source process of very long period events accompanying long period signals at cotopaxi volcano ecuador abstract renewed seismic activity of cotopaxi ecuador began in january 2001 with the increased number of long period lp events followed by a swarm of volcano tectonic vt earthquakes in november 2001 in late june 2002 the activity of very long period vlp 2 s events accompanying lp 0 5 1 s signals began beneath the volcano the vlp waveform was characterized by an impulsive signature which was accompanied by the lp signal showing non harmonic oscillations we observed temporal changes of both the vlp and lp signals from the beginning until september 2003 the vlp signal gradually disappeared and the lp signal characterized by decaying harmonic oscillations became dominant assuming possible source geometries we applied a waveform inversion method to the observed waveforms of the largest vlp event our inversion and particle motion analyses point to volumetric changes of a sub vertical crack as the vlp source which is located at a depth of 2 3 km beneath the northeastern flank the spectral analysis of the decaying harmonic oscillations of lp events shows frequencies between 2 0 and 3 5 hz with quality factors significantly above 100 the increased vt activity and deformation data suggest an intrusion of magma beneath the volcano a release of gases with small magma particles may have repetitively occurred due to the pressurization which was caused by sustained bubble growth at the magma ceiling the released particle laden gases opened a crack above the magma system and triggered the resonance of the crack we interpret the vlp and lp events as the gas release process and the resonance of the crack respectively

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

aragonite crystal fans in neoproterozoic cap carbonates a case study from brazil and implications for the post snowball earth coastal environment abstract neoproterozoic cap carbonates are characterized by anomalous sedimentary features including sea floor precipitates represented by aragonite pseudomorph cement crusts and crystal fans these features are found in restricted periods of geological history and their generation in the context of the neoproterozoic has been attributed to very specific postglacial conditions leading to alkalinity oversaturation new sedimentary and geochemical results on well preserved neoproterozoic deposits of aragonite pseudomorph crystal fans at the base of the sete lagoas formation bambui group central brazil are reported the micrite settling facies shows the highest abundance of crystal fans arranged in centimeter scale layers interfingered with the micrite matrix this facies is interpreted as a result of postglacial calcium carbonate oversaturation in restricted areas characterized by marine dysoxic waters a numerical model constrains the kinetics of formation of aragonite crystals or micrite by calculating the induction times and precipitation rates of both carbonate species for postglacial conditions of elevated temperature and high atmospheric pco2 in these conditions the mg ca ratio of the neoproterozoic seawater is calculated at ca 1 2 alkalinity oversaturation is monitored by a variable evaporation degree aragonite formation is kinetically favored and the discrepancy between calcite and aragonite precipitation rate is greater as atmospheric pco2 hence alkalinity is higher these modeling conditions do not preclude the contribution of incomplete organic matter degradation to alkalinity as suggested by negative carbon isotope signatures in addition the large number of aragonite micrite pairs suggests a seasonal or paleoclimatic forcing other cases of abiotic aragonite precipitation through time are also briefly examined by comparison

structure and emplacement of the pliocene roque nublo debris avalanche deposit gran canaria spain abstract collapse of the flanks of the pliocene roque nublo stratocone on gran canaria lead to large debris avalanches that traveled far beyond the coastline with velocities that may have exceeded 100 m s the deposits comprised at least 14 km 3 of debris and covered an area of about 180 km 2 in the southern half of the island the debris filled deep canyons are largely exhumed at present incomplete disintegration poor fluidization and a good preservation of megablocks are thought to be mainly due to the confinement of the debris avalanche within deep canyons the rheological behavior of lithologic domains varies with their size internal strength and relative position within the deposit the deformation structures indicate that distinct components flowed whereas others slid throughout the transport in a relatively dense mode the following factors are believed to have been important in generating the roque nublo debris avalanche deposit 1 unusual abundance of pyroclastic flow and other volcaniclastic deposits making up the upper roque nublo cone 2 highly asymmetric basement beneath the cone with a very high southern ridge and a steep erosional southern slope leading to major instabilities 3 intrusion of dikes and cryptodomes as well as hydrothermal alteration in the crater area further weakening the volcano

structural analysis of the early stages of catastrophic stratovolcano flank collapse using analogue models many major volcanic flank collapses involve the failure of low angle strata in or under the edifice such failures produce voluminous destructive debris avalanches that are a major volcanic hazard at socompa las isletas mombacho and parinacota volcanoes field studies have shown that during catastrophic flank collapse a significant segment of their substrata was detached and expelled from beneath the volcanic edifice and formed a mobile basal layer on which the sliding flanks were transported previous studies have proposed that gravitational flank spreading was likely involved in the onset of sudden substrata failure the early stages of this particular type of flank collapse can be modelled under laboratory conditions using analogue models this allows us to study the development of structures accommodating early deformation of the sliding flank during catastrophic collapse in the experiments the detached substratum segment low viscosity basal layer was modelled with a silicone layer and the overlying stratovolcano with a layered sand cone the first structure developed in the models is a graben rooted in the low viscosity basal layer this graben forms the limits of the future avalanche amphitheatre and divides the sliding flank into a toreva domain upper sliding flank and a hummock domain lower sliding flank these domains display distinctive structural patterns and kinetic behaviour normal faults develop in the toreva domain and inside the graben while the hummock domain is characterised by transtensional structures the hummock domain also over thrusts the lower amphitheatre sides which allows subsequent sideways avalanche spreading measurements show that horizontal speeds of the hummock domain are always higher than that of the toreva domain during model collapse the main role played by the low viscosity basal layer during this type of collapse is to control the size shape and structural complexity of the sliding flank it also transmits mass and momentum from the toreva to the hummock domain

quilotoa volcano ecuador an overview of young dacitic volcanism in a lake filled caldera abstract quilotoa volcano an example of young dacitic volcanism in a lake filled caldera is found at the southwest end of the ecuador s volcanic front it has had a long series of powerful plinian eruptions of moderate to large size vei 4 6 at repetitive intervals of roughly 10 15 thousand years at least eight eruptive cycles labeled q i to q viii with increasing age over the past 200 ka are recognized often beginning with a phreatomagmatic onset and followed by a pumice rich lapilli fall and then a sequence of pumice crystal and lithic rich deposits belonging to surges and ash flows these unwelded pyroclastic flows left veneers on hillsides as well as very thick accumulations in the surrounding valleys the farthest ash flow having traveled about 17 km down the toachi valley the bulk volumes of the youngest flow deposits are on the order of 5 km 3 but that of q i s 800 yr bp ash fall unit is about 18 km 3 in the last two eruption cycles water has had a more important role upon quilotoa s low relief volcanic edifice three calderas are recognized the formation of the oldest one predates the q iv cycle and the others occurred during the q ii and q i cycles dacite lava domes are common along the present caldera rim and most were emplaced at the end of the q ii cycle older domes of dark dacite belong to the q iii and iv cycles the explosive onset of the q i cycle expulsed as much as 250 million m 3 of the lake s water resulting in large debris flows that scoured the eastern flanks of the edifice and descended the toachi river little variation in the mineralogy and chemistry of quilotoa s eruptive products is observed suggesting that the source is a homogeneous magma body at shallow depth both the pyroclastic material and the domes are composed chiefly of gray porphyritic dacites carrying large phenocrysts of plagioclase amphibole biotite and occasionally quartz

physical models of rock avalanche spreading behaviour with dynamic fragmentation the dynamic fragmentation of rock during avalanche motion has been postulated as a mechanism explaining the long runout of large rock avalanches or sturzstrome this paper investigates whether test

obliquity tides do not significantly heat enceladus recently tyler tyler r h 2009 geophys res lett 36 l15205 tyler r 2011 icarus 211 770 779 proposed that the tide due to an obliquity of greater than 0 1 might drive resonant flow in a liquid ocean at enceladus and that dissipation of the ocean s kinetic energy may be an alternate source for the observed global heat flux while there is currently no measurement of enceladus obliquity dissipation is expected to drive the spin pole to a cassini state under this assumption we find that enceladus should occupy cassini state 1 and that the obliquity of enceladus should be less than 0 0015 for values of the degree 2 gravity coefficient c2 2 between 1 0 10 3 and 2 5 10 3 unless there is a

geological and geotechnical characterization of the debris avalanche and pyroclastic deposits of cotopaxi volcano ecuador a contribute to instability related hazard studies abstract the huge volcanic debris avalanche occurred at 4 5 ka is a major event in the evolution of the cotopaxi volcano ecuador the present volcanic hazard in the cotopaxi region is related to lahars generated by volcanic eruptions and concurrent ice melting this paper presents the geological and geotechnical field and laboratory characterization of the 4 5 ka cotopaxi debris avalanche deposit and of the younger unconsolidated pyroclastic deposits representing the probable source of future shallow landslides the debris avalanche formed a deposit with a well developed hummocky topography and climbed a difference in height of about 260 m along the slopes of the adjacent sincholagua volcano the debris avalanche deposit includes four lithofacies megablock block mixed and sheared facies that represent different flow regimes and degrees of substratum involvement the facies distribution suggests that in the proximal area the debris avalanche slid predominantly confined to the valleys along the n and ne flank of the volcanic cone emplacing a stack of megablocks when the flow reached the break in slope at the base of the edifice it became unconfined and spread laterally over most of the area of the rio pita valley a dynamic block fragmentation and dilation occurred during the debris avalanche transport emplacing the block facies the incorporation of the older chalupas ignimbrite is responsible for the mixed facies and the sheared facies geotechnical results include a full range grain size characterization which enabled to make broader considerations on possible variability among the sampled facies consolidated drained triaxial compression tests carried out on the fine fraction the investigated post 4 5 pyroclastic deposits constitute a 5 12 m thick sequence of poorly consolidated materials that are interlayered with lava flows their geotechnical analyses have evidenced a strong variability in grain size distribution reflecting the depositional processes and a generally high porosity consolidated drained triaxial compression tests delineated a similar shear stress strain behaviour among the different units where shear strength is only due to friction angle failure surfaces are always well developed indicating that the poorly consolidated pyroclastic cover could undergo failure leading to the formation of a gravity driven instability phenomena like granular or debris flows which are mainly controlled by the fine fraction this work underlies the general necessity for a site specific and interdisciplinary approach in the characterization of volcanic successions to provide reliable data for gravitational instability studies

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

lahar hazard assessment in the southern drainage system of cotopaxi volcano ecuador results from multiscale lahar simulations abstract the ice capped cotopaxi volcano is known worldwide for the large scale catastrophic lahars that have occurred in connection with historical explosive eruptions the most recent large scale lahar event occurred in 1877 when scoria flows partially melted ice and snow of the summit glacier generating debris flows that severely impacted all the river valleys originating from the volcano the 1877 lahars have been considered in the recent years as a maximum expected event to define the hazard associated to lahar generation at cotopaxi conversely recent field based studies have shown that such debris flows have occurred several times during the last 800 years of activity at cotopaxi and that the scale of lahars has been variable including events much larger than that of 1877 despite a rapid retreat of the summit ice cap over the past century in fact there are no data clearly suggesting that future events will be smaller than those observed in the deposits of the last 800 years of activity in addition geological field data prove that the lahar triggering mechanism also has to be considered as a key input parameter and under appropriate eruptive mechanisms a hazard scenario of a lahar with a volume 3 times larger than the 1877 event is likely in order to analyze the impact scenarios in the southern drainage system of the volcano simulations of inundation areas were performed with a semi empirical model laharz using input parameters including variable water volume results indicate that a lahar 3 times larger than the 1877 event would invade much wider areas than those flooded by the 1877 lahars along the southern valley system eventually impacting highly urbanized areas such as the city of latacunga

rock mass strength and slope stability of the hilina slump kīlauea volcano hawai i abstract stability of the hilina slump on the south flank of k lauea volcano hawai i is investigated using slope stability analyses based on rock mass mechanics the hilina slump is an active example of the giant landslides that are observed around submarine flanks of ocean island volcanoes based on edifice topology along with derived rock mass strength and deformability parameters slope stability analyses predict that the geometries of present day failure surfaces of the hilina slump are shallow located at less than 3 5 km depth below the upper surface of the edifice the failure surfaces at the base of the hilina slump are predicted to be structurally independent from a previously interpreted subjacent detachment at the contact between the k lauea edifice and the oceanic crust based on these model results the hilina slump is envisioned to ride atop the south flank of k lauea as it spreads seaward along this slipping basal detachment under present day slope and sea level configurations local horizontal ground accelerations greater than 0 4 0 6 g are predicted to cause slip along failure surfaces within hilina slump therefore dynamic stress changes due to slip along the subjacent detachment may potentially trigger slip along failure surfaces of the hilina slump model derived stability and failure surface geometries can account for the distinct observed distribution of slip along specific hilina faults following the m fa 7 9 1868 ka u and m s 7 2 1974 kalapana earthquakes further the spatial distribution of south flank aftershocks m 1 5 recorded between 1950 and 1976 are consistent with the predicted distribution of potential earthquake induced slip of the hilina faults

sequencing events across the permian triassic boundary guryul ravine kashmir india abstract the permian triassic boundary ptb section at guryul ravine kashmir india comprises a 100 m thick apparently conformable succession of mixed siliciclastic carbonate sediments deposited in a deep shelf or ramp setting this section although long important in debates concerning placement of the ptb has not previously been the focus of an integrated chemostratigraphic study in the present study samples from a 20 m thick interval straddling the ptb were analyzed for major and trace element concentrations toc tic rees and organic 13c 15n to investigate contemporaneous environmental changes the guryul ravine section exhibits a sequence of discrete events that provide potentially important information about the character and cause s of the ptb two transient negative c isotopic excursions within the upper changxingensis zone predate the late permian event horizon lpeh i e the global mass extinction event by 200 400 kyr and are associated with the onset of a major eustatic rise and with secondary extinction peaks these excursions may record minor environmental disturbances prior to the main end permian crisis supporting an intrinsic mechanism such as volcanism and climate change rather than an extrinsic mechanism such as a bolide impact the onset of a large 4 0 to 4 5 sustained negative c isotope shift marks the lpeh which is located at the zewan khunamuh formation contact 260 cm below the biostratigraphically defined ptb the guryul ravine section exhibits a stepwise extinction pattern with the largest peak between the lpeh and ptb and a secondary peak just above the ptb a pattern similar to that observed in the meishan d gssp

stromatolites of the lower triassic union wash formation ca evidence for continued post extinction environmental stress in western north america through the spathian abstract recent studies have documented the complexity of biotic recovery from the permian triassic mass extinction by revealing that recovery began quickly in some regions while the biota in other areas continued to suffer as the result of widespread harsh environmental conditions throughout much of the early triassic period examination of lower triassic rocks from the southwestern u s has produced a variety of sedimentologic and biotic evidence that point to persistent environmental stress following the extinction specifically anoxic alkaline waters in the deep ocean and possible high carbon dioxide levels in the surface ocean and have also documented trends in the long suffering biota present in that region the shoaling facies of the upper member of the union wash formation at the cerro gordo ca usa locality contain stratiform stromatolites that suggest harsh environmental conditions in the area may have lingered until the late spathian latest early triassic the stromatolites are laterally extensive some layers persist for at least 1 km and typically exhibit planar to wavy laminations with some development of small domes up to 10 cm in height a shallow subtidal depositional environment is suggested by evidence of eroded or planed surfaces within the stromatolites as well as channelization of the stromatolites and the occurrence of ooids and coated grains within the interval the stromatolites documented here occur stratigraphically higher than previously documented inorganic calcium carbonate precipitates from the union wash formation e g woods a d bottjer d j corsetti f a 2007 calcium carbonate seafloor precipitates from the outer shelf to slope facies of the lower triassic smithian spathian union wash formation california u s a sedimentology and palaeobiologic significance palaeogeography palaeoclimatology palaeoecology 252 281 290 woods a d bottjer d j mutti m morrison j 1999 lower triassic large seafloor carbonate cements their origin and a mechanism for the prolonged biotic recovery from the end permian mass extinction geology 27 645 648 and microbialites from the virgin limestone e g schubert j k bottjer d j 1992 early triassic stromatolites as post mass extinction disaster forms geology 20 883 886 pruss s b bottjer d j 2004 late early triassic microbial reefs of the western united states a description and model for their deposition in the aftermath of the end permian mass extinction palaeogeography palaeoclimatology palaeoecology 211 127 137 therefore these stromatolites may represent the last known occurrence of anachronistic facies and associated unusual palaeoceanographic conditions in eastern panthalassa following the permian triassic mass extinction

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

tidal heating in icy satellite oceans abstract tidal heating plays a significant role in the evolution of many satellites in the outer solar system however it is unclear whether tidal dissipation in a global liquid ocean can represent a significant additional heat source tyler tyler r h 2008 nature 456 770 772 tyler r h 2009 geophys res lett 36 doi 10 1029 2009gl038300 suggested that obliquity tides could drive large scale flow in the oceans of europa and enceladus leading to significant heating a critical unknown in this previous work is what the tidal quality factor q of such an ocean should be the corresponding tidal dissipation spans orders of magnitude depending on the value of q assumed to address this issue we adopt an approach employed in terrestrial ocean modeling where a significant portion of tidal dissipation arises due to bottom drag with the drag coefficient o 0 001 being relatively well established from numerical solutions to the shallow water equations including nonlinear bottom drag we obtain scalings for the equivalent value of q as a function of this drag coefficient in addition we provide new scaling relations appropriate for the inclusion of ocean tidal heating in thermal orbital evolution models our approach is appropriate for situations in which the ocean bottom topography is much smaller than the ocean thickness using these novel scalings we calculate the ocean contribution to the overall thermal energy budgets for many of the outer solar system satellites although uncertainties such as ocean thickness and satellite obliquity remain we find that for most satellites it is unlikely that ocean tidal dissipation is important when compared to either radiogenic or solid body tidal heating of known satellites triton is the most likely icy satellite to have ocean tidal heating play a role in its present day thermal budget and long term thermal evolution

estimating volcanic deformation source parameters with a finite element inversion the 2001 2002 unrest at cotopaxi volcano ecuador deformation at cotopaxi was observed between 2001 and 2002 along with recorded seismicity beneath the northeast ne flank despite the fact that the last eruption occurred in 1942 we use electronic distance meter deformation data along with the patterns of recorded seismicity to constrain the cause of this unrest episode to solve for the optimum deformation source parameters we employ inverse finite element fe models that account for material heterogeneities and surface topography for a range of source shapes the models converge on a shallow reservoir beneath the southwest sw flank the individual best fit model is a small oblate shaped source approximately 4 5 km beneath the summit with a volume increase of roughly 20 10 6 m 3 this sw source location contrasts with the ne seismicity locations subsequently further fe models that additionally account for temperature dependent viscoelasticity are used to reconcile the deformation and seismicity simultaneously comparisons of elastic and viscous timescales allude to aseismic pressurization of a small magma reservoir in the sw seismicity in the ne is then explained through a mechanism of fluid migration from the sw to the ne along fault systems we extend our analyses to further show that if future unrest crises are accompanied by measurable seismicity around the deformation source this could indicate a higher magma supply rate and increased likelihood of a forthcoming eruption

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

volcanic rock mass properties from snowdonia and tenerife implications for volcano edifice strength although volcano instability is increasingly recognized as a societal hazard numerical data on the relevant mechanical properties remain sparse we report new field data on the rock mass properties of volcanic materials from snowdonia north wales uk and tenerife canary islands using rock types that range in composition from phonolite to rhyolite we summarize a method for estimating the overall strength of a volcanic edifice based on the rock mass rating index rmr and the hoek brown criterion we show that the average rock mass compressive cm and cohesive c strengths decrease exponentially with rmr according to cm 0 652 0 0559rmr and c 0 035 0 0669rmr respectively and appear insensitive to both initial magma composition and relative age this exponential relationship provides a new predictive tool for directly estimating rock mass strength from the rmr our analysis further predicts a marked reduction of up to 96 in the rock mass compressive strength relative to the intact rock value based on laboratory tests and that overall the combined results from both study areas yield cohesive strength values from 4 8 to 0 44 mpa estimated values of rock mass angle of friction range from 28 to c 38 recent modifications to the hoek brown criterion in particular the inclusion of the disturbance factor d suggest that even these low values of rock mass strength and cohesion may be optimistic and the true values of rock parameters relevant for accurate predictions of volcano edifice strength may be up to 30 weaker still

enceladus s ice shell structure as a window on internal heat production abstract its extraordinary level of geologic activity its potential for habitability and the prospects of returning samples from its plume of erupting water ice make saturn s small 500 km diameter moon enceladus a high priority target for future exploration and a key to our developing understanding of icy ocean worlds the structure of its outer ice shell is particularly important as it relates to the global heat budget the global scale response to tidal forces and the nature of the ongoing eruptions it is also diagnostic of how and where heat is dissipated internally here using the most recent shape model and a new approach to modeling isostasy we obtain a shell structure that simultaneously accommodates the shape gravity and libration observations and suggests that tidal dissipation near the base of the ice shell is likely an important mode of internal heating the implied conductive heat loss is greater than the heat loss associated with the eruptions but is nevertheless compatible with the condition of steady state

textural features as indicators of debris avalanche transport and emplacement taranaki volcano the pungarehu debris avalanche deposit was emplaced by the largest known collapse of the proto taranaki volcano ca 25 000 calibrated cal years ago this debris avalanche deposit displays a highly contrasting sedimentary character between its proximal and distal reaches examination of the deposit granulometry sedimentary structures and microscopic particle attributes provides new insights into debris avalanche transport and internal evolution processes initial collapse of the proto taranaki volcano during this event occurred near the last glacial maximum with snow and ice cover and substantial groundwater present the collapsing sliding large blocks of edifice material megaclasts were highly fractured by the landslide generation and the depressurization event forming pervasive jigsaw textures as the megaclasts moved shear was focused in softer domains between the hardest lava dominated lithologies these crush and shear zones developed a complex pattern of relative motion between horizontal and vertical parts of the landslide rather than a simple basal shear zone that supported an upper pluglike mass the sheared zones concentrated in soft pyroclastic lithologies were areas of intense synflow fragmentation producing a proto interclast matrix between large blocks of coherent albeit jigsaw fractured lavas down flow the interclast matrix component increased to become pervasive by 23 25 km from the source enveloping and preserving large megaclasts out to at least 30 km the most distal exposures limited by coastal erosion to 25 27 km show that the matrix was not completely water saturated with only superficial penetration of the sand dominated material into the margins of fractured lava domains which still contained central void space evidence of multiple generations of particle fracturing is seen under scanning electron microscopy of sand grade clasts with initial decompression fractures crosscut by later cracks pits and scratches produced by collisional and frictional processes during transport the findings from this study help to explain the formation of the highly irregular topography of debris avalanche deposits with chaotically distributed and probably temporary zones of shear developing where softer lithologies occur in a collapsing mass thus leading to differential velocity profiles of portions of the flowing mass in vertical and horizontal planes

stability assessment of the crater lake te wai ā moe overflow channel at mt ruapehu new zealand and implications for volcanic lake break out triggers abstract the presence of lakes on active volcanoes gives rise to several unique volcano hydrologic hazards including those directly related to volcanic activity e g phreatic explosions and non volcanic phenomena e g lake outbursts mt ruapehu volcano hosts the 107 m3 crater lake te wai moe in the active summit crater making it prone to lahars due to the abundance of water stored at high elevation apart from eruptive periods when water is commonly ejected from the lake large lahar events can occur when portions of the crater rim fail during quiescent periods leading to partial lake drainage the latter occurred recently in 1953 and 2007 here we investigate the potential of future lahars due to rim failure at the current overflow channel considering several triggering scenarios during non eruptive periods the geomechanical properties of a matrix dominated breccia unit composing part of the overflow channel were analyzed using physical and mechanical laboratory methods these properties combined with previous geomechanical studies of lava units in the overflow channel were used in finite element and limit equilibrium method based groundwater and stability models groundwater models indicate that a low permeability barrier inside the crater rim is preventing water from seeping through the unconsolidated and potentially permeable breccia unit of the overflow channel the removal of this barrier or weathering of a resistive lava cap could cause water to seep through the overflow channel elevating the potential of collapse slope stability models indicate that under certain conditions the overflow channel is below a conservative threshold of stability and can be destabilized with continued mechanical or chemical weathering that reduces strength properties this is also true during high magnitude tectonic or volcanic earthquakes where large ground accelerations could result in several centimeters of displacement at the overflow channel corresponding to high hazard categories of stability in the worst case scenario modeled here full collapse of the overflow channel could result in the release of c 2 4 million m3 of lake water this could drive a lahar substantially larger than well documented historic events including the more common lahars produced during eruptions the identification of key factors affecting stability can be used to inform future monitoring and the risk of these high impact events

rock avalanche elements of the shadow valley basin eastern mojave desert california processes and problems abstract an impressive record of mass wasting is preserved in the shadow valley basin california chiefly rock avalanche breccias and gravity driven glide blocks the rock avalanche breccias show commonly described features including penetrative fragmentation and preserved stratigraphy inherited from their source terrane basal contacts may have substantial 5 60 m relief and a well developed mixed zone a variety of transport indicators show predominant transport from an eastern source to a western depositional site across a variety of facies structural reconstructions suggest that shadow valley rock avalanches had unusually long run outs that are not obviously due to variations in substrate drop height or mechanism of avalanche initiation many features observed in the shadow valley rock avalanche breccias demonstrate significant internal and basal shear as well as a prolonged interaction with depositional substrate as such the basal contacts were not frictionless and basal shear stresses probably were transmitted through the breccia mass during transport if so then many common features of megabreccia deposits including long run out inherited stratigraphy and crackle or jigsaw textures may be consistent with intergranular actions and collisions granular mechanics may be sufficient to produce long run out and these other features suggesting that no special mechanism is required to produce shadow valley type deposits recent two dimensional numerical models and new observations of the physics of granular m dia support this conclusion

coupled δ44 40ca δ88 86sr and 87sr 86sr geochemistry across the end permian mass extinction event abstract we report high resolution high precision 44 40ca 88 86sr and 87sr 86sr records spanning the permian triassic boundary ptb from the meishan and dajiang carbonate successions in south china the goal of the study was to understand the behavior of ca and sr isotopes during a time period in earth history characterized by severe biological and environmental perturbations including a major mass extinction flood basalt volcanism ocean acidification and sea level fluctuations dajiang displays negative 44 40ca and 88 86sr excursions and invariant 87sr 86sr ratios in the

enceladus s and dione s floating ice shells supported by minimum stress isostasy enceladus gravity and shape have been explained in terms of a thick isostatic ice shell floating on a global ocean in contradiction of the thin shell implied by librations here we propose a new isostatic model minimizing crustal deviatoric stress and demonstrate that gravity and shape data predict a 38 4km thick ocean beneath a 23 4km thick shell agreeing with but independent from libration data isostatic and tidal stresses are comparable in magnitude south polar crust is only 7 4km thick facilitating the opening of water conduits and enhancing tidal dissipation through stress concentration enceladus resonant companion dione is in a similar state of minimum stress isostasy its gravity and shape can be explained in terms of a 99 23km thick isostatic shell overlying a 65 30km thick global ocean thus providing the first clear evidence for a present day ocean within dione

the shiveluch volcanic eruption of 12 november 1964 explosive eruption provoked by failure of the edifice abstract restudy of deposits at shiveluch in comparison with other data has shown that the sequence of eruptive events at shiveluch volcano on 12 november 1964 was the following edifice failure involving 1 154 km3 of material at 07 07 a m phreatic explosion with ejection of resurgent ash with a volume of 0 01 km3 plinian activity between 07 20 and 07 47 a m during which andesitic juvenile tephra with a volume of 0 3 km3 erupted during the final stage of the eruption between 07 47 and 08 22 a m pyroclastic flows with a volume of 0 3 0 5 km3 were erupted in this sequence there was no catastrophic directed blast with generation of a destructive pyroclastic density current like those that took place at bezymianny volcano in 1956 and at mount st helens in 1980 the absence of a directed blast is attributed to the fact that the 1964 eruption occurred before magma had enough time to intrude into the edifice and build a cryptodome the failure of the edifice depressurized only a hydrothermal system that existed around the old domes this appears to have been insufficient for the generation of a catastrophic directed blast the case history of volcanic activity at shiveluch before 1964 suggests that if the edifice of the young shiveluch had been stronger and had not failed by landsliding the eruption of 1964 might have consisted of prolonged dome extrusion with relatively weak explosive activity

comment on permian triassic boundary interval in the abadeh section of iran with implications for mass extinction part 1 sedimentology by e heydari j hassanzadeh w j wade and a m ghazi palaeogeography palaeoclimatology palaeoecology 193 405 424 2003 b

tidal dynamical considerations constrain the state of an ocean on enceladus abstract in previous work solutions to the non dissipative laplace tidal equations lte were used to provide bounds on the heat generated by the response of a subsurface ocean on enceladus to an obliquity component of tidal forces here we improve these bounds using solutions from the lte with a generic dissipation term explicitly added we find solutions for a wider range of ocean tidal responses that include both unstratified barotropic and stratified baroclinic flow responses to obliquity as well as eccentricity components of the tidal forces we consolidate the results in three ocean tidal scenarios on enceladus that can explain the high heat fluxes 7 mw m 2 globally averaged inferred from measurements by the cassini spacecraft 1 a deep 1 50 km barotropic ocean responding to obliquity tidal forces where obliquity is at least 0 1 2 a shallow 360 m barotropic ocean responding to eccentricity tidal forces 3 a stratified baroclinic ocean responding to eccentricity tidal forces where the density weighted equivalent depth typically much smaller than the ocean s physical depth is near 360 m the ocean is assumed to be global but extensions for a semi global case are also described a more general result which is independent of the specific scenarios proposed is that an ocean attempting to freeze with an associated decrease in its liquid depth which affects the ocean s dynamical response to the tidal forcing must first pass through resonant configurations with a greatly increased generation of ocean tidal heat exceeding 1 w m 2 to 1 kw m 2 that would act to halt further freezing and stagnate the ocean state in this configuration so long as there is still orbital energy to provide the tidal forces with an additional assumption that the ocean has evolved from a more energetic state where the depth of the liquid ocean was greater we obtain the three scenarios proposed

geochemical evidence from bio apatite for multiple oceanic anoxic events during permian triassic transition and the link with end permian extinction and recovery abstract a detailed 20 myr redox history of permian to triassic oceans changhsingian to carnian stages has been constructed using ce anomaly ce and th u ratios from conodont albid crown apatite material the results show that the well established phenomenon of intense ocean anoxia coincident with the end permian mass extinction is faithfully recorded in conodont ce and th u data extending this conodont redox record shows that end permian anoxia persisted possibly into the earliest dienerian stage and that two intense oceanic anoxic events also occurred later in the early triassic earliest smithian earliest spathian and middle spathian followed by a weaker manifestation of anoxia in the anisian stage seen in ce data marine benthic radiation following the end permian mass extinction began after the smithian earliest spathian anoxic event suggesting a suppression of evolution prior to this due to these inimical conditions the failure of the middle spathian anoxic event to retard the evolutionary rebound implies shallow shelf seas remained well ventilated at this time even if the oceans did not other attributes of the early triassic record also closely coincide with redox fluctuations phases of anoxia intensification saw the proliferation of microbial carbonates and major negative carbon isotope swings that can be attributed to chemocline shallowing causing alkalinity pulses and enrichment in light remineralised carbon and or indicate a trigger meachnaims related to increased fluxes of light c from siberian volcanic sources

the attenuation rates of ocean waves in the marginal ice zone during field operations in the greenland and bering seas in 1978 1979 and 1983 a number of experiments were carried out in which wave energy was measured along a line of stations running from the open sea deep into an icefield wave buoys in the water and accelerometer packages on floes were the instruments employed with airborne vertical photography to supply information on floe size distribution it was found that the decay of waves is exponential with a decay coefficient which generally increases with frequency except for a roll over at the highest frequencies the observations can be fitted reasonably well to a theory of one dimensional scattering

nonlinear tidal dissipation in the subsurface oceans of enceladus and other icy satellites abstract subsurface ocean tides act as a mechanism to dissipate tidal energy in icy satellite interiors we numerically model the effect of an ice shell on ocean tides using non linear bottom drag for the first time we demonstrate that subsurface oceans experience tidal pressurization due to the confining nature of the ice shell and find that enceladus eccentricity forcing can generate up to 2 2 kpa of pressure excess at the ocean surface existing free surface oceanic energy dissipation scaling laws are extended to subsurface oceans and are benchmarked against our numerical results to within 10 we show that for the large bodies ganymede europa and titan an ice shell increases eccentricity tidal heating due to self gravity whereas the shell s suppressive mechanical forcing reduces eccentricity tide dissipation on enceladus and dione by several orders of magnitude due to their high effective rigidities in contrast the ice shell enhances obliquity forced dissipation in all satellites investigated except triton because the largely divergence free ocean response is unaffected by the shell s rigidity but is still enhanced by self gravity we conclude that the fundamental difference in ocean response to obliquity and eccentricity forcing combined with self gravity results in increased obliquity heating and suppressed eccentricity heating in small satellites for large satellites with low effective rigidities the type of ocean response is less important because the shell s mechanical forcing has little impact on the flow whereas self gravity will enhance the response and consequently dissipation regardless of the forcing overall obliquity tides are likely to dominate the tidal heating budget of icy satellite oceans remaining the most prominent source of fluid dissipation in subsurface barotropic ocean tides

determination of the largest clast sizes of tephra deposits for the characterization of explosive eruptions a study of the iavcei commission on tephra hazard modelling the distribution of clasts deposited around a volcano during an explosive eruption typically contoured by isopleth maps provides important insights into the associated plume height wind speed and eruptive style nonetheless a wide range of strategies exists to determine the largest clasts which can lead to very different results with obvious implications for the characterization of eruptive behaviour of active volcanoes the iavcei commission on tephra hazard modelling has carried out a dedicated exercise to assess the influence of various strategies on the determination of the largest clasts suggestions on the selection of sampling area collection strategy choice of clast typologies and clast characterization i e axis measurement and averaging technique are given mostly based on a thorough investigation of two outcrops of a plinian tephra deposit from cotopaxi volcano ecuador located at different distances from the vent these include 1 sampling on a flat paleotopography far from significant slopes to minimize remobilization effects 2 sampling on specified horizontal area sections with the statistically representative sampling area depending on the outcrop grain size and lithic content 3 clast characterization based on the geometric mean of its three orthogonal axes with the approximation of the minimum ellipsoid lithic fragments are better than pumice clasts when present and 4 use of the method of the 50th percentile of a sample of 20 clasts as the best way to assess the largest clasts it is also suggested that all data collected for the construction of isopleth maps be made available to the community through the use of a standardized data collection template to assess the applicability of the new proposed strategy on a large number of deposits and to build a large dataset for the future development and refinement of dispersal models

transport and emplacement mechanisms of large volcanic debris avalanches evidence from the northwest sector of cantal volcano france abstract large volcanic debris avalanche vda deposits of miocene age occur within the stratigraphic sequence of cantal stratovolcano central france the vda of cantal volcano were initiated by sector collapse of a cone of high elevation up to 4500 m a s l two distinct superimposed vda deposit units breccias i and ii resulted from at least two successive large scale collapse events during the evolution of the volcanic complex breccia i the oldest one is very thick up to 200 m and heterolithologic it is overlain by breccia ii which is thinner up to 50 m and contains more heterometric clasts ranging from hectometer to millimeter size the vda deposits are poorly sorted clasts are angular and highly fractured at different scales often with jigsaw fit in breccia ii jigsaw megaclasts have usually subspheric shapes with size decreasing distally basal deposits commonly display thin inversely graded layers reorientated clasts along ramp structures and cataclasis of the substratum some units have a distal fabric in the form of a poorly developed clast imbrication the clasts are commonly sub rounded thereby indicating abrasion during viscous flow anisotropy of magnetic susceptibility a m s measurements indicate absence of a preferentially oriented matrix fabric magnetic foliation parallel to the bedding suggests that the depositional process is dominated by particle settling the magnetic fabric is better organized in distal deposits where magnetic carriers are imbricated moreover the fragmented clasts and megaclasts are not abraded rather inflation led to isotropic spherical dispersion of clastic material isotropic dispersive inflation which fed the interclast matrix this is also confirmed by the lack of rotation at the individual crystal level all these data strongly suggest transport of vda by liquified non turbulent granular flows distally imbricated deposits suggest more turbulent flow emplacement of the vda results from progressive upward aggradation of the particles by volume reduction and deflation loss the non turbulent liquified stage of the vda disappears the vda behaves as a sliding rigid mass plug flow that exerts strong friction on the basement leading to gouge formation

crustal control of dissipative ocean tides in enceladus and other icy moons abstract could tidal dissipation within enceladus subsurface ocean account for the observed heat flow earthlike models of dynamical tides give no definitive answer because they neglect the influence of the crust i propose here the first model of dissipative tides in a subsurface ocean by combining the laplace tidal equations with the membrane approach for the first time it is possible to compute tidal dissipation rates within the crust ocean and mantle in one go i show that oceanic dissipation is strongly reduced by the crustal constraint and thus contributes little to enceladus present heat budget tidal resonances could have played a role in a forming or freezing ocean less than 100 m deep the model is general it applies to all icy satellites with a thin crust and a shallow ocean scaling rules relate the resonances and dissipation rate of a subsurface ocean to the ones of a surface ocean if the ocean has low viscosity the westward obliquity tide does not move the crust therefore crustal dissipation due to dynamical obliquity tides can differ from the static prediction by up to a factor of two

volcanic dry avalanche deposits identification and comparison with nonvolcanic debris stream deposits abstract a volcanic dry avalanche deposit is defined as a volcaniclastic deposit formed as a result of a large scale sector collapse of a volcanic cone associated with some form of volcanic activity avalanche transport occurred in response to the gravitational field in a manner similar to the transport of nonvolcanic debris streams e g hsu 1975 such deposits are characterized by megablock structure deformed and fractured large blocks up to several hundreds meters in diameter a megablock preserves original layering intrusive contacts or weathered surfaces of the source volcanic edifice surface topography of the deposit is characterised with hummocky relief ratios of fell height to travel distance for volcanic dry avalanche deposits are between 0 18 and 0 06 this range is similar but smaller than the value of 0 58 to 0 08 for nonvolcanic debris stream deposit this similarity suggests similar transportation mechanisms excessive travel distances as defined by hsu 1975 calculated for volcanic dry avalanche deposits give values larger than for debris stream deposits of the same volume the difference is explained by lower rigidity of the collapsing mass due to the existence of soft pyroclastic layers alteration around the vent development of fractures owing to new cryptodome intrusion and boiling of supercritical fluid contained within the collapsed mass

extensional tectonics and volcano lateral collapses insights from ollague volcano chile bolivia and analogue modelling understanding the process of volcanic lateral collapse which may be governed by numerous possible factors can be significantly improved by identifying the role of each factor here we test the perturbation induced in a volcano by tectonic normal faulting in the basement magma inflation and multiple flank deformation based on fieldwork and analogue experiments ollague volcano chile bolivia provides a good example of a sector collapse with exposed substrate extensional tectonics and our experiments have been done with conditions consistent with field data results show that none of the possible tectonic conditions led to complete lateral failure in agreement also with the field data sector collapse of the model cone occurred only when a shallow magmatic intrusion within the volcano was reproduced we also found out that volcano flank deformation is enhanced if a previous flank destabilization occurred interleaved by new cone growth terra nova 18 282 289 2006

late early triassic microbial reefs of the western united states a description and model for their deposition in the aftermath of the end permian mass extinction abstract research in the western united states to reinvestigate and characterize the previously reported stromatolites of the latest early triassic spathian virgin limestone member of the moenkopi formation has shown that these microbial build ups formed patch reef mounds detailed field analysis of these reef mounds and the surrounding beds has established that they attained 1 2 m of topographic relief above the seafloor a petrographic study of these microbial mounds illustrates that they consisted of microbial fabrics as well as voids with early marine cements and formed in the absence of in situ metazoans these reef mounds formed during the aftermath of the end permian mass extinction that spanned the early triassic due to the devastation of marine metazoans at this extinction the early triassic has often been deemed a reef gap because no metazoan reefs are found at this time whereas colonial metazoan reefs are globally absent from lower triassic strata microbial build ups similar to these described from the western united states have been found in south china armenia southern turkey and greenland a regional early permian to late early triassic unconformity exists in the study region however analysis of these microbial reefs within a global context suggests that conditions favouring microbial reef development must have existed as long as 4 8 m y after the end permian mass extinction a depositional model of these microbial mounds indicates that flooding of the shelf with anoxic and or co2 rich deep waters may have fostered their occurrence

enceladus s internal ocean and ice shell constrained from cassini gravity shape and libration data the intense plume activity at the south pole of enceladus together with the recent detection of libration hints at an internal water ocean underneath the outer ice shell however the interpretation of gravity shape and libration data leads to contradicting results regarding the depth of ocean ice interface and the total volume of the ocean here we develop an interior structure model consisting of a rocky core an internal ocean and an ice shell which satisfies simultaneously the gravity shape and libration data we show that the data can be reconciled by considering isostatic compensation including the effect of a few hundred meter thick elastic lithosphere our model predicts that the core radius is 180 185 km the ocean density is at least 1030 kg m3 and the ice shell is 18 22 km thick on average the ice thicknesses are reduced at poles decreasing to less than 5 km in the south polar region

chronology and dispersal characteristics of recently last 5000 years erupted tephra of cotopaxi ecuador implications for long term eruptive forecasting abstract cotopaxi the highest active volcano on earth and one of the most dangerous of ecuador is constituted by a composite cone made up of lava and tephra erupted from the summit crater the activity of the present volcano begun with large volume plinian eruptions followed by a succession of small volume lava emissions and pyroclastic episodes which led to the edification of a symmetrical cone the growth of the cone was broken by an episode of slope failure the scar of which is now obliterated by recent and historical products volcanic history eruptive frequency and characteristics of the activity were investigated by studying the stratigraphy of tephra and carrying out fifteen new 14 c dating on paleosols and charcoals the investigated period is comprised between the slope failure and the present the deposit of the volcanic landside dry debris avalanche of rio pita previously believed to be between 13 000 and 25 000 yr b p is now considered to have an age slightly older than 5000 yr b p the stratigraphy of tephra of the last 2000 years reveals the existence of 22 fallout layers seven of them were dated with 14 c whereas three were ascribed to the eruptions of 1534 1768 and 1877 on the basis of comparison with historical information maximum clast size distribution isopleths of 9 tephra layers points out that the sustained explosive eruptions of cotopaxi during the last 2000 years are characterized by very high dispersive power plinian plumes with column heights between 28 and 39 km and high intensity peak mass discharges from 1 1 to 4 1 10 8 kg s the magnitude mass of tephra fallout deposits calculated from distribution of thickness isopaches are however moderate from 0 8 to 7 2 10 11 kg the limited volume of magma erupted during each explosive episode is consistent with the lack of caldera collapses small volume pyroclastic flows and surges virtually accompanied all identified tephra fallouts during such an activity large scale snow ice melting of the summit glacier produced devastating mudflows comparable in scale to those of 1877 eruption by assuming a 1 1 correspondence between fallout episodes and generation of large scale lahar we have estimated an average recurrence of one explosive lahartriggering event every 117 years over the last two millennia this value compares well with that calculated by considering the period since spanish conquest the probability of having an eruption like this in 100 or 200 years is respectively of 0 57 and 0 82 such an high probability underscores the need for quick actions aimed at the mitigation of cotopaxi lahar hazard along all the main valleys which originate from the volcano

parallel adaptive numerical simulation of dry avalanches over natural terrain high fidelity computational simulation can be an invaluable tool in planning strategies for hazard risk mitigation the accuracy and reliability of the predictions are crucial elements of these tools being successful we present here a new simulation tool for dry granular avalanches using several new techniques to create a highly accurate tool with a combination of good models and numerical methodologies highlights of our methodology are the use of a depth averaged model of the conservation laws and an adaptive grid godunov solver to solve the resulting equations the software is designed to run on distributed memory supercomputers and make use of digital elevation data dynamically i e refine the grid and input data to finer resolutions to better capture flow features as the flow evolves our simulations are validated using quantitative and qualitative comparisons to tabletop experiments and data from field observations our software is freely available and can be used on a range of hardware from inexpensive desktop computers to the largest supercomputers

no abrupt change in redox condition caused the end permian marine ecosystem collapse in the east greenland basin abstract multiple observations have revealed that environmental disturbances may have been linked to the end permian mass extinction and delayed biotic recovery biogeochemical constraints on the temporal and spatial changes of oceanic redox chemistry during the permian triassic interval are essential to evaluate global significance of previous hypotheses and to improve our understanding of extinction and recovery processes to investigate redox ocean chemistry change associated with the end permian extinction and subsequent delayed biotic recovery we examine framboidal pyrites as well as sulfur isotopic compositions of pyrites from the east greenland basin the size distributions of framboidal pyrites in sediments from a continuous section across the permian triassic boundary reveal that sulfidic conditions in water columns were established about 0 7 m above the extinction event in the east greenland basin our detailed examination of framboidal pyrites challenges a leading hypothesis that euxinia in the photic zone caused the end permian ecosystem collapse we identify several positive and negative s isotopic shifts before and after the extinction event and demonstrate that a positive s isotopic shift is not indicative of an abrupt change of redox chemistry in water columns in contrast to previous claims the integration of isotope and framboidal pyrite data provides a nearly continuous record of ocean chemistry evolution and new insights into the end permian extinction and delayed biotic recovery in the east greenland basin

anachronistic facies from a drowned lower triassic carbonate platform lower member of the alwa formation ba id exotic oman mountains abstract the lower member of the alwa formation lower olenekian found within the ba id exotic in the oman mountains sultanate of oman consists of ammonoid bearing pelagic limestones that were deposited on an isolated drowned carbonate platform on the neotethyan gondwana margin the strata contain a variety of unusual carbonate textures and features including thrombolites frutexites bearing microbialites that contain synsedimentary cements matrix free breccias surrounded by isopachous calcite cement and fissures and cavities filled with large botryoidal cements thrombolites are found throughout the study interval and occur as 0 5 1 0 m thick lenses or beds that contain laterally laterally linked stromatactis cavities the frutexites bearing microbialites occur less frequently and also form lenses or beds up to 30 cm thick the microbialites may be laminated and often developed on hardgrounds in addition the frutexites bearing microbialites also contain synsedimentary calcite cement crusts and botryoids typically frutexites bearing microbialites low level of calcium carbonate supersaturation associated with anoxic conditions and deposition below a stable chemocline formed the results of this study point to continued environmental stress in the region during the early triassic that likely contributed to the uneven recovery from the permian triassic mass extinction

an integrated field numerical approach to assess slope stability hazards at volcanoes the example of pacaya guatemala pacaya is an active stratovolcano located 30 km south of guatemala city guatemala a large 0 65 km3 sector collapse of the volcano occurred 0 6 1 6 ka b p producing a debris avalanche that traveled 25 km sw of the edifice the current cone has since rebuilt within the scarp of this ancestral collapse the structural setting of the volcano along with two recent smaller volume collapses in 1962 and 2010 suggests gravitational instability of this volcano to assess pacaya s stability and potential for another large lateral collapse of the active cone standard engineering methodologies for studying non volcanic slopes were used to examine the sw flank of the edifice a geomechanical model was developed based on the physical mechanical material properties of pacaya s intact rocks and rock mass characteristics found through field observations and laboratory tests slope stability was analyzed in several scenarios with the limit equilibrium method lem and finite element method fem including static conditions i e under gravity forces only and considering the application of magma pressure and seismic force as triggering mechanisms for slope failure results show that the edifice remains stable under gravity alone however a large scale collapse could be triggered by reasonable ranges of magma pressure 7 7 mpa if constant along a dyke or peak ground acceleration 460 cm s2 results also suggest that a layer of pyroclastics beneath the edifice could have controlled the ancestral sector collapse structural analysis shows that a transtensional stress regime is causing a nw se orientation of aligned features at the surface and may be a controlling mechanism for the direction of a future collapse fem results are concordant with those from lem and reveal that maximum shear strain patterns within the edifice may account for long lava flows erupted from lower vent elevations

cassini observes the active south pole of enceladus cassini has identified a geologically active province at the south pole of saturn s moon enceladus in images acquired by the imaging science subsystem iss this region is circumscribed by a chain of folded ridges and troughs at 55 s latitude the terrain southward of this boundary is distinguished by its albedo and color contrasts elevated temperatures extreme geologic youth and narrow tectonic rifts that exhibit coarse grained ice and coincide with the hottest temperatures measured in the region jets of fine icy particles that supply saturn s e ring emanate from this province carried aloft by water vapor probably venting from subsurface reservoirs of liquid water the shape of enceladus suggests a possible intense heating epoch in the past by capture into a 1 4 secondary spin orbit resonance

on the energy budgets of fragmenting rockfalls and rockslides insights from experiments the travel lengths of rockfalls and rockslides can be difficult to predict due to complex interactions of numerous physical processes such as fragmentation of the rock mass and its effect on the energy dissipation through basal and internal friction previous studies have shown that the front of the rockslide deposits travels farther with increased fragmentation however little is known about the displacement of the center of mass which is the relevant parameter for studying the energy budget leaving open the question whether fragmentation acts as an effective sink or source of energy taking advantage of a newly developed rock analogue material we perform a total of 109 experiments to study the effect of fragmentation on the displacement of the center of mass and the energy budget of experimental rockslides to determine the degree of fragmentation we define a characteristic fragment size from the total mass of the experimental sample and the mass of the largest fragment the degree of fragmentation is seen to depend linearly on the aspect ratio of the experimental sample and as a power law on its cohesion similar to the previous studies our results show that the travel distance of the front of the deposits increases with the degree of fragmentation in contrast displacement of the center of mass is reduced with the degree of fragmentation suggesting increased energy consumption consistent with the assumption that fragmentation acts effectively as an energy sink

objective delineation of lahar inundation hazard zones a new method of delineating lahar hazard zones in valleys that head on volcano flanks provides a rapid objective reproducible alternative to traditional methods the rationale for the method derives from scaling analyses of generic lahar paths and statistical analyses of 27 lahar paths documented at nine volcanoes together these analyses yield semiempirical equations that predict inundated valley cross sectional areas a and planimetric areas b as functions of lahar volume v the predictive equations a 0 05v 2 3 and b 200v 2 3 provide all information necessary to calculate and plot in

catastrophic sector collapse at usu volcano hokkaido japan failure of a young edifice built on soft substratum catastrophic sector collapse is a destructive volcanic process that occurs during the growth history of a volcano understanding the timing and causal mechanisms of sector collapse at individual volcanoes is essential for evaluating long term volcano evolution and associated hazards this paper describes the lithofacies tephrostratigraphy and radiocarbon dating of a debris avalanche deposit at usu volcano japan based on detailed field geological surveys and proposes that uplift of soft substratum played an important role in destabilizing the young volcanic edifice usu is a quaternary basaltic to andesitic stratovolcano that has an amphitheater at the summit the basement of the volcano has been uplifted by 300 400 m relative to the surrounding area the debris avalanche deposit is 0 3 km3 in volume and displays well preserved hummocky topography the hummocks are composed of andesite blocks derived from the stratovolcano and non welded pyroclastic flow and fluvial deposits derived from the basement of the stratovolcano tephrostratigraphy and radiocarbon dating of charcoal samples from the debris avalanche deposit indicate that the sector collapse occurred at 16 ka the age of sector collapse combined with previous geochronological data enables reconstruction of the eruptive history of usu as follows 1 andesitic explosive eruption at 18 19 ka 2 stratovolcano growth between 18 and 16 ka 3 sector collapse at 16 ka 4 hiatus in volcanic activity for 15 000 years 5 rhyolitic plinian eruption in ad 1663 and 6 dacitic dome forming eruptions after ad 1663 this eruptive history indicates that the sector collapse occurred within 3000 years of the onset of stratovolcano growth much sooner than at other volcanoes where the timing of sector collapse is known we infer that the sector collapse of such a young volcanic edifice was caused by a combination of dome like uplifting tilting forced folding of soft substratum overloading of the volcanic edifice on the soft substratum a ne sw trending fault system that deeply cuts the substratum and possible magma intrusion within the edifice and associated earthquakes usu provides an excellent example of edifice instability that is characterized by uplift of soft substratum our new view of causal mechanisms of the sector collapse provides invaluable information for hazard assessment of quaternary volcanoes

do tidally generated inertial waves heat the subsurface oceans of europa and enceladus some of the moons of the outer solar system harbour subsurface liquid oceans tidal dissipation plays an important role in preventing these oceans from freezing in the past most studies considered only tidal dissipation in the solid layers of these bodies rock and ice recently new studies considering tidal dissipation in the oceans of these moons have appeared all of them make use of the shallow water approximation however the use of this approximation might not be adequate here we consider the linear non hydrostatic three dimensional response of these oceans to tidal forcing with the full coriolis force to do so we consider an ocean of homogeneous density contained within a perfectly spherical shell and neglect the effect of the ice shell we force the ocean with a time changing tidal potential and observe patterns of periodic inertial waves that take energy from the global tidal forcing and focus it along thin shear layers that propagate in the fluid we focus on europa and enceladus showing that inertial waves result in fluid flows of significant amplitude a few cm s nevertheless we find that under the previously mentioned assumptions tidal dissipation due to inertial waves is several orders of magnitude smaller than europa s radiogenic heating and enceladus observed heat flux finally we propose additional dissipation mechanisms that might play a relevant role in europa and enceladus and could be further investigated

significant dissipation of tidal energy in the deep ocean inferred from satellite altimeter data how and where the ocean tides dissipate their energy are long standing questions1 that have consequences ranging from the history of the moon2 to the mixing of the oceans3 historically the principal sink of tidal energy has been thought to be bottom friction in shallow seas4 5 there has long been suggestive evidence6 7 however that tidal dissipation also occurs in the open ocean through the scattering by ocean bottom topography of surface tides into internal waves but estimates of the magnitude of this possible sink have varied widely3 8 9 10 11 here we use satellite altimeter data from topex poseidon to map empirically the tidal energy dissipation we show that approximately 1012 watts that is 1 tw representing 25 30 of the total dissipation occurs in the deep ocean generally near areas of rough topography of the estimated 2 tw of mixing energy required to maintain the large scale thermohaline circulation of the ocean12 one half could therefore be provided by the tides with the other half coming from action13 on the surface of the ocean

subsurface oceans on europa and callisto constraints from galileo magnetometer observations magnetic field perturbations measured during galileo flybys of europa and callisto are consistent with dipole fields induced by the temporal variations of the ambient jovian magnetospheric field these fields are close to those expected for perfectly conducting moons we investigate the implications of these observations for the electrical structure of the moon s interiors using a simple shell model it is found that europa and callisto must possess regions where the conductivity exceeds 0 06 and 0 02 s m at a depth of less than 200 and 300 km below the surface respectively this conductivity is unattainable in ice or silicates unless the ice layer is at least partially molten or very large temperature gradients can be maintained below the ice an ionosphere or a cloud of pick up ions are probably also insufficiently conductive global earth like oceans under the surface of both moons could account for the observations provided they are at least a few kilometers thick c 2000 academic press

reorientation of sputnik planitia implies a subsurface ocean on pluto to explain the position of the sputnik planitia basin on pluto the feature would need to have formed via impact and pluto would need to have a subsurface ocean the present location of sputnik planitia the prominent deep icy basin on pluto is close to one of the longitudes of the dwarf planet s tidal axis by analogy with other large basins in the solar system it is thought to be an impact feature although reorientation arising from tidal and rotational torques can explain the present day location of the basin it requires the feature to be a positive gravity anomaly despite its negative topography francis nimmo et al argue that if sputnik planitia formed via impact and if pluto possesses a subsurface ocean a positive gravity anomaly would naturally result because of shell thinning and ocean uplift followed by later modest nitrogen deposition this is one of four papers on the geology of sputnik planitia in this issue of nature in news views amy barr puts these latest contributions into context the deep nitrogen covered basin on pluto informally named sputnik planitia is located very close to the longitude of pluto s tidal axis1 and may be an impact feature2 by analogy with other large basins in the solar system3 4 reorientation5 6 7 of sputnik planitia arising from tidal and rotational torques can explain the basin s present day location but requires the feature to be a positive gravity anomaly7 despite its negative topography here we argue that if sputnik planitia did indeed form as a result of an impact and if pluto possesses a subsurface ocean the required positive gravity anomaly would naturally result because of shell thinning and ocean uplift followed by later modest nitrogen deposition without a subsurface ocean a positive gravity anomaly requires an implausibly thick nitrogen layer exceeding 40 kilometres to prolong the lifetime of such a subsurface ocean to the present day8 and to maintain ocean uplift a rigid conductive water ice shell is required because nitrogen deposition is latitude dependent9 nitrogen loading and reorientation may have exhibited complex feedbacks7

ocean tidal heating in icy satellites with solid shells abstract as a long term energy source tidal heating in subsurface oceans of icy satellites can influence their thermal rotational and orbital evolution and the sustainability of oceans we present a new theoretical treatment for tidal heating in thin subsurface oceans with overlying incompressible elastic shells of arbitrary thickness the stabilizing effect of an overlying shell damps ocean tides reducing tidal heating this effect is more pronounced on enceladus than on europa because the effective rigidity on a small body like enceladus is larger for the range of likely shell and ocean thicknesses of enceladus and europa the thin shell approximation of beuthe 2016 is generally accurate to less than about 4 explaining enceladus endogenic power radiated from the south polar terrain by ocean tidal heating requires ocean and shell thicknesses that are significantly smaller than the values inferred from gravity and topography constraints the time averaged surface distribution of ocean tidal heating is distinct from that due to dissipation in the solid shell with higher dissipation near the equator and poles for eccentricity and obliquity forcing respectively this can lead to unique horizontal shell thickness variations if the shell is conductive the surface displacement driven by eccentricity and obliquity forcing can have a phase lag relative to the forcing tidal potential due to the delayed ocean response for europa and enceladus eccentricity forcing generally produces greater tidal amplitudes due to the large eccentricity values relative to the obliquity values despite the small obliquity values obliquity forcing generally produces larger phase lags due to the generation of rossby haurwitz waves if europa s shell and ocean are respectively 10 and 100 km thick the tide amplitude and phase lag are 26 5 m and

sector collapse of the sw flank of volcan de colima mexico the 3600 yr bp la lumbre los ganchos debris avalanche and associated debris flows abstract some 3600 years ago the sw flank of volcan de colima collapsed generating a debris avalanche that travelled 25 km to the armeria river and stopped against the cerro grande limestone escarpment the debris avalanche deposit covers an area of 48 km2 has an average thickness of 35 m and a volume of 1 7 km3 with an h l ratio of 0 13 along the la lumbre ravine the deposit forms a series of flat terraces up to 65 m thick a pyroclastic flow deposit overlies the debris avalanche deposit suggesting that the colima collapse was accompanied by a magmatic component the debris avalanche deposit dammed the armeria river forming a temporary lake that accumulated a water volume of 0 19 km3 the subsequent breaking of the dam formed a debris flow that travelled at least 20 km along the armeria river emplacing 15 70 m thick deposits the debris flow deposits cover a surface of 6 4 km2 and have a volume of 0 2 km3 the avalanche deposit contains fragments of carbonized wood that where dated at 3600 120 yr bp by komorowski et al 1997 this deposit underlies a younger debris avalanche 2505 45 yr bp and a debris flow deposit with pottery shards and charcoal dated at 1940 90 yr bp these pottery shards likely related to the capacha people 820 300 yr bc indicating that the region has been inhabited during the last 3000 years a future collapse of volcan de colima in the same direction may affect several towns for a total population of circa 40 000

heating of enceladus due to the dissipation of ocean tides abstract given cassini observations of a large and unexplained endogenic heat source the subsurface ocean on enceladus is an important test bed for modeling icy satellite ocean tides and the dissipative heat generated here we revisit and expand estimates of the ocean tidal power heating rate to describe how the power depends on input parameter and process assumptions the approach taken in this and previous work by this author is that the dissipation process in enceladus ocean is unknown and cannot be reliably modeled from first principles considered instead are generic dissipation forms that cover specific physical dissipation processes as special cases specific cases described here include linear nonlinear drag eddy viscosity viscoelastic ice coupling and vertical wave damping the justification for basing conclusions primarily on the generic rather than specific dissipation forms is that whatever the ocean dissipation process it must draw from the stored energy kinetic or potential in the ocean tidal response and this process must have an associated time scale for the dissipation to take place by treating this time scale as well as the lamb number wave speed as free parameters millions of tidal solutions are calculated to sample the full domain of tidal scenarios that arrive from different combinations of these two parameters as well as the assumed dissipation form conclusions drawn from the general behavior in this larger solution domain are then considered to be more robust than conclusions drawn from the subdomain that assumes the validity of a specific physical dissipation process the results show plausible states whereby the ocean tides even if enceladus is covered with thick ice generate the observed heat flux while the same results show that low power non resonant states are also allowed an argument is presented that these low power states may not be stable in the presence of secular trends e g cooling stratification rather self tuned resonance stabilizes the tidal configuration in a near resonant forced state with high power and dissipative heat

can libration maintain enceladus s ocean abstract the process by which the subsurface ocean on enceladus is heated remains a puzzle tidal interaction with saturn and dione is the leading candidate but whether the dominant heating occurs in the solid core ice crust or in the ocean itself is an outstanding question here we consider the driving effect of the longitudinal libration of the ice crust on the subsurface ocean and argue that the flow response should be turbulent even in the most benign situation of a smooth spherical ice shell when the motion of the boundary is only transmitted viscously a rigorous upper bound on the turbulent viscous dissipation rate is then derived and used to argue that libration should be potent enough to explain the observed heat flux emanating out of enceladus when the effects of tidal distortion and roughness of the ice crust are included

comment on heating of enceladus due to the dissipation of ocean tides by r tyler abstract dissipation of ocean potential energy is proposed by tyler 2020 as a new mechanism leading to possible high power states for enceladus i show here that this process actually results from viscoelastic dissipation within the crust for plausible values of enceladus s ocean thickness crustal dissipation can be computed with the standard approach of static deformations of solid layers by equilibrium tides

a string function for describing the propagation of baroclinic anomalies in the ocean the authors derive a string function that describes the propagation of large scale potentially large amplitude baroclinic energy anomalies in a two layer ocean with variable topography and rotation parameter the generality of the two layer results allows results for the 1 layer 1 5 layer inverted 1 5 layer lens and dome models to be produced as limiting cases the string function is a scalar field that acts as a streamfunction for the propagation velocity in the linear case the string function is simply c2o f where co is the background baroclinic shallow water wave speed and typically describes propagation poleward on the eastern boundaries westward with some topographic steering over the middle ocean and equatorward on the western boundaries in the more general nonlinear case the string function is locally distorted by the anomaly in the fully nonlinear examples of a lens or dome there is no rest or background string function the string function is generated entirely by the disturbance and propagation is due to asymmetric distribution of the anomalous mass over the string function contours it is shown that conventional beta topographic propagation results e g beta drift of eddies the nof speed of cold domes can be obtained as limiting cases of the string function the string function provides however more general propagation velocities that are also usually simpler to derive the first baroclinic mode string function for the global oceans is calculated from hydrographic data the westward propagation speeds in the ocean basins as derived from the meridional gradient of the string function are typically two to five times faster than those expected from standard theory and agree well with the propagation speeds observed for long baroclinic rossby waves in the topex poseidon data

deev jahi model of the permian triassic boundary mass extinction a case for gas hydrates as the main cause of biological crisis on earth the smoking gun revealing the secrets of the end permian mass mortality is a unique 1 2 m thick layer consisting of 5 20 cm long crystals of calcite that occurs precisely at the permian triassic boundary ptb in iran armenia turkey and china this layer is interpreted as synsedimentary abiotic seafloor cement indicative of precipitation from a highly carbonate supersaturated seawater its 13 c composition 13 c 0 pdb is 4 to 5 pdb lower than the typical upper permian values 4 to 5 pdb suggesting the involvement of massive amounts of gas hydrate ch 4 13 c 60 pdb the temporal coincidence of the cement layer with the ptb suggests that the process that promoted seafloor cementation was also responsible for the biological crisis a cementation model is developed based on accumulation dissociation cycle of gas hydrates which also explains the mass extinction at the ptb the upper permian accumulation period of gas hydrates ended abruptly adjacent to the ptb and the dissociation event began releasing 3 2 to 4 7 10 18 g ch 4 into the ocean oxidation of ch 4 in the water column created a seawater that was charged with co 2 an oceanic acid bath and had lower than normal o 2 content but not anoxic this oceanic acid bath first dissolved suspended fine grained carbonate particles and small calcareous organisms followed by extensive dissolution of platform carbonates raising ca 2 and hco 3 concentrations of seawater when the release of ch 4 declined the acid bath ocean became a soda ocean precipitating massive amount of seafloor cements observed globally at the ptb the study suggests that prior to cement precipitation the ptb ocean was charged with co 2 warm had low oxygen high ca 2 and high hco 3 concentrations these conditions collectively created stressful conditions causing the marine mass mortality the leakage of ch 4 to the atmosphere produced a super hot climate resulting in the biological devastation on land the proposed kill mechanism is developed on the basis of the physical clue the cement layer left behind by the killing process the change in ocean chemistry the accumulation dissociation cycles of gas hydrates also explain the 13 c pattern of marine carbonates and the periodicity of mass extinction events during the phanerozoic accumulation periods were long 5 to 20 my providing favorable conditions for ecosystem development pardeess phase the dissociation events were short and catastrophic 10 to 500 ky causing low oxygenation super hot climate and biological devastation doozakh phase it appears that most mass extinctions of the phanerozoic have been related to the internal working of the earth system during the phanerozoic methane has played the role of the deev jahi a female demon in persian mythology whose task is to attack the earth every so often to kill life on land and in sea

ocean tides heat enceladus 1 with a young highly reflective surface and vigorous geological activity saturn s tiny moon enceladus has been one of the most mysterious planetary bodies in the solar system recent observations from the cassini spacecraft show vast plumes of vapor erupting from geysers near the south pole and inferred heat fluxes of about 100 mw m2 for the same region have helped consolidate the essential enigma of enceladus there must be a relatively large and unidentified source of heat in the tiny moon here we present a case for heating from dissipation by tidal flow in an ice covered ocean we show that if the spin axis of enceladus is tilted with respect to its orbital plane by at least 0 05 degree then strong tidal flow will be generated with enough dissipative heating to explain the observed heat flux in an alternative case of a shallow 10 km or less ocean comparable flow velocities and heating may be obtained by eccentricity tidal forces

small fast moving flow like landslides in volcanic deposits the 2001 las colinas landslide el salvador abstract fast moving landslides are one of the most significant dangers deriving from slope instabilities landslides involving large volumes can develop in rock or debris avalanches with extreme mobility and enormous destructiveness nevertheless a relevant number of casualties and damages derive from small fast moving landslides with flow like behaviour the las colinas landslide occurred at santa tecla el salvador central america during a strong earthquake it slid off the northern flank of the balsamo ridge and resulted in almost 500 casualties and can be considered one of the most destructive landslides ever known earthquake shaking was amplified by the rock mass and the steep ridge topography we collected original geological geomorphological and geophysical data in the cordillera del balsamo area the involved materials ranging from lapilli to tuff layers of different strength have been mapped and characterized slope stability analyses have been performed both under static and dynamic conditions through limit equilibrium and finite element methods hazard zonation for this type of landslides requires the forecast of the movement velocity and final deposition area we used a fully two dimensional fem model to simulate landslide spreading downslope the developed code allows the use of different constitutive models and yield rules with the possibility to model and study internal deformation of the landslide mass as well material entrainment and deposition

galileo magnetometer measurements a stronger case for a subsurface ocean at europa on 3 january 2000 the galileo spacecraft passed close to europa when it was located far south of jupiter s magnetic equator in a region where the radial component of the magnetospheric magnetic field points inward toward jupiter this pass with a previously unexamined orientation of the external forcing field distinguished between an induced and a permanent magnetic dipole moment model of europa s internal field the galileo magnetometer measured changes in the magnetic field predicted if a current carrying outer shell such as a planet scale liquid ocean is present beneath the icy surface the evidence that europa s field varies temporally strengthens the argument that a liquid ocean exists beneath the present day surface

long term stability of enceladus uneven ice shell abstract we present a new model of enceladus internal structure based on the recent shape model by tajeddine et al 2017 and the gravity model by iess et al 2014 assuming that the rocky core is homogeneous and in hydrostatic equilibrium we derive a set of structural models that accurately reproduce the main characteristics of enceladus gravity field in order to restrict the range of acceptable models we analyze the degree of compensation ratio of the bottom to the surface load at spherical harmonic degrees well constrained by the gravity data in agreement with previous studies we find that enceladus ice shell is close to equilibrium with the degree of compensation approaching one for models with a hydrostatic core having a radius between 190 km and 195 km by computing the flow of ice driven by variations in hydrostatic pressure on the ice water interface we demonstrate that the ice shell is in steady state as suggested by the gravity and shape data only if the viscosity of ice at the melting temperature is equal to or higher than 3 1014 pa s corresponding to diffusion creep with a grain size of 1 mm or larger the topographic anomalies are maintained by phase changes at the ice water interface with a melting freezing rate of a few mm yr or smaller this process is controlled by the heat flux at the top of the ocean characterized by a strong degree 2 zonal component with amplitudes exceeding 60 mw m2 in both south and north polar regions

transport and sedimentation dynamics of transitional explosive eruption columns the example of the 800 bp quilotoa plinian eruption ecuador abstract impact of large scale explosive eruptions largely depends on the dynamics of transport dispersal and deposition of ash by the convective system in fully convective eruptive columns ejected gases and particles emitted at the vent are vertically injected into the atmosphere by a narrow buoyant column and then dispersed by atmosphere dynamics on a regional scale in fully collapsing explosive eruptions ash partly generated by secondary fragmentation is carried and dispersed by broad co ignimbrite columns ascending above pyroclastic currents in this paper we investigate the transport and dispersion dynamics of ash and lapillis during a transitional plinian eruption in which both plinian and co ignimbrite columns coexisted and interacted the 800 bp eruptive cycle of quilotoa volcano ecuador produced a well exposed tephra sequence our study shows that the sequence was accumulated by a variety of eruptive dynamics ranging from early small phreatic explosions to sustained magmatic plinian eruptions to late phreatomagmatic explosive pulses the eruptive style of the main 800 bp plinian eruption u1 progressively evolved from an early fully convective column plinian fall bed to a late fully collapsing fountain dense density currents passing through an intermediate transitional eruptive phase fall syn plinian dilute density currents in the transitional u1 regime height of the convective plinian column and volume and runout of the contemporaneous pyroclastic density currents generated by partial collapses were inversely correlated the convective system originated from merging of co plinian and co surge contributions this hybrid column dispersed a bimodal lapilli and ash fall bed whose grain size markedly differs from that of classic fall deposits accumulated by fully convective plinian columns sedimentological analysis suggests that ash dispersion during transitional eruptions is affected by early aggregation of dry particle clusters

endogenic heat from enceladus south polar fractures new observations and models of conductive surface heating linear features dubbed tiger stripes in the south polar region of enceladus have anomalously high heat fluxes and are the apparent source of the observed plume several explanations for the observed activity have been proposed including venting from a subsurface reservoir of liquid water sublimation of surface ice dissociation of clathrates and shear heating thermal modeling presented in this work coupled with observations from the cassini composite infrared spectrometer cirs instrument seeks to elucidate the underlying physical mechanism by constraining vent temperatures and thermal emission sources using a model in which the observed thermal signature results primarily from conductive heating of the surface by warm subsurface fractures the fractures feed surface vents which may themselves contribute to the observed thermal emission model variables include vent temperature presence of a surface insulating layer vent width time variable heat input and heat sources other than the central vent results indicate

the tancitaro debris avalanche characterization propagation and modeling abstract the tancitaro volcano 3860 m is an andesitic dacitic stratovolcano located in the western portion of the trans mexican volcanic belt within the state of michoacan mexico the tectonic activity of this area has likely contributed to a large sector collapse of the volcano the first findings of a multidisciplinary investigation into this debris avalanche are presented here geomorphological analyses based on the interpretation of orthophotos satellite imagery and on gis elaborations had the objective of determining the main morphometric features of the landslide the collapse structure is an east facing horseshoe shaped crater 4 km wide and 5 3 km long while the deposit forms a large fan that is 66 km long covers an area of approximately 1155 km2 and has an estimated volume of 18 km3 event volume was established by reconstructing the paleo edifice in a gis and taking into account volumetric expansion cross sections measured in the field were also used for this purpose field investigations also highlighted the presence of two texturally distinct units which are referred to as the block facies and the matrix facies respectively the first is responsible for the typical hummock morphologies found in the proximal area a transitional zone contains a mixed block and matrix facies while in the distal portion blocks and megablocks some of which have a jigsaw puzzle texture gradually decrease in size until they disappear entirely a number of matrix samples were collected to conduct direct shear tests granulometric analyses and classification of the materials the data and analyses described above were used to discuss the mechanism controlling the long runout of the avalanche based on the comparison between the tancitaro debris avalanche and similar events we propose that mechanical fluidization was the mechanism responsible for the remarkable mobility of the landslide the predisposing factors leading to the collapse were also considered field observations suggest that these are mainly related to weakening processes operating both in volcanoes and in non volcanic areas the runout of the tancitaro debris avalanche was numerically modeled using dan w the geotechnical parameters determined in the field and from the laboratory analyses were used as input the dan w code models longitudinal spreading and the thickness and velocity of the failed mass by opportunely selecting a specific rheological model voellmy frictional bingham thus it was determined that the two parameter voellmy model provided the best simulation of the tancitaro debris avalanche movement and the best fitting rheological parameters have been found through back analysis

calcium and calcium isotope changes during carbon cycle perturbations at the end permian negative carbon and calcium isotope excursions as well as climate shifts took place during the most severe mass extinction event in earth s history the end permian 252 ma investigating the connection between carbon and calcium cycles during transient carbon cycle perturbation events such as the end permian may help resolve the intricacies between the coupled calcium carbon cycles as well as provide a tool for constraining the causes of mass extinction here we identify the deficiencies of a simplified calcium model employed in several previous studies and we demonstrate the importance of a fully coupled carbon cycle model when investigating the dynamics of carbon and calcium cycling simulations with a modified version of the long term ocean atmosphere sediment carbon cycle reservoir model which includes a fully coupled carbon calcium cycle indicate that increased weathering rates and ocean acidification potentially caused by siberian trap volcanism are not capable of producing trends observed in the record as previously claimed our model results suggest that combined effects of carbon input via siberian trap volcanism 12 000 pg c the cessation of biological carbon export and variable calcium isotope fractionation due to a change in the seawater carbonate ion concentration represents a more plausible scenario this scenario successfully reconciles 13c and 44ca trends observed in the sediment record as well as the proposed warming of 6 c

geomechanical characterization of the volcaniclastic material involved in the 2002 landslides at stromboli during the 2002 eruption the nw flank of stromboli volcano southern italy experienced large landslides that produced tsunami waves with a maximum runup of 10 m in height this paper focuses on the geomechanical behavior of the loose volcaniclastic layers the weakest component of the deposit forming the volcano flank tests on the coarse grained volcaniclastic soil and on the rock material forming the grains were conducted in dry conditions a feature of the subaerial slope the rock material in spite of its high porosity exhibits relatively high stiffness and strength due to the remarkable continuity of the solid skeleton accordingly the volcaniclastic soil is characterized by high shear strength during shear tests however significant grain crushing occurs which partly explains the nonlinear shear strength envelope and the strain softening associated with contractive behavior grain crushing was also found to affect compressibility and its time dependency investigated under oedometric conditions

the enormous chillos valley lahar an ash flow generated debris flow from cotopaxi volcano ecuador the chillos valley lahar cvl the largest holocene debris flow in area and volume as yet recognized in the northern andes formed on cotopaxi volcano s north and northeast slopes and descended river systems that took it 326 km north northwest to the pacific ocean and 130 km east into the amazon basin in the chillos valley 40 km downstream from the volcano depths of 80 160 m and valley cross sections up to 337 000 m2 are observed implying peak flow discharges of 2 6 6 0 million m3 s the overall volume of the cvl is estimated to be 3 8 km3 the cvl was generated approximately 4500 years bp by a rhyolitic ash flow that followed a small sector collapse on the north and northeast sides of cotopaxi which melted part of the volcano s icecap and transformed rapidly into the debris flow the ash flow and resulting cvl have identical components except for foreign fragments picked up along the flow path juvenile materials including vitric ash crystals and pumice comprise 80 90 of the lahar s deposit whereas rhyolitic dacitic and andesitic lithics make up the remainder the sand size fraction and the 2 to 10 mm fraction together dominate the deposit constituting 63 and 15 wt of the matrix respectively whereas the silt size fraction averages less than 10 wt and the clay size fraction less than 0 5 wt along the 326 km runout these particle size fractions vary little as does the sorting coefficient average 2 6 there is no tendency toward grading or improved sorting limited bulking is recognized the cvl was an enormous non cohesive debris flow notable for its ash flow origin and immense volume and peak discharge which gave it characteristics and a behavior akin to large cohesive mudflows significantly then ash flow generated debris flows can also achieve large volumes and cover great areas thus they can conceivably affect large populated regions far from their source especially dangerous therefore are snow clad volcanoes with recent silicic ash flow histories such as those found in the andes and alaska

a global marine sedimentary response to the end permian mass extinction examples from southern turkey and the western united states the end permian mass extinction greatly diminished marine diversity and brought about a whole scale restructuring of marine ecosystems these ecosystem changes also profoundly affected the sedimentary record data presented here attained through facies analyses of strata deposited during the immediate aftermath of the end permian mass extinction southern turkey and at the close of the early triassic southwestern united states in combination with a literature review show that sedimentary systems were profoundly affected by 1 a reduction in biotic diversity and abundance and 2 long term environmental fluctuations that resulted from the end permian crisis lower triassic strata display widespread microbialite and carbonate seafloor fan development and contain indicators of suppressed infaunal bioturbation such as flat pebble conglomerates and wrinkle structures facies considered unusual in post cambrian subtidal deposits our observations suggest that depositional systems too respond to biotic crises and that certain facies may act as barometers of ecologic and environmental change independent of fossil assemblage analyses close investigation of facies changes during other critical times in earth history may serve as an important tool in interpreting the ecology of metazoans and their environment

effect of enceladus s rapid synchronous spin on interpretation of cassini gravity enceladus s degree 2 gravity determined by cassini is nominally nonhydrostatic to 3 j2 c22 3 38 3 63 as opposed to 10 3 iess et al 2014 interpret this in terms of a hydrostatic interior core and isostatic not hydrostatic floating ice shell enceladus s rapid 1 37 d synchronous spin and tide distorts its shape substantially though enough that the predicted hydrostatic j2 c22 is not 10 3 but closer to 3 25 this leads to the following revision to the internal picture of enceladus compared with iess et al 1 the satellite s core is somewhat smaller and slightly denser 190 km radius and 2450 kg m3 2 the compensation depth shell thickness of the global degree 2 ice shell is 50 km rather close to the base of the modeled ice water layer and 3 the compensation depth shell thickness beneath the south polar terrain from j3 remains shallower thinner at 30 km independent of but influenced by the degree 2 solution

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

the rhyolitic andesitic eruptive history of cotopaxi volcano ecuador at cotopaxi volcano ecuador rhyolitic and andesitic bimodal magmatism has occurred periodically during the past 0 5 ma the sequential eruption of rhyolitic 70 75 sio2 and andesitic 56 62 sio2 magmas from the same volcanic vent over short time spans and without significant intermingling is characteristic of cotopaxi s holocene behavior this study documents the eruptive history of cotopaxi volcano presenting its stratigraphy and geologic field relations along with the relevant mineralogical and chemical nature of the eruptive products in order to determine the temporal and spatial relations of this bimodal alternation cotopaxi s history begins with the barrancas rhyolite series dominated by pumiceous ash flows and regional ash falls between 0 4 and 0 5 ma which was followed by occasional andesitic activity the most important being the ample andesitic lava flows 4 1 km3 that descended the n and nw sides of the edifice following a 400 ka long repose without silicic activity cotopaxi began a new eruptive phase about 13 ka ago that consisted of seven rhyolitic episodes belonging to the holocene f and colorado canyon series the onset of each episode occurred at intervals of 300 3 600 years and each produced ash flows and regional tephra falls with dre volumes of 0 2 3 6 km3 andesitic tephras and lavas are interbedded in the rhyolite sequence the colorado canyon episode 4 500 years bp also witnessed dome and sector collapses on cotopaxi s ne flank which with associated ash flows generated one of the largest cohesive debris flows on record the chillos valley lahar a thin pumice lapilli fall represents the final rhyolitic outburst which occurred at 2 100 years bp the pumices of these holocene rhyolitic eruptions are chemically similar to those of older rhyolites of the barrancas series with the exception of the initial eruptive products of the colorado canyon series whose chemistry is similar to that of the 211 ka ignimbrite of neighboring chalupas volcano since the colorado canyon episode andesitic magmatism has dominated cotopaxi s last 4 400 years characterized by scoria bomb and lithic rich pyroclastic flows infrequent lava flows that reached the base of the cone andesitic lapilli and ash falls that were carried chiefly to the w and large debris flows andesitic magma emission rates are estimated at 1 65 km3 dre ka for the period from 4 200 to 2 100 years bp and 1 85 km3 dre ka for the past 2 100 years resulting in the present large stratocone

lower triassic large sea floor carbonate cements their origin and a mechanism for the prolonged biotic recovery from the end permian mass extinction precipitation of inorganic calcium carbonate is a common occurrence in both modern and ancient marine environments however synsedimentary growth of large 5 10 cm crystalline carbonate cements directly onto the sea floor has been thought to be limited to the proterozoic when seawaters were highly oversaturated with calcium carbonate compared to average phanerozoic values outer shelf to slope deposits of the lower triassic union wash formation in east central california deposited in oxygen restricted settings contain crystalline calcium carbonate cements that appear to have grown directly on the sea floor paleoenvironmental analyses indicate that these large calcium carbonate cements grew under conditions that were similar to those proposed for the precipitation of inorganic calcite in the black sea sulfate reduction of organic matter led to an increase in the amount of bicarbonate ion in deep waters and a concomitant increase in co 2 and alkalinity mixing with surface waters led to co 2 degassing and precipitation of cements from waters supersaturated with calcium carbonate the presence of these cements and associated facies thus provides evidence of harsh environmental conditions in the early triassic at the regional level which may have acted in concert with biotic effects of the end permian mass extinction as well as similar deleterious conditions e g shelf anoxia in other regions to produce a prolonged as well as temporally and geographically variable biotic recovery from this mass extinction