geophysical and geochemical methods applied to investigate fissure related hydrothermal systems on the summit area of mt etna volcano italy abstract a multidisciplinary approach integrating self potential soil temperature heat flux co 2 efflux and gravity gradiometry signals was used to investigate a relatively small fissure related hydrothermal system near the summit of mt etna volcano italy measurements were performed through two different surveys carried out at the beginning and at the end of july 2009 right after the end of the long lived 2008 2009 flank eruption and in coincidence with an increase in diffuse flank degassing related to a reactivation of the volcano leading to the opening of a new summit vent nsec the main goal was to use a multidisciplinary approach to the detection of hidden fractures in an area of evident near surface hydrothermal activity despite the different methodologies used and the different geometry of the sampling grid between the surveys all parameters concurred in confirming that the study area is crossed by faults related with the main fracture systems of the south flank of the volcano where a continuous hydrothermal circulation is established results also highlighted that hydrothermal activity in this area changed both in space and in time these changes were a clear response to variations in the magmatic system notably to migration of magma at various depth within the main feeder system of the volcano the results suggest that this specific area initially chosen as the optimal test site for the proposed approach can be useful in order to get information on the potential reactivation of the summit craters of mt etna

highly isotopically depleted isoprenoids molecular markers for ancient methane venting abstract we propose that organic compounds found in a miocene limestone from marmorito northern italy are source markers for organic matter present in ancient methane vent systems cold seeps the limestone contains high concentrations of the tail to tail linked acyclic c20 isoprenoid 2 6 11 15 tetramethylhexadecane crocetane a c25 homolog 2 6 10 15 19 pentamethylicosane pme and a distinctive glycerol ether lipid containing 3 7 11 15 tetramethylhexadecyl phytanyl moieties the chemical structures of these biomarkers indicate a common origin from archaea their extremely 13c depleted isotope compositions 13c 108 to 115 6 pdb suggest that the respective archaea have directly or indirectly introduced isotopically depleted methane derived carbon into their biomass we postulate that a second major cluster of biomarkers showing heavier isotope values 13c 88 is derived from sulfate reducing bacteria srb the observed biomarkers sustain the idea that methanogenic bacteria in a syntrophic community with srb are responsible for the anaerobic oxidation of methane in marine sediments marmorito may thus represent a conceivable ancient scenario for methane consumption performed by a defined two membered bacterial consortium 1 archaea that perform reversed methanogenesis by oxidizing methane and producing co2 and h2 and 2 srb that consume the resulting h2 furthermore the respective organic molecules are unlike other compounds tightly bound to the crystalline carbonate phase the marmorito carbonates can thus be regarded as cold seep microbialites rather than mere authigenic carbonates

methane derived authigenic carbonates formed by subduction induced pore water expulsion along the oregon washington margin authigenic magnesian calcite dolomite and aragonite are precipitated in the uppermost terrigenous sediments of the washington oregon accretionary prism by subduction induced dewatering these distinctive carbonates are methane derived and occur at sites of concentrated pore water expulsion unique biologic communities that subsist at least indirectly on methane suess et al 1985 are also found at some of these sites the methane which is dominantly biogenic is carried to the uppermost sediments of the prism by fluids and is oxidized by sulfate reducers before being incorporated into a carbonate cement carbonate precipitation occurs below the oxic layer probably no deeper than several centimetres to a few metres below the seabed cementation may be induced by three factors 1 increased carbonate alkalinity resulting from microbial sulfate reduction 2 decreased co 2 solubility resulting from a pressure decrease when the pore water escapes the prism and or 3 the addition of ca 2 and mg 2 ions from sea water near the sediment water interface the convergent margin setting engenders precipitation of authigenic carbonates in several ways compressive stresses induce anomalously rapid compaction and dewatering rates and they may cause overpressuring in migrating pore water thereby delaying precipitation of carbonates until pressure is released near the sediment water interface structural deformation of the accretionary prism creates pathways such as fault zones secondary fracture porosity and dipping permeable layers often exposed by mass movement for efficient advection and expulsion of methane enriched pore water these characteristic conditions which lead to the precipitation of methane derived carbonates may be found at other convergent margins

microbial methane turnover at mud volcanoes of the gulf of cadiz the gulf of cadiz is a tectonically active area of the european continental margin and characterised by a high abundance of mud volcanoes diapirs pockmarks and carbonate chimneys during the r v sonne expedition gap gibraltar arc processes so 175 in december 2003 several mud volcanoes were surveyed for gas seepage and associated microbial methane turnover pore water analyses and methane oxidation measurements on sediment cores recovered from the centres of the mud volcanoes captain arutyunov bonjardim ginsburg gemini and a newly discovered mud volcano like structure called no name show that thermogenic methane and associated higher hydrocarbons rising from deeper sediment strata are completely consumed within the seabed the presence of a distinct sulphate methane transition zone smt overlapping with high sulphide concentrations suggests that methane oxidation is mediated under anaerobic conditions with sulphate as the electron acceptor anaerobic oxidation of methane aom and sulphate reduction sr rates show maxima at the smt which was found between 20 and 200 cm below seafloor at the different mud volcanoes in comparison to other methane seeps aom activity 383 mmol m 2 year 1 and diffusive methane fluxes 321 mmol m 2 year 1 in mud volcano sediments of the gulf of cadiz are low to mid range corresponding lipid biomarker and 16s rdna clone library analysis give evidence that aom is mediated by a mixed community of anaerobic methanotrophic archaea and associated sulphate reducing bacteria srb in the studied mud volcanoes little is known about the variability of methane fluxes in this environment carbonate crusts littering the seafloor of mud volcanoes in the northern part of the gulf of cadiz had strongly 13c depleted lipid signatures indicative of higher seepage activities in the past however actual seafloor video observations showed only scarce traces of methane seepage and associated biological processes at the seafloor no active fluid or free gas escape to the hydrosphere was observed visually at any of the surveyed mud volcanoes and biogeochemical measurements indicate a complete methane consumption in the seafloor our observations suggest that the emission of methane to the hydrosphere from the mud volcano structures studied here may be insignificant at present

an enigmatic kilometer scale concentration of small mytilids late miocene guadalquivir basin s spain abstract upper miocene heterozoan carbonates crop out extensively in a ne sw trending belt 42 km long and 1 5 8 km wide along the so called el alcor topographic high from carmona to dos hermanas seville s spain these carbonates formed at the southern active margin of the guadalquivir basin the foreland basin of the betic cordillera they change to marls basinward ne and to sands landward se and sw therefore carbonate production was constrained to a limited area in an otherwise siliciclastic shelf the carbonates up to 40 m thick overlie a gradually coarsening upward succession of marls followed by silts and sandstones the carbonate sequence can be divided into three subunits corresponding from bottom to top to lowstand transgressive and highstand system tract deposits the lower subunit exhibiting extensive trough cross bedding is interpreted as a shallow water bar deposit the intermediate subunit onlaps underlying sediments and was deposited in deeper low turbulence conditions the upper subunit deposits accumulated in a well oxygenated outer platform based on benthic foraminiferal assemblages the presence of hummocky and swaley cross stratification in these latter deposits suggests that they were affected by storms pervasive fluid escape structures are also observed throughout the carbonates the three subunits consist of bioclastic packstones to rudstones made up of abundant fragments of small mytilids isotopic data from serpulid polychaete ditrupa tubes show 13c depleted values up to 16 1 whereas 18o yields normal marine values additional isotopic data on shells of scallops oysters and small mussels as well as bulk sediment show diagenetic alterations based on actualistic examples of massive concentrations of mussels the nearly monospecific composition of the el alcor deposits together with negative 13c values of ditrupa tubes indicates that cold seeps presumably promoted carbonate formation however the absence of typical features of cold seep deposits such as authigenic carbonates mediated by anaerobic bacterial activity and the typical chemosynthetic shelly organisms makes the large carbonate body of el alcor an unusual cold seep deposit

hydrothermal circulation beneath mount pelee inferred by self potential surveying structural and tectonic implications abstract self potential sp surveys were made on mount pelee volcano martinique island french west indies in 1991 and 1992 in order to recognize its hydrothermal system the associated groundwater channeling and the main superficial structures of the massif almost 70 km of profiles were carried out with an average sample spacing of 50 m measurements essentially reveal negative sp anomalies down to 1700 mv with high gradients 1 83 mv m due to the infiltration of meteoric water into the massif rims of summit calderas morne macouba and etang sec present sharp negative sp anomalies on the western northern and eastern flanks negative sp anomalies indicate no upward water flow beneath mount pelee summit on the southwestern volcano flank a 3 5 6 km horseshoe shaped structure corresponding to a southwest flank collapse event older than 25 000 years bp is clearly identified by the sp mapping high gradients border the inner southern rim from morne calebasse to st pierre town and the caribbean sea along the northern rim of the horseshoe shaped structure the negative sp anomalies give place to a positive sp anomaly up to 200 mv of sw ne trend this zone covers the area of two active hot springs sources chaudes and puits chaud 40 65 c marine magnetic surveys and bathymetry show that the horseshoe shaped structure spreads into the caribbean sea up to about 10 km from the coast buried structural discontinuities are evidenced inside the flank collapse structure the upper one deviates the groundwater flow coming from the summit toward the south flank where the flow finds an indentation to expand again downwards this discontinuity is either an old hypothetical caldera rim partly destroyed by the collapse of the south southwestern flank and covered by recent pyroclastic deposits or more probably the trace of a bulge landslide a circulation model of the hydrothermal waters is proposed rainfall 5 6 m year is partly drained inside the summital calderas and the flank collapse zone through pyroclastic flows down to an impermeable basement there the groundwater constitutes perched aquifers at the contact of the bulge landslide or of the hypothetical old caldera rim along the inner northern border of the flank collapse structure the phreatic water is reheated warm groundwater flows along the northern avalanche structure rim and discharges near the coast in ground and marine outcrops of medium temperature finally the main part of the meteoric water is channeled along the old caldera rim or along the bulge landslide towards the south flank of mount pelee where some gaps in the rim exist there the groundwater finds again a subhorizontal gravitational circulation along mount pelee slopes into the caribbean sea

combined electromagnetic geochemical and thermal surveys of taal volcano philippines during the period 2005 2006 since 1572 33 phreatic to phreatomagmatic eruptions have occurred on taal volcano philippines some of them causing several hundred casualties considering the time delay between two consecutive eruptions there is an 88 probability that taal volcano should have already erupted since 1992 several phases of seismic activity have been recorded accompanied by ground deformation opening of fissures and surface activity the volcanic activity of taal appears to be controlled by dike injections and magma supply buffered by a hydrothermal system that releases fluids and heat through boiling and subsequent steaming in early 2005 a multidisciplinary project was launched for studying the hydrothermal activity to map the hydrothermal system combined surveys were carried out to investigate self potential total magnetic field ground temperature and carbon dioxide soil degassing along with satellite thermal imaging of the main crater lake the elevated temperatures and high concentrations of carbon dioxide as well as electromagnetic anomalies indicate large scale hydrothermal degassing this process is enhanced along the tectonic features e g crater rim and faults of the volcano while active fissures opened along the e w northern flank during the 1992 1994 seismic activity heat and fluids from the hydrothermal system are essentially released in the northern part of the crater which is bounded to the south by a suspected nw se fault along which seismicity seems to take place and dikes are thought to be intruded during the january 2005 surveys a new seismic crisis started and the felt earthquakes prompted spontaneous evacuation of hundreds of inhabitants living on the volcano repeated surveys show changes of self potential total magnetic field and ground temperature with time without any noticeable spatial enlargement these observations suggest that the northern flank located between the crater rim and the 1992 1994 fissures is connected with a deep thermal source in main crater and is reactivated during seismic crises this sector could be subjected to flank failure

case study of a volcanic geothermal system mount pelee martinique abstract mount pelee is one of the active volcanoes of the lesser antilles arc with more than 20 eruptions during the last 5000 years despite this abundant potential heat flow there are few surface manifestations indicative of the existence of a large high temperature hydrothermal system a few na hco 3 so 4 type hot springs with emergence temperatures not exceeding 65 c occur on the south and west flanks of the volcano two small hydrothermal eruptions occurred in 1792 and 1851 on the southwestern flank on the site of now extinct sulfur springs the heat source provided by the mount pelee magma chamber should occur according to petrologic data at shallow depth 5 8 km beneath the summit region we assume abundant groundwater recharge to take place within the central calderas where faults and magmatic conduits provide vertical channelways for deep infiltration of cold meteoric water this would be expected to depress a presumed nacl hydrothermal system located deep in the core of the volcano upwelling of high temperature fluids and gases is thought to be found at the periphery of the central calderas along the arcuate caldera related faults and or along regional faults and any permeable stratigraphic levels connected to the central caldera structure steam heating of shallow meteoric waters by a degassing nacl system could produce a na hco 3 so 4 type system which would develop preferentially on the periphery of the central caldera structure or even outside it in an adjacent zone of fracture permeability caldera or regional faults where cold meteoric flows are less abundant this na hco 3 so 4 system is assumed to be located beneath the south flank of the volcano and the major upflow zone seems to be the southern limit of the intermediate caldera as evidenced by the location of hot springs and hydrothermal eruptions the scarcity of thermal manifestations on mount pelee is not surprising in view of its groundwater hydrogeology the na hco 3 so 4 fluids which ascend will be masked wherever a highly permeable subhorizontal aquifer occurs near the surface and they commonly mix with cold waters before discharging

spontaneous potentials and resistivity surveys applied to hydrogeology in a volcanic area case history of the chaine des puys puy de dome france two geophysical methods resistivity soundings and spontaneous potentials sp are used to investigate aquifers in the quaternary volcanic formations of the chaine des puys france the interpretation of the resistivity soundings required a specific work of determination of the resistivity of the formations concerned the basement topography characterized by axial horst and graben structures and perpendicular palaeovalleys was revealed sp was developed experimentally in the field and theoretically it is shown that the sp anomalies can be considered as double layer potentials with their source on the aquifers interfaces the most significant of them is the water table which creates an sp anomaly of similar but inverted form sp anomalies due to flows in unconfined aquifers in palaeovalleys and in volcanic ranges are computed and compared with the observed ones these two methods have determined the extent and the boundary conditions of the different hydrogeological basins and have determined the major drainage axes and the groundwater flow pattern

pore water anomalies of submarine gas hydrate zones as tool to assess hydrate abundance and distribution in the subsurface what have we learned in the past decade abstract the most significant new contributions to the study of natural gas hydrates in the past decade have come from findings of the ocean drilling program odp notably legs 112 141 146 and 164 and to a lesser extent legs 131 160 170 and 186 leg 164 in particular was dedicated to gas hydrate drilling in the blake ridge gas hydrate field in the west atlantic in an unprecedented multidisciplinary research effort paull et al 1996 proc ocean drill program initial rep 164 623 pp paull c k matsumoto r wallace p j dillon w p eds 2000a proc ocean drill program sci results 164 ocean drilling program college station tx 459 pp most important for the progress of hydrochemical studies related to gas hydrates has been the growing awareness of the significance of diffusion modulated advective processes shaping the chemical and isotopic pore water profiles in hydrate zones this started with qualitative evidence for advective flow from drilling the hydrate bearing peru and hydrate free barbados active margins continued with the nankai trough accretionary prism the japan trench slope and the cascadia and costa rica active margins and culminated in the quantitative advection diffusion model of egeberg and dickens chem geol 153 1999 53 for the passive margin setting of the blake ridge advective flow regimes are different at active and passive margins as there is a tendency for the flow at active margins to be focussed along landward dipping thrust planes and faults in the wedge of imbricated thrust sheets that finds expression in a step pattern of the pore water profiles for passive margins but also for some active margin sites advection is from sources below the drilled section either through subvertical faults passive margins or from the decollement zone active margins we have learned that the well known coupled pore water anomalies that are ascribed to hydrate dissociation downward chlorinity decrease combined with 18 o increase hesse and harrison 1981 earth planet sci lett 55 1981 453 need not occur together in the presence of hydrates because the isotope effect may be overprinted by the effects of other reactions such as volcanic ash alteration or by the advection of low 18 o fluids however if the anomalies show up hydrates are present almost invariably with the exception of advected low cl high 18 o waters coming to terms with the effects of advection and diffusion has allowed successful modeling of the simpler hydrate affected pore water profiles at passive margins instrumental for modeling are chlorine isotopes which provide an effective tool to assess advection rates the egeberg and dickens model allows estimation of hydrate concentration and distribution in the subsurface because it separates the effects of advection diffusion and hydrate dissociation but critically depends on samples taken under in situ pressure and temperature conditions modeling the more complex pore water profiles of active margins is a challenge for the future compared to geophysical methods to estimate hydrate concentration the geochemical method gives minimum amounts

a large self potential anomaly on unzen volcano shimabara peninsula kyushu island japan self potential sp observation was carried out in the summit area of unzen one of the active volcanoes in kyushu island japan we found a positive sp anomaly in the vicinity of the newly extruded lava dome the potential difference across the anomaly exceeds 1000mv per 500m streaming potentials associated with subsurface hydrothermal convection seem to be the most reasonable mechanism for the positive anomaly in association with the first emergence of the lava dome a sharp increase of sp was detected which is considered to be a result of the growth of the hydro thermal system

stable isotopes 14c dating and geochemical characteristics of carbonate nodules and sediment from an active vent field northern juan de fuca ridge northeast pacific abstract a record of early uplift events foreshadowing development of an active vent field in middle valley on northern juan de fuca ridge is preserved in a core taken on the margin of the field by a near surface mud fragment breccia dated 8 300 to 11 500 yr b p cementation of the breccia with low mn methanogenic calcite at 5 c formed a carbonate nodule layer by 6 800 yr b p recent hydrothermal overprinting at 6 m in the same core resulted in formation of carbonate nodules with late stage high mn calcite cements oxygen isotopic temperatures of 55 85 c and more positive 13 c values reworked vent detritus suggests that surface venting began by at least 2 900 yr b p localized lateral flow of hydrothermal fluid tens of cm below the seafloor is suggested by a barite rich zone in a permeable interval bounded sharply below by relatively impervious mud clast breccia carbonate and barite cementation near the seabed could eventually result in localized ponding or redirection of fluid flow in the shallow subsurface near the center of the active field a barite zone originating from reaction of hydrothermal ba with residual highly fractionated seawater sulfate barite 34 s 44 5 is found at 6 m below the seafloor

fluid circulation in the active emerged asal rift east africa djibouti inferred from self potential and telluric telluric prospecting abstract in 1996 self potential sp and telluric telluric tt surveys were performed in the asal rift in the republic of djibouti in order to study water circulation through the rift from ghoubbet strait to asal lake located 11 km northwest and at the altitude of 155 m below sea level sp surveys reveal two main positive anomalies several kilometres wide up to 150 mv in amplitude parallel to the rift and separated by a relatively large 1 km negative anomaly the northern anomaly is well centred above the active rift the central part of the anomaly is cut by a sharp and narrow negative anomaly 200 mv in amplitude 150 m width due to a major fault running from ghoubbet strait to asal lake the two positive anomalies are interpreted by ground seawater flowing toward asal lake and warmed up during their advance by the strong geothermal flux existing beneath the rift the negative anomalies are most probably due to large and rapid fluid transfer along faults and high permeable geologic beds bending toward asal lake the rapid flow would prevent any large heating of the ground water the largest negative anomaly which isolates the two positive ones gives new valuable information on the tectonics the extension of the northern positive anomaly to the southwest is stopped by a fault located about 1 km to the north of a normal fault considered until now as a major rift structure the 16 telluric telluric tt surveys point out three behaviours of the telluric field near ghoubbet strait and inland the telluric field is well polarised in a n90 100 e direction and the amplitude expresses a medium to a low resistivity beneath the recording sites this pattern is the signature of the coast effect and the regional polarisation of the field along normal faults bordering the rift the se nw polarisation seems to be controlled by the rift tectonics inside the rift the telluric field becomes weaker indicating a decay of the resistivity in the central part of the rift the telluric field amplitude becomes 1 3 of the generally recorded amplitude and the polarisation cannot be estimated it is corresponding to very low resistive areas in agreement with high positive sp values

methane derived carbonate cementation of marine sediments from the kattegat denmark geochemical and geological evidence abstract methane derived carbonate cementation of holocene marine sediment occurs at several locations in the kattegat denmark generally the carbonate cemented sandstones occur at the seafloor as individual slabs or widely distributed thinly lithified pavements in some areas the lithified sandstones take the form of large and spectacular vertical pillar and mushroom like bodies standing up from the seafloor the carbonate cement consists of aragonite high mg calcite and dolomite the high mg calcite is the most widespread carbonate solid phase found aragonite is primarily associated with shell accumulations in the sediments so far dolomite has only been recorded as cement in the large vertical lithified sandstone bodies the carbonates are remarkably depleted in 13c i e generally in the range of 55 to 45 pdb and are therefore interpreted as being the result of methane oxidation by sulphate reducing bacteria in the anaerobic diagenetic zone of the sediments however the oxygen isotopic composition and the concentrations of minor elements indicate that carbonate precipitation took place under relatively constant temperature and salinity conditions in normal marine pore fluids the habit and mineralogy of the carbonate cemented sandstone observed most likely are controlled by the effect of bacterial activity and upward gas migration on the interstitial geochemical microenvironment the lithified sediments were subsequently exposed as spectacular sandstone formations on the seafloor by submarine erosion data from onshore exploration wells reveal that methane is encountered in eemian early weichselian late quaternary marine deposits the chemical composition and the isotopic signatures of the methane suggest a gas of microbial origin and it is thought that the gas is generated within the host marine quaternary sediment the locations of submarine gas seeps along with those of the carbonate cemented sandstone formations and the onshore gas seeps show a linear distribution which largely coincides with the extension of the fennoscandian border zone thus the seeps may be controlled by the structural framework in the northeastern part of the danish subbasin

rare earth elements in cold seep carbonates from the southwestern dongsha area northern south china sea the circulation of methane rich fluids at cold seeps often leads to the precipitation of seep carbonates close to the seafloor along continental margins which can be used as records of past fluid seepage rare earth element ree concentrations in seep carbonates have been used to trace fluid sources and provide information on associated biogeochemical processes at cold seeps the ree concentrations of a series of carbonates collected from cold seeps in the southwestern dongsha area of the northern south china sea are analyzed in this study the total ree contents sigma ree of the seep carbonates analyzed show a wide variation from 17 ppm to 523 ppm with an average sigma ree value of 54 ppm which are higher than the carbonates from other cold seep areas a positive correlation between fe mn content and sigma ree was observed these results suggest that the seep carbonates of this study were primarily controlled by the methane derived fluid from which they precipitated the fe rich dolomite and siderite which are the main components of the carbonates are responsible for the enrichment of the ree a slight positive ce anomaly observed in the shale normalized ree patterns of the studied seep carbonates suggests that they formed in anoxic conditions and the correlations between ce ce and la n sm n ce ce and dy n sm n ce ce and sigma ree further reveal that the ree characteristics of most seep carbonate samples preserve the original redox conditions in which they precipitated and late diagenesis has had little effect on the ree however the ree characteristics of sub samples ds2 2b ds1 6a and ds1 7a are very different from those of the other sub samples indicating a greater impact of late diagenesis and post oxidation favored ree enrichment c 2014 elsevier ltd all rights reserved

macro and micro fauna from cold seeps in the palmahim disturbance israeli off shore with description of waisiuconcha corsellii n sp bivalvia vesicomyidae abstract chemosymbiotic micro and macro fauna related to cold seep sites were recovered in the palmahim disturbance pd offshore israel during eu eurofleets2 semseep cruise by box coring and remotely operated vehicle rov dives no live macrofauna was identified in the collected sediments with the exception of the seep related crustacean calliax lobata de gaillande and lagardere 1966 numerous calliax claws testify the past colonization of these soft bottoms by several generations of this ghost shrimp after sediment sieving on 1 mm we identified gastropods belonging to the families trochidae eucyclidae unassigned seguenzioidea genus anekes rissoidae elachisinidae raphitomidae mangeliidae architectonicidae orbitestellidae and acteonidae the identified bivalves belong to the families nuculidae yoldiidae mytilidae lucinidae thyasiridae semelidae kelliellidae vesicomyidae xylophagidae and cuspidariidae a seep related group of chemosymbiotic molluscs was detected including taranis moerchii malm 1861 lurifax vitreus waren and bouchet 2001 idas ghisottii waren and carrozza 1990 lucinoma kazani salas and woodside 2002 thyasira biplicata philippi 1836 isorropodon perplexum sturany 1896 and the newly described vesicomyid species waisiuconcha corsellii n sp that represents also the first record of the genus waisiuconcha in recent mediterranean sediments the rov dives recorded local patches of several m2 of seafloor covered by dead shells of l kazani with a density of up to about 200 loose shells per square meter the potential occurrence of seep related foraminifera among low oxygen tolerant species was explored by comparison with previously sampled adjacent localities and lead to the identification of chilostomella oolina globobulimina affinis and g pseudospinescens as potential foraminiferal seep indicators in the southeastern mediterranean sea the absence of live seep related fauna in surface sediments in the pd where seepage has been confirmed suggests intermittent activity and a pause or decline of the investigated seeps

large scale flank collapse events during the activity of montagne pelee martinique lesser antilles 1 a horseshoe shaped structure already identified on the southwestern flank of montagne pelee martinique lesser antilles arc was previously interpreted as resulting of a flank collapse event but no debris avalanche deposits were observed at the time new offshore high resolution bathymetry and geophysical data aguadomar cruise december 1998 to january 1999 r v l atalante lead us to identify three debris avalanche deposits on the submarine western flank of montagne pelee extending down to the grenada basin they display morphological fronts and hummocky morphology on bathymetric data speckled pattern on backscatter data and hyperbolic facies on 3 5 khz and seismic profiles new on land geological studies lead us to identify two other horseshoe shaped structures on the same flank of the volcano the three submarine deposits have been traced back to the structures identified on land which confirms the occurrence of repeated flank collapse events during the evolution of montagne pelee the ages of the last two events are estimated at 9 ka and 25 ka on the basis of 14c and 238u 230th dates every flank collapse produced debris avalanches which flowed down to the caribbean sea we propose that the repeated instabilities are due to the large asymmetry of the island with western aerial and submarine slopes steeper than the eastern slopes the asymmetry results from progressive loading by accumulation of volcanic products on the western slopes of the volcano and development of long term gravitational instabilities meteoric and hydrothermal fluid circulation on the floor of the second flank collapse structure also creates a weakened hydrothermalized area which favors the recurrence of flank collapses

fluid flow and mass flux determinations at vent sites on the cascadia margin accretionary prism fluid venting from the toe of the accretionary prism off oregon was measured in situ during a series of dives with dsrv alvin in 1987 and 1988 a benthic chamber was placed over active vent sites to sequentially collect samples of venting fluids and to make direct measurements of discharge rates calibrated flow meter measurements and flow rates determined from dissolved methane transfer indicate that discharge from two vent sites alvin 1428 and alvin 1900 ranges roughly between 100 and 500 l m 2 d 1 with the most reliable estimates falling in the range of 125 150 l m 2d 1 these rates imply subsurface advective flow on the order of 100 m yr 1 comparison of observed discharge rates with rates calculated for steady state expulsion supported by accretion related compaction indicates that the observed flow is greater than predicted flow by several orders of magnitude the disparity dictates that fluids are not derived locally but are transported laterally within the prism or that flow is not steady state and that individual vents are short lived features in the ongoing accretion process

analysis of bubble plume distributions to evaluate methane hydrate decomposition on the continental slope cascadia margin sediments contain a rich reservoir of carbon derived both from terrestrial input and sea surface productivity a portion of this carbon exists as solid gas hydrate within sediment pore spaces which previous studies have shown to be a methane reservoir of substantial size on both the vancouver island and oregon portions of the cascadia margin multichannel seismic reflection profiles on the cascadia margin show the widespread presence of bottom simulating reflectors bsrs within the sediment column indicating the gas hydrate reservoir extends from the deformation front at 3000 m depth to the upper limit of gas hydrate stability near 500 m water depth in this study we compile an inventory of methane bubble plume sites on the cascadia margin identified in investigations carried out for a range of interdisciplinary goals that also include sites volunteered by commercial fishermen high plume density anomalies are associated with both the continental shelf 180 m and the depth of the upper limit of methane hydrate stability depth mhsd that occurs near 500 m in the ne pacific the observed anomalies on the cascadia slope may be due to the warming of seawater at intermediate depths suggesting that modern climate change has begun to destabilize the climate sensitive hydrate reservoir within the cascadia margin sediments reanalysis of similar plume images on the north american atlantic slope suggests a lack of correlation between observed plume depths and the mhsd for much of the latitudinal range

deep water hydrocarbon seeps in guaymas basin gulf of california abstract acoustically discovered hydrocarbon seeps along a transform fault zone on the sonoran margin of guaymas basin and in the southern trough of guaymas basin were examined and sampled during dives of dsv alvin seepage of methane and heavier hydrocarbons occurs through shallow pockmarks along the eroding crest of a steep anticline 1600 m below sea level extensive ledges of aragonite crop out around the rims of the pockmarks isotopic analysis indicates that carbonate precipitation is a result of methane oxidation seepage zones within the pockmarks support dense communities of calyptogena half buried in the mud tubeworms lamellibracheae sp have colonized many of the aragonite outcrops though the margin site is only a few kilometers from a high temperature sulfide precipitating and petroleum discharging vent system at a nearby center its structural setting is more akin to pockmarks described from continental shelves and its chemosynthetic fauna is more like that around low temperature seeps on other continental slopes and margins e g oregon u s a and japan the seep in the southern trough is a condensate type petroleum c 1 c 40 and rises as a plume from a young vent mound system about 2000 m below sea level

a study of the chemistry of pore fluids and authigenic carbonates in methane seep environments kodiak trench hydrate ridge monterey bay and eel river basin analyses of the chemical and isotopic composition of carbonates rocks recovered from methane seepage areas of the kodiak trench hydrate ridge monterey bay clam flats and the eel river basin coupled with the studies of the chemistry of the pore fluids have shown that these carbonates have grown within the sediment column geochemical profiles of pore fluids show that in deep water seeps kodiak trench 4450 m monterey bay 1000 m hydrate ridge 650 m 13c dic values are low isotopically light whereas in the eel river area 350 500 m 13c dic values are much higher isotopically heavier in all cases the 13c values indicate that processes of methane oxidation associated with sulfate reduction are dominant in the shallow sediments data on the isotopic composition of authigenic carbonates found at sites in kodiak trench eel river basin south and eel river basin north indicate a variable composition and origin in different geochemical environments some of the authigenic carbonates from the study sites show a trend in their 13c values similar to those of the pore fluids obtained in their vicinity suggesting formation at relatively shallow depths but others indicate formation at greater sediment depths the latter usually consist of high magnesium calcite or dolomite which from their high values of 13c up to 23 and 18o up to 7 5 suggest formation in the deeper horizons of the sediments in the zone of methanogenesis these observations are in agreement with observations by other workers at hydrate ridge in monterey bay and in the eel river basin

microbial methane oxidation and sulfate reduction at cold seeps of the deep eastern mediterranean sea abstract the eastern mediterranean hosts a variety of active cold seep systems such as gas chimneys mud volcanoes and pockmarks in water depths of 500 to 3200 m as part of the nautinil expedition in 2003 the sediments of cold seeps on the nile deep sea fan ndsf were sampled for the first time for biogeochemical and microbiological analyses here we compare rates of the anaerobic oxidation of methane aom and sulfate reduction sr as well as the microbial community structure of a variety of cold seep systems including mud volcanoes pockmarks and brine seeps our results revealed strong differences in microbial activity among the different seep systems of the eastern central and western provinces of the ndsf as well as the olimpi field central mediterranean ridge integrated over a sediment depth of 10 cm below the seafloor sr rates ranged from 0 1 66 mmol m 2 d 1 and aom rates from 0 1 3 6 mmol m 2 d 1 sr was often considerably higher than methane oxidation indicating that electron donors other than methane were utilized in general the lowest rates were associated with pockmarks and carbonate pavements and highest rates with bacterial mats above the gassy sediments of mud volcano centers 16s rrna gene analysis and fluorescence in situ hybridization fish revealed the presence of all known groups of marine methane oxidizing archaea i e anme 1 2 3 and also of methane oxidizing bacteria i e methylobacter sp and relatives in some seep sediments presumably syntrophic sulfate reducing bacterial partners of anmes were also detected in association with the anmes several anmes formed consortia with unknown bacterial partners the microbial community structure reflected the presence of typical seep microorganisms at all sites investigated but differed to varying extents between the different types of seeps despite the high availability of methane and sulfate methanotrophic microbial activity and biomass were lower at the seeps of the eastern mediterranean compared to those of other continental margins for unknown reasons

paleo methane emissions recorded in foraminifera near the landward limit of the gas hydrate stability zone offshore western svalbard we present stable isotope and geochemical data from four sediment cores from west of prins karls forland ca 340 m water depth offshore western svalbard recovered from close to sites of active methane seepage as well as from shallower water depths where methane seepage is not presently observed our analyses provide insight into the record of methane seepage in an area where ongoing ocean warming may be fueling the destabilization of shallow methane hydrate the 13c values of benthic and planktonic foraminifera at the methane seep sites show distinct intervals with negative values as low as 27 8 that do not coincide with the present day depth of the sulfate methane transition zone smtz these intervals are interpreted to record long term fluctuations in methane release at the present day landward limit of the gas hydrate stability zone ghsz shifts in the radiocarbon ages obtained from planktonic foraminifera toward older values are related to methane derived authigenic carbonate overgrowths of the foraminiferal tests and prevent us from establishing the chronology of seepage events at shallower water depths where seepage is not presently observed no record of past methane seepage is recorded in foraminifera from sediments spanning the last 14 ka cal bp 14c ams dating 13c values of foraminiferal carbonate tests appear to be much more sensitive to methane seepage than other sediment parameters by providing nucleation sites for authigenic carbonate precipitation foraminifera thus record the position of even a transiently stable smtz which is likely to be a characteristic of temporally variable methane fluxes

resistivity and self potential changes associated with volcanic activity the july 8 2000 miyake jima eruption japan abstract the miyake jima volcano abruptly erupted on july 8 2000 after 17 years of quiet and gave birth to a crater 1 km in diameter and 250 m deep this expected unrest was monitored during the years 1995 2000 by electromagnetic methods including dc resistivity measurements and self potential sp surveys beneath the 2500 yr old hatcho taira summit caldera audio magnetotelluric soundings made in 1997 98 identified a conductive medium 200 500 m thick within the 50 m isoline located at a few hundred metres depth it was associated with the active steady state hydrothermal system centred close to the 1940 cone and extending southward a dc resistivity meter set in a schlumberger array with 600 1000 and 1400 m long injection lines evidenced strong resistivity changes between september 1999 and july 3 2000 in the vicinity of the newly formed crater the apparent resistivity has reached about three times its initial values on the 1400 m long line and has lowered to about 20 on the 600 m line just prior to the july 8 2000 eruption sp mapping made inside the summit hatcho taira caldera revealed negative anomalies where positive ones had occurred during the previous tens of years the largest negative anomaly 225 mv in amplitude mainly took place above the 1940 cone which collapsed in the crater formation a permanent 1 km long sp line across the caldera suggests accelerating changes during the 3 months preceding the eruption on a larger scale the comparison between 1995 and 2000 surveys has shown a global increase of the hydrothermal activity beneath the volcano its source could have been 250 m to the south of the crater these observations suggest that the hydrothermal system was slowly disturbed in the months preceding the eruption while drastic changes have occurred during the 2 weeks before the summit collapse when tectonic and volcanic swarms have appeared

anaerobic oxidation of methane in a cold water coral carbonate mound from the gulf of cadiz the gulf of cadiz is an area of mud volcanism and gas venting through the seafloor in addition several cold water coral carbonate mounds have been discovered at the pen duick escarpment amidst the el arraiche mud volcano field on the moroccan margin one of these mounds named alpha mound has been studied to examine the impact of the presence of methane on pore water geochemistry potential sulphate reduction sr rate and dissolved inorganic carbon dic budget of the mound in comparison with off mound and off escarpment locations pore water profiles of sulphate sulphide methane and dic from the on mound location showed the presence of a sulphate to methane transition zone at 350 cm below the sea floor this was well correlated with an increase in sr activity 13c depleted dic at the transition zone 21 9 vs vienna pee dee belemnite indicated that microbial methane oxidation significantly contribute to the dic budget of the mound the alpha mound thus represents a new carbonate mound type where the presence and anaerobic oxidation of methane has an important imprint on both geochemistry and dic isotopic signature and budget of this carbonate mound

characteristics and possible origin of native aluminum in cold seep sediments from the northeastern south china sea abstract although native aluminum al has been reported to occur in various geological settings for more than 20 locations but its mechanism of formation still remains to be elucidated we report the occurrence and characterization of al particles recovered from the surface sediment cf4 and a short core sediment rov g 37 cm length obtained at cold seeps in the northeastern continental slope ncs of the south china sea scs x ray diffraction analysis shows that the collected particles are metallic aluminum with the unit cell edge a of 4 059 0 005 a cf4 2 and 4 029 0 004 a t26 28 2 rov g the al particles occur as spherules irregular plates and elongated forms with typical lamellar structures their chemical compositions are 95 07 99 84 al the average values is 98 42 with very small amounts of si fe ti s zn mg ca k na cu co and p and are similar to al particles from the east pacific rise and the central indian basin but differ markedly to those from other locations after ruling out several possibilities of al sources and mechanism of formation an alternative cold seep mechanism is proposed for the origin of al in the scs during the processes of anaerobic oxidation of methane aom and pyrite formation high h2s and h2 partial pressures result in strong reducing micro environments under which al oh 4 is reduced to its metallic state by the microbial bacterial processes

a late miocene methane seep deposit bearing methane trapping silica minerals at joetsu central japan abstract the modern japan sea is characterized by active methane seeps associated with gas hydrates but their ancient counterparts are not fully understood this study describes a newly discovered methane seep carbonate block the nakanomata seep deposit from the upper miocene nodani formation in joetsu city central japan the age of this deposit is constrained to 7 5 6 5 ma based on its fossil diatom assemblage the deposit contains molluscan fossils typical of methane seeps including vesicomyid and bathymodiolin bivalves and provannid gastropods and it retains an almost entirely aragonitic mineralogy despite its miocene age it is composed of clotted microcrystalline aragonite containing nodules and intraclasts and is crosscut by vein like networks of voids and cavities rimmed with acicular aragonite the 13c values of the carbonate phases are as low as 41 1 and the presence of lipid biomarkers pentamethylicosane and crocetane suggests that the deposit originated from the anaerobic oxidation of methane it is suggested that an initially diffuse methane seepage formed the micritic nodules followed by a more rapid and intense methane seepage that led to the development of abundant voids in the sediment finally the sediment was cemented by microcrystalline aragonite and void lining acicular aragonite the seep deposit also contains peculiar globular silica minerals and authigenic quartz during their precipitation these globular silica minerals may have trapped methane gas bubbles and the minerals may be pseudomorphs after silica clathrate sufficient increase in ph and supersaturation of silica which led to the dissolution and subsequent precipitation of these silica minerals could have resulted from the degassing of carbon dioxide promoted by an effective supply of methane and its supersaturation thus forming gas bubbles

last glacial emplacement of methane derived authigenic carbonates in the sea of japan constrained by diatom assemblage carbon 14 and carbonate content abstract we studied diatom assemblages and caco 3 contents of methane derived authigenic carbonates from the eastern margin of the sea of japan and assessed the formation time of these samples radioactive 14 c date was determined in selected samples to obtain the maximum age of the time the results of our study suggest mass formation of carbonate nodules in a glacial period within 40 ky consistent with a published u th dating result of carbonate nodules in the study area diatom assemblages and contents in the carbonate nodules abundance of 10 6 g dominance of neritic littoral species warm cold water species ratio lower than 25 differ from the near seafloor sediments in the study area which have characteristics of holocene sediments in the sea of japan and suggest cementation of glacial sediments laminated sediments in some nodule samples are glacial sediments because laminations are records of a low sea level period in the semi enclosed ocean similarity of diatom assemblages and contents in all carbonate samples is another evidence of glacial sediments in nodules glacial sediments with oceanic cold water species as low as holocene sediments restricts the sediment age to before 20 cal ky bp carbonate contents higher than 78 wt suggest the cementation of poorly compacted sediments near the seafloor and the date of carbonate cementation is therefore close to that of the cemented sediments most carbonate nodule samples in this study were formed in a glacial period and detection of 14 c restricts this period to within 40 ky

integrated geophysical studies in the east indian geothermal province integrated geophysical surveys using vertical electrical sounding ves very low frequency vlf em radiation counting total magnetic field and self potential sp measurements are carried out to characterize the geothermal area around a hot spring in the nayagarh district orissa india that lies in the east indian geothermal province the study was performed to delineate the fracture pattern contaminated groundwater movement and possible heating source ves interpretations suggest a three to four layer structure in the area resistivity survey near the hot spring suggests that weathered and fractured formations constitute the main aquifer system and extend to 60 m depth current flow measured at various electrode separations normalized by the applied voltage suggests that fractures extend to a greater depth detailed vlf study shows that fractures extend beyond 70 m depth vlf anomaly has also very good correlation with the total magnetic field measured along the same profiles study results suggest that a gridded pattern of vlf survey could map the underground conductive fracture zones that can identify the movement of contaminated groundwater flow therefore precautionary measures can be taken to check further contamination by delineating subsurface conducting structures self potential sp measured over the hot spring does not show a large anomaly in favor of the presence of a sulphide mineral body a small positive 5 15mv sp anomaly is measured which may be streaming potential due to subsurface fluid flow a high radiation is measured about four kilometers from the hot spring suggesting possible radiogenic heating however the exact nature of the heating source and its depth is not known in the area deep resistivity followed by a magneto telluric survey could reveal the deeper structures

u th dating and post depositional alteration of a cold seep carbonate chimney from the campos basin offshore brazil abstract dating authigenic cold seep carbonates allows determining the timing of active seepage of hydrocarbon rich fluids at continental margins and ultimately the detection of the geological factors affecting it u th dating has been selected in this study the method having been successfully used before however incorporation of initial thorium in substantial amounts of detrital material due to the precipitation of carbonates within the seabed and post depositional alteration potentially pose a major problem violating the basic assumptions of the method here we report results from several samples from the campos basin off the coast of brazil they are unusual in their high 13 c values mean of 10 0 vpdb high detrital contents and being dominantly dolomite elevated 230 th 238 u activity ratios indicate that most of the carbonates lost uranium during diagenesis isochrones are obtained from the unaffected samples yielding an age of 140 4 3 1 ka vertical growth of the chimney must have been short and rapid since results from the top and bottom parts of the chimney concur within analytical uncertainties furthermore profiles of u th radioisotope specific activity 234 u and 232 th specific activity on two quarter slices of a carbonate chimney reveal the occurrence of three distinct diagenetic processes u loss u exchange with seawater and th gain

the past 5 000 years of volcanic activity at mt pelee martinique f w i implications for assessment of volcanic hazards the history of mt pelee martinique was subdivided into three stages based on field geology and 14c data the two first stages constructed an ancient mt pelee and an intermediate cone between 0 4 m y and 19 500 y b p the third or present stage started 13 500 years ago after a repose of 6 000 years this paper focuses on the activity of mt pelee during the past 5 000 years as a means to assess and zone volcanic hazards of the 23 magmatic eruptions during the past 5 000 years the ages of 21 eruptions of this period are based on 75 new 14c dates the types of phenomena and distribution of pyroclasts relate to four main types of activity the first type consists of pumice and ash flows that are not preceded by a plinian fall two eruptions named p6 and p4 illustrate this type for which the mixture of gas ash and pumice simply overflow the vent and flood several valleys the second type differs from the first by the occurrence of a preliminary moderate plinian fall stage four eruptions p5 p31 p2 and p1 illustrate this type two eruptions p32 and p33 experienced cataclysmic plinian explosions and pumiceous surges the third type is related to dome growth with the rise of viscous spines and the production of related block and ash flows five eruptions 1929 sept 1902 1904 npm nab2 and nmp illustrate this type the fourth type is characterized by violent ejection of more or less heterogeneous nuees ardentes the direction of the blast dictated by the morphology of the crater has been towards the south several times at mt pelee four eruptions may 1902 nab1 nrp2 and nrp3 belong to this type future magmatic eruptions at mt pelee will very likely belong to one of these four types assessment of hazards at mt pelee is based upon the behavior of the volcano during the past 5 000 years because 1 recognition of past magmatic eruptions is quite complete and well dated and 2 no structural change has occurred in the volcano a probabilistic and statistical approach has been tentatively followed stochastic models of wickman indicate a the chance that contemporary abnormal seismic and or phreatic activity at the volcano would signal an impending magmatic eruption is 20 percent b mt pelee exhibits a complex loading time behavior that may be related to the buffering effect of a magma chamber time is needed following a single or several closely spaced eruptions to establish conditions to initiate a new eruption and c if the 1929 event can be regarded as the last episode of the major 1902 eruption the volcano could remain in a dormant stage with respect to magmatic events for another century

ζ potential measurement of volcanic rocks from aso caldera 1 we deduced the z potential of various rocks in aso caldera from streaming potential measurements in laboratory in contrast to the conventional observation that the z potential of crustal rocks is mostly negative under typical geologic conditions almost half of the samples equilibrated with dilute kcl solution show positive values of z potential at ph 4 5 5 5 the samples showing positive z are characterized by relatively low sio2 content and abundance of elements having high isoelectric points and found to be localized around the summit of mt takadake where the positive correlation between self potential sp and altitude is observed we emphasize that measurements of z potential of volcanic rocks are very important to give more appropriate interpretations of sp data from volcanic fields index terms 0634 electromagnetics measurement and standards 0925 exploration geophysics magnetic and electrical methods 5199 physical properties of rocks general or miscellaneous 8499 volcanology general or miscellaneous 1832 hydrology groundwater transport citation hase h t ishido s takakura t hashimoto k sato and y tanaka z potential measurement of volcanic rocks from aso caldera geophys res lett 30 23 2210 doi 10 1029 2003gl018694 2003

zeta potential estimation of volcanic rocks on 11 island arc type volcanoes in japan implication for the generation of local self potential anomalies 1 from streaming potential measurements we deduced the zeta potential of 73 volcanic rock samples collected in 11 volcanoes where self potential sp surveys had also been conducted experiments with crushed rock samples and 0 001 mol l nacl solution showed a large variation in streaming potential coefficient which ranged from 2860 to 2280 mv mpa deduced zeta potential ranged from 45 1 to 37 2 mv among the 73 samples 9 samples showed positive values and 11 samples showed small absolute values less than 10 mv even in a volcano the zeta potential values of rocks were sometimes highly variable to investigate the reason for the variation in zeta potential we performed x ray fluorescence xrf measurements on the rock samples however no significant correlations between zeta potential or isoelectric point and weight percentage of major elements were found implying that the zeta potential of the volcanic rocks is not controlled by chemical composition but by mineralogical composition or crystalline structure in volcanic areas rocks with positive or small absolute values of zeta potential which are considered to be unusual frequently exist in areas along with local positive sp anomalies although positive sp anomalies are usually interpreted as an indication of hydrothermal upflow this correlation suggests that in addition to the groundwater flow pattern the polarity of zeta potential should also be considered for interpretation of sp data therefore in cases where detailed zeta potential measurements have not been conducted local positive sp anomalies should be interpreted with caution

mapping and surveillance of active fissure zones on a volcano by the self potential method etna sicily abstract the self potential s p method often employed in base metal exploration has successfully been applied to volcanological problems test surveys on the site of mount etna sicily have revealed some positive anomalies as high as a few hundred millivolts over recent and old eruptive fissures the s p technique allows one to determine the precise location of the fissures the interpretation of the geophysical results including s p taking into account the structure of mount etna has shown two important zones upon which several s p investigations have been carried out studies of the causes of these s p anomalies have shown the importance of the streaming potential as the principal source mechanism

fluid flow and origin of a carbonate mound offshore vancouver island seismic and heat flow constraints a 1 5 km long 1 km wide and 70 80 m high carbonate mound was identified on the mid slope region of the subduction accretionary sedimentary prism offshore vancouver island 3 5 km west of ocean drilling program odp site 889 and integrated ocean drilling program iodp site u1327 seabed video images show the presence of seafloor carbonate as well as chemosynthetic communities a high resolution single channel seismic survey with close line spacing recording coherent reflectivity down to about 400 m beneath the seafloor provided acoustic images of this mound and of the gas hydrate bottom simulating reflector bsr beneath it the mound is interpreted to have developed as a structural topographic high in the hanging wall of a large reverse fault formed at the base of the current seaward slope the fault zone provides pathways for fluids including gas to migrate to the seafloor where diagenetic carbonate forms and cements the near surface sediments to examine the thermal effect of possible upward fluid flow beneath the mound heat flow at the mound and in the neighbouring region was calculated from the depth of the bsr below the seafloor these data were combined with heat flow calculated over a broader region from previous multi channel seismic data heat flow within the flattest portion of the surrounding 4 km by 8 km region averages 74 mw m2 taking this value to represent the regional or background heat flow a simple 2d analytical method was used to calculate theoretical heat flow variations due to topography across the mound most of the variability is explained by topographic effects including a local 6 mw m2 negative anomaly over the central mound and a large 20 mw m2 positive anomaly over the mound steep side slope however just south of the mound there is a 6 7 mw m2 positive anomaly in a 2 km long band that has predominantly flat seafloor most of this anomaly is probably unrelated to topographic effects but rather likely due to warm upward fluid flow along faults or fracture zones

interaction between hemipelagic sediment and a hydrothermal system middle valley northern juan de fuca ridge subarctic northeast pacific abstract slightly hydrothermally altered sediments were recovered from a sedimented rift valley with active hydrothermal discharge the sediment consists mainly of terrigenous material with a low content of biogenic components in spite of the alteration glacial and non glacial periods are still discernable based on lithology mineralogy carbonate content and bulk sediment geochemistry in the vicinity of the core studied extremely high heat flow anomalies and the presence of active black smokers suggest a rapid discharge of hydrothermal fluids along discrete pathways such as coarse grained turbidite layers or faults in the biogenic rich fine grained sediments diffuse transport can supply the components and allow the time necessary for the formation of authigenic phases such as carbonate concretions gypsum barite often mg rich amorphous silica and mg rich silicates stevensite mg rich amorphous silica could be the precursor of the mg rich silicates commonly found associated with hydrothermal deposits carbon and oxygen isotopic results on the carbonate nodules suggest 1 that the carbon in the nodules could be partly derived from methane which would have been oxidized at the oxic anoxic boundary and in the sulphate reduction zone and 2 that successive cycles of hydrothermal fluid migration through the sediment could explain the variability in the results

preliminary video spatial analysis of cold seep bivalve beds at the base of the continental slope of israel palmahim disturbance abstract seafloor video surveys were carried out with the rov max rover in the palmahim disturbance pd area offshore israel in september 2016 during the eurofleets2 semseep cruise on board the r v aegaeo preliminary observations of distribution and frequencies of bivalve accumulations show that they are mostly composed by lucinoma kazani shells valves are distributed mainly along the base of authigenic carbonate crusts in association with bacterial mats and inside inactive chimney like structures sometimes associated with crabs and living tubeworms however no living molluscs were observed the relation between distribution of bivalve beds and seepage activity is not straightforward in the pd area however the presence of these accumulations and the size of l kazani suggest that seepages may have lasted for at least one decade before its reduction cessation that induced l kazani mortality the presence of few articulated valves of this species indicates that they were alive up to one year before the rov observations and their different preservation state may imply different seepage phases this research shows that chemosymbiotic benthic communities may be used as a proxy for better understanding the past dynamics of fluid emissions at the seafloor however further quantitative studies are needed to confirm these observations

geological imprint of methane seepage on the seabed and biota of the convergent hikurangi margin new zealand box core and grab carbonate results abstract short box cores to 30 cm bsf and seafloor carbonate grab samples were acquired at mapped hydrocarbon seep sites 600 1200 m water depths during the 2007 rv sonne so191 cruise on the hikurangi margin offshore eastern north island new zealand to evaluate the influence of methane seepage on sedimentologic biotic mineralogic and stable isotopic attributes of seabed sediments sedimentary horizons in the box cores consist of siliciclastic silts and sands shell beds and nodular microcrystalline aragonite bands up to 15 cm thick the megafauna is dominated by infaunal to semi infaunal chemosymbiotic bivalves calyptogena lucinoma and acharax as well as associated worms and carnivorous and grazing gastropods burrows in silts some occupied by worms or juvenile acharax mainly have simple morphologies more typical of high energy nearshore settings than deep sea environments while a few are large and sparsely branched with wall scratch marks inferred to be of decapod crustacean origin the box core silts and nodular carbonate samples vary in toc content from 0 2 to 0 9 wt carbonate content from 4 to 78 and 13 c and 18 o values from 50 3 to 0 6 pdb and 0 77 to 3 2 pdb respectively low carbonate content silt samples have the most enriched 13 c values implying a seawater source for their pore water bicarbonate negative 13 c and positive 18 o values typify the nodular microcrystalline aragonite bands indicating formation during microbially mediated sulphate dependent anaerobic oxidation of methane aom in a cold near seafloor environment as is also supported by lipid biomarker data a clear isotopic mixing trend of decreasing 13 c and increasing 18 o and carbonate content in the fine seafloor grab carbonate samples show greater textural variability and are divided into two types fresh appearing grey to white blocks yield similar mineralogic isotopic and biomarker signatures to the nodular carbonate bands in the cores a largely seep related epifauna affiliated with these grab samples include chemosymbiotic bathymodiolin mussels siboglinid tube worms methanotrophic suberitid sponges and grazing limpets which in places are entombed within the carbonate by contrast some dark reddish to brown iron stained microcrystalline dolomitic slabs and tubular concretions support abundant non seep epifaunal encrusters from the surrounding deep sea indicative of long exposure on the seafloor distinct stable isotopic signatures of these exhumed dolostones 13 c c 20 pdb 18 o up to 7 pdb suggest derivation from an oxidised methane pool and pore fluid freshening by gas hydrate dissociation or from mobilized burial fluids that have undergone clay mineral dehydration

self potential modeling from primary flows this paper discusses a new method for the investigation of self potentials sp based on induced current sources the induced current sources are due to divergences of the convection current which is driven in turn by a primary flow either heat or fluid as a result of using this approach there is a shift in emphasis toward the vector flow field and its interaction with current cross coupling structure when compared with the total potential approach of nourbehecht 1963 which emphasized the primary flow potential and the voltage cross coupling this shift in emphasis is advantageous because it is analogous to the actual physical processes for example fluid flow in the ground gives rise to drag convection currents and the interaction of the convection currents with the electrical structure gives rise to the electrical potentials sp this simple physical picture should aid in developing a better intuitive understanding of the generation of sp effects the convective current approach is easily ada

fluid expulsion from the cascadia accretionary prism evidence from porosity distribution direct measurements and gloria imagery fluid expulsion from the cascadia accretionary prism off oregon results from porosity reduction by compaction and by cementation as methane rich pore waters precipitate diagenetic carbonate deposits near the sediment water interface porosity changes suggest that dewatering begins 5 6 km west of the base of the slope in a proto deformation zone gloria imagery of surficial carbonate deposits confirms that fluid is actively expelled from this zone there is no such evidence further west in cascadia basin within the uncertainties of the data porosities do not decrease landward beneath the prism this pattern is consistent with imbricate thrust faulting on the slope which provides the vertical load to induce compactive dewatering and may physically import as much as 50 of the total fluid volume in the section a simple vertical compaction model suggests that significant pore water volumes have been expelled from the lower slope but at flux rates 10 11 10 12 m 3 m 2 s 1 which are orders of magnitude less than those measured at individual vent sites 10 6 m 3 m 2 s 1 faulting clearly controls some fluid expulsion but gloria data suggest that repeated local discharge cementation and abandonment lead to dispersed accumulations of diagenetic carbonate

fluid venting in the eastern aleutian subduction zone fluid venting has been observed along 800 km of the alaska convergent margin the fluid venting sites are located near the deformation front are controlled by subsurface structures and exhibit the characteristics of cold seeps seen in other convergent margins the more important characteristics include 1 methane plumes in the lower water column with maxima above the seafloor which are traceable to the initial deformation ridges 2 prolific colonies of vent biota aligned and distributed in patches controlled by fault scarps over steepened folds or outcrops of bedding planes 3 calcium carbonate and barite precipitates at the surface and subsurface of vents and 4 carbon isotope evidence from tissue and skeletal hard parts of biota as well as from carbonate precipitates that vents expel either methane or sulfide dominated fluids a biogeochemical approach toward estimating fluid flow rates from individual vents based on oxygen flux measurements and vent fluid analysis indicates a mean value of 5 5 0 7 l m 2 d 1 for tectonics induced water flow wallmann et al 1997b a geophysical estimate of dewatering from the same area von huene et al 1997 based on sediment porosity reduction shows a fluid loss of 0 02 l m 2 d 1 for a 5 5 km wide converged segment near the deformation front our video guided surveys have documented vent biota across a minimum of 0 1 of the area of the convergent segment off kodiak island hence an average rate of 0 006 l m 2 d 1 is estimated from the biogeochemical approach the two estimates for tectonics induced water flow from the accretionary prism are in surprisingly good agreement

the primitive volcano of mount pelee its construction and partial destruction by flank collapse abstract the geology of mount pelee the active volcano of martinique lesser antilles has been actively studied during the past decade this paper reviews the current knowledge about the oldest least well known part of the volcano here called paleo pelee and the relations between paleo pelee and the mont conil volcanic complex paleo pelee consists mostly of volcanic breccias with a few lava flows it differs in this respect from neighbouring active volcanoes such as the grande decouverte soufriere in guadeloupe and the soufriere in st vincent the oldest products of which are mainly lava flows paleo pelee initially formed a regular cone which was comparable in size with the present edifice it is now largely eroded and its products form prominent radial ridges on the western flank of mount pelee these are buried under younger deposits on the eastern flank the uniformly andesitic breccias of paleo pelee are for the most part brecciated lava flows it is inferred that the activity of mount pelee was less explosive at this stage than during following periods neo pelee the paleo pelee formations overlap those of mont conil the geology of mont conil is poorly known however its lowest exposed products are submarine andesitic breccias cut by many dikes this contrasts with paleo pelee where all breccias are of subaerial origin pleistocene limestones are interbedded within the mont conil breccias between 120 and 150 m above sea level though mont conil seems to be closely linked to mount pelee on the basis of available petrological data a major uplift must have occurred sometime during or after the construction of mont conil and forms a recognizable geological boundary between the two volcanic systems the paleo pelee edifice was partially destroyed by a flank collapse event that occurred on the southwest flank during the early stage 40 000 20 000 y b p of neo pelee this event is evidenced by a large 6 2 5 km horseshoe shaped structure which is limited by well preserved morphological scarps on land and by a 300 m offshore scarp as shown by seabeam bathymetry paleo pelee breccias and lava flows are truncated by the boundary of the collapse structure lava domes occupied the upslope part of the structure at a later time these domes are intersected by the present crater etang sec which has probably been the active vent for at least 2000 years the active crater is located at the intersection between the flank failure depression and an older caldera formed at the paleo pelee stage but probably enlarged later the flank failure structure appears as a major structure of the volcano and creates a strong structural asymmetry in the edifice this fact should be considered when dealing with such various aspects as the hydrogeology of the volcano the structural control of past and future eruptions and the volcanic hazards

microbialite formation in seawater of increased alkalinity satonda crater lake indonesia abstract the crater lake of the small volcanic island satonda indonesia is unique for its red algal microbial reefs thriving in marine derived water of increased alkalinity the lake is a potential analogue for ancient oceans sustaining microbialites under open marine conditions current reef surfaces are dominated by living red algae covered by non calcified biofilms with scattered cyanobacteria and diatoms minor caco3 precipitates are restricted to the seasonally flooded reef tops which develop biofilms up to 500 m thick dominated by the cyanobacteria pleurocapsa calothrix phormidium and hyella microcrystalline aragonite patches form within the biofilm mucilage and fibrous aragonite cements grow in exopolymer poor spaces such as the inside of dead lysed green algal cells and reef framework voids cementation of lysed hadromerid sponge resting bodies results in the formation of wetheredella like structures hydrochemistry data and model calculations indicate that co2 degassing after seasonal mixis can shift the carbonate equilibrium to cause caco3 precipitation increased concentrations of dissolved inorganic carbon limit the ability of autotrophic biofilm microorganisms to shift the carbonate equilibrium therefore photosynthesis induced cyanobacterial calcification does not occur instead passive diffusion controlled eps mediated permineralization of biofilm mucus at contact with the considerably supersaturated open lake water takes place in contrast to extreme soda lakes the release of ca2 from aerobic degradation of extracellular polymeric substances does not support caco3 precipitation in satonda because the simultaneously released co2 is insufficiently buffered subfossil reef parts comprise green algal tufts encrusted by microstromatolites with layers of fibrous aragonite and an amorphous unidentified mg si phase the microstromatolites probably formed when lake satonda evolved from seawater to ca2 depleted raised alkalinity conditions because of sulfate reduction in bottom sediments and pronounced seasonality with deep mixing events and strong co2 degassing the latter effect caused rapid growth of fibrous aragonite while mg si layers replaced the initially mg calcite impregnated biofilms this could be explained by dissolution of siliceous diatoms and sponge spicules at high ph followed by mg calcite dissolution and mg silica precipitation at low ph due to heterotrophic activity within the entombed biofilms

lipid biomarkers preserved in hydrate associated authigenic carbonate rocks of the gulf of mexico anaerobic oxidation of methane aom is common in ocean margin sediments where it is mediated by consortia of archaea and bacteria and can result in the formation of authigenic carbonate including extensive carbonate crusts previous work indicates that aom is associated with gulf of mexico hydrocarbon seeps and is mediated by similar organisms as identified in other settings however biological investigations have not been done on the associated 13c depleted carbonates here we show that 13c depleted archaeal and bacterial biomarkers are abundant in gulf of mexico authigenic carbonate rocks revealing that aom mediating organisms are closely associated with carbonate authigenesis moreover the rocks share general characteristics of the background soft sedimentary archaeal and bacterial community inferred from biomarker analysis suggesting that the organisms associated with carbonate authigenesis are the same as those that live elsewhere in the hydrocarbon seep environment this provides further evidence that aom by archaea and sulfate reducing bacteria can result in the sequestration of significant quantities of methane derived carbon in carbonate rocks

fluid expulsion sites on the cascadia accretionary prism mapping diagenetic deposits with processed gloria imagery point discharge fluid expulsion on accretionary prisms is commonly indicated by diagenetic deposition of calcium carbonate cements and gas hydrates in near surface 10 m below seafloor mbsf hemipelagic sediment the contrasting clastic and diagenetic lithologies should be apparent in side scan images however sonar also responds to variations in bottom slope so unprocessed images mix topographic and lithologic information we have processed gloria imagery from the oregon continental margin to remove topographic effects a synthetic side scan image was created initially from sea beam bathymetric data and then was subtracted iteratively from the original gloria data until topographic features disappeared the residual image contains high amplitude backscattering that we attribute to diagenetic deposits associated with fluid discharge based on submersible mapping ocean drilling program drilling and collected samples diagenetic deposits are concentrated 1 near an out of sequence thrust fault on the second ridge landward of the base of the continental slope 2 along zones characterized by deep seated strikeslip faults that cut transversely across the margin and 3 in undeformed cascadia basin deposits which overlie incipient thrust faults seaward of the toe of the prism there is no evidence of diagenetic deposition associated with the frontal thrust that rises from the decollement if the decollement is an important aquifer apparently the fluids are passed either to the strike slip faults which intersect the decollement or to the incipient faults in cascadia basin for expulsion diagenetic deposits seaward of the prism toe probably consist dominantly of gas hydrates

snowball earth termination by destabilization of equatorial permafrost methane clathrate the recovery from the marinoan snowball ice age of about 635 million years ago is one of the most severe climate change events known to have occurred on earth hypotheses accounting for the abruptness of deglaciation include ice albedo feedback deep ocean out gassing during post glacial oceanic overturn or methane hydrate destabilization martin kennedy and colleagues now report the broadest range of oxygen isotope values yet measured in marine sediments in methane seeps in marinoan deglacial sediments underlying a thin interval of carbonate these deposits are thought to record widespread oceanic carbonate precipitation during postglacial sea level rise the range of values is likely the result of mixing between ice sheet derived meteoric waters and clathrate derived fluids during the flushing and destabilization of a clathrate field by glacial meltwater their findings suggest that methane released from low latitude permafrost clathrates acted as a trigger and or strong positive feedback for deglaciation and warming this paper reports the broadest range of oxygen isotope values yet measured in marine sediments in methane seeps in marinoan deglacial sediments underlying a thin interval of carbonate these deposits are thought to record widespread oceanic carbonate precipitation during postglacial sea level rise the range of values is likely the result of mixing between ice sheet derived meteoric waters and clathrate derived fluids during the flushing and destabilization of a clathrate field by glacial meltwater the start of the ediacaran period is defined by one of the most severe climate change events recorded in earth history the recovery from the marinoan snowball ice age 635 myr ago ref 1 marinoan glacial marine deposits occur at equatorial palaeolatitudes2 and are sharply overlain by a thin interval of carbonate that preserves marine carbon and sulphur isotopic excursions of about 5 and 15 parts per thousand respectively3 4 5 these deposits are thought to record widespread oceanic carbonate precipitation during postglacial sea level rise1 3 4 this abrupt transition records a climate system in profound disequilibrium3 6 and contrasts sharply with the cyclical stratigraphic signal imparted by the balanced feedbacks modulating phanerozoic deglaciation hypotheses accounting for the abruptness of deglaciation include ice albedo feedback3 deep ocean out gassing during post glacial oceanic overturn7 or methane hydrate destabilization8 9 10 here we report the broadest range of oxygen isotope values yet measured in marine sediments 25 to 12 in methane seeps in marinoan deglacial sediments underlying the cap carbonate this range of values is likely to be the result of mixing between ice sheet derived meteoric waters and clathrate derived fluids during the flushing and destabilization of a clathrate field by glacial meltwater the equatorial palaeolatitude implies a highly volatile shelf permafrost pool that is an order of magnitude larger than that of the present day a pool of this size could have provided a massive biogeochemical feedback capable of triggering deglaciation and accounting for the global postglacial marine carbon and sulphur isotopic excursions abrupt unidirectional warming cap carbonate deposition and a marine oxygen crisis our findings suggest that methane released from low latitude permafrost clathrates therefore acted as a trigger and or strong positive feedback for deglaciation and warming methane hydrate destabilization is increasingly suspected as an important positive feedback to climate change11 12 13 that coincides with critical boundaries in the geological record14 15 and may represent one particularly important mechanism active during conditions of strong climate forcing

origin of ultramafic hosted vein magnesite deposits abstract large deposits of magnesite mgco3 occur either as carbonated ultramafic rocks or as sedimentary beds the origins of both sedimentary and ultramafic hosted deposits remain controversial as does the relationship between them ultramafic hosted deposits are reviewed herein with an emphasis on veins rather than massive bodies magnesium apparently has been supplied to magnesite veins by their ultramafic host uncertainties concerning ultramafic hosted deposits include the source state and mode of transportation of carbon the cause of its precipitation and the mineralogy of the initial precipitate genetic questions about ultramafic hosted vein deposits are summarized with the aid of flow charts the preferred route through these charts attributes most vein magnesite to an influx of metamorphic degassing co2 and ch4 into groundwater which flows through serpentinite or peridotite the source of co2 ch4 is considered to be deeper than 10 km because metamorphism 300 c is required to release carbonaceous volatiles of the type which apparently induced observed magnesite mineralization however vein magnesite precipitation generally has occurred within just a few hundred meters of the earth s surface vein deposits are considered to be genetically related to massive bodies but the massive bodies typically contain less 12c the 12c rich co2 which has produced vein deposits is attributed to a fluid phase variably mixed ch4 co co2 which rose until it reached upper crustal groundwater the hypothetical water poor fluid presumably became slightly oxidized hence richer in soluble co2 as it encountered near surface sulfate bearing water co2 enriched water is envisioned to have been expelled regionally due to tectonic processes leaving little mineralogical evidence of its expulsion through non ultramafic rock co2 rich water which happened to encounter either serpentinite or peridotite presumably has produced magnesite vein deposits and a common silicate byproduct nontronite according to the following reaction 12 mg3si2o5 oh 4 serpentine 36 hco3 4 fe3o4 o2 12 fesi2o5 oh nontronite 36 mgco3 magnesite 36 oh 18h2o

the role of low temperature organic matter diagenesis in carbonate precipitation within a marine deposit abstract carbonate minerals in veins can record paleo hydrogeological information that enables the reconstruction of groundwater history this paper investigates the cause of differences in the occurrence of carbonate veins in the koetoi and wakkanai formations both neogene mudstone units in northwestern hokkaido from the perspective of controls on co2 supply from the alteration of organic matter carbonate veins are rare in the koetoi formation but are widespread in the wakkanai formation this area is a region of oil and gas accumulation where deep groundwater is saturated mainly with ch4 and co2 the results show high 13c values in co existing ch4 32 6 and co2 31 0 gases an investigation of 13c d systematics among these gases indicates that isotopic fractionation was caused by microbial co2 reduction although total organic carbon content in the koetoi formation decreases with increasing depth total organic content in the wakkanai formation remains roughly constant with depth furthermore although 13c values also show depth dependence values from the wakkanai formation are higher than those from the koetoi formation this 13c enrichment could be explained by rayleigh fractionation in a closed system based on these results the processes behind the formation of the carbonate veins can be summarized as follows carbon dioxide behavior is thought to play an important role with respect to carbonate formation because co2 abundance is closely linked to ph and pressure in shallow sedimentary rocks such as the koetoi formation that have started to experience diagenetic alteration of organic matter co2 in groundwater is supplied by microbial decomposition of organic matter and is reduced to ch4 by methanogens in deep sedimentary rocks such as the wakkanai formation that have undergone diagenesis but have only experienced moderate temperatures so that thermal decomposition of organic matter has not yet begun microbial degradation of organic matter has proceeded too far for any more co2 to be produced thus carbonate precipitation is initiated when ph rises due to microbial co2 reduction the contrast between the occurrence of carbonate veins in the koetoi and wakkanai formations can be explained by our results which can also be applied to general carbonate behavior in marine sedimentary rocks

the structure of a hydrothermal system from an integrated geochemical geophysical and geological approach the ischia island case study the complexity of volcano hosted hydrothermal systems is such that thorough characterization requires extensive and interdisciplinary work we use here an integrated multidisciplinary approach combining geological investigations with hydrogeochemical and soil degassing prospecting and resistivity surveys to provide a comprehensive characterization of the shallow structure of the southwestern ischia s hydrothermal system we show that the investigated area is characterized by a structural setting that although very complex can be schematized in three sectors namely the extra caldera sector ecs caldera floor sector cfs and resurgent caldera sector rcs this contrasted structural setting governs fluid circulation geochemical prospecting shows in fact that the caldera floor sector a structural and topographic low is the area where co2 rich 40 cm3 l hydrothermally mature log mg na ratios 150 g m 2 d 1 is clearly captured by electrical resistivity tomography ert and transient electromagnetic tem surveys as a highly conductive resistivity 10 000 mg l and poorly conductive meteoric derived tds 4 000 mg l waters are observed respectively we finally integrate our observations to build a general model for fluid circulation in the shallowest 0 5 km part of ischia s hydrothermal system

continental margin tectonics submarine accretionary prisms submarine accretionary prisms are sites of incipient mountain building where sediments and rocks of the deep ocean are uplifted deformed and ultimately transformed to continental crust accretionary prisms develop at sites of lithospheric convergence that is subduction zones commonly accretionary prisms form along continental margins although accretionary prisms may also occur adjacent to island arcs which are ultimately coalesced into continental landmasses here we review the studies of submarine accretionary prisms during the past four years with primary focus on the contributions of geoscientists from the united states

a geochemical and geophysical investigation of the hydrothermal complex of masaya volcano nicaragua abstract masaya volcano nicaragua is a persistently active volcano characterized by continuous passive degassing for more than 150 years through the open vent of santiago crater this study applies self potential soil co 2 and ground temperature measurements to highlight the existence of uprising fluids associated to diffuse degassing structures throughout the volcano the diffuse degassing areas are organized in a semi circular pattern and coincide with several visible and inferred surface volcanic structures cones fissure vents and likely consist of a network of buried faults and dykes that respectively channel uprising flow and act as barrier to gravitational groundwater flow water depths have been estimated by multi scale wavelet tomography of the self potential data using wavelets from the poisson kernel family compared to previous water flow models our water depth estimates are shallower and mimic the topography typically less than 150 m below the surface between 2006 and 2010 the depths of rising fluids along the survey profiles remained stable suggesting that hydrothermal activity is in a steady state this stable activity correlates well with the consistency of the volcanic activity expressed at the surface by the continuously passive degassing when compared to previous structural models of the caldera floor it appears that the diffuse degassing structures have an important effect on the path that shallow groundwater follows to reach the laguna de masaya in the eastern part of the caldera the hydrogeological system is therefore more complex than previously published models and our new structural model implies that the flow of shallow groundwater must bypass the intrusions to reach the laguna de masaya furthermore these diffuse degassing structures show clear evidence of activity and must be connected to a shallow magmatic or hydrothermal reservoir beneath the caldera as such the heat budget for masaya must be significantly larger than previously estimated

chlorine isotopes of thermal springs in arc volcanoes for tracing shallow magmatic activity the evaluation of the status of shallow magma body i e from the final intrusion stage to quiescence and back to activity one of the key parameters that trigger and sustain volcanic eruptions has been challenging in modern volcanology among volatile tracers chlorine cl uniquely exsolves at shallow depths and is highly hydrophilic consequently cl enrichment in volcanic gases and thermal springs has been proposed as a sign for shallow magmatic activities however such enrichment could also result from numerous other processes e g water evaporation dissolution of old chloride mineral deposits seawater contamination that are unrelated to magmatic activity here based on stable isotope compositions of chloride and dissolved inorganic carbon as well as previous published 3he 4he data obtained in thermal springs from two recently erupted volcanoes la soufriere in guadeloupe and montagne pelee in martinique in the lesser antilles arc we show that the magmatic cl efficiently trapped in thermal springs displays negative 37cl values 0 65 0 65 consistent with a slab derived origin but distinct from the isotope compositions of chloride in surface reservoirs e g seawater local meteoric waters rivers and cold springs displaying common 37cl values of around 0 using this 37cl difference as an index of magmatic cl we further examined thermal spring samples including a 30 year archive from two thermal springs in guadeloupe covering samples from its last eruption in 1976 1977 to 2008 and an island wide sampling event in martinique in 2008 to trace the evolution of magmatic cl in the volcanic hydrothermal systems over time the results show that magmatic cl can be rapidly flushed out of the hydrothermal systems within 30 to 80 years after the eruption much quicker than other volatile tracers such as co2 and noble gases which can exsolve at greater depths and constantly migrate to the surface because arc volcanoes often have well developed hydrothermal systems where magmatic cl is easily transferred to the surface following its exsolution from shallow magma body we suggest that 37cl has great potential to be a unique proxy to monitor the cessation and revival of infrequent arc volcanoes particularly at centennial time scales

hydrothermal system beneath aso volcano as inferred from self potential mapping and resistivity structure abstract we conducted self potential sp surveys sequentially from part to part over the central cones of aso volcano since august 1998 by december 2001 the compiled sp map revealed large sp anomalies on the central cones the main feature of the sp map is a w shaped profile along the ns transect over the central cones it is probable that this characteristic sp profile is produced by the combination of hydrothermal upwelling in the middle and topographic effect a positive anomaly showing a large concentric pattern has appeared after correcting the topographic effect to evaluate this sp anomaly we implemented a numerical code that calculates electric potential produced by arbitrarily positioned current sources and sinks in any three dimensional resistivity structure a layered structure obtained from a time domain electromagnetic tdem field experiment was used for the resistivity model the estimated current source is 300 a being located in a conductive layer around the sea level meanwhile sinks were estimated to sit on a circular area corresponding to the marginal part of the conductive layer water and heat budget study gives a lower limit of water mass transfer from depth to the bottom of the crater lake of nakadake this value was used to estimate the equivalent current in either case of electro kinetic ek mizutani h ishido t 1976 a new interpretation of magnetic field variation associated with the matsushiro earthquakes j geomag geoelectr 28 179 188 or rapid fluid disruption rfd process johnston m j s byerlee j d lockner d 2001 rapid fluid disruption a source for self potential anomalies on volcanoes j geophys res 106 b3 4327 4335 this comparison suggests that the former process is preferable to explain the observed sp anomaly from these results we infer a large scale hydrothermal system beneath the central cones of aso volcano in which the fluid flow initiates from the surrounding area converging to the central vent to transport the heat and materials up to the crater lake of nakadake through a vapor filled conduit

implications for focused fluid transport at the northern cascadia accretionary prism from a correlation between bsr occurrence a d near sea floor reflectivity anomalies imaged in a multi frequency seismic data set a high resolution seismic survey was carried out at the accretionary prism on the continental slope off vancouver island canada two gi gun data sets with different source frequency ranges of 50 150 and 100 500 hz were combined with 4 khz narrow beam echosounding data parasound the data allow spatial correlation between a gas hydrate bottom simulating reflector bsr and distinct areas of high near sea floor reflectivity an integrated interpretation of the multi frequency data set provides insight into the regional distribution of tectonically induced fluid migration and gas hydrate formation in the vicinity of odp leg 146 sites 889 and 890 the bsr at the base of the gas hydrate stability field is observed within accreted and deformed sediments but appears to be absent within bedded slope basin deposits it is suggested that these basin deposits inhibit vertical fluid flow and prevent the formation of a bsr whereas the hydraulic conductivity of the accreted sediments is sufficiently high to allow for pervasive gas migration an elevation of the bsr beneath the flanks of a topographic high is interpreted as an indicator for local upflow of warm fluids along permeable pathways within outcropping accreted sediments parasound data reveal discontinuous zones of high reflectivity at or directly beneath the sea floor which may indicate local cementation of surface sediments in combination with gi gun data the occurrence of these reflective areas can be related to the location of slope sedimentary basins acting as hydraulic seals it is proposed that the seals sometimes fail along faults extending beneath the bsr leading to focused upflow of methane bearing fluid and the formation of carbonate pavements at the sea floor

temporal variation of the hawaiian plume flux abstract the magnitude of the hawaiian swell which surrounds the hawaiian volcanic chain does not decline monotonically and smoothly with distance along the chain the observed undulations are interpreted here as reflecting past variations in the buoyancy flux of the hawaiian plume rather than the monotonic thermal decline of the swell with age as has been inferred previously this interpretation is supported by seismic evidence that indicates there has been little thinning of the lithosphere which it is shown further implies that the time scale for thermal subsidence will be very long the largest change in flux was an increase in the plume flux by more than a factor of two about 25 30 myr ago the size of the volcanic edifices shows a broad correlation with the variations in the swell supporting this interpretation

anomalous sea floor backscatter patterns in methane venting areas dnepr paleo delta nw black sea the relation between acoustic sea floor backscatter and seep distribution is examined by integrating multibeam backscatter data and seep locations detected by single beam echosounder this study is further supported by side scan sonar recordings high resolution 5 khz seismic data pore water analysis grain size analysis and visual sea floor observations the datasets were acquired during the 2003 and 2004 expeditions of the ec funded crimea project in the dnepr paleo delta area northwestern black sea more than 600 active methane seeps were hydroacoustically detected within a small 3 96 km by 3 72 km area on the continental shelf of the dnepr paleo delta in water depths ranging from 72 m to 156 m multibeam and side scan sonar recordings show backscatter patterns that are clearly associated with seepage or with a present dune area seeps generally occur within medium to high backscatter areas which often coincide with pockmarks high resolution seismic data reveals the presence of an undulating gas front i e the top of the free gas in the subsurface which domes up towards and intersects the sea floor at locations where gas seeps and medium to high backscatter values are detected pore water analysis of 4 multi cores taken at different backscatter intensity sites shows a clear correlation between backscatter intensity and dissolved methane fluxes all analyzed chemical species indicate increasing anaerobic oxidation of methane aom from medium to high backscatter locations this is confirmed by visual sea floor observations showing bacterial mats and authigenic carbonates formed by aom grain size analysis of the 4 multi cores only reveals negligible variations between the different backscatter sites integration of all datasets leads to the conclusion that the observed backscatter patterns are the result of ongoing methane seepage and the precipitation of methane derived authigenic carbonates mdacs caused by aom the carbonate formation also appears to lead to a gradual self sealing of the seeps by cementing fluid pathways horizons followed by a relocation of the bubble releasing locations

streaming potential properties of westerly granite with applications this paper reports on laboratory measurements of the streaming potential properties of common minerals and in particular of westerly granite data are presented for these solids in contact with simple electrolytic solutions and in one case for temperature variation in the range 5 70 c for 1 1 electrolytes the ratio of the streaming potential coupling coefficient to fluid resistivity was approximately 4 mv atm m and for 2 1 electrolytes 2 mv atm m the effect of temperature was small 0 05 mv c temperature increase and indicates that the zeta potential was independent of temperature preliminary experimental results using mixed electrolytic solutions nacl cacl2 and two phase fluid flow are also described two phase flow can enhance streaming potentials by as much as a factor of 3 or 4 the laboratory data are used to interpret streaming potentials in geological problems such as earthquake prediction geothermal prospecting using the self potential method and surface conductivity contribution to the electrical resistivity of rocks

methane derived authigenic carbonates of mid cretaceous age in southern tibet types of carbonate concretions carbon sources and formation processes abstract methane derived authigenic carbonates with distinctive structures and morphologies have been documented worldwide but they are rarely found from ancient strata in the eastern tethys ocean the methane derived authigenic carbonates found in southern tibet are developed in calcareous or silty shales of mid cretaceous age in the xigaze forearc basin and in the tethyan himalaya tectonic zone the morphology mineralogy elemental geochemistry and composition of carbon and oxygen isotopes of these carbonates are studied in detail the carbonates have nodular tubular and tabular morphologies they are primarily composed of carbonate cement that binds and partly replaces host sediment grains host siliciclastic sediments are composed mainly of quartz and plagioclase feldspar a few foraminifers and framboidal or subhedral to euhedral pyrite carbonate cements dominantly are micritic calcite with minor contribution of dolomite nodular concretions are characterized by depleted 13c values commonly ranging from 30 to 5 the 13c values show a gradual decrease from the periphery to the center and the cao sio2 fe2o3 al2o3 k2o and tio2 contents generally show a gradual change these features indicate that the nodular concretions grew from an early formed center toward the periphery and that the carbon source of the nodular concretions was derived from a mixture of methane methanogenic co2 and seawater dissolved inorganic carbon the tubular concretions are characterized by 13c values of 8 85 to 3 47 in the shangba section and 27 37 to 23 85 in the upper gamba section unlike the nodular concretions the tubular concretions show central conduits which are possible pathways of methane rich fluids suggesting that the cementation of tubular concretions begins at the periphery and proceeds inward moreover the tubular concretions show morphological similarity with the methane derived carbonate chimneys pipes and slabs reported in present day cold seep settings we suggest that the carbon source of the tubular concretions was derived from a mixture of seawater dissolved inorganic carbon and oxidized methane formed by released hydrate the tabular concretions are characterized by 13c values of 21 87 to 6 67 in the xiege sections these depleted 13c values suggest that the carbon of the tabular concretions was derived at least in part from aom the tabular concretions are characterized by 13c values of 28 81 to 12 99 in the gamba section according to the 13c values and field observation we infer that their carbon source was more likely to be a mixture of the oxidized methane formed by released hydrate and seawater dissolved inorganic carbon

3d electrical imaging of the inner structure of a complex lava dome puy de dome volcano french massif central france abstract lava domes result from extrusion of massive lava frequent explosions and collapses this contribution focuses on a complex trachytic lava dome the puy de dome volcano located in the chaine des puys volcanic field french massif central france we performed electrical resistivity tomography ert acquisitions on the entire edifice in order to investigate its overall inner structure as well as to detail its summit area the resulting large ert dataset integrated a recently developed 3d inversion code based on an unstructured discretization of the geometrical model the 3d inversion models obtained refine the existing geological model of the puy de dome s inner structure obtained by previous geophysical studies these results also highlight the strong fracturing and fumarolic alteration that affect the summit part of the volcano

structural controls on seepage of thermogenic and microbial methane since the last glacial maximum in the harstad basin southwest barents sea the harstad basin is a structural block on the continental shelf of sw barents sea where gas hydrates likely occurred below the grounded ice sheet during the last glaciation and it hosts active gas seepage at numerous seafloor sites we present an integrated study of fluid flow systems in the harstad basin by combining seismic profile interpretations and gas flare mapping data with the geochemical results obtained on seafloor seeping gas and methane derived carbonate crusts more than 190 acoustic gas flares were registered in water column many of them in association with pockmarks and carbonate crust fields however weak or absent seepage observed during remotely operated underwater vehicle transects across many pockmarks and crust fields suggests that seepage activity may have decreased since the last deglaciation in the western harstad basin seeps of microbial methane occur mainly above tertiary formations that are pinching out below the glacial sediments high amplitude seismic anomalies suggest the presence of gas pockets at the base of the glacial sediments and within tertiary deposits in contrast gas seeping in the eastern harstad basin originates from a biodegraded thermogenic source tentatively connected to the deeply faulted mesozoic rocks occurring below glacial sediments this spatial variability in fluid sources is also recorded in the carbon isotope data of seafloor carbonate crusts with 13 c values typically between 55 and 42 and 40 and 20 vpdb for carbonate crusts associated with microbial and thermogenic fluids respectively u th chronology combined with the stable isotope data suggests that this discrepancy in fluid sources over a distance of about 20 km has been stable since the last glaciation and highlights the significance of regional underlying geology in mediating fluid supply to the seafloor

a methane derived carbonate build up at a cold seep on the crimean slope north western black sea abstract a unique chimney shaped carbonate build up was produced by microbially mediated anaerobic oxidation of methane at a deep sea cold seep the build up was sampled from 1600 m water depth in the area of the lomonosov rise nw black sea crimean shelf slope the carbonate chimney grew free into the anoxic water column with its base attached to a steep slope composed of plagiogranite and void of sediments the perfectly preserved 1 5 m high chimney stores reliable records of the diversity of mineralogy geochemistry and stable isotope composition of deep sea methane related carbonates never studied before the build up consists of mg calcite mgco 3 9 13 mol with minor aragonite the carbonate matrix encloses organic matter and emiliania huxleyi coccoliths as well as minor framboidal pyrite gypsum barite and diatomite fragments the contribution of detrital silicate material is negligible micritic mg calcite in the inner zone of the chimney forms obtuse rhombohedrons clustered in hemispherical aggregates clots and hosts isolated prismatic aragonite 1 vol in the outer zone mg calcite exists as foliated crystals and spherulites while aragonite spherulites are restricted to the top surface the carbon isotope compositions of carbonates 13 46 5 to 33 0 vpdb and remnant bacterial mats 13 76 9 to 81 6 vpdb provide evidence of a biogenic methane source for the build up formation oxygen came mainly from sea water judging by a narrow range of 18 o values in carbonates 0 2 to 1 3 vpdb the prevalence of mg calcite throughout the build up indicates an anme 2 sbr consortium being the main component of the bacterial mats living at the seep aragonite grew mostly late in the seep history which hints to environmental changes and the ensuing predominance of the anme 1 sbr consortium the observed relationship between the prokaryotic communities and the main carbonate phases is common to the microbial mats of the black sea but is actually opposed to the pattern of aom community and aom related carbonates found in sediments different morphologies of carbonates in the outer and inner zones of the build up point to variations in the methane flux gradient which controlled the biomass density of the aom consortia the ree y patterns of mg calcite from the inner zone are typical of carbonates crystallised in a freshened sea water environment while both mg calcite and aragonite from the outer zone show distinct sea water signatures inasmuch as the time span of build up growth radiocarbon ages from 9000 180 to 7500 180 year bp overlaps the period when the black sea lake reconnected to the mediterranean sea the progressive arrival of sulphate rich waters can be inferred to be another possible control of ree y patterns in seep carbonates besides the methane flux gradient and related activity of aom consortia

first observations of deep sea coral reefs along the angola margin the west african continental slope is an important theatre for geological survey prospecting and drilling for hydrocarbons but little is known about local deep sea biological communities at these depths while shallow water reefs are common and well known features in the tropics only few records of deep water corals exist at low latitudes and most of them have been reported by historical oceanographic cruises undertaking circum navigations of the world this study based on a multidisciplinary approach presents a description of newly discovered deep water coral reef communities along the angola margin data from rov multibeam bathymetry side scan sonar and seismics from a deep towed acoustic system sar were used to describe the morphology of the coral mounds and their relationship with the local geological setting the reef building scleractinian coral lophelia pertusa has colonised carbonate mounds that reach heights of ca 30 m and follow an orientation that is correlated with salt tectonic processes recent erosion is suggested as a process that influences the shape of the mounds sixteen fish taxa were identified during the rov video surveys with some of them likely to have a strong affinity with dense living corals the species observed belong to families commonly associated with deep water corals i e sebastidae berycidae lophiidae and chaunacidae except an abundant species belonging to the family zoarcidae rarely observed in this type of environment lucinidae shells were found around mounds as this bivalve family is indicative of reduced sediment and generally associated with cold seep environments this finding could revive the debate over the relationship between the distribution of cold water coral habitat and gas seeps however there is no present day nutritional relationship between living coral and chemosynthetic derived biomass the possible role of fluid expulsion in carbonate precipitation acting as the first step for coral colonisation is nevertheless discussed

formation of methane related authigenic carbonates within the bioturbated zone an example from the upwelling area off vietnam abstract in the biologically high productive area off vietnam authigenic carbonates formed in the bioturbated zone while methane was oxidized microbially under anaerobic conditions open crustacean burrows spongeliomorpha connected to the seafloor acted as conduits for methane as suggested by intense cementation of burrow walls having a light c isotope signature although seawater circulated within these open inhabited tubes conditions favorable for anaerobic oxidation of methane aom occurred trypanites cementation started at several spots that coalesced later to form the nodule carbon isotopes indicate a biogenic methane source 13 c carb reaching 49 to 40 v pdb while higher 13 c values imply mixing with carbon from other sources that is very likely within the bioturbated zone the cement is generally fine grained 18 o values of 5 1 reflect the general 18 o enriched isotope signature of the bottom water in south china sea especially during glacial times but influence of water released from decaying gas hydrate cannot be excluded the studied nodule was found on top of a slump that displaced it

structural control of collapse events inferred by self potential mapping on the piton de la fournaise volcano la reunion island abstract field surveys were performed on the terminal cone of piton de la fournaise in 2006 and 2008 to precisely map the self potential sp signal and determine the zonation of the hydrothermal activity both on the flanks of the cone and in the summit area including inside the bory and dolomieu craters sp maps inside the craters have been performed 8 months before the 5 7 april 2007 caldera collapse zonations appear both at the scale of the cone and of the summit and allow new interpretation of the electrical signal distribution on the terminal cone of piton de la fournaise superimposed to the sp maxima linked to the rift zones several areas of sp maxima associated with collapse structures have been detected 1 in the summit area the bory and dolomieu craters show the strongest sp values with amplitudes exceeding 2 v with respect to the base of the cone and with a sharp lateral variation to the east corresponding to the inner boundary of the dolomieu caldera collapsed on 5 7 april 2007 and 2 in the paleo pit craters surrounding the summit which show amplitudes similar to the dolomieu bory craters the analysis of the variations of the signal with time evidences a modification of the fluid flow pattern with a higher associated sp signature to the east in 2008 we interpret the amplification of fluid flow to the east in 2008 as a consequence of the eastward motion of the eastern flank of the volcano during the april 2007 eruption the acquisition of sp data during two periods separated by the april 2007 eruption turns out to be a good opportunity to correlate the sp signal to the piton de la fournaise structure and to its evolution in term of hydrothermal and eruptive activity

cretaceous cold seep communities and methane derived carbonates in the canadian arctic lower cretaceous cold seep fossil assemblages have been found in the canadian arctic archipelago serpulid worm tubes and bivalves are most abundant in these communities in contrast fossils are scarce in the surrounding strata the fossils are contained in an isotopically light delta 13 c 25 to 50 per mil carbonate rock groundmass that is interpreted to have formed from bacterial oxidation of methane the rocks were deposited at intermediate depth 400 meters in a cold marine environment nearby normal faults may have provided a conduit for seeping methane and hydrogen sulfide needed to fuel chemosynthetic bacteria and in turn the higher life forms

tracing organic compounds in aerobically altered methane derived carbonate pipes gulf of cadiz sw iberia abstract the primary geochemical process at methane seeps is anaerobic oxidation of methane aom performed by methanotrophic archaea and sulfate reducing bacteria srb the molecular fingerprints biomarkers of these chemosynthetic microorganisms can be preserved in carbonates formed through aom however thermal maturity and aerobic degradation can change the original preserved compounds making it difficult to establish the relation between aom and carbonate precipitation here we report a study of amino acid and lipid abundances in carbonate matrices of aerobically altered pipes recovered from the seafloor of the gulf of cadiz sw iberian peninsula this area is characterized by a complex tectonic regime that supports numerous cold seeps studies so far have not determined whether the precipitation of carbonate pipes in the gulf of cadiz is a purely chemical process or whether microbial communities are involved samples from this site show signs of exposure to oxygenated waters and of aerobic alteration such as oxidation of authigenic iron sulfides in addition the degradation index calculated from the relative abundance of preserved amino acids indicates aerobic degradation of organic matter although crocetane was the only lipid identified from methanotrophic archaea the organic compounds detected n alkanes regular isoprenoids and alcohols are compatible with an origin from aom coupled with bacterial sulfate reduction bsr and subsequent aerobic degradation we establish a relation among aom bsr and pipe formation in the gulf of cadiz through three types of analysis 1 stable carbon and oxygen isotopic composition of carbonate minerals 2 carbonate microfabrics and 3 mineralogical composition our results suggest that carbonate pipes may form through a process similar to the precipitation of vast amounts of carbonate pavements often found at cold seeps our approach suggests that some organic compound patterns in combination with additional evidence of aom and bsr may help indicate the source of altered methane derived carbonates commonly occurring in ancient and modern deposits

structure of the nemrut caldera eastern anatolia turkey and associated hydrothermal fluid circulation abstract plio quaternary volcanism played an important role in the present physical state of eastern anatolia mount nemrut situated to the west of lake van is one of the main volcanic centers in the region with a spectacular summit caldera 8 5 7 km in diameter the most recent eruptions of the volcano were in 1441 1597 and 1692 nemrut lake covers the western half of the caldera it is a deep half bowl shaped lake with a maximum depth of 176 m numerous eruption centers are exposed within the caldera as a consequence of magma water interaction current activity of nemrut caldera is revealed as hot springs fumaroles and a small hot lake self potential and bathymetric surveys carried out in the caldera were used to characterize the structure of the caldera and the associated hydrothermal fluid circulation in addition analyses based on digital elevation models and satellite imagery were used to improve our knowledge about the structure of the caldera according to sp results the flanks of the volcano represent the hydrogeologic zone whereas the intra caldera region is an active hydrothermal area where the fluid circulation is controlled by structural discontinuities there is also a northern fissure zone which exhibits hydrothermal signatures nemrut caldera collapsed piecemeal with three main blocks stress controlling the collapse mechanism seems to be highly affected by the regional neotectonic regime in addition to the historical activity current hydrothermal and hydrogeologic conditions in the caldera in which there is a large lake and shallow water table increase the risk of the quiescent volcano

streaming potential in volcanic rocks from mount pelee streaming potential and electric conductivity have been measured in a laboratory on 11 consolidated samples coming from five deposits of the different evolutionary stages of mount pelde volcano the streaming potential coupling coefficient ranges from 35 to 4905 mv mpa 1 and increases with increasing permeability this increase is mainly due to the dependency of rock effective conductivity with permeability the permeability of the samples varies from 0 146x10 12 to 34x10 12 m 2 the zeta potential at ph 7 and water conductivity of 2 1x10 4 s m l is relatively small for the majority of the samples it ranges from 4 to 19 rev according to water conductivity analysis on mount pel e streaming potential coupling coetficients of 25 to 406 mv mpa 1 can be expected for this volcano

u th chronology and formation controls of methane derived authigenic carbonates from the hola trough seep area northern norway abstract we investigated methane derived authigenic carbonate mdac crusts and nodules from a cold seep site on the northern norwegian continental shelf in ca 220 m water depth to determine the timing and mode of their formation gas bubbling observed during remotely operated vehicle rov assisted sampling of mdac crusts revealed ongoing seep activity authigenic carbonates were present as crusts on the seafloor and as centimetre size carbonate cemented nodules at several intervals within an adjacent sediment core aragonite dominated mineralogy of the mdac crusts suggests formation close to the seafloor at higher rates of sulphate dependent anaerobic oxidation of methane aom in contrast dolomite cemented nodules are consistent with the formation at the sulphate methane transition zone deeper within the sediment at lower rates of aom the 13c carbonate values of bulk rock and of micro drilled aragonite samples vary between 22 2 and 34 6 vpdb we interpret the carbon in aragonite to be mainly derived from the anaerobic oxidation of thermogenic methane with a minor contribution from seawater dissolved inorganic carbon dic aom activity is supported by high concentrations of aom related biomarkers of archaea archaeol and 2 sn hydroxyarchaeol and sulphate reducing bacteria iso and anteiso c15 0 fatty acids in the crusts the dolomite nodules exhibit higher 13c carbonate values 12 vpdb suggesting a smaller amount of methane derived carbon presumably due to the contribution of dic migrating from depth and lower aom rates the latter is supported by orders of magnitude lower concentrations of archaeol and sn 2 hydroxyarchaeol in the sediment interval containing the largest dolomite nodules 18o values of pure aragonite samples and dolomite nodules indicate the precipitation of carbonate close to isotopic equilibrium with seawater and no influence of gas hydrate derived water u th dating of two mdac crusts shows that they formed between 1 61 0 02 and 4 39 1 63 ka bp and between 2 65 0 02 and 4 32 0 08 ka bp we infer both a spatial and temporal change in methane flux and related mdac formation at this seep site these changes might be caused by regional seismic events that can affect pore pressure or re activation of migration pathways thus facilitating fluid flow from deep sources towards the seabed

reconnaissance de structures tectoniques et volcaniques sous marines de l arc recent des petites antilles kick em jenny qualibou montagne pelee nordouest de la guadeloupe abstract a multibeam bathymetric survey seacarib 1 was carried out in april 1985 on board the r v conrad lamont doherty geological observatory off the western coasts of several islands of the lesser antilles complementing a previous survey of the same type arcante 2 thermosite 1980 devoted to adjoining areas in guadeloupe martinique and st lucia it allowed us to precisely map submarine volcanoes in a marginal setting behind the recent arc the main volcanic axis of the archipelago emplaced during the neogene the kick em jenny volcano south of the grenadines is the only active submarine volcano of the lesser antilles it is a small and very young cone probably only tens or hundreds of years old which was hydrothermally active during the survey the directeur volcano guadeloupe is the largest submerged volcanic centre thus far detected in the lesser antilles having been formed between 3 3 and 2 9 ma during the 1980 survey two other large volcanoes were discovered off southern basse terre guadeloupe vieux fort volcano 2 5 2 0 ma and in front of fort de france bay martinique schoelcher volcano older than 4 2 ma several other much smaller volcanoes have been mapped off the same coasts particularly the bouillante seapeaks guadeloupe moreover large tectonic structures cut the recent arc transversally and obliquely the well known qualibou depression on the island of st lucia was interpreted in various ways neither the hypothesis of a large caldera the western side of which collapsed offshore nor the suggestion of a huge rotational gravity slide are confirmed the depression seems more likely to have been controlled by tectonic factors shaping a complex graben structure the seaward extension appears to be restricted to a northern channel the soufriere channel the st pierre fault in martinique is a large transverse feature extending seaward down to some 2000 m depth to the south it bounds the mount pelee active volcanic system and the escarpment of the fault forms a dam against subaqueous pyroclastic flows running down from the volcano these flows are responsible for the unusually smooth morphology of the submarine flanks the zombi fault of northwest guadeloupe is part of a first order feature extending along at least 130 km from montserrat in the north to marie galante in the east this curved fracture cuts across the northern central part of the lesser antilles passing progressively from a subparallel to a transverse orientation with respect to the axis of the island arc these types of surveys are important because they provide better understanding of the structure and recent geological evolution of the recent volcanic arc they are also a useful complementary tool for geothermal and seismological studies

self potential and ground temperature at merapi volcano prior to its crisis in the rainy season of 2000 2001 abstract rainwater infiltration into the active lava dome of merapi volcano central java has often been suggested as a triggering mechanism for partial dome collapse and subsequent eruptive behavior however the phenomenon has not been systematically investigated we use a multi parametric approach to study the interaction of the hydrologic and magmatic system near the lava dome prior to its crisis in early 2001 we describe the hardware concept for a continuous monitoring system for self potentials u sp and ground temperature t installed in august 2000 at the solfatara woro only 150 m from the active lava dome relating the data from this station to measurements of rainfall air pressure solfatara temperature and seismicity several effects can be distinguished a a long term correlation is observed between electrode temperature difference and sp with estimated coupling coefficients of 2 1 0 5 mv c b after individual rainfall events u t signatures show a typical pattern of positive charge accumulation at the hot electrodes near the fumarolic vents c an exceptional anti correlation between u and t is observed in january 2001 during a period of rapid dome growth prior to the collapse and eruptive crisis d wavelet analysis of sp reveals the sporadic occurrence of periodic fluctuations with a clear 12 h s2 component because of their amplitude of up to 100 mv km and their periodicity s2 but not 24 h or lunar 12 h 25 min these fluctuations are unlikely to be caused by natural magnetic field variation or by earth tides instead they do seem correlated but not in phase with atmospheric pressure changes we discuss effects a d in the framework of source mechanisms related to water lava interactions

volcano flank instability in the lesser antilles arc diversity of scale processes and temporal recurrence 1 the 1997 boxing day collapse a remarkable feature of the ongoing eruption of soufriere hills on montserrat has prompted new interest in the study of volcano stability in the lesser antilles building on a few cases documented in the literature we have now identified at least 47 flank collapse events on volcanoes of the caribbean arc where this type of behavior is characteristic and repetitive about 15 events occurred on active volcanoes within the last 12 000 years in the northern part of the arc flank collapses are repetitive do not exceed 1 km3 in volume occur in all directions and are promoted by intense hydrothermal alteration and well developed fracturing of the summit part of the edifices in contrast infrequent but large sector collapses with volumes up to tens of km3 are typical of the southern volcanoes they are always directed to the west as a result of the high overall slopes of the islands toward the deep back arc grenada basin because caribbean islands are small a large part of the resulting debris avalanches have flowed into the sea thus contributing voluminous and sudden inputs of volcaniclastic sediments to the grenada basin deposits from such submarine flows have been identified during the recent aguadomar and caraval oceanographic cruises and traced to their source structures on land edifice collapses have a major influence on subsequent volcanic activity but also are of high concern because of their tsunamigenic potential

shallow water methane derived authigenic carbonate mounds at the codling fault zone western irish sea abstract methane derived authigenic carbonate mdac mound features at the codling fault zone cfz located in shallow waters 50 120 m of the western irish sea were investigated and provide a comparison to deep sea mdac settings carbonates consisted of aragonite as the major mineral phase with 13 c depletion to 50 and 18 o enrichment to 2 these isotope signatures together with the co precipitation of framboidal pyrite confirm that anaerobic oxidation of methane aom is an important process mediating methane release to the water column and the atmosphere in this region 18 o enrichment could be a result of mdac precipitation with seawater in colder than present day conditions or precipitation with 18 o enriched water transported from deep petroleum sources the 13 c depletion of bulk carbonate and sampled gas 70 suggests a biogenic source but significant mixing of thermogenic gas and depletion of the original isotope signature cannot be ruled out active seepage was recorded from one mound and together with extensive areas of reduced sediment confirms that seepage is ongoing the mounds appear to be composed of stacked pavements that are largely covered by sand and extensively eroded the cfz mounds are colonized by abundant sabellaria polychaetes and possible nemertesia hydroids which benefit indirectly from available hard substrate in contrast to deep sea mdac settings where seep related macrofauna are commonly reported seep specialist fauna appear to be lacking at the cfz in addition unlike mdac in deep waters where organic carbon input from photosynthesis is limited lipid biomarkers and isotope signatures related to marine planktonic production e g sterols alkanols were most abundant evidence for microbes involved in aom was limited from samples taken possibly due to this dilution effect from organic matter derived from the photic zone and will require further investigation