Fallout Deposits Research Articles

Analysis of the vertical distribution of 137Cs and 239,240Pu in waterlogged and non-boggy soils by the sequential extraction method

Mobile capabilities of 137Cs, 239,240Pu and some stable element physicochemical forms were studied in soil layers at a depth of 6–8 cm (maximum concentrations of radionuclides) of non-boggy and waterlogged soil cores sampled on the shores of Lake Bedugnis (Lithuania). Soil samples were acidic with small amount of clay (muscovite). The radionuclide activity concentrations were about 2.5 times higher in non-boggy soil. It was explained by different conditions of deposition of radioactive fallout at these sampling sites and density of the soil samples. The value of the exchangeable fraction of radionuclides is shown to be an indicator of their migration capabilities in the soil. Under anaerobic conditions in waterlogged soil (stagnant pore water conditions) and due to the presence of clay admixture, ∼90% of 137Cs was concentrated in the residual fraction and its mobility was low. 239,240Pu was concentrated mainly in organic matter with rather large exchangeable fractions (∼9.6–∼13.9%). Under oxidizing conditions in non-boggy soil (dynamic pore water conditions in the case of rain), 239,240Pu was mostly concentrated in the oxide fraction. Its exchangeable fractions were less than those in waterlogged soil and, respectively, its mobility was lower. In non-boggy soils, exchangeable fractions of 137Cs were large and varied in the range of 10.1–12.2%, which indicated its high mobility. In the case, 137Cs adsorption by clay materials was reduced and its residual fraction did not exceed 71.3%. The obtained data show that in the area of Lake Bedugnis, the migration capabilities of 137Cs and 239,240Pu change in antiphase.

Forecasting and communicating the dispersion and fallout of ash during volcanic eruptions: lessons from the September 20, 2020 eruptive pulse at Sangay volcano, Ecuador

Volcanic ash is a hazard to human health and activities. Accurate and timely forecasts coupled with effective communication about the dispersion and fallout of volcanic ash during explosive events are essential to reduce impacts on local communities and limit economic losses. In this study, we present the first detailed description of an eruptive pulse at Sangay volcano and its eruption source parameters. The eruptive pulse on September 20, 2020, started at about 9:20 UTC and lasted between 90 and 100 min, producing an eruptive column that rapidly separated into (1) a higher (15.2 km above sea level, asl), gas-rich cloud moving east-southeast and (2) a lower (12.2 km asl), ash-rich cloud moving west and causing ash fallout up to 280 km from the volcano. Field data collected immediately after the event allow estimating the volume of bulk tephra to be between 1.5 and 5.0 × 106 m3, corresponding to a volcanic explosivity index of 2. The eruptive pulse, identified as violent Strombolian, emitted andesitic ash that was more mafic than products ejected by Sangay volcano in recent decades. Component analysis and glass chemistry of juvenile particles support the hypothesis that this event excavated deeper into the upper conduit compared to typical Strombolian activity at Sangay volcano, while grain-size analysis allows reconstruction of the total grain-size distribution of the fallout deposit. The discrepancies between the ash fallout simulations performed with the Ash3D online tool and the actual deposit are mainly the result of inaccurate pre- and syn-eruptive configurations and highlight the importance of additional processes such as aggregation. Communication products issued during the event included (1) several standard short reports, (2) volcano observatory notices for aviation, (3) social media posts, and (4) a special report providing the results of the ash fallout simulation. Although communication was effective with the authorities and the connected population, an effort must be made to reach the most vulnerable isolated communities for future events. This study shows that forecasting ash dispersion and fallout during volcanic eruptions can guide early warnings and trigger humanitarian actions, and should become a standard in volcano observatories worldwide.

The eruptive chronology of the Carihuairazo volcano (Ecuador): Recurrent sector collapses of a Middle Pleistocene stratovolcano of the northern andes

The eruptive chronology of arc volcanoes consists of construction stages usually punctuated by large collapse events affecting the edifice. In this paper, we reconstruct the eruptive chronology of Carihuairazo volcano, a Middle Pleistocene edifice from the Ecuadorian segment of the Andean Northern Volcanic Zone. This study is based on extensive fieldwork on both the proximal flanks of the volcano and the medial-to-distal deposits of the nearby Ambato basin, as well as a large dataset of geochronological (40K-40Ar, 14C) and geochemical (major and trace element) data. The Basal Carihuairazo edifice is mainly composed of an andesitic lava flow succession dated at 230–200 ka. The resulting edifice suffered a first sector collapse that was responsible for a relatively large (4 ± 1 km3) debris avalanche deposit (DAD-1) that covers the entire Ambato basin. This event occurred between 206 ± 4 and 216 ± 5 ka. Then, Carihuairazo started a succession of construction (Intermediate and Terminal lava flow successions) and destruction stages lasting about 50 ky (i.e., from 200 to 150 ka), which are composed by thick block-and-ash flow deposits (L- and U-BAFD) and debris avalanche deposits (DAD-2). This volcanic succession is recorded in the Ambato basin, interlayered with several tephra fallout deposits (TFD-1 to −4) whose source is the neighbouring Huisla-Mulmul volcanic complex. The current morphology of Carihuairazo results from two additional sector collapses (DAD-3 and -4) that occurred during the past 40–50 ka, i.e., following a long period (at least 100 ka) without volcanic activity. We stress these debris avalanches were not related with magmatic activity. Samples from the Carihuairazo volcano defines a medium-K magmatic trend composed of andesites and dacites with a mineral assemblage of plagioclase, amphibole, ortho- and clino-pyroxene, and Fe–Ti oxides. The evolution of the Carihuairazo edifice, recorded in the medial-distal deposits of the Ambato basin, represents a unique example in the Ecuadorian arc of an edifice that experienced successive destruction and construction stages during a major part of its volcanic history.

Inflated pyroclasts in proximal fallout deposits reveal abrupt transitions in eruption behaviour

During explosive eruption of low viscosity magmas, pyroclasts are cooled predominantly by forced convection. Depending on the cooling efficiency relative to other timescales, a spectrum of deposits can be formed. Deposition of hot clasts, above their glass transition temperature, can form spatter mounds, ramparts and clastogenic lava flows. Clasts may also be deposited cold, producing tephra cones and blankets. Thus, the deposit and pyroclast type can provide information about eruption dynamics and magma properties. Here we examine pyroclasts from Tseax volcano, British Columbia, Canada. These newly identified inflated pyroclasts, are fluidal in form, have undergone post-depositional expansion, and are found juxtaposed with scoria. Detailed field, chemical and textural observations, coupled with high temperature rheometry and thermal modelling, reveal that abrupt transitions in eruptive behaviour — from lava fountaining to low-energy bubble bursts — created these pyroclastic deposits. These findings should help identify transitions in eruptive behaviour at other mafic volcanoes worldwide.

Degassing from magma reservoir to eruption in silicic systems: The Li elemental and isotopic record from rhyolitic melt inclusions and host quartz in a Yellowstone rhyolite

Lithium and hydrogen are volatile elements which diffuse rapidly in crystals and melt, making them powerful geochemical tools to reconstruct geological processes that take place on short time scales, such as syn- and post-eruptive degassing. Although the dynamics of hydrogen are fairly well understood to better constrain such processes, the assessment of Li behaviour within the magma reservoir relevant for ascent-related degassing still lacks detailed evaluation. Here, the first in situ Li concentrations and isotopic compositions (using SIMS analysis) of rhyolitic quartz-hosted, naturally glassy and crystallised melt inclusions (MIs) and groundmass glass (Mesa Falls Tuff, Yellowstone) are used to reconstruct Li elemental and isotopic evolution in the magma reservoir. Lithium concentrations in quartz-hosted glassy MIs (10–61 ppm) from a fallout deposit overlap with their groundmass glass (32–46 ppm) and their host quartz (8–15 ppm). Crystallised MIs from a later erupted flow pumice clast sample have higher Li concentrations (8–190 ppm) compared to the groundmass glass (32–51 ppm) and their host quartz (15–24 ppm). Lithium content in quartz from the early erupted sample is relatively homogenous, whereas it is up to a factor of two higher and heterogeneous in the later erupted sample, with a simultaneous increase in Li versus a decrease in H towards crystal rims. The δ7Li difference (expressed as Δ7LiMI–glass) between MIs (−8.0‰ to + 12.3‰) and groundmass glass (+9.0‰ to + 20.5‰) of two pyroclastic deposits reaches up to 29‰. Glassy MIs are internally heterogeneous in δ7Li and Li abundance. The cores of the glassy MIs record the δ7Li of the least modified melt during entrapment and the data distribution can be modelled by equilibrium fractionation between the melt and vapour phase during early open-system degassing in the magma reservoir. Late degassing during eruption triggers Li–H diffusional exchange between quartz and melt, as the degassing of H2O and the accompanying pressure change trigger H diffusion out of the host quartz and the MIs, which is charge balanced by inward Li diffusion. This results in the modification of Li contents in quartz and δ7Li values in the rims of the glassy MIs. Crystallised MIs reflect the loss of H2O from the MIs and the resulting enrichment of Li during the crystallisation. Additionally, the variations of δ7Li in the groundmass glass can be explained through modelling by kinetic fractionation between the melt and vapour during late stage open-system degassing linked with magma ascent.

Analysis of the 2020 Taal Volcano tephra fall deposits from crowdsourced information and field data

After 43 years of dormancy, Taal Volcano violently erupted in January 2020 forming a towering eruption plume. The fall deposits covered an area of 8605 km2, which includes Metro Manila of the National Capital Region of the Philippines. The tephra fall caused damage to crops, traffic congestion, roof collapse, and changes in air quality in the affected areas. In a tropical region where heavy rains are frequent, immediate collection of data is crucial in order to preserve the tephra fall deposit record, which is readily washed away by surface water runoff and prevailing winds. Crowdsourcing, field surveys, and laboratory analysis of the tephra fall deposits were conducted to document and characterize the tephra fall deposits of the 2020 Taal Volcano eruption and their impacts. Results show that the tephra fall deposit thins downwind exponentially with a thickness half distance of about 1.40 km and 9.49 km for the proximal and distal exponential segments, respectively. The total calculated volume of erupted fallout deposit is 0.057 km3, 0.042 km3, or 0.090 km3 using the exponential, power-law, and Weibull models, respectively, and all translate to a VEI of 3. However, using a probabilistic approach (Weibull method) with 90% confidence interval, the volume estimate is as high as 0.097 km3. With the addition of the base surge deposits amounting to 0.019 km3, the volume translates to a VEI of 4, consistent with the classification for the observed height and umbrella radius of the 2020 main eruption plume. VEI 4 is also consistent with the calculated median eruption plume height of 17.8 km and sub-plinian classification based on combined analysis of isopleth and isopach data. Phreatomagmatic activity originated from a vent located in Taal Volcano’s Main Crater Lake (MCL), which contained 42 million m3 of water. This eruptive style is further supported by the characteristics of the ash grain components of the distal 12 January 2020 tephra fall deposits, consisting dominantly of andesitic vitric fragments (83–90%). Other components of the fall deposits are lithic (7–11%) and crystal (less than 6%) grains. Further textural and geochemical analysis of these tephra fall deposits contributes to better understand the volcanic processes that occurred at Taal Volcano, one of the 16 Decade Volcanoes identified by the International Association of Volcanology and Chemistry of the Earth’s Interior (IAVCEI) because of its destructive nature and proximity to densely populated areas. The crowdsourcing initiative provided a significant portion of the data used for this study while at the same time educating and empowering the community to build resilience.

Non-linear radar response to the radial structure of Europa plume fallout deposits

Observations of water vapor plumes emanating from Europa's surface provide direct evidence of on-going activity within the ice shell that may have important implications for the potential habitability of Europa's putative global ocean. However, the scarcity of repeated observations suggest that Europa plumes are sporadic and may prove elusive when attempting to sample them directly with the instruments on-board either NASA's Europa Clipper or ESA's JUpiter ICy moons Explorer (JUICE) spacecraft. An alternative approach is then to search for and characterize the remnant plume fallout deposits preserved on Europa's surface. To this end, in this study we investigate the radar response of surficial plume fallout deposits when illuminated by both the Radar for Europa Assessment and Sounding: Ocean to Near-surface (REASON) instrument on-board Europa Clipper as well as the Radar for Icy Moons Exploration (RIME) instrument on-board JUICE. Our results reveal distinct patterns in radial coherent surface reflectivity associated with different families of plume heights. Uniform fallout depositional rates surrounding low (≤25 km) altitude plumes result in a radially-constant coherent surface reflectivity that oscillates as a function of plume duration. In contrast, fallout deposits from high (≥50 km) altitude plumes exhibit radially variable, ripple-like patterns in coherent surface reflectivity as the velocity at which a particle is ejected from the plume is size dependent. The amplitude of the reflectivity oscillations as a function of fallout deposit thickness is directly dependent on porosity, with greater oscillation amplitudes being associated with older fallout deposits that have undergone some degree of densification (as opposed to the young, porous deposits of very recently active plumes). Finally, the results highlight that in the presence of near-surface structure, there is no direct proportionality between observed radar surface reflectivity and near-surface bulk density.

A Methodology for Estimating External Doses to Individuals and Populations Exposed to Radioactive Fallout from Nuclear Detonations.

A methodology of assessment of the doses from external irradiation resulting from the ground deposition of radioactive debris (fallout) from a nuclear detonation is proposed in this paper. The input data used to apply this methodology for a particular location are the outdoor exposure rate at any time after deposition of fallout and the time-of-arrival of fallout, as indicated and discussed in a companion paper titled "A Method for Estimating the Deposition Density of Fallout on the Ground and on Vegetation from a Low-yield Low-altitude Nuclear Detonation." Example doses are estimated for several age categories and for all radiosensitive organs and tissues identified in the most recent ICRP publications. Doses are calculated for the first year after the detonation, when more than 90% of the external dose is delivered for populations close to the detonation site over a time period of 70 y, which is intended to represent the lifetime dose. Modeled doses in their simplest form assume no environmental remediation, though modifications can be introduced. Two types of dose assessment are considered: (1) initial, for a rapid but only approximate dose estimation soon after the nuclear detonation; and (2) improved, for a later, more accurate, dose assessment following the analysis of post-detonation measurements of radiation exposure and fallout deposition and the access of information on the lifestyle of the exposed population.

Unveiling the occurrence of transient, multi-contaminated mafic magmas inside a rhyolitic reservoir feeding an explosive eruption (Nisyros, Greece)

The investigation of heterogeneous magma systems enhances the understanding of magma differentiation and transfer processes in active volcanoes, thus constraining the dynamics driving the eruptions and the related hazard. Magma heterogeneity is generally preserved in the coeval juvenile products of explosive eruptions, as it occurs in the Upper Pumice sequence, emplaced by the last sub-Plinian explosive eruption at Nisyros volcano (Greece). The deposit comprises a basal fallout, overlaid by pyroclastic density current units, followed by a lag-breccia level. White-yellow, porphyritic, rhyolitic pumices constitute the main juvenile component. Grey, crystal-rich juvenile clasts (CRCs) are less abundant (up to 10–15%), and are characterised by three different texture types (Type-A, -B and -C), with specific recurrence in the different depositional units and well correlated to the magma evolution. In the basal unit CRCs occur as andesitic to dacitic lapilli with Type-A and -B vesicular textures associated with highly variable trace element and isotopic compositions. In the lag-breccia deposit, the juvenile clasts occur as bombs with crenulated or bread-crust surfaces, displaying diktytaxitic Type-C textures and less evolved andesitic compositions, covering a larger Nd-isotope range at lower Sr-isotopes compared to the others.The CRCs are interpreted as the result of the rapid cooling of more mafic magma blobs sequentially intruded in the cooler rhyolitic host magma, in which they attained variable textures by different undercooling conditions, due to their variable compositions. We suggest that a two-stage AFC (Assimilation plus Fractional Crystallisation) process occurred at different pressures, before intrusion in the host magma, accounting for their heterogeneous chemical and isotopic characteristics. Firstly, the most primitive melts variably assimilated gneissic wallrock at depth, acquiring a variable Nd-isotope signature. On the way to the surface, they later experienced shallow AFC processes within different small magma reservoirs, involving heterogeneous carbonate-rocks such as pure limestone, metasomatised marble and skarn. Sequential dynamics of ascent and intrusion into the rhyolitic magma chamber lead the more evolved and skarn-contaminated Type-A and -B melts to firstly move in the upper part of the reservoir to be erupted in the early fallout deposits. Type-C more mafic melts later intruded the rhyolitic reservoir and were erupted in the lag-breccia deposit. The lowest Nd-isotopes recorded by CRCs, with respect to all the volcanic products of the Kos-Nisyros volcanic field, reveal the peculiar transient history for these magmas at relatively shallow levels in the crust. The CO2 release from the carbonate-rock assimilation has also possibly contributed to trigger the explosive eruption, discharging a large amount of CO2 into the atmosphere.

Lahar risk assessment from source identification to potential impact analysis: the case of Vulcano Island, Italy

Lahars are rapid flows composed of water and volcaniclastic sediments, which have the potential to impact residential buildings and critical infrastructure as well as to disrupt critical services, especially in the absence of hazard-based land-use planning. Their destructive power is mostly associated with their velocity (related to internal flow properties and topographic interactions) and to their ability to bury buildings and structures (due to deposit thickness). The distance reached by lahars depends on their volume, on sediments/water ratio, as well as on the geometrical properties of the topography where they propagate. Here we present the assessment of risk associated with lahar using Vulcano island (Italy) as a case study. First, we estimated an initial lahar source volume considering the remobilisation by intense rain events of the tephra fallout on the slopes of the La Fossa cone (the active system on the island), where the tephra fallout is associated with the most likely scenario (e.g. long-lasting Vulcanian cycle). Second, we modelled and identified the potential syn-eruptive lahar impact areas on the northern sector of Vulcano, where residential and touristic facilities are located. We tested a range of parameters (e.g., entrainment capability, consolidation of tephra fallout deposit, friction angle) that can influence lahar propagation output both in terms of intensity of the event and extent of the inundation area. Finally, exposure and vulnerability surveys were carried out in order to compile exposure and risk maps for lahar-flow front velocity (semi-quantitative indicator-based risk assessment) and final lahar-deposit thickness (qualitative exposure-based risk assessment). Main outcomes show that the syn-eruptive lahar scenario with medium entrainment capability produces the highest impact associated with building burial by the final lahar deposit. Nonetheless, the syn-eruptive lahar scenario with low entrainment capacity is associated with higher runout and results in the highest impact associated with lahar-flow velocities. Based on our simulations, two critical infrastructures (telecommunication and power plant), as well as the main road crossing the island are exposed to potential lahar impacts (either due to lahar-flow velocity or lahar-deposit thickness or both). These results show that a risk-based spatial planning of the island could represent a valuable strategy to reduce the volcanic risk in the long term.

Quaternary basaltic volcanic fields of the American Southwest

AbstractThe southwestern United States contains numerous monogenetic basaltic volcanoes distributed in intraplate volcanic fields. We review, on a regional scale, our current understanding of the Quaternary basalts with a focus on aspects pertinent to hazard assessment, such as physical volcanology and geochronology, while also summarizing the several petrogenetic conceptual models that have been proposed for the range of local tectonic settings in the region. We count 2229 volcanoes in 37 volcanic fields (including the Pinacate volcanic field, which is mostly in northern Sonora, Mexico). Volcanic landforms are dominantly scoria cones and ramparts with attendant lava fields that have a spectrum of ‘a'ā and blocky to pāhoehoe morphologies, while a small percentage of the volcanoes are maars and tuff cones. Explosive eruption styles that were driven mainly by magmatic volatiles, where they have been studied in detail, included Hawaiian, Strombolian, violent Strombolian, and sub-Plinian activity. The latter two have resulted in substantial fallout deposits that can be traced tens of kilometers from source vents. Phreatomagmatic styles have produced pyroclastic current (mainly pyroclastic surges), ballistic, and fallout deposits. These eruption styles pose hazards to humans when they occur in populated areas and to air travel and regional infrastructure even in sparsely populated areas. All but one of the major volcanic fields (fields that contain ∼100 or more Quaternary volcanoes) together form a northwest-southeast–trending band, which we suggest may reflect an influence of plate-boundary-related shearing on melt segregation in the upper mantle along with other factors; this view is consistent with recent global positioning system (GPS) and structural geologic data indicating the influence of dextral motion along the North America-Pacific plate boundary deep inside the Southwest. Of the 2229 Quaternary volcanoes identified, ∼548 (25%) have been dated, and only ∼15% have been dated with methods such as 40Ar/39Ar and cosmogenic surface exposure methods that are considered optimal for young basalts. Acknowledging the large uncertainty due to the poor geochronological data coverage, we use a simple Poisson model to provide a first-order estimate of recurrence rates of monogenetic volcanoes on the scale of the region as a whole; recurrence rates using our compiled age data set range from 3.74 × 10−4 yr−1 to 8.63 × 10−4 yr−1. These values are only based on dated and mapped volcanoes, respectively, and do not account for undated and buried volcanoes or other uncertainties in the volcano count. The time between monogenetic eruptions in the Southwest is similar to the repose times of some polygenetic volcanoes, which suggests that the regional hazard is potentially commensurate with the hazard from a reawakening stratovolcano such as those in the Cascade Range. Notable in our review is that only a few volcanoes have been the subject of physical volcanological characterization, interpretation, and detailed petrologic study that may elucidate factors such as magma generation, ascent (including time scales), and controls on eruption style.

Uniform “water” content in quartz phenocrysts from silicic pyroclastic fallout deposits – implications on pre-eruptive conditions

Abstract. Structural hydroxyl content of volcanic quartz phenocrysts was investigated with unpolarized Fourier-transform infrared spectroscopy. The phenocrysts originated from five pyroclastic fallout deposits from the Bükk Foreland Volcanic Area (BFVA), Hungary, and two from the AD 1314 Kaharoa eruption (KH eruption), Okataina Volcanic Complex (Taupo Volcanic Zone), New Zealand. All investigated quartz populations contain structural hydroxyl content in a narrow range with an average of 9.3 (±1.7) wt ppm. The earlier correlated horizons in the BFVA had the same average structural hydroxyl content (within uncertainty). Thus, it can be concluded that the structural hydroxyl content does not depend on the geographical distance of outcrops of the same units or the temperature or type of the covering deposit. The rare outlier values and similar structural hydroxyl contents show that the fallout horizons cooled fast enough to retain their original structural hydroxyl content. The similarity of the structural hydroxyl contents may be the result of similar P, T, and x (most importantly H2O and the availability of other monovalent cations) conditions in the magmatic plumbing system just before eruption. Therefore, we envisage common physical–chemical conditions, which set the structural hydroxyl content in the quartz phenocrysts and, consequently, the water content of the host magma (∼ 5.5 wt %–7 wt % H2O) in a relatively narrow range close to water saturation.

Deciphering anthropogenic uranium sources in the equatorial northwest Pacific margin

This work reports the first high-resolution deposition records of anthropogenic uranium (236U and 233U) in a sediment core taken at the continental slope of the Philippine Sea off Mindanao Island in the equatorial northwest Pacific Ocean. Two notable peaks were observed in both profiles of 236U and 233U concentrations, with a narrower peak in 1951–1957 corresponding to close-in Pacific Proving Grounds (PPG) signal, and a broader peak in 1960s–1980s corresponding to the global fallout from nuclear weapons testing. 236U and 233U areal cumulative inventories in the studied sediment core are (2.79 ± 0.20) ∙ 1012 atom ∙ m−2 and (3.12 ± 0.41) ∙ 1010 atom ∙ m−2, respectively, about 20–30% of reported 233U and 236U inventories from the direct global fallout deposition. The overall 233U/236U atomic ratios obtained in this work vary within (0.3–3.5) ∙ 10−2, with an integrated 233U/236U atomic ratio of (1.12 ± 0.17) ∙ 10−2. The contribution from global fallout and close-in PPG fallout to 236U in the sediment core is estimated to be about 69% and 31%, respectively. We believe the main driving process for anthropogenic uranium deposition in the Philippine sediment is continuous scavenging of dissolved 236U from the surface seawater by sinking particles.

New observations on the recent eruptive activity of Sumaco Volcano (Ecuador), based on geochronology, stratigraphy and petrography

Sumaco is a stratovolcano located in the northern SubAndean zone of Ecuador, 105 km east of Quito. The flanks of Sumaco are jungle-covered, and scarce outcrops are found along stream banks, trails and, in quarries. Based on our field studies, eruptions of Sumaco during the historical era were associated with small-scale Strombolian activity. Earlier more robust activity, which pertains to the last 4400 years, had vigorous eruptions whose ∼10 cm thickness ash fallout deposits are identified more than 20 km from the vent.Stratigraphic sections studied around the volcano's outer flanks identify five principal ash-fall layers corresponding to Sumaco's activity. The ash layers contain white micro-vesiculated pumice, displaying clinopyroxene, plagioclase, traces of amphibole, and biotite crystals. Also, gray lithics with pyroxene phenocrysts and scarce plagioclase crystals are present. The amount of volcanic glass shards is meager in almost all samples. The thickest ash layer, “SUM-JS-44″, was dated by 14C, obtaining an age of 3029-2888cal AD.Analysis of a sediment core obtained from the “Guagua Sumaco” near-source lagoon allowed us to identify nine ash layers; seven are from Sumaco. Dating an underlying layer of peat (OL3) beneath the six ash layers provides an age of 1483–1644 cal AD, showing that Sumaco volcano experienced at least six separate eruptive pulses during the last centuries, and thus it should be considered potentially active.Based on morphological observations, Sumaco's edifice consists of three phases: PaleoSumaco, Recent Sumaco, and Current Sumaco, differentiated mainly by two scars representing flank collapses that produced far-reaching debris avalanches, whose breccia deposits are observed around the cone's depositional apron.The aim of our research is to understand the evolution of Sumaco's edifice and verify the relative youthfulness of the volcano and its eruption styles. These inputs are then applied in determining three eruption scenarios.

Pre-eruptive conditions and reheating of dacitic magma (Malinche Pumice II Plinian eruption) at La Malinche volcano, Central Mexico

The Malinche Pumice II is a fallout deposit produced by a Plinian-type eruption during the Pleistocene-Holocene at La Malinche volcano. La Malinche (4461 masl) is an active stratocone located in central Mexico, in the Trans-Mexican Volcanic Belt province. It is 26 km to the NE of the City of Puebla and 22 km to the SE of the City of Tlaxcala. The Malinche Pumice II was produced by one of the largest explosive eruptions of this volcano, involving a dacitic magma (63.6–65.3 wt% SiO2, anhydrous basis) with a mineral assemblage of plagioclase + amphibole + FeTi oxides and ± biotite phenocrysts. Larger plagioclase crystals are up to 1.2 mm in diameter, with resorbed margins and complex zoning (An26 to An43), whereas microcrysts are euhedral with homogeneous composition (An42 to An55). Amphibole is mainly magnesio-ferri-hornblende (Mg# = 0.65–0.82) and lesser amounts of pargasite. Geothermometry performed using FeTi oxides yields an average temperature of 873 ± 2 °C and oxygen fugacity of 1.8 units above the NNO buffer. Amphibole geothermobarometry yields a lower temperature (809 ± 19 °C) and a pressure of 230 ± 100 MPa, assuming 4.4 wt% of H2O. Considering an average density of 2650 kg/m3 for the upper crust in central Mexico, the storage region of the Malinche Pumice II dacitic magma was located at 8 ± 2 km depth. Biotite could be antecrystic or xenocrystic in origin, based on its reacted texture, large sizes (0.85–2 mm), and reaction rims. Similarly, pargasite that provides higher temperature estimates (900 ± 18 °C) and low anorthite plagioclase (An26) could also be antecrysts or xenocrysts. The Plinian eruption was likely triggered by an input of a hotter and deeper magma batch that overpressurized the dacitic magma system that eventually provoked vesiculation and fragmentation. The eruption shifted to a hydromagmatic style because of external water's entrainment that decreased the vesicularity of pumice. Our results are in good agreement with recent seismicity recorded at depths of ~7 km probably associated with activity of the Malinche's magmatic system.

High-precision measurement of U-Pu-Np-Am concentrations and isotope ratios in environmental reference materials by mass spectrometry

We report results of precise and sensitive mass spectrometric measurements of uranium, plutonium, neptunium, and americium concentrations and isotope ratios in a variety of environmental reference materials. Most of our work has been done on NIST SRM 4350b, River Sediment, but we also present results for NIST SRM 4354, Lake Sediment; NIST SRMs 4355 and 4355a, Peruvian Soil; NIST SRM 4357, Ocean Sediment; NIST SRM 1648a, Urban Particulate Material; NIST SRM 1649b, Urban Dust; IAEA CRM 385, Ocean Sediment; USGS BCR-2, Columbia River Basalt; and USGS BHVO-2, Hawaiian Volcanic Observatory Basalt. These materials reflect a wide range in long-lived actinide concentrations (e.g. 1E4 to 1E10 atoms 239Pu/g) and isotope ratios. Measurements were performed in a clean laboratory by isotope dilution, multi-collector thermal ionization and multi-collector inductively coupled plasma mass spectrometry. In general, our results are in agreement with, but lower the uncertainty of, literature or certificate values for these reference materials. Our uranium results for the basalts also confirm previously reported high-precision mass spectrometric results from our laboratory. In many cases our measurements of U-Pu-Np-Am nuclides appear to be novel.Extensive results for NIST SRM 4350b, River Sediment, indicate that this material is heterogeneous for Pu-Np-Am concentrations and isotope ratios at a sample size of 5 g or lower. Pu–Np isotope ratios and a241Pu-241Am model age of 1954 reflect a mix of plutonium production operations at the nearby Hanford, Washington site, and global atmospheric fallout from nuclear weapons testing. Results for the oceanic sediment materials (NIST SRM 4357 and IAEA 385) collected near Sellafield, U.K. vary but are also indicative of local anthropogenic sources of varying Pu isotopic composition and a mean 241Pu-241Am model age of 1964. Large environmental fractionation between Pu and Np is observed for the ocean, river, and lake sediment reference materials. Novel measurements for the two air particulate SRMs indicate high U, Pu and Np concentrations for these collections in 1976–1977 with an anomalous regional fallout Pu isotopic signature. Results for BHVO-2 and other Hawaiian basalts indicate that those which erupted before or during the period of abundant atmospheric nuclear weapons testing (1950–1970) contain significant levels of Pu (on the order of 1E7 atoms 239Pu/g) with a global fallout Pu isotopic composition, compared to more recent eruptions which incorporated less Pu. Hence, Hawaiian basalts may provide an integrated temporal record of anthropogenic actinide fallout deposition from the atmosphere since eruption.

Explosive caldera-forming eruptions and debris-filled vents: Gargle dynamics

AbstractLarge explosive volcanic eruptions are commonly associated with caldera subsidence and ignimbrites deposited by pyroclastic currents. Volumes and thicknesses of intracaldera and outflow ignimbrites at 76 explosive calderas around the world indicate that subsidence is commonly simultaneous with eruption, such that large proportions of the pyroclastic currents are trapped within the developing basins. As a result, much of an eruption must penetrate its own deposits, a process that also occurs in large, debris-filled vent structures even in the absence of caldera formation and that has been termed “gargling eruption.” Numerical modeling of the resulting dynamics shows that the interaction of preexisting deposits (fill) with an erupting (juvenile) mixture causes a dense sheath of fill material to be lifted along the margins of the erupting jet. This can cause an eruption that would otherwise produce a buoyant plume and fallout deposits to instead form pyroclastic currents as the dense sheath drives pulsing jet behavior. Increasing thickness of fill amplifies the time variation in jet height. Increasing the fill grain size relative to that of the juvenile particles can result in a much higher jet due to poorer mixing between the dense sheath and the dilute jet core. In all cases, material collapses along the entire height of the dense sheath rather than from the top of a simple fountain. These gargle dynamics provide strong backing for processes that have been inferred to result in intraplinian ignimbrites and simultaneous deposition from high- and low-energy pyroclastic currents.

Nuclear Emergency: A Review of Radioactivity in Human Ecosystem

One of the serious impacts on the environment and human health is the proper evaluation of radioactivity from elevated naturally occurring isotopes or those from industrial activities. Radionuclides produced from nuclear explosions and nuclear facilities when released into the environment may reach the human body through the food pathways. Radionuclides from environmental sources have the ability to cause a hazard to human health through food sources. There is the need for radiological estimation for transfers from the vegetative covers through the human ecosystem. The assessment models are subdivided mainly into three categorical states; that is from the soil-plant transfer, the transfer to animals, and spatial models. Radionuclides may enter the human ecosystem through atmospheric releases from nuclear facilities. Freshwater contamination happens via the release of water bodies which may affect aquatic lives. Various assessment models have been developed based on the fallout deposition from the Chernobyl accident, however, the distinct uncertainties involved in propagating this data to a completely different geographical location cannot be ignored. This is a review paper that analysis the Absalom model, its application in system assessment models, and how they can be applied in country-specific data to achieve a realistic model prediction in food safety from radionuclide release and the need for further research.

The Ediacaran volcano-sedimentary succession in the Western Skoura inlier (Central High Atlas, Morocco): facies analysis, geochemistry, geochronology and geodynamic implications

The Skoura inlier in the Moroccan High Atlas consists of thick Precambrian–Paleozoic formations. It displays, in the western part near Aguerzega village, a volcano-sedimentary succession of about 400 m thickness. It includes a variety of welded and non-welded ignimbrites, lapilli-tuff fallout deposit, coherent lava, sedimentary mass flow deposit and fluvial sediments, which are grouped into three lithofacies associations, corresponding to different depositional environments. The volcanic activity in the studied area represents successive volcanic eruptions, alternating with phases of quiescence (sedimentary beds). The Ediacaran volcano-sedimentary succession of the Skoura inlier represents an evolution in four stages in a subaerial environment. The geochemical results obtained from Skoura volcanic rocks display high silica-rich composition ranging from dacite to rhyolite. Major and trace elements show high-K calc-alkaline and alkali-calcic to alkaline affinities and reflect an active continental margin signature. In addition, the studied rocks show enriched LILE compared to HFSE with negative Nb-, Ta- and Ti anomalies. This is consistent with a post-collisional setting, documented for the final phase of the Pan-African orogeny. Laser ablation U–Pb zircon dating on three rhyolitic ignimbrites from the base and top of two profiles, yielded ages of 580 ± 7 Ma, 574 ± 14 Ma and 571 ± 4 Ma. These ages compare well with the lower Ouarzazate Supergroup, widespread in the Anti-Atlas, as well as in the High Atlas and with rare exposures in the Meseta domain in northern Morocco.

Early Miocene calc-alkaline felsic tuffs within deep-marine turbidites in the Kyrenia Range, north Cyprus, with a possible post-collisional eruptive centre in western Anatolia

AbstractFelsic tuff as a direct fallout deposit is known from one small area in the Kyrenia Range, north Cyprus, within deep-sea terrigenous turbidites. Nearby tuffaceous siltstones contain compositionally similar felsic volcanic rocks (c. 5–10%), mixed with terrigenous material. Sedimentary evidence indicates that the fallout tuff was variable reworked locally, whereas the tuffaceous siltstones are interpreted as turbidites mixed with terrigenous material derived from Anatolia. U–Pb dating of zircons that were extracted from a sample of relatively homogeneous tuff yielded a dominant age of 16.64 ± 0.12 Ma (Burdigalian). Zircon trace-element analysis indicates predominant derivation from within-plate-type felsic magma. Whole-rock chemical analysis of the tuffaceous sediments as a whole is compatible with a felsic arc source, similar to the post-collisional magmatism within Anatolia. Regional comparisons suggest that the nearest volcanism of similar age and composition is locatedc. 500 km away, within the Kırka area (Eskişehir region) of the Western Anatolia Volcanic Province. Evidence of tephra dispersal in the western Mediterranean region and climatic modelling suggests E-wards prevailing winds and therefore tephra transport over southern Anatolia and adjacent areas during early Miocene time. The north Cyprus tuffs could represent powerful Minoan (Plinian)-type eruptions in western Anatolia, coupled with SE-wards tephra transport during and soon after the onset of post-collisional magmatism.