role of straining and advection in the intratidal evolution of stratification vertical mixing and longitudinal dispersion of a shallow macrotidal salt wedge estuary 1 a month of flow observations in the snohomish river estuary reveals the complex intratidal and fortnightly stratification mixing and dispersion dynamics in this macrotidal shallow salt wedge estuary system both salt wedge propagation and concomitant straining of the density field dominate temporal and spatial variations in stratification leading to intratidal variability of shear and mixing that differs in important ways from observations in partially mixed estuaries bottom generated turbulent kinetic energy production is enhanced during spring tides and acts in concert with straining to counteract advection and minimize vertical stratification during the spring flood tides this bottom generated mixing contributes to a buoyancy flux near the top of a well mixed layer during strong flood tides during strong ebb tides interfacial shear production and buoyancy flux occur along the sharp straining enhanced interface just before the system becomes well mixed longitudinal dispersion is less sensitive to the spring neap cycle yet exhibits strong intratidal variability reduced longitudinal dispersion is observed during the large floods relative to the rest of the tidal cycle behavior we attribute to a lack of vertical shear overall ebb tide advection and straining enhance stratification and longitudinal dispersion and allow for interfacial mixing intratidal variability which varies on the spring neap scale is a dominant feature of this estuary suggesting the importance of intratidal processes and tidally varying mixing coefficients in similar strongly stratified strongly forced estuaries

deep seated gravitational slope deformations related landslides and tectonics abstract deep seated gravitational slope deformations and their relationships with tectonic deformation of rocks is considered to examine the viewpoint of tectonics as a causative factor in slope deformation first a distinction is made between the different types of deep seated gravitational slope deformation then the geomorphological and structural effects of the different macrostructural deformations induced by tectonics on the scale of the whole deforming ridge is briefly discussed finally some case studies that represent either verified or possible cases of gravity deformation in response to tectonic activity are used as illustration

structure and flow induced variability of the subtidal salinity field in northern san francisco bay abstract the structure of the salinity field in northern san francisco bay and how it is affected by freshwater flow are discussed two datasets are examined the first is 23 years of daily salinity data taken by the u s bureau of reclamation along the axis of northern san francisco bay the second is a set of salinity transects taken by the u s geological survey between 1988 and 1993 central to this paper is a measure of salinity intrusion x2 the distance from the golden gate bridge to where the bottom salinity is 2 psu using x2 to scale distance the authors find that for most flow conditions the mean salinity distribution of the estuary is nearly self similar with a salinity gradient in the center 70 of the region between the golden gate and x2 that is proportional to x 12 analysis of covariability of q and x2 showed a characteristic timescale of adjustment of the salinity field of approximately 2 weeks the steady state response deduced from the x2 time series implies that x2 is proportional

very shallow earthquakes and brittle deformation in active volcanic areas the eatnean region as an example abstract some aspects of the stress field acting in active volcanic areas were investigated by studying the relationship between surficial seismicity h 1 2 km and the brittle deformation pattern of the etna volcano the magmatic composition and structural character of mt etna are described together with its geodynamic regional context after a discussion of the problem of the state of stress in active volcanoes and a definition of very shallow seismicity the high level of surficial seismicity the morphology of the sedimentary basement and the kinematic behaviour of the faults suggest that the eastern flank of mt etna is a shallow seismotectonic domain structurally decoupled from the rest of the volcanic body this flank shows a tendency to slide in an eastern direction and is bound to the north by a left lateral oblique slip normal fault trending e w and in the south by an arcuate fault system with right lateral features right lateral oblique slip normal faults

giant quaternary landslides in the evolution of la palma and el hierro canary islands in the past large morphological escarpments in the canaries have been generally related to explosive and or erosive processes recent onshore and offshore investigations drastically changed this interpretation by providing evidence of the importance of giant lateral collapses in the evolution of the islands especially in their earlier stages of growth giant landslide scars and deposits are readily observed both onshore and offshore in the younger western canaries and seem to be a common feature of the development of the entire archipelago at least one catastrophic collapse is apparent on la palma the cumbre nueva giant landslide which occurred about 560 ka ago this collapse removed some 200 km3 of central western la palma forming a large embayment three successive giant landslides and evidence of an aborted attempt at another are seen in the island of el hierro the combined volume of those collapses estimated at about 400 500 km3 considerably exceeds the present subaerial volume of the island about 140 km3 giant landslides and erosion during the past million years have removed more than half of the total subaerial volume of la palma and el hierro

observations of stratified turbulent mixing in an estuary neap to spring variations during high river flow abstract observations of turbulent mixing stratification and currents were made with a free falling microstructure profiler and a 600 khz adcp in the hudson river off manhattan in may 1994 the ship was anchored in a relatively straight and uniform channel about 15 m deep over 4 days of intense observations from 19 to 24 may 1994 the progression from neap tides to spring tides caused a severe reduction in stratification from an initial top to bottom salinity difference of 18 to 3 6 while low gradient richardson numbers ri occurred only in the weakly stratified bottom layer on flood during neap tides low ri spanned the water column on the second half of ebb during spring tides turbulent dissipation rates varied roughly inversely to ri during neap conditions turbulent mixing was intense only in the bottom layer on flood where eddy diffusivities k reached more than 10 2 m 2 s 1 while mixing was weak in the centre of the halocline near 5 m during spring tides strong mixing occurred throughout the water column during the latter part of ebb with typical k 5 10 3 m 2 s 1 and typical vertical salt flux of 0 0015 kg m 2 s 1 if it existed in isolation this flux would eliminate the haline stratification on a time scale of 4 h ebb time bands of low ri and intense mixing showed increasing phase lag with increasing distance from the bottom the spring tide ebb time internal turbulent stress was relatively uniform with depth with a typical magnitude of 0 4 pa 4 dyne cm 2 turbulent overturning thorpe scales ranged from below 1 cm in the neap tide halocline to a few metres in the weakly stratified bottom layer on flood the strong spring tide ebb time mixing had thorpe scales of typically 0 5 m throughout the water column ozmidov scales tracked thorpe scales except in the weakly stratified layer above the bottom

causes and mobility of large volcanic landslides application to tenerife canary islands abstract giant volcanic landslides are one of the most hazardous geological processes due to their volume and velocity since the 1980 eruption and associated debris avalanche of mount st helens hundreds of similar events have been recognised worldwide both on continental volcanoes and volcanic oceanic islands however the causes and mobility of these enormous mass movements remain unresolved tenerife exhibits three voluminous subaerial valleys and a wide offshore apron of landslide debris produced by recurrent flank failures with ages ranging from upper pliocene to middle pleistocene we have selected the la orotava landslide for analysis of its causes and mobility using a variety of simple numerical models first the causes of the landslide have been evaluated using limit equilibrium method and 2d finite difference techniques conventional parameters including hydrostatic pore pressure and material strength properties together with three external processes dike intrusion caldera collapse and seismicity have been incorporated into the stability models the results indicate that each of the external mechanism studied is capable of initiating slope failures however we propose that a combination of these processes may be the most probable cause for giant volcanic landslides second we have analysed the runout distance of the landslide using a simple model treating both the subaerial and submarine parts of the sliding path the effect of the friction coefficient drag forces and hydroplaning has been incorporated into the model the results indicate that hydroplaning particularly can significantly increase the mobility of the landslide which may reach runout distances greater than 70 km the models presented are not considered definite and have mainly a conceptual purpose however they provide a physical basis from which to better interpret these complex geologic phenomena and should be taken into account in the prediction of future events and the assessment of landslide related hazards

spatial probability distribution of future volcanic eruptions at el hierro island canary islands spain abstract the 2011 submarine eruption that took place in the proximity of el hierro island canary islands spain has raised the need to identify the most likely future emission zones even on volcanoes characterized by low frequency activity here we propose a probabilistic method to build the susceptibility map of el hierro i e the spatial distribution of vent opening for future eruptions based on the probabilistic analysis of volcano structural data of the island collected through new fieldwork measurements bathymetric information as well as analysis of geological maps orthophotos and aerial photographs these data have been divided into different datasets and converted into separate and weighted probability density functions which were included in a non homogeneous poisson process to produce the volcanic susceptibility map the most likely area to host new eruptions in el hierro is in the south western part of the west rift high probability locations are also found in the northeast and south rifts and along the submarine parts of the rifts this map represents the first effort to deal with the volcanic hazard at el hierro and can be a support tool for decision makers in land planning emergency measures and civil defense actions

vertical and lateral collapses on tenerife canary islands and other volcanic ocean islands recent studies demonstrate that tenerife has undergone large lateral collapses this has led to the suggestion that the las canadas caldera one of the best exposed calderas in the world is the result of lateral collapse we have tested this idea using the available structural stratigraphic volcanological and geochronological data we conclude that the las canadas caldera is the result of a complex sequence of vertical collapse events associated with a long history of phonolitic explosive activity in the central part of tenerife our results indicate however that vertical collapses may have played a major role in triggering lateral collapses we propose that the association of vertical and lateral collapse events such as inferred for tenerife can also explain similar sequences of events interpreted to have affected other large volcanic ocean islands

intratidal variations in stratification and mixing in the hudson estuary this study represents a detailed examination of intratidal variations in boundary layer structure in a relatively narrow straight section of the hudson river estuary during high river discharge the presence of active mixing is inferred from estimates of the richardson number the maximum height above bed to which mixing occurs is comparable during flood and ebb however the regions of mixing differ in density structure during the flood active mixing is confined to a well mixed near bed layer whereas during the ebb active mixing occurs throughout regions of significant stratification tidal straining maintains stratification during the ebb while it promotes the growth of a uniform bottom mixed layer during the flood in general maximum and minimum near bed stratification occur during late ebb and flood respectively reflecting the dominant role played by tidal straining in determining intratidal variation vertical stretching was also found to be an important term in the stratification balance during the ebb

the influence of flow inertia buoyancy wind and flow unsteadiness on mixing at the asymmetrical confluence of two large rivers summary the rates and patterns of mixing of two large rivers with large density differences at a strongly asymmetrical confluence in northern spain are analyzed we assess the factors controlling the site where the denser river plunges and the mixing rates between the rivers in particular we focus on the interaction between inertial and buoyancy forces the effect of wind forcing and the unsteady nature of the hydraulic forcing the steady state location of the plunge line is shown to be controlled by an inertia buoyancy balance which accounts for the relative magnitude of the buoyancy forcing associated with density differences between the confluent rivers and the magnitudes of both the main stream and the side flow tributary inertia the plunge line moves to upstream locations as the inertia of the tributary increases for low tributary inertia and or the density contrast between the rivers increases this has important consequences for river mixing since mixing rates increase as the plunging occurs at the confluence the high mixing rates in this case occur as a result of a large mixing interface surface area and high diffusivities as the plunging area moves upstream or downstream of the confluence vertical diffusivities or the area of contact available for mixing decrease and constrain mixing rates wind forcing depending on its velocity and direction affects mixing rates through 1 altering the buoyancy inertia equilibrium and so changing the location of the plunge line 2 altering the pattern of secondary circulation within the confluence and or 3 increasing shear at the confluence flow unsteadiness can lead to changes in the location of the plunge line through time and thus can strongly modify mixing rates at the confluence the downstream movement of the plunge line is advection dominated while its upstream movement seems to respond to a baroclinic response of the confluence

development and recent activity of the san andres landslide on el hierro canary islands spain abstract extremely voluminous landslides with a long run out also known as megalandslides on oceanic volcanic islands are infrequent denudational processes on such islands at the same time they represent a major geological hazard that must be looked into to avoid negative consequences for the inhabitants of these islands their occurrence can be related to periods of intense seismo volcanic activity similar to that which occurred on el hierro island over 2011 2012 landslides on volcanic islands are studied using onshore and offshore geological geophysical and geomorphological records considering their unique triggering conditions e g lava intrusions eruptive vents magma chamber collapses previous work has pointed out similarities between specific cases of landslides on volcanic islands and deep seated gravitational slope deformations dsgsds which are typical in high mountain settings nevertheless the methodological approaches and concepts used to investigate dsgsds are not commonly applied on volcanic islands studies even though their use may provide new information about the development stage recent movements and future hazards therefore this approach for studying the san andres landslide sal on el hierro canary islands has been developed applying a detailed morphological field mapping an interpretation of digital elevation models structural measurements kinematic testing and a precise movement monitoring system the acquired information revealed a strong structural influence on the landslide morphology and the presence of sets of weakened planes acting as the sliding surfaces of the sal or secondary landslides within its body the presence of secondary landslides deep erosive gullies coastal cliffs and high on shore relative relief also suggests a high susceptibility to future landslide movement direct monitoring on the landslide scarps and the slip plane performed between february 2013 and july 2014 using an automated optical mechanical crack gauge with a precision of up to 10 2 mm detected creep movement in the order of 1 mm yr 1 with a persistent sinistral component as well as episodic horizontal and a subtle vertical movement this monitoring will continue in the future in order to verify the initial observations which instead of long term movement patterns could represent a landslide response to the period of an intense seismo volcanic activity during 2011 12

hotspot volcanism close to a passive continental margin the canary islands the canarian archipelago is a group of volcanic islands on a slow moving oceanic plate close to a continental margin the origins of the archipelago are controversial a hotspot or mantle plume a zone of lithospheric deformation a region of compressional block faulting or a rupture propagating westwards from the active atlas mountains fold belt have been proposed by different authors however comparison of the canarian archipelago with the prototypical hotspot related island group the hawaiian archipelago reveals that the differences between the two are not as great as had previously been supposed on the basis of older data quaternary igneous activity in the canaries is concentrated at the western end of the archipelago close to the present day location of the inferred hotspot this is the same relationship as seen in the hawaiian and cape verde islands the latter archipelago associated with a well defined but slow moving mantle plume shows anomalies in a plot of island age against distance which are comparable to those seen in the canary islands these anomalies cannot therefore be used to argue against a hotspot origin for the canaries individual islands in both archipelagoes are characterized by initial rapid growth the shield building stages of activity followed by a period of quiescence and deep erosion erosion gap which in turn is followed by a post erosional stage of activity the absence of post shield stage subsidence in the canaries is in marked contrast with the major subsidence experienced by the hawaiian islands but is comparable with the lack of subsidence evident in other island groups at slow moving hotspots such as the cape verdes comparison of the structure and structural evolution of the canary islands with other oceanic islands such as hawaii and reunion reveals many similarities these include the development of triple mercedes star rift zones and the occurrence of giant lateral collapses on the flanks of these rift zones the apparent absence of these features in the post erosional islands may in part be a result of their greater age and deeper erosion which has removed much of the evidence for their early volcanic architecture we conclude that the many similarities between the canary islands and island groups whose hotspot origins are undisputed show that the canaries have been produced in the same way

large scale mass wasting in ancient volcanic materials abstract giant landslides are significant hazards associated with many active volcanic edifices we describe a similar feature on ancient 4 ma volcanic deposits subject to active tectonism the landslide is approximately 3 km long by 1 km wide with an estimated depth of 400 m side margins are straight and parallel mimicking regional structure narrow valleys incised down these margins provide low strength side release surfaces between these is a giant slump consisting of at least four largely intact discrete blocks that have moved down dip a distance of 500 m a series of flows with areal extents ranging from 0 01 to 0 5 km 2 extends from the front of the failure the materials represent an eroded sequence of andesite flows on the flanks of a stratovolcano these have undergone two phases of hydrothermal alteration and are deeply weathered to low density 1040 80 kg m 3 silt 59 and clay 35 materials with strength properties typical of weathered silts c 26 3 kn m 2 42 8 the size and location of this landslide preclude detailed geotechnical investigation of the failure the worth of numerical stability analysis as an alternative technique in assessing the nature of the failure and hence the risk it poses to nearby communities is investigated sensitivity analysis identified likely conditions under which initial failure may have occurred analyses for sensitivity to strength and earthquake acceleration needed conversion to critical combinations f 1 0 of water table and strength acceleration to remove the overriding influence of water table fluctuations failure was likely initiated either by a high water table level 83 84 or some combination of intensity vii ix earthquake waves together with water table heights of 40 80 a general hazard assessment indicates that the risk associated with creep and catastrophic failure of the main mass is small whereas the risk from flow failures near the toe of the landslide may be high important parameters hydrological regime flow failure morphology age of initiation and rates of movement requiring closer investigation are identified development of a model is crucial to assessing the hazard associated with a feature such as that described here with limited resources a detailed stability analysis is a powerful tool as an initial stage in hazard analysis

assessing landslide movements in volcanic islands using near shore marine geophysical data south pico island azores marine geophysical data from around the submarine flanks of volcanic islands can potentially help to resolve whether large scale instability of an edifice has been geologically recently active we use geophysical data to investigate part of the coast of pico island of the azores where above sea level a major slump of topo volcano has been interpreted previously from arcuate escarpments and a rugged irregular topography seaward of them multibeam echo sounder data collected offshore of this feature show remarkably little evidence for slump fault movements in the island s submarine slope mid slope benches like those associated with the hilina slump of kilauea are absent the high resolution data extends onto the island s shelf allowing us to evaluate evidence for continuing activity there in particular as the shelf s rock platform will have been last modified by surf erosion during the postglacial period of sea level transgression it provides a reference surface of intermediate age 7 19 ka that can potentially reveal whether any movements occurred in pre historic times where the arcuate escarpments are continued offshore the modern seabed shows no bathymetric evidence for active faults where the shelf rock platform crops out in the multibeam data elsewhere mobile shelf sediments could be disguising evidence for active faulting so we examined boomer profiles able to image the rock platform beneath them the data reveal a platform that is steep 6 6 compared with the dips of platforms that we have studied previously around the coast of adjacent faial island and steeper than the platform outside the proposed slump this suggests that it was created by coastal erosion over a shorter period and hence is consistent with a younger age of the coastline as with the multibeam data where escarpments are continued offshore onto the shelf the rock surface imaged with these boomer data also shows no clear evidence of major slump related fault displacements this study therefore illustrates how high resolution boomer seismic and multibeam data could usefully contribute to hazard assessment of volcanic islands by helping to evaluate areas with no historical movements explanations to reconcile the onshore and offshore data here are also put forward

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

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

submarine landslides around the canary islands the morphology and structure of the submarine flanks of the canary islands were mapped using the gloria long range side scan sonar system bathymetric multibeam systems and sediment echosounders twelve young 2 ma giant landslides have been identified on the submarine flanks of the canary islands up to now older landslide events are long buried under a thick sediment cover due to high sedimentation rates around the canary islands most slides were found on the flanks of the youngest and most active islands of la palma el hierro and tenerife but young giant landslides were also identified on the flanks of the older 15 20 ma but still active eastern islands large scale mass wasting is an important process during all periods of major magmatic activity the long lived volcanic constructive history of the islands of the canary archipelago is balanced by a correspondingly long history of destruction resulting in a higher landslide frequency for the canary islands compared to the hawaiian islands where giant landslides only occur late in the period of active shield growth the lower stability of the flanks of the canaries is probably due to the much steeper slopes of the islands a result of the abundance of highly evolved intrusive and extrusive rocks another reason for the enhanced slope instability is the abundance of pyroclastic deposits on canary islands resulting from frequent explosive eruptions due to the elevated volatile contents in the highly alkalic magmas dike induced rifting is most likely the main trigger mechanism for destabilization of the flanks flank collapses are a major geological hazard for the canary islands due to the sector collapses themselves as well as triggering of tsunamis in at least one case a giant lateral blast occurred when an active magmatic or hydrothermal system became unroofed during flank collapse

on nonhydrostatic coastal model simulations of shear instabilities in a stratified shear flow at high reynolds number the nonhydrostatic surface and terrain following coastal model nhwave is utilized to simulate a continually forced stratified shear flow in a straight channel which is a generic problem to test the existing nonhydrostatic coastal models capability in resolving shear instabilities in the field scale the resolved shear instabilities in the shear layer has a reynolds number of about 1 4 106 which is comparable to field observed value using the standard smagorinsky closure with a grid size close to the ozmidov length scale simulation results show that the resolved energy cascade exceeds 1 order of magnitude and the evolution and turbulent mixing characteristics are predicted well two different approaches are used to estimate the turbulent dissipation rate namely using the resolved turbulent energy spectrum and the parameterized subgrid turbulent dissipation rate and the predicted results provide the upper and lower bounds that encompass the measured values model results show significantly higher turbulence in braids of shear instabilities which is similar to field observations while both the subgrid turbulent dissipation rate and resolved vorticity field can be used as surrogates for measured high acoustic backscatter signals simulation results also reveal that the surface velocity divergence convergence is an effective identifier for the front of the density current and the shear instabilities to guide future numerical studies in more realistic domains an evaluation on the effects of different grid resolutions and subgrid viscosity on the resolved flow field and subgrid dissipation rate are discussed

age of the el golfo debris avalanche el hierro canary islands new contraints from laser and furnace 40ar 39 ar dating abstract the life cycle of ocean island volcanoes is commonly punctuated by large scale flank collapse events which may generate far reaching tsunami estimates exist though are poorly constrained for worldwide recurrence time intervals of giant landslides however individual events are often difficult to date the el golfo debris avalanche on the island of el hierro canary islands is a young feature although its exact formation age remains elusive using both furnace and laser heating 40 ar 39 ar dating techniques on groundmass separates we obtained new ages for the altitudinally highest lava flows cut by the el golfo landslide headwall as well as a post collapse lava flow erupted from within the embayment the new data significantly improve limits on the age of the debris avalanche which we propose occurred between 87 8 ka and 39 13 ka ago this age range raises doubts on the previously proposed correlation between this event and the glacial to interglacial transition at 130 ka

large eddy simulation of turbulence and solute transport in a forested headwater stream the large eddy simulation les module of the virtual streamlab vsl3d model is applied to simulate the flow and transport of a conservative tracer in a headwater stream in minnesota located in the south twin cities metropolitan area the detailed geometry of the stream reach which is 135 m long 2 5 m wide and 0 15 m deep was surveyed and used as input to the computational model the detailed geometry and location of large woody debris and bed roughness elements up to 0 1 m in size were also surveyed and incorporated in the numerical simulation using the curvilinear immersed boundary approach employed in vsl3d the resolution of the simulation which employs up to a total of 25 million grid nodes to discretize the flow domain is sufficiently fine to directly account for the effect of large woody debris and small cobbles on the streambed on the flow patterns and transport processes of conservative solutes two tracer injection conditions a pulse and a plateau release and two cross sections of measured velocity were used to validate the les results the computed results are shown to be in good agreement with the field measurements and tracer concentration time series to our knowledge the present study is the first attempt to simulate via high resolution les solute transport in a natural stream environment taking into account a range of roughness length scales spanning an order of magnitude from small cobbles on the streambed 0 1 m in diameter to large woody debris up to 3 m long

vertical boil propagation from a submerged estuarine sill 1 surface disruptions by boils during strong tidal flows over a rocky sill were observed in thermal infrared imagery collected at the snohomish river estuary in washington state locations of boil disruptions and boil diameters at the surface were quantified and are used to test an idealized model of vertical boil propagation the model is developed as a two dimensional approximation of a three dimensional vortex loop and boil vorticity is derived from the flow shear over the sill predictions of boil disruption locations were determined from the modeled vertical velocity the sill depth and the over sill velocity predictions by the vertical velocity model agree well with measured locations rms difference 3 0 m and improve by using measured velocity and shear rms difference 1 8 m in comparison a boil surfacing model derived from laboratory turbulent mixed layer wakes agrees with the measurements only when stratification is insignificant

structural constraints on deep seated slope deformation kinematics abstract a significant sackung type deep seated slope gravitational deformation dsgsd was recognised for the first time by the authors in the middle part of valfurva east of bormio rhaetian alps italy the reconstruction of its kinematics age and state of activity is presented through a detailed description of its morphological geomechanical and structural features an integrated multi disciplinary approach was performed to achieve a clear comprehension of the phenomenon field surveys and aero photo interpretation were carried out in order to clarify the structural geological and geomorphological setting in which the dsgsd developed a kinematic conceptual model of the slope deformation was developed through the analysis of morpho structures of their significance and relationships with lithological markers and quaternary deposits after a geomechanical characterisation of the rock mass involved in the slope deformation numerical modelling was performed to verify the hypotheses made on kinematics and driving factors of the phenomenon the sackung affects pre permian metapelites metabasites and marbles belonging to the upper austroalpine basement of the campo nappe as well as late pleistocene and holocene glacial and rock glacier deposits the deformation started after the late wurmian age 15 000 11 000 years b p and continued until few centuries ago not excluding a present day low rate activity deformation consists in a large oblique sagging along a deep confined sliding surface associated with gravitational reactivation of pre existing late alpine and recent tectonic brittle structures leading to the formation of n s and wnw ese trending gravitational morpho structures the evolution of the wnw ese trending system resulting in asymmetric trenches led to progressive failure of the lower part of the slope during the last 10 000 years as testified by large paleo landslide accumulations and it is still in progress numerical modelling indicates post glacial unloading as the main triggering factor of the slope deformation the importance of this deep seated slope deformation is enhanced by the occurrence of the 30 mm 3 active ruinon landslide in the lower part of the slope such landslide is subjected to rapid evolution and threatens the valley floor establishing an important risk factor connected to human lives and socio economic activities

morphological and geological aspects related to large slope failures on oceanic islands the huge la orotava landslides on tenerife canary islands huge volcanic landslides are one of the most hazardous geomorphological processes that can occur during the evolution of volcanic ocean islands the causes of these phenomena however are very complex and combine non volcanic and volcanic factors in the canary islands more than 20 events have been detected during the last decades a detailed analysis was carried out for la orotava amphitheatre on tenerife in order to understand the relationship between geomorphological and geological aspects and huge volcanic landslides the results indicated four major features that play a significant role in such mass movements deep erosive canyons high coastal cliffs widespread residual soils and structural axes high coastal cliffs and deep erosive canyons locally reduce the stability conditions and control both the seaward and the lateral boundary of the landslide weak residual soils formed above phonolitic pyroclastic deposits occur repeatedly in the stratigraphic column of la orotava and are characterised by their large extent thus one of these soils may have evolved into the slip surface of the failure part of the head scarp of the amphitheatre is defined by a volcanic rift zone as indicated by the measurement of dike orientation and a density map of eruptive vents the four features are not able to trigger a failure but to destabilise the volcano flank and determine the boundary of the slide therefore information on depth and orientation of canyons location and height of coastal cliffs stratigraphic repetition extension and thickness of residual soils and orientation and density of dikes and eruptive vents along structural axes should be incorporated into a hazard assessment on large landslides on volcanic islands

the relationship between seismic deformation and deep seated gravitational movements during the 1997 umbria marche central italy earthquakes abstract this paper re evaluates the origin of some peculiar patterns of ground deformation in the central apennines observed by space geodetic techniques during the two earthquakes of the colfiorito seismic sequence on september 26th 1997 the surface displacement field due to the fault dislocation as modelled with the classic okada elastic formulations shows some areas with high residuals which cannot be attributed to non simulated model complexities the residuals were investigated using geomorphological analysis recognising the geologic evidence of deep seated gravitational slope deformations dsgsd of the block slide type the shape and direction of the co seismic ground displacement observed in these areas are correlated with the expected pattern of movement produced by the reactivation of the identified dsgsd at least a few centimetres of negative line of sight ground displacement was determined for the costa picchio mt pennino and mt prefoglio areas a considerable horizontal component of movement in the costa picchio dsgsd is evident from a qualitative analysis of ascending and descending interferograms the timing of the geodetic data indicates that the ground movement occurred during the seismic shaking and that it did not progress appreciably during the following months this work has verified the seismic triggering of dsgsd previously hypothesized by many researchers a further implication is that in the assessment of dsgsd hazard seismic input needs to be considered as an important cause of accelerated deformation

multiple sector collapses at stromboli volcano italy how they work this paper demonstrates that four large sector collapses have affected the nw flank of the stromboli volcano in the past 13 ka alternating with growth phases in order to contribute to the evaluation of the critical conditions which trigger lateral collapses a reconstruction of the geometry of each collapse of the volcano edifice in the four stages that preceded the relative collapse events is also presented and a computation of the landslide volume this reconstruction is based on new field data plotted in three dimensions prior to the initial 13 ka collapse the volcano was 1125 100 m high above sea level the collapse had a volume of 2 23 0 87 km3 whereas the pre collapse volcano volume was 218 8 7 7 km3 the next edifice that failed was 900 70 m high a s l the collapse volume was 1 0 54 km3 with a precollapse volcano volume of 201 4 5 4 km3 the edifice then grew to 1000 60 m a s l the third collapse had a volume of 1 08 0 39 km3 and occurred within a volcano with a volume of 209 1 4 6 km3 this was followed by a new growth phase followed by the last collapse with a volume of 0 73 0 22 km3 the volcano volume was about the same as the present one the present active crater zone is at 780 m a s l in the first three collapses sliding surfaces cut the main magma conduit in the last collapse the upper scarp coincided with the conduit location dyking along a main ne trending weakness zone across the volcano summit exerted a lateral force for collapse inception the decrease of the landslide volumes with the age and the concentric scarps of the four collapses suggest that the younger sliding planes tended to become more superficial and to decrease the areal extent this is interpreted as due to a successively weaker eruptive products from dominantly lavas to dominantly pyroclastics and b the feedback effects between collapses and dykes that injected along the lateral segments of the first collapse slide plane

deep seated gravitational slope deformations in the highest parts of the czech flysch carpathians evolutionary model based on kinematic analysis electrical imaging and trenching deep seated gravitational slope deformations dsgsds played an important role during the quaternary evolution of mountain ridges formed by anisotropic flysch rocks of the outer western carpathians owc four dsgsd affected ridges in the highest part of the czech sector of the owc have been subjected to multidisciplinary investigation involving mapping structural and kinematic analysis geoelectrical imaging trenching and dating all the studied dsgsds are strongly predisposed by regional structural fabric given by the intersection of bedding planes joint sets and faults performed research suggests high diversity of mechanisms leading to the origin of individual dsgsds the area of a single dsgsd can be affected by various types of movements such as sackung lateral spreading toppling or incipient sliding electrical imaging and trenching revealed that besides these mechanisms anisotropic flysch massifs formed by thick bedded sandstones are strongly exposed to subsurface opening of air filled voids related to widened crevices such a process is driven by deep seated creep and translational sliding of sandstone beds upon plastic claystones whose strength has been reduced to residual values of the angle of internal friction performed radiocarbon and osl dating revealed that some of the studied dsgsds originated in the holocene period particularly in the atlantic and subboreal chronozones

kinematics of a landslide derived from archival photogrammetry and gps data abstract the evolution of the patigno landslide a deep seated gravitational slope deformation in the northern apennine range italy was investigated using archival photogrammetry and gps observations from a permanent station located inside the landslide historical aerial photographs of the area taken in 1975 scale 1 13 000 1987 1 13 000 and 2004 1 30 000 were co registered into the same reference frame using an unconventional method based on the detection of homologous points in multi temporal models three dtms were produced using a digital photogrammetric workstation and compared the displacement vectors of 293 points in the landslide were determined the average movement velocity of the gps station since 2004 about 3 5 cm yr 1 agrees with the mean displacement rate obtained from photogrammetry furthermore the estimated velocity varies seasonally between 3 and 6 cm yr 1 this variability correlated with rainfall suggests that the creep of the landslide is influenced by hydrological factors

numerical modeling of an estuary a comprehensive skill assessment i numerical simulations of the hudson river estuary using a terrain following three dimensional model regional ocean modeling system roms are compared with an extensive set of time series and spatially resolved measurements over a 43 day period with large variations in tidal forcing and river discharge the model is particularly effective at reproducing the observed temporal variations in both the salinity and current structure including tidal spring neap and river discharge induced variability large observed variations in stratification between neap and spring tides are captured qualitatively and quantitatively by the model the observed structure and variations of the longitudinal salinity gradient are also well reproduced the most notable discrepancy between the model and the data is in the vertical salinity structure while the surface to bottom salinity difference is well reproduced the stratification in the model tends to extend all the way to the water surface whereas the observations indicate a distinct pycnocline and a surface mixed layer because the southern boundary condition is located near the mouth the estuary the salinity within the domain is particularly sensitive to the specification of salinity at the boundary a boundary condition for the horizontal salinity gradient based on the local value of salinity is developed to incorporate physical processes beyond the open boundary not resolved by the model model results are sensitive to the specification of the bottom roughness length and vertical stability functions insofar as they influence the intensity of vertical mixing the results only varied slightly between different turbulence closure methods of k e k and k kl

subtidal salinity and velocity in the hudson river estuary observations and modeling a tidally and cross sectionally averaged model based on the temporal evolution of the quasi steady hansen and rattray equations is applied to simulate the salinity distribution and vertical exchange flow along the hudson river estuary the model achieves high skill at hindcasting salinity and residual velocity variation during a 110 day period in 2004 covering a wide range of river discharges and tidal forcing the approach is based on an existing model framework that has been modified to improve model skill relative to observations the external forcing has been modified to capture meteorological time scale variability in salinity stratification and residual velocity due to sea level fluctuations at the open boundary and alongestuary wind stress to reflect changes in vertical mixing due to stratification the vertical mixing coefficients have been modified to use the bottom boundary layer height rather than the water depth as an effective mixing length scale the boundary layer parameterization depends on the tidal amplitude and the local baroclinic pressure gradient through the longitudinal richardson number and improves the model response to spring neap variability in tidal amplitude during periods of high river discharge finally steady state model solutions are evaluated for both the hudson river and northern san francisco bay over a range of forcing conditions agreement between the model and scaling of equilibrium salinity intrusions lends confidence that the approach is transferable to other estuaries despite significant differences in bathymetry discrepancies between the model results and observations at high river discharge are indicative of limits at which the formulation begins to fail and where an alternative approach that captures two layer dynamics would be more appropriate

major changes in volcano behaviour after a sector collapse insights from stromboli italy in recent years increasing numbers of volcanoes are being recognized as having undergone large sector collapses how far such events can change the succeeding behaviour of the volcano is poorly known despite the importance for natural hazards and economic applications by analysing the last 100 kyr geological history of stromboli italy which has involved multiple collapses this paper illuminates the feedback effect between sector collapse and magma upwelling and emplacement the collapsed zone of stromboli is episodically unbuttressed draining magma preferentially with formation of eruptive centres in the collapse amphitheatre and dyking along the collapse shoulders after a collapse there were no further linear eruptions across the cone on opposing middle lower slopes but these occurred again after rebuilding of the cone the time averaged eruption rate increased immediately before the first collapse and remained higher during the succeeding period of frequent collapses

geomorphological research of large scale slope instability at machu picchu peru a multidisciplinary approach has been adopted to study the slope movements and landscape evolution at the archaeological site of machu picchu and its immediate surroundings the basic event in the paleogeomorphological evolution of the area was the large scale slope movement which destroyed the originally higher ridge between mt machupicchu and mt huaynapicchu within remnants of that primary deformation several younger generations of slope movements occurred the laboratory analyses of granitoids revealed highly strained zones on the slopes of mt machupicchu which strongly affect the largest slope deformation the borders of the largest slope deformation are structurally predisposed by the existence of fault zones the majority of various types of slope movements on the so called front slope e facing and back slope w facing are influenced by the alignment between topography and joints along with slope movements fluvial erosion and tectonic disturbance of the rocks have been affecting the evolution of the landscape a monitoring network for dilatometric and extensometric measurements was used to detect the present day activity of rock displacements within the archaeological site in addition to standard mapping of surface hydrogeological phenomena eleven express slug tests were conducted to verify the infiltration potential of precipitation the results of these surveys indicate that recent large scale slope movement as suggested by some previous studies is doubtful and the detected movements can be explained by individual movements of rock blocks or several other mechanisms including sinking of archaeological structures subsurface erosion and annual changes in the water content of the soils

three armed rifts or masked radial pattern of eruptive fissures the intriguing case of el hierro volcano canary islands abstract using new surface structural data as well as subsurface structural data obtained from seventeen water galleries we provide a comprehensive model of the volcano tectonic evolution of el hierro canary islands we have identified measured and analysed more than 1700 volcano structural elements including vents eruptive fissures dykes and faults the new data provide important information on the main structural patterns of the island and on its stress and strain fields all of which are crucial for reliable hazard assessments we conducted temporal and spatial analyses of the main structural elements focusing on their relative age and association with the three main cycles in the construction of the island the tinor edifice the el golfo las playas edifice and the rift volcanism a radial strike distribution which can be related to constructive episodes is observed in the on land structures a similar strike distribution is seen in the submarine eruptive fissures which are radial with respect to the centre of the island however the volcano structural elements identified onshore and reflecting the entire volcano tectonic evolution of the island also show a predominant ne sw strike which coincides with the main regional trend of the canary archipelago as a whole two other dominant directions of structural elements n s and wnw ese are evident from the establishment of the el golfo las playas edifice during the second constructive cycle we suggest that the radial striking structures reflect comparatively uniform stress fields during the constructive episodes mainly conditioned by the combination of overburden pressure gravitational spreading and magma induced stresses in each of the volcanic edifices by contrast in the shallower parts of the edifice the ne sw n s and wnw ese striking structures reflect local stress fields related to the formation of mega landslides and masking the general and regional radial patterns

using depth normalized coordinates to examine mass transport residual circulation in estuaries with large tidal amplitude relative to the mean depth abstractresidual subtidal circulation profiles in estuaries with a large tidal amplitude to depth ratio often are quite complex and do not resemble the traditional estuarine gravitational circulation profile this paper describes how a depth normalized coordinate system allows for a more physical interpretation of residual circulation profiles than does a fixed vertical coordinate system in an estuary with a tidal amplitude comparable to the mean depth depth normalized coordinates permit the approximation of lagrangian residuals performance of empirical orthogonal function eof analysis estimation of terms in the along stream momentum equations throughout depth and computation of a tidally averaged momentum balance the residual mass transport velocity has an enhanced two layer exchange flow relative to an eulerian mean because of the stokes wave transport velocity directed upstream at all depths while the observed coordinate profiles resemble gravitational circulation and pressure and fricti

residual circulation in shallow estuaries 2 weakly stratified and partially mixed narrow estuaries long wave theory is used herein to analyze circulation in weakly stratified and partially mixed estuaries unlike the highly stratified systems considered in part 1 the flows considered here have only a minimal tidal frequency internal wave component these estuaries may therefore be modeled as the sum of weakly interacting barotropic and baroclinic modes the dominant factors driving the residual flow are finite amplitude barotropic effects in weakly stratified estuaries and a combination of barotropic effects and steady horizontal density gradient forcing in partially mixed estuaries the dominant vertical exchange mechanism in the weakly stratified case is bottom boundary induced turbulence and that in partially mixed estuaries is believed to be random internal wave interactions a model of the columbia river estuary under weakly stratified conditions accurately predicts the observed residual velocity and salinity fields and the tidal amplitude at which a transition to a highly stratified state takes place the partially mixed state is unstable in the columbia river estuary because the tides and buoyancy input are both too strong

reconstructing temperature during the last glacial maximum from lyndon stream south island new zealand using beetle fossils and maximum likelihood envelopes this paper presents fossil beetle data from a last glacial maximum site at the lyndon stream in the canterbury foothills south island new zealand paleotemperatures are derived using the maximum likelihood envelope mle model developed for regions where modern distribution data are incomplete marra et al 2004 late quaternary climate change in the awatere valley south island new zealand using a sine model with a maximum likelihood envelope on fossil beetle data quaternary science reviews 23 1637 1650 the mle model results indicate that summer temperatures in the canterbury foothills in close proximity to the major rakaia glacier at ca 22 000 c 14 yr bp were between 0 5 degrees c warmer and 1 9 degrees c cooler than present day in february summer mean minimum winter temperatures ranged between 1 degrees c warmer and 2 2 degrees c cooler than the present day these apparently surprising results confirm and quantify existing climate reconstructions from plant macrofossils from this site soons j m burrows c j 1978 dates for otiran deposits including plant microfossils and macrofossils from rakaia valley new zealand journal of geology and geophysics 21 607 615 they are consistent with new evidence of relatively mild conditions at least during some periods within the last glacial maximum chron in new zealand c 2006 elsevier ltd all rights reserved

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

influence of structural framework on mountain slope deformation in the maiella anticline central apennines italy abstract relationships between tectonic framework and gravity driven phenomena have been investigated in an area of the central apennines italy characterised by high relief the north south half dome shaped maiella anticline lies in the easternmost part of the apennine fold and thrust belt its backlimb is bordered by the caramanico fault a normal fault with a maximum downthrown of about 3 5 km that separates the western slope of the maiella massif from the caramanico valley the southwestern maiella area is affected by deep seated gravitational slope deformation indicated by major double crest lines down hill and up hill facing scarps a pattern of crossing trenches bulging at the base of slopes and the presence of different types of landslide and talus slope deposits the onset and development of deep seated gravitational slope deformations and the location of quaternary massive rockslope failures have been strongly influenced by the structural framework and tectonic pattern of the anticline deep seated gravitational slope deformation at mt macellaro mt amaro ridge has developed along the maiella western reverse slope in correspondence with the anticline axial culmination it is bordered at the rear by a nnw sse oriented dextral strike slip fault zone and has an e w direction of rock mass deformation closer to the southern plunging area of the anticline gravity driven phenomena show instead a n s and nw se direction influenced by bedding attitude 3d topographic models illustrate the relationship between deep seated gravitational slope deformation and massive rockslope failures the campo di giove rock avalanche a huge quaternary failure event was the result of an instantaneous collapse on a mountaine slope affected by a long term gravity driven deformation

lateral spreading processes in mountain ranges insights from an analogue modelling experiment abstract the results of a study on gravitational induced lateral spreading phenomena are here reported the lateral spreading processes are widely represented in the italian apennines due to the widespread overlapping of stiff rock masses on more ductile ones the stress strain evolution of these processes was investigated by combining an analogical and a numerical modelling approach the analogue modelling reproduced the evolution of a carbonate ridge thrust over a clayey flysch with reference to the case study of mt roccatagliata mt sant angelo ridge the rock mass juxtaposition was reproduced in a laboratory experiment by overlapping a brittle concrete on a viscous ductile material these materials were selected with rheological properties physically scaled with respect to the natural rock mass prototypes the spreading phenomenon was modelled by opening horizontal panels in sequential stages and monitoring the resulting stresses within the ductile material during the experiment a stress strain modelling was also performed by an fdm numerical solution this modelling replied the laboratory experiment by testing the use of different rheological constitutive laws the resulting stresses and morphological evolutions are comparable with the analogical laboratory experiment only if a time dependent rheological behaviour is assumed for the ductile material the results show that lateral spreading processes can be properly investigated by combining analogue and numerical modelling techniques which take into account the viscous plastic behaviour of the used materials

monitoring the volcanic unrest of el hierro canary islands before the onset of the 2011 2012 submarine eruption 1 on 10 october 2011 a submarine volcanic eruption started 2 km south from el hierro island spain since july 2011 a dense multiparametric monitoring network was deployed all over the island by instituto geografico nacional ign by the time the eruption started almost 10000 earthquakes had been located and the deformation analyses showed a maximum deformation of more than 5 cm earthquake migration from the north to the south of the island and acceleration of seismicity are in good correlation with changes in the deformation pattern as well as with some anomalies in geochemical and geomagnetic parameters an earthquake of local magnitude 4 3 at 12 km depth 8 october 2011 and shallower seismicity a day after preceded the onset of the eruption this is the first time that a volcanic eruption is fully monitored in the canary islands data recorded during this unrest episode at el hierro will contribute to understand reawakening of volcanic activity in this region and others of similar characteristics

structural analysis of turtle mountain alberta using digital elevation model toward a progressive failure abstract in 1903 the eastern slope of turtle mountain alberta was affected by a 30 m m 3 rockslide named frank slide that resulted in more than 70 casualties assuming that the main discontinuity sets including bedding control part of the slope morphology the structural features of turtle mountain were investigated using a digital elevation model dem using new landscape analysis techniques we have identified three main joint and fault sets these results are in agreement with those sets identified through field observations landscape analysis techniques using a dem confirm and refine the most recent geology model of the frank slide the rockslide was initiated along bedding and a fault at the base of the slope and propagated up slope by a regressive process following a surface composed of pre existing discontinuities the dem analysis also permits the identification of important geological structures along the 1903 slide scar based on the so called sloping local base level slbl an estimation was made of the present unstable volumes in the main scar delimited by the cracks and around the south area of the scar south peak the slbl is a method permitting a geometric interpretation of the failure surface based on a dem finally we propose a failure mechanism permitting the progressive failure of the rock mass that considers gentle dipping wedges 30 the prisms or wedges defined by two discontinuity sets permit the creation of a failure surface by progressive failure such structures are more commonly observed in recent rockslides this method is efficient and is recommended as a preliminary analysis prior to field investigation

landslides and the evolution of el hierro in the canary islands seismic and sonar data have been used to evaluate the extent and characteristics of giant landslides on the flanks of el hierro in the canary islands as the youngest and most southwesterly of the canary islands el hierro has experienced rapid growth and destructive events in its 1 12 million year history at least four giant landslides el golfo el julan san andres and las playas have modified 450 km3 of el hierro during the last 200 300 thousand years with each landslide event removing around 3 of the total edifice volume the extent of landsliding indicates that it is the main process of decay we characterise flank morphology around el hierro and distinguish between rugged unfailed flank failed flank and steep gullied ridge flanks affected by landsliding have downslope long profiles with distinctive b coefficients and exponential forms the el golfo landslide is the most recent 15 ka best described and clearly defined landslide in the canary islands the el julan landslide sw flank has an estimated volume of 130 km3 an age of 200 ka and is characterised by gravitational slumping on the se flank two new landslide events are reported the younger landslide las playas occurred 145 176 ka has a narrow steep sided embayment and a corresponding blocky debris avalanche deposit the older landslide san andres is recognised on the basis of a highly chaotic seismic facies offshore and reduced upper flank gradients its lack of an upper flank embayment and offshore blocky debris avalanche lead us to interpret that the landslide involved gravitational slumping possibly a series of events which reduced upper flank gradients but did not catastrophically collapse to produce a debris avalanche

k ar ages and magnetic stratigraphy of a hotspot induced fast grown oceanic island el hierro canary islands abstract the combined use of accurate radiometric dating and magnetic stratigraphy can be applied to define the main stages of the building of oceanic volcanic islands this method has been successfully applied on the island of el hierro the westernmost island of the canaries archipelago for the emerged part of this island built in the last 1 2 ma magnetic stratigraphy and mapping show the presence of four consecutive subchrons k ar dating of eighteen samples in stratigraphic sequences using an unspiked technique produced ages consistent with the general volcanic stratigraphy the ages show that the magnetic polarity zones correlate to the upper part of the matuyama and to the brunhes chrons the jaramillo normal polarity subchron of the upper part of the matuyama reverse polarity chron is recorded in one of the lava sequences the lower limit of this event is constrained by two ages of 1 04 0 02 ma and one of 1 05 0 02 ma close to the value deduced from the astronomically tuned magnetic polarity time scale apts the volcanic history can be summarised by two consecutive main basaltic volcanic edifices the el tinor active during the upper part of the matuyama chron and the el golfo edifice constructed during the brunhes chron

a giant landslide on the southern flank of tahiti island french polynesia we present evidence for an ancient and voluminous subaerial landslide of the southern flank of tahiti society islands during a marine geophysical survey in 1996 submarine mass wasting deposits were mapped as far as 60 km from the southern shore of the island acoustic imagery reveals a surface of 2950 km of debris avalanche and hummocky terrain based on bathymetric data the volume of the debris is estimated to be 1150 km in comparison with hawaiian and other oceanic island landslides it can be classified as a giant rapid and cataclysmic event tahiti morphology and the distribution of volcanic ages over the island strongly suggest that the slope failure initiated near the top of the southern island flank between 650 and 850 ka the landslide scar was subsequently filled by eruptions the estimated volume of the subaerial removed material exhibits a large discrepancy with the volume of the submarine deposits that can be explained by recurrent slide events

morphology and kinematic of a very large deep seated structural rock slide located in the fusch valley eastern alps austria in this paper we present a structurally controlled deep seated gravitational slope deformation located in the fusch valley eastern alps austria which is potentially endangering infrastructure in the framework of a landslide risk analysis a danger characterisation of this slope is presented the characterisation is based on strong geomorphological geological and hydrological evidence on which both a kinematical and a stability model of that slope could be developed unlike the majority of case studies where type and position of basal slip surfaces remain unknown the present models seem capable of delivering characterisations on the classification of the potential slope instability its spatial extents and likely physical reasons for its pre and post failure behaviour with high consistency and likelihood

numerical investigation of split flows by gravity currents into two layered stratified water bodies the behavior of a two dimensional 2 d gravity current impinging upon a density step in a two layered stratified basin is analyzed using a high resolution reynolds averaged navier stokes model the gravity current splits at the density step and the portion of the buoyancy flux becoming an interflow is largely controlled by the vertical distribution of velocity and density within the gravity current and the magnitude of the density step between the two ambient layers this is in agreement with recent laboratory observations the strongest changes in the ambient density profiles occur as a result of the impingement of supercritical currents with strong density contrasts for which a large portion of the gravity current detaches from the bottom and becomes an interflow we characterize the current partition process in the simulated experiments using the densimetric froude number of the current fr across the density step upstream and downstream when underflows are formed more supercritical currents are observed downstream of the density step compared to upstream fru frd which indicates lower mixing between the current and ambient water after the impingement due to the significant stripping of interfacial material at the density step

slope instability induced by volcano tectonics as an additional source of hazard in active volcanic areas the case of ischia island italy ischia is an active volcanic island in the gulf of naples whose history has been dominated by a caldera forming eruption ca 55 ka and resurgence phenomena that have affected the caldera floor and generated a net uplift of about 900 m since 33 ka the results of new geomorphological stratigraphical and textural investigations of the products of gravitational movements triggered by volcano tectonic events have been combined with the information arising from a reinterpretation of historical chronicles on natural phenomena such as earthquakes ground deformation gravitational movements and volcanic eruptions the combined interpretation of all these data shows that gravitational movements coeval to volcanic activity and uplift events related to the long lasting resurgence have affected the highly fractured marginal portions of the most uplifted mt epomeo blocks such movements mostly occurring since 3 ka include debris avalanches large debris flows lahars smaller mass movements rock falls slumps debris and rock slides and small debris flows and deep seated gravitational slope deformation the occurrence of submarine deposits linked with subaerial deposits of the most voluminous mass movements clearly shows that the debris avalanches impacted on the sea the obtained results corroborate the hypothesis that the behaviour of the ischia volcano is based on an intimate interplay among magmatism resurgence dynamics fault generation seismicity slope oversteepening and instability and eruptions they also highlight that volcano tectonically triggered mass movements are a potentially hazardous phenomena that have to be taken into account in any attempt to assess volcanic and related hazards at ischia furthermore the largest mass movements could also flow into the sea generating tsunami waves that could impact on the island s coast as well as on the neighbouring and densely inhabited coast of the neapolitan area

observations of turbulence in a partially stratified estuary the authors present a field study of estuarine turbulence in which profiles of reynolds stresses were directly measured using an adcp throughout a 25 h tidal day the dataset that is discussed quantifies turbulent mixing for a water column in northern san francisco bay that experiences a sequence of states that includes a weak ebb and flood that are stratified followed by a strong and eventually unstratified ebb and flood these measurements show that energetic turbulence is confined to a bottom mixed layer by the overlying stratification examination of individual reynolds stress profiles along with profiles of richardson number and turbulent froude number shows that the water column can be divided into regions based on the relative importance of buoyancy effects using the measured turbulence production rate p the dissipation rate e is estimated the observed turbulence had values of e nn 2 20 all of the time and e nn 2 200 most of the time suggesting that the observed motions were buoyancy affected turbulence rather than internal waves however at times turbulent froude numbers in much of the upper water column were less than one indicating important stratification effects taken as a whole the data show that stratification affects the turbulent velocity variance q2 most severely that is observed reductions in u9w9 are largely associated with small values of q2 rather than with a dramatic reduction in the efficiency with which turbulent motions produce momentum fluxes finally the dataset is compared to predictions made using the popular mellor yamada level 2 5 closure these comparisons show that the model tends to underestimate the turbulent kinetic energy in regions of strong stratification where the turbulence is strongly inhomogeneous and to overestimate the turbulent kinetic energy in weakly stratified regions the length scale does not appear to compensate for these errors and as a result similar errors are seen in the eddy viscosity predictions it is hypothesized that the underestimation of q2 is due to an inaccurate parameterization of turbulence self transport from the near bed region to the overlying stratification

geomechanical parameters of intact rocks and rock masses from the canary islands implications on their flank stability abstract new data on the geomechanical properties of the highly cohesive volcanic rocks of the canary archipelago and their role in the flank stability on oceanic islands are provided in this work on the basis of the textural and petrological features a preliminary classification of rocks grouped into lithotypes was carried out this classification includes vesicular and non vesicular basalts trachybasalts trachytes phonolites welded and non welded ignimbrites strength and strain related features are summarized here for each distinctive lithotype taking into account the results of the uniaxial and triaxial compressive tests the geological strength index of rock masses and their textural structural features an estimate of the rock mass parameters and mohr coulomb fit has been carried out a final discussion on the impact of those geomechanical parameters as factors governing the stability of steep slopes in volcanic islands is then made here as a contribution in volcanic risk

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

modeling intrajunction dispersion at a well mixed tidal river junction abstractthe relative importance of small scale intrajunction flow features such as shear layers separation zones and secondary flows on dispersion in a well mixed tidal river junction is explored a fully nonlinear nonhydrostatic and unstructured three dimensional 3d model is used to resolve supertidal dispersion via scalar transport at a well mixed tidal river junction mass transport simulated in the junction is compared against predictions using a simple node channel model to quantify the effects of small scale 3d intrajunction flow features on mixing and dispersion the effects of three dimensionality are demonstrated by quantifying the difference between two dimensional 2d and 3d model results an intermediate 3d model that does not resolve the secondary circulation or the recirculating flow at the junction is also compared to the 3d model to quantify the relative sensitivity of mixing on intrajunction flow features resolution of complex flow features simulated by the full 3d model is not

stratification and turbulence in subtidal channels through intertidal mudflats 1 field observations in san francisco bay of subtidal channels that drain through intertidal mudflats indicate that substantial periodic stratification develops in very shallow flows with distinct asymmetries between flood and ebb conditions the greatest variability in salinity and stratification occurs during the wet winter months very strong longitudinal salinity gradients develop across the intertidal zone between salty subtidal water and fresher water draining into the marsh upstream tidal straining of the longitudinal gradient creates the periodic stratification stratifying through ebbs and destratifying through floods the stratification can be very strong in very shallow flows with n2 0 1 s 2 in about 0 5 m water depth analysis of the data with dimensionless numbers shows that at times the stratification is strong enough to suppress turbulence and mixing the asymmetry in stratification between ebbs and floods results in asymmetries in eddy viscosity and eddy diffusivity with lower values during the stratified ebbs because of the intertidal elevation of the system the strong longitudinal salinity gradient is regenerated each time the mudflats and marsh drain the system approaches a tidally periodic steady state where the flow dynamics are dominated by the sharp front of salty water that advects into the intertidal zone on the rising tide and exits the system by each lower low water the field data are supported by a numerical model with simple mudflat channel bathymetry both the field and numerical work indicate that the shallow low energy flows in mudflat channels transition between strongly stratified suppressed turbulence and relatively unstratified active turbulence each tidal cycle

modeling and understanding turbulent mixing in a macrotidal salt wedge estuary 1 a high resolution three dimensional numerical simulation is performed with the parallel unstructured grid suntans model to study the spatiotemporal dynamics of turbulent mixing in a shallow macrotidal salt wedge estuary that experiences periodic mixing and strong stratification unresolved vertical mixing is parameterized with the k kl closure scheme with the canuto a stability functions based on a careful comparison of multiple two equation closure schemes and stability functions via the generic length scale approach the predictions of velocity salinity richardson number and reynolds stress are in good agreement with field observations and the top and bottom salinity predictions achieve skill scores of 0 86 and 0 91 respectively the model shows that the salt wedge starts to strengthen upstream at the beginning of weak ebb and gradually expands downstream during the weak tide mixing is most active along a density interface during the weak ebb while it is most active in a bottom mixed layer during weak flood consistent with the findings inferred from the observations stratification decays during the strong ebb in a mixing event along the horizontal extent of the salt wedge while it is also being advected offshore local mixing is shown to account for roughly half of the decay rate of the stratification in this process numerical experiments are performed to investigate the response of stratification and mixing to changes in the magnitude of the buoyancy high sensitivity is shown under intermediate levels of stratification that occur in the real system which becomes considerably weaker under more extreme conditions

catastrophic collapse of the volcanic island of hierro 15 ka ago and the history of landslides in the canary islands landslides play an important role in the evolution of many volcanic islands producing huge fields of blocky volcanic debris on their submarine slopes sidescan sonar images presented in this paper provide evidence for a large debris avalanche el golfo on the northern flank of hierro island in the canary islands angular blocks as much as 1 2 km across and 200 m high cover the debris avalanche surface el golfo avalanche is related to both the canary debris flow and a volcaniclastic turbidite found in the madeira abyssal plain 600 km west of the canaries dating of the turbidite and the failure scarp onshore indicates that the failure probably occurred between 13 and 17 ka there appears to be a general correlation between volcaniclastic turbidites in the abyssal plain sequence and landslides in the canaries during the past 750 ka tentatively this correlation suggests that seven major landslides have affected the canaries in that time

how multiple foliations may control large gravitational phenomena a case study from the cismon valley eastern alps italy abstract the right slope of the high cismon valley trento province italy carved into the poly deformed phyllites of the south alpine basement shows evidence of differential quaternary slope evolution which highly depends on how the slope intersects the inherited structures in the study area the regional schistosity outlines a kilometer scale nnw sse trending fold with close flanks and an axial plane dipping to the ne the structure obliquely intersects the nne ssw trending slope so that the northern part of the slope follows the upper limb of the fold and the southern sector coincides with the lower limb and the hinge the secondary axial plane foliation is typically incipient at the fold flanks and much more pervasive and fan shaped near the hinge zone this foliation as well as the asymmetric polyharmonic secondary folds has significant consequences on rock mass mechanical properties and on mechanisms and timing of the gravitational phenomena developed along the slope in particular the joint compressive strength jcs and the geological strength index gsi obtained on stable outcrops outside the deforming area display a decrease from north to south this points to a progressive deterioration of the rock mass strength which directly reflects the influence of the pre existing fabric the results obtained by the analysis of lidar derived digital elevation model show evidence of two different gravitational movements located in the northern and southern sectors of the slope respectively the northern side is characterized by an ongoing deep seated gravitational slope deformation dsgsd likely triggered by post glacial unloading derived from the retreat of the ice tongue that filled the cismon valley during the last glacial maximum lgm conversely the southern part of the slope is the expression of a fully evolved pre lgm gravitational collapse this heterogeneous behavior of the slope is most likely controlled by the secondary foliation and asymmetric polyharmonic folds the former being of paramount importance for the release of the mobilized mass at the crown area and the latter easing or impeding the downslope movement although it is widely accepted that the regional foliation is the dominant controlling factor of dsgsds on poly deformed and highly foliated metamorphic basement our work suggests that the secondary foliation as well as parasitic folds may also have remarkable effects on slope evolution if favorably oriented and sufficiently pervasive

a simple model of mixing in stratified tidal flows we use a simple model of vertical mixing in a stratified tidal flow to study flows that might be observed in shallow estuaries in the model flow is driven by a specified surface pressure gradient due to barotropic tidal motions the model incorporates two means for accomplishing vertical mixing 1 shear instability and 2 bottom mixed layer deepening by turbulence produced at the estuary bottom and in the shear layer at the top of the mixed layer we discuss model results that show how the combined action of shear instability and tidal stirring accomplishes vertical mixing the interaction between the instabilities that develop because of the substantial tidal timescale velocity shear caused by stratification is the key feature of mixing shear instability weakens the stability of the mixed layer allowing stirring to efficiently entrain lighter fluid into the mixed layer the importance of shear is found to depend on the stability of the water column and on the relative importance of frictional forces

tide induced variation of the dynamics of a salt wedge estuary abstract the time variations of the salt wedge intrusion in the fraser estuary british columbia were monitored during a variety of tidal and run off conditions using instruments and sampling methods that provided high resolution of the velocity and water properties in space and time the salt wedge was found to vary considerably in position and vertical structure through the tidal cycle due to the interaction of the tidal flow with the density driven motion of the salt wedge during the flood the salt wedge progressed up the estuary as a gravity current while during the ebb the salinity structure was eroded by shear instability the difference in character of the flow between flood and ebb is attributed to the transition between a subcritical and supercritical internal froude number during flood tide the internal state is subcritical and the estuarine shear flow is maintained with a small amount of vertical mixing while in the supercritical ebb flow vertical shears become so large that the pycnoc

characterisation of a volcanic residual soil and its implications for large landslide phenomena application to tenerife canary islands large landslides are common processes during the evolution of volcanoes and individual events can exceed several cubic kilometres in volume volcanic slope failures are a significant risk for the neighbouring population due to their huge volumes and great runout distances around the canary archipelago a total of seventeen deposits of large landslides have been found and on tenerife seven large landslides have affected the subaerial and submarine morphology during the last 6 ma however the causes of such mass movements are still poorly understood this work analyses the events around the canary islands and focuses on the ones that occurred on tenerife in order to obtain new insights into the mechanisms of large volcanic landslides the study is divided into a first part that includes site investigations examining the general features favouring large scale failures at volcanoes the second part describes the laboratory tests used to analyse a residual soil that may be the potential slip surface of the slides on tenerife the site investigation revealed that regional tectonics and the climate have a significant influence on the spatial distribution of the landslides moreover morphological and geological features such as deep fluvial canyons a high coastal cliff and persistent dike intrusion may favour the initiation of slope failure a typical residual soil sample from the lateral scarp of the la orotava amphitheatre on tenerife was studied by carrying out standard laboratory tests the microstructure was analysed using environmental scanning electron microscopy and a particular bonding was found this bonding was also detected by the geotechnical tests consolidation tests and direct shear tests revealed that the mechanical behaviour of the residual soil changes greatly if the bonding of the soil is broken the bonded structure generally fails when the effective normal stress surpasses the yield strength of the bonding in the case of large volcanic landslides with thicknesses up to several hundred meters the high overburden easily exceeds this yield strength and generates a broken bonding therefore volcanic residual soils such as the one analysed in this study are perfect candidates for the potential failure surfaces of large volcanic landslides referring to the la orotava events we assume that residual soil layers and morphological geological and climatic features reduced the slope stability to critical conditions whereas a strong earthquake associated with a caldera collapse episode may have finally triggered the landslide the results obtained indicate that the residual soils play an important role in affecting the stability of volcano slopes and their destabilising influence significantly favours large scale sliding we suggest that the results obtained from this study can be applied to other locations since volcanic residual soils are common in volcanic areas

remotely sensed river surface features compared with modeling and in situ measurements 1 images of river surface features that reflect the bathymetry and flow in the river have been obtained using remote sensing at microwave visible and infrared frequencies the experiments were conducted at jetty island near the mouth of the snohomish river at everett washington where complex tidal flow occurs over a varied bathymetry which was measured as part of these experiments an x band 9 36 ghz doppler radar was operated from the river bank and produced images of normalized radar cross sections and radial surface velocities every 20 min over many tidal cycles the visible and infrared instruments were flown in an airplane all of these techniques showed surface evidence of frontal features flow over a sill and flow conditioned by a deep hole these features were modeled numerically and the model results correspond well to the remote observations in situ measurements made near the hole showed that changes in measured velocities correlate well with the occurrence of the features in the images in addition to tidal phase the occurrence of these features in the imagery depends on tidal range the surface roughness observed in the imagery appears to be generated by the bathymetry and flow themselves rather than by the modulation of wind waves

structure variability and salt flux in a strongly forced salt wedge estuary this researchwas funded by national science foundation grant oce 0452054 ralston also received partial support from the penzance endowed fund in support of assistant scientists and the john f and dorothy h magee fund in support of scientific staff at woods hole oceanographic institution