sector collapse sedimentation and clast population evolution at an active island arc volcano stromboli italy sciara del fuoco is the subaerial part of a partially filled sector collapse scar that extends to 700 m below sea level on stromboli volcano the collapse occurred 2200 m and 10 km from the shore to the nnw a fan shaped mounded feature comprises debris avalanche deposits 4 km3 from two or more sector collapses volcaniclastic density currents originating from sciara del fuoco follow the topographic margin of the debris avalanche deposits although overbank currents and other unconfined currents widely cover the mounded feature with turbidites historical recorded eruptive activity in sciara del fuoco is considerably less than that which occurred earlier and much of the partial fill may have formed from eruptions soon after the sector collapse it is possible that a mass of eruptive products similar to that in the collapse scar is dispersed as volcanogenic sediment in deep water of the tyrhennian basin evidence that the early post collapse eruptive discharge was greater than the apparent recent flux 2kg s counters suggestions that a substantial part of stromboli s growth has been endogenous the partial fill of sciaria del fuoco is dominated by lava and spatter layers rather than by the scoria and ash layers classically regarded as main constituents of strombolian cinder cones much of the volcanic slope beneath the vents is steeper than the angle of repose of loose tephra which is therefore rapidly transported to the sea delicate pyroclasts that record the magmatic explosivity are selectively destroyed and diluted during sedimentary transport mainly in avalanches and by shoreline wave reworking and thus the submarine deposits do not record well the extent and diversity of explosive activity and associated clast forming processes considerable amounts of dense non vesicular fine sand and silt grains are produced by breakage and rounding of fragments of lava and agglutinate the submarine extension of the collapse scar and the continuing topographic depression to 2200 m below sea level are zones of considerable by passing of fine sand and silt which are transported in turbidity currents evidently volcanogenic sediments dispersed around island volcanoes by density currents are unlikely to record well the true spectrum and relative importance of clast forming processes that occurred during an eruption marine sedimentary evidence of magmatic explosivity is particularly susceptible to partial or complete obliteration unless there is a high rate of discharge of pyroclastic material into the sea

the petrology of a large intra oceanic silicic eruption the sandy bay tephra kermadec arc southwest pacific abstract the pumiceous pyroclastic deposits known as the sandy bay tuff on macauley island in the kermadec group represent a medium scale silicic eruption in an oceanic subduction setting the sandy bay eruption occurred about 6310 yr bp forming a large submarine caldera in the summit of the mainly submarine and essentially basaltic macauley volcano the sandy bay magma contained

generation of annual rossby waves in the north pacific abstract a new mechanism is proposed for the generation of the annual period baroclinic rossby waves which have been observed in the central north pacific by kang and magaard it is shown that annual north south fluctuations in the eastern boundary current off vancouver island can efficiently generate first baroclinic mode rossby waves throughout the central north pacific in particular to the southwest of vancouver island the direction wavelength and speed of phase propagation associated with the far field asymptotic wave solution agree favorably with observations also along and fixed latitude contained within the observed latitude band 30 40 n the amplitudes of the vertical displacement at 300 m and surface horizontal current speed both monotonically increase to the west in agreement with the observed trends for these quantities however the existence of this monotonicity in the solution appears to be quite sensitive to the north south spatial structure of the fluctuating coastal current for

formation of an a ā lava delta insights from time lapse multibeam bathymetry and direct observations during the stromboli 2007 eruption five consecutive multibeam bathymetries collected before during and after the 2007 stromboli eruption combined with visual inspections allowed us to document the morphological evolution of an a lava fed delta and to reconstruct the main processes acting during its submarine emplacement the 2007 stromboli delta extended down to 600 m water depth and covered an area of 420 103 m2 with a maximum thickness of 65 m and a total estimated volume of 7 106 m3 i e three times larger than its subaerial counterpart the lava delta grew mainly through the emplacement of discrete lobes about 50 150 m in size lobes were fed from point sources along the paleoshoreline and their subaqueous pathways seem to be mainly controlled by the submarine morphology with flows mostly filling in depressions left by previous lobes the main controlling factors on the lobe morphology and thickness are the effusion rates and the pre eruption morphology i e the geometry and gradients of the basal surface data also shows that sudden slope failure of portions of the submarine delta may occur simultaneously with accretion implying that a significant part of the delta material can be transported to greater depths by submarine gravity flows the present study is relevant for future monitoring and hazard assessment during the growth of active lava fed deltas as well as for a better interpretation of ancient volcaniclastic successions inland

recent emerged reef terraces of the yenkahe resurgent block tanna vanuatu implications for volcanic landslide and tsunami hazards emerged reef terraces record the extraordinarily rapid holocene uplift rate of the fault bounded yenkahe resurgent block yrb located within a partially submerged quaternary caldera on tanna island vanuatu southwest pacific the presently active volcano yasur is located at the western end of the yrb episodic uplift of the yrb is probably associated with the movement of magma below the yenkahe area a historically recorded uplift at port resolution bay in a d 1878 raised the shoreline 15 m this a d 1878 event was accompanied by a local earthquake and a tsunami that reached 12 m elevation coral samples from terraces at mean altitudes of 155 m and 15 m above present sea level yield 230 th 234 u dates of a d 1002 pm 10 and a d 1868 pm 4 respectively these ages imply a mean uplift of 156 mm yr for the yrb since a d 1002 until a d 1992 this volcanically related uplift occurs within the context of regional uplift of the southern new hebrides arc the late holocene uplift r

origin of spectacular fields of submarine sediment waves around volcanic islands understanding how large eruptions and landslides are recorded by seafloor morphology and deposits on volcanic island flanks is important for reconstruction of volcanic island history and geohazard assessment spectacular fields of bedforms have been recognised recently on submerged flanks of volcanic islands at multiple locations worldwide these fields of bedforms can extend over 50 km and individual bedforms can be 3 km in length and 150 m in height the origin of these bedform fields however is poorly understood here we show that bedforms result from eruption fed supercritical density flows turbidity currents in some locations but most likely rotational landslides at other locations general criteria are provided for distinguishing between submarine bedforms formed by eruptions and landslides and emphasise a need for high resolution seismic datasets to prevent ambiguity bedforms associated with rotational landslides have a narrower source with a distinct headscarp they are more laterally confined and internal bedform structure does not suggest upslope migration of each bedform eruption fed density currents produce wide fields of bedforms which extend radially from the caldera internal layers imaged by detailed seismic data show that these bedforms migrated up slope indicating that the flows that produced them were froude supercritical due to the low density contrast between interstitial fluid and sediment the extent and dimensions of submarine eruption fed bedforms is much greater than those produced by pyroclastic density currents on land

la fossa caldera breaching and submarine erosion vulcano island italy abstract la fossa caldera lfc on vulcano island in the aeolian archipelago italy is a multi collapse caldera whose north eastern part lies underwater through the integration of marine geophysical surveys and sampling carried out in the last decade its submarine extension and offshore areas have been reconstructed in unprecedented detail strong erosive processes breached the submarine portion of lfc and gradually dismantled the caldera rims and infill leading to the emplacement of a wide volcaniclastic fan from the base of lfc down to over 1000 m the bathy morphologic setting seismoacoustic facies and analyses of sediment samples from the fan together with volumetric considerations suggest that this feature is the pathway deposit of submarine unconfined gravity flows and turbidity currents deriving from the gradual dismantling of lfc submarine erosive processes are still active and the progressive erosion of the northern caldera sector threatens the stability of the active la fossa cone and the nearby coastal settlements

large scale sediment waves and scours on the modern seafloor and their implications for the prevalence of supercritical flows large scale 20 m to 7 km wavelength bedforms are common on the seafloor yet there is a lack of consensus on how they form and thus what to call them we conducted statistical analysis on a dataset of 82 seafloor bedforms that span a range of water depths and environments the data form three distinct groups 1 small scale 20 300 m wavelength sediment waves with mixed relief made of medium sand to cobble sized sediment that form in confined settings which we call small sediment waves 2 large scale 300 7000 m wavelength sediment waves with mixed relief made of fine grained sediment that form in relatively unconfined settings which we call large sediment waves and 3 large scale fully enclosed depressions in the seafloor which we call scours there is a statistically significant data gap in the size of bedforms between small sediment waves and large sediment waves that does not appear to be a sampling artefact this data gap probably results from the environments in which sediment waves form being either confined e g channel or canyon or unconfined e g open slope bedform migration direction is available for 36 of the data and includes small and large scale sediment waves of these examples all are shown to migrate up current up current migration is indicative of supercritical flow thus this data suggests that supercritical flows operate in a wide range of environments and can generate both small and large sediment waves therefore we suggest that small and large sediment waves form by similar processes despite the gap in bedform wavelength and sediment size the migration direction for scours remains unknown scours may form from similar processes to small and large sediment waves or alternatively they may be a completely separate bedform type that form when erosive flows exploit pre existing defects in the seafloor this novel statistical analysis of a global database shows that up current migrating bedforms associated with supercritical flow are unusually widespread and are recognised at two distinct scales

mass fluxes in the canary basin abstract ocean studies in the 1970s provided an improved knowledge of the coastal upwelling region off nw africa while in the 1980s and 1990s they led to a good description of the open ocean flow patterns in the canary basin it was not until the late 1990s that major research addressed the open coastal ocean coupled response here we examine the mean and seasonal circulation patterns in the canary basin with data from four hydrographic cruises carried out in the region between cape ghir madeira island and the canary islands we apply an inverse box model to an ocean divided into 14 layers with several layers representing each water mass or stratum to obtain mass fluxes consistent with the thermal wind equation an optimum flow description is obtained using conservation of mass salt and heat anomaly biologically corrected oxygen and silicate and allowing for ekman transport in the surface layer and dianeutral mixing between adjacent layers the deep waters show no predominant flow direction while the intermediate waters display localized southward flowing mediterranean water far from shore and northward flowing antarctic intermediate water near the continental slope specially in the passage between the eastern canary islands and the african slope the mean upper thermocline canary current composed of north atlantic central water flows south with an open ocean branch transporting about 3 1 sv 1 sv 10 6 m 3 s 1 10 9 kg s 1 and an upwelling related branch near the continental slope carrying 1 0 3 sv the seasonal transport by the open ocean branch intensifies and moves offshore from spring to fall 2 8 1 2 sv in spring 2 9 1 1 sv in summer and 4 5 1 2 sv in fall while it carries its lowest southward mass flux in winter 1 7 1 0 sv possibly as a result of a migration offshore the sampled region upwelling related southward flow is present in spring and summer 1 9 0 1 sv and 2 4 0 1 sv respectively while in fall and winter it merges with the offshore southward branch this westward migration allows a northward mass flux between the canary islands and the african coast 1 8 0 1 sv that by winter reaches cape ghir 0 5 0 2 sv seasonal air sea heat fluxes fit well with the climatological values the net phosphate transport in the surface layer indicates that primary production was negligible in this region during january 1997 and april 1998 though in this last month production was probably starting as a result of significant nutrient supply

the insular shelves of the faial pico ridge azores archipelago a morphological record of its evolution shelves surrounding reefless volcanic ocean islands are formed by surf erosion of their slopes during changing sea levels posterosional lava flows if abundant can cross the coastal cliffs and fill partially or completely the accommodation space left by erosion in this study multibeam bathymetry high resolution seismic reflection profiles and sediment samples are used to characterize the morphology of the insular shelves adjacent to pico island the data show offshore fresh lava flow morphologies as well as an irregular basement beneath shelf sedimentary bodies and reduced shelf width adjacent to older volcanic edifices in pico these observations suggest that these shelves have been significantly filled by volcanic progradation and can thus be classified as rejuvenated despite the general volcanic infilling of the shelves around pico most of their edges are below the depth of the last glacial maximum revealing that at least parts of the island have subsided after the shelves formed by surf erosion prograding lava deltas reached the shelf edge in some areas triggering small slope failures locally decreasing the shelf width and depth of their edges these areas can represent a significant risk for the local population hence their identification can be useful for hazard assessment and contribute to wiser land use planning shelf and subaerial geomorphology magnetic anomalies and crustal structure data of the two islands were also interpreted to reconstruct the long term combined onshore and offshore evolution of the faial pico ridge the subaerial emergence of this ridge is apparently older than previously thought i e before 850 ka

late quaternary tephra layers around raoul and macauley islands kermadec arc implications for volcanic sources explosive volcanism and tephrochronology a suite of deep sea cores were collected along transects up to 100 km across the fore arc and back arc regions of the predominantly submarine kermadec arc near raoul and macauley islands southwest pacific the cores reveal a macroscopic tephra record extending back 50 ka this is a significant addition to the dated record of volcanism previously restricted to fragmented late holocene records exposed on the two islands the 27 macroscopic tephra layers display a wide compositional diversity in glass 50 78 wt sio2 many tephra layers comprise silicic shards with a subordinate mafic shard population this could arise from magma mingling and may reflect mafic triggering of the silicic eruptions broadly the glass compositions can be distinguished on diverging high k and low k trends most likely arising from different source volcanoes this distinction is also reflected in the tephra records exposed on raoul low k and macauley high k islands the likely source areas heterogeneous tephra comprising shards of both high and low k affinity silicic and mafic compositions and more homogeneous tephra with subordinate outlier shard compositions are best explained by post depositional mixing of separate eruption deposits or contemporaneous eruptions evidently the slow sedimentation rates of the calcareous oozes 101 102 mm ka 1 were insufficient to adequately separate and preserve closely spaced eruption deposits this exemplifies the difficulty in assessing eruption frequencies and magmatic trends and erecting a tephrostratigraphy using geochemical fingerprinting in such environments despite these difficulties the ca 5 7 ka sandy bay tephra erupted from macauley island can be correlated over a distance of 100 km extending east and west of the island showing that the mostly submerged volcanoes are capable of wide tephra dispersal hence there is potential for developing chronostratigraphies for the southwest pacific beyond the region covered by the extensive rhyolite marker beds from the taupo volcanic zone

turbidity current sediment waves on the submarine slopes of the western canary islands two sediment wave fields have been identified on the flanks of the western canary islands of la palma and el hierro using a high quality 2 d and 3 d dataset that includes geosea and tobi imagery 3 5 khz profiles and short sediment cores the la palma sediment wave field covers some 20 000 km2 of the continental slope and rise and consists of sediment waves with wave heights of up to 70 m and wavelengths of up to 2 4 km the wave crestlines have a complex morphology with common bifurcation and a clear sinuosity waves have migrated upslope through time cores recovered from the wave field contain volcaniclastic turbidites interbedded with pelagic hemipelagic layers the wave field is interpreted as having formed beneath unconfined turbidity currents a simple previously published two layer model is applied to the waves revealing that they formed beneath turbidity currents flowing at 10 100 cm s 1 with a flow thickness of 60 400 m and a sediment concentration of 26 427 mg l the el julan sediment wave field lies within a turbidity current channel on the southwest flank of el hierro the sediment waves display wave heights of about 6 m and wavelengths of up to 1 2 km the waves are migrating upslope and migration is most rapid in the centre of the channel where the flow velocity is highest this wave field has been formed by channelised turbidity currents originating on the flanks of el hierro

bedforms on the submarine flanks of insular volcanoes new insights gained from high resolution seafloor surveys a comparative analysis of bedform fields along the submarine flanks of insular volcanoes characterized by different morpho structural settings volcanic and meteo marine regimes vanuatu kermadec bismark madeira and aeolian archipelagos is presented here to provide insights on the size distribution morpho dynamic and genesis of such bedforms two main types of bedforms are recognized according to their size location and preconditioning triggering processes small scale bedforms have wavelengths of tens to hundreds of metres and wave heights of metres because of their small size they are typically not recognizable at water depths greater than 400 m from vessel mounted bathymetric surveys however few examples of small scale bedforms are reported from upper volcanic flanks where steep gradients commonly hinder their formation their recognition is mostly limited to the thalweg of shallow and flat bottomed channels that carve the insular shelf on slope gradients 15 small scale bedforms are mostly related to erosional depositional processes due to sedimentary gravity flows that are often the result of a cascading effect between volcanic and non volcanic processes for example flood discharges and retrogressive landslides large scale bedforms occur at all water depths having wavelengths of hundreds thousands of metres and wave heights up to few hundreds of metres the origin of large bedforms is more difficult to ascertain especially if only bathymetric data are available some diagnostic criteria are presented to distinguish between bedforms associated with landslide deposits and those associated with density currents in this latter case relevant sediment sources and slope gradients 8 are key factors for bedform development erosional depositional bedforms are typically related to eruption fed density flows formed during large caldera collapses or to large turbidity flows bedforms generated by turbidity flows are often observed in the lower volcanic flanks where an abrupt decrease of gradients is present often matching a change from confined to unconfined settings in summary this study provides insights to interpret bedforms in modern and ancient marine volcaniclastic settings elsewhere

the west mariana ridge western pacific ocean geomorphology and processes from new multibeam data the western flank of the west mariana ridge and the distal parece vela basin have been mapped for the first time using a modern multibeam echosounder the new data reveal the ridge to be composed of 82 volcanic peaks of which 25 have summits with water depths of 1000 m and 11 have summits with depths of 500 m deep five of the volcanoes have summit craters and two are guyots the remaining 75 seamounts are peaked volcanoes one volcanic peak has a summit water depth of 16 m and two in the central region have summits as shoal as 7 m the erosional character of the volcanoes suggests a younging toward the south the western flank of the west mariana ridge is buried by a sediment apron that merges with the distal parece vela basin the sediment apron is incised by a series of canyon channel systems that head on the upper flank or summit of the west mariana ridge and trend downslope to the west several of the channels are sediment filled with an incised thalweg suggesting a multiphase evolution to the channel systems none of the channels have a pelagic drape whereas the seafloor adjacent to the channels does suggesting recent activity the lack of guyots the apparent younging of the volcanoes to the south and the youth of channel activity suggest the west mariana ridge may be either recently or is presently tectonically active with the evidence suggesting uplift

marine terrace development on reefless volcanic islands new insights from high resolution marine geophysical data offshore santa maria island azores archipelago abstract submerged marine terraces are relict coastal erosional landforms now underwater due to rising sea level and or land subsidence using as case study the shelf around santa maria island north atlantic ocean we intend to advance our knowledge on the formation and preservation of these features on reefless volcanic islands santa maria is an ideal place to study their combined generation since it displays a sequence of subaerial and submerged marine terraces the latter not studied before distributed between 7 230 m in elevation and 40 140 m in depth respectively based on some geological constraints we investigated a possible correlation between the formation of the different terraces with known sea level changes our results suggest that the spatial distribution of marine terraces at santa maria depends on the complex interplay between glacio eustatic sea level fluctuations the island s vertical motion trends the morphology of the shelf and the intensity of marine erosion subaerial terraces probably developed from 3 5 ma to 1 ma following a fortuitous conjugation of optimal exposure to energetic waves and a suitable arrangement lithology of the stratigraphic units promoting easier erosion their preservation was likely promoted by the uplift trend the island experienced in the last 3 5 ma which was rapid enough to prevent their destruction by subsequent highstands the submerged terraces presumably all younger than 1 ma were largely influenced by shelf gradient leading to more developed and preserved terraces in wider and low gradient sectors displacement by active faults also conditioned the formation and further development of both subaerial and submerged terraces with tectonic activity documented for the 0 693 ma 2 7 ma period

morphological expression of bedforms formed by supercritical sediment density flows on four fjord lake deltas of the south eastern canadian shield eastern canada high resolution swath bathymetry data collected in fjord lakes pentecote walker and pasteur eastern quebec canada allowed imaging in great detail the deltas of four rivers in order to understand the factors controlling the formation and downslope evolution of bedforms present on their slopes the morphometry and morphology of 199 bedforms reflect the behaviour of sediment density flows the shape of the bedforms mostly crescentic and the relationships between their morphological properties indicate that they were formed by supercritical density flows and that they are cyclic steps the crescentic shape suggests an upslope migration while the aspect ratios and increasing wavelengths with distance from the shore and decreasing slopes are compatible with a cyclic step origin at the rollover point the acceleration of the density flows on steep slopes produces tightly spaced hydraulic jumps and favours short wavelength and symmetrical bedforms further downslope decreasing slopes and increasing specific discharge increase the wavelength and asymmetry of the bedforms the wavelength and asymmetry are increased because density flows require longer distances to become supercritical again on lower slopes after each successive hydraulic jump bedform morphometry and morphology are used to reconstruct density flow behaviour downslope froude numbers are high near the rollover point and gradually decrease downslope as the slope becomes gentler conversely the specific discharge and flow depth are low near the rollover point and gradually increase downslope as the flow either erodes sediments or becomes more dilute due to sediment deposition and water entrainment the supercritical density flows are believed to be triggered mainly by hyperpycnal flows but some evidence of delta front slope failures is also observed the differences in delta morphology and bedform development between the four deltas are linked to basin morphology and watershed hydrology but also mainly to the fjord heritage of the lakes that allowed the focusing of sediment at the delta front

the northeast pacific ocean response to the 1982 1983 el nino the ocean s response to atmospheric forcing and to forcing along the coast by kelvin waves is examined in light of nearshore seasonal variability and the major 1982 1983 el nino in addition to driving the northeast pacific gyre and local currents the wind modifies the depth to the main thermocline changing the apparent westward phase speed of rossby waves excited by passing kelvin waves the amplitude of the passing kelvin wave determines whether the rossby wave depresses or raises the thermocline while propagating westward along the northeast pacific coast from oregon to washington model results suggest that the wind raises the main thermocline during the 1982 1983 el nino generally the coastal response off oregon and washington appears to be strongly driven by the large scale atmosphere while along the california coast and south to the equator the dominant el nino signal has an oceanic origin that signal with periods between 2 and 5 years originates in the western equatorial pacific ocean and is tracked eastward through the equatorial waveguide and then poleward along the coast to 50 n using data from two reduced gravity primitive equation models coupled at 18 n at shorter seasonal time scales the acceleration of the wind appears to be an important mechanism in driving coastal currents

the emergence of volcanic oceanic islands on a slow moving plate the example of madeira island ne atlantic the transition from seamount to oceanic island typically involves surtseyan volcanism however the geological record at many islands in the ne atlantic all located within the slow moving nubian plate does not exhibit evidence for an emergent surtseyan phase but rather an erosive unconformity between the submarine basement and the overlying subaerial shield sequences this suggests that the transition between seamount and island may frequently occur by a relative fall of sea level through uplift eustatic changes or a combination of both and may not involve summit volcanism in this study we explore the consequences for island evolutionary models using madeira island portugal as a case study we have examined the geologic record at madeira using a combination of detailed fieldwork biostratigraphy and 40ar 39ar geochronology in order to document the mode timing and duration of edifice emergence above sea level our study confirms that madeira s subaerial shield volcano was built upon the eroded remains of an uplifted seamount with shallow marine sediments found between the two eruptive sequences and presently located at 320 430 m above sea level this study reveals that madeira emerged around 7 0 5 6 ma essentially through an uplift process and before volcanic activity resumed to form the subaerial shield volcano basal intrusions are a likely uplift mechanism and their emplacement is possibly enhanced by the slow motion of the nubian plate relative to the source of partial melting alternating uplift and subsidence episodes suggest that island edifice growth may be governed by competing dominantly volcanic and dominantly intrusive processes

onset of the persistent activity at stromboli volcano italy stromboli known worldwide as the lighthouse of the mediterranean is commonly believed to have been in a state of persistent activity for the past 2000 2500 years however historical sources older than 1000 a d are not accurate enough to assess if the activity of the volcano was exactly the same as we see at present in order to attempt to identify the onset of the present eruptive regime and assess if it has been maintained with the same characteristics through time stratigraphic and radiometric studies of the recent tephra deposits were undertaken up to 4 m deep stratigraphic trenches dug at a height of approximately 500 m on the ne flank of the volcano exposed a conformable tephra pile containing charcoal fragments one of the most interesting finds was the discovery of a 7 cm thick weathered bed rich in organic matter thin palaeosol approximately 3 m below the surface the sequence underneath the palaeosol consists of decimetre thick lapilli fallout beds alternating with ash deposits bearing small charcoals with calibrated ages of between the fourth century b c and the first century a d the sequence above the palaeosol is charcoal free and consists of coarse ash deposits with discrete centimetre thick lapilli fallout beds composed of crystal poor golden pumice and subordinate crystal rich black scoriae similar to scoria pumice pairs emitted during the more energetic explosions of the present day activity the data collected indicate that between the third and seventh centuries a d after a period of quiescence the activity resumed with an eruptive style identical to the present one we conclude that the lighthouse of the mediterranean actually began its activity in a period much later than previously thought

long period transport changes in the eastern north atlantic and their simulation by propagating waves an analysis is presented of geostrophic volume transport across a zonal line along 28 degrees n in the eastern atlantic the data are from an array of five moorings with 200 km spacing carrying temperature sensors and one current meter each for 1 or 2 years transport changes in the main thermocline relative to a fixed depth level are obtained by the use of temperature salinity relationships the transport variability is simulated by two propagating waves with first order baroclinic mode structure solutions exist with annual and semi annual periods and zonal wavelengths of 100 200 km and 300 km respectively assuming quasi geostrophic dynamics and using results on the reynolds stress the dominating waves of annual and semi annual period are found to propagate to the southwest with 45 degrees 60 degrees and 25 degrees to the south off the westward direction respectively wave solutions with a 90 day period and a zonal wavelength of about 300 km are interpreted as an effect of barotropic waves arising due to horizontal temperature inhomogeneity the propagation is about 25 degrees off the westward direction in general good approximations are obtained with the propagating wave simulations in the western and central part of the array while large differences occur between observation and simulation close to the canary archipelago possible causes for these differences are discussed

mean temperature salinity salinity depth and temperature depth curves for the north atlantic and the north pacific abstract all available hydrographic data are used to compute average temperature salinity salinity depth and temperature depth curves for 5 squares in the north atlantic and north pacific 10 s to 60 n both objective and subjective methods are used to filter out obviously erroneous data summary maps of all 5 square mean curves and their corresponding standard deviations are used to select regions of spatial homogeneity over which the curves are averaged scatter diagrams of each parameter pair are used to identify 5 squares containing a variety of water masses the area average curves and their standard deviations are presented individually along with tables of the parameter values these curves in conjunction with the 5 square summary maps provide a comprehensive picture of the distributions of these properties in the upper and mid depth portions of these oceans this well resolved picture of the water mass structure both confirms and adds new insights into the traditional concepts of these property distributions the application of the mean temperature salinity and salinity depth curves to the inference of salinity from observed temperature profiles is examined shallow 0 500 db dynamic heights calculated from observations of temperature and salinity true dynamic height are compared with dynamic heights computed from observed temperature profiles and salinities inferred from the mean property curves maps of the rms differences between true and inferred dynamic heights by 5 square reveal those areas where salinities inferred from either temperature salinity or salinity depth curves yield reliable dynamic heights

a 25 000 year record of earthquakes on the owens valley fault near lone pine california implications for recurrence intervals slip rates and segmentation models seven trenches in eastern california across the owens valley fault near lone pine expose two episodes of faulting since early holocene time in the form of 1 m throw in lacustrine beds with liquefaction that were buried and then faulted again 1 m by the m 7 5 to 7 75 a d 1872 owens valley earthquake geomorphic maps applications of sequence stratigraphy and analyses of radiocarbon from charcoal and tufa deposits indicate that the paleoearthquake the penultimate event here occurred between 10 200 200 and 8800 200 cal yr b p the cumulative vertical displacement from these last two earthquakes in three trenches averages 2 4 0 3 m 2 and the penultimate event has slightly larger displacements a synthesis of available data indicates that the antepenultimate event was probably as large and occurred between ca 24 000 and 14 000 cal yr b p 2 thus the two interseismic intervals between the last three surface faulting earthquakes on the southern owens valley fault are each 10 000 yr this 25 000 year record indicates that the two event normal oblique slip rate on the owens valley fault near lone pine is 1 0 0 5 m k y this result is similar to that of several previous geological studies here yet it is still slower than slip rates on the northern owens valley fault and several factors slower than contemporary geodetic measurements this study attempts to account for different dating methods and interpretational uncertainties to acknowledge how little is known about the slip history of the owens valley fault and adjacent faults and to consider the role of segmentation as well as splay and distributed faulting in comparisons of displacement data among different sites along the entire 100 10 km length of the owens valley fault

traveling wave like mesoscale perturbations in the north pacific current abstract individual seasonal mean maps of temperature at 300 m in the north pacific current cast of 180 from 1976 to 1980 were constructed from transpac xbt data the long term annual mean map is relatively smooth with some weak quasi stationary meander activity most of the total variance was due to large scale interannual variability i e 60 loss to the mesoscale perturbations i e 30 and least to the annual cycle i e 10 however individual mesoscale perturbations were significant clearly wave like with a wavelength scale of 500 1000 km and a period scale of 1 2 years and generally coherent in phase over 10 of latitude these wave like mesoscale perturbations emanated from the eastern boundary and propagated westward as coherent features at the phase speed of linear non dispersive baroclinic long waves the latitudinal reduction in phase speed from 2 7 cm s 1 at 35 n to 1 4 cm s 1 at 45 n was consistent with baroclinic long wave theory an increase in time scale of these wave l

turbidity current sediment waves on irregular slopes observations from the orinoco sediment wave field abstract the orinoco sediment wave field covers an area of at least 29 000 km2 on the southern margin of the orinoco valley at a water depth of 4400 4825 m wave dimensions are highly variable across the wave field with wavelengths of 110 2600 m and wave heights of 1 15 m slope gradients are also very variable with values of 0 14 0 48 overall the sedimentary sequence on the upslope wave flanks is about 40 thicker than that on the downslope flanks leading to upslope wave migration in the manner of antidunes in addition reflectors on the upslope flanks generally display higher reflectivity than those on the downslope flanks suggesting that a higher proportion of coarser sediment occurs on the upslope flank an unconfined turbidity current origin is proposed for the orinoco sediment waves based upon detailed analysis of regional stratigraphic seismic facies and sediment wave distribution morphology and dimensions sediment waves are not related to flows passing along or spilling out of the orinoco valley or to bottom currents flowing parallel to the slope turbidity currents responsible for wave generation are interpreted as originating from slope failures on the adjacent venezuela guyana and suriname continental margins simple numerical modelling has enabled turbidity current flow characteristics across the orinoco sediment waves to be estimated internal froude number 0 7 1 1 flow thickness 24 645 m and flow velocity 31 82 cm s 1 a key finding of this study is that there appears to be a close relationship between the changes in slope gradient and those in wave dimensions across the wave field the irregular gradient of the present day wave field is partly a reflection of the irregular bounding surface of the sediment waves which is represented by mass flow deposits and associated mud diapirs the changes in slope gradient along this lower boundary lead to variations in the flow thickness and flow velocity of passing turbidity currents which in turn control the wave dimensions generally on lower gradients beyond minor breaks of slope flow thickness increases and flow velocity decreases leading to an increase in wavelength and a decrease in height

growth and mass wasting of volcanic centers in the northern south sandwich arc south atlantic revealed by new multibeam mapping new multibeam swath bathymetric sonar data acquired using an em120 system on the rrs james clark ross supplemented by sub bottom profiling reveals the underwater morphology of a not vert similar 12 000 km2 area in the northern part of the mainly submarine south sandwich volcanic arc the new data extend between 55 45 s and 57 20 s and include protector shoal and the areas around zavodovski visokoi and the candlemas islands groups each of these areas is a discrete volcanic center the entirely submarine protector shoal area close to the northern limit of the arc forms a 55 km long east west trending seamount chain that is at least partly of silicic composition the seamounts are comparable to small subaerial stratovolcanoes in size with volumes up to 83 km3 indicating that they are the product of multiple eruptions over extended periods zavodovski visokoi and the candlemas island group are the summits of three 3 3 5 km high volcanic edifices the bathymetric data show evidence for relationships between constructional volcanic features including migrating volcanic centers structurally controlled constructional ridges satellite lava flows and domes and mass wasting of the edifices mass wasting takes place mainly by strong erosion at sea level and dispersal of this material along chutes probably as turbidity currents and other mass flows that deposit in extensive sediment wave fields large scale mass wasting structures include movement of unconsolidated debris in slides slumps and debris avalanches volcanism is migrating westward relative to the underlying plate and major volcanoes are asymmetrical being steep with abundant recent volcanism on their western flanks and gently sloping with extinct eroded volcanic sequences to their east this is consistent with the calculated rate of subduction erosion of the fore arc

currents fronts and eddy fluxes in the canary basin hydrographic data from two cruises in the canary basin meteor 57 july 1981 poseidon 86 april 1982 are analysed with respect to current distribution and lateral heat flux in the azores madeira region the first part of the data base consists of long transects of xbt and g e k measurements between cape finisterre north west spain and the northern canary basin where several year long current meter records exist further information is obtained by thermosalinograph surface data and by expendable current profilers xcp geostrophic currents are derived from xbt profiles using the tight temperature salinity relationship in the depth range of the warmwassersphare the results compare well with the g e k and xcp current observations the second part consists of ctd data from an eddy resolving box shaped ctd survey 500 500 km2 centered at the mooring location 33 n 22 w the observations are supplemented by satellite buoy trajectories horizontal parameter distribution is shown in terms of objectively contoured maps bands of spatially enhanced energetic structures seen in the long transects are further resolved by the box survey as a deep jet like current system cross the canary basin in a west east direction associated with this azores current is a frontal zone with near surface temperature and salinity steps of order 2 k and 0 3 practical salinity units the dynamic topography field can be decomposed into a linear background field a rossby wave and a mesoscale eddy field we find that major contributions to the meridional eddy heat flux are confined to the vicinity of the azores current frontal zone it is shown that the principal balance in the temperature equation is between heating by the mean horizontal advection terms and cooling by the eddy flux divergence

a numerical model study of the effects of interannual time scale wave propagation on the predictability of the atlantic meridional overturning circulation we investigate processes leading to uncertainty in forecasts of the atlantic meridional overturning circulation amoc a climate model is used to supply initial conditions for ensemble simulations in which members initially have identical ocean states but perturbed atmosphere states baroclinic transports diverge on interannual timescales even though the ocean is not eddy permitting interannual fluctuations of the model amoc in the subtropical gyre are caused by westward propagating rossby waves divergence of the predicted amoc with time occurs because the waves develop different phases in different ensemble members predominantly due to differences in eastern boundary windstress curl these windstress fluctuations communicate with interior ocean transports via modifications to the vertical velocity and the vortex stretching term dw dz consequently errors propagate westwards resulting in longer predictability times in the interior ocean compared with the eastern boundary another source of divergence is transport anomalies propagating along the gulf stream and other boundary currents the propagation mechanism seems to be predominantly advection by mean currents and we show that the arrival of westward propagating waves can trigger development of these anomalies the mean state of the amoc has a small effect on interannual predictability in the subtropical gyre most likely because eastern boundary windstress curl predictability is not strongly dependent on the state of the amoc in the subtropics eastern boundary windstress curl was more predictable at 45 degree sign n when the amoc was in a strongly decreasing state but unlike at 30 degree sign n no mechanism was found linking windstress curl fluctuations with deep transports

earlier history of the 70 ma old canary hotspot based on the temporal and geochemical evolution of the selvagen archipelago and neighboring seamounts in the eastern north atlantic major element trace element and sr nd pb isotope data combined with 40ar 39ar age determinations of volcanic rocks from the selvagen islands and neighboring seamounts in the eastern north atlantic reveal the earlier history of the 70 ma old canary hotspot a basanitic to phonolitic late shield stage intrusive complex 29 ma is exposed on selvagem pequena the evolution of selvagem grande can be divided into three magmatic phases a tephritic to phonolitic late shield stage intrusive complex 24 26 ma and two rejuvenated or post erosional stages 8 12 and 3 4 ma consisting of alkali basalt basanite and rare phonolite during the early to mid miocene volcanic hiatus 12 24 ma the top of the volcano was beneath sea level as evidenced by marine carbonate sediments 13 24 ma dated through correlation of 87sr 86sr with the seawater sr isotope curve the geochemistry of the shield stage lavas indicates that they derive from plume sources whereas the post erosional lavas are derived from metasomatized lithospheric sources five sampled seamounts to the east and northeast of the islands range in composition from alkali basalt and basanite to phonolite samples from dacia conception bank and lars were dated at 9 17 and 68 ma respectively geochemical data suggest that the dredged samples come from the post erosional stage of volcanism and therefore the dates represent minimum ages for the seamount volcanoes the elevation of erosional platforms formed at wave base decrease from selvagen grande 100 m above sea level to lars seamount 900 m below sea level suggesting a southwest to northwest age progression and that all of these seamounts are older than the selvagen islands trace element and sr nd pb isotopic composition of the selvagen islands and neighboring seamounts are consistent with their origin from the canary plume interaction of the weak canary mantle plume with a slow moving plate appears to be responsible for generating a 450 km wide irregular hotspot track extending 800 km from the youngest canary island of hierro in the southwest to lars seamount in the northeast

the stromboli 2002 tsunamigenic submarine slide characteristics and possible failure mechanisms 1 on 30 december 2002 a major instability event deeply involving the submarine slope occurred on the sciara del fuoco on the western flank of stromboli volcano in the aeolian islands tsunami waves with a maximum runup of over 10 m in stromboli were generated having a measurable impact as far as the sicily coast just 10 months before the event a multibeam bathymetry had been collected in the area down to 1000 m of depth a repetition of the survey after the slide allowed the unique opportunity to verify the occurrence of a large submarine slide and to define volumes involved and morphology generated by the event through the comparison of the preevent and postevent bathymetric grids a morphological characterization of the slope before and after the submarine landslide is presented showing how the preexisting features interacted with the slide event in controlling the instability mechanisms of the submarine failure are discussed on the basis of the geometrical characters of the landslide event structural and stratigraphic setting of the submerged slope and geotechnical considerations on the behavior of slope material

preconditioning and triggering of offshore slope failures and turbidity currents revealed by most detailed monitoring yet at a fjord head delta rivers and turbidity currents are the two most important sediment transport processes by volume on earth various hypotheses have been proposed for triggering of turbidity currents offshore from river mouths including direct plunging of river discharge delta mouth bar flushing or slope failure caused by low tides and gas expansion earthquakes and rapid sedimentation during 2011 106 turbidity currents were monitored at squamish delta british columbia this enables statistical analysis of timing frequency and triggers the largest peaks in river discharge did not create hyperpycnal flows instead delayed delta lip failures occurred 8 11 h after flood peaks due to cumulative delta top sedimentation and tidally induced pore pressure changes elevated river discharge is thus a significant control on the timing and rate of turbidity currents but not directly due to plunging river water elevated river discharge and focusing of river discharge at low tides cause increased sediment transport across the delta lip which is the most significant of all controls on flow timing in this setting

categorizing the morphologic variability of siliciclastic passive continental margins the basic morphology of the continental shelf slope and rise on passive continental margins has many variations in the modern ocean environment through using a satellite derived bathymetric data set of the global ocean we have developed a classification for the shape of modern siliciclastic dominated passive margins the classification subdivides 50 margins into five distinct shape categories based on each margin s pattern of sea floor slopes as a function of depth by comparing these shape categories with the underlying stratal architecture sediment input and present degree of canyon incision of the margins we find apparent correlations between these factors and basic margin shape in general gently sloped margins tend to occur in regions with high sediment input few modern canyons and unstable substrates higher gradient margins tend to have lower sediment input more modern canyons and a variety of subsurface architectures these results suggest two important conclusions 1 morphology differences among modern siliciclastic passive margins can be objectively and systematically categorized and 2 these shape differences seem to be related to aspects of the modern sedimentary environment despite the fact that the margins have evolved over geologic time

the morphology of insular shelves as a key for understanding the geological evolution of volcanic islands insights from terceira island azores shelves from volcanic ocean islands result from the competition between two main processes wave erosion that forms and enlarges them and volcanic progradation that reduces their dimension in places where erosion dominates over volcanism shelf width can be used as a proxy for the relative age of the subaerial volcanic edifices and reconstruction of their extents prior to erosion can be achieved in this study new multibeam bathymetry and high resolution seismic reflection profiles are exploited to characterize the morphology of the insular shelves adjacent to each volcanic edifice of terceira island in order to improve the understanding of its evolution subaerial morphological and geological stratigraphic data were also used to establish the connection between the onshore and offshore evolution shelf width contiguous to each main volcanic edifice is consistent with the known subaerial geological history of the island most of the older edifices have wider shelves than younger ones the shelf edge proved to be a very useful indicator in revealing the original extent of each volcanic edifice in plan view its depth was also used to reconstruct vertical movements showing that older edifices like serra do cume ribeirinha guilherme moniz and pico alto have subsided while more recent ones have not the morphology of the shelf namely the absence presence of fresh lava flow morphologies and several types of erosional depositional and tectonic features integrated with the analysis of the coastline morphology allowed us to better constrain previous geological interpretations of the island evolution

volcano collapse and tsunami generation in the bismarck volcanic arc papua new guinea during a cruise on the r v kilo moana in 2004 we mapped 12 debris avalanches from volcanoes in the bismarck volcanic arc estimated their sizes and computed the size of potential tsunami run up in major local population centers from these features we used the towed side scan instrument hawaii mr1 the hull mounted em120 system for swath bathymetry and backscatter intensity a shallow penetration chirp system several bottom camera tows and selected cores we calibrate our computations with the known tsunami run up of the ritter collapse even the small collapses may have had significant run up on near by coastlines had any of the collapses we have identified occurred in modern times each would affect a presently populated region of the coastline to a moderate or significant degree

lateral collapses and active sedimentary processes on the northwestern flank of stromboli volcano italy abstract the marine volcaniclastic system extending to 3 km water depth on the northwest flank of stromboli volcano has been surveyed using seismo acoustic profiling multibeam bathymetry deep towed long range side scan sonar imaging and box core sampling deposits and sea floor topography record repeated flank collapses that have occurred during the last 13 ka and created the present sciara del fuoco scar an extensive 170 km2 debris avalanche deposit characterized by subdued hummocks megablocks is buried by turbidites formed from gravity currents that originated in sciara del fuoco the currents were mainly deflected along the margin of the avalanche deposit but also spilt over onto it the turbidites reflect topographic flow stripping and their thinning towards slightly steeper slopes indicates that some material that settled there drained further downslope as secondary higher concentration flows the estimated volume of the entire fan shaped bulge amounts to 12 2 5 km3 about 3 5 km3 of which is attributed to the post collapse sedimentation the remaining 8 5 2 5 km3 is in the order of the volume computed for the material removed by the multiple sector collapses that affected the nw stromboli flank two units are identified in the distal part of the bulge through the recognition of their fronts and these indicate a layered structure for successive debris avalanche deposits granulometric and particle type characterization of seabed samples shows clast population evolution with sedimentary transport distance from the main entrance point of debris in sciara del fuoco to the confluence with the stromboli canyon and into the marsili basin some 45 km from the island changes in particle populations are due to selective sedimentation and also mixing with a wide range of terrigenous detritus brought by currents that descended the main stromboli canyon from the continental shelf abundant fine sand and silt is produced at the volcano and occurrence of mainly coarse grained material along the channel to the marsili basin indicates that a considerable volume of volcaniclastic material from stromboli lies in the sedimentary succession accumulating on the distal basin floor where a deep sea fan is growing

different origins of seafloor undulations in a submarine canyon system northern south china sea based on their seismic character and relative location abstract high resolution 2d and 3d seismic data are used to investigate the morphology internal architecture and origin of widespread seafloor undulations in the eastern area of a submarine canyon system northern south china sea the seafloor undulations reveal similar seafloor morphologies and three different types types a b and c can be classified based on their relative locations and internal seismic characters types a and b are observed in the canyon areas whereas type c occurs in the canyon heads seismic reflections within types a and c are continuous and have an upslope migrating trend while type b seafloor undulations are separated by listric faults our analysis reveals the origins of these three different types of seafloor undulations type a seafloor undulations are sediment waves formed by turbidity currents flowing through the submarine canyons gravity driven submarine creep resulted in the formation of type b seafloor undulations type c undulations are sediment waves generated by internal waves interacting with the continental slope our results provide information about the origin of widespread seafloor undulations in other submarine canyon systems it is also of great significance to future risk assessments as the study area now is one of the most active regions for hydrocarbon exploration in se asia

generation and migration of coarse grained sediment waves in turbidity current channels and channel lobe transition zones large scale sediment waves composed of gravels and sands have been studied using deep water sidescan systems new data are presented from submarine channels off the canary islands and from canyon mouths off portugal data from other areas are briefly reviewed including a re interpretation of data from laurentian fan in order to summarise the varied morphology and setting of these bedforms coarse grained sediment waves are found in the proximal dominantly bypassing areas of deep water turbidite systems within canyons channels and channel lobe transition zones wave heights are in the region of 1 10 m and wavelengths are up to several hundred metres the distribution of waves and sparse sedimentological evidence from modern and ancient sediment wave fields suggests that initial transport and deposition of coarse sediment occurs within a high density turbidity current and not as a non newtonian debris flow in some cases the development of pronounced wave asymmetry and evidence of wave disruption and reworking suggests that the wave morphology is at least partially controlled by a later phase of low density turbidity flow grain size also appears to exert some control on wave morphology for example gravel rich waves have a greater height for the same wavelength than sand rich waves coarse grained sediment waves are often difficult to recognise on the seafloor because of reworking or burial by younger turbidity currents and are equally difficult to recognise in outcrop because of their large size

morphology of the faial island shelf azores the interplay between volcanic erosional depositional tectonic and mass wasting processes 1 the extents of volcanic island shelves result from surf erosion which enlarges them and volcanic progradation which reduces them however mass wasting tectonics and sediment deposition also contribute to their morphology in order to assess the relative significance of these various processes we have mapped in detail faial island s shelf in the azores archipelago based on interpretation of geophysical and geological data the nearshore substrates of the island down to 30 50 m depth are rocky and covered by volcaniclastic boulder deposits formed by surf action on now submerged lava flows below those depths sandy and gravel volcaniclastic beds dominate building clinoforms up to the shelf edge in some sectors of the coast prograding lava has narrowed the shelf but in contrast to nearby pico island we find fewer submarine emplaced lavas on the shelf in this island we interpret the distance between the coastline and the shelf edge as almost entirely a result of a straightforward competition between surf erosion and lava progradation in which erosion dominates therefore shelf width can be used as a proxy for coastline age as well as for wave energy exposure the stratigraphy of shelf deposits in boomer seismic data is examined in detail to assess the roles of different sediment sources accommodation space and wave exposure in creating these deposits we also show evidence of mass wasting at the shelf edge and discuss the possible origins of slope instability finally we discuss the contributing role of tectonics for the development of the shelf

upslope migrating bedforms in a proglacial sandur delta cyclic steps from river derived underflows abstract backstepping cross strata on steep foresets of a gilbert type proglacial fluviodeltaic system are ascribed to cyclic steps and other associated supercritical bedforms they provide insight into how sandur river flows transition into the marine realm these sedimentary structures are located on steep foresets up to 17 with corresponding top lying flat based topsets in an upper pleistocene delta on the north shore of the gulf of st lawrence quebec canada packages of backstepping cross strata of sand and gravel lying in the lower part of the delta front outcrop are organized in 10 20 m spaced pseudo foresets with a mean slope of 11 12 seawards backstepping strata include frequent internal erosion surfaces that onlap upslope on pseudo foresets and are interpreted as cyclic steps narrow deep and asymmetrical scours and upslope climbing cross beds are interpreted as chutes and pools and antidunes respectively very shallow 15 m depositional paleo bathymetry is inferred from the preservation of the delta brink the well organized stratal pattern in cyclic step to antidune deposits indicates relatively steady and uniform flow patterns there is insufficient distance for a headscarp large enough to transform to the volume of observed accreted sands or for a flow transformation from a gravitational collapse to net depositional cyclic steps these deposits are sandier than the topsets beds and are thus not derived from them but rather correspond to topset erosional surfaces the development of cyclic steps from hyperpycnal flows was likely enhanced by tidal drawdown processes the resulting sediment laden supercritical flows plunged inertially and evolved into an underflow that generated the cyclic steps on the upper foresets the cyclic steps have a high aspect ratio and represent an end member of coarse grained sediment deposited on steep slopes in contrast to low gradient low aspect ratio muddy deposits

the volcanic environment for 40 000 years of human occupation on the willaumez isthmus west new britain papua new guinea abstract the stratigraphic sequence of 22 tephra beds and their associated paleosols at two sites selected from our studies in west new britain papua new guinea provide the essential environmental background for understanding human responses to c 40 ka years of volcanic activity lithology grain size and mineralogy of the tephras interpreted for the first time elucidate the varying volcanic provenance especially of the pleistocene beds and the environmental conditions which former inhabitants experienced this sequence provides an important long term record of how humans coped with volcanic adversity in papua new guinea the stratigraphic record contains abundant evidence for human settlement during the intervals between volcanic eruptions following plinian and subplinian eruptions people abandoned the region for significant periods of time in some cases these cataclysmic events caused major cultural disasters characterised by local population extinction and loss of some significant types of cultural behaviour despite the punctuated record of settlement and changes in material culture over the long term human populations found effective ways to maintain themselves within an active volcanic environment key responses included persistence of mobile and flexible settlement patterns planned and staged uses of raw materials social exchange and increasing levels of landscape management

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

seasonal variability of the canary current a numerical study 1 a high resolution numerical model study of the canary basin in the northeast subtropical atlantic ocean is presented a long term climatological solution from the regional oceanic modeling system roms reveals mesoscale variability associated with the azores and canary current systems the northwest african coastal upwelling and the canary island archipelago the primary result concerns the canary current canc which in the solution transports 3 sv southward in line with observations the simulated canc has a well defined path with pronounced seasonal variability this variability is shown to be mediated by the westward passage of two large annually excited counterrotating anomalous structures that originate at the african coast the anomalies have a sea surface expression permitting their validation using altimetry and travel at the phase speed of baroclinic planetary rossby waves the role of nearshore wind stress curl variability as a generating mechanism for the anomalies is confirmed through a sensitivity experiment forced by low resolution winds the resulting circulation is weak in comparison to the base run but the propagating anomalies are still discernible so we cannot discount a further role in their generation being played by annual reversals of the large scale boundary flow that are known to occur along the african margin an additional sensitivity experiment where the azores current is removed by closing the strait of gibraltar presents the same anomalies and canc behavior as the base run suggesting that the canc is rather insensitive to upstream variability from the azores current

large scale seafloor waveforms on the flanks of insular volcanoes aeolian archipelago italy with inferences about their origin abstract high resolution multibeam data in the central and eastern part of the aeolian volcanic arc southern tyrrhenian sea reveal widespread large scale waveforms on the submarine flanks of these insular volcanoes these features show high variability in wave parameters wavelength of 60 1600 m and wave height of 4 200 m and morphology from sinuous to arcuate in plan view and from undulating to stepped with very steep scarps in cross section indicating that different processes at variable spatial and temporal scale are responsible for their genesis by relating the morphological characters of the different waveforms and the local boundary conditions morphological setting regional slope gradients sediment source and dynamics where these features form we were able to distinguish bedforms formed by sedimentary gravity flows from bedform like features due to gravity instability processes in detail bedforms have been interpreted as coarse grained sediment waves according to their wave parameters geometry and texture bedforms are always found where the slope gradients markedly decrease to values

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

development of volcanic insular shelves insights from observations and modelling of faial island in the azores archipelago a variety of geological processes contribute to the development of volcanic island shelves although their relative importance remains unclear we have mapped the morphology of faial island s shelf in the azores from geophysical multibeam sonar chirp and boomer seismic reflection and geological data sediment sampling a wave erosional model and a eustatic record of glacially induced oscillations of sea level which modulated the elevation at which the waves operated through time was used to determine the contribution of mechanical wave erosion to shelf development wave regimes varied according to the orientation of the coast the model was run for 10 to 800 ka depending on the age of the various coastal sectors based on published radiometric data the modelling replicated the shape of the island s shelf reasonably well supporting the contention that it developed primarily through mechanical wave erosion operating in an intertidal zone that migrated landwards and seawards with changes in the level of the sea disparities between modelled and actual shelf morphologies may reflect varied geological resistance to erosion errors in the radiometric dates more recent unrecognised volcanic deposits sediment deposition and tectonic vertical movements there were some variation in rates of shelf development over different time scales but over the long term the relationship between shelf age and width was essentially linear the depth of the shelf break in some areas suggests that there have been differential vertical movements of the land around the island probably related to local faults the poor development or absence of terraces on the shelf may be attributed either to recent volcanic progradation or to sediment infilling of the space created by earlier erosion however poorly developed terraces on the southern shelf of faial are similar to those predicted by the model given appropriate adjustments for vertical movements of the land

a structural outline of the yenkahe volcanic resurgent dome tanna island vanuatu arc south pacific abstract a structural study has been conducted on the resurgent yenkahe dome 5 km long by 3 km wide located in the heart of the siwi caldera of tanna island vanuatu arc south pacific this spectacular resurgent dome hosts a small caldera and a very active strombolian cinder cone the yasur volcano in the west and exhibits an intriguing graben in its central part detailed mapping and structural observations make it possible to unravel the volcano tectonic history of the dome it is shown that following the early formation of a resurgent dome in the west a complex collapse caldera plus graben occurred and this was associated with the recent uplift of the eastern part of the present dome eastward migration of the underlying magma related to regional tectonics is proposed to explain this evolution

morpho bathymetric and seismo stratigraphic analysis of the insular shelf of salina aeolian archipelago to unveil its late quaternary geological evolution abstract the distribution and morphological characteristics of the shelves around salina island have been analyzed and integrated with observations from onshore geological field studies in order to improve knowledge about its evolution and to demonstrate how shelf width depth can be used as proxies for reconstructing the development of the volcanic edifice insular shelves form essentially through marine erosion of volcanic centres during stages of reduced or inactive volcanism and are representative of their original extension shelves having larger widths commonly 1000 m and deeper edges over 125 m depth experienced wave erosion during successive cycles of sea level fluctuations and subsidence after their formation thus being indicative of a relatively older age of the eroded volcanic centres accordingly we document offshore salina the occurrence of presently submerged and largely dismantled volcanic centres namely pizzo capo north and fossa delle felci south predating the oldest subaerial products exposed on the adjacent coastal sectors these offshore centres have subsided after their erosion and are no more documented on land furthermore the finding of the largest and deepest shelf around the subaerial remnants of pizzo di corvo volcanic edifice allows relating it to an earlier stage of evolution of salina shedding light on contradictory radiometric ages on land narrower shelves commonly on the whole our results show the importance of integrated field and marine studies to unravel the geological evolution of insular volcanoes and to obtain inferences on their vertical mobility

gravitational erosional and depositional processes on volcanic ocean islands insights from the submarine morphology of madeira archipelago abstract the submarine flanks of volcanic ocean islands are shaped by a variety of physical processes whilst volcanic constructional processes are relatively well understood the gravitational erosional and depositional processes that lead to the establishment of large submarine tributary systems are still poorly comprehended until recently few studies have offered a comprehensive source to sink approach linking subaerial morphology with near shore shelf slope and far field abyssal features in particular few studies have addressed how different aspects of the subaerial part of the system island height climate volcanic activity wave regime etc may influence submarine flank morphologies we use multibeam bathymetric and backscatter mosaics of an entire archipelago madeira to investigate the development of their submarine flanks crucially this dataset extends from the nearshore to the deep sea allowing a solid correlation between submarine morphologies with the physical and geological setting of the islands in this study we also established a comparison with other island settings which allowed us to further explore the wider implications of the observations the submarine flanks of the madeira archipelago are deeply dissected by large landslides most of which also affected the subaerial edifices below the shelf break landslide chutes extend downslope forming poorly defined depositional lobes around the islands a large tributary system composed of gullies and channels has formed where no significant rocky ridge outcrops are present in madeira island these were likely generated by turbidity currents that originated as hyperpycnal flows whilst on porto santo and desertas their origin is attributed to storm induced offshore sediment transport at the lower part of the flanks 3000 to 4300 m where seafloor gradients decrease to 0 5 3 several scour and sediment wave fields are present with the former normally occurring upslope of the latter sediment waves are often associated with the depositional lobes of the landslides but also occur offshore poorly developed tributary systems sediment wave fields and scours are mostly absent in areas where the tributary systems are well developed and or are dominated by rocky outcrops this suggests that scours and sediment wave fields are probably generated by turbidity currents which experience hydraulic jumps where seafloor gradients are significantly reduced and where the currents become unconfined the largest scours were found in areas without upslope channel systems and where wave fields are absent and are also interpreted to have formed from unconfined turbidity currents our observations show that tributary systems are better developed in taller and rainy islands such as madeira on low lying and dry islands such as porto santo and desertas tributary systems are poorly developed with unconfined turbidite currents favouring the development of scours and sediment wave fields these observations provide a more comprehensive understanding of which factors control the gravitational erosional and depositional features shaping the submarine flanks of volcanic ocean islands

how to recognize crescentic bedforms formed by supercritical turbidity currents in the geologic record insights from active submarine channels submarine channels have been important throughout geologic time for feeding globally significant volumes of sediment from land to the deep sea modern observations show that submarine channels can be sculpted by supercritical turbidity currents seafloor sediment flows that can generate upstream migrating bedforms with a crescentic planform in order to accurately interpret supercritical flows and depositional environments in the geologic record it is important to be able to recognize the depositional signature of crescentic bedforms field geologists commonly link scour fills containing massive sands to crescentic bedforms whereas models of turbidity currents produce deposits dominated by back stepping beds here we reconcile this apparent contradiction by presenting the most detailed study yet that combines direct flow observations time lapse seabed mapping and sediment cores thus providing the link from flow process to depositional product these data were collected within the proximal part of a submarine channel on the squamish delta canada we demonstrate that bedform migration initially produces back stepping beds of sand however these back stepping beds are partially eroded by further bedform migration during subsequent flows resulting in scour fills containing massive sand as a result our observations better match the depositional architecture of upstream migrating bedforms produced by fluvial models despite the fact that they formed beneath turbidity currents

on the potential energy of baroclinic rossby waves in the north pacific abstract estimates of baroclinic rossby wave potential energy spectra for various parts of the north pacific were calculated from published material containing information about this energy in many different formats definitions and units the standardized results lead to frequency spectra of potential energy ranging from 0 1 to 0 45 cpy cycles per year in 34 5 squares between 20 and 30 n to energy spectra ranging from 0 28 to 2 11 cpy in eight subsections of the great circle route from honolulu to san francisco and to a map of annual rossby wave energy between 30 and 40 n the most remarkable finding is a consistent sequence of interannual rossby wave spectra with a peak at 0 15 cpy i e at a wave period of 6 7 years covering the area 20 25 n and 175 130 w the most complete information is available for a 5 square east of the hawaiian islands there the spectrum shows besides the 0 15 cpy peak another broad peak ranging from about 0 4 to 1 4 cycles per year

generation and propagation of annual rossby waves in the north atlantic abstract results of a nonlinear quasi geostrophic mode model on the plane with topography and coastal geometry of the north atlantic in the area 10 50 n 10 80 w are presented two modes are used in this study the baroclinic one is based on the mean density profile from the levitus dated at 30 n mean and annual variations of the wind stress curl which drive the model were obtained from the bunker climatic atlas annual rossby waves emanating off the eastern coast are strongly influenced by the mid atlantic ridge west of the mar a relative minimum of energy is observed the waves are influenced and modified by variable bottom topography in the western basin two regions are identified where rossby waves are generated the gulf stream and its extension towards the east and the southern flank of the subtropical gyre compared to the north pacific annual rossby waves seem to be less energetic in the north atlantic

the evolution of craters and calderas on young seamounts insights from sea marc i and sea beam sonar surveys of a small seamount group near the axis of the east pacific rise at 10 n a northwest trending group of seamounts located just west of the east pacific rise epr axis has been mapped using high resolution sea marc i side scan sonar and sea beam multibeam bathymetry these seamounts have 9 13 km basal diameters and the shapes of the volcanos change from conical domes near the epr axis to truncated cones and larger elliptical truncated cones farther away from the rise axis the detailed resolution of constructional volcanic features on these seamounts and the progressive development of summit depressions craters to large complex calderas and summit plateaus suggest to us a succession of evolutionary stages through which seamounts grow our evolutionary scheme for constructing these volcanos calls for the development of satellite extrusive centers around the base of a growing seamount which serve to drain off magmas and precipitate summit collapse the creation of a summit depression on a seamount will structurally constrain the style of eruptive volcanism to be principally along ring fractures which localize vents around the margin of a crater or caldera the concentration and channelization of volcanic eruptions around the top of the volcano lead to a progradation of the summit area and the establishment of a summit plateau the steep sides of a seamount reflect growth of the summit area out over the upper flanks of the volcano caused by continued eruption of lavas around the margin of the caldera the steep constructional slopes are sites for vigorous mass wasting that shapes and modifies flank terrain as a seamount evolves the crestal topography is the product of many volcanic cycles characterized by filling and subsequent draining of the caldera and expansion of caldera area through progressive collapse and migration of primary magmatic conduits the final phase of volcanism may be a calderafilling episode that builds a rough conical mount over the summit plateau

the canary basin contribution to the seasonal cycle of the atlantic meridional overturning circulation at 26 n this study examines the seasonal cycle of the atlantic meridional overturning circulation amoc and its eastern boundary contributions the cycle has a magnitude of 6 sv as measured by the rapid mocha wbts project array at 26 n which is driven largely by the eastern boundary the eastern boundary variations are explored in the context of the regional circulation around the canary islands there is a 3 month lag between maximum wind forcing and the largest eastern boundary transports which is explained in terms of a model for rossby wave generated at the eastern boundary two dynamic processes take place through the lanzarote passage lp in fall the recirculation of the canary current and the northward flow of the intermediate poleward undercurrent in contrast during the remaining seasons the transport through the lp is southward due to the canary upwelling current these processes are linked to the seasonal cycle of the amoc

from seamount to oceanic island porto santo central east atlantic the uplifted and deeply eroded volcanic succession of porto santo central east atlantic is the product of a wide spectrum of dynamic processes that are active in shoaling to emergent seamounts two superimposed lapilli cones marking the base of the exposed section are interpreted as having formed from numerous submarine to subaerial phreatomagmatic explosions pyroclastic fragmentation being subordinate the lower basaltic and the upper mugearitic to trachytic sections are dominated by redeposited tephra and are called lapilli cone aprons vertical growth due to accumulation of tephra voluminous intrusions and minor pillowed lava flows produced ephemeral islands which were subsequently leveled by wave erosion as shown by conglomerate beds periods of volcanic quiescence are represented by abundant biocalcarenite lenses at several stratigraphic levels the loose tephra piles became stabilized by widespread syn volcanic intrusions such as dikes and trachytic to rhyolitic domes welding the volcanic and volcaniclastic ensemble into a solid edifice shattering of a submarine extrusive trachytic dome by pyroclastic and phreatomagmatic explosions accentuated by quench fragmentation resulted in pumice and crystal rich deposits emplaced in a prominent submarine erosional channel the dome must have produced an island as indicated by a collapse breccia comprising surf rounded boulders of dome material subaerial explosive activity is represented by scoria cones and tuff cones basaltic lava flows built a resistant cap that protected the island from wave erosion some lava flows entered the sea and formed two distinct types of lava delta 1 closely packed pillow lava and massive tabular lava flows along the southwestern coast of porto santo and 2 a steeply inclined pillow hyaloclastite breccia prism composed of foreset bedded hydroclastic breccia variably shaped pillows and thin sheet flows capped by subhorizontal submarine to subaerial lava flows along the eastern coast of porto santo the facies architectures indicate emplacement 1 on a gently sloping platform in southwestern porto santo and 2 on steep offshore slopes along high energy shorelines in eastern porto santo growth of the pillow hyaloclastite breccia prism is dominated by the formation of foreset beds but various types of syn volcanic intrusions contributed significantly submarine flank eruptions occurred in very shallow water on the flanks of the hyaloclastite prism in eastern porto santo the island became consolidated by intrusion of numerous dikes and by emplacement of prominent intrusions that penetrate the entire volcanic succession volcanic sedimentation ended with the emplacement of a debris avalanche that postdates the last subaerial volcanic activity

structureless coarse tail graded bouma ta formed by internal hydraulic jump of the turbidity current abstract turbidity currents are commonly super critical if they travel on slopes steeper than 0 001 hence upon deceleration such flows must pass a hydraulic jump it is therefore surprising that sedimentary features related to the hydraulic jump are so poorly known and not clearly related to the bouma sequence to study this missing link a stability diagram of bed forms generated by decelerating initially super critical turbidity currents is presented here to sketch the position of hydraulic jump deposits relative to super and sub critical bed forms observed in turbidites the axes of the diagram are formed by the densiometric froude number the grain size and the particle fall out rate experimental evidence shows that the hydraulic jump is hardly manifested in the deposit if turbidity currents pass the jump as a low concentration single phase suspension flow only those turbidity currents that develop two phase suspension flow with a super critical flowing traction carpet cause vigorous erosion and liquefaction of the substrate at the jump locality to produce rip up of the substrate rip up clasts and flame structures which are trapped in structureless coarse tail graded deposits characteristic of the classic bouma ta unit the location of the jump is sensitive to density velocity variations of the traction carpet and can shift rapidly up and down the slope this would explain why structureless coarse tail graded deposits such as bouma ta develop sheet like

persistent westward flow in the azores current as seen from altimetry and hydrography temporal and spatial variability of the eastward flowing jet like azores current is investigated by applying a new method for combining altimetry with hydrography in order to produce absolute surface geostrophic currents challenor et al 1996 the altimeter surface measurements contain information about both the geoid and the geostrophic ocean circulation the geoid signal dominates and is generally not sufficiently well known at the small length scales required to identify the mesoscale ocean signal in this study hydrography is used to distinguish the mean ocean signal from the geoid along an ers 1 satellite track south of the azores during both 3 day repeat phases and thereby determine cross stream absolute dynamic topography of the azores current at high temporal resolution hydrographic data collected near 28 w in march 1992 is combined with ers 1 altimeter data from january march 1992 and january to early april 1994 time series of 3 day repeat profiles of absolute surface geostrophic velocity perpendicular to the altimeter cruise track are examined the azores current absolute velocity profile along this track is rather coherent the current variability is less than the mean surprisingly a persistent westward flow of 25 cm s 1 is observed near 35 n 28 w this flow appears to be a retroflection from the main eastward flowing current an isopycnal analysis reveals the westward flow to be cooler by 0 5 c and fresher by 0 15 practical salinity units than the main body of the azores current the flow appears to persist throughout each of the above 3 month periods in late winter early spring but the question of whether this is a seasonal feature or more permanent remains open it is suggested that the westward flow is topographically controlled

volcanic tectonic and mass wasting processes offshore terceira island azores revealed by high resolution seafloor mapping terceira island in the azores archipelago lies at the intersection of four submarine volcanic ridges new high resolution bathymetric and seismic reflection data have been used to analyze the main volcanic tectonic and mass wasting features of the island offshore volcanic features such as linear volcanic centers and pointy and flat topped cones are mainly concentrated on the narrow western and north western ridges characterized by an overall rugged morphology fault scarps dominate mainly the broad eastern and south eastern ridges which are characterized by an overall smooth and terrace like morphology on the eastern ridge faults form a series of horsts and grabens related to the onshore lajes graben the strikes of the fault scarps linear volcanic centers and alignment of volcanic cones on the ridges reveal two main structural trends wnw ese and nnw sse consistent with the main tectonic structures observed on the azores plateau in contrast a large variability of strike was observed in inter ridge areas reflecting the relative importance of regional and local stresses in producing these structures mass wasting features are subordinate and mostly represented by hundred meter wide scars that indent the edge of the insular shelf surrounding the island apart from two large deeper scars identified on the southern steep flank of the western ridge finally the remarkable morpho structural differences between the western and eastern ridges are discussed in the framework of the evolution of the terceira volcanic edifice and hypothesized to reflect successive stages of ridge evolution

sources of interannual baroclinic waves in the eastern subtropical north pacific abstract subsurface temperature and surface salinity observations along the great circle transect between san francisco and honolulu are used to investigate the source of annual baroclinic long waves in the eastern subtropical north pacific ocean long term mean 15 day values 1966 74 of depth of the 9 c isotherm indicative of thermocline depth and of surface salinity are each fit by least squares method with a time varying cosine yielding phase and amplitude of the mean annual cycle at standard locations every 92 6 km 50 mi along the transect local wind stress curl is expected to influence the observed depth of the 9 c isotherm through the mechanism of ekman pumping therefore its annual cycle is computed in a manner like that of the depth of the 9 c isotherm and its effect removed from the latter the residual annual cycle has phase and amplitude profiles along the transect that closely resemble that of model annual baroclinic long waves emanating from a line source of large amplitude wind st

collision propagation in papua new guinea and the solomon sea the mountain system in papua new guinea png is growing by accretion of australian margin strata to the front of the papuan fold and thrust belt in the south and by accretion of exotic terranes along its ne margin presently the finisterre terrane is being accreted along the ne margin of png and the collision point is migrating eastward within the solomon sea east of the collision point the new britain trench marks the tectonic front between the solomon sea and south bismarck sea plates whereas to the west the tectonic front lies in the southern part of the papuan fold and thrust belt present day sedimentary environments within the western solomon sea are inferred from interpretation of seismic reflection data similar facies are observed accreted to the front of the finisterre terrane in the markham valley the frontal leron formation is largely fluvial and shallow marine and the erap complex contains elements of turbidites and pelagic deposits there appears to be a smaller volume of coarse proximal marine strata accreted to the front of the finisterre terrane than is expected from interpretation of reflection profiles in the western solomon sea this difference may be attributed to a combination of submarine erosion in the markham canyon partial incorporation of these deposits into the erap complex and a difference in depositional rates and products carried to the solomon sea in the past relative to what is observed today based on plate motions alternative collision geometries and the youngest dates available for the erap complex we determine a rate of progression of the collision point of about 212 km m y during the past 1 m y

the 40ar 39ar age dating of the madeira archipelago and hotspot track eastern north atlantic the 40ar 39ar ages for 35 volcanic rocks and 14c ages for two charcoal samples from the madeira archipelago and ampere seamount eastern north atlantic are presented the volcanic evolution of madeira can be divided into a voluminous shield stage 4 6 0 7 ma and a subsequent low volume posterosional stage 70 myr old hotspot which formed porto santo island 11 1 14 3 ma seine ampere 31 ma corral patch and ormond 65 67 ma feraud et al 1982 1986 seamounts and the serra de monchique 70 72 ma mcintyre and berger 1982 complex in southern portugal age and spatial relationships result in a calculated absolute african plate motion above the hotspot of 1 2 cm yr around a rotation pole located at 43 36 n 24 33 w

distinguishing sediment waves from slope failure deposits field examples including the humboldt slide and modelling results abstract migrating sediment waves have been reported in a variety of marine settings including submarine levee fan systems floors of fjords and other basin or continental slope environments examination of such wave fields reveals nine diagnostic characteristics when these characteristics are applied to several features previously attributed to submarine landslide deformation they suggest that the features should most likely be reinterpreted as migrating sediment wave fields sites that have been reinterpreted include the humboldt slide on the eel river margin in northern california the continental slope in the gulf of cadiz the continental shelf off the malaspina glacier in the gulf of alaska and the adriatic shelf a reassessment of all four features strongly suggests that numerous turbidity currents separated by intervals of ambient hemipelagic sedimentation deposited the wave fields over thousands of years a numerical model of hyperpycnal discharge from the eel river for example shows that under certain alongshore current conditions such events can produce turbidity currents that flow across the humboldt slide serving as the mechanism for the development of migrating sediment waves numerical experiments also demonstrate that where a series of turbidity currents flows across a rough seafloor i e numerical steps sediment waves can form and migrate upslope hemipelagic sedimentation between turbidity current events further facilitates the upslope migration of the sediment waves physical modelling of turbidity currents also confirms the formation and migration of seafloor bedforms the morphologies of sediment waves generated both numerically and physically in the laboratory bear a strong resemblance to those observed in the field including those that were previously described as submarine landslides

direct sediment transfer from land to deep sea insights into shallow multibeam bathymetry at la reunion island abstract submarine canyon heads are key areas for understanding the triggering factors of gravity currents responsible for the transfer of detrital sediment to the deep basins this contribution offers a detailed picture of canyon heads off la reunion island with high resolution multibeam bathymetry in the water depth range of 4 220 m the present feeding of the cilaos turbidite system one of the largest modern volcaniclastic systems in the world is deduced from morphological and sedimentological interpretations of newly acquired data the study highlights small scale sedimentary features indicating hydrodynamic and sedimentary processes a direct connexion between the saint etienne river mouth and submarine canyons is evidenced by the complete incision of the shelf and the presence of canyon heads connected to the modern deltaic bar this direct connection supplied by river torrential floods cyclonic floods every two or three years suggests the continuity of high density fluvial flows to submarine gravity flows forming hyperpycnal flows in the canyon the initiation of secondary submarine gravity flows by storm waves large austral waves and cyclonic waves is also proposed for submarine canyons with large canyon heads developed in the surf zone from a sandy coastal bar bedforms in active canyon axis are considered as an indicator of the frequent activity of high density turbidity currents moreover a morphological record of last glacial and deglacial sea level variations is preserved and particularly the last glacial maximum sea level with the presence of small vertical cliffs observed in this bathymetric data which likely corresponds to a paleo shoreline or paleo reefs

on the origin of the azores current the azores current south of the azores archipelago is part of the subtropical north atlantic gyre using an international hydrographic data set we analyze mean and seasonal geostrophic transport fields in the upper 800 m of the ocean in order to determine the origin of the azores current in the western basin and seasonal changes in the related flow geostrophic currents are obtained by using the method applied by stramma 1984 in the eastern basin the azores current is found to originate in the area of the southwest newfoundland rise figure 10 in winter an almost uniform current connects this region of origin with the azores current while a branching into two current bands is observed in summer with the southern band forming a marked cyclonic loop within the upper 800 m all of the transport in the northern band and about 70 of the transport in the southern band recirculates in the eastern basin additionally expendable bathythermograph data from the azores current region indicate an increase of eddy potential energy from winter to summer

rossby wave analysis of subsurface temperature fluctuations along the honolulu san francisco great circle abstract seven years of xbt observations collected between honolulu and san francisco reveal subsurface temperature fluctuations with strong in phase vertical coherence and fair horizontal coherence over 1000 km distance their annual and semi annual harmonics exhibit randomness of phase suggesting that the fluctuations are modeled better as a stochastic process than as a deterministic signal cross spectral fitting of a stochastic first baroclinic mode rossby wave model to the fluctuations demonstrates the rossby waves could be producing 50 60 of the observed subsurface covariance at periods exceeding nine months phase is seen to propagate northwestward and energy westward and southwestward the corresponding sea surface velocities and sea level fluctuations are of the order 1 cm s 1 and 1 5 cm

physical oceanography of the azores front abstract there is a considerable body of evidence for the existence of a permanent front sw of the azores surveys in the summer of 1981 show the structure to penetrate to a depth of 2 000 m and suggest that its meandering is related to the alignment of the atlantis gt meteor seamount chain the total volume transport above 2 000 m is between 10 and 12 106 m3 s 1 towards the east the main water mass contrasts across the front are confined to the upper 400 m of the water column only a small change in mediterranean water strength was seen across the front satellite tracked drogued buoys seeded into the front showed surface speeds of up to 40 cm sec 1 and revealed the formation of a closed cold core eddy some 100 115 km in diameter which propagated westward at 2 2 km day 1 over a 200 day period sea surface temperature contrasts across the frontal boundary are small and together with frequent cloud cover prevent the detection of the front and associated eddies by satellite infra red imagery the front apparently marks the eastward extension of the southern branch of the gulf stream recirculation and the northern limit of the 18 c water mass eddies formed at the front could propagate westward into the interior of the sargasso sea but have not yet been observed to cross the mid atlantic ridge

supercritical and subcritical turbidity currents and their deposits a synthesis common facies models of turbidite deposits are based on idealized sequences of turbidite units which are assumed to reflect the depositional processes of a decelerating turbidity current we show how suites of turbidite units i e distinct turbidite facies associations that are easily described from core and outcrop may characterize the entire range of large scale dynamics of turbidity currents enabling estimates of their densimetric froude number fr subcritical versus supercritical and suspension fall out rate stratified versus nonstratified flows the linking of facies associations with large scale flow dynamics resolves process facies links that were hitherto unresolved by the common turbidite facies models

unexpected fast rate of morphological evolution of geologically active continental margins during quaternary examples from selected areas in the italian seas abstract in the last few decades seafloor imagery systems have drastically changed our vision of a mostly regular and depositional marine landscape evidencing how erosive and mass wasting processes are widespread in the marine environments with particular reference to geologically active areas most of the previous studies have focused on the characterization of these features whereas a very few ones have tried to estimate what is the extent and order of magnitude of erosion rates in these areas in this paper we show several examples from some of the most geologically active margins off southern italy aimed to a quantify the spatial extent of such processes b better understand the role of submarine erosion in the morphogenesis of the coastal sector and c try to roughly estimate the order of magnitude of erosion rates in these areas the results are impressive with mass wasting features widespread from coast down to 2600 affecting from the 52 up to 97 of the whole continental slope because of the narrow or totally lacking shelves in these areas mass wasting processes often occur close to the coast and match embayment of the coast so indicating a key role in the morphogenesis of coastal sector with significant implication on the related geohazard finally based on a morphological approach integrated by available stratigraphic constraints we have roughly estimated average erosion rates in these areas ranging from at least some mm year to a few cm year i e some hundreds of meters up to kilometers eroded in each eustatic cycle despite the large uncertainties of these estimates as well as their spatial and temporal variability in response to regional and local factors the obtained values are very high and they should be considered for future model of margin evolution source to sink computation and marine coastal geohazard assessment

coastal evolution on volcanic oceanic islands a complex interplay between volcanism erosion sedimentation sea level change and biogenic production abstract the growth and decay of oceanic hotspot volcanoes are intrinsically related to a competition between volcanic construction and erosive destruction and coastlines are at the forefront of such confrontation in this paper we review the several mechanisms that interact and contribute to the development of coastlines on oceanic island volcanoes and how these processes evolve throughout the islands lifetime volcanic constructional processes dominate during the emergent island and subaerial shield building stages during the emergent island stage surtseyan activity prevails and hydroclastic and pyroclastic structures form these structures are generally ephemeral because they can be rapidly obliterated by marine erosion with the onset of the subaerial shield building stage coastal evolution is essentially characterized by rapid but intermittent lateral growth through the formation of lava deltas largely expanding the coastlines until they typically reach their maximum extension with the post shield quiescence in volcanic activity destructive processes gradually take over and coastlines retreat adopting a more prominent profile mass wasting and marine and fluvial erosion reshape the landscape and if conditions are favorable biogenic processes assume a prominent role post erosional volcanic activity may temporarily reverse the balance by renewing coastline expansion but islands inexorably enter in a long battle for survival above sea level reef growth and or uplift may also prolong the island s lifetime above the waves the ultimate fate of most islands however is to be drowned through subsidence and or truncation by marine erosion

an examination of froude supercritical flows and cyclic steps on a subaqueous lacustrine delta lake chelan washington u s a density driven submarine flows including turbidity currents play an important role in the transfer of sediment into deep water these bottom hugging flows often produce flow transverse bedforms along their path a sedimentological and geophysical survey of the stehekin river delta in lake chelan washington reveals a downslope elongate field of bedforms on the delta foreset associated with hyperpycnal discharges of the stehekin river an analysis of the bedform morphologies delta geometry and density contrast between lake and river water suggests that these hyperpycnal flows are froude supercritical the bedforms are likely cyclic steps flow transverse bedforms that are bounded by stable hydraulic jumps between alternating subcritical and supercritical flow regimes the ability to examine the three dimensional bed configuration produced by natural density driven flows adds valuable information to the body of experimental work focused on the behavior of cyclic steps in flumes

the morphology of the submarine flanks of volcanic ocean islands a comparative study of the canary and hawaiian hotspot islands the submarine flanks of volcanic islands are shaped by volcanic constructional processes landslides erosion sediment deposition and tectonic movements we use a newly acquired multibeam sonar dataset from the westerly canary islands el hierro la palma and tenerife to develop a comparison with the hawaiian islands which suggests differences in the processes constructing and modifying their flanks landslides affect the flanks of both island groups debris avalanches fast moving shallow landslides have left smooth chutes and blocky deposits in both cases but blocks within some hawaiian avalanche deposits are markedly larger we attribute the larger block sizes in the hawaiian islands to the fact that their avalanches were relatively unconfined whereas many canary and hawaiian avalanches with small block sizes appear to have been constrained down narrow chutes forcing interactions between blocks within the flows and encouraging disintegration furthermore the hawaiian avalanches with the largest blocks initiated near sea level whereas many of the canary avalanches initiated above sea level so hydraulic resistance of water entering cracks may be an additional factor in resisting block disintegration during flow slow moving deep seated slumps or volcanic spreading have produced submarine benches and tabular escarpments due to thrust faulting adjacent to several hawaiian rift zones but are not well developed in the canaries although volcanic morphology is partly obscured by sedimentation in the canaries we are able to interpret lava terraces around the deep flanks of el hierro which are similar to those found in the hawaiian islands however cones rather than terraces are the most common volcanic forms in the canary islands implying that flank eruptions have involved magma with significant volatile contents assuming that volatile contents dictate whether cones or terraces are formed these differences may ultimately originate from the different building rates of the two island groups for example the lack of evidence for high level magma chambers in the canaries associated with their lower outputs implies that there is less possibility for degassing of magma below the summit before lateral intrusion down rift zones hence cones rather than lava terraces are more commonly observed the apparent lack of slumping or volcano spreading could also reflect a lack of driving pressure from extensive high level magma chambers in the canaries

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

meandering of the subtropical front south east of the azores a subtropical front was observed in the area south and southeast of the azores during cruises of fs meteor and fs poseidon in early 1982 the front has a basically west east extension with considerable meandering observed meso scale eddies are found on both sides the overall flow pattern corresponds to earlier results on geopotential differences in the upper northeast atlantic but the baroclinic transport of the order of 107 m3 s 1 is found to be concentrated in a 60 km wide jet we suggest here that the current band is part of the gyre circulation resulting from a branching of the north atlantic current