Fluorescence lifetime Hong-Ou-Mandel sensing

Fluorescence Lifetime Imaging Microscopy in the time domain is typically performed by recording the arrival time of photons either by using electronic time tagging or a gated detector. As such the temporal resolution is limited by the performance of the electronics to 100’s of picoseconds. Here, we demonstrate a fluorescence lifetime measurement technique based on photon-bunching statistics with a resolution that is only dependent on the duration of the reference photon or laser pulse, which can readily reach the 1–0.1 picosecond timescale. A range of fluorescent dyes having lifetimes spanning from 1.6 to 7 picoseconds have been here measured with only ~1 s measurement duration. We corroborate the effectiveness of the technique by measuring the Newtonian viscosity of glycerol/water mixtures by means of a molecular rotor having over an order of magnitude variability in lifetime, thus introducing a new method for contact-free nanorheology. Accessing fluorescence lifetime information at such high temporal resolution opens a doorway for a wide range of fluorescent markers to be adopted for studying yet unexplored fast biological processes, as well as fundamental interactions such as lifetime shortening in resonant plasmonic devices.

The passive sampler assisted human exposure risk characterization for tetrachloroethene soil vapor intrusion scenario

The potential human health risks associated with soil vapor intrusion and volatile organic compounds (VOCs) exposure were characterized at an industrialized site by the quantification of gaseous VOCs in soil pores using a passive sampling technique. The gaseous tetrachloroethene (PCE) in soil pores varied between 12 and 5,400 μg m−3 showing 3 orders of magnitude variation with dependence on groundwater PCE concentrations. Though the PCE concentration in the air only varied between 0.45 and 1.5 μg m−3 showing negligible variations compared to the variation observed in soil pores. The PCE concentration in the air varied between 0.45 and 1.5 μg m−3. The calculation of fugacity suggested that the PCE in the test site originated from groundwater. Measured PCE in groundwater ranged from 14 to 2,400 times higher than PCE in soil gas. This indicates that conducting a vapor intrusion risk assessment using passive soil gas sampling is critical for accurate risk characterization and assessment. Estimated PCE inhalation cancer risks for street cleaners and indoor residents varied between 10−6 and 10−4 with a low plausible hazard, and between 10−3 and 10−2 with a high risk, respectively. The results of this study demonstrate that passive sampling offers a significantly lower cost and labor-intensive approach compared to traditional methods for assessing pollution distribution in contaminated sites and characterizing risks. This highlights the potential for wider application of passive sampling techniques in environmental studies.

The effect of in-situ metasomatism on the electrical resistivity of the lower crust

Improved estimates of composition and temperature in the lower crust are vital in characterising crustal rheology and better understanding tectonic processes. Fluids introduced into the lower crust during collisional events leave behind large domains of metasomatised crust which are long-lived and should be observable via magnetotelluric sounding. With this in mind, the electrical conductivity of a subduction-related eclogite and its anhydrous, anorthositic granulite protolith were experimentally determined at atmospheric pressure and lower crustal temperatures (773–1123 K). Complex impedance spectra were collected between 20 Hz and 2 MHz while oxygen fugacity was controlled about the quartz-fayalite-magnetite (QFM) buffer using a CO:CO2 gas mix. At <1000 K, both samples are characterised by impurity conduction with low observed activation enthalpies of 0.48 ± 0.03 eV and 0.39 ± 0.02 eV for the granulite and eclogite respectively. High temperature data from the granulite (>1000 K) indicates a switch to small polarons with an activation enthalpy of 1.02 ± 0.02 eV. Results indicate that conversion of Fe-poor mafic granulite to eclogite does not enhance conductivity at lower crustal temperatures. Comparisons with previous experiments reveal a much stronger relationship between conductivity and FeOT than previously anticipated. Modelling indicates that an increase in FeOT of 2 wt% is equivalent to a temperature increase of 100 K and reasonable variations in FeOT in the lower crust may account for ∼4 orders of magnitude variation in conductivity. Elevated FeOT up to 20 wt% may enhance conductivity to ∼100 S m−1 at a moderate 873 K. A system of linear equations is derived to estimate iron content, electrical conductivity or temperature within dry, mafic lower crust. For the temperature range 773–973 K, conductivity may be predicted to within 0.16 log units using log σ(T,FeOT) = 0.006 T + 0.3FeOT − 11.35. Under the same conditions, FeOT may be predicted to within 0.51 wt% using FeOT (T,σ) = 37–0.0193 T + 3.24 log σ. Finally, lower crustal temperatures may be estimated to within 24 K using T(FeOT,σ) = 1728 − 42FeOT + 139 log σ.

Transport and distribution of residual nitrogen in ion-adsorption rare earth tailings

A large amount of nitrogen remains in ion-absorption rare earth tailings with in-situ leaching technology, and it continually ends up in groundwater sources. However, the distribution and transport of ammonium nitrogen (NH4+-N) and nitrate nitrogen (NO3−-N) across tailings with both depth and hill slopes is still unknown. In this study, the amount of NH4+-N and nitrate nitrogen (NO3−-N) was determined in tailings, and a soil column leaching experiment, served to assess the transport and distribution following mine closure. Firstly, a high concentration of NH4+-N in the leachate at the initial leaching stage was detected, up to 2000 mg L−1, and the concentration of NH4+-N clearly diminished as time passed. Meanwhile, the NH4+-N contents remained relatively high in soil. Secondly, both the content of NH4+-N and NO3−-N varied greatly according to vertical distribution after leaching lasting several years. The amounts of NH4+-N and NO3−-N in surface soil were much smaller than those in deep soil, with 3–4 orders of magnitude variation with depth. Thirdly, when disturbed by NH4+-N, the pH not only diminished but also changed irregularly as depth increased. Fourthly, although the amount of NO3−-N was smaller than that of NH4+-N, both their distribution trend was similar with depth. In fact, NH4+-N and NO3−-N were significantly correlated but this declined from the knap to the piedmont. Based on these results, it is suggested that mining activity could cause nitrogen to be dominated by NH4+-N and acidification in a tailing even if leaching occurs over several years. NO3−-N derived from NH4+-N transports easily and it becomes the main nitrogen pollutant with the potential to be a long-lasting threat to the environment around a mine.

X-ray emission from pre-main sequence stars with multipolar magnetic fields

ABSTRACT The large-scale magnetic fields of several pre-main sequence (PMS) stars have been observed to be simple and axisymmetric, dominated by tilted dipole and octupole components. The magnetic fields of other PMS stars are highly multipolar and dominantly non-axisymmetric. Observations suggest that the magnetic field complexity increases as PMS stars evolve from Hayashi to Henyey tracks in the Hertzsprung–Russell diagram. Independent observations have revealed that X-ray luminosity decreases with age during PMS evolution, with Henyey track PMS stars having lower fractional X-ray luminosities (LX/L*) compared to Hayashi track stars. We investigate how changes in the large-scale magnetic field topology of PMS stars influences coronal X-ray emission. We construct coronal models assuming pure axisymmetric multipole magnetic fields, and magnetic fields consisting of a dipole plus an octupole component only. We determine the closed coronal emitting volume, over which X-ray-emitting plasma is confined, using a pressure balance argument. From the coronal volumes, we determine X-ray luminosities. We find that LX decreases as the degree ℓ of the multipole field increases. For dipole plus octupole magnetic fields, we find that LX tends to decrease as the octupole component becomes more dominant. By fixing the stellar parameters at values appropriate for a solar mass PMS star, varying the magnetic field topology results in two orders of magnitude variation in LX. Our results support the idea that the decrease in LX as PMS stars age can be driven by an increase in the complexity of the large-scale magnetic field.

Hydrological and Geological Controls for the Depth Distribution of Dissolved Oxygen and Iron in Silicate Catchments

AbstractDissolved Oxygen (DO) plays a key role in reactive processes and microbial dynamics in the critical zone. Recent observations showed that fractures can provide rapid pathways for oxygen penetration in aquifers, triggering unexpected biogeochemical processes. In the shallow subsurface, DO reacts with electron donors, such as Fe2+ coming from mineral dissolution. Yet, little is known about the factors controlling the spatial heterogeneity and distribution of oxygen with depth. Here we present a reduced analytical model describing the coupled evolution of DO and Fe2+ as a function of fluid travel time in silicate catchments. Our model, validated from fully resolved reactive transport simulations, predicts a linear decay of DO with time, followed by a rapid non‐linear increase of Fe2+ concentrations up to a far‐from‐equilibrium steady‐state. The relative effects of geological and hydrological forcings are quantified through a Damköhler number (Da) and a lithological number (Λ). We use this framework to investigate the depth distribution of DO and Fe2+ in two catchments with similar environmental contexts but contrasted hydrochemical properties. We show that hydrochemical differences are explained by small variations in Da but orders of magnitude variations in Λ. Therefore, we demonstrate that the hydrological and geological drivers controlling hydrochemistry in silicate catchments can be discriminated by analyzing jointly the O2 and Fe2+ evolution with depth. These findings provide a new conceptual framework to understand and predict the evolution of DO in modern groundwater, which plays an important role in critical zone processes.

Key factors for regulation of cell morphology in supercritical CO2 direct rapid depressurization foaming silicone rubber process

Silicone rubber foam was prepared by direct rapid depressurization foaming process using supercritical CO2 as foaming agent. It was found that under high temperature and pressure, the dissolution of CO2 and the vulcanization reaction occurred simultaneously. The vulcanization degree range with good cell morphology was between 19.8% and 48.2%. When the saturation pressure exceeded 16 MPa, the cell morphology did not depend on foaming pressure. When the temperature was increased from 110 °C to 140 °C, the degree of vulcanization increased from 1.8% to 60.5%, and the cell size ranged from 13.9 µm to 646.4 µm, with an order of magnitude variation in cell density. This study identified the key control factors for supercritical CO2 relief foaming of silicone rubber and provided a fast and efficient preparation method, as well as theoretical guidance, for obtaining lightweight microporous silicone rubber foams.

Ocular following responses of the marmoset monkey are dependent on postsaccadic delay, spatiotemporal frequency, and saccade direction.

Ocular following is a short-latency, reflexive eye movement that tracks wide-field visual motion. It has been studied extensively in humans and macaques and is an appealing behavior for studying sensory-motor transformations in the brain because of its rapidity and rigidity. We explored ocular following in the marmoset, an emerging model in neuroscience because their lissencephalic brain allows direct access to most cortical areas for imaging and electrophysiological recordings. In three experiments, we tested ocular following responses in three adult marmosets. First, we varied the delay between saccade end and stimulus motion onset, from 10 to 300 ms. As in other species, tracking had shorter onset latencies and higher eye speeds with shorter postsaccadic delays. Second, using sine-wave grating stimuli, we explored the dependence of eye speed on spatiotemporal frequency. The highest eye speed was evoked at ∼16 Hz and ∼0.16 cycles per degree (cpd); however, the highest gain was elicited at ∼1.6 Hz and ∼1.2 cpd. The highest eye speed for each spatial frequency was observed at a different temporal frequency, but this interdependence was not consistent with complete speed tuning of the ocular following response. Finally, we found the highest eye speeds when saccade and stimulus motion directions were identical, although latencies were unaffected by direction difference. Our results showed qualitatively similar ocular following in marmosets, humans, and macaques, despite over an order of magnitude variation in body and eye size across species. This characterization will help future studies examining the neural basis of sensory-motor transformations.NEW & NOTEWORTHY Previous ocular following studies focused on humans and macaques. We examined the properties of ocular following responses in marmosets in three experiments, in which postsaccadic delay, spatial-temporal frequency of stimuli, and congruence of saccade and motion directions were manipulated. We have demonstrated short-latency ocular following in marmosets and discuss the similarities across three species that vary markedly in eye and head size. Our findings will help future studies examining the neural mechanism of sensory-motor transformations.

The Explosive Activity of the 2021 Tajogaite Eruption (La Palma, Canary Islands, Spain)

AbstractThe explosive activity of the 2021 Tajogaite eruption eludes pigeonholing into well‐defined eruption styles, with a variety of pyroclast ejection modes occurring both alternately and simultaneously at multiple vents. Visually, we defined four endmembers of explosive activity, referred to as fountaining, spattering, ash‐poor jets and ash‐rich jets. To capture the physical parameters of these activities, we deployed a camera array including one high‐speed camera and three high‐definition cameras in two field campaigns. Transitions between and fluctuations within activity occurred at the time scale of minutes to hours, likely driven by the same shallow conduit and vent processes controlling Strombolian activity at other volcanoes, but at higher gas and magma fluxes. From a physical standpoint, mean pyroclast rise velocity ranged 5–50 m/s, maximum ejection velocity 10–220 m/s, and sub‐second mass flux of lapilli to bomb‐sized pyroclasts at the vent 0.2–200 × 103 kg/s. The largest mass flux occurred during fountaining, which contributed by far more than other activities to cone building. All explosive activity exhibited well‐defined pyroclast ejection pulses, and we found a positive correlation between the occurrence rate of ejection pulses and maximum pyroclast ejection velocity. Despite orders of magnitude variations, physical parameters shift gradually with no boundary from one activity endmember to another. As such, attributing this explosive activity specifically to any currently defined style variations is arbitrary and potentially misleading. The highly variable explosive activity of the Tajogaite eruption recalls previous definitions of violent Strombolian eruptions, an eruption style whose pyroclast ejection dynamics, however, were so far largely undefined.

Are We Recording? Putting Embayment Speedometry to the Test Using High Pressure‐Temperature Decompression Experiments

AbstractDespite its increasing application to estimate magma decompression rates for explosive eruptions, the embayment speedometer has long awaited critical experimental evaluation. We present the first experimental results on the fidelity of natural quartz‐hosted embayments in rhyolitic systems as recorders of magma decompression. We conducted two high pressure‐temperature isobaric equilibrium experiments and 13 constant‐rate, continuous isothermal decompression experiments in a cold‐seal pressure vessel where we imposed rates from 0.005 to 0.05 MPa s−1 in both H2O‐saturated and mixed‐volatile (H2O + CO2)‐saturated systems. In both equilibrium experiments, we successfully re‐equilibrated embayment melt to new fluid compositions at 780°C and 150 MPa, confirming the ability of embayments to respond to and record changing environmental conditions. Of the 32 glassy embayments recovered, seven met the criteria previously established for successful geospeedometry and were thus analyzed for their volatile (H2O ± CO2) concentrations, with each producing a good model fit and recovering close to the imposed decompression rate. In one H2O‐saturated experiment, modeling H2O concentration gradients in embayments from three separate crystals resulted in best‐fit decompression rates ranging from 0.012 to 0.021 MPa s−1, in close agreement with the imposed rate (0.015 MPa s−1) and attesting to the reproducibility of the technique. For mixed‐volatile experiments, we found that a slightly variable starting fluid composition (2.4–3.5 wt.% H2O at 150 MPa) resulted in good fits to both H2O + CO2 profiles. Overall our experiments provide confidence that the embayment is a robust recorder of constant‐rate, continuous decompression, with the model successfully extracting experimental conditions from profiles representing nearly an order of magnitude variation (0.008–0.05 MPa s−1) in decompression rate.