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Coastal environments are highly recognized for their spectacular morphological features and economic activities, such as agriculture, maritime traffic, fishing, and tourism. In the context of climate change and the evolution of physical processes, the occurrence of intense natural phenomena adjacent to populated coastal areas may result in natural hazards, causing human and/or structural losses. As an outcome, scientific interest in researching and assessing multi-hazard susceptibility techniques has increased rapidly in an effort to better understand spatial patterns that are threatening coastal exposed elements, with or without temporal coincidence. The islands of Milos and Thira (Santorini Island) in Greece are prone to natural hazards due to their unique volcano-tectonic setting, the high number of tourist visits annually, and the unplanned expansion of urban fabric within the boundaries of the low-lying coastal zone. The main goal of this research is to analyze the onshore coastal terrain’s susceptibility to natural hazards, identifying regions that are vulnerable to soil erosion, torrential flooding, landslides and tsunamis. Therefore, the objective of this work is the development of a multi-hazard approach to the South Aegean Volcanic Arc (SAVA) islands, integrating them into a superimposed susceptibility map utilizing Multi-Criteria Decision-Making (MCDM) analysis. The illustrated geospatial workflow introduces a promising multi-hazard tool that can be implemented in low-lying coastal regions globally, regardless of their morphometric and manmade characteristics. Consequently, findings indicated that more than 30% of built-up areas, 20% of the transportation network, and 50% of seaports are within the high and very high susceptible zones, in terms of the Extended Low Elevation Coastal Zone (ELECZ). Coastal managers and decision-makers must develop a strategic plan in order to minimize potential economic and natural losses, private property damage, and tourism infrastructure degradation from potential inundation and erosion occurrences, which are likely to increase in the foreseeable future.

Nitrogen (N) dominates Earth's atmosphere (78% N2) but occurs in trace abundances in silicate minerals, making it a sensitive tracer of recycled surface materials into the mantle. The mechanisms controlling N transfer between terrestrial reservoirs remain uncertain because low N abundances in mineral‐hosted fluid inclusions (FIs) are difficult to measure. Using new techniques, we analyzed N and He isotope compositions and abundances in olivine‐ and pyroxene‐hosted FIs from arc volcanoes in Southern Chile, Cascadia, Central America, and the Southern Marianas. These measurements enable an estimate of the global flux of N outgassing from arcs (4.0 × 1010 mol/yr). This suggests that Earth is currently in a state of net N ingassing, with roughly half of subducted N returned to the mantle. Additionally, the N outgassing flux of individual arcs correlates with the thickness of subducting pelagic sediment, suggesting that N cycling in the modern solid Earth is largely controlled by sediment subduction. Plain Language Summary Nitrogen (N) largely behaves like an inert gas, and so it is substantially more concentrated at Earth's surface than in Earth's deep interior. Over geologic time, N can be transported between the solid Earth and the surface, and its concentration can change in both of these settings. Volcanic gases transport N from the interior to the surface, while some surface N returns into the solid Earth via plate subduction. Here, we present measurements of N and helium (He) gas trapped within crystals in volcanic rocks to determine how much N is transported to the surface through volcanism associated with plate subduction. We find that the amount of N returning to the surface through volcanism is less than estimates of how much N is transported into the solid Earth, suggesting that, overall, N is being returned to the planet's deep interior. Additionally, we observe that the amount of oceanic sediment that is subducted correlates with the amount of N that comes out of volcanoes, making it the primary carrier of N into the solid Earth. Key Points Arc lavas yield fluxes of 4.0 × 1010 mol N/yr, similar to estimates from volcanic arc gases, likely resulting in net mantle ingassing of N Nitrogen isotopes and N‐He mixing models highlight that small contributions of sediment dominate volcanic arc N budgets Subducted sediment thickness correlates with N2/3He ratios, and likely controls arc N fluxes rather than slab parameters or thermal state

The 2015 VESPA voyage (Volcanic Evolution of South Pacific Arcs) was a seismic and rock dredging expedition to the Loyalty and Three Kings Ridges and South Fiji Basin. In this paper we present 33 40Ar/39Ar, 22 micropaleontological, and two U/Pb ages for igneous and sedimentary rocks from 33 dredge sites in this little‐studied part of the southwest Pacific Ocean. Igneous rocks include basalts, dolerites, basaltic andesites, trachyandesites, and a granite. Successful Ar/Ar dating of altered and/or low‐K basalts was achieved through careful sample selection and processing, detailed petrographic and element mapping of groundmass, and incremental heating experiments on both phenocryst and groundmass separates to interpret the complex spectra produced by samples having multiple K reservoirs. The 40Ar/39Ar ages of most of the sampled lavas, irrespective of composition, are latest Oligocene to earliest Miocene (25–22 Ma); two are Eocene (39–36 Ma). The granite has a U/Pb zircon age of 23.6 ± 0.3 Ma. 40Ar/39Ar lava ages are corroborated by microfossil ages from associated sedimentary rocks. The VESPA lavas are part of a >3,000 km long disrupted belt of Eocene to Miocene subduction‐related volcanic rocks. The belt includes arc rocks in Northland New Zealand, Northland Plateau, Three Kings Ridge, and Loyalty Ridge and, speculatively, D’Entrecasteaux Ridge. This belt is the product of superimposed Eocene and Oligocene‐Miocene remnant volcanic arcs that were stranded along and near the edge of Zealandia while still‐active arc belts migrated east with the Pacific trench. Plain Language Summary Samples of lava from the seabed between New Zealand and New Caledonia have been dated using atomic clocks and fossils. Most lavas erupted in a big pulse of volcanic activity between 25 and 22 million years ago. They are part of a belt of now‐extinct undersea volcanoes that stretches for more than 3,000 km between New Zealand and the Solomon Islands. These volcanoes were formed by subduction of the Pacific Plate under the Australian Plate. Key Points A major pulse of 25–22 Ma volcanism is documented on the Loyalty and Three Kings Ridges, southwest Pacific Ocean The ridges are part of a more than 3,000 km long belt of Eocene to Miocene remnant volcanic arcs, stranded along the edge of Zealandia With care in sample selection, and petrological work, meaningful Ar/Ar ages can be obtained from altered and/or very low‐K submarine basalts

Geological and tectonic characteristics of the Mekong River Rapids in Chiang Khan District, Northern Loei Province, are investigated within the structural context of the Loei-Phetchabun Foldbelt. A multidisciplinary approach – including detailed fieldwork, petrographic analysis, whole-rock geochemistry (major, trace, and rare earth elements), and structural interpretation – reveals a complex lithological assemblage spanning the Middle Devonian to Jurassic periods. Volcanic sequences, including rhyolite, rhyodacite, dacite, and andesite, exhibit calc-alkaline arc signatures. Associated intrusive rocks (aplite and microgranodiorite) are enriched in LREEs and exhibit elevated LaN/YbN (10.06–15.89) and LILE/HFSE ratios, indicating subduction-related magmatism. Sedimentary formations reflect fore-arc basin settings, with Carboniferous strata dominating the east and Permian units in the west. Contact metamorphism has produced marble, garnet-pyroxene skarn, and spotted phyllite. Structural evidence documents multiphase deformation, linked to Indosinian compression followed by post-orogenic extension. The differential persistence of rapids is governed by lithological variability, tectonic uplift, intense monsoonal regimes, and pervasive silica-rich hydrothermal alteration that enhances bedrock competence through silicification. These factors collectively increase resistance to fluvial incision despite pronounced seasonal erosional forces. The findings underscore the complex interplay between lithology, structural deformation, and climatic dynamics in controlling the long-term stability and geomorphic evolution of rapids in tectonically active fluvial landscapes.

A variety of subaerial and submarine events, including mass‐wasting and volcanism, can generate sediment gravity flows and fallout deposits that are preserved in deep‐water stratigraphic records. This study examines whether event beds with differing depositional and transport histories exhibit distinct thickness‐frequency distributions. Analyzing over 4,500 event beds from seven drilling sites near Montserrat, the Izu Arc, the Kyushu‐Palau Ridge, and Gran Canaria, the analyses explore variations in event‐bed characteristics across different climatic periods, volcanic stages, and geomorphological settings. Statistical methods include characterizing thickness‐frequency distributions and assessing subset similarity using t‐tests and smoothed distribution patterns. The data‐driven results indicate discernible differences where dominant geological processes vary. For example, volcanic growth stages at the Kyushu–Palau Ridge produced thicker, coarser, and more frequent event beds compared with quiescent stages. Similarly, beds from the north slope of Gran Canaria—where submarine canyons enhanced sediment delivery—were nearly twice as thick as those from the south. In contrast, indistinguishable characteristics between the rear and frontal Izu Arc subsets after 3 Ma are attributed to the development of an extensional zone supplying material to both arc sides. Comparable distributions were also observed within intervals with minimal geological differences. The reliability of this analytical approach depends on high‐quality sediment recovery, as drilling‐related disturbances may obscure primary depositional signals. Beyond stratigraphic characterization, the method shows broader potential for identifying the provenance of volcanic glass shards through geochemical comparisons and for evaluating the statistical compatibility of data sets from neighboring sites, ensuring sufficient sample size for robust integrated analyses.

Understanding the origin of Late Jurassic volcanism in southern Patagonia is crucial for unraveling the early Andean orogenic evolution. However, radiometric dating is not connected to stratigraphic analysis along the South Patagonian Andes, which obscures the real duration of the Late Jurassic magmatic activity. In this contribution, we present the results of a volcanic stratigraphy analysis, complemented by structural and petrographic data, on a thick succession of acidic volcanogenic rocks in the Laguna Verde district of southern Chile located along the south shore of General Carrera-Buenos Aires Lake. Through the recognition of igneous stratigraphy, we strategically sampled representative volcanogenic rocks that cover the entire duration of eruptive activity. By doing so, the new U–Pb zircon magmatic ages, combined with a compilation of U–Pb crystallization ages from the South Patagonian Andes, allows us to constrain the volcanic activity in the study area to a period of 8 My (~ 155–146 Ma, V3 stage) and 11 My considering age inherent errors. The field recognition of normal faults and the syn-kinematic emplacement of sub-volcanic bodies, which are inferred to conform to a ring-fault system, along with the presence of a thick succession of ignimbrites, suggest that the syn-extensional volcanic emplacement occurred in a caldera volcanic environment. This setting was responsible for the short-lived, voluminous eruptions. Furthermore, the high Th/U zircon ratios identified for the ~ 155–150 Ma period indicate the climax of extensional tectonics. The integration of these data supports the hypothesis that retreating-mode subduction played a major role in producing ignimbrite flare-ups. Graphical abstract

The Kolumbo submarine volcano in the southern Aegean (Greece) is associated with repeated seismic unrest since at least two decades and the causes of this unrest are poorly understood. We present a ten‐month long microseismicity data set for the period 2006–2007. The majority of earthquakes cluster in a cone‐shaped portion of the crust below Kolumbo. The tip of this cone coincides with a low Vp‐anomaly at 2–4 km depth, which is interpreted as a crustal melt reservoir. Our data set includes several earthquake swarms, of which we analyze the four with the highest events numbers in detail. Together the swarms form a zone of fracturing elongated in the SW‐NE direction, parallel to major regional faults. All four swarms show a general upward migration of hypocenters and the cracking front propagates unusually fast, compared to swarms in other volcanic areas. We conclude that the swarm seismicity is most likely triggered by a combination of pore‐pressure perturbations and the re‐distribution of elastic stresses. Fluid pressure perturbations are induced likely by obstructions in the melt conduits in a rheologically strong layer between 6 and 9 km depth. We conclude that the zone of fractures below Kolumbo is exploited by melts ascending from the mantle and filling the crustal melt reservoir. Together with the recurring seismic unrest, our study suggests that a future eruption is probable and monitoring of the Kolumbo volcanic system is highly advisable. Key Points Seismicity is clustered in a cone‐shaped volume beneath Kolumbo; the cone's tip coincides with a melt reservoir at 2–4 km depth Seismicity swarms occupy nearby, yet different portions of the crust, ruling out an origin on a single fault Swarms were likely triggered by a combination of fluid pressure perturbations and redistribution of elastic stresses

Quantitative isotopic paleoaltimetry has been applied in regions where Rayleigh distillation controls isotopic lapse rates. Air mass mixing and moisture recycling are viewed as complicating factors. We show here that, because of such effects, a cross‐Andean transect of meteoric water δD values precisely marks the geographic position of the Western Cordillera crest. This modern water signal is also recorded in Pliocene‐Pleistocene hydrated volcanic glass δD values. δD values between the Pacific coast and Western Cordillera exhibit no trend up to 2.5 km elevation and 100 km inboard, consistent with an arid climate in which Amazonian moisture is topographically blocked and Pacific moisture is efficiently recycled. The result is a large δD lapse rate (−98‰/km) and an abrupt horizontal δD shift (2‰/km) at the Western Cordillera crest. Therefore, we conclude that cross‐orogen δD transects could locate the ancient Western Cordillera crest. Plain Language Summary Mountains have an outsized control on climate. Moist air masses rise and cool to cross high elevations, resulting in enhanced precipitation on the windward side and dry conditions downwind These processes influence the isotopic compositions of rainfall and of materials preserved in the geologic record that form from the interaction of rain with near‐surface materials. Here we report data from transects across the Peruvian Central Andes and show that the isotopic compositions shift abruptly at the position of highest topography (the crest of the Western Cordillera). This suggest that isotopic compositions of materials preserved in the geologic record might help establish the geographic position of the crests of mountain belts in the past. Key Points There is a substantial shift in the hydrogen isotope ratios of meteoric water at the Andean Western Cordillera crest Volcanic glass younger than 5 million years old shows similar ratio distributions to modern soil and precipitation water values Volcanic arc migration over time can be identified with meteoric water stable isotope records

This study employs advanced synthetic aperture radar (SAR) techniques, specifically the small baseline subset (SBAS) method, to analyze ground deformation dynamics on Aegina, a volcanic island within the Hellenic Volcanic Arc. Using Sentinel-1 satellite data spanning January 2016 to May 2023, this research reveals different deformation behaviors. The towns of Aegina and Saint Marina portray regions of stability, contrasting with central areas exhibiting subsidence rates of up to 1 cm/year. The absence of deformation consistent with volcanic activity on Aegina Island aligns with geological records and limited seismic activity, attributing the observed subsidence processes to settlement phenomena from past volcanic events and regional geothermal activity. These findings reinforce the need for continuous monitoring of the volcanic islands located in the Hellenic Volcanic Arc, providing important insights for local risk management, and contributing to our broader understanding of geodynamic and volcanic processes.

A global study of subduction zone dynamics indicates that the thermal structure of the overriding plate may control arc location. A fast convergence rate and a steep slab dip bring a hotter mantle further into the wedge corner, forming arc volcanoes closer to the trench. Separately, laboratory and numerical experiments showed that the development of a back‐arc spreading center (BASC) is driven by the migration of the subducting hinge, especially following changes in the slab geometry. As both arc location and the deformation regime of the overriding plate depend on slab kinematics and geometry, we investigate the possible correlations between BASC, the position of volcanic arcs, and slab dip at the scale of individual subduction zones. To do this, we compare the distance from trench to arc and trench to BASC at the Mariana, Scotia, Vanuatu, Tonga, and Kermadec subduction zones. In most cases, the arc and BASC are closer to the trench when the slab is dipping steeply. The correlation could result from an interplay between progressive changes in slab geometry and overriding plate deformation. This assumes, on the one hand, that the isotherm at the apex of which the arc forms is tied to a constant slab decoupling depth and, on the other hand, that back‐arc opening accommodates a change in slab dip. As slab dip decreases, both the BASC and the apex of the isotherm controlling the melt focusing move further from the trench. The observed trends are consistent with a slab anchored at 660 km depth. Plain Language Summary At subduction zones, where oceanic plates are recycled into the Earth's interior, water released by the downgoing plate initiates volcanism that forms arc volcanoes. Back‐arc basins sometimes develop beyond the volcanic arc as the upper plate stretches and thins under extensional stress, to the point of forming a back‐arc spreading center (BASC). Subduction parameters such as slab dip and plate velocity remain the dominant control of the arc location globally. The arc and BASC location, expressed as the distance from the trench, are negatively correlated with slab dip in most cases. We show here that the correlation may result from two separate phenomena stemming from variations in slab dip in the upper mantle. Extension in the back‐arc is induced by the retreating motion of the trench as a response to the slowdown of slab dip after reaching the mantle with higher viscosity. As the back‐arc opens, the spreading ridge keeps moving away from the trench, and the slab dip in the upper mantle decreases. As the slab dip decreases, the trenchward limit of the hot mantle flow is located further from the trench, resulting in further distance from the trench to the arc. Key Points The distance from the trench to the arc is negatively correlated with the slab dip within each subduction zone The thermal structure of the upper plate, which is tied to the depth of the slab coupling/decoupling transition, controls arc location Variations in the location of the spreading center in a given subduction zone can be linked to changes in slab dip during trench retreat