Orals: Thu, 1 May | Room K1
In this study, the geochemistry of acidic-intermediate dykes cutting basaltic volcanics around Elazığ (Osmanağa, Kuşsarayı, İçme and Harput) were discussed. The samples studied are of subalkaline character and are predominantly rhyodacite/dacite and, to a lesser extent andesite in composition. Two main groups can be distinguished for the rocks in the studied region: (1) aphanitic andesite, rhyolite, and dacite dykes (2) phaneritic tonalite, granodiorite dykes. While the Al2O3, TiO2, Fe2O3, MgO, CaO, P2O5, Co, and V contents of the samples decrease with increasing SiO2, Zr, Hf, and Nb show a slight increase. In N-MORB (Normal mid-ocean ridge basalt) and ORG (ocean ridge granite) normalizations, large ionic radius lithophile elements (LILE) (e.g. K, Rb, Ba), Th, and La, are enriched compared to Nb, Zr, Hf, Ti, and heavy REE. All samples are characterized by high Th/Nb and La/Nb ratios (average [Th/Nb]M = 18.3; average [La/Nb]M = 3.5), indicating negative Nb anomalies.Chondrite-normalized patterns are parallel to each other and slightly REE enriched ([La/Sm]N = 1.6-5.4), while medium and heavy REEs have a flat-slightly down-concave pattern. Both the initial Nd and Pb isotopes of the samples are in a narrow range (143Nd/144Nd(i)=0.51285 - 0.51290; 206Pb/204Pb(i)=17.95-18.67, 207Pb/204Pb(i)=15.54 - 15.64, 208Pb/204Pb(i)=37.89 - 38.65), while εNd(i) is between +6.4 and +7.2. All samples have positive and variable Δ7/4, Δ8/4 values (∆7/4Pb = +3.75 to +12.54; ∆8/4Pb = +12.65 to +48.76).High Zr/Nb (43.4-55.7) and εNd(i) values indicate a depleted mantle source. Considering the negative Nb anomalies, the mantle source of the samples can be suggested as a depleted mantle source metasomatically enriched by the slab-derived materials. The relatively high Pb isotopic values over DMM (depleted MORB mantle) can be attributed to the contribution of slab-derived sediment. The isotopic compositions of basaltic lithologies and the intruding acidic-intermediate dykes appear similar. The dykes show no sign of crustal contamination and reflect depleted mantle contribution (high, positive ε values). The negative Nb anomalies, low HFSE and HREE abundances (relative to ORG), and relatively low Th-La enrichment levels of the samples, coupled with high Zr/Nb and εNd(i) values, suggest an oceanic arc environment.
How to cite: Ural, M., Sayit, K., Koralay, O. E., and Goncuoglu, M. C.: Geochemistry and petrogenesis of acidic-intermediate dykes from the Yüksekova Complex around Elazığ (Eastern Anatolia, Turkey), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5066, https://doi.org/10.5194/egusphere-egu25-5066, 2025.
Seven short-lived basaltic fissure eruptions took place from December 2023 to December 2024 at the Sundhnúkur crater-row on the Svartsengi intra-transform spreading centre. The duration and magma volume of each eruption increased with time until the last event. The whole-rock major-element composition of the basalt produced is limited (with 7-8.5% MgO) whereas incompatible element and Sr-Nd isotope ratios vary (e.g. 87Sr/86Sr: 0.70312 - 0.70323 and 143Nd/144Nd: 0.51302-0.51295) irregularly with time (Matthews et al. 2024) until June 2024. Similar variability was observed for the isotope ratios during the six-months long 2021 eruption at Fagradalsfjall (87Sr/86Sr: 0.70310 - 0.70323 and 143Nd/144Nd: 0.51302-0.51295); Halldórsson et al., 2022; Marshall et al. 2024). An important difference is that the Sr isotope ratios are significantly higher for a given Nd isotope ratio in the 2024 Sundhnúkur basalt. Mass-balance criteria exclude significant crustal interaction and consequently, the two eruptions are fed from different deep-seated magma aggregation zones. The main difference is that since late 2023 the basalt has ascended into a mid-crustal domain causing a regular inflation until eruption. The eruptions at Sundhnúkur crater-row all start as an intense but short-lived phase on several km long erupting fissures reflecting pressure release in a magma chamber and consequent deflation.
After June 2024, the Sr- and Nd isotope ratios as well as the incompatible element ratios reached the background values of the historical basalts on the Reykjanes Peninsula. Therefore, the evacuation of the “enriched” (high 87Sr/86Sr and K2O/TiO2) basalt compositions, erupted from late April 2021, through 2022 and July 2023 in the Fagradalsfjall region and from December 2023 to June 2024 at Sundhnúkur, from the trans crustal magma domain may be over.
Correlations between Th, Sr and Nd with Th/U revealing magma mingling in an aggregation zone and/or during transport and corresponding timescales of ascent through the oceanic crust will be discussed.
References:
Halldórsson, S.A. et al 2022. Rapid source shifting of a deep magmatic system revealed by the Fagradalsfjall eruption, Iceland. Nature 609, 529-534.
Marshall et al. 2024. The near-Moho magmatic system of the 2021 Fagradalsfjall eruption, Iceland: insights into melt aggregation processes at divergent plate boundaries. AGU Advances 5, AV001310.
Matthews et al. 2024. A dynamic mid-crustal magma domain revealed by the 2023-24 Sundhnúksgígar eruptions, Iceland. Science DOI: 10.1126/science.adp8778.
How to cite: Sigmarsson, O.: Thorium, Sr and Nd isotope study of basalt erupted 2021-2024 on the Reykjanes Peninsula, Iceland , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15066, https://doi.org/10.5194/egusphere-egu25-15066, 2025.
Magma is transported through the Earth’s crust via thin fractures called dykes that cut through layers of bedrock towards the surface to feed volcanic eruptions. Dyke propagation is a multiphase problem where fluid dynamics control propagation velocities and solid mechanics determine dyke pathways. Numerical models are essential tools for understanding the hidden processes of magma transport and interpreting the geophysical and geodetic signals (e.g. earthquakes and surface deformations) that are released during dyke propagation. The complex physical processes governing propagation are challenging to implement in a numerical model, and simplifying assumptions must be made. Common simplifications include neglecting magma flow and assuming that buoyancy drives propagation, or assuming a viscosity-dominant unidirectional flow within a single, vertically oriented dyke. However, such models represent only a small subset of natural cases, and there is motivation for a new model that can simulate a wider range of dyke behaviour. We propose a phase field approach, where a continuous variable (the phase field) denotes the presence or absence of a fracture. Phase field evolution (i.e. dyke propagation) is governed by a simple equation which enables the simulation of nonlinear fracture pathways, whilst the continuous nature of the approach makes it well suited for multiphase fracture problems. We have developed a three-variable φ-p-u model that solves for the phase field φ, magma pressure p, and solid rock displacement u. Real-time simulations of an experimental dyke show promising results, suggesting that the phase field approach could bring significant advancements to models of natural dyke propagation.
How to cite: Chalk, C., Quintanas-Corominas, A., Kavanagh, J., Houzeaux, G., Costa, A., and Folch, A.: A phase field model of magma transport in dykes: validation with small-scale experiments, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9211, https://doi.org/10.5194/egusphere-egu25-9211, 2025.
Terrestrial volcanism is the result of a series of magmatic processes governed by the plumbing system architecture and the timescales of melt migration. It has been proposed that large stratovolcanoes are fed by transcrustal magmatic systems with crystals and melts erupted from a range of reservoir depths. At the other end of the spectrum, mafic monogenetic volcanoes are generally thought to be fed directly from the mantle and thus may lack a plumbing system. The presence or absence of a range of magma reservoirs prior to eruption has implications for the timescales of unrest and magma transport to the surface. Here we address these issues by a petrological and mineralogical study of six scoria cones representing the mafic endmember of the Chaîne des Puys (Massif Central, France). This monogenetic intracontinental volcanic province dominates the Clermont-Ferrand agglomeration and its 400,000 inhabitants, with the first eruptions starting about 100 kyr ago and the last only 6.7 kyr ago. Although very active at certain times, the Chaîne des Puys has also been inactive on several occasions over periods of several thousand years.
We investigated the composition and textures of several hundred clinopyroxene and olivine phenocrysts and applied crystal system analyses to propose a range of magmatic environments and also timescales of transfer between them and eruption using diffusion chronometry methods. We found that all scoria cones were fed by two or three magmatic reservoirs and that crystals circulated between them prior to eruption on a range of timescales. We propose that magmas migrate repetitively from the deepest basaltic reservoir (R1; ~25 km depth), partially in the mantle, to slightly more evolved and shallower reservoirs (R2) where they interact with the host magma before eruption onset. Occasionally, magmas from R2 migrate and interact with trachy-basaltic R3 reservoirs (~18 km). The R1 reservoir was involved in both the oldest and most recent eruptions studied (~40 kyr difference), demonstrating its stability over time. The timescale of eruptions triggered by magma transfer from R1 to R2 ranges from about six months to a few years, while the timescale for magma transfer from R2 to R3 ranges from about one week to five months.
How to cite: Pereira, T., France, L., Costa, F., and Villeneuve, J.: Kinetics of mafic magma transfer and destabilization of the deep plumbing system in monogenetic volcanic provinces (Chaîne des Puys, France)., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9908, https://doi.org/10.5194/egusphere-egu25-9908, 2025.
The plumbing system beneath Mauna Loa, Hawai'i, has been understudied relative to its younger neighbor, Kīlauea. It is particularly interesting to ponder whether Mauna Loa’s larger size and greater maturity is reflected in its magma storage geometry. For example, prior work has suggested the presence of a deep (>18 km) storage system based on the presence of high Mg# (>84) Opx, from which magmas may ascend within days towards the surface. This would have very different implications for hazards and effective monitoring than at Kīlauea, where eruptions mobilize mostly from 1-5 km depth. To assess the possibility of deep storage, we examine crystal cargoes from picritic to aphanitic basalts erupted in 1852, 1855, 1868, 1949, 1950, 1984 and 2022 from the summit and rift zones, including harzburgitic xenoliths present in lavas erupted on the south flank. We use confocal Raman Spectroscopy to analyze fluid inclusions (small pockets of CO2-rich fluid trapped within crystals), coupled with Energy Dispersive Spectroscopy to determine the chemistry of the host crystal. Fluid inclusion barometry provides a precise determination of the pressures at which fluids were trapped within crystals, and thus the depths at which crystals grew and/or stalled for prolonged periods. Analyses of ~300 fluid inclusions from seven effusive eruptions and ~80 from xenoliths show that magma is predominantly stored at 1-5.5 km depth, which is slightly deeper than similar measurements at Kīlauea. These results contrasts with past studies which have suggested that the high Mg# orthopyroxenes in the xenoliths formed at > 6 kbar based on pMELTS modelling of orthopyroxene stability. We show that different thermodynamic models (pMELTS, rhyoliteMELTS, MageMIN) disagree greatly on the depth of Opx stability, indicating that the high pressures of magma storage previously suggested for Mauna Loa are not required. The poikilitic textures within the xenoliths with rounded, resorbed olivine chadocrysts within large Opx oikocrysts suggest that the high Mg# Opxs within these samples formed from a reaction between a higher SiO2 melt (~52 vs 49 wt%) and the olivine cumulate pile, at 3-5 km depth based on fluid and melt inclusion pressures from the olivine chadocrysts. The observed phase assemblage can be reproduced with melt-mush reaction models in rhyoliteMELTS. In summary, we suggest that the presence/absence of high Mg# Opx in shield Hawaiian volcanoes may instead reflect differences in bulk SiO2 between the two chemical trends present in the Hawaiian hotspot (Loa and Kea trend), rather than drastic differences in the depth of magma storage.
How to cite: Wieser, P., Rangel, B., Bearden, A., DeVitre, C., Lynn, K., and Gleeson, M.: Assessing magma storage beneath Mauna Loa, the world's largest active volcano, using combined barometric and microstructural constraints, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3884, https://doi.org/10.5194/egusphere-egu25-3884, 2025.
Crystals and glass discharged as tephra during explosive volcanic eruptions provide a valuable window into magmatic processes. Kolumbo, a shallow submarine volcano on the Hellenic Arc of the southern Aegean Sea, recently erupted in 1650 CE and was both violently explosive and tsunamigenic, resulting in significant loss of life on neighboring Santorini. Developing a conceptual model of the magma storage and eruption processes at Kolumbo is crucial for improving preparedness in this volcanically active and densely populated region. Using in situ tephra deposits cored during the International Ocean Discovery Program Expedition 398, this study aims to reconstruct the temporal evolution of the magma plumbing system at Kolumbo over the two most recent eruptive units at Kolumbo (1650 CE and an earlier eruption). This research aims to (1) infer pre-eruption magmatic processes and eruption initiation mechanisms, (2) determine magma storage conditions, including pressure, temperature, and H₂O content, and (3) assess temporal variations in the magmatic system at Kolumbo. Methods include the traditional petrologic toolbox of major- and trace-element geochemistry, focusing on minerals and glass to delineate crystallization histories, identify zonation patterns, and infer pressures and temperatures of the crystallizing assemblages. Preliminary results suggest significant differences in eruption initiation mechanisms and magmatic histories between the two eruptive units. The 1650 CE tephra exhibits multiple populations of phenocrysts that preserve textures such as reverse zoning and sieving, consistent with mafic recharge into a silicic reservoir as suggested by previous research. Plagioclase-hosted melt inclusions reveal water content of 4.0–5.25 wt.% for 1650 CE at a storage temperature of 807–847ºC, determined using plagioclase-liquid hygrometry and thermometry (Waters and Lange, 2015; Putirka, 2008). Clinopyroxene-liquid barometry (Petrelli, 2020; Jorgenson, 2022) identifies two clinopyroxene populations, yielding pressures of 4 and 6 kbar, respectively (±0.3 kbar) and temperatures of 914–953ºC (±<3ºC) supportive of mafic injection from a deeper magma source that triggered the 1650 CE eruption. The newly analyzed older eruption was initiated by some other mechanism than mafic injection - either heating from below or depressurization of a highly evolved silicic reservoir. Plagioclase-liquid hygrometry and thermometry indicate water contents of 4.25–5.0 wt.% at a storage temperature of 797–817ºC, though pressures remain unconstrained. These findings offer critical insights into the contrasting magmatic processes driving eruptions at Kolumbo, highlighting the dynamic interplay between mafic recharge and silicic storage.
How to cite: Maher, T., DeBari, S., Druitt, T., Kutterolf, S., McIntosh, I., Metcalfe, A., and Ronge, T.: Characterizing eruption initiation mechanisms and storage conditions at the high-threat Kolumbo volcano, Greece., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-729, https://doi.org/10.5194/egusphere-egu25-729, 2025.
Phenocrysts in magmas are often assumed to be the product of crystallization directly from a host magma. However, decades of research suggests that crystals carried in magmas (crystal cargo) are far more complex. We test the hypothesis that textural and chemical characteristics of phenocrysts (both native and disaggregated from crystal clots) in andesitic and dacitic lavas and tephras can be used to develop models for spatial arrangement of subcrustal magma systems and their evolution over time. To do this, we use geochemical fingerprinting of complex crystal cargo in a compositionally diverse set of lavas and tephras erupted over the last hundred thousand years at the very high-threat Mount Baker volcanic center in the northern Cascade Arc. These eruptive products, whose composition ranges from basaltic andesite to dacite, contain crystals of plagioclase (pl), clinopyroxene (cpx), orthopyroxene (opx), and sometimes olivine (ol). Multiple populations of each of these crystal types, even within a single thin section, show that they are not typical phenocrysts. Their textures and zoning profiles, especially within crystal clots, lead us to identify as many as five distinct co-crystallizing assemblages of pl-opx-cpx-ol that exist within each individual eruptive product. Careful work parsing out these assemblages has led us to infer that they are liquid-poor remnants of basaltic (B), basaltic andesite (BA), andesite (A), and dacite (D) mushes that exist in the subsurface. These crystal assemblages were first identified in mafic lavas that span ages of 110 ka to 9.8 ka, but we have also recently identified a subset of them in dacitic lava flows and a 6.7 ka dacitic tephra. The interpretation of these data is that multiple crystal mushes beneath Kulshan are tapped by multiple passing magmas that erupt at the surface at different times, producing the same array of crystal clot types/co-crystallizing assemblages in subsequent eruptive products for at least 100 ka. We use thermobarometry to constrain the depths of these mushes and textural/chemical characteristics to infer eruption triggers. We also show that a Holocene monogenetic flank eruption taps a very different mush system and has distinct eruption triggers. Our work shows that meticulous characterization of crystals is invaluable for development of conceptual models of individual volcanic centers to aid in hazard planning.
How to cite: DeBari, S., Escobar-Burciaga, R., Aughenbaugh, K., Cunningham, D., Florea, A., Garvey, B., Kaplan, E., Shamloo, H., Tucker, D., Walowski, K., and Yoder, E.: Phenocryst or not? Using a stratovolcano’s crystal cargo to explore crustal-scale magmatic systems through time, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14391, https://doi.org/10.5194/egusphere-egu25-14391, 2025.
At active volcanoes, observed surface deformation results from the complex interaction between the magma and the host rock in the magmatic plumbing system. One common source of deformation is magmatic recharge, resulting in pressurisation of the magma chamber. All active systems, from the most basaltic to the most silicic magmatic composition, are subject to magma chamber replenishment. The majority of numerical models used to invert surface deformation focus on the effect of over-pressure and neglect the effect of the fluid buoyancy. In the case of silicic magma, the buoyancy is positive and can further be increased by the gas exsolution that occurs at shallow depths. Basaltic magma, on the other hand, has a negative buoyancy which is measurable by gravimetry. We present here experiments investigating the effect of buoyancy on surface deformation. Surface deformation, the shear strain pattern and the chamber overpressure are measured throughout the injection of liquid at constant volumetric flux. Then, we use the McTigue (1987) model to predict the surface displacement from the measured overpressure in the chamber, and conversely. We show that predictions are 7% below the observation when the liquid buoyancy is positive (ẟρ =-81 kg⋅m-3) and 9% above it when the liquid buoyancy is negative (ẟρ =-157 kg⋅m-3). Even if the effect of buoyancy is small, this highlights the possible error made on source overpressure when inverting surface deformation. This call to a careful consideration of the geological context in unrest period at active systems when volume change needs to be precisely estimated.
How to cite: Morand, A., Rust, A. C., Burgisser, A., and Biggs, J.: Highlighting the buoyancy effects on surface deformation above an inflating magma chamber from analogue experiments, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11951, https://doi.org/10.5194/egusphere-egu25-11951, 2025.
The pre- and syn-eruptive magma decompression rate is recognized as a key parameter modulating eruption dynamics, with explosive eruptions being generally associated with much larger decompression rates than effusive ones. Magma decompression rates cannot be directly measured and thus are typically inferred from petrological, geochemical, numerical modelling, and seismic data. Most studies use petrological information of volatile element diffusive equilibration in glass and crystals to infer a single value for the magma ascent rate for a given eruption, even though numerical volcano conduit simulations show that changes of velocity are expected during magma ascent. Here we integrate magma ascent conduit models with diffusion chronometry of volatiles in melt embayments and phenocrysts to obtain a more comprehensive understanding of magma ascent rates. We find that incorporating a more realistic boundary condition that depends on the magma ascent path with variable velocities gives time estimates that can be up to a factor of 7 longer than from the standard assumption of constant magma ascent rate. Therefore, previous magma ascent rates from diffusion chronometry of volatiles in crystals and melts with a fixed boundary condition may be significantly overestimated. Overall, we show that coupling of magma ascent models with diffusion chronometry can provide more robust inferences of magma ascent and thus improve the understanding of the role of this parameter into the explosive and effusive eruption controls.
How to cite: Bernard, O. and Costa, F.: Coupling magma ascent models with volatile diffusion chronometry, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5867, https://doi.org/10.5194/egusphere-egu25-5867, 2025.
Caldera resurgence is rare at mafic volcanoes. Here we consider the well-exposed resurgence at Sierra Negra caldera (Galápagos), to investigate how resurgence develops at a mafic system. Based on topographic and field analysis, the structure of the resurgence consists of an eastward tilted block bounded by a fault-propagation fold activated by a steep inward-dipping reverse fault with dip decreasing towards the surface. Extension of the uplifted part of the reverse fault results from gravitational instability, and is accommodated by horst-and-graben structures over a several hundred meter wide zone. Extension culminates in the main normal fault responsible for the inward-tilt of the lava pile, forming a distinctive ridge. The resurgence results from spatially and temporally distinct unrest episodes, promoted by the shallow accumulation of large volumes of magma. Sierra Negra is the first documented example of piecemeal resurgence, as shown by the recent uplift episodes associated with eruptions in 2005 and 2018. The example of Sierra Negra suggests that the formation of resurgent blocks depends on the initial location of the feeding system, with non-centered feeding systems developing asymmetric (trapdoor) blocks. Finally, Sierra Negra demonstrates that mafic volcanoes without well-developed rift zones may promote resurgence when reaching a mature stage with significant amounts of viscous cumulates, favoring shallow magma accumulation.
How to cite: Acocella, V., Galetto, F., Amelung, F., and Aguaiza, S.: Sierra Negra, Galápagos: a resurgent-block basaltic caldera , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5817, https://doi.org/10.5194/egusphere-egu25-5817, 2025.
Calderas often experience prolonged periods of unrest that are challenging to attribute to magmatic or hydrothermal origins, making it critical to develop a clear picture of these dynamics. The Campi Flegrei caldera (CFc), in southern Italy, is a striking example. Since 2005, the caldera has been undergoing its most recent phase of unrest, marked by increased ground uplift, seismicity and hydrothermal activity, the nature of which remains under debate. Understanding the past and ongoing behaviour of this volcanic system is far from trivial, yet it is of crucial importance. To address this, we focus on investigating the chemico-physical and mechanical properties as well as the dynamics of the CFc shallow crustal structure (first 4 km of depth), where most earthquakes and deformation occur, and their role during periods of unrest. Our study employs a multiscale analysis, integrating results from 4D X-ray microtomography (i.e., 3D imaging during in-situ experiments) of core samples from a ~3 km-deep geothermal well located near the caldera’s center with 3D high-resolution seismic tomography, complemented by magmatic dyke path simulations. At a depth of approximately 2.5–3.0 km, we identify a transition to a weak tuff layer likely acting as a trap for magmatic fluids. Simulations of magma pathways suggest that past intrusions may have stalled at these depth, influenced by caldera unloading stress and magma's neutral buoyancy level. These stalled dykes deformed, heated, and released magmatic fluids, weakening the surrounding rocks. This weak layer may play a pivotal role in generating overpressure, driving deformation and seismicity, and shaping the dynamics of recent CFc unrest episodes, as well as potential future magma ascent events.
How to cite: Buono, G., Maccaferri, F., Pappalardo, L., Tramelli, A., Caliro, S., Chiodini, G., Pinel, V., Rivalta, E., Spagnuolo, E., Trasatti, E., and Di Vito, M. A.: Weak crustal layer beneath Campi Flegrei (Italy) identified: what's its impact on unrest?, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19156, https://doi.org/10.5194/egusphere-egu25-19156, 2025.
IODP Expedition 398 to the Christiana-Santorini-Kolumbo Volcanic Field unearthed the largest shallow submarine explosive eruption from ancestral Santorini: The Archaeos Tuff (AT). This ~90 km3 eruption erupted at water depths of 200–1000 m, forming a megaturbidite up to 150 m thick in the surrounding marine basins1. Shipboard biostratigraphic constraints initially suggested an age of 520 ± 10 ka, though nannofossils are subject to post-eruptive upward remobilization in active marine basins1. Here, we present preliminary 40Ar/39Ar and U-Pb age determinations for AT from 5 samples at sites U1591 and U1593 that redefine AT as a stratigraphic marker approximately 250 kyrs older than shipboard estimates. Plagioclase and sufficiently degassed glass were separated from recovered pumice and lapilli by crushing, heavy liquid and/or magnetic separation, and subsequently leached and handpicked. Following irradiation, the samples were analyzed on the ARGUS-VI noble gas multi-collector mass spectrometer in the 40Ar/39Ar Geochronology lab at Oregon State University. In parallel, zircons were separated from the residual sample powders (<150 µm) as well as one AT onshore equivalent and analyzed by secondary ionization mass spectrometry (SIMS) at Curtin University. Preliminary age determinations from Sites U1591 and U1593 in the Christiana and Anhydros Basins, respectively, of glass and plagioclase indicate a new stacked eruptive age that is tentatively constrained at 764 ± 3.5 . Tentative U-Pb crystallization ages from zircons collected from the same samples, after filtering for high-radiogenic (>90% 206Pb) spots, range from a minimum crystallization age of 775 ± 18 Ma, over a a (geologically meaningless) central age of 810 ± 19 Ma (MSWD = 3.1; n = 49), to a minor xenocrystic population with ages between 2.1 and 8.6 Ma (n = 5). Compared to other highly explosive arc systems, the equivalence between 40Ar/39Ar ages and those of a significant zircon population with near-eruption crystallization ages suggests rapid magma accumulation prior to the AT event. This highlights the importance of integrated, high-resolution radiometric age constraints in tephrochronostratigraphy and multi-chronometer assessments of recharge timescales in arc settings.
1Druitt, T., Kutterolf, S., Ronge, T.A. et al. Giant offshore pumice deposit records a shallow submarine explosive eruption of ancestral Santorini. Commun Earth Environ 5, 24 (2024). https://doi.org/10.1038/s43247-023-01171-z
How to cite: Beethe, S., Schmitt, A. K., Koppers, A. A. P., Pank, K., Metcalfe, A., Druitt, T. H., Kutterolf, S., Preine, J., and Ronge, T. and the IODP Expedition 398 Scientists: New Age for the Archaeos Tuff: Using 40Ar/39Ar and U-Pb to Redefine Ancestral Santorini’s Tephrochronostratigraphy and Implications for Rapid Magma Accumulation, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12976, https://doi.org/10.5194/egusphere-egu25-12976, 2025.
Lava flow emplacement depends on the effusion rate, the viscosity of the lava and the topography. The transport of lava within lava flows usually occurs through the formation of lava channels or by the development of lava tubes. Lava flows that form tubes are able to feed their front with molten lava, due to the insulation of the erupted lava by the roof of the tubes, preventing atmospheric cooling. These tube-fed lava flows can thus emplace over longer distances, increasing the hazard caused by lava flows. Lava tube formation within a lava flow can be influenced by different factors such as: eruption rate, pre-eruptive topography, geochemical composition, and lava viscosity. Understanding how these mechanisms influence the formation of a lava tube is of great importance to better assess the hazard caused by lava flows and better react in case of eruptive crisis. In this study, the 1858 lava flow field formed during the 1858-1861 eruption at Vesuvius was examined as it formed several lava tubes, including one which can be accessed. The 1858 lava flow field and the largest lava tubes were sampled from the vent to the front and from the inside to the outside respectively. We performed Electron Microprobe Analysis (EMPA) to measure crystal and glass compositions, and used phase-contrast synchrotron X-ray computed microtomography (µ-CT) to retrieve the 3D structure of our samples and characterize the crystal phases. Our results show a variation between the microlitic matrix of the samples in terms of size and number of crystals, suggesting different cooling conditions during lava flow emplacement and lava tube development. Moreover, the volume fractions of the different phases composing the lava, leucites and plagioclase, clinopyroxenes, oxides, also show variations. These variations in volume fraction, number and size of the microlitic matrix can be used to decipher the local conditions of emplacement within the lava flow and lava tube. Understanding the petrology and geochemistry of the lavas forming the flow field and the lava tube help us to further comprehend lava flow emplacement and lava tube formation at Vesuvius.
How to cite: Lemaire, T., Morgavi, D., Arzilli, F., Calvari, S., Bamber, E. C., La Spina, G., Cucciniello, C., Prasek, M., Mancini, L., and Petrosino, P.: Chemical and textural analysis by EMPA and synchrotron X-ray micro-CT: insights into lava tube formation at Vesuvius (Italy), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18854, https://doi.org/10.5194/egusphere-egu25-18854, 2025.
This study investigates the nucleation and growth of nanometric crystals within basaltic glass to understand their impact on the mechanical properties of the host medium. Our findings reveal that the evolution of the crystalline mass is far more complex than previously anticipated. Samples subjected to different thermal treatments—single ramp heating versus double-step annealing—exhibited dramatically enhanced toughness. These variations underscore the critical role of crystallization pathways in defining the mechanical performance of the material. Using advanced characterization techniques, including Transmission Electron Microscopy (TEM), Raman spectroscopy, and X-ray Diffraction (XRD), we analyzed the interplay between nanocrystals, gas bubbles, and cracks within the remelted volcanic rock samples. Our results have implications for understanding the rheological evolution of volcanic systems during eruptions and for optimizing industrial processes in glass ceramics. This work sheds light on how nanocrystal formation and growth can significantly modify both natural and engineered materials.
Contribution of PRIN2022PXHTXM- STONE project, funded by EU - NextGeneration, PNRR-M4C2- CUP: D53D23004840006
How to cite: La Felice, S., Capitani, G. C., Chaudary, R., Giordano, D., Biesuz, M., Daldosso, N., and Cassetta, M.: Nanocrystal Nucleation and Growth in Basaltic Glass: Implications for Mechanical Properties and Crystallization Pathways, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10314, https://doi.org/10.5194/egusphere-egu25-10314, 2025.
Small crystals (below 100 microns ca.) in pyroclasts from explosive volcanic eruptions are often fractured, with fractures that are both empty or filled with the same groundmass that surrounds the microlite, usually made of glass. Textural observations and experiments show that microlites are fractured during the same process of fragmentation that causes the transition from a continuum of liquid magma to a gas-pyroclast dispersion. However, the timing and dynamics of the fracturing process are still poorly defined. Aiming at constraining how and when crystals are fractured, we investigated the chemical and textural features of glass that entered into fractures within crystals. Under Scanning Transmission Electron Microscope (STEM), these glasses reveal inhomogeneities that are otherwise invisible. In particular, nanometer-sized patches of variable composition are outlined, which are present in the glass only inside the fractures but are lacking outside of them. These features, tentatively interpreted as incipient immiscibility leading to nanolite crystallization, testify local disequilibrium conditions between the melt and the newly-formed crystal fracture surface, and could provide a mean to define the timing intervening between crystal (and magma) fracturing and pyroclast quenching upon eruption.
How to cite: Taddeucci, J., Pontesilli, A., Di Fiore, F., and Scarlato, P.: Scanning Transmission Electron Microscope (STEM) features of glass in crystal fractures, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16475, https://doi.org/10.5194/egusphere-egu25-16475, 2025.
Posters on site: Fri, 2 May, 14:00–15:45 | Hall X1
The volcanic landscapes of Iceland's Westfjords are marked by the intriguing of Plagioclase Ultraphyric Basalts (PUBs), distinctive lava formations characterized by plagioclase contents so high (up to 50-60%) that they approach the crystallinity of a crystal mush. This research investigates the magmatic origin, emplacement mechanisms, and flow dynamics of these unusual lavas through an interdisciplinary approach combining petrographical, geochemical, and rock magnetic analyses. Thermobarometric calculations reveal magma equilibration conditions at mid-crustal depths (11.6±2.5 km) and temperatures of 1204.5±9.7°C. Mineral-melt relationships reveal a mush origin for the macrocrysts cores, with high An-cores for the plagioclases (An85-89) and high Fo-cores for the olivines (Fo83-86), whereas the rims show more evolved rims with compositions ranges of An50-70 for the plagioclases and Fo48-84 for the olivines, indicating a complex crystallization history. Trace element concentrations in the lava matrix are similar to other non-PUB westfjords basalts. Plagioclase trace element compositions are nearly in equilibrium with the composition of the host lava, unlike most modern Icelandic PUBs that typically show plagioclase-melt disequilibrium. Despite calculated viscosities suggesting potentially explosive behaviour (with viscosity values (log η) = 6.2 Pa·s and crystal volume fractions (φ) = 0.59 at 900ºC), field evidence indicates effusive emplacement, explained by several mechanisms including crystal alignment, thermal exchange, and shear thinning behavior. Anisotropy of Magnetic Susceptibility (AMS) measurements reveal flow directions predominantly oriented WNW-ESE, consistent with the location of the Arnarfjörður central volcano. However, scattered AMS distributions in crystal-rich samples suggest that elevated crystal content influenced the flow dynamics.
These findings enhance our understanding of crystal-rich magmatic systems and their emplacement mechanisms, contributing to refined models of magma dynamics. The results highlight the importance of considering more complex emplacement mechanisms when studying crystal-rich magmas that appear to defy traditional rheological models.
How to cite: Jones, P., Piispa, E. J., Caracciolo, A., and Marshall, E. W.: Understanding the flow dynamics of a Plagioclase Ultraphyric Basalt- a case study from the Westfjords, Iceland, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2586, https://doi.org/10.5194/egusphere-egu25-2586, 2025.
Mt. Etna is one of the most active basaltic volcanoes on Earth, producing a wide range of eruptive styles, from relatively gentle effusive eruptions to highly hazardous explosive eruptions. During the last three decades, Etna has produced numerous highly explosive paroxysmal events, generating intense lava fountaining and ash clouds that reached several kilometres in height. In particular, between 13 December 2020 and 21 February 2022, a series of 62 paroxysms occurred at Mt. Etna. Petrological and geochemical analyses of erupted samples collected throughout the entire eruptive period suggest that the activity can be divided into two main sequences. These two sequences are both associated with the arrival of a more primitive, hotter, and volatile-rich magma from an intermediate magma chamber at a depth of 9 km (relatively to the vent of the conduit) into a shallower magma chamber at a depth of 3 km where a more evolved, colder and volatile-poor magma was present.
Here, we investigate the role of the evolution in magma composition and the resulting variations in the pre-eruptive conditions (pressure, temperature, crystal and volatile content) on the magma ascent dynamics observed during the 2020-2022 paroxysmal activity at Mt. Etna. Specifically, we use a 1D steady-state model of magma ascent to simulate the ascent dynamics at Mt. Etna. We consider different magma compositions, emulating the progressive mixing between a more evolved magma with a more primitive magma, as suggested by petrological and geochemical analyses. We also explore different thermodynamic conditions of the shallow magma chamber, simulating the evolution of the pre-eruptive conditions due to the interaction of the two magmas.
How to cite: La Spina, G., Corsaro, R. A., and Miraglia, L.: The role of pre-eruptive conditions on magma ascent dynamics during the 2020-2022 paroxysmal activity at Mt. Etna: a numerical investigation, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5641, https://doi.org/10.5194/egusphere-egu25-5641, 2025.
Volcano-tectonic (VT) earthquakes can occur during the movement of magma when it exerts pressure on surrounding rock. During the 1998 dike-fed eruption at Piton de la Fournaise (PdF), over 500 VT events were documented, offering a rare chance to analyze the volcano's stress conditions. We derived double-couple fault plane solutions (FPS) for these events. The main orientation of the compressional (P) axes varied with depth: between approximately 2 and 6 km below sea level, the P-axes were vertical, while above 2 km BSL, they became horizontal. This horizontal orientation is perpendicular to regional compression at depths of 0–2 km BSL, then aligns with regional compression between 0–2 km above sea level. By integrating edifice loading with stress alterations from dike activity through an innovative damage-based model for dike propagation, we examined various factors influencing the stress field at PdF, including rock strength, density, and magma viscosity, thereby enhancing our understanding of the volcano's stress state before an eruption.
How to cite: Huang, Y. and Zhan, Y.: Dike-Induced Earthquakes as Probes of the Local Stress Field Prior to the 1998 Eruption of the Piton de la Fournaise Volcano, La Reunion, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7688, https://doi.org/10.5194/egusphere-egu25-7688, 2025.
Mt. Etna, the most active volcano of Europe, produces both summit and flank eruptions. In recent decades, the summit eruptions have been more common than flank ones. They occur from the four summit craters, namely the South-East Crater, the youngest and the most active, the North-East Crater, the Voragine Crater and the Bocca Nuova Crater. Summit eruptions can also be generated by branching of the central conduits opened in sub-terminal position, i.e. slightly downslope from the summit craters. Besides the location of the eruptive vents, summit eruptions show a range of eruptive style, from discrete Strombolian explosions to high-intensity paroxysmal events characterized by lava fountains producing high-altitude ash plumes, and associated with lava effusion.
Here, we study a period of summit activity that began after the end of the long-lasting 2008-2009 eruption. More precisely, we investigate from 2010 to 2024, focusing on distinctive paroxysmal sequences, which mostly involved the South-East Crater (SEC) and, to a lesser extent, the Voragine Crater (VOR). Overall, The SEC produced 25 episodes in 2011–2012 and 23 in 2013–2014, while 4 and 2 episodes occurred at the VOR in December 2015 and May 2016, respectively. In recent years, more than 60 episodes took place at the SEC in December 2020-February 2022, and 7 at the VOR in July and November 2024. Noteworthy, the characteristics of paroxysmal activity at the two summit craters differ significantly for the number of events, the duration of each sequence, the repose period between episodes, the total volume of the erupted products, the proportion of tephra and lavas, the impact of the eruptive activity on the morphology of the summit area, as well as the texture and composition of the erupted products.
Although several petrological studies have considerably improved the knowledge of Etna’s summit explosive activity in the last decades, long-term investigations focused on paroxysms are scarce. Therefore, in the framework of petrological monitoring of the Etna Observatory, we carried out a regular sampling of the products erupted from 2010 to 2024, which have been analysed for petrographic textures and the compositions of glass, major and trace elements, as well as Sr-Nd isotopes. The research is still in progress.
The expected results will help to: i) deepen the knowledge of the magmatic processes (mafic recharge, magma mixing and crystallization), ii) investigate if/how pre-eruptive magma dynamics influence the syn-eruptive processes driving paroxysmal activity at SEC and VOR, iii) gain insight into the role that tectonic and /or geometry of the shallow plumbing system can play in determining different characteristics of paroxysmal activity at the SEC and the VOR, and finally iv) explore if the products erupted before a paroxysmal sequence show textural and compositional features heralding the onset of paroxysms.
The scientific community has the important goal of deeply understanding the magmatic processes and mechanisms at the root of the paroxysmal activity in order to provide crucial information to the authorities in charge of mitigating hazard associated with such activity.
How to cite: Corsaro, R. A. and Miraglia, L.: Summit activity at Mt. Etna, Sicily, Italy: long-period (2010-2024) petrologic study to investigate the high-energetic paroxysmal activity, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10212, https://doi.org/10.5194/egusphere-egu25-10212, 2025.
Violent eruptive events in basaltic systems often follow input of hot, undegassed magmas in shallow magmatic reservoirs. Investigating how crystal and glass chemistry record such physicochemical changes in the system is critical to reconstruct the mechanisms driving sudden large scale explosive events in such settings, and may be integrated with crystal stratigraphy to recover the relative and absolute timing of eruption triggers. As such, it is of utmost importance to reconstruct such changes in natural systems through the record provided by crystals and glasses in the eruption products.
The reconstruction of crystal-melt equilibria is crucial for a thermodynamically rigorous assessment of intensive properties of the magmatic system based on mineral compositions. In this respect, experimental constraints on crystal-melt partitioning are quintessential to the modeling of melt compositions and intensive parameters, performed by minimizing the strain energy determined by the substitution of isovalent trace cations in crystal lattice sites. In this contribution we combine numerical modeling with a multi-elemental approach to the study of intracrystalline compositional variations in a statistically representative data set of plagioclase compositions from Stromboli volcano. This approach, applied to a well-studied volcanic system, allows to constrain the chemical evolution of the system, assessing the role of disequilibrium effects and transient melt compositions existing ephemerally during crystal growth and dissolution episodes. Implications of this work extend from the reconstruction of magma dynamics at Stromboli to the definition of best practices to deal with the interdependence inherent in the treatment of intensive thermodynamic properties of magmatic systems.
How to cite: Pontesilli, A., Di Fiore, F., Mollo, S., Ellis, B., Andronico, D., Taddeucci, J., Bachmann, O., and Scarlato, P.: Multi-elemental assessment of plagioclase-melt equilibria unravels episodes of crystal growth and provides clues on magma evolution, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12168, https://doi.org/10.5194/egusphere-egu25-12168, 2025.
Eruption dynamics and eruptive style are controlled by the interplay and feedback of non-linear conduit processes during magma ascent, such as gas exsolution, bubble expansion, outgassing and crystallisation. These processes control the evolution of magma viscosity and how easily the gas and melt phase decouple during ascent. Volcanism associated with intermediate and evolved alkaline magmas (from phonotephritic to phonolitic) is characterised by a wide range of eruptive styles, from lava flow to Plinian eruptions. This diversity in eruptive behaviour makes the eruption dynamics of alkaline volcanic systems challenging to predict.
The volcanic history of Vesuvius (Italy) is characterised by complex transitions in eruptive behaviour, producing eruptions that are amongst the most catastrophic volcanic eruptions in human history. Here, we combine synchrotron X-ray microtomography with a numerical conduit model to investigate the processes and the pre-eruptive conditions that control the style of activity of alkaline magmas, using Vesuvius as a case study. We quantify crystallinity, vesicularity and connectivity of pore networks in pyroclasts from deposits of the 79 AD Plinian eruption and of the 1944 lava fountaining eruption of Vesuvius using 3D textural analysis. Our results reveal that heterogeneous bubble nucleation, driven by leucite crystals, contributes to the formation of large bubble populations during Plinian eruptions, with vesicle number densities exceeding 10⁴ mm⁻¹. The numerical results, obtained using a 1D steady-state model, indicate that phonolitic magmas are prone to fragmentation considering a wide range of pre-eruptive conditions, including temperatures from between 830 and 970 ºC and crystal fractions up to 0.40.
How to cite: Arzilli, F., La Spina, G., Bamber, E., Morgavi, D., Fedele, L., Mancini, L., Prašek, M., Lemaire, T., Santangelo, I., Chiominto, G., Perrotta, A., Balcone-Boissard, H., Giordano, D., and Scarpati, C.: The role of bubble-crystal interactions in the eruption dynamics of alkaline magmas: implications for Vesuvius volcano, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12502, https://doi.org/10.5194/egusphere-egu25-12502, 2025.
Monte Amiata is a small linear Pleistocenic volcano emplaced in a short period of time (between 303 ka and 299 ka) and located in Southern Tuscany. It is made monotonously by silicic massive lava flows and exogenous domes, grouped in two main volcanic periods: the Bagnore Synthem and the Monte Amiata Synthem. Massive lavas and domes host rounded to sub-rounded Mafic Magmatic Enclaves (MMEs). They are abundant in the youngest period of activity (i.e., Monte Amiata Synthem), increasing, apparently in the most recent eruptions. Volcanic rocks and their MMEs range in composition from trachydacites to olivine latites. Here, we present the results of our detailed study about the distribution, origin, and evolution of the mafic magmatic enclaves hosted by Monte Amiata lavas and domes in the frame of the evolution of the short-lived volcanic activity at surface. In order to do this, fieldwork observations were made, thin sections were studied under the petrographic microscope and chemical and isotopic analyses on whole MMEs and their forming minerals were performed. Fieldwork observations, supported by image analysis, showed a variation of the outcropping percentage abundance of the magmatic enclaves within the Monte Amiata domes. The estimated mafic enclaves outcropping abundance percentage varies between ca. 5.5% for La Montagnola dome and ca. 0.8% in the case of the Pratini dome. This suggests a variable degree of interaction between the magmas involved in the mingling process and, in some cases, it remarks the occurrence of the mechanical fractionation. Through the petrographic investigation of the magmatic enclaves five groups of enclaves can be identified. They are diversified by type of phenocrysts, micro-phenocrysts and microliths, the degree of porphyricity and the presence and abundance of xenocrysts (such as, for example, sanidine, biotite, plagioclase and orthopyroxene). Their chemical composition range from olivine latite, with enclaves characterized by abundant xenocrysts of sanidine (Or75-Or82), anhedral orthopyroxene (Mg# = 0.42-0.72), anhedral biotite (Mg# = 0.40-0.686), and copious plagioclase phenocrysts (An89-An44) with sieved texture, to potassic trachybasalt, where the most representative enclaves group is marked by the occurrence of phenocrysts of clinopyroxene (Mg# = 0.15-0.92) and abundant acicular biotite to phlogopite (Mg# = 0.30-0.82). A similar group is also characterized by the presence of olivine phenocrysts and micro-phenocrysts (Fo90-Fo56), often entirely surrounded by acicular microcrystals of phlogopite or biotite. The other two more mafic groups are respectively made up of: i) aggregates of large and abundant clinopyroxene crystals (Mg# = 0.85-0.91) with a groundmass characterized mainly by plagioclase with a feathery texture; ii) large phenocrysts of olivine (Fo87-Fo53) and clinopyroxene (Mg# = 0.61-0.93) and a groundmass rich in microliths of olivine and plagioclase euhedral, as in the case of the most mafic sample among those sampled. Several traces of disequilibrium processes among the crystals of the magmatic enclaves, such as sanidine, orthopyroxene, olivine crystals were observed.
How to cite: Valeriani, L., Paternostro, S., Sepulveda Birke, J. P., Casalini, M., Braschi, E., Orlando, A., Cioni, R., Avanzinelli, R., Francalanci, L., Tommasini, S., and Conticelli, S.: A journey into the Monte Amiata volcanic system: data from field observations to petrography and chemistry of igneous enclaves, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13221, https://doi.org/10.5194/egusphere-egu25-13221, 2025.
Campi Flegrei caldera is an active volcanic system in southern Italy. The caldera was formed by the collapses associated with the Campanian Ignimbrite (CI; 40 ka BP) and the Neapolitan Yellow Tuff (NYT; 15 ka BP) eruptions. After the NYT, three volcanic epochs (i.e. 15-10.6, 9.6-9.1 and ~5.5-3.7 ka BP) of mainly mild to moderate explosive volcanic activity occurred. No effusive eruption has been documented in the first epoch, unlike Epochs 2 and 3. Due to their impact, the explosive eruptions at Campi Flegrei have been well studied over the years, but there are few studies on the lava domes/flows in the literature. Moreover, the shift in the eruption style during an eruption at Campi Flegrei has never been investigated by the scientific community. The infrequent observable eruptions of highly viscous and silicic alkaline lavas have hampered understanding of their mechanism as well. To bridge this knowledge gap, we studied the explosive and effusive products of Accademia eruption that followed the uplift phase after the Plinian eruption of Agnano-Monte Spina (4.55 ka BP). A fieldwork was carried out to distinguish the eruptive sequence and the pre-eruptive topography, and collect samples. Thin sections were prepared and observed under an optical microscope for petrographic characterization. The samples were also analysed with X-ray fluorescence (XRF) spectroscopy and scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS). The fieldwork data, petrological characterisation and geochemical analysis were used to understand: (1) the pre-eruptive topography; (2) the volume of the eruption; and (3) the geochemical evolution, crystal size distribution and viscosity of the eruptive products. Our work aims to improve the knowledge about the transition from an explosive to an effusive event and, in general, the significance of effusive eruptions during resurgence phases at Campi Flegrei.
How to cite: Ebrahimi, P., Morgavi, D., Natale, J., Arzilli, F., Di Fiore, F., and Petrosino, P.: Unravelling the processes behind the explosive to effusive transition during the ~4.3 ka Accademia volcanic eruption of Campi Flegrei, southern Italy, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13759, https://doi.org/10.5194/egusphere-egu25-13759, 2025.
Krafla is located in the Mývatn region (North-East Iceland), on the axis of the Icelandic rift valley. The last episode of intense activity, examined in this study, remains the most important in the site’s history, and is called the ‘Krafla fires’ (1975-1984). Like most of Icelandic volcanoes, the Krafla eruptions are fissural and produce tholeiitic basaltic lavas (Nicholson, 1990).
The aim of this study is to determine whether it is possible to simulate a basaltic flow that is consistent to the reality in the field, based on morphologies observed in the field and on a very high-resolution numerical model. The focus of this study is an auxiliary flow, 605 m long and covering 0.04 km², positioned at the southern end of the main Krafla flow. In the field, variations in width (spreading and channeling) and thickness (in the centre and at the edge of the flow) were assessed at regular intervals. These were supplemented by a high-resolution drone survey of the upstream part of the flow (300 m), covering 0.05 km². The georeferenced pictures were computed to generate a Very High-Resolution Digital Surface Model (2 cm). The internal rheological parameters, such as yield stress and viscosity, are determined using the morphological approaches presented by (Chevrel et al., 2013) : The first approach evaluates these two parameters for Newtonian and Bingham behaviour. The second approach is based on lateral spread, excluding slope-related effects. Finally, the third approach evaluates these parameters in the context of channelized flows.
Field observations show that this bayonet-shaped flow has a range of thicknesses from 35 cm to 3.5 m. It has an average width of 48.5 m (with a minimum width of 15.7 m and a maximum width of 75.8 m) and slopes between 4° and 21°. In addition, upstream to downstream, the facies tend to have an increasingly rough and disturbed texture as they approach the flow terminations. Regarding internal parameters: these 3 approaches show a convergence of viscosity values between 2.1 and 4.2.103 Pa.s with ranges of values between 0.5 and 11.103 Pa.s ; and yield strength values which tend to converge towards 1.9 to 6.0.103 Pa with ranges of values between 0.9 and 105.103 Pa. Those orders of magnitude are consistent with the values obtained by (Chevrel et al., 2013) for other cases of the spreading of icelandic basaltic flows.
This study provided an initial assessment of the morphological and rheological characteristics of a basaltic flow, based on field observations and high-resolution numerical models. Internal parameters such as viscosity and yield strength were assessed using several morphological approaches, yielding values consistent with similar studies carried out on other icelandic basaltic flows. Exploratory use of numerical simulation would allow further refinement of the model's internal parameters and external parameters, in order to assess and rank their relative influence on emplacement behavior.
Chevrel, M.O., Platz, T., Hauber, E., Baratoux, D., Lavallée, Y., Dingwell, D.B., 2013. Earth and Planetary Science Letters, volume 384, p. 109-120. DOI : 10.1016/j.epsl.2013.09.022
Nicholson, H., 1990. university of Edinburgh. 301 p.
How to cite: Louis-Sylvestre, I., Demeestere, V., Leyrit, H., Ottavi Pupier, E., Le Bivic, R., Dujany, A., Denis, M., and Duquennoy, J.: Basaltic lava flow characterization and modelling using a geomorphological approach: integration of field and drone acquired data (Krafla, Iceland), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16018, https://doi.org/10.5194/egusphere-egu25-16018, 2025.
The Late Pleistocene-Holocene Dilo-Dukana and Mega volcanic fields (Ririba rift, South Ethiopia) formed through monogenetic eruptions of limited volumes of alkaline basalts containing abundant mantle and crustal xenoliths. This activity postdated the emplacement of voluminous Pliocene subalkaline basaltic lavas related to the main rifting phase. Several NE-SW aligned vents, that abruptly cut the rift-related structures, form the two volcanic fields, indicating the occurrence of magmatism disconnected from the main rift activity (Corti et al., 2019).
New detailed petrological and mineral chemistry data (major and trace elements) on these products allow us to investigate the ascent pathways and plumbing system architecture of the related magmas, as well as their magmatic evolution. Alkaline lavas are dominated by olivines and pyroxenes phenocrysts, with minor oxides. Olivines are commonly dendritic or show jagged rims. Feldspar is the main phase found in the groundmass, together with clinopyroxenes, olivines and oxides. Occurrence of feldspathoids in the groundmass is also observed in some samples.
Two different olivine populations can be recognized according to their composition and zoning. Most olivines are normal zoned, with Fe-enriched rims. Minor reversed zoned crystals or complex banding zoning are also found. CaO contents in olivines increase from core to rim, regardless of the zoning pattern. This feature can be related to the dynamic of magmatic processes (i.e. heating due to recharge events, decompression). Orthopyroxenes are always in disequilibrium with the groundmass showing olivine coronas or clinopyroxene armored-rims, which supports silica-under saturation conditions in the host melt. Clinopyroxenes show complex sector zoning, especially in the microlites of the groundmass, indicating rapid crystallization rates. Some clinopyroxene phenocrysts and micro-phenocrysts show resorbed cores with Ti-, Al-, Fe-enriched (coupled with Si-, Cr-, Mg-, Na-depleted) rims suggesting rapid cooling and/or decompression during magma ascent, or an increase of the activity of oxygen.
All these features point to the important role of kinetic processes during magma crystallization and indicate the fundamental role of rapid decompression related to magma ascent. The occurrence of xenoliths agrees with this hypothesis, testifying the high “erosion and transport capacity” of these magmas. However, the presence of complex zoning or discordant trace elements behavior suggests the possibility of more complex processes in the feeding system.
Pliocene rift-related magmatic products were also investigated and compared with the Quaternary volcanics indicating a change in the magmatic system, especially in the upward melt transfer mode (ascent dynamic, storage levels) related to variations of the thermal and rheological state of the extensional lithosphere associated with the transitions from the main rift phase (Pliocene) to the later rift deactivation (Quaternary).
Reference: Corti, G., Cioni, R., Franceschini, Z., Sani, F., Scaillet, S., Molin, P., Isola, I., Mazzarini, F., Brune, S., Keir, D., Erbello, A., Muluneh, A., Illsley-Kemp, F., Glerum, A., (2019). Aborted propagation of the Ethiopian rift caused by linkage with the Kenyan rift. Nat. Commun. 10, 1309. https://doi.org/10.1038/s41467-019-09335-2.
How to cite: Orlando, A., Braschi, E., Petrone, C. M., Franceschini, Z., Buret, Y., Broderick, C., Cortes-Calderon, E. A., Filfilu Gebru, E., Cioni, R., Tommasini, S., and Corti, G.: Mineral chemistry investigations of the Quaternary alkaline basalts erupted at Dilo-Dukana and Mega volcanic fields (Ririba rift, South Ethiopia), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18893, https://doi.org/10.5194/egusphere-egu25-18893, 2025.
Magmatism in extensional tectonic settings, such as the East African Rift System, is mainly modulated by the interaction of plume upwelling and plate dynamics, resulting in complex tectonic processes associated to rifting (e.g., rift migration, focusing) and generating a large compositional variability of the erupted products, even over small distances and short time periods. The Ririba rift, formed from the southward propagation of the Main Ethiopian Rift, well exemplifies these complexities providing a unique opportunity to investigate in detail both the spatial and temporal evolution of mantle sources involvement and magma ascent dynamics related to tectonics. The activity of the Ririba rift is associated to the emplacement of subalkaline basalts producing a widespread basaltic lava basement during Pliocene. Later, the Quaternary Dilo-Dukana and Mega volcanic fields (VFs) formed through monogenetic eruptions of limited volumes of alkaline-basalts, rich in mantle and crustal xenoliths. Both volcanic fields form lineaments that abruptly cut the rift-related features, suggestive of an emplacement after rift abandonment.
We provide new petrological, geochemical and isotopic data on both Pliocene and Quaternary products aimed at investigating the nature of mantle component(s) contributing to magma genesis during the two periods of activity and detail the processes driving magma evolution during the more recent magmatic phase.
All data discriminate the younger alkaline lavas from the Pliocene products, indicating they originated from different mantle sources. The Quaternary Dilo-Dukana and Mega products, on the contrary, overlap in major, trace elements and radiogenic (Sr-Nd-Pb) isotopes. No clear geochemical correlation is observed with respect to vent location (rift floor, scarp or plateau), xenoliths content or eruptive style (lava flows or tuff cones). However, well-defined trends, displayed by major and incompatible trace elements, coupled with the absence of a correlation between the evolutionary degree and isotopes, indicate the prominent role of fractional crystallization driving magma differentiation. The small variation in silica, decorrelated from MgO variation, indicates fractionation of mainly femic phases, probably in deep, transient, storage levels. Only light-REEs, together with some HFSE ratios and LILE contents, roughly discriminate between the products erupted at Dilo-Dukana and Mega VFs pointing to variations in the degree of partial melting and/or different phase proportion in the crystallizing assemblage of the ascending magmas between the two VFs.
We infer that the Dilo-Dukana and Mega VFs were fed by two different systems of deep structures, unrelated to rifting but associated to old inherited fabrics, directly transferring mantle melts to the surface without important differentiation in shallow storage levels before eruption. Moreover, from rift-related Pliocene sub-alkaline basalts to the Quaternary basanites, the nature of the involved mantle source changed towards a more plume-dominated signature with minor contribution from the sub-continental lithosphere mantle (SCLM). This can be correlated to a variation in the thermal and rheological state of the lithosphere following the transitions from the main rift phase (Pliocene) to the later rift deactivation (Quaternary) that limited the SCLM melting and promote a direct magma uprise in the more recent activity.
How to cite: Braschi, E., Franceschini, Z., Cioni, R., Corti, G., Sani, F., Casalini, M., and Muluneh, A.: Geochemical and isotopic constraints on the recent magmatic activity of the Dilo-Dukana and Mega volcanic fields (Ririba rift, South Ethiopia), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-21008, https://doi.org/10.5194/egusphere-egu25-21008, 2025.
We propose the existence of a previously undocumented monogenetic volcanic field in northwest Colombia, near Venecia and Fredonia in Antioquia, potentially marking the northernmost Andean volcanic field known to date. This field, situated within the Combia Volcanic Formation, encompasses Cerro Tusa, Cerro El Sillón, and Cerro Bravo—three features traditionally described as hypabyssal bodies but now reinterpreted as volcanic in origin. Petrographic observations of lava flows and bread-crust block deposits suggest a magmatic emplacement, linked to regional fault systems trending N-S and SE-NW, as well as local SW-NE structures, some of which intersect the volcanic features and may correlate with recent earthquake activity.
Petrographic and geochemical analyses conducted at the University of South Florida reveal a calc-alkaline dacitic composition characteristic of subduction-related volcanism. Textural features, including sieve textures, glomerocrysts, and oxidation rims, point to rapid magma ascent and disequilibrium processes. Geochemical diagrams (TAS, AFM, and spider) indicate advanced differentiation, aligning with trends observed in regional monogenetic volcanic fields.
Ongoing Ar/Ar geochronology aims to establish eruption timelines and temporal relationships among sampled units, refining connections to adjacent volcanic fields. These findings contribute to understanding magmatic evolution in the northern Andes and have broader implications for interpreting tectonomagmatic processes in subduction zone settings.
How to cite: Rave Bonilla, Y. P., Cáceres, A., Sánchez, J. J., Germa, A., Ricci, J., and Rodgers, M.: Evidence for the Venecia-Fredonia Monogenetic Volcanic Field as the northernmost Andes volcanism, supported by new geochemical, geochronological and structural data, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-21226, https://doi.org/10.5194/egusphere-egu25-21226, 2025.
Posters virtual: Tue, 29 Apr, 14:00–15:45 | vPoster spot 1
EGU25-17683 | ECS | Posters virtual | VPS22
Impact of Cooling Rate on Rheology and Emplacement Dynamics of Basaltic Lava Flows: Insights from the 2023-2024 Sundhnúksgígar Eruption (Iceland)Tue, 29 Apr, 14:00–15:45 (CEST) | vP1.9
The 2023-2024 eruptions at Sundhnúksgígar in Iceland produced tholeiitic basaltic lavas that traveled at high velocities, affecting vast areas. In this context, disequilibrium crystallization can play a fundamental role in modulating the lava flow dynamic and inundation capacity. To investigate this phenomenon, we performed a comprehensive rheological characterization of the Sundhnúksgígar basaltic liquid and crystal-bearing suspension under both disequilibrium and near-equilibrium conditions. Compared to other basalts erupted worldwide, our results reveal unique features of the Sundhnúksgígar melt: i) exceptionally low solidification rates and ii) the ability to crystallize even at the highest cooling rates applied during the experiments. These characteristics enhance the efficiency of external crust formation, minimizing heat loss from the inner portion of the lava flow, which consequently experiences slower cooling rates. As a result, the lava is able to flow for longer times and travel greater distances than other basaltic flows. Our findings underscore the critical influence of disequilibrium crystallization on the rheological evolution and emplacement behavior of basaltic lavas, with implications for hazard assessment and risk mitigation during effusive eruptions.
How to cite: Di Fiore, F., Vona, A., Di Genova, D., Caracciolo, A., Pontesilli, A., Calabro', L., Giuliani, G., Mollo, S., Bondar, D., Nazzari, M., Romano, C., and Scarlato, P.: Impact of Cooling Rate on Rheology and Emplacement Dynamics of Basaltic Lava Flows: Insights from the 2023-2024 Sundhnúksgígar Eruption (Iceland), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17683, https://doi.org/10.5194/egusphere-egu25-17683, 2025.
