tectonics fluids and ore deposits mobilization and remobilization abstract the mobilization of metals leading to the formation of many known types of metallic resource involves the focussed flow of very large km 3 fluid volumes different types of fluids such as sea water and metamorphic and meteoric fluids with or without biomolecules may be specific for certain metals or suites of metals where large fluid volumes are part of a geologic process there is potential for local metal enrichment examples of such processes within the context of plate tectonics include convective flow of sea water at ocean ridges in relation to ophiolite cu zn mineralization and black smokers subduction of metal enriched sediments and the tectonic recycling of sn w mineralization metamorphic dewatering of subducted oceanic crust in the context of au deposits metamorphic degassing around high level granitic plutons and metamorphic re equilibration of the underthrust plate in relation to continental thrusting in addition during weathering processes short term leaching produces fertile soils whereas long term leaching can result in lateritic ores the large scale remobilization of ore deposits or of mineralization where metal enrichment is currently sub economic is improbable unless large fluid volumes are involved or the crust undergoes major tectonic re arrangement but it is perhaps possible that these situations are more common than we suppose and that such multistage events are indicated by the long term persistence of metallogenic provinces

catastrophic debris avalanche deposit of socompa volcano northern chile between 10 000 and 500 yr ago the socompa volcano in northern chile experienced a catastrophic collapse of a 70 deg sector of the original cone causing a debris avalanche that descended nearly 3000 m vertically and traveled more than 35 km from the volcano the deposits cover some 490 sq km and have a minimum volume of 15 cu km parts of the original cone slumped in a nearly coherent form and are now preserved as large blocks more than 400 m high the primary avalanche traveled northwestward over sloping ground before coming to rest transiently forming a prominent marginal ridge and then slid away northeastward to form a secondary flow overriding much of the primary avalanche deposit abundant prismatic jointed dacite blocks within the debris avalanche deposit and a thin fine grained pumiceous deposit beneath it suggest that the collapse was triggered by magmatic activity and may have been accompanied by a violent lateral blast collapse was followed by eruption of pumiceous pyroclastic flows and extrusion of voluminous dacite domes

lessons from ontake san a comparative analysis of debris avalanche dynamics abstract dynamic aspects of the long runout ontake san debris avalanche are evaluated by a comparison of several models an unsteady numerical model assumes two dimensional flow of an incompressible biviscous or newtonian fluid represented as a continuum with a free surface internal deformation of the flowing mass is considered as well as boundary resistances thus flow thinning and deposit shape as well as flow kinematics may be modeled parameters are adjusted to match observed runout with additional constraints on velocity and emplacement time with abundant constraints for ontake san from careful field investigations by japanese research teams our analysis indicates that a substantial decrease in flow resistance occurred as a function of displacement constant property models that match runout tend to overestimate the peak velocities and to underestimate the emplacement times a staged increase in mobility in both constant volume and variable volume models leads to results consistent with field data runout in a channel overflow area was also modeled qualitatively similar results have been obtained by other researchers using simple sliding block models with empirical parameters a slide block model with rational parameter selection a modified flood simulation and a multi element frictional slide model the relative merits of these models are compared the field mechanisms associated with this mobility increase with displacement are poorly understood but the question is now identified as a target for future research at debris avalanche sites and some plausible mechanisms are considered the main reason probably involves the entrainment of river water and saturated sediment leading to enhanced efficiency of fluid pressure mechanisms with undrained shear in addition progressive shearing reduced the mean particle size and angularity and the cohesion and friction and apparent viscosity of avalanche debris near the wetted perimeter hydroplaning the shearing of water films and slurries may have occurred locally

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

flow of variably fluidized granular masses across three dimensional terrain 2 numerical predictions and experimental tests numerical solutions of the equations describing flow of variably fluidized coulomb mixtures predict key features of dry granular avalanches and water saturated debris flows measured in physical experiments these features include time dependent speeds depths and widths of flows as well as the geometry of resulting deposits three dimensional 3 d boundary surfaces strongly influence flow dynamics because transverse shearing and cross stream momentum transport occur where topography obstructs or redirects motion consequent energy dissipation can cause local deceleration and deposition even on steep slopes velocities of surge fronts and other discontinuities that develop as flows cross 3 d terrain are predicted accurately by using a riemann solution algorithm the algorithm employs a gravity wave speed that accounts for different intensities of lateral stress transfer in regions of extending and compressing flow and in regions with different degrees of fluidization field observations and experiments indicate that flows in which fluid plays a significant role typically have high friction margins with weaker interiors partly fluidized by pore pressure interaction of the strong perimeter and weak interior produces relatively steep sided flat topped deposits to simulate these effects we compute pore pressure distributions using an advection diffusion model with enhanced diffusivity near flow margins although challenges remain in evaluating pore pressure distributions in diverse geophysical flows riemann solutions of the depth averaged 3 d coulomb mixture equations provide a powerful tool for interpreting and predicting flow behavior they provide a means of modeling debris flows rock avalanches pyroclastic flows and related phenomena without invoking and calibrating rheological parameters that have questionable physical significance

the chimborazo sector collapse and debris avalanche deposit characteristics as evidence of emplacement mechanisms abstract chimborazo is a late pleistocene to holocene stratovolcano located at the southwest end of the main ecuadorian volcanic arc it experienced a large sector collapse and debris avalanche da of the initial edifice ch i this left a 4 km wide scar removing 8 0 0 5 km 3 of the edifice the debris avalanche deposit dad is abundantly exposed throughout the riobamba basin to the rio chambo more than 35 km southeast of the volcano the dad averages a thickness of 40 m covers about 280 km 2 and has a volume of 11 km 3 two main dad facies are recognized block and mixed facies the block facies is derived predominantly from edifice lava and forms 80 vol of the dad with a probable volume increase of 15 25 vol the mixed facies was essentially created by mixing brecciated edifice rock with substratum and is found mainly in distal and marginal areas the dad has clear surface ridges and hummocks and internal structures such as jigsaw cracks injections and shear zone features are widespread structures such as stretched blocks along the base contact indicate high basal shear substratum incorporation is directly observed at the base and is inferred from the presence of substratum derived material in the dad body based on the facies and structural interpretation we propose an emplacement model of a lava rich avalanche strongly cataclased before and or during failure initiation the flow mobilises and incorporates significant substrata 10 14 vol while developing a fine lubricating basal layer the substrata dominated mixed facies is transported to the dad interior and top in dykes invading previously formed fractures

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

catastrophic debris avalanche from ancestral mount shasta volcano california a debris avalanche deposit extends 43 km northwestward from the base of mount shasta across the floor of shasta valley california where it covers an area of at least 450 km 2 the surface of the deposit is dotted with hundreds of mounds hills and ridges all formed of blocks of pyroxene andesite and unconsolidated volcaniclastic deposits derived from an ancestral mount shasta individual hills are separated by flat topped laharlike deposits that also form the matrix of the debris avalanche and slope northwestward about 5 m km radiometric ages of rocks in the deposit and of a postavalanche basalt flow indicate that the avalanche occurred between about 300 000 and 360 000 yr ago an inferred average thickness of the deposit plus a computed volume of about 4 km 3 for the hills and ridges indicate an estimated volume of about 26 km 3 making it the largest known quaternary landslide on earth

structural mapping of enceladus and implications for formation of tectonized regions global structural mapping of high resolution cassini images of enceladus reveals a richly varied surface most notable are three main regions of deformation each containing multiple structural units in addition to the well known south polar terrain spt there are two other large regions of deformation that we term leading hemisphere terrain lht and trailing hemisphere terrain tht each of these three terrains includes a circumferential belt that encloses one or more other structurally deformed units areal extents range from about 80 000 km2 spt to 195 000 km2 lht or 160 to 250 km equivalent circular radius based on relative crater densities the tht is inferred to be older than the lht the geologically active spt is the youngest the overall similarities in shape and dimension of the three tectonized terrains suggest similar formational processes plausibly related to broad loading of a thin elastic shell a viable scenario is that each tectonized terrain formed above a large scale region of warm upwelling ice with subsequent downwarping triggered by cooling and or subsurface melting however differences in morphological detail suggest that the specific evolution of each tectonized terrain has been different

the 1883 and late prehistoric eruptions of augustine volcano alaska abstract the eruptive history of augustine volcano has been characterized by cycles of growth and destruction of the volcano repeated failure of 5 10 of the edifice has produced mobile debris avalanches that reached the sea on all sides high lava extrusion rates rapidly restore the volcano to its pre failure configuration this equilibrium between constructive and destructive processes has resulted in a relatively low lava dome complex surrounded by an apron of volcaniclastic debris three times the volume of the dome complex the most recent edifice collapse occurred in 1883 producing the 0 3 km3 burr point debris avalanche deposit three major slide blocks extended the shoreline up to 2 km and produced a tsunami that swept across cook inlet hummock morphologies change from a proximal radial orientation to a dominantly transverse alignment reflecting deceleration and compression of the avalanches as they enter the sea the breached crater formed by collapse was then largely filled by a 0 09 km3 lava dome and a 0 04 km3 lava flow travelled down the north flank lithic block and ash flows and pyroclastic surges reached the coast the burr point avalanche deposit partially overlaps the rocky point debris avalanche deposit to the west that was probably emplaced 200 400 years b p a major collapse event at ca 1540 110 a d produced the west island debris avalanche ending a period of expansion of the western side of the island an accompanying lateral blast overtopped the avalanche covering a 40 sector of the west flank the plinian tephra layer b may also have been erupted at the time of the west island eruption today augustine volcano has rebuilt itself to a size similar to that which preceded the last edifice failure in 1883 the frequency of past collapses three in the last 500 years suggests that summit collapse is a possibility during any future eruption the next major collapse is expected to involve 0 1 0 5 km3 of the summit the ensuing debris avalanche would likely reach the coast producing a tsunami that could impact populated areas of the kenai peninsula the largest tsunami would result from collapse in directions other than to the north or west tsunami magnitude is contingent on failure volume direction and timing with respect to tides

grain size evolution and fractionation trends in an experimental regolith the comminution of blocky planetary surfaces into fine grained regoliths was simulated by impacting a fragmental gabbro target 200 times with stainless steel projectiles diameter 6 35 mm mass 1 2g vi 1 35 km s initially the target fragments were 2 32 mm in size with a mean diameter of 15 2 mm which was reduced to 0 4 mm after 200 shots for the first 60 shots comminution was linear with cumulative kinetic energy and thus essentially linear with time the comminution efficiency however decreased at later stages this could be due to a change in fracture mechanism from predominantly intergranular to predominantly intragranular and or due to a change in partitioning of the projectile s kinetic energy from collisional fragmentation or large fragments at early times to cratering in a progressively finer grained medium at later stages mineral specific preferential comminution is abundantly observed in the modal make up of various grain size fractions plagioclase comminutes more readily than pyroxenes plagioclase initially present at 54 vol comprises typically 65 70 of the 125 250 m fraction pyroxenes initially at 33 are depleted to 20 25 this fractionation occurs in the earliest samples analyzed and is not a time dependent phenomenon bulk chemical analyses reveal a corresponding increase in al2o3 cao and na2o and a decrease in feo and mgo the finest grain sizes are generally the most severely affected by differential comminution similar if not exactly identical trends are abundantly documented for lunar soil samples these experimental findings illustrate that differential comminution is capable of producing fractionation in the finest grain sizes they diminish the need for prominent lateral and vertical transport of components otherwise foreign to a lunar soil sampling site as postulated by some workers on the basis of multivariate chemical mixing models

flow of variably fluidized granular masses across three dimensional terrain 1 coulomb mixture theory rock avalanches debris flows and related phenomena consist of grain fluid mixtures that move across three dimensional terrain in all these phenomena the same basic forces govern motion but differing mixture compositions initial conditions and boundary conditions yield varied dynamics and deposits to predict motion of diverse grain fluid masses from initiation to deposition we develop a depth averaged three dimensional mathematical model that accounts explicitly for solid and fluid phase forces and interactions model input consists of initial conditions path topography basal and internal friction angles of solid grains viscosity of pore fluid mixture density and a mixture diffusivity that controls pore pressure dissipation because these properties are constrained by independent measurements the model requires little or no calibration and yields readily testable predictions in the limit of vanishing coulomb friction due to persistent high fluid pressure the model equations describe motion of viscous floods and in the limit of vanishing fluid stress they describe one phase granular avalanches analysis of intermediate phenomena such as debris flows and pyroclastic flows requires use of the full mixture equations which can simulate interaction of high friction surge fronts with more fluid debris that follows special numerical methods described in the companion paper are necessary to solve the full equations but exact analytical solutions of simplified equations provide critical insight an analytical solution for translational motion of a coulomb mixture accelerating from rest and descending a uniform slope demonstrates that steady flow can occur only asymptotically a solution for the asymptotic limit of steady flow in a rectangular channel explains why shear may be concentrated in narrow marginal bands that border a plug of translating debris solutions for static equilibrium of source areas describe conditions of incipient slope instability and other static solutions show that nonuniform distributions of pore fluid pressure produce bluntly tapered vertical profiles at the margins of deposits simplified equations and solutions may apply in additional situations identified by a scaling analysis assessment of dimensionless scaling parameters also reveals that miniature laboratory experiments poorly simulate the dynamics of full scale flows in which fluid effects are significant therefore large geophysical flows can exhibit dynamics not evident at laboratory scales

internal structural variations in a debris avalanche deposit from ancestral mount shasta california usa various parameters of the internal structure of a debris avalanche deposit from ancestral mount shasta size and percentage of block facies in each exposure number and width of jigsaw cracks and number of rounded clasts in matrix facies were measured in order to study flow and emplacement mechanisms three types of coherent blocks were identified blocks of massive or brecciated lava flows or domes blocks of layered volcaniclastic deposits and blocks of accidental material typically from sedimentary units underlying shasta valley the mean maximum dimension of the three largest blocks of layered volcaniclastic material is 220 m and that of the lava blocks 110 m this difference may reflect plastic deformation of blocks of layered volcaniclastic material blocks of massive or brecciated volcanic rock deformated brittly and may have split into several smaller blocks the blocks in the deposit are one order of magnitude larger and the height of collapse 1100 m higher than the pungarehu debris avalanche deposit at mount egmont new zealand although the degree of fracturing is about the same this suggests either that the shasta source material was less broken or that the intensity of any accompanying explosion was smaller at ancestral mount shasta the shasta debris avalanche deposit covered the floor of a closed basin the flanks of the basin may have retarded the opening of jigsaw cracks and the formation of stretched and deformed blocks such as those of the pungarehu debris avalanche deposit

the rain triggered atenquique volcaniclastic debris flow of october 16 1955 at nevado de colima volcano mexico abstract on october 16 1955 at 10 45 a m local time after three days of intense rain 140 mm that was twice the monthly average precipitation a devastating flood surge formed a volcaniclastic debris flow on the eastern slopes of nevado de colima volcano nearly simultaneous flood surges formed in the arroyo seco los platanos and dos volcanes ravines that coalesced with the larger flow in the atenquique ravine at each confluence with a tributary the flow was diluted the texture and structure of the preserved 1955 deposits near high water marks indicate that the downstream flow was mainly in the lower range of debris flow concentration 60 sediment concentration by weight downstream the tributaries the flood encountered a 0 06 10 6 m 3 water reservoir that failed significantly increasing the surge volume additional entrained sediment also increased the flow volume downstream the flood wave reached the town of atenquique as an 8 9 m catastrophic wave causing the death of more than 23 people the partial destruction of the town and losses of 13 000 000 pesos 1 million us dollars today to a paper mill and company facilities according to eyewitness accounts the flood wave had a peak discharge that lasted ca 10 to 15 minutes at atenquique deposits at the site and the high water marks observed from photographs of the town s church indicate that sediment concentration was ca 60 wt the flood continued for about 1 km to its junction with the tuxpan river where it was diluted by mixing with normal flood flow the deposits covered an area of 1 2 km 2 and had a minimum volume of 3 2 10 6 m 3 the main deposit consists of a single unit averaging 4 m in thickness with weak textural variations that suggest surging within the flood wave the deposit is heterolithologic and consists of boulders set in a matrix of sand size sediment with polymodal or bimodal distributions and normal grading varying with distance from source the town of atenquique has been reconstructed largely within the area inundated by the 1955 flood wave thus creating the conditions for a future disaster a rainfall intensity warning system and an educational program for inhabitants are strategies to mitigate this risk

downstream dilution of a lahar transition from debris flow to hyperconcentrated streamflow nearly instantaneous melting of snow and ice by the march 19 1982 eruption of mount st helens released a 4 106 m3 flood of water from the crater that was converted to a lahar volcanic debris flow through erosion and incorporation of sediment by the time it reached the base of the volcano over the next 81 km that it traveled down the toutle river the flood wave was progressively diluted through several mechanisms a transformation from debris flow to hyperconcentrated streamflow began to occur about 27 km downstream from the crater when the total sediment concentration had decreased to about 78 by weight 57 by volume the hyperconcentrated lahar runout flood wave transporting immense quantities of sand in suspension continued to experience progressive downstream dilution although turbulence was significantly dampened by the extremely high suspended load very large standing waves and antidune waves were observed the hyperconcentrated lahar runout flow deposited an unusual faintly stratified coarse sand which locally contained small isolated gravel lenses very similar deposits in the quaternary stratigraphy of mount st helens and other cascades volcanoes suggest that lahars may be more frequent than previously recognized

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

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

ongoing hydrothermal activities within enceladus analysis of silicon rich nanometre sized dust particles near saturn shows them to consist of silica which was initially embedded in icy grains emitted from enceladus subsurface waters and released by sputter erosion in saturn s e ring their properties indicate their ongoing formation and transport by high temperature hydrothermal reactions from the ocean floor and up into the plume of enceladus hsiang wen hsu et al have analysed the silicon rich nanometre sized dust stream particles in the saturnian system using the cosmic dust analyser cda onboard the cassini spacecraft with the help of experiments and modelling the particles are interpreted as silica grains that were initially embedded in the icy plume emitted from subsurface waters on enceladus and released by sputter erosion in saturn s e ring their properties indicate their formation and transport by high temperature hydrothermal reactions from the ocean floor and up into the plume of enceladus detection of sodium salt rich ice grains emitted from the plume of the saturnian moon enceladus suggests that the grains formed as frozen droplets from a liquid water reservoir that is or has been in contact with rock1 2 gravitational field measurements suggest a regional south polar subsurface ocean of about 10 kilometres thickness located beneath an ice crust 30 to 40 kilometres thick3 these findings imply rock water interactions in regions surrounding the core of enceladus the resulting chemical footprints are expected to be preserved in the liquid and subsequently transported upwards to the near surface plume sources where they eventually would be ejected and could be measured by a spacecraft4 here we report an analysis of silicon rich nanometre sized dust particles5 6 7 8 so called stream particles that stand out from the water ice dominated objects characteristic of saturn we interpret these grains as nanometre sized sio2 silica particles initially embedded in icy grains emitted from enceladus subsurface waters and released by sputter erosion in saturn s e ring the composition and the limited size range 2 to 8 nanometres in radius of stream particles indicate ongoing high temperature 90 c hydrothermal reactions associated with global scale geothermal activity that quickly transports hydrothermal products from the ocean floor at a depth of at least 40 kilometres up to the plume of enceladus

is io s mantle really molten abstract the tremendous heating dissipated by jovian tides in io s interior is essentially evacuated by an intense volcanic activity so that the heat is removed from the interior to the surface much more by advection than by conduction through the lithosphere the efficiency of this heat pipe cooling process is investigated through numerical models of convection performed in spherical geometry with a permeable top boundary this new heat transfer model provides a cooling twice as efficient as that obtained with an impermeable condition traditionally used in mantle convection modeling the globally averaged temperature varies as ra 1 2 where ra is the rayleigh number whereas the power law exponent is classically 1 4 so that the expected ra would not be in excess of 10 7 if the whole mantle of io is involved in the convection process the major portion could remain solid while a possible molten zone could be confined to a 100 km thick layer between the solid part and the core this model predicts the existence of a strong lithosphere which is required to support the observed topographic amplitude of the io s relief

keeping enceladus warm abstract despite its small size enceladus emits considerable heat especially at its south pole even long after simple thermal models predict it should be frozen several sources of energy have been proposed as responsible for this heating such as tidal dissipative heating tdh convection and shearing in the ice shell and exothermic chemical reactions e g serpentine formation crater relaxation simulations suggest that episodic heating events have occurred over long stretches of enceladus history thermal history and hydrothermal simulations reported here show that a combination of steady plus episodic tdh heating could maintain at least a polar ocean to the present time hydrothermal circulation can play a significant role in mining enceladus internal heat facilitating the persistence of an ocean even to the present by focusing internal heat to the polar regions

ocean worlds in the outer solar system many outer solar system bodies are thought to harbor liquid water oceans beneath their ice shells this article first reviews how such oceans are detected we then discuss how they are maintained when they formed and what the oceans likely characteristics are we focus in particular on europa ganymede callisto titan and enceladus bodies for which there is direct evidence of subsurface oceans we also consider candidate ocean worlds such as pluto and triton

textural analysis of particles from el zaguan debris avalanche deposit nevado de toluca volcano mexico evidence of flow behavior during emplacement abstract el zaguan deposit originated at 28 000 yrs b p from the flank collapse of nevado de toluca a dacitic stratovolcano of the transmexican volcanic belt scanning electron microprobe analyses sem were performed on some particles from this deposit to observe microtextures produced during transport and emplacement of the debris avalanche flow particles from 2 250 m 0 1 mm and 2 4 mm granulometric classes were randomly selected at different outcrops and their surface textures were described the observed textures are divided in two groups basal and upper textures each one indicating different clast interactions basal textures are observed predominantly in the lower part of the deposit and consist of parallel ridges parallel grooves scratches and lips upper textures are mainly present in the upper part of the deposit and consisted of fractures percussion marks and broken or grinded crystals these characteristics coupled with field observations such as the presence of clastic dikes and deformed lacustrine mega blocks indicate that the basal part of the debris avalanche was moving in a partially liquefied state by contrast the particles in the upper part were able to move freely interacting by collision these microscopic textures are in agreement with previously described emplacement behaviors in debris avalanches of volcanic origin suggesting a stratified flow dominated by different transport and depositional mechanisms depending upon flow depth and possible fluid content at their base