numerical modeling of the emplacement of socompa rock avalanche chile 1 the 7 5 ka socompa sector collapse emplaced 25 km3 of fragmented rock as a thin but widespread 500 km2 avalanche deposit followed by late stage sliding of 11 km3 as toreva blocks most of the avalanche mass was emplaced dry although saturation of a basal shear layer cannot be excluded modeling was carried out using the depth averaged granular flow equations in order to provide information on the flow behavior of this well preserved long run out avalanche results were constrained using structures preserved on the surface of the deposit as well as by deposit outline and run up a proxy for velocity models assuming constant dynamic friction fail to produce realistic results because the low basal friction angles 1 to 3 5 necessary to generate observed run out permit neither adequate deposition on slopes nor preservation of significant morphology on the deposit surface a reasonable fit is obtained however if the avalanche is assumed simply to experience a constant retarding stress of 50 100 kpa during flow this permits long run out as well as deposition on slopes and preservation of realistic depositional morphology in particular the model explains a prominent topographic escarpment on the deposit surface as the frozen front of a huge wave of debris reflected off surrounding hills the result that socompa avalanche experienced a small approximately constant retarding stress during emplacement is consistent with a previously published analysis of avalanche data

initiation movement and run out of the giant tsaoling landslide what can we learn from a simple rigid block model and a velocity displacement dependent friction law abstract tsaoling landslide is the largest and best documented landslide among several large landslides induced by the 1999 taiwan chi chi earthquake pliocene sedimentary rocks of about 125 mm 3 in volume slid along very flat bedding planes dipping by 14 with an average speed of 35 40 m s for about 1650 m before hitting the bank of the chinshui river during the landslide detailed analysis of dtms before and after the earthquake using a gis software leads to an accurate determination of the locations of the centroids of landslide mass revealing the horizontal and vertical displacements of the 2524 m and 524 m respectively those displacements and landslide mass give an apparent friction coefficient of 0 21 and the release of the potential energy of 1 6 10 15 j we conducted rotary shear high velocity friction experiments on fault gouge from bedding parallel faults under semi wet conditions and at 3 mpa normal stress corresponding to the overburden pressure of the landslide mass we also compiled reported data on the frictional properties on shale powders and fault gouge from the landslide site under both dry and wet conditions and proposed a velocity displacement dependent friction law that can describe most experimental data newmark analysis of landslide motion with six scenarios for different landslide materials and conditions assuming a simple rigid block sliding and using measured frictional parameters revealed that the landslide did not occur with dry frictional properties and that the landslide occurred at 38 39 s with accumulated displacements of 0 62 m 1 09 m and reached at the river bank at 82 87 s after the generation of chi chi earthquake at its epicenter those timings are consistent with high frequency signals at 32 40 s and at 76 s recorded at a nearby seismic station and with a survivor s witness that the landslide initiated 10 s after he felt strong ground motion possible s wave arrival at 25 2 s slip weakening is essential in initiating the landslide and low friction coefficient 0 08 0 1 allowed high speed of the landslide possible the landslide was caused by a few peaks of northeast oriented strong accelerations of the ground motion frictional work during the sliding of the landslide mass was estimated to be of about 23 of potential energy and the rest of the released energy is likely to have been consumed during the stopping phase of the landslide after hitting the river bank in complex processes such as fragmentation heat dissipation and spreading of the landslide deposits

a statistical description of the mean circulation and eddy variability in the northwestern atlantic using sofar floats abstract velocity data obtained from trajectories of sofar floats launched as part of several experiments carried out in the northwest atlantic during the last two decades are used to give a statistical description of the mean gulf stream and its recirculation the distribution of eddy variability in the region is also presented a mean gulf stream which bifurcates between 55 and 45 w to feed the north atlantic current and a southern recirculation can be clearly identified a weak interior sverdrup flow is also suggested the spatial distribution of eddy variability is consistent with previous descriptions showing a maximum near the gulf stream

interaction between landsliding materials and the underlying erodible bed in a loess flowslide abstract loess landslides exhibit strong interactions with the terrace sediments of the jing river on the south jingyang platform jingyang xi an china analysis of past landslide events revealed that the sand layer of this terrace was thrust up to the surface accompanied by other terrace sediments of carrying this led to the formation of a thrust nappe structure over a long distance we performed ring shear tests to examine the shear behavior of this sand layer with the finding that saturated sand was highly susceptible to liquefaction induced failure the groundwater level of the study area is high resulting in near saturation of the sand layer therefore topographic interferences contributed additional variables and increased interaction complexities simulations indicated that the liquefied sand layer was compressed and forced due to the absence of constraints the sand layer near the bottom of the slope was sheared out over a relatively short distance on the other hand particle interia and constraints of the stable layer resulted in the sand layer near the distal part of the deposits being sheared upward to the ground finally an initiation movement model of loess flowslides is proposed it describes static liquefaction of the loess layer of the slope resulted in occurrence of flowslides collisions between the deposits from the platform edge slope and terrace sediments resulted in the shear liquefaction of sands the landslide experienced four stages as they moved scraping collisions floating scrapes folded thrusts and nappe accumulation

the north atlantic current and surrounding waters at the crossroads the north atlantic current is a well defined western boundary current that flows north along the east side of the grand banks from 40 to 51 n where it turns sharply to the east and begins its journey across the ocean the current is unique in transporting warm tropical waters to much higher latitudes than any other western boundary current and thus plays a crucial role in ameliorating the climate of the european subcontinent the north atlantic current originates in the gulf stream when the latter curves north around the southeast newfoundland rise a major submarine ridge that stretches se from the grand banks a well defined front delineates the path of the current as long as it flows north as a western boundary current after the current turns east in the north it broadens into a widening band of eastward drift without a sharp or permanent front in the sense of the eastward flowing gulf stream after it separates from cape hatteras the north atlantic current transports more than 40 sv 1 sv 106 m s 1 in the south and about 20 sv by the time it flows east across the mid atlantic ridge the currents along the northward flowing front are quite swift with typical maximum average speeds in the upper 300 m near 1 m s 1 2 knots the current meanders almost as wildly as a snaking river but unlike steep meanders in the gulf stream these meanders appear to be stable and with one exception have not been observed to break off to form pools of warm and or cold waters as frequently occurs in the gulf stream the meanders appear to be induced by major topographic features along the path of the current namely the southeast newfoundland rise the newfoundland seamounts and flemish cap strong recirculations develop on the concave side of the meanders one of these the mann eddy at the first meander crest of the north atlantic current should be regarded as a permanent feature of the north atlantic circulation other meanders also contain recirculations that can persist for months under certain conditions these can merge together to form an extended sw flow recirculation just east of the north atlantic current

dynamics of the bingham canyon rock avalanches utah usa resolved from topographic seismic and infrasound data the 2013 bingham canyon mine rock avalanches represent one of the largest cumulative landslide events in recorded u s history and provide a unique opportunity to test remote analysis techniques for landslide characterization here we combine aerial photogrammetry surveying topographic reconstruction numerical runout modeling and analysis of broadband seismic and infrasound data to extract salient details of the dynamics and evolution of the multi phase landslide event our results reveal a cumulative intact rock source volume of 52 mm3 which mobilized in two main rock avalanche phases separated by 1 5 h we estimate the first rock avalanche had 1 5 2 times greater volume than the second each failure initiated by sliding along a gently dipping 21 highly persistent basal fault before transitioning to a rock avalanche and spilling into the inner pit the trajectory and duration of the two rock avalanches were reconstructed using runout modeling and independent force history inversion of intermediate period 10 50 s seismic data intermediate and shorter period 1 50 s seismic data were sensitive to intervals of mass redirection and constrained finer details of the individual slide dynamics back projecting short period 0 2 1 s seismic energy we located the two rock avalanches within 2 and 4 km of the mine further analysis of infrasound and seismic data revealed that the cumulative event included an additional 11 smaller landslides volumes 104 105 m3 and that a trailing signal following the second rock avalanche may result from an air coupled rayleigh wave our results demonstrate new and refined techniques for detailed remote characterization of the dynamics and evolution of large landslides

isopycnal lagrangian statistics from the north atlantic current rafos float observations one hundred isopycnal floats were tracked on the 27 2 and 27 5 surfaces in the newfoundland basin nfb from july 1993 to july 1995 to study the current structure and exchanges of waters between the subtropical and subpolar gyres the float mapped mean flow consists of weak flows in the nfb and a strong boundary current the north atlantic current nac which separates from the boundary at the northwest corner becoming a diffusive zonal drift the nac meanders are linked to topography and have similar patterns on the two isopycnals despite the fact that the upper layer velocities are twice as fast as the lower layer ones perturbation velocity from the mean is used to compute isopycnal turbulent dispersion and diffusivity this large data set allows us to resolve a narrow mean nac and results in a gaussian turbulence the turbulence approximately follows the classic taylor dispersion theory integral timescales and length scales and turbulent isopycnal diffusivity are of 1 5 2 5 days 20 30 km and 1 7 103 m2 s 1 respectively the timescale increases with depth and decreases with latitude the length scale decreases with depth and longitude and the diffusivity decreases with depth and from nac to nfb compared to previous results from surface drifters and isobaric floats our isopycnal statistics are more isotropic and agree better with the taylor dispersion theory because 1 the mean velocity has a better resolution and 2 the isopycnal floats are better lagrangian followers the diffusivity scales better with the rms velocity and length scale than with the velocity variance and timescale

the climatology of the north atlantic abstract data from approximately 144 000 hydrographic stations in the north atlantic have been retrieved from the national oceanic data centre and analysed to produce maps of mean pressure temperature salinity and oxygen on selected potential density surfaces for the domain bounded by 0 85 w and 0 65 n the data span the period from 1904 to 1990 with the majority of the data from the last four decades the data set for this region is 60 larger than that used in the production of levitus climatological world atlas this increase in stations coupled with smoothing scales specific to the north atlantic rather than the global ocean considerably improves the resolution of the basin s features the mean property fields and their associated standard deviations are resolved on a one degree grid with little smoothing contrasting with the levitus atlas where properties although presented on a one degree grid have been smoothed on the order of 1000km another important feature of this database is the process by which irregularly spaced data are averaged onto a regular grid in a significant departure from the levitus analysis which averaged on depth surfaces these data were averaged on potential density surfaces thus eliminating an artificial mixing of water mass properties the database is used to describe the baroclinicity of well known features such as the gulf stream the north atlantic current and the deep western boundary current and to elucidate the recirculations associated with these currents it additionally resolves several new features in the intermediate and deep north atlantic these features include the signature of a large scale deep recirculation that extends southwestward from the eastward extension of the north atlantic current to the separation point of the gulf stream near cape hatteras this recirculation which spans approximately 2000m of the water column encompasses more local recirculations and potentially mixes subpolar and subtropical waters furthermore in the upper thermocline this database reveals a coherent azores current that stretches from the gulf stream system south of the tail of the grand banks to madeira this flow is marked by divergences to the south and convergences from the north such that its downstream transport is not much changed

experiments on the flow behaviour of granular materials at high velocity in an open channel a series of laboratory flume experiments has been conducted to investigate the flow behaviour of dry sand at high velocities the first incentive for this experimental programme was an attempt to explain the high mobility of apparently dry masses of rapidly moving broken rock during rock avalanches sturzstroms test velocities of over 5 m s and most other parameters of the tests were found to be dimensionally similar to those for a typical rock avalanche yet the conclusion was negative even the most rapid of the experiments indicated flow behaviour which is in conformity with the constant volume uniform coulomb friction relationship as applicable to slow shearing this conclusion was confirmed independently both by direct measurements of base friction and mean density of the flows and by detailed observations of flow uniformity acceleration and velocity profiles the surprising mobility of st umlrzstroms therefore requires a different explanation une serie de tests a canaux a ete entreprise dans le

dynamics and physical parameters of the lastarria debris avalanche central andes abstract volcanic debris avalanches are extremely destructive phenomena with the potential to travel many kilometers from their source region either as rockslides or as mass flows given that they may even be triggered at inactive volcanoes their hazard is often underestimated understanding the dynamics of such mass movements is essential for evaluating and mitigating hazards a number of case studies have been carried out around the world but there is still a need for further studies of flow dominated avalanches which remain poorly constrained these studies would have high educational value providing striking examples to teach decision makers and at risk populations about the hazard in this study we investigate the 7500 cal year b p lastarria debris avalanche it is a 7 km long deposit with exceptional preservation of both the flow structures and the collapse scar detailed fieldwork morphometric mapping of over 600 surface features and numerical modelling was carried out to constrain the avalanche s trigger and flow parameters numerical models and field scaling relationships are in good agreement suggesting maximum velocities of 210 to 270 km h 1 negligible basal friction low cohesion 50 kpa and an intermediate friction coefficient structures are dominantly oriented parallel to transport direction suggesting minimal influence from a smooth paleotopography lastarria provides an example of a shallow flank failure initiated along stratigraphic planes that allowed low strength pyroclastic strata to disaggregate rapidly and then quickly accelerate to flow as a granular material at high velocity beyond the base of the volcano overall lastarria provides excellent constraints on granular avalanche initiation and flow which are valuable for hazard assessments and for the study of less well preserved flow deposits elsewhere the question of which precursory signs may warn of such a flank failure remains open and is important to address in future studies

evolution of a mediterranean salt lens scalar properties abstract the evolution of a mediterranean salt lens meddy over a two year period is examined several nondimensional numbers can be used to describe the overall decay in the structure of the moddy two rossby numbers one using the central relative vorticity and another using the radius and velocity of the azimuthal velocity maximum did not change over the two year period however the burger number n2h2 f2l2 increased as the meddy decayed another burger number the ratio of total kinetic energy to total available potential energy decreased from 1 1 to 0 6 over a one year period the rates at which the meddy lost salt and heat are consistent with estimates of horizontal fluxes by intrusions a horizontal diffusivity of o 5 m2 s 1 is needed if this flux by intrusions is parameterized by an eddy coefficient simple models of the evolution of an isolated eddy by horizontal and vertical mixing of mass and momentum are examined these simple attempts to explain the evolution of the meddy suggest more c

two years in the life of a mediterranean salt lens abstract a lens of mediterranean water meddy was tracked in the eastern north atlantic for two years with sofar floats the meddy was first found between the canary islands and the azores in october 1984 it center moved in an irregular pattern at speeds of a few cm s 1 and translated 1100 km to the south in two years this meddy was surveyed four times by ctd and velocity profilers and once with the microstructure profiler epsonde when observed during the first two surveys the meddy had a core that was stably and smoothly stratified in both salinity and temperature nearly uniform in the horizontal and was saltier than the surrounding ocean by 0 65 psu the meddy was eroded from its edges top and bottom and lost salt and hat with an e folding time of about one year the salinity at the center remained at its original value during the first year and decreased during the second year evidence was seen for mixing by lateral intrusions double diffusion and turbulence the intrusions are thought to

rheological changes induced by clast fragmentation in debris flows on the basis of rotating drum analogue experiments we describe a fragmentation process acting within debris flows during transport and its influence on rheologic behavior our hypothesis is based on a detailed textural analysis including granulometry clast morphology and rheologic properties of the fluid matrix results of the experiments point out that breakage of certain granulometric classes produces fine particles like fine sand and silt the population growth of fine clasts with time leads to an increase in yield strength and viscosity that progressively modifies the rheologic behavior from a textural point of view this is reflected in a bimodal granulometric distribution up to now this characteristic has been explained as the effect of bulking and or sedimentation processes during transport our experimental results show that the type of fragmentation depends on particle size and is the consequence of strong clast clast interaction and clast fluid interactions coarse particles develop small fractures which cause the loss of sharp edges and asperities medium sized particles develop through going fractures that cause them to break apart the latter process explains why intermediate granulometric classes progressively diminish with time in debris flows analogue experiments enable us to study the efficacy of clast fragmentation in modifying the textural character and flow behavior of debris flows without the influence of external factors such as erosion and sedimentation the obtained results constitute the base of a new approach for modeling debris flow dynamics

the subthermocline lens d1 part i description of water properties and velocity profiles abstract one remarkable result of the local dynamics experiment in polymode is the discovery of a large number of small energetic eddies using ctd data sofar float tracks and profiles of absolute velocity we describe one of these features the subthermocline eddy d1 the feature has an advective time scale of 1 day and its primary mode of movement is advection by the ambient flow field the eddy is resolved into a coordinate system moving with the velocity of the ambient flow which ranges from 11 16 cm s 1 its phase speed is less than 2 cm s 1 the eddy is a lens centered at 1500 db velocity profiles show the lens has no detectable signal in and above the main thermocline or below about 3000 db its subsurface velocity maximum is 28 6 cm s 1 at 1500 db 15 km from the center the radial variation of the azimuthal velocity is gaussian inside the velocity maximum but decays as e br beyond there is little evidence of the eddy beyond a radius of 25 km inside the velocity maximum the eddy is characte

observational evidence of salt lens formation in the iberian basin the quasi synoptic picture of the mesoscale eddy field off portugal is presented on the basis of recent hydrographic measurements the dynamic topography and the salinity field at middepths 900 1300 m is shown to be dominated by several isolated meddy structures superimposed on a general east west gradient deduced from the actual dynamical situation there is evidence for meddy generation in this region numerical process studies demonstrate the possibility of vortex formation by baroclinic instability of a northward middepth jet of mediterranean water and by fragmentation of larger scale mediterranean water blobs

influence of runout path material on emplacement of the round top rock avalanche new zealand factors influencing the distance a disintegrating rock mass travels as it spreads across the landscape after detaching from a slope include the volume and mechanical properties of the material local topography and the materials encountered in the runout path here we investigate the influence of runout path material on the mobility and final morphology of the round top rock avalanche deposit new zealand this rock avalanche of mylonitic schist ran out over a planar surface of saturated fluvial gravel longitudinal ridges aligned radial to source grade into smaller aligned hummocks and digitate lobes in the distal reach soils and river gravels in the runout path are found bulldozed at elongate ridge termini where they formed local obstacles halting avalanche motion at these locations thus aiding development of prominent elongate ridges on the deposit further travel over the disrupted substrate led to avalanche substrate mixing at the base of the debris mass field observations combined with subsurface geophysical investigations and laboratory analogue models illustrate the processes of substrate deformation features at the round top rock avalanche copyright 2009 john wiley sons ltd

volcanic avalanche fault zone with pseudotachylite and gouge in french massif central abstract structures and textures with sedimentological variations at different scales of the lithofacies assemblage help us to constrain the basal kinematic transition from non depositional to depositional conditions during volcanic avalanche emplacement in the well exposed impact sheared contact along volcanic avalanche fault zone in the french massif central we observe how the granular textures of the pseudotachylite and fault gouge have recorded the propagation of shock wave with granular oscillatory stress sequential events of basal aggradation along avalanche fault zone have been established related to fractal d values temperature pressure regime and oscillatory stress during slow wave velocity a typical lithofacies assemblage with a reverse grading shows the pseudotachylite and fault gouge a cataclastic gradient is characterised by the fractal d values from 2 7 in jigsaw breccias with pseudotachylite partial melt to 2 6 in the polymodal gouge shock brecciation and comminution produce cataclastic shear bands in the pseudotachylite and quartz microstructures along the basal contact of the volcanic debris avalanche deposit gouge microstructures show granular segregation cataclasis with antithetic rotational riedel shear and an arching effect between the riedel shear bands x ray microtomography provided 3d microfabrics along the clastic vein in the sandy gouge from the available statistical dataset a few equations have been developed implicating the same cataclastic origin with a co genetic evolution of lithofacies an impact wave during primary shear propagation may contribute to produce hydroclastic matrix pseudotachylite partial melt and proximal gouge thixotropy with v 50m s and a t

granular flow experiments on the interaction with stationary runout path materials and comparison to rock avalanche events the central focus of this work is to study the processes acting well below the surface of a moving rock or debris avalanche during travel over stationary substrate material small scale physical models at a linear scale of 1 104 used coal as avalanche analogue material and different granular material simulating sedimentary substrates varying in frictional resistance thickness and relative basal boundary roughness as well as inerodible non deformable runout path conditions substrate materials with the least frictional resistance showed the greatest response to granular flow overriding becoming entirely mobilized beneath and ahead of the moving mass and producing the longest runout observed with a unique deposit profile shape with a smooth substrate basal contact failure occurred along this plane and avalanche and substrate became coupled during runout with a rough base however temporary force chains of grain contacts in the substrate prevailed longer imparted their resistance to motion shear into the granular flow and the flow rear section consequently halted earlier than when moving over substrates with a weak base reducing substrate thickness diminished the effect of basal contact roughness on granular flow runout and deposit length inerodible non deformable substrate conditions caused changes in granular flow behaviour from essentially en masse sliding on low friction surfaces to increasing granular agitation over rougher paths copyright 2012 john wiley sons ltd

on variations in static stability along lagrangian trajectories abstract by causing an isopycnal float to rise and sink to neighboring density surfaces one can measure layer thickness along a float trajectory and thus variations in static stability we report here on layer thickness measurements that were obtained from the nearly 100 isopycnal floats that were deployed in the 1993 1995 lagrangian study of the north atlantic current layer thickness variations depend significantly upon location and process in the high velocity core of the meandering north atlantic current layer thickness changes correlate with curvature of the flow stretching in troughs compression in crests but this correlation fails in unsteady flows or outside the high velocity center of the current floats also register significant changes in stratification when they cross between the warm waters in the newfoundland basin and the cold waters from the labrador sea as floats enter and exit what appear to be coherent eddy structures significant but not necessarily predictable changes in layer thickness can occur while the technology to measure layer thickness variations performed as well and reliably as we had hoped for the presence of ubiquitous small scale features in the density field together with the fact that the thickness measurements sampled only o 100 m of the total water column limited our ability to isolate and identify the cause of thickness variations to only relatively energetic features

grain size distribution and sedimentology in volcanic mass wasting flows implications for propagation and mobility the sedimentological characteristics of mass wasting flow deposits are important for assessing the differences between phenomena and their propagation and emplacement mechanisms in the present study nine volcanic debris avalanche deposits and eight lahar deposits are considered from the literature their sedimentology is expressed in the descriptive statistics median grain size sand gravel and finer particle fractions skewness and sorting analysis of the data confirms that lahars and debris avalanches diverge in their grain size distribution and in their evolution during propagation water saturation in lahars is the main factor enabling debulking a mechanism that is not recorded in the data derived from debris avalanches deposits on the contrary evidence of comminution of particles due to particle particle interactions is observed in debris avalanches and not in lahars these findings support previous studies suggesting that although water content in debris avalanches plays a role in propagation the effects of inertial collision of solid fragments are more important than fluid effects confirming that particle particle interactions are the main factor influencing the mobility of non saturated mass wasting flows

runout of the socompa volcanic debris avalanche chile a mechanical explanation for low basal shear resistance we propose a mechanical explanation for the low basal shear resistance about 50 kpa previously used to simulate successfully the complex well documented deposit morphology and lithological distribution produced by emplacement of the 25 km3 socompa volcanic debris avalanche deposit chile stratigraphic evidence for intense basal comminution indicates the occurrence of dynamic rock fragmentation in the basal region of this large granular mass flow and we show that such fragmentation generates a basal shear stress retarding motion of the avalanche that is a function of the flow thickness and intact rock strength the topography of the socompa deposit is realistically simulated using this fragmentation derived resistance function basal fragmentation is also compatible with the evidence from the deposit that reflection of the avalanche from topography caused a secondary wave that interacted with the primary flow

shear localisation strain partitioning and frictional melting in a debris avalanche generated by volcanic flank collapse abstract the arequipa volcanic landslide deposit to the east of arequipa peru originated from the pichu pichu volcanic complex covering an area 100 km2 the debris avalanche deposit exhibits internal flow structures and basal pseudotachylytes we present field microstructural and chemical observations from slip surfaces below and within the deposit which show varying degrees of strain localisation at one locality the basal shear zone is localised to a 1 2 cm thick extremely sheared layer of mixed ultracataclasite and pseudotachylyte containing fragments of earlier frictional melts rheological modelling indicates brittle fragmentation of the melt may have occurred due to high strain rates at velocities of 31 m s 1 and that frictional melting is unlikely to provide a mechanism for basal lubrication elsewhere we observe a

current broadening as a mechanism for anticyclogenesis at the northwest corner of the north atlantic current 1 the warm north atlantic current flowing north just east of the grand banks makes an abrupt turn to the east near 51 n as the waters flow through this region known as the northwest corner the current broadens and weakens effectively splitting into two zonal yet variable flows forming what is generally known as the subpolar front the northwest corner also has the curious property that it expands and expels anticyclonic vortices on a quasi regular basis approximately every 2 1 2 months using an energy budget approach we show that this anticyclogenesis can be accounted for in terms of a kinetic energy convergence due to the broadening of the flow as it passes through the region the principal export route for the newly formed eddies appears to be density driven subduction i e sinking driven by severe heat loss due to the exposed position of these warm waters in the southern labrador sea

tracking three meddies with sofar floats abstract three meddies were tracked for up to two years in the canary basin using neutrally buoyant sofar floats these meddies have cores of warm salty mediterranean water and are approximately 100 km in diameter 800 m thick and are centered at a depth of 1100 m meddy 1 was tracked for two years 1984 86 with five floats as it drifted 1090 km southward with a mean velocity of 1 8 cm s 1 four shipboard surveys made during these two years revealed the nearly total decay of meddy 1 by gradual mixing processes meddy 2 drifted 530 km southwestward over 8 5 months with a mean velocity of 2 3 cm s 1 until it collided with hyeres seamount near 31 n 29 w the floats trapped in this meddy then stopped looping abruptly implying a major disruption of this meddy meddy 3 drifted 500 km southwestward for a year and a half with a mean translation velocity of 1 1 cm s 1 a comparison of the velocity of meddies to the velocity of nearby floats at 1100 m depth outside of the meddies shows clearly that all three m

thickness of the seismic slip zone this article reviews geologic and other evidence constraining the thickness of the principal slip zone psz that accommodates the bulk of coseismic shear displacement during an individual rupture event surface deformation from rupturing may occupy swaths tens of meters or more in width but trenches across active faults generally reveal that incremental slip is accommodated by a psz that is tens of centimeters or less in thickness geomorphic evidence coupled with the observations from trenching suggest a psz may stay well localized for distances of several kilometers through many rupture episodes mine exposures and exhumed fault zones demonstrate that pszs separating different lithologies within the fault core although contained within damage zones of variably fractured rock ranging up to hundreds of meters in thickness often comprise just a few centimeters of gouge ultracataclasite that have accommodated large finite displacements 1 km microstructural studies demonstrate incremental slip localized still further down to 1 10 mm as do other fault rock assemblages slickensides and slickenfibers fault veins of pseudotachylyte friction melt intravein septa in hydrothermal fault infills the accumulated evidence indicates that localization of coseismic shearing to less than 10 cm on planar faults is widespread throughout the crustal seismogenic zone with extreme localization to less than 1 cm not uncommon however some distributed coseismic shear may also develop especially at rupture irregularities coseismic reduction of shear resistance from friction melting t 1000 c or from transient thermal pressurization of aqueous fluids t 100 c requires slip during moderate to large earthquakes u 1 m to be restricted to narrow zones respectively a few centimeters or tens of centimeters in thickness given the evidence for slip localization the apparent scarcity of pseudotachylyte suggests either that seismic friction melting is a rare phenomenon or that pseudotachylyte is only rarely preserved in recognizable form within mature hydrated fault zones

mechanical origin of power law scaling in fault zone rock 1 a nearest neighbor fragmentation model previously developed to explain observations of power law particle distributions in 3d with mass dimension d 3 2 6 d 2 2 6 in 2d section in low strain fault gouge and breccia is extended to the case of large strains to explain recent observations of d 3 3 0 d 2 2 0 in 2d section in the highly strained cores of many exhumed fault zones at low strains the elimination of same sized nearest neighbors has been shown to produce a power law distribution which is characterized by a mass dimension near d 3 2 6 with increasing shear strain these isolated same size neighbors can collide in which case one of them fractures the probability of two same size neighbors colliding and fragmenting in a simple shear flow is a function of the size and density of the two particles only for a power law distribution with d 3 3 0 is this collision probability independent of the size of the particles citation sammis

observations of an intense anticyclonic warm eddy in the newfoundland basin an intense anticyclonic warm eddy was sampled in february 1997 in the newfoundland basin its presence detected during a hydrographic survey was further corroborated through ers topex sea surface height anomaly and satellite tracked drifters this 120 km wide eddy was very homogeneous in temperature and salinity down to 800 m and its transport 15 1800 dbar reached 27 sv its location 49 n 40 w in the warm and saline waters of the northwest corner the northernmost position reached by the north atlantic current is clearly exceptional although intense anticyclonic eddies have previously been observed with satellite tracked buoys and rafos floats this is the first eddy to our knowledge ever documented at such a high latitude in the north atlantic current system its formation is discussed in term of thermohaline processes

the subpolar mode water of the north atlantic ocean abstract the warm waters of the subtropical and subpolar basins of the north atlantic have tight regional temperature salinity relationships and are conventionally called the regional central waters a volumetric census of the temperature salinity characteristics of the north atlantic by wright and worthington 1970 shows that waters characterized by certain segments of the t s relationships have large volumes compared to those of other segments volumetric mode waters such mode waters appear as layers with increased vertical separation between isopycnals pycnostads the present study reports on the existence of pycnostads in the central and eastern north atlantic these subpolar mode waters are formed by deep winter convection in the subpolar north atlantic and participate in the upper water circulation of the northern north atlantic the seasonal outcropping of the pycnostads occurs within and adjacent to the north atlantic current the irminger current the east and west greenland currents and

rock avalanche deposits store quantitative evidence on internal shear during runout we investigated the quantitative effect of internal shear on grain breakage during rock avalanche runout by means of 38 ring shear experiments on identical sand samples at different normal stresses shear strains and shear strain rates we compared sample grain size characteristics before and after shearing we found that grain size decreased with increase in normal stress and shear strain reduction in grain size was inferred to occur through grain breakage associated with grain interactions in strong force chains during strain the results were consistent with observations of both inverse grading structure in deep rock avalanche exposures and fining and grading of particles with increasing rock avalanche travel distance our study suggested that with appropriate calibration variations in grain size distributions within a rock avalanche deposit would provide quantitative information on the distribution of internal shear during its runout

semi brittle deformation of granitoid gouges in shear experiments at elevated pressures and temperatures abstract the physical and chemical processes acting in the brittle to plastic transition are of great interest for a better understanding of fault rheology we performed a series of experiments on granitoid gouge material under high confining pressures pc 500 1500 mpa temperatures t 300 c and 500 c and fast shear strain rates 1 8 10 4 s 1 where the material deforms by semi brittle flow samples deformed at 500 c are systematically weaker than samples deformed at 300 c over the whole examined confining pressure range indicating a non frictional component of the deformation all samples develop an s c fabrics and deformation localizes in slip zones containing amorphous feldspar material with an intermediate composition na ca and k rich further we observe changes in composition of feldspars enrichment in the albite component in the highly fragmented but crystalline regions with increasing finite shear strain our results indicate that mass transfer processes keep pace with frictional deformation even at high strain rates and together with viscous flow of the amorphous material are responsible for the observed strength difference

fragmentation in the val pola rock avalanche italian alps 1 grain size data from the deposit of the 1987 val pola rock avalanche central italian alps are compared with data concerning rock avalanching rock fragmentation and comminution the weibull distribution fits a small part of the entire particle size distribution of debris samples with a mean value of the curve shape factor of 0 54 0 28 this is typical of multiple comminution or fragmentation with much shearing a fractal distribution fits over a greater size range computed fractal dimensions range between 1 3 and 3 2 within the deposit with average values of about 2 6 2 7 these values cover the range between the theoretical values of the plane of weakness model 1 97 and the pillar of strength model 2 84 and are close to the theoretical value for the constrained comminution model 2 58 these suggest that both texturally mature and immature deposits are present and that more than a single comminution process acted during the rock avalanche motion variation of the grain size distribution within the deposit and grain size segregation show as trends in the fractal dimension and arise from variation in the fragmentation process a variety of different physical and empirical laws suggest that 1 30 of the energy expended in the rock avalanche was consumed in fragmentation

heavy rainfall triggered loess mudstone landslide and subsequent debris flow in tianshui china abstract continuous and heavy precipitation triggered a large loess landslide at the southern dagou village of mapaoquan town tianshui city gansu province of china on july 21 2013 the landslide debris rapidly turned into a debris flow that was deposited in the ravine mouth with the volume of 1 9 105 m3 detailed field mapping three dimensional laser scanning aerial photograph interpretation and laboratory tests were carried out to study the formation and moving characteristics of the landslide and subsequent debris flow the results showed that 1 the peak flow velocity and peak discharge of the debris flow were estimated to be approximately 7 2 m s and 730 m3 s respectively the velocity had a tendency to first increase and then decrease from the head to entrance in the dagou gully 2 the analysis of rainfall conditions showed that the effective antecedent rainfall within 7 days and hourly rainfall intensity which triggered the slide debris flows was 239 mm and 20 mm h respectively compared with the critical rainfall in this area the effective antecedent rainfall was found to be more significant in triggering this event 3 the mean and effective particle sizes were approximately 0 73 1 3 mm and 0 036 0 087 mm respectively and had the same distribution along the gully as the velocity which confirmed the process of the variation in the flow velocity 4 the scale amplification was very obvious in the formation and moving process of the slide debris flows

diagrammatize movement disintegration patterns of bedding rockslide disintegration in a bedding rockslide often results in damage to structures and lands on the slide mass three disintegration patterns have been proposed through the analysis of bedding rockslide causes in the three gorges area of china using a tree diagram seven affecting factors have been identified and classified by literature analysis and field surveying of 21 bedding rockslides both rough set and synthetic index methods have been employed to analyze the susceptibility of the seven factors and to determine disintegration patterns three main disintegration patterns are indicated for bedding rockslides whole translation and minor disintegration of the slide mass type 1 rapid translation and partial disintegration of the slide mass type 2 and rapid translation and complete disintegration of the slide mass type 3 the slip surface shape a2 the ratio of mass thickness to acceleration distance a4 the profile terrain a5 and the triggering factor a7 are susceptive factors affecting disintegration a matrix graph depicts the criterion that either of the two sets of a2 a5 a7 or a2 a4 a7 can determine the disintegration pattern of a bedding rockslide thereby guiding land use decisions on a bedding rockslide

meddy trajectories in the canary basin measured during the semaphore experiment 1993 1995 as part of the structures des echanges mer atmosphere proprietes des heterogeneites oceaniques recherche experimentale semaphore experiment four mediterranean water eddies meddies were identified in the canary basin and tracked with freely drifting rafos floats one large and energetic meddy discovered 1700 km west of cape saint vincent portugal set a distance and speed record as it translated another 1700 km southwestward at 3 9 cm s during 1 5 years this meddy traveled 57 of the distance from cape saint vincent toward the spot mcdowell and rossby 1978 found a possible meddy north of the dominican republic two meddies were observed to interact with the azores current as they passed underneath or through it three meddies collided with tall seamounts which seemed to disrupt the normal swirl velocity perhaps fatally in two cases one meddy appeared to bifurcate when it collided with seamounts

insights into the kinematics and dynamics of the luanshibao rock avalanche tibetan plateau china based on its complex surface landforms abstract complex topographic features on the surfaces of rock avalanche deposits have been regarded as important indicators for understanding avalanche kinematics and dynamics based on a combination of remote sensing data and in situ observations of surface landforms including toreva blocks transverse and longitudinal ridges ridges separated by conjugate troughs and hummocks a giant holocene rock avalanche on the tibetan plateau is recognized this work aims to understand the kinematics of this event in planview the tongue shaped rock avalanche exhibits a clear sequential distribution of various landforms the translation zone ii is characterised by toreva blocks originating from extension in subzone iii 1 of the accumulation zone iii compression related transverse ridges are well developed longitudinal ridges resulting from lateral velocity differences due to radial spreading are present in the front part of subzone iii 1 farther down ridges separated by conjugate troughs generated by a combination of compression and radial spreading are common in subzone iii 2 subzone iii 3 is characterised by abundant scattered hummocks with circular to oval shapes based on the distributions of these landforms this rock avalanche is proposed to have mainly experienced a motion featuring laminar flow with radial spreading in its distal and marginal parts during transport three distinct processes appear to have occurred in the avalanche mass from the proximal to the distal zones extension dominated sliding in zone ii compression dominated sliding in subzones iii 1 and iii 2 and rapid radial spreading in subzone iii 3

geomorphology lithofacies and block characteristics to determine the origin and mobility of a debris avalanche deposit at apacheta aguilucho volcanic complex aavc northern chile abstract understanding the evolution of a volcanic edifice is important in establishing its associated geological hazards apacheta and aguilucho volcanoes northern chile formed a volcanic complex with known fumaroles and geothermal potential among the products resulting from the evolution of the apacheta aguilucho volcanic complex aavc a new volcanoclastic deposit has been recognized towards the eastern flank of the volcanic complex this deposit is constituted by fragments of andesitic to dacitic lava and hydrothermally altered lava blocks these fragments which reach up to 5 m in diameter form geomorphological structures such as hummocks levees and ridges using these geomorphological characteristics the distribution of the main lithological facies or lithofacies and fragment features jigsaw cracks and impact marks we proposed that this deposit was generated by a debris avalanche this debris avalanche was triggered by partial collapse of an ancestral volcanic edifice occurred between 100 and 700 ka the collapse of the aavc ancestral edifice was influenced by hydrothermal alteration and the extensional tectonic setting that characterize the cerro pabellon dome area the mobility of the avalanche and the genesis of the main geomorphological features associated with the deposit are related to fragmentation of material during avalanche genesis and movement

direct observations of formation and propagation of subpolar eddies into the subtropical north atlantic abstract subsurface float and moored observations are presented to show for the first time the formation and propagation of anticyclonic submesoscale coherent vortices that transport relatively cold fresh subpolar water to the interior subtropical north atlantic acoustically tracked rafos floats released in the southward flowing western boundary current at the exit of the labrador sea reveal the formation of three of these eddies at the southern tip of the grand banks 42 n 50 w using a recently developed method to detect eddies in float trajectories and estimate their kinematic properties it was found that the eddies had average rotation periods of 5 7 day at radii of 10 25 km with mean rotation speeds of up to 0 3 m s 1 one especially long lived 5 1 months eddy crossed under the gulf stream path and translated southwestward in the subtropical recirculation to at least 35 n where it hit one of the corner rise seamounts velocity temperature and salinity measurements from a nine month deployment of two moorings south of the gulf stream at 38 n 50 w reveal the passage of at least two eddies with similar hydrographic and kinematic properties the core temperature and salinity properties of the eddies imply their formation at intermediate levels of the labrador current south of the tail of the grand banks these observations confirm earlier speculation that eddies form in this region and transport anomalously cold low salinity water directly into the subtropical interior possible formation mechanisms and potential importance of these eddies to interior ventilation and the equatorward spreading of labrador sea water are discussed

kinetic characteristics of debris flows as exemplified by field investigations and discrete element simulation of the catastrophic jiweishan rockslide china abstract the jiweishan rockslide of june 5 2009 in china provides an important opportunity to elucidate the kinetic characteristics of high speed long runout debris flows a 2d discrete element model whose mechanical parameters were calibrated using basic field data was used to simulate the kinetic behavior of this catastrophic landslide the model output shows that the jiweishan debris flow lasted about 3 min released a gravitational potential energy of about 6 10 13 j with collisions and friction dissipating approximately equal amounts of energy and had a maximum fragment velocity of 60 70 m s almost twice the highest velocity of the overall slide mass 35 m s notable simulated characteristics include the high velocity and energy of the slide material the preservation of the original positional order of the slide blocks the inverse vertical grading of blocks and the downslope sorting of the slide deposits field observations that verify these features include uprooted trees in the frontal collision area of the air blast wave downslope reduction of average clast size and undamaged plants atop huge blocks that prove their lack of downslope tumbling the secondary acceleration effect and force chains derived from the numerical model help explain these deposit features and the long distance transport our back analyzed frictions of the motion path in the pfc model provide a reference for analyzing and predicting the motion of similar geological hazards

dynamic simulation of the motion of fragmenting rock avalanches a mass referenced continuum model for dynamic analysis of rapid mass movement dan is verified by laboratory and field data increased earth pressure coefficients are used in this model to represent the dispersive pressures caused by fragmentation within a translating rock avalanche the numerical model demonstrates that increased runout in large rock avalanches can occur with normal friction coefficients if higher than normal internal pressures such as those believed to be generated by fragmentation are present the extent of the falling mountain rock avalanche deposit in new zealand is reproduced in the model with normal friction and high earth pressure coefficients to represent by analogy the additional internal pressures due to fragmentation it appears that if internal friction is changed by fragmentation it is only by a small amount and may increase rather than decrease to test this and to move beyond the present analogue model requires a better understanding of the rheology of fragmenting ro

an alternative hypothesis for the origin of the mediterranean salt lens observed off the bahamas in the fall of 1976 abstract a hypothesis is presented that the original salt lens or meddy observed off the bahamas in the fall of 1976 may have been formed not near the mediterranean outflow but instead in the vicinity of the northwest corner 51 n 43 w of the north atlantic current an eddy was observed near the northwest corner by an isopycnal rafos float deployed during the 1993 95 north atlantic current experiment and had nearly identical temperature salinity properties as those of the bahamas lens hydrographic evidence of thick homogeneous layers with similar properties near the northwest corner suggest a possible formation mechanism by which surface eddies containing warm and saline waters are cooled and subducted a plausible scenario is made whereby a northwest corner eddy might be advected southward in the newfoundland basin by the flow around the high pressure ridge east of the north atlantic current and then enter the recirculation gyre immediately south of the gulf stream such an eddy could be advect

minor inheritance inhibits the calibration of the 10be production rate from the ad 1717 val ferret rock avalanche european alps to calibrate the in situ 10be production rate we collected surface samples from nine large granitic boulders within the deposits of a rock avalanche that occurred in ad 1717 in the upper ferret valley mont blanc massif italy the 10be concentrations were extremely low and successfully measured within 10 analytical uncertainty or less the concentrations vary from 4829 448 to 5917 476 at g 1 using the historical age exposure time we calculated the local and sea level high latitude i e 60 cosmogenic 10be spallogenic production rates depending on the scaling schemes these vary between 4 60 0 38 and 5 26 0 43 at g 1 a 1 although they correlate well with global values our production rates are clearly higher than those from more recent calibration sites we conclude that our 10be production rate is a mean and an upper bound for production rates in the massif region over the past 300 years this rate is probably influenced by inheritance and will yield inaccurate e g too young exposure ages when applied to surface exposure studies in the area other independently dated rock avalanche deposits in the region that are approximately 103 years old could be considered as possible calibration sites

grain fracture in 3d numerical simulations of granular shear we present a new method to implement realistic grain fracture in 3d numerical simulations of granular shear we use a particle based model that includes breakable bonds between individual particles allowing the simulation of fracture of large aggregate grains during shear grain fracture simulations produce a comminuted granular material that is texturally comparable to natural and laboratory produced fault gouge our model is initially characterized by monodisperse large aggregate grains and gradually evolves toward a fractal distribution of grain sizes with accumulated strain comminution rate and survival of large grains is sensitive to applied normal stress the fractal dimension of the resultant grain size distributions 2 3 0 3 and 2 9 0 5 agree well with observations of natural gouges and theoretical results that predict a fractal dimension of 2 58 copyright 2005 by the american geophysical union

micromechanical modeling of cracking and failure in brittle rocks dynamic micromechanical models are used to analyze crack nucleation and propagation in brittle rock models of rock are created by bonding together thousands of individual particles at points of contact the feasibility of using these bonded particle models to reproduce rock mechanical behavior is explored by comparing model behavior to results from actual laboratory tests on different rock types the behavior of two granite models are examined in detail to study cracking and failure patterns that occur during compressional loading because discontinuum models are being used the rock models are free to crack and break apart under stress such that the micromechanics of cracking can be examined stress waves are allowed to propagate outward from each crack and it is shown that these dynamic waves significantly affect the rock behavior as the peak stress in the modeled rock is approached and many of the bonds are close to breaking a passing wave from a nearby crack is sufficient to break more bonds this causes clusters of cracks to be created and then eventual macroscopic shear failure occurs as these clusters connect to bisect the sample the failure patterns observed in the granite models are similar to those observed in actual laboratory tests

nature of stress accommodation in sheared granular material insights from 3d numerical modeling active faults often contain distinct accumulations of granular wear material during shear this granular material accommodates stress and strain in a heterogeneous manner that may influence fault stability we present new work to visualize the nature of contact force distributions during 3d granular shear our 3d discrete numerical models consist of granular layers subjected to normal loading and direct shear where gouge particles are simulated by individual spheres interacting at points of contact according to simple laws during shear we observe the transient microscopic processes and resulting macroscopic mechanical behavior that emerge from interactions of thousands of particles we track particle translations and contact forces to determine the nature of internal stress accommodation with accumulated slip for different initial configurations we view model outputs using novel 3d visualization techniques our results highlight the prevalence of transient directed contact force networks that preferentially transmit enhanced stresses across our granular layers we demonstrate that particle size distribution psd controls the nature of the force networks models having a narrow i e relatively uniform psd exhibit discrete pipe like force clusters with a dominant and focussed orientation oblique to but in the plane of shear wider psd models e g power law size distributions d 2 6 also show a directed contact force network oblique to shear but enjoy a wider range of orientations and show more out of plane linkages perpendicular to shear macroscopic friction level is insensitive to these distinct force network morphologies however force network evolution appears to be linked to fluctuations in macroscopic friction our results are consistent with predictions based on recent laboratory observations that force network morphologies are sensitive to grain characteristics such as particle size distribution of a sheared granular layer our numerical approach offers the potential to investigate correlations between contact force geometry evolution and resulting macroscopic friction thus allowing us to explore ideas that heterogeneous force distributions in gouge material may exert an important control on fault stability and hence the seismic potential of active faults 2007 elsevier b v all rights reserved

observations in the northwest corner of the north atlantic current abstract the north atlantic current a northern branch of the gulf stream flows in a northerly direction to the east of the grand banks of newfoundland and turns sharply to the right north of flemish cap in the northwest corner the currents and water masses in and near this turn are described using data from batfish satellite tracked drifters ctds and current meters drifter trajectories and water mass properties indicate that the northward current toward the northwest corner is sometimes well defined narrow converging and accelerating at other times it is poorly defined weaker less coherent and diverging when it is well defined the current turns sharply eastward between 51 and 52 n but rather than continuing east it forms 100 km anticyclonic eddies which persist for at least 1 2 months records from 16 current meters placed on four moorings across the current show the flow direction to be variable in time but nearly constant throughout the water column speed is also constant with depth

discrete element simulations of bed force anomalies due to force chains in dense granular flows abstract surficial flows on volcanic edifices are often comprised of high concentrations of granular materials either derived from juvenile eruptive material or material sourced from an unstable edifice although much attention has been given to granular flow mobility the physics that govern flow internal behavior and substrate interaction are still poorly understood recent laboratory experiments have shown that force chains transmit extreme localized forces to the substrates of free surface granular flows in this work we combine computational and experimental approaches to investigate the forces at the bed of a simplified granular flow a photoelastic experimental approach is used to resolve discrete forces in the granular flows we also conduct discrete element model dem simulations using input parameters derived from measureable physical material properties of experimental and natural materials that successfully reproduce the experimental bed forces generated by filamentary force chain structures observed in free surface granular flows the dem results show particular sensitivity to values prescribed for contact stiffness which is in contrast with previous reports indicating that stiffness values have insignificant influence on flow behavior the transient forces at the bed generated by force chain structures can greatly exceed by several 100 the bed forces predicted from continuum approaches and our simulation results imply that natural materials are more prone to excessive bed forces than photoelastic materials due to their larger contact stiffnesses this work suggests that force chain activity may play an important role in the bed physics of dense volcanic flows by influencing substrate entrainment

baroclinic eddy interaction with isolated topography point vortex and finite difference methods are used to study baroclinic eddies advected into weak and strong encounters with topography it is argued that weak interactions often scatter radially symmetric eddies into generalized hetons the dipole moments so generated within the eddy result in eddy propagations at various angles to the current strong interactions can result in the complete separation of the upper and lower layer circulations subsequent evolution in this case depends on many factors although strong topographic obstacles i e seamounts permit a reorganization of the centers into a coherent structure weaker topography confined to the deep ocean can disrupt the lower center although the upper center typically survives disassociation of the centers with both retaining their integrity is also possible heton generation can occur for eddies with weak lower layer expressions demonstrating a potentially strong control of shallow eddy propagation by deep sea bathymetry analytical and numerical estimates of the induced propagation speeds are sizable arguing topographic scattering is a potentially powerful mechanism influencing eddy propagation

reconstruction of seismic faulting by high velocity friction experiments an example of the 1995 kobe earthquake 1 high velocity friction experiments on a fault gouge collected from the nojima fault activated during the 1995 kobe earthquake showed that the friction coefficient decreased from 0 63 to 0 18 over a slip weakening distance dc at high slip rates of 1 m s the dramatic drop in friction coefficient of more than 0 3 is consistent with that for the kobe earthquake estimated from seismological observations experimentally determined dc becomes 5 m at a higher normal stress of 1 85 mpa close to the order of magnitude of seismologically determined dc of 0 5 to 1 m the difference in dc is not significant because the fracture energy consumed during frictional slip is the same order of 106 n m for both cases here we show that frictional behavior of a fault during an earthquake can be predicted by conducting high velocity friction experiments

kinematics and dynamics of a mediterranean salt lens abstract two surveys of the absolute velocity field of an eddy of mediterranean water meddy in the eastern north atlantic were conducted one year apart in 1984 and 1985 two velocity regimes were revealed within the radius of maximum velocity the meddy rotated anticyclonically as a solid body with a depth dependent rotation period near 6 days at its mid depth 1000 m one year later the radius of the core had decreased by one third the rotation rate of the lens also decreased except at its mid depth where there was a small but perceptible increase there was a sharp 5 km or less transition between the core and the outer region where the velocity decayed exponentially with radius a strong potential vorticity front due to the abrupt change in sign of horizontal shear kept the core isolated from the outer region potential vorticity was nearly constant within the upper confines of the core over the study period whereas there was a notable increase in potential vorticity in the lower portion of

fault textures in volcanic debris avalanche deposits and transformations into lahars the pichu pichu thrust lobes in south peru compared to worldwide avalanche deposits abstract structures lithofacies and semi quantitative sedimentological analysis of volcanic debris avalanche deposits are essential to constrain syn emplacement processes along avalanche fault zones in the setting of mass flow runout distances at a distance of 28 km from the extinct pichu pichu compound volcano we show how internal structures of thrust lobes faulted as to form horst and graben like structures have recorded the brecciation with granular segregations cataclastic gradients have been recognized in more than eleven breccia structures with statistical grain size parameters among them fractal d values between 1 96 and 2 53 related to an extensional fracturing in dads with fractal d values between 2 and 2 5 leading to granular disaggregation with fractal d values between 2 13 and 2 22 primary fractures related to transport processes and the secondary cataclasis produced during emplacement are quantified as having 50 matrix the hybrid lithofacies in graben like structures may be the precursory stages of the matrix transformation into lahar deposits volcanic debris avalanche structures of eleven worldwide volcanoes that belong to the central andes and the cascades volcanic arc have been compared using sedimentary and statistical methods 156 sieved samples and shape preferred orientation measured on 30 342 clasts median diameter sorting index skewness and kurtosis values help differentiate four deposits and processes 1 the proximal gravitational collapse deposits 2 the avalanche thrust lobes located in inverted extensional fault zones and 3 the hybrid and mixed deposits with polymodal distributions and 4 the bimodal transformed matrix with clast sorting the fractal d values of avalanche matrix range between 2 3 and 2 7 suggesting that extensional fractures have led to granular disaggregation from the available statistical dataset a few equations have been developed that help pointing to a syn emplacement cataclastic gradient along avalanche fault zone three textural classes of avalanche fault zones have been identified based on the ellipse a b values of 2 14 for the planar collapse in fault zone 1 75 to 2 for the crushing of volcanic avalanche breccias and

new constraints on the slate islands impact structure ontario canada the slate islands in northern lake superior represent the eroded remains of a complex impact crater originally approximately 32 km in diameter new field studies there reveal allogenic crater fill deposits along the eastern and northern portions of the islands indicating that this 500 800 ma impact structure is not as heavily eroded as previously thought near the crater center on the western side or patterson island massive blocks of target rocks enclosed within a matrix of fine grained polymict breccia record the extensive deformation associated with the central uplift shatter cones are a common structural feature on the islands and range from less than 3 cm to over 10 m in length although shatter cones are powerful tools for recognizing and analyzing eroded impact craters their origin remains poorly constrained

large lenses of highly saline mediterranean water isolated compact anticyclonic eddies or salt lenses were found in the canary basin hydrographic surveys of three such lenses show large anomalies of salinity and temperature 0 8 2 5 c they are centered at 1100 m have a vertical extent of up to 900 m and radii of 50 km current meter records indicate anticyclonic velocities up to 29 cm s 1 fine structure with vertical scales of 20 m and less possibly due to intrusive decay appears at the outer edges of the lenses whereas the centers are free of such structure the probability of finding a salt lens at any station in the canary basin is fairly high 0 08

chemical weathering in active mountain belts controlled by stochastic bedrock landsliding in active mountain belts erosion is driven by bedrock landsliding river water chemistry in new zealand s southern alps suggests that stochastic mass wasting processes also enhance chemical weathering in such environments a link between chemical weathering and physical erosion exists at the catchment scale over a wide range of erosion rates1 2 however in mountain environments where erosion rates are highest weathering may be kinetically limited3 4 5 and therefore decoupled from erosion in active mountain belts erosion is driven by bedrock landsliding6 at rates that depend strongly on the occurrence of extreme rainfall or seismicity7 although landslides affect only a small proportion of the landscape bedrock landsliding can promote the collection and slow percolation of surface runoff in highly fragmented rock debris and create favourable conditions for weathering here we show from analysis of surface water chemistry in the southern alps of new zealand that weathering in bedrock landslides controls the variability in solute load of these mountain rivers we find that systematic patterns in surface water chemistry are strongly associated with landslide occurrence at scales from a single hillslope to an entire mountain belt and that landslides boost weathering rates and river solute loads over decades we conclude that landslides couple erosion and weathering in fast eroding uplands and thus mountain weathering is a stochastic process that is sensitive to climatic and tectonic controls on mass wasting processes

giant rockslides from the inside the growing body of research on large scale mass wasting events so far has only scarcely investigated the sedimentology of chaotic deposits from non volcanic terrestrial landslides such that any overarching and systematic terminological framework remains elusive yet recent work has emphasized the need for better understanding the internal structure and composition of rockslide deposits as a means to characterise the mechanics during the final stages of runout and emplacement we offer a comprehensive overview on the occurrence of rock fragmentation and frictional melt both at different geographic locations and different sections within large 10 6 m 3 rockslide masses we argue that exposures of pervasively fragmented and interlocked jigsaw cracked rock masses basal melange containing rip up clasts and phantom blocks micro breccia and thin bands of basal frictionite are indispensable clues for identifying deposits from giant rockslides that may remain morphologically inconspicuous otherwise these sedimentary assemblages are diagnostic tools for distinguishing large rockslide debris from macro and microscopically similar glacial deposits tectonic fault zone breccias and impact breccias and thus help avoid palaeoclimatic and tectonic misinterpretations let alone misestimates of the hazard from giant rockslides moreover experimental results from mossbauer spectroscopy of frictionite samples support visual interpretations of thin sections and demonstrate that short lived 1500 degrees c in the absence of water occurred at the base of several giant moving rockslides this finding supports previous theories of dry excess runout accompanied by comminution of rock masses down to gm scale and indicates that catastrophic motion of large fragmenting rock masses does not require water as a potential lubricant

fragmentation energy in rock avalanches fragmentation is one of the mechanisms involved in rock avalanches quantifying the associated energy dur ing a rock avalanche can help to assess the influence of fragmentation on post failure mass movements in this paper in situ block size distributions of the intact rock mass and the debris deposits are presented and analyzed for nine rock avalanches five in the canadian rocky mountains and four in the european alps degrees of fragmentation are esti mated from these data two methods are examined to assess fragmentation energy one based on the comminution the ory and one on the blasting energy used in the mining industry the results show that for the studied rock avalanches there is a relationship between the reduction in diameter ratio rr d50 d50 where d50 and d50 are the mean diameter of the intact rock mass and the mean diameter of the debris respectively and the potential energy per unit volume normalized with respect to the point load strength of rock hg c where is the unit weight of the material hg is the vertical distance between the centres of gravity of the mass at the start and end positions and c is the point load strength for the cases studied fragmentation energy calculations average 20 of the potential energy an empirical relationship between rr and hg c has been established and is used in the definition of a disintegration index id this index seems to reflect the physics of the disintegration process since it accounts for the fact that the reduction in diameter ratio is a function of the dissipated energy and the strength of the rock these factors have long been known to affect fragmentation but have never been presented in a coherent manner for rock avalanches

effects of rock avalanches on glacier behaviour and moraine formation although large rock avalanches are infrequent sediment production in active orogens is dominated by such events which may strongly influence geomorphic processes where rock avalanches fall onto glaciers they may affect glacier behaviour and moraine formation we outline the processes of rock avalanche initiation and motion and show that supraglacial deposits of rock avalanche debris have distinct sedimentological and thermal properties laboratory experiments on the effects of such debris on ice ablation are supplemented by field data from two rock avalanches in the southern alps new zealand their effects are compared with those of the thinner supraglacial debris that results from small rockfalls and melt out of englacial debris implications of rock avalanche debris cover for glacier behaviour are explored using a mass balance model of the franz josef glacier in new zealand demonstrating a likely supraglacial rock avalanche origin for the waiho loop moraine and considering the potential hazard of a large rock avalanche onto the present day glacier

revised palaeoclimatic significance of mueller glacier moraines southern alps new zealand a sequence of late holocene moraines on the foreland of the mueller glacier southern alps new zealand forms part of a local moraine age database used to establish a regional glacier chronology and subsequently to investigate potential intra hemispheric and global climate forcing mechanisms we present new sedimentological and geomorphological evidence that a set of these moraine ridges previously considered to represent individual advances constitutes a single moraine complex the mueller memorial moraine formed by supraglacial transport of a large volume of landslide debris to the glacier terminus because a moraine formed in this way is not necessarily associated with an advance triggered by a climate event we question the palaeoclimatic significance of the mueller memorial moraine as well as that of other moraines in comparable settings our findings suggest that the mode of formation and glacio dynamical context of moraines whose ages contribute to existing palaeoclimate reconstructions need to be re examined in order to assess the reliability of these reconstructions copyright 2015 john wiley sons ltd

a hydrological continuum in permafrost environments the morphological signatures of melt driven hydrology on earth and mars abstract this paper examines relationships between the morphology of cold desert hydrological features and the water sources and it relates the formation of diagnostic deposits and erosion patterns to environmentally controlled patterns of discharge in particular three sets of landforms found in the mcmurdo dry valleys of antarctica are compared to similar features on mars antarctic streams rivers to amazonian valleys terrestrial gullies to martian gullies and water tracks to recurring slope lineae similarities in landform morphology are highlighted for each set hydrological characteristics are aggregated or calculated and they are shown to scale comparably across the landforms for the terrestrial and martian groups accordingly a hydrological continuum is proposed linking the magnitude and the persistence of water sources in cold desert environments to flow response and the formation of diagnostic landforms this concept provides a framework for examining the relationships between climate hydrology and geomorphology in the cold desert environments of these two worlds

dynamics and emplacement mechanisms of the successive baige landslides on the upper reaches of the jinsha river china abstract two successive baige landslides are presented in this study to investigate the dynamics and emplacement mechanisms field survey shows that the deposit characteristics of the first landslide are affected by the extremely fractured rock masses and the complex spatial distribution of lithologies in the source area this deposit consists of abundant angular megablocks on the surface supported by clasts with a relatively abundant content of rubble ranging from micrometre to decimetre sizes and rarely well preserved original stratigraphic sequence diapiric structure and convoluted structure these sedimentological characteristics imply that a simple differential shear process induced by compression is distributed through the entire avalanche masses with low internal disturbance during the emplacement of the first landslide the three dimensional discrete element simulations show that i the first landslide reaches its maximum average velocity of 41 m s in 28 s and eventually is bulldozed to a halt in the river within 80 s ii the second landslide is controlled by entrainment which impedes the avalanche from further accelerating and simultaneously imparts kinematic energy to the substrate eventually becoming entirely mobilized and reaching a maximum average velocity of 35 m s in 36 s in the dynamic process of the second landslide the significant entrainment induced enlarged volume its entrainment ratio reaches 3 3 is associated with the steep concave terrain water bearing substrate and lower roughness substrate basal boundary and overloading impact induced erosion is proposed to be the most significant contribution to this entrainment

fragmentation and boosting of rock falls and rock avalanches fragmentation has been proposed as an important dynamical process in the propagation of rock avalanches the occurrence of an intense block fragmentation inside a rock avalanche traveling on smooth inclined terrain followed by a flat region a geometry common to many landslides is first studied numerically by means of a discrete element 2 d code in which blocks are subjected to mutual collisions and impact with the terrain this numerical model confirms that the locations where fragmentation is more likely to occur are those in correspondence of abrupt slope changes we thus analyze this geometry of impact in two cases low and high impact energy in the first case where recent experimental data are available a kinematic analysis shows that the energy released at impact causes high velocities of the smallest fragments a highly probable scenario in rock avalanche dynamics when the impact is so energetic to disintegrate the landslide we find that explosive fragmentation at the slope break provides an extra horizontal boost to a rock avalanche via a peculiar mechanism coupling the geometry of the slope path to the dynamics of the rock avalanche as a consequence a net momentum gain boost results along the horizontal direction due to the terrain asymmetry however under normal field conditions only when the slope angle is greater than 70 and fragmentation produces clasts of fairly uniform size the momentum and runout distance are significantly enhanced allowing for a spectrum of fragment sizes and velocities we find a relationship between the degree of fragmentation and the magnitude of the extra boost

on the use of a split hopkinson pressure bar in structural geology high strain rate deformation of seeberger sandstone and carrara marble under uniaxial compression abstract there is increasing evidence that seismogenic fractures can propagate faster than the shear wave velocity of the surrounding rocks strain rates within the tip region of such super shear earthquake ruptures can reach deformation conditions similar to impact processes resulting in rock pulverization the physical response of brittle rocks at high strain rates changes dramatically with respect to quasi static conditions rocks become stiffer and their strength increases a measure for the dynamic behavior of a rock and its strain dependency is the dynamic increase factor dif which is the ratio of the dynamic compressive strength to the quasi static uniaxial compressive strength to investigate deformation in the high strain rate regime experimentally we introduce the split hopkinson pressure bar technology to the structural geology community a method that is frequently used by rock and impact engineers we measure the stress strain response of homogeneous fine grained seeberger sandstone and carrara marble in uniaxial compression at strain rates ranging from 10 1 to 10 2 s 1 with respect to tangent modulus and dynamic uniaxial compressive strength we present full stress strain response curves of seeberger sandstone and carrara marble at high strain rates and an evaluation method to determine representative rates of deformation results indicate a rate dependent elastic behavior of carrara marble where an average increase of 18 could be observed at high strain rates of about 100 s 1 dif reaches a factor of 2 2 2 4 seeberger sandstone does not have a rate dependent linear stress strain response at high strain rates its dif was found to be about 1 6 1 7 at rates of 100 s 1 the onset of dynamic behavior is accompanied with changes in the fracture pattern from single to multiple fractures to pervasive pulverization for increasing rates of deformation seismogenic shear zones and their associated fragment size spectra should be carefully revisited in the light of dynamic deformation

high velocity ring shear tests on sand ring shear tests on sand materials have been carried out to show whether there is a change in the behaviour of these materials at high shearing rates and normal stresses this question is relevant to the problem of the mobility of large rock avalanches sturzstroms but is also of more general academic interest a ring shear apparatus of unusual although simple design has been constructed capable of achieving circumferential velocities of 2 m s at normal stresses of up to 200 kpa tests were carried out on two types of coarse sand wet or dry sand rock flour mixtures and polystyrene beads perfect frictional behaviour was observed in all the tests uninfluenced by either velocity or normal stress over the entire range of these variables change in frictional behaviour due to high rate of shearing therefore cannot be used to explain the high observed mobility of sturzstroms des essais de cisaillement circulaire par torsion ont ete effectes afin de decouvrir si un changement ait lieu dans le comportem

fracture surface energy of the punchbowl fault san andreas system the energetics of earthquake rupture slip weakening and rupture surface formation are poorly understood by measuring the energy associated with fracture damage along the punchbowl fault in the devil s punchbowl los angeles county park part of the san andreas system chester et al show that the fracture surface energy for rupture along a mature fault of this type accounts for only a small fraction of the energy released during large earthquakes as determined by seismologists this suggests that mechanisms such as melt lubrication and thermal pressurization are responsible for slip weakening fracture energy is a form of latent heat required to create an earthquake rupture surface and is related to parameters governing rupture propagation and processes of slip weakening1 2 3 fracture energy has been estimated from seismological and experimental rock deformation data4 5 6 7 8 yet its magnitude mechanisms of rupture surface formation and processes leading to slip weakening are not well defined8 9 10 here we quantify structural observations of the punchbowl fault a large displacement exhumed fault11 12 in the san andreas fault system and show that the energy required to create the fracture surface area in the fault is about 300 times greater than seismological estimates would predict for a single large earthquake if fracture energy is attributed entirely to the production of fracture surfaces then all of the fracture surface area in the punchbowl fault could have been produced by earthquake displacements totalling 1 km but this would only account for a small fraction of the total energy budget and therefore additional processes probably contributed to slip weakening during earthquake rupture

a comparison of pyroclastic flow and debris avalanche mobility many pyroclastic flows have runout distances longer than expected from basic frictional arguments in these cases the ratio of the height descended h and the runout l are as small as 0 2 a feature which has been attributed to fluidization however significant fluidization by gases is now considered unlikely during emplacement of debris avalanches where h l and volume are inversely related we determine whether pyroclastic flows are more mobile than debris avalanches of the same volume and if different emplacement mechanisms are needed to describe their runout h l and volume data were compiled for 34 nonvolcanic and 40 volcanic debris avalanche deposits as well as 15 pyroclastic flow deposits systematic differences in the volume versus h l plots were explored by statistical analysis results show an inverse relationship between h l and volume for both nonvolcanic and volcanic debris avalanche deposits as expected and also for pyroclastic flow deposits regression lines for plots of pyroclastic flow and volcanic debris avalanche data are statistically indistinguishable and the non volcanic debris avalanche line is parallel to the other two we argue that the nonvolcanic and volcanic debris avalanche differences are due to material properties rather than emplacement mechanisms therefore since pyroclastic flows and volcanic debris avalanches have indistinguishable h l versus volume it is unlikely that pyroclastic flows have a significantly different primary emplacement mechanism based on the data in hand we conclude that it is unnecessary to invoke gas fluidization to explain the mobility of the types of pyroclastic flows examined or the excess runout of large volume debris avalanches

characteristics and transport mechanism of the nyixoi chongco rock avalanche on the tibetan plateau china abstract for studying rock avalanches complex surficial and internal characteristics have been regarded as important indicators for understanding avalanche transport mechanism in the present study deposits of a massive holocene rock avalanche termed the nyixoi chongco rock avalanche located on the lhasa terrane of tibetan plateau in china are investigated based on a combination of remote sensing data and in situ observations it is revealed that abundant surface landforms including toreva blocks longitudinal and transverse ridges en echelon ridges and hummocks are commonly developed corresponding to these surface morphologies a series of internal sedimentary structures including jigsaw structures inner shear zones aligned clasts diapiric structures convoluted laminations and basal decollements are also well developed through an analysis of these surficial and internal characteristics we propose that a rapid motion similar to a laminar flow most likely occurred after the avalanche mass detaching from the source area in this process the detached avalanche mass was mainly emplaced by a frictional simple shear process characterized by a bulldozing effect that occurred between the sliding mass and the substrate from the proximal to the distal sections of the avalanche the transport of the rock mass can be classified into four major processes an extension dominated sliding process in the transition zone a compression dominated sliding process in subzones iii 1 and iii 2 of the accumulation zone iii a sliding process co dominated by compression and lateral spreading in subzone iii 3 and a rapid radial spreading process in subzone iii 4 the results of our study provided an improved understanding of the transport mechanisms of this rock avalanche

the role of rock fragmentation in the motion of large landslides abstract by considering the implications of the comminution generally associated with very large landslides we arrive at a simple explanation for the remarkably low frictional resistance to motion demonstrated by large intact blockslides e g waikaremoana new zealand volcanic debris avalanches e g socompa chile and large rock avalanches e g falling mountain n z which allows such mass movements to achieve unexpectedly high velocities and long runout distances during rapid grain flow under high direct stress the overall grain motion generates stresses in many force chains that strain individual grains to failure most of the elastic strain energy accumulated in these force chains before failure is returned at failure to the resulting grain fragments resulting in apparent instantaneous pressures of 3q on the surroundings where q is the ambient strength of the previously intact grains gpa these intense pressures support some of the direct force on the shear layer so that the effective intergranular stress in the shear layer is reduced because frictional resistance is proportional to effective stress this reduces the overall frictional resistance to shear the steady state effective stress is that which just allows fragmentation to continue the resistance to motion estimated from this relationship explains to much better than order of magnitude accuracy the reported motions of the large rapid mass movements we also deduce that grain fragmentation can be sustained for sufficiently long to explain the phenomena without reducing the mean grain size by volume in the granular layer to unrealistically small values the presence of pore fluid does not appear to influence the effect of fragmentation dynamics in a major way the proposed mechanism requires further laboratory and simulation studies to reduce its current dependence on limited field data but its success suggests that it is worthwhile investigating further as an explanation for large mass movements in the types of brittle rock in which fragmentation occurs

discrete element modeling of the mass movement and loose material supplying the gully process of a debris avalanche in the bayi gully southwest china abstract the dynamic process of a debris avalanche in mountainous areas is influenced by the landslide volume topographical conditions mass material composition mechanical properties and other factors a good understanding of the mass movement and loose material supplying the gully process is very important for understanding the dynamic properties of debris avalanches three dimensional particle flow code pfc3d was used to simulate a debris avalanche in quaternary deposits at the bayi gully southwest china fortran and autocad were used for the secondary development to display the mass movement process and to quantitatively describe the mass movement and loose material supplying the gully process the simulated results show that after the landslide is initiated the gravitational potential energy is converted into kinetic energy with a variation velocity for the sliding masses two stages exist for the average movement velocity the acceleration stage and the slowdown stage which are influenced by the topographical conditions for the loose materials supplying the gully process the cumulative volume of the sliding masses into the gully gradually increases over the time when the landslide volume is not large enough the increasing landslide volume does not obviously influence the movement process of the sliding masses the travel distance and movement velocity increase with the decreasing numerical parameters and the mass movement process is finished more quickly using low value parameters the deposition area of the sliding masses decreases with the increasing numerical parameters and the corresponding deposition thickness increases the mass movement of the debris avalanche is not only influenced by the mechanical parameters but is also controlled by the topographical conditions

a census of meddies tracked by floats recent subsurface float measurements in 27 mediterranean water eddies meddies in the atlantic are grouped together to reveal new information about the pathways of these energetic eddies and how they are often modified and possibly destroyed by collisions with seamounts twenty meddies were tracked in the iberian basin west of portugal seven in the canary basin during february 1994 14 meddies were simultaneously observed 11 of them in the iberian basin most 69 of the newly formed meddies in the iberian basin translated southwestward into the vicinity of the horseshoe seamounts and probably collided with them some meddies 31 passed around the northern side of the seamounts and translated southwestward at a typical velocity of 2 0 cm s into the canary basin some meddies observed there were estimated to be up to 5 yr old four meddies in the canary basin collided with the great meteor seamounts and three meddies were inferred to have been destroyed by the collision overall an estimated 90 of meddies collided with major seamounts the mean time from meddy formation to a collision with a major seamount was estimated to be around 1 7 yr combined with the estimated meddy formation rate of 17 meddies yr from previous work this suggests that around 29 meddies co exist in the north atlantic therefore during february 1994 we observed about half of the population of meddies

particle size and energetics of gouge from earthquake rupture zones surprisingly considering the forces that we see at the surface not all the energy involved in an earthquake is transformed into ground motion much of it is consumed by frictional heating and rock pulverization an analysis of pulverized rock or gouge collected from the san andreas fault in california and from a rupture zone at 2 km depth in a south african gold mine contradicts the commonly held view that gouge surface energy is a negligible component of earthquake energy balance the analysis reveals unexpected diminutive particles in gouge samples indicating that pulverization not frictional heating is the major consumer of earthquake energy at depth this might explain the heat flow anomaly seen in the san andreas fault system and perhaps some other long standing puzzles in earthquake energetics grain size reduction and gouge formation are found to be ubiquitous in brittle faults at all scales1 2 3 4 and most slip along mature faults is observed to have been localized within gouge zones5 6 this fine grain gouge is thought to control earthquake instability3 6 7 8 and thus understanding its properties is central to an understanding of the earthquake process7 9 here we show that gouge from the san andreas fault california with 160 km slip and the rupture zone of a recent earthquake in a south african mine with only 0 4 m slip display similar characteristics in that ultrafine grains approach the nanometre scale gouge surface areas approach 80 m2 g 1 and grain size distribution is non fractal these observations challenge the common perception that gouge texture is fractal10 11 and that gouge surface energy is a negligible contributor to the earthquake energy budget3 9 12 we propose that the observed fine grain gouge is not related to quasi static cumulative slip but is instead formed by dynamic rock pulverization during the propagation of a single earthquake

meddy seamount interactions implications for the mediterranean salt tongue abstract a quasigeostrophic point vortex numerical model is used to explore interactions of eddies and seamounts the ultimate objective of this study is to assess the role of meddy seamount interaction as an input to mediterranean salt tongue maintenance secondary objectives are to clarify the dynamics of meddy seamount interaction the results suggest that meddies survive seamount collisions with 60 70 of their initial cores remaining intact as coherent vortices given observed formation rates it appears meddies in their interactions with seamounts inject between one quarter and one half of the salt anomaly necessary to sustain the mediterranean salt tongue other considerations suggest the anomalous mass flux by meddies is comparable to that due to the mean flow in summary meddies are important to the maintenance of the salt tongue although other mechanisms are needed coherent vortex transport of which meddies are one example is a mesoscale process not well described by the downgradient mix

sedimentology of rock avalanche deposits case study and review abstract detailed sedimentological studies concerning different facies types and the factors influencing their development such as lithology topography substrates etc were carried out at the carbonate tschirgant rockslide rock avalanche deposit in the eastern alps of austria several depositional facies and sub facies have been identified at this and other sites by many researchers these facies are found throughout the debris regardless of depth or travel distance and result from highly heterogeneous stress distributions in time and space during emplacement one of the most important recent observations in terms of emplacement dynamics is that shear is not confined to the base but is distributed throughout the debris except the coarse carapace due to the preservation of source stratigraphy in these non turbulent mass movements any horizontal facies or grain size variations need to be regarded in context since they strongly depend on source stratigraphy and hence the spatial distribution of lithologies i e geological units of different mechanical properties for example some lithologies do not form a boulder carapace due to absence of large in situ blocks in the source rock mass however at tschirgant slight facies maturation with distance within the same lithology is observed i e clast fragmentation progresses to create the distinct facies characteristic grain size distribution only after some distance travelled these details are revealed through facies based sampling and analysis studies based on bulk sampling in some cases observed progressively reduced grain sizes with distance and depth which might be a function of added variations within different facies sampled together in this paper the wealth of observations on rockslide and rock avalanche sedimentology of the past decades is combined with a detailed case study of a lithologically relatively simple deposit to outline global and site specific depositional structures and facies with the aim to summarize review and refine the current state of knowledge on rock avalanche and rockslide emplacement processes

a model for the runout analysis of rapid flow slides debris flows and avalanches runout analyses are used for risk assessment and design of remedial measures against rapid landslides such as debris flows debris avalanches rockslide avalanches large scale liquefaction failure

isopycnal rafos floats as roving hydrographers in the north atlantic current region the properties measured by isopycnal floats can be compiled to provide hydrographic information about the sampled surfaces the height and temperature of two specific volume anomaly surfaces reported by 84 rafos floats deployed in the north atlantic current nac region are compared here with the climatological hydrographic database the mean pathway of the nac and other prominent features of the region are similar in float derived and climatological surfaces the most striking difference between floats and climatology an extended trough in the nac path at 44 n in the float derived surface reflects the sampling time scales the baroclinic transport of the nac estimated from rafos floats using the observed climatological relationship between the potential energy anomaly and the height of the specific volume anomaly surfaces was 42 sv at 42 n and 24 sv at 47 n in reasonable agreement with climatological estimates

characterization of the cubilche debris avalanche deposit a controversial case from the northern andes ecuador abstract in areas characterized by many volcanoes identifying the source of a deposit may not be trivial this becomes much more complicated when looking for the source of a debris avalanche deposit dad the common products of catastrophic volcanic edifice collapses to overcome this problem in this work a methodology is proposed based on the integration of texture features and areal distribution of the deposit comparison between the petrography of the coarser clasts within the dad and of the proximal products grain size analysis and the volumetric estimations of the deposit and the volume missing from the volcanic edifice this methodology has been tested to a dad occurred near the city of ibarra imbabura province northern ecuador having a controversial source two main volcanic edifice are located in proximity of the dad the cubilche volcano 3826 m a s l located immediately south of and east of the colossal dormant imbabura volcano the former displays a sharp horseshoe shaped scar towards the north and inside this post collapse edifice that we name old cubilche volcano ocv is located the young cubilche volcano ycv that refilled a portion of the collapse scar and partially covered the southern flank of the ocv detailed knowledge of cubilche volcano is critical because of its close proximity and interspersed activity with imbabura volcano in fact imbabura most recent edifice was built over the northwestern slope of the ocv and partially covered it recent studies linked the studied dad to both imbabura volcano as a product of its northern sector collapse as well as neighboring cubilche volcano our data points to cubilche as the most likely source for this dad a perspective view of the shaded relief image of the present day ocv shows that the morphology of the volcano is well preserved on its southern eastern and western flanks this allows us to reconstruct the morphology of the ocv previous to the collapse through interpolation of elevation and altitude data of preserved flanks a dem of the present day topography was used for extrapolating the morphology using similar methodology the post collapse base of the amphitheater was reconstructed by removing the relief of the present day ycv the reconstructed topography of the ocv shows that it could have been a symmetric cone reaching a maximum elevation of 4100 m a s l with a lack volume of 3 5 km3 based on this scenario the deposit originated from the ocv main collapse should have a volume 3 3 5 km3 in accordance to the volume calculated for the studied dad

a gravitational spreading origin for the socompa debris avalanche abstract socompa volcano arguably provides the world s best exposed example of a sector collapse derived debris avalanche deposit new observations lead us to re interpret the origin of the sector collapse we show that it was triggered by failure of active thrust anticlines in sediments and ignimbrites underlying the volcano the thrust anticlines were a result of gravitational spreading of substrata under the volcano load about 80 of the resulting avalanche deposit is composed of substrata formerly residing under the volcano and in the anticlines the collapse scar can be traced up to 5 km from the edifice truncating two spreading related anticlines which collapsed in the event outcrops near the volcano preserve evidence of edifice material being carried along on top of mobilised substrata on the north side of the scar the avalanche motion was initially at right angles to the failure edge structural relations indicate that immediately prior to collapse the substrata disintegrated became effectively liquidised and were ejected from beneath the edifice catastrophic mobilisation of substrata probably resulted from breakdown of ignimbrite clasts and cement it may have occurred through progressive rock fracture by high shear strain during spreading material ejected from under socompa formed a layer on which volcanic edifice debris was transported this interpretation of events explains the puzzling observation that avalanche units with the lowest gravitational potential energy moved the furthest it can also account for avalanche motion normal to the collapse scar walls ignimbrites and other rock types probably capable of similar behaviour underlie many other volcanoes identification of spreading at other sites could therefore be a first step towards assessment of the potential for this style of catastrophic sector collapse

gouge formation by dynamic pulverization during earthquake rupture it is proposed here that fault gouge forms by rock pulverization within the tip region of a fast propagating earthquake due to the intensity of stress and rates of strain in this zone to examine this mechanism we calculate the deformation conditions of a dynamic shear fracture propagating close to the limiting rayleigh wave velocity the mechanical conditions close to the fracture tip are extreme tensile stresses approach 5 gpa volumetric strain rates exceed 105 s 1 and volumetric expansion alternates with volumetric contraction it is expected that a localized zone a few millimeters wide will be pulverized under these conditions this mechanism of dynamic gouge formation provides new insight to recent observations of the texture of gouge from the san andreas fault zone and from rupture zones in south african mines further as such extreme conditions develop only during fast propagating earthquakes presence or absence of pulverized gouge may serve as an indicator of earthquake propagation velocity

unraveling driving factors for large rock ice avalanche mobility large rock ice avalanches have attracted attention from scientists for decades and some of these events have caused high numbers of fatalities a relation between rock slope instabilities in cold high mountain areas and climate change is currently becoming more evident and questions about possible consequences and hazard scenarios in densely populated high mountain regions leading beyond historical precedence are rising to improve hazard assessment of potential rock ice avalanches their mobility is a critical factor this contribution is an attempt to unravel driving factors for the mobility of large rock ice avalanches by synthesizing results from physical laboratory experiments and empirical data from 64 rock ice avalanches with volumes 1x106 m3 from glacierized high mountain regions around the world the influence of avalanche volume water and ice content low friction surfaces and topography on the apparent coefficient of friction as a measure of mobility is assessed in laboratory experiments granular ice in the moving mass was found to reduce bulk friction up to 20 while water led to a reduction around 50 for completely saturated material compared with dry flows evidence for the effects of water as a key driving factor to enhance mobility was also found in the empirical data while the influence of the ice content could not be confirmed to be of much relevance in nature besides liquefaction it was confirmed that mobility increases with volumes and that frictional surface characteristics such as flow paths over glaciers are also dominant variables determining mass movement mobility effects of the topography along the flow path as well as channeling are assumed to be other critical factors the results provide an empirical basis to roughly account for different path and flow characteristics of large rock ice avalanches and to find appropriate ranges for friction parameters for scenario modeling and hazard assessments copyright 2011 john wiley sons ltd

a fragmentation spreading model for long runout rock avalanches based on the observation that deposits of large rock avalanches consist predominantly of intensely fragmented rock debris it is proposed that the processes of rock fragmentation are significant ca