Dispersal Axis Research Articles

A Kernel-Based Calibration Algorithm for Chromatic Confocal Line Sensors.

In chromatic confocal line sensors, calibration is usually divided into peak extraction and wavelength calibration. In previous research, the focus was mainly on peak extraction. In this paper, a kernel-based algorithm is proposed to deal with wavelength calibration, which corresponds to the mapping relationship between peaks (i.e., the wavelengths) in image space and profiles in physical space. The primary component of the mapping function is depicted using polynomial basis functions, which are distinguished along various dispersion axes. Considering the unknown distortions resulting from field curvature, sensor fabrication and assembly, and even the inherent complexity of dispersion, a typical kernel trick-based nonparametric function element is introduced here, predicated on the notion that similar processes conducted on the same sensor yield comparable distortions.To ascertain the performance with and without the kernel trick, we carried out wavelength calibration and groove fitting on a standard groove sample processed via glass grinding and with a reference depth of 66.14 μm. The experimental results show that depths calculated by the kernel-based calibration algorithm have higher accuracy and lower uncertainty than those ascertained using the conventional polynomial algorithm. As such, this indicates that the proposed algorithm provides effective improvements.

Reconstructing the Belbaşhanı Pumice Plinian eruption, Hasandağ Volcano, Turkey

Hasandağ volcano (Central Anatolia, Turkey) has recently underwent an increase in local seismicity and fumarolic activity since 2013. In the past, this volcano has produced multiple large explosive eruptions during the last million years. The Belbaşhanı Pumice is the product of a sub-Plinian to Plinian eruption dated at ~ 417 ± 20.5 ka (40Ar/39Ar). Here, we present a complete volcanological study including stratigraphy, glass chemistry, pumice morphology, geochronology, and eruption source parameters with the associated uncertainties, to characterize the Belbaşhanı Pumice eruption. The eruption involved a column of 18–29 km in height, with the main dispersal axis towards the northeast. A pumice layer up to ~ 17-m-thick accumulated in proximal deposits along the Belbaşhanı path, and up to 2-m-thick in medial-distal areas (~ 18 km northeast from the vent). The high and tubular vesicularity of the pumice clasts indicates that the Belbaşhanı eruption was predominantly magmatic. The bulk volume of the Belbaşhanı Pumice fallout deposit has been estimated as 0.5 and 8 km3 (with ~ 2 km3 being the mean value), which corresponds to Volcanic Explosivity Index (VEI) of at least 4 and up to 6. Both isopach and isopleth maps indicate that the volcanic vent may have been located at the intersection of the Tuz Gölü fault and Ulukışla caldera, within the Hasandağ volcanic complex. The glass composition of Belbaşhanı Pumice confirms that the eruption belongs to the Hasandağ magmatic system. The reconstruction of the Belbaşhanı Pumice eruption represents an essential baseline in providing volcanological constraints for further investigations of tephra fallout hazard assessment in Central Anatolia, especially considering that a new Plinian eruption cannot be ruled out at Hasandağ volcano in the future. The chemical and geochronological datasets presented here could aid in refining tephrochronological correlations, with the goal of synchronizing paleoenvironmental and paleoclimatic records alongside archaeological sites.

Electrocardiographic characteristics of pediatric and adolescent football players

Electrocardiographic characteristics of children and adolescents present differences compared to adults. The aim of our work was to study electrocardiograms (ECGs) of football male players from childhood to late adolescence and examine if the ECG parameters are influenced by systematic exercise. One thousand fifty-four football players participated and formed four groups. Group A included 89 players aged 5–7 years, group B 353 players aged 8–11 years, group C consisted of 355 football players 12-15 yearsold and group D of 257 players with 16–18 years of age. All participants underwent preparticipation screening, including 12-lead surface ECG. Heart rate (HR), PR, RR, QRS, QT, QTc intervals, QT dispersion (QTdisp) and QRS axis were calculated. All ECGs were evaluated according to the current preparticipation cardiac screening guidelines, that refer to athletes aged 12–35 years and do not include pediatric players. Eleven percent of the participants presented an ECG finding. Group D obtained the lowest values of HR, QTc and the highest of PR, RR, QRS, QT intervals and QTdisp, whereas no differences in QRS axis were reported. Incomplete Right Bandle Branch Block (RBBB) was the most frequent ECG peculiarity, detected in 7.3% of the participants. Years of training were statistically significantly correlated to HR, PR, RR, QRS and QT intervals. In conclusion, guidelines for ECG interpretation of athletes in childhood, early and late adolescence are needed.

Radiocarbon dating, magnitude, and catastrophic impact of Popocatépetl's Terminal Preclassic “Lorenzo pumice” Plinian eruption and paleomagnetic age constraints on the Nealtican lava flow field (central Mexico)

The “Lorenzo pumice” (LP) fallout was produced by a Plinian (VEI = 4) eruption of Popocatépetl volcano ∼40 cal BCE during the Terminal Preclassic period. It is part of a pyroclastic sequence that consists in stratigraphic order of fall, pyroclastic density current, and lahar deposits, which in turn are partly covered by the 70 km2 andesitic-dacitic “Pedregal de Nealtican” lava flow field on the eastern slope of the volcano.The composition of the pumice varies insignificantly (SiO2 = 61.0 to 63.5 wt%) with phenocrysts of euhedral plagioclase > orthopyroxene > clinopyroxene ± olivine ± hornblende ± opaques.Sizes of lithics and the isopach map indicate an eruption column height of ∼28 km and a dispersal axis toward the ENE, where an area of ∼600 km2 that included pre-Hispanic dispersed villages was buried under >10 cm of pumice. The minimum volume for the LP fallout was calculated at ∼0.6 km3 corresponding to ∼0.2 km3 of dense rock equivalent (DRE).The short Plinian phase ended when the column collapsed abruptly, generating lethal pyroclastic density currents that were emplaced around the volcano. It was followed by periodic flooding by rain lahars that originated from the slopes of Popocatépetl and from neighboring Iztaccíhuatl, severely affecting ravines and large portions of the plains of Puebla in the east.After the cataclysmic phase, the El Ombligo vent alignment opened at ∼4000 m a.s.l. on Popocatépetl's NE upper slope from which the lavas that form the Nealtican lava flow field emanated, an effusive activity that lasted >30 years. Paleomagnetic data for these lavas and stratigraphic evidence indicate that the lava flows with a total volume of 4.2 km3 were emplaced shortly after the explosive Plinian phase and represent the degassed portion of the LP magma.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, Cholula, and Cantona.

Dispersal and grain size characteristics of the May 14, 2018 Shinmoedake eruption deposit, Kirishima Volcano, Japan, based on post-eruption field survey and meteorological datasets

This study describes the dispersal and grain size characteristics of the May 14, 2018 Shinmoedake eruption deposits of Kirishima Volcano in southern Kyushu, southwestern Japan. We discuss the eruption sequence, including the temporal variations in the behavior of the plume, by combining field and meteorological datasets. Following a magmatic activity in 2011 characterized by a substantial change in the eruption style (from subplinian eruptions to lava effusion) and subsequent vulcanian explosions, the Shinmoedake crater experienced intermittent eruptions in 2018. The May 14, 2018 eruption began at 14:44 with a vulcanian eruption, with the eruption plume rising 4500 m above the crater rim. Thereafter, it transitioned to an ash eruption; the plume height decreased gradually until the eruption ceased at 16:10. The tephra fall deposits were distributed more than 27 km to the southeast of the source crater; the mass of the tephra fall deposit was approximately 2.1 × 107 kg, calculated based on an isomass map. The deposit incidence differed between the east and west sides of the major dispersal axis. The deposits found east of the main dispersal axis were primarily composed of coarse to medium sand-sized particles with no fine fraction (fine sand to silt in size). In contrast, the deposits west of the axis were finer-grained than those east of the axis. We analyzed photographs of the eruption plume, along with the regional meteorological data and the dispersal and grain-size characteristics of the deposits, and reached the following conclusion: during the May 14, 2018 eruption, the wind directions above the Shinmoedake crater fluctuated across altitudes. The westerly winds dispersed the eruption plume that rose to a higher altitude, containing coarser tephra associated with the initial vulcanian eruption, further to the east rather than along the main axis. In contrast, a lower-altitude ash eruption plume that was rich in fine materials was dispersed westward rather than along the main axis, which was influenced by northerly winds. The findings of this study can support the analysis of similar volcanic events.Graphical

Marsupial position on life-history continua and the potential contribution of life-history traits to population growth.

Previous studies have suggested that mammal life history varies along the fast-slow continuum and that, in eutherians, this continuum is linked to variation in the potential contribution of survival and reproduction to population growth rate (λ). Fast eutherians mature early, have large litters and short lifespans, and exhibit high potential contribution of age at first reproduction and fertility to λ, while slow eutherians show high potential contribution of survival to λ. However, marsupials have typically been overlooked in comparative tests of mammalian life-history evolution. Here, we tested whether the eutherian life-history pattern extends to marsupials, and show that marsupial life-history trade-offs are organized along two major axes: (i) the reproductive output and dispersion axis, and (ii) the fast-slow continuum, with an additional association between adult survival and body mass. Life-history traits that potentially drive changes in λ are similar in eutherians and marsupials with slow life histories, but differ in fast marsupials; age at first reproduction is the most important trait contributing to λ and fertility contributes little. Marsupials have slower life histories than eutherians, and differences between these clades may derive from their contrasting reproductive modes; marsupials have slower development, growth and metabolism than eutherians of equivalent size.

The Kormendy relation of early-type galaxies as a function of wavelength in Abell S1063, MACS J0416.1-2403, and MACS J1149.5+2223

Context. The wavelength dependence of the projection of the fundamental plane along the velocity dispersion axis, namely the Kormendy relation, is well characterised at low redshift but poorly studied at intermediate redshifts. The Kormendy relation provides information on the evolution of the population of early-type galaxies (ETGs). Therefore, by studying it, we may shed light on the assembly processes of these objects and their size evolution. As studies at different redshifts are generally conducted in different rest-frame wavebands, it is important to investigate whether the Kormendy relation is dependent on wavelength. Knowledge of such a dependence is fundamental to correctly interpreting the conclusions we might draw from these studies. Aims. We analyse the Kormendy relations of the three Hubble Frontier Fields clusters, Abell S1063 at z = 0.348, MACS J0416.1-2403 at z = 0.396, and MACS J1149.5+2223 at z = 0.542, as a function of wavelength. This is the first time the Kormendy relation of ETGs has been explored consistently over such a large range of wavelengths at intermediate redshifts. Methods. We exploit very deep Hubble Space Telescope photometry, ranging from the observed B-band to the H-band, and VLT/MUSE integral field spectroscopy. We improve the structural parameter estimation we performed in a previous work by means of a newly developed PYTHON package called MORPHOFIT. Results. With its use on cluster ETGs, we find that the Kormendy relation slopes increase smoothly with wavelength from the optical to the near-infrared (NIR) bands in all three clusters, with the intercepts becoming fainter at lower redshifts due to the passive ageing of the ETG stellar populations. The slope trend is consistent with previous findings at lower redshifts. Conclusions. The slope increase with wavelength implies that smaller ETGs are more centrally concentrated than larger ETGs in the NIR with respect to the optical regime. As different bands probe different stellar populations in galaxies, the slope increase also implies that smaller ETGs have stronger internal gradients with respect to larger ETGs.

Dispersed fringe cophasing method based on principal component analysis.

With the success of the Webb telescope, dispersed fringe sensing (DFS), with the significant merit of a large capture range, is proving to be a promising cophasing approach for a large-aperture segmented telescope. In this Letter, a novel, to the best of our knowledge, piston error extraction method based on principal component analysis (PCA) technology is proposed. In this method, all the one-dimension intensity distributions along the dispersion axis for different interference positions are regarded as a set of random phase-shifted interference signals. PCA technology is utilized to obtain its corresponding continuous principal phase and the piston error could be directly estimated proportionally from the slope of the phase-wavenumber line. This method avoids nonlinear operations, similar to Shi's traditional framework; no active move is needed for fine cophasing, and the method is also free of characteristic constant calibration in sidelobe peak displacement- and slope-based methods. Preliminary simulations of the method's coarse-then-fine cophasing ability with high accuracy are presented here to show its potential.

Using Eruption Source Parameters and High-Resolution Grain-Size Distributions of the 7.7 ka Cleetwood Eruption of Mount Mazama (Oregon, United States) to Reveal Primary and Secondary Eruptive Processes

Numerical simulations of real-time volcanic ash dispersal forecasts and ensuing tephra hazard assessments rely on field-derived Eruption Source Parameters (ESPs) such as plume height, erupted volume, mass eruption rate and the Total Grain-Size Distribution (TGSD) of particles ejected from a volcano into the atmosphere. Here we calculate ESPs for the ∼7.7 ka Cleetwood eruption of Mount Mazama (Crater Lake/giiwas, Oregon, United States) that immediately preceded the caldera-forming eruption. We also introduce a novel approach to produce high-resolution grain-size distributions (GSDs) of individual samples over a wide range of particle sizes (0.00035–35 mm) by combining laser diffraction with dynamic image analysis. Detailed field analysis allows us to divide the Cleetwood eruptive sequence into a series of two distinct and consecutive VEI 4 eruptions: the lower (∼0.98 km3) and upper (∼0.20 km3) Cleetwood units. The lower Cleetwood was the most intense with a plume height of ∼19 km and an average mass discharge rate of ∼3.1 × 107 kg s−1. Its TGSD yields a fractal dimension D∼3.1, like other similar eruptions. All twelve high-resolution GSDs produced in this study exhibit two systematic breaks in slope from a power-law relationship at ∼0.125 and ∼0.510 mm. These breaks in slope create three segments: S1 (<0.125 mm), S2 (0.125–0.510 mm), and S3 (>0.510 mm) that can be fit by power-law relationships with fractal dimensions of D1 = 2.5 ± 0.2, D2 = 0.5 ± 0.1, and D3 = 3.6 ± 1.1, respectively. Together with ESPs and detailed componentry, D values at various locations give insight into magma fragmentation and tephra transport. We find that D1 values are positively correlated with the median grain-size and are similar to values found in rapid decompression magma fragmentation experiments. We infer that D1 values reflect the size distribution of the primary products of magma fragmentation and could thus be used to infer the potential energy at fragmentation. We interpret the relatively low values of D2 to an increase in dense components due to particle rafting. Our work shows that comparing high-resolution GSDs at several locations on the dispersal axis can further constrain primary and secondary eruptive processes, which prove crucial to improving tephra hazard assessments and dispersal forecasting.

The explosive, basaltic Katla eruption in 1918, south Iceland, II: Isopach map, ice cap deposition of tephra and layer volume

Due to poor preservation and lack of proximal tephra thickness data, no comprehensive isopach map has existed for the tephra layer from the major eruption of the Katla volcano in 1918. We present such a map obtained by combining existing data on the thickness of the 1918 tephra in soil profiles with newly acquired data from the 590 km² Mýrdalsjökull ice cap which covers the Katla caldera and its outer slopes. A tephra thickness of 20–30 m on the ice surface proximal to the vents is inferred from photos taken in 1919. The greatest thicknesses presently observed, 30–35 cm, occur where the layer outcrops in the lowermost parts of the ablation areas of the Kötlujökull and Sólheimajökull outlet glaciers. A fallout location within the Katla caldera is inferred for the presently exposed tephra in both outlet glaciers, as estimates of balance velocities imply lateral transport since 1918 of ∼15 km for Kötlujökull, ∼11 km for Sólheimajökull and about 2 km for Sléttjökull. Calculations of thinning of the tephra layer during this lateral transport indicate that the presently exposed tephra layers in Kötlujökull and Sólheimajökull were respectively over 2 m and about 1.2 m thick where they fell while insignificant thinning is inferred for the broad northern lobe of Sléttjökull. The K1918 layer has an estimated volume of 0.95±0.25 km³ (corresponding to 1.15±0.30×1012 kg) whereof about 50\% fell on Mýrdalsjökull. About 90\% of the tephra fell on land and 10\% in the sea to the south and southeast of the volcano. The volume estimate obtained contains only a part of the total volume erupted as it excludes water-transported pyroclasts and any material that may have been left on the glacier bed at the vents. While three main dispersal axes can be defined (N, NE and SE), the distribution map is complex in shape reflecting tephra dispersal over a period of variable wind directions and eruption intensity. In terms of airborne tephra, Katla 1918 is the largest explosive eruption in Iceland since the silicic eruption of Askja in 1875.

Formation and Dispersal of Ash at Open Conduit Basaltic Volcanoes: Lessons From Etna

Open conduit volcanoes are characterized by frequent, small scale explosive eruptions, which have a significant impact. Ash-forming explosions are impacting over larger areas with respect to effusive or poorly explosive events and, consequently, are more significant for hazard assessments. Quantifying the hazard associated with them requires understanding the processes and parameters controlling explosive style, and tephra dispersal and obtaining a comprehensive dataset to constrain syn-eruptive dynamics and particle transport in the volcanic plume. We present a study focused on Etna volcano (Italy), which, despite its continuous outgassing through the summit vents, has very frequent explosive eruptions dispersing ash along the southern Mediterranean area. The goal of this study is to obtain a statistically valid dataset on ash morphology and texture and investigate how various particle types distribute spatially in the tephra blanket. We chose a small scale, ash-forming eruption occurred in May 2016, sampled a few hours after tephra deposition. Analyses of grainsize distribution were coupled with further data on tephra texture and morphology, and numerical simulations. Several components were identified based either on purely textural or purely shape characteristics. Shape parameters related to the form of the grains (aspect ratio) are consistent across grainsizes and components. However, roughness parameters (solidity, convexity, concavity index) vary non-uniformly with particle size and componentry. Ash was formed through complex fragmentation of heterogenous magma, starting in the conduit, extending to the explosion jet, and resulting into a large variability of particle shapes, density and textures which distribute non-uniformly across grainsizes. This variability determines variable traveling potential within the volcanic plume and thus non uniform distribution in the deposit. Componentry variations along the dispersal axis suggest that density is the most effective parameter in controlling particle settling. However, extreme shapes, such as very elongated particles formed by surface tension instabilities in the jet, have the largest potential of being transported in the plume and can disperse downwind up to tens of km. Our results suggest that heterogeneities in textures and morphologies of particles are fundamental characteristics of tephra from frequently erupting volcanoes and should be accounted for plume dispersal modelling and hazard assessment.

Reconstructing fallout features and dispersal of Cretaio Tephra (Ischia Island, Italy) through field data analysis and numerical modelling: Implications for hazard assessment

The magnitude and intensity of the 60 CE Cretaio Tephra, the largest historical explosive eruption at Ischia caldera (Italy), was studied integrating field data and numerical modelling in order to reconstruct the dispersal of the fallout related to the climax phase of the eruption and characterize its physical parameters.A field survey of the main fall unit (EUC) of Cretaio Tephra and its sampling was performed on the island, which is the proximal area of dispersal, and for the first time outcrops of this tephra were found southward on the Capri Island. The dataset is completed by a distal tephra sampled in the offshore and described in the literature, allowing the analysis of samples of intermediate and distal deposits. Grain size analysis of the samples collected on the island show bimodal distributions due to the presence of a ballistic component, especially in the most proximal sampling sites around the inferred and buried vent. Tails of fine ash in the distributions can be associated with settling enhanced by ash aggregation processes in the moisture-rich plume. Tephra dispersal was reconstructed using the HAZMAP tephra dispersal model by minimizing the difference between the simulations obtained exploring plausible ranges of eruption source parameters and the available thickness and grain-size measurements. Results show that the dispersal axis of EUC is to the south-southeast, the best guess for the total erupted volume of tephra is 0.075 km3, the plume height ranges between 5 and 13 km, for an average mass eruption rate (MER) of 105 kg/s, hence a duration of the eruption of a few days. Considering an eruptive scenario given by the eruption parameters and diffusion coefficient of the Cretaio Tephra, together with a statistical set of wind profiles, HAZMAP modelling allowed us to generate tephra loading probability maps, needed to assess the impact of such an eruption at Ischia Island and the Neapolitan metropolitan area, pivotal for civil protection purposes.Another important outcome of the study is that, for volcanic islands, the reconstruction of eruption parameters may benefit much more from the search of even few medial and distal offshore outcrops than from implementing the on-island proximal dataset only.

Association of Electrocardiographic P-Wave Markers and Atrial Fibrillation in Embolic Stroke of Undetermined Source

Background: Several P-wave indices are thought to represent underlying atrial remodeling and have been associated with ischaemic stroke even in the absence of atrial fibrillation (AF). However, the utility of these P-wave indices in predicting outcomes in patients with embolic stroke of undetermined source (ESUS) has not been studied. The aim of this study is to examine these different P-wave indices towards predicting new-onset AF and stroke recurrence in a cohort of patients with ESUS, thereby demonstrating the value of these electrocardiographic markers for stroke risk stratification. Methods: Between October 2014 and October 2017, consecutive patients diagnosed with ESUS were followed for new-onset AF and ischaemic stroke recurrence. The various P-wave indices, namely, the P-terminal force in the precordial lead V1 (PTFV1), P-wave duration, P-wave dispersion, interatrial blocks, and P-wave axis, were assessed on the initial electrocardiogram on presentation and studied for their relation to eventual AF detection and recurrent stroke. Results: 181 ischaemic stroke patients with ESUS were recruited and followed up for a median duration of 2.1 years. An abnormal PTFV1 was associated with occult AF detection but not with recurrent ischaemic strokes. No significant association was observed between the other P-wave indices with either occult AF or stroke recurrence. Conclusion: PTFV1 is associated with AF detection but not recurrent strokes in ESUS patients and can be a useful electrocardiographic marker for further risk stratification in ESUS patients.

Influence of particle aggregation on the tephra dispersal and sedimentation from the October 8, 2016, eruption of Aso volcano

The phreatomagmatic eruption at Aso volcano on October 8, 2016, released PDC and fallout up to 320 km from the vent, providing an opportunity to study the dispersal and sedimentation of tephra bearing wet and dry aggregates. We investigated fresh air-fall tephra and conducted both dry- and wet-sieving to assess the size distribution of both aggregate-bearing deposits on the ground and particles in the plume prior to aggregation. The tephra was asymmetrically distributed in the ENE direction, with a relatively wide distribution and small maximum grain sizes north of the depositional axis, reflecting different wind directions at each altitude. The secondary accumulation maxima at 4–8 km NE from the vent was characterized by the segregation of lapilli followed by accretionary pellets that were rapidly created by aggregation in the wet plume, thereby enhancing the removal of airborne ash. Coalesced aggregates possibly arose from salt precipitation processes. For dry aggregates fallen in medial-to-distal regions, observed deposition duration and fall velocity calculations concluded that fine ash was deposited not as individual particles but as aggregates. Most grain-size distributions along the dispersal axis based on the two sieving methods used were multimodal, with the coarser mode fining according to distance from the vent and the finer mode stabilizing at around 4ϕ; this is interpreted as resulting from the mixture of grain-size distributions with different origins, i.e., the normal settling of individual clasts and particle aggregation. The wet-sieved total grain-size distribution included 20.4 wt% fine ash compared with only 2.4 wt% fine ash in the dry-sieved distribution, suggesting that aggregated particles accounted for 18 wt% of the deposit. Total grain-size distributions based on wet-sieving showed extremely poor sorting that could be explained by the following causes: the release of coarse-grained ejecta originating from the host rock of the crater, fine particles due to fragmentation from a phreatomagmatic eruption, the supply of water and salt from the crater to the plume, and aggregation enhancement of the fine ash on the ground, reflecting the effect of the crater lake as external water source.

A new method to identify the source vent location of tephra fall deposits: development, testing, and application to key Quaternary eruptions of Western North America

A new method to identify the source vent location of tephra fall deposits based on thickness or maximum clast size measurements is presented in this work. It couples a first-order gradient descent method with either one of two commonly used semi-empirical models of tephra thickness distribution. The method is applied to three tephra thickness and one maximum clast size datasets of the North Mono and Fogo A tephra deposits. Randomly selected and localized subsets of these datasets are used as input to evaluate its performance. The results suggest the utility of the method and show that estimating the dispersal axis is a more robust way to constrain the vent location compared with directly estimating the vent coordinates given sparse observations. Local change in dispersal direction can be detected given localized observations. Bootstrap aggregating and visualizing the surface of the cost function are used to analyze epistemic uncertainty for the method. Our discussion focuses on how different features of tephra deposits and technical aspects of the method would affect the performance of the method. Suggestions on how to use the method given limited observations are listed. One subset of the North Mono Bed 1 thickness dataset and thickness datasets of the Trego Hot Springs and Rockland tephras are used as case studies. The method is then applied to the well-correlated tephra sub-units within the Wilson Creek Formation to estimate their vent location and volume. The simplicity and flexibility of the method make it a potentially useful tool for analyzing tephra fall deposits.

Impact of wind direction variability on hazard assessment in Martinique (Lesser Antilles): The example of the 13.5 ka cal BP Bellefontaine Plinian eruption of Mount Pelée volcano

The threat posed by powerful Plinian explosive eruptions, which inject large quantities of ash into the atmosphere and produce pyroclastic density currents (PDC) on ground, is mainly controlled by eruptive parameters and by the direction and strength of the wind field during the eruption. In most studies, mean wind profiles are used to investigate potential tephra deposit dispersion and to assess volcanic risk. Here we present a detailed reconstruction and reinterpretation of a poorly-understood eruption of Mount Pelée volcano (Martinique), and use it to demonstrate that exclusive use of the average trade wind profile can lead to a misrepresentation of the volcanic risk. The great interest of this eruption stems from its unusual southward dispersion, which encompasses areas that are considered to be safe in current hazard maps and that host major infrastructure. Our new field study and radiocarbon dating show that these deposits are not part of the 2010 BP P3 eruptive sequence as previously thought, but define a so far unknown eruptive event dating back to 13,516 cal BP, which we propose to name the Bellefontaine eruption. The Bellefontaine sequence consists of a basal grey lithic-rich layer resulting from an explosive opening phase that destroyed a pre-existing lava dome, immediately followed by a much thicker, slightly reverse-graded white pumice-fall layer. Their dispersal, thickness, and grain-size distribution are used together with physical models of a volcanic plume to reconstruct the time evolution of the eruption. We find that the mass eruption rate reached 5 × 107 kg s−1, producing a 20-km-high Plinian plume, and that the minimum volume of pyroclastic deposits was 0.18 km3 DRE. 2D simulations of tephra dispersion in the atmosphere performed with HAZMAP show that, unlike the recent eruptions at Mount Pelée volcano, mean seasonal wind profiles cannot explain the southward dispersal of the Bellefontaine deposits. To understand the origin of this unusual dispersion axis, we retrieve forty years of wind data over Martinique by using global atmospheric reanalyses from 1979 by the European Center for Medium-Range Weather Forecasts ERA Interim (hereafter ERA-Interim) and ERA5 (hereafter ERA5). We find that, contrary to previous assumptions, this eruption did not necessarily occur during extreme weather conditions associated with the passing of a hurricane. Looking in detail into the ERA Interim datasets, we observe that the wind direction variability over the past 40 years is very low during the dry season (from December to May), and much larger during the wet season (from June to November), even in the troposphere (≈0 to 18 km), which can occasionally result in northerly winds in the mid- to high troposphere over Martinique. As a similar eruption today would spread volcanic material as far as the prefecture of Fort-de-France and its international airport, a zone classified as safe in current hazard maps, this study highlights the importance of including daily variability of winds in hazard assessment models when considering Plinian eruptions.

Two dimensions of demographic differentiation of species in a mountain grassland community: An experimental test

Abstract There is remarkable variation in life histories of coexisting plant species. These “alternative designs” for the given set of environmental conditions are likely to play a role in species niche differences and thus may underlie species coexistence, although there is no clear demonstration of it. Currently available data on within‐community differentiation concern primarily easy and measurable traits that are not fully informative of life history variation. Their relevance for functional differentiation of species and species coexistence is far from clear. Here, we examined differentiation of coexisting species in demographic parameters and how it determines species’ response to neighbours. We determined these parameters for a set of 21 co‐occurring species by fitting a process‐based model to a long‐term (30 years) data series of shoot counts. We examined the functional relevance of these parameters using species responses in a field removal experiment. We further asked with which functional traits they are correlated. Species were differentiated along two largely independent axes: (a) slow vs. fast, separating species according to instantaneous growth rate, competitive response and intraspecific density dependence; and (b) dispersal vs. local dynamics, which separated species with strong dispersal (by seeds or vegetative) from species that tended to stay in the occupied spot. While the slow‐fast axis was associated with commonly used leaf and seed traits, the dispersal axis was best predicted by lateral spreading distance. Each of these two axes predicted different components of species’ responses to neighbour competition: the slow‐fast axis was a good predictor of the short‐term response, whereas dispersal axis was a good predictor of the long‐term response. Synthesis. Demographic differentiation of coexisting species resembles to an important degree demographic differentiation known from large‐scale comparisons. This differentiation is functionally meaningful also at the fine scale; its role in species’ responses to competition implies it is involved in species niche differentiation and coexistence. While seed and leaf traits are important correlates of demographic differentiation, a hitherto underappreciated trait, viz. lateral spreading distance, is an important predictor of the dispersal axis at the fine scale and should be more widely used. A plain language summary is available for this article.

Rhyolitic and dacitic component of the Askja 1875 tephra in southern and central Finland: first step towards a Finnish tephrochronology

ABSTRACTTephra from Icelandic volcanic eruptions is frequently dispersed to northern Europe, but so far tephra has not been detected in Finnish sedimentary records. We report the first finding of a cryptotephra layer in southern and central Finland. Sediment samples from five lakes and 10 peatlands, most of them located in the tephra fallout zone of the Hekla 1947 eruption, were investigated for the presence of cryptotephra to assess the potential for tephrochronology in Finland. Tephra shards were extracted from their host matrix and electron probe microanalysis was conducted on single shards for geochemical characterization. Our results confirm the presence of Askja 1875 tephra in Finland, thus extending the known dispersal area of the Askja 1875 tephra eastwards. Most of the shards are rhyolitic, but a minor concentration of tephra with dacitic composition forms a narrow dispersal zone extending from Sweden to southern Finland. This zone possibly represents the main dispersal axis of the tephra in the distal area. Our results suggest that Finnish environmental research could benefit greatly from adding tephrochronology to the array of dating methods commonly used. Additionally, the absence of Hekla 1947 tephra in the previously inferred fall‐out zone is an important result indicating the complexity of tephra deposition and preservation.

Intricate episodic growth of a Hawaiian tephra deposit: case study of the 1959 Kīlauea Iki eruption

The 1959 Kīlauea Iki eruption on Hawai’i generated a succession of fountains, most reaching hundreds of meters high. The 16 episodes of fountaining persisted intermittently (with repose periods of between 7 h and 4 days) for 36 days. They produced tephra deposits that were dispersed several kilometers downwind of the vent, and a much larger volume of clastogenic lava which drained into the Kīlauea Iki crater to form a > 100 m deep lava lake. Field data from 211 tephra sample pits downwind of the vent reflect imperfectly the episodic nature of the fountaining behavior: only five composite stratigraphic subunits from the total of 16 fountaining episodes can be mapped in the field. However, isopach maps of these subunits were generated and, by the application of empirical deposit thinning relationships, volumes of each subunit were estimated. In combination with detailed observations made in 1959, our field data allow us to assign stratigraphic subunits to either single or aggregates of several fountaining episodes. The most voluminous subunits are linked with the highest fountaining, not with the longest in duration. In fact, significant downwind dispersal was possible only if the top part of the fountains reached above the crater rim, which was located about 100 m above the vent. The end of high fountaining episodes produced ash-rich partings, which are found on top of the lapilli-sized products of some episodes. However, the ash-rich intervals are strongly attenuated by wind advection and so are only present along the dispersal axes. The subunits follow slightly different dispersal axes. The maximum spread of 28 degrees between various dispersal axes is predominantly controlled by changing wind directions and spatter cone collapse into the vent, which modified its geometry. This study outlines the dependency of tephra dispersal on fountain height and emphasizes the capability of an episodic Hawaiian fountaining eruption to generate a seemingly monotonous downwind tephra deposit.

Total grain-size distribution of four subplinian–Plinian tephras from Hekla volcano, Iceland: Implications for sedimentation dynamics and eruption source parameters

The size distribution of the population of particles injected into the atmosphere during a volcanic explosive eruption, i.e., the total grain-size distribution (TGSD), can provide important insights into fragmentation efficiency and is a fundamental source parameter for models of tephra dispersal and sedimentation. Recent volcanic crisis (e.g. Eyjafjallajökull 2010, Iceland and Córdon Caulle 2011, Chile) and the ensuing economic losses, highlighted the need for a better constraint of eruption source parameters to be used in real-time forecasting of ash dispersal (e.g., mass eruption rate, plume height, particle features), with a special focus on the scarcity of published TGSD in the scientific literature. Here we present TGSD data associated with Hekla volcano, which has been very active in the last few thousands of years and is located on critical aviation routes. In particular, we have reconstructed the TGSD of the initial subplinian–Plinian phases of four historical eruptions, covering a range of magma composition (andesite to rhyolite), eruption intensity (VEI 4 to 5), and erupted volume (0.2 to 1km3). All four eruptions have bimodal TGSDs with mass fraction of fine ash (<63μm; m63) from 0.11 to 0.25. The two Plinian dacitic-rhyolitic Hekla deposits have higher abundances of fine ash, and hence larger m63 values, than their andesitic subplinian equivalents, probably a function of more intense and efficient primary fragmentation. Due to differences in plume height, this contrast is not seen in samples from individual sites, especially in the near field, where lapilli have a wider spatial coverage in the Plinian deposits. The distribution of pyroclast sizes in Plinian versus subplinian falls reflects competing influences of more efficient fragmentation (e.g., producing larger amounts of fine ash) versus more efficient particle transport related to higher and more vigorous plumes, displacing relatively coarse lapilli farther down the dispersal axis.