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This review focuses on the recognition of volcanic ash occurrences in marine sediment cores and on using their appearance and properties to deduce their origin. Widespread marine tephra layers are important marker horizons for both volcanological as well as general geological investigations. We describe ash detection by visual inspection and logging of sediment cores. Ash layer structure and texture, particle morphologies and lithological compositions of primary volcanic deposits are summarized and processes modifying them are discussed, both natural processes acting on and in the seafloor, i.e. erosion and bioturbation, and anthropogenic modifications during drilling/coring and core preparation. We discuss primary emplacement processes of marine fall and flow tephra deposits derived from either subaerial or submarine sources in order to identify distinguishing properties. We also elaborate on processes generating secondary, resedimented volcaniclastic layers such as submarine landslides and shelf erosion as well as fluvial input and ice-rafting, and how they can be distinguished from primary volcaniclastic deposits, which is essential in tephrostratigraphy. Finally, methods of tephra correlation between cores and on-land deposits/volcanoes are illustrated because they allow us to extend the 1D information from single cores to 3D distribution and facies changes of tephras and to bridge the land–sea gap.

Geological histories of volcanic ocean islands can be revealed by the sediments shed by them. Hence there is an interest in studying cores of volcaniclastic sediments that are particularly preserved in the many flat-floored basins lying close to the Azores islands. We analyse four gravity cores collected around the central group of the islands. Three sedimentary facies (F1-F2a, F2b) are recognized based on visual core logging, particle morphometric and geochemical analyses. F1 is clay-rich hemipelagite comprising homogeneous mud with mottled structures from bioturbation. F2a and F2b are both clay-poor volcaniclastic deposits, which are carbonate-rich and carbonate-poor, respectively. More biogenic carbonate in F2a reflects the incorporation of unconsolidated calcareous material from island shelves or bioturbation. Within F2a and F2b we identify deposits emplaced by pyroclastic fallout, primary or secondary turbidity currents by combining multiple information from lithological composition, sedimentary structures, chemical composition of volcanic glass shards and morphometric characteristics of volcanic particles. Primary volcaniclastic sediments were found in all four cores, echoing activity known to have occurred up to historical times on the adjacent islands. These preliminary results suggest that greater details of geological events could be inferred for other volcanic islands by adopting a similar approach to core analysis.

Magmatic heat and fluids can interact with a volcanic host rock to form secondary minerals, such as phyllosilicates, zeolites, sulfates, sulfides and oxides. The water-rock reactions, inducing alteration of the primary volcanic material, strongly depend on the magma chemistry and volatile flux, and the nature of the aquatic environment (i.e., sea/ocean and meteoric) and its properties such as temperature, salinity, redox and pH. The newly-grown alteration minerals result from the chemical reaction between the host rock and they can indicate particular physico-chemical conditions. Hence, the mechanisms controlling the formation of secondary mineral associations can be critical, not only for assessing the role of hydrothermally altered host rocks in moderating eruptions styles but also for volcano flank instabilities. In this study, we applied mass balance calculations and thermodynamic modelling to establish the formation and equilibria environments of alteration minerals and hydrothermal fluids at three active volcanic suites: Ruapehu (New Zealand), Mt. Zao (Japan) and Deception Island (Antarctica). Results indicate that the secondary minerals follow different precipitation sequences as a function of the magma composition and the primary mineral assemblage (basalt-andesitic to dacitic for Ruapehu, andesitic for Mt. Zao, and basaltic for Deception Island). Temporal variations in composition and abundances of the hydrothermal paragenesis in Ruapehu and Mt. Zao determinate the evolution of acid¿sulfate alteration zones. We conclude that the combination of the proposed petrologic-geochemical approach, the regional and local tectonic features, and the spatial distribution of the alteration minerals within the volcanic edifices can be used for the assessment of future hydrovolcanic eruptions (including multiple eruption phases) and/or instability flanks episodes. In addition, the biological submarine and global change communities can also benefit from this geochemical pro

Geological histories of volcanic ocean islands can be revealed by the sediments shed by them. Hence there is an interest in studying cores of volcaniclastic sediments that are particularly preserved in the many flat-floored basins lying close to the Azores islands. We analyse four gravity cores collected around the central group of the islands. Three sedimentary facies (F1-F2a, F2b) are recognized based on visual core logging, particle morphometric and geochemical analyses. F1 is clay-rich hemipelagite comprising homogeneous mud with mottled structures from bioturbation. F2a and F2b are both clay-poor volcaniclastic deposits, which are carbonate-rich and carbonate-poor, respectively. More biogenic carbonate in F2a reflects the incorporation of unconsolidated calcareous material from island shelves or bioturbation. Within F2a and F2b we identify deposits emplaced by pyroclastic fallout, primary or secondary turbidity currents by combining multiple information from lithological composition, sedimentary structures, chemical composition of volcanic glass shards and morphometric characteristics of volcanic particles. Primary volcaniclastic sediments were found in all four cores, echoing activity known to have occurred up to historical times on the adjacent islands. These preliminary results suggest that greater details of geological events could be inferred for other volcanic islands by adopting a similar approach to core analysis.

This review focuses on the recognition of volcanic ash occurrences in marine sediment cores and on using their appearance and properties to deduce their origin. Widespread marine tephra layers are important marker horizons for both volcanological as well as general geological investigations. We describe ash detection by visual inspection and logging of sediment cores. Ash layer structure and texture, particle morphologies and lithological compositions of primary volcanic deposits are summarized and processes modifying them are discussed, both natural processes acting on and in the seafloor, i.e. erosion and bioturbation, and anthropogenic modifications during drilling/coring and core preparation. We discuss primary emplacement processes of marine fall and flow tephra deposits derived from either subaerial or submarine sources in order to identify distinguishing properties. We also elaborate on processes generating secondary, resedimented volcaniclastic layers such as submarine landslides and shelf erosion as well as fluvial input and ice-rafting, and how they can be distinguished from primary volcaniclastic deposits, which is essential in tephrostratigraphy. Finally, methods of tephra correlation between cores and on-land deposits/volcanoes are illustrated because they allow us to extend the 1D information from single cores to 3D distribution and facies changes of tephras and to bridge the land–sea gap.

Deception Island (South Shetland Islands) is one of the most active volcanoes in Antarctica, with more than 20 explosive eruptive events registered over the past centuries. Recent eruptions (1967, 1969, and 1970) and volcanic unrest episodes (1992, 1999, and 2014–2015) demonstrate that volcanic activity is likely occurring in the future. This is of special concern for scientists, logistic personnel, and tourists, since the South Shetland Islands are an important tourist destination and host numerous year-round and seasonal scientific stations and base camps. Significant efforts have been made to understand the complex magmatic and volcanic evolution of Deception Island with special interest on its subaerial part. However, studies on submerged volcanic cones within Port Foster, the sea-flooded part of Deception Island's caldera depression, are comparatively scarce. Here, we provide a full characterization of Stanley Patch volcano, the largest of these volcanic edifices. Estimated morphometric parameters based on new multibeam bathymetric data, supported by petrographic and chemical observations from rock samples collected on the crater rim, reveal that Stanley Patch volcano grew in a subaerial environment. This result, combined with previous findings and new sedimentological evidence from our ultra-high resolution seismic profiles, allow to further detail the island's geologic evolution since the caldera collapse. We conclude that the complete flooding of Port Foster could have only occurred after the formation of Stanley Patch volcano, i.e. during the last ~2000 years, and in a time period of a few days or less.

Deception Island is amongst the most active volcanoes in the Southern Ocean, with over 20 explosive eruptions in the last ca. 200 years. The eruption that formed the caldera at Deception Island occurred 3980 ± 125 calendar years Before Present, and it is the largest eruptive event documented in Antarctica during Holocene. Since then, post-caldera volcanic activity has comprised many scattered eruptive vents across the island. Mortality of benthic organisms has been reported during the most recent eruptions occurred on the island, in 1967, 1969, and 1970 Common Era (CE), with very low abundances of organisms during the 1967–1973 CE period. Within the sea-flooded part of the caldera depression, named Port Foster, a submarine volcanic axis with several volcanic cones is observed. An interdisciplinary team sampled the best morphologically preserved volcanic edifice within Port Foster, the so-called Stanley Patch. Geophysical data traced the volcano and characterized its morphology and inner structure. Underwater scuba sampling allowed to acquire sediment and rock samples, photographs and video images of the benthic organisms and seascape. Morphology of Stanley Patch cone and textural characteristics of the collected pyroclastic rocks indicate that the volcanic edifice was originated during an explosive eruption. Furthermore, the lack of palagonitization, quenched pyroclast margins, and hyaloclastite deposits indicate that this cone has formed on-land, before the caldera floor became inundated by the seawater, highlighting the complex intra-caldera evolution of Deception Island. A sediment core from the crater was collected for sedimentological, and geochemical analysis. Antarctic climate and seasonal sea ice, together with organic degradation due to high sedimentation rates, explain the low total organic carbon data measured. The volcanic history of the island has probably avoided the development of a stable benthic community over time, similar to other Antarctic shallo

Isla Decepción es uno de los volcanes más activos de la Antártida, con más de veinte erupciones explosivas en los últimos dos siglos. Las variaciones isotópicas de hidrógeno y oxígeno en los volátiles atrapados en las muestras recogidas (vidrio volcánico e inclusiones de fundido en fenocristales) proporcionan información esencial sobre los mecanismos que controlan la historia eruptiva en este sistema volcánico. Los nuevos resultados isotópicos combinados con un exhaustivo conocimiento petrológico de este volcán revela (i) un ascenso rápido y el enfriamiento de los magmas preservando el contenido de agua magmática pre-eruptiva, con ligeras variaciones por rehidratación debido a la exposición del vidrio volcánico a aguas marinas, meteóricas y fumarólicas; (ii) un sistema(s) magmático(s) variable en el tiempo y actualmente dominado por una desgasificación en sistema cerrado que conduce a erupciones explosivas; (iii) el control que ejercen los dos sistemas de fallas principales de la isla sobre las profundidades de estancamiento de los magmas, así como sobre las interacciones de los magmas con las aguas superficiales que dan lugar a una actividad hidrovolcánica.

Deception Island (DI) is amongst the most active volcanoes, with >20 explosive eruptions in the last two centuries. DI¿s caldera-forming eruption, a volcano-climatic event with hemispheric impact occurred 3980 ± 125c.y. before present, is the largest eruption documented in Antarctica during Holocene. Mortality of benthic organisms occurredby eruptions in 1967, 1969, 1970, with very low abundances from 1967-1973. Volcanic activity post-caldera-forming comprises many scattered eruptive vents across the island. A submarine volcanic axis with several volcanic cones is observed within the caldera, and volcanic edifices, morphologically well-preserved in the southern part of the bay raise from the seafloor up to >50 m. A multidisciplinary team sampled one of the submerged volcanoes, Stanley Patch (SP), in Port Foster (PF). Geophysical data allocated the volcano and characterized its morphology and inner structure. Direct sampling by SCUBA provided sediment and rocks, and photographs/video images of benthic organisms and landscape. Morphology of SP cone and textural characteristics of pyroclastic rocks (vesiculation, bubble shape) indicate an explosive volcanism origin, and fits with the post-caldera magmatic trend. A sediment core from the crater (4 cm Ø, 8 cm length) was collected for sedimentological, geochemical and geochronological analysis. Antarctic climate and seasonal sea ice, together with organic degradation due to high sedimentation rates, explain low TOC data. SP, and the whole PF, provide a unique, great natural laboratory for benchmarking the reestablishment of benthic communities on avolcanological-influenced shallow marine environment, offering relevant data for future studies evaluating global change effects on Antarctic seabed.

Interest in monogenetic volcanism, with special reference to volcanic hazards and risk studies, has risen in the last decade. This is especially true in areas where monogenetic volcanic fields are close to population centres, critical infrastructure, and shipping routes, as for example the Michoacán-Guanajuato and Chichinautzin Volcanic Fields in Mexico, Auckland Volcanic Field in New Zealand, Deception Island in the Antarctica, Garrotxa Volcanic Field and Canary Islands in Spain. Volcanic hazard assessment requires information to be obtained from the geomorphology of volcanic edifices and deposit characteristics, such as volumes, crater shapes, grain size distributions, and edifice geometries. Such attributes of a volcanic edifice often provide quantitative information for long-term eruptive volumes, magma eruption rates, and relative chronologies (Conway et al. 1998; Guilbaud et al. 2012).

Deception Island is one of the most active volcanoes in Antarctica, with more than 20 monogenetic eruptions during the Holocene. The latest episodes of 1967, 1969, and 1970 have shown that volcanic activity on Deception Island can become a concern for tourists, scientists, and military personnel working on or near the island. The objective of this work is to identify eruptive processes and the geomorphic evolution of post-caldera monogenetic volcanic edifices at Deception Island by morphometric analyses, supported by field observations. Morphometric analysis has been used since the 1970s to analyse scoria cones, but it has rarely been applied to other monogenetic volcanoes, such as tuff cones and tuff rings. Tuff cones and tuff rings represent the most common landforms during Deception Island's recent geological past, with over 70 scattered eruptive vents inside and along the caldera rim. These volcanic landforms have been studied based on field observations and later, Digital Elevation Model analyses. Their geometry ranges from 10 to 100 m in height, and diameters vary between 300 and 2500 m. The morphometric data suggest that tuff cones have a more circular crater than tuff rings, with a significant separation between the two landforms using the height (Hco) and basal width (Wco) parameters. Tuff cones have Hco/Wco ratios with values between 0.04 and 0.16 and outer slopes between 7° and 34°. Tuff rings have lower Hco/Wco ratios that are between 0.01 and 0.04 and lower outer slopes between 3° and 21°. This study shows that basic shape parameters in combination with slope angle analysis can be used to discriminate among different types of monogenetic volcanoes. The initial eruptive-related morphometric diversity, however prevents correlation of eruption ages with morphometric parameters, or constructing a relative chronology of the monogenetic eruptions. This work provides a better comprehension of the potential evolution of a future eruption and a broader understan

Deception Island is one of the most active volcanoes in Antarctica, with more than 20 monogenetic eruptions during the Holocene. The latest episodes of 1967, 1969 and 1970 have shown that volcanic activity on Deception Island can become a concern for tourists, scientists, and military personnel working on or near the island. The objective of this work is, therefore to identify eruptive processes and the evolution of post-caldera volcanic edifices at Deception Island by morphometric analysis, supported by field observations. This methodology has been used since the 1970s to analyse mafic monogenetic volcanoes but it has not been fully developed until recently. Tuff cones and rings, as a result of magma-water interaction, represent the most common eruptive events occurring during Deception Island's recent geological past and are therefore the most likely to occur in the near future. This work provides an opportunity to incorporate for the first time at Deception Island geomorphological observations for a better comprehension of the potential evolution of a future eruption and for a broader understanding of volcanic hazards on this island.

Geochemistry of volatiles in active volcanoes provides insights into the magmatic processes and evolution at depth, such as magma evolution and degassing, which can be implemented into volcanic hazards assessment. Deception Island is one of the most active volcanoes in Antarctica, with more than twenty explosive eruptions documented over the past two centuries. Hydrogen and oxygen isotopic variations in the volatiles trapped in the Deception Island rocks (glass and melt inclusions in phenocrysts) provide essential information on the mechanisms controlling the eruptive history in this volcanic suite. Thus, understanding the petrological and related isotopic variations in the island, has the potential to foresee the possible occurrence and its main eruptive features of a future eruption. Information from hydrogen and oxygen stable isotopes combined with detailed petrologic data reveal in Deception Island (i) fast ascent and quenching of most magmas, preserving pre-eruptive magmatic signal of water contents and isotopic ratios, with local modification by rehydration due to glass exposition to seawater, meteoric and fumarolic waters; (ii) a plumbing system(s) currently dominated by closed-system degassing leading to explosive eruptions; (iii) control on the interactions of ascending magmas with the surface waters producing hydrovolcanic activity throughout the two main fault systems in Deception Island. These results can be considered in further studies of volcanic monitoring to improve the capability to interpret geophysical data and signals recorded during volcanic unrest episodes, and hence, forecast volcanic eruptions and related hazards. This research was partially funded by the following projects: POSVOLDEC (CTM2016¿79617¿P) (AEI/FEDER¿UE), VOLGASDEC (PGC2018-095693-B-I00) (AEI/FEDER¿UE) and Programa Propio Ib-2019 (USAL). This research is also part of POLARCSIC activities.

Deception Island is one of the most active volcanoes in Antarctica, with more than twenty explosive eruptions documented over the past two centuries. Volatiles can provide insights into the magmatic processes and evolution of active volcanoes, which can be implemented into volcanic hazards assessment. Stable isotopes (hydrogen and oxygen) on trapped volatiles in volcanic rocks of Deception Island give essential information for better understanding the genesis, eruptive mechanism(s) and volcanic hazards underneath this active volcano. The results combined with exhaustive petrologic information [1] have direct implications on the future eruption forecasting in the island by revealing (i) clear systematics among D/H values, volcanic stage (pre-, syn- and post-caldera), water source (meteoric vs. oceanic), and location over two main fault systems within the island, favouring magma ascent; (ii) a significant rapid magma ascent rates during the explosive hydrovolcanic eruptions evidenced by the negligible secondary hydration by meteoric or glacial melt waters after degassing of the primary magma.

Deception Island (DI), one of the most active volcanoes in Antarctica, had more than 20 monogenetic eruptions during the Holocene. The latest episodes in 1967, 1969 and 1970 destroyed, or severely damaged, the scientific bases that operated on the island. It is not possible to rule out the possibility of a future eruption in the future and in order to evaluate the eruptive recurrence is important to know the ages of most of the post-caldera edifices. This is one of the main problems at DI, due to the lack of data. The objective of this study is to carry out the morphometric analysis of the volcanic edifices and craters recognisable on the island, to establish a correlation between morphometry and the age of the post-caldera monogenetic landforms. This methodology has been used since the 70¿s to analyse mafic monogenetic volcanoes but it has not been fully developed until recently. One of the main peculiarity of DI is that these structures were probably affected by post-eruptive volcanic or erosive processes and that most of the volcanic edifices are tuff cones, due to magma-water interaction. The results obtained will allow improving the estimation of the eruptive recurrence of the island and, in turn, fundamental point for the advising of the volcanic hazard.

Deception Island (DI) is one of the most active volcanoes in Antarctica, with more than 20 monogenetic eruptions during the Holocene. The latest episodes of 1967, 1969 and 1970 destroyed, or severely damaged, the scientific bases that operated on the island and have shown that volcanic activity on DI can become a concern for tourists, scientists and military personnel working on or near the island. Indeed, it is not possible to rule out the possibility of a future eruption in the future. One of the main problems at DI is related to the lack of data about the ages of most of the edifices, in order to evaluate the eruptive recurrence. The objective of this study is to carry out the morphometric analysis of the post-caldera volcanic structures (volcanic edifices and craters) recognizable on the island. This methodology has been used since the 700s to analyse mafic monogenetic volcanoes but it has not been fully developed until recently. Several works were carried out in Campo de Calatrava-Ciudad Real, Tenerife, Gran Canaria and Lanzarote (Spain), Mauna Kea (USA) and Highlands of Bakony-Batalon (Hungary). This approach has been used at DI with the aim to establish a correlation between morphometry and the age of the post-caldera monogenetic landforms. The morphometric parameters include Crater maximum (Crmax) and minor (Crmin) diameter, Cone height (Hcomax and Hcomin), Crater depth (Cdep), Cone major (Comax) and minor (Comin) diameter, Cone slope (Scomax and Scomin) and Crater slope (Scrmax and Scrmin). One of the main peculiarity of DI is that these structures were probably affected by post-eruptive volcanic or erosive processes and that most of the volcanic edifices are tuff cone, as results of magma-water interaction. The results obtained will allow improving the estimation of the eruptive recurrence of the island and, in turn, fundamental point for the advising of the volcanic hazard.