evidence of active ground deformation on the mid ocean ridge axial seamount juan de fuca ridge april june 1988 since september 1987 a precision bottom pressure recorder bpr has been deployed within the summit caldera of axial seamount on the central juan de fuca ridge the instrument is capable of measuring pressure to 1 mbar resolution and recording these measurements at 64 samples per hour for up to 15 months after removal of oscillatory signals due to tidal and oceanographic effects and linear trends caused by sensor drift any significant change in the pressure record should indicate a change of depth associated with vertical ground movement in subaerial volcanic systems such ground movements commonly indicate active inflation or deflation of underlying magma bodies and are frequently coincident with rift eruptions axial seamount was selected for this pilot study for three primary reasons 1 its tectonic setting 2 the presence of a well formed summit caldera and 3 observational evidence of geologically recent volcanic activity results from the first 9 months of the bpr deployment revealed a significant change in pressure which is interpreted to represent a 15 cm subsidence of the caldera floor during two 2 to 3 week periods in april june 1988 also during these periods an anomalous decline in temperature at the site was recorded that is correlated with an apparent increase in current velocity at the axial seamount hydrothermal emissions study ashes vent field suggesting vigorous advection of cold water into the caldera concurrent oceanographic data from geosat and from current meter arrays do not indicate any large scale oceanographic phenomena capable of generating these simultaneous events one mechanism to explain simultaneous ground subsidence and temperature decline at the caldera center and increased bottom current at the caldera margin is the generation of a buoyant parcel of heated water in response to the intrusion or the eruption of magma associated with volcanic deflation such a parcel must have been sufficiently buoyant and proximal to induce horizontal entrainment currents capable of producing the bottom water conditions that were observed at both sites similar volcanic events also may have generated large midwater plumes that have been described previously along the southern juan de fuca ridge

laboratory study of hydraulic fracturing laboratory tests on teton dam soil were performed by increasing the water pressure in model bore holes and in simulated rock joints the water pressure required to cause hydraulic fracturing was found to depend on soil density water content confining stress and test duration on the basis of the test results it was hypothesized that 1 hydraulic fracturing is a weak link phenomenon in that fracturing will occur in the least resistant soil subjected to increased water pressure and 2 hydraulic fracturing can probably occur only in the presence of a discontinuity within which the water pressure can act to create a wedging mechanism thus creating tensile stresses in the soil

the distribution of geothermal fields on the juan de fuca ridge near bottom water temperatures were mapped along 400 km of the strike of the juan de fuca ridge as part of a combined sea marc seabeam experiment to image the variability of morphology and structure along a spreading center segment the water temperature data collected by a continuously towed thermistor chain in addition to salinity data indicate that there are four geothermal areas spaced at distances of 100 km from each other south of the cobb propagator and one field just to the north of the propagator on the endeavor ridge segment each thermal region is located above a morphological dome on the spreading center these domes are an average of 100 200 m shallower than the rest of the axis the structure of bottom water suggests that the geothermal regions are on average 20 km long and that the heat from these fields raises the temperature in the water column by a minimum of 0 06 sup 0 c up to 300 m above the bottom two simple models are used to estimate the heat flux associated with these features

water column hydrothermal plumes on the juan de fuca ridge hydrographic surveys on the juan de fuca ridge jdfr carried out from 1980 to 1987 show a complex pattern of sup 3 he and mn rich water column plumes produced by venting from several submarine hot spring areas in the vicinity of axial volcano at latitude 46 degree n distinct plumes were detected in 1980 1982 and 1983 with sup 3 he signatures up to delta sup 3 he 64 at approximately 1 500 m depth at distances of approximately 10 km from the seamount summit however the same plumes had no detectable thermal signature a paradox which is attributed to the high sup 3 he heat ratios and low salinities of the fluids venting within the caldera of axial volcano profiles directly over the seamount show hydrothermal sup 3 he in the water column up to 300 m above the caldera floor with the sup 3 he signal increasing with depth to very high and uniform ratios of delta sup 3 he 108 150 below the approximately 1 500 m caldera sill depth another apparent locus of hydrothermal input is helium basin a depression on the northeast flank of axial volcano which had delta sup 3 he 51 when first sampled in 1980 however subsequent hydrocasts into helium basin in 1982 and 1983 yielded lowermore helium enrichments suggesting either a decrease in hydrothermal input or flushing of the basin via a mixing event to the south of axial volcano high delta sup 3 he values of approximately 40 observed over the ridge axis at 45 degree 18 prime n and 45 degree 39 prime n indicate venting on this previously unexplored section of the ridge the water column plumes over the us geological survey vent site at approximately 44 degree 40 prime n on the southern jdfr have very high mn sup 3 he ratios of 4 600 mol cm sup 3 an apparently unique characteristic which can be used to distinguish these plumes from those originating at other jdfr vent fields less

the first measurements of hydrothermal heat output at 9 50 n east pacific rise abstract despite the importance of the heat output of seafloor hydrothermal systems for the earth s energy budget hydrothermal heat output measurements have been very limited in this paper we report the first measurements of hydrothermal heat output at the ridge 2000 integrated study site on the east pacific rise we focused our work on the bio 9 complex situated at 9 50 n where there has been an extensive measurement and sampling program since 1991 this site is located along the eruptive fissure of the 1991 1992 event and the site of the 1995 earthquake swarm we made direct measurements of advective heat output at several individual vents and at one site of diffuse flow tica although these data do not describe the complete heat flux picture at this vent field the data yield a total hydrothermal heat output of 325 160 mw with 42 21 mw coming from high temperature vents along this 2 km segment of ridge this result assumes a diffuse flux similar to that measured at tica occurs at each high temperature vent site our initial measurements thus suggest that the heat output of the low temperature diffuse venting is approximately 10 times that of the high temperature vents but may also be one or two orders of magnitude greater

water column anomalies associated with hydrothermal activity in the guaymas basin gulf of california abstract sea floor hydrothermal activity in the guaymas basin gulf of california is quite different from that associated with ridge crest spreading centers injection of hydrothermal fluids occurs in the bottom of a semi enclosed basin and water column anomalies produced by this activity increase to much higher values than in the open ocean in the guaymas basin the hydrothermal venting generates large clouds of fine suspended particulate matter spm 100 300 m above active mounds and chimneys these hydrothermal clouds have potential temperature anomalies of about 0 010 0 020 c are enriched in dissolved silica particulate manganese and depleted in dissolved oxygen relative to areas away from the vents the particulate manganese values increase from about 3 nmol kg at 1000 m well above the enclosing topography of the subsill basin to 100 150 nmol kg in the clouds of spm and in the bottom nepheloid layer the particulate mn in the hydrothermal clouds appears to originate from both direct precipitation of dissolved mn2 injected by the vents and entrainment of mn rich spm in the rising hydrothermal plumes injection of silica rich vent fluids into the basin bottom waters produces a silica anomaly of 10 15 mol relative to the other deep basins of the gulf of california spillover of guaymas basin deep water produces a silica plume just above the basin sill depth which is detectable to the mouth of the gulf a simple two endmember mixing model indicates that the deep waters of the guaymas basin contain approximately 0 1 hydrothermal fluid oxygen anomalies associated with the hydrothermal clouds are on the order of 5 mol relative to regions away from active vents the basin as a whole shows a depletion in oxygen of about 13 mol relative to the other deep basins of the gulf the mixing model shows that this oxygen consumption can be explained by the oxidation of dissolved sulfide and methane injected by the hydrothermal vents box models of the deep basins of the southern gulf of california indicate that the guaymas basin has a significantly higher source term for dissolved silica and sink term for dissolved oxygen than the other basins the calculated flux of hydrothermal fluids into the guaymas basin is 10 12 m3 s

the magnetic structure of axial seamount juan de fuca ridge axial seamount is a large volcanically active seamount located in the eastern pacific on the central juan de fuca jdf ridge at 46 n 130 w sea surface magnetic anomaly data show that axial lies completely within crust formed during the brunhes normal polarity epoch the edifice however does not produce a simple positive magnetic anomaly related to the excess mass above mean seafloor several pronounced negative magnetic anomalies are associated with the seamount including both a circular shaped low located west of the summit and an elongate low trending nw on the southeast flank of the volcano these two anomalies form part of a nw se magnetic trough which extends across the seamount edifice oblique to the general jdf ridge trend of n20 e a third negative anomaly is observed on the northern flank of the seamount associated with north helium basin a deep elongate basin which indents the northeast flank of the seamount both inversion of sea surface magnetics data and forward modelling of topography constrained by magnetization values of dredged samples show that bathymetric effects can explain the helium basin anomaly but topography alone cannot produce the low magnetization values which extend across the seamount summit magnetization of crustal rocks does not vary spatially over the seamount so that negative anomalies at the summit can be explained by variations in the effective thickness of the magnetic source layer a simple forward model of uniform magnetization shows that the anomaly source layer would have to thin by 50 to less than 700 m thick in order to generate the observed magnetic response a thinned source layer is consistent with the presence of either a substantial magma chamber at depth beneath the summit of axial or a zone of substantial crustal alteration the shape of the anomaly implies the trend of either of these sources must be oriented obliquely to the general ridge trend but parallel to the direction of the absolute plate motion

hydrothermal cooling of midocean ridge axes do measured and modeled heat fluxes agree abstract accurate estimates of near axis hydrothermal cooling are keys to understanding many geological chemical and biological processes at midocean ridges at present however field observations h heat flux vent field are few and imprecise and model results h m heat flux km of axis vary widely depending on assumptions about crustal formation crustal composition and the cooling efficiency and spatial and temporal extent of hydrothermal circulation in this paper i compare all published vent field scale measurements of h to a range of published h m for slow 40 mm yr and fast 40 mm yr ridges to assess the present state of knowledge about the magnitude of near axis hydrothermal cooling h has been evaluated 28 times either by point measurements using inventories of individual sources 362 552 mw n 12 measurements or by integrated measurements using water column observations 876 1011 mw n 16 comparable estimates of mean vent field expected h at any spreading rate can be derived by merging h m from various models with the predicted global inventory of active vent sites these estimates range from 1 1 5 gw field and are approximately constant for all spreading rates this range agrees with the best constrained results of h from slow ridge vent fields 1669 1354 mw but is considerably higher than those from fast ridges 245 170 mw inferences about the spatial and temporal variability of h can be gained by defining the parameter l h h m equivalent to the axis length needed to continuously power a hydrothermal field the resultant large l values 13 333 km for slow ridges 1 32 km for fast demand punctuated cooling where for short periods h h m the percentage of time that a given vent field might be active can be speculatively estimated by dividing l by the length of axis the field cools examples of this percentage range from a low of 50 for some fast ridge fields

flow to fracture transition in a volcanic mush plug may govern normal eruptions at stromboli stromboli is a model volcano for studying eruptions driven by degassing the current paradigm posits that strombolian eruptions represent the bursting of gas slugs ascending through melt filled conduits but petrological observations show that magma at shallow depth is crystalline enough to form a three phase plug consisting of crystals bubbles and melt we combine a 1d model of gas flushing a crystalline mush with a 3d stress model our results suggest that localized gas segregation establishes hot conduits of mobile magma within a stagnant plug the plug is prone to tensile failure controlled by gas over pressure and tectonic stress with failure most likely beneath the observed vent locations we hence argue that strombolian eruptions are related to plug failure rather than flow our proposed three phase model of the shallow plumbing system may provide a promising framework for integrating geophysical petrological and morphological observations at stromboli and in open system volcanism more generally

gis techniques and statistical models in evaluating landslide hazard geographical information systems gis and numerical cartography may greatly facilitate the development and use of statistical models for the assessment of regional landslide hazard from a small drainage basin located in central italy relevant geological and geomorphological factors were collected and processed by applying gis technology in particular modules were used which both generate high fidelity digital terrain models and automatically partition the terrain into main slope units the resulting information was then analysed by discriminant analysis which enabled landslide hazard and risk to be evaluated in each slope unit although not lacking drawbacks the method proved to be a feasible and cost effective approach to landslide susceptibility assessment and mapping

fluid driven fractures in uncemented sediments underlying particle level processes article i nfo granular materials subjected to fluid flow may experience fracture formation and fluid flow localization current explanations for hydraulic fracture in soils fail to satisfy the inherent characteristics of granular materials effective stress dependent cohesionless frictional strength we apply complementary experi mental and numerical techniques to identify the underlying particle scale mechanisms first we show that the miscibility of the invading fluid with the host fluid leads to distinct localization processes that depend on the balance between particle level skeletal forces effective stress dependent capillary forces the invasion of the interfacial membrane when immiscible fluids are involved and seepage drag forces associated with fluid flow velocity then we identify the positive feedback mechanisms at surface defects and fracture tips that promote fracture initiation and sustain fracture propagation these include increased porosity at the tip due to strains preferentially normal to the fracture alignment either eased membrane invasion immiscible fluids or higher hydraulic conductivity miscible fluids and the emergence of particle level forces that promote opening mode particle displacement this effective stress compatible sequence of events helps identify the parameters that govern fluid driven fracture formation in uncemented sediments and explain experimental observations

geochemistry of axial seamount lavas magmatic relationship between the cobb hotspot and the juan de fuca ridge axial seamount located along the central portion of the juan de fuca ridge axis and at the eastern end of the cobb eickelberg seamount chain is the current center of the cobb hotspot the axial seamount lavas are transitional between n type and e type mid ocean ridge basalt morb characteristics that they share with lavas along the rest of the juan de fuca ridge there are however subtle but distinct differences between the seamount lavas and those of the adjoining ridge segments these include higher na2o cao and sr at a given mgo content and lower silica saturation in the seamount lavas as compared with the ridge lavas lava chemistry and bathymetry indicate that axial seamount is a discrete volcanic unit with a more productive shallow magmatic plumbing system separate from the adjacent ridge segments these high magma supply rates have sustained a continuously replenished steady state magma reservoir that has erupted remarkably homogeneous lavas over a long time period despite this classic association of spreading center and hotspot volcanic activity there is no evidence in the lavas for geochemical or isotopic enrichment typical of hotspot or mantle plume activity the differences in composition between the axial seamount lavas and the juan de fuca ridge lavas are attributed to melting processes rather than to any fundamental differences in their mantle source compositions the higher magma production rates higher sr and lower silica saturation in the seamount lavas relative to the ridge lavas are thought to be a consequence of melt initiation at greater depths the melting column producing the seamount lavas is thought to be initiated in the stability field of spinel peridotite whereas the ridge lavas are produced from a melting column initiated at shallower levels possibly within or close to the stability field of plagioclase peridotite implicit in this interpretation is the conclusion that the juan de fuca ridge lavas and by analogy most morb are generated at shallow mantle levels mostly within the stability field of plagioclase peridotite this interpretation also requires that for the upwelling mantle to intersect the solidus at different depths the mantle supplying axial seamount must be hotter than the rest of the juan de fuca ridge axial seamount therefore reflects a thermal anomaly in the mantle rather than a geochemically enriched ocean island basalt type mantle plume

hydrography and geochemistry of sea surface hydrothermal plumes resulting from hawaiian coastal volcanism the entry of lava into the ocean at kilauea volcano hawaii has produced extensive sea surface hydrothermal plumes studies at this site over 1989 1991 showed that particle rich chemically altered thermal plumes of 1 3 m thickness can be mapped for distances up to 2 km from the entries using an array of physical and chemical tracers particle concentrations in the plumes were as high as 65 mg l 1 and produced light attenuation anomalies exceeding 11 m 1 the maximum observed seawater temperature was 69 c the following extremes in plume chemical markers were measured h2 2 1 m dissolved mn 320 nm dissolved si 55 m co2 1 6 mm alkalinity 1 5 meq l 1 and ph 7 1 dissolved h2 linearly increased and co2 ph and total alkalinity decreased with increasing seawater temperature dissolved mn and si also increased with increasing temperature but were better correlated with each other indicating that heat is not conserved in the surface plumes heat and mass inputs to the ocean are comparable to those from mid ocean ridge crest vent fields

high resolution studies of the summit of axial volcano sea beam bathymetry sea marc i side scan 30 khz towed camera and submersible data from axial volcano juan de fuca ridge jdfr have been integrated to produce detailed maps of the volcano s summit region in order to elucidate its volcanic and tectonic evolution the proximity of axial volcano the youngest edifice of the cobb eickelberg seamount chain to the jdfr superposes a hotspot derived radial stress pattern onto the linear stress field of a mid ocean ridge spreading center the morphology of the summit of axial volcano reflects the differing eruptive styles produced from this superposition long rift zones begin at the edges of the caldera and extend as much as 75 km to the north and south axial volcano has a distinct summit plateau similar to those found on many other submarine volcanos the process by which summit plateaus are constructed is illustrated by the lava flows originating from the south rift zone which have partially filled the southern half of the caldera and have smoothed the flanks the summit plateau contains penetrative ne sw fracturing that is approximately parallel to the jdfr the unusual rectangular caldera is 3 8 km in size and its trend is about 160 three possible mechanisms are discussed for the caldera s formation 1 canary island type trapdoor formation 2 overlapping spreading center interaction and 3 magma source migration although none of these models is fully compatible with the present data base the overlapping spreading center model is preferred postcaldera volcanism probably began with the formation of the central caldera eruptive complex which was characterized by relatively low volume high viscosity flows the most recent volcanism has apparently taken place along the northern and southern rift zones which have erupted more fluid lavas resulting in areally extensive flows covering up to 60 of the caldera floor extensive low temperature venting and areas of high temperature venting near the northern and southern rift zones and caldera walls suggest a shallow magmatic source beneath the summit of axial volcano

a comparison of the gis based landslide susceptibility assessment methods multivariate versus bivariate the purpose of this study is to evaluate and to compare the results of multivariate logical regression and bivariate landslide susceptibility methods in geographical information system gis based landslide susceptibility assessment procedures in order to achieve this goal the asarsuyu catchment in nw turkey was selected as a test zone because of its well known landslide occurrences interfering with the e 5 highway mountain pass

gradients in the composition of hydrothermal fluids from the endeavour segment vent field phase separation and brine loss hydrothermal fluid samples collected in 1984 1987 and 1988 from a large vent field near 47 57 n on the endeavour segment of the juan de fuca ridge jfr have been analyzed for major and minor elements and gases there are of the order of 100 individual smoker vents on 10 large sulfide structures which are localized along faults and fault intersections across the vent field each sulfide structure has a characteristic fluid composition which varies very little from one vent orifice to the next or from year to year on a given structure however there are large gradients in fluid composition across the vent field with endmember chlorinity increasing from 255 mmol kg in the sw to 505 mmol kg in the ne end member concentrations of major elements are well correlated with chlorinity and endmember volatile concentrations in the lowest chlorinity fluids are approximately twice as high as in the highest chlorinity fluids the gradients in composition across the vent field and measured vent fluid temperatures 400 c are consistent with supercritical phase separation and loss of brine phase below the seafloor the factor of 2 variation in co2 and h2s is larger than expected for loss of a very high chlorinity brine concentrations of iron and manganese are not positively correlated with chlorinity suggesting that temperature and ph are more important in controlling metal solubility elevated ammonia and bromide chloride ratios indicate that there has been subseafloor interaction between the hydrothermal fluids and organic matter and high boron concentrations point to a sedimentary source

hydrothermal anomalies in the lucky strike segment on the mid atlantic ridge 37 17 n abstract as part of the fara french american ridge atlantic project the northern mid atlantic ridge mar was surveyed for hydrothermal activity between 33 and 40 n during the fazar cruise in august october 1992 after detection of hydrothermal activity in the lucky strike segment 37 17 n a detailed water column survey was undertaken in this region during a follow up cruise with the dsrv alvin several active high temperature vents were found on the summit of an central seamount here we focus on the results of the water column survey undertaken during the fazar cruise the influence of mediterranean water and the site s shallow depth complicates the hydrography at lucky strike background temperature and salinity gradients are usually too complex to indicate hydrothermal anomalies clearly light transmission anomalies within the lucky strike region were small but were detected throughout the segment from mid depth 1500 m all the way to the valley seafloor 2300 m depth the large depth range covered by these anomalies probably results from vertical mixing as well as the presence of multiple vent sources at various depths methane anomalies and a temperature anomaly observed deeper than the vents documented by alvin further support the idea of additional deeper vents within this segment particle samples of the deep particle layer are enriched in fe and trace metals

gis based detachment susceptibility analyses of a cut slope in limestone ankara turkey due to the rapidly growing population of the city of ankara turkey and increased traffic congestion it has become necessary to widen the ankara eskisehir e 90 highway connecting the newly built areas west of the city to the city center during widening several cut slopes were formed along the highway route as a result some instability problems small sized rock falls sliding sloughing raveling produced detachment zones along a cut slope in highly jointed folded and sheared limestone causing local degradation of the cut slope identification of the areas that are likely to detach from the cut slope in the future is considered to be very important for the application of remedial measures for this purpose the relationships between the existing detachment zones and various parameters e g point load strength index weathering block size daylighting shear zone were investigated using gis based statistical detachment susceptibility analyses in order to predict the further aerial extension of the detachment zones with time during the overlay analyses statistical index and weighting factor methods were used the outcomes of the analyses were compared and evaluated with the field observations to check the reliability of the methods and to assess the detachment zones that may develop in the future the detachment susceptibility map without the block size layer gives the best result and indicates some risky zones where detachments are likely to occur in the future recommendations on remedial measures of the cut slope should consider these risky zones

a model of an atlantic and pacific hydrothermal plume a turbulent entrainment model of a hydrothermal plume was modified to include the effects of vertical structure in the background temperature and salinity fields owing to the stably stratified salinity field in the pacific relatively warm salty water spreads at an equilibrium level where the plume density equals the ambient density in contrast the unstable salinity profile in the atlantic gives the plume added buoyancy and it continues to rise to an equilibrium level where it is relatively cool and fresh these attributes result from the mixing between the plume and the surrounding seawater at each level below the spreading layer the equilibrium temperature anomaly is not directly proportional to the source strength but depends on the mixing and background salinity gradient the net entrainment of surrounding seawater is greater in the atlantic plume model than in the pacific plume model for the same buoyancy flux recent data from the tag hydrothermal field at 26 n on the mid atlantic ridge and data from a vent field on the endeavor segment of the juan de fuca ridge are compared to model results the model predicts the penetration height and s characteristics of the atlantic plume and it explains some of the differences between the observed atlantic and pacific hydrothermal plumes

hydrothermal venting and the apparent magmatic budget of the juan de fuca ridge the fact that vigorous hydrothermal discharge occurs on ridge segments with a variety of spreading rates and morphological characteristics makes it difficult to discern the large scale geological controls on the distribution of hydrothermal venting along the mid ocean ridge we undertook to simplify this problem by mapping the distribution of hydrothermally produced thermal and light attenuation anomalies along the crest of the juan de fuca ridge a medium rate spreading center with segments of markedly differing morphology hydrothermal anomalies were detected by towing a high precision conductivity temperature depth transmissometer ctdt package in a sawtooth pattern through the lowermost 1000 m of the water column above each segment these surveys conducted between 1985 and 1989 have produced the first quantitative and continuous visualizations of hydrothermal plumes along a multisegment portion of the mid ocean ridge hydrothermal discharge is strongest on those segments or portions of segments where the apparent magmatic budget is highest as indicated by the degree of along axis inflation and other morphological characteristics this correspondence implies that magma is episodically delivered in small and spatially discontinuous bodies of melt rather than by the constant resupply of a steady state magma chamber we propose that the probability of discharge occurring at any point on the mid ocean ridge is proportional to the spreading rate this probability scaled by the observation that significant plumes presently emanate from 20 of the juan de fuca ridge is expected to range from 5 on the slowest spreading ridge to 50 on the fastest spreading ridge

grain displacive gas migration in fine grained sediments support for this research was provided by the kaust endowment g e abelskamp edited the manuscript data sets presented as part of this study are available from the kaust repository http hdl handle net 10754 630965

estimation of hydraulic fracture pressure in clay for offshore drilling and in particular when drilling from fixed platforms in deep waters the mud pressure will be high compared with the hydraulic fracture pressure i e the formation strength close to the sea floor the first casing the conductor should therefore be installed to a depth where the formation strength is sufficient to prevent hydraulic fracturing of the soil the consequences of hydraulic fracture could be mud flowing into the formation and loss of mud circulation this slows down the drilling and in cases where large quantities of mud flow into the formations beneath the platform may even threaten the integrity of the foundation soils and create a safety problem a conservative approach with too deep conductor setting depths will on the other hand lead to high unnecessary costs this paper presents a new approach for calculating hydraulic fracture pressures the new calculation approach considers two important factors that are generally not covered by theories found in the lite

submarine venting of phase separated hydrothermal fluids at axial volcano juan de fuca ridge since the discovery of high temperature venting on the east pacific rise in 19791 it has been expected2 3 because of the physical properties of sea water at pressures and temperatures encountered during submarine hydrothermal circulation4 5 that phase separated fluids would discharge from ridgecrest vents although this notion is supported by the reported large deviations in vent fluid chlorinity relative to that of sea water 40 200 6 7 by observations of venting at p t conditions clearly within the two phase region 220 bar and 420 c 8 and by fluid inclusion data9 10 unequivocal identification11 of phase separated venting fluids has remained elusive here we report observations of chloride and metal depleted gas enriched fluids from a shallow vent field on the juan de fuca ridge which confirm the expectation that phase separated effluents are delivered to the deep ocean from some sea floor venting systems

chemistry of hydrothermal solutions from the southern juan de fuca ridge fluids from three vent fields on the southern juan de fuca ridge were sampled in september 1984 using the dsrv alvin the fluids are uniquely high in both chloride which ranges up to twice the seawater value and in metal content simple vapor liquid phase separation could not have produced both the high chlorinity and gas concentrations observed in these fluids the cause of the elevated chlorinity can not be uniquely identified but may be the result of either or a combination of two processes 1 subsurface formation of a degassed brine and subsequent mixing of a small amount of this brine with a hydrothermal seawater which has not undergone a phase separation and 2 dissolution of a chloride rich phase combined with a possible small loss of gas during sampling procedures although measured temperatures were all less than 300 sup 0 c quartz geothermometry suggests that the fluids have equilibrated at greater than 340 sup 0 c quartz geobarometry is also in agreement with geophysical estimates of depth to the local magma chamber copyright american geophysical union 1987

spatial and temporal patterns in larval supply at hydrothermal vents in the northeast pacific ocean larval supply in marine benthic invertebrates influences patterns of settlement and recruitment to adult populations to successfully colonize newly formed or distant hydrothermal vents which are discontinuous and ephemeral habitats larvae of vent invertebrates must possess long range dispersal abilities however a significant proportion of locally produced larvae must remain within the adult habitat to maintain the observed dense assemblages of invertebrates i compared spatial and temporal patterns in larval availability flux and abundance at hydrothermal vents within and between ridge segments in the northeast pacific ocean at axial seamount and endeavour segment on the juan de fuca ridge and at magic mountain on explorer ridge near bottom within 50 cm larval supply individuals m 2 d 1 at five vents on axial seamount measured with passively collecting traps in 2000 and 2001 varied temporally by an order of magnitude but not spatially at scales of tens of meters to kilometers the most abundant larval taxa were gastropods particularly the limpet lepetodrilus fucensis and polychaetes larval abundance in the water column within the axial valley was measured with net tows by the remotely operated vehicle ropos at the three ridge segments axial seamount 2000 2001 endeavour segment 2001 2002 magic mountain 2002 abundance was greater by an order of magnitude at the endeavour segment than at axial seamount and magic mountain and it did not differ between on vent within tens of meters and off vent up to 5 km from the venting source locations within the axial valley the uniformly high abundance of larvae within axial valleys suggests that larval supply within a ridge segment is most likely localized implying significant larval retention on the scale of vent fields and possibly ridge segments

decay of hydrothermal output following the 1998 seafloor eruption at axial volcano observations and models 1 observations of the decay of heat and particle discharge following the reinvigoration of a hydrothermal field by a dike intrusion and eruption can provide insights about subsurface hydrothermal circulation in january 1998 a lava eruption at the summit of axial volcano juan de fuca ridge created numerous new vents along a 5 km length of the caldera boundary five cruises over the next 3 5 years found the inventory of hydrothermal heat and particles determined by optical backscattering in the overlying plume decaying as time t 0 9 these results are consistent with the 1993 coaxial eruption where the heat flux decayed as t 1 2 and t 0 7 at the flow and floc sites respectively all three eruption sites decayed significantly faster than t 0 5 the rate attributable to cooling only by simple conduction through the impermeable layer separating magma from hydrothermal circulation we present a more realistic model of hydrothermal cooling that adds conductive heat loss by ascending fluid to the surrounding rock walls increasing the theoretical loss rate to t 0 75 we suggest that variability in the observed decay rates are not sampling variations but reflect real differences in the local heat supply and cooling processes the decay rate was slowest and matched our model result where no seafloor eruption occurred and a long lasting heat source was likely present floc the rate was fastest where a shallow source erupted a thick lava pavement flow the axial eruption where a substantial magma chamber emplaced only a thin sheet flow may be intermediate between these extremes

an approach for methane hydrates reservoir dissociation in a marine setting krishna godhavari basin east coast india abstract gas hydrates are considered to be potential sources of clean energy various methods of gas hydrates extraction such as thermal stimulation depressurization and inhibitor injection have been proposed but each of them has some advantages and disadvantages depending upon reservoir conditions this study deals with a production method applicable to the fine grained clay rich reservoir conditions in the krishna godhavari kg basin of india by means of introducing an electrode into a gas hydrate reservoir to confine the energy delivery for dissociation and continue with depressurization for sustained production the simulation of electrical heating using matlab and hydrate dissociation quantification using tough hydrate modeling programs supported by laboratory studies indicate that the reservoir temperature can be raised to 21 5 c in one hour at a distance of 1 m from the electrode results indicate that 20 1 m3 of hydrate bearing reservoir section with 90 hydrate saturation can be dissociated in 72 h at a given power of 90 kw the energy balance calculations show that the energy supplied to produce is at the ratio of 1 3 5 to enhance the energy efficiency after 15 h of heating either the input power is increased in incremental stages or thermal stimulation is stopped and extraction is continued with the depressurization technique by pumping out dissociated freshwater from the zone of dissociation within the reservoir at a rate of 144 m3 h with a perforated borehole area of 2 m2 in the reservoir

helium and methane measurements in hydrothermal fluids from the mid atlantic ridge the snake pit site at 23 n methane and helium isotopes concentrations have been measured in hydrothermal fluids of black smoker vents at the snake pit area mar 23 n as part of the hydrosnake cruise with the submersible nautile the samples contain large quantities of helium and methane with endmember values of 4 6 10 5 cm3 stp g for helium and 1 38 10 3 cm3 stp g for methane the helium isotopic ratio 3he 4he is 8 4 times the atmospheric ratio these values are strikingly similar to those already obtained on the east pacific rise the ch4 3he ratio is also quite similar ch4 3he 2 6 106 suggesting a non biogenic origin of this gas in the fluids assuming that the range of variation of the 3he concentration data obtained so far from various tectonic settings is close to the genuine range of values encountered on mid ocean ridges the global mass flow involved in the hydrothermal circulation at the ridge s axis is estimated between 1000 and 3000 m3 of water sec leading to a residence time of the global ocean with respect to the hydrothermal circulation between 15 and 45 million years this estimate implies that in addition to the individual vents smokers there is an extensive diffuse circulation of hydrothermal fluids along the ridges in agreement with recent observations concerning heat budgets at hydrothermal sites in the eastern pacific

distribution and composition of hydrothermal plume particles from the ashes vent field at axial volcano juan de fuca ridge in 1986 and 1987 buoyant and neutrally buoyant hydrothermal plume particles from the ashes vent field within axial volcano were sampled to study their variations in composition with height above the seafloor individual mineral phases were identified using standard x ray diffraction procedures elemental composition and particle morphologies were determined by x ray fluorescence spectrometry and scanning electron microscopy x ray energy spectrometry techniques the vent particles were primarily composed of sphalerite anhydrite pyrite pyrrhotite chalcopyrite barite hydrous iron oxides and amorphous silica grain size analyses of buoyant plume particles showed rapid particle growth in the first few centimeters above the vent orifice followed by differential sedimentation of the larger sulfide and sulfate minerals out of the buoyant plume the neutrally buoyant plume consisted of a lower plume which was highly enriched in fe s zn and cu and an upper plume which was highly enriched in fe and mn the upper plume was enriched in fe and mn oxyhydroxide particles and the lower plume was enriched in suspended sulfide particles in addition to the fe and mn oxyhydroxide particles the chemical data for the water column particles indicate that chemical scavenging and differential sedimentation processes are major factors controlling the composition of the dispersing hydrothermal particles short term sediment trap experiments indicate that the fallout from the ashes vent field is not as large as some of the other vent fields on the juan de fuca ridge

heterogeneous hydrofracture development and accretionary fault dynamics ocean drilling program observations at many accretionary wedges indicate that fluid flow in low permeability sediments is focused along faults rich in clay minerals recent ring shear experiments show that shear failure generally reduces permeability in muddy faults to values well below the surrounding sediments and that very little increase occurs in the fault permeability even when continued failure proceeds under steadily reduced effective loads it is thus unlikely that observed focused flow occurs through the matrix of muddy faults and we suggest that focused flow can only be explained by the development of open fracture systems the lithostatic fluid pressures necessary for hydrofracturing in weak sediments cannot however exist throughout the imbricate thrust system and basal decollement zone because a zero basal shear stress condition would result in regional instability and accretionary wedge collapse we propose that the regional hydrofracture networks must propagate heterogeneously leaving relatively strong asperity regions at sublithostatic fluid pressures to balance forces in the wedge in three dimensions

distribution of hydrothermal manganese over the juan de fuca ridge bottom waters from five hydrographic stations spaced equally along a 400 km section of the juan de fuca ridge north of the blanco fracture zone contain anomalously high concentrations of total dissolvable manganese tdm the two bottom most bottles from each hydrocast approx 100 to 200 m above bottom range from 8 3 to 108 9 nmol kg sup 1 with a median value of 12 0 nmol kg sup 1 this median is nearly a factor of 10 higher than similar near bottom samples obtained from two off axis locations analogy to work on the east pacific rise implies that hydrothermal activity along the ridge axis is contributing substantially to the manganese content of the water column in this portion of the northeastern pacific

the application of gis based logistic regression for landslide susceptibility mapping in the kakuda yahiko mountains central japan as a first step forward in regional hazard management multivariate statistical analysis in the form of logistic regression was used to produce a landslide susceptibility map in the kakuda yahiko mountains of central japan there are different methods to prepare landslide susceptibility maps the use of logistic regression in this study stemmed not only from the fact that this approach relaxes the strict assumptions required by other multivariate statistical methods but also to demonstrate that it can be combined with bivariate statistical analyses bsa to simplify the interpretation of the model obtained at the end in susceptibility mapping the use of logistic regression is to find the best fitting function to describe the relationship between the presence or absence of landslides dependent variable and a set of independent parameters such as slope angle and lithology here an inventory map of 87 landslides was used to produce a dependent variable which takes a value of 0 for the absence and 1 for the presence of slope failures lithology bed rock slope relationship lineaments slope gradient aspect elevation and road network were taken as independent parameters the effect of each parameter on landslide occurrence was assessed from the corresponding coefficient that appears in the logistic regression function the interpretations of the coefficients showed that road network plays a major role in determining landslide occurrence and distribution among the geomorphological parameters aspect and slope gradient have a more significant contribution than elevation although field observations showed that the latter is a good estimator of the approximate location of slope cuts using a predicted map of probability the study area was classified into five categories of landslide susceptibility extremely low very low low medium and high the medium and high susceptibility zones make up 8 87 of the total study area and involve mid altitude slopes in the eastern part of kakuda mountain and the central and southern parts of yahiko mountain

crustal magnetization and the subseafloor structure of the ashes vent field axial seamount juan de fuca ridge implications for the investigation of hydrothermal sites

circulation near axial seamount year long moored current measurements from 1987 to 1988 on the saddle 1860 m between axial volcano and brown bear seamount show an oscillating flow with a broadband frequency centered at about 4 days and a long term average flow of about 4 cm s southward the measurements at sill depth also suggest a possible alternating exchange of water north and south of the cobb eickelberg seamount chain with warmer water 0 05 c coming from the north however measurements near the top of the volcano at about 1400 m show a weaker but northward mean flow and the 4 day oscillation barely exists conductivity temperature and depth ctd observations on the east side of the volcano infer possible intensification of southward flow adjacent to the juan de fuca ridge similar to that found with combined ctd and current meter observations about 100 km to the south southward flow is hypothesized along the entire east side of the ridge on the west side the axial brown bear saddle may be near a convergence zone between southward and northward currents which then flow westward the highly energetic environment on the saddle suggests other gaps in the ridge and seamount chains may be important in determining the fate of the hydrothermal effluents the general oceanic flow at the top of the caldera however is more tenuous and the depth of change between these two regimes cannot be determined

hydrothermal venting from the summit of a ridge axis seamount axial volcano juan de fuca ridge we have mapped the distribution and intensity of submarine hydrothermal emissions from the summit caldera of axial volcano by means of hydrographic and chemical sampling of the water column during annual cruises in four consecutive years 1985 1988 these investigations were undertaken to ascertain the strength of hydrothermal venting relative to other vent fields on the juan de fuca ridge and to gauge the importance of axial volcano as a source of hydrothermal emissions to the northeast pacific ocean measurable temperature anomalies are mostly restricted to a 200 m thick water column within the caldera where they range from a background level of 0 01 c to local maxima of 0 02 0 1 c above known high temperature vent fields the temperature anomaly plume is significantly smaller in both extent and intensity than plumes emitted by vent fields on other segments of the juan de fuca ridge a maximum estimate of the total heat flux from the summit based on the total excess heat and advective velocity of the plume is 8 108 w hydrothermal venting seems surprisingly small for an edifice that testifies to a long term oversupply of magma at a single axial location we speculate that additional heat may be lost from axial volcano by diffuse percolation of sea water over broad areas of its flanks and by magma eruption and venting along flank rift zones

assessment of landslide susceptibility on the natural terrain of lantau island hong kong steep terrain and the high frequency of tropical rainstorms make landslide occurrence on natural terrain a common phenomenon in hong kong for example more than 800 slope failures were triggered by a rainstorm in november 1993 on lantau island hong kong maps of recent landslides interpreted from aerial photographs in combination with a geographical information system were used to evaluate the frequency and distribution of landslides with particular reference to such physical parameters as lithology slope gradient slope aspect elevation vegetation cover and proximity to drainage line all of which are considered to be influential in the occurrence of landslides a stepwise logistic regression model was obtained between landslide susceptibility and the above mentioned physical parameters the study area has been classified into five classes of relative landslide susceptibility namely very low low moderate high and very high based on this methodology

discrete and diffuse heat transfer atashes vent field axial volcano juan de fuca ridge abstract heat fluxes of discrete and diffuse components of hydrothermal discharge are estimated from submersible measurement in the ashes vent field located in the caldera of axial volcano on the central juan de fuca ridge the discrete component comprises discharge from individual vents and the diffuse component comprises seepage from large areas of the seafloor the investigation centered on the high temperature portion of the field a 100 100 m area of fractured lobate and sheet lava flows encompassing discrete discharge 326 c from seven individual vents and diffuse flow from intervening areas a total of 4 4 2 10 6 w was estimated for the discrete heat flux based on measurements of effluent temperature flow rate and orifice diameter at all the known individual vents by d s v alvin in september 1987 a total of 15 75 10 6 w was calculated with a standard plume model for the diffuse flux based on a grid of temperature measurements at altitudes of 1 m and 20 m above the study area using a 1 m long vertical array of temperature sensors mounted at the front of alvin s instrument platform the study indicates that 1 the diffuse component rises separately from the discrete component of hydrothermal discharge and is laterally advected by a prevailing current below the discrete component and that 2 the diffuse component of convective heat flux is approximately an order of magnitude greater than the discrete component in the high temperature portion of the ashes vent field

seismic characteristics of fluid escape pipes in sedimentary basins implications for pipe genesis abstract fluid escape pipes were first documented from 3d seismic data over a decade ago and have subsequently been identified in many petroliferous basins worldwide they are characterized on seismic data by vertical to sub vertical zones of reduced reflection continuity that have a columnar geometry in three dimensions the upper terminations of these pipes commonly coincide with pockmarks or palaeo pockmarks signifying a close connection of pipe formation with a high flux fluid expulsion process dimensions range from tens to hundreds of metres in diameter and hundreds to over a thousand metres in height and the slenderness ratio defined as height diameter ranges from 0 8 to over 20 pipes are frequently associated with sub vertical clustering of amplitude anomalies on seismic data related either to the presence of free gas or to cementation linked to the passage of hydrocarbons three mechanisms have been suggested to explain pipe genesis 1 hydraulic fracturing 2 erosional fluidisation and 3 capillary invasion we suggest a further two possible mechanisms in the form of localised collapse by volume loss and synsedimentary flow localisation we review all five mechanisms and conclude that it is unlikely that a single mechanism applies but that combinations of these processes may all occur in particular contexts fluid escape pipes may be far more widespread that currently appreciated and they may play a critical role in secondary hydrocarbon migration and in providing leakage pathways for trapped hydrocarbons through overlying seals

landslide inventory of northwestern anatolia turkey turkey is heavily exposed to natural hazards such as earthquakes landslides and floods the total loss caused by landslides in terms of affected buildings in a period of 35 years between 1959 and 1994 constitutes 27 of the entire loss from all natural hazards and is second after earthquakes there are no other available data on either direct or indirect losses due to landslides on a national scale the general directorate of mineral research and exploration mta started the turkish landslide inventory mapping project in 1997 to improve understanding of regional and national landslide processes the purpose of the project is to establish landslide inventory maps at medium 1 25 000 regional 1 100 000 and national 1 500 000 scales existing landslides are mapped on 1 25 000 scale topographic base maps by interpretation of aerial photographs and field investigations the base maps are then digitized and stored in a geographic information system gis database by the geological research department of mta hence regional and national scale landslide maps will be available as well as the work progresses landslides are classified as fall topple slide and flow and are broadly characterized as active or inactive the landslides are also classified according to their relative depths as shallow depth 5 m the present paper will attempt to describe the project standards and its application to the area of 1 500 000 scale zonguldak quadrangle the study area extends to 39 081 km2 and 7 1 of the area was found to be affected by landslides a total 10 007 landslides 392 shallow seated 8020 deep seated active and 1595 deep seated inactive were mapped in the area covering 2768 km2 cretaceous flysch paleocene eocene flysch and paleocene middle miocene volcanics are the most landslide prone units and constitute 27 8 29 9 and 7 2 of the all landslides respectively

geochemistry of hydrothermal fluids from axial seamount hydrothermal emissions study vent field juan de fuca ridge subseafloor boiling and subsequent fluid rock interaction hydrothermal fluids collected from the ashes vent field in 1986 1987 and 1988 exhibit a very wide range of chemical composition over a small area 60 m in diameter compositions range from a 300 c gas enriched 285 mmol kg co2 low chlorinity 33 of seawater fluid to a 328 c relatively gas depleted 50 mmol kg co2 high chlorinity 116 of seawater fluid the entire range of measured compositions at ashes is best explained by a single hydrothermal fluid undergoing phase separation while rising through the ocean crust followed by partial segregation of the vapor and brine phases other mechanisms proposed to produce chlorinity variations in hydrothermal fluids precipitation dissolution of a chloride bearing mineral or crustal hydration cannot produce the covariation of chlorinity and gas content observed at ashes there is good agreement of the measured fluid compositions with compositions generated by a simple model of phase separation in which gases are partitioned according to henry s law and all salt remains in the liquid phase significant enrichments in silica lithium and boron in the low chlorinity fluids over levels predicted by the model are attributed to fluid rock interaction in the upflow zone depletions in iron and calcium suggest that these elements have been removed by iron sulfide and anhydrite precipitation at some time in the history of the low chlorinity fluids the distribution of low and high chlorinity venting is consistent with mechanisms of phase segregation based on differential buoyancy or relative permeability the relatively shallow depth of the seafloor 1540 m and the observed chemistry of ashes fluids are consistent with phase separation in the sub critical or near critical region

geologic history of the summit of axial seamount juan de fuca ridge 1 multibeam 1 m resolution and side scan data collected from an autonomous underwater vehicle and lava samples radiocarbon dated sediment cores and observations of flow contacts collected by remotely operated vehicle were combined to reconstruct the geologic history and flow emplacement processes on axial seamount s summit and upper rift zones the maps show 52 post 410 ce lava flows and 20 precaldera lava flows as old as 31 2 kyr the inferred age of the caldera clastic deposits 1 2 m thick accumulated on the rims postcaldera between 31 ka and 410 ce there are no known lava flows near the summit the oldest postcaldera lava 410 ce is a pillow cone se of the caldera two flows erupted on the w rim between 800 and 1000 ce from 1220 to 1300 ce generally small eruptions of plagioclase phyric depleted mafic lava occurred in the central caldera and on the east rim larger post 1400 ce eruptions produced inflated lobate flows of aphyric less depleted and less mafic lava on the upper rift zones and in the n and s caldera all caldera floor lava flows and most uppermost rift zone flows postdate 1220 ce activity shifted from the central caldera to the upper s rift outside the caldera to the n rift and caldera floor and then to the s caldera and uppermost s rift where two historical eruptions occurred in 1998 and 2011 the average recurrence interval deduced from the flows erupted over the last 800 years is statistically identical to the 13 year interval between historical eruptions

pore pressure generation in sedimentary basins overloading versus aquathermal the principal mechanism for abnormally high pore pressure generation has been an important matter of debate for more than a decade among the various mechanisms proposed mechanical overloading and aquathermal pressuring have probably received the greatest attention most previous discussions however have been based upon qualitative conceptual models here we propose a quantitative analysis by first examining the basic principles of porous flow and the fundamental properties of sediments and second by comparing the relative importance of the overloading versus the aquathermal mechanisms the coupling between pore pressure and compaction as well as the nonlinear and path dependent material properties are found to be critical in the present analysis we find that although changes in stress and temperature both contribute to pressure generation mechanical overloading is the main mechanism under normal geological conditions and is capable of producing the observed pore pressure profiles

the physics of bubbles in surficial soft cohesive sediments abstract this paper reviews current understanding of the physics of bubbles in soft unlithified cohesive sediments certainly in the top 100 m from the sediment water interface but likely much deeper experimental evidence primarily ct scans and internal pressure records indicate that near surface bubbles grow by elastically compressing and fracturing these sediments which results in thin irregular disks of gas these data do not suggest either plastic or fluid behavior on the part of the bulk sediment in addition there is no hint of capillary invasion of gas into the pores of fine grained sediments the growth rate of an elastic fracturing disk shaped bubble can vastly exceed that of a spherical bubble depending on the eccentricity of the bubble this effect results from the far more favorable surface to volume ratio of flattened bubbles the initial rate of rise of bubbles in cohesive sediments also appears to be governed by a fracture process which is driven by pseudo buoyancy the rate of bubble rise could be controlled by various possible mechanisms but only the predictions from a visco elastic fracture propagation model seem to produce rise velocities that are not ballistic experimental evidence demonstrates that a rising bubble can deviate from its path to the surface if it encounters a zone of sediment with lower lateral fracture toughness such a bubble will begin to move in a lateral direction but stall because pseudo buoyancy is no longer operative subsequent bubbles will do the same and accumulate in the low fracture toughness zone this explains the occurrence of shallow sub seafloor domes of gas and modeling of this process predicts only modest over pressures in such structures

estimation of heat and chemical fluxes from a seafloor hydrothermal vent field using radon measurements the circulation of seawater through newly formed ocean crust at mid ocean ridge spreading centres is important in the oceanic heat and chemical budgets the heat transfer in submarine hydrothermal systems accounts for 25 of the total global heat loss1 the transfer of mass resulting from basaltic alteration affects the geochemistry of seawater2 and is responsible for the formation of ore deposits on and beneath the seafloor3 various geophysical techniques have been employed in efforts to determine the heat output from hydrothermal vent fields4 9 however the magnitudes of the heat and chemical fluxes through these systems remain uncertain here we introduce a geochemical approach for estimating the flux from a vent field based on radon 222rn measurements in the overlying effluent plume this method was applied successfully in september 1986 during a 23 day expedition to an active vent field on the 170 km endeavour segment of the juan de fuca ridge fig la we estimate the heat flux from this site to be l 5 l09 w

characteristics of hydrothermal plumes from two vent fields on the juan de fuca ridge northeast pacific ocean deep ctd transmissometer tows and water bottle sampling were used during 1985 to map the regional distribution of the neutrally buoyant plumes emanating from each of two major vent fields on the southern symmetrical segment sss and endeavour segment es of the juan de fuca ridge at both vent fields emissions from point and diffuse hydrothermal sources coalesced into a single 200 m thick plume elongated in the direction of current flow and with characteristic temperature anomalies of 0 02 0 05 c and light attenuation anomalies of 0 01 0 08 m 1 10 80 g l above background temperature anomalies in the core of each plume were uniform as far downcurrent as the plumes were mapped 10 15 km downcurrent light attenuation trends were non uniform and differed between plumes apparently because different vent fluid chemistries at each field cause significant differences in the settling characteristics of the hydrothermal precipitates vent fluids from the sss are metal dominated and mostly precipitate very fine grained hydrous fe oxides that remain suspended in the plume vent fluids from the es are sulfur dominated and precipitate a high proportion of coarser grained fe sulfides that rapidly settle from the plume the integrated flux of each vent field was estimated from measurements of the advective transport of each plume heat flux was 1700 1100 mw from the es and 580 351 mw from the sss particle flux varied from 546 312 g s to 204 116 g s at the es depending on distance from the vent field and was 92 48 g s from the sss

relationships between lava types seafloor morphology and the occurrence of hydrothermal venting in the ashes vent field of axial volcano deep towed and submersible photographic surveys within the caldera of axial volcano have been integrated with high resolution bathymetry to produce a geological map of the most active vent field axial seamount hydrothermal expeditions ashes in the caldera the ashes vent field encompasses an approximately 200 m 1200 m area of active venting which is located adjacent to the southwest caldera wall locations for over 2000 photographs in and near the vent field were determined using a seafloor transponder network then each photograph was described utilizing a classification system which provides detailed information concerning lava type hydrothermal activity sediment cover geological structure and biology resulting data were entered into a digital data base and computer generated maps were created that portray spatial relationships between selected geological variables in general the entire ashes field is characterized by pervasive low temperature venting the most vigorous venting is concentrated in an approximately 80 m 80 m area where there are several high temperature vents including some which are producing high temperature vapor phase fluids derived from a boiling hydrothermal system lava types within the ashes vent field are grouped into three distinct morphologies 1 smooth flat surfaced ropy and whorled sheet flows 2 lobate flows and 3 jumbled sheet flows the most intense hydrothermal venting is concentrated in the smooth sheet flows and the lobate flows the location of the ashes field is mainly attributable to faulting which defines the southwest caldera wall but the concentration of intense venting appears to be related also to the spatial distribution of lava types in the vent field and their contrasting permeabilities other structural trends of faults and fissures within the field also influence the location of individual vents

hydrothermal venting at vailulu u seamount the smoking end of the samoan chain 1 the summit crater of vailulu u seamount the youngest volcano in the samoan chain hosts an active hydrothermal system with profound impact on the ocean water column inside and around its crater 2 km wide and 407 m deep at a 593 m summit depth the turbidity of the ocean water reaches 1 4 ntu values that are higher than in any other submarine hydrothermal system the water is enriched in hydrothermal mn 3 8 ppb and 3he 1 10 11 cc g and we measured water temperature anomalies near the crater floor up to 0 2 c the hydrothermal system shows complex interactions with the ocean currents around vailulu u that include tidally modulated vertical motions of about 40 50 m and replenishment of waters into the crater through breaches in the upper half of the crater wall inside and outside potential density gradients suggest that hydrothermal venting exports substantial amounts of water from the crater 1 3 0 2 108 m3 day which is in good agreement with fluxes obtained from a tracer release experiment inside the crater of vailulu u 0 8 108 m3 day hart et al 2003 this mass flux in combination with the differences in the inside and outside crater temperature yields a power output of around 760 megawatts the equivalent of 20 100 mor black smokers the mn output of 300 kg day is approximately ten times the output of a single black smoker

discontinuity controlled probabilistic slope failure risk maps of the altindag settlement region in turkey the evaluation of potential rock slope problems using stereographic projection techniques known as kinematic analysis is one of the most important parts of a slope stability investigation to be carried out in jointed rock media in conventional stereoprojection techniques for the assessment of possible rock slope failures the peak orientations of joints together with the slope geometry and the friction angle of the weakness planes are used other possible joint orientations which may be encountered in the rock media are ignored although they belong to the group of joint peak orientations in this study nearly vertical jointed andesites cropped out at the altindag settlement region in ankara were studied in order to evaluate the relevance of this ignored discontinuity orientation data on slope stability as a result probabilistic risk maps for planar toppling and wedge failures were produced using the kinematic rules and digital elevation model of the study area the comparison of the distribution of the actual failures in the area and the probabilistic risk maps prepared for the study area revealed that all of the identified failures are found to be located in the higher risk zones on the probabilistic risk maps

hydrothermal methane venting between 12 n and 26 n along the mid atlantic ridge hydrographic surveys along the mid atlantic ridge mar between 12 n and 26 n carried out from 1984 to 1990 show a variable pattern of ch4 rich water column plumes the vertical distribution of ch4 at stations located every 20 40 km is presented along this 1200 km long section of the mar ch4 venting is clearly demonstrated ch4 enriched fluids rise from vents as plumes spreading is confined to the axial valley due to the topography of the mar ch4 contents from 45 nmol to 675 nmol kg are measured in the buoyant plumes above the two active hydrothermal sites mark 23 n tag 26 n known at present whereas ch4 anomalies up to 3 6 nmol kg are typically observed in plumes emitted either on the inner floor on the walls and or at the top of the rift mountains along the studied ridge section ch4 concentrations 45 mol to 144 mol kg in mark and tag vent fluids are of the same order of magnitude as those found in the east pacific rise fluids even though ch4 is known to be unstable with respect to oxidation by dissolved oxygen and in spite of its microbial oxidation in plumes these results confirm ch4 to be a good indicator to track hydrothermal plumes and to map the variation of hydrothermal activity along mid oceanic ridges moreover between 12 and 26 n along the mar ch4 results show that while hydrothermal activity is present everywhere along the ridge it is predominant near fracture zones fz kane fz 15 20 n fz comparison of ch4 tracer with total dissolvable manganese tdm tracer in plumes allows us to differentiate subseafloor hydrothermal processes the high tdm ch4 found above tag and mark areas is indicative of basalt seawater interaction while at 15 n the low tdm ch4 provides evidence of fluid circulation in ultrabasic rocks ch4 data confirm the association between mantle degassing hydrothermal activity and serpentinization along this 12 26 n section of the mid atlantic ridge

landslide susceptibility mapping for a landslide prone area findikli ne of turkey by likelihood frequency ratio and weighted linear combination models landslides are very common natural problems in the black sea region of turkey due to the steep topography improper use of land cover and adverse climatic conditions for landslides in the western part of region many studies have been carried out especially in the last decade for landslide susceptibility mapping using different evaluation methods such as deterministic approach landslide distribution qualitative statistical and distribution free analyses the purpose of this study is to produce landslide susceptibility maps of a landslide prone area findikli district rize located at the eastern part of the black sea region of turkey by likelihood frequency ratio lrm model and weighted linear combination wlc model and to compare the results obtained for this purpose landslide inventory map of the area were prepared for the years of 1983 and 1995 by detailed field surveys and aerial photography studies slope angle slope aspect lithology distance from drainage lines distance from roads and the land cover of the study area are considered as the landslide conditioning parameters the differences between the susceptibility maps derived by the lrm and the wlc models are relatively minor when broad based classifications are taken into account however the wlc map showed more details but the other map produced by lrm model produced weak results the reason for this result is considered to be the fact that the majority of pixels in the lrm map have high values than the wlc derived susceptibility map in order to validate the two susceptibility maps both of them were compared with the landslide inventory map although the landslides do not exist in the very high susceptibility class of the both maps 79 of the landslides fall into the high and very high susceptibility zones of the wlc map while this is 49 for the lrm map this shows that the wlc model exhibited higher performance than the lrm model