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

continental like crust beneath the andaman island through joint inversion of receiver function and surface wave from ambient seismic noise abstract we study shear wave velocity structure of the crust beneath the andaman island through joint inversion of the teleseismic receiver function and rayleigh wave group velocity measurements from 10 broadband seismographs over the island the group velocities in the periods from 5 to 21 s are obtained using cross correlation of six month s ambient seismic noise data recorded by these seismic stations joint inversion results show 2 to 6 km thick subsurface low shear velocity vs 1 3 2 5 km s layer followed by a 12 14 km thick layer of silicic material average vs 3 5 km s the lower crust is mapped as an 8 12 km thick mafic layer with vs 4 0 km s uppermost mantle shear wave velocity is 4 55 km s the near surface low velocity layer is interpreted as the andaman flysch sediments the crustal thickness beneath the andaman island varies from 24 km in the north to 32 km in the south the shear wave velocity depth results show that the crustal structure beneath the andaman island is akin to continental crust possibly the burma continental crust the subducting indian plate may lie down below this overriding plate

new insights into the tectonic evolution of the andaman basin northeast indian ocean multibeam swath bathymetry data acquired over an area of about 30 000 km2 together with magnetic and single channel seismic data have been analyzed to understand the tectonic evolution of the andaman basin northeast indian ocean swath bathymetry data revealed several morphotectonic features that divide the basin into a complex western part comprising arc parallel seamount chains and n s trending fault systems and a relatively smooth eastern part a sw ne trending spreading ridge bisects the basin an offset of about 11 8 km at 94 21 e longitude divides the spreading ridge into sw and ne segments high resolution bathymetry and magnetic data enabled us to identify two finer scale segments over the sw part of the ridge that display distinct topographic fabric compared to the ne segment thin sediment cover and presence of axial seamounts characterize sw segments of the ridge whereas the ne segment has thick sediment cover and well maintained rift valley kinematics of basin evolution derived from the identification of the seafloor spreading magnetic anomalies suggest very slow initial opening rates of about 1 6 cm yr and an increase in the spreading rate to about 3 8 cm yr from anomaly 2 to present although this interpretation relies only on magnetic anomalies in the two westernmost segments it is suggested that the true seafloor spreading started about 4 ma in the andaman backarc basin rather than the 11 ma postulated previously we infer based on the integrated analysis of swath bathymetry magnetic and seismological data that the basin has evolved as a consequence of extrusive tectonics that prompted extension and rifting along the plane joining the sagaing and semengko fault systems extension by seafloor spreading during the past 4 myr resulted in the formation of the deep andaman backarc basin this phase has also experienced westward propagation of the spreading center

the lithobiontic ecological niche with special reference to microorganisms abstract revised terminology is proposed that describes the ecological niches of microorganisms within hard mineral substrates organisms attached to the external surfaces of the rock are termed epiliths while those in the interior of the rock are all termed endoliths the latter are called chasmoendoliths if they inhabit fissures in rocks cryptoendoliths if they dwell within structural cavities and euendoliths if they actively penetrate calcareous substrates

ignimbrites of amazonis planitia region of mars a series of postulated ignimbrite units is mapped in the amazonis memnonia and aeolis quadrangles of mars the units cover about 2 2 106 km2 within a broad but discontinuous and irregular belt trending east west along the highland lowland boundary the ignimbrites overlie parts of the western and southern aureole materials of olympus mons but are embayed in places by the lava plains of the lowlands stratigraphic relations between the basalt flows from the tharsis montes region and the ignimbrites are not clearly defined crater counts suggest that the younger ignimbrites postdate the lava flows crater counts per square kilometer for the ignimbrites range from 7 29 1 95 10 4 to 6 36 2 01 10 5 for craters larger than 1 km in diameter the ignimbrite materials form thick 100 m extensive relatively flat sheets that are smooth to grooved or gently undulating grooved surfaces appear to be yardangs and in most places are not alined with prevailing wind directions the seven mapped ignimbrite units are characterized by morphologic expression stratigraphic position and crater counts similarities to ignimbrites in the pancake range of central nevada include 1 rounded patches of smooth high albedo nonwelded material superposed on jointed low albedo welded material 2 local complementary joint sets in welded materials and 3 thick flow sheets of great areal extent that follow but subdue underlying topography four major eruptive centers occur in areas where units are thickest and where a dominant nnw sse structural trend is expressed locally by unit margins elongate collapse features and normal faulting a minimum volume of 3 85 106 km3 for the deposits has been calculated from thickness estimates based on shadow measurements and crater rim height relations

long term seismic observations along myanmar sunda subduction margin insights for 2004 m w 9 0 earthquake the present study investigates the temporal variation of few seismic parameters between the myanmar zone i andaman nicobar northwest sumatra zone ii southeast sumatra west indonesia zone iii and east indonesia zone iv converging boundaries in reference to the generation of 26 december 2004 mw 9 0 off sumatra mega earthquake event the four segments are distinguished based on tectonics parameters distinct geological locations great earthquake occurrences and the wadati benioff zone characteristics two important seismic parameters such as seismic energy and b values are computed over a time window of 6 month period during the entire 1976 2013 period for these segments the b values show a constant decrease in zones ii iii and iv whereas the zone i does not show any such pattern prior to the 2004 mega event the release of seismic energy was also gradually decreasing in zones ii and iii till the 2004 event and little similar pattern was also noted in zone iv this distinct observation might be indicating that the stress accumulation was dominant near the sumatra java area located towards southeast of zone ii and northwest of zone iii the released strain energy during the 2004 event was subsequently migrated towards north rupturing 1300 km of the boundary between the northwest sumatra and the north andaman the occurrence of 2004 mega event was apparently concealed behind the long term seismic quiescence existing near the sumatra and nicobar margin a systematic study of the patterns of seismic energy release and b values and the long term observation of collective behaviour of the margin tectonics might have had given clues to the possibility of the 2004 mega event

anomalous phase association of ree in ferromanganese crusts from indian mid oceanic ridges evidence for large scale dispersion of hydrothermal iron abstract ferromanganese crusts collected at selected locations along the 7000 km long stretch of carlsberg central indian and southwest indian ridges are studied for bulk geochemical composition and distribution of rare earths and yttrium in major geochemical phases exchangeable carbonate mn oxide fe oxyhydroxide and residual silicate the crusts are dominated by vernadite with traces of quartz and calcite a high concentrations of major fe mn trace co ni cu zn and rare earth elements indicates that these crusts are hydrogenous in nature however the negative or no cerium anomalies in the shale normalized ree pattern indicates that some of these crusts are of mixed type hydrogenous and hydrothermal irrespective of their nature mixed or hydrogenous the phase distribution of ree y shows 70 83 of total ree y are associated with fe oxyhydroxide phase whereas only about 17 30 are associated with mn oxide phase such phase distribution is expected in mixed type crusts because it is a combination of hydrothermal where 90 of the total ree y is associated with only fe oxyhydroxide phase and hydrogenous processes where 50 of the total ree y is associated with only fe oxyhydroxide phase conversely the hydrogenous crusts also shows similar phase distributions 70 83 association with fe oxyhydroxide phase which is certainly different from typical hydrogenous crusts where both fe oxyhydroxide and mn oxide phases host equal amounts 50 each the large scale dispersion of hydrothermal particulate iron along the indian ocean ridges is likely to contribute an additional fe bound ree y pool to these crusts the positive yttrium anomaly in mn oxide phase of all these crusts substantiates the hydrothermal contribution

earthquake swarms reveal submarine magma unrest induced by distant mega earthquakes andaman sea region abstract little is known about earthquake triggered magma intrusions or eruptions of submarine volcanoes the analysis of teleseismic earthquake occurrence performed in this study offers a tool to address such enigmatic and inaccessible processes in the past ten years the andaman sea region repeatedly became a site of shallow earthquake swarms that followed distant mega earthquakes by days to weeks the mw 9 1 december 26 2004 sumatra andaman earthquake was followed by two earthquake swarms about 600 km northward in the andaman sea region delayed by 30 and 35 days respectively earthquakes of one of these seismic episodes the extensive january 2005 earthquake swarm migrated laterally at a rate of about 0 25 km per hour during the swarm evolution the strong indian ocean mw 8 6 and 8 2 april 11 2012 earthquake doublet west of northern sumatra was followed by an earthquake swarm approximately 800 km northward in the andaman sea region delayed by 13 days all the three swarms that followed the 2004 and 2012 mega earthquakes occurred beneath distinct seamounts and seafloor ridges based on the observations of migration of earthquakes during the swarm and swarm occurrence beneath distinct highs at the seafloor we conclude that these earthquake swarms probably resulted as a consequence of magma unrest induced by static and or dynamic stress changes following the distant mega earthquakes repeated occurrence of such a phenomenon suggests that the arc magma reservoirs beneath the andaman sea have recently reached some form of criticality and are vulnerable to even small stress changes the andaman seafloor could thus become a site of submarine volcanic eruptions in near future and deserves close attention of earth scientists

earth s free oscillations excited by the 26 december 2004 sumatra andaman earthquake at periods greater than 1000 seconds earth s seismic free oscillations have anomalously large amplitude when referenced to the harvard centroid moment tensor fault mechanism which is estimated from 300 to 500 second surface waves by using more realistic rupture models on a steeper fault derived from seismic body and surface waves we approximated free oscillation amplitudes with a seismic moment 6 5 10 22 newton meters that corresponds to a moment magnitude of 9 15 with a rupture duration of 600 seconds the fault rupture models represent seismic observations adequately but underpredict geodetic displacements that argue for slow fault motion beneath the nicobar and andaman islands

soil deformation measurement using particle image velocimetry piv and photogrammetry a deformation measurement system based on particle image velocimetry piv and close range photogrammetry has been developed for use in geotechnical testing in this paper the theory underlying this system is described and the performance is validated digital photography is used to capture images of planar soil deformation using piv the movement of a fine mesh of soil patches is measured to a high precision since piv operates on the image texture intrusive target markers need not be installed in the observed soil the resulting displacement vectors are converted from image space to object space using a photogrammetric transformation a series of validation experiments are reported these demonstrate that the precision accuracy and resolution of the system are an order of magnitude higher than previous image based deformation methods and are comparable to local instrumentation used in element testing this performance is achieved concurrent with an order of magnitude increase in the number of meas

base stability of multi propped excavations in soft clay subjected to hydraulic uplift excavations in soft clay underlain with an aquifer may be destabilized by hydraulic uplift previous studies on this subject are based mainly on field observations dewatering from the aquifer is a

genesis of ferromanganese crusts from the tag hydrothermal field the rare earth element ree geochemistry and nd isotopic composition of marine ferromanganese crusts allow insight into their environment of deposition we present ree along with major and trace element data from a suite of samples collected near an active hydrothermal site from the mid atlantic ridge and demonstrate extreme ree variability over short spatial scales both positive and negative ce anomalies are observed along with varied fractionation of the rees some of the fe mn crusts are formed directly from low temperature hydrothermal fluids channelled over 3 km from any high temperature vent site a significant hydrothermal component is observed in one fe mn crust sampled other samples collected from the same area are predominantly hydrogenous and form at a wide range of accumulation rates depending on the hydrothermal plume input the identification of extreme heterogeneity in source and depositional environment within one hydrothermal field suggests that 1 this variability can be resolved both spatially and temporally within a fossil hydrothermal deposit and 2 the integrated record provided by bulk analysis should be interpreted with caution

endolithic cyanobacteria in soil gypsum occurrences in atacama chile mojave united states and al jafr basin jordan deserts 1 soil sulfates are present in arid and hyperarid environments on earth and have been found to be abundant in soils on mars examination of soil gypsum from the atacama desert chile the mojave desert united states and al jafr basin jordan revealed endolithic cyanobacteria communities just below the surface of soil gypsum samples optical and scanning electron microscope observations of the colonized layers indicated that the unicellular chroococcidiopsis is the dominant cyanobacterium in all studied communities 16s rrna gene analysis revealed that in addition to chroococcidiopsis a few other cyanobacteria are present heterotrophic bacteria are also abundant in the colonized zones of the fine grained gypsum from the atacama and mojave desert but insignificant in the fibrous gypsum from the jordan desert endolithic life forms similar to these described here may exist or have existed on mars and should be targeted by the mars science laboratory and future in situ missions

initiation and failure mechanism of base instability of excavations in clay triggered by hydraulic uplift excavations in clay overlying an aquifer may cause catastrophic basal failure due to hydraulic uplift although case histories with hydraulic uplift failures are reported worldwide from time to time the initiation and failure mechanism of the base instability are not well studied and understood to address these two issues dimensional analysis is firstly conducted to propose dimensionless groups dgs possibly relevant to this subject effects of these dgs on the initiation and failure mechanism of base instability are then investigated by carrying out a series of finite element analyses in which constitutive models and model parameters have been previously validated against centrifuge test results it is revealed that the initiation and failure mechanism of base instability due to hydraulic uplift is mainly governed by a ratio of excavation width over the thickness of soft clay inside excavation b d as excavation becomes narrower i e b d decreases the hydraulic pressure pi required to initi

earthquake clustering in the tectonic pattern and volcanism of the andaman sea region abstract seismicity pattern in the andaman sea region has been analysed to interpret recent dynamics of regional submarine volcanic provinces hypocentral determinations and focal mechanisms of available global seismological data have been used frequent occurrence of earthquake swarms proved to be an important characteristic of seismicity pattern in the investigated region epicenters of the earthquake swarms are situated almost exclusively along a narrow belt forming the easternmost limit of the epicentral area of the andaman sea region the southern zone of the belt between 6 and 10 5 n is trench parallel and coincides with the northward prolongation of the sumatra volcanic arc the northern zone of the belt between 10 5 and 13 n is deflected by about 45 northeast and precisely follows the complicated zigzag pattern of the rift system in the middle of the andaman basin earthquake occurrence in these two zones the northern and the southern differs by several aspects by shape of the epicentral zones of individual swarms by focal mechanisms and by response to the 2004 sumatra andaman great earthquake these differences together with available information on composition of magmas found at the seafloor lead us to the conclusion that the swarms of the southern zone are induced by intrusions of subduction generated calc alkaline magmas whereas the swarms in the northern zone by intrusions of basaltic magmas associated with the seafloor spreading earthquake swarm occurrence defines a brittle seismogenic layer at depths between 9 and 35 km excludes the existence of large magma reservoirs in respective depth interval and puts their hypothetical location to a greater depth episodes of magma ascent from deeper reservoir to shallow magma chamber depth

regional earthquake as a trigger for enhanced volcanic activity evidence from modis thermal data 1 the magnitude 6 4 earthquake that occurred in java on 26 may 2006 provided us with data capable of revealing an immediate eruptive response at two javanese volcanoes merapi and semeru the availability of pre processed thermal data for volcanic hot spots detected by the moderate resolution imaging spectrometer modis and provided on http hotspot higp hawaii edu allowed us to produce heat and volume flux time series for these two erupting volcanoes covering a 35 day period spanning the earthquake our results revealed a coupled response by the volcanoes to the earthquake both experiencing increases in heat and volume flux beginning 3 days after the earthquake with the response lasting 9 days the response was felt at both volcanoes as a factor of two to three increase in the rate of volumetric output after which output returned to the pre response rates this implies that the earthquake triggered enhanced output at two erupting volcanoes 50 and 300 km distant from the earthquake epicenter and separated from each other by 260 km

submersible observations of hydrothermal manganese deposits on the kaikata seamount izu ogasawara bonin arc abstract during dive 408 of shinkai 2000 on the flank of the kaikata seamount located on the volcanic front of the izu ogasawara bonin arc possibly recent hydrothermal manganese deposits were observed on sandy volcanic sediments at water depths of between 800 and 1200 m the deposits cover almost the entire surface sediment across the manganese belt on the northwestern flank on the seamount on a scale of kilometers the occurrence of the deposits seafloor morphology and temperature of the sediments together with previous shipboard results lead to a possible model for the formation of the manganese deposits a low temperature hydrothermal solution ascends through fractures or faults in the volcanic substrate into permeable volcanic sands and precipitates manganate minerals which cement several centimeters of surface sand as hardpan more intense and probably intermittent discharge of hydrothermal solution follows and forms many typical ridge like vents and mounds on the seafloor subsequently pure dense manganate layers developed beneath the semi consolidated volcanic sandstone and act as a cap to the ascending fluids the proposed mechanism may be the dominant type of low temperature hydrothermal mineralization in submarine island arc volcanoes and rifts similar hydrothermal manganese deopsits most probably occur in other active areas of the modern seafloors and in inactive island arcs

undrained bearing capacity factors for conical footings on clay introduction the bearing capacity of circular foundations on undrained clay is of fundamental importance in many geotechnical problems in particular there are a number of designs of offshore foundations where the foundation can be treated approximately as a large circular footing for instance some gravity bases the spudcan foundations of jack up units and the more recently developed caisson foundations in most cases the footing is not placed at the ground surface and it is important to take into account the depth of embedment furthermore the base of a spudcan is generally not flat but approximates a shallow cone for foundations on soft clays the effect of the increase of strength of the soil with depth needs to be taken into account and this is particularly important for large foundations the purpose of this note is to present calculations of bearing capacity factors for shallow circular foundations accounting for embedment cone angle rate of increase of strength with depth and surface roughness of the foundation the results have widespread application particularly in the offshore industry the soil is assumed to be rigid plastic with yield determined by the tresca condition with an undrained strength su the method of characteristics is used for the bearing capacity calculation as described by shield 1955 eason shield 1960 houlsby 1982 and houlsby wroth 1982a for application to undrained axisymmetric problems some previous results have been published for this problem using similar numerical techniques e g houlsby wroth 1982b salencon matar 1982 houlsby wroth 1983 tani craig 1995 martin 2001 but the study presented here involves a much more comprehensive coverage of the parameters where comparisons can be made with the previous solutions the factors differ by up to about 0 5 which gives some indication of the level of accuracy attainable with this numerical technique exceptionally the rough footing results given by tani craig 1995 are higher by up to about 5 but this may be due to a problem with their numerical integration procedures see martin randolph 2001

the january 1998 earthquake swarm at axial volcano juan de fuca ridge hydroacoustic evidence of seafloor volcanic activity on january 25 1998 at 11 33z an intense swarm of earthquakes began within the summit caldera of axial volcano central juan de fuca ridge jdfr the earthquake swarm was detected using the u s navy hydrophones in the northeast pacific ocean the earthquake swarm lasted 11 days and produced 8247 detected 1037 located earthquakes during the first two days of the swarm earthquake activity migrated from the summit caldera 50 km along the south rift zone of axial volcano at rates of 0 92 0 13 and 0 23 0 09 m s 1 earthquake epicenter migration is characteristic of a lateral magma dike injection the largest three swarm earthquakes occurred within the caldera their timing and mechanisms are consistent with adjustment of the caldera floor as magma is removed from beneath the summit earthquakes with short t wave rise times shallow focal depths cluster at two spots along the summit and south rift zone and are considered possible seafloor eruption sites in situ ground deformation and hydrothermal plume monitors and later shipboard observations confirmed the occurrence of a seafloor volcanic eruption at the volcano s summit

the west andaman fault and its influence on the aftershock pattern of the recent megathrust earthquakes in the andaman sumatra region 1 distinctly different rupture patterns of december 2004 and march 2005 megathrust earthquakes occurred in the andaman sumatra region suggest strong influence of tectonic and structural elements we have analysed the shipboard gravity bathymetry and seismic data across the west andaman fault waf a major tectonic feature in the andaman sea to infer the crustal structure and to examine its influence in controlling the aftershock pattern our results support the idea of singh et al 2005 that waf forms a lithospheric scale boundary and together with other tectonic elements modulate the occurrence of large earthquakes and their rupture pattern the active strike slip motion along the waf presence of backarc spreading coupled with increased obliquity of subduction in the andaman sector reduce the probability of occurrence of major or great earthquakes north of 10 n

volcanology and eruptive styles of barren island an active mafic stratovolcano in the andaman sea ne indian ocean barren island india is a relatively little studied little known active volcano in the andaman sea and the northernmost active volcano of the great indonesian arc the volcano is built of prehistoric possibly late pleistocene lava flows dominantly basalt and basaltic andesite with minor andesite intercalated with volcaniclastic deposits tuff breccias and ash beds deposited by pyroclastic falls and surges which are exposed along a roughly circular caldera wall there are indications of a complete phreatomagmatic tephra ring around the exposed base of the volcano a polygenetic cinder cone has existed at the centre of the caldera and produced basalt basaltic andesite aa and blocky aa lava flows as well as tephra during historic eruptions 1787 1832 and three recent eruptions 1991 1994 95 2005 06 the recent aa flows include a toothpaste aa flow with tilted and overturned crustal slabs carried atop an aa core as well as locally developed tumuli like elliptical uplifts having corrugated crusts based on various evidence we infer that it belongs to either the 1991 or the 1994 95 eruptions the volcano has recently 2008 begun yet another eruption so far only of tephra we make significantly different interpretations of several features of the volcano than previous workers this study of the volcanology and eruptive styles of the barren island volcano lays the ground for detailed geochemical isotopic and petrogenetic work and provides clues to what the volcano can be expected to do in the future

structural features and formation conditions of mud diapirs in the andaman sea basin data from offshore oil and gas explorations have revealed that mud diapirs occur widely not only at continental margins but also in foreland basins and may have played an important role in the entrapment of oil and gas although the structural features and formation mechanism of salt diapirs have been extensively investigated mud diapirs are still not fully understood largely due to the difficulty of identifying them from seismic data in this paper the structural features and main controlling factors of mud diapirs in the andaman sea basin are investigated based on seismic profiles combined with drilling data and regional tectonic settings the results show that there are five types of mud diapir in the andaman sea basin turtleback mud diapir mud dome piercing mud diapir mud volcano and gas chimney like mud diapir turtleback mud diapirs mainly occur in the southern segment of the accretionary wedge of the andaman sea basin which is far from the bengal fan and characterized by low deposition rate and strong compression tectonic setting piercing mud diapirs exist mainly in the central segment of the accretionary wedge which is close to provenances of sediments and characterized by rapid sedimentation rates large mudstone thickness and transpressional tectonic setting mud domes and mud volcanoes mainly occur in the northern segment of the accretionary wedge which is characterized by rapid sedimentation rates large mudstone thickness and sedimentary wedge growth tectonic setting the gas chimney like mud diapirs only occur in the northern segment of the back arc depression close to the sagaing strike slip fault belt which is characterized by high deposition rate large mudstone thickness and high geothermal gradient these features suggest that thick mudstone deposit rapid sedimentation rates large geothermal gradient strong tectonic stress and gravitational spreading and sliding may have prompted the formation of mud diapirs in the andaman sea basin

k o ocr relationships in soil the relationships between k o and ocr are investigated for primary loading unloading reloading conditions the study reviews laboratory data from over 170 different soils and presents an approach common to clays silts and sands simple empirical methods for predicting k o for normally consolidated and overconsolidated soils are evaluated the validity of the methods is supported by statistical analyses on the basis of the findings only the effective stress friction angle o and prior stress history ocr and ocrmax are needed to predict approximate values of k o

the great sumatra andaman earthquake of 26 december 2004 the two largest earthquakes of the past 40 years ruptured a 1600 kilometer long portion of the fault boundary between the indo australian and southeastern eurasian plates on 26 december 2004 seismic moment magnitude mw 9 1 to 9 3 and 28 march 2005 mw 8 6 the first event generated a tsunami that caused more than 283 000 deaths fault slip of up to 15 meters occurred near banda aceh sumatra but to the north along the nicobar and andaman islands rapid slip was much smaller tsunami and geodetic observations indicate that additional slow slip occurred in the north over a time scale of 50 minutes or longer

low temperature hydrothermal deposits of franklin seamount woodlark basin papua new guinea abstract hydrothermal deposits of siliceous fe mn oxides from a few cm to 7 m in height are widespread at the summit and caldera floor of franklin seamount a 250 m high edifice of basaltic andesite lava tubes pillows and talus located near the western propagating tip of the woodlark spreading axis some deposits are venting clear fluid at about 30 c the hydrothermal constructions are composed predominantly of x ray amorphous protoferrihydrite mixed with variable amounts of opaline silica and greenish nontronite most deposits are covered by mm thick black crusts of vernadite and feroxyhyte which are mineralised bacterial formations genus leptothrix of hydrogenous origin microbes also influenced formation of the fe rich parts of the deposits as evidenced by filamentous protoferrihydrite pseudomorphs of gallionella blocky inorganic particles of protoferrihydrite and ferrihydrite occur as rare interior phases nontronite formed by precipitation from hydrothermal solutions commonly involving replacement of microbial protoferrihydrite and silica patchy and lenticular birnessite partly altered by biogenic processes to vernadite occurs within siliceous protoferrihydrite matrices in dark cm thick outer margins of some edifices this is considered hydrothermal in origin reflecting percolation of hydrothermal fluids through porous protoferrihydrite opal aggregates to more oxidised conditions near the exterior related to mixing with seawater the different mineralogical associations are reflected by geochemistry trace elements in the manganiferous phases were derived partly from the primary hydrothermal solution and partly from seawater with which this was extensively diluted at the depositional site and also deeper within the volcanic structure of franklin seamount most of the fe mn cu zn and pb was derived from the primary hydrothermal fluid from limited data nontronitic portions of the deposits contain more cu zn and pb than the siliceous protoferrihydrite rich portions migration of redox boundaries and redistribution of elements during flow through processes influence development of the typical zoned structure of the deposits uranium thorium decay series equilibria at both actively venting and inactive sites at franklin seamount yield ages not exceeding 43 years

hydrothermal manganese oxide deposits from baby bare seamount in the northeast pacific ocean abstract manganese oxide crusts were recovered from baby bare seamount in order to investigate the history of off axis hydrothermal venting baby bare is a small basement high protruding from a regional sediment cover on the eastern flank of the juan de fuca ridge that acts as a focus for discharging crustal fluids stratabound mn oxide crusts were collected where warm venting has been observed near the seamount summit mn oxide crusts are composed primarily of 10 a manganate pyrolusite with minor nontronite saponite and or barite these assemblage and chemical characteristics such as high mn fe ratios and low trace metal and ree concentrations are indicative of a hydrothermal origin minimum ages for these deposits calculated using growth rates 324 to 1800 mm ma and estimated thicknesses of manganese outcrops show that baby bare has been hydrothermally active for at least 0 5 myr and possibly since its formation 1 7 2 7 ma hydrothermal manganese oxide crusts such as these from baby bare record interactions between the hydrothermal fluids and seawater and are important tools for estimating the longevity of off axis hydrothermal activity

neotectonics of the sumatran fault indonesia the 1900 km long trench parallel sumatran fault accommodates a significant amount of the right lateral component of oblique convergence between the eurasian and indian australian plates from 10 n to 7 s our detailed map of the fault compiled from topographic maps and stereographic aerial photographs shows that unlike many other great strike slip faults the sumatran fault is highly segmented cross strike width of step overs between the 19 major subaerial segments is commonly many kilometers the influence of these step overs on historical seismic source dimensions suggests that the dimensions of future events will also be influenced by fault geometry geomorphic offsets along the fault range as high as 20 km and may represent the total offset across the fault if this is so other structures must have accommodated much of the dextral component of oblique convergence during the past few million years our analysis of stretching of the forearc region near the southern tip of sumatra constrains the combined dextral slip on the sumatran and mentawai faults to be no more than 100 km in the past few million years the shape and location of the sumatran fault and the active volcanic arc are highly correlated with the shape and character of the underlying subducting oceanic lithosphere nonetheless active volcanic centers of the sumatran volcanic arc have not influenced noticeably the geometry of the active sumatran fault on the basis of its geologic history and pattern of deformation we divide the sumatran plate margin into northern central and southern domains we support previous proposals that the geometry and character of the subducting investigator fracture zone are affecting the shape and evolution of the sumatran fault system within the central domain the southern domain is the most regular the sumatran fault there comprises six right stepping segments this pattern indicates that the overall trend of the fault deviates 4 clockwise from the slip vector between the two blocks it separates the regularity of this section and its association with the portion of the subduction zone that generated the giant m w 9 earthquake of 1833 suggest that a geometrically simple subducting slab results in both simple strike slip faulting and unusually large subduction earthquakes

toothpaste lava from the barren island volcano andaman sea abstract toothpaste lava is a basaltic lava flow type transitional between pahoehoe and aa and has been described from paricutin kilauea and etna volcanoes here we describe a spectacular example of toothpaste lava forming part of a recent possibly 1994 95 aa flow on the active volcano of barren island andaman sea this flow of subalkalic basalt shows abundant squeeze ups of viscous toothpasate lava near its entry into the sea the squeeze ups are sheets and slabs up to several meters across and tens of centimeters thick extruded from boccas they are often prominently curved have striated upper surfaces with close spaced en echelon linear ridges and grooves broad wave like undulations perpendicular to the striations and sometimes clefts textural geochemical and sr nd isotopic data on the squeeze ups and the exposed aa flow core indicate very crystal rich viscous and isotopically very homogeneous lava we envisage that a greatly reduced speed of this viscous flow at the coastline possibly aided by a shallowing of the basal slope led to lateral spreading of the flow which caused tension in its upper parts this with continued albeit dwindling lava supply at the back led to widespread tearing of the flow surface and extrusion of the squeeze ups the larger slabs while extruding in a plastic condition curved under their own weight whereas their surfaces experienced brittle deformation forming the en echelon grooves the extruded detached and rotated sheets and slabs were carried forward for some distance atop the very slowly advancing aa core before the flow solidified

hirise images of yardangs and sinuous ridges in the lower member of the medusae fossae formation mars abstract hirise images of the lower member of the medusae fossae formation mff were used to identify characteristics of two specific landforms that are well expressed in this particular geologic unit yardangs and sinuous ridges yardangs are wind eroded ridges that are usually confined to arid environments where the bedrock materials can be easily eroded by windblown sand yardangs are common in the lower member of mff where many individual yardangs show evidence of a caprock unit overlying a more friable unit most consistent with an ignimbrite origin for these mff deposits heights of the yardangs in the lower member materials are generally less than a few tens of meters in contrast to yardangs in the thicker middle member mff materials to the east of the study area the yardangs may form in materials comprised of discrete depositional units and there is good evidence that at least a dozen such depositional events contributed to the emplacement of the lower member of mff the lower member yardang heights indicate aeolian erosion has removed at least 19 000 km 3 of lower member mff materials sinuous ridges are elongate positive relief landforms that have been attributed to a variety of possible fluvial flow processes on mars sinuous ridges are very common within exposures of the lower member of mff multiple ridge types are present but all forms seen at hirise scale are most consistent with some form of aqueous channel flow rather than other possible origins the results from this initial examination of hirise images indicate the potential utility of comparing yardangs and sinuous ridges in the lower member to other members of mff although it remains to be determined if sinuous ridges are abundant in the younger mff members

constraints on 2004 sumatra andaman earthquake rupture from gps measurements in andaman nicobar islands the 26 december 2004 sumatra andaman earthquake mw 9 0 9 3 is the greatest earthquake of the modern seismological era the rupture characteristics of the earthquake particularly in the andaman nicobar region are not well resolved from seismological or far field geodetic data here in this article we present campaign mode global positioning system gps measurements of coseismic displacements at 13 sites in the andaman nicobar islands before and after the 2004 sumatra andaman earthquake these measurements provide improved estimates of rupture characteristics in the region coseismic horizontal ground displacement of 1 5 6 5 m towards the southwest and coseismic vertical displacement mostly subsidence of 0 5 2 8 m occurred along the andaman nicobar islands with maximum displacements in the nicobar islands we estimate coseismic slip under the andaman and nicobar islands as 3 8 7 9 m and 11 15 m respectively the length of the rupture is estimated to be about 1500 km with a width varying from 120 km under middle andaman island to 160 km under great nicobar island gps measurements during january 11 22 2005 from port blair suggest rapid afterslip in the postseismic period limited gps data available from 1995 measurements at two sites in andaman provide evidence of strain accumulation that varied significantly in the 10 yr preceding the earthquake d 2005 elsevier b v all rights reserved

coseismic slip distributions of the 26 december 2004 sumatra andaman and 28 march 2005 nias earthquakes from gps static offsets static offsets produced by the 26 december 2004 m 9 sumatra andaman earthquake as measured by global positioning system gps reveal a large amount of slip along the entire 1300 km long rupture most seismic slip inversions place little slip on the andaman segment whereas both near field and far field gps offsets demand large slip on the andaman segment we compile available datasets of the static offset to render a more detailed picture of the static slip distribution we construct geodetic offsets such that postearthquake positions of continuous gps sites are reckoned to a time 1 day after the earthquake and campaign gps sites are similarly corrected for postseismic motions the newly revised slip distribution m w 9 22 reveals substantial segmentation of slip along the andaman islands with the southern quarter slipping 15 m in unison with the adjacent nicobar and northern sumatran segments of length 700 km we infer a small excess of geodetic moment relative to the seismic moment a similar compilation of gps offsets from the 28 march 2005 nias earthquake is well explained with dip slip averaging several meters mw 8 66 distributed primarily at depths greater than 20 km online material offset estimation procedure comparison of results to other stud ies and simpler solutions and tables of coseismic offsets

what drives centuries long polygenetic scoria cone activity at barren island volcano abstract barren island in the andaman sea is an active mafic stratovolcano which had explosive and effusive eruptions followed by caldera formation in prehistoric time poorly dated a scoria cone within the caldera marking volcanic resurgence was active periodically from 1787 to 1832 the historic eruptions since 1991 the same scoria cone has produced six eruptions commonly including lava flows links between barren island s eruptions and giant earthquakes such as the 26 december 2004 great sumatra megathrust earthquake have been suggested though there is no general correlation between them the 227 year long activity of the scoria cone named here shanku cone is normally driven by purely magmatic processes i present a source to surface model for barren island and shanku including the source region deeper and shallow magma chambers volcanotectonics dyking from magma chambers and eruptions and eruptive style as controlled by crustal stresses composition and volatile content calculations show that dykes 0 5 m thick and a few hundred meters long originating from shallow level magma chambers 5 km deep are suitable feeders of the shanku eruptions shanku a polygenetic scoria cone at least 13 eruptions since 1787 has three excellent analogues namely anak krakatau 40 eruptions since 1927 cerro negro 23 eruptions since 1850 and yasur persistent activity for the past hundreds of years this is an important category of volcanoes gradational between small monogenetic scoria cones and larger polygenetic volcanoes

distribution of rees and yttrium among major geochemical phases of marine fe mn oxides comparative study between hydrogenous and hydrothermal deposits abstract mineralogy and geochemistry of the ferromanganese oxides collected from two seamounts in the andaman sea have been investigated with special reference to the solid phase partitioning behavior of rare earth elements rees bulk elemental compositions indicate that the oxides from a volcanic cratered seamount csm are hydrothermal while those from another seamount sm2 are hydrogenous in origin the distributions of rees and yttrium in four geochemical phases viz easily exchangeable mn oxide fe oxyhydroxide and residual of csm oxides were distinctly different from that of sm2 oxides in csm oxides the rees and yttrium are mainly associated with fe oxyhydroxide phase while in sm2 oxides both mn oxide and fe oxyhydroxide phases contain the major fraction of these elements the exchangeable and residual phases of both hydrothermal and hydrogenous oxides have extremely low ree content the shale normalized negative ce anomalies and relative enrichment of heavy ree characteristic of hydrothermal oxides are retained in fe oxyhydroxide phase in hydrogenous oxides the positive ce anomalies occurred in both fe and mn oxide phases while negative y anomalies were found only in fe oxyhydroxide phase the phase distribution of rees and yttrium in hydrothermal oxides is described in terms of co precipitation and adsorption of their halide complexes and available free ions in hydrothermal solutions instead adsorption of major carbonate species from seawater primarily regulates the partitioning of rees among the co existing phases of hydrogenous oxides

the effect of plume processes on the fe isotope composition of hydrothermally derived fe in the deep ocean as inferred from the rainbow vent site mid atlantic ridge 36 14 n abstract the rainbow hydrothermal vent site which is the largest known point source for dissolved fe delivered to the deep north atlantic ocean has remained invariant in its fe isotope composition over at least the past 16 000 years based on analysis of metalliferous sediments beneath the plume because of the conservative behavior of fe in the rainbow plume 56 fe values of particles in the neutrally buoyant plume 0 18 0 05 and underlying sediments 0 19 0 05 are indistinguishable from the 56 fe values of the high temperature fluid sources 0 23 0 04 particles from the near vent buoyant stage of the plume however have higher 56 fe values 0 15 to 1 20 relative to the original vent fluid consistent with fractionation during oxidation of fe ii aq to fe iii aq isotope compositions become invariant in the plume once all fe ii aq is fully oxidized preserving the original composition of the vent fluid the constant fe isotope compositions of the vent fluids over time implies that changes in seawater fe isotope composition of the north atlantic ocean as they are recorded in fe mn crusts requires changes in the relative fluxes of fe to the ocean

liquefaction and flow failure during earthquakes two aspects of seismically induced liquefaction are discussed which are of vital engineering significance the triggering condition and the consequences of liquefaction the triggering condition is examined with respect to liquefaction analysis note being taken of the onset condition which is governed by cyclic strength consequences of liquefaction are discussed with respect to post seismic stability analysis in which the residual strength plays a major role procedures used for liquefaction analysis based on the results of in situ sounding tests are introduced and the applicability of this method for estimating associated ground settlements is discussed the evaluation of residual strength requires a better understanding of undrained sand behaviour results of extensive laboratory rests on japanese standard sand are examined and new index parameters are proposed to quantify undrained sand behaviour better the results of laboratory tests on silty sands are examined in the same way ah the results are

the nature and distribution of upper cenozoic ignimbrite centres in the central andes abstract a wide variety of upper cenozoic ignimbrite centres have been identified and studied on landsat imagery of the central andes some have been investigated in the field lower miocene ignimbrite centres are distributed along an arc which in north chile diverges markedly from the line of the present trench and parallels an arc of lower miocene plutons in the eastern cordillera of bolivia much of the ignimbrite erupted since the late miocene has been erupted around the faulted margins of the altiplano basin of western bolivia particularly where the western and eastern cordilleras converge typical examples of ignimbrite centres are described some centres take the form of ignimbrite shield volcanoes other ignimbrite sheets are more widely dispersed the degree of dispersal probably relates to the height of the eruption column partial or total caldera formation sometimes took place and a few of these calderas have resurgent centres late stage lava extrusions are common and some of these are located on caldera ring fractures

oblique convergence and deformation along the kuril and japan trenches the hypothesis that present day deformation within the southern kuril forearc is driven by oblique subduction of the pacific plate is tested using 397 horizontal slip directions derived from shallow thrust earthquakes from the kuril and japan trenches for the period 1963 1991 a simple two plate model fits the 397 slip vectors significantly worse than a model that permits strike slip motion of the southern kuril forearc relative to the overlying plate weighted mean slip directions along the southern kuril trench are systematically rotated toward the direction orthogonal to the trench which implies that the net convergence is partitioned into less oblique subduction and trench parallel displacement of the southern kuril forearc the angular discrepancy between the observed slip direction and the direction predicted by the nuvel 1 pacific north america euler vector implies that the southern kuril forearc translates 6 11 mm yr 1 to the southwest relative to the overlying north american plate these results are consistent with geologically geodetically and seismologically observed convergence at the leading edge of the forearc sliver in southern hokkaido and with previously inferred extension at the trailing edge of the sliver which is located at the bussol strait at 46 n the percentage of the oblique component of the rigid plate convergence vector that is transferred into forearc strike slip motion is only 30 which may be evidence that the hokkaido honshu bend in the trench hinders southwest forearc motion or that the greater strength of oceanic forearcs impedes motion along forearc strike slip faults

the limiting pressure on a circular pile loaded laterally in cohesive soil in the analysis of the undrained loading of laterally loaded piles an important quantity is the ultimate lateral resistance at depth to purely horizontal movement if the soil is modelled as a perfectly plastic cohesive material then the calculation of this quantity reduces to a plane strain problem in plasticity theory in which the load is calculated on a long cylinder which moves laterally through an infinite medium an exact calculation of the load on such a cylinder is presented if this load is non dimensionalized with respect to the soil strength and the diameter of the pile it is found that the load factor varies between for a perfectly smooth pile and for a perfectly rough pile this result is discussed in the context of previous calculations for the lateral load capacity of piles and is compared with approximate calculations using cavity expansion theory and a wedge failure near the soil surface la resistance laterale limite en profondeur au seul mouvement horizontal represente un parametre im

iron isotope fractionation during oceanic crust alteration abstract the purpose of this work is to study the mobility and budget of fe isotopes in the oceanic crust and in particular during low temperature interaction of seawater with oceanic basalt we carried out this investigation using samples from ocean drilling program odp site 801c drilled during leg 129 and leg 185 in jurassic pacific oceanic crust seaward of the mariana trench the site comprises approximately 450 m of sediment overlying a section of 500 m of basalt which includes intercalated pelagic and chemical sediments in the upper basaltic units and two low temperature 10 30 c ocherous si fe hydrothermal deposits fe was chemically separated from 70 selected samples and 57fe 54fe ratios were measured by mc icp ms isoprobe the isotopic ratios were measured relative to an internal standard solution and are reported relative to the international fe standard irmm 14 based on duplicate measurements of natural samples an external precision of 0 2 2 has been obtained the results indicate that the deep sea sediment section has a restricted range of 57fe which is close to the igneous rock value in contrast large variations are observed in the basaltic section with positive 57fe values up to 2 05 for highly altered basalts and negative values down to 2 49 for the associated alteration products and hydrothermal deposits secondary fe minerals such as fe oxyhydroxides or fe bearing clays celadonite and saponite have highly variable 57fe values that have been interpreted as resulting from the partial oxidation of fe2 leached during basalt alteration and precipitated as fe3 rich minerals in contrast altered basalts at site 801c which are depleted in fe up to 80 display an increase in 57fe values relative to fresh values which suggest a preferential leaching of light iron during alteration the apparent fractionation factor between dissolved fe2 and fe remaining in the mineral is from 0 5 to 1 3 and may be consistent with a kinetic isotope fractionation where light fe is stripped from the minerals alternatively the formation of secondary clays minerals such as celadonite during basalt alteration may incorporate preferentially the heavy fe isotopes resulting in the loss of light fe isotopes in the fluids because microbial processes within the oceanic crust are of potential importance in controlling rates of chemical reactions fe redox state and fe isotope fractionation we evaluated the possible effect of this deep biosphere on fe isotope signatures the fe isotope systematics presented in this study suggest that even though iron behavior during seafloor weathering may be mediated by microbes such as iron oxidizers 57fe variations of more than 4 may also be explained by abiotic processes further laboratory experiments are now required to distinguish between various processes of fe isotope fractionation during seafloor weathering

petrology and geochronology of basalt breccia from the 1996 earthquake swarm of loihi seamount hawaii magmatic history of its 1996 eruption samples of basalt were collected during the rapid response cruise to loihi seamount from a brec cia that was probably created by the july to august 1996 loihi earthquake swarm the largest swarm ever recorded from a hawaiian volcano 210 po 210 pb dating of two fresh lava blocks from this breccia indicates that they were erupted during the first half of 1996 making this the first documented historical eruption of loihi sonobuoys deployed during the august 1996 cruise re corded popping noises north of the breccia site indicat ing that the eruption may have been continuing during the swarm all of the breccia lava fragments are tho leiitic like the vast majority of loihi s most recent lav as reverse zoning at the rim of clinopyroxene pheno crysts and the presence of two chemically distinct oliv ine phenocryst populations indicate that the magma for the lavas was mixed just prior to eruption the trace element geochemistry of these lavas indicates there has been a reversal in loihi s temporal geochemical trend although the new loihi lavas are similar isotopically and geochemically to recent kilauea lavas and the man tle conduits for these two volcanoes appear to converge at depth distinct trace element ratios for their recent lavas preclude common parental magmas for these two active volcanoes the mineralogy of loihi s recent tho leiitic lavas signify that they crystallized at moderate depths f8 9 km within the volcano which is approx imately 1 km below the hypocenters for earthquakes from the 1996 swarm taken together the petrological and seismic evidence indicates that loihi s current magma chamber is considerably deeper than the shal low magma chamber f3 4 km in the adjoining active shield volcanoes

medusae fossae formation new perspectives from mars global surveyor 1 the nature and origin of the medusae fossae formation mff on mars has been debated since the return of the first viking images the mff s young age distinctive surface texture and lack of obvious source have prompted multiple hypotheses for its origin this study uses data from the mars global surveyor mgs mission to examine the mff at all available scales we discuss and quantify observations from mars orbiter laser altimeter mola topography and mars orbiter camera moc images to better constrain the origin of the mff topographic grid estimates yield a present extent of 2 1 106 km2 and a volume of 1 4 106 km3 however remnant yardang deposits observed far from the thicker lobes of mff material suggest that it may have once covered up to 5 106 km2 we do not find compelling evidence for extensive fluvial reworking of the mff however in several regions buried channels are apparent in the mff because the formation is draped over underlying topography layering is apparent at all scales from submeter to hundreds of meters with variable resistance to weathering continuity of layers appears to be local to regional but not likely formation wide yardangs form both parallel and bidirectional patterns with resistant layers and jointing probably influencing their orientations a comparative study of mff regional topography and surface expression indicates that the mff is quantitatively dissimilar to martian polar layered deposits the material is most likely a friable and irregularly consolidated air fall deposit of probable volcanic origin

constraints on the configuration of andaman nicobar subduction zone from em modeling abstract the electrical conductivity structures using long period magneto telluric data at three sites nbg nabagram hav havelock in andaman and cby campbell bay in nicobar region are investigated after obtaining 1d responses 2d forward models of electrical structure are constructed along profiles across north andaman middle andaman and nicobar islands the initial configuration along each profile is constrained from models based on seismic reflection data the responses obtained after iterative forward computations match the observed data at respective sites reasonably well new structures within the forearc high are discerned from north to south we delineate a moderately conductive body beneath north andaman which is associated with the presence of ophiolites around this location in the middle andaman a highly conductive body below the island is interpreted as presence of fluids along the active diligent fault facilitated by the barrier of the invisible bank a complex geometry of resistive material embedded in a highly conductive body inferred beneath at great nicobar at cby is commensurate with the presence of a layered magmatic body possibly linked to the volcanic seamount to the east near the tear of the subducting plate

biosignatures and microbial fossils in endolithic microbial communities colonizing ca sulfate crusts in the atacama desert abstract since the description of microbial communities colonizing ca sulfate crusts in the atacama desert there has been much interest in the mechanisms that could lead to the formation and preservation of biosignatures or microbial fossils of these communities a key to understanding physico chemical processes of taphonomy and early diagenesis is to examine microfossils in their natural environment in this study we characterize organomineral traces and microbial fossils found around microbial communities present in these ca sulfate crusts through scanning electron microscopy microanalytical eds and raman spectroscopy techniques calcium carbonate precipitates were detected around remnants of cryptoendolithic algae beneath the crust surface as what seems to be the final step in the organomineralization of these cryptoendolithic communities we also observed alga cell remains permineralized by mg si rich minerals inside gypsum crystals additionally mg si bearing minerals formed a web like structure within the hypoendolithic cyanobacterial habitat via permineralization of extracellular polymeric substances our observations indicate that despite the extremely hyperarid environment microenvironmental conditions may be appropriate for the formation of biosignatures and microbial fossils of extinct endolithic microbial communities a model of the possible organomineralization processes involved is presented

structural geology and the seismotectonics of the 2004 great sumatran earthquake y the authors acknowledge funding support from the australian research council discovery project dp120103554 a unified model for the closure dynamics of ancient tethys constrained by geodesy structural geology argon geochronology and tectonic reconstruction and linkage project lp130100134 where to find giant porphyry and epithermal gold and copper deposits the research was also supported by the satellites seismometers and mass spectrometers initiative within the research school of earth sciences at anu bob engdahl is thanked for his support during earlier versions and for providing data

raman spectroscopic and scanning electron microscopic analysis of a novel biological colonisation of volcanic rocks a novel type of colonisation of a basaltic rock collected on the arctic island of svalbard norway during the amase expedition in 2004 was characterised using raman spectroscopy and scanning electron microscopy sem the sample contains two different types of extremophile communities one occurring behind a radial white crystallisation and the other occurring inside a dark vacuole several types of minerals and microbial colonies have been identified by both raman spectroscopy and sem analyses it is the first time that photosynthetic communities have been documented to colonise the inside of dark basaltic rocks our discovery has important implications for planetary exploration because it extends the analytical capability and our understanding of microbial rock colonisations to subaerial volcanic outcrops and has wide implications towards the search for life in extraterrestrial planets in this work we also demonstrate that the use of different laser wavelengths for raman spectroscopic studies and complementary microscopic analysis are critical for a comprehensive organic and inorganic compound identification

mineralogical characterization and genesis of hydrothermal mn oxides from the flank of the juan the fuca ridge several sites of active hydrothermal flow have been found on the eastern flank of the juan de fuca ridge these sites are typically located along the edge of basaltic outcrops where sediment is thin we present data on mn oxides formed on such outcrops zona bare and grinin bare these oxides are either black layered crust or soft micro concretions found in partially altered sediments x ray diffraction xrd and scanning electron microscopy sem analyses of mn crusts indicate the presence of well crystallized todorokite and birnessite encrusting detrital minerals and replacing siliceous fossil transmission electron microscopy tem and energy dispersive x ray spectroscopy edx analyses were used to identify amorphous and poorly crystallized mn rich phases in partially altered sediments and crusts tem of impregnated samples showed textural evidence suggesting that amorphous mn oxides are incrusting cellular structures that could be bacteria the valence state of mn in these oxides was determined by parallel electron energy loss spectroscopy peels results indicate that todorokite and birnessite have an average valence state of about 3 7 whereas the poorly crystallized mn rich phases have a lower valence state these data suggest that the formation of hydrothermal mn concretions occurs in several steps the initial step is the adsorption or precipitation of mn fe and si around cell wall bacteria extracellular polymers and siliceous fossil remains these mineralizations are poorly crystallized phyllomanganates which progressively increase in size and crystallinity to give the final birnessite and todorokite products all of these mn rich phases are the result of interactions between hydrothermal fluid and sediments and formed in areas where hydrothermal fluids discharge through the sediment

rupture process of the 2004 sumatra andaman earthquake the 26 december 2004 sumatra andaman earthquake initiated slowly with small slip and a slow rupture speed for the first 40 to 60 seconds then the rupture expanded at a speed of about 2 5 kilometers per second toward the north northwest extending 1200 to 1300 kilometers along the andaman trough peak displacements reached 15 meters along a 600 kilometer segment of the plate boundary offshore of northwestern sumatra and the southern nicobar islands slip was less in the northern 400 to 500 kilometers of the aftershock zone and at least some slip in that region may have occurred on a time scale beyond the seismic band

tectonic and volcanic implications of a cratered seamount off nicobar island andaman sea the region of the nicobar earthquake swarm of january 2005 has been explored during a recent cruise using multibeam swath bathymetry seafloor imaging and tv guided sampling to decipher the seafloor morphology nature and tectonic frame work a seamount with well developed crater at the summit was discovered near to the center of the nicobar swarm rock samples collected by tv guided grab from the seamount crater are dacite rhyolite and andesite type with a veneer of ferromanganese oxide coating the aggregates recovered from the slope consisted of manganese globules the geochemistry of the globules suggests 66 97 mn oxide indicative of hydrothermal origin the morphology of the seamount seafloor video footage and geochemistry of the seabed samples suggest that the cratered seamount has erupted in the recent geological past and is dormant at present this is the first documented report of submarine arc volcanism in the andaman sea this finding substantiates the prediction of a submarine volcano east of nicobar island study of the seismicity and the stress pattern in the region suggest that the earthquake swarm in the region occurred due to 2004 sumatra andaman megathrust earthquake the derived stress pattern suggests that the 2004 earthquake greatly reduced the normal stress in the region of west andaman fault from the planes or unclamped them thus unclamping of the region by the 2004 sumatra andaman earthquake led to the initiation of the swarm through predominantly strike slip faulting the newly discovered dormant submarine volcano indicates the volcanic nature of the region we suggest that this submarine volcano is a link between sub aerial volcanoes of barren narcondam islands of the andaman sea and the volcanoes of sumatra

present day crustal deformation around sagaing fault myanmar 1 global positioning system gps measurement campaigns in myanmar conducted in 1998 and 2000 allow quantifying the present day crustal deformation around the sagaing fault system in central myanmar both a regional network installed at four points within the country and a local 18 station network centered on the city of mandalay across the sagaing fault demonstrate that active deformation related to the northward motion of india is distributed across myanmar in a platelet that extends from the western edge of the shan plateau in the east to the andaman trench in the west in this platelet deformation is rather diffuse and distributed over distinct fault systems in the east the sagaing shan scarp fault system absorbs 10 mm yr this gps study combined with an on land geotectonic survey demonstrate that oblique slip of india along the rigid sundaland block is accommodated by a partitioned system characterized by distribution of deformation over a wide zone index terms 1206 geodesy and gravity crustal movements interplate 8155 1243 geodesy and gravity space geodetic surveys 8110 tectonophysics continental tectonics general 0905 8158 tectonophysics plate motions present and recent 3040 keywords tectonics gps fault southeast asia

understanding the signature of rock coatings in laser induced breakdown spectroscopy data surface compositional features on rocks such as coatings and weathering rinds provide important information about past aqueous environments and water rock interactions the search for these features represents an important aspect of the curiosity rover mission with its unique ability to do fine scale chemical depth profiling the chemcam laser induced breakdown spectroscopy instrument libs onboard curiosity can be used to both identify and analyze rock surface alteration features in this study we analyze a terrestrial manganese rich rock varnish coating on a basalt rock in the laboratory with the chemcam engineering model to determine the libs signature of a natural rock coating results show that there is a systematic decrease in peak heights for elements such as mn that are abundant in the coating but not the rock there is significant spatial variation in the relative abundance of coating elements detected by libs depending on where on the rock surface sampled this is due to the variability in thickness and spatial discontinuities in the coating similar trends have been identified in some martian rock targets in chemcam data suggesting that these rocks may have coatings or weathering rinds on their surfaces

earthquake occurrence reveals magma ascent beneath volcanoes and seamounts in the banda region characteristic seismicity patterns beneath the volcanic arcs of the banda region se asia suggest that magmatic processes have recently occurred beneath submarine portions of the arcs forming yet unrecognised submarine volcanoes we have found that almost 50 of earthquakes spatially associated with the banda and ambon volcanic arcs occurred in sequences with epicenters often concentrated in a small area and foci distributed in vertically elongated domains the most pronounced occurrence of such earthquake series and swarms was observed in the area of the manipa submarine basin latitude 3 75 s longitude 127 5 e ese of buru island the remarkable morphology of which resembles a huge caldera 60 km in diameter with a distinct cone seamount in its center reaching almost 3000 m above seafloor another candidate for an unrecognised submarine volcano is an area between volcanoes banda api and manuk with a huge 1973 74 earthquake swarm we assume that such a specific occurrence of earthquakes is induced by magma ascent and migration along faults above the subducting slab with magma possibly occasionally reaching the sea floor utilization of teleseismic data can thus reveal activation of plumbing systems of submarine volcanoes and highlight areas with the potential of near future volcanic events

mafic pyroclastic flows at tyrrhena patera mars constraints from observations and models abstract tyrrhena patera 22 s 104 e mars is a low relief 1800 m maximum relief central vent volcano whose flanks are dissected with broad 5 km wide flat floored channels the easily eroded nature of the shield materials combined with extremely low flank slopes 2 0 suggest that tyrrhena patera is composed of pyroclastic materials these shield deposits are observed to crop out 600 km from the volcano s summit with measured thicknesses of 100 150 m at these distances such dimensions strongly suggest emplacement via pyroclastic flows currently available data indicate that these deposits have a mafic composition application of models derived for terrestrial pyroclastic flow emplacement reveals that aside from environmental parameters atmospheric density gravity if all else is held equal a pyroclastic flow should travel a factor of 3 to 4 times farther on mars than on earth the observed tyrrhena patera deposits extend even farther suggesting that some emplacement mechanism may be enhancing pyroclastic flow runout distances on mars

evidence from the ad 2000 izu islands earthquake swarm that stressing rate governs seismicity magma intrusions and eruptions commonly produce abrupt changes in seismicity far from magma conduits that cannot be associated with the diffusion of pore fluids or heat such swarm seismicity also migrates with time and often exhibits a dog bone shaped distribution the largest earthquakes in swarms produce aftershocks that obey an omori type exponential temporal decay but the duration of the aftershock sequences is drastically reduced relative to normal earthquake activity here we use one of the most energetic swarms ever recorded to study the dependence of these properties on the stress imparted by a magma intrusion a 1 000 fold increase in seismicity rate and a 1 000 fold decrease in aftershock duration occurred during the two month long dyke intrusion we find that the seismicity rate is proportional to the calculated stressing rate and that the duration of aftershock sequences is inversely proportional to the stressing rate this behaviour is in accord with a laboratory based rate state constitutive law suggesting an explanation for the occurrence of earthquake swarms any sustained increase in stressing rate whether due to an intrusion extrusion or creep event should produce such seismological behaviour

characteristics of the landslide dams induced by the 2008 wenchuan earthquake and dynamic behavior analysis using large scale shaking table tests abstract the ms 8 0 wenchuan earthquake triggered at least 257 landslide dams more than 300 aftershocks with the magnitudes higher than ms 4 0 occurred after the formation of these landslide dams which might largely influence the structure and soil properties of these dams this paper aims to comprehensively investigate the characteristics of the landslide dams induced by the 2008 wenchuan earthquake and study the dynamic behaviors of the landslide dams under aftershocks using large scale shake table tests first the characteristics of the landslide dams including the distribution geometric parameters stability and longevity mitigation measures and the influence of the aftershocks are proposed then two groups of shaking table tests to simulate the dynamic behaviors of two types of landslide dams under aftershocks are illustrated one with quartz sand contained 10 kaolin dam i and the other with quartz sands all dam ii finally the results of the tests including the acceleration distribution dam deformation and dam breaching process are discussed through this study it is found that the landslide dams caused by high magnitude earthquakes have distinctive characteristics which may largely influence the stability breach process and risks of these dams in the model tests the accelerations are generally higher on the surface of the dams either on the crest or on the both upstream and downstream slopes the dam i was prone to settlement and cracking the aftershocks may not directly trigger the failures of landslide dams but accelerate the overtopping failures by lowering the dam crest with settlement and cracking

tectonics and history of the andaman sea region abstract the andaman sea is an active backarc basin lying above and behind the sunda subduction zone where convergence between the overriding southeast asian plate and the subducting australian plate is highly oblique the effect of the oblique convergence has been formation of a sliver plate between the subduction zone and a complex right lateral fault system the late paleocene collision of greater india and asia with approximately normal convergence started clockwise rotation and bending of the northern and western sunda arc the initial sliver fault which probably started in the eocene extended through the outer arc ridge offshore from sumatra through the present region of the andaman sea into the sagaing fault with more oblique convergence due to the rotation the rate of strike slip motion increased and a series of extensional basins opened obliquely by the combination of backarc extension and the strike slip motion these basins in sequence are the mergui basin starting at 32 ma the conjoined alcock and sewell rises starting at 23 ma east basin separating the rises from the foot of the continental slope starting at 15 ma and finally at 4 ma the present plate edge was formed alcock and sewell rises were separated by formation of the central andaman basin and the faulting moved onshore from the mentawai fault to the sumatra fault system bisecting sumatra

origin of the medusae fossae formation mars insights from a synoptic approach 1 the geologic origin of the medusae fossae formation mff has remained a mystery despite three decades of research to better constrain its formation an in depth analysis of observations made in the literature was combined with a new survey of over 700 mars orbiter camera narrow angle images of the mff to identify morphologic characteristics and material properties that define this formation as a whole while previous work has identified clear agreement on some characteristics our analysis identifies yardangs collapse features and layering as pervasive features of the mff whereas collapse features and layering may implicate several different physical and chemical processes yardangs provide vital information on material properties that inform about mechanical properties of the mff lithology aspect ratios of megayardangs range from 3 1 to 50 1 and slope analyses reveal heights of up to 200 m with cliffs that are almost vertical other yardangs show lower aspect ratios and topographic profiles these characteristics coupled to the presence of serrated margins suggest that mff lithology must be of weakly to heavily indurated material that lends itself to jointing the characteristics and properties of the mff are inconsistent with those of terrestrial pyroclastic fall deposits or loess but are in common with large terrestrial ignimbrites a hypothesis that explains all key observations with a single mechanism yardang fields developed in regionally extensive ignimbrite sheets in the central andes display morphologic characteristics that correlate with degree of induration of the host lithology and suggest an origin by pyroclastic flow for the mff

paleoclimate of mars as captured by the stratigraphic record in gale crater a kilometers thick sedimentary sequence in gale crater exhibits stratigraphic changes in lithology that are consistent with transitions in aqueous and climatic conditions purported to be global in scale the sequence is divided into two formations where the lower formation exhibits a net transition in mineralogy from clay sulfate to sulfate oxide assemblages and is separated from the overlying upper formation by an erosional unconformity superposition and crater counts suggest strata in the lower formation lie along the noachian hesperian time stratigraphic boundary whereas beds in the upper formation which lack signatures indicative of clay minerals or sulfates are thinner more regularly spaced and clearly younger the observed stratigraphic trends are consistent with the rocks at gale crater recording a global transition from a climate favorable to clay mineral formation to one more favorable to forming sulfates and other salts

experimental study of uplift resistance of shallow skirted foundations in clay under transient and sustained concentric loading wind wave and current forces cause significant overturning loads to be transmitted to foundation systems of fixed bottom offshore structures while buoyancy forces in conjunction with environmental loading impart direct tensile loads to foundations of floating facilities shallow skirted foundations are a potentially attractive foundation solution when overturning or tension loading is significant as suctions mobilised within the soil plug provide tensile resistance while passive suctions are maintained undrained reverse end bearing will govern failure providing enhanced uplift resistance compared with vented pull out of the foundation unit with or without the soil plug governed by skirt soil friction currently uncertainty exists over the limiting ratio of skirt depth to foundation diameter to mobilise undrained reverse end bearing and the duration over which passive suctions can be sustained this paper reports results from beam centrifuge tests investigating the response of shallow skirted fou

strain partitioning and fault slip rates in the northeastern caribbean from gps measurements 1 gps data collected in the dominican republic from 1994 to 2001 show that oblique convergence between the north american and caribbean plates is partitioned between 5 2 2 mm yr 1 of dip slip reverse motion on the north hispaniola thrust approximately n s and 12 8 2 5 mm yr 1 and 9 0 9 0 mm yr 1 of approximately e w left lateral strike slip motion on the septentrional and enriquillo faults 95 confidence the agreement between gps and paleoseimological slip rates on the septentrional fault together with the 770 960 years since the last major earthquake and the 800 1200 years maximum repeat time of major earthquakes may indicate that the septentrional fault is currently in the late phase of its rupture cycle

role of biomineralization as an ultraviolet shield implications for archean life cyanobacteria isolated from the krisuvik hot spring iceland were mineralized in an iron silica solution and irradiated with high levels of ultraviolet light analysis of the rates of photosynthesis chlorophyll a content and phycocyanin autofluorescence revealed that these mineralized bacteria have a marked resistance to uv compared to nonmineralized bacteria naturally occurring sinters composed of iron silica biominerals collected from

burma plate motion 1 plate motion in the indo burmese arc andaman sumatra region of burma plate is poorly resolved this is mainly due to lack of relevant data and complex tectonics of the region we analyze 1 azimuths of coseismic displacements due to the 2004 sumatra andaman and 2005 nias earthquakes 2 estimates of interseismic deformation in the indo burmese arc andaman sumatra and sagaing fault regions all based on gps measurements 3 long term plate motion rates across sumatra fault system sagaing fault and andaman sea from geomorphological and other geophysical studies and 4 the earthquake focal mechanisms in the region we suggest that the ssw motion of sunda plate with respect to indian plate may be partitioned into the dextral strike slip motion across the sagaing fault in the north and sumatra fault system in south in the back arc region and the arc normal motion across the sumatra subduction zone which becomes oblique in andaman and southern indo burmese arc region and dextral in the northern indo burmese arc region of the fore arc under the rigid plate approximation we estimate a pole for india burma plate pair at 27 1 n 82 1 1 e with an angular velocity of 0 845 0 12 ma and for burma sunda at 22 3 1 1 n 109 3 2 5 e with an angular velocity of 0 67 0 12 ma thus the plate motion in the northern and southern regions of burma plate namely the indo burmese arc and andaman sumatra arc may be explained by a single pole and does not require a boundary between the two

evidence of a microbial community associated with rock varnish at yungay atacama desert chile 1 rock varnish is a very slow growing nanostratigraphic coating consisting of approximately 70 fine grained clay and 30 iron and manganese oxides that forms on the surfaces of rocks in arid and semiarid climates the microbial diversity associated with rock varnish collected from the hyperarid yungay region of the atacama desert was investigated using culture independent biomolecular methods and an adenosine triphosphate atp assay the extraction of dna from rock varnish collected at yungay a region in which little to no dna has been extracted from the surface soil 1 cm to date indicates that rock varnish may provide a niche habitat for microbial life where water is essentially absent the clone library constructed suggests the presence of numerous phylogenetically distinct microorganisms ranging in diversity from cyanobacterial to a proteobacteria lineages the findings also show that only a few micrometers of varnish material are enough to shelter microbes like chroococcidiopsis spp from the intense ultraviolet radiation present in the atacama desert whether or not microorganisms are involved in its nucleation and or growth rock varnish appears to provide a microhabitat resembling cryptoendolithic communities seen on a larger scale

topography of apollinaris patera and ma adim vallis automated extraction of digital elevation models we have used automatic extraction of digital elevation models dems from stereo imagery of mars to produce dems of parts of the aeolis quadrangle of mars the method uses automated stereo matching based on an adaptive least squares correlation technique which can be applied to viking orbiter imagery a demonstration of the technique is presented which focuses on the volcano apollinaris patera 186 w 9 s and the channel ma adim vallis 183 w 20 s the topographic information derived is compared with previous determinations of topography and a brief discussion of the relationship of the topography to the processes that have acted in the area is given dems derived from stereomatching are an invaluable resource for terrain interpretation and will provide a complementary technique to direct topographic measurements such as future missions to mars will provide

effects of multipropped excavation on an adjacent floating pile abstractdeep excavations inevitably induce stress relief and soil movement which may affect the safety and serviceability of nearby existing pile foundations although the effects of excavation on

seismic images of the sliver strike slip fault and back thrust in the andaman nicobar region 1 the sliver strike slip great sumatra fault gsf traverses mainland sumatra from the sunda strait in the southeast to banda aceh in the northwest and defines the present day plate boundary between the sunda plate in the north and the burmese sliver plate in the south it has been well studied on mainland sumatra but poorly north of banda aceh in the andaman sea here we present deep seismic reflection images along the northward extension of the gsf over 700 km until it joins the andaman sea spreading centre and we interpret these images in the light of earthquake gravity and bathymetry data we find that the gsf has two strands between banda aceh and nicobar island a transpression in the south and a deep narrow active rift system in the north dotted with volcanoes in the center suggesting that the volcanic arc is coincident with rifting farther north of nicobar island an active strike slip fault the andaman nicobar fault cuts through a rifted deep basin until its intersection with the andaman sea spreading centre the volcanic arc lies just east of the rift basin the western margin of this basin seems to be a rifted continental margin tilted westward and flooring the andaman nicobar fore arc basin the andaman nicobar fore arc basin is bounded in the west by back thrusts similar to the west andaman and mentawai faults the cluster of seismicity after the 2004 great andaman sumatra earthquake just north of nicobar island coincides with the intersection of two strike slip fault systems

compositional and dynamic controls on mafic silicic magma interactions at continental arc volcanoes evidence from cordon el guadal tatara san pedro complex chile

atmospheric storm triggered and intensified by geodynamics case studies from andaman sea and bay of bengal region in the indian ocean the study analyses the possible connection between the onset of cyclone and volcano tectonic seismicity in the andaman region the historical data of the major volcanic seismic and atmospheric events from the region show that several of the geodynamic activities were followed by severe atmospheric disturbances over the region in this study we consider the case of three recent cyclones phailin hudhud and nilam that either originated or were intensified over the andaman sea and bay of bengal and examine their correlation with the volcano tectonic seismic events during the cyclone occurrence the zenith total delay ztd time series derived from global positioning system data from the pbr2 station on andaman island overlapping with the period of the cyclone occurrence were examined to distinguish the onset and intensification of the atmospheric events the comparison of the sharp changes in ztd associated with the cyclone and the seismic events during the period indicates that the atmospheric changes almost coincide or follow the geodynamic activity our study illustrates that volcano tectonics of the region plays a role in the triggering of atmospheric disturbances

a reevaluation of using laboratory shear tests the expression for the average undrained shear strength mobilized on a slip surface in the field resulted from in situ vane and oedometer data combined with a correction factor obtained from the computed factor of safety of unstable embankments footings and excavations it is shown here that the same expression for mobilized undrained strength of soft clays is also obtained from laboratory shear tests by taking into account anisotropy and time effects this result is highly significant since the laboratory undrained shear strength data as well as the correction factor for the time effect are completely unrelated to the in situ data that previously resulted in the expression for field mobilized undrained shear strength key words mobilized undrained shear strength in situ vane test laboratory shear tests

geophysical characteristics of the ninetyeast ridge andaman island arc trench convergent zone abstract the convergence tectonics of the ninetyeast ridge ner upon the andaman island arc trench system is examined through an analysis of etopo2 bathymetry satellite derived free air gravity and seismic data oblique subduction and the buoyancy forces arising from subduction of the ner render the subduction processes near the andaman arc highly complex the bathymetric expression of the ner is visible up to lat 10 n but seismic reflection data indicate that it extends up to about lat 17 n the gravity anomalies are strongly positive over the exposed segment of the ridge but are subdued over the buried portion there is a prominent break in the continuity of the trench gravity low where the ner seems to impinge upon the island arc further a strong curvilinear belt of negative anomalies just behind and running parallel to the island arc associated with the forearc basin is a dominant feature of the gravity map an offset in the continuity of this strong negative anomaly occurs at about the same latitude where the ner seems to be converging upon the island arc seismic reflection data indicate that the ner is very close to the trench flexural modeling of the gravity anomalies for the subducting indian ocean lithosphere loaded by sediments and the ner indicates that the ner is at the starting phase of its collision with the island arc and may not have started affecting the subduction process itself we infer that the en echelon block structure of the ner in the proximity of the convergent zone is a consequence of complex strike slip and subduction related tectonic forces

chronology eruption duration and atmospheric contribution of the martian volcano apollinaris patera geologic mapping thermal inertia measurements and an analysis of the color visual wavelengths of the martian volcano apollinaris patera indicate the existence of two different surface materials comprising an early easily eroded edifice and a more recent competent fan on the southern flank a chronology of six major events that is consistent with the present morphology of the volcano has been identified we propose that large scale explosive activity occurred during the formation of the main edifice and that the distinctive fan on the southern flank appears to have been formed by lavas of low eruptive rate similar to those that form compound pahoehoe flow fields on earth a basal escarpment typically 500 m in relief and morphologically similar to the one surrounding olympus mons was produced between the formation of the main edifice and the fan indicating multistage eruptions over a protracted period of time contact relations between the volcanic units and the adjacent chaotic material indicate that formation of the chaotic material occurred over an extended period of time and may be related to the volcanic activity that formed apollinaris patera stereophotogrammetric measurements permit the volume of the volcano to be estimated at 105 km3 from this volume measurement and an inferred eruption rate 1 5 10 2 km3 yr 1 we estimate the total eruption duration for the main edifice to be 107 yrs plausible estimates of the exsolved volatile content of the parent magma imply that greater than 1015 kg of water vapor was released into the atmosphere as a consequence of this activity this large amount of water vapor as well as other exsolved gases must have had a significant impact on local and possibly global climatic conditions

ignimbrite as a substrate for endolithic life in the hyper arid atacama desert implications for the search for life on mars the hyper arid core of the atacama desert in chile is considered the driest and most life limited place on earth with few habitats capable of sustaining an active microbial ecosystem as such it is one of the best terrestrial analogues of the extreme arid conditions on mars and an ideal environment to explore survival and biological adaptation strategies as the environment becomes increasingly dry here we show that weakly welded rhyolitic ignimbrites in this desert are abundantly colonized by endolithic cyanobacteria and associated heterotrophic bacteria we propose that the porous ignimbrite interior provides protection from damaging uv radiation and excessive levels of visible light rock porosity also favors cell hydration through water retention after scarce rainfall events even when the surrounding environment remains stubbornly dry this is the first known example of an endolithic microbial community colonizing ignimbrite rocks in an extremely dry environment the existence of a habitat capable of supporting abundant phototrophic and heterotrophic communities in an environment that precludes most life forms suggests that if similar deposits are found on mars these should be considered important targets in the search for life indeed ignimbrite rocks have been tentatively identified in gale crater the landing site of the mars science laboratory msl mission and could be directly analyzed by its rover curiosity

volcaniclastic processes on modern submarine arc stratovolcanoes sidescan and photographic evidence from the rumble iv and v volcanoes southern kermadec arc sw pacific abstract studies of volcaniclastic processes on modern submarine arc stratovolcanoes are rare facies models of submarine volcanism and associated volcaniclastic deposits have to date emphasized general and or regional processes two andesite alkali basaltic volcanoes rumble iv and v volcanoes from the southern kermadec arc are mapped with swath bathymetry and sidescan imagery and photographic data to characterise volcaniclastic processes on these modern submarine arc stratovolcanoes and their interaction with ambient marine processes the principal observation from the rumble iv and v data is the fine scale spatial variability in the distribution of effusive lavas various volcaniclastic deposits and hemipelagic pelagic sediments mass movement of volcaniclastic deposits is common and includes 1 epiclastic debris flows 2 pillow breccia talus deposition penecontemporaneous with lava eruption 3 traction particulate gravity flows and possibly 4 sector collapse epiclastic redeposition is inferred to be mobilised by episodic but frequent localised small volume flows which largely redeposit debris on the edifice winnowed and rippled volcaniclastic sediment indicates bottom current activity is common but localised over the entire height of both volcanoes down to a water depth of 2200 m these currents also possibly entrain detritus for subsequent mobilisation by particulate gravity flows irregular and ragged spatter agglutinates on rumble iv interpreted as evidence of lava fountaining and wellsorted fines poor scoriaceous material on rumble v interpreted as evidence of explosive eruption indicate the transition between effusive and explosive volcanism is between 650 and 700 m water depth other southern kermadec volcanoes e g tangaroa have scoriaceous detritus at 960 970 m water depth positions of these effusive explosive transition zones are likely to oscillate up and down the volcano during glacioeustatic fluctuations

submarine hydrothermal activity and mineralization on the kurile and western aleutian island arcs n w pacific the kurile arc consists of at least 100 submarine volcanoes and 5 submarine caldera located mainly in the rear arc the arc is seismically very active particularly in the south and is characterized by extensive volcanism and hydrothermal activity at least one subaerial volcano on the arc medvezhy located on iturup island has an extremely shallow magma chamber and is intensely active three types of submarine hydrothermal deposit were recovered from this area hydrothermal manganese crusts nontronite and hydrothermal manganese crusts overlain by hydrogenous manganese oxides in addition submarine hydrothermal fe oxyhydroxides enriched in p were sampled from the submerged caldera of kraternaya bight in the central part of the arc these deposits appear to be analagous to deposits from santorini caldera on the aegean arc piip submarine volcano located in the western aleutian arc is characterized by two shallow summit craters both intermediate temperature anhydrite gypsum barite amorphous silica pyrite calcite and aragonite and low temperature nontronite fe oxyhydroxides hisingerite and ferromanganese crusts hydrothermal minerals were recovered from this seamount together with bacterial mats and giant clams the maximum measured temperature of the hydrothermal fluids was 133 c although the actual temperature may have reached 250 c both the kurile and aleutian arcs have the potential to host major submarine hydrothermal systems detailed exploration of these poorly studied areas using modern geophysical geochemical and sampling techniques is therefore strongly recommended

non biological fractionation of stable ca isotopes in soils of the atacama desert chile abstract we measured ca stable isotope ratios 44 40 ca in an ancient 2 my hyperarid soil where the primary source of mobile ca is atmospheric deposition most of the ca in the upper meter of this soil 3 5 kmol m 2 is present as sulfates 2 5 kmol m 2 and to a lesser extent carbonates 0 4 kmol m 2 in aqueous extracts of variably hydrated calcium sulfate minerals 44 40 ca e values vs bulk earth increase with depth 1 4 m from a minimum of 1 91 to a maximum of 0 59 the trend in carbonate 44 40 ca in the top six horizons resembles that of sulfate 44 40 ca but with values 0 1 0 6 higher the range of observed ca isotope values in this soil is about half that of 44 40 ca values observed on earth linear correlation among 44 40 ca 34 s and 18 o values indicates either a a simultaneous change in atmospheric input values for all three elements over time or b isotopic fractionation of all three elements during downward transport we present evidence that the latter is the primary cause of the isotopic variation that we observe sulfate 34 s values are positively correlated with sulfate 18 o values r 2 0 78 and negatively correlated with sulfate 44 40 ca e values r 2 0 70 if constant fractionation and conservation of mass with downward transport are assumed these relationships indicate a 44 40 ca fractionation factor of 0 4 in caso 4 the overall depth trend in ca isotopes is reproduced by a model of isotopic fractionation during downward ca transport that considers small and infrequent but regularly recurring rainfall events near surface low ca isotope values are reproduced by a rayleigh model derived from measured ca concentrations and the ca fractionation factor predicted by the relationship with s isotopes this indicates that the primary mechanism of stable isotope fractionation in caso 4 is incremental and effectively irreversible removal of an isotopically enriched dissolved phase by downward transport during small rainfall events

volcanic geology of hadriaca patera and the eastern hellas region of mars hadriaca patera is a low relief volcano in the southern highlands of mars northeast of the hellas basin layered friable deposits composing the extensive channeled flanks of the volcano surround a well defined summit caldera containing late stage eruptive products the morphologic characteristics of the channels suggest erosion by groundwater sapping and surface runoff the erosional morphology of the volcano the lack of lava flow features and the friable nature of the flank materials indicate that hadriaca patera consists predominantly of pyroclastic deposits gravity driven flow models demonstrate that the distribution of flank materials can be attributed to the emplacement of pyroclastic flows both magmatic and hydromagmatic eruption models are viable for the magmatic case the necessary mass eruption rates 107 108 kg s ejection velocities 400 m s and volatile contents 1 5 3 0 wt h2o are consistent with parameters derived for terrestrial plinian eruptions for the hydromagmatic case the required energy conversion efficiencies are comparable to those of laboratory experiments and the inferred permeability of the martian crust allows large amounts of groundwater to be transported rapidly at flow rates of 103 104 m3 s into the region models of cooling during emplacement indicate that welding of pyroclastic flows can occur at large distances hundreds of kilometers from a source vent on mars the layering within hadriaca patera could be attributed to welding of pyroclastic flows that would control its susceptibility to erosion morphologic similarities between hadriaca and tyrrhena paterae suggest a similar volcanic history with an early pyroclastic dominated shield building phase followed by effusive eruptions at their summit calderas and on the flank of tyrrhena patera the formation of the extensive ridged plains of hesperia planum following the formation of the highland paterae supports the interpretation of a transition from explosive to effusive volcanism in the eastern hellas region a progressive depletion of volatiles on mars is consistent with the morphologic properties of highland paterae and other central vent volcanoes a predominance of hydrovolcanic eruptions in the development of hadriaca and tyrrhena paterae would imply that the transition in volcanic eruption style can be attributed to a volatile depletion of the crust whereas magmatic eruptions at the paterae would be indicative of temporal changes in martian magmas

facilitation of endolithic microbial survival in the hyperarid core of the atacama desert by mineral deliquescence 1 the hyperarid core of the atacama desert is considered the dry limit for life on earth soils in this region have very low abundance of heterotrophic bacteria and are practically barren of photosynthetic microorganisms because of the extreme dry conditions 2 mm a 1 rainfall however relatively abundant endolithic communities of cyanobacteria chroococcidiopsis occur within halite crusts in paleolake evaporitic deposits by means of continuous monitoring of the microclimate conditions temperature relative humidity water vapor density wetness and photosynthetically active radiation inside and around the halite crusts we demonstrate here that water vapor condenses within the pore space of the halite at relative humidity rh levels that otherwise hinder the occurrence of liquid water in the surrounding environment water condensation occurs at rh 75 which corresponds to the deliquescence point of halite we have estimated a total of 57 deliquescence events i e water condensation within the halite crusts as opposed to only 1 liquid water event outside these wet events resulted in a total of 213 8 h of potential photosynthetic activity for the endolithic microorganisms versus only 6 h for organisms outside the halite crusts halite crusts may therefore represent the last available niche for photosynthetic activity in extreme arid environments on earth

coeval compressional deformation and volcanism in the central andes case studies from northern chile 23 s 24 s received 22 may 2009 revised 6 august 2009 accepted 24 august 2009 published 1 december 2009 1 in this contribution we examine the relationship between active compression and construction of pleistocene volcanoes in the present day magmatic arc of the central andes 23s 24s deformation producedseveraln sstriking 40kmlongsubparallel ridges these ridges formed by folding of pliocene ignimbrites and upper pliocene and pleistocene lavas they are asymmetrical in profile and have a gentle back limb and steeper frontal limb andesitic monogenetic volcanoes show a close spatial relationship with the ridges some volcanoes are on the hinge zone whereas others lay on the sides of the ridges we interpret this spatial pattern as a result of magma storage and migration along a system of subhorizontal reservoirs and reverse faults magma reservoirs probably formed along flat portions of reverse faults between ramp structures that serve as episodic magma transport

submarine hydrothermal venting related to volcanism in the lesser antilles evidence from ferromanganese precipitates 1 radiogenic isotope compositions sr nd pb hf and os of sediment hosted seafloor ferromanganese crusts and sediments incrusted with ferromanganese oxyhydroxides from the lesser antilles island arc were measured to distinguish between hydrogenous seawater derived and hydrothermal metal sources the ages of the precipitates range between recent last few thousand years and a few 100 kyr as deduced from 10be and co concentrations evidence from the presence of bladed todorokite and nontronite together with the major element and ree composition suggests that a significant proportion of these sediment hosted precipitates formed at relatively low temperatures from a mixture of seawater and hydrothermal fluids associated with island arc volcanism the radiogenic isotope compositions of all metals mentioned above except pb show large differences in hydrothermal versus hydrogenous contributions over space and time in contrast to precipitates of high temperature fluids which mainly scavenge their ree contents from seawater the crusts of this study show 143nd 144nd of up to 0 512817 nd 3 5 this is close to the signature of the nearby island arc rocks and far above the expected local seawater ratio of 0 51209 nd 10 7 these crusts also show high 176hf 177hf up to 0 283102 low 87sr 86sr up to 0 7069 and low 187os 188os up to 0 16 compared with local seawater as expected from hydrothermal island arc derived metal contributions in contrast the pb isotope signatures of the crusts cannot be explained by mixing between seawater and hydrothermal sources it is suggested that pb was either removed from the ascending fluids within the sediment column before they reached seawater or the temperatures were too low to leach significant amounts of pb from the rocks or sediments external sources such as saharan dust particulate inputs from the orinoco river or even incongruent release of pb isotopes from the island arc rock derived particles must have contributed to the observed pb isotope variability our results suggest that submarine hydrothermalism originating from intraoceanic island arc volcanism creates distinct geochemical environments for the dispersion of hydrothermal fluids and may be an important mechanism to supply metals of hydrothermal origin to seawater