Inverting sediment bedforms for evaluating the hazard of dilute pyroclastic density currents in the field

Pyroclastic density currents are ground hugging gas-particle flows associated to explosive volcanic eruptions and moving down a volcano's slope, causing devastation and deaths. Because of the hostile nature they cannot be analyzed directly and most of their fluid dynamic behavior is reconstructed by the deposits left in the geological record, which frequently show peculiar structures such as ripples and dune bedforms. Here, a set of equations is simplified to link flow behavior to particle motion and deposition. This allows to construct a phase diagram by which impact parameters of dilute pyroclastic density currents, representing important factors of hazard, can be calculated by inverting bedforms wavelength and grain size, without the need of more complex models that require extensive work in the laboratory

Ash leachates from some recent eruptions of Mount Etna (Italy) and Popocatépetl (Mexico) volcanoes and their impact on amphibian living freshwater organisms

Leaching experiments were carried out on fresh ash samples from Popocatépetl 2012, Etna 2011, and Etna 2012 eruptions, in order to investigate the release of compounds in both double-deionized and lake (Lake Ohrid, FYR of Macedonia) waters. The experiments were carried out using different grain sizes and variable stirring times (from 30 min to 7 days). Results were discussed in the light of changing pH and release of compounds for the different leachates. In particular, Etna samples induced alkalinization, and Popocatépetl samples induced acidification of the corresponding leachates. The release of different elements does not show correlation with the stirring time, with the measured maximum concentrations reached in the first hours of washing. General inverse correlation with grain size was observed only for Na+, K+, Cl-, Ca2+, Mg2+, SO2-4 , and Mn2+, while the other analysed elements show a complex, scattering relationship with grain size. Geochemical modelling highlights leachates' saturation only for F and Si, with Popocatépetl samples sometimes showing saturation in Fe. The analysed leachates are classified as undrinkable for humans on the basis of European laws, due to excess in F-, Mn2+, Fe, and SO2-4 (the latter only for Popocatépetl samples). Finally, the Etna 2012 and Popocatépetl leachates were used for toxicity experiments on living biota (Xenopus laevis). They are mildly toxic, and no significant differences exist between the toxic profiles of the two leachates. In particular, no significant embryo mortality was observed; while even at high dilutions, the leachates produced more than 20% of malformed larvae

Influence of particle density on flow behavior and deposit architecture of concentrated pyroclastic density currents over a break in slope: Insights from laboratory experiments

Geological granular flows are highly complex, gravity-driven phenomena whose different behaviors depend on the mechanical properties, density and granulometric distributions of the constituent materials. Years of research have produced significant advances in understanding transport and deposition processes in granular flows. However, the role and effects of clast densities and density contrast in a granular flow are still not fully understood. In this paper we show the effect that pumice has on dry granular flows; specifically on flow velocity and longitudinal segregation of the deposits. Our work confirms, by experimental results, field observations on pumice/lithic segregation and longer pumice runout. We report results of velocity decay and deposit architecture for a granular flow passing over a break in slope (from 38° to 4° inclination). The 30 experimental runs were carried out in a five-meter long laboratory flume equipped with a series of sensors that include laser gates and high-speed cameras (400 fps). We used two polydisperse mixtures of dacitic lithics and rhyolitic pumice in varying amounts, with Weibull and Gaussian particle size distributions. The pumice/lithic ratio changes the flow response passing over a break in slope. This effect is particularly evident starting from 10% of pumice volume into the flow mixture, independently of its granulometric distribution. Runout relates to mass following a power law, with an exponent close 0.2. The experiments confirm that pumice segregation affects polydispersed mixtures, similarly to what has been observed in real field deposits, where density decoupling produces lithic-enriched proximal areas and pumice-enriched distal areas. The results obtained prove that the presence of low-density materials in a dense granular flow has a strong influence on its behavior

Vegetation, climate and environmental history of the last 4500 years at lake Shkodra (Albania/Montenegro)

Three parallel overlapping cores have been taken in the Albanian side of Lake Shkodra (Albania/Montenegro). The chronological frame of the record, spanning approximately the last 4500 years, has been assessed using four radiocarbon dates and four well-known tephra layers of Italian volcanoes. Multidisciplinary analyses turned out to be decisive to understand environmental, climatic changes and human impact. Here, we focus on palynology. The humidity at Shkodra was always enough to allow the developing of a luxuriant arboreal vegetation. The pollen percentage diagram does not record important changes in terrestrial plants percentages. Arboreal pollen (AP) shows only a rather slight decrease, with ‘natural forests’ replaced by intensive cultivation of chestnut and walnut in the last seven/eight centuries. The rather minimal changes in composition and dominance are because of the fact that the pollen rain comes from different vegetation belts, from the Mediterranean to the alpine one. Two major periods of humidity are found, one at the base of the pollen concentration and influx diagram, before 4100 yr BP, the other at 1300 yr BP. Minima in pollen influx and concentration occurred soon before 4000, at ca. 2900 and at ca. 1450 yr BP These minima, interpreted as aridity crises, show a temporal coincidence with the so-called Bond events 1-3 already found in other central and eastern Mediterranean records. The minimum in AP occurring after 500 yr BP could represent the record of the ‘Little Ice Age’, even if it could be the effect of a strong land use

Shallow-water models for volcanic granular flows: a review of strengths and weaknesses of TITAN2D and FLO2D numerical codes

The behaviour of dry and wet volcanic granular flows is one of the main research topics in present day geophysics and volcanology. It involves various disciplines (e.g. sedimentology, geophysics, fluid dynamics) and investigation techniques (e.g. field studies, laboratory experiments, computational fluid dynamics). The vast interest is justified by the complex nature of these flows and their very dangerous nature that threaten millions of people around the world. In the last decade, computational fluid dynamics has become one of the main instruments used to reproduce past events of volcanic granular flows or to predict their behaviour and potential hazard. In this study, we tested two of the most used codes for simulating volcanic granular flows, TITAN2D and FLO2D, against well studied natural cases (the 1998 wet granular flows in the Sarno area and the 2005 block and ash flows at Colima volcano) and large-scale experiments on granular flows. Comparison between simulated parameters and real ones were carried out in order to evaluate strengths and weaknesses of the two numerical codes. TITAN2D results showed how the basal friction angle is fundamental to control numerical simulations and its dependence on the topographic complexities, DEM resolution and slope-angle ratio. Simulation of large scale experiments offered a good relationship between slope angle ratio at break in slope and basal friction angle, which is useful for application to small drainage basins with not complex channel morphology. FLO2D suffers the lack of rheometric parameters for volcaniclastic material, but is less sensitive of DEM resolution with respect to TITAN2D

Analysing stress field conditions of the Colima Volcanic Complex (Mexico) by integrating finite-element modelling (FEM) simulations and geological data

In recent decades, finite-element modelling (FEM) has become a very popular tool in volcanological studies and has even been used to describe complex system geometries by accounting for multiple reservoirs, topography, and het- erogeneous distribution of host rock mechanical properties. In spite of this, the influence of geological information on numerical simulations is still poorly considered. In this work, 2D FEM of the Colima Volcanic Complex (Mexico) is pro- vided by using the Linear Static Analysis (LISA) software in order to investigate the stress field conditions with increas- ingly detailed geological data. By integrating the published geophysical, volcanological, and petrological data, we mod- elled the stress field considering either one or two magma chambers connected to the surface via dykes or isolated (not connected) in the elastic host rocks (considered homoge- neous and non-homogeneous). We also introduced tectonic disturbance, considering the effects of direct faults bordering the Colima Rift and imposing an extensional far-field stress of 5 MPa. We ran the model using the gravity in calculations. Our results suggest that an appropriate set of geological data is of pivotal importance for obtaining reliable numerical out- puts, which can be considered a proxy for natural systems. Beside and beyond the importance of geological data in FEM simulations, the model runs using the complex feeding system geometry and tectonics show how the present-day Col- ima volcanic system can be considered in equilibrium from a stress state point of view, in agreement with the long-lasting open conduit dynamics that have lasted since 1913

Lake Ohrid’s tephrochronological dataset reveals 1.36 Ma of Mediterranean explosive volcanic activity

Tephrochronology relies on the availability of the stratigraphical, geochemical and geochronological datasets of volcanic deposits, three preconditions which are both often only fragmentary accessible. This study presents the tephrochronological dataset from the Lake Ohrid (Balkans) sediment succession continuously reaching back to 1.36 Ma. 57 tephra layers were investigated for their morphological appearance, geochemical fingerprint, and (chrono-)stratigraphic position. Glass fragments of tephra layers were analyzed for their major element composition using Energy-Dispersive-Spectroscopy and Wavelength-Dispersive Spectroscopy and for their trace element composition by Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry. Radiometric dated equivalents of 16 tephra layers and orbital tuning of geochemical proxy data provided the basis for the age-depth model of the Lake Ohrid sediment succession. The age-depth model, in turn, provides ages for unknown or undated tephra layers. This dataset forms the basis for a regional stratigraphic framework and provides insights into the central Mediterranean explosive volcanic activity during the last 1.36 Ma

A simple two-state model interprets temporal modulations in eruptive activity and enhances multivolcano hazard quantification

Volcanic activity typically switches between high-activity states with many eruptions and low-activity states with few or no eruptions. We present a simple two-regime physics-informed statistical model that allows interpreting temporal modulations in eruptive activity. The model enhances comprehension and comparison of different volcanic systems and enables homogeneous integration into multivolcano hazard assessments that account for potential changes in volcanic regimes. The model satisfactorily fits the eruptive history of the three active volcanoes in the Neapolitan area, Italy (Mt. Vesuvius, Campi Flegrei, and Ischia) which encompass a wide range of volcanic behaviors. We find that these volcanoes have appreciably different processes for triggering and ending high-activity periods connected to different dominant volcanic processes controlling their eruptive activity, with different characteristic times and activity rates (expressed as number of eruptions per time interval). Presently, all three volcanoes are judged to be in a low-activity state, with decreasing probability of eruptions for Mt. Vesuvius, Ischia, and Campi Flegrei, respectively

The late MIS 5 Mediterranean tephra markers: A reappraisal from peninsular Italy terrestrial records

We present new tephrostratigraphic records from the late MIS 5 (ca 110e80 ka) terrestrial sediments from southern and central Italy. On the one hand, the central Italy record consists of an outcropping lacustrine sequence from the Sulmona intermountain basin that contains four trachyticephonolitic tephra layers (POP3, POP2a, POP2b, POP1), all of which show a K-alkaline affinity that is typical for the Roman co-magmatic Province. The POP3 and POP1 layers were dated by 40Ar/39Ar method at 106.2 1.3 ka (2s) and 92.4 4.6 ka (2s), respectively. The sequence in southern Italy, on the other hand, is represented by post-Tyrrhenian coastal deposits of the Cilento area, Campania, which contain two trachytic layers (CIL2, CIL1) that show the same K-alkaline affinity. Based on their chemical compositions and radiometric ages, POP3 and POP1 are firmly correlated with the marine tephra layers X-5 (105 2 ka) and C-22 (ca 90 ka), which, in turn, match tephras TM-25 and TM-23-11, respectively, in the lacustrine sequence of Lago Grande di Monticchio (southern Italy). Of note, the POP1 layer also matches the Adriatic Sea tephra PRAD 2517 that was previously correlated with the older X-5 layer. The tephra couplet POP2a and POP2b (ca 103 and 103.5 ka, extrapolated ages) are compatible with the TM- 24b and TM-24-3 tephras in Monticchio, which match both the stratigraphic positions and the chemical compositions. In the Cilento area, as well as the already described X-6 layer (ca 108 ka) (CIL2), we recognise a new stratigraphic superimposed layer (CIL1) that matches the POP3/TM-25/C-27/X-5 Mediterranean marker(s). In summary, the data presented here provide new chemical and 40Ar/39Ar chronological constraints towards a robust late MIS 5 tephrostratigraphy of the central Mediterranean, although at the same time, they also reveal how the tephrostratigraphy itself might be flawed when dealing with tephra markers that are not adequately constrained and characterised.Published31-451V. Storia eruttivaJCR Journa