imaging subduction from the trench to 300 km depth beneath the central north island new zealand with vp and vp vs summary recent dense deployments of portable digital seismographs have provided excellent control on earthquakes beneath the central north island of new zealand here we use a subset of the best recorded earthquakes in an inversion for the 3 d vp and vp vs structure the data set includes 39 123 p observations and 18 331 s observations from 1239 earthquakes and nine explosions the subducted plate is imaged as a high vp low vp vs feature vp within the mantle of the subducted slab is almost always 8 5 km s 1 which requires the ca 120 myr slab to be unusually cold the low vp vs within the subducted plate closely parallels the lower plane of the dipping seismic zone it most likely indicates fluid resulting from dehydration of serpentine in the slab mantle and the earthquakes themselves are likely to be promoted by dehydration embrittlement we identify a region with vp 8 0 km s 1 directly above the dipping seismic zone can be interpreted as sinking entrained with the motion of the subducted slab and forming a viscous blanket that insulates the slab from the high temperature mantle wedge material in the overlying low vp region can be interpreted as rising within a return flow within the wedge the volcanic front appears to be controlled by where this dipping low vp region meets the base of the crust the thickness of the backarc crust also shows significant variation along strike in the central taupo volcanic zone tvz the crust is ca 35 km thick while southwest of mt ruapehu the crust thickens by ca 10 km there is no significant low vp zone in the mantle wedge in this southwestern region suggesting that this thicker crust has choked off mantle return flow the seismic tomography results when combined with constraints on mantle flow from previous shear wave splitting results provide a plausible model for both the distribution of volcanism in the central north island and the exceptional magmatic productivity of the central tvz

intra oceanic subduction related hydrothermal venting kermadec volcanic arc new zealand intra oceanic volcanic arcs mark the boundaries between converging lithospheric plates where subduction produces volcanic and tectonic activity that ensures a steady supply of magmatic heat and hydrothermal fluids to the seafloor here we report on the first broad and systematic survey of hydrothermal emissions generated along a submarine arc front more than half seven of 13 of the volcanoes surveyed along 260 km of the southern kermadec arc ne of new zealand are hydrothermally active our results indicate that volcanic arcs represent a previously unheeded but potentially extensive source of shallow 2 km water depth vent fields expelling fluids of a unique and heterogeneous composition into the oceans

ocean current and temperature time series at brothers volcano 1 time series of currents and temperatures were acquired near surface and at depth on three moorings above brothers volcano 34 52 25 s 179 04 e 25 km west of the kermadec ridge and 300 km northeast of the north island new zealand from september 2004 to may 2005 ocean current time series were previously unavailable within 300 km of this site and few such measurements exist anywhere near magmatically or hydrothermally active volcanoes such as brothers energy in near surface currents 163 527 m depth was primarily subtidal 64 subtidal motions to 527 m depth are shown to be reasonably well correlated with geostrophic currents derived from satellite sea level anomalies although the moorings were separated laterally by only 11 km the upper current meters also recorded significant differences in m2 tidal currents indicating the presence of significant internal tides at this site below volcano summit depth 1220 m the kinetic energy of currents was primarily tidal 54 longer period currents at depth evidenced the influence of volcano topography temperature time series showed a 3 month period of sharply decreased temperature that extended in depth from 163 m to at least 1260 m advanced very high resolution radiometer avhrr sea surface temperature data show colder surface water immediately above and north of brothers over the same time period these data together with the velocity records suggest an anomalous deep cold water mass arrived and lingered over brothers for 3 months in the austral late spring and early summer of 2004 2005

high resolution water column survey to identify active sublacustrine hydrothermal discharge zones within lake rotomahana north island new zealand abstract autonomous underwater vehicles were used to conduct a high resolution water column survey of lake rotomahana using temperature ph turbidity and oxidation reduction potential orp to identify active hydrothermal discharge zones within the lake five areas with active sublacustrine venting were identified 1 the area of the historic pink terraces 2 adjacent to the western shoreline subaerial steaming cliffs boiling springs and geyser 3 along the northern shoreline to the east of the pink terrace site 4 the newly discovered patiti hydrothermal system along the south margin of the 1886 tarawera eruption rift zone and 5 a location in the east basin northeast of patiti island the pink terrace hydrothermal system was active prior to the 1886 eruption of mount tarawera but venting along the western shoreline in the east basin and the patiti hydrothermal system appear to have been initiated in the aftermath of the eruption similar to waimangu valley to the southwest different combinations of turbidity ph anomalies both positive and negative and orp responses suggest vent fluid compositions vary over short distances within the lake the seasonal period of stratification limits vertical transport of heat to the surface layer and the hypolimnion temperature of lake rotomahana consequently increases with an average warming rate of 0 010 c day due to both convective hydrothermal discharge and conductive geothermal heating a sudden temperature increase occurred during our 2011 survey and was likely the response to an earthquake swarm just 11 days prior

submarine hydrothermal activity along the mid kermadec arc new zealand large scale effects on venting 1 the 2 500 km kermadec tonga arc is the longest submarine arc on the planet here we report on the second of a series of cruises designed to investigate large scale controls on active hydrothermal venting on this arc the 2002 nzaplume ii cruise surveyed 12 submarine volcanic centers along 580 km of the middle kermadec arc mka extending a 1999 cruise that surveyed 260 km of the southern kermadec arc ska average spacing between volcanic centers increases northward from 30 km on backarc crust along the ska to 45 km on backarc crust along the southern mka to 58 km where the mka joins the kermadec ridge volcanic cones dominate in the backarc and calderas dominate the kermadec ridge the incidence of venting is higher along the mka 83 10 of 12 volcanic centers than the ska 67 8 of 12 but the relative intensity of venting as given by plume thickness areal extent and concentration of dissolved gases and ionic species is generally weaker in the mka this pattern may reflect subduction of the 17 km thick oceanic hikurangi plateau beneath the ska subduction of this basaltic mass should greatly increase fluid loss from the downgoing slab initiating extensive melting in the upper mantle wedge and invigorating the hydrothermal systems of the ska conversely volcanic centers in the southern mka are starved of magma replenishment and so their hydrothermal systems are waning farther north where the mka centers merge with the kermadec ridge fewer but larger magma bodies accumulate in the thicker older crust ensuring more widely separated caldera dominated volcanic centers

backarc rifting constructional volcanism and nascent disorganised spreading in the southern havre trough backarc rifts sw pacific high resolution multibeam em300 and seabeam data of the southern havre trough sht combined with observations and sample collections from the submersible shinkai6500 and deep tow camera are used to develop a model for the evolution and magmatism of this backarc system the havre trough and the associated kermadec arc are the product of westward subduction at the pacific australian plate boundary detailed studies focus on newly discovered features including a seamount saito seamount and a deep graben ngatoroirangi rift 4000 m water depth floored with a constructional axial volcanic ridge 5 km in length and in excess of 200 m high both of which are characterised by pillow and lobate flows estimated at elongate volcanic ridges at 35 15 s and 34 30 s and backarc seamounts 35 30 s 178 30 e occur at the eastern margin of the sht similar seafloor morphology is observed in the central and western portions of the basin suggesting that recent volcanism may be broadly distributed across the backarc mass balance modelling indicates a maximum crustal thickness of 11 km to 4000 m spreading systems these discontinuous spreading systems are characterised by failed rifts rift segmentation and propagation successive episodes of magmatic intrusion into thinned faulted arc basement results in defocused asymmetrical accretion cross arc volcanic chains isolated volcanoes and underlying basement plateaus are interpreted to represent a cap of recent extrusives however they may also be composed entirely of newly accreted crust and the spatially extensive basement fabric of elongated volcanic ridges may be the surface expression of pervasive dike intrusion that has thoroughly penetrated and essentially replaced the original arc crust with newly accreted intrusives

hydrothermal venting at hinepuia submarine volcano kermadec arc understanding magmatic hydrothermal fluid chemistry the hinepuia volcanic center is made up of two distinct edifices aligned northwest to southeast with an active cone complex in the se hinepuia is one of several active volcanoes in the northern segment of the kermadec arc regional magnetic data shows no evidence for large scale hydrothermal alteration at hinepuia yet plume data confirm present day hydrothermal discharge suggesting that the hydrothermal system may be too young to have altered the host rocks with respect to measurable changes in magnetic signal gravity data are consistent with crustal thinning and shallow mantle under the volcanic center following the discovery of hydrothermal plumes over hinepuia the submersible shinkai 6500 was used to explore the se cone and sample hydrothermal fluids the chemistry of hydrothermal fluids from submarine arc and backarc volcanoes are typically dominated by water rock interactions and or magmatic degassing chemical analyses of vent fluids show that hinepuia does not quite fit either traditional model moreover the hinepuia samples fall between those typically ascribed to both end member fluid types when plotted on a k mg so4 ternary diagram due to evidence of strong degassing abundant native sulfur deposition and h2s presence the vent sampled at hinepuia is ultimately classified as a magmatic hydrothermal system with a water rock influence this vent is releasing water vapor and magmatic volatiles with a notable lack of salinity due to subcritical boiling and phase separation magmatic hydrothermal fluid chemistry appears to be controlled by a combination of gas flux phase separation processes and volcano evolution and or distance from the magma source

the tectonomagmatic source of ore metals and volatile elements in the southern kermadec arc deciphering the ultimate source of chalcophile metals e g cu zn pb in volcanogenic massive sulfide vms deposits and the volatiles that help drive their formation is critical for understanding where how and why vms deposits form the southern kermadec arc volcanic front is known to be highly hydrothermally active and host to at least three vms deposits whereas the associated back arc system is apparently hydrothermally inactive although this may simply be due to a lack of exploration in this region we have analyzed major trace and volatile element concentrations in a suite of basaltic glasses and olivine hosted melt inclusions from volcanoes ridges and rifts of the southern kermadec arc volcanic front and havre trough back arc basin these data indicate clear compositional differences in the mantle beneath the arc front and the back arc with the arc front having higher extents of prior melt extraction and enrichment in volatile and metal elements from slab derived aqueous fluids the magmatic budget of pb is supplied to the mantle source by these slab derived fluids whereas magmatic concentrations of zn and cu are primarily controlled by the degree of partial melting with a cu bearing residual phase required in the mantle consequently the relative enrichment of chalcophile metals in the mantle derived melts is pb cu zn the magma volatile history recorded by the glasses and melt inclusions indicates that degassing during crystal fractionation is significant and notably leads to the reduction of sulfur in the evolving magma as oxidized sulfur degasses preferentially the apparent absence or retention of volatiles notably co 2 and so 3 in magma chambers lack of magmatic activity and absence of hot mafic dikes beneath volcanoes may be important factors in inhibiting the formation of active hydrothermal venting and by extension the potential for vms deposition

trace element systematics of pyrite from submarine hydrothermal vents abstract submarine hydrothermal sulfide ores occur at mid ocean ridges intra oceanic arcs and in back arc basins associated with host rocks of highly variable composition pyrite is the dominant sulfide mineral in most samples presented within this study and thus the trace element composition of pyrite may reflect the different metal sources and precipitation processes here we report on a systematic study of minor and trace element contents in pyrite from active and inactive submarine hydrothermal vent fields at different plate tectonic settings including the indian and mid atlantic ridges the tonga kermadec intra oceanic arc the lau back arc and the central okinawa trough our results show that the trace element contents of pyrite from different locations vary significantly but for most elements without any systematic correlation to the concentration in the magmatic host rocks only as appears to be depleted in pyrite from ultramafic hosted vent systems that are affected by serpentinization these as depleted pyrites preferentially host au 0 micro or nano particles bismuth is enriched in pyrite from hydrothermal systems that contain a sedimentary component and micro inclusions of sphalerite are either due to fluid sediment interaction or phase separated fluid venting pyrites from individual locations have highly variable concentrations of elements like au co cu se mo ag and sb that are most likely related to fluid evolution and changes in fluid composition sub seafloor hydrothermal fluid seawater mixing influences the distribution of au co cu se and mo in pyrite elements like au ag sb and pb often have a characteristic affinity to as while cd correlates closely with zn a magmatic volatile contribution to the hine hina hydrothermal system may result in the precipitation of cu enriched pyrite our results show that the concentrations of most trace metals in pyrite are a function of the physicochemical parameters of the fluid phase rather than a reflection of the magmatic host rock composition

migration of fluid phases and genesis of basalt magmas in subduction zones dehydration and hydration reactions in both the downgoing lithosphere and the overlying mantle wedge have been examined in order to understand the role of h2o in the production of magmas at convergent plate boundaries the subduction of oceanic lithosphere occurring with increasing pressures and rising temperatures causes liberation of h2o from the slab amphibole which can be stable to the highest pt conditions among hydrous phases in the slab decomposes at around 90 km depth it follows that the subducted lithosphere is essentially anhydrous beneath volcanic arcs lying more than 110 km above the slab and that the supply of slab derived h2o is not a direct trigger for the production of arc magmas instead the h2o released from downgoing lithosphere reacts with the forearc mantle wedge to crystallize hydrous minerals serpentine talc amphibole chlorite and phlogopite this hydrated peridotite is dragged downward on the slab toward higher pt regions and releases h2o to shallower potential magma source regions in the mantle wedge combining experimental data on the stability of serpentine and talc with the thermal structure in the mantle wedge it is concluded that those minerals decompose beneath the forearc region on the other hand high pt experimental and thermodynamic data suggest that dehydration of amphibole and chlorite in the downdragged hydrated peridotite can take place just beneath a volcanic front phlogopite in the peridotite decomposes to release h2o at a deeper level about 200 km h2o liberated from the hydrated peridotite causes partial melting of overlying mantle wedge peridotites along with the migration of h2o through the above processes subduction components especially large ion lithophile elements can be overprinted on the magma source region which governs the geochemical characteristics of arc magmas

fore arc deformation and underplating at the northern hikurangi margin new zealand geophysical investigations of the northern hikurangi subduction zone northeast of new zealand image fore arc and surrounding upper lithospheric structures a seismic velocity vp field is determined from seismic wide angle data and our structural interpretation is supported by multichannel seismic reflection stratigraphy and gravity and magnetic modeling we found that the subducting hikurangi plateau carries about 2 km of sediments above a 2 km mixed layer of volcaniclastics limestone and chert the upper plateau crust is characterized by vp 4 9 6 7 km s overlying the lower crust with vp 7 1 km s gravity modeling yields a plateau thickness around 10 km the reactivated raukumara fore arc basin is 10 km deep deposited on 5 10 km thick australian crust the fore arc mantle of vp 8 km s appears unaffected by subduction hydration processes the east cape ridge fore arc high is underlain by a 3 5 km deep strongly magnetic 3 3 a m high velocity zone interpreted as part of the onshore matakaoa volcanic allochthon and or uplifted raukumara basin basement of probable oceanic crustal origin beneath the trench slope we interpret low seismic velocity high attenuation low density fore arc material as accreted and recycled suggesting that underplating and uplift destabilizes east cape ridge triggering two sided mass wasting mass balance calculations indicate that the proposed accreted and recycled material represents 25 100 of all incoming sediment and any remainder could be accounted for through erosion of older accreted material into surrounding basins we suggest that continental mass flux into the mantle at subduction zones may be significantly overestimated because crustal underplating beneath fore arc highs have not properly been accounted for

active hydrothermal discharge on the submarine aeolian arc 1 in november 2007 we conducted a water column and seafloor mapping study of the submarine volcanoes of the aeolian arc in the southern tyrrhenian sea aboard the r v urania on 26 conductivity temperature depth casts and tows we measured temperature conductivity pressure and light scattering and also collected discrete samples for helium isotopes methane and ph the 3he 4he isotope ratio an unambiguous indicator of hydrothermal input showed a clear excess above background at 6 of the 10 submarine volcanoes surveyed marsili seamount had the highest anomaly where the 3he 4he ratio reached a 3he value of 23 at 610 m depth compared with background values of 5 smaller but distinct 3he anomalies occurred over palinuro enarete eolo sisifo and secca del capo although hydrothermal emissions are known to occur offshore of some aeolian subaerial volcanoes and hydrothermal deposits have been sampled throughout the arc our results are the first to confirm active discharge on marsili enarete eolo sisifo and secca del capo samples collected over lametini filicudi north alicudi north and alcione had 3he near the regional background values suggesting either absence of or very weak hydrothermal activity on these seamounts hydrocasts between the volcanoes revealed a consistent 3he maximum between 11 and 13 at 2000 m depth throughout the se tyrrhenian sea the volcanoes of the aeolian arc and the marsili back arc all 1000 m deep cannot contribute directly to this maximum this deep 3he excess may be a remnant of tritium decay or may have been produced by an unknown deep hydrothermal source

the abundance of seafloor massive sulfide deposits the possibility of mining seafl oor massive sulfide deposits has stirred debate about the sustainable use of this new resource and whether commercial development is worth the risk among the outstanding questions is how many deposits might be accessible to deep sea mining more than 300 sites of high temperature hydrothermal venting have been identifi ed since the discovery of black smokers but signifi cant massive sulfide accumulation has been found at only 165 of these sites estimates of the total number of vent fields and associated mineral deposits based on plume studies and deposit occurrence models range from 500 to 5000 we have used new deposit occurrence data from 10 000 km of ridge arc and backarc spreading centers to estimate the amount of massive sulfide in the easily accessible neovolcanic zones of the global oceans the total accumulation in these areas is estimated to be on the order of 6 108 tonnes containing 3 107 tonnes of copper and zinc this is similar to the total discovered copper and zinc in cenozoic massive sulfi de deposits mined on land but is insuffi cient to satisfy a growing global demand for these metals

forearc structures and tectonic regimes at the oblique subduction zone between the hikurangi plateau and the southern kermadec margin the convergent southern kermadec margin is examined to study the structural development and mechanical parameters of the inner trench slope in response to the oblique subduction of the oceanic hikurangi plateau swath bathymetric data have been combined with other geophysical data to reveal that the south kermadec inner trench wall is segmented into distinct upper middle and lower margins the lower margin is a nongrowing compressionally unstable accretionary wedge that is dissected by transcurrent faults the wedge has been thinned and narrowed as a result of tectonic erosion the middle margin is stable by comparison and separated from the lower margin by the 220 km long awanui fault this fault is a landward dipping strike slip reverse fault the middle upper margin including east cape ridge ecr forms a deforming backstop with a sharp along strike change in tectonic regime south of 36 40 s transpression characterizes the ecr shear zone north of 36 40 s the ecr is marked by uplift by extension and farther north by subsidence it is suggested that subsidence and subsequent tectonic erosion of the margin north of 35 50 s in the wake of hikurangi plateau subduction have broken the link between once continuous segments of the ecr tonga platform the unstable nature of the southern kermadec wedge under compression together with a comparison of its taper characteristics with those of modern convergent margins implies that the wedge deforms under a relatively high internal pore pressure but high effective basal friction regime strike slip deformation in the wedge is attributable to a relatively strong interplate coupling related to the buoyancy and ruggedness of the hikurangi plateau

collapse and reconstruction of monowai submarine volcano kermadec arc 1998 2004 monowai submarine volcano is one of the three most historically active volcanoes of the kermadec arc repeat multibeam surveys of monowai cone from september 1998 and september 2004 and t wave data recorded by the reseau sismique polynesien network for the same period document the collapse and subsequent regrowth of the cone within this 6 a period grid differencing of the two bathymetric data sets acquired 6 a apart reveals that a landslide 2230 m long occurred between the surveys within which a postcollapse cone and talus ridge 0 023 km3 in volume subsequently formed the volume of this collapse minus postcollapse construction is 0 085 km3 we interpret an unusual strong amplitude t wave event on 24 may 2002 as recording hot landsliding where the 100 to 160 m thick collapse has unroofed the uppermost parts of the vent conduit with the subsequent explosive interaction and cooling of hot magma and volcaniclastic rubble with ambient seawater this interpretation is consistent with the lack of emergent events sharp onset and large amplitude of the 24 may 2002 t waves the subsequent 2500 t wave events between november 2002 and september 2004 occurred in swarms with emerging and waning activity and with typical explosive volcanic acoustic signatures which are interpreted as recording the regrowth of an 90 m high cone back to a near 1998 elevation at an average rate of 47 m a 1 this study provides 1 a lower bound for frequency magnitude relationships of landsliding for submarine arc volcanoes and 2 estimates of 0 013 km3 a 1 of submarine cone growth during eruptive cycles

metallogenesis and mineralization of intraoceanic arcs i kermadec arc introduction the kermadec intraoceanic arc marks the southernmost section of the pacific ring of fire in the western pacific region a chain of mostly underwater volcanoes that stretches from north of japan southward to new zealand the kermadec arc striking for 1 200 km from monowai volcano to the north island of new zealand represents the southern portion of the contiguous 2 500 km kermadec tonga arc fig 1 de ronde et al 2003 the kermadec arc is populated by almost 30 volcanic centers comprising single large caldera or cone volcanoes or less commonly groups of relatively smaller cones de ronde et al 2001 2007 graham et al 2008 all of these volcanic centers lie to the west of the kermadec ridge in the southern and mid parts of the arc by up to 70 km in the case of rumble ii west then merge with the kermadec ridge near the kermadec islands around 30 s the volcanoes then diverge away westward from the kermadec ridge in the northern reaches of the arc fig 1 fig 1 location map for the kermadec arc and the various volcanoes referred to in the papers of this special volume the kermadec arc havre trough system is made up from east to west of a number of tectonic elements including the kermadec trench the kermadec ridge the havre trough or kermadec back arc and the colville ridge the volcanoes of the active arc front lie immediately west of the kermadec ridge in the southern and mid parts of the arc then merge with the kermadec ridge to the north the underlying bathymetry in shaded relief is derived from the satellite altimetry grid of smith and sandwell 1997 with more up to date bathymetry over top especially in the southern

hydrothermal venting and mineralization in the crater of kick em jenny submarine volcano grenada lesser antilles kick em jenny is a frequently erupting shallow submarine volcano located 7 5 km off the northern coast of grenada in the lesser antilles subduction zone focused and diffuse hydrothermal venting is taking place mainly within a small 70 110 m depression within the 300 m diameter crater of the volcano at depths of about 265 m much of the crater is blanketed with a layer of fine grained tephra that has undergone hydrothermal alteration clear fluids and gas are being discharged near the center of the depression from mound like vents at a maximum temperature of 180 c the gas consists of 93 96 co2 with trace amounts of methane and hydrogen gas flux measurements of individual bubble streams range from 10 to 100 kg of co2 per day diffuse venting with temperatures 5 35 c above ambient occurs throughout the depression and over large areas of the main crater these zones are colonized by reddish yellow bacteria with the production of fe oxyhydroxides as surface coatings fragile spires up to several meters in height and elongated mounds up to tens of centimeters thick a high resolution photomosaic of the inner crater depression shows fluid flow patterns descending the sides of the depression toward the crater floor we suggest that the negatively buoyant fluid flow is the result of phase separation of hydrothermal fluids at kick em jenny generating a dense saline component that does not rise despite its elevated temperature

3 d focused inversion of near seafloor magnetic data with application to the brothers volcano hydrothermal system southern pacific ocean new zealand 1 we describe and apply a new inversion method for 3 d modeling of magnetic anomalies designed for general application but which is particularly useful for the interpretation of near seafloor magnetic anomalies the crust subsurface is modeled by a set of prismatic cells each with uniform magnetization that together reproduce the observed magnetic field this problem is linear with respect to the magnetization and the number of cells is normally greater than the amount of available data thus the solution is obtained by solving an under determined linear problem a focused solution exhibiting sharp boundaries between different magnetization domains is obtained by allowing the amplitudes of magnetization to vary between a pre determined range and by minimizing the region of the 3 d space where the source shows large variations i e large gradients a regularization functional based on a depth weighting function is also introduced in order to counter act the natural decay of the magnetic field intensity with depth the inversion method has been used to explore the characteristics of the submarine hydrothermal system of brothers volcano in the kermadec arc by inverting near bottom magnetic data acquired by autonomous underwater vehicles auvs different surface expressions of the hydrothermal vent fields show specific vertical structures in their underlying demagnetization regions that we interpret to represent hydrothermal upflow zones for example at focused vent sites the demagnetized conduits are vertical pipe like structures extending to depths of 1000 m below the seafloor whereas at diffuse vent sites the demagnetization regions are characterized by thin and inclined conduits

eruption fed particle plumes and volcaniclastic deposits at a submarine volcano nw rota 1 mariana arc 1 nw rota 1 is an active submarine volcano in the mariana arc with a summit depth of 517 m and an explosively erupting volcanic vent southwest of the summit at a depth of 530 560 m during a period of ongoing explosive eruptions particle plumes surrounded the volcano and at least 3 3 107 m3 of volcaniclastic material was deposited on the southern flank particle plumes over the summit were magmatic hydrothermal in origin characterized by 3he enrichment hydrothermal precipitates and low ph values plumes at multiple depths below the summit surrounded the volcano and were composed overwhelmingly of fresh glassy shards of basalt rare anhydrite particles were present but there was a complete absence of other hydrothermal components in the deep plume samples these short lived anhydrite particles indicate the source of the deep plumes is from within or very near the eruptive vent and the mechanism for transport down the flanks of the volcano must be far faster than settling of individual particles the deep plumes most likely originated from sediment gravity flows generated by explosive eruptions or slope failure and landslides of unstable materials that had accumulated near the eruptive vent suspended sediments detach from the volcano slopes at multiple depths and are transported laterally up to tens of kilometers where they contribute to fall out deposits in distal sediments these observations link mechanisms for the transport of volcanic ash in the submarine environment to the types of deposits common in volcaniclastic aprons and fine ash layers in distal sediments

geometrical and mechanical properties of four species of northern european brown macroalgae abstract aquatic vegetation interacts with the flow by posing an obstruction and in return experiences drag and is reconfigured by acting forces it is suggested that plant buoyancy and stiffness affect these bio physical interactions and hence should be considered when including vegetation in physical and numerical hydrodynamic models however data on these parameters is either lacking for many species or existing information is insufficient to model flexible aquatic vegetation correctly previous studies have focused on plant stems but did not take plant foliage into account the present study extends the existing knowledge base by providing data for four northern european brown macroalgae and also provides a comparison between the mechanical properties of stem and blade tissue for these species specimens of alaria esculenta laminaria digitata fucus serratus and fucus vesiculosus were collected from a small tidal inlet in norway other than f serratus the macroalgae were positively buoyant and all stems showed bending moduli in agreement with previous studies with respect to their order of magnitude only l digitata exhibited a significant difference between bending moduli for stems and blades and also between the tip and the base of the blades however there were differences in flexural rigidities product of bending modulus and second moment of cross sectional area of both stems and blades and the tip and the base of blades of all but f serratus this highlights the important influence of cross sectional area and cross sectional shape on stiffness

hot fingers in the mantle wedge new insights into magma genesis in subduction zones abstract quaternary volcanoes in the northeast japan arc can be grouped into 10 volcanic clusters striking transverse to the arc these have an average width of 50 km and are separated by parallel gaps 30 75 km wide this clustering of volcanic centres topographic profiles low velocity regions in the mantle wedge and local negative bouguer gravity anomalies along the japan sea side of the volcanic arc are closely correlated all these observations may be related to locally developed hot regions within the mantle wedge that have the form of inclined 50 km wide fingers each of the 10 fingers recognised extends from deep mantle 150 km below the back arc region towards the shallower mantle 50 km beneath the volcanic front quaternary volcanoes are built immediately above the hot mantle fingers the volcanic basement along the fingers has been uplifted by repeated injection of magmas into the crust accompanied by quaternary volcanic activity at the surface although volcanic activity is rare along the japan sea coast tomographic results show that hot low velocity mantle fingers exist within the mantle wedge the negative bouguer anomalies at the rear of the volcanic arc could be caused by magmas supplied from the hot mantle fingers these have not yet been erupted but have accumulated at the moho discontinuity

geochemical characterization of highly diverse hydrothermal fluids from volcanic vent systems of the kermadec intraoceanic arc abstract during the r v sonne cruise so253 in 2016 2017 hydrothermal vent sites along the kermadec intraoceanic arc were sampled for hydrothermal fluids at four active volcanoes macauley haungaroa brothers and rumble iii respectively water depths ranged between 290 m and 1700 m a new vent field was discovered at haungaroa the samples were taken from diffuse flow sites as well as from white and black smokers rich in metals and gases with discharge temperatures as high as 311 c their fluid composition is very variable but basically divides into two types one that indicates distinct magmatic input and another that shows evidence for intense water rock interaction under hot acidic conditions fluid samples from macauley the shallowest sampling site 300 m had fe concentrations as high as 1 7 mm al concentrations up to 122 m and h2s up to 10 mm at a ph of only 1 2 at brothers the deepest sampling site down to 1600 m we identified two different fluid types 1 a magmatically influenced type at the upper and lower cone with highest temperatures of 115 c up to 95 6 mm mg the highest mg concentration measured in fluids from intraoceanic arc systems so far elevated so42 76 9 mm high h2s 5 0 mm but fe concentrations of only 15 m and 2 a fluid with low mg 5 4 mm low h2s 1 1 mm temperatures reaching 311 c and high fe contents 12 4 mm at the upper caldera and nw caldera wall typical of a black smoker fluid chloride concentrations in all fluids were similar or highly enriched when compared to seawater e g up to 787 mm brine fluids with also one low chlorinity vapor phase fluid sample recovered indicating that phase separation is occurring at brothers unusual highly elevated mg concentrations in fluids from the brothers lower cone 95 6 mm compared to 53 2 mm in ambient seawater combined with highly elevated concentrations of so42 76 9 mm compared to 29 0 mm in ambient seawater indicate dissolution of mg and so42 bearing minerals in the subsurface such as caminite our data show how highly diverse and variable island arc systems can be with respect to their fluid chemistry both spatially and temporally it adds to the still limited data set of arc systems compared to mid ocean ridges and supplies an important contribution towards a better understanding of geochemical processes along arc volcanoes the higher range in fluid chemistry together with shallower water depth implies that the fluids from intraoceanic arcs may contribute a significant fraction of dissolved metals not only to the global oceanic biogeochemical cycle but also into the photic zone the area of highest bioproductivity

multiple hydrothermal sources along the south tonga arc and valu fa ridge 1 quantifying hydrothermal venting at the boundaries of tectonic plates is an outstanding geoscience problem considerable progress has been made by detailed surveys along mid ocean ridges mors but until recently little was known about fluid venting along volcanic arcs we present the first systematic survey for hydrothermal venting along the 425 km long south tonga arc and new chemistry data for particle and thermal plumes previously reported along an adjacent 88 km long section of the back arc valu fa ridge vfr eleven hydrothermal plumes recognized by their anomalous light backscattering eh temperature ph dissolved he 3 ch4 and total dissolvable fe and mn were identified arising from seven volcanic centers along the arc five plumes on the vfr were characterized chemically vent field density for the south tonga arc was 2 6 sites 100 km of arc front comparable to that found by surveys of the kermadec arc 1 9 to 3 8 sites 100 km and to mors in the eastern pacific average value for 2280 km of surveyed ridgecrest 3 2 sites 100 km a vent gap occurs along a 190 km section of the arc closest to the vfr and a site density twice the average for mors on the eastern edge of the pacific plate was found on this part of the vfr 6 6 sites 100 km we suggest magmas ascending under the adjacent south tonga arc have been captured by the vfr while chemical enrichments of plumes on the south tonga arc were in general slightly less than those on the kermadec arc several instances of excessive anomalies in ph suggest a similar presence of fluids enriched in magmatic volatiles co2 so2 h2s locally venting on the vfr has contributed to accumulations of 3 he fe and mn within the southern lau basin on a broader scale our results provide considerable support for the notion that venting from intraoceanic arcs on the convergent margin of the pacific plate adds significantly to the total hydrothermal input into the pacific ocean

drilling shallow water massive sulfides at the palinuro volcanic complex aeolian island arc italy a subseafloor replacement style barite and sulfide occurrence was drilled in shallow waters at the palinuro volcanic complex the northernmost aeolian arc volcano in the tyrrhenian sea italy using a lander type drilling device 11 successful drill holes yielded a total of 13 5 m of core from a sediment filled depression located at a water depth of 630 to 650 m the longest continuous drill core recovered consists of 4 84 m of massive to semimassive barite and sulfides with abundant late native sulfur overprint seafloor observations suggest that the hydrothermal system associated with the formation of the subseafloor barite and sulfide ore zone is still active although black smoker activity does not occur on the seafloor the recovered drill core shows that the subseafloor deposit is zoned with depth the top of the mineralized zone is comprised of a variably silicified vuggy barite sulfide facies that shows notable polymetallic metal enrichment while the deeper portion of the mineralized zone is dominated by massive pyrite having distinctly lower base and precious metal grades metal zonation of the barite and sulfide deposit is related to the evolution of the hydrothermal fluids in space and time the barite cap and the massive pyrite present in the deeper portion of the mineralized zone appear to have formed early in the paragenesis during the main stage of the mineralization the barite cap was brecciated and cemented by a polymetallic assemblage of barite and pyrite with minor chalcopyrite and tetrahedrite trace famatinite and rare cinnabar lower temperature precipitates formed during the main stage of mineralization include sphalerite galena pyrite opal a and barite which are associated with traces of pb sb as sulfosalts such as bournonite seligmannite or semseyite a distinct mineral assemblage of fine grained anhedral enargite hypogene covellite chalcopyrite and galena is commonly associated with colloform sphalerite galena and pyrite as a late phase of this main stage colloform pyrite and marcasite are the last sulfides formed in the paragenetic sequence the deposit is interpreted to have formed from fluids having an intermediate sulfidation state although excursions to high and very high sulfidation states are indicated by the presence of abundant enargite and hypogene covellite laser ablation and conventional sulfur isotope analyses show that pyrite formed close to the seafloor within the zone of polymetallic metal enrichment has a variable sulfur isotope composition 34s 39 to 3 whereas a more narrow range is observed in the massive pyrite at depth 34s 10 to 0 similar variations were also documented for the late native sulfur overprint overall the negative sulfur isotope ratios at depth the intermediate to very high sulfidation conditions during mineralization and the abundance of native sulfur suggest contributions of magmatic volatiles to the mineralizing fluids from a degassing magma chamber at depth biological processes are interpreted to have played a major role during late stages of ore formation the combination of a subseafloor replacement deposit with a massive to semimassive barite cap rock overlying massive pyrite the intermediate to high sulfidation characteristics and the strong biological influence on the late stages of mineralization are distinct from other modern seafloor massive sulfide deposits and represents a style of submarine mineralization not previously recognized in a modern volcanic arc environment the barite and sulfide occurrence at palinuro shares many characteristics with porphyry related base metal veins and intermediate sulfidation epithermal deposits suggesting that metallogenic processes associated with arc related magmatic hydrothermal systems are not restricted to the subaerial environment

zonal currents in the f region deduced from swarm constellation measurements the swarm constellation has been used to estimate zonal currents in the topside f region ionosphere at about 500 km near simultaneous magnetic field measurements from two altitudes but the same meridian are used for the current density calculations we consider the period 15 february to 23 june 2014 for deriving a full 24 h local time coverage of the latitudinal distribution over 50 in magnetic latitude intervals with close orbital phasing at the two heights are considered which repeat every 6 days from such days seven successive orbits are used where the epochs of equator crossings differ by less than 2 min deduced current densities are predominantly eastward about 20 na m2 on the dayside and westward about 10 na m2 on the nightside a number of different drivers contribute to the observed total current we identified the gravity driven eastward current as the most prominent at low latitudes eastward currents in the northern hemisphere are clearly stronger than in the south this is attributed to the proximity of our study period to june solstice when the solar radiation is stronger in the north in addition interhemispheric winds from the northern summer to the southern winter hemisphere contribute they cause eastward currents in the north and westward in the south we find a relatively large variability of the zonal currents both in space and time the standard deviation is at least twice as large as the mean value of current density this large variability is suggested to be related to gravity wave forcing from below

venting of a separate co2 rich gas phase from submarine arc volcanoes examples from the mariana and tonga kermadec arcs submersible dives on 22 active submarine volcanoes on the mariana and tonga kermadec arcs have discovered systems on six of these volcanoes that in addition to discharging hot vent fluid are also venting a separate co2 rich phase either in the form of gas bubbles or liquid co2 droplets one of the most impressive is the champagne vent site on nw eifuku in the northern mariana arc which is discharging cold droplets of liquid co2 at an estimated rate of 23 mol co2 s about 0 1 of the global mid ocean ridge mor carbon flux three other mariana arc submarine volcanoes nw rota 1 nikko and daikoku and two volcanoes on the tonga kermadec arc giggenbach and volcano 1 also have vent fields discharging co2 rich gas bubbles the vent fluids at these volcanoes have very high co2 concentrations and elevated c 3he and 13c co2 ratios compared to mor systems indicating a contribution to the carbon flux from subducted marine carbonates and organic material analysis of the co2 concentrations shows that most of the fluids are undersaturated with co2 this deviation from equilibrium would not be expected for pressure release degassing of an ascending fluid saturated with co2 mechanisms to produce a separate co2 rich gas phase at the seafloor require direct injection of magmatic co2 rich gas the ascending co2 rich gas could then partially dissolve into seawater circulating within the volcano edifice without reaching equilibrium alternatively an ascending high temperature co2 rich aqueous fluid could boil to produce a co2 rich gas phase and a co2 depleted liquid these findings indicate that carbon fluxes from submarine arcs may be higher than previously estimated and that experiments to estimate carbon fluxes at submarine arc volcanoes are merited hydrothermal sites such as these with a separate gas phase are valuable natural laboratories for studying the effects of high co2 concentrations on marine ecosystems

subaerial and sublacustrine hydrothermal activity at lake rotomahana abstract lake rotomahana is a crater lake in the okataina volcanic centre new zealand that was significantly modified by the 1886 tarawera rift eruption the lake is host to numerous sublacustrine hydrothermal vents water column studies were conducted in 2011 and 2014 along with sampling of lake shore hot springs and crater lakes in waimangu valley to complement magnetic seismic bathymetric and heat flux surveys helium concentrations below 50 m depth are higher in 2014 compared to 2011 and represent some of the highest concentrations measured at 6 10 7 ccstp g with an end member 3he 4he value of 7 1 ra the high concentrations of helium when coupled with ph anomalies due to high dissolved co2 content suggest the dominant chemical input to the lake is derived from magmatic degassing of an underlying magma the lake shore hot spring waters show differences in source temperatures using a na k geothermometer with inferred reservoir temperatures ranging between 197 and 232 c water 18o and d values show isotopic enrichment due to evaporation of a steam heated pool with samples from nearby waimangu valley having the greatest enrichment results from this study confirm both pre 1886 eruption hydrothermal sites and newly created post eruption sites are both still active

helium isotope studies of geothermal fields in the taupo volcanic zone new zealand abstract we report new measurements of 3he 4he and ne on 69 samples of gas from geothermal fields in the central section of the ne sw trending taupo volcanic zone tvz we find 3 he 4 he ratios in the range 5 9 7 3 times the atmospheric ratio 5 9 7 3ra typical of subduction zone systems in some areas near the boundaries of the volcanic zone the ratio is much lower 2 4ra the values in the wairakei field are extremely uniform and vary by only a few per cent from 7 2 ra in contrast the wells in the ohaaki broadlands field show a striking factor of two variation with the west bank section characterised by values near 6 ra while the east bank section has values as low as 3 0 ra this suggests that mixing of two types of geothermal source fluids may be occurring at ohaaki broadlands an inverse relationship has been found between the 3 he 4 he ratio of the gases and the b cl ratios in the associated fluids thus the helium isotope ratios appear to be affected both by the flux of mantle helium associated with mantle subduction and also by the presence of sedimentary rocks beneath the geothermal field leaching by the hot ascending fluid of radiogenic 4he together with boron from the underlying high boron low chloride mesozoic greywacke basement is thought to be the cause of this inverse relationship the co 2 3 he ratio in the tvz exceeds the morb ratio by a factor of up to 100 with higher values corresponding to higher b cl fluid ratios suggesting that the greywacke may also be the major source of the co2 we have also measured argon concentrations and isotopes on 19 samples in the ohaaki broadlands area in order to further elucidate the nature of the striking helium isotope variations the argon isotope ratios are relatively close to atmospheric indicating that the majority of the argon comes from recirculated groundwater the simplified boiling model of mazor et al 1990 has been used to calculate the 3 he heat ratio in the ohaaki broadlands and wairakei fields the values obtained fall within the range previously reported for mid ocean ridge systems this model has been extended and has led us to the conclusion that compared to the 3 he 4 he ratio the 3 he 36 ar asw ratio is a much better indicator of the potential geothermal heat the 4 he 40 ar na where na non atmospheric ratio of both the high mantle derived and low crustal derived 3 he 4 he end members of the analyses reported here is about 3 6 but for samples with low 3 he 36 ar ratio this ratio falls to values below 0 5 the value of 3 6 is in the range which is expected for the radiogenic component and although considerably lower than that often found in subduction type mantle gases it is still within the accepted range of values

submarine magmatic hydrothermal systems at the monowai volcanic center kermadec arc the monowai volcanic center is located at the midpoint along the 2 530 km long tonga kermadec arc system the monowai volcanic center is comprised of a large elongate caldera monowai caldera area 35 km2 depth to caldera floor 1 590 m which has formed within an older caldera some 84 km2 in area to the south of this nested caldera system is a large composite volcano monowai cone which rises to within 100 m of the sea surface and which has been volcanically active for the past several decades mafic volcanic rocks dominate the monowai volcanic center basalts are the most common rock type recovered from the cone whereas basaltic andesites are common within the caldera hydrothermal plume mapping has shown at least three major hydrothermal systems associated with the caldera and cone 1 the summit of the cone 2 low temperature venting 60 c mussel ridge on the southwestern wall of the caldera and 3 a deeper caldera source with higher temperature venting that has yet to be observed the cone summit plume shows large anomalies in ph a shift of 2 00 ph units and 3he 358 and noticeable h2s up to 32 m and ch4 up to 900 nm the summit plume is also metal rich with elevated total dissolvable fe tdfe up to 4 200 nm tdmn up to 412 nm and tdfe tdmn up to 20 4 particulate samples have elevated fe si al and ti consistent with addition to the hydrothermal fluid from acidic water rock reaction plumes extending from 1 000 to 1 400 m depth provide evidence for a major hydrothermal vent system in the caldera the caldera plume has lower values for tdfe and tdmn although some samples show higher tdmn concentrations than the cone summit plume caldera plume samples are also relatively gas poor i e no h2s detected ph shift of 0 06 ph units ch4 concentrations up to 26 nm the composition of the hydrothermal plumes in the caldera have higher metal contents than the sampled vent fluids along mussel ridge requiring that the source of the caldera plumes is at greater depth and likely of higher temperature minor plumes detected as light scattering anomalies but with no 3he anomalies down the northern flank of the monowai caldera most likely represent remobilization of volcanic debris from the volcano flanks we believe the monowai volcanic center is host to a robust magmatic hydrothermal system with significant differences in the style and composition of venting at the cone and caldera sites at the cone the large shifts in ph very high 3he values elevated tdfe and tdfe tdmn and the h2s and ch4 rich nature of the plume fluids together with elevated ti p v s and al in hydrothermal particulates indicates significant magmatic volatile metal contributions in the hydrothermal system coupled with aggressive acidic water rock interaction by contrast the caldera has low tdfe tdmn in hydrothermal plumes however elevated al and ti contents in caldera particulate samples combined with the presence of alunite pyrophyllite sulfide minerals and native sulfur in samples from mussel ridge suggest past and perhaps recent acid volatile rich venting and active fe sulfide formation in the subsurface

vortex structure and sediment deposition in the wake behind a finite patch of model submerged vegetation abstracta submerged patch of finite width vegetation may produce vortex structures in its wake in both the vertical and horizontal planes this experimental study used velocity and deposition measu

crustal magnetization of brothers volcano new zealand measured by autonomous underwater vehicles geophysical expression of a submarine hydrothermal system near bottom magnetic anomaly data have been acquired using autonomous underwater vehicles at brothers volcano southern kermadec arc new zealand crustal magnetization for the study area was obtained by inverting the magnetic data and shows a strong correlation between areas of low magnetization and four hydrothermal fields one of which was unknown prior to our surveys the magnetization pattern is consistent with a model of discrete individual zones of fluid upflow focused along caldera ring faults that provide preferred pathways for the ascent of the hydrothermal fluids differences in the amplitude of the magnetization over the vent fields appear to correlate with age and temperature variations of the hydrothermal fields

geology hydrothermal activity and sea floor massive sulfide mineralization at the rumble ii west mafic caldera abstract sea floor imagery volcanic rock massive sulfide and hydrothermal plume samples 3 he ph dissolved fe and mn and particulate chemistry have been collected from the rumble ii west volcano southern kermadec arc new zealand rumble ii west is a caldera volcano with an 3 km diameter summit depression bounded by ring faults with a resurgent central cone rocks recovered to date are predominantly mafic in composition i e basalt to basaltic andesite with volumetrically lesser intermediate rocks i e andesite on the basis of its size geometry volcanic products and composition rumble ii west can be classified as a mafic caldera volcano rumble ii west has a weak hydrothermal plume signature characterized by a small but detectable 3 he anomaly 25 time series light scattering data though obtained from vertical casts and tow yos do show that hydrothermal activity has increased in intensity between 1999 and 2011 massive sulfides recovered from the eastern caldera wall and eastern flank of the central cone are primarily comprised of barite and chalcopyrite with lesser sphalerite pyrite and traces of galena the weak hydrothermal plume signal indicates that the volcano is in a volcanic hydrothermal quiescent stage compared to other volcanoes along the southern kermadec arc although the preponderance of barite with massive sulfide mineralization indicates higher temperature venting in the past of the volcanoes along the kermadec tonga arc known to host massive sulfides i e clark rumble ii west brothers monowai volcano 19 and volcano 1 the majority five out of six are dominantly mafic in composition and all but one of these mafic volcanoes form moderate size to large calderas to date mafic calderas have been largely ignored as hosts to sea floor massive sulfide deposits that 75 of the presently known massive sulfide bearing calderas along the arc are mafic in composition the dacitic brothers volcano is the exception has important implications for sea floor massive sulfide mineral exploration in the modern oceans and ancient rock record on land

mineralized microbes from giggenbach submarine volcano 1 the giggenbach submarine volcano which forms part of the kermadec active arc front is located 780 km nne of the north island of new zealand samples collected from chimneys associated with seafloor hydrothermal vents on this volcano at a depth of 160 180 m contain silicified microbes and microbes entombed in reticular fe rich precipitates the mineralized biota includes filamentous rod shaped and rare coccoid microbes in the absence of organic carbon for rdna analysis or preserved cells the taxonomic affinity of these microbes in terms of extant taxa remains questionable because of their architectural simplicity and the paucity of taxonomically significant features the three dimensional preservation of the microbes indicates rapid mineralization with a steady supply of supersaturated fluids to the nucleation sites present on the surfaces of the microbes the mineralization styles evident in the microbes from the giggenbach submarine volcano are similar to those associated with mineralized microbes found in terrestrial hot spring deposits in new zealand iceland yellowstone and kenya these similarities exist even though the microbes are probably different and the fluids become supersaturated with respect to opal a by different mechanisms for ancient rocks it means that interpretations of the depositional settings cannot be based solely on the silicified microbes or their style of silicification

high resolution hydrothermal mapping of brothers caldera kermadec arc submarine edifices with caldera summits are common along volcanic arcs and much more likely than simple cones to host hydrothermal venting compared with cones however locating all vent field locations on a caldera s complex bathymetry is a daunting logistical challenge here we describe the first use of an autonomous underwater vehicle abe to fully map the distribution of near bottom hydrothermal tracers over the caldera walls and cone complex of brothers volcano the most active hydrothermal source on the southern kermadec arc sensors on abe simultaneously measured hydrothermal plume anomalies in temperature light backscattering particle concentration and oxidation reduction potential dissolved reduced species every 2 to 3 m along track local maxima in these tracers confirmed known sites on the northwestern wall and the cone summits and more precisely mapped their extents we discovered evidence for new sites throughout the entire northwestern half of the caldera wall at the base of the southeastern wall and on the flanks of both cones systematic variations in the backscattering temperature ratio identified different types of fluid discharge plumes from high temperature metal rich sources dominated the caldera wall while on top of the caldera wall and on the cones we found only plumes from low temperature diffuse flow including occasional s rich plumes source distribution on the walls appears fault controlled but we detected no sources along the deepest fault defining the rim of the downdropped caldera floor advanced deep sea survey techniques using autonomous vehicles is an indispensible and cost effective tool for acquiring a comprehensive understanding of the relationship between hydrothermal discharge and geology on individual volcanoes

detailed morphology and structure of an active submarine arc caldera brothers volcano kermadec arc a survey of the brothers caldera volcano kermadec arc with the autonomous underwater vehicle abe has revealed new details of the morphology and structure of this submarine frontal arc caldera and the geologic setting of its hydrothermal activity brothers volcano has formed between major sw netrending faults within the extensional field of the havre trough brothers may be unique among known submarine calderas in that it has four active hydrothermal systems two high temperature sulfide depositing sites associated with faulting on the northwestern and western walls i e the nw caldera and w caldera hydrothermal sites respectively and gas rich sites on the summits of the constructional cones that fill most of the southern part of the caldera i e the upper and lower cone sites the 3 0 3 4 km caldera is well defined by a topographic rim encompassing 320 of its circumference and which lies between the bounds of two outer half grabenshaped faults in the northwest and southeast sectors there is not a morphologically well defined continuous ring fault at the map resolution although near vertical scarps are present discontinuously at the base of sections of the wall the width of the wall varies from 200 m at its southwest portion to 750 m on its northern section the widest part of the wall is its northwest sector which also has the largest documented area of hydrothermal alteration and where sea floor magnetization is lowest in addition to primary northwest southeast elongation and southwest northeast structures caused by faulting within the regional back arc strain field there are also less well developed west southwestnorth northeast regional structures intersecting the volcano that is appar ent on the abe bathymetry and at outcrop scale from submersible observations asymmetrical trap doorstyle caldera collapse is considered a possible mechanism for the formation of the brothers caldera

the importance of accurately representing submerged vegetation morphology in the numerical prediction of complex river flow this paper reports a novel method for the incorporation of complex plant morphologies into a computational fluid dynamics cfd model allowing the numerical prediction of flows around individual plants the morphological complexity which comprises the vertical and lateral distribution of individual branches and leaves is captured through terrestrial laser scanning tls and is maintained in the numerical prediction of flow fields this is achieved where the post processed voxelised plant representation is incorporated into a cfd scheme through a mass flux scaling algorithm mfsa flow around prunus laurocerasus has been modelled under foliated and defoliated states following the removal of leaves the complex plant morphologies are shown to produce spatially heterogeneous downstream velocity fields with velocity profiles that deviate significantly from the idealised inflected shape rapid transition between the high velocity free stream zone and the zone of reduced velocity in the plant wake indicate shearing of flow with the point of reattachment extending up to seven plant lengths downstream the presence of leaves significantly modifies the flow field response with development of a second more pronounced wake structure around the dense foliage this approach provides a full flow numerical description of the pressure field enabling the vegetative drag force to be quantified for the example given here drag force is an order of magnitude greater for the foliated state the methodology outlined here demonstrates the importance of accurately representing complex plant morphology in hydraulic models and allows drag forces and coefficients to be calculated for specific plant species this article is protected by copyright all rights reserved

hydrothermal activity and volcano distribution along the mariana arc 1 submarine volcanic arcs extend for fully a third of the length of the mid ocean ridge system but systematic investigation of hydrothermal venting on those arcs is sparse here we report on the distribution of hydrothermal activity along the intraoceanic mariana arc we identify 76 volcanic edifices along 1370 km of arc grouped into 60 volcanic centers of which at least 26 20 submarine are hydrothermally or volcanically active the overall volcanic center density is 4 4 100 km of arc and that of active centers is 1 9 100 km an equal length of the tonga kermadec arc holds fewer centers 2 9 100 km but a similar density of active centers 1 8 100 km the lower percentage of active centers on the mariana arc results from its having both fewer caldera volcanoes since on both arcs calderas are twice as likely as cones to be active and a lower percentage of active calderas and cones active centers are found from 80 to 230 km above the subducting pacific slab and a quarter lie behind the arc front the frequency distribution of center spacing along the arc front peaks between 20 and 30 km and shows the asymmetric long tail shape typical for many other arcs especially those with volcano populations 20 there is no evidence for a regular spacing of volcanic centers using the new mariana data and recent data from the tonga kermadec arc we estimate that all intraoceanic arcs combined may contribute hydrothermal emissions equal to 10 of that from the global mid ocean ridge

the rapuhia scarp northern hikurangi plateau its nature and subduction effects on the kermadec trench abstract multibeam bathymetric data seismic reflection and magnetic data are used to examine the nature of the 1 km high rapuhia scarp and the tectonic effects of its subduction on the kermadec margin the rapuhia scarp is the boundary between the hikurangi plateau and 85 ma oceanic crust its intersection with the kermadec trench moves south at 4 cm yr magnetic modelling indicates that the northern hikurangi plateau may be formed of 5 km of relatively strongly magnetised extrusive and intrusive volcanics rocks uplift of the rapuhia scarp near the trench is consistent with vertical motion on a tear fault in the subducting plate the coincident intersection of the subducting rapuhia scarp with a nnw trending volcanic ridge intersection ridge and the kermadec trench results in an abrupt 1 5 km increase in the trench depth and inner margin topography the rapuhia scarp boundary sweeps south along the margin slumping and subsidence of the inner margin resulting from this transition occur on a variety of scales from 5 km wide 1 km high arcuate frontal erosion slumps to regional subsidence of up to 4 km across the 50 100 km wide mid upper inner trench margin as it adjusts to the new subduction geometry the pattern of inner margin subsidence involving the entire forearc is broadly similar to that observed 1200 km further north in the wake of subduction of the louisville ridge seamount chain subsidence of the inner trench margin results in the loss of approximately 400 km3 per kilometre of margin as the subducting hikurangi plateau support is removed we estimate however only one fifth of the above subsidence is frontal or basal erosion highlighting the risks of estimating tectonic erosion from margin subsidence if the cause of subsidence is mis identified the remaining 320 km2 of subsidence is due to the steeper dip of the subducting plate associated with subduction of the comparatively dense 85 ma oceanic crust

flow structure in canopy models dominated by progressive waves summary laboratory experiments were carried out to study the flow structure both inside and above different canopy models which were dominated by progressive waves a set of experimental conditions were considered in a laboratory flume three vegetation models submerged rigid submerged flexible and emergent rigid three plant densities 128 640 and 1280 stems m 2 and three wave frequencies f 0 8 1 and 1 4 hz the progressive waves followed the second order stokes theory in the intermediate depth range the observations revealed that submerged and emergent rigid vegetation models modified the wave induced velocities i e both mean current and wave velocity the submerged rigid vegetation model for plant densities higher than 640 plants m 2 and wave frequency higher than 1 hz acted akin to a false floor confining the mean current to above the plant bed a penetration depth around 2 cm below the top of submerged rigid vegetation was found for the other runs the vertical profile of mean current did not present changes with respect to runs without plants the emergent rigid vegetation model reversed the direction of the induced mean current with the highest velocity corresponding to the highest plant density in contrast the submerged flexible vegetation model had a weak effect on the mean current with the vertical velocity profile similar to that found in experiments without vegetation the wave velocities inside the vegetation for the densest submerged rigid vegetation were found to be reduced by 20 when compared to the wave velocities without vegetation while in emergent rigid vegetation this reduction was of 45

plant patch hydrodynamics in streams mean flow turbulence and drag forces 1 this paper investigates the effects of a finite size vegetation patch on flow turbulence variations in drag forces experienced by individual plants within the patch and flow drag interrelations the experiments were conducted in a 32 m long laboratory flume with a 2 8 m long artificial patch the plants were arranged to form a staggered pattern and three flow scenarios were tested velocities were recorded with an acoustic doppler velocimeter whereas specifically designed devices were used to simultaneously measure the drag forces acting on nine plants within the patch for all studied cases the results show zones of increased turbulent energy close to the leading edge and along the patch canopy top where turbulence shear production is enhanced zones of negative reynolds stresses u w are found inside the patch and they reflect the influence of plant morphology which affects the shape of the longitudinal velocity profile and associated turbulent fluxes modifications to the power spectral densities of velocity by the plants indicate the emergence of two plant induced mechanisms of energy production which are most likely related to the wake turbulence and shear layer turbulence drag fluctuations appear to be correlated with the velocity field with this correlation being especially profound at the highest studied flow rate the data suggest that the highlighted correlation stems from flow plant interactions at the top of the vegetation canopy likely due to the presence of large three dimensional coherent structures

reactivation of tectonics crustal underplating and uplift after 60 myr of passive subsidence raukumara basin hikurangi kermadec fore arc new zealand implications for global growth and recycling of continents we use seismic reflection and refraction data to determine crustal structure to map a fore arc basin containing 12 km of sediment and to image the subduction thrust at 35 km depth seismic reflection megasequences within the basin are correlated with onshore geology megasequence x late cretaceous and paleogene marine passive margin sediments megasequence y a similar to 10 000 km 3 submarine landslide emplaced during subduction initiation at 22 ma and megasequence z a neogene subduction margin megasequence the moho lies at 17 km beneath the basin center and at 35 km at the southern margin beneath the western basin margin we interpret reflective units as deformed gondwana fore arc sediment that was thrust in cretaceous time over oceanic crust 7 km thick raukumara basin has normal faults at its western margin and is uplifted along its eastern and southern margins raukumara basin represents a rigid fore arc block 150 km long which contrasts with widespread faulting and large neogene vertical axis rotations farther south taper of the western edge of allochthonous unit y and westward thickening and downlap of immediately overlying strata suggest westward or northwestward paleoslope and emplacement direction rather than southwestward as proposed for the correlative onshore allochthon spatial correlation between rock uplift of the eastern and southern basin margins with the intersection between moho and subduction thrust leads us to suggest that crustal underplating is modulated by fore arc crustal thickness the trench slope has many small extensional faults and lacks coherent internal reflections suggesting collapse of indurated rock rather than accretion of 1 km of sediment from the downgoing plate the lack of volcanic intrusion east of the active arc and stratigraphic evidence for the broadening of east cape ridge with time suggests net fore arc accretion since 22 ma we propose a cyclical fore arc kinematic rock moves down a subduction channel to near the base of the crust where underplating drives rock uplift oversteepens the trench slope and causes collapse toward the trench and subduction channel cyclical rock particle paths led to persistent trench slope subsidence during net accretion existing global estimates of fore arc loss are systematically too high because they assume vertical particle paths citation sutherland r et al 2009 reactivation of tectonics crustal underplating and uplift after 60 myr of passive subsidence raukumara basin hikurangi kermadec fore arc new zealand implications for global growth and recycling of continents tectonics 28 tc5017 doi 10 1029 2008tc002356

hydrothermal helium plumes in the pacific ocean hydrothermal activity along the global mid ocean ridge system and at active seamounts introduces a 3 he rich signal into the deep ocean basins which can be used to trace patterns of ocean circulation and mixing this hydrothermal helium signal is especially strong in the pacific ocean where the spreading rate of the ridges is the greatest in several areas of the pacific the hydrothermal activity is of sufficient strength to produce intense helium plumes which clearly define the regional circulation among these are 1 a pair of helium plumes at 2500 m depth which extend westward from the east pacific rise at 10 n and 15 s into the interior of the pacific basin 2 a helium plume at 2000 m depth extending southwest from sources on the juan de fuca ridge in the northeast pacific and 3 a plume at 1100 m depth emanating from loihi seamount at 20 n which extends eastward from hawaii to the coast of mexico the flow field implied by the helium distribution appears to be in reasonable agreement with reid s 1997 steric height analysis for the pacific

crustal structure of the kermadec arc from mango seismic refraction profiles three active source seismic refraction profiles are integrated with morphological and potential field data to place the first regional constraints on the structure of the kermadec subduction zone these observations are used to test contrasting tectonic models for an along strike transition in margin structure previously known as the 32 s boundary we use residual bathymetry to constrain the geometry of this boundary and propose the name central kermadec discontinuity ckd north of the ckd the buried tonga ridge occupies the forearc with vp 6 5 7 3 km s 1 and residual free air gravity anomalies constrain its latitudinal extent north of 30 5 s width 110 20 km and strike 005 south of 25 s south of the ckd the forearc is structurally homogeneous down dip with vp 5 7 7 3 km s 1 in the havre trough backarc crustal thickness south of the ckd is 8 9 km which is up to 4 km thinner than the northern havre trough and at least 1 km thinner than the southern havre trough we suggest that the eocene arc did not extend along the current length of the tonga kermadec trench the eocene arc was originally connected to the three kings ridge and the ckd was likely formed during separation and easterly translation of an eocene arc substrate during the early oligocene we suggest that the first order crustal thickness variations along the kermadec arc were inherited from before the neogene and reflect mesozoic crustal structure the cenozoic evolution of the tonga kermadec hikurangi margin and along strike variations in the duration of arc volcanism

trace element mapping of copper and zinc rich black smoker chimneys from brothers volcano kermadec arc using synchrotron radiation xfm and la icp ms

laboratory measurements of flow and turbulence in discontinuous distributions of ligulate seagrass turbulent flow characteristics were investigated in laboratory flume studies of a ligulate plant canopy interrupted by a gap representing discontinuities observed in seagrass prairies the reliability of velocity measurements obtained using an acoustic doppler velocimeter within the canopy was shown using specifically designed experiments in relatively fast flow mean velocity 5 5 cm s 1 the mean flow profile was logarithmic above the canopy had an inflection point near its top and uniformly low values within it within the gap a recirculation cell formed reynolds stress maxima were approximately coincident with the mean flow inflection point quadrant analysis revealed an ejection dominated upper layer a sweep dominated region around the top of the canopy and within the gap and no dominant quadrant within the canopy in slower flow mean velocity 1 7 cm s 1 the plants were quasiemergent and the flow fields more uniform sweeps similarly dominated the region near the top of the canopy and within the gap in both flows autocorrelation of longitudinal velocity fluctuations showed a lagrangian time scale maximum at the downstream end of the gap

hikurangi plateau a cretaceous large igneous province in the southwest pacific ocean the first dredge haul of basement rocks obtained from the hikurangi plateau in the southwest pacific ocean consists dominantly of volcanic and volcaniclastic rocks of probable pre late cretaceous age all samples have undergone extensive seafloor weathering to phyllosilicate and zeolite bearing assemblages petrography mineral chemistry and whole rock element concentrations and ratios of the least altered lavas e g tio2 1 3 1 6 wt cr 132 224 ppm zr y 2 9 3 6 zr nb 19 29 ti v 22 29 suggest a restricted igneous compositional range broadly comparable with normal to enriched mid ocean ridge basalt however isotopic compositions of leached samples 87sr 86sri 0 70361 0 70374 endi 5 7 6 2 are comparable with oceanic island basalt suites collectively these petrological characteristics are similar to rocks from large igneous provinces of cretaceous age in the western pacific ocean e g manihiki and ontong java plateaus consequently we interpret the hikurangi plateau as another of these early cretaceous basaltic oceanic plateaus speculatively parts of the obducted tangihua and matakaoa igneous complexes of the north island may have been derived from the hikurangi plateau as the plateau collided with the new zealand continent in the early miocene

submarine volcanoes and high temperature hydrothermal venting on the tonga arc southwest pacific submarine hydrothermal vents and associated seafloor mineralization on the tonga arc have been found for the first time in the summit calderas of two shallow water volcanoes greatly extending the known areas and diversity of seafloor hydrothermal activity in the western pacific region the highest temperature vents 245 265 c occur at water depths of 385 540 m near the summit of one volcano at 24 s the vents are spatially related to basaltic dike swarms exposed at a summit cone and in the caldera walls clusters of large to 10 m high barite anhydrite and sulfide chimneys on the summit cone are vigorously discharging clear hydrothermal fluids with temperatures on the seawater boiling curve there is abundant evidence of phase separation which can be seen as flame like jets of steam h2o vapor at the chimney orifices pyrite marcasite sphalerite and chalcopyrite line the interiors of the highest temperature vents similar to black smoker chimneys on the mid ocean ridges

helium isotopic composition of the tabar lihir tanga feni island arc papua new guinea helium abundances and isotopic ratios have been measured in samples of geothermal gases submarine ultramafic xenoliths and subaerial mafic phenocrysts and xenoliths from the tabar lihirtanga feni tltf arc in the bismarck archipelago of papua new guinea these unusual volcanoes are produced by adiabatic decompression melting of subduction modified upper mantle and apparently carry an exceptionally large slab derived component they therefore provide an ideal setting for studying the role of subducted helium in arc volcanoes helium isotopic ratios in the geothermal fluids submarine xenoliths and most helium rich subaerial samples indicate the mantle source regions beneath the tabar island group and lihir island have 3he 4he ratios of about 7 2 times the atmospheric ratio r a whereas the mantle source for ambitle island feni group in the more southern tltf arc has a lower ratio of about 6 6 r a these ratios are only slightly lower than typical depleted upper mantle values of about 8 5 r a indicating that even severely slab modified mantle wedge carries a relatively minor slab derived helium component the systematically lower 3he 4he ratios of the ambitle samples are interpreted to reflect a slightly greater slab derived helium component helium isotopic ratios as low as 2 r a which are correlated with low total helium abundances were observed in subaerial augitic clinopyroxene phenocrysts coexisting olivine and sodium rich acmitic clinopyroxene have higher helium abundances and isotopic ratios this isotopic disequilibrium between coexisting mineral phases is interpreted as crustal level addition of a low 3he 4he component to an actively outgassing magma from which different mineral phases trap helium sequentially

slow wavespeeds and fluid overpressure in a region of shallow geodetic locking and slow slip hikurangi subduction margin new zealand abstract travel times recorded onshore from active source marine seismic surveys were used to determine hikurangi forearc wavespeeds ray path midpoints sample forearc crust above the shallow v p from the seabed to 4 km depth consistent with rapidly deposited clastic sediments and near constant v p 5 0 0 2 km s at depths of 4 10 km within the forearc the northern region has slow slip events at shallow depths of c 5 15 km beneath the volume sampled by our analysis average travel times at offsets of 20 80 km are 1 s more than at equivalent offsets in the south and v p increases with depth within the forearc from 3 5 0 1 km s at 4 km depth to 4 5 0 2 km s at 10 km depth we interpret the low wavespeeds in terms of compaction disequilibrium and compare seismic inferences of anomalously high porosity 10 with hydrostatic reference compaction models to show effective stress is low in both the north 27 10 mpa and south 36 14 mpa in the south pore space and conduits have a high chance of being localized on faults or sand layers the wedge is clearly compressionally critical and we suggest the higher seismic velocities recorded primarily reflect higher effective stress levels transmitted through the rock framework the observed wedge geometry and our estimate of fluid pressure within the wedge 0 87 0 05 suggest a weak overpressured subduction thrust in the north we suggest high fluid pressure is maintained by a large fluid inventory from subducting sediment a pore space geometry characterized by pervasively fractured rock and mudstone and a lower mean stress due to its stable and non critical wedge geometry we consider both end member assumptions of convergent and tensile failure the latter of which reveals the possibility of near lithostatic fluid pressure on the north hikurangi subduction interface although this remains unproven our observations are consistent with high fluid pressures encountered in petroleum wells at depths

experimentally based water budgets for dehydrating slabs and consequences for arc magma generation phase diagrams of hydrous mid ocean ridge mor basalts to 330 km depth and of hydrous peridotites to 250 km depth are compiled for conditions characteristic for subduction zones a synthesis of our experimentally determined phase relations of chlorite lawsonite epidote zoisite amphibole paragonite chloritoid talc and phengite in basalts and of phase relations from the literature of serpentine talc chlorite amphibole and phase a in ultramafics permits calculation of h2o contents in hydrous phase assemblages that occur in natural compositions this yields the information necessary to calculate water budgets for descending slabs starting from low grade blueschist conditions 10 20 km depth with h2o contents between 5 and 6 wt for hydrated oceanic crust complete dehydration is achieved between 70 and 300 km depth as a function of individual slab geotherms hydrous phases which decompose at depth below volcanic arcs are lawsonite zoisite chloritoid and talc phengite in mafic compositions and chlorite and serpentine in peridotite approximately 15 35 of the initially subducted h2o are released below volcanic arcs the contribution of amphibole dehydration to the water budget is small 5 20 and occurs at relatively shallow depth 65 90 km in any predicted thermal structure dehydration is a combination of a stepwise and a continuous process through many different reactions which occur simultaneously in the different portions of the descending slab such a dehydration characteristic is incompatible with single phase dehydration models which focus fluid flow through a unique major dehydration event in order to explain volcanic fronts as a consequence of continuously progressing dehydration water ascending from the slab will be generally available to depth of ca 150 200 km the fluid rising from the subducting lithosphere will cause partial melting in the hot portion of the mantle wedge we propose that the volcanic front simply forms above the mantle wedge isotherm where the extent of melting is sufficient to allow for the mechanical extraction of parental arc magmas thermal models show that such an isotherm ca 1300oc locates below volcanic fronts slab surface depths below such an isotherm are compatible with the observed depths of the slab surface below volcanic fronts 1998 elsevier science b v all rights reserved

new multibeam mapping and geochemistry of the 30 35 s sector and overview of southern kermadec arc volcanism new multibeam mapping and whole rock geochemistry establish the first order definition of the modem submarine kermadec arc between 30 degrees and 35 degrees s twenty two volcanoes with basal diameters 5 km are newly discovered or fully mapped for the first time giggenbacb macauley havre haungaroa kuiwai ngatoroirangi sonne kibblewhite and yokosuka for each large volcano edifice morphology and structure surficial deposits lava fields distribution of sector collapses and lava compositions are determined macauley and havre are large silicic intra oceanic caldera complexes for both concentric ridges on the outer flanks are interpreted as recording mega bedforms associated with pyroclastic density flows and edifice foundering other stratovolcanoes reveal complex histories with repeated cycles of tectonically controlled construction and sector collapse extensive basaltic flow fields and the development of summit craters and or small nested calderas combined with existing data for the southernmost arc segment we provide an overview of the spatial distribution and magmatic heterogeneity along similar to 780 km of the kermadec arc at 30 degrees 36 degrees 30 s coincident changes in arc elevation and lava composition define three volcano tectonic segments a central deeper segment at 32 degrees 20 34 degrees 10 s has basement elevations of 3200 m water depth and relatively simple stratovolcanoes dominated by low k series basalt basaltic andesite in contrast the adjoining arc segments have higher basement elevations typically 3 km coincide with the shallower arc segments the dominant mode of large caldera formation is interpreted as mass discharge pyroclastic eruption with syn eruptive collapse hence the shallower arc segments are characterized by both the generation of volatile enriched magmas from crustal melting and a reduced hydrostatic load allowing magma vesiculation and fragmentation to initiate and sustain pyroclastic eruptions proposed initiation parameters for submarine pyroclastic eruptions are water depths 70 wt sio2 and a high discharge rate c 2005 elsevier b v all rights reserved

near field hydrothermal plume dynamics at brothers volcano kermadec arc a short lived radium isotope study abstract the naturally occurring radium ra isotope quartet was measured for the first time at an intraoceanic arc hydrothermal setting along the kermadec island arc sw pacific 224ra 3 7 d half life and 223ra 11 4 d half life are assumed to be tracers solely originating from hydrothermal discharge and have been used to resolve near field hydrothermal plume dynamics by applying both advection and eddy diffusion based dispersion models assuming dominant advective processes we identified different horizontal plume age structures at brothers volcano with a slow moving plume inside the caldera 0 060 cm s and a faster moving plume outside the caldera 0 323 cm s indicating a longer plume residence time within the caldera structure the decreasing trend in ra activity also allows the calculation of horizontal eddy diffusion coefficients inside and outside of the caldera with 0 164 m2 s and 3 545 m2 s for 224ra respectively these trends are in accordance with the radial horizontal eddy diffusion model our results reveal that net advection might not necessarily play a major role at brothers as radial horizontal eddy diffusion reproduces the observed ra activity distribution to the same degree additional model simulations based on a combination of advection and diffusion favor slow net advection to explain the ra activity distribution within the rising non buoyant plume ra isotopes suggested constant dilution along the first 170 m of the vertical water column and a vertical transport velocity on the order of 0 156 cm s for altitudes up to 150 m above the vent and around 0 004 cm s for altitudes above 150 m when a common source of diffuse and focused venting is assumed and only small amounts of ra are added to the ascending plume due to recoil originating from high water to rock ratios fluids from diffuse vents show a slower migration rate through the subsurface than fluids from focused vents our data imply that the fluids from diffuse vents needed approximately five days longer to percolate through the underlying subsurface to reach the water column plume compared to the fluids from direct vents which emanate through chimney structures this study demonstrates the potential of short lived ra isotopes as tracers of near field plume dynamics which will improve our understanding of hydrothermal vents as sources for various trace elements to the global ocean

sediment deposition and production in se asia seagrass meadows abstract seagrass meadows play an important role in the trapping and binding of particles in coastal sediments yet seagrass may also contribute to sediment production directly through the deposition of detritus and also the deposition of the associated mineral particles this study aims at estimating the contribution of different seagrass species growing across an extensive range of deposition to inorganic carbonate and non carbonate and organic sediment production total daily deposition measured with sediment traps varied from 18 8 2 0 g dw m 2 d 1 in silaqui philippines to 681 1 102 g dw m 2 d 1 in bay tien vietnam these measurements correspond to a single sampling event and represent sedimentation conditions during the dry season in se asia coastal areas enhalus acoroides was the most common species in the seagrass meadows visited and together with thalassia hemprichii was present at sites from low to very high deposition halodule uninervis and cymodocea species were present in sites from low to medium deposition the mineral load in seagrass leaves increased with age and was high in e acoroides because it had the largest and long lived leaves up to 417 mg calcium carbonate per leaf and 507 mg non carbonate minerals per leaf and low in h uninervis with short lived leaves 4 mg calcium carbonate per leaf and 2 mg non carbonate minerals per leaf in se asia seagrass meadows non carbonate minerals accumulate at slower rates than the production of calcium carbonate by the epiphytic community consequently the final loads supported by fully grown leaves were as average lower than calcium carbonate loads our results show that organic and inorganic production of the seagrasses in se asia represents a small contribution maximum of 15 of the materials sedimented on a daily base by the water column during the sampling period the contribution of the carbonate fraction can be locally significant i e 34 in silaqui in areas where the depositional flux is low but is minor

three dimensional measurement of river channel flow processes using acoustic doppler velocimetry this paper describes and assesses i the use of a new instrument for the determination of three dimensional flow velocities in natural rivers the acoustic doppler velocimeter adv and ii a method for positioning and orienting such measurements relative to a single local coordinate system to relate flow velocity vectors with the bed and water surface the adv uses the doppler shift principle to measure the velocity of small particles assuming to be moving at velocities similar to the fluid velocity is resolved into three orthogonal components and measured in a volume 5 cm below the sensor head minimizing interference of the flow field and allowing measurements to be made close to the bed a simple method for positioning and orienting the instrument using digital tacheometry is described and is used to obtain velocity measurements concurrently with measurements of both bed and water surface topography the paper includes a preliminary field assessment of the adv by comparing velocity profiles with those generated from marsh mcbirney electromagnetic current meters and a full field assessment of the position and orientation methodology these results suggest that the recommended methods in combination with an adv are able to provide reliable mean three dimensional velocity field information and accurate bed and surface topography copyright 1998 john wiley sons ltd

microthermometric evidence for the formation of permian vhms deposits in tasik chini area central belt of peninsular malaysia abstract the vhms deposits of tasik chini area are located in the pahang state of central belt peninsular malaysia the deposits occur in a package of permian volcanics within mixed volcano sedimentary sequence and have been exploited from the bukit botol and bukit ketaya deposits they have many similarities with kuroko style massive sulfide deposits the host rocks at both deposits are felsic volcanic rocks of rhyolitic to rhyodacitic composition mineralization occurs as distinct ore zonation forming a stringer to massive sulfide zone at the footwall followed by barite lenses and exhalite layers fe mn si ore at the stratigraphic top the sulfide phases are characterized by pyrite as the major sulfide mineral with subordinate chalcopyrite sphalerite and rare galena traces of gold silver and sn bearing minerals occur in the massive sulfide and barite ores primary fluid inclusions within quartz and barite occur as two types 1 type i two phase liquid vapour inclusions without daughter minerals and 2 type ii three phase liquid co2 bearing carbonic inclusions these three phase inclusions include liquid h2o liquid co2 and vapour co2 with variable co2 content and often decrepitate before complete homogenization microthermometric measurements of the type i inclusions show that the temperature of homogenization th varies between 180 c and 310 c with salinities ranging from 1 0 to 15 0 wt nacl equivalent in the quartz samples homogenization temperatures th of 190 c to 300 c and salinities between 1 0 and 13 0 wt nacl equivalent are recorded from the barite samples type ii inclusions have an initial melting temperature range of 57 1 c to 57 5 c clathrate melting temperature tmclathrate of 7 4 c to 8 0 c and co2 homogenization temperature thco2 between 30 1 c and 30 3 c and salinity ranging from 4 0 to 5 1 wt nacl equivalent densities pressure and depth of ore forming fluids range from 0 711 to 0 970 g cm3 12 to 93 bars and 1500 m depth of seawater laser raman spectroscopic analysis shows the presence of co2 in the carbonic inclusions the fluid inclusion results suggest that the main ore fluid during the formation of the tasik chini vhms deposit is a seawater dominated fluid but contribution from a modified seawater or possibly magmatic origin is also indicated by higher salinities relative to seawater 3 2 wt nacl and the presence of co2 taking into account the regional geodynamic evolution it is also concluded that the formation of vhms deposits in the tasik chini area occurred in a back arc geotectonic setting

extreme spatial and temporal variability of hydrothermal microbial mat communities along the mariana island arc and southern mariana back arc system 1 twenty five microbial communities were sampled from 18 different hydrothermal systems located at seven different sites along the mariana island arc and at a single site from the southern mariana spreading center over a 3 year period terminal restriction fragment length polymorphism t rflp analysis of the small subunit rrna gene revealed that the microbial community diversity is much greater along the mariana arc back arc than at either hot spot volcanoes or mid ocean ridges along the same spatial scale cluster analysis of t rflp fingerprints reveals the microbial communities formed three distinct clusters designated mariana clusters i ii and iii microbial communities in mariana cluster i are all associated with iron rich microbial mats and are dominated by members of the proteobacteria and by unique phylotypes clustering deeply in the proteobacteria and within the nitrospira division mariana cluster ii communities are all from shallow hydrothermal systems and mostly from colder sediments or microbial mats that are dominated by putative heterotrophic phylotypes usually associated with seawater and sediments not generally associated with hydrothermal fluid inputs mariana cluster iii is generally from much hotter vent sites and is dominated by sulfur oxidizing proteobacteria quantitative polymerase chain reaction q pcr of archaeal abundance reveal that all of the microbial communities are dominated by members of the bacterial domain sampling of microbial mats from iceberg vent at nw rota 1 in 2004 and again in 2006 reveal the community has shown a transition from caminibacter group proteobacteria phylotypes to a mixed population of caminibacter sulfurovum and sulfurimonas group proteobacteria

influences of the buoyancy of partially molten rock on 3 d plume patterns and melt productivity above retreating slabs using 3 d petrological thermo mechanical subduction models we investigate how the buoyancy of partially molten rock affects the development of thermal chemical plumes and melt productivity in the mantle wedge as a first order approximation we limit the positive buoyancy of partially molten rock compared to non molten rock which can be decreased due to rapid melt extraction and removal to the surface our simulations show that a large to moderate density contrast of 200 kg m

hydrodynamics of model posidonia oceanica patches in shallow water the hydrodynamics of simulated patches of the mediterranean seagrass posidonia oceanica were studied in laboratory flume experiments in which the height of the pronated canopy was always greater than half the total water depth the effects of variations in speed from 0 08 m s 21 to 0 24 m s 21 and patch configuration on the hydrodynamics were investigated significant speeds penetrated the patches to approximately half their height reducing speed did not change the flow patterns observed except to weaken and blur them flow encountering a single patch formed a turbulent wake at the height of the top of the canopy within this wake the vertical shear stress decreased monotonically downstream but the reynolds stress increased initially and then decayed when a second patch was positioned within the region where reynolds stress increased referred to as the 06 patch the wake center penetrated it causing average turbulent velocities with horizontal components 3 3 times higher and vertical components 4 2 times higher than in the upstream patch when this patch was positioned where the reynolds stress decayed referred to as the 14 patch the wake center rose above it nevertheless the turbulence in the 14 patch had horizontal components 12 higher and vertical components 22 higher on average than in the 06 patch because its upstream end was closer to the reynolds stress maximum thus the ratio of the patch separation to the length of wake in which the reynolds stress increased was identified as central to quantifying the turbulence within the downstream patch the increased turbulence is likely to be important in determining sedimentary and ecological patch characteristics by increasing retention of particulates in suspension and thus reducing depositional rates of for example larvae nutrients and dead organic matter

hydrothermal methane and manganese variation in the plume over the superfast spreading southern east pacific rise abstract onboard analyses of dissolved ch4 and mn were conducted on the water column along the southern east pacific rise between 13 50 and 18 40 s during the 1993 ridge flux cruise many hydrothermal plumes were identified by chemical anomalies which overlie more than half of the surveyed ridge crest the ch 4 mn ratio in the plumes shows wide variability ranges from about 0 05 to 3 9 due to wide range of ch 4 concentration the ch 4 rich plumes were detected in the region of 16 00 18 40 s where vigorous magmatic budget was confirmed by previous studies moreover the ch 4 mn ratio of the plumes is highly correlated with other volatile metal parameters such as the s fe ratio in plume particulate these results strongly suggest that volatile input caused by magmatic perturbation to hydrothermal systems is responsible for the ch 4 mn variability in the southern epr plumes based on analogy of the case at the epr 9 50 n site the detection of several volatile rich plumes and the extensive hydrothermal flux of volatile species are attributed to frequent magmatic events in the superfast spreading southern epr

evidence for iron and sulfur enrichments in hydrothermal plumes at axial volcano following the january february 1998 eruption in response to 12 days of seismic activity at axial volcano juan de fuca ridge in january february 1998 the nsf noaa sponsored axial response team conducted three response cruises in february august and august september to map and sample hydrothermal plumes over the region vertical profiles of particulate fe and s over the eruption site show high concentrations from about 1400 m to the bottom chemical and scanning electron microscope analysis of the february plume samples revealed anhydrite fe ferrihydrites elemental sulfur and angular glassy basalt shards up to 190 m in the longest dimension many of these shards had halite coatings which is consistent with subseafloor basalt seawater reactions at temperatures 450 c at 1500 m depth in august and september cruises the basalt shards were no longer present in the hydrothermal plumes instead the plumes were predominantly composed of fe ferrihydrites elemental sulfur and sulfur filaments a unique feature of this data set is the high concentrations of elemental sulfur in the lower 60 m of the water column the sulfur results are suggestive of a significant enrichment of the bacterial biomass in the water column over the eruption site with time within the axial caldera approximately 10 20 of the total sulfur is present as sulfur filaments these post eruption particle compositional changes have strong similarities to the results from the 1993 coaxial eruption on the juan de fuca ridge

rapid rates of growth and collapse of monowai submarine volcano in the kermadec arc most of earth s volcanoes are under water as a result of their relative inaccessibility little is known of the structure and evolution of submarine volcanoes advances in navigation and sonar imaging techniques have made it possible to map submarine volcanoes in detail and repeat surveys allow the identification of regions where the depth of the sea floor is actively changing here we report the results of a bathymetric survey of monowai submarine volcano in the tonga kermadec arc which we mapped twice within 14 days we found marked differences in bathymetry between the two surveys including an increase in seafloor depth up to 18 8 m and a decrease in depth up to 71 9 m we attribute the depth increase to collapse of the volcano summit region and the decrease to growth of new lava cones and debris flows hydroacoustic t wave data reveal a 5 day long swarm of seismic events with unusually high amplitude between the surveys which directly link the depth changes to explosive activity at the volcano the collapse and growth rates implied by our data are extremely high compared with measured long term growth rates of the volcano demonstrating the pulsating nature of submarine volcanism and highlighting the dynamic nature of the sea floor

submarine hydrothermal activity and gold rich mineralization at brothers volcano kermadec arc new zealand brothers volcano of the kermadec intraoceanic arc is host to a hydrothermal system unique among seafloor hydrothermal systems known anywhere in the world it has two distinct vent fields known as the nw caldera and cone sites whose geology permeability vent fluid compositions mineralogy and ore forming conditions are in stark contrast to each other the nw caldera site strikes for 600 m in a sw ne direction with chimneys occurring over a 145 m depth interval between 1 690 and 1 545 m at least 100 dead and active sulfide chimney spires occur in this field and are typically 2 3 m in height with some reaching 6 7 m their ages at time of sampling fall broadly into three groups 4 23 and 35 years old the chimneys typically occur near the base of individual fault controlled benches on the caldera wall striking in lines orthogonal to the slopes rarer are massive sulfide crusts 2 3 m thick two main types of chimney predominate cu rich up to 28 5 wt cu and more commonly zn rich up to 43 8 wt zn geochemical results show that mo bi co se sn and au up to 91 ppm are correlated with the cu mineralization whereas cd hg sb ag and as are associated with the dominant zn rich mineralization the cone site comprises the upper cone site atop the summit of the recent main dacite cone and the lower cone site that straddles the summit of an older smaller more degraded dacite cone on the ne flank of the main cone huge volumes of diffuse venting are seen at the lower cone site in contrast to venting at both the upper cone and nw caldera sites individual vents are marked by low relief 0 5 m mounds comprising predominately native sulfur with bacterial mats vent fluids of the nw caldera field are focused hot 300 c acidic ph 2 8 metal rich and gas poor calculated end member fluids from nw caldera vents indicate that phase separation has occurred with cl values ranging from 93 to 137 of seawater values by contrast vent fluids at the cone site are diffuse noticeably cooler 122 c more acidic ph 1 9 metal poor and gas rich higher than seawater values of so4 and mg in the cone vent fluids show that these ions are being added to the hydrothermal fluid and are not being depleted via normal water rock interactions iron oxide crusts 3 years in age cover the main cone summit and appear to have formed from fe rich brines evidence for magmatic contributions to the hydrothermal system at brothers includes high concentrations of dissolved co2 e g 206 mm kg at the cone site high co2 3he negative d and 18oh2o for vent fluids negative 34s for sulfides to 4 6 sulfur to 10 2 and 15n2 to 3 5 vent fluid ph values to 1 9 and mineral assemblages common to high sulfidation systems changing physicochemical conditions at the brothers hydrothermal system and especially the cone site occur over periods of months to hundreds of years as shown by interlayered cu au and zn rich zones in chimneys variable fluid and isotopic compositions similar shifts in 3he 4he values for both cone and nw caldera sites and overprinting of magmatic mineral assemblages by water rock dominated assemblages metals especially cu and possibly au may be entering the hydrothermal system via the dissolution of metal rich glasses they are then transported rapidly up into the system via magmatic volatiles utilizing vertical 2 5 km long narrow 300 m diameter pipes consistent with evidence of vent fluids forming at relatively shallow depths the nw caldera and cone sites are considered to represent stages along a continuum between water rock and magmatic hydrothermal dominated end members

mean and turbulent velocity fields near rigid and flexible plants and the implications for deposition 1 the transport of fine sediment and organic matter plays an important role in the nutrient dynamics of shallow aquatic systems and the fate of these particles is closely linked to vegetation we describe the mean and turbulent flow near circular patches of synthetic vegetation and examine how the spatial distribution of flow is connected to the spatial distribution of suspended sediment deposition patches of rigid emergent and flexible submerged vegetation were considered with two different stem densities for the rigid emergent vegetation flow adjustment was primarily two dimensional with flow deflected in the horizontal plane horizontal shear layers produced a von karman vortex street flow through the patch shifted the vortex street downstream resulting in a region directly downstream of the patch in which both the mean and turbulent velocities were diminished net deposition was enhanced within this region in contrast for the flexible submerged vegetation flow adjustment was three dimensional with shear layers formed in the vertical and horizontal planes because of strong vertical circulation turbulent kinetic energy was elevated directly downstream of the patch consistent with this deposition was not enhanced at any point in the wake this comparison suggests that morphological feedbacks differ between submerged and emergent vegetation further enhanced deposition occurred only in regions where both turbulent and mean velocities were reduced relative to the open channel reduced deposition indicating enhanced resuspension occurred in regions of high turbulence kinetic energy regardless of local mean velocity these observations highlight the importance of turbulence in controlling deposition

mixing layers and coherent structures in vegetated aquatic flows 1 to date flow through submerged aquatic vegetation has largely been viewed as perturbed boundary layer flow with vegetative drag treated as an extension of bed drag however recent studies of terrestrial canopies demonstrate that the flow structure within and just above an unconfined canopy more strongly resembles a mixing layer than a boundary layer this paper presents laboratory measurements obtained from a scaled seagrass model that demonstrate the applicability of the mixing layer analogy to aquatic systems specifically all vertical profiles of mean velocity contained an inflection point which makes the flow susceptible to kelvin helmholtz instability this instability leads to the generation of large coherent vortices within the mixing layer observed in the model at frequencies between 0 01 and 0 11 hz which dominate the vertical transport of momentum through the layer the downstream advection of these vortices is shown to cause the progressive coherent waving of aquatic vegetation known as the monami when the monami is present the turbulent vertical transport of momentum is enhanced with turbulent stresses penetrating an additional 30 of the plant height into the canopy

hydrothermal exploration of mid ocean ridges where might the largest sulfide deposits be forming highlights black smokers on slow spreading ridges can host larger seafloor massive sulfide sms deposits than on fast ridges the largest slow ridge sms deposits are typically associated with long lived tectonic fractures sustained fluid flow ultramafic tectonic hosted sites exhibit high average cu 10wt and au 3ppm contents in their surface sms samples hydrothermal plume surveys are consistent with equal abundances of magmatic vs tectonic vent control along ultraslow ridges the first black smokers on any ultraslow ridges exhibit high cu au sms contents at both magmatic and tectonic vent sites abstract here we review the relationship between the distribution of modern day seafloor hydrothermal activity along the global mid ocean ridge crest and the nature of the mineral deposits being formed at those sites since the first discovery of seafloor venting a sustained body of exploration has now prospected for one form of hydrothermal activity in particular high temperature black smoker venting along 30 of the global mid ocean ridge crest while that still leaves most of that 60 000 km continuous network to be explored some important trends have already emerged first it is now known that submarine venting can occur along all mid ocean ridges regardless of spreading rate and in all ocean basins further to a first approximation the abundance of currently active venting as deduced from water column plume signals can be scaled linearly with seafloor spreading rate a simple proxy for magmatic heat flux what can also be recognized however is that there is an excess of high temperature venting along slow and ultra slow spreading ridges when compared to what was originally predicted from seafloor spreading magmatic heat budget models an examination of hydrothermal systems tracked to source on the slow spreading mid atlantic ridge reveals that no more than half of the sites responsible for the black smoker plume signals observed in the overlying water column are associated with magmatic systems comparable to those known from fast spreading ridges the other half of all currently known active high temperature submarine systems on the mid atlantic ridge are hosted under tectonic control these systems appear both to be longer lived than and to give rise to much larger sulfide deposits than their magmatic counterparts presumably as a result of sustained fluid flow a majority of these tectonic hosted systems also involve water rock interaction with ultramafic sources importantly from a mineral resource perspective this subset of tectonic hosted vent sites also represents the only actively forming seafloor massive sulfide deposits on mid ocean ridges that exhibit high concentrations of cu and au in their surface samples 10 wt average cu content and 3 ppm average au along ultraslow spreading ridges first detailed examinations of hydrothermally active sites suggest that sulfide deposit formation at those sites may depart even further from the spreading rate model than slow spreading ridges do hydrothermal plume distributions along ultraslow ridges follow the same 50 50 distribution of black smoker plume signals between magmatic and tectonic settings as the slow spreading mar however the first three black smoker sites tracked to source on any ultra slow ridges have all revealed high temperature vent sites that host large polymetallic sulfide deposits in both magmatic as well as tectonic settings further deposits in both types of setting have now been revealed to exhibit moderate to high concentrations of cu and au respectively an important implication is that ultra slow ridges may represent the strongest mineral resource potential for the global ridge crest despite being host to the lowest magmatic heat budget

exploring the ocean for hydrothermal venting new techniques new discoveries new insights abstract enumerating active hydrothermal fields on the seafloor has been a challenge since their discovery almost 40 years ago high temperature hydrothermal fields are readily discoverable primarily by detecting mineral laden plumes but low temperature particle poor vent fields resist discovery decades of exploration for vent fields have covered though often cursorily about one third of the global lengths of both oceanic spreading ridges osrs and volcanic arcs identifying some 630 active vent fields about 80 of these fields are on osrs and the spatial frequency of those fields is currently estimated as 0 5 5 100 km generally increasing with spreading rate over the last decade however a few detailed surveys have added sensors capable of detecting ephemeral chemical tracers oxidation reduction potential in addition to standard sensors that detect quasi conservative optical tracers such as light backscattering this approach has revealed a new view of the distribution of venting fields along fast spreading 55 mm yr osrs studies of four such ridge sections totaling 1470 km length suggest that the present inventory of vent fields may underestimate the true global population of vent fields on fast spreading osrs by a factor of 3 6 this increase implies that ridge axes are unexpectedly leaky reservoirs from which hydrothermal fluids escape at far more sites than presently assumed that the supply of dissolved hydrothermal iron which may be fertilizing the primary production of the southern ocean is higher than now calculated and that present estimates of recoverable sulfide tonnage from ridge axes may be too low along slow spreading ridges which account for 60 of the global osr length and 86 of known sulfide tonnage expansive axial valleys present special exploration challenges that will not be easily overcome

tsunami hazard posed to new zealand by the kermadec and southern new hebrides subduction margins an assessment based on plate boundary kinematics interseismic coupling and historical seismicity we assess the tsunami hazard posed to new zealand by the kermadec and southern new hebrides subduction margins neither of these subduction zones has produced tsunami large enough to cause significant damage in new zealand over the past 150 years of well recorded history however as this time frame is short compared to the recurrence interval for major tsunamigenic earthquakes on many of the earth s subduction zones it should not be assumed that what has been observed so far is representative of the long term for each of these two subduction zones we present plate kinematic and fault locking results from block modelling of earthquake slip vector data and gps velocities the results are used to estimate the current rates of strain accumulation on the plate interfaces where large tsunamigenic earthquakes typically occur we also review data on the larger historical earthquakes that have occurred on these margins as well as the global cmt catalogue of events since 1976 using this information we have developed a set of scenarios for large earthquakes which have been used as initial conditions for the comcot tsunami code to estimate the subsequent tsunami propagation in the southwest pacific and from these the potential impact on new zealand has been evaluated our results demonstrate that there is a significant threat posed to the northland and coromandel regions of new zealand should a large earthquake m w 8 5 occur on the southern or middle regions of the kermadec trench and that a similarly large earthquake on the southern new hebrides trench has the potential to strongly impact on the far northern parts of new zealand close to the southern end of the submarine three kings ridge we propose logic trees for the magnitude frequency parameters of large earthquakes originating on each trench which are intended to form the basis for future probabilistic studies