Erupted Lavas Research Articles

Hydroacoustic Evidence for Offshore Lava Emplacement During the 2018 Kīlauea Eruption

AbstractDuring the 2018 Kīlauea eruption, over half the erupted lava was deposited on the seafloor. Lava flows crossing the shoreline generated sounds that were recorded by a network of hydrophones. We show that short‐duration, broadband signals associated with lava‐water interactions occurred throughout the eruption but increased in number when the Ahalanui ocean entry initiated on July 11. These terminated in early August coincident with the eruption's end. We compare hydroacoustic data with transmission loss models and eruption photographs to show that coastal explosive activity was poorly recorded by the hydrophone network. Similarly, strong hydroacoustic signals did not correlate with observed activity. These results suggest that acoustic signals were generated by lava flowing up to 100 s of meters offshore. Offshore lava flows can be hazardous to boaters, but hydrophones provide a means by which these hazards can be detected.

Effects of cohesion and viscosity on lava dome growth following repose

Lava domes result from effusive eruption of high viscosity lava. These viscous lava extrusions range in shape from flat-topped domes with small height-to-width aspect ratios, to spine-like columns exhibiting large height-to-width aspect ratios. A primary control on morphology during early dome growth is thought to be the variation in rheological characteristics of extruded material. In this work, we present new scaled analogue models of lava dome growth that consider extrusion of a frictional plastic upper-conduit plug followed by viscous magma. We simulate the brittle plug using a sand-plaster mixture, the cohesion of which is varied by plaster content. We model the magma using sugar syrup, the viscosity of which is controlled by the weight percent of added crystalline sugar. The models both qualitatively and quantitatively reproduce part of the spectrum of natural dome morphology not previously obtained in most past analogue modelling studies. Model aspect ratios of 0.02 to 0.9 capture approximately 90 % of the reported aspect ratio variation in nature. Increasing plug cohesion results in extrusions with higher aspect ratios and spinier morphologies. Low viscosity fluid typically erupts through the brittle dome, whilst high viscosity fluid tends to promote endogenous growth or emerge as exogenous lobes. Particle Image Velocimetry shows that fracture localisation at the dome surface is cohesion-dependent, and eruption of fluid follows shear fractures within the dome. Where fluid remains contained within the dome, we see lateral spread leading to a wider and flatter dome morphology. Evolution of lava dome morphology, deformation, and associated hazards is guided by the complex rheological properties of the extruded material; we suggest that during episodic dome growth, these properties are largely defined in the conduit prior to their eruption.

A Geodetically Constrained Petrogenetic Model for Evolved Lavas from the January 1997 Fissure Eruption of Kīlauea Volcano

Abstract Magmatic systems below volcanoes are often dominated by partially crystalline magma over the long term. Rejuvenation of these systems during eruptive events can impact lava composition and eruption style—sometimes resulting in more violent or explosive activity than would be expected, as was the case at Fissure 17 during Kīlauea’s 2018 eruption. Here, we explore how the crystallinity of unerupted intrusion magmas affect hybrid magma compositions and petrological signatures by constructing phase-equilibria models to evaluate mineral and melt compositions of low-MgO lavas erupted along the East Rift Zone of Kīlauea volcano on 30 to 31 January 1997 (Episode 54, Fissures A-F). We then compare calculated mixing proportions and petrologically derived magma volumes to GPS-based geodetic inversions of ground deformation and intrusion growth in an attempt to reconcile geodetic and petrologically estimated magma volumes. Open-system phase-equilibria thermodynamic models were used to constrain the composition, degree of differentiation, and thermodynamic state of a rift-stored, two pyroxene + plagioclase saturated low-MgO magma body immediately preceding its mixing with high-MgO recharge and degassed drainback (lava lake) magma from Pu‘u‘ō‘ō‘, shortly before fissure activity within Nāpau Crater began on 29 January 1997. Mixing models constructed using the Magma Chamber Simulator reproduce the mineralogy and compositions of Episode 54 lavas within uncertainties and suggest that the identity of the low-MgO magma body may be either variably differentiated remnants of un-erupted magmas intruded into Nāpau Crater in October 1968, or another spatially and compositionally similar magma body. We find that magmas derived from a single, compositionally stratified magma emplaced beneath Nāpau Crater in 1968 can mix with mafic Kīlauea magmas to reproduce average Episode 54 bulk lava, mineralogy and mineral compositions without necessitating the interaction of multiple, low-MgO rift-stored magma bodies to produce Episode 54 lava compositions. Further, by constructing phase equilibria-based mixing models of Episode 54, we can better define the pre-eruptive state of the magmatic system. The resultant mineral assemblages and compositions are consistent with the possibility that the now-fractionated, rift-stored magma body was compositionally stratified and ~ 40% to 50% crystalline at the time of mixing. Finally, we estimate the volume of the low-MgO magma body to be ~7.51 Mm3. Phase-equilibria model results corroborate field and geochemical relationships demonstrating how shallow intrusions at intraplate shield volcanoes can crystallize, evolve, and then be remobilized by new, later batches of mafic magma. Most notably, our MCS models demonstrate that the pre-eruptive conditions of an intrusive body may be recovered by examining mineral compositions within mixed lavas. Discrepancies between the geodetic constraints on volumes of stored rift versus newly intruded (recharge) magma and our best-fit results produced by MCS mixing models (which respectively are mmafic:mlow-MgO ≈ 2 vs. mmafic:mlow-MgO ≈ 0.75) are interpreted to highlight the complex nature of incomplete mixing on more localized scales as reflected in erupted lavas, compared to geodetically constrained volumes that likely reflect large spatial scale contributions to a magmatic system. These dissimilar volume relationships may also help to constrain eruptive versus unerupted volumes in magmatic systems undergoing mixing. By demonstrating the usefulness of MCS in modeling past eruptions, we highlight the potential to use it as a tool to aid in petrologic monitoring of ongoing activity.

Melt-Rock Reaction in the Lower Oceanic Crust and the Influence on the Evolution of Mid-Ocean Ridge Basalts at the Central Indian Ridge (7°50′–8°30′S)

Abstract Various crustal processes shape both the lower oceanic crust and mid-ocean ridge basalts (MORBs). To better understand how these crustal processes influence MORB compositions, we conducted comprehensive petrographic and geochemical investigations on gabbroic rocks and erupted lavas dredged from a segment of the Central Indian Ridge (CIR) spanning from 7°50′S to 8°30′S. The petrographic and geochemical analyses of the gabbroic rocks revealed evidence of melt-rock reaction through reactive porous flow in olivine gabbro and gabbro. This process resulted in distinctive features in clinopyroxene, including disequilibrium textures with a troctolite/anorthosite matrix, complex variations in Mg#-Cr-Ti [Mg# = molar Mg/(Mg + Fe2+)] relationships, and considerable enrichment and fractionation of incompatible trace elements. A significant finding of our study is the close resemblance of trace element ratios in MORB and olivine-hosted melt inclusions to those of melts in equilibrium with clinopyroxene from olivine gabbro and gabbro with Sr anomaly (Sr/Sr* = SrN/sqrt[PrN*NdN]; N refers to chondrite-normalized values) greater than ~0.7. This observation strongly indicates that the composition of MORB is influenced by the melt-rock reaction taking place in the lower oceanic crust. Furthermore, our findings suggest that evolved melts in equilibrium with clinopyroxene having Sr/Sr* values lower than ~0.7 are less likely to erupt onto the seafloor and are instead trapped within the lower oceanic crust. Oxide gabbronorite is characterized by coarse-granular, pegmatitic textures and exhibits mineralogically and chemically more evolved characteristics compared to olivine gabbro and gabbro. It is inferred that the oxide gabbronorite formed through the in situ freezing of highly evolved melts within a melt-rich layer. Finally, we present a comprehensive model for melt evolution in the lower oceanic crust at the 7°50′S–8°30′S CIR by integrating all petrological and geochemical data obtained from gabbroic rocks, MORB, and olivine-hosted melt inclusions. This holistic model contributes to a better understanding of the intricate processes governing MORB composition in the context of the lower oceanic crust dynamics at slow-spreading ridges.

The Volcanism of the Meseta del Lago Buenos Aires, Patagonia: the Transition from Subduction to Slab Window

Abstract The Meseta del Lago Buenos Aires (MLBA) in southern Patagonia, a volcanic plateau formed from ~12 Ma to present, provides an opportunity to investigate the temporal evolution in volcanism as this region transitions from the subduction of the Nazca plate to the formation of the slab window produced by the collision of the Chile Ridge and the Andean subduction zone. Here, we report new major, minor, and trace element contents, as well as Sr, Nd, Pb, and Hf isotopes of the MLBA lavas. Three distinct geochemical endmembers can be distinguished in the MLBA basalts: a subduction-influenced endmember, a transitional component similar to the South Atlantic enriched mid-ocean ridge basalts, and an enriched component akin to the EM1 mantle composition. Lavas older than ~1.5 Ma define a compositional continuum between the subduction-influenced and transitional endmembers; this trend is also present in many other southern Patagonian plateaus regardless of their distance to the trench, eruption age, and the composition of the continental blocks where they are located. In contrast, MLBA basalts younger than ~1.5 Ma uniquely define a transition into the EM1 mantle component at the time when this region was affected by the slab window. The estimated pressures and temperatures of mantle-melt equilibration for the MLBA basalts indicates an increase in both parameters after the formation of the slab window that roughly correlate with the changes in lava composition. The basalts’ composition from all southern Patagonia plateaus points to the presence of the South Atlantic mid-ocean ridge basalt mantle influenced by the Discovery, Shona, and Bouvet hotspots rather than the sub-slab mantle, as represented by the Chile Ridge basalts. This observation challenges the hypothesis that the sub-slab mantle within the slab window has had an important role in the composition of the erupted lavas. Instead, it suggests the presence of a South Atlantic mantle beneath southern Patagonia either within the mantle wedge, consistent with a long-lasting South Atlantic convection cell beneath South America, or in the subcontinental lithospheric mantle metasomatized before or just after the opening of the South Atlantic basin, as demonstrated by the composition of southern Patagonia mantle xenoliths. Although it is difficult to precisely distinguish the contributions of the asthenosphere from that of the metasomatized subcontinental lithospheric mantle beneath this region, our work suggests significant contributions from the latter in the composition of the MLBA lavas.

Internal structure of the volcanic island of Surtsey and surroundings: Constraints from a dense aeromagnetic survey

Surtsey, a young basaltic island off the south coast of Iceland, was built by volcanic activity in 1963–1967 from a pre-eruption oceanic seafloor depth of 130 m. An aeromagnetic survey was carried out in October 2021 over a 60 km2 area covering Surtsey and its surroundings. It aimed to explore the internal structure and the possible existence of basaltic intrusions associated with the five vents active at different times over the 3.5 years of eruptive activity. The survey line spacing was 200 m and the flying altitude was generally 90 m a.s.l. The strongest anomalies (amplitude ∼700 nT) are caused by the 30–100 m thick subaerially erupted lava field on the southern part of Surtsey, formed in two episodes of effusive activity:1964–1965 and 1966–1967. 2D spectral analysis and Euler deconvolution indicate that the causative bodies of anomalies outside the island of Surtsey are located within the uppermost 300 m of the seafloor and their horizontal dimensions are similar to or smaller than their depth. 3D forward modeling of the island and its surroundings, constrained by observations during the formation of the island and drill cores extracted in 1979 and 2017, is consistent with an absence, at all vents, of pillow lava and therefore effusive activity in their opening phases. However, the data support the existence of a 10–20 m thick pillow lava field on the seafloor, 2.5–3 km2 in area, extending about ∼1 km to the south of Surtsey. The field is considered to have been fed by magma reaching the seafloor via channelized intrusive flow through the foreset breccia constituting the submarine part of an emerging lava delta during the early stage of effusive eruption in May–July 1964. The general scarcity of significant magnetic bodies within the edifices is consistent with magma fragmentation dominating the submarine eruptions from the onset of activity. A small magnetic anomaly is observed over the submarine edifice of Surtla, built during short-lived activity over ∼10 days in 1963–1964. This anomaly is consistent with observed subaqueous weak or moderate explosive activity that may have allowed a dyke to be preserved within the submarine tephra mound. More violent Surtseyan activity was observed at other vents, however, and may have destroyed any initial dykes that, if preserved, might have been resolved magnetically. Indications of magnetized volcanic rocks of unknown age predating the Surtsey eruption are found beneath the flank of the ephemeral island of Jólnir, the southernmost of the Surtsey vents.

Magma Evolution During Main‐Phase Continental Flood Basalt Volcanism: A Case for Recharge‐Evacuation‐Assimilation‐Fractional Crystallization in the Ethiopian Low‐Ti Province

AbstractLavas erupted in Continental Flood Basalt (CFB) provinces are not primary magmas; they are differentiated products that result from large volumes of melt migrating and stalling in the lithosphere prior to eruption, resulting in complex liquid lines of descent. Geochemical models can be used to constrain the various influencers of magma differentiation (recharge, assimilation, fractional crystallization (FC), eruption, and mixing). Temporal constraints for changes in plumbing system dynamics are recorded in the petrography and stratigraphy of the erupted lava flows. This study focuses on the flow‐stratigraphy preserved within the Oligocene Ethiopian low‐Ti flood basalt province, located on the NW Ethiopian Plateau. We present new bulk rock geochemistry from 107 lavas and interpret these data within a petrostratigraphic framework. Our model results suggest that both a deep (∼0.6 GPa) and shallow (<0.2 GPa) magmatic system are active throughout the main phase of volcanism. Our recharge evacuation assimilation and fractional crystallization models (REAFC) show that during the main phase of magmatism evacuation from both the deep (65%) and shallow (55%) systems reached an apex. During the terminal phases, magma evacuation from the deeper system ceases while evacuation from the shallow system is much reduced (25%). The degree of crustal contamination predicted by REAFC (4%–10%) is lower than previous estimates determined for this region using assimilation with FC only models (12%–25%). Our study highlights the importance of evaluating petrography while interpreting geochemical models in CFB.

Geomorphology mapping and landslide susceptibility for disaster risk reduction and sustainability environment in the Sub DAS Maspo, Mt. Welirang, East Java, Indonesia

Landslides are still problematic for areas with rough surface shapes and high rainfall. Landslides are still causing human life losses, so mitigation efforts for disaster risk reduction must be prioritized. The purpose of this study is geomorphological mapping and landslide hazard mapping as a basis for disaster risk reduction efforts. The method used integrates remote sensing data using geographic information systems. Geomorphology mapping is processed and analyzed using four geomorphological approaches, while for landslide susceptibility maps are analyzed using the Weight of Evidence (WoE) method using existing landslide variables and 17 landslide control factors. The geomorphological mapping results show that in the Maspo sub-watershed, there are 25 landform units based on geomorphological mapping. There are five classes of landslide vulnerability indices, i.e very low index (0.001-0.341) namely 9.38%; low index (0.341-0.471) that is 26.18%; moderate index (0.471-0.584) that is 28.49%; high index (0.584-0.741) that is 23.94% and very high index (0.714-1) that is 12.02%. The accuracy of the landslide hazard map results is 88%, indicating that the landslide hazard map has good accuracy. Dominant landslides of 26.98% and 23.59% occurred in the HS2V1/ME landform, which is the middle slope of the steep hills of the lava eruption of the 2nd Mt. Welirang with moderate geomorphic processes and HS2V1/VSE which is the middle slope of the steep hills of the 2nd eruption of Welirang volcano with the process strong geomorphism. The results of geomorphology mapping and landslide susceptibility can be used as an information base for disaster risk reduction strategies and sustainable environmental management.

Synthesis of micropaleontological age constraints for the reconstruction of the Tethyan realm in the Lesser Caucasus (Armenia, Karabagh)

We present new biostratigraphic results from two ophiolite outcrops in Armenia. The discovery of upper Tithonian–lower Berriasian diagnostic radiolarian species (Vallupus gracilis Li and Sashida) in the lower radiolarites of the Dali section allows to date more accurately submarine lava eruptions of transitional to alkaline composition. The radiolarian results also indicate that blocks of shallow-water carbonates slid into the basin during this time interval. At Vedi, upper Coniacian–Santonian calcareous nannofossils identified in marls of the post-obduction sedimentary cover refine previous age data. Synthesis of the existing bio-chronostratigraphic constraints in Armenia and Karabagh sheds light to the depositional and magmatic history of Tethys in the Lesser Caucasus and highlights the age constraints of fossils on the timing of ophiolite obduction in the region.

Integrated photogrammetry, lava geochemistry and palynological re-evaluation of the early evolution of the topographically constrained Mull Lava Field, Scotland

ABSTRACTPhotogrammetry was used to elucidate complex strata relationships between isolated outcrops of the Palaeocene lava fields of SW Mull, part of the North Atlantic Igneous Province. Subsequent sampling for lava geochemistry and palynology was undertaken based on interpretation of these photogrammetry models. Coherent units of Plateau- and Staffa-type lavas were identified using lava geochemistry, in particular using rare earth elements (REEs), divisions supported by multivariate statistics. Lavas with three different REE compositional clusters were identified within the Staffa magma type and four within the Plateau type of SW Mull. Understanding the distribution of these lava types was achieved using the interpreted photogrammetry models and analysis of prominent interbedded sedimentary rock units and their correlative unconformities. Probably the most renowned rocks of SW Mull are the thick columnar jointed lavas, including those of the Isle of Staffa. REE geochemistry reveals that lavas of both Staffa- and Plateau-type geochemistry occur as columnar jointed facies associated with what has previously been attributed to the Staffa Lava Formation. Instead, the SW Mull Lava Field was initiated by eruption of Plateau-type lava into a fault-controlled valley. Subsequent eruptions of Staffa-type lavas partially infilled this structure, which was finally overfilled by a thick succession of younger Plateau-type lavas. The geochemical characteristics of this Plateau–Staffa–Plateau lava succession indicate that magma reservoirs deep in the crust were succeeded by shallow melts during a period of crustal extension. This phase of shallow melting induced topographical instability and formation of sedimentary interbeds and correlative unconformities that characterise the Staffa-type lava succession. Subsequent compressive tectonics forced a return to deep crustal melts. Interbed palynofloral compositional data indicate that eruption of the later Plateau-type lavas likely took place within a period of ~2.5 million years during the Selandian to early Thanetian period.

Aero Mapping Application for Affected Area Detection by the Semeru Volcano Eruption in 2022

The development of geospatial technology, especially Unmanned Aerial vehicles (UAV) or drones, has been growing rapidly. One of the uses of UAV is to detect disaster hazards, the extent of the affected area, and the element of risks. The latest UAV technology in the form of Aero Mapping is beneficial for mapping disaster-affected areas, in this case, post-volcanic eruption lava flows. Aero mapping with the rotary wing type is low-cost (<$ 2000/Rp.29.500.000) but a potent tool for collecting spatial data quickly and accurately. This application is applied to detect areas affected by volcanic eruptions. The photo image produced by the UAV can be used to analyze lava flows, lava deposits, changes in landforms, and changes in land cover due to volcanic eruptions. This study aims to detect the area affected by the eruption of Semeru Volcano post-eruption in 2022. In the research study area, there is no detailed scale mapping can detect the direction/path of post-eruptive lahars. This research seeks to detail the description of the affected areas. The results of aerial photographs show that low-cost UAVs are capable of producing high-resolution data of up to 2.86 cm/px (Orthomosaic), 6.94 cm/px (DSM), and 3.94 cm/px (GSD) with a total area of up to 755 Ha. This area is obtained from 34 flight processes at an altitude of 120 meters with 70% front and side overlap. These findings prove that aero mapping is a low-cost technique that can be used to map new lava flows after the 2022 eruption at Semeru Volcano.

Remobilization and eruption of an upper crustal cumulate mush at the Singkut caldera (North Sumatra, Indonesia)

Understanding the conditions and timescales of storage and remobilization of magma bodies in the upper crust is key to interpreting the signals of potential reawakening at active volcanoes. In this paper, we provide the first volcanological and petrochronological characterization of the Singkut caldera, a young volcanic system located in northern Sumatra (Indonesia), in close proximity to Medan, one of the country's most popoluous cities. Singkut formed at ∼44 ka during a VEI 6 explosive eruption that deposited at least ∼26 km3 of tephra (dense rock equivalent, DRE). The cataclysmic eruption was preceded by >200 ky of mostly effusive pre-caldera activity and followed by effusive to mildly explosive post-caldera activity. The lavas and pumices have high crystallinity (up to 62% crystals) with andesitic to dacitic bulk-rock composition and rhyolitic glass. Mineral textures and matrix glass compositions indicate resorption of quartz, plagioclase and zircon. Zircon crystallization ages show a complete overlap with the eruption ages in pre-caldera lavas, while a time gap in zircon crystallization (>50 ky) is identified in the caldera-forming tuff and post-caldera lavas. Ti-in-zircon thermometry shows that the Singkut magma body experienced a temperature increase starting approximately upon eruption of the pre-caldera lavas (∼254 ka). Such thermal perturbation determined progressive melting of mineral phases in the cumulate crystal mush, caused the resorption of the youngest zircon domains before the caldera-forming eruption, and hampered zircon crystallization between the caldera-forming eruption and the effusion of the post-caldera lavas (∼16 ka). Our data demonstrate how cumulate melting processes played a key role in leading the volcanic system towards a caldera-forming eruption and controlled the transitions in eruptive style between the effusive phases and the explosive climactic eruption.

Unveiling the formation and magma transport dynamics of the Ulanqab maar volcanic cluster in the western North China Craton: Insights from 40Ar-39Ar geochronology, mineral chemistry, and Sr-Nd-Mg isotopes

The chemical composition of eastern North China Craton (NCC)'s alkaline basaltes likely influenced by subducting Pacific Plate. Nonetheless, the influence of these processes on the western craton remains uncertain due to the lack of geochemical evidence. The recent discovery of Ulanqab maar volcanic cluster (UMVC) in the western NCC has become significant research windows. However, their petrogenesis and magmatic processes remain poorly understood. In the present study, 40Ar/39Ar, whole rock and mineral geochemistry, and Sr–Nd–Mg isotope data for the UMVC in the western NCC are reported. These data reveal that the UMVC was formed during the Neogene (7.60 ± 0.04 Ma), diverging from Quaternary basalts or as part of the Hannuoba basalts (eastern Ulanqab). The UMVC rocks, featuring typical oceanic island basalts traits with moderate (87Sr/86Sr)i values (0.70487–0.70524) and εNd(t) values from −4.95 to + 0.82, likely originated from an enriched EMI-type mantle source during the mid-Proterozoic. This involved mixing melts from 30 to 50 % partial melting of garnet lherzolite and 5–15 % partial melting of garnet pyroxenite in a deep magma chamber. Crystallization of clinopyroxene and garnet in this chamber created high-Ti alkaline lavas, with limited presence in erupted lavas due to sluggish magma ascent in the profound lithospheric mantle. In shallower lithospheric mantle regions, interactions between alkaline magma and orthopyroxenite improved transport kinetics, enabling clinopyroxene and olivine crystallization under lower pressure. These magmas integrated mafic crystal mushes from accumulation chambers. The study also identified a low Mg isotope composition (δ26Mg = − 0.56 ‰ to − 0.42 ‰) in samples, suggesting a hybrid source influenced by early decarbonation in Precambrian subduction zones. This finding indicates the incorporation of Mg-rich carbonate minerals from marine sediments into the magma source, contributing to the observed variations in eastern China's alkaline basalts.

Chemostratigraphy of the extrusive sequence of a Late Cretaceous Neotethyan ophiolite in southern Iran and its significance for the mode and tempo of subduction initiation magmatism and melt evolution in forearc tectonic settings

Chemostratigraphy of lavas in extrusive sequences of modern and ancient forearc environments provides significant information on oceanic crust formation through progressive stages of melt evolution from subduction initiation magmatism (SIM) to arc infancy, and arc maturation-related magmatism. We present here new trace element and radiogenic Sr–Nd–Pb isotopic data from a Late Cretaceous ophiolite in the Outer Zagros Belt of southern Iran and discuss its magmatic development through SIM in a Neotethyan forearc setting. Initial volcanism produced the stratigraphically oldest boninitic (BON) lavas in the Haji-Abad ophiolite whose trace element ratios as well as Pb isotopic signatures indicate a refractory mantle source, which was contaminated by subducting slab-derived fluids. The BON lavas change structurally upwards into island-arc tholeiitic (IAT) lavas and their fractionated felsic derivatives that display isotopic evidence for the contribution of sediment-derived melts in their magmatic source(s). This melt evolution pattern of the Haji-Abad ophiolite marks a major difference from the progressive melt evolution trends reported from the Izu–Bonin–Mariana (IBM) forearc lava sequence, which starts at the bottom with forearc basalts (FAB) phasing up-section into BON and IAT affinity lavas. IAT lavas in the IBM are in turn overlain by calc-alkaline (CAL) lavas. Our geochemical modelling points to a probable existence of a less depleted, pre-subduction mantle whose partial melting probably generated primary magmas before the eruption of boninitic lavas, although the record of such magmas is missing in the Haji-Abad ophiolite. Our comparison of the chemostratigraphy of the Outer Zagros ophiolites with the documented record of subduction initiation generated volcanic rocks in the other Neotethyan ophiolites in the region and the IBM forearc setting strongly suggests that there is no single rule or template for SIM. Supplementary material: Details of analytical procedures and supplementary figures and tables are available at https://doi.org/10.6084/m9.figshare.c.6837597 Thematic collection: This article is part of the Ophiolites, melanges and blueschists collection available at: https://www.lyellcollection.org/topic/collections/ophiolites-melanges-and-blueschists

The noble gas signature of the 2021 Tajogaite eruption (La Palma, Canary Islands)

Here, we characterize the temporal evolution of volatiles during the Tajogaite eruption by analyzing the elemental (He-Ar-CO2-N2) and isotopic (He-Ar-Ne) composition of fluid inclusions (FI) in phenocrysts (olivine+pyroxene) identified in erupted lavas. Our 2021 lava samples identify substantial temporal variations in volatile composition. We show that, during the 2021 Tajogaite eruption, the He-CO2-N2 concentrations in FI increased since October 15th; this increase was accompanied by increasing 40Ar/36Ar ratios (from ∼300 to >500), and paralleled a major shift in bulk lava chemistry, with increasing Mg contents (Mg#, from 47 to 52 to 55–59), CaO/Al2O3 (from 0.65 to 0.74 to 0.75–0.90), Ni and Cr, and decreasing TiO2, P2O5 and incompatible elements. The olivine core composition also became more forsteritic (from Mg# = 80–81 to Mg# = 84–86). Mineral thermobarometry and FI barometry results indicate that the eruption was sustained by magmas previously stored in at least two magma accumulation zones, at respectively ∼6–12 km and 15–30 km, corroborating previous seismic and FI evidence. We therefore propose that the compositional changes seen throughout the eruption can be explained by an increased contribution - since early/mid-October - of more primitive, less-degassed magma from the deeper (mantle) reservoir. Conversely, Rc/Ra values (3He/4He ratios corrected for atmospheric contamination) remained constant throughout the whole eruption at MORB-like values (7.38 ± 0.22 Ra, 1σ), suggesting an isotopically homogeneous magma feeding source. The Tajogaite He isotope signature is within the range of values observed for the 1677 San Antonio lavas (7.37 ± 0.17Ra, 1σ), but is more radiogenic than the 3He/4He values (>9 Rc/Ra) observed in the Caldera de Taburiente to the north. The 3He/4He ratios (6.75 ± 0.20 Ra, 1σ) measured in mantle xenoliths from the San Antonio volcano indicate a relatively radiogenic nature of the mantle beneath the Cumbre Vieja ridge. Based on these results and mixing modeling calculations, we propose that the homogeneous He isotopic signatures observed in volatiles from the Tajogaite/San Antonio lavas reflect three component mixing between a MORB-like source, a radiogenic component and small additions (6–15%) of a high 3He/4He reservoir-derived (>9Ra) fluid components. The simultaneous occurrence of high 3He/4He (>9Ra)- and MORB-like He signatures in northern and southern La Palma is interpreted to reflect small-scale heterogeneities in the local mantle, arising from spatially variable proportions of MORB, radiogenic, and high 3He/4He components.

Global radiant flux from active volcanoes: the 2000–2019 MIROVA database

Since 2000, the Moderate Resolution Imaging Spectroradiometer (MODIS) has acquired infrared images of the Earth’s surface daily. These data have made it possible to measure the thermal energy radiated by the world’s most famous volcanoes and also to discover and track eruptions in remote and poorly monitored regions. In this work, we present the database of Volcanic Radiative Power (VRP, in W) time series, recorded by the MIROVA (Middle Infrared Observation of Volcanic Activity) system over 2 decades of MODIS observations (2000–2019) at 111 active volcanoes. The database reveals that globally, the number of thermally active volcanoes each year varies between 60 and 80, almost equally partitioned between volcanoes with a basic (50%) and intermediate (45%) composition, while only 5% is represented by volcanoes erupting acidic lavas. Within the investigated period, the global-scale heat flux was almost stationary, and occasionally punctuated by peaks associated with the largest effusive eruptions (e.g., Bardarbunga and Kilauea). The Volcanic Radiative Energy (VRE, in J) emitted by basic volcanoes (∼1.8 × 1018 J) in 20 years constitutes 91% of the total, while intermediates and acids contribute only 8% (∼1.8 × 1017 J) and 1% (∼1.7 × 1016 J), respectively. A comparison with the volume of lava erupted effusively by the same volcanoes reveals that this difference is attributed to the lower efficiency in radiating thermal energy of increasingly acidic (viscous) lava bodies. Each compositional group is associated with a specific relationship between VRE and erupted volume which characterises most of the effusive volcanoes. On the other hand, some open-vent volcanoes reveal that much more heat is released than that theoretically radiated by the erupted lava. This imbalance (hereby called excess radiation) is attributed to an additional heat source, likely associated with an underlying convective magma column and/or to outgassing through a permeable conduit. We are convinced that the database presented in this work will be useful to support new emerging studies on global-scale volcanism and will contribute to a better understanding of each volcanic system.

Local Infrasound Monitoring of Lava Eruptions at Nyiragongo Volcano (D.R. Congo) Using Urban and Near‐Source Stations

AbstractDuring eruptions, volcanoes produce air‐pressure waves inaudible for the human ear called infrasound, which are very helpful for detecting early signs of magma at the surface. Compared to violent ash‐rich explosions, recording more discrete atmospheric disturbances from effusive eruptions remains a practical challenge depending on the distance to the source. At Nyiragongo volcano (D.R. Congo), towering above a 1‐million urban area, we analyzed local infrasonic records between January 2018 and April 2022. An acoustic signature from this open‐vent volcano is detected up to the volcano observatory facilities in Goma city center about 17 km from its crater. We compared infrasound signals with space‐based observations of the intra‐crater activity (SO2 emissions, thermal anomalies, crater depth/radius). We thus obtain a comprehensive picture of Nyiragongo's eruptive activity during this period, encompassing the drainage of its lava lake during its third known flank eruption on 22 May 2021.

Eruption of stagnant lava from an inactive perched lava lake

Lava flow hazards are usually thought to end when the erupting vent becomes inactive, but this is not always the case. At Kīlauea in August 2014, a spiny ʻaʻā flow erupted from the levee of a crusted perched lava lake that had been inactive for a month, and the surface of the lava lake subsided as the flow advanced downslope over the following few days. Topography constructed from oblique aerial photographs using structure-from-motion (SfM) software shows that the volume of the flow (∼68,000 m3) closely matches the volume of subsidence of the crusted lava lake (∼64,000 m3). The similarity of these volumes, along with the textural characteristics of the lava, shows that the lava that fed the flow had been stored beneath the surface of the perched lava lake, and that the flow was not generated by reactivation of the vent. This extends the duration of the local lava flow hazard presented by perched lava lakes and similar flow field structures that store lava, such as rootless shields. The flow probably occurred because the density of the lava beneath the crusted surface of the perched lava lake increased through loss of gas bubbles until it was able to penetrate the less-dense levee, which was composed of relatively vesicular overflows. The flow is thus equivalent to the lava seeps described previously at Kīlauea and elsewhere. We present a simple physical model for the pressure change at the base of a densifying body of lava, which we apply to this case study, and which could be applied to similar scenarios elsewhere.

Composition of Phenocrysts in Lamproites of Gaussberg Volcano, East Antarctica

—This paper presents numerous new data on the geochemical composition of olivine, clinopyroxene, and leucite phenocrysts, as well as spinel inclusions in olivine and quench glass from lamproites of Gaussberg volcano (East Antarctica). Most of the olivine phenocrysts in the Gaussberg lamproites are high Mg varieties (Fo89–91) with elevated Ni contents (up to 4900 ppm) and high Ni/Co ratios. According to data of about 320 clinopyroxene analyses, two groups of diopsidic phenocrysts have been established. Group I consists mainly of high-Mg varieties (Mg#>80), while group II clinopyroxenes are less magnesian (Mg# 52–80). The main difference between the clinopyroxenes of the two groups is the elevated contents of Al2O3, FeO and reduced TiO2, Cr2O3, and NiO in the compositions of group II compared to group I, as well as different contents of trace elements, which may reflect their crystallization from different types of primary melts. According to the study of ~550 grains of leucite phenocrysts in the Gaussberg lamproites, it was shown that they correspond to the ideal stoichiometry of leucite K[AlSi2O6] and are enriched in Na2O (0.05–0.35 wt %), but depleted in K2O (19.9–20.9 wt %) compared to leucites from lamproites of other provinces. The BaO content reaches 0.3 wt %, SrO –0.04 wt %. The iron content in most leucite phenocrysts varies within 0.7–1.2 wt % Fe2O3, but some grains have the low Fe2O3 contents (<0.5 wt %). In leucite microlites of the groundmass and rims of phenocrysts, the Fe2O3 content can reach 2.4 wt %, which may indicate more oxidized conditions at lava eruption. Based on the study of natural samples, existing experimental data and numerical models, the order and conditions of crystallization of the Gaussberg lamproites were obtained. Crystallization proceeded in the following order: chromian spinel → chromian spinel + olivine → olivine + leucite (± chromian spinel) → olivine + leucite + clinopyroxene (± chromian spinel). The near-liquidus assemblage represented by high-Mg olivine phenocrysts with inclusions of Cr-spinel was formed in the temperature range from 1180 to 1250°C. Further crystallization of the melt with the formation of an association of olivine+leucite+clinopyroxene phenocrysts could occur at pressures below 2 GPa and temperatures of 1070–1180°C, corresponding to the presence of water in the magmatic system. Estimates of the redox conditions of crystallization of lamproites obtained using different oxybarometers vary in a wide range from QFM-0.5 to QFM+2.3. The elevated Ni contents in liquidus olivines of Gaussberg indicate the high nickel contents in the source. It is shown that the formation of ultra-alkaline magmas in the Gaussberg volcano area is likely related to melting of the continental lithosphere, which was heterogeneous and included both the peridotite mantle and hydrous pyroxenite fragments.

Mercury stratigraphy of early Danian sediments from the Rio Grande Rise and the timing of Deccan volcanism

The Maastrichtian - Danian transition is characterized by one of the largest mass extinctions recorded in the geological history of Earth, the Cretaceous-Paleogene (K-Pg boundary). Chemostratigraphic indicators (e.g. Mercury) are of fundamental importance for understanding the causes of this extinction and its effects on the environment in which life after the K-Pg boundary flourished. This study presents a new mercury (Hg) concentrations and Hg/TOC dataset for Deep Sea Drilling Project (DSDP) Site 516F (Rio Grande Rise), in the framework of carbon cycle proxies that depict the Dan-C2 event within the ∼500 kyr that followed the K-Pg event, from 66.05 to 65.55 Ma, and their temporal relationship with the Deccan Traps (DT) volcanic event. Enriched Hg and Hg/TOC values were observed between ∼65.89 Ma (963.45 mbsf) and 65.98 Ma (963.73 mbsf), ∼60 kyr before (or 40 cm below) the Dan-C2 event. Furthermore, the stratigraphic position with the highest Hg and/or Hg/TOC values is ∼40 kyr after the K-Pg boundary. Our results suggest that the DT volcanism is unrelated with the Dan-C2 event observed at Site 516, and that the highest Hg/TOC appear to be coeval with the eruption of the Deccan Ambenali Formation lavas at about ∼65.90–65.95 Ma.