scaling characteristics of local geomagnetic field and seismicity at etna volcano and their dynamics in relation to the eruptive activity abstract the evolution of scaling characteristics of the local geomagnetic field and of the seismicity at etna volcano is studied in relation to the strong eruptive activity occurred here from 2000 to 2002 scaling laws are found in the hourly time variability of magnetic data and in the seismicity pattern the scaling exponents suggest the presence of persistent temporal fluctuations clear links between the dynamics of the measured data and the eruptive volcanic episodes are revealed fractal dimensions of seismicity seem to be always correlated to the beginning of main eruptive events while strong alterations of the dynamics of the local magnetic field take place only when the eruptive fractures opened very close to the magnetic sites

carbonate dissolution on the muir seamount western north atlantic interglacial glacial changes abstract although the history of carbonate dissolution has been studied for many years few records of dissolution through an entire glacial cycle are available for the western north atlantic north american basin using 14 cores from the muir and siboney seamounts located about 240 km northeast of bermuda changes in carbonate dissolution were examined over the last 125 000 years the core depth range spans more than 3000 m 1780 m 4980 m insuring that major changes in dissolution will be recorded weight percent carbonate was plotted as a function of water depth for five stratigraphically defined levels to determine temporal changes in the sedimentary lysocline and calcite compensation depth ccd during the holocene the lysocline is located between 4050 m and 4350 m the ccd is not pre ent even in the deepest sample 4980 m the late glacial 18 000 years b p lysocline may have shoaled to about 2500 m whereas during early glacial time 72 000 years b p it deepened to about 3400 m the mid glacial carbonate maximum 60 000 years b p interstadial is marked by a deepening of the lysocline to about 3800 m during the entire glacial episode the ccd aappears to have remained fixed at 4650 m the last interglacial 125 000 years b p was a time favorable to carbonate preservation the lysocline was deeper than 4650 m the deepest core containing sediments of this age increased glacial dissolution appears to result from changes in deep circulation the establishment of the ccd during glacial time is interpreted as indicating increased antarctic bottom water flow the lysocline on the other hand may reflect the degree of stagnation of north atlantic deep water

long term 17 ma turbidite record of the timing and frequency of large flank collapses of the canary islands volcaniclastic turbidites on the madeira abyssal plain provide a record of large volume volcanic island flank collapses from the canary islands this long term record spans 17 ma and comprises 125 volcaniclastic beds determining the timing provenance and volumes of these turbidites provides key information about the occurrence of mass wasting from the canary islands especially the western islands of tenerife la palma and el hierro these turbidite records demonstrate that landslides often coincide with protracted periods of volcanic edifice growth suggesting that loading of the volcanic edifices may be a key preconditioning factor for landslide triggers furthermore the last large volume failures from tenerife coincide with explosive volcanism at the end of eruptive cycles many large volume canary island landslides also occurred during periods of warmer and wetter climates associated with sea level rise and subsequent highstand however these turbidites are not serially dependent and any association with climate or sea level change is not statistically significant

estimation of surface roughness and stone cover in burnt soils using sar images abstract in many quartzitic slopes in the nw of the iberian peninsula there is a high topsoil stoniness which produces a random surface roughness the surface roughness is one of the control parameters in the signal of synthetic aperture radar sar images in this work we test the use of the sar images for distinguishing and mapping areas with different surface roughness which in this study correspond with areas with different surface stoniness in accordance with the geographic location the relief of the study area and the aims of the project jers and envisat sar images were used the images are characterized by the high view angles between 33 and 42 alternating polarization hh hv vv vh data and ascending and descending passes in order to describe the soil roughness various measuring methods were applied in plot parcels direct measurements of height of clasts and laser scanning and different roughness models were tested the results show that there are relation between sar signal dn and the soil roughness classes dn a b and the b parameter is correlated with the roughness the best fit between roughness model and sar data was found for mean standard deviation rms height of clasts once verified that the correlation between sar signal and surface roughness exists the envisat images were classified into three successive surface roughness classes in order to facilitate the classification principal components analysis were carried out over all polarization bands and the object oriented classification was applied to validate the accuracy of the sar images classification we elaborated by photointerpretation a surface condition map for an area of 10 700 ha the sar classification and photointerpreted map were compared for three classes surface without stones surface with stones low and medium stoniness and total cover of loose clasts the overall coincidence between the maps is about 70 besides large areas located in the northwest of the iberian peninsula suffer soil degradation caused by wildfires and the increase of surface stoniness is one of the effects described in the postfire erosion the influence of wildfires and the associated erosion is particularly important on quartzitic slopes partially covered by coarse grain supported deposits like the ones considered in this study the available data for the area of study suggest the high correlation between the different classes of surface roughness and stoniness obtained from sar imagery and the gradual different status of postfire soil erosion

itrax description and evaluation of a new multi function x ray core scanner a new automated multi function core scanning instrument named itrax has been developed that records optical radiographic and elemental variations from sediment half cores up to 1 8 m long at a resolution as fine as 200 m an intense micro x ray beam focused through a flat capillary waveguide is used to irradiate samples to enable both x radiography and x ray fluorescence xrf analysis data are acquired incrementally by advancing a split core via a programmable stepped motor drive through the flat rectangular section x ray beam traditional xrf determination of element composition in sediments provides high quality data but it takes a considerable time and normally consumes gram quantities of material that is often only available in limited quantities the itrax core scanner non destructively collects optical and x radiographic images and provides high resolution elemental profiles that are invaluable for guiding sample selection for further destructive detailed sampling this paper presents a description of the construction characteristics and capabilities of the itrax system high resolution itrax data obtained from sediment cores are also presented and compared with results from traditional wavelength dispersive xrf analysis at lower resolution finally some recent technical developments linked to the second generation itrax are presented

multistage collapse of eight western canary island landslides in the last 1 5 ma sedimentological and geochemical evidence from subunits in submarine flow deposits volcaniclastic turbidites in the madeira abyssal plain provide a record of major landslides from the western canary islands in the last 1 5 ma these volcaniclastic turbidites are composed of multiple fining upward turbidite sands known as subunits the subunits indicate that the landslides responsible for the sediment gravity flows occurred in multiple stages the subunits cannot result from flow reflection or splitting because the compositions of volcanic glasses from each individual subunit in an event bed are subtly different this indicates that each subunit represents a discrete failure as part of a multistage landslide this has significant implications for geohazard assessments as multistage failures reduce the magnitude of the associated tsunami the multistage failure mechanism reduces individual landslide volumes from up to 350 km3 to less than 100 km3 thus although multistage failure ultimately reduce the potential landslide and tsunami threat the landslide events may still generate significant tsunamis close to source

frequency and timing of landslide triggered turbidity currents within the agadir basin offshore nw africa are there associations with climate change sea level change and slope sedimentation rates abstract older sequence stratigraphic models suggested that submarine landslide and turbidite activities are greatest during sea level lowstands however growing evidence indicates that many turbidite systems are also active during sea level transgressions and highstands the moroccan turbidite system comprises three depocentres of which agadir basin is closest to the moroccan slope and canary archipelago the very large volumes of sediment transported by individual sediment flows in this system suggest that they are triggered by landslides extensive core coverage and dating control for the agadir basin deposits have provided an excellent opportunity to derive accurate records of turbidite and associated landslide frequency for the last 600 ka previous studies in the more distal madeira abyssal plain depocentre have indicated that large volume 50 km 3 turbidites occurred at oxygen isotope stage ois boundaries this study of agadir basin confirms that two major turbidites beds a5 and a12 occurred during glacial interglacial transitions associated with ois4 and ois6 however this association is based on just two examples and two other large volume turbidites beds a7 and a11 did not occur at a stage boundary the main conclusion of this study is that 90 of turbidites and landslides occurred during rising and high sea level which represents 40 of the total time during the last 600 ka only 10 of the turbidites and landslides occurred during glacials 40 of the time with a paucity of turbidites and landslides at peak glacial lowstands a comparison to sediment accumulation rates in the source area of the turbidite suggests that landslides did not occur preferentially during periods of more rapid sedimentation rate although sedimentation rates in this area only varied from 4 to 6 g cm 2 ka 1

slope failures on the flanks of the western canary islands abstract landslides have been a key process in the evolution of the western canary islands the younger and more volcanically active canary islands el hierro la palma and tenerife show the clearest evidence of recent landslide activity the evidence includes landslide scars on the island flanks debris deposits on the lower island slopes and volcaniclastic turbidites on the floor of the adjacent ocean basins at least 14 large landslides have occurred on the flanks of the el hierro la palma and tenerife the majority of these in the last 1 million years with the youngest on the northwest flank of el hierro as recent as 15 thousand years in age older landslides undoubtedly occurred but are difficult to quantify because the evidence is buried beneath younger volcanic rocks and sediments landslides on the canary island flanks can be categorised as debris avalanches slumps or debris flows debris avalanches are long runout catastrophic failures which typically affect only the superficial part of the island volcanic sequence up to a maximum thickness of 1 to 2 km they are the commonest type of landslide mapped in contrast slumps move short distances and are deep rooted landslides which may affect the entire thickness of the volcanic edifice debris flows are defined as landslides which primarily affect the sedimentary cover of the submarine island flanks some landslides are complex events involving more than one of the above end member processes individual debris avalanches have volumes in the range of 50 500 km3 cover several thousand km2 of seafloor and have runout distances of up to 130 km from source overall debris avalanche deposits account for about 10 of the total volcanic edifices of the small relatively young islands of el hierro and la palma some parameters such as deposit volumes and landslide ages are difficult to quantify the key characteristics of debris avalanches include a relatively narrow headwall and chute above 3000 m water depth on the island flanks broadening into a depositional lobe below 3000 m debris avalanche deposits have a typically blocky morphology with individual blocks up to a kilometre or more in diameter however considerable variation exists between different avalanche deposits at one extreme the el golfo debris avalanche on el hierro has few large blocks scattered randomly across the avalanche surface at the other icod on the north flank of tenerife has much more numerous but smaller blocks over most of its surface with a few very large blocks confined to the margins of the deposit icod also exhibits flow structures longitudinal shears and pressure ridges that are absent in el golfo the primary controls on the block structure and distribution are inferred to be related to the nature of the landslide material and to flow processes observations in experimental debris flows show that the differences between the el golfo and icod landslide deposits are probably controlled by the greater proportion of fine grained material in the icod landslide this in turn relates to the nature of the failed volcanic rocks which are almost entirely basalt on el hierro but include a much greater proportion of pyroclastic deposits on tenerife landslide occurrence appears to be primarily controlled by the locations of volcanic rift zones on the islands with landslides propagating perpendicular to the rift orientation however this does not explain the uneven distribution of landslides on some islands which seems to indicate that unstable flanks are a weakness that can be carried forward during island development this may occur because certain island flanks are steeper extend to greater water depths or are less buttressed by the surrounding topography and because volcanic production following a landslide my be concentrated in the landslide scar thus focussing subsequent landslide potential in this area landslides are primarily a result of volcanic construction to a point where the mass of volcanic products fails under its own weight although the actual triggering factors are poorly understood they may include or be influenced by dyke intrusion pore pressure changes related to intrusion seismicity or sealevel climate changes a possible relationship between caldera collapse and landsliding on tenerife is not in our interpretation supported by the available evidence

tsunami wave height dependence on landslide volume tsunami generation from submarine landslides depends mainly on the volume of the slide material and also on other factors which include angle of the slide water depth density of the slide material the speed with which the material moves duration of the slide etc based on an incomplete data set of volume v of slide versus maximum amplitude h of the resulting tsunami waves gleaned through available literature a simple linear regression relationship was developed another partial data set was developed also from published literature on v versus h values based on numerical models it was found that the agreement between the results of the numerical simulations and the observations is rather poor it is not clear why this is so and which data set is of questionable relevance this is not to cast doubt on numerical models that do not use volume of the slide in an explicit manner

numerical modelling of the tsunami triggered by the guimar debris avalanche tenerife canary islands comparison with field based data abstract some tsunami deposits have been previously identified 41 188 m asl in the agaete valley on the northwest coast of the island of gran canaria in the canary islands in this paper the guimar sector collapse tenerife 0 83 ma and its expected associated tsunami that is thought to be at the origin of these tsunami deposits are tentatively reproduced using a two fluid numerical code two failure processes are considered 1 the whole 44 km 3 volume is released in one go or 2 the 44 km 3 are released in five retrogressive failures of equal volume occurring each 120 s in both cases two rheologies are used to simulate the landslide propagation the mohr coulomb frictional law and a constant retarding stress two hypotheses concerning the origin of the offshore mapped deposits are also considered 1 the mapped deposits are the direct result of a single collapse event occurring either in one go or by near retrogressive failures or 2 the mapped deposits result from a collapse followed by later partial remobilization of its deposits in all scenarios the subaerial destabilisation spreads out eastwards into the sea triggering waves 390 500 m high when considering a collapse in one go and 225 380 m when considering successive retrogressive failures the first wave reaches the coast of gran canaria located at 70 km from the scar 495 560 s after the collapse onset whatever the scenario considered water enters the agaete valley on gran canaria 555 690 s after the onset of collapse reaching up to 9 1 km inland for a collapse in one go and 5 0 km when considering five retrogressive failures in this valley the simulated waves inundate all the locations where tsunami deposits were identified with the flow depth measured reaching a maximum of 50 m collapse by retrogressive failures to 150 m collapse in one go at these particular places the directions of maximum kinetic energy as a function of time for the simulated waves are consistent with the current directions recorded by the cobble fabrics present in the run up and backwash layers of the tsunami deposits at one outcrop this study shows that the major source of uncertainty when reproducing landslide triggered tsunamis is linked to the way the landslide happens failure mechanisms that should be thus more precisely taken into account for landslide triggered tsunamis hazard assessment the rheology chosen to simulate the landslide propagation has only a second order impact on the produced waves

composition and provenance of turbidite sands late quaternary madeira abyssal plain abstract late quaternary sediments from the madeira abyssal plain map consist of metre thick fine grained distal turbidites separated by centimetre thick layers of pelagic clay marl and or ooze three major compositional groups of turbidites have been defined by previous work volcanic organic rich and calcareous the coarse to medium grained sand fraction from the basal parts of the volcanic turbidites is predominantly composed of volcanic glass pumice and foraminifera whereas heavy mineral and plagioclase feldspar grains plus basalt and trachyte clasts become more abundant in the overlying fine grained sands and silts the bases of organic rich turbidites consist of fine grained sands and silts which are rich in foraminifera quartz and alkali feldspar grains and altered lithic clasts calcareous turbidites have bases composed of medium to fine grained foraminiferal sand devoid of terrigenous coarse grained material new mineralogical data are used to define grain assemblages in the sand silt fraction from these turbidite groups these assemblages are comparable to mineral assemblages from alkali olivine basalts trachybasalts to trachyandesites and trachytes phonolites on the azores canary islands and madeira and with sediments from the continental margin of northwestern africa volcanic glass chemistry however distinguishes the canary islands as the principal island provenance of the volcaniclastic sands volcaniclastic material probably originated either from reactivation of basic volcanism on tenerife and gran canaria in the quaternary or during the development of the western islands of la palma and hierro 5 ma recent trachytic and phonolitic material was derived from the more fractionated volcanic complexes on the central and eastern islands of the canary islands tenerife gran canaria fuerteventura and lanzarote organic rich turbidites consist of two mineralogical subgroups which originated from two distinct source areas along the continental margin of northwestern africa 1 north of the canaries off morocco 2 south of the canaries off senegal differences in the mineralogy between source areas reflect geographical variations in the weathering of continental granitic rocks which were subsequently transported off shore mainly by aeolian processes calcareous turbidites were derived from the great meteor cruiser seamount chain west of the map

volcanic development of small oceanic central volcanoes on the flanks of the east pacific rise inferred from narrow beam echo sounder surveys abstract narrow beam bathymetric surveys of about 30 volcanoes on young crust of the cocos plate were collected in order to help determine the origin and evolution of oceanic central volcanoes the volcanoes are located on ocean crust 1 5 7 5 m y in age and range in size from to 600 km 3 these volcanoes differ greatly in shape development of linear features small scale morphologic characteristics and crater development we conclude that these large differences in morphologic characteristics are due to the complex interaction of many factors in their development such as conduit geometry magma ascent rates eruption rate history tectonic activity crater formation and filling and others elongation directions of individual volcanoes and clear linear bathymetric features near these volcanoes are among the lines of evidence that strongly suggest these volcanoes originate and evolve on and near oceanic fracture zones their origin and morphologic evolution is thus closely tied to the tectonic processes and thermal regimes at fractures we speculate that these volcanoes on fast spreading lithosphere are generated by episodic pulses of melt production beneath ridge crests in the vicinity of fracture zones petrologic evidence shows that these volcanoes cannot be fed from sub axial magma chambers beneath the east pacific rise instead they tap the same mantle source as the ridge crest at mantle depth

seismic image of the cantabrian mountains in the western extension of the pyrenees from integrated escin reflection and refraction data abstract integrated analysis of normal incidence and large aperture seismic reflection data collected in 1992 and 1993 within the spanish escin and complementary projects provide a first complete n s crustal transect across the northern iberian peninsula and continental margin images of the crustal structure of the cantabrian mountains and their transition to the duero basin and to the cantabrian margin are obtained from a a 65 km long vertical reflection profile escin 2 on land b a 200 km long reversed refraction profile and c wide angle recordings of the marine escin 4 profile consistent results between reflectivity pattern and velocity depth distribution reveal important lateral variations in the deep structure the reflective crust imaged in the escin 2 profile changes its attitude from sub horizontal beneath the duero basin to north dipping beyond the mountain front basement thrusts are observed in the upper crust merging into a detachment at 6 s twt and may have triggered the alpine uplift of the range the moho is identified at the bottom of the reflective lower crust and deepens from 12 to 15 s at the northern end of the profile about 35 km inland modelling of the refraction data laterally extends the seismic image and provides evidence for variscan crustal features beneath the duero basin northwards the velocity in the lower crust decreases and the moho constrained by the wide angle data from profile escin 2 deepens to about 60 km ending abruptly at the shoreline the velocity depth model is constrained along the asturian platform up to the continental slope where the crust mantle boundary is located at 24 km depth this margin moho shows a progressive deepening southwards and extends to the coast where it is found at 30 km depth the present seismic data support an important alpine reworking and thickening of the crust under the cantabrian mountains the onshore offshore transition is marked by an imbrication of two crusts of very different thicknesses this signature offers a strong parallelism with the one previously observed further east across the pyrenees in the ecors seismic profile

the lifecycle of mid ocean ridge seamounts and their prodigious flank collapses abstract volcanic seamounts are spectacular bathymetric features representing undersea mountains comparable in size to volcanic islands they are often sites of active volcanism represent major marine habitats and contain potentially globally significant commodities of trace metals however we know comparatively little about how they form the extent of their volcanic lifecycle and what risks they pose from periodic flank collapse here we study a uniquely extensive 43 myr record of volcaniclastic and calciclastic turbidites accumulated on the madeira abyssal plain in the ne atlantic which originate from large submarine landslides from the adjacent great meteor cruiser seamount complex on the flanks of the mid atlantic ridge these turbidites present the first long term temporal record of the recurrence magnitude and emplacement mechanism of seamount flank collapses from a single seamount complex throughout its lifecycle landslides from the great meteor cruiser seamount complex are comparable size to those from the canary islands with average volumes of 30 40 km3 but can be as large as 130 km3 comparable to many volcanic island landslides these seamount landslides were predominantly multi stage failures similar to those form neighbouring volcanic islands but in contrast occurred preferentially during sea level lowstands we show that volcanic seamounts above mantle plumes have long protracted lifecycles and that substantial flank failures are capable of occurring at all stages of development temporal change in turbidite composition has for the first time enabled reconstruction of the inception around 43 45 myrs ago ascension taking around 20 25 myrs emergence after 30 myrs and later recession last 9 myrs cessation in volcanism last 4 myrs and subsidence of the seamounts from 2 myrs onwards these seamounts above a mantle plume have taken around 26 myrs to emergence above sea level from inception while their volcanic island contemporaries only took 2 to 5 myrs here we use the history of turbidites derived from landslides from the seamounts to show how the seamounts developed and suffered mass wasting during their life cycles

a susceptibility model for post wildfire soil erosion in a temperate oceanic mountain area of spain abstract in the north west of the cantabrian range north of spain the climate is oceanic and vegetation cover is continuous in those areas where livestock farming prevails wildfires are common although small in size their recurrence makes the phenomenon critical for the conservation of soils in this study we propose that the structural stability of soil associated with the type and size of the structural aggregates may be a useful indicator to assess erosion susceptibility in burnt soils we have chosen an area of approximately 485 km2 over quartzitic lithologies where a high recurrence of wildfires has been noted and which displays several forms of erosion gullying rilling and erosion by overland flow we have measured texture percentage and degree of structural aggregate stability and the rate of infiltration in soils that have been burnt up to 3 times over the last 20 years and also in unburnt soils the results obtained enable us to establish connections between wildfires soil deterioration and macro aggregate stability we have used the stability of macro aggregates as an indicator to elaborate a soil erosion susceptibility model for a large area of 10 600 km2 with sharp relief and atlantic climate the model was constructed by combining three main factors soil structural stability fire intensity and relief variables related to soil structural stability and presence of basic cations have been derived from lithology clay and silt fine sand the availability of humified organic material has also been taken into account as an additional variable in the formation of stable macro aggregates the expected fire intensity was calculated from the amount of inflammable material and the structure of the different vegetation types finally the influence of relief was analyzed by considering the slope steepness the resultant cartographic model presents five types of post wildfire soil erosion susceptibility those areas with the highest risk correspond to quartzite lithology regions with long steep hillsides covered with heaths those with the lowest risk correspond to limestone bedrock areas with gentle slopes and herbaceous vegetation the accuracy of the model is determined by the scale of the original thematic cartography 1 25000 and the cell size of the digital terrain model is 50 50 m

a new empirical model to retrieve soil moisture and roughness from c band radar data abstract a new empirical model for the retrieval at a field scale of the bare soil moisture content and the surface roughness characteristics from radar measurements is proposed the derivation of the algorithm is based on the results of three experimental radar campaigns conducted under natural conditions over agricultural areas radar data were acquired by means of several c band space borne sir c radarsat or helicopter borne erasme sensors operating in different configurations of polarization hh or vv and incidence angle simultaneously to radar acquisitions a complete ground truth data base was built up with different surface condition measurements of the mean standard deviation rms height s the correlation length l and the volumetric surface moisture m v this algorithm is more specifically developed using the radar cross section 0 hh polarization and 39 incidence angle off nadir namely 0 hh 39 and the differential hh polarization radar cross section 0 0 23 0 39 in terms of an original roughness parameter z s namely z s s 2 l and m v a good agreement is observed between model outputs and backscattering measurements over different test fields eventually an inversion technique is proposed to retrieve z s and m v from radar measurements

cold water coral banks and submarine landslides a review this paper aims to review the relation between cold water coral bank development and submarine landslides both are common features on continental margins but so far it has not been reviewed which effect if at all they may have upon each other indirect and direct relations between coral banks and landslides are evaluated here based on four case studies the magellan mound province in the porcupine seabight where fossil coral banks appear partly on top of a buried slide deposit the sula ridge reef complex and the storegga landslide both off mid norway and the mauritania coral bank province associated with the mauritanian slide complex for each of these locations positive and negative relationships between both features are discussed based on available datasets locally submarine landslides might directly favour coral bank development by creating substratum where corals can settle on enhancing turbulence due to abrupt seabed morphological variations and in some cases causing fluid seepage in turn some of these processes may contribute to increased food availability and lower sedimentation rates landslides can also affect coral bank development by direct erosion of the coral banks and by the instantaneous increase of turbidity which may smother the corals on the other hand coral banks might have a stabilising function and delay or stop the headwall retrogradation of submarine landslides although local relationships can be deduced from these case studies no general and direct relationship exists between submarine landslides and cold water coral banks

jasper seamount seven million years of volcanism jasper seamount is a young mid sized 690 km sup 3 oceanic intraplate volcano located about 500 km west southwest of san diego california reliable sup 40 ar sup 39 ar age data were obtained for several milligram sized samples of 4 to 10 ma plagioclase by using a defocused laser beam to clean the samples before fusion gee and staudigel suggested that jasper seamount consists of a transitional to tholeiitic shield volcano formed by flank transitional series lavas overlain by flank alkalic series lavas and summit alkalic series lavas twenty nine individual sup 40 ar sup 39 ar laser fusion analyses on nine samples confirm the stratigraphy 10 3 10 0 ma for the flank transitonal series 8 7 7 5 ma for the flank alkalic series and 4 8 4 1 ma for the summit alkalic series the alkalinity of the lavas clearly increases with time and there appear to be 1 to 3 m y hiatuses between each series the age data are consistent with the complex magnetic anomaly of jasper however the dominant reversed polarity inferred from the anomaly suggests that most of the seamount formed at ca 11 ma prior to the onset of chron c5n the duration of volcanism of jasper seamount is slightly longer than the duration of volcanism at hawaiian volcanoes suggesting thatmore individual age data from seamounts may constrain the age of a seamount only to within about 7 m y unless the stage of volcanism can be unambiguously determined extrapolating from the results of our study similar precision in age determinations should be possible on 50 mg of 1 ma plagioclase from mid ocean ridge basalt opening new possibilities in the geochronology of young low potassium volcanic rocks less

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

variation of rock fragment cover and size along semiarid hillslopes a case study from southeast spain abstract the spatial variation of rock fragment cover rc and rock fragment size rs along semiarid hillslopes and transects in the mediterranean is largely controlled by hillslope gradient total rock fragment cover rc 5 mm often increases in a convex upward curve with hillslope gradient while the d50 of the surface rock fragments 5 mm increases linearly with hillslope gradient on south facing slopes rc 5 mm is slightly higher than on north facing slopes lithology controls the size distribution of the stone pavement rather than its cover percentage spatial variation of rock fragment cover reflects spatial variation in past erosion and deposition rates hillslope sections that are steep south facing or have been abandoned a long time ago have undergone intense interrill and rill erosion and thus have high rock fragment covers tillage erosion leads to high rock fragment covers on convex hillslopes in intensively cultivated areas thus using information on hillslope gradient aspect lithology and landuse we have been able to describe the spatial variation of rock fragment cover and size along semiarid hillslopes in southeast spain such information is crucial for understanding and modelling the spatial variation of the hydrological and erosion response of semiarid hillslopes under environmental change especially in semiarid environments of the mediterranean where vegetation cover is predicted to decrease due to climatic or landuse changes and rock fragments at the surface become the only soil surface stabilisers

northwest african continental margin history of sediment accumulation landslide deposits and hiatuses as revealed by drilling the madeira abyssal plain 1 odp drill sites in the madeira abyssal plain reveal sequences of organic rich turbidites derived from the northwest african margin in which each turbidite has a volume of tens to hundreds of cubic kilometers the frequency of turbidite emplacement has been combined with core and seismic data to show the volume of redeposited sediment the basin began to fill about 22 ma with numerous small turbidites up to 100 per million years each with volumes of a few cubic kilometers the total volume of turbidites deposited increased between 16 and 11 ma as did their individual volumes and then declined to 7 ma at 7 ma there was a dramatic increase in the amount of turbidite input to 768 km3 myr and a rise in the average volume of each unit to 59 km3 these high values have been maintained to the present day the variations in the amount of redeposited sediment most likely reflect the rates of sedimentation on the northwest african margin since high sedimentation leads to oversteepening of the slopes and eventual mass wasting the dramatic changes at about 7 ma may be due to a large increase in upwelling off northwest africa caused by circulation changes associated with increased glaciation of the poles up to 20 of sediment may be remobilized by landslides with each event leaving a hiatus each of these hiatuses extends over an average area of 4800 km2 and represents removal of sediment layers several tens of meters thick and of several hundred thousand years duration

evidence of climatic control on hydrocarbon seepage in the miocene of the northern apennines the case study of the vicchio marls abstract the vicchio outcrop in the tuscan apennines contains excellent exposures of a miocene methane derived carbonate system made up of more than 80 carbonate bodies enclosed in marly sediments facies analysis composition and a detailed biostratigraphic study of the carbonates and enclosing vicchio marls allowed us to document the role of climatic changes and eustasy on seepage in these ancient deposits results of our study indicate that the stratigraphic horizon bearing seep carbonates is constrained by two planktonic foraminiferal events the acme end ae of turborotalita cf t quinqueloba 13 75 ma and the acme 1 beginning a 1 b of paragloborotalia siakensis 13 32 ma encompassing about 400 000 years the ae of t cf t quinqueloba approximates the mid miocene global cooling event mi3b as defined by the 18 o maxima 13 78 ma the glacio eustatic sea level drop associated with this cooling event is estimated to be approximately 60 m assuming that the highest rates of glacio eustatic sea level fall coincide with 18 o maxima the timing of the seepage onset at about 13 75 ma is concomitant with the phase of sea level lowering the ascent and emission of methane rich fluids may have been triggered by pressure drop due to the eustatic fall associated with the mi3b event the moderate intensity of fluid expulsion is suggested by the lack of brecciation by the scarcity of detrital particles in the carbonates and by the pervasive occurrence of carbonate in the enclosing marls this type of seepage differs from focused fault confined fluid flows typical of other tectonically controlled apenninic seep carbonates

modeling scour and deposition in ephemeral channels after wildfire the area burned by wildfire in the states of arizona and new mexico in the southwestern us has been increasing in recent years in many cases high severity burns have caused dramatic increases in runoff and sediment yield from burned watersheds this paper describes the potential and limitations of the hec6t sediment transport model to describe changes in channel scour and deposition following the cerro grande fire near los alamos new mexico following the fire pueblo canyon near los alamos was subject to a peak flow two orders of magnitudes higher than any discharge in the 7 year period of record and twice the initial post fire estimate of the 100 year event hec6t requires that the limits of scour and deposition on a cross section be specified prior to application this was achieved by using geomorphologic principles predicted post burn hydrology and longterm estimates of channel change derived from air photos to estimate post fire channel widths because significant quantities of silt and clay were present in the runoff erosion shear stress and erosion rate parameters for cohesive sediments had to be obtained experimentally after a sensitivity analysis an optimization routine was used to estimate the optimal model parameter values for sensitive parameters hec6t was able to accurately model the change in cumulative sediment volume change derived from airborne laser swath mapping alsm often called lidar taken before and after the large post fire event one discrepancy between the hec6t model prediction and the alsm estimated change was that the alsm estimated change showed the greatest amount of deposition in a portion of the canyon with increasing slope which the hec6t model did not predict

turbidite record of frequency and source of large volume 100 km3 canary island landslides in the last 1 5 ma implications for landslide triggers and geohazards during the last two decades numerous studies have focused on resolving the landslide histories of the canary islands issues surrounding the preservation and dating of onshore and proximal submarine landslide deposits precludes accurate determination of event ages however submarine landslides often disaggregate and generate sediment gravity flows volcaniclastic turbidites sampled from madeira abyssal plain piston cores represent a record of eight large volume failures from the western canary islands in the last 1 5 ma during this time there is a mean recurrence rate of 200 ka while the islands of el hierro and tenerife have individual landslide recurrences of 500 ka and 330 ka respectively deposits from the 15 ka el golfo landslide from el hierro and 165 ka icod landslide from tenerife are examined this study also identifies potential deposits associated with the orotava 535 ka guimar 850 ka and rogues de garcia landslides 1 2 ma from tenerife el julan 540 ka and el tinor 1 05 ma landslides from el hierro and the cumbre nueva landslide 485 ka from la palma seven of eight landslides occurred during major deglaciations or subsequent interglacial periods which represent 55 of the time however all of the studied landslides occur during or at the end of periods of protracted island volcanism which generally represent 60 of the island histories although climate may precondition failures it is suggested that volcanism presents a more viable preconditioning and trigger mechanism for canary island landslides

gravitational erosional sedimentary and volcanic processes on the submarine environment of selvagens islands madeira archipelago portugal abstract volcanic oceanic islands are the emerged portions of large volcanoes that rise abruptly from the ocean floor although the geological record of these islands provide some insights into the evolution of their entire volcanic edifices for a complete picture it is essential to study the islands submarine pedestals and surrounding settings in this study we document the submarine morphology of the selvagens islands madeira archipelago portugal and relate it with their subaerial evolution in order to gain a more complete insight on the evolutionary history of these islands to this purpose we employed bathymetric surfaces backscatter mosaics and subbottom profiler data integrated with geological observations of the subaerial part of the islands our study reveals the presence of a complex submarine morphology composed mainly of two deeply eroded central volcanoes the edifices of selvagem grande and selvagem pequena and a less eroded saddle like ridge related to a fissural volcanic system located between them other secondary landforms generated by volcanism erosion gravitational collapses and possible faulting activity are also present whilst the building of the two central volcanoes relates to the older volcanic stages of both islands the fissural system with a general ne sw trend is probably contemporaneous of the younger volcanic stages of selvagem grande the shelf of selvagem grande also features the eroded remains of numerous relatively young volcanic cones seemingly forming several nw se and ne sw lineaments the same direction observed onshore for the younger volcanic stage of this edifice the shelves break of both selvagens was affected by multiple landslide scars and channel headwalls the channels constitute a large drainage network that fans out in a radial pattern along the flanks of both central edifices in the deeper parts of this submarine drainage large sediment wave fields are observed in some locations with wavelengths of 300 1 900 m and 2 45 m in height these tend to form cyclic steps that change gradually downslope to antidunes and their origin is attributed to sediment density flows that suffer hydraulic jumps when their channel confinement ends and the slope gradient decreases from 7 to 2 5 several scour features are also found at 3 300 4 000 m water depth being 3 20 km in width 10 20 km in length rectangular or u shaped in cross section and 40 100 m deep they occur around the base of the submarine edifices where seafloor gradients change to 3 0 0 5 their origin is also related to hydraulic jumps of unconfined sediment density flows which are able to erode the seafloor and create these features these morphologies are a testimony to how volcanic erosional and depositional processes conjugate to shape the flanks of a very long lived volcanic island system one of the oldest in the north atlantic ocean

formation of carbonate chimneys in the mediterranean sea linked to deep water oxygen depletion marine sediments at ocean margins vent substantial amounts of methane1 2 microbial oxidation of the methane released can trigger the precipitation of carbonate within sediments and support a broad diversity of seafloor ecosystems3 4 the factors controlling microbial activity and carbonate precipitation associated with the seepage of submarine fluid over geological time remain poorly constrained here we characterize the petrology and geochemistry of rocks sampled from metre size build ups of methane derived carbonate chimneys located at the amon mud volcano on the nile deep sea fan we find that these carbonates comprise porous structures composed of aggregated spherules of aragonite and closely resemble microbial carbonate reefs forming at present in the anoxic bottom waters of the black sea5 using u series dating we show that the amon carbonate build ups formed between 12 and 7 thousand years ago contemporaneous with the deposition of organic rich sediments in the eastern mediterranean the so called sapropel layer s1 we propose that the onset of deep water suboxic or anoxic conditions associated with sapropel formation resulted in the development of intense anaerobic microbial activity at the sea floor and thus the formation of carbonate chimneys

sedimentological and geochemical evidence for multistage failure of volcanic island landslides a case study from icod landslide on north tenerife canary islands 1 volcanic island landslides can pose a significant geohazard through landslide generated tsunamis however a lack of direct observations means that factors influencing tsunamigenic potential of landslides remain poorly constrained the study of distal turbidites generated from past landslides can provide useful insights into key aspects of the landslide dynamics and emplacement process such as total event volume and whether landslides occurred as single or multiple events the northern flank of tenerife has undergone multiple landslide events the most recent being the icod landslide dated at 165 ka the icod landslide generated a turbidite with a deposit volume of 210 km3 covering 355 000 km2of seafloor off northwest africa the icod turbidite architecture displays a stacked sequence of seven normally graded sand and mud intervals named subunits sbu1 7 evidence from subunit bulk geochemistry volume basal grain size volcanic glass composition and sand mineralogy combined with petrophysical and geophysical data suggests that the subunit facies represents multistage retrogressive failure of the icod landslide the basal subunits sbu1 3 indicate that the first three stages of the landslide had a submarine component whereas the upper subunits sbu4 7 originated above sea level the presence of thin non bioturbated mud intervals between subunit sands suggests a likely time interval of at least several days between each stage of failure these results have important implications for tsunamigenesis from such landslides as multistage retrogressive failures separated by several days and with both a submarine and subaerial component will have markedly lower tsunamigenic potential than a single block failure

fluvial response a decade after wildfire in the northern yellowstone ecosystem a spatially explicit analysis forest fire is a vital ecological process capable of inducing complex fluvial response but the integration of these effects across entire watersheds remains poorly understood we collected downstream cross sectional and geomorphic data acquired geographic information on land cover and forest fire and performed spatially explicit statistical analyses to examine fire related impacts in catchments burned to varying degrees generalized least squares gls regression models suggested that channels with a greater percentage of burned drainage area were associated with markedly higher cross sectional stream power relatively smaller width depth ratios and lower bank failure rates 12 to 13 years after the fires these results implied that streams became more powerful in the aftermath of forest fire and that net incision had been the primary response in second to fourth order channels since the 1988 yellowstone fires the extensive geographic coverage of our data spanning multiple basins with measurements spaced every 100 m allowed us to hypothesize a process response model based on these results we suggest that a wave of fire related sediment propagates through burned catchments high runoff events or even moderate flows provide sufficient energy to evacuate the finer grained material delivered from burned hillslopes to the channel network over a period of 5 10 years the combination of elevated post fire discharges and decreased sediment supply then induces an episode of incision site specific channel changes are highly variable because streams can accommodate post fire increases in energy and sediment supply through multiple modes of adjustment characterizing the spatial distribution of stream power would provide a valuable management tool because this variable is strongly associated with percent burned drainage area and integrates several elements of complex fluvial response future research focused on the channel substrate and its evolution through time is needed but our results indicate a fundamental linkage between fire and fluvial processes d 2002 elsevier science b v all rights reserved

correlation frequency of emplacement and source directions of megaturbidites on the madeira abyssal plain abstract this paper describes the sediments of the whole madeira abyssal plain including the madcap area to the south previous studies have centred on the central sub basin which occupies most of the plain and which has become one of the most studied areas of seafloor the plain is made up of a series of large turbidites separated by thin pelagic layers which can be used to provide a high resolution stratigraphy back to about 750 000 years many of the turbidites were deposited close to oxygen isotope stage boundaries suggesting a strong relationship to sea level climate change although the exact initiation mechanism for the flows is not known data from the northern and southern extensions of the plain shows the effects of different entry points for the four main turbidite groups volcanic rich turbidites enter from the ne and e calcareous turbidites from the w one group of organic rich turbidites enters from the se and one group from the ne and e different turbidite sources operate for limited periods before switching to one of the other source areas it is very rare for two sources to provide turbidites at the same isotope stage boundary

sluggish and steady focussed flows through fine grained sediments the methane derived cylindrical concretions of the tertiary piedmont basin nw italy abstract in the cenozoic succession of the tertiary piedmont basin nw italy a wide array of methane derived carbonate rocks including both seafloor and sub seafloor products have been reported in the last decades the most intriguing features are cylindrical concretions more than 1 m long and around 10 cm across that were found within fine grained sediments of messinian age in their original stratigraphic position crossing the bedding planes at high angles these concretions result from cementation of the host muddy sediments by intergranular dolomite microcrystals and lack any evidence of exposure at the sea floor their c and o stable isotope signature suggests that dolomite precipitation was induced by anaerobic oxidation of methane possibly sourced by gas hydrate destabilization such cylindrical morphologies are interpreted as the result of carbonate precipitation and cementation of the sediments around fluid conduits and record a relatively long period of steady sluggish flux of methane rich fluids that opened their way rising up through fine grained unconsolidated sediments they formed immediately below the sea floor in a narrow horizon bracketed between the sulphate methane interface and the oxic anoxic interface cylindrical concretions represent only the highest part of pipes through which methane rich fluids flowed up the deeper part of the conduits conversely left no trace in the stratigraphic record because of the lack of chemical microbiological conditions favourable for carbonate precipitation

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

age determinations of eastern pacific seamounts henderson 6 and 7 implications for near ridge and intraplate volcanism abstract we report 40ar 39ar stepwise heating ages for basalt samples from three seamounts in the eastern pacific the first henderson seamount is located on pacific lithosphere that is 22 ma old while an alkalic basalt sample dredged from near its summit yields a good age about 7 8 ma this suggests that henderson not a member of a linear hotspot chain probably did not form at the east pacific rise but rather is an intraplate volcano henderson is the first well dated volcano of this type to be identified in the eastern pacific seamounts 6 and 7 are located on the cocos plate upon lithosphere 3 4 ma old samples from these seasmounts yield poor isochrons with individual data points scattering between 0 and 3 ma these data are consistent with geologic observations in situ magnetic gradiometer measurements and modeling of the total magnetic fields indicating that seamounts 6 and 7 formed near but not on the axis of the east pacific rise the data from henderson seamount confirm that some isolated volcanoes represent non hotspot intraplate volcanism as suggested earlier by the abundance and distribution of seamounts

subduction related structures in the north iberian margin the oblique convergence of eurasia and iberia since the early cretaceous caused the formation of the pyrenean intracontinental collisional orogen in the east and progressed to continent ocean collision with subduction of the bay of biscay oceanic crust beneath the north iberian margin in the west two deep multichannel seismic profiles iam 12 and escin 4 integrated with gravity modeling and other geological and geophysical data provide the crustal scale architecture of this margin and its tectonic evolution during the convergence the north iberian margin is modeled with a south or south southeast dipping oceanic crust beneath the outer part of the continental shelf mesozoic basins on the shelf were inverted during the tertiary and compressional activity continued until recent times in the escin 4 section while a shallower probably neogene age basin is subjected to active recent erosion in the iam 12 section in the oceanic areas a marginal trough deepens and widens toward the east as a result of the regional east dip of the oceanic basement the accretionary prism increases in size from west to east 18 56 km and its internal structure and morphology varies along strike the prism is buried by postcorivergence sediments in both sections and in the iam 12 section appears to have been active at least during lutetian to burdigalian times the crustal scale structure of the north iberian margin is that of an arrested subduction zone in which a remnant oceanic basin was being consumed near two continental plates that collided obliquely

deep water seamounts a potential source of tsunami generated by landslides the hirondelle seamount ne atlantic abstract submarine mass failures represent one of the most significant marine geo hazards their importance as a major contributor to tsunami generation and hazard has been recognized over the last 20 30 years this study investigates a newly mapped submarine landslide the south hirondelle landslide shl and its potential to generate a tsunami and to threat the surrounding coasts the shl is located 150 km offshore south west iberia along the southern flank of the hirondelle seamount here available swath bathymetry and one multichannel seismic profile show the presence of large geometrically well constrained deep water landslide deposit of about 500 km 3 and its associated scar the failure likely occurred in one single event and according to a detailed numerical modelling of the landslide dynamics and of the resulting water propagation the mass failure generated a mega tsunami with significant impact along the surrounding coastal areas of iberia and morocco this result strongly supports the inclusion of tsunami induced by deep water submarine landslides in the marine geo hazard assessment of the north east atlantic region

growth structure instability and collapse of canarian volcanoes and comparisons with hawaiian volcanoes recent onshore and offshore investigations in the canarian archipelago especially in the western islands of la palma and el hierro have greatly improved the understanding of the genesis and evolution of these islands and allow interesting comparisons with other hotspot induced oceanic island volcanoes especially the hawaiian archipelago genesis induced by hotspot activity and consequently shield and post erosional stages of growth allow the definition of similar main stratigraphic units the canarian and hawaiian volcanoes show common constructional and structural features such as rift zones progressive volcano instability and multiple gravitational collapses however the canaries present some important geological differences from the prototypical hotspot volcanoes of the hawaiian islands particularly the absence of significant subsidence the canarian volcanoes remain emergent until completely mass wasted by gravitational collapses and erosion volcanic formations over 20 million years are observable in outcrop in the canaries including the seamount stages of growth in several of the islands

turbidite depositional architecture across three interconnected deep water basins on the north west african margin the moroccan turbidite system mts on the north west african margin extends 1500 km from the head of the agadir canyon to the madeira abyssal plain making it one of the longest turbidite systems in the world the mts consists of three interconnected deep water basins the seine abyssal plain sap the agadir basin and the madeira abyssal plain map connected by a network of distributary channels excellent core control has enabled individual turbidites to be correlated between all three basins giving a detailed insight into the turbidite depositional architecture of a system with multiple source areas and complex morphology large volume 100 km3 turbidites sourced from the morocco shelf show a relatively simple architecture in the madeira and seine abyssal plains sandy bases form distinct lobes or wedges that thin rapidly away from the basin margin and are overlain by ponded basin wide muds however in the agadir basin the turbidite fill is more complex owing to a combination of multiple source areas and large variations in turbidite volume a single very large turbidity current 200 300 km3 of sediment deposited most of its sandy load within the agadir basin but still had sufficient energy to carry most of the mud fraction 500 km further downslope to the map large turbidity currents 100 150 km3 of sediment deposit most of their sand and mud fraction within the agadir basin but also transport some of their load westwards to the map small turbidity currents 35 km3 of sediment are wholly confined within the agadir basin and their deposits pinch out on the basin floor turbidity currents flowing beyond the agadir basin pass through a large distributary channel system individual turbidites correlated across this channel system show major variations in the mineralogy of the sand fraction whereas the geochemistry and micropalaeontology of the mud fraction remain very similar this is interpreted as evidence for separation of the flow with a sand rich erosive basal layer confined within the channel system overlain by an unconfined layer of suspended mud large volume turbidites within the mts were deposited at oxygen isotope stage boundaries during periods of rapid sea level change and do not appear to be specifically connected to sea level lowstands or highstands this contrasts with the classic fan model which suggests that most turbidites are deposited during lowstands of sea level in addition the three largest turbidites on the map were deposited during the largest fluctuations in sea level suggesting a link between the volume of sediment input and the magnitude of sea level change

evidence for age and evolution of corner seamounts and great meteor seamount chain from multibeam bathymetry the comer seamounts in the western north atlantic and great meteor seamount chain in the eastern north atlantic are thought to progress in age from late cretaceous through late cenozoic they both presumably formed by volcanism above the new england hotspot when first the north american plate and then the mid atlantic ridge axis and african plate moved over the hotspot high resolution multibeam bathymetry of the seamounts shows geomorphic features such as guyots terraces and a base level plateau cruiser plateau that we interpret to have formed at sea level we have backtracked these features to sea level along the north atlantic crustal age depth curve in order to estimate their ages the derived age pattern of volcanism indicates formation of the comer seamounts at ca 80 ma to 76 ma with migration of the mid atlantic ridge plate boundary over the hotspot and formation of the cruiser plateau about 76 ma seamount ages suggest that subsequent volcanism on the african plate moved first northward in the late cretaceous to early cenozoic plato tyro and atlantis seamount groups then southward to great meteor seamount in the late cenozoic recurrent volcanism appears to have occurred at some seamounts up to 20 30 m y after their initial passage over the hotspot it would thus appear that intralithospheric conduits can link the hotspot to old seamounts several hundred kilometers away

climatic control of turbidite deposition on the madeira abyssal plain studies of sedimentation in the southwestern part of the madeira abyssal plain have revealed sequences of turbidites correlatable over thousands of square kilometres turbidites are sediments transported by turbidity currents and represent rapidly accumulated sedimentary units1 in this case in the distal part of the flow they are very fine grained and homogeneous occasionally with silty bases individual turbidites are separated by thin pelagic units which alternate from oozes to pelagic clays a stratigraphy for these pelagic units has been produced from combining coccolith distributions and lithological changes which enables comparison to cores containing only pelagic sediments from outside the turbidite province these comparisons show that turbidity currents cause no significant erosion in the area the major turbidites occur between lithological alternations which reflect global climate changes associated with glaciations and related eustatic sea level fluctuations turbidites have been linked with eustacy on previous occasions but only with low stands of sea level2 3 our work shows that turbidites are more likely to occur during regressions and transgressions rather than in the quiet periods between

turbidites from giant hawaiian landslides results from ocean drilling program site 842 pliocene to pleistocene volcanic sand turbidites recovered 320 km west of the island of hawaii at ocean drilling program site 842 contain fragments off fresh weakly vesicular glass and tests of pleistocene and eocene radiolarians this sand is probably related to turbidity currents generated from debris avalanches produced by giant landslides on the flanks of the hawaiian islands on their way to site 842 the currents flowed over the m bigh ha waiian arch indicating that the turbidity currents were at least 325 m thick similar sand has been reported 930 km south of the islands thus hawaiian giant landslides play a significant role in central pacific deep sea sedimentary processes

nonvolcanic tectonic islands in ancient and modern oceans 1 most oceanic islands are due to excess volcanism caused by thermal and or compositional mantle melting anomalies we call attention here to another class of oceanic islands due not to volcanism but to vertical motions of blocks of oceanic lithosphere related to transform tectonics sunken tectonic islands capped by carbonate platforms have been previously identified along the vema and romanche transforms in the equatorial atlantic we reprocessed seismic reflection lines did new facies analyses and 87sr 86sr dating of carbonate samples from the carbonate platforms a 50 km long narrow paleoisland flanking the vema transform underwent subsidence erosion and truncation at sea level it was then capped by a 500 m thick carbonate platform dated by 87sr 86sr at 11 10 ma three former islands on the crest of the romanche transverse ridge are now at 900 m bsl they show horizontal truncated surfaces of oceanic crust capped by 300 m thick carbonate platforms with 10 6 ma sr isotopic ages these sunken islands formed due to vertical tectonics related to transtension transpression along long offset slow slip transforms another tectonic sunken island is atlantis bank an uplifted gabbroic block along the atlantis ii transform sw indian ridge 700 m bsl a modern tectonic island is st peter and st paul rocks a rising slab of upper mantle located at the st paul transform equatorial atlantic cold tectonic islands contrast with hot volcanic islands related to mantle thermal and or compositional anomalies along accretionary boundaries and within oceanic plates or to supra subduction mantle melting that gives rise to islands arcs

seamount morphology in the bowie and cobb hot spot trails gulf of alaska full coverage multibeam bathymetric mapping of twelve seamounts in the gulf of alaska reveals that they are characterized by flat topped summits rarely with summit craters and by terraced or step bench flanks these summit plateaus contain relict volcanic features e g flow levees late stage cones and collapse craters and as such must have been constructed by volcanic processes such as lava ponding above a central vent rather than by erosion above sea level the terraced flanks are composed of a sequence of stacked lava deltas and cones probably tube fed from a central lava pond a morphology which is suggestive of long lived stable central lava sources and low to moderate eruption rates indicative of significant time spent above a hot spot outlet most of these seamounts have summit plateaus surrounded and cut into by amphitheater headwall scarps and flanks that are scarred by debris chutes but lack visible debris accumulations at their base we interpret the lack of blocky debris fields as evidence that the slope failures are mainly small scale debris flows rather than large scale flank collapses however we cannot rule out the possibility that large flank collapse blocks from early in the histories of these seamounts are now hidden beneath the thick glacio fluvial fan deposits that cover the gulf of alaska seafloor these slope failure features become smoother and longer and increase in size and abundance with increasing age of a seamount suggesting that slope failure processes continue long after volcanic activity ceases

prodigious submarine landslides on the hawaiian ridge the extensive area covered by major submarine mass wasting deposits on or near the hawaiian ridge has been delimited by systematic mapping of the hawaiian exclusive economic zone using the side looking sonar system gloria these surveys show that slumps and debris avalanche deposits are exposed over about 100 000 km2 of the ridge and adjacent seafloor from kauai to hawaii covering an area more than 5 times the land area of the islands some of the individual debris avalanches are more than 200 km long and about 5000 km3 in volume ranking them among the largest on earth the slope failures that produce these deposits begin early in the history of individual volcanoes when they are small submarine seamounts culminate near the end of subaerial shield building and apparently continue long after dormancy consequently landslide debris is an important element in the internal structure of the volcanoes the dynamic behavior of the volcanoes can be modulated by slope failure and the structural features of the landslides are related to elements of the volcanoes including rift zones and fault systems the landslides are of two general types slumps and debris avalanches the slumps are slow moving wide up to 110 km and thick about 10 km with transverse blocky ridges and steep toes the debris avalanches are fast moving long up to 230 km compared to width and thinner 0 05 2 km they commonly have a well defined amphitheater at their head and hummocky terrain in the lower part oceanic disturbance caused by rapid emplacement of debris avalanches may have produced high level wave deposits such as the 365 m elevation hulopoe gravel on lanai that are found on several islands most present day submarine canyons were originally carved subaerially in the upper parts of debris avalanches subaerial canyon cutting was apparently promoted by the recently steepened and stripped slopes of the landslide amphitheaters

flocculent layers and bacterial mats in the mudstone interbeds of the primary lower gypsum unit tertiary piedmont basin nw italy archives of palaeoenvironmental changes during the messinian salinity crisis abstract the recognition of peculiar laminated layers atypically rich in a biogenic intrabasinal component in the mudstone intervals from the messinian late miocene primary lower gypsum unit 5 97 5 60 ma of the piedmont basin nw italy provides information on the palaeoenvironmental evolution at precessional insolation maxima these cyclic layers consist of irregular alternation of cm thick grey terrigenous laminae and whitish composite packets the latter is in turn composed of sub mm thick wrinkled dolomite rich laminae that alternate with terrigenous ones two types of layers can be distinguished i peloidal layers composed of faecal pellets and irregular diatom rich aggregates interpreted as marine snow floccules and ii filament bearing layers composed of interwoven filaments up to 150 m across corresponding to remains of beggiatoa like giant sulphide oxidising bacteria by comparison with present day settings the peloidal layers are interpreted as flocculent layers deposited on anoxic sea bottoms following episodes of phytoplankton bloom in the upper water column the filament bearing layers are considered as chemotrophic microbial mats growing on dysaerobic sea bottoms the uncommon preservation of both kinds of layers is the result of extensive dolomite precipitation in the shallow subsurface induced by bacterial sulphate reduction the laminated layers are the first reported example of a high frequency climate driven cyclicity in the non evaporitic portion of the primary lower gypsum unit their stacking pattern within the mudstone intervals reflects the gradual increase of the oxygen content of bottom waters during the humid precessional hemicycle culminating with gypsum deposition at the onset of the arid phase

a geochemical application of the itrax scanner to a sediment core containing eastern mediterranean sapropel units the itrax micro x ray fluoresence xrf core scanner has been applied in a sediment geochemistry investigation the core sections selected contain examples of the organic rich sedimentary units sapropels that form periodically in the eastern mediterranean basin sapropels are visually obvious from their dark coloration but the itrax x radiograph also reveals physical property changes that result mainly from the high pore water content of sapropels a consideration of wavelength dispersive xrf data from discrete samples of the most recent sapropel s1 was made along with the set of elements reported by the itrax instrument s energy dispersive xrf system over core sections containing s1 this allowed selection of a suite of eight inter element ratios or element integrals through which characteristic features of sapropel development and geochemistry were revealed while recognizing that the measured xrf element integrals from the itrax do not have an exact constant relationship with element concentration over changing sediment types this combination of ratios provides significant information for geochemical interpretation these include evidence for i the presence of high corg contents in the visual sapropel from ba ti and br cl ratios ii a thinning of the original sapropel thickness by post depositional oxidation from mn ti and cu ti ratios iii pyrite authigenesis in the residual visual sapropel from fe ti and s cl ratios and the as integral and iv aragonite formation in and around the sapropel from the sr ca ratio these same ratios were then used to interpret itrax data from a deeper section of the same core containing the older sapropel s3 where the same characteristics including the relict post depositional oxidative thinning of the original unit could be identified with only minor differences of detail directions of supply of fe as and cu into the sapropels could be inferred from profile shapes

temporal changes in soil aggregates and water erosion after a wildfire in a mediterranean pine forest abstract the evolution of soil structure after a forest fire was studied on two zones representatives of a typical mediterranean pine forest these zones were in opposite slope orientation but with similar topographical and pedological characteristics changes in soil macro aggregation and water stable micro aggregation were monitored seasonally during a year after the fire the water erosion patterns were also studied from august 1993 immediately after the fire to the end of 1996 the first 5 cm of soil depth were the most affected by fire temperature showing clear differences on aggregate distribution and temporal variability between zones in the north facing soil a substantial and gradual recovery on soil aggregation was observed mainly in the fraction greater than 5 mm diameter this reached an increase of 27 in mass of aggregates in the south slope the evolution of aggregation was smooth and restricted to the fraction minor than 0 1 mm these differences between zones are reflected also in their values on soil cohesiveness and compaction being lesser in the south oriented soils values of erosion parameters show that both zones have the higher soil losses during the immediate period 4 months after the fire being more important in the south zone this zone produced more sediment and runoff 52 42 and 29 95 respectively than north facing soils for the whole period studied

soil surface roughness measurement methods applicability and surface representation abstract in a laboratory rainfall simulator study soil surface roughness was measured using contact roller chain pin meter and noncontact devices laser scanner photogrammetry soil surfaces with two initial roughness conditions aggregates as for the contact methods resolution cm range and precision mm range is limited which constrains their application to calculation of simple surface parameters resolution and precision in the sub millimeter range could be obtained with the laser scanner while for the photogrammetric method the measurement uncertainty was approximately 1 2 mm measurement time was highest 90 min for the pin meter technique though data were ready to use for analyses laser scanner measurements took 34 min several steps of data post processing required 30 more minutes data acquisition was fastest for photogrammetry 5 min but expert knowledge as well as special hard and software were necessary for time consuming photo analyses taking about 120 min the chain and pin meter were compared using a profile index profile lengths matched well for smooth surfaces on rough surfaces the chain meter gave shorter profile lines between profile index from chain measurements and the random roughness derived from pin meter data a polynomial regression could be found parameters of distributions of elevations as well as inclinations and depressions were used to compare the laser scanner and the photogrammetric technique generally the laser scanner was able to reproduce small aggregates as well as voids in between them while dem from stereophotos was smoothed between major aggregates this led to skewed distributions of elevations and inclinations as well as to a lower surface area up to 39 and a lower depression volume up to 68 shapes of depressions were significantly different as well the used photogrammetric technique is supposed to be successful in producing adequate dems for already smoothed surfaces e g after rainfall events the study revealed different fields of application and limitations of the compared devices using a non adequate technique for certain situations will definitely have implications on further analyses concerning connectivity of runoff pathways surface protection from raindrop impact or runoff detachment and sediment transport

identifying and quantifying erosion beneath the deposits of long runout turbidity currents along their pathway variations between the geochemical compositions coccolith species compositions and the physical properties of turbidite muds and their underlying hemipelagites can be used to understand the erosive nature of sediment gravity flows large volume submarine landslides on the nw moroccan continental margin produce long runout turbidity currents capable of traversing hundreds to thousands of kilometres across the adjacent moroccan turbidite system mts these turbidity currents are responsible for turbidites that are among the largest volume most aerially extensive and longest runout deposits recorded these resulting turbidite beds can be correlated over distances of 1800 km across the full 250 000 km2 area of the mts due to the ability to trace these individual flow deposits throughout the mts large volume beds a5 a7 a11 a12 and a15 can be shown to be erosive upon debouching agadir canyon whilst smaller volume flows were not erosive these aforementioned large volume flows have been capable of eroding up to 15 km3 of material in the canyon mouth equating to as much as 50 of the later deposit volume evidence suggests individual flows erode up to 4 5 m of sediment within scours in the mouth of agadir canyon however these scours are 8 0 m deep indicating that several flows contribute to forming the scours in a series of cut and fill episodes several flows including beds a5 a7 a11 and a12 were also erosive in agadir basin up to 210 km from the canyon the present study indicates that large volume flows a5 a7 and a12 are also erosive within the channel lobe transition zone within the proximal madeira abyssal plain after exiting the madeira channels over 800 km from agadir canyon studying the deposits of these flows and their compositional changes along their entire pathway has provided invaluable information of whether the flows are erosive where this erosion takes place and to what extent they erode the seafloor there are also broader implications towards gaining information about flow processes at the bed interface calculating basin sediment budgets and better understanding discontinuous stratigraphy in distal turbidite systems