Decompression Rate Research Articles

Study on Overburden Movement and Fissure Evolution Law of Protective Layer Mining in Shallow Coal Seam

This study aims to effectively solve the problem of the destruction of the coal roof and floor overlying rock after mining the protective layer, and determines whether the gas in the protected layer can be effectively released. We do this based on the engineering background of the Weng’an Coal Mine; research and analysis of the movement of the roof and floor overlying rocks; the evolution of cracks and the pressure relief characteristics of the protected layer after mining the protective layer; and through theoretical analysis and similar simulation experiments. Through numerical simulation, it was found that the protected layer was depressurized due to the mining of the protective layer, and the decompression rate of the protected layer was 0.2–0.8. In addition, the overall expansion rate of the protected layer was greater than the requirements of the “Detailed Rules for Prevention and Control of Coal and Gas Outbursts” for coal mines, and the investigation of the residual gas pressure and content of the protected layer revealed that the protected coal seam had been mined in the upper protective layer coal face. The gas pressure dropped to 50.7% of the original coal seam gas pressure, the rate of decrease was 49.3%, the residual gas content dropped by 68.67%, and the gas concentration in the return airway was 0.31% on average, meeting the national regulations that require its value to be less than or equal to 1%. The study comprehensively demonstrates that mining of the protective layer is beneficial to the release of gas from the protected layer, and provides a practical reference for coal and gas outbursts in mines.

118 Delayed Cranial Decompression Rates After Initiation of Unfractionated Heparin Versus Low-Molecular-Weight Heparin in Traumatic Brain Injury

INTRODUCTION: Both unfractionated heparin (UH) and low-molecular weight heparin (LMWH) are routinely used prophylactically after traumatic brain injury (TBI) to prevent deep vein thrombosis. Their comparative risk for intracranial hemorrhage (ICH) development or worsening necessitating cranial decompression after prophylaxis initiation is unclear. Furthermore, the absence of a specific antidote for LMWH may lead to UH being used more often for high-risk patients. METHODS: We compared the incidence of delayed cranial decompression occurring after initiation of prophylactic UH vs. LMWH using the National Trauma Data Bank. Cranial decompression procedures included craniotomy, craniectomy, and external ventricular drain placement. Multiple imputation was utilized for missing data. To account for selection bias between UH and LMWH, we conducted propensity score matching using factors that were significantly different between the two groups. The matched UH and LMWH groups were then compared using logistic regression for the primary outcome of post-prophylaxis cranial decompression. RESULTS: A total of 218,594 TBI patients were included, with 61,998 (28.3%) receiving UH and 156,596 (71.7%) receiving LMWH as DVT prophylaxis. The UH group had significantly higher patient age, BMI, comorbidity rates, injury severity score, and worse motor Glasgow coma scale. After matching the UH and LMWH groups for these factors, logistic regression demonstrated lower rates of post-prophylaxis cranial decompression for the LMWH group (OR 0.13, 95% CI 0.11-0.16, P < 0.001). CONCLUSION: Despite the absence of a specific antidote, LMWH was associated with substantially lower rates of post-DVT-prophylaxis cranial decompression. This indicates that UH may not be the safer alternative in TBI patients at high risk for intracranial hemorrhagic complications.

The late Holocene Nealtican lava-flow field, Popocatépetl volcano, central Mexico: Emplacement dynamics and future hazards

Abstract Popocatépetl, one of the most hazardous volcanoes worldwide, poses significant threats for nearby populations in central Mexico. Therefore, it is important to reconstruct its eruptive history, including estimates of lava-flow emplacement times and their rheological properties. These studies define possible future eruptive scenarios and are necessary to mitigate the risk. Stratigraphic studies of the cal 350–50 B.C. Lorenzo Plinian pumice sequence indicate that effusive activity (Nealtican lava-flow field) occurred shortly after explosive activity, reflecting drastic changes in the eruptive dynamics. It was likely due to the efficient degassing of the magma during the Plinian phase and a decrease of magma ascent and decompression rates. Magma mixing, fractional crystallization, and a minor crust assimilation are the processes controlling the differentiation of the Nealtican lavas. We used lava chemical and mineralogical composition to estimate lava-flow viscosities, and used high-resolution elevation data to estimate emplacement times. Results indicate that lava viscosities of andesites and dacites ranged from 109 to 1012 Pa·s and emplacement durations were between ~1 and ~29 years, depending on the flow unit and morphological method employed. Considering the entire volume of emitted lava (4.2 km3) and a mean output rate of ~1 m3/s to ~15 m3/s, we estimated that the effusive phase that produced the Nealtican lava-flow field may have lasted ~35 years. This eruption had a considerable impact on pre-Hispanic settlements around the volcano, whose population exodus and relocation probably contributed to the rise of important cities in central Mexico, such as Teotihuacán and Cholula.

In situx-ray diffraction study of dynamically compressedα-cristobalite using a dynamic diamond anvil cell

In this study we present results of the dynamic compression of $\ensuremath{\alpha}$-cristobalite up to a pressure of 106 GPa with the use of the dynamic diamond anvil cell. X-ray diffraction images were recorded at different ramp compression and decompression rates to investigate in situ the high-pressure phase transitions of $\ensuremath{\alpha}$-cristobalite. Our results suggest that the pressure onset of the phase transformation of $\ensuremath{\alpha}$-cristobalite to cristobalite II, cristobalite X-I, and ultimately to seifertite ($\ensuremath{\alpha}\text{\ensuremath{-}}{\mathrm{PbO}}_{2}$ type ${\mathrm{SiO}}_{2}$) is dependent on the applied compression rates and stress conditions of the experiment. Increasing compression rates in general shift the studied phase transitions to higher pressures. Furthermore, our results indicate for single crystals under hydrostatic conditions a suppression of a phase transition from cristobalite X-I to seifertite at pressures of up to 82 GPa.

Crystallization of peralkaline rhyolitic magmas: pre- and syn-eruptive conditions of the Pantelleria system

Pantelleritic magmas are low-viscosity peralkaline rhyolites which exhibit large differences in eruptive style (explosive to effusive). The processes that promote fragmentation and explosive eruptions of pantelleritic magma remain subject to debate, but undoubtedly variations of magma viscosity during magma ascent and degassing contribute to differences in eruptive style. Because crystallization can significantly influence magma rheology, we present a review of equilibrium and disequilibrium crystallization experiments of pantellerites, focusing on the crystallization of the main phases, alkali feldspar, and (lesser) clinopyroxene. Our analysis of data for several explosive pantelleritic eruptions on Pantelleria suggests pre-eruptive pressures of 50–100 MPa, temperatures of 700–800 °C for water-saturated conditions. Given these conditions, we show that the low pre-eruptive crystal fractions (0.08 to 0.15), temperatures between 700 and 800 °C, and the decrease of melt H2O content during magma ascent/decompression can promote a significant change in viscosity (up to 106–107 Pa·s), leading to magma brittle fragmentation and explosive eruptions. Because of their typical range of viscosity, pantelleritic magmas may show greater variations in eruptive style due to differences in ascent (decompression) rate when compared with metaluminous rhyolites.

Coalescence of two growing bubbles in a Hele\u2013Shaw cell

An understanding of the dynamics of growth-driven coalescence is important in diverse fields across natural science and engineering. Motivated by the bubble coalescence in magma during volcanic eruptions, we study both experimentally and theoretically the coalescence of two growing bubbles in a Hele–Shaw cell. In our system, bubbles grow by gas expansion due to decompression and the diffusional influx of dissolved gas in the liquid. Our experiments show that the evolution of film thickness and bubble shape depends on viscosity, decompression rate, and cell gap. Through a scaling analysis and a perturbation approximation, we find that the hydrodynamic interaction between two bubbles is characterized by a film capillary number Ca_f=(eta {dot{R}}/sigma )(R/D)^2 depending on viscosity eta, bubble radius R, growth rate {dot{R}}, interfacial tension sigma, and cell gap D. The experimental results demonstrate that the film capillary number solely determines the bubble distortion just before coalescence. Under our experimental conditions, bubble coalescence occurs below a critical value of a nominal film capillary number defined as a film capillary number evaluated when two undeformed circular bubbles come into contact.

Analyzing giant pituitary adenomas: An 8-year review (2012–2020) at a reference center in Brazil

PurposeThis study aimed to review the cases of giant adenomas that were operated on from 2012 to 2020 and to analyze the epidemiological profile, complications, and resection rates using the transseptal/transnasal endoscopy technique. We also compared the results with data from revised literature. MethodsThis is an observational, retrospective study includes a review of the medical records of 26 patients diagnosed with giant adenomas (diameter > 4 cm or volume >10 cm3) who underwent 28 surgical procedures. ResultsOf the 57 patients operated for pituitary adenoma, 26 (50.8%) had giant adenomas. The mean volume was 17.28 cm3 (95% confidence interval [CI], 8.3359–26.2241). Moreover, 64.28% of the patients were graded Knosp 3 (p < 0.0001). Most cases were of nonsecretory adenomas (88.46%). Visual impairment was present in 89.2% of the patients and hormonal deficit and headache affected 53.5% of them. The visual impairment improved in 60% of the patients. The most common surgical complication was cerebrospinal fluid fistula (10.71%). Tumor resection > 90% was achieved in 53.56% of the cases, and the mean resection rate was 78.36% (95% CI, 71.316–87.956). ConclusionsThe endoscopic endonasal technique is a good treatment option for giant adenomas, showing satisfactory optic apparatus decompression rates and a low incidence of complications when performed by surgeons with expertise in this approach.

Millisecond time-resolved synchrotron radiation X-ray diffraction and high-pressure rapid compression device and its application

Non-equilibrium transition dynamics under high pressure depends on temperature, pressure and (de)compression rate. The studies require combination of time-resolved probe and rapid compression device on different time scales. Here we report the time-resolved X-ray diffraction (XRD) and dynamic diamond anvil cell (dDAC) system, which were recently developed at the BL15U1 beamline of Shanghai Synchrotron Radiation Facility (SSRF). There are two rapid loading methods for dDAC. One uses membrane control and the other is piezoelectric actuator driven dDAC. Both methods can dynamically compress the DAC sample chamber up to 300 GPa on millisecond scale (20 μm culet is used), and the time-resolved XRD data are obtained correspondingly. A new type of piezoelectric ceramic dDAC is designed with single-side drive or double-side drive, which allows us to realize extremely high pressure (above 300 GPa) with a fast compression rate of 13 TPa/s. During the rapid compression process, the X-ray diffraction spectra are collected continuously and simultaneously. The XRD detector is Pilatus 3X 900K, which has 2-ms resolution with 500 kHz frame rate. The millisecond time-resolved XRD and high pressure rapid compression system developed at BL15U1 of SSRF enrich the high-pressure experimental methods and enable the beamline to carry out ultra-high pressure experiments, non-equilibrium phase transition and relevant scientific researches.

Downward-propagating eruption following vent unloading implies no direct magmatic trigger for the 2018 lateral collapse of Anak Krakatau

The lateral collapse of Anak Krakatau volcano, Indonesia, in December 2018 highlighted the potentially devastating impacts of volcanic edifice instability. Nonetheless, the trigger for the Anak Krakatau collapse remains obscure. The volcano had been erupting for the previous six months, and although failure was followed by intense explosive activity, it is the period immediately prior to collapse that is potentially key in providing identifiable, pre-collapse warning signals. Here, we integrate physical, microtextural and geochemical characterisation of tephra deposits spanning the collapse period. We demonstrate that the first post-collapse eruptive phase (erupting juvenile clasts with a low microlite areal number density and relatively large microlites, reflecting a crystal-growth dominated regime) is best explained by instantaneous unloading of a relatively stagnant upper conduit. This was followed by the second post-collapse phase, on a timescale of hours, which tapped successively hotter and deeper magma batches, reflected in increasing plagioclase anorthite content and more mafic glass compositions, alongside higher calculated ascent velocities and decompression rates. The characteristics of the post-collapse products imply downward propagating destabilisation of the magma storage system as a response to collapse, rather than pre-collapse magma ascent triggering failure. Importantly, this suggests that the collapse was a consequence of longer-term processes linked to edifice growth and instability, and that no indicative changes in the magmatic system could have signalled the potential for incipient failure. Therefore, monitoring efforts may need to focus on integrating short- and long-term edifice growth and deformation patterns to identify increased susceptibility to lateral collapse. The post-collapse eruptive pattern also suggests a magma pressurisation regime that is highly sensitive to surface-driven perturbations, which led to elevated magma fluxes after the collapse and rapid edifice regrowth. Not only does rapid regrowth potentially obscure evidence of past collapses, but it also emphasises the finely balanced relationship between edifice loading and crustal magma storage.

Mafic explosive volcanism at Llaima Volcano: 3D x-ray microtomography reconstruction of pyroclasts to constrain shallow conduit processes

Mafic volcanic activity is dominated by effusive to mildly explosive eruptions. Plinian and ignimbrite-forming mafic eruptions, while rare, are also possible; however, the conditions that promote such explosivity are still being explored. Eruption style is determined by the ability of gas to escape as magma ascends, which tends to be easier in low-viscosity, mafic magmas. If magma permeability is sufficiently high to reduce bubble overpressure during ascent, volatiles may escape from the magma, inhibiting violent explosive activity. In contrast, if the permeability is sufficiently low to retain the gas phase within the magma during ascent, bubble overpressure may drive magma fragmentation. Rapid ascent may induce disequilibrium crystallization, increasing viscosity and affecting the bubble network with consequences for permeability, and hence, explosivity. To explore the conditions that promote strongly explosive mafic volcanism, we combine microlite textural analyses with synchrotron x-ray computed microtomography of 10 pyroclasts from the 12.6 ka mafic Curacautín Ignimbrite (Llaima Volcano, Chile). We quantify microlite crystal size distributions (CSD), microlite number densities, porosity, bubble interconnectivity, bubble number density, and geometrical properties of the porous media to investigate the role of magma degassing processes at mafic explosive eruptions. We use an analytical technique to estimate permeability and tortuosity by combing the Kozeny-Carman relationship, tortuosity factor, and pyroclast vesicle textures. The groundmass of our samples is composed of up to 44% plagioclase microlites, > 85% of which are < 10 µm in length. In addition, we identify two populations of vesicles in our samples: (1) a convoluted interconnected vesicle network produced by extensive coalescence of smaller vesicles (> 99% of pore volume), and (2) a population of very small and completely isolated vesicles (< 1% of porosity). Computed permeability ranges from 3.0 × 10−13 to 6.3 × 10−12 m2, which are lower than the similarly explosive mafic eruptions of Tarawera (1886; New Zealand) and Etna (112 BC; Italy). The combination of our CSDs, microlite number densities, and 3D vesicle textures evidence rapid ascent that induced high disequilibrium conditions, promoting rapid syn-eruptive crystallization of microlites within the shallow conduit. We interpret that microlite crystallization increased viscosity while simultaneously forcing bubbles to deform as they grew together, resulting in the permeable by highly tortuous network of vesicles. Using the bubble number densities for the isolated vesicles (0.1-3−3 × 104 bubbles per mm3), we obtain a minimum average decompression rate of 1.4 MPa/s. Despite the textural evidence that the Curacautín magma reached the percolation threshold, we propose that rapid ascent suppressed outgassing and increased bubble overpressures, leading to explosive fragmentation. Further, using the porosity and permeability of our samples, we estimated that a bubble overpressure > 5 MPa could have been sufficient to fragment the Curacautín magma. Other mafic explosive eruptions report similar disequilibrium conditions induced by rapid ascent rate, implying that syn-eruptive disequilibrium conditions may control the explosivity of mafic eruptions more generally.

Syn-Eruptive Conditions of the AD 1530 Sub-Plinian Eruption of La Soufrière of Guadeloupe (Lesser Antilles)

A prerequisite in refining volcanic hazard at explosive volcanoes is a better quantification of the timescales of the syn-eruptive processes, such as magma degassing and crystallization prior to eruption. To this aim, new data on the matrices (microlites, residual glasses, and bubbles) of pumice, scoria, and dense clasts erupted during the AD 1530 andesitic eruption of La Soufrière of Guadeloupe are combined with published data from phase-equilibrium and kinetic experiments, in order to estimate pressures of microlite crystallization and magma ascent rates. From the timescale data, we infer that the AD 1530 eruption started with phreatomagmatic explosions tapping magmas that ascended during about 1 month (decompression rate of ∼50 Pa/s) from the coldest parts of the reservoir (∼825°C and a 74 wt% SiO2 melt). These magmas continuously crystallized microlites (∼25 vol% plagioclase, orthopyroxene, clinopyroxene, magnetite, quartz, and apatite), but did not outgas likely due to sealed conduit margins. The flank collapse (preexisting “cold” edifice) that followed the phreatomagmatic phase triggered a sub-Plinian eruption that progressively tapped the hotter main reservoir (∼875°C and 71 wt% SiO2 interstitial melt), emitting banded and homogeneous pumice. The banded pumice did not significantly outgas and mostly lack decompression-induced microlites, suggesting short ascent durations of the order of 0.5–1 day (decompression rates of 1,400–4,000 Pa/s). The following Strombolian phase emitted dark scoria that did not significantly outgas and only crystallized rare microlites, suggesting ascent duration of the order of 2 days (decompression rates of ∼550 Pa/s). The terminal lava dome growth involved fully outgassed magmas ascended during more than 1 month, giving time for microlite crystallization (∼40 vol% plagioclase, orthopyroxene, clinopyroxene, magnetite, and cristobalite). The detection of any shallow new magmatic intrusion is crucial, since it can trigger a sequence of conduit processes leading to an eruption marked by a succession of different and disastrous eruptive styles, following a scenario similar to the AD 1530 eruption. Overall, we provide a combined approach of petrological, geochemical, and experimental data that may be used to infer ascent conditions and rates at other volcanic systems.

Protective Effect of Hyperbaric Oxygen Treatment on Axon Degeneration after Acute Motor Axonal Neuropathy.

Objectives Acute motor axonal neuropathy (AMAN) is a disease that leads to acute flaccid paralysis and may result from the binding of antibody and antigen to the spinal cord. The objective of this study is to evaluate the protective effect of hyperbaric oxygen treatment (HBOT) on axon degeneration of the spinal cord and sciatic nerve of the AMAN model rabbit. Axonal degeneration was assessed by evaluating glutathione (GSH) activity, interleukin-1β (IL-1β) expression, and clinical and histopathological features. Methods Twenty-one New Zealand rabbits were divided into three groups. The treatment group was exposed to 100% oxygen at 2.4 ATA 90 minutes for 10 days at a decompression rate of 2.9 pounds per square inch/minute. GSH level was evaluated using an enzyme-linked immune-sorbent assay. An expression of IL-1β in the spinal cord was determined by immunohistochemistry. Clinical appearances were done by motor scale and body weight. Histological features observed neuronal swelling and inflammatory infiltration in the sagittal lumbar region and the undulation of the longitudinal sciatic nerve. Results Rabbits exposed to HBO had high GSH activity levels (p < 0.05) but unexpectedly had high IL1β expression (p > 0.05). In addition, the HBO-exposed rabbits had a better degree of undulation, the size of neuronal swelling was smaller, the number of macrophages was higher, and motor function was better than the AMAN model rabbits (p < 0.05). Conclusions These findings indicate that HBO therapy can decrease axon degeneration by triggering GSH activity, increasing IL-1β level, and restoring tissues and motor status. In conclusion, HBO has a protective effect on axon degeneration of the spinal cord and sciatic nerve of the AMAN model rabbit.

Episodic transport of discrete magma batches beneath Aso volcano

Magma ascent, storage, and discharge in the trans-crustal magmatic system are keys to long-term volcanic output and short-term eruption dynamics. How a distinct magma batch transports from a deep reservoir(s) to a pre-eruptive storage pool with eruptible magma remains elusive. Here we show that repetitive very-long-period signals (VLPs) beneath the Aso volcano are preceded by a short-lived (~50–100 s), synchronous deformation event ~3 km apart from the VLP source. Source mechanism of a major volumetric component (~50–440 m3 per event) and a minor low-angle normal-fault component, together with petrological evidence, suggests episodic transport of discrete magma batches from an over-pressured chamber roof to a pre-eruptive storage pool near the brittle-ductile transition regime. Magma ascent velocity, decompression rate, and cumulative magma output deduced from recurrent deformation events before recent 2014 and 2016 eruptions reconcile retrospective observations of the eruption style, tephra fallouts, and plume heights, promising real-time evaluation of upcoming eruptions.

Cycling versus Continuous High Pressure treatments at moderate temperatures: Effect on bacterial spores?

The advantage of using high pressure (HP) cycling treatment compared with continuous HP treatment was investigated for the inactivation of bacterial spores. The effects of parameters such as pulse number, pressure level, treatment temperature, compression and decompression rates, and time between pulses were evaluated. For this purpose, Bacillus subtilis and B. cereus spores (108 and 106 CFU/mL respectively) were suspended in 2-(N-morpholino) ethanesulfonic acid (MES) buffer solution, tryptone salt (TS) buffer solution, or infant milk and treated by HP cycling at 300–400 MPa, at 38–60 °C, for 1–5 pulses. Pressure cycling reduced the number of viable spores by 1.8 and 5.9 log respectively for B. subtilis and B. cereus species. Continuous HP treatments were performed at the same pressure and temperature for similar treatment durations. Our results showed that the spore inactivation ratio was correlated with the cumulative exposure time to pressure rather than to effects of the cycling process. Greater spore inactivation caused by HP cycling was observed only when faster compression and decompression rates were applied, probably due to adiabatic heating. A three-step kinetic model was developed, which seemed to support our hypothesis regarding the mechanisms of inactivation by pressure cycling and continuous HP treatments. Industrial relevanceThe resistance of bacterial spores to HP limits the industrial applications to refrigerated food products. In this study, we investigated the use of pressure cycling as a means to improve spore baroinactivation at moderate temperatures (T < 60 °C). We showed that cycling pressure does not significantly increase bacterial spore inactivation in comparable treatment duration, but certainly increases material fatigue in HP vessels. Thus, under moderate temperature, cycling pressure treatment is not industrially relevant.

Liquid–liquid phase transition in simulations of ultrafast heating and decompression of amorphous ice

• Ultrafast heating experiments on amorphous ice clarified by simulations. • High density amorphous ice heated to liquid state by ultrafast laser pulse. • Decompression of high density liquid reveals liquid–liquid transition. • Simulations detect structural transition along out-of-equilibrium paths. A recent experiment [K. H. Kim, et al. , Science 370 , 978 (2020)] showed that it may be possible to detect a liquid–liquid phase transition (LLPT) in supercooled water by subjecting high density amorphous ice (HDA) to ultrafast heating, after which the sample reportedly undergoes spontaneous decompression from a high density liquid (HDL) to a low density liquid (LDL) via a first-order phase transition. Here we conduct computer simulations of the ST2 water model, in which a LLPT is known to occur. We subject various HDA samples of this model to a heating and decompression protocol that follows a thermodynamic pathway similar to that of the recent experiments. Our results show that a signature of the underlying equilibrium LLPT can be observed in a strongly out-of-equilibrium process that follows this pathway despite the very high heating and decompression rates employed here. Our results are also consistent with the phase diagram of glassy ST2 water reported in previous studies.

Independent Living 1 Year After Balloon Kyphoplasty for Osteoporotic Vertebral Compression Fracture

The prevalence of osteoporotic vertebral compression fracture (OVCF) is increasing. The indications for and efficacy of balloon kyphoplasty (BKP) are controversial. We sought to identify predictors of outcome after BKP in patients with OVCF. Between January 2001 and December 2019, 152 patients underwent BKP for painful OVCFs at our institution. This study included 115 patients who were followed for >12 months, and their data were retrospectively analyzed. With regard to the degree of independent living 1 year after BKP, patients were divided into a good outcome group (composed of patients who could independently go indoors) and a poor outcome group. We analyzed factors associated with outcome and subsequent OVCF. Mean age of patients was 77.9 years, 58.2% were female, 81% had a good outcome, and 19% had a poor outcome. Univariable analysis revealed significant differences in age, bone mineral density, preoperative vertebral body decompression rate, body mass index (BMI), preoperative Japanese Orthopaedic Association score, preoperative modified Rankin Scale score, and subsequent OVCF. Multivariable logistic analysis showed that low BMI (odds ratio 1.415, 95% confidence interval 1.06-1.87, P= 0.046) and subsequent OVCF (odds ratio 0.13, 95% confidence interval 0.02-0.69, P= 0.044) were independent risk factors. The incidence of subsequent OVCF was also lower among patients with higher BMI (odds ratio 0.83, 95% confidence interval 0.72-0.95, P= 0.001). BMI and subsequent OVCF are the most influential predictors of independent living 1 year after BKP for OVCF.

Magma Decompression Rate Calculations With EMBER: A User‐Friendly Software to Model Diffusion of H2O, CO2, and S in Melt Embayments

AbstractMagma decompression rate is one of the most important parameters in controlling eruption dynamics. One way to determine decompression rate is by fitting a volatile elements diffusion profile to a concentration gradient in crystal‐hosted embayments. Previous studies have used a variety of diffusion models, limiting the possibility for inter‐study comparison. Here, we introduce EMBayment‐Estimated Rates (EMBER), a standalone versatile tool that models diffusion of volatile elements along melt embayments. Our model relies on the pdepe function of MATLAB to calculate diffusion profiles of H2O, CO2, and S through the finite difference method. EMBER uses a grid search seeking out the best fits for decompression rates, initial dissolved concentration of each studied volatile and initial exsolved gas content, while setting three constants: temperature along the ascent and pressure at the beginning and end of the ascent. Our model can compute the rate for basaltic, intermediate, and rhyolitic compositions. We applied EMBER to previous studies to evaluate and validate our model. We then reprocessed “homogeneously” the raw data from the literature for a comparison. In other words, the same protocol was used for each diffusion profiles removing the literature‐specific strategies used to constrain unknown parameters. With this comparison, we found a statistically significant positive correlation between maximum magma decompression rates and explosivity of the related eruption. EMBER is expected to help increase the number of volatile diffusion in embayments studies aiming at constraining magma decompression and ascent rates and to facilitate inter‐study comparisons.

The Ins and Outs of Water in Olivine-Hosted Melt Inclusions: Hygrometer vs. Speedometer

The amount of water dissolved in magmas at depth beneath volcanoes is fundamental to a wide range of magmatic and eruptive processes due to water’s dominant control on magma generation, viscosity, and buoyancy. Since magmas degas most of their initial water content upon ascent and eruption, the primary record of magmatic water evolution exists within melt inclusions trapped inside crystals, especially olivine. However, the discovery of rapid H+ diffusion through olivine has called into question the fidelity of the melt inclusion water record. How compromised is the vast existing and growing dataset of melt inclusion water contents? What are the circumstances favorable for recording primary or pre-eruptive water concentration? Even if inclusions are compromised, diffusive water loss can be exploited to constrain magma decompression rates, a critical parameter that affects conduit processes. Here, we outline the current understanding of factors controlling water loss: the olivine/melt partition coefficient, the diffusive transport of water through olivine, the distance between inclusion and crystal rim, the melt inclusion size, and the exterior magma’s water evolution. We combine these parameters into a regime diagram that can be used to guide when melt inclusions may be used as hygrometers and when they are better suited to act as magma speedometers. We develop diagnostic tools to recognize where and when water loss has occurred in a magma’s ascent history, and we outline quantitative tools that may be used to restore the primary and/or pre-eruptive water content. The intent of this paper is to guide researchers in the interpretation of existing melt inclusion data, and to aid in the design of new studies that maximize the valuable information that melt inclusions may convey on the evolution of water in magmas prior to eruption.

Using Volatile Element Concentration Profiles in Crystal‐Hosted Melt Embayments to Estimate Magma Decompression Rate: Assumptions and Inherited Errors

AbstractMagma decompression rate has profound impacts on volcanic eruption style as it determines the time available for most kinetic processes (e.g., volatile exsolution, crystal nucleation and growth) that influence the explosive‐effusive eruption transition. Thus, accurately quantifying decompression rate is a critical goal for understanding volcanic eruption dynamics. A recently developed technique uses crystal‐hosted pockets of melt that remain open to the host magma (melt embayments) to calculate an average decompression rate. Diffusion of volatile elements (e.g., H2O, CO2) out of the embayment during decompression creates “frozen” concentration gradients upon quenching that can be modeled to calculate the time needed to create the gradients. This geospeedometer is increasingly used, but inherent assumptions associated with the modeling and their impact on calculated decompression rates are poorly quantified. Therefore, we have conducted a numerical investigation to assess the impact of three common model simplifications pertaining to rhyolitic magmas: 1D diffusion models, equilibrium degassing, and isothermal decompression. We find that the greatest deviation between imposed and calculated decompression rates occur when 1D models are applied to “necked” embayments that have a constriction where the embayment joins with the far field melt. Simplifying to equilibrium degassing can also introduce modeling errors when disequilibrium conditions exist, though the prevalence of one or the other condition in nature is currently under debate. Assuming isothermal conditions introduces little error into modeled timescales. All of our modeling results are summarized into a list of best practices to minimize error in modeled timescales due to modeling assumptions.

Comparison of Follow-Up Length-Matched Single-Center Myelomeningocele Postnatal Closure Cohort to the Management of Myelomeningocele Study (MOMS) Trial Results

Objective: We sought to compare our large single-institution cohort of postnatal myelomeningocele closure to the 2 arms of the Management of Myelomeningocele Study (MOMS) trial at the designated trial time points, as well as assess outcomes at long-term follow-up among our postnatal cohort. Methods: A single-institutional retrospective review of myelomeningocele cases presenting from 1995 to 2015 at Children’s Hospital of Pittsburgh was performed. We compared outcomes at 12 and 30 months to both arms of the MOMS trial and compared our cohort’s outcomes at those designated time points to our long-term outcomes. Univariate statistical analysis was performed as appropriate. Results: One-hundred sixty-three patients were included in this study. All patients had at least 2-year follow-up, with a mean follow-up of 10 years (range 2–20 years). There was no difference in the overall distribution of anatomic level of defect. Compared to our cohort, the prenatal cohort had a higher rate of tethering at 12 months of age, 8 versus 1.8%. Conversely, the Chiari II decompression rate was higher in our cohort (10.4 vs. 1.0%). At 30 months, the prenatal cohort had a higher rate of independent ambulation, but our cohort demonstrated the highest rate of ambulation with or without assistive devices among the 3 groups. When comparing our cohort at these early time points to our long-term follow-up data, our cohort’s ambulatory function decreased from 84 to 66%, and the rate of detethering surgery increased almost 10-fold. Conclusions: This study demonstrated that overall ambulation and anatomic-functional level were significantly better among our large postnatal cohort, as well as having significantly fewer complications to both fetus and mother, when compared to the postnatal cohort of the MOMS trial. Our finding that ambulatory ability declined significantly with age in this patient population is worrisome for the long-term outcomes of the MOMS cohorts, especially given the high rates of cord tethering at early ages within the prenatal cohort. These findings suggest that the perceived benefits of prenatal closure over postnatal closure may not be as substantial as presented in the original trial, with the durability of results still remaining a concern.