Submarine Volcano Research Articles

Imaging of CO2 bubble plumes above an erupting submarine volcano, NW Rota‐1, Mariana Arc

AbstractNW Rota‐1 is a submarine volcano in the Mariana volcanic arc located ∼100 km north of Guam. Underwater explosive eruptions driven by magmatic gases were first witnessed there in 2004 and continued until at least 2010. During a March 2010 expedition, visual observations documented continuous but variable eruptive activity at multiple vents at ∼560 m depth. Some vents released CO2 bubbles passively and continuously, while others released CO2 during stronger but intermittent explosive bursts. Plumes of CO2 bubbles in the water column over the volcano were imaged by an EM122 (12 kHz) multibeam sonar system. Throughout the 2010 expedition numerous passes were made over the eruptive vents with the ship to document the temporal variability of the bubble plumes and relate them to the eruptive activity on the seafloor, as recorded by an in situ hydrophone and visual observations. Analysis of the EM122 midwater data set shows: (1) bubble plumes were present on every pass over the summit and they rose 200–400 m above the vents but dissolved before they reached the ocean surface, (2) bubble plume deflection direction and distance correlate well with ocean current direction and velocity determined from the ship's acoustic doppler current profiler, (3) bubble plume heights and volumes were variable over time and correlate with eruptive intensity as measured by the in situ hydrophone. This study shows that midwater multibeam sonar data can be used to characterize the level of eruptive activity and its temporal variability at a shallow submarine volcano with robust CO2 output.

Layered Hydrothermal Barite-Sulfide Mound Field, East Diamante Caldera, Mariana Volcanic Arc

East Diamante is a submarine volcano in the southern Mariana arc that is host to a complex caldera ~5 × 10 km (elongated ENE-WSW) that is breached along its northern and southwestern sectors. A large field of barite-sulfide mounds was discovered in June 2009 and revisited in July 2010 with the R/V Natsushima , using the ROV Hyper-Dolphin . The mound field occurs on the northeast flank of a cluster of resurgent dacite domes in the central caldera, near an active black smoker vent field. A 40Ar/39Ar age of 20,000 ± 4000 years was obtained from a dacite sample. The mound field is aligned along a series of fractures and extends for more than 180 m east-west and >120 m north-south. Individual mounds are typically 1 to 3 m tall and 0.5 to 2 m wide, with lengths from about 3 to 8 m. The mounds are dominated by barite + sphalerite layers with the margins of each layer composed of barite with disseminated sulfides. Rare, inactive spires and chimneys sit atop some mounds and also occur as clusters away from the mounds. Iron and Mn oxides are currently forming small (<1-m diam, ~0.5-m tall) knolls on the top surface of some of the barite-sulfide mounds and may also drape their flanks. Both diffusely and focused fluids emanate from the small oxide knolls. Radiometric ages of the layered barite-sulfide mounds and chimneys vary from ~3,920 to 3,350 years. One layer, from an outcrop of 10- to 100-cm-thick Cu-rich layers, is notably younger with an age of 2,180 years. The Fe-Mn oxides were <5 years old at the time of collection in 2009. Most mound, chimney, and layered outcrop samples are dominated by barite, silica, and sphalerite; other sulfides, in decreasing order of abundance, are galena, chalcopyrite, and rare pyrite. Anglesite, cerussite, and unidentified Pb oxychloride and Pb phosphate minerals occur as late-stage interstitial phases. The samples contain high Zn (up to 23 wt %), Pb (to 16 wt %), Ag (to 487 ppm), and Au (to 19 ppm) contents. Some layered outcrop samples are dominated by chalcopyrite resulting in ≤4.78 wt % Cu in a bulk sample (28 wt % for a single lens), with a mean of 0.28 wt % for other samples. Other significant metal enrichments are Sb (to 1,320 ppm), Cd (to 1,150 ppm), and Hg (to 55 ppm). The East Diamante mound field has a unique set of characteristics compared to other hydrothermal sites in the Mariana arc and elsewhere. The geochemical differences may predominantly reflect the distribution of fractures and faults and consequently the rock/water ratio, temperature of the fluid in the upper parts of the circulation system, and extensive and prolonged mixing with seawater. The location of mineralization is controlled by fractures. Following resurgent doming within the caldera, mineralization resulted from focused flow along small segments of linear fractures rather than from a point source, typical of hydrothermal chimney fields. Based on the mineral assemblage, the maximum fluid temperatures were ~260°C, near the boiling point for the water depths of the mound field (367–406 m). Lateral fluid flow within the mounds precipitated interstitial sphalerite, silica, and Pb minerals within a network of barite with disseminated sulfides; silica was the final phase to precipitate. The current low-temperature precipitation of Fe and Mn oxides and silica may represent rejuvenation of the system.

Near-Bottom Magnetic Signatures of Submarine Hydrothermal Systems at Marsili and Palinuro Volcanoes, Southern Tyrrhenian Sea, Italy

Research Article| December 01, 2014 Near-Bottom Magnetic Signatures of Submarine Hydrothermal Systems at Marsili and Palinuro Volcanoes, Southern Tyrrhenian Sea, Italy F. Caratori Tontini; F. Caratori Tontini † 1GNS Science, P.O. Box 30368, Lower Hutt, New Zealand †Corresponding author: e-mail, f.caratori.tontini@gns.cri.nz Search for other works by this author on: GSW Google Scholar G. Bortoluzzi; G. Bortoluzzi 2CNR, Ismar, via Gobetti, 101, 40129, Bologna, Italy Search for other works by this author on: GSW Google Scholar C. Carmisciano; C. Carmisciano 3INGV, U.P. Geofisica e Tecnologie Marine, via Pezzino Basso, 2, 1902, Fezzano (SP), Italy Search for other works by this author on: GSW Google Scholar L. Cocchi; L. Cocchi 3INGV, U.P. Geofisica e Tecnologie Marine, via Pezzino Basso, 2, 1902, Fezzano (SP), Italy Search for other works by this author on: GSW Google Scholar C.E.J. de Ronde; C.E.J. de Ronde 1GNS Science, P.O. Box 30368, Lower Hutt, New Zealand Search for other works by this author on: GSW Google Scholar M. Ligi; M. Ligi 2CNR, Ismar, via Gobetti, 101, 40129, Bologna, Italy Search for other works by this author on: GSW Google Scholar F. Muccini F. Muccini 3INGV, U.P. Geofisica e Tecnologie Marine, via Pezzino Basso, 2, 1902, Fezzano (SP), Italy Search for other works by this author on: GSW Google Scholar Author and Article Information F. Caratori Tontini † 1GNS Science, P.O. Box 30368, Lower Hutt, New Zealand G. Bortoluzzi 2CNR, Ismar, via Gobetti, 101, 40129, Bologna, Italy C. Carmisciano 3INGV, U.P. Geofisica e Tecnologie Marine, via Pezzino Basso, 2, 1902, Fezzano (SP), Italy L. Cocchi 3INGV, U.P. Geofisica e Tecnologie Marine, via Pezzino Basso, 2, 1902, Fezzano (SP), Italy C.E.J. de Ronde 1GNS Science, P.O. Box 30368, Lower Hutt, New Zealand M. Ligi 2CNR, Ismar, via Gobetti, 101, 40129, Bologna, Italy F. Muccini 3INGV, U.P. Geofisica e Tecnologie Marine, via Pezzino Basso, 2, 1902, Fezzano (SP), Italy †Corresponding author: e-mail, f.caratori.tontini@gns.cri.nz Publisher: Society of Economic Geologists First Online: 09 Mar 2017 Online Issn: 1554-0774 Print Issn: 0361-0128 © 2014 Society of Economic Geologists. Economic Geology (2014) 109 (8): 2119–2128. https://doi.org/10.2113/econgeo.109.8.2119 Article history First Online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation F. Caratori Tontini, G. Bortoluzzi, C. Carmisciano, L. Cocchi, C.E.J. de Ronde, M. Ligi, F. Muccini; Near-Bottom Magnetic Signatures of Submarine Hydrothermal Systems at Marsili and Palinuro Volcanoes, Southern Tyrrhenian Sea, Italy. Economic Geology 2014;; 109 (8): 2119–2128. doi: https://doi.org/10.2113/econgeo.109.8.2119 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyEconomic Geology Search Advanced Search Abstract Near-bottom magnetic field data were collected using a towed magnetometer over selected parts of Palinuro and Marsili submarine volcanoes in the southern Tyrrhenian Sea, Italy. We obtained equivalent magnetizations maps at these sites by inverting the corresponding magnetic anomalies, highlighting the seafloor expression of hydrothermal alteration. Zones of reduced magnetization are interpreted as evidence for alteration related to hydrothermal processes; they are associated with water-column and seafloor observations of hydrothermal activity and altered host rocks. At Marsili volcano, a large elliptical area of reduced magnetization is located south of the summit cone and perpendicular to the trend of Marsili volcano itself. This confirms the presence of a large hydrothermal system centered over the more recent eastern volcanic ridge and its associated magma chamber. Similarly, areas of reduced magnetization over Palinuro caldera are consistent with hydrothermal venting occurring along the caldera walls, consistent with permeability structures related to caldera ring faults providing preferred pathways for the upflow of hydrothermal fluids. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Submarine eruption-fed and resedimented pumice-rich facies: the Dogashima Formation (Izu Peninsula, Japan)

In the Izu Peninsula (Japan), the Pliocene pumice-rich Dogashima Formation (4.55 ± 0.87 Ma) displays exceptional preservation of volcaniclastic facies that were erupted and deposited in a below wave-base marine setting. It includes high-concentration density current deposits that contain clasts that were emplaced hot, indicating an eruption-fed origin. The lower part of the Dogashima 2 unit consists of a very thick sequence (<12 m) of massive grey andesite breccia restricted to the base of a submarine channel, gradationally overlain by pumice breccia, which is widespread but much thinner and finer in the overbank setting. These two breccias share similar mineralogy and crystal composition and are considered to be co-magmatic and derived from the destruction of a submarine dome by an explosive, pumice-forming eruption. The two breccias were deposited from a single, explosive eruption-fed, sustained, sea floor-hugging, water-supported, high-concentration density current in which the clasts were sorted according to their density. At the rim of the channel, localised good hydraulic sorting of clasts and stratification in the pumice breccia are interpreted to reflect local current expansion and unsteadiness rather than to be the result of hydraulic sorting of clasts during fall from a submarine eruption column and/or umbrella plume. A bimodal coarse (>1 m) pumice- and ash-rich bed overlying the breccias may be derived from delayed settling of pyroclasts from suspension. In Dogashima 1 and 2, thick cross- and planar-bedded facies composed of sub-rounded pumice clasts are intercalated with eruption-fed facies, implying inter-eruptive mass-wasting on the flank of a submarine volcano, and reworking and resedimentation by high-energy tractional currents in a below wave-base environment.

The Black Sea basins structure and history: New model based on new deep penetration regional seismic data. Part 1: Basins structure and fill

This work is based upon results of interpretation of about 8872 km-long regional seismic lines acquired in 2011 within the international project Geology Without Limits in the Black Sea. The seismic lines cover nearly the entire Black Sea Basins, including Russia, Turkey, Ukraine, Romania and Bulgaria sectors. A new map of acoustic basement relief and a new tectonic structure scheme are constructed for the Black Sea Basins. The basement of the Black Sea includes areas with oceanic crust and areas with highly rifted continental crust. A chain of buried seamounts, which were interpreted as submarine volcanoes of Late Cretaceous (Santonian to Campanian) age, has been identified to the north of the Turkish coast. On the Shatsky Ridge, probable volcanoes of Albian age have also been recognized. Synorogenic turbidite sequences of Paleocene, Eocene and Oligocene ages have been mapped. In the Cenozoic, numerous compressional and transpressional structures were formed in different parts of the Black Sea Basin. During the Pleistocene–Quaternary, turbidites, mass-transport deposits and leveed channels were formed in the distal part of the Danube Delta.

Breakdown of under-water gas hydrate deposits

At the floor and upper sediment layers of the submarine volcano Hakon Mosby gas (methane) hydrate deposits have been discovered. Measurements of the water-dissolved methane concentration at different depths near the volcano have shown that its level is higher than the average level in the Ocean. In order to understand the effects observed in concentration distribution, a model is proposed for describing the propagation of methane formed as a result of decomposition of depth and floor hydrate over the hydrosphere. Within the framework of physical modeling the kinetics of methane dissolution and its distribution in the hydrosphere are traced numerically with account for transfer anisotropy in different directions and undercurrents. The dissolution rate and the mass transfer directions are determined and the concentration fields in the floor layers are calculated. It is shown that methane is rapidly dispersed in the hydrosphere and, thus, significant volumes with high methane concentration cannot be formed. Practical recommendations are given for hunting hydrate deposits in water areas. The model proposed is applicable to describing the propagation of any admixture in different anisotropic media.

Active undersea volcanoes pose increased corrosion risk

Active undersea volcanoes pose increased corrosion risk

Hydrodynamic modeling of magmatic–hydrothermal activity at submarine arc volcanoes, with implications for ore formation

Subduction-related magmas have higher volatile contents than mid-ocean ridge basalts, which affects the dynamics of associated submarine hydrothermal systems. Interaction of saline magmatic fluids with convecting seawater may enhance ore metal deposition near the seafloor, making active submarine arcs a preferred modern analogue for understanding ancient massive sulfide deposits.We have constructed a quantitative hydrological model for sub-seafloor fluid flow based on observations at Brothers volcano, southern Kermadec arc, New Zealand. Numerical simulations of multi-phase hydrosaline fluid flow were performed on a two-dimensional cross-section cutting through the NW Caldera and the Upper Cone sites, two regions of active venting at the Brothers volcanic edifice, with the former hosting sulfide mineralization. Our aim is to explore the flow paths of saline magmatic fluids released from a crystallizing magma body at depth and their interaction with seawater circulating through the crust. The model includes a 3×2 km2 sized magma chamber emplaced at ∼2.5 km beneath the seafloor connected to the permeable cone via a ∼200 m wide feeder dike. During the simulation, a magmatic fluid was temporarily injected from the top of the cooling magma chamber into the overlying convection system, assuming hydrostatic conditions and a static permeability distribution.The simulations predict a succession of hydrologic regimes in the subsurface of Brothers volcano, which can explain some of the present-day hydrothermal observations. We find that sub-seafloor phase separation, inferred from observed vent fluid salinities, and the temperatures of venting at Brothers volcano can only be achieved by input of a saline magmatic fluid at depth, consistent with chemical and isotopic data. In general, our simulations show that the transport of heat, water, and salt from magmatic and seawater sources is partly decoupled. Expulsion of magmatic heat and volatiles occurs within the first few hundred years of magma emplacement in the form of rapidly rising low-salinity vapor-rich fluids. About 95% of the magmatically derived salt is temporarily trapped in the crust, either as dense brine or as precipitated halite. This retained salt can only be expelled by later convection of seawater during the waning period of the hydrothermal system (i.e., “brine mining”).While the abundant mineralization of the NW Caldera vent field at Brothers could not be classified as an economic ore deposit, our model has important implications for submarine metal enrichment and the origin of distinct ore types known from exposed systems on land. Sulfide-complexed metals (notably Au) will preferentially ascend during early vapor-dominated fluid expulsion, potentially forming gold ± copper rich vein and replacement deposits in near-seafloor zones of submarine volcanoes. Dense magmatic brine will initially accumulate chloride-complexed base metals (such as Cu, Fe, Pb and Zn) at depth before they are mobilized by seawater convection. The resulting mixed brines can become negatively buoyant when they reach the seafloor and may flow laterally towards depressions, potentially forming layers of base metal sulphides with distinct zonation of metals.

Cold seeps associated with a submarine debris avalanche deposit at Kick’em Jenny volcano, Grenada (Lesser Antilles)

Remotely operated vehicle (ROV) exploration at the distal margins of a debris avalanche deposit from Kick’em Jenny submarine volcano in Grenada has revealed areas of cold seeps with chemosynthetic-based ecosystems. The seeps occur on steep slopes of deformed, unconsolidated hemipelagic sediments in water depths between 1952 and 2042m. Two main areas consist of anastomosing systems of fluid flow that have incised local sediments by several tens of centimeters. No temperature anomalies were observed in the vent areas and no active flow was visually observed, suggesting that the venting may be waning. An Eh sensor deployed on a miniature autonomous plume recorder (MAPR) recorded a positive signal and the presence of live organisms indicates at least some venting is still occurring. The chemosynthetic-based ecosystem included giant mussels (Bathymodiolus sp.) with commensal polychaetes (Branchipolynoe sp.) and cocculinid epibionts, other bivalves, Siboglinida (vestimentiferan) tubeworms, other polychaetes, and shrimp, as well as associated heterotrophs, including gastropods, anemones, crabs, fish, octopods, brittle stars, and holothurians. The origin of the seeps may be related to fluid overpressure generated during the collapse of an ancestral Kick’em Jenny volcano. We suggest that deformation and burial of hemipelagic sediment at the front and base of the advancing debris avalanche led to fluid venting at the distal margin. Such deformation may be a common feature of marine avalanches in a variety of geological environments especially along continental margins, raising the possibility of creating large numbers of ephemeral seep-based ecosystems.

Mount Woolnough: the submerged volcano, SE of Sydney, NSW

Part of a larger investigation of the sea bed off Sydney was a study of the extinct submarine volcano Mount Woolnough. It is located approximately 41 km east of Kurnell, NSW, and protrudes 175 m above the sediment cover at depths of approximately −550 to −375 m. Volcanic rock, approximately 2.2 km in diameter, is exposed above the sediment sea floor and is much smaller than its magnetic expression (approximately 13 km in diameter). Samples dredged from Mount Woolnough were conglomerates with phosphatic nodules and volcanic fragments set in a fine foraminiferal sediment matrix. Zircons within the mafic fragments yielded a minimum age of 261 Ma.

Anatomy of an active submarine volcano

Research Article| August 01, 2014 Anatomy of an active submarine volcano A.F. Arnulf; A.F. Arnulf 1Cecil H. and Ida M. Green Institute of Geophysics and Planetary Physics, Scripps Institution of Oceanography, University of California–San Diego, La Jolla, California 92093, USA Search for other works by this author on: GSW Google Scholar A.J. Harding; A.J. Harding 1Cecil H. and Ida M. Green Institute of Geophysics and Planetary Physics, Scripps Institution of Oceanography, University of California–San Diego, La Jolla, California 92093, USA Search for other works by this author on: GSW Google Scholar G.M. Kent; G.M. Kent 2Nevada Seismological Laboratory, 0174, University of Nevada–Reno, Reno, Nevada 89557, USA Search for other works by this author on: GSW Google Scholar S.M. Carbotte; S.M. Carbotte 3Lamont-Doherty Earth Observatory, Columbia University, Palisades, New York 10964, USA Search for other works by this author on: GSW Google Scholar J.P. Canales; J.P. Canales 4Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02540, USA Search for other works by this author on: GSW Google Scholar M.R. Nedimović M.R. Nedimović 3Lamont-Doherty Earth Observatory, Columbia University, Palisades, New York 10964, USA5Department of Earth Sciences, Dalhousie University, Halifax, Nova Scotia B3H4J1, Canada Search for other works by this author on: GSW Google Scholar Author and Article Information A.F. Arnulf 1Cecil H. and Ida M. Green Institute of Geophysics and Planetary Physics, Scripps Institution of Oceanography, University of California–San Diego, La Jolla, California 92093, USA A.J. Harding 1Cecil H. and Ida M. Green Institute of Geophysics and Planetary Physics, Scripps Institution of Oceanography, University of California–San Diego, La Jolla, California 92093, USA G.M. Kent 2Nevada Seismological Laboratory, 0174, University of Nevada–Reno, Reno, Nevada 89557, USA S.M. Carbotte 3Lamont-Doherty Earth Observatory, Columbia University, Palisades, New York 10964, USA J.P. Canales 4Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02540, USA M.R. Nedimović 3Lamont-Doherty Earth Observatory, Columbia University, Palisades, New York 10964, USA5Department of Earth Sciences, Dalhousie University, Halifax, Nova Scotia B3H4J1, Canada Publisher: Geological Society of America Received: 28 Feb 2014 Revision Received: 12 May 2014 Accepted: 13 May 2014 First Online: 09 Mar 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 © 2014 Geological Society of America Geology (2014) 42 (8): 655–658. https://doi.org/10.1130/G35629.1 Article history Received: 28 Feb 2014 Revision Received: 12 May 2014 Accepted: 13 May 2014 First Online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation A.F. Arnulf, A.J. Harding, G.M. Kent, S.M. Carbotte, J.P. Canales, M.R. Nedimović; Anatomy of an active submarine volcano. Geology 2014;; 42 (8): 655–658. doi: https://doi.org/10.1130/G35629.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Most of the magma erupted at mid-ocean ridges is stored in a mid-crustal melt lens that lies at the boundary between sheeted dikes and gabbros. Nevertheless, images of the magma pathways linking this melt lens to the overlying eruption site have remained elusive. Here, we have used seismic methods to image the thickest magma reservoir observed beneath any spreading center to date, which is principally attributed to the juxtaposition of the Juan de Fuca Ridge with the Cobb hotspot (northwestern USA). Our results reveal a complex melt body, which is ∼14 km long, 3 km wide, and up to 1 km thick, beneath the summit caldera. The estimated volume of the reservoir is 18–30 km3, more than two orders of magnitude greater than the erupted magma volumes of either the A.D. 1998 or 2011 eruption. Our images show a network of sub-horizontal to shallow-dipping (<30°) features that we interpret as pathways facilitating melt transport from the magma reservoir to the eruption sites. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Geochemistry of granitoids from the basement of the Kuril island arc system

This paper reports the characteristics of granitoids from the Pacific slope of the Kuril island arc system, which were discovered by the authors during geological and geophysical operations in three cruises of the R/V Akademik M. Lavrent’ev. The major and trace element compositions of these rocks were determined, their role in the formation of the submarine Vityaz Ridge was evaluated, and they were compared with granitoids from the Brouton group of submarine volcanoes and xenoliths from Simushir Island and the Sea of Okhotsk. Granitoids from various structures of the basement of the Kuril island arc system are hypabyssal rocks derived from andesite magmas. Their common features are related to the formation on the continental crust under convergent geodynamic conditions involving compression due to the movement and subduction of the Pacific plate beneath the Asian continent. The problem of the basement of the Kuril island arc system was discussed, the composition and age of its rocks were determined, and the history of the geologic development of the Pacific slope of the arc starting from the Late Mesozoic was briefly described.

The submarine volcano eruption off El Hierro Island: effects on the scattering migrant biota and the evolution of the pelagic communities.

The submarine volcano eruption off El Hierro Island (Canary Islands) on 10 October 2011 promoted dramatic perturbation of the water column leading to changes in the distribution of pelagic fauna. To study the response of the scattering biota, we combined acoustic data with hydrographic profiles and concurrent sea surface turbidity indexes from satellite imagery. We also monitored changes in the plankton and nekton communities through the eruptive and post-eruptive phases. Decrease of oxygen, acidification, rising temperature and deposition of chemicals in shallow waters resulted in a reduction of epipelagic stocks and a disruption of diel vertical migration (nocturnal ascent) of mesopelagic organisms. Furthermore, decreased light levels at depth caused by extinction in the volcanic plume resulted in a significant shallowing of the deep acoustic scattering layer. Once the eruption ceased, the distribution and abundances of the pelagic biota returned to baseline levels. There was no evidence of a volcano-induced bloom in the plankton community.

Louisville Seamount Chain: Petrogenetic processes and geochemical evolution of the mantle source

AbstractThe Louisville Seamount Chain is a ∼4300 km long chain of submarine volcanoes in the southwestern Pacific that spans an age range comparable to that of the Hawaiian‐Emperor chain and is commonly thought to represent a hot spot track. Dredging in 2006 recovered igneous rocks from 33 stations on 22 seamounts covering some 49 Myr of the chain's history. All samples are alkalic, similar to previous dredge and drill samples, providing no evidence for a Hawaiian‐type tholeiitic shield‐volcano stage. Major and trace element variations appear to be predominantly controlled by small but variable extents of fractional crystallization and by partial melting. Isotopic values define only a narrow range, in agreement with a surprising long‐term source homogeneity—relative to the length scale of melting—and overlap with proposed fields for the “C” and “FOZO” mantle end‐members. Trace element and isotope geochemistry is uncorrelated with either seamount age or lithospheric thickness at the time of volcanism, except for a small number of lavas from the westernmost Louisville Seamounts built on young (&lt;20 Ma old) oceanic crust. The Louisville hot spot has been postulated to be the source of the ∼120 Ma Ontong Java Plateau, but the Louisville isotopic signature cannot have evolved from a source with isotopic ratios like those measured for Ontong Java Plateau basalts. On the other hand, this signature can be correlated with that of samples dredged from the Danger Islands Troughs of the Manihiki Plateau, which has been interpreted as a rifted fragment of the “Greater” Ontong Java Plateau.

Seafloor Geodesy

Seafloor geodetic techniques allow for measurements of crustal deformation over the ∼70% of Earth's surface that is inaccessible to the standard tools of tectonic geodesy. Precise underwater measurement of position, displacement, strain, and gravity poses technical, logistical, and cost challenges. Nonetheless, acoustic ranging; pressure sensors; underwater strain-, tilt- and gravimeters; and repeat multibeam sonar and seismic measurements are able to capture small-scale or regional deformation with approximately centimeter-level precision. Pioneering seafloor geodetic measurements offshore Japan, Cascadia, and Hawaii have substantially contributed to advances in our understanding of the motion and deformation of oceanic tectonic plates, earthquake cycle deformation in subduction zones, and the deformation of submarine volcanoes. Nontectonic deformation related to down-slope mass movement and underwater extraction of hydrocarbons or other resources represent other important targets. Recent technological advances promise further improvements in precision as well as the development of smaller, more autonomous, and less costly seafloor geodetic systems.

Rare earth elements as indicators of hydrothermal processes within the East Scotia subduction zone system

The East Scotia subduction zone, located in the Atlantic sector of the Southern Ocean, hosts a number of hydrothermal sites in both back-arc and island-arc settings. High temperature (>348°C) ‘black smoker’ vents have been sampled at three locations along segments E2 and E9 of the East Scotia back-arc spreading ridge, as well as ‘white smoker’ (<212°C) and diffuse (<28°C) hydrothermal fluids from within the caldera of the Kemp submarine volcano. The composition of the endmember fluids (Mg=0mmol/kg) is markedly different, with pH ranging from <1 to 3.4, [Cl−] from ∼90 to 536mM, [H2S] from 6.7 to ∼200mM and [F−] from 35 to ∼1000μM. All of the vent sites are basalt- to basaltic andesite-hosted, providing an ideal opportunity for investigating the geochemical controls on rare earth element (REE) behaviour. Endmember hydrothermal fluids from E2 and E9 have total REE concentrations ranging from 7.3 to 123nmol/kg, and chondrite-normalised distribution patterns are either light REE-enriched (LaCN/YbCN=12.8–30.0) with a positive europium anomaly (EuCN/Eu∗CN=3.45–59.5), or mid REE-enriched (LaCN/NdCN=0.61) with a negative Eu anomaly (EuCN/Eu∗CN=0.59). By contrast, fluids from the Kemp Caldera have almost flat REE patterns (LaCN/YbCN=2.1–2.2; EuCN/Eu∗CN=1.2–2.2).We demonstrate that the REE geochemistry of fluids from the East Scotia back-arc spreading ridge is variably influenced by ion exchange with host minerals, phase separation, competitive complexation with ligands, and anhydrite deposition, whereas fluids from the Kemp submarine volcano are also affected by the injection of magmatic volatiles which enhances the solubility of all the REEs. We also show that the REE patterns of anhydrite deposits from Kemp differ from those of the present-day fluids, potentially providing critical information about the nature of hydrothermal activity in the past, where access to hydrothermal fluids is precluded.

Bubbled lava from the floor of the Sea of Okhotsk

A sample of bubbled lava raised from a submarine volcano in the Sea of Okhotsk was analyzed by means of electron microscopy and the ICP-MS technique. The outside of the sample is flecked with rounded micro- and macrocavities, and the inner part is characterized by a liquation structure. Along with this, the unstructured mass of the rock contains globular particles of nearly the same diameters as the cavities. The lava is close to andesites and volcanic ashes of Kamchatka Peninsula in the macro- and microelemental composition but different in the somewhat increased content of barium, strontium, lithium, niobium, tungsten, uranium, and thorium. It is suggested that the cavities were formed during the eruption of the submarine volcano owing to contact of the boiling gas-saturated lava with seawater accompanied by the ejection of ash, which was spread by marine currents over long distances.

A comparative analysis of magnetic properties in rocks: Five active submarine volcanoes in the western Pacific

We studied the petrophysical and magnetic properties of dredged rocks that compose the edifices of five active submarine volcanoes in the Pacific Ocean, viz., the Fukujin, Esmeralda, Kovachi, and Simbo at island arcs, and Ile des Cendres in a marginal sea. We measured the standard petrophysical and magnetic characteristics and performed three kinds of thermomagnetic analysis as well as an electron-probe analysis. Comparative analysis of magnetic properties in rocks showed that they are strongly differentiated by the value of natural remanent magnetization and of magnetic susceptibility. The greatest values are shown by the Esmeralda aphyric basaltic andesites, the lowest occur in the Ile des Cendres xenoliths. The principal carriers of magnetization in the rocks are grains of unaltered and/or oxidized titanomagnetite with varying domain structures. All the samples are magnetically isotropic.

The emergence and growth of a submarine volcano: The Kameni islands, Santorini (Greece)

The morphology of a volcanic edifice reflects the integrated eruptive and evolutionary history of that system, and can be used to reconstruct the time-series of prior eruptions. We present a new high-resolution merged LiDAR-bathymetry grid, which has enabled detailed mapping of both onshore and offshore historic lava flows of the Kameni islands, emplaced in the centre of the Santorini caldera since at least AD 46. We identify three new submarine lava flows: two flows, of unknown age, lie to the east of Nea Kameni and a third submarine flow, located north of Nea Kameni appears to predate the 1925–1928 lava flows but was emplaced subsequent to the 1707–1711 lava flows. Yield strength estimates derived from the morphology of the 1570/1573 lobe suggest that submarine lava strengths are approximately two times greater than those derived from the onshore flows. To our knowledge this is the first documented yield strength estimate for submarine flows. This increase in strength is likely related to cooling and thickening of the dacite lava flows as they displace sea water. Improved lava volume estimates derived from the merged LiDAR-Bathymetry grid suggest typical lava extrusion rates of ∼2–3m3s−1 during four of the historic eruptions on Nea Kameni (1707–1711, 1866–1870, 1925–1928 and 1939–1941). They also reveal a linear relationship between the pre-eruption interval and the volume of extruded lava. These observations may be used to estimate the size of future dome-building eruptions at Santorini volcano, based on the time interval since the last significant eruption.

Numerical simulations of tsunamis generated by underwater volcanic explosions at Karymskoye lake (Kamchatka, Russia) and Kolumbo volcano (Aegean Sea, Greece)

Abstract. Increasing human activities along the coasts of the world provoke the necessity to assess tsunami hazard from different sources (earthquakes, landslides, volcanic activity). In this paper, we simulate tsunamis generated by underwater volcanic explosions from (1) a submerged vent in a shallow water lake (Karymskoye Lake, Kamchatka), and (2) from Kolumbo submarine volcano (7 km NE of Santorini, Aegean Sea, Greece). The 1996 tsunami in Karymskoye lake is a well-documented example and thus serves as a case study for validating the calculations. The numerical model reproduces realistically the tsunami run-ups measured onshore. Systematic numerical study of tsunamis generated by explosions of the Kolumbo volcano is then conducted for a wide range of energies. Results show that in case of reawakening, the Kolumbo volcano might represent a significant tsunami hazard for the northern, eastern and southern coasts of Santorini, even for small-power explosions.