Mass Discharge Research Articles

Marginally stable recent Plinian eruptions of Mt. Pelée volcano (Lesser Antilles): the P2 AD 280 eruption

Major volcanic hazards in the Lesser Antilles arc include powerful Plinian explosive eruptions that inject ash high into the atmosphere and produce dangerous pyroclastic density currents (PDC) on the ground. Understanding the key physical processes governing the dynamics and stability of past volcanic columns is a fundamental problem in volcanology as well as being central to assessing specific hazards in this region and elsewhere. However, the number of cases for which the transition of regime between a stable and collapsing eruptive plume is described in detail remains too small to constrain fully theoretical models of volcanic plumes. Here we present a detailed reconstruction of the time evolution of the P2 AD 280 eruption at Mt. Pelee volcano in Martinique, to expand the database available to test physical models. The P2 sequence, which forced the first inhabitants to flee to other islands for decades as suggested by archaeological evidence, starts with a basal ash layer interpreted as the result of an initial violent laterally directed explosion to the NE of the volcano. Most of the deposit sequence is made of a pumice fall deposit interbedded with a low-concentration PDC deposit interpreted as the result of a partial column collapse. The upper pumice fall unit shows an inverse gradation and is overlain by a final high-concentration PDC deposit or locally by the correlative low-concentration PDC deposit. Field data on deposit dispersal, thickness, and grain-size distribution are used together with physical models to reconstruct the dynamic evolution of this eruption. Empirical models of deposit thinning suggest that the minimum volume of pyroclastic deposits is 0.67–0.88 km3 dense rock equivalent (DRE), much larger than the 0.17 km3 DRE previously estimated. We find that the mass eruption rate increased from 6 × 107 to 1.1 × 108 kg s−1, producing an initially stable 23- to 26-km-high Plinian plume, which ultimately collapsed to form a fountain. We discuss the mechanisms leading to column collapse based on published data on magmatic water contents and our estimates of grain-size distributions and mass discharge rates. The eruption started close to the plume/fountain transition and the volcanic column ultimately collapsed mainly due to an increase in mass discharge rate. This marginally stable evolution was also inferred from analysis of the P1 AD 1300 eruption deposits, suggesting consistent behavior during the recent Plinian eruptions of Mt. Pelee volcano. In these two eruptions, the transition occurred at conditions well predicted by our theoretical model of volcanic plumes.

Effects of wind velocity and soil characteristics on dust storm generation in Hawr-al-Azim Wetland, Southwest Iran

Nowadays, dust storms are an important environmental problem in Iran (especially in Khuzestan Province). The Hawr-al-Azim Wetland is a source for generation of dust storms. One-third area of this wetland is located in Iran. In this study, dust discharge is calculated using wind velocity, mean soil grain size (D50) and soil dry density. Soil characteristics were determined by data collected from 16 boreholes drilled in this wetland. Distributions of D50 and soil dry density in the wetland were determined using ordinary kriging method. Then critical wind speed was calculated in different regions of the wetland. The wetland soil is composed of medium and coarse silty soil. The dust mass discharge has reduced from 2003. The maximum monthly dust discharge mass occurs in June and July (along with a mean monthly wind velocity of 4.42 m s-1 and 4.27 m s-1, respectively). Because of the little amount of clay particles and the high wind velocity, increased soil moisture content cannot help in neither raise inthe critical shear velocity nor decreased dust mass discharge. Also, the produced dust is transported towards Northwest Iran because the dominant direction of wind is 270° to 300° relative to the north.

Experimental and Numerical Modeling of DNAPL Mass Discharge from the Elliptic Pool in Saturated Homogeneous Sandy Soil

"The present study aims to study the dissolution and mass transport of trichloroethylene (TCE) as Dense Non Aqueous Phase Liquid (DNAPL) in saturated porous media." A rectangular Perspex tank of internal dimensions (150cm length 20cm width and 40 cm height) used to represent the model aquifer. The tank was packed with homogenous soil (Karbala sand)"."Unidirectional flow at five different interstitial velocities (0.9, 1.8, 2.34, 2.7, and 3.6) cm/hr assumed to study the process. The average mass transfer coefficient" was determined for each velocity .Their values were increased with increasing the velocity reaching a limit value" .A conservative tracer is used to obtain the longitudinal and transverse aquifer dispersivities"."An elliptic shape of (TCE) pool was used to carry out the dissolution processes. Steady state dissolved (TCE) concentrations at downstream were collected from ten ports with two different depths under five interstitial velocities". Two linear relationships are created from an elliptic trichloroethylene pool: these relationships were between the average Peclet number in x-direction (Pe*x(e)) with the overall Sherwood number (Sh*(e )), and the other between the average Peclet number in y-direction (Pe*y(e) ) with the overall Sherwood number (Sh*(e))". A numerical modeling was achieved using COMSOL software.

Partitioning of poly- and perfluoroalkyl substances from soil to groundwater within aqueous film-forming foam source zones

Metadata from on-going site investigations at U.S. Air Force sites impacted by Aqueous Film-Forming Foam (AFFF) were used to evaluate primary factors that affect transport of poly- and perfluoroalkyl substances (PFAS) within source zones. Soil-to-groundwater ratios (γSoil-GW) were calculated for each site and PFAS as an empirical transport metric and regressed against select soil chemical and physical properties, as well as relevant interactions thereof, using analysis of covariance (ANCOVA). Total organic carbon and percent total clay content were significant covariates and best fit log-transformed γSoil-GW with a parallel lines model. Regression parameters were used to derive apparent KOC estimates for 15 perfluoroalkyl acids, perfluorooctane sulfonamide, and the 6:2 and 8:2 fluorotelomer sulfonates, which were bimodal where significant differences were primarily observed between PFAS with fewer than 8 perfluorinated carbons (including perfluorooctoanoic acid; PFOA) and those with 8 or more (including perfluorooctane sulfonate; PFOS). Surprisingly, clay content was observed with a negative slope (i.e., γSoil-GW decreased with increasing clay content), which may reflect greater retardation at more permeable sites due to air-water interfacial partitioning. Further analysis demonstrated that γSoil-GW is also affected by the degree of flushing in a way that suggests mass transfer (as opposed to hysteretic desorption) primarily controls mass discharge at poorly flushed sites. Overall, this meta-analysis demonstrates that PFAS retention in soil is significant, but depends on a combination of fundamental partitioning mechanisms that may not be predictable in all cases based on transport models that assume an equilibrium condition.

Determining the long-term operational performance of pump and treat and the possibility of closure for a large TCE plume.

The purpose of this study is to evaluate the impact of heterogeneity on the long-term performance of a large pump-and-treat (PAT) system that has been in operation for 30 years at a site located in Tucson, AZ. A 3D numerical model was developed. Three different concentrations were examined: composite concentration in the influent to the treatment plant, resident concentration in the aquifer, and concentration for downgradient boundary discharge. The time scales needed for concentrations measured in these ways to reach the Maximum Contaminant Levels (MCLs) are significantly different, with ∼125 years required for treatment-plant influent compared to ∼225 years for downgradient boundary discharge and >>227 years (total simulated time) for the resident concentration in the aquifer. These large time scales, compared to 36 years for a hypothetical homogeneous system, demonstrate the significant impacts of permeability heterogeneity on remediation at this site. The possibility of closure of the site was investigated by examining the mass discharge from the site boundary and the concentration rebound after simulating shutdown of the PAT system. The results of this study provide insight on evaluation of closure potential for large, complex contamination sites and a reference on selecting performance metrics for site management.

Theoretical and experimental investigation of low-power AF-MPDT performance in the high mass flow rate low discharge current regime

We performed a test campaign in order to fill the gaps in the experimental data and understanding of the performance of the Applied Field Magnetoplasmadynamic Thruster in low current, high mass flow rate regime. Thrust and discharge voltage were measured for two anode geometry configurations with different mass flow rate distribution, discharge current and external magnetic field strength. The general trends in thruster behavior using argon as propellant are analyzed in this paper and an approach for thruster optimization is investigated. We find an unexpectedly weak dependence of thrust efficiency on discharge current in low current, high mass flow rate regimes. Using a cylindrical anode configuration, we managed to achieve thrust efficiency of 21%, which is significantly higher than that reported in literature for AF-MPDTs operating in this regime.

Impact of The Method of Diagnosis on The Stage of Breast Carcinoma.

Screening mammography is recommended to women at a certain age to achieve an early diagnosis. The purpose of this study is to find out how breast carcinoma was diagnosed and the impact of the method of diagnosis on the stage of the tumor. In this study, 903 operated breast cancer patients, between 2010-2016, in a large volume Marmara University Istanbul Pendik Education and Research Hospital were analyzed retrospectively. Patients presenting with clinical symptoms and those diagnosed with screening were investigated separately. The percentage of the patients diagnosed with symptoms and the impact of the method of diagnosis on the stage of the tumor was the primary outcome of the study. 738 patients fulfilling inclusion criteria with complete clinical records were analyzed. 126 patients (17%) were in the age range of 19-39 years, while 32% (236 patients) were 40-50 and 51% (376 patients) were older than 50 years.485 patients (65.7%) were diagnosed with a mass in the breast, while 241 (32.6%) patients were diagnosed with screening with mammography. Twelve patients (1.7%) presented with nipple discharge. Median tumor sizes measured in the resected specimen were 22 mm, 21 mm, and 21 mm in patients diagnosed with a mass, screening, and nipple discharge respectively. The difference among the groups were not significant (p=0.460).Axillary lymph nodes were positive in 210 (43.3%) of patients presenting with a mass in the breast while 85 patients (35.3%) diagnosed with screening had metastatic lymph nodes in the axilla. Three patients presenting with nipple discharge had positive axillary lymph nodes (p=0.137). This study demonstrated that breast cancer screening programs in Turkey needs improvement and at the same time shows that screening with mammography after 40 years of age should be done annually despite Ministry of Health recommendations.

Source strength functions from long-term monitoring data and spatially distributed mass discharge measurements

Source strength functions (SSF), defined as contaminant mass discharge or flux-averaged concentration from dense nonaqueous phase liquid (DNAPL) source zones as a function of time, provide a quantitative model of DNAPL source-zone behavior. Such information is useful for calibration of screening-level models to assist with site management decisions. We investigate the use of historic data collected during long-term monitoring (LTM) activities at a site in Rhode Island to predict the SSF based on temporal mass discharge measurements at a fixed location, as well as SSF estimation using mass discharge measurements at a fixed time from three spatially distributed control planes. Mass discharge based on LTM data decreased from ~300 g/day in 1996 to ~70 g/day in 2012 at a control plane downgradient of the suspected DNAPL source zone, and indicates an overall decline of ~80% in 16 years. These measurements were compared to current mass discharge measurements across three spatially distributed control planes. Results indicate that mass discharge increased in the downgradient direction, and was ~6 g/day, ~37 g/day, and ~400 g/day at near, intermediate, and far distances from the suspected source zone, respectively. This behavior was expected given the decreasing trend observed in the LTM data at a fixed location. These two data sets were compared using travel time as a means to plot the data sets on a common axis. The similarity between the two data sets gives greater confidence to the use of this combined data set for site-specific SSF estimation relative to either the sole use of LTM or spatially distributed data sets.

Estimates of Horizontal Groundwater Flow Velocities in Boreholes.

Currently, monitoring tools can be deployed in observation boreholes to better assess groundwater flow, flux of dissolved contaminants and their mass discharge in an aquifer. The relationship between horizontal water velocity in observation boreholes and Darcy fluxes in the surrounding aquifer has been studied for natural flow conditions (i.e., no pumping). Interpretation of measurements taken with dilution tests, the colloidal borescope, the Heat Pulse Flowmeter, and other techniques require the conversion of observed borehole velocity u to aquifer Darcy flux q∞ . This conversion is typically done through a proportionality factor α = u/q∞ . In experimental studies as well as in theoretical developments, reported values of α vary almost three orders of magnitude (from 0.5 to 10). This large variability in reported values of α could be explained by: (1) unclear distinction between Darcy flux and water seepage velocity, (2) unclear definition of water velocity in the borehole, (3) effects of well screen and the presence of the measurement device itself on the observable velocities, and (4) hydraulic conditions in the borehole annulus. We address (1), (2) from a conceptual/theoretical perspective, and (3) by means of numerical simulations. We show that issue (1) in low porosity aquifers can yield to order-of-magnitude discrepancies in estimates of q∞ ; (2) may result in discrepancies of up to 50%, and (3) can cause differences up to 20% of water velocity in the borehole void space compared to the theoretical case of an open borehole.

Prediction of hopper discharge rate using combined discrete element method and artificial neural network

An Artificial Neural Network (ANN) was developed to predict the mass discharge rate from conical hoppers. By employing Discrete Element Method (DEM), numerically simulated flow rate data from different internal angles (20°–80°) hoppers were used to train the model. Multi-component particle systems (binary and ternary) were simulated and mass discharge rate was estimated by varying different parameters such as hopper internal angle, bulk density, mean diameter, coefficient of friction (particle-particle and particle-wall) and coefficient of restitution (particle-particle and particle-wall). The training of ANN was accomplished by feed forward back propagation algorithm. For validation of ANN model, the authors carried out 22 experimental tests on different mixtures (having different mean diameter) of spherical glass beads from different angle conical hoppers (60° and 80°). It was found that mass discharge rate predicted by the developed neural network model is in a good agreement with the experimental discharge rate. Percentage error predicted by ANN model was less than ±13%. Furthermore, the developed ANN model was also compared with existing correlations and showed a good agreement.

Geophysics‐Based Contaminant Mass Discharge Quantification Downgradient of a Landfill and a Former Pharmaceutical Factory

AbstractContaminant mass discharge is a commonly applied tool to evaluate the environmental impact of contaminated sites on water resources. At large contaminated sites with heterogeneous sources, such as landfills, the number of wells available is often not sufficient, leading to a high uncertainty of mass discharge estimates. In this study, we tackle the uncertainty of the contaminant mass discharge due to low sampling densities by interpolating limited water‐sample data with the support of surface direct current resistivity and induced polarization geophysical data. The method relies on finding a conceptual link between the bulk conductivity imaged from geophysics and the contaminant concentrations. We investigate the link between (1) imaged bulk and electrical water conductivity, (2) water conductivity and conservative ionic species, (3) water conductivity and redox‐sensitive species, (4) water conductivity and semipersistent organic species, and (5) water conductivity and biodegradable organic compounds. The method successfully identify similarities between the distribution of the bulk conductivity and chloride and pharmaceutical compounds in a landfill leachate plume and between the bulk conductivity data and benzene and chlorinated ethenes for a contaminant plume from a former pharmaceutical factory. Contaminant concentrations were interpolated through regression kriging, using geophysical data as the dependent variable. The distribution of concentration determined with the novel method showed a lower mean relative estimation error than the traditional method of kriging only contaminant concentration data. At large sites, the method can improve contaminant mass discharge estimates, especially if surface geophysical measurements are integrated in the site investigation at an early stage.

Understanding eruptive style variations at calc-alkaline volcanoes: the 1913 eruption of Fuego de Colima volcano (Mexico)

The 1913 sub-Plinian eruption of Fuego de Colima volcano (Mexico) occurred after almost 100 years of effusive and (minor) Vulcanian explosive activity, which modulated dome growth and destruction. Dome extrusion persisted from 1869 to 1913. The transition to explosive eruption started on 17 January 1913, and it progressed in three phases: (1) opening, with the generation of block-and-ash flows, (2) vent clearing, with strong explosions that destroyed the summit dome and decompressed the magmatic system, and (3) sustained column (sub-Plinian fallout) with final collapse producing pyroclastic density currents. Because of this succession of events, the 1913 activity represents an excellent case-study for investigating the eruptive style changes at calc-alkaline volcanoes. We investigated the conditions that led to eruptive style transition from effusive (dome growth) to explosive (the final sub-Plinian fallout) through steady-state numerical simulations, using subsurface data and independently inferred (from volcanological data) mass discharge rates as constraints. Results show good matches for hybrid geometrical settings of the shallow conduit-feeding system (i.e., dyke developing into a shallower cylindrical conduit), and the magma chamber top at 6 km of depth. The fragmentation level was shallower than 2 km, as inferred from the lithics contained in the sub-Plinian fall deposits of Phase (3). The most likely solution is represented by a dyke having major axis between 200 and 2000 m and the minor axis of 40 m. The dyke-cylinder transition was set at a depth of 500 m, with a cylinder diameter of 40 m. It emerges that at least two main mechanisms may be responsible for the effusive to explosive transition that led to the Phase (3) of the 1913 eruption: (i) an increase in magma chamber overpressure (magmatic triggering) or (ii) decrease of lithostatic stress acting on the volcano (non-magmatic triggering). The former implies arrival into the magma chamber of a batch of fresh magma, which can have volume between 10 and 200 × 106 m3, depending on the values of magma and host rock compressibility. The latter requires decompression-induced emptying of at least the equivalent of 1000 m of the magma column to produce the necessary unloading of the conduit-feeding system. A sudden jerk in the lateral spreading of the Fuego de Colima cone would be a reliable mechanism for decompressing the upper conduit and driving fragmentation processes over a time period of few hours. The results are not conclusive on an internal (magma chamber overpressure), external (lowering of lithostatic load), or mixed (internal and external) trigger of the observed eruptive style transition. This work highlights how different processes can have non-linear cascade effects on close-to-equilibrium volcanic systems like Fuego de Colima volcano.

Lichen Sclerosus Accompanied by Urethral Squamous Cell Carcinoma: A Retrospective Study From a Urethral Referral Center.

To evaluate the characteristics of lichen sclerosus (LS) accompanied by urethral squamous cell carcinoma (USCC) and to raise urologists’ awareness about the early management of LS, a retrospective analysis was performed on the clinical features, diagnosis, treatment, and prognosis of 18 male genital LS accompanied by USCC patients who were referred to Shanghai Sixth People’s Hospital between June 2000 and August 2014. All of the patients had a long-term history of LS, urethral strictures, and urethral dilatation. Seven patients are with distal (glanular or penile) USCC, 10 patients with proximal USCC, and one with entire USCC. The most common presentation, except for LS and urethral strictures, was periurethral abscess, followed by extraurethral mass, pelvic pain, urethrocutaneous fistula, hematuria, and bloody urethral discharge. All had primary surgical excision that was adapted to tumor location and extension. All of the USCC were positive for P53 and Ki-67. P16 was positive in four cases of human papillomavirus (HPV)-associated USCC and negative in 14 cases of HPV-independent USCC. Patients with distal USCC had a significant longer survival time than proximal USCC (p < .05). LS should be treated early to prevent the disease progression. LS probably has some associations with USCC. Distal USCC has a relatively better prognosis than proximal USCC.

Priority substances and emerging pollutants in urban rivers in Ukraine: Occurrence, fluxes and loading to transboundary European Union watersheds

The occurrence and fluxes of 18 priority substances and emerging pollutants listed in the European Union Water Framework Directive and a Watch List (trace metals (Cd, Pb and Ni), nonylphenols, octylphenols, 8 polyaromatic hydrocarbons, 4 dioxin-like polychlorinated biphenyls and diclofenac) were investigated in a Ukrainian city and the mass discharge loads of these compounds into EU-transboundary watersheds were estimated. Fluxes of chemicals were calculated per capita and per area of the Ukrainian urban territory and used to estimate mass loading of priority and emerging concern compounds from Lviv, Uzhorod and Chernivtsi (West Ukraine) to neighbouring EU-transboundary rivers. The highest loading was found for trace metals (1.15 t a−1), diclofenac (0.7 t a−1) and nonylphenols (0.4 t a−1). Transboundary water contamination must be considered in order to successfully manage water resources in a manner that fulfils the requirements of EU environmental quality standards.

Topographic Steering of Enhanced Ice Flow at the Bottleneck Between East and West Antarctica

AbstractHypothesized drawdown of the East Antarctic Ice Sheet through the “bottleneck” zone between East and West Antarctica would have significant impacts for a large proportion of the Antarctic Ice Sheet. Earth observation satellite orbits and a sparseness of radio echo sounding data have restricted investigations of basal boundary controls on ice flow in this region until now. New airborne radio echo sounding surveys reveal complex topography of high relief beneath the southernmost Weddell/Ross ice divide, with three subglacial troughs connecting interior Antarctica to the Foundation and Patuxent Ice Streams and Siple Coast ice streams. These troughs route enhanced ice flow through the interior of Antarctica but limit potential drawdown of the East Antarctic Ice Sheet through the bottleneck zone. In a thinning or retreating scenario, these topographically controlled corridors of enhanced flow could however drive ice divide migration and increase mass discharge from interior West Antarctica to the Southern Ocean.

Evaluating the combined effects of source zone mass release rates and aquifer heterogeneity on solute discharge uncertainty

Abstract Quantifying the uncertainty in solute mass discharge at an environmentally sensitive location is key to assess the risks due to groundwater contamination. Solute mass fluxes are strongly affected by the spatial variability of hydrogeological properties as well as release conditions at the source zone. This paper provides a methodological framework to investigate the interaction between the ubiquitous heterogeneity of the hydraulic conductivity and the mass release rate at the source zone on the uncertainty of mass discharge. Through the use of perturbation theory, we derive analytical and semi-analytical expressions for the statistics of the solute mass discharge at a control plane in a three-dimensional aquifer while accounting for the solute mass release rates at the source. The derived solutions are limited to aquifers displaying low-to-mild heterogeneity. Results illustrate the significance of the source zone mass release rate in controlling the mass discharge uncertainty. The relative importance of the mass release rate on the mean solute discharge depends on the distance between the source and the control plane. On the other hand, we find that the solute release rate at the source zone has a strong impact on the variance of the mass discharge. Within a risk context, we also compute the peak mean discharge as a function of the parameters governing the spatial heterogeneity of the hydraulic conductivity field and mass release rates at the source zone. The proposed physically-based framework is application-oriented, computationally efficient and capable of propagating uncertainty from different parameters onto risk metrics. Furthermore, it can be used for preliminary screening purposes to guide site managers to perform system-level sensitivity analysis and better allocate resources.

Worldwide Distribution of Novel Perfluoroether Carboxylic and Sulfonic Acids in Surface Water.

Driven by increasingly stringent restrictions on long-chain per- and polyfluoroalkyl substances (PFASs), novel fluorinated compounds have emerged on the market. Here we report on the occurrences of several perfluoroalkyl ether carboxylic and sulfonic acids (PFECAs and PFESAs), including hexafluoropropylene oxide dimer and trimer acids (HFPO-DA and HFPO-TA), ammonium 4,8-dioxa-3 H-perfluorononanoate (ADONA), chlorinated polyfluorinated ether sulfonic acid (6:2 Cl-PFESA), and its hydrogen-substituted analogue (6:2 H-PFESA) in surface waters from China ( n = 106), the United States ( n = 12), the United Kingdom ( n = 6), Sweden ( n = 10), Germany ( n = 14), The Netherlands ( n = 6), and Korea ( n = 6). Results showed that HFPO-DA, HFPO-TA, and 6:2 Cl-PFESA (median = 0.95, 0.21, and 0.31 ng/L, respectively) were frequently detected in all countries, indicating ubiquitous dispersal and distribution in global surface waters. The presence of 6:2 H-PFESA was widely detected in China (detection rate > 95%) but not in any other country. Only trace levels of ADONA (0.013-1.5 ng/L) were detected in the Rhine River flowing through Germany. The estimated total riverine mass discharges of HFPO-DA, HFPO-TA, and ΣPFESAs reached 2.6, 6.0, and 4.3 ton/year in five of the major river systems in China. Our results indicated that novel PFECAs and PFESAs might become global contaminants, and future investigations are warranted.

A revisit of the role of gas entrapment on the stability conditions of explosive volcanic columns

Explosive volcanic eruptions produce high-velocity turbulent jets that can form either a stable buoyant Plinian column or a collapsing fountain producing pyroclastic density currents (PDC). Determining the source conditions leading to these extreme regimes is a major goal in physical volcanology. Classically, the regime boundary is defined as the critical eruptive mass discharge rate (MDR) before collapse for a given amount of free gas in the eruptive mixture (free gas + pyroclasts) at the vent. Previous studies have shown that an agreement between theory and field data can be achieved in two different frameworks: (i) by accounting for the effect of gas entrapment in large pumice fragments, which lowers the effective gas content, depending on the total grain-size distribution (TGSD) of pyroclastic fragments, or (ii) by accounting for the reduction of turbulent entrainment at the base of the volcanic column due to its negative buoyancy. Here, we aim at combining these two using a 1D model of volcanic column that includes sedimentation to follow the evolution of the TGSD. In powerful (≥ 107 kg s−1) Plinian eruptions, the loss of particles by sedimentation acts as to decrease the load of particles during the plume rise, which favors the formation of a stable column. In this case, we obtain that coarse TGSD promote the formation of stable plumes, a result at odds with the predictions of models considering gas entrapment in large pyroclastic fragments. To interpret this conclusion, we reconsider the effect of gas entrapment and show that in general, it has a dominant role on column collapse compared to particle sedimentation, and hinders the formation of buoyant columns. This drastic effect is reduced when incorporating open porosity, e.g. by considering that some bubbles inside a fragment are connected to the exterior. The characteristics of the PDC produced by column collapse are then predicted as a function of the TGSD and MDR at the source. We further test the model using two well-documented historical events, the ≈186 CE Taupo and 79 CE Vesuvius eruptions. Our model predictions are consistent with the Taupo eruption record, but not with the Vesuvius one. In this latter case, we suggest that the characteristics of the TGSD imply to take into account the thermal disequilibrium between gas and pyroclasts.

Application of new point measurement device to quantify groundwater-surface water interactions

The streambed point velocity probe (SBPVP) measures in situ groundwater velocities at the groundwater-surface water interface without reliance on hydraulic conductivity, porosity, or hydraulic gradient information. The tool operates on the basis of a mini-tracer test that occurs on the probe surface. The SBPVP was used in a meander of the Grindsted Å (stream), Denmark, to determine the distribution of flow through the streambed. These data were used to calculate the contaminant mass discharge of chlorinated ethenes into the stream. SBPVP data were compared with velocities estimated from hydraulic head and temperature gradient data collected at similar scales. Spatial relationships of water flow through the streambed were found to be similar by all three methods, and indicated a heterogeneous pattern of groundwater-surface water exchange. The magnitudes of estimated flow varied to a greater degree. It was found that pollutants enter the stream in localized regions of high flow which do not always correspond to the locations of highest pollutant concentration. The results show the combined influence of flow and concentration on contaminant discharge and illustrate the advantages of adopting a flux-based approach to risk assessment at the groundwater-surface water interface. Chlorinated ethene mass discharges, expressed in PCE equivalents, were determined to be up to 444 kg/yr (with SBPVP data) which compared well with independent estimates of mass discharge up to 438 kg/yr (with mini-piezometer data from the streambed) and up to 372 kg/yr crossing a control plane on the streambank (as determined in a previous, independent study).

Recent high-resolution Antarctic ice velocity maps reveal increased mass loss in Wilkes Land, East Antarctica

We constructed Antarctic ice velocity maps from Landsat 8 images for the years 2014 and 2015 at a high spatial resolution (100 m). These maps were assembled from 10,690 scenes of displacement vectors inferred from more than 10,000 optical images acquired from December 2013 through March 2016. We estimated the mass discharge of the Antarctic ice sheet in 2008, 2014, and 2015 using the Landsat ice velocity maps, interferometric synthetic aperture radar (InSAR)-derived ice velocity maps (~2008) available from prior studies, and ice thickness data. An increased mass discharge (53 ± 14 Gt yr−1) was found in the East Indian Ocean sector since 2008 due to unexpected widespread glacial acceleration in Wilkes Land, East Antarctica, while the other five oceanic sectors did not exhibit significant changes. However, present-day increased mass loss was found by previous studies predominantly in west Antarctica and the Antarctic Peninsula. The newly discovered increased mass loss in Wilkes Land suggests that the ocean heat flux may already be influencing ice dynamics in the marine-based sector of the East Antarctic ice sheet (EAIS). The marine-based sector could be adversely impacted by ongoing warming in the Southern Ocean, and this process may be conducive to destabilization.