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The morphology of the shield volcanoes on Bioko, a volcanic island in central Africa, is controlled both by tectonic and volcanic processes, but the complex interplay of these regional and local mechanisms is poorly understood. Using a TanDEM-X digital elevation model, we are able to create an inventory of 436 vents and monogenetic cones, and over 1330 structural elements and lineaments, and perform a comprehensive morphological and geospatial analysis. We provide detail on the general geomorphology of Bioko Island, and describe its flat top, apical graben-like structures, and the setting of the structural inventory created. Based on vent density and lineament mapping, we are able to identify volcanic rift zones that are governed by vent clustering and the asymmetry of associated monogenetic cones. Specifically, we find that eruption vents are not only clustered but aligned and follow the principal NE-SW axis, although we also highlight evidence for complex structures such as side-stepping alignments and en échelon patterns indicative of strike-slip contributions to the volcano-tectonic fabrics. We discuss possible volcano-tectonic and regional tectonic contributors, such as the Cameroon Volcanic Line and intersecting fracture zones, as well as gravity-tectonic processes dominant at Bioko Island. In this view, our results are relevant for understanding the past and recent volcanic activity and discuss the influence of regional and local volcano-tectonic architectures.

Pelado volcano is a typical example of an andesitic Mexican shield with a summital scoria cone. It erupted ca. 10 ka in the central part of an elevated plateau in what is today the southern part of Mexico City. The volcano forms a roughly circular, 10-km wide lava shield with two summital cones, surrounded by up to 2.7-m thick tephra deposits preserved up to a distance of 3 km beyond the shield. New cartographic, stratigraphic, granulometric, and componentry data indicate that Pelado volcano was the product of a single, continuous eruption marked by three stages. In the early stage, a > 1.5-km long fissure opened and was active with mild explosive activity. Intermediate and late stages were mostly effusive and associated with the formation of a 250-m high lava shield. Nevertheless, during these stages, the emission of lava alternated and/or coexisted with highly explosive events that deposited a widespread tephra blanket. In the intermediate stage, multiple vents were active along the fissure, but activity was centered at the main cone during the late stage. The final activity was purely effusive. The volcano emitted > 0.9 km3 dense-rock equivalent (DRE) of tephra and up to 5.6 km3 DRE of lavas. Pelado shares various features with documented “violent Strombolian” eruptions, including a high fragmentation index, large dispersal area, occurrence of plate tephra, high eruptive column, and simultaneous explosive and effusive activity. Our results suggest that the associated hazards (mostly tephra fallout and emplacement of lava) would seriously affect areas located up to 25 km from the vent for fallout and 5 km from the vent for lava, an important issue for large cities built near or on potentially active zones, such as Mexico City.

The Paleogene lava flows of the Faroe Islands Basalt Group are divided into three relatively thick formations. The oldest, the Beinisvørð Formation is separated from the second lava flow succession, the Malinstindur Formation, by two formations composed primarily of volcaniclastic rocks. The oldest of these, the Prestfjall Formation has been interpreted as a period of eruptive quiescence and linked to changes in mantle melting. It is characterised in the south by the occurrence of coals, while the overlying Hvannhagi Formation is a sequence of primary and remobilised volcaniclastic strata. Field, laboratory, palynology, and photogrammetry studies have been used to investigate variations in facies and architecture within these volcaniclastic formations. The data reveal significantly different depositional systems in the Prestfjall and Hvannhagi formations over the ~40 km from the island of Vágar in the north to the island of Suðuroy in the south. Facies distribution in both the Prestfjall and Hvannhagi formations was found to have been controlled by a complex interaction of regional paleoslope, pre-existing topography, the eruption and local collapse of low-angle shield volcanoes, and minor brittle deformation. Lithological data and photogrammetry have enabled the identification of a > 180 m thick succession of volcaniclastic conglomerates deposited by lahars reworking a low-angle shield sector collapse. Co-occurrence of facies characteristic of the Prestfjall, Hvannhagi and Malinstindur formations indicate that volcanic eruption continued at a lower tempo throughout the Prestfjall Formation interval. Identification of a Beinisvørð Formation low-angle volcano shield northwest of the Faroe Islands alters the previous eruption model for this extensive lava field.

This study signifies the compositional variability of Mare Tranquillitatis basalt and the Irregular Mare patches (IMPs) – the youngest volcanic feature on the Moon, using hyperspectral data from Moon Mineralogy Mapper (M 3 ) for the first time. Along with composition, the topographic and morphological mapping has been done to understand the possible evolutionary history of this mare. Total 22 spectral units has been identified based on Integrated Band Depth (IBD) parameter technique. Number of reflectance spectra were collected from the fresh craters of each spectral unit and quantitative mineralogical abundances estimated using band parameters like band centre, band strength and band area. The result shows abundances of olivine and pyroxene mixture bearing material in the mare basalt. The compositional map shows smaller spectral units in the western-low lying half and larger spatial distribution of spectral unit in the eastern half depicts probable large-scale volcanic eruption in the eastern part that may have flowed to longer distances from the Cauchy shield to the central mare. This study marks 61 new domes in the Cauchy shield area and also depicts possible formation and evolutionary history of the Mare Tranquillitatis.

The Karacadag Volcanic Complex (KVC) is the largest volcanic unit in SE Turkey. It is also defined as a shield volcano on the northernmost part of the Arabian Plate. The main goal of this study is to investigate the geothermal potential of this region associated with the magnetic signature of this volcanic complex and surrounding area. Besides this primary objective, the possibility of there being volcanic intrusion into the buried fault zones under the volcanic cover are also investigated to determine the interrelations between the active tectonics and heat flow in the area. A spectral analysis method is applied to the magnetic anomalies of the volcanic rocks to identify the Curie point depth (CPD) and geothermal gradient, as well as to estimate heat flow and radiogenic heat production of radioactive minerals in the complex. A tilt angle map is also presented, in correlation with instrumentally recorded earthquake magnitudes, to indicate tectonic trends that are consistent with the maps of the thermal parameters in this study. In contrast with expectations for the KVC area, the region around Akcakale and Suruc Grabens is the most prolific zone for geothermal potential, despite them not showing strong magnetic anomalies. Curie point depths are shallow, down to 18 km, around the Akcakale Graben, and deeper, down to 22 km, around the Bitlis-Zagros Suture Zone where the geothermal gradients increase from 26 to 32 °C km−1 through the graben area. Heat flows in this zone are in the range from 75 to 90 mW m−2 depending on the thermal conductivity coefficient (2.3, 2.5, 2.7, and 3.0 W m−1 K−1) used. Radiogenic heat production values also indicate slightly changing spectra in the range 0.19 to 0.25 μW m−3). None of these parameters are focused around Mt. Karacadag. However, the earthquake epicenters (generally M ≤ 4) are aligned with the boundary faults of the Akcakale Graben where the CPD, geothermal gradient, and heat flow maps indicate relatively high potential. We thus suggest that this graben area would be good for future geothermal exploration. On the contrary, considering the low geothermal gradient and heat flow values, Mt. Karacadag can be accepted as being an extinct volcano, despite its apparent, high, magnetic anomalies.

A clear model of structures and associated stress fields of a volcano can provide a framework in which to study and monitor activity. We propose a volcano-tectonic model for the dynamics of the summit of Piton de la Fournaise (La Reunion Island, Indian Ocean). The summit contains two main pit crater structures (Dolomieu and Bory), two active rift zones, and a slumping eastern sector, all of which contribute to the actual fracture system. Dolomieu has developed over 100 years by sudden large collapse events and subsequent smaller drops that include terrace formation. Small intra-pit collapse scars and eruptive fissures are located along the southern floor of Dolomieu. The western pit wall of Dolomieu has a superficial inward dipping normal fault boundary connected to a deeper ring fault system. Outside Dolomieu, an oval extension zone containing sub-parallel pit-related fractures extends to a maximum distance of 225 m from the pit. At the summit the main trend for eruptive fissures is N80°, normal to the north–south rift zone. The terraced structure of Dolomieu has been reproduced by analogue models with a roof to width ratio of approximately 1, suggesting an original magma chamber depth of about 1 km. Such a chamber may continue to act as a storage location today. The east flank has a convex–concave profile and is bounded by strike-slip fractures that define a gravity slump. This zone is bound to the north by strike-slip fractures that may delineate a shear zone. The southern reciprocal shear zone is probably marked by an alignment of large scoria cones and is hidden by recent aa lavas. The slump head intersects Dolomieu pit and may slide on a hydrothermally altered layer known to be located at a depth of around 300 m. Our model has the summit activity controlled by the pit crater collapse structure, not the rifts. The rifts become important on the mid-flanks of the cone, away from pit-related fractures. On the east flank the superficial structures are controlled by the slump. We suggest that during pit subsidence intra-pit eruptions may occur. During tumescence, however, the pit system may become blocked and a flank eruption is more likely. Intrusions along the rift may cause deformation that subsequently increases the slump’s potential to deform. Conversely, slumping may influence the east flank stress distribution and locally control intrusion direction. These predictions can be tested with monitoring data to validate the model and, eventually, improve monitoring.

Volcanic activity disturbs the existing magnetic field, and analysis of the resulting magnetic anomalies provides information about the internal structure and evolution of active systems within edifices. This study focuses on the South-East Rift Zone (SERZ) of Piton de la Fournaise, specifically the eruptive site of September 2022, which offers a unique opportunity to characterise the thermal state, the subsurface structures, and to obtain information about the global fluid dynamics of this highly active area. For this purpose, we performed high-resolution aeromagnetic surveys using an Unmanned Aerial Vehicle (UAV) in November 2022 and May 2024 to investigate the evolution of the eruptive site. At a regional scale, first order 3D modelling of the magnetic anomalies primarily reveals a negative magnetic axis with a N120° orientation. Comparative analysis with 3D Interferometric Synthetic Aperture Radar data modelling shows a significant correlation between this demagnetised axis, the depth, and the volume of magmatic intrusions along the rift-zone. This result suggests the presence of a N120°-trending mechanical weakness intersecting the SERZ that has some control over the internal dynamics of the magmatic and hydrothermal fluids in the area. In addition, we quantify the temporal evolution of the magnetic signals associated with the September 2022 lava flow by means of repeated UAV measurements from May 2024 and estimate a global increase of several hundreds of nanoteslas (between 150 and 900 nT) linked to the magnetisation caused by the lava cooling during this time. We then successfully explore on a more local scale the ability of UAV magnetic prospecting to detect lava tubes using semi-quantitative 2D models. These results demonstrate the potential of UAV magnetic surveys to characterise the spatio-temporal evolution of magnetic signals from Piton de la Fournaise. Such multi-scale analysis of magnetic structures within the edifice indicates the potential of 4D monitoring for obtaining a better understanding of the volcano’s evolution. Graphical Abstract

Bagana is a remote, highly active volcano, located on Bougainville Island in southeastern Papua New Guinea. The volcano has exhibited sustained and prodigious sulfur dioxide gas emissions in recent decades, accompanied by frequent episodes of lava extrusion. The remote location of Bagana and its persistent activity have made it a valuable case study for satellite observations of active volcanism. This remoteness has also left many features of Bagana relatively unexplored. Here, we present the first measurements of volcanic gas composition, achieved by unoccupied aerial system (UAS) flights through the volcano's summit plume, and a payload comprising a miniaturized MultiGAS. We combine our measurements of the molar CO2/SO2 ratio in the plume with coincident remote sensing measurements (ground‐ and satellite‐based) of SO2 emission rate to compute the first estimate of CO2 flux at Bagana. We report low SO2 and CO2 fluxes at Bagana from our fieldwork in September 2019, ∼320 ± 76 td−1 and ∼320 ± 84 td−1, respectively, which we attribute to the volcano's low level of activity at the time of our visit. We use satellite observations to demonstrate that Bagana's activity and emissions behavior are highly variable and advance the argument that such variability is likely an inherent feature of many volcanoes worldwide and yet is inadequately captured by our extant volcanic gas inventories, which are often biased to sporadic measurements. We argue that there is great value in the use of UAS combined with MultiGAS‐type instruments for remote monitoring of gas emissions from other inaccessible volcanoes. Plain Language Summary Bagana is a remote and highly active volcano in southeastern Papua New Guinea (PNG). Historically, it has been among the most active volcanoes in PNG, notable for its long‐lived eruptions and sustained gas emissions. Bagana has only been infrequently studied before now. We use unoccupied aerial systems (drones) along with ground‐ and satellite‐based remote sensing data to characterize the chemical composition and flux of Bagana's gas emissions and place these in the context of global volcanic emissions. Owing to low activity during the time of our fieldwork, we report lower than anticipated emissions of carbon dioxide and sulfur dioxide from Bagana. We argue that characterizing highly variable volcanic emissions is challenging without long‐term continuous observations and that, for remote volcanoes like Bagana, both drones and satellite observations are powerful tools to undertake these observations. Key Points We present the first measurements of volcanic gas composition at Bagana volcano CO2 and SO2 fluxes at Bagana vary widely with levels of unrest, from ∼102 to ∼104 td−1 Unoccupied aerial systems (drones) are of great value in monitoring emissions from inaccessible volcanic summits

Kauaʻi shield‐stage lavas are central to understanding the origin of the distinct Kea and Loa Hawaiian geochemical trends in Hawaiian basalts. These trends reflect two geochemically distinct sides in the Hawaiian plume, with Loa to the southwest and Kea to the northeast. The geochemistry and Sr‐Nd‐Hf isotopic compositions of shield‐stage lavas from Kauaʻi show a transition from Kea to Loa across the island with the Loa mantle source becoming dominant as the volcano grew. This geochemical transition is gradual from west to east Kauaʻi and supports the hypothesis that the Kauaʻi volcano sampled both sides of the bilateral Hawaiian plume, a phenomenon that is unusual for a Hawaiian volcano. Notably, Kauaʻi marks the arrival of progressively larger volumes of Loa compositions within the Hawaiian mantle plume. The new data from Kauaʻi, combined with an updated and comprehensive database of Hawaiian shield‐stage major element oxides, trace element concentrations, and isotopic compositions normalized to the same standard values, allows for the Pb‐Sr‐Nd‐Hf isotopic compositions of the Average Loa (‘ALOA’) common geochemical component to be estimated. Despite the bilateral Loa‐Kea geochemical trend beginning at Molokaʻi, Loa compositions dominate the erupted volume of Hawaiian volcanoes younger than 3 Ma, validating the volumetric importance of the Loa source in the lower mantle portion of the Hawaiian plume. Plain Language Summary Hawaiian volcanoes are arranged along two parallel geographic trends named Loa and Kea. Volcanoes belonging to either trend have distinct geochemical compositions that are linked to their deep mantle sources as sampled by the Hawaiian mantle plume. The Kea composition has been present in shield‐stage basalts for ∼81 Ma, however the Loa composition is relatively new and has mainly been measured in volcanoes formed since 3–4 Ma. We used the geochemistry and isotopic compositions of shield‐stage basalts from the island of Kauaʻi to show that Loa compositions began to appear in larger amounts in the Hawaiian plume around 5 Ma. These new data, combined with a large and carefully curated geochemical data set of Hawaiian samples, has allowed us to estimate the average composition of Loa and its associated isotopic end‐member compositions. This work demonstrates that Loa was an important mantle source for the older Hawaiian volcanoes such as Kauaʻi and dominates shield lavas along the Hawaiian chain. Notably, the geochemistry of Kauaʻi’s volcanic rocks represents the long‐term establishment of Loa compositions in the Hawaiian plume. Key Points Radiogenic (Sr‐Nd‐Hf, and Pb) isotopic compositions change from west to east across Kauaʻi and broadly correlate with age Kauaʻi records the first large‐scale and long‐lasting occurrence of Loa‐trend Hawaiian compositions The average Loa composition is constrained in Pb‐Sr‐Nd‐Hf isotopes and dominates compositions along the Hawaiian chain

Most oceanic plateaux are massive basaltic volcanoes. However, the structure of these volcanoes, and how they erupt and evolve, is unclear, because they are remote and submerged beneath the oceans. Here we use multichannel seismic profiles and rock samples taken from Integrated Ocean Drilling Program core sites to analyse the structure of the Tamu Massif, the oldest and largest edifice of the Shatsky Rise oceanic plateau in the north-western Pacific Ocean. We show that the Tamu Massif is a single, immense volcano, constructed from massive lava flows that emanated from the volcano centre to form a broad, shield-like shape. The volcano has anomalously low slopes, probably due to the high effusion rates of the erupting lavas. We suggest that the Tamu Massif could be the largest single volcano on Earth and that it is comparable in size to the largest volcano in the Solar System, Olympus Mons on Mars. Our data document a class of oceanic volcanoes that is distinguished by its size and morphology from the thousands of seamounts found throughout the oceans. The structure of oceanic plateaux is unclear, as they are remote and submerged beneath the seas. Seismic images of the Tamu Massif, part of the Shatsky Rise oceanic plateau in the northwestern Pacific Ocean, show that it is a single immense volcano, potentially the largest on Earth.