Paolo Papale

The role of magma composition and water content in explosive eruptions: 1. Conduit ascent dynamics

Abstract The role of anhydrous magma composition, water content, and crystal content on the dynamics of explosive eruptions is investigated by modeling the ascent of magma along volcanic conduits and the subsequent pyroclastic dispersion in the atmosphere, described in a companion paper [Neri, A., Papale, P., Macedonio, G., 1998. The role of magma composition and water content in explosive eruptions: 2. Pyroclastic dispersion dynamics. J. Volcanol. Geotherm. Res., 87, 95–115.]. The conduit model used is based on the solution of the fundamental transport equations assuming steady-state and isothermal flow conditions, and includes a composition-based description of magma properties and their variations along the conduit. This study stems from the well-documented vertical compositional variation of many pyroclastic deposits, often associated with reconstructed variations in initial water content. The results of the modeling show complex and sometimes non-intuitive dependence of the distribution of the flow variables on magma composition, crystal and water contents. In general, a water content decrease is expected to produce a decrease in mass flow-rate, decrease in pressure and velocity along the conduit, an increase in the exit gas volume fraction, and a decrease in velocity, pressure, and mixture density at the conduit exit. Reverse variations are expected to occur by decreasing the degree of chemical evolution of the liquid at a constant water content, apart from exit velocities which show more complex variations. The overall effect of increasing crystals is in general similar to that of increasing the degree of chemical evolution of the liquid, or decreasing the water content. The above results are to a large extent interpreted in terms of variations in magma viscosity, which is recognized as the critical magma property besides water content in the dynamics of magma ascent. The common compositional trend of explosive eruptions characterized by chemically evolved, water-richer and crystal-poorer magma erupted first is predicted to be associated with variations in the evolution of the eruption dynamics, depending on the relative magnitude of the changes. However, the exit velocity always decreases in the above trend, and the mass flow-rate increases in most relevant cases, comparing well with the results of chemical and stratigraphic studies of the deposits from explosive eruptions.

Modeling of the ascent of magma during the plinian eruption of Vesuvius in A.D. 79

Abstract The ascent of magma during the A.D. 79 eruption of Vesuvius was studied by a steady-state, one-dimensional, and nonequilibrium two-phase flow model. The gas exsolution process was modeled by assuming a chemical equilibrium between the exsolved and dissolved gas, whereas the magma density and viscosity were modeled by accounting for the crystal content in magma. The exsolution, density, and viscosity models consider the effect of different compositions of the white and gray magmas. By specifying the conduit geometry and magma composition, and employing the model to search for the maximum discharge rate of magma which is consistent with the specified geometry and magma composition, the model was then used to establish the two-phase flow parameters along the conduit. It was found that for all considered conditions the magma pressure in the conduit decreases below the lithostatic pressure near the magma fragmentation level, and that in the deep regions of the conduit the white magma pressure is larger and the gray magma pressure is lower than the lithostatic one. The exsolution and fragmentation levels were found to be deeper for the white than for the gray magma, and the changing composition during the eruption causes an increase of the exit pressure and decrease of the exit gas volumetric fraction. The model also predicted a minimum conduit diameter which is consistent with the white and gray magma compositions and mass flow-rates. The predictions of the model were shown to be consistent with column collapses during the gray eruption phase, large presence of carbonate lithics in the gray pumice fall deposit, and magma-water interaction during a late stage of the eruption.

The evolution of lava flows from ephemeral vents at Mount Etna: Insights from vesicle distribution and morphological studies

Abstract Lava flow units from ephemeral vents at Mount Etna are characterized by a cross-flow subdivision into zones with different surface morphology, symmetrically distributed with respect to the centerline of the flow. These zones are: (1) a central zone (cp zone) with a relatively smooth surface near the vent; (2) a lateral zone (lp zone) covered by a carpet of clinkers overlying the massive lava body; and (3) a lateral levee zone (ll zone). In many cases the cp and lp zones are separated by an inward-dipping groove, and the cp zone is from some decimeters up to more than 1 m thicker than the adjacent lp zone. In sections perpendicular to the flow direction, the vesicles corresponding with the cp zone are systematically distributed in a ring-like region and are characterized by a sub-elliptical shape with their minor axes along a direction radial to the center of such region. Vesicles corresponding with the lp zone are still elliptical and their major axes tend to be parallel to the nearest cooling surface. Vesicularity is the lowest at the center of the ring-like region where vesicles approach a spherical shape. In the upper part of the ring-like region, vesicle accumulation and coalescence below the crust produces one or more gas-rich layers which act as levels of preferential detachment for the formation of lava tubes. The observed morphological characteristics and reconstructed vesicle distribution patterns are consistent with a radial distribution of velocity within the lava flow unit and suggest the existence of an inner plug flow region where the velocity gradient is zero. A simple evolution scheme is proposed in which a lava flow unit from ephemeral vent invariably evolves to a lava tube through the downward migration of the plug flow region. The progressive reduction of the cross-flow section due to cooling produces a pressure increase within the flowing lava body and the thickening of the active central portion of the lava flow unit in order to satisfy mass conservation.

The role of magma composition and water content in explosive eruptions : 2. Pyroclastic dispersion dynamics

Abstract The net effect of magma composition and water content on the behavior of explosive volcanic eruptions was investigated by the use of thermofluid-dynamic models and numerical simulation. The two-phase flow models employed allowed the description of the eruptive process from the conduit entrance at the top of the magma chamber up to the pyroclastic dispersion process in the atmosphere. In this paper, vent conditions computed in the companion paper by Papale et al. [Papale, P., Neri, A., Macedonio, G., this issue. The role of magma composition and water content in explosive eruptions: I. Conduit ascent dynamics. J. Volcanol. Geotherm. Res.], as a function of magma composition and water content, are employed as boundary conditions at the crater base of the pyroclastic dispersion model. The eruptive mixture was described as a two-phase gas–particle fluid. Pyroclasts are represented as solid particles of one size whereas the gas phase consists of superheated water vapor leaving the vent and atmospheric air. Simulations were performed on physical domains extending several kilometers in both radial and vertical directions and for several minutes of real time. The results clearly show the net effects of the anhydrous magma composition, crystals, and water content on the spatial and temporal distribution of pyroclastic material during the first minutes of eruption. In detail, the results indicate a strong influence of magma composition on eruption intensity, whereas the eruptive style, i.e., the generation of Plinian, transitional, or collapsing columns, appears to be mainly controlled by the total water content of the magma, i.e., the weight fraction of water with respect to the entire magmatic mixture. The main effect of the crystals is to reduce the total water content of the mixture and lead to a less buoyant behavior of the column. As a summary, for the investigated ranges of variations, simulation results indicate a progressive change to a more collapsing behavior of the column whenever water-poorer or crystal-richer magma is erupted from the vent with the anhydrous composition of magma affecting just the intensity of the eruption. For most conditions, such a conclusion does not appear to be strongly dependent on a relatively large variation of vent diameter and, therefore, of the scale of the event. Simulation results appear to be consistent with field studies even though more complete data on specific eruptions are recommended for a more thorough comparison.

Coupled conduit and atmospheric dispersal dynamics of the AD 79 Plinian eruption of Vesuvius

Abstract The AD 79 eruption of Vesuvius is certainly one of the most investigated explosive eruptions in the world. This makes it particularly suitable for the application of numerical models since we can be quite confident about input data, and the model predictions can be compared with field-based reconstruction of the eruption dynamics. Magma ascent along the volcanic conduit and the dispersal of pyroclasts in the atmosphere were simulated. The conduit and atmospheric domain were coupled through the flow conditions computed at the conduit exit. We simulated two different peak phases of the eruption which correspond to the emplacement of the white and gray magma types that produced Plinian fallout deposits with interlayered pyroclastic flow units during the gray phase. The input data, independently constrained and representative of each of the two eruptive phases, consist of liquid magma composition, crystal and water content, mass flow rate, and pressure–temperature–depth of the magma at the conduit entrance. A parametric study was performed on the less constrained variables such as microlite content of magma, pressure at the conduit entrance, and particle size representative of the eruptive mixture. Numerical results are substantially consistent with the reconstructed eruptive dynamics. In particular, the white eruption phase is found to lead to a fully buoyant eruption plume in all cases investigated, whereas the gray phase shows a more transitional character, i.e. the simultaneous production of a buoyant convective plume and pyroclastic surges, with a significant influence of the microlite content of magma in determining the partition of pyroclast mass between convective plumes and pyroclastic flows.

Modality-independent encoding of individual concepts in the left parietal cortex

ABSTRACT The organization of semantic information in the brain has been mainly explored through category‐based models, on the assumption that categories broadly reflect the organization of conceptual knowledge. However, the analysis of concepts as individual entities, rather than as items belonging to distinct superordinate categories, may represent a significant advancement in the comprehension of how conceptual knowledge is encoded in the human brain. Here, we studied the individual representation of thirty concrete nouns from six different categories, across different sensory modalities (i.e., auditory and visual) and groups (i.e., sighted and congenitally blind individuals) in a core hub of the semantic network, the left angular gyrus, and in its neighboring regions within the lateral parietal cortex. Four models based on either perceptual or semantic features at different levels of complexity (i.e., low‐ or high‐level) were used to predict fMRI brain activity using representational similarity encoding analysis. When controlling for the superordinate component, high‐level models based on semantic and shape information led to significant encoding accuracies in the intraparietal sulcus only. This region is involved in feature binding and combination of concepts across multiple sensory modalities, suggesting its role in high‐level representation of conceptual knowledge. Moreover, when the information regarding superordinate categories is retained, a large extent of parietal cortex is engaged. This result indicates the need to control for the coarse‐level categorial organization when performing studies on higher‐level processes related to the retrieval of semantic information. HighlightsWe studied the semantic representation of concrete nouns in the left lateral parietal cortex.Four models were used to predict fMRI responses to individual nouns from different categories.Posterior and middle IPS retained high‐level perceptual and semantic information.Information about superordinate categories yielded a different recruitment of parietal regions.

When Neuroscience 'Touches' Architecture: From Hapticity to a Supramodal Functioning of the Human Brain.

In the last decades, the rapid growth of functional brain imaging methodologies allowed cognitive neuroscience to address open questions in philosophy and social sciences. At the same time, novel insights from cognitive neuroscience research have begun to influence various disciplines, leading to a turn to cognition and emotion in the fields of planning and architectural design. Since 2003, the Academy of Neuroscience for Architecture has been supporting ‘neuro-architecture’ as a way to connect neuroscience and the study of behavioral responses to the built environment. Among the many topics related to multisensory perceptual integration and embodiment, the concept of hapticity was recently introduced, suggesting a pivotal role of tactile perception and haptic imagery in architectural appraisal. Arguments have thus risen in favor of the existence of shared cognitive foundations between hapticity and the supramodal functional architecture of the human brain. Precisely, supramodality refers to the functional feature of defined brain regions to process and represent specific information content in a more abstract way, independently of the sensory modality conveying such information to the brain. Here, we highlight some commonalities and differences between the concepts of hapticity and supramodality according to the distinctive perspectives of architecture and cognitive neuroscience. This comparison and connection between these two different approaches may lead to novel observations in regard to people–environment relationships, and even provide empirical foundations for a renewed evidence-based design theory.

Foreground-Background Segmentation Revealed during Natural Image Viewing

Abstract One of the major challenges in visual neuroscience is represented by foreground-background segmentation. Data from nonhuman primates show that segmentation leads to two distinct, but associated processes: the enhancement of neural activity during figure processing (i.e., foreground enhancement) and the suppression of background-related activity (i.e., background suppression). To study foreground-background segmentation in ecological conditions, we introduce a novel method based on parametric modulation of low-level image properties followed by application of simple computational image-processing models. By correlating the outcome of this procedure with human fMRI activity, measured during passive viewing of 334 natural images, we produced easily interpretable “correlation images” from visual populations. Results show evidence of foreground enhancement in all tested regions, from V1 to lateral occipital complex (LOC), while background suppression occurs in V4 and LOC only. Correlation images derived from V4 and LOC revealed a preserved spatial resolution of foreground textures, indicating a richer representation of the salient part of natural images, rather than a simplistic model of object shape. Our results indicate that scene segmentation occurs during natural viewing, even when individuals are not required to perform any particular task.

Eight Weddings and Six Funerals: An fMRI Study on Autobiographical Memories

“Autobiographical memory” (AM) refers to remote memories from ones own life. Previous neuroimaging studies have highlighted that voluntary retrieval processes from AM involve different forms of memory and cognitive functions. Thus, a complex and widespread brain functional network has been found to support AM. The present functional magnetic resonance imaging (fMRI) study used a multivariate approach to determine whether neural activity within the AM circuit would recognize memories of real autobiographical events, and to evaluate individual differences in the recruitment of this network. Fourteen right-handed females took part in the study. During scanning, subjects were presented with sentences representing a detail of a highly emotional real event (positive or negative) and were asked to indicate whether the sentence described something that had or had not really happened to them. Group analysis showed a set of cortical areas able to discriminate the truthfulness of the recalled events: medial prefrontal cortex, posterior cingulate/retrosplenial cortex, precuneus, bilateral angular, superior frontal gyri, and early visual cortical areas. Single-subject results showed that the decoding occurred at different time points. No differences were found between recalling a positive or a negative event. Our results show that the entire AM network is engaged in monitoring the veracity of AMs. This process is not affected by the emotional valence of the experience but rather by individual differences in cognitive strategies used to retrieve AMs.

Non‐Newtonian flow of bubbly magma in volcanic conduits

The dynamics of magma ascent along volcanic conduits toward the Earths surface affects eruptive styles and contributes to volcanic hazard. The rheology of ascending magmatic mixtures is known to play a major role on mass flow rate as well as on pressure and exit velocity at the vent, even determining effusive versus explosive eruptive behavior. In this work we explore the effects of bubble-induced non-Newtonian rheology on the dynamics of magma flow in volcanic conduits. We develop a quasi 2-D model of magma ascent that incorporates a rheological constitutive equation describing the strain-dependent effect of gas bubbles on the viscosity of the multiphase magma. Non-Newtonian magma flow is investigated through a parametric study where the viscosity of the melt and the water content are varied over natural ranges. Our results show that non-Newtonian rheology leads to greater exit velocity, mass flow, and density. The pressure distribution along the conduit remains very similar to the Newtonian case, deviating only at the conduit exit. Plug-like velocity profiles develop approaching the conduit exit, when mixture velocity is high, and are favored by smaller liquid viscosity. Since the mass flow rate, the density and the velocity of the mixture exiting from the conduit are fundamental for quantifying and assessing the transport and emplacement dynamics, neglecting that the non-Newtonian effect of bubble-bearing magmas may result in misinterpretation of the deposit and, consequently, eruptive behavior.