Strombolian activity is common in low-viscosity volcanism. It is characterised by quasi-periodic, short-lived explosions, which, whilst typically weak, may vary greatly in magnitude. The current ...paradigm for a strombolian volcanic eruption postulates a large gas bubble (slug) bursting explosively after ascending a conduit filled with low-viscosity magma. However, recent studies of pyroclast textures suggest the formation of a region of cooler, degassed, more-viscous magma at the top of the conduit is a common feature of strombolian eruptions. Following the hypothesis that such a rheological impedance could act as a ‘viscous plug’, which modifies and complicates gas escape processes, we conduct the first experimental investigation of this scenario. We find that: 1) the presence of a viscous plug enhances slug burst vigour; 2) experiments that include a viscous plug reproduce, and offer an explanation for, key phenomena observed in natural strombolian eruptions; 3) the presence and extent of the plug must be considered for the interpretation of infrasonic measurements of strombolian eruptions. Our scaled analogue experiments show that, as the gas slug expands on ascent, it forces the underlying low-viscosity liquid into the plug, creating a low-viscosity channel within a high-viscosity annulus. The slug's diameter and ascent rate change as it enters the channel, generating instabilities and increasing slug overpressure. When the slug reaches the surface, a more energetic burst process is observed than would be the case for a slug rising through the low-viscosity liquid alone. Fluid-dynamic instabilities cause low and high viscosity magma analogues to intermingle, and cause the burst to become pulsatory. The observed phenomena are reproduced by numerical fluid dynamic simulations at the volcanic scale, and provide a plausible explanation for pulsations, and the ejection of mingled pyroclasts, observed at Stromboli and elsewhere.
•We present laboratory experiments in which gas slugs ascend a pipe plugged with a viscous liquid.•The presence of a viscous plug enhances burst vigour.•Slug–plug interaction causes pulsatory bursting resembling natural strombolian eruptions.•Experiments indicate slug passage promotes mingling between vertically stratified magmas.
Ash deposited during volcanic eruptions can be resuspended by wind and become hazardous for health and infrastructure hours to decades after an eruption. Accurate resuspension forecasting requires ...accurate modelling of the threshold friction velocity of the volcanic particles (U
*), which is the key parameter controlling volcanic ash detachment by wind. Using an environmental wind tunnel facility this study provides much needed experimental data on volcanic particle resuspension, with the first systematic parameterization of U
* for ash from the regions Campi Flegrei in Italy and also Eyjafjallajökull in Iceland. In this study atmospheric relative humidity (and related ash moisture content) was systematically varied, from <10% to >90%, which in the case of the Eyjafjallajökull fine ash (<63 μm) produced a twofold increase in U
*. Using the Campi Flegrei fine ash (<63 μm) an increase in U
* of only around a factor of 1.5 was observed. Reasonable agreement with force balance resuspension models was seen, which implied an increase in interparticle adhesion force of up to a factor of six due to high humidity. Our results imply that, contrary to dry conditions, one single modelling scheme may not satisfy the resuspension of volcanic ash from different eruptions under wet conditions.
The explosive activity of the 2021 Tajogaite eruption eludes pigeonholing into well‐defined eruption styles, with a variety of pyroclast ejection modes occurring both alternately and simultaneously ...at multiple vents. Visually, we defined four endmembers of explosive activity, referred to as fountaining, spattering, ash‐poor jets and ash‐rich jets. To capture the physical parameters of these activities, we deployed a camera array including one high‐speed camera and three high‐definition cameras in two field campaigns. Transitions between and fluctuations within activity occurred at the time scale of minutes to hours, likely driven by the same shallow conduit and vent processes controlling Strombolian activity at other volcanoes, but at higher gas and magma fluxes. From a physical standpoint, mean pyroclast rise velocity ranged 5–50 m/s, maximum ejection velocity 10–220 m/s, and sub‐second mass flux of lapilli to bomb‐sized pyroclasts at the vent 0.2–200 × 103 kg/s. The largest mass flux occurred during fountaining, which contributed by far more than other activities to cone building. All explosive activity exhibited well‐defined pyroclast ejection pulses, and we found a positive correlation between the occurrence rate of ejection pulses and maximum pyroclast ejection velocity. Despite orders of magnitude variations, physical parameters shift gradually with no boundary from one activity endmember to another. As such, attributing this explosive activity specifically to any currently defined style variations is arbitrary and potentially misleading. The highly variable explosive activity of the Tajogaite eruption recalls previous definitions of violent Strombolian eruptions, an eruption style whose pyroclast ejection dynamics, however, were so far largely undefined.
Plain Language Summary
The 2021 Tajogaite volcanic eruption offered a rare opportunity to study in detail the physical properties and the controlling factors of explosive activity driven by basaltic magmas. The activity lasted almost uninterrupted for almost 3 months and had visually different manifestations occurring simultaneously and alternating at different volcanic vents. To study the explosive activity, we used one high‐speed camera, taking short, slow motion videos, and three commercial grade high‐definition camcorders recording for many hours. We found that the activity changed in features and intensity at the time scale of minutes to hours, largely controlled by changes in the size and debris cover of the vent, magma viscosity, and magma flux and gas content. The ejection velocity of large volcanic particles ranged 5–220 m/s, with mean values around 10–50 m/s. The mass flux of particles erupted reached peaks of 200 metric tons per second. Particle ejection was never steady but always proceeded in pulses, which were more frequent if the ejection velocity was higher. Our measurements show that the current classification schemes for explosive eruptions of basaltic magmas do not adequately describe the activity of the Tajogaite eruption, which represents a type of eruption that was not yet measured in detail.
Key Points
High‐definition and high‐speed imaging record the velocity, size, and mass flux of pyroclasts
Activity shifted in location, nature and vigor at the time scale of hours and progressed in ejection pulses at the time scale of seconds
Physical parameters of explosive activity vary gradually between apparently different activity styles, without any clear boundary
Despite recent research showing that early childhood education and daycare settings (ECEC) have an important role in promoting toddlers’ physical activity (PA), crucial information gaps remain ...regarding toddlers' PA and sedentary behavior (SB) in these outdoor settings. We aimed in this study to: (a) analyze PA patterns and SB during unstructured outdoor play time in preschool and daycare environments using accelerometry and systematic observation; (b) provide concurrent accelerometry and observational data to help validate the Observational System for Recording Physical Activity in Children-Preschool Version (OSRAC-P); and (c) examine individual, social and environmental correlates of PA and SB during toddlers’ unstructured outdoor play time. We found that: (a) toddlers displayed high amounts of PA with no sex, BMI, and/or age differences in PA and SB levels,; (b) environmental variables (e.g., fixed equipment and playground density) were not associated with PA levels or SB intensity; (c) the OSRAC-P was a reliable and valid means of observing and analyzing toddlers’ PA patterns during unstructured outdoor play time; and (e) different social patterns between boys and girls did not impact PA levels or patterns. Combining different measurement methods permitted an improved understanding of unstructured outdoor play in preschool and daycare settings.
Centimeter to meter‐sized volcanic ballistic projectiles from explosive eruptions jeopardize people and properties kilometers from the volcano, but they also provide information about the past ...eruptions. Traditionally, projectile trajectory is modeled using simplified ballistic theory, accounting for gravity and drag forces only and assuming simply shaped projectiles free moving through air. Recently, collisions between projectiles and interactions with plumes are starting to be considered. Besides theory, experimental studies and field mapping have so far dominated volcanic projectile research, with only limited observations. High‐speed, high‐definition imaging now offers a new spatial and temporal scale of observation that we use to illuminate projectile dynamics. In‐flight collisions commonly affect the size, shape, trajectory, and rotation of projectiles according to both projectile nature (ductile bomb versus brittle block) and the location and timing of collisions. These, in turn, are controlled by ejection pulses occurring at the vent. In‐flight tearing and fragmentation characterize large bombs, which often break on landing, both factors concurring to decrease the average grain size of the resulting deposits. Complex rotation and spinning are ubiquitous features of projectiles, and the related Magnus effect may deviate projectile trajectory by tens of degrees. A new relationship is derived, linking projectile velocity and size with the size of the resulting impact crater. Finally, apparent drag coefficient values, obtained for selected projectiles, mostly range from 1 to 7, higher than expected, reflecting complex projectile dynamics. These new perspectives will impact projectile hazard mitigation and the interpretation of projectile deposits from past eruptions, both on Earth and on other planets.
Key Points
Volcanic Ballistic Projectiles (VBPs) in volcanic deposits, theory, and direct observations are reviewed
High‐speed imaging and measurements of VBPs spinning, deforming, fragmenting, colliding, and impacting with the ground are provided
In‐flight fragmentation, collisions, and spinning are important for VBPs dynamics, and apparent drag coefficient can be higher than expected
Plain Language Summary
Explosive volcanic eruptions launch incandescent fragments, sometimes partially molten, to distances of up to several kilometers from the volcano. The largest fragments, from the size of an apple to that of a van, travel in air following the same laws that control the flight of artillery shells and, on landing, may cause the same harmful consequences. To protect people and properties from these volcanic projectiles, their occurrence in volcanic rocks is documented, and their motion is simulated by computer models. However, both field studies and computer models require validation, but in‐flight observation of the projectiles have been sparse, so far. We used state‐of‐the‐art high‐speed cameras, filming volcanic projectiles in slow motion to understand and measure the processes that control their flight dynamics. We found that the in‐flight deformation, rotation, and collision of the projectiles have a deep impact on their trajectory. We also measured the size of craters left by the projectiles on landing, and we derived specific parameters that are essential to model projectiles flight. We found that currently used models often do not account for all the in‐flight dynamics. Our findings will improve interpreting the motion of the projectiles and mitigating their hazard.
Open‐conduit conditions characterize several of the most hazardous and active volcanic systems of basaltic composition worldwide, persistently refilled by magmatic inputs. Eruptive products with ...similar bulk compositions, chemically buffered by continual mafic inputs, nevertheless exhibit heterogeneous glass compositions in response to variable magma mixing, crystallization, and differentiation processes within different parts of the plumbing system. Here, we document how multivariate statistics and magma differentiation modeling based on a large data set of glass compositions can be combined to constrain magma differentiation and plumbing system dynamics. Major and trace elements of matrix glasses erupted at Stromboli volcano (Italy) over the last 20 years provide a benchmark against which to test our integrated petrological approach. Principal component analysis, K‐means cluster analysis, and kernel density estimation reveal that trace elements define a multivariate space whose eigenvectors are more readily interpretable in terms of petrological processes than major elements, leading to improved clustering solutions. Comparison between open‐ and closed‐system differentiation models outlines that steady state magma compositions at constantly replenished and erupting magmatic systems approximate simple fractional crystallization trends, due to short magma residence times. Open‐system magma evolution is associated with magma storage crystallinities that are lower than those associated with closed‐system scenarios. Accordingly, open‐system dynamics determine the efficient crystal‐melt separation toward the top of the reservoir, where eruptible melts continuously supply the ordinary activity. Conversely, a mush‐like environment constitutes the bottom of the reservoir, where poorly evolved magmas result from mixing events between mush residual melts and primitive magmas injected from deeper crustal levels.
Plain Language Summary
Volcanoes characterized by continuous eruptive activity are typified by constant replenishment of new magma, rising from deeper regions of the crust. The volcanic glass (supercooled silicate melt), represents the residual liquid of magma crystallization, and is found as the intracrystalline matrix of eruptive products. The study of its chemical composition may provide insight into the processes occurring at depths beneath the volcanic vent, where magma compositional changes result from crystallization and mixing with new magma rising from depth. We combine statistical analyses and analytical equations based on the chemical composition of the matrix glasses from Stromboli volcano, in order to constrain the processes which produce their chemical variations, identifying different environments where magmas are stored at depth. Our results also show that when magma is stored for a short period of time, the chemical changes to which the magma is subjected in a constantly replenished system are similar to those occurring in a system which is closed to new inputs of magma.
Key Points
The combination of multivariate statistics with geochemical modeling provides new constraints on magma differentiation processes
Multivariate statistics based on trace elements allow better retrieval of petrological information than those based on major elements
Magma differentiation in open systems approximates that occurring in closed systems when magma residence timescales are short
Early childhood education (ECE) teachers have traditionally been trained as generalists. However, there is now a growing awareness of the potential importance of having pedagogical content knowledge ...(PCK) of physical activity opportunities in the ECE curriculum. Furthermore, several scholars argue that movement content knowledge in physical education (PE) teacher education needs to be revisited. The aim of this study is to analyze ECE teachers’ and student teachers’ perception of PCK in the teaching and learning process of the structured movement sessions. Using a deductive coding scheme, we identified fourteen initial categories and consolidated them into three major categories. The first, the disregard for psychomotricity in the ECE curriculum, can be explained by (a) the perception that ECE is less important than elementary education, and (b) the lack of importance given to psychomotricity by society and schools, which have been responsible for exacerbating this distortion. Secondly, there are several barriers that threaten PCK during structured movement sessions: (a) lack of content knowledge; (b) lack of confidence; (c) lack of interest; (d) lack of training; (e) the non-standardized curriculum; (f) personal negatives experiences related to PE; and (g) lack of context-specific PE teacher education for ECE. Finally, we identified the following facilitating factors challenging these barriers: (a) interaction among members of the school community; (b) personal intrinsic motivation; (c) the role of university training and continuous professional development for exposing teachers to alternatives ways of thinking; and (d) teachers’ feelings of professional responsibility for modifying the reality of the educational context to generate positive practices.
To our knowledge, there are no published studies that describe the physical activity (PA) levels and objectively measure them through accelerometry in toddlers (2-3 years old) attending early ...childhood education and care (ECEC) institutions during the COVID-19 pandemic. The aims of this study were two-fold: (a) to analyse toddlers' PA levels and sedentary behaviour (SB) during school hours in ECEC institutions, as well as the rate of adherence to specific recommendations on total PA (TPA) and moderate-vigorous PA (MVPA); and (b) to evaluate the characteristics correlates (age, gender, and body mass index -BMI) of young children and the school environment on toddlers' TPA, light PA (LPA), MVPA, and SB during school hours in ECEC institutions. PA was evaluated with ActiGraph accelerometers. The main findings were that: (a) toddlers engaged in very high amounts of TPA and MVPA during ECEC hours; (b) girls and boys displayed similar levels of LPA, TPA, and SB, while girls had lower levels of MVPA, compared to boys, and younger toddlers were less active than older ones; (c) BMI was not associated with PA of any intensity or SB; (d) playground and classroom density were not associated with higher levels of PA of any intensity, though classroom density was associated with SB. These ECEC institutions provide and challenge the new COVID-19 scenario, as well as supportive environments for toddlers' PA.
Several aspects of the indoor early childhood education (ECE) environment may be associated with physical activity (PA), including indoor areas. Modifying the indoor physical environment in ...classrooms could have significant potential to influence PA in young children. However, to our knowledge, PA promotion interventions involving changes to the ECE indoor physical environment have not been empirically implemented or monitored by accelerometry and direct observation. Therefore, the aims of this study were twofold: (a) to evaluate personal, social, and environmental correlates of moderate-vigorous PA (MVPA) in young children during indoor free play time; and (b) to assess the impact of incorporating a physical activity area in an indoor ECE environment on PA patterns during recess and the overall school day. Outcomes were measured at baseline, at 1 week post-intervention, and at 6 weeks’ follow-up. We studied contextual variables such as the presence of others, location, availability of equipment, and gender-based group interactions during indoor free play. It is notable that at 1-week post-intervention, both girls and boys increased their PA levels, but by the 6-week follow-up, the increase in MVPA was significantly higher in boys compared to girls, suggesting that our PA area is not benefitting girls to the same extent as their male counterparts. In addition, at all time points, boys spent more time during recess and overall in MVPA minutes than girls. MVPA is below the recommended levels for this age during the school day, the role of the indoor physical environment and context should be revised.
Little is known about the modes of active commuting to and from school (ACS) in toddlers (2-3 years old). The aims of the present study are threefold: (a) to describe the modes of transport to and ...from early childhood education and care (ECEC) institutions in toddlers; (b) to analyze the role of different barriers and neighbourhood characteristics, as perceived by parents, in ACS; and (c) to examine the contribution of ACS on levels of PA. Parents provided written input through a questionnaire about the modes of transport to school they use with their young children, the weekly use-frequency of each mode, as well as the barriers they perceived to walking or riding a bike to ECEC institutions. The final sample consisted of 154 young children from Valencia (Spain). In a randomly selected subsample of 44 children, PA was measured using accelerometers. Cars and strollers were the most common modes of transport in toddlers. Perceived distance to school was negatively correlated to ACS, whereas parents' perceptions around planning/psychosocial barriers was also negatively associated with ACS. There was a significant and positive association between ACS and total PA. However, ACS contributes positively to toddlers' overall PA levels. This study provides information about planning/psychosocial barriers as significant predictors of ACS in toddlers.
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