estimating phase velocity and attenuation of guided waves in acoustic logging data in acoustic logging the guided waves which propagate along the borehole are affected by the properties of the formation for acoustic logging tools with many receivers array processing methods can be used to calculate the phase velocity and attenuation of these waves this information is crucial in estimating formation properties like permeability transverse isotropy and s wave velocity

evolution of the canadas edifice and its implications for the origin of the canadas caldera tenerife canary islands the volcano stratigraphic and geochronologic data presented in this work show that the tenerife central zone has been occupied during the last 3 ma by shield or central composite volcanoes which reached more than 3000 m in height the last volcanic system the presently active teide pico viejo complex began to form approximately 150 ka ago the first canadas edifice ce volcanic activity took place between about 3 5 ma and 2 7 ma the ce i is formed mainly by basalts trachybasalts and trachytes the remains of this phase outcrop in the canadas wall cw sectors of la angostura 3 5 3 0 ma and 3 0 2 7 ma boca de tauce 3 0 ma and in the bottom of some external radial ravines 3 5 ma the position of its main emission center was located in the central part of the cc the volcano could have reached 3000 m in height this edifice underwent a partial destruction by failure and flank collapse forming debris avalanches during the 2 6 2 3 ma period the debris avalanche deposits can be seen in the most distal zones in the n flank of the ce i tigaiga breccia a new volcanic phase whose deposits overlie the remains of ce i and the former debris avalanche deposits constituted a new volcanic edifice the ce ii the dyke directions analysis and the morphological reconstruction suggest that the ce ii center was situated somewhat westward of the ce i reaching some 3200 m in height the ce ii formations are well exposed on the cw especially at the el cedro 2 3 2 00 ma sector they are also frequent in the s flank of the edifice 2 25 1 89 ma in tejina 2 5 1 87 ma as well as in the tigaiga massif to the n 2 23 ma during the last periods of activity of ce ii important explosive eruptions took place forming ignimbrites pyroclastic flows and fall deposits of trachytic composition their ages vary between 1 5 and 1 6 ma adeje ignimbrites to the w in the cw the upper ucanca phonolitic unit 1 4 ma could be the last main episode of the ce ii afterwards the can adas iii phase began it is well represented in the cw sectors of tigaiga 1 1 ma 0 27 ma las pilas 1 03 ma 0 78 ma diego hernandez 0 54 ma 0 17 ma and guajara 1 1 ma 0 7 ma the materials of this edifice are also found in the se flank these materials are trachybasaltic lava flows and abundant phonolitic lava and pyroclastic flows 0 6 ma 0 5 ma associated with abundant plinian falls the ce iii was essentially built between 0 9 and 0 2 ma a period when the volcanic activity was also intense in the dorsal edifice situated in the easterly wing of tenerife the so called valleys of la orotava and gu imar transversals to the ridge axis also formed during this period in the central part of tenerife the ce iii completed its evolution with an explosive deposit resting on the top of the ce for which ages from 0 173 to 0 13 ma have been obtained the cc age must be younger due to the fact that the present caldera scarp cuts these deposits on the controversial origin of the cc central vertical collapse vs repeated flank failure and lateral collapse of mature volcanic edifices the data discussed in this paper favor the second hypothesis clearly several debris avalanche type events exist in the history of the volcano but most of the deposits are now under the sea the caldera wall should represent the proximal scarps of the large slides whose intermediate scarps are covered by the more recent teide pico viejo volcanoes

numerical simulation of the landslide induced tsunami of 1988 on vulcano island italy on 20 april 1988 a landslide of approximately 200 000 m3 occurred on the northeastern flank of the volcano la fossa on the island of vulcano the landslide fell into the sea producing a small tsunami in the bay between punte nere and punta luccia that was observed locally in the neighbouring harbour called porto levante the slide occurred during a period of unrest at the volcano that was monitored very accurately the study of this event is composed of two parts the simulation of the landslide and the simulation of the ensuing tsunami the former is studied by means of a lagrangian type numerical model in which the landslide is seen as a multibody system an ensemble of material deforming blocks interacting together during their motion the latter is simulated according to the eulerian view by solving the shallow water approximation to navier stokes equations of fluid dynamics with the incorporation of a forcing term depending on the slide motion technically the slide evolution is computed first and this result is then used to evaluate the excitation term of the hydraulic equations and to calculate the tsunami propagation computed wave fronts radiate both toward the open sea with rapid amplitude decay and along the shore in the form of edge waves that lose energy slowly comparison between model outputs and observations can be carried out only in a qualitative way owing to the absence of tide gauge records and results are satisfactory

volcanic evolution of the island of tenerife canary islands in the light of new k ar data new age determinations from tenerife together with those previously published 93 in all provide a fairly comprehensive picture of the volcanic evolution of the island the oldest volcanic series with ages starting in the late miocene are formed mainly by basalts with some trachytes and phonolites which appear in anaga teno and roque del conde massifs in anaga ne three volcanic cycles occurred one older than 6 5 ma a second one between 6 5 and 4 5 ma with a possible gap between 5 4 and 4 8 ma and a late cycle around 3 6 ma in teno nw after some undated units the activity took place between 6 7 and 4 5 ma with two main series separated by a possible pause between 6 2 and 5 6 ma in the zone of roque del conde s the ages are scattered between 11 6 and 3 5 ma between 3 3 and 1 9 ma the whole island underwent a period of volcanic quiescence and erosion the large canadas volcano made up of basalts trachytes and phonolites was built essentially between 1 9 and 0 2 ma to the ne of this central volcano linking it with anaga is a chain of basaltic emission centers with a peak of activity around 0 8 ma the canadas caldera had several collapse phases associated with large ignimbrite emissions there were at least an older phase more than 1 ma old on the western part of the volcano and a younger one less than 0 6 ma old in the eastern side the two large valleys of guimar and la orotava were formed by large landslides less than 0 8 ma ago and probably before 0 6 ma ago the present canadas caldera was formed by another landslide less than 0 2 ma ago this caldera was later filled by the huge teide volcano which has been active even in historic times during the same period a series of small volcanoes erupted at scattered locations throughout the island the average eruptive rate in tenerife was 0 3 km3 ka with relatively small variations for the different eruptive periods this island and la gomera represent a model of growth by discontinuous pulses of volcanic activity separated by gaps often coinciding with episodes of destruction of the edifices and sometimes extended for several million years the neighbouring gran canaria on the other hand had an initial rapid shield building phase during which more than 90 of the island was built and a series of smaller pulses at a much later period a comparison between these three central islands indicates that the previously postulated westward displacement in time of a gap in the volcanic activity is valid only as a first approximation several gaps are present on each island overlapping in time and not clearly supporting either of the models proposed to explain the evolution of the canaries

flank collapse and large scale landsliding in the cape verde islands off west africa large scale landslides occur on the flanks of many volcanic oceanic islands worldwide none have taken place in historical time but their geohazard potential especially their ability to generate tsunamis is large the cape verde islands are a group of 10 large and several smaller volcanic islands off the coast of west africa between 15 and 17 n a single flank landslide has previously been described from the island of fogo but systematic analysis of the cape verde group has until now been lacking this paper describes and interprets a multibeam bathymetry data set covering the slopes of the western cape verde islands including those of the islands with the most recent volcanic activity fogo in the southwest and santo antao in the northwest all of the larger islands show evidence of large flank landslides although only fogo and the southwest part of santo antao have failed in the last 400 ka tope de coroa the volcano at the southwest end of santo antao has been inactive for the past 170 ka and is judged to have a low landslide potential unless volcanic activity resumes in contrast there would seem to be a high probability of a future east directed landslide on fogo from the area of the highly active pico do fogo volcano although it is impossible to predict a timescale for such an event a tsunami generated by such a landslide could have a catastrophic effect on the adjacent island of santiago and possibly even farther afield on the west african coast

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 simulations of large water waves due to landslides a mathematical model based on the hydrodynamic shallow water equations is developed for numerical simulation of slide generated waves in fjords the equations are solved numerically by a finite difference technique to examine the performance of the numerical model we have simulated the slide catastrophe in tafjord western norway 1934 the predicted runup heights are in good agreement with measured runup heights the effects of wave amplification are estimated in runup zones with gentle beach slopes the model results reveal wave energy trapping due to the fjord geometry this causes standing wave oscillations in accordance with the observations

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

computer simulations of tsunamis due to sector collapse at stromboli italy abstract stromboli is an island volcano of the aeolian volcanic arc characterised by persistent activity the cone rises about 2500 3000 m from its submarine base with very steep slopes its summit at 924 m above the sea level the subaerial growth of stromboli occurred in the last 100 ka has been marked by repeated episodes of large gravitational collapses especially affecting the nw flank of the island in the last 13 ka the last one occurred less than 5000 years ago forming the deep depression on the nw seaward flank named sciara del fuoco sdf and it produced very likely large water waves this paper envisages a scenario where a huge mass of volcanic material collapses into the sea in the same sector in which the sdf collapse took place in holocenic times and it computes possible tsunami evolutions assuming the present day bathymetry numerical simulations are performed by means of two distinct models one for the mass collapse and one for the tsunami slope failure dynamics are calculated with the aid of a lagrangian model the landslide is subdivided into blocks and the motion of each constituent block is calculated by applying the basic principle of mechanical momentum conservation with block block and block ambient interactions being taken into account water waves are computed by solving a system of shallow water equations including a forcing term dependent on the sliding mass motion the finite element fe technique is employed since it permits the use of non uniform grids which are adequate to account for marine basins with irregular coastlines in addition to the sensitivity analysis concerning the main parameters governing the slide motion two main cases are explored differing in the slide path followed by the mass the resulting tsunami is very large with giant waves as high as several meters tens of meters in the worst cases impinging the coast due to the strong wave refraction induced by bathymetry waves travel around the island affecting even the island coast opposite the source

new sonar evidence for recent catastrophic collapses of the north flank of tenerife canary islands previous sonar surveys show that the north flank of tenerife has been subject to at least four major landslides during the past 1 ma the youngest icod affected the region to the north of the teide pico viejo complex the world s third highest oceanic volcano recently we obtained the first detailed acoustic images of icod using a deep tow side scan sonar the images suggest that tenerife s north flank has experienced at least two types of flow deposit in the recent past the older flow deposit icod i is characterised by a 15 to 20 km wide 65 km long chaotic debris avalanche deposit which includes several very large blocks we believe the deposit to be 170 ka and that it represents the mass wasting products of the canadas edifice remnants of which are now found in the las canadas caldera wall the younger flow deposit icod ii associated with a shute in its proximal part appears to have produced a less chaotic deposit in its distal part which clearly preserves flow structures such as latitudinal boulder ridges and longitudinal shear structures the sonar images cannot determine how much younger icod ii is than icod i although it is likely that they are a consequence of the same lateral collapse event there is evidence from the shute area for erosional scour and sediment deposition since the icod landslide if this is correct then it suggests that mass wasting is an ongoing process that has already started to modify the teide pico viejo complex itself

fundamental mechanisms for tsunami generation by submarine mass flows in idealised geometries tsunami generation from submarine gravity mass flows is investigated using linear two dimensional analytical models a simplified slide geometry and a prescribed sub critical slide velocity slide characteristics as maximum slide velocity initial acceleration slide length and thickness are all found to determine the characteristics of the tsunami effects of dispersion usually turn out to be of minor practical importance tsunamis due to retrogressive slides are generally smaller than for a similar fixed shaped slide with the same characteristics due to an increased duration of slide mass mobilisation however above the rear of the slide the surface elevation can also be increased for small time lags

the quaternary pyroclastic succession of southeast tenerife canary islands explosive eruptions related caldera subsidence and sector collapse a much revised quaternary stratigraphy is presented for ignimbrites and pumice fall deposits of the bandas del sur in southern tenerife new ar 41 ar 39 data obtained for the arico granadilla fasnia poris la caleta and abrigo formations are presented allowing correlation with previously dated offshore marine ashfall layers and volcaniclastic sediments we also provide a minimum age of 287 7 ka for a major sector collapse event at the gaimar valley the bandas del sur succession includes more than seven widespread ignimbrite sheets that have similar characteristics including widespread basal plinian layers predominantly phonolite composition ignimbrites with similar extensive geographic distributions thin condensed veneers with abundant diffuse bedding and complex lateral and vertical grading patterns lateral gradations into localized massive facies within palaeo wadis and widespread lithic breccia layers that probably record caldera forming eruptions each ignimbrite sheet records substantial bypassing of pyroclastic material into the ocean the succession indicates that las canadas volcano underwent a series of major explosive eruptions each starting with a plinian phase followed by emplacement of ignimbrites and thin ash layers some of coignimbrite origin several of the ignimbrite sheets are compositionally zoned and contain subordinate mafic pumices and banded pumices indicative of magma mingling immediately prior to eruption because passage of each pyroclastic density current was characterized by phases of non deposition and erosion the entire course of each eruption is incompletely recorded at any one location accounting for some previously perceived differences between the units because each current passed into the ocean estimating eruption volumes is virtually impossible nevertheless the consistent widespread distributions and the presence of lithic breccias within most of the ignimbrite sheets suggest that at least seven caldera collapse eruptions are recorded in the bandas del sur succession and probably formed a complex nested collapse structure detailed field relationships show that extensive ignimbrite sheets e g the arico poris and la caleta formations relate to previously unrecognized caldera collapse events we envisage that the evolution of the nested las cahadas caldera is more complex than previously thought and involved a protracted history of successive ignimbrite related caldera collapse events and large sector collapse events interspersed with edifice building phases

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

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

island edifice failures and associated tsunami hazards volcanic ocean islands are prone to structural failure of the edifice that result in landslides that can generate destructive tsunamis these island landslides range enormously in size varying from small rock falls to giant sector failures involving tens of cubic kilometers of debris a survey of literature has allowed us to identify twenty three processes that contribute to edifice collapse these have been divided into endogenetic and exogenetic sources of edifice failure endogenetic sources of instability and failure include unstable foundations volcanic intrusions thermal alteration edifice pore pressures unbuttressed structures and buried faults exogenetic sources of instability and failure include collapse of subaerial or submarine deposits endo upwelling karst megaporosity fractures oversteepening overloading sea level change marine erosion weathering including hurricanes glacial response volcanic activity regional uplift or subsidence tectonic seismicity and anthropogenic agents while the endogenetic sources dominate during periods of active volcanism and cone building the exogenetic sources may cause failure at any time tsunamis both small and large are associated with these edifice failures

a parametric study of tsunamis generated by submarine slides in the ormen lange storegga area off western norway tsunami generation by submarine slides have been a major concern in the risk assessment for the ormen lange gas field off western norway tsunamis are analysed with a numerical model supplemented by an analytical one both models show how slide extensions and slide dynamics influence the tsunamigenic potential for a large region several combinations of slide parameters were tested and the product of initial acceleration and the volume of the slide gave the best correlation with the maximum surface elevation for the near coastal domain

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

evolution of the north flank of tenerife by recurrent giant landslides geomorphologic analysis of submarine and subaerial surface features using a combined topographic bathymetric digital elevation model coupled with onshore geological and geophysical data constrain the age and geometry of giant landslides affecting the north flank of tenerife shaded relief and contour maps and topographic profiles of the submarine north flank permit the identification of two generations of post shield landslides older landslide materials accumulated near the shore 40 km and comprise 700 km3 of debris thickening towards a prominent axis suggests one major landslide deposit younger landslide materials accumulated 40 70 km offshore and comprise the products of three major landslides the la orotava landslide complex the icod landslide and the east dorsal landslide complex each with an onshore scar a proximal submarine trough and a distal deposit lobe estimated lobe volumes are 80 80 and 100 km3 respectively the old post shield landslide scar is an amphitheatre 20 25 km wide partly submarine now completely filled with younger materials age width relationships for tenerife s coastal platform plus onshore geological constraints suggest an age of ca 3 ma for the old collapse young landslides are all less than 560 ka old the la orotava and icod slides involved failures of slabs of subaerial flank to form the subaerial la orotava and icod valleys offshore they excavated troughs by sudden loading and basal erosion of older slide debris the onshore east dorsal slide also triggered secondary failure of older debris offshore the slab like geometry of young failures was controlled by weak layers deep drainage channels and flank truncation by marine erosion the partly submarine geometry of the older amphitheatre reflects the absence of these features relatively low h l ratios for the young slides are attributed to filling of the slope break at the base of the submarine edifice by old landslide materials low aspect ratios of the failed slabs and channelling within troughs post shield landslides on tenerife correlate with major falls in sea level reflecting increased rates of volcanism and coastal erosion and reduced support for the flank landslide head zones have strongly influenced the pattern of volcanism on tenerife providing sites for major volcanic centres

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

tsunamis of volcanic origin summary of causes with particular reference to krakatoa 1883 known tsunamis of volcanic origin are reviewed and classified according to their causes earthquakes accompanying eruptions excluding tectonic events which apparently triggered eruptions pyroclastic flows and submarine explosions have each accounted for about 20 of cases ten causes of volcanic tsunamis are discussed from the risk point of view those due to landslides are particularly dangerous eruptions at calderas are more likely to generate tsunamis than eruptions elsewhere of those killed directly by volcanic eruptions nearly a quarter have died as a result of tsunamis by transfer of energy to sea waves a violent eruption which would be comparatively harmless on land extends greatly the radius over which destruction occurs

reflected turbidity currents on an ordovician basin floor canadian appalachians sedimentary structures associated with turbidity current deposits show either partial or complete bouma ta e sequences1 that suggest deposition of sediment from a waning decelerating unidirectional flow2 bathymetric highs and basin margins can cause turbidity currents to reflect back along their original flow paths a rare situation in both ancient3 4 and modern5 marine basins the internal structures of such contained or reflected turbidites have only been described in one case the contessa bed ref 4 pp 268 300 our data from 1 6 m thick graded mud dominated turbidites from the quebec appalachians using mainly sole marks megaripple ripple and grain fabric data suggest that during the deposition of these beds the turbidity currents were reflected several times from either internal basin highs or basin slopes the recognition of such beds not only provides an insight into the depositional environment deep water basin floor but also allows detailed bed by bed correlations over tens of kilometres of coastal sections since the beds are reliable chronostratigraphical datum lines

observations of hydrography and downflow of brine enriched shelf water in the storfjorden polynya svalbard 1 observations of hydrography and currents in the active storfjorden polynya during fieldwork in april 2004 and 2006 are presented the polynya adds salt from its efficient ice production usually increasing the density 0 15 kg m 3 downflow of dense water from the coastal polynya to the deeper basin enclosed by the storfjorden sill was captured in both years april 2006 had a period of strong heat loss and intense frazil ice growth in the polynya this created downflow of brine enriched shelf water bsw with a maximum salinity of 35 25 i e an increased density 0 4 kg m 3 above that of the source water in april 2004 the salinity remained lower than bsw s 34 8 reflecting the fresh source water in fall 2003 due to the heavy ice conditions in the western barents sea that year a portion 0 05 sv of such source water probably enters storfjorden through freemansundet where the mean current transports less saline and warmer water from the northwestern barents sea freemansundet has additionally a strong tidal current peaking at 53 cm s 1 dominated by the m2 component the tidal wave propagates through the narrow sound producing shallow water components and a locally well mixed water column the estimated ice production in winter 2004 twice as large as that of winter 2006 could not overcome this less saline well mixed source water bsw downflow within storfjorden was both observed and modeled to occur in areas with steep bathymetry our observations show that high resolution hydrographical data spacing less than 0 5 km are necessary to resolve such downflow consistent with the observed polynya water salinity current data at the sill showed weaker overflow in 2004 than in 2006 overflow of bsw was observed on the eastern part of the storfjorden sill in april 2006 indicating that overflow occurs across the entire sill width during the freezing period current temperature and salinity data from the overflow indicate a time lag of 12 18 days between the bsw production and the sill this downflow overflow link is confirmed by a numerical experiment and analytical scaling making results applicable to other polynyas

stratigraphy structure and geochronology of the las canadas caldera tenerife canary islands after a long period of subaerial fissure fed extrusions of basaltic magmas 12 to 3 ma volcanic activity was then concentrated in the central part of tenerife phonolitic magma chambers formed and a central volcanic complex was constructed the las canadas edifice the formation of a large depression the las canadas caldera truncated the top of the edifice the active twin strato cones teide pico viejo are sited in this depression the history of the las canadas caldera and edifice are established from stratigraphy geochronology k ar dates and volcanological studies two different groups are recognized separated by a major unconformity the lower group is dated at 2 to 3 ma and includes the products of several volcanic centres which together represent several cycles the upper group ranges from 1 56 to 0 17 ma and includes three different formations representing three long term 100 to 300 ka volcanic cycles the periods of dormancy between each formation were of 120 to 250 ka duration the las canadas caldera is a multicyclic caldera which formed over the period 1 18 0 17 ma each cycle of activity represented by a formation culminated in caldera collapse which affected different sectors of the las canadas edifice geological observation and geochronology support an origin by collapse into a magma chamber the minimum volume of pyroclastic ejecta is substantially greater than the present caldera depression volume 45 km3 but approaches the inferred volume of the original caldera depression 140 km3 after the formation of the caldera sector collapses could also occur at the northern flank of the volcano causing the disappearance of the northern side of the caldera wall

a deep scar in the flank of tenerife canary islands geophysical contribution to tsunami hazard assessment abstract among the high intensity on earth tsunami generating events seismicity submarine landslides and volcano lateral collapses are the most important ward s h 2001 landslide tsunami j geophy res 106 11201 11215 holcomb r t searle r c 1991 large landslides from oceanic volcanoes mar geotech 10 19 32 tinti s bortolucci e romagnoli c 2000 computer simulations of tsunamis due to the sector collapse ar stromboli italy j volcano geotherm res 96 103 128 ward s n day s 2003 ritter island volcano lateral collapse and the tsunami of 1888 geophys j int 154 891 902 macguire w j 2003 volcano instability and lateral collapse revista 1 33 45 offshore bathymetry studies highlighted huge accumulations of large mass waste flows up to thousands cubic kilometres inherited from past lateral collapses or submarine landslides le friant a boudon g deplus c villemant b 2003 large scale flank collapse events during the activity of montagne pelee martinique lesser antilles j geophys res 108 ecv13 moore j g et al 1989 prodigious submarine landslides on the hawaiian ridge j geophys res 94 17465 17484 which spread over more than 100 km off the northern tenerife canary islands coastline watts a b masson d g 1995 a giant landslide on the north flank of tenerife canary islands j geophys res 100 24487 24498 although mechanics and dynamics triggering such catastrophic events follow from combined complex processes and interactions hurlimann m garcia piera j o ledesma a 2000 causes and mobility of large volcanic landslides application to tenerife canary islands j volcano geotherm res 103 121 134 masson d g et al 2002 slope failures on the flanks of the western canary islands earth sci rev 57 1 35 reid m e sisson t w brien d l 2001 volcano collapse promoted by hydrothermal alteration and edifice shape mount rainier washington geology 29 779 782 potential movable volume is an unavoidable parameter to quantify and constrain tsunamigenic hazard numerical modelling of a tsunami generated by the potential la palma landslide concluded that high amplitude waves threaten north atlantic shorelines ward s n day s j 2001 cumbre vieja volcano potential collapse and tsunami at la palma canary islands geophys res lett 28 397 400 new audiomagnetotelluric results provide for the first time a good estimation of the icod valley tenerife canary islands volume a potential giant landslide threatening the same shorelines two profiles image its electrically conductive roots with a characteristic of a u shaped cross section thought to be the consequence of previous landslides by this study we show that north atlantic ocean shorelines might be exposed to a destructive tsunami generated by a subaerial lateral collapse of at least 120 km 3 during the next strong felsic eruptive activity of the teide pico viejo complex this article highlights the degree of urgency of carrying out geophysical investigations on the flanks of most volcanic islands prone to potential flank collapse these investigations will contribute to the understanding of their structure a key parameter in the sliding process finally all results should be included in model providing a global map of tsunami hazard assessment