iceberg scours along the southern u s atlantic margin rapid climate fluctuations associated with ice sheet oscillations have resulted in pulses of iceberg discharge that are recorded by iceberg scour marks along continental shelves and ice rafted debris deposits across the north atlantic iceberg transport is largely controlled by ocean surface currents therefore iceberg trajectories can serve as a proxy for paleo circulation studies records of iceberg transport from ice rafted debris i e heinrich layers in the north atlantic suggest that most icebergs released during quaternary glaciations were entrained in a cyclonic subpolar gyre restricted to polar and mid latitudes however new data suggest that there may have been an additional southerly component of transport along the western atlantic margin here we present evidence of extensive iceberg scouring across the upper slope offshore of south carolina 1000 km south of the proximal ice margin during quaternary glacial maximums the location and orientation of the keel marks suggest that icebergs were entrained in a southwestward flowing coastal current at present warm waters of the rapid northeastward flowing gulf stream bathe the upper slope off the southeastern united states an offshore shift in the gulf stream axis during sea level lowstand may have allowed glacially fed coastal currents to penetrate farther south this may be the first evidence of iceberg rafting to subtropical latitudes in the north atlantic

crustal seismic velocity structure near faial and pico islands azores from local earthquake tomography the azores archipelago portugal is located on an oceanic plateau in a geodynamic environment prone to intense seismic and volcanic activity in order to investigate the crustal structure in this region we have conducted a local earthquake tomography study in the area of the islands of faial pico and s jorge using data recorded in july 1998 the july 9th 1998 earthquake near faial island triggered an aftershock sequence of thousands of events that lasted for several months and were recorded by a total of 14 stations located on the three islands surrounding the epicentral area in the upper crustal layers consistency is seen between the tomographic results and the islands surface volcanic units beneath the faial central volcano a low vp b6 0 km s anomaly roughly located at 3 7 km depth suggests a connection to the plumbing system possibly the presence of a magma chamber in ne faial a high vp n6 3 km s body was found located at mid lower crust most likely an intrusion of gabbroic composition that is bordered by the registered seismic activity its shape suggesting a tectonic controlled mechanism the relocated hypocenters together with the overall analysis of the tomographic model suggest a tectonic segmentation of faial island the crustal thickness under the islands volcanic buildings of the faial pico area was estimated at around 14 km 2007 elsevier b v all rights reserved

the role of seamount volcanism in crustal construction at the mid atlantic ridge 24 30 n an analysis of approximately 6000 km2 of sea beam swaths indicates that the floor of the median valley of the mid atlantic ridge mar between 24 30 n is strewn with near circular volcanoes we have identified 481 seamounts in the height range 50 650 m because many of the features which appear to be seamounts do not meet our criteria fully they have not been counted and our numbers are likely a minimum estimate of the population the large abundance of seamounts on the median valley floor indicates that seamount volcanism plays an important role in the accretionary processes at this section of the mar the summit height distribution of the mar seamount population is consistent with the exponential frequency size distribution model for off axis eastern pacific seamounts jordan et al 1983 smith and jordan 1987 the model parameters for the mar population yield an average of about 195 seamounts per one thousand square kilometers and a characteristic height of about 60 m shape statistics compiled from the 481 seamounts give parameters that are exactly the same or cover the same range in values as those obtained from a study of pacific seamounts in the height range 140 3800 m smith 1988 implying a universal control on seamount construction based on the volcanic morphology we identify 18 spreading segments along the ridge all except two contain a prominent axial volcanic ridge many of the seamounts identified are associated with the axial ridges from the sea beam swaths we infer that the ridges are composed of piled up seamounts and hummocky flows and interpret them to be the primary sites of crustal construction this style of volcanism contrasts strongly with that observed at the east pacific rise where seamounts are virtually absent at the spreading axis the construction of seamounts and hummocky flows may be directly related to the fact that the mar is fed by magma chambers that are limited in size and frequency we suggest that small magma pockets with slow eruption rates produce seamounts either from pipes or initial fissure eruptions that collapse to construct a single edifice small magma bodies with somewhat higher eruption rates produce hummocky fissure fed flows using buoyancy arguments the heights of the mar seamounts are related to the depth of the magma bodies we hypothesize that small magma bodies rise buoyantly to the base of the hydrothermally cooled brittle lid where they are trapped and then erupt if this hypothesis is correct the thickness of the brittle lid controls seamount height and the exponential distribution of seamount summit heights implies that the thickness of the brittle hd follows an exponential distribution in time and space with characteristic thickness 1 4 1 9 km if seamounts and hummocky flows are fed each from their own discrete magma body trapped at the brittle ductile transition then the lower crust of the mar will be made up of the products of a multitude of small plutons

climate and vegetation history of the midcontinent from 75 to 25 ka a speleothem record from crevice cave missouri usa four missouri stalagmites yield consistent overlapping records of oxygen and carbon isotopic changes and provide a climate and vegetation history with submillennial resolution from 75 to 25 thousand years ago ka the thorium 230 dated records reveal that between 75 and 55 ka the midcontinental climate oscillated on millennial time scales between cold and warm and vegetation alternated among forest savanna and prairie temperatures were highest and prairie vegetation peaked between 59 and 55 ka climate cooled and forest replaced grassland at 55 ka when global ice sheets began to build during the early part of marine oxygen isotope stage 3

modelled atmospheric temperatures and global sea levels over the past million years the climate has passed through a series of glacials and interglacials over the past million years but the nature of this cyclicity in terms of temperature ice volume and sea level and the underlying causes are not well known bintanja et al use a new method to deduce a one million year time series of these variables the reconstructed records are much longer than other methods have provided for any of these variables individually the most intense glacial stages were 17 c colder than today and most of the continental ice was present in north america strong cooling in the beginning of glacials was found to precede ice sheet build up these findings may shed light on the causes of ice age cycles marine records of sediment oxygen isotope compositions show that the earth s climate has gone through a succession of glacial and interglacial periods during the past million years but the interpretation of the oxygen isotope records is complicated because both isotope storage in ice sheets and deep water temperature affect the recorded isotopic composition1 2 3 4 5 separating these two effects would require long records of either sea level or deep ocean temperature which are currently not available here we use a coupled model of the northern hemisphere ice sheets6 and ocean temperatures forced to match an oxygen isotope record for the past million years compiled from 57 globally distributed sediment cores to quantify both contributions simultaneously we find that the ice sheet contribution to the variability in oxygen isotope composition varied from ten per cent in the beginning of glacial periods to sixty per cent at glacial maxima suggesting that strong ocean cooling preceded slow ice sheet build up the model yields mutually consistent time series of continental mean surface temperatures between 40 and 80 n ice volume and global sea level we find that during extreme glacial stages air temperatures were 17 1 8 c lower than present with a 120 10 m sea level equivalent of continental ice present

seismic and bathymetric evidence for four different episodes of iceberg scouring on the new jersey outer shelf possible correlation to heinrich events abstract re analysis of dense chirp seismic surveys on the outer new jersey shelf reveals two sets of shallowly buried incisions the incisions are linear to slightly sinuous oriented ne sw and exhibit cross cutting relationships we interpret both sets as paleo iceberg scours one set cuts into the r horizon a regional unconformity that formed 45 40 ka and which was subsequently buried by the finer grained outer shelf sediment wedge osw the second set is part of an erose boundary between a layered lower unit of the osw and an upper more transparent unit the erose boundary scours are deeper and have steeper slopes than the r horizon scours the latter often exhibit bermed edges whereas the former do not these differences in cross sectional morphology are likely determined by the material properties of the sediments being scoured sand at the r horizon and clay at the erose boundary the orientation of both sets of scours is consistent with previously recognized iceberg scours in stratigraphically younger seafloor on the outer new jersey shelf in 110 150 m water depths located 40 km to the northeast we argue that heinrich events recurring periods of massive iceberg flux into the north atlantic represent the most likely times for transporting icebergs to these latitudes based on stratigraphic relationships a recently published ambient sea level curve and radiocarbon age constraints we attribute the r horizon scours to heinrich event h4 37 cal ka the erose boundary scours to h3 30 cal ka and the seafloor scours to h2 23 cal ka and or h1 17 cal ka facies changes immediately following the r horizon and erose boundary scours may be related to heinrich event forced climate changes perhaps the onset of interstadial conditions and associated melt water pulses floods these pulses floods repeatedly carried fine grained rock flour produced by widespread glacial erosion to the new jersey shelf

faulting associated with historical and recent earthquakes in the eastern mediterranean region summary this paper summarizes evidence for surface faulting in historical and recent earthquakes in the eastern mediterranean region and in the middle east such information is particularly important for studies of active tectonics and for palaeoseismology we have found 78 cases of faulting pre 1900 and 72 post 1900 some of which show that faults that have apparently been inactive this century had already ruptured before 1900 for some cases faulting could not have been predicted from 20th century activity and in others it could have been expected but has not been observed during the instrumental period the data are suycient to allow the derivation of relationships between magnitude and rupture length

reconstructing the architectural evolution of volcanic islands from combined k ar morphologic tectonic and magnetic data the faial island example azores the morpho structural evolution of oceanic islands results from competition between volcano growth and partial destruction by mass wasting processes we present here a multi disciplinary study of the successive stages of development of faial azores during the last 1 myr using high resolution digital elevation model dem and new k ar tectonic and magnetic data we reconstruct the rapidly evolving topography at successive stages in response to complex interactions between volcanic construction and mass wasting including the development of a graben we show that 1 sub aerial evolution of the island first involved the rapid growth of a large elongated volcano at ca 0 85 ma followed by its partial destruction over half a million years 2 beginning about 360 ka a new small edifice grew on the ne of the island and was subsequently cut by normal faults responsible for initiation of the graben 3 after an apparent pause of ca 250 kyr the large central volcano cv developed on the western side of the island at ca 120 ka accumulating a thick pile of lava flows in less than 20 kyr which were partly channelized within the graben 4 the period between 120 ka and 40 ka is marked by widespread deformation at the island scale including westward propagation of faulting and associated erosion of the graben walls which produced sedimentary deposits subsequent growth of the cv at 40 ka was then constrained within the graben with lava flowing onto the sediments up to the eastern shore 5 the island evolution during the holocene involves basaltic volcanic activity along the main southern faults and pyroclastic eruptions associated with the formation of a caldera volcano tectonic depression we conclude that the whole evolution of faial island has been characterized by successive short volcanic pulses probably controlled by brief episodes of regional deformation each pulse has been separated by considerable periods of volcanic inactivity during which the faial graben gradually developed we propose that the volume loss associated with sudden magma extraction from a shallow reservoir in different episodes triggered incremental downward graben movement as observed historically when immediate vertical collapse of up to 2 m was observed along the western segments of the graben at the end of the capelinhos eruptive crises 1957 58

large earthquakes kill coral reefs at the north west gulf of aqaba down faulting at the north west margins of the gulf of aqaba is inferred to have triggered a catastrophic sedimentary event at 2 3 ka that killed the elat fringing coral reef whereas segments of the holocene reef were perfectly fossilized and preserved beneath a veneer of siliciclastic sediments other segments were abraded settled by nomads and later re submerged under 4 m of water repeated damage triggered by down throwing earthquakes degenerate the fringing reefs of the north west end of the gulf conversely on the north eastern and southern parts of the gulf where earthquakes uplift the margins modern reefs are thriving attached to uplifted fossil reef terraces therefore coastal subsidence moderates the development of fringing coral reefs during the late holocene sea level stand still

morphometry of scoria cones located on a volcano flank a case study from mt etna italy based on high resolution lidar data abstract by using new high resolution 2 m digital elevation model derived from the 2005 lidar survey of mt etna volcano italy our study measured the classical morphometrical parameters for scoria cones i e w co cone width w cr crater diameter h cone height as well as volume inclination of cone slope and substrate and a number of other parameters for 135 scoria cones of mt etna volume and age distribution of cones shows that there is no direct structural control on their emplacement in terms of etna s rift zones the cones are progressively smaller in size toward summit which can be explained by the large volcano s feeding system and progressively frequent lava burial toward top a careful analysis of h w co ratio determined as 0 18 for other volcanic fields worldwide shows that this ratio strongly depends on 1 the calculation method of h and 2 lava burial of cone for etnean cones applying an improved method for calculating h relative to the dipping substrate results in a significantly lowered standard h w co ratio 0 137 which in turn questions the validity of the classical value of 0 18 in the case of large central volcanoes the reduction of the ratio is not only due to methodology but also to the common lava burial this can be expressed even better if h mean is used instead of h max h mean w co 0 098 using this measure at etna well formed cones have higher ratios than structurally deformed e g double or rifted cones furthermore although the sampled scoria cones at etna have formed in a relatively narrow time interval h w co corresponding to erosional changes detected globally h w co 0 143 0 135 and 0 115 for three age classes of etna s scoria cones corresponding to average slopes of 26 6 23 9 and 23 7 because the morphometrical effect of position on a dipping substrate as well as lava burial exceeds the effect of erosion we call attention to use caution in simply using the h w co ratio of scoria cones for detecting age especially on large active volcanoes

the use of distinct disciplines to investigate past earthquakes abstract the investigation of past earthquakes can be approached in many different ways with a large variety of methods and techniques this is mainly due to the complexity of this natural phenomenon in both its genetic aspects and consequential ones in the present note we briefly analyse the peculiarities of instrumental seismology historical seismology archaeoseismology and earthquake geology but especially we emphasise the major differences among these four distinct approaches in order to better define and clearly separate these disciplines in terms of appropriate tools to be applied and possible outcomes to be expected an alternative point of view is proposed based on the source of information and not on a chronological distribution as commonly accepted in the literature although multidisciplinarity is a common approach for investigating past earthquakes each one of the discussed disciplines has its own peculiarities advantages and limitations and researchers should be aware of this

boomerang seamount the active expression of the amsterdam st paul hotspot southeast indian ridge during a survey of the axis of the southeast indian ridge seir we discovered a 1100 m tall volcanically active submarine volcano boomerang seamount near the spreading center on the amsterdam st paul asp plateau the summit of the volcano is 650 m below sea level and has a 200 m deep 2 km wide circular caldera samples of very fresh volcanic glass dated by the 210po 210pb technique at 5 months old were collected from the floor of the caldera in march 1996 the volcano is 18 km northeast of amsterdam island near the intersection of a long spreading segment and the boomerang transform fault it is built on the stationary antarctic plate where widely scattered volcanic activity thickens the crust continuing to build the plateau water column profiles reveal a 1 7 c temperature anomaly and a 0 3 v stepped nephelometer water column turbidity anomaly within the caldera nearly an order of magnitude larger than other hydrothermal plume anomalies we measured these anomalies suggest hydrothermal activity within the caldera volcanic glass compositions at two sample sites on the volcano summit are similar to each other and to amsterdam and st paul island basalts but have some important differences as well k2o tio2 ratios in boomerang seamount glasses are similar to st paul island samples but differ significantly from amsterdam island samples rare earth element patterns in lavas from boomerang amsterdam and st paul are similar sr nd and pb isotope ratios in samples from the boomerang caldera floor are similar to samples from amsterdam island however another sample from boomerang seamount deviates from a seir st paul amsterdam mixing trend and shows evidence of mixing with a kerguelen like source component the geochemical complexity of these three closely spaced volcanic edifices on the asp plateau suggests that the boomerang seamount source is heterogeneous on a very small scale

a palaeoseismological and geoarchaeological investigation of the eliki fault gulf of corinth greece abstract palaeoseismological and morphotectonic analyses enable us to define a 400 m wide actively deformed zone associated with the active eliki normal fault central greece bounded on the south by a second order fault and on the north by a composite and prominent fault scarp this scarp is further analysed by trenching based on colluvium stratigraphy displacement of distinct horizons and deposition of sedimentary layers three faulting events have been identified along four fault strands affecting unconsolidated sediments in the trench the two younger events with throws of 0 93 and 1 37 m respectively the third event with a throw of 0 44 m and the penultimate 373 bc event suggest a variable seismic history the entire alluvial plain of the kerynitis and vouraikos rivers which cross the eliki fault has subsided at a rate of 1 4 mm year resulting in the burial of the late hellenistic roman occupation horizons under 3 m of fluvial and colluvial sediments in places extension in the broader area is accommodated by the seismically active eliki and egion faults structural and palaeoseismological analysis of those two faults indicates that they accommodate 1 5 mm year or about 10 of the geodetically estimated extension of up to 13 mm year

mass wasting and subaerial weathering in guyot formation the hawaiian and canary ridges as examples by using a combination of bathymetry and topography in the computerized grass 3d package guyot evolution has been determined on the fast moving pacific plate for the subaerial low sloped hawaiian island chain on the slow moving african plate the timing of guyot formation has been determined for the subaerial steeper sloped canary islands chain in the hawaiian chain the niihau island platform was already essentially formed although there is a platform at the 180 m elevation on kauai island if the remaining peaks are discounted by fuerteventura island in the canary chain the seamount island has already been flattened both of these platforms are far above the influence of wave cutting the causal agent of flattening is primarily mass wasting by landsliding caused in part by earthquake activity on the moving plates this disproves the subsidence and wavecut theory of guyot formational processes in that the guyot is already formed before it subsides the islands lie in the tropical coral zone yet coral formation has little effect on the flattening process this may be because the turbidity from slumps kills the coral this exercise also gives a time limit for the reduction of pristine volcanic slopes to the typical guyot surface that time being between one and four million years it is apparent that wave cutting merely polishes the stone applying the finishing patina

condor seamount azores ne atlantic a morpho tectonic interpretation abstract high resolution datasets collected by multibeam and acoustic backscatter surveys were used to produce fine scale seafloor nature and morpho tectonic interpretations of the condor seamount condor constitutes an elongated volcanic ridge that extends for 39 km and rises more than 1800 m from the surrounding seafloor constructive morphologies include i linear eruptive centres ii volcanic cones with or without summit depressions iii lava flows and iv hummocky sectors eruptive type is interpreted to vary with depth on the deeper seamount extremities the predominance of highly acoustically backscattering volcanic cones and hummocky terrain is interpreted to result from effusive eruptions not yet covered by sediment deposits in contrast the smoother relief of the central seamount flanks is interpreted as draping and infilling of the underlying effusive relief by i primary volcaniclastic deposits produced by explosive eruptions on the shallowest parts of the ridge together with ii secondary volcanigenic sediments resulting from truncation of the seamount top by swell erosion and iii sediments resulting from biogenic production a set of wnw ese to nw se trending volcano tectonic structures are shown to control most of the fissural volcanism that formed the ridge a network of nnw sse trending faults is identified on the sea floor around condor but they show little relation with the distribution of volcanic edifices or with post emplacement dismantling of the seamount these fault sets are related to the transtensional regime acting on the azorean segment of the eurasia nubia plate boundary erosional features include i palaeo wave cut platforms on the seamount summit ii landslide scars produced by lateral collapses of the ne and sw facing flanks iii gullies and turbidity current channels and iv mass wasting deposits iceberg drag and bump marks are also identified on the seamount upper flanks representing the first reference to such features in the azores and an additional low latitude record given the lack of major erosional and tectonic dismantling condor is suggested to be a relatively young seamount a revised factoring of eustatic erosional and isostatic processes does not exclude that the summit may have been eroded as late as the last glacial maximum

merging gps and atmospherically corrected insar data to map 3 d terrain displacement velocity a method to derive accurate spatially dense maps of 3 d terrain displacement velocity is presented it is based on the merging of terrain displacement velocities estimated by time series of interferometric synthetic aperture radar insar data acquired along ascending and descending orbits and repeated gps measurements the method uses selected persistent scatterers pss and gps measurements of the horizontal velocity an important step of the proposed method is the mitigation of the impact of atmospheric phase delay in insar data it is shown that accurate vertical velocities at ps locations can be retrieved if smooth horizontal velocity variations can be assumed furthermore the mitigation of atmospheric effects reduces the spatial dispersion of vertical velocity estimates resulting in a more spatially regular 3 d velocity map the proposed methodology is applied to the case study of azores islands characterized by important tectonic phenomena

application of tree ring analysis to paleoseismology knowledge of the seismicity for a region is one of the keys to estimating earthquake hazards unfortunately historical records are generally inadequate for evaluations of seismicity paleoseismology addresses this problem using various techniques for determining the times and locations of earthquake disturbances trees with widespread geographical distribution identifiable annual growth increments and sensitivity to environmental changes can provide an almost unique tool for dating past earthquake events geomorphic and hydrologic changes and dynamic stress resulting from earthquakes can cause a variety of effects in trees and communities of trees tree ring analysis can 1 produce the actual year and sometimes the season for disturbance events and 2 establish synchronicity for events that may be beyond the range of absolute calendar dating tree ring dating or dendrochronology is used to establish exact dates based on patterns of annual ring variations through time mere counting of rings is inadequate and may lead to errors in assigning dates to rings because of possible missing micro or false rings trees ranging in age from 300 500 years grow in many places and can be used to identify previously unknown seismic events or to better define events that are partially known longer time spans can be covered in some instances earthquakes may be more precisely located in space and time or have their magnitudes and displacements better estimated by analysis of tree rings a number of studies have established the validity of tree ring application to paleoseismology but only a few studies have contributed new information to the paleoseismic record a review of the application of tree ring analysis to paleoseismology is in jacoby 1997 the science should now move from the discovery phase to a wider application phase successful applications will add important information to the records of seismicity and the evaluation of earthquake hazards

the relative motion between africa and eurasia as derived from itrf2000 and gps data 1 studies of intra and inter plate deformation typically need a model describing the motions of the stable part of the tectonic plates for reference purposes we have developed deos2k a model for the current motion of seven major tectonic plates derived from space geodetic observations this paper focuses on relative motion between africa and eurasia in the past this motion has been poorly established because of poor data coverage for africa deos2k is based on itrf2000 altamimi et al 2002 and new african gps observations it is an improvement over the nuvel 1a model for predicting the present day relative motions of these two plates deos2k predicts in northeastern africa that africa eurasia relative motion is about 40 smaller in magnitude than nuvel 1a and trends more to the northwest this is consistent with independent local geodetic observations a similar shift in orientation clockwise is observed at the western tip of the plate boundary

cone morphologies associated with shallow marine eruptions east pico island azores eruptions in shallow water typically produce cones of volcaniclastic material in order to identify any systematic effects of water depth and other environmental parameters on cone morphology we have measured the heights and widths of cones in multibeam echo sounder data from a submarine ridge extending southeast from pico island azores xrf analyses of dredged samples show that lavas here vary compositionally from alkali basalt to trachybasalt and trachyandesite cones in deeper water are generally steep sided with upper flanks close to 30 the dip of talus at the angle of repose however height width ratios of cones vary more in shallow water 200 400 m summit depth with extreme values below 0 1 while some shallow water cones are steep sided as in deep water others are much flatter three such cones lie on a bench at 300 m depth immediately east of pico island and have flank slopes of only 10 20 we speculate that exceptionally shallow cone slopes here were produced by forced spreading of the erupting columns on reaching the water air density barrier

high resolution geological record of historic earthquakes in the dead sea basin a 2000 year paleoseismic record of the dead sea area was recovered from a lacustrine sedimentary section the section is being exposed at the ze elim terrace on the shores of the dead sea due to the fast retreat of the lake the section consists of laminated detrital and chemical mainly aragonite sediments that were deposited in the holocene paleo dead sea eight layers in the section show deformed sedimentary structures and are identified as seismites their chronology was determined by radiocarbon dating on organic remains the seismite ages are well correlated with the historically documented earthquakes of 64 and 31 b c and 33 363 1212 1293 1834 and 1927 a d the few historically documented earthquakes that have no correlatives in the ze elim seismite record occurred in times of sedimentary hiatuses at this site e g 749 a d based on modern analogues and the association of similar disturbed layers with syndepositional faults the ze elim terrace seismites indicate m 5 5 earthquakes the average recurrence interval is estimated as 100 300 years and represents slip events on different faults in the dead sea area the ze elim section provides a unique opportunity to correlate two independent and extensive data sets the historical and sedimentary records this study opens the way for better understanding of spatial and temporal distribution of earthquakes along the dead sea transform and elsewhere

geodynamic models for the azores triple junction a contribution from tectonics abstract the american eurasian and african lithospheric plates meet at the azores triple junction the nature of the northern and southern branches of the junction is well known and uncontroversial the american plate is separated from eurasia and africa by the mid atlantic ridge mar the western group of islands of the azores archipelago flores and corvo lies on the american plate just west of the rift and their tectonic features agree with that location the nature of the third branch of the junction to the east of the mar is however still controversial some authors believe that a ridge ridge ridge junction occurs in the azores area and adopt the structure known as the terceira ridge working as a simple rift boundary as the third branch another model proposes a triangular microplate in the azores region bounded by the mid atlantic rift to the west the east azores fault zone to the south and a fault crossing s miguel and the terceira islands to the northeast in this model the fault zones are pure dextral strike slip boundaries both models would create space problems at gloria fault a well known pure dextral strike slip structure in the first model transtension would be necessary at gloria fault to accommodate plate motion while the second would require a transpressive regime on that structure neotectonic and seismotectonic data in the azores indicate a transtensile regime in the central and eastern island groups in present and recent times this is compatible with a leaky transform structure acting as the third branch of the junction in the azores area a model which has already been presented by several authors in the past stress trajectories deduced from neotectonic studies in some of the islands suggest that the main plate boundary passes between the islands of s jorge and pico south of s miguel and joins gloria fault east of santa maria this model and boundary location is also compatible with seismotectonic and magnetic data

interaction between the mid atlantic ridge and the azores hot spot during the last 85 myr emplacement and rifting of the hot spot derived plateaus 1 multiple and single beam bathymetric data are compiled over the azores plateau to produce a 1 km 1 km grid between latitudes 32 n and 49 n and longitudes 22 w and 43 w mantle bouguer anomalies are then calculated from this grid and the satellite derived gravity these grids provide new insights on the temporal and spatial variations of melt supply to the ridge axis the elevated seafloor of the azores plateau is interpreted as resulting from the interaction of a mantle plume with the mid atlantic ridge mar the presence of a large region of elevated seafloor associated with a thick crust between the great meteor seamounts and the azores platform on the africa plate and less developed conjugate structures on the north america plate favors genetic relations between these hot spot derived structures this suggests that a ridge hot spot interaction has occurred in this region since 85 ma this interaction migrated northward along the ridge axis as a result of the sse absolute motion of the africa plate following a direction grossly parallel to the orientation of the mar kinematic reconstructions from chron 13 35 ma to the present allow a proposal that the formation of the azores plateau began around 20 ma and ended around 7 ma a sharp bathymetric step is associated with the beginning of important melt supply around 20 ma the excess of melt production is controlled by the interaction of the ridge and hot spot melting zones the geometry and distribution of the smaller scale features on the plateau record episodic variations of the hot spot melt production the periodicity of these variations is about 3 5 myr following the rapid decrease of widespread volcanism the plateau was subsequently rifted from north to south by the mid atlantic ridge since 7 ma this rifting begins when the mar melting zone is progressively shifted away from the 200 km plume thermal anomaly these results bear important consequences on the motion of the africa plate relative to the azores hot spot they also provide an explanation to the asymmetric geochemical signature of the azores hot spot along the mid atlantic ridge

record of seamount production and off axis evolution in the western north atlantic ocean 25 25 27 10 n using multibeam bathymetry we identified 86 axial and 1290 off axis seamounts near circular volcanoes with heights 70 m in an area of 75 000 km2 on the western flank of the mid atlantic ridge mar 25 25 n to 27 10 n extending 400 km from the inner rift valley floor to 29 ma crust our study shows that seamounts are a common morphological feature of the north atlantic seafloor seamount producing volcanism occurs primarily on the inner rift valley floor and few if any seamounts are formed on the rift valley walls or the ridge flank the high abundance of off axis seamounts is consistent with 1 3 km wide sections of oceanic crust being transferred intact from the axial valley to the ridge flank on crust 4 ma significant changes in seamount abundances sizes and shapes are attributed to the effects of faulting between 0 6 and 2 m y off axis in the lower rift valley walls few seamounts are completely destroyed by inward facing faults and population abundances are similar to those on axis however faulting reduces the characteristic height of the seamount population significantly in the upper portions of the rift valley on 2 4 ma crust crustal aging processes sedimentation and mass wasting together with additional outward facing faults destroy and degrade a significant number of seamounts beyond the crest of the rift mountains 4 ma crust faulting is no longer active and changes in the off axis seamount population reflect crustal aging processes as well as temporal changes in seamount production that occurred at the ridge axis estimates of population density for off axis seamounts show a positive correlation to crustal thickness inferred from analysis of gravity data suggesting that increased seamount production accompanies increased magma input at the ridge axis we find no systematic variations in seamount population density along isochron within individual ridge segments possible explanations are that along axis production of seamounts is uniform or that seamount production is enhanced in some regions e g segment centers but many seamounts do not meet our counting criteria because they are masked by younger volcanic eruptions and low relief flows

seafloor slopes at mid ocean ridges from submersible observations and implications for interpreting geology from seafloor topography abstract observations from 145 submersible dives are used to create a database of mid ocean ridge scarp topography and lithology seafloor lithologies are classified into extrusives basaltic talus dykes gabbros and serpentinites and the dive locations are broadly classified according to whether they are close to transform valleys and as a function of ridge spreading rate the database is used to determine whether there is any difference in the maximum slope for each rock type which might relate to differences in rock jointing cohesion or friction properties there is a common perception that lower crustal rocks form steeper slopes than shallower crustal rocks but until now there has been little evidence to support or refute this idea from our analysis we find a tendency for gabbro and dykes to form steeper slopes than serpentinite the 90th percentile of each lithology slope distribution used as a measure of limiting slope is 43 39 and 32 for gabbro dykes and serpentinite respectively lithologic control on slope is weak however compared to overall slope variability in these mid ocean ridge settings so seafloor relief is likely to be a poor guide to underlying geology we speculate on the structure of eroding fault scarps outline the implications for attempts to infer active faults from talus ramp activity and discuss more generally factors affecting the geomorphology of mid ocean ridge slopes

susceptibility of mid ocean ridge volcanic islands and seamounts to large scale landsliding 1 with a view to assessing the incidence of large scale landsliding a morphologic database was created for volcanic islands and seamounts on young oceanic lithosphere the database included 44 mid ocean ridge seamounts jasper seamount and the islands of ascension bouvet guadalupe and several of the galapagos and azores islands supplemented with published reports from a further five volcanic edifices the data reveal that major landslides are common on edifices taller than 2500 m but are rare in shorter edifices implying a threshold of instability at around 2500 m a number of causes of this threshold are discussed for example many structures taller than 2500 m are or were originally volcanic islands and therefore their flanks probably include extensive weak hyaloclastite built up from lava sea interactions around coasts compaction of hyaloclastites in larger edifices lead to regions of low permeability which may help to explain the more deeply seated slope failures it is intriguing that the threshold also coincides with the edifice height at which volcanic ridges become observable a stage at which dike intrusion is probably common because slope oversteepening or excess pore pressure associated with dike intrusions have been proposed elsewhere as landslide triggers the current indications of landsliding reveal no observable relation to rainfall as landslides occur equally in wet and dry climates and no relation to tectonic setting as there are relatively few major landslides in the seismically active azores group

a pliocene shoaling basaltic seamount ba volcanic group at rakiraki fiji abstract at rakiraki in northeastern viti levu the pliocene ba volcanic group comprises gently dipping pyroxene phyric basaltic lavas including pillow lava and texturally diverse volcanic breccia interbedded with conglomerate and sandstone three main facies associations have been identified 1 the primary volcanic facies association includes massive basalt flows and sills pillow lava and related in situ breccia pillow fragment breccia autobreccia in situ hyaloclastite peperite 2 the resedimented volcaniclastic facies association consists of bedded monomict volcanic breccia and scoria lapilli rich breccia 3 the volcanogenic sedimentary facies association is composed of bedded polymict conglomerate and breccia together with volcanic sandstone and siltstone mudstone facies pillow lava and coarse hyaloclastite breccia indicate a submarine depositional setting for most of the sequence thick massive to graded beds of polymict breccia and conglomerate are interpreted as volcaniclastic mass flow deposits emplaced below wave base well rounded clasts in conglomerate were reworked during subaerial transport and or temporary storage in shoreline or shallow water environments prior to redeposition red oxidised lava and scoria clasts in bedded breccia and conglomerate also imply that the source was partly subaerial the facies assemblage is consistent with a setting on the submerged flanks of a shoaling basaltic seamount the coarse grade and large volume of conglomerate and breccia reflect the high supply rate of clasts and the propensity for collapse and redeposition on steep palaeoslopes the clast supply may have been boosted by vigorous fragmentation processes accompanying transition of lava from subaerial to submarine settings the greater proportion of primary volcanic facies compared with resedimented volcaniclastic and volcanogenic sedimentary facies in central and northwestern exposures near rakiraki indicates they are more proximal than those in the southeast towards viti levu bay the proximal area coincides with one of two zones where nw se trending mafic dykes are especially abundant and it is close to several small dome like intrusions of intermediate and felsic igneous rocks the original surface morphology of the volcano is no longer preserved though the partial fan of bedding dip azimuths in the south and east and the wide diameter exceeding 20 km are consistent with a broad shield

poseidon s horses plate tectonics and earthquake storms in the late bronze age aegean and eastern mediterranean abstract in light of the accumulated evidence now published the oft denigrated suggestion that major earthquakes took place in the aegean and eastern mediterranean areas during the late 13th and early 12th centuries bc must be reconsidered a new study of earthquakes occurring in the aegean and eastern mediterranean region during the 20th century utilizing data recorded since the invention of seismic tracking devices shows that this area is criss crossed with major fault lines and that numerous temblors of magnitude 6 5 enough to destroy modern buildings let alone those of antiquity occur frequently it can be demonstrated that such major earthquakes often occur in groups known as sequences or storms in which one large quake is followed days months or even years later by others elsewhere on the now weakened fault line when a map of the areas in the aegean and eastern mediterranean region affected i e shaken by 20th centuryad earthquakes of magnitude 6 5 and greater and with an intensity of vii or greater is overlaid on robert drews map of sites destroyed in these same regions during the so called catastrophe near the end of the late bronze age it is readily apparent that virtually all of these lba sites lie within the affected high shaking areas while the evidence is not conclusive based on these new data we would suggest that an earthquake storm may have occurred in the late bronze age aegean and eastern mediterranean during the years 1225 1175bc this storm may have interacted with the other forces at work in these areas c 1200bc and merits consideration by archaeologists and prehistorians

earthquakes and archaeology abstract this article examines the use of archaeological evidence for the assessment of historical earthquakes in the eastern mediterranean region and middle east long before the advent of modern seismology we ask the questions when and where have large earthquakes happened in the past how can this evidence contribute to our scientific understanding of earthquake activity is it possible on literary and archaeological grounds to distinguish between earthquake damage and damage from other causes it is found that archaeological evidence for an earthquake is not always clear or unambiguous and that there is a need for collaboration between archaeologists historians geologists engineering seismologists and workers in other disciplines to evaluate the traces of earthquakes in excavations both for understanding their effects at the site and for the information they can provide about the nature of the earthquake implicated

the submarine flanks of anatahan volcano commonwealth of the northern mariana islands abstract the submarine flanks of anatahan volcano were surveyed comprehensively for the first time in 2003 and 2004 with multibeam and sidescan sonar systems a geologic map based on the new bathymetry and backscatter data shows that 67 of the volcano s submarine flanks are covered with volcaniclastic debris and 26 is lava flows cones and bedrock outcrops the island of anatahan is only 1 of the volume of the entire volcano which has a height from its submarine base of 3700 m and an average diameter of 35 km ne anatahan is a prominent satellite volcano located 10 km ne of the island but it is only 6 of anatahan s volume 40 km 3 vs 620 km 3 seventy eight submarine eruptive vents are mapped associated with lava flows and cones between depths of 350 and 2950 m and 80 of these vents are located in a cluster on the east flank of the volcano the distribution of cones and lava flows vs depth suggests a possible change in eruptive style from explosive to effusive between 1500 and 2000 m eruptive vents below 2000 m have produced mostly lava flows there is no evidence of major landslides on the submarine flanks of anatahan volcano in contrast to many basaltic islands and seamounts suggesting that mass wasting at felsic oceanic arc volcanoes may be characterized by sediment flows of unconsolidated volcaniclastic debris instead of mass movements of relatively large intact blocks

constraining models of postglacial rebound using space geodesy a detailed assessment of model ice 5g vm2 and its relatives summary using global positioning system very long baseline interferometry satellite laser ranging and doppler orbitography and radiopositioning integrated by satellite observations including the canadian base network and fennoscandian bifrost array we constrain in models of postglacial rebound the thickness of the ice sheets as a function of position and time and the viscosity of the mantle as a function of depth we test model ice 5g vm2 t90 rot which well fits many hundred holocene relative sea level histories in north america europe and worldwide ice 5g is the deglaciation history having more ice in western canada than ice 4g vm2 is the mantle viscosity profile having a mean upper mantle viscosity of 0 5 1021 pa s and a mean uppermost lower mantle viscosity of 1 6 1021 pa s t90 is an elastic lithosphere thickness of 90 km and rot designates that the model includes rotational feedback earth s response to the wander of the north pole of earth s spin axis towards canada at a speed of 1 myr 1 the vertical observations in north america show that relative to ice 5g the laurentide ice sheet at last glacial maximum lgm at 26 ka was 1 much thinner in southern manitoba 2 thinner near yellowknife northwest territories 3 thicker in eastern and southern quebec and 4 thicker along the northern british columbia alberta border or that ice was unloaded from these areas later thicker or earlier thinner than in ice 5g the data indicate that the western laurentide ice sheet was intermediate in mass between ice 5g and ice 4g the vertical observations and grace gravity data together suggest that the western laurentide ice sheet was nearly as massive as that in ice 5g but distributed more broadly across northwestern canada vm2 poorly fits the horizontal observations in north america predicting places along the margins of the laurentide ice sheet to be moving laterally away from the ice centre at 2 mm yr 1 in ice 4g and 3 mm yr 1 in ice 5g in disagreement with the observation that the interior of the north american plate is deforming more slowly than 1 mm yr 1 substituting vm5a t60 for vm2 t90 that is introducing into the lithosphere at its base a layer with a high viscosity of 10 1021 pa s greatly improves the fit of the horizontal observations in north america ice 4g vm5a t60 rot predicts most of the north american plate to be moving horizontally more slowly than 1 mm yr 1 in agreement with the data ice 5g vm5a t60 rot well fits both the vertical and horizontal observations in europe the space geodetic data cannot distinguish between models with and without rotational feedback in the vertical because the velocity of earth centre is uncertain and in the horizontal because the areas of the plate interiors having geodetic sites is not large enough to detect the small differences in the predictions of rotational feedback going across the plate interiors

tree damage and surface displacement the 1931 m 8 0 fuyun earthquake trees often suffer damage during large earthquakes due to shaking and rupturing of the ground surface from associated faults the damage may result in temporary asymmetric growth and reduction in the width of annual growth rings observation of tree displacement and tree ring analysis of the circle shrub sabina pseudosabina on the fuyun fault zone in northwest china reveals dextral displacement as much as 10 8 m along the surface rupture located near the epicenter of the 1931 m 8 fuyun earthquake tree ring analysis indicates a sharp change in ring width in 1931 rings of 1931 1934 are much narrower in width than those formed immediately before 1931 and after 1934 no obvious abnormalities in average temperature or rainfall during 1931 1934 were recorded the results of ring analysis and the displacement of trees indicate that the sharp change of tree ring width and the maximum displacements of 10 15 m near the epicentral area were generated by surface rupturing in the 1931 m 8 0 fuyun earthquake

en echelon axial volcanic ridges at the reykjanes ridge a life cycle of volcanism and tectonics abstract new deep towed sidescan records and multibeam bathymetric data along the reykjanes ridge allow us to assess the varying thermal effect of the icelandic hotspot the increasing predominance of faulting speculated to be derived from mantle upwelling and outflow over simple extensional neotectonics is traced from northeast to southwest numerous en echelon volcanic ridges built along the plate boundary are seen in various stages of growth and decay and a cycle of alternating construction and dismemberment is proposed unfaulted short narrow lensoid ridges occasionally in small groups are interpreted as immature and developing axial volcanic ridges broad convex flanked ridges appear to be mature sites of volcanic construction where the magma supply has been maintained narrow bow form ridges occasionally with rectilinear flanks represent axial volcanic ridges which have ceased construction and are in initial stages of disaggregation isolated polygonal blocks generally seen off axis represent the most advanced stage of dismantling of the surface crustal accretionary features while this cyclicity is speculated to be related to periodic magmatic and tectonic focusing and defocusing along the axis due to the restricted magma supply at this slow spreading ridge it is recognised that this needs modelling although the oblique spreading of the reykjanes ridge allows one to clearly distinguish between structures attributable to plate spreading from those related to small scale accretionary processes we propose that the major processes identified in this study are directly applicable to all slow spreading sections of mid ocean ridges

meiofauna assemblages of the condor seamount north east atlantic ocean and adjacent deep sea sediments seamounts are currently considered hotspots of biodiversity and biomass for macro and megabenthic taxa but knowledge of meiofauna is still limited studies have revealed the existence of highly diverse meiofauna assemblages however most data are mainly qualitative or focused only on specific groups thus preventing comparisons among seamounts and with other deep sea areas this study conducted on condor seamount azores north east atlantic ocean describes variation in abundance biomass community structure and biodiversity of benthic meiofauna from five sites located on the condor seamount and one site away from the seamount while the summit of the seamount hosted the highest alpha biodiversity the flanks and the bases showed a rich meiofauna assemblage in terms of abundance and biomass the observed marked differences in grain size composition of sediments reflected the oceanographic conditions impacting different sectors of the condor seamount and could play an important role in the spatial distribution of different meiofaunal taxa trophic conditions biochemical composition of organic matter explained 78 of the variability in the meiofauna biomass pattern while sediment grain influenced the vertical distribution of meiofauna and only partially explained meiofaunal taxa composition this study provides a further advancement in the knowledge of meiofaunal communities of seamounts only a deeper understanding of the whole benthic communities including meiofauna will allow to elaborate effective management and conservation tools for seamount ecosystems

submarine volcaniclastic rocks in this chapter we are concerned with underwater volcaniclastic eruptions and products as well as pyroclastic flows and debris generated on land and transported by mass flowage into the sea submarine fallout deposits derived from land based eruptions are treated in chapter 7 clastic materials redistributed as mass flows or turbidity currents originating from the rapid build up of tephra and epiclastic volcanic debris along coastal parts of volcanoes are also discussed in various places throughout the text e g chap 13

the submarine eruption and erosion of surtla surtsey iceland abstract surtla is the site of a short lived submarine vent which built basaltic elastic deposits almost to sea level in 1963 early in the eruption of surtsey since then wave and current activity have eroded the volcanic pile such that in july 1981 its top was a fairly level plateau 45 m below sea level and its surface comprised a lag deposit of sparse blocks of lava in a bed mainly of glass granules this winnowed layer was underlain by a nonreworked poorly sorted and finer deposit of glassy clasts formed by a combination of disruption by magmatic volatiles steam explosions and quench brecciation during the eruption the explosion violence and associated comminution increased as the pile built up to shallower water depths it is argued that at times of continuous effusion a cupola of steam was situated over the vent as indicated by scoriaceous spatter which shows agglutination and bread crust features that can only have developed in conditions more akin to subaerial than hitherto envisaged in a subaqueous eruption

high resolution geophysical observations of the yermak plateau and northern svalbard margin implications for ice sheet grounding and deep keeled icebergs high resolution geophysical evidence on the seafloor morphology and acoustic stratigraphy of the yermak plateau and northern svalbard margin between 79 20 and 81 30 n and 5 and 22 e is presented

transition from circular to stellate forms of submarine volcanoes large volcanic islands and guyots have stellate forms that reflect the relief of radiating volcanic rift zones multiple volcanic centers and embayments due to giant flank failures small mid ocean ridge volcanoes in contrast are commonly subcircular in plan view and show only embryonic rift zones in order to characterize the transition between these two end members the morphology of 141 seamounts and guyots was studied using the shape of the depth contour at half the height of each edifice irregularity was characterized by measuring perimeter distance elongation and moment of inertia of the contours assuming an ideal edifice is circular the analysis reveals a general transition over 2 4 km edifice height best transition estimate 3 km while some large edifices 4 5 km high show no major embayments or ridges suggesting considerable variation in the effectiveness of mechanisms that cause flank instability and growth of rift zones the various origins of the transition are discussed and the upper limit of magma chambers many of which lie above the basement of the larger edifices is proposed to affect the morphologic complexity via a number of mechanisms and is an important factor affecting the mode of growth the origins of the truncated cone shape of mid ocean ridge volcanoes are also discussed of the eruption mechanisms that have been proposed to explain their flat summits the most likely mechanisms involve eruption from small ephemeral magma bodies lying within the low density upper oceanic crust the discussion includes speculations on factors affecting the depths of magma chambers beneath oceanic volcanoes supporting table is available via web browser or via anonymous ftp from ftp kosmos agu org directory append username anonymous password guest subdirectories in the ftp site are arranged by paper number information on searching and submitting electronic supplements is found at http www agu org pubs csupp about html

serreta 1998 2001 submarine volcanic eruption offshore terceira azores characterization of the vent and inferences about the eruptive dynamics abstract high resolution bathymetric data and seafloor sampling were used to characterize the most recent volcanic eruption in the azores region the 1998 2001 serreta submarine eruption the vent of the eruption is proposed to be an asymmetric topographic high composed of two coalescing volcanic cones underlying the location where lava balloons had been observed at the sea surface during the eruption the volcanic products related to the 1998 2001 eruption are constrained to an area of 0 5 km2 around the proposed vent position a submarine strombolian style eruption producing basaltic lava balloons ash and coarse scoriaceous materials with limited lateral dispersion led to the buildup of the cones the 1998 2001 serreta eruption shares many similarities with other intermediate depth lava balloon forming eruptions e g the 1891 eruption offshore pantelleria and the 2011 2012 eruption south of el hierro revealing the particular conditions needed for the production of this unusual and scarcely documented volcanic product

the azores triple junction evolution since 10 ma from an aeromagnetic survey of the mid atlantic ridge abstract in the past two decades several models have been presented to describe the evolution and the present structure of the azores triple junction these models were mainly based on morphological analysis of sea bottom topography sparse magnetic profiling sidescan sonar surveying over the plateaus and global plate kinematic considerations for the north atlantic in this paper we follow a different approach from a detailed aeromagnetic survey covering both sides of the mid atlantic ridge between 37 n and 40 30 n the magnetic anomalies up to anomaly 5 are accurately identified allowing careful modelling of the kinematics of this region for the past 10 ma and thus establishing a coherent framework for the design of geophysical models for the azores triple junction the analysis of magnetic anomalies and the use of fourier domain inversion techniques show that the ridge is made up of six segments each one varying in length from 50 to 60 km the more continuous section of the ridge can be defined from the first four northern segments although the north azores fracture zone right offsets the ridge at 39 30 n 29 40 w the fifth and sixth segments are respectively right offset by the acor fracture zone at 38 23 n 30 15 w and by the princess alice fracture zone at 38 00 n 30 50 w anomaly identifications using a two dimensional model and plate tectonics reconstruction techniques allowed the calculation of rotation pole parameters the results thus obtained reveal that at least between anomalies 5 and 3 10 3 85 ma the azores displayed an independent motion relative to the neighbouring plates and after anomaly 2a 2 45 ma the azores moved attached to the eurasian plate the triple junction azores north america africa or eurasia north america africa moved northward from 38 00 n 30 50 w to 38 20 n 30 15 w between 4 and 3a and probably to 38 50 n 30 00 w at anomaly 2a time a detailed reconstruction model is presented

storm induced sediment gravity flows at the head of the eel submarine canyon northern california margin 1 as part of the strataform program a bottom boundary layer bbl tripod was deployed at 120 m depth in the northern thalweg of the eel canyon during winter 2000 increases of the near bottom suspended sediment concentrations ssc recorded at the canyon head were not directly related to the eel river discharge but were clearly linked to the occurrence of storms bbl measurements revealed that during intensifications of the wave orbital velocity sediment transport at the head of the canyon occurred as sediment gravity flows directed down canyon observational evidence for near bed sediment gravity flow transport included an increase toward the bed of the down canyon component of wave averaged velocity and high estimated ssc at higher sampling frequencies 1 hz the current components during these events fluctuated at the same periodicity as the pressure reflecting a clear influence of the surface wave activity on the generation and maintenance of the sediment gravity flows the origin of such flows is not related to the formation of fluid muds on the shelf or to intense wave current sediment resuspension around the canyon head region rather liquefaction of sediment deposited at the head of the canyon induced by wave load excess pore water pressures during storms combined with elevated slopes around the canyon head appear to be the mechanisms initiating sediment transport the resulting fluidized sediment layer can easily be eroded entrained into the water column and transported down canyon as a sediment gravity flow results from this study reveal that storm induced sediment gravity flows occur periodically in the eel canyon head and suggest that this kind of sediment transport process can occur in other submarine canyons more frequently than previously expected

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

mid ocean ridge eruptive vent morphology and substructure evidence for dike widths eruption rates and evolution of eruptions and axial volcanic ridges high resolution side scan sonar data of mid atlantic ridge mar inner valley floor axial volcanic ridges reveal details of their architectural elements we develop quantitative models for basaltic eruptions from dikes and compare the predicted products of these eruptions with the observed morphologic features inhibition of gas exsolution lack of magma disruption and hydrothermal effects combine to decrease the rise speed of magma in submarine dikes and enhance cooling leading to more rapid centralization of eruptions along the widest places in the dike dikes are predicted to initially feed eruptions from fissure vents producing lines of hummocky ridges centralization of activity to several adjacent vents produces chains of hummocky bulbous mounds and can enhance the effusion rate at a single vent to produce small seamounts the widest dikes are predicted to produce smooth flows up to several kilometers in length which should pond in adjacent lows edifice sizes predicted on the basis of volume fluxes and flow lengths implied by the widths of dikes observed on the seafloor in iceland and in ophiolite complexes are in quantitative agreement with the dimensions of observed features each ridge is made up of the products of a variety of these individual dike emplacement and extrusive events involving various dike widths cooling times and eruption durations on the basis of typical mar spreading rates about one dike emplacement event would be expected every 40 years since not all dikes reach the surface the actual mean interval between eruptions will exceed this mar dikes should solidify between average dike emplacement events dike emplacement events are more frequent on the east pacific rise epr and thus new dikes are more likely to reoccupy the sites of incompletely solidified older dikes differences between the morphology of the mar axial volcanic ridge and the sheet flow dominated epr are attributed to on average wider dikes erupting with greater frequency along the epr

formation of submarine flat topped volcanic cones in hawai i high resolution bathymetric mapping has shown that submarine flat topped volcanic cones morphologically similar to ones on the deep sea floor and near mid ocean ridges are common on or near submarine rift zones of kilauea kohala or mauna kea mahukona and haleakala volcanoes four flat topped cones on kohala were explored and sampled with the pisces v submersible in october 1998 samples show that flat topped cones on rift zones are constructed of tholeiitic basalt erupted during the shield stage similarly shaped flat topped cones on the northwest submarine flank of ni ihau are apparently formed of alkalic basalt erupted during the rejuvenated stage submarine postshield stage eruptions on hilo ridge mahukona hana ridge and offshore ni ihau form pointed cones of alkalic basalt and hawaiite the shield stage flat topped cones have steep 25 sides remarkably flat horizontal tops basal diameters of 1 3 km and heights 300 m the flat tops commonly have either a low mound or a deep crater in the center the rejuvenated stage flat topped cones have the same shape with steep sides and flat horizontal tops but are much larger with basal diameters up to 5 5 km and heights commonly greater than 200 m the flat tops have a central low mound shallow crater or levees that surrounded lava ponds as large as 1 km across most of the rejuvenated stage flat topped cones formed on slopes 10 and formed adjacent semicircular steps down the flank of ni ihau rather than circular structures all the flat topped cones appear to be monogenetic and formed during steady effusive eruptions lasting years to decades these and other submarine volcanic cones of similar size and shape apparently form as continuously overflowing submarine lava ponds a lava pond surrounded by a levee forms above a sea floor vent as lava continues to flow into the pond the lava flow surface rises and overflows the lowest point on the levee forming elongate pillow lava flows that simultaneously build the rim outward and upward but also dam and fill in the low point on the rim the process repeats at the new lowest point forming a circular structure with a flat horizontal top and steep pillowed margins there is a delicate balance between lava heat supply to the pond and cooling and thickening of the floating crust factors that facilitate construction of such landforms include effusive eruption of lava with low volatile contents moderate to high confining pressure at moderate to great ocean depth long lived steady eruption years to decades moderate effusion rates probably ca 0 1 km3 year and low but not necessarily flat slopes with higher effusion rates sheet flows flood the slope with lower effusion rates pillow mounds form hawaiian shield stage eruptions begin as fissure eruptions if the eruption is too brief it will not consolidate activity at a point and fissure fed flows will form a pond with irregular levees the pond will solidify between eruptive pulses if the eruption is not steady lava that is too volatile rich or that is erupted in too shallow water will produce fragmental and highly vesicular lava that will accumulate to form steep pointed cones as occurs during the post shield stage the steady effusion of lava on land constructs lava shields which are probably the subaerial analogs to submarine flat topped cones but formed under different cooling conditions

faulting and effects of earthquakes on minoan archaeological sites in crete greece abstract examination of damages affecting the buildings of the archaeological sites of phaistos and agia triada southern crete suggests that these minoan settlements were probably destroyed by two major seismic events characterized by mks intensities of ix x and occurred at the end of the protopalatial 1700 bc and the neopalatial 1450 bc periods geological and morphological studies carried out in the neighbouring areas show the occurrence of e w trending quaternary normal fault segments spili and agia galini faults that control the present topography and morphology and exhibit steep young scarps mostly holocene in age these fault segments are related to a nw se extension direction which is consistent with that indicated by the available focal mechanisms of the earthquakes occurring in this area in the last 50 years combining structural and seismic data we can infer that the spili and agia galini fault segments could represent good candidates to be considered active faults generating large earthquakes m 6 5 that were responsible for the damages of phaistos and agia triada this hypothesis suggests that the minoan palatial centres were destroyed by several large earthquakes related to ruptures along distinct fault segments rather than by a single catastrophic event that caused the abrupt destruction of the minoan civilisation in the eastern mediterranean

structure and development of an axial volcanic ridge mid atlantic ridge 45 n we describe the most comprehensive and detailed high resolution survey of an axial volcanic ridge avr ever conducted at 45 n on the mid atlantic ridge we use 3 m resolution sidescan sonar deep towed magnetic field measurements video observations from eleven rov dives and two very high resolution bathymetry and magnetic surveys the most recently active avr has high topographic relief high acoustic backscatter high crustal magnetization and little faulting it is sharp crested 25 4 km in extent and 500 m high and is covered by approximately 8000 volcanic hummocks whose detailed nature is revealed for the first time each is an individual volcano 450 m in diameter and 200 m high ranging from steep sided 45 cones to low domes many have suffered significant flank collapse hummocks tend to align in rows parallel to the avr axis parallel to its ne trending spurs or on its lower flanks sub normal to the avr trend these latter are spaced 1 2 km apart and comprise 1 2 km long rows of single volcanoes we infer that their emplacement is controlled by down flank magma transport possibly via lava tubes the avr contains only one large flat topped seamount the flanking median valley floor consists of either older hummocky volcanic terrain or flat lying mostly sediment covered lavas these typically have low relief lobate surfaces inflation and collapse structures and occasional lava tubes and tumuli the avr displays open fissures mostly along its crest there is direct evidence for only a few small faults on the avr though steep outward facing slopes draped by elongate pillows may be small normal faults covered by lava the surrounding median valley floor is heavily fissured normal faults cut it and an older avr the latter displaying significant outward facing faults high crustal magnetization an approximate proxy for crustal age within the brunhes is confined to the active avr magnetic palaeointensity measurements are consistent with ages up to 12 ka for several samples from the active avr and 12 ka for one sample from the median valley floor this is much less than the predicted spreading age implying distribution of melt off axis or episodic avr growth

recognition of earthquake related damage in archaeological sites examples from the dead sea fault zone abstract archaeological structures that exhibit seismogenic damage expand our knowledge of temporal and spatial distribution of earthquakes afford independent examination of historical accounts provide information on local earthquake intensities and enable the delineation of macroseismic zones they also illustrate what might happen in future earthquakes in order to recover this information we should be able to distinguish earthquake damage from anthropogenic damage and from other natural processes of wear and tear the present paper reviews several types of damage that can be attributed with high certainty to earthquakes and discusses associated caveats in the rare cases where faults intersect with archaeological sites offset structures enable precise determination of sense and size of slip and constrain its time among the characteristic off fault damage types i consider horizontal shifting of large building blocks downward sliding of one or several blocks from masonry arches collapse of heavy stably built walls chipping of corners of building blocks and aligned falling of walls and columns other damage features are less conclusive and require additional evidence e g fractures that cut across several structures leaning walls and columns warps and bulges in walls circumstantial evidence for catastrophic earthquake related destruction includes contemporaneous damage in many sites in the same area absence of weapons or other anthropogenic damage stratigraphic data on collapse of walls and ceilings onto floors and other living horizons and burial of valuable artifacts as well as associated geological palaeoseismic phenomena such as liquefaction land and rock slides and fault ruptures additional support may be found in reliable historical accounts special care must be taken in order to avoid circular reasoning by maintaining the independence of data acquisition methods

morphology and shallow structure of seafloor mounds in the canary basin eastern central atlantic ocean abstract the increasing volume of high resolution multibeam bathymetry data collected along continental margins and adjacent deep seafloor regions is providing further opportunities to study new morphological seafloor features in deep water environments in this paper seafloor mounds have been imaged in detail with multibeam echosounders and parametric sub bottom profilers in the deep central area of the canary basin 350 550 km west off el hierro island between 4800 and 5200 mbsl these features have circular to elongated shapes with heights of 10 to 250 m diameters of 2 24 km and with flank slopes of 2 50 based on their morphological features and the subsurface structures these mounds have been classified into five different types of mounds that follow a linear correlation between height and slope but not between height and size the first second subgroup a and third mound types show heights lower than 80 m and maximum slopes of 35 with extension ranging from 2 to 400 km2 and correspond to domes formed at the surface created by intrusions located at depth that have not outcropped yet the second subgroup b fourth and fifth mound types show higher heights up to 250 m high maximum slopes of 47 and sizes between 10 and 20 km2 and are related to the expulsion of hot and hydrothermal fluids and or volcanics from extrusive deep seated systems based on the constraints on their morphological and structural analyses we suggest that morphostructural types of mounds are intimately linked to a specific origin that leaves its footprint in the morphology of the mounds we propose a growth model for the five morphostructural types of mounds where different intrusive and extrusive phenomena represent the dominant mechanisms for mound growth evolution these structures are also affected by tectonics bulge like structures clearly deformed by faulting and mass movements slide scars and mass transport deposits in this work we report how intrusive and extrusive processes may affect the seafloor morphology identifying a new type of geomorphological feature as intrusive domes that have to date only been reported in fossil environments but might extend to other oceanic areas

organic matter composition and macrofaunal diversity in sediments of the condor seamount azores ne atlantic in recent years increasing knowledge has been accumulated on seamounts ecology however their sedimentary environments and associated biological communities remain largely understudied in this study we investigated quantity and biochemical composition of organic matter and macrofaunal diversity in sediments of the condor seamount ne atlantic azores in order to test the effect of the seamount on organic matter distribution sediment samples were collected in 6 areas the summit the northern and southern flanks and bases and in an external far field site macrofauna abundance and diversity were investigated on the summit the southern flank and in the far field site the organic matter distribution reflected the complex hydrodynamic conditions occurring on the condor concentrations of organic matter compounds were generally lower on the whole seamount than in the far field site and on the seamount summit compared to flanks and bases a clear difference was also evident between the northern and southern slopes of the condor suggesting a role of the seamount in conditioning sedimentation processes and distribution of food resources for benthic consumers macrofauna assemblages changed significantly among the three sampling sites high abundance and dominance accompanied by low biodiversity characterized the macrofauna community on the condor summit while low dominance and high biodiversity were observed at the flank our results although limited to five samples on the seamount and two off the seamount do not necessarily support the paradigm that seamounts are more biodiverse than the surrounding seafloor however the abundance and biomass functional diversity and taxonomical distinctiveness of the macrofaunal assemblages from the condor seamount suggest that seamounts habitats may play a relevant role in adding to the regional biodiversity

the terceira rift as hyper slow hotspot dominated oblique spreading axis a comparison with other slow spreading plate boundaries abstract we suggest the 550 km long terceira rift tr azores plateau is the world s slowest spreading hyper slow 4 mm a plate separation 2 3 3 8 mm a perpendicular to oblique axial segments organized accreting plate boundary in its slightly sinuous ca 300 km radius of curvature axial trace its oblique spreading angles ca 40 65 and in frequency and first motions of earthquakes the tr resembles better known ultra or super slow spreading ridges e g gakkel and southwest indian ridges interpreted simply as volcanically unfilled rift valley segments the inter island basins e g the 3200 m deep hirondelle basin are slightly wider 30 60 km but not significantly deeper 1000 2200 m than the mid atlantic ridge mar median valley 20 28 mm a 10 n 53 n however along axis segmentation wavelengths ca 100 km are double those along the central mar but make tr comparable to the ultra slow 15 16 mm a southwest indian and gakkel 7 13 mm a ridges if this segmentation wavelength reflects rayleigh taylor instabilities the viscosity contrast between the overlying axial lithosphere and the partial melt zones is about an order of magnitude greater at ca 4 16 mm a than at 20 30 mm a the tr differs dramatically from ultra slow ridges only in the large amplitude of along strike topography 2000 4000 m 4200 m total variation owing perhaps to a copious melt flux from the azores hotspot combined with a spreading rate determined greater axial flexural strength and plate thickness and slower export of volcanics from the rift axis the probable tr youth ca 1 ma requiring less than 4 km new oceanic crust suggests lack of steady state spreading conditions which may explain the published gravity evidence against tr spreading absolute plate motions support the creation of the azores plateau by successive ne jumps of the rift axis to maintain its position over a fixed hotspot

timing of the last glacial maximum from observed sea level minima during the last glacial maximum ice sheets covered large areas in northern latitudes and global temperatures were significantly lower than today but few direct estimates exist of the volume of the ice sheets or the timing and rates of change during their advance and retreat here we analyze four distinct sediment facies in the shallow tectonically stable bonaparte gulf australia each of which is characteristic of a distinct range in sea level to estimate the maximum volume of land based ice during the last glaciation and the timing of the initial melting phase we use faunal assemblages and preservation status of the sediments to distinguish open marine shallow marine marginal marine and brackish conditions and estimate the timing and the mass of the ice sheets using radiocarbon dating and glacio hydroisostatic modelling our results indicate that from at least 22 000 to 19 000 calendar years before present land based ice volume was at its maximum exceeding today s grounded ice sheets by 52 5 x 10 exp 6 cu km a rapid decrease in ice volume by about 10 percent within a few hundred years terminated the last glacial maximum at 19 000 250 years

submarine explosive volcanism in the southeastern terceira rift sao miguel region azores abstract morphologic studies with sonar data and in situ observations of modern eruptions have revealed some information suggesting how submarine volcanic cones develop but the information only addresses the modern surfaces of these features here we describe a study combining morphological data with high resolution seismic reflection data collected over cones within the southeastern terceira rift a succession of deep basins volcanic bathymetric highs and islands e g sao miguel representing the westernmost part of the eurasian nubian plate boundary the cones 252 are distributed in depths down to 3200 m and exhibit an average diameter of 743 m an average slope of 20 and heights mainly between 50 and 200 m the cones are here classified into three different categories by physiographic or tectonic setting we find no particular morphometric differences in cone shapes between these areas first numerous cones located at the submarine flanks of sao miguel s sete cidades and fogo volcano are considered to be parasitic structures second in the southeast of the island they form a superstructure possibly reflecting an early submarine stadium of a posterior subaerial stratovolcano third some cones are controlled by faults mostly in a graben system southwest of the island high resolution multichannel seismic data indicates that the graben cones evolved synchronously with the graben formation bottom currents then probably removed the surficial fine grain size fraction leaving rough surface textures of the cones which backscatter sonar signals strongly in the data recorded here however a young cone investigated in detail is characterized by a smooth surface a marked increase of internal stratification with increasing distance from the summit and upwards concave flanks others exhibit central craters suggesting an explosive than an effusive evolution of these structures the morphological characteristics of these submarine cones show that they have similar sizes and shapes to cinder cones onshore sao miguel

mixed layer deepening during heinrich events a multi planktonic foraminiferal δ18o approach proxies from greenland ice cores and north atlantic marine sediment cores document repeated extreme climate swings of a few decades to millennia during the last glacial cycle including periods of intense ice rafting called heinrich events hes we have found similar oxygen isotope variations recorded in mixed layer and thermocline dwelling planktonic foraminifera during hes 0 1 and 4 suggesting that three foraminiferal taxa calcified their shells at similar temperatures in a homogenized upperwater column this implies that the surface mixed layer was deeper during hes similar deepening occurred on the northern margin of the ice rafted debris belt implying that these deep mixed layers during hes were widespread in the region we suggest that an increase in storminess during hes intensified the vertical mixing of meltwater from ice rafting in the upper ocean

recurrence pattern of holocene earthquakes along the dead sea transform revealed by varve counting and radiocarbon dating of lacustrine sediments abstract a high resolution holocene seismic history of the dead sea transform dst is established from laminated sedimentary cores recovered at the shores of the dead sea radiocarbon dating and annual laminae counting yield excellent agreement between disturbed sedimentary structures identified as seismites and the historical earthquake record all recent and historical strong events of the area were identified including the major earthquakes of a d 1927 1837 1212 1033 749 and 31 b c the total of 53 seismites recognized along the entire holocene profile indicate varying recurrence intervals of seismic activity between a few and 1000 years with a conspicuous minimum rate at 2100 31 b c and a noticeable maximum during the past six to eight centuries most of the epicenters of the correlated earthquakes are situated very close to the dead sea within 150 km or up to 400 km north of it along the dst between 1000 b c and a d 1063 and from a d 1600 to recent time the epicenters are all located on the northern segment of the dst whereas prior to 1000 b c and between a d 1000 and 1600 they appear to scatter along several segments of the dst we establish how the local intensity exerts a control on the formation of seismites at historically estimated intensities greater than vii all well documented earthquakes are correlated whereas at intensities smaller than vi none are matching the periods with enhanced earthquake rate along the dst correlate with those along the north anatolian fault as opposed to the intervening east anatolian fault this may indicate some elastic coupling on plate boundary scale that may also underlie escape and extrusion tectonics typical of continental collision

life and death of axial volcanic ridges segmentation and crustal accretion at the reykjanes ridge abstract in this paper we present a description of ridge segmentation and segment evolution at the slow spreading reykjanes ridge based on the combined and integrated interpretation of several geophysical datasets acquired along this section of the mid atlantic ridge at the reykjanes ridge segmentation is manifest at the seabed most clearly as axial volcanic ridges avrs these correspond to third order segments while multiple adjacent avrs collectively represent the larger scale pattern of second order segmentation avrs are known to undergo a life cycle of multiple phases of magmatic accretion tectonic extension and dismemberment our combined interpretation of the results of the previously independently analysed datasets indicates that magma influx from the mantle to the crust associated with these cycles is initially focused towards second order segment centres adjacent avrs within a second order segment are progressively rejuvenated from the segment centre towards the segment tips during each cycle with the redistribution of magma along axis occurring within individual avrs at mid crustal to upper crustal level during the magmatic phase in some cases offset basins between adjacent avrs are characterised by significant crustal melt accumulation and increased crustal thickness indicating that they are currently sites of incipient avr growth the initiation of new avrs within former offset basins and the abandonment of other avrs indicates that third order segments have a finite and limited life span as part of this study we have mapped the geometry and location of all abandoned inactive relict avrs preserved off axis to form the basis of a reconstruction of the pattern of asymmetric spreading using this reconstruction we have developed a new model of avr evolution spanning 2 myr of crustal accretion that reveals nested scales and phases of accretion in which each avr undergoes multiple tectonomagmatic cycles before ending its life once it has migrated sufficiently far across the median valley to become isolated from its melt supply once extinct avrs are rafted further off axis and are preserved in the morphology of the seabed and the thickness of layer 2a

crusader castle torn apart by earthquake at dawn 20 may 1202 the crusader castle of vadum jacob an outpost overlooking the jordan river was deformed during a destructive earthquake triggered by motion along the dead sea transform the m 7 earthquake occurred at dawn 20 may 1202 and offset the castle walls by 1 6 m this exceptional precision in dating and estimating displacement was achieved by combining accounts from primary historical sources by excavating the dead sea transform where it bisects the castle and by dating faulted archaeological strata the earthquakes of october 1759 and or january 1837 may account for the remaining 0 5 m out of a total 2 1 m of offset our study exploits the potential embodied in interdisciplinary historical archaeological geological research and illustrates how detailed histories of seismogenic faults can be reconstructed

reevaluation of magnetic chrons in the north atlantic between 35 n and 47 n implications for the formation of the azores triple junction and associated plateau 1 in this paper we present a new magnetic compilation for an area of the north atlantic located between 35 n and 47 n and up to anomaly 33r we also present a strategy to pick magnetic isochrones and compute finite rotation poles this technique is based on a continuous reduction to the pole technique and some basic assumptions regarding the direction of the remanent magnetization vector a cost function that measures the misfit between interpreted and rotated isochrones and the systematic exploitation of the parameter space is used to compute the best set of finite eulerian rotations for the chrons 5 6 6c 11 12 13 18 20 21 22 23 24 25 26 28 29 30 32 33 and 33r this set of chrons and poles is used to discuss the evolution of the north atlantic close to iberia and in particular the onset and early development of the azores triple junction area we show that the relative motion between the eurasian and the african plates can be coherently described in terms of rigid plate kinematics respecting both the anomalies shapes and the precise location of the main structural elements of the area the pico fracture zone the east azores fracture zone and the gloria fault we distinguish from the magnetic point of view two different areas of the azores plateau the south azores domain where almost undisturbed nnw magnetic lineations can be found and the azores domain close to the topographic highs and with no systematic magnetic stripping with the exception of a few recent lineations probably matuyama and brunhes we present an approximate reconstruction of the plate configuration after chron 18 to conclude that the attachment of iberia to eurasia was younger than previously thought lower miocene triggering the formation of the azores domain in which stretching took place essentially in the last 20 ma at an average rate of 3 8 mm a and progressively attaching the south azores domain to the african plate by a northward progression of the triple junction

sources of the large a d 1202 and 1759 near east earthquakes the sources of the may 1202 and november 1759 m 7 5 near east earthquakes remain controversial because their macroseismal areas coincide straddling subparallel active faults in the lebanese restraining bend paleoseismic trenching in the yammouneh basin yields unambiguous evidence both for slip on the yammou neh fault in the twelfth thirteenth centuries and for the lack of a posterior event this conclusion is supported by comparing the freshest visible fault scarps which imply more recent slip on the r chaiya serghaya system than on the yammouneh fault our results suggest that the recurrence of an a d 1202 type earthquake might be due this century as part of a sequence similar to that of a d 1033 1202 possibly heralded by the occurrence of the 1995 mw 7 3 aqaba earthquake the seismic behavior of the levant fault might thus be characterized by millennial periods of quiescence separated by clusters of large earthquakes