sedimentary features of the seismo turbidites lake biwa japan abstract seismo turbidite layers are deposited at the foot of the steep slope of the half graben in which lake biwa has accumulated sedimentary studies especially of grain size distribution of selected turbidites provide excellent information for clarifying the distinctive features of general seismo turbidites development of the two constituent sublayers lower sandy sublayer and upper silt sublayer lack or limited appearances of traction indicating structures and characteristic grain size distribution in the two constituent sublayers are most remarkable and significant the characteristic grain size distribution features are coarse tail grading in a relatively thick sandy sublayer exceptionally rapid distribution grading through the thin boundary interval between the two sublayers height increase and fluctuation of the silt mode and high clay content brief discussion was made on the causes of these sedimentary features the need and importance of further comparative studies of various turbidites known triggering forces are emphasized

quartz cemented breccias from the mid atlantic ridge samples of a high salinity hydrothermal upflow zone textural mineralogical chemical and fluid inclusion studies on a suite of quartz rich sulfide bearing greenstone breccias indicate that high salinity high fluid flow systems were recently active on the mid atlantic ridge south of the kane fracture zone these systems involved fluids with temperatures close to 300 c and salinities almost 3 times that of seawater rounded pebblelike fragments enclosed within a matrix of euhedral quartz crystals appear to have been cemented by quartz deposition from a moving fluid which attained velocities in excess of 1 m s homogenization temperatures and freezing point depression effects in fluid inclusions from texturally early and late quartz crystals indicate temporal evolution of fluid temperatures and nacl equivalent salinities from 290 c and 10 wt to 200 c and 4 7 wt during alteration and cementation of the breccias highly variable cobalt concentrations in the evolving hydrothermal solutions are indicated by fine scale oscillatory zoning in euhedral pyrite within the breccias a continuous supply of the high salinity fluids may be generated either by supercritical two phase separation at depths well below the level of inclusion entrapment or by retrograde dissolution of hydroxy chloride phases in the deeper portions of the hydrothermal system either model requires the initial temperature of the deeply circulating fluids to have been distinctly higher than 415 c and the fluid to have been cooled by conduction or by mixing with lower temperature seawater prior to entrapment within the inclusions

analysis of fluid inclusions in seafloor hydrothermal precipitates testing and application of an integrated gc ic technique the principal research objective was to test an integrated gas gc and ion chromatographic ic technique for analysis of trapped fluids in seafloor hydrothermal precipitates and to compare the results with independently analyzed vent fluids twenty three samples of chalcopyrite pyrite sphalerite barite and anhydrite from hydrothermal chimneys from four seafloor sites axial seamount juan de fuca ridge the vai lili vent field lau basin the tag hydrothermal field mid atlantic ridge and the 21 n vent field east pacific rise as well as of pyrite marcasite and quartz from the tag mound were analyzed a new type of blank for sulphides and sulphates was also developed water contents obtained by gc analysis are in agreement with known compositions of seafloor hydrothermal solutions also the volatiles occur in the same order of abundance as in vent fluids co2 n2 co ar o2 ch4 cos c2 c3 hydrocarbons for all analyzed hydrothermal fluids the mean cl concentrations are similar to those for the respective measured vent fluid compositions furthermore the gc ic results are directly comparable to salinity data determined by microthermometric methods nh4 can be enriched and is most probably formed by decomposition of organic matter volatile concentrations in fluid inclusions and data from vent fluids differ significantly for some of the investigated sites furthermore the gc data indicate systematic variations regarding the volatile contents of trapped fluids from different active seafloor hydrothermal systems fluid inclusion volatile data of samples from the ashes vent field at axial seamount define an inclined array consistent with phase separation

turbidite chronostratigraphy off algiers central algerian margin a key for reconstructing holocene paleo earthquake cycles northern algeria is threatened by moderate to large magnitude earthquakes resulting from the slow convergence between the african and european plates main active faults are located offshore along the algerian coast as exemplified by the 2003 mw 6 8 boumerdes earthquake this event triggered numerous and widespread turbidity currents over 150 km along strike in the algerian basin reaching 2800 m of water depth and demonstrates the multi source and multi path characteristics of earthquake triggered turbidity flows along this margin segment we rely on the sedimentological analysis of five cores located at the toe of the algiers margin close to the 2003 cable break sites to explore the potential for holocene turbidite paleoseismology radiocarbon measurements provide age models for hemipelagic sediments based on sedimentary facies identification analysis of depositional sequences stacking pattern and a stratigraphic framework established by age models a first correlation of turbidites between the 5 cores is attempted the number of turbidites is constant at the base of the continental slope and decreases seawards over 80 km away from the coast from turbidite correlations 36 synchronous events are identified along the algiers margin segment over the last 9 kyr and are tentatively interpreted as seismically triggered providing a 250 yr mean recurrence interval the main historical earthquakes in the algiers area 2003 1716 and 1365 ce reasonably correlate with three out of the four last turbidites strengthening the hypothesis that turbidites are suitable markers for holocene paleoseismology recurrence intervals of turbidites range between 50 and 900 yr defining quiescence periods exceeding 450 yr three quiescence periods lasting about 800 1400 and 500 yr 7 6 2 ka bp 5 4 4 ka bp and 1 5 1 ka bp respectively support irregular earthquake cycling earthquake triggered turbidites are more frequent in the study area than in the western adjacent margin segment offshore el asnam this higher frequency could arise from the close location of the seismogenic faults beneath the continental slope whereas they are located several tenths of kilometers onland in the el asnam area implying less instabilities of the submarine slope

consequences of phase separation on the distribution of hydrothermal fluids at ashes vent field axial volcano juan de fuca ridge recent studies of hydrothermal fluid chemistry at the axial seamount hydrothermal emissions study ashes vent field of axial volcano indicate separation of liquid and vapor phases during the migration of fluids to the seafloor the brine phase liquid emanates from discrete sulfide chimneys while fluid which has been through vapor phase separation flows diffusely from fissures in the surrounding basalt one possible mechanism to explain this spatial segregation of the fluid phases is based on the relative permeability terms in the equations of two phase flow a qualitative model for the distribution of fluids observed at ashes is postulated in which brine phase fluids are confined within flow conduits by a surrounding relative permeability barrier while vapor phase fluids flow diffusely into the surrounding host rock

a search for hydroacoustic signals associated with the 2 june 1988 temperature anomaly at axial seamount data from the wake island hydrophone array is examined for signals possibly associated with sudden decreases in bottom temperature at axial seamount which is located on the juan de fuca ridge in spite of the extreme sensitivity of the wake hydrophones to small explosive charges and unreported shallow focus earthquakes along the juan de fuca ridge and to unreported episodes of submarine volcanism no sustained signals were found which appear to be related to the observed temperature anomalies because of intermittent recording problems some hydroacoustic signals of extremely short duration possibly associated with the temperature anomalies could have escaped detection in the eight hours subsequent to the occurrence of these anomalies however no such signals could have escaped detection during an eight hour period prior to the onset of the observed anomalies since the recording system was working properly the absence of signals indicates that sustained teleacoustically detectable submarine volcanism was not associated with the 2 june 1988 temperature anomaly

axial load transfer in liquefiable soils for free standing piles the shaft friction capacity of a piled foundation is commonly linked to the effective stresses acting on the pile and hence it is assumed that if the surrounding soil liquefies following an earthquake event the shaft friction capacity of a pile drops to zero in this paper an investigation into the axial load transfer during a liquefaction event based on dynamic centrifuge test results is presented a free standing pile group with the pile cap clear of the ground surface is considered to clarify the mechanism of load transfer the pile group was instrumented to measure axial loading at several locations along the pile length and was embedded in a saturated soil profile where a dense permeable base layer was overlain by a layer of loose liquefiable sand the results show that shaft friction continues to be maintained during an earthquake in both loose and dense soil in the case of loose soils the apparent shaft friction capacity is proposed with reference to the shear taking place at the pile soil i

geochemical modeling of the zoned footwall alteration pipe hellyer volcanic hosted massive sulfide deposit western tasmania australia the mineralogy of hydrothermal alteration assemblages siliceous core chlorite zone sericite zone in the footwall pipe of the hellyer volcanic hosted massive sulfide vhms deposit is controlled mainly by the temperature ph and redox state of the hydrothermal fluids based on the results of our numerical modeling the zoned alteration system could have formed by a combination of water rock interaction and cooling with a siliceous core predicted to form at the center of the conduit passing outward to a chlorite dominated zone a sericite rich zone and finally grading out to unaltered andesite these mineralogical changes relate to a gradual evolution of fluid chemistry water rock ratio ph and temperature from the core to the margin of the system initial temperatures were probably close to 350 degrees c and the hydrothermal fluids were reduced h2s dominated at low temperatures 200 degrees c a peripheral alteration zone consisting mostly of k feldspar chlorite sericite and hematite is predicted to form this low temperature zone has not been recognized at hellyer but elevated k2o contents and local k feldspar development have been noted at other vhms deposits suggesting that this zone might form at low temperatures and low water rock ratios in the footwall of vhms deposits if the existence of barren outer k feldspar alteration zones is confirmed the findings could have important implications for exploration specifically with regards to distinguishing ore related alteration zones from barren alteration systems

chloride depletions and enrichments in seafloor hydrothermal fluids constraints from experimental basalt alteration studies na k ca cl fluid was reacted with diabase at 400 and 425 c 400 bars and fluidrock mass ratio of 0 5 to assess the relative mobility of dissolved cl fluids from the present experiments reveal relatively large time and temperature dependent decreases in cl temperature increase enhances cl removal whereas reaction progress has the opposite effect these changes are not due to boiling and or phase separation at 400 and 425 c 400 bars cl removal from solution is accompanied by ca and na fixation respectively both experiments produced mixed layer chlorite smectite clinozoisite and albite olivine was not detected by x ray diffraction or petrographic analysis of run products from either experiment however we propose that the time dependent changes in dissolved cl result from olivine replacement by an fe hydroxy chloride phase followed by hydration effects quenched and washed alteration products however did not reveal anomalous cl which suggests that the cl bearing phase is characterized by retrograde solubility this is consistent with the relative magnitude of cl fixation observed for experiments at both temperatures and from results of an isobaric cooling experiment the experiments provide evidence for the non conservative behavior of cl during hydrothermal alteration of basalt the data are particularly important in light of the cl depleted nature of some ridge crest hot spring fluids and suggest temperatures of formation for these fluids of approximately 410 c assuming sub seafloor pressure of 400 bars in addition the retrograde solubility of the cl bearing phase responsible for cl fixation during high temperature basalt alteration may help to explain cl enrichment in hot spring fluids which have conductively cooled below 350 c

re mobilization of pile shaft friction after an earthquake during strong earthquakes significant excess pore pressures can develop in saturated soils after shaking ceases the dissipation of these pressures can cause significant soil settlement creating downward acting frictional loads on piled foundations additionally if the piles do not support the full axial load at the end of shaking then the proportion of the superstructure s vertical loading carried by the piles may change as a result of the soil settlement further altering the axial load distribution on piles as the soil consolidates in this paper the effect of hydraulic conductivity and initial post shaking pile head loading is investigated in terms of the changing axial load distribution and settlement responses the investigation is carried out by considering the results from four dynamic centrifuge experiments in which a 2 2 pile group was embedded in a two layer profile and subjected to strong shaking it is found that large contrasts in hydraulic conductivity between the two layers of the soil model affected both the pile group settlements and axial load distribution both these results stem from the differences in excess pore pressure dissipation part of which took place very rapidly when the underlying soil layer had a large hydraulic conductivity

supercritical two phase separation of hydrothermal fluids in the troodos ophiolite the hot 350 c black smoker springs of the ocean floor are the vents of hydrothermal systems in which cold seawater descends below the ocean floor is heated reacts with the host rock and is transformed into metal bearing brine the salinity of these brines varies between vents from 0 7 to 2 0 times seawater salinity1 4 this variation has been ascribed to crustal hydration5 crystallization of chloride bearing minerals6 or two phase separation of seawater into components of differing salinity4 7 12 here we present fluid inclusion evidence for two phase separation in the ancient troodos sulphide forming systems of cyprus and discuss with the nacl h2o system as a model how this process could explain observed salinity variations in hydrothermal fluids

frequent sediment density flows during 2006 to 2015 triggered by competing seismic and weather events observations from subsea cable breaks off southern taiwan at least 17 subsea telecommunications cables cross the gaoping canyon and manila trench system in the strait of luzon between taiwan and the philippines there cable breaks record rapid 5 16 ms 1 long run out 300 km sediment density flows triggered by earthquakes and typhoons four major cable breaking events have occurred in the last decade in 2006 the pingtung ml 7 0 earthquakes formed up to 3 individual flows some of which ran out for up to 460 km in 2009 typhoon morakot generated two sediment flows the first was triggered by hyperpycnal river discharge whereas a second flow formed 3 days later possibly due to failure of recently deposited flood sediment in upper gaoping canyon a flow in 2010 formed during a swarm of ml 3 5 earthquakes that followed the ml 6 4 jiashian earthquake finally typhoon soudelor of 2015 caused the gaoping river to form a hyperpycnal plume that failed to break cables at 2600 m depth but broke at least 6 cables in deeper water the 2006 pingtung earthquakes produced the largest sediment flow s that produced 22 cable breaks the other events were less destructive with each causing 6 9 breaks sources of the sediment flows varied with the triggering mechanism those associated with hyperpycnal discharges probably began near the mouth of the gaoping river in contrast earthquake triggered landslides and subsequent sediment density flows formed anywhere on the adjacent continental margin flow speeds generally declined with increased run out lower seabed slope and increased channel width most variability 7 20 ms 1 was observed over the 0 4 1 0 slopes of gaoping canyon but speeds were mainly restricted to 5 8 ms 1 in the 0 3 sloping manila trench the 2006 2015 period of frequent cable damaging flows is the first for the past two decades or longer in the absence of evidence for increased seismic or anthropogenic activity this disruptive period may reflect increased typhoon intensity and fluvial sediment discharge such typhoon related flows may complicate interpretation of palaeo seismic records derived from turbidites in such settings

very large subaqueous sand dunes on the upper continental slope in the south china sea generated by episodic shoaling deep water internal solitary waves abstract very large subaqueous sand dunes were discovered on the upper continental slope of the northern south china sea the dunes were observed along a single 40 km long transect southeast of 21 93 n 117 53 e on the upper continental slope in water depths of 160 m to 600 m the sand dunes are composed of fine to medium sand with amplitudes exceeding 16 m and crest to crest wavelengths exceeding 350 m the dunes apparent formation mechanism is the world s largest observed internal solitary waves which generate from tidal forcing on the luzon ridge on the east side of the south china sea propagate west across the deep basin with amplitudes regularly exceeding 100 m and dissipate extremely large amounts of energy via turbulent interaction with the continental slope suspending and redistributing the bottom sediment while subaqueous dunes are found in many locations throughout the world s oceans and coastal zones these particular dunes appear to be unique for two principal reasons their location on the upper continental slope away from the influence of shallow water tidal forcing deep basin bottom currents and topographically amplified canyon flows and their distinctive formation mechanism approximately 60 episodic extremely energetic large amplitude events each lunar cycle

first observations of high temperature submarine hydrothermal vents and massive anhydrite deposits off the north coast of iceland high temperature 250 c hydrothermal vents and massive anhydrite deposits have been found in a shallow water sediment filled graben near 66 36 n in the tjornes fracture zone north of iceland the site is located about 30 km offshore near the small island of grimsey the main vent field occurs at a depth of 400 m and consists of about 20 large diameter up to 10 m mounds and 1 3 m chimneys and spires of anhydrite and talc a north south alignment of the mounds over a 1 km strike length of the valley floor suggests that their distribution is controlled by a buried fault widespread shimmering water and extensive white patches of anhydrite in the sediment between the mounds indicates that the entire 1 km2 area occupied by the vents is thermally active a 2 man research submersible jago was used to map the area and to sample vent waters gases and chimneys actively boiling hydrothermal vents occur on most of the mounds and extensive two phase venting indicates that the field is underlain by a large boiling zone 200 300 m the presence of boiling fluids in shallow aquifers beneath the deposits was confirmed by sediment coring the highest temperature pore fluids were encountered in talc and anhydrite rich sedimentary layers that occur up to 7 m below the mounds baked muds underlie the talc and anhydrite layers and pyrite is common in stockwork like fractures and veins in the hydrothermally altered sediments however massive sulfides pyrite marcasite crusts were found in only one relict mound subseafloor boiling has likely affected the metal carrying capacity of the hydrothermal fluids and deposition of sulfides may be occurring at greater depth although the mounds and chimneys at grimsey resemble other deposits at sedimented ridges e g middle valley escanaba trough guaymas basin the shallow water setting and extensive boiling of the hydrothermal fluids represent a distinctive new type of seafloor hydrothermal system

geomorphic tectonic control of sediment discharge to the ocean the importance of small mountainous rivers analysis of data from 280 rivers discharging to the ocean indicates that sediment loads yields are a log linear function of basin area and maximum elevation of the river basin other factors controlling sediment discharge e g climate runoff appear to have secondary importance a notable exception is the influence of human activity climate and geology on the rivers draining southern asia and oceania sediment fluxes from small mountainous rivers many of which discharge directly onto active margins e g western south and north america and most high standing oceanic islands have been greatly underestimated in previous global sediment budgets perhaps by as much as a factor of three in contrast sediment fluxes to the ocean from large rivers nearly all of which discharge onto passive margins or marginal seas have been overestimated as some of the sediment load is subaerially sequestered in subsiding deltas before the proliferation of dam construction in the latter half of this century rivers

velocity field of gps stations in the taiwan area abstract the 131 stations of the taiwan gps network were surveyed 4 6 times from 1990 to 1995 with dual frequency geodetic receivers the standard deviation of an observed baseline length with its linear trend removed is in the range of 6 10 mm for a 3 120 km long baseline the average rates of length change for all baselines of the network and those from nine continuously monitoring permanent stations are used in a least squares adjustment to estimate the velocities of the gps stations relative to paisha penghu situated at the chinese continental margin to the south of fengping in the northern coastal range the velocity vectors of stations in lanhsu lutao and the coastal range trend in the directions of 306 322 with rates of 56 82 mm yr in contrast there is a dramatic decrease in the rates to the north of fengping this may be caused by the motion along the ne sw trending thrusts which obliquely cut the northern coastal range a discontinuity of about 30 mm yr in the rates along with a remarkable change in the directions of station velocity is observed across the longitudinal valley then the moving directions gradually shift to the west for the stations in the western foothills in the kaohsiung pingtung coastal area the station velocities are even directed toward the southwest to the north of the peikang high the velocity vectors of the stations change direction from the west gradually to the north and finally to the east and southeast significant nw se extensional deformation is found in the ilan plain and northern taiwan in general the pattern of the velocity field for gps stations in the taiwan area is quite consistent with the directions of present day tectonic stress

systematics of and postulated controls on submarine hydrothermal solution chemistry the chemical compositions of seafloor hydrothermal solutions from the galapagos spreading center 21 n and 13 n on the east pacific rise the southern juan de fuca ridge and the guaymas basin gulf of california are examined for systematic variations several elemental ratios elemental products and empirical geothermometers show much consistency among the various areas in spite of large absolute differences in elemental concentrations the results suggest that most of the major cations in these solutions are solubility controlled with respect to a similar phase assemblage at all of the sites examination of the solution chemistry in conjunction with experimental results and seafloor rock alteration data permits identification of phases which may be important in controlling the solution chemistry as potassium appears to be solubility controlled its use to calculate water rock ratios is inappropriate lithium appears to be a better element to use in these calculations a model to explain the observed solution chemistries as a result of three component mixing is discussed all of the solutions are postulated to be either the result of mixing between a seawater hydrothermal solution which has not undergone a phase separation and is hence gas containing a gas rich vapor phase and a gas poor brine phase or any one of these individual components alone the vapor and brine phases are the result of phase separation which may have occurred at some time in the past essentially all of the reported data fall within the field defined by these three components the solutions apparently have had sufficient time after the mixing event s to reequilibrate with the rock this is true for quartz as well as other chemical components the best test of this model is chloride together with gas and isotropic data as the model predicts that solutions with elevated chlorinities will be depleted in gases and enriched in 18 o and low chlorinity solutions will have elevated gas contents and lower 18 o

paleoseismicity of the cascadia subduction zone evidence from turbidites off the oregon washington margin cores from cascadia deep sea channel contain sequences of turbidites that can be correlated and dated by the first occurrence of volcanic glass from the mount mazama eruption 6845 50 radiocarbon yrbp turbidity currents from the tributaries appear to have occurred synchronously to form single deposits in the main channel there being only 13 turbidite deposits in the lower main channel since the mazama eruption instead of the twice as many expected if the tributaries had behaved independently in addition to the cascadia channel 13 post mazama turbidites have been deposited in the astoria canyon and at two sites off cape blanco sample locations that span 580 km of the oregon washington margin pelagic intervals deposited between the turbidites suggest that in each place the turbidity currents occurred fairly regularly every 590 170 years on average the best explanation of the spatial and temporal extent of the data is that the turbidity currents were triggered by 13 great earthquakes on the cascadia subduction zone the variability of turbidite timing is similar to that for great earthquake cycles the thickness of the topmost pelagic layer suggests the last event was 300 60 years ago from three places along the margin but this number may be a biased underestimate it is however consistent with the youngest sudden subsidence event on the washington coast the turbidite data demonstrate that the near term hazard of a great earthquake on the cascadia subduction zone is of the order of 2 10 in the next 50 years

cyclone induced hyperpycnal turbidity currents in a submarine canyon 1 density currents such as turbidity currents are major transport agents in various terrestrial lacustrine and marine environments worldwide however a gap exists between those who study the deposits by turbidity currents turbidite on a field scale and those who study turbidity currents using small scale laboratory experiments and theoretical numerical models we report two typhoon triggered hyperpycnal turbidity current events observed in a submarine canyon our findings verify turbidite sequences with the characteristics of suspended sediment carried by passing turbidity currents that displayed distinct waxing and waning phases our study also confirms the direct link between typhoon triggered hyperpycnal flows in a small mountainous river and turbidity currents in a nearby submarine canyon that transport sediment to the deep sea efficiently

topographic characteristics of the submarine taiwan orogen a complete digital elevation and bathymetry model of taiwan provides the opportunity to characterize the topography of an emerging mountain belt the orogen appears to form a continuous wedge of constant slope extending from the subaerial peaks to the submarine basin we compare submarine channel systems from the east coast of taiwan with their subaerial counterparts and document a number of fundamental similarities between the two environments the submarine channel systems form a dendritic network with distinct hillslopes and channels there is minimal sediment input from the subaerial landscape and sea level changes are insignificant suggesting that the submarine topography is sculpted by offshore processes alone we implement a range of geomorphic criteria widely applied to subaerial digital elevation models and explore the erosional processes responsible for sculpting the submarine and subaerial environments the headwaters of the submarine channels have steep straight slopes and a low slope area scaling exponent reminiscent of subaerial headwaters that are dominated by bedrock landslides the main trunk streams offshore have concave up longitudinal profiles extensive knickpoints and a slope area scaling exponent similar in form to the onshore fluvial domain we compare the driving mechanisms of the likely offshore erosional processes primarily debris flows and turbidity currents with subaerial fluvial incision the results have important implications for reading the geomorphic signals of the submarine and subaerial landscapes for understanding the links between the onshore and offshore environments and more widely for focusing the future research of the submarine slope

comment on consequences of phase separation on the distribution of hydrothermal fluids at ashes vent field axial volcano juan de fuca ridge by christopher g fox

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

the formation and fate of internal waves in the south china sea internal oceanic waves are subsurface gravity waves that can be enormous and travel thousands of kilometres before breaking but they are difficult to study here observations of such waves in the south china sea reveal their formation mechanism extreme turbulence relationship to the kuroshio current and energy budget internal waves are the underwater version of more familiar surface waves they can be enormous and travel thousands of kilometres before breaking the south china sea is known to be home to the largest internal waves in the world s oceans but their size generation mechanisms and role in the regional energy budget are unknown matthew alford and colleagues now present the results from the iwise observational campaign and reveal that internal waves more than 200 metres high break in the south china sea and create turbulence that is orders of magnitude larger than in the open ocean and that wave formation is influenced by the kuroshio current these results now allow for a complete energy budget of the south china sea and for a more accurate incorporation of internal waves into climate models internal gravity waves the subsurface analogue of the familiar surface gravity waves that break on beaches are ubiquitous in the ocean because of their strong vertical and horizontal currents and the turbulent mixing caused by their breaking they affect a panoply of ocean processes such as the supply of nutrients for photosynthesis1 sediment and pollutant transport2 and acoustic transmission3 they also pose hazards for man made structures in the ocean4 generated primarily by the wind and the tides internal waves can travel thousands of kilometres from their sources before breaking5 making it challenging to observe them and to include them in numerical climate models which are sensitive to their effects6 7 for over a decade studies8 9 10 11 have targeted the south china sea where the oceans most powerful known internal waves are generated in the luzon strait and steepen dramatically as they propagate west confusion has persisted regarding their mechanism of generation variability and energy budget however owing to the lack of in situ data from the luzon strait where extreme flow conditions make measurements difficult here we use new observations and numerical models to 1 show that the waves begin as sinusoidal disturbances rather than arising from sharp hydraulic phenomena 2 reveal the existence of 200 metre high breaking internal waves in the region of generation that give rise to turbulence levels 10 000 times that in the open ocean 3 determine that the kuroshio western boundary current noticeably refracts the internal wave field emanating from the luzon strait and 4 demonstrate a factor of two agreement between modelled and observed energy fluxes which allows us to produce an observationally supported energy budget of the region together these findings give a cradle to grave picture of internal waves on a basin scale which will support further improvements of their representation in numerical climate predictions

chemical controls on the composition of vent fluids at 13 11 n and 21 n east pacific rise six vent fields sampled at 13 11 n east pacific rise epr in may 1984 exhibit large interfield variations and a much wider range of chemical compositions than previously observed at 21 n measured ph at 25 c are acidic ranging from 3 1 to 3 7 sodium and chloride vary from 40 lower to 30 higher than seawater iron concentrations range from 2 to 10 mmol kg compared with 0 7 2 5 mmol kg at 21 n other sulfide forming metals cu zn cd and pb are generally lower at 11 13 n than at 21 n reliable temperature measurements were obtained at only two of the six vents and both were 350 5 c the vent fields at 21 n epr were resampled in august 1985 thus extending to almost 6 years the time period over which they have been monitored previous expeditions were made in november 1979 and november 1981 campbell et al this issue have shown that the chemistry of the hydrothermal fluids from these fields has been very stable over the period of repeated observation equilibrium calculations for the fluids from the fields at 13 n and 21 n using a greatly improved thermodynamic data base are described in this report they indicate that the chemistry is rock buffered and that the stability of these systems over time is a result of equilibrium control with respect to a greenschist type mineral assemblage at depth calculated high temperature ph of the fluids range from 4 1 to 4 7 with those from 13 11 n at the more acidic end of the range calculated affinities show that the fluids are close to or at saturation with respect to quartz albite muscovite smectite chlorite epidote and pyrrhotite the computations imply that lower temperature vents such as national geographic smoker ngs 273 c may have their silica concentrations controlled by equilibrium with respect to a phase other than quartz a comparison of fluid chemistry between ngs and vent 5 at 11 n suggests that the latter vent may also have a temperature 300 c while the fluid chemistry of a given field is compositionally stable the compositions themselves are unique for a particular field and cover a wide range between fields the processes controlling this variability probably include the depth of reaction i e pressure which is difficult to treat thermodynamically at present in addition increasing depth in the crust may be accompanied by decreasing permeability and hence a probable decrease in the water rock ratio it may be difficult to separate these two effects if the age differences between the fields at present unknown are of the order of decades then their temporal histories may have an important influence on their particular chemistries

long term in situ observations on typhoon triggered turbidity currents in the deep sea this work is supported by the national science foundation of china grants 91528304 41576005 and 41530964 we thank j li x lyu p li k duan j ronan y wang p ma and y li for cruise assistance g de lange and j hinojosa for editing an early version of manuscript and e pope and two anonymous reviewers for their reviews

cyclone driven deep sea injection of freshwater and heat by hyperpycnal flow in the subtropics china 973 program 2009cb421200 program of introducing talents of discipline to universities b07034 academia sinica thematic program afobi taiwan nsc 98 2116 m 001 005

damaging sediment density flows triggered by tropical cyclones the global network of subsea fibre optic cables plays a critical role in the world economy and is considered as strategic infrastructure for many nations sediment density flows have caused significant disruption to this network in the recent past these cable breaks represent the only means to actively monitor such flows over large oceanic regions here we use a global cable break database to analyse tropical cyclone triggering of sediment density flows worldwide over 25 yrs cable breaking sediment density flows are triggered in nearly all areas exposed to tropical cyclones but most occur in the nw pacific they are triggered by one of three sets of mechanisms tropical cyclones directly trigger flows synchronous to their passage as a consequence of storm waves currents and surges cyclones also trigger flows indirectly with near synchronous timing to their passage as a consequence of peak flood discharges last cyclones trigger flows after a delay of days as a consequence of the failure of large volumes of rapidly deposited sediment no clear relationship emerges between tropical cyclone activity i e track frequency and intensity and the number of sediment density flows triggered this is a consequence of the short period of observation however expansion of the cable network and predicted changes to cyclone activity in specific regions increases the likelihood of increasing numbers of damaging flows

sources of baroclinic tidal energy in the gaoping submarine canyon off southwestern taiwan 1 a three dimensional model driven by tidal constituents o1 k1 m2 and s2 was adopted to evaluate the sources of baroclinic tidal energy in the gaoping submarine canyon gpsc off southwestern taiwan the model domain covered the probable primary generation sites including the luzon strait ls and the southeastern taiwan strait ts the simulated baroclinic tides agreed with the observations of tidal current velocity isotherm vertical displacement and baroclinic tidal energy flux fbc in the gpsc the depth integrated seven day averaged fbc computed from the model result was 2 2 kw m 1 in the gpsc and the corresponding area integrated fbc reached 189 4 mw the results obtained from the model suggest that the baroclinic tides lead to strong turbulent mixing near the canyon head with a vertical diffusivity of 3 5 10 3 m2 s 1 baroclinic tidal energy in the gpsc is mainly generated on the western ridge in the ls and on the steep topography in the southeastern ts the local generation of baroclinic energy only accounts for 4 4 of the total value the other 95 6 of the baroclinic tidal energy is remotely generated at the ls and the southeastern ts of which 31 9 and 8 8 are directly emanated respectively into the gpsc the northwestward and southeastward baroclinic energy beams radiating from the ls and the southeastern ts respectively meet each other and form internal partial standing tides outside the gpsc the transverse baroclinic energy from the internal partial standing tides accounts for the remaining 54 9 of the baroclinic tidal energy in the gpsc

geology geography and humans battle for dominance over the delivery of fluvial sediment to the coastal ocean abstract sediment flux to the coastal zone is conditioned by geomorphic and tectonic influences basin area and relief geography temperature runoff geology lithology ice cover and human activities reservoir trapping soil erosion a new model termed bqart in recognition of those factors accounts for these varied influences when applied to a database of 488 rivers the bqart model showed no ensemble over or underprediction had a bias of just 3 across six orders of magnitude in observational values and accounted for 96 of the between river variation in the long term 30 years sediment load or yield of these rivers the geographical range of the 488 rivers covers 63 of the global land surface and is highly representative of global geology climate and socioeconomic conditions based strictly on geological parameters basin area relief lithology ice erosion 65 of the between river sediment load is explained climatic factors precipitation and temperature account for an additi

the abrupt shift of typhoon activity in the vicinity of taiwan and its association with western north pacific east asian climate change bayesian analysis is applied to detect changepoints in the time series of seasonal typhoon counts in the vicinity of taiwan an abrupt shift in the typhoon count series occurs in 2000 on average 3 3 typhoons per year have been noted before 2000 1970 99 with the rate increasing to 5 7 typhoons per year since 2000 2000 06 this abrupt change is consistent with a northward shift of the typhoon track over the western north pacific east asian region and an increase of typhoon frequency over the taiwan east china sea region the northward shift of the typhoon track tends to be associated with typhoon enhancing environmental conditions over the western north pacific namely the weakening of the western north pacific subtropical high the strengthening of the asian summer monsoon trough and the enhanced positive vorticity anomalies in the lower troposphere based on observational analysis and model simulations warm sea surface temperature anomalies over the equatorial western and central pacific appear to be a major factor contributing to a northward shifted typhoon track

effects of a major typhoon on sediment accumulation in fangliao submarine canyon sw taiwan abstract the fangliao submarine canyon cuts across the shelf and slope of southwest taiwan unlike other canyons along this margin there is no obvious connection to an individual fluvial sediment source on land two recent cruises to fangliao canyon provide insight into sedimentation associated with a major typhoon box and piston cores were retrieved from fangliao canyon in early january 2007 after a local earthquake and an extended period of low to moderate river flow in streams that are suspected of contributing sediment to the canyon similar cores were collected from the canyon in early october 2009 following one of the largest typhoons to hit taiwan in the past several decades typhoon morakot delivered several meters of rain to taiwan with the largest river floods occurring in the south and southwest regions in addition the coastal ocean environment was energized by significant wave heights 12 m comparisons of textural radioisotopic and geochemical data reveal likely sediment transport and depositional processes within and surrounding fangliao canyon typhoon morakot caused a layer 10 cm thick and greater throughout the canyon x radiographs of the 2007 cores show limited physical structure in most cases and the 2009 radiographs display obvious changes in sediment density relative to the underlying sediment as well as distinct physical lamination examining signals from different geochemical and radiochemical tracers for terrestrial sediment source indicates that the flood layer deposited by typhoon morakot came from several small mountainous rivers by comparing the results of the 2007 cruise with those from 2009 we gain significant insight to the close linkage between a line source of fluvial sediment and deposition in a submarine canyon as well as the role that tropical storm events can play in delivering sediment to these environments

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

liquefaction induced settlement of pile groups in liquefiable and laterally spreading soils the results of a series of dynamic centrifuge tests on model pile groups in level liquefied and laterally spreading soil profiles are presented the piles are axially loaded at typical working loads which has enabled liquefaction induced settlements of the foundations to be studied the development of excess pore pressures within the bearing layer dense sand was found to lead to a reduction in pile capacity and potentially damagingly large coseismic settlements as the excess pore pressure increased these settlements were observed to exceed postshaking downdrag induced settlements which occur due to the reconsolidation of liquefied sand around the pile shaft in resisting settlement the pile cap was found to play an important role by compensating for the capacity lost by the piles this was shown to be achieved by the development of dilative excess pore pressures beneath the pile cap within the underlying loose liquefied sand which provide increasing bearing capacity with settlement the centrifuge test data show good qualitative and quantitative agreement with the limited amount of model and full scale data currently available in the literature the implications of settlement for the design of piled foundations to serviceability conditions in both level and sloping ground are discussed with settlement becoming an increasingly important consideration for laterally stiffer piles finally empirical relationships have been derived from the test data to relate suitable static safety factors to given increases in excess pore pressure in the bearing layer within a performance based design framework i e based on limiting displacements

what determines the downstream evolution of turbidity currents abstract seabed sediment flows called turbidity currents form some of the largest sediment accumulations deepest canyons and longest channel systems on earth only rivers transport comparable sediment volumes over such large areas but there are far fewer measurements from turbidity currents ensuring they are much more poorly understood turbidity currents differ fundamentally from rivers as turbidity currents are driven by the sediment that they suspend fast turbidity currents can pick up sediment and self accelerate ignite whilst slow flows deposit sediment and dissipate self acceleration cannot continue indefinitely and flows might reach a near uniform state autosuspension here we show how turbidity currents evolve using the first detailed measurements from multiple locations along their pathway which come from monterey canyon offshore california all flows initially ignite typically initially faster flows then achieve near uniform velocities autosuspension whilst slower flows dissipate fractional increases in initial velocity favour much longer runout and a new model explains this bifurcating behaviour however the only flow during less stormy summer months is anomalous as it self accelerated which is perhaps due to erosion of surficial mud layer mid canyon turbidity current evolution is therefore highly sensitive to both initial velocities and seabed character

water and sediment discharge from small mountainous rivers taiwan the roles of lithology episodic events and human activities national science council of taiwan nsc96 2628 m 001 028 u s national science foundation and naval oceanographic office

from the highest to the deepest the gaoping river gaoping submarine canyon dispersal system abstract there are many different source to sink dispersal systems around the world and the gaoping river gpr gaoping submarine canyon gpsc provides an example especially as a canyon captured system the gpr a small mountainous river having an average gradient of 1 150 and the gpsc which links the river catchment to the deep sea basin represent two major topographic features around sw taiwan together they constitute a terrestrial to marine dispersal system that has an overriding impact on the source to sink transport of sediment in this region the gpsc extents from the mouth of the gpr through the shelf and slope and into the northeastern manila trench a distance of about 260 km it is a major conduit for the transport of terrestrial sediment and carbon to the south china sea and the landward transport of particles of marine and biological origin in the gpsc the dominant mode of suspended sediment transport is tidal oscillations and the net direction is up canyon in contrast sediment transport associated with episodic gravity driven events is down canyon the steady sedimentation of the tidal regime results in hemipelagic mud across the canyon floor whereas the gravity driven hyperpycnal regime causes turbidite erosion and deposition along the canyon thalweg typhoon induced river floods often lead to hyperpycnal plumes at the river mouth which directly and indirectly ignite hyperpycnal turbidity currents in the canyon forming an effective agent for transporting large amounts of terrestrial organic material modern and fossil carbon to the south china sea basin therefore the gpr gpsc represents a source to sink system in which terrestrial sediment in a mountainous catchment is promptly removed and transported to the deep sea by episodic gravity flows this is also a pathway by which modern terrestrial organic carbon is quickly and effectively delivered to the deep sea

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

seismic reversal pattern for the 1999 chi chi taiwan mw 7 6 earthquake we in this study have calculated the standard normal deviate z value to investigate the variations in seismicity patterns in the taiwan region before and after the chi chi earthquake we have found that the areas with relatively high seismicity in the eastern taiwan became abnormally quiet before the chi chi earthquake while the area in the central taiwan with relatively low seismicity showed unusually active such a spatially changing pattern in seismicity strikingly demonstrates the phenomenon of seismic reversal and we here thus present a complete representative cycle of seismic reversal embedding in the changes of seismicity patterns before and after the chi chi earthquake

earthquake triggered increase in sediment delivery from an active mountain belt in tectonically active mountain belts earthquake triggered landslides deliver large amounts of sediment to rivers we quantify the geomorphic impact of the 1999 mw 7 6 chi chi earthquake in taiwan which triggered 20 000 landslides coseismic weakening of substrate material caused increased landsliding during subsequent typhoons most coseismic landslides remained confined to hillslopes downslope transport of sediment into the channel network occurred during later storms the sequential processes have led to a factor of four increase in unit sediment concentration in rivers draining the epicentral area and increased the magnitude and frequency of hyperpycnal sediment delivery to the ocean four years after the earthquake rates of hillslope mass wasting remain elevated in the epicentral area

conditions for the ignition of catastrophically erosive turbidity currents abstract the basic impediment to a clear understanding of eroding and depositing turbidity currents has been the lack of a proper formulation of bed sediment entrainment this problem is addressed herein a detailed analysis indicates that the bagnold criterion is necessary but insufficient for self sustaining turbidity currents the analysis reveals two possible equilibrium states a relatively low velocity ignitive state and a high velocity dense catastrophic state a stability analysis indicates that the ignitive state is unstable flows below it invariably die out and flows above it ignite i e accelerate and entrain sediment to the catastrophic state which is stable the ignitive state thus defines the criterion for a self sustaining turbidity current estimates of the catastrophic state suggest that it is highly erosive and competent to scour out submarine canyons

near synchronous and delayed initiation of long run out submarine sediment flows from a record breaking river flood offshore taiwan subsea fiber optic telecommunication cables can break under fast sediment flows that travel 100s of kilometers through the deep ocean in response to earthquakes and submarine landslides similar flows are inferred to form from major river floods whose sediment laden waters plunge and travel along the seabed however the complex initiation of flood related flows and their hazard potential have not been observed until now here we use cable fault data from the gaoping canyon manila trench off taiwan to show that a major river flood formed during typhoon morakot 2009 generated two long run out destructive sediment flows one during peak flood and the other 3 days later the latter flow was more damaging with speeds and run out similar to that of landslide triggered turbidity currents formed in the same catchment if the second flow was due to remobilized canyon sediment it occurred during low earthquake mw 2 0 activity suggesting other triggering mechanisms

earthquake cycle in western taiwan insights from historical seismicity summary we attempt at providing new insights about the earthquake behaviour in western taiwan based on a comparison between historical information and present day instrumental records we provide a consistent picture of the earthquake history during the last four centuries and draw some inferences in terms of seismic cycle before instrumental seismic observation in taiwan started at the end of the 19th century ancient written earthquake records are available from the ancient chinese governments and the public concerning the 17th 18th and 19th centuries distribution of casualties and property damage indicating seismic intensity can be estimated from archives using the central weather bureau cwb intensity scale we calibrate the intensity magnitude relationships from the instrumental seismicity recorded from 1995 to 2005 showing that within the range of historical uncertainties and earthquake depths in western taiwan 0 40 km the depth is not critical in these relationships with estimated intensities the magnitudes of historical earthquakes can be evaluated based on a single average empirical relationship between ml the local magnitude and i0 the epicentral intensity ml 0 08i0 2 0 04i0 3 41 three types of diagrams are then proposed to describe the historical seismicity the first type involves simple representation of earthquake events according to time and magnitude the second type involves cumulative plot of the released elastic energy with time as calculated from reconstructed magnitudes the third type of diagram shows the evolution of cumulative seismic strain release with time based on a benioff s law indicating that the release of elastic strain related to an earthquake is proportional to the square root of the dissipated energy these curves highlight inferences of historical seismicity analysis in terms of earthquake frequency and seismic cycle duration in the different segments of the front belt and foreland zones of western taiwan with large contrasts suggesting different levels in earthquake hazard

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

response of two phase fluids to fracture configurations within submarine hydrothermal systems submarine hydrothermal systems at mid ocean ridges evolve within a region of brittle deformation overlying a region of ductile deformation the interplay between brittle and ductile modes of deformation and the geometry of fracture systems within the brittle zone can exert a significant influence on fluid flow especially under conditions leading to aqueous two phase separation within the brittle region fractures vary between large conduits directly open to the seafloor and small veins and microcracks with constricted or indirect connections to the seafloor in the ductile region fluids may be trapped under near lithostatic pressure while fluids within throughgoing veins in the brittle region will experience hydrostatic pressure in a narrow transition zone between these two extremes a steep pore fluid pressure gradient must exist in the brittle region itself fluid pressures will vary between lithostatic and hydrostatic as fluid occupies interstices varying from isolated pores through tortuous microcracks to channels directly connected to the main upflow conduits a hydrostatic gradient modified by the decreased density of hot fluid and the effects of the flow itself should be applicable in major conduits open to the seafloor fluctuating pressure conditions in the transition zone may induce phase changes in a fluid remaining at constant depth as a result of the large volume increase that accompanies two phase separation a two phase fluid must either accelerate upward or exert an increased pressure on its surroundings possibly leading to enhanced fracturing the fracture configuration will also affect the behavior of the mixed fluid after phase separation a two phase fluid experiencing rapid turbulent flow in a large open conduit is more likely to remain a well mixed suspension of vapor and liquid whereas a two phase mixture in a constricted branching series of channels moving more slowly in a laminar flow regime is more likely to undergo physical isolation of the phases leading to venting of a vapor phase and retention of a saline brine phase at depth we propose a possible configuration for the fracture pattern within a submarine hydrothermal system consisting of a feeder zone comprised of anastomozing microcracks and veinlets progressively increasing in diameter and decreasing in abundance feeding into a main upflow stockwork zone in which flow directly to the surface takes place in relatively large unconstricted conduits fluid movement within a feeder zone may be modified by capillary flow tortuous channelways disconnected fractures blocking of cracks by mineral deposition and opening of new fractures

large scale scours formed by supercritical turbidity currents along the full length of a submarine canyon northeast south china sea abstract high resolution multibeam bathymetric and seismic data enables a detailed morphological investigation of a submarine canyon west penghu canyon on the northeastern south china sea margin where twenty three 23 scours are observed along the canyon thalweg these scours form narrow topographic depressions in plan view and show asymmetrical morphologies in cross section the identified scours can be further divided into two groups types a and b based on their sizes and relative locations they are separated by a slope break at a water depth of 2850 m type a scours s1 s18 occur upslope from the slope break whereas type b scours s19 s23 lie downslope from this same break the scours are interpreted as net erosional cyclic steps associated with turbidity currents flowing through the west penghu canyon the currents that form type a scours reflect higher v q and el compared to the currents forming type b scours a change in slope gradient and loss of lateral confinement are proposed to control the change from type a to type b scours furthermore coriolis force influences the flow direction of turbidity currents leading to the preferential development and larger incision depths of scours towards the southwestern flank of the west penghu canyon our results contribute to a better understanding on the origin of scours in submarine canyons across the world

deep sea smokers windows to a subsurface biosphere since the discovery of hyperthermophilic microbial activity in hydrothermal fluids recovered from smoker vents on the east pacific rise the widely accepted upper temperature limit for life based on pure culture data has risen from below the boiling point of water at atmospheric pressure to approximately 115 degrees c many microbiologists seem willing to speculate that the maximum may be closer to 150 degrees c we have postulated not only higher temperatures than these under deep sea hydrostatic pressures but also the existence of a biosphere subsurface to accessible seafloor vents new geochemical information from the endeavour segment of the juan de fuca ridge indicative of subsurface organic material caused us to re examine both the literature on hyperthermophilic microorganisms cultured from deep sea smoker environments and recent results of microbial sampling efforts at actively discharging smokers on the endeavour segment here we offer the case for a subsurface biosphere based on an interdisciplinary view of microbial and geochemical analyses of endeavour smoker fluids a case in keeping with rapidly evolving geophysical understanding of organic stability under deep sea hydrothermal conditions