configurational energy and the formation of mixed flowing powder snow and ice avalanches a long standing problem in avalanche dynamics is to model the flow of a mixed flowing powder avalanche here we use the thermodynamic concept of configurational energy to describe the blow out of air from the avalanche core configurational energy is the mean potential energy associated with the location of snow and ice particles in the avalanche core as such configurational energy determines the avalanche flow density expansion of the particle ensemble reduces the flow density and leads to the intake of air compression of the particle ensemble causes the blow out of the intaken air now laden with ice dust once formed the cloud moves independently of the flowing avalanche with the initial momentum acquired in the core configurational energy changes in the avalanche core are therefore intimately related to the formation of the powder suspension cloud in this paper we use the concept of configurational energy to predict the mass of air taken into and blown out of the core this requires calculating the dispersive pressure arising from random particle movements and configuration changes related to the expansion and collapse of the flowing particle ensemble the ice avalanche that struck the everest base camp on 25 april 2015 is simulated using the proposed concept

measured shear rates in large dry and wet snow avalanches we present estimates of internal shear rates of real scale avalanches that are based on velocity measurements optical velocity sensors installed on the instrument pylon at the swiss vallee de la sionne test site are used to measure flow velocities at different flow heights of three large dry and wet snow avalanches possible sources of error in the correlation analysis of the time lagged reflectivity signals measured by optical sensors are identified for real size avalanches these include spurious velocities due to noise and elongated peaks an appropriate choice of the correlation length is essential for obtaining good velocity estimates placing restrictions on the maximum possible accelerations in the flow improves the analysis of the measured data coherent signals are found only in the dense flowing cores we observe the evolution of shear rates at different depths between the front and tail of the flowing avalanche at the front large shear rates are found throughout the depth at the tail plug flows overriding highly sheared layers near the bottom of the flow are observed the measured velocities change strongly with height above the ground and fluctuations around the measured mean velocity can be identified we find that the dense flows are laminar undergoing a transition from supercritical to subcritical flow behaviour from the head to the tail furthermore we provide real scale experimental evidence that the mean shear rate and the magnitude of velocity fluctuations increase with the mean discharge

interaction between an inclined gravity current and a pycnocline in a two layer stratification a series of laboratory experiments were conducted to investigate the characteristics of a dense gravity current flowing down an inclined slope into a quiescent two layer stratification the presence of the pycnocline causes the gravity current to split and intrude into the ambient at two distinct levels of neutral buoyancy as opposed to the classical description of gravity currents in stratified media as being either a pure underflow or interflow the splitting behaviour is observed to be dependent on the richardson number ri unicode stix x1d70c of the gravity current formulated as the ratio of the excess density and the ambient stratification for low ri unicode stix x1d70c underflow is more dominant while at higher ri unicode stix x1d70c interflow is more dominant as ri unicode stix x1d70c increases however we find that the splitting behaviour eventually becomes independent of ri unicode stix x1d70c additionally we have also identified two different types of waves that form on the pycnocline in response to the intrusion of the gravity current an underflow dominated regime causes a pycnocline displacement where the speed of the wave crest is locked to the gravity current whereas an interflow dominated regime launches an internal wave that moves much faster than the gravity current head or interfacial intrusion

exploring the significance of the fluidized flow regime for avalanche hazard mapping observational and experimental evidence suggests that it is important to explicitly account for the uidised ow regime in avalanche hazard mapping due to its high mobility intermediate density and high velocity we explore the di erences to conventional runout modelling by implementing an extension of the norem irgens schieldrop rheology in a simple mass point model when the dispersive stresses and the excess pore pressure equal the overburden pressure the ow height increases and the density diminishes until a new equilibrium is reached determined by the di erent density dependences of the two parameters of the dispersive stresses fluidization requires su ciently steep terrain when it occurs it leads to substantially higher velocities than in the dense ow regime the model parameters are strongly constrained by their physical meaning and vary little between widely di erent avalanches yet in all test cases we obtained better agreement between simulated and observed runout distances and pressure e ects than with conventional models fig 1 deposit area of the albristhorn avalanche of 30 january 1995 adelboden switzerland the deposit of the dense part is clearly visible greyish outline the area reached by the uidised part is black outlined the suspension layer continued for several hundred meters uphill to the left photo stefan keller

deformation metamorphism and imbrication of the indian plate south of the main mantle thrust north pakistan south of the main mantle thrust in north pakistan rocks of the northern edge of the indian plate were deformed and metamorphosed during the main southward thrusting phase of the himalayan orogeny in the hazara region between the indus and kaghan valleys metamorphic grade increases northwards from chlorite zone to sillimanite zone rocks in a typically barrovian sequence metamorphism was largely synchronous with early phases of the deformation the metamorphic rocks were subsequently imbricated by late north dipping thrusts each with higher grade rocks in the hanging wall than in the footwall such that the metamorphic profile shows an overall tectonic inversion the rocks of the hazara region form one of a number of internally imbricated metamorphic blocks stacked after the metamorphic peak on top of each other during the late thrusting this imbrication and stacking represents an early period of post himalayan uplift

metamorphic response to collision in the central himalayan orogen abstract closure of the neotethys ocean and high angle continent continent collision between india and asia after about 55 ma resulted in low angle subduction of the indian plate below the tibetan plateau and by 30 ma established an arcuate 2300 km long shallow north dipping metamorphic fold thrust belt in the foreland this himalayan metamorphic front quickly established an upper plate lower plate paired metamorphic architecture centred on the median high himal thrust that largely controlled subsequent evolution the upper plate is a thick slab of high t moderate p high grade migmatized metamorphic rocks whereas the lower plate is an inverted series of moderate t high p schists in two crustal wedges the broad main central thrust zone and at lowest structural levels the footwall below the basal main central thrust spatial and temporal patterns of metamorphic response in the evolving himalayan metamorphic front has been characterized in a large scale integrated structural metamorphic study based on 8 profiles across eastern nepal metamorphic response at all structural levels is established using a large dataset n 160 of internally consistent quantitative pt determinations petrology of metapelite samples semi quantitative p t paths metamorphic mapping and metamorphic field gradients these results are integrated with previously published metamorphic studies structural profiles and metamorphic chronology from these datasets the architecture and evolution of the himalayan metamorphic front is constrained by rock kinematics metamorphic field gradients showing discontinuities and diachronous metamorphism with contrasting p t evolutions at different structural levels each of the three panels constituting the himalayan metamorphic front upper plate main central thrust zone and footwall experienced distinctly different tectono metamorphic histories crustal processes operating during metamorphism and exhumation differ between the upper and lower plates the upper plate experienced long lived metamorphism starting from at least 28 38 ma and tracking low p t clockwise p t paths that culminated at 19 27 ma in peak high grade condition with 27 31 c km thermal regimes protracted high grade conditions produced significant partial melt which facilitated gravity driven southward extrusion involving internal ductile flow processes southward extrusion of the upper plate was accommodated by coeval reverse movement on the high himal thrust and top down to the north normal reactivation of the south tibet detachment system between 22 10 ma transport of this thick slab to the south resulted in further prograde burial of the lower plate below culminating in peak metamorphism at the highest pressures attained in the lower plate rocks the lower plate consists of at least two deeply buried 7 5 9 4 kb crustal wedges both of which experienced steep p t hairpin clockwise p t paths with isothermal decompression the main central thrust zone experienced 20 26 c km metamorphism at 12 22 ma and was exhumed along the basal main central thrust after 11 ma whereas loading by the main central thrust zone gave rise to further prograde burial of the footwall which experienced 16 21 c km metamorphism at 4 10 ma and was exhumed along the main boundary thrust at 3 9 ma in contrast to the upper plate both crustal wedges were exhumed by a process of out wedging which involved upthrusting along basal and internal thrusts with coeval extensional slip in the hanging walls this three stage foreland propagating lateral exhumation history resulted in telescoping of the himalayan metamorphic front in concert with peak metamorphic events at different structural levels during main phase orogenesis and is not the result of superimposed retrograde reactivation of the belt

collision tectonics in the nw himalayas west himalayan tectonics involve the collision of microplates between the indian and asian plates the kohistan complex consists largely of tightly folded basic volcanics and sediments generated as late jurassic to late cretaceous island arcs these were intruded by post folding mid cretaceous eocene plutonics produced from continued subduction of the indian plate after closure of a suture between kohistan and the karakorum the himalayan structures show major thrust sheets and the kohistan arc is essentially a crustal pop up with southward upright and northward verging structures developed above a thick ductile decoupling zone the indus suture which can be traced for 100 km beneath kohistan on large reentrants this pop up formed by a two stage process closure of the northern suture followed by closure of the southern indus suture granitic rocks of the kohis tan ladakh batholith dated at 100 40 ma post date most of the structures related to the northern suture but were deformed and carried southwards on shear structures related to the indus suture postcollisional deformation carried this kohistan complex on deep decoupling zones over the indian plate on a series of imbricated gneiss sheets the thrusts climbing up section in the movement direction so that in the far s some override their own molasse debris folds above these deep decoupling zones deformed their overlying thrust sheets into large antiforms i e the nanga parbat and hazara syntaxes the nanga parbat syntaxis probably formed due to a shear couple near a branch line where one of the main himalayan thrusts joined the indus suture beneath kohistan crustal delamination to produce the imbricated gneiss sheets could not account for all the displacement of india into asia suggested by palaeomagnetic data there must also have been lateral displacement as demonstrated by the large oblique slip shear zone in the hunza valley n of kohistan

thermal evolution and exhumation in obliquely convergent transpressive orogens most p t t path models to date have considered a linear erosion rate for exhumation from burial depth related to isostatic readjustment of crustal thickness a few have discussed extension enhanced exhumation erosional exhumation can only restore lower crustal rocks from the thickened mountain root to their previous original depth in the pre collisional crust one major assumption of all models to date is that the compressive forces responsible for crustal thickening cease before elevation and erosion begins however compression is often still active even if the crustal thickening has stopped further compression of the thickened and strongly deformed orogenic root is responsible for forceful exhumation extrusion of softened rocks upwards hence the rate of exhumation is related to the rate of convergence of colliding plates extrusional exhumation can elevate buried rocks to any depth depending on the action of fault shear systems in the extrusional exhumation models examined here the ascending rocks cool faster because they approach the zero temperature surface conditions more rapidly than by isostatic erosion the exhumation rate is also governed by the angle between the plate boundary and the displacement vector implying that the convergent plate boundaries are regarded as complex transpressive systems in which the degree of obliquity can be expressed by the ratio of pure to simple shear components a low ratio of pure simple shear typical for wrench dominated plate boundaries implies long distance horizontal transport from the buried position in the original orogen and longer periods during which metamorphic heating occurs a high ratio of pure simple shear characteristic for frontal like convergence implies a rapid exhumation without significant heating thus granulites barrovian type and blueschist facies metamorphism are characterised by increasing angle of obliquity 10 30 90 respectively the high temperature limit at low ratio of pure simple shear is the geotherm t and lies at temperatures that would commonly be taken to indicate that addition of mantle heat was required to generate hot geotherms and p t t paths wrench faulting over 100 s of kilometres at reasonable slow convergence rates could lead to extensive dehydration melting and granulite formation in large scale collisional orogens

u pb monazite ages from the pakistan himalaya record pre himalayan ordovician orogeny and permian continental breakup the greater himalayan sequence in india and nepal records crustal thickening processes that took place during and following the onset of india asia collision ca 54 50 ma these resulted in late eocene early miocene kyanite and sillimanite grade regional metamorphism and oligocene miocene crustal anatexis which formed migmatites and leucogranites we present new u pb monazite data for kyanite and sillimanite grade gneisses of the neoproterozoic to cambrian tanawal formation in the pakistan himalaya which have metamorphic ages of 482 4 7 9 ma and 464 5 4 0 ma respectively these ages together with along strike equivalent rocks in the lesser himalaya of india and nepal help to define an ordovician orogeny the bhimpedian orogeny also called the kurgiakh orogeny spanning at least from 490 to 460 ma which followed neoproterozoic cambrian sedimentation and preceded late ordovician silurian postorogenic molasse deposition and development of a stable shelf margin at 460 440 ma these new ages for peak metamorphism of neoproterozoic rocks in the pakistan himalaya overlap with those of widespread s type granites that exist along the length of the lesser himalaya e g mansehra mandi and kathmandu granites greater himalaya e g nanga parbat kinnaur kailas and ama drime and in the north himalayan domes e g the tso morari kangmar and kampa domes thus based on stratigraphic metamorphic and u pb geochronological criteria we equate rocks of the tanawal formation gneisses to the lesser himalayan rocks to the east and rocks of the alpurai group to the higher himalaya our data also confirm that the lesser greater and tethyan himalaya are all part of a single contiguous plate staurolite grade schists from a higher structural level of the tanawal formation record u pb monazite ages of ca 272 267 ma indicating the occurrence of permian regional metamorphism in the area concomitant with major rifting and extrusion of the panjal trap volcanics

the crystalline units of the high himalayas in the lahul zanskar region northwest india metamorphic tectonic history and geochronology of the collided and imbricated indian plate in the high himalayan belt of northwest india crustal thickening linked to palaeogene collision between india and eurasia has led to the formation of two main crystalline tectonic units separated by the syn metamorphic miyar thrust the high himalayan crystallines sensu stricto hhc at the bottom and the kade unit at the top these units are structurally interposed between the underlying lesser himalaya and the very low grade sediments of the tibetan nappes they consist of paragneisses orthogneisses minor metabasics and chiefly in the hhc leucogranites the hhc registers a polyphase metamorphism with two main stages designated as m1 and m2 a metamorphic zonation with high temperature recrystallization and migmatization at middle structural levels and medium temperature assemblages at upper and lower levels in contrast the kade unit underwent a low temperature metamorphism rb sr and u th pb isotope data point to derivation of the orthogneisses from early palaeozoic granitoids while the leucogranites formed by anatexis of the hhc rocks and were probably emplaced during miocene time most of the complicated metamorphic setting is related to polyphase tectonic stacking of the hhc with the cooler kade unit and lesser himalaya during the himalayan history however a few inconsistencies exist for a purely himalayan age of some ml assemblages of the hhc as regards the crustal derived leucogranites the formation of a first generation mixed with quartzo feldspathic leucosomes was possibly linked to melt lubricated shear zones which favoured rapid crustal displacements at upper levels they intruded during stage m2 and the latest movements along the syn metamorphic miyar thrust but before juxtaposition of the tibetan nappes along the late metamorphic zanskar fault

coupling of turbulent and non turbulent flow regimes within pyroclastic density currents the internal dynamics of pyroclastic density currents are not easily observed experiments reveal how the underflow and turbulent ash cloud regimes within pyroclastic flows are dynamically coupled through a zone of intermediate turbulence volcanic eruptions are at their most deadly when pyroclastic density currents sweep across landscapes to devastate everything in their path1 2 the internal dynamics underpinning these hazards cannot be directly observed3 here we present a quantitative view inside pyroclastic density currents by synthesizing their natural flow behaviour in large scale experiments the experiments trace flow dynamics from initiation to deposition and can explain the sequence and evolution of real world deposits we show that inside pyroclastic density currents the long hypothesized non turbulent underflow and fully turbulent ash cloud regions4 5 are linked through a hitherto unrecognized middle zone of intermediate turbulence and concentration bounded by abrupt jumps in turbulence the middle zone couples underflow and ash cloud regions kinematically inside this zone strong feedback between gas and particle phases leads to the formation of mesoscale turbulence clusters these extremely fast settling dendritic structures dictate the internal stratification and evolution of pyroclastic density currents and allow the underflows to grow significantly during runout our experiments reveal how the underflow and ash cloud regions are dynamically related insights that are relevant to the forecasting of pyroclastic density current behaviour in volcanic hazard models

cr bearing tourmaline associated with emerald deposits from swat nw pakistan genesis and its exploration significance carbonate talc altered ultramafic and mafic rocks of the obducted oceanic lithosphere along the main mantle thrust in the swat valley host emerald deposits and are invaded by quartz veins and stockworks both the quartz veins and carbonate talc altered rocks contain discrete grains and clusters of tourmaline crystals which may be associated with emerald and or chromian muscovite tourmalines from the mingora and gujar kili emerald mines and the spin obo kuh area are ni bearing cr rich dravites and oxy dravites that exhibit substantial chemical variability with 2 0 2 5 atoms per formula unit apfu mg relatively low al 4 8 5 8 apfu high cr 0 5 1 8 apfu high cr cr al ratios of 0 08 0 28 significant amounts of ni up to 0 11 apfu and variable calculated w site o 2 0 2 0 8 apfu the mechanisms that appear to control the tourmaline chemistry at these localites are combinations of the dominant substitution al cr with lesser amounts of the mg oh 1 al cr o 2 and al 3 fe 3 substitutions relative to the mingora gujar kili and spin obo kuh areas the charbagh tourmalines are oxy dravites that have comparable mg contents 2 2 2 3 apfu with variable calculated w site o 2 0 6 0 9 apfu but are more fe rich 0 5 apfu and al rich 6 0 6 3 apfu with low cr 0 00 0 01 apfu and ni contents 0 01 0 02 apfu the mechanism that appears to control the variable chemistry of the charbagh tourmalines is primarily mg oh 1 al o 2 the chemical characteristics of tourmalines from the various localities relate most clearly to differences in host rock chemistry tourmalines from the carbonate talc altered ultramafic mafic rocks and the invasive quartz veins have a common hydrothermal origin associated with emplacement and crystallization of younger granitoids furthermore the occurrence of swat emeralds in quartz tourmaline chromian muscovite veins suggests that the tourmaline is cogenetic with emerald formation the quality and quantity of swat emeralds depend on the 1 host rock composition and 2 nature of the hydrothermal fluids large deposits of gem quality emerald occur in carbonate altered ultramafic rocks which also contain cr rich dravites and oxy dravites this suggests that the presence of high cr magnesian tourmalines particularly in magnesite talc altered ultramafic rocks can represent a criterion for further emerald exploration in the lower swat region of pakistan and comparable ultramafic hosted emerald producing regions

inferences on flow mechanisms from snow avalanche deposits the deposit structure of 20 very small to large avalanches that occurred in the davos area eastern swiss alps during winters 2004 05 and 2005 06 was investigated snow cover entrainment was significant in the majority of events and likely to have occurred in all cases evidence was found both for plough like frontal entrainment especially in wet snow avalanches and more gradual erosion along the base of dry snow avalanches several of the dry snow avalanches both small and large showed a fairly abrupt decrease in deposit thickness in the distal direction often accompanied by changes in the granulometry and the deposit density combined with other observations snow plastered onto tree trunks deposit less flow marks in bends etc and measurements at instrumented test sites this phenomenon is best explained as being due to a fluidized low density flow regime that formed mostly in the head of some dry snow avalanches the mass fraction of the fluidized deposits ranged from less than 1 to 25 of the total deposit mass fluidization appears to depend rather sensitively on snow conditions and path properties

deformation partitioning and porphyroblast rotation in meta morphic rocks a radical reinterpretation abstract most porphyroblasts never rotate during ductile deformation provided they do not intern ally deform during subsequent events with the exception of relatively uncommon but spectacular examples of spiralling garnets instead the sur rounding foliation rotates and reactivates due to partitioning of the deformation around the porphyroblast consequently porphyroblasts commonly preserve the orientation of early foliations and stretching lineations within strain shadows or inclusion trails even where these structures have been rotated or obliterated in the matrix due to subsequent deformation these relationships can be readily used to help develop an understanding of the processes of foliation development and they demonstrate the prominent role of reactivation of old foliations during subse quent deformation they can also be used to determine the deformation history as porphyro blasts only rotate when the deformation cannot partition and involves progressive shearing with no combined bulk shortening component

variation of deposition depth with slope angle in snow avalanches measurements from vallee de la sionne 1 the snow surface height was precisely measured with a laser scanner before and after the passage of two dry mixed avalanches in vallee de la sionne during the winter of 2005 2006 the measurements were used to calculate the depth of the deposited snow along each entire avalanche path with a height resolution of 100 mm and a horizontal resolution of 500 mm these data are much more accurate than any previous measurements from large avalanches and show that the deposit depth is strongly negatively correlated with the slope angle that is on steep slopes the deposit is shallow and on gentle slopes the deposit is deep the time evolution of the snow depth showing the initial erosion and final deposition as the avalanche passed was also observed at one position using a frequency modulated continuous wave radar measurements at a nearby position gave flow speed profiles and showed that the avalanche tail consists of a steady state subcritical flow that lasts for about 100 s eventually the tail slowly decelerates as the depth slightly decreases and then it comes to rest we show that the dependency between the slope angle and the deposition depth can be explained by both a cohesive friction model and the pouliquen h stop model

size of snow particles in a powder snow avalanche little quantitative information is available concerning the size of ice particles in the turbulent clouds of powder snow avalanches to quantify particle size distributions we have developed an experimental device that collects particles in real scale powder avalanches the device was placed on the concrete bunker of the swiss vallee de la sionne avalanche dynamics test site on 31 january 2003 a large powder snow avalanche struck the bunker and we were able to collect particle samples the collected particles have been photographed and the pictures digitized an image analysis tool allows us to determine an equivalent particle radius the captured particles have a geometric mean of 0 16 mm the largest particles were 0 8 mm in size and the smallest particles 0 03 mm

geothermometry geobarometry and the al2sio5 triple point at mt moosilauke new hampshire the distribution of aluminum silicate minerals in pelitic schists constrains pressure and temperature conditions during the acadian orogeny to have been approximately those of the al 2 sio 5 invariant point thus providing an excellent opportunity to evaluate the internal consistency of a variety of published geothermometers and geobarometers with the al 2 sio 5 invariant point of holdaway 1971 four fluid independent equilibria yield p t estimates consistent with holdaway 1971 two fluid dependent equilibria yield internally consistent but unrealistically high temperatures our data are consistent with the conclusions that 1 only pyrope grossular mixing in the quaternary garnet system is significantly non ideal and 2 the activity coefficient for the anorthite component in plagioclase is approximately 2 at triple point p t conditions modified journal abstract

high resolution radar measurements of snow avalanches 1 two snow avalanches that occurred in the winter 2010 2011 at vallee de la sionne switzerland are studied using a new phased array fmcw radar system with unprecedented spatial resolution the 5 3 ghz radar penetrates through the powder cloud and reflects off the underlying denser core data are recorded at 50 hz and have a range resolution better than 1 m over the entire avalanche track we are able to demonstrate good agreement between the radar results and existing measurement systems that record at particular points on the avalanche track the radar data reveal a wealth of structure in the avalanche and allow the tracking of individual fronts and surges down the slope for the first time

pedo and biogeochemical studies of mafic and ultramfic rocks in the mingora and kabal areas swat pakistan this study highlights the heavy metals hms distribution in soils and their uptake by wild plants grown in the soils derived from the mafic and ultramafic terrains plant and soil samples were analyzed for cu pb zn cr ni and cd using atomic absorption spectrophotometer the data indicate that almost all the hms in the soil samples collected from the study area exceeded the reference and normal agricultural soils greater variability was noticed in the uptake of hms by various plants grown on the studied soils high concentrations of cu and zn in cannabis sativa l seft hemp pb in ailanthus altissima mill ailanto ni and cr in indigofrra gerardiana wall ex baker sage and saccharum griffihii munro ex boiss plume grass were noticed among the studied plants the multifold enrichments of cr and ni in the indigofrra gerardiana and saccharum griffihii as compared to the other plants of the study area suggested that these plants have the ability to uptake and translocate high concentrations of cr and ni the excessive concentrations of cr and ni in these plants can be used for mineral prospecting but their main concern could be of serious environmental problems and health risks in the inhabitants of the study areas

a multi parameter criterion for layer formation in a stratified shear flow using sorted buoyancy coordinates here we examine the conditions for layer formation in a stratified shear flow we reformulate the conditions for amplification of small perturbations to a uniform stratification first proposed by phillips deep sea research and oceanographic abstracts vol 19 1972 pp 79 81 elsevier and posmentier j phys oceanogr vol 7 2 1977 pp 298 300 using the sorted buoyancy coordinates introduced by nakamura j atmos sci vol 53 11 1996 pp 1524 1537 and winters d asaro j fluid mech vol 317 1996 pp 179 193 we consider the possible dependence of the effective diffusivity on three non dimensional parameters the gradient richardson number the buoyancy reynolds number and the prandtl number and obtain a simple expression for conditions favourable for layer formation the new framework is applied to direct numerical simulations of stratified shear flow we then apply a recent multi parameter parameterization developed by salehipour et al geophys res lett vol 43 7 2016 pp 3370 3379 which suggests that layer formation is favoured for large prandtl numbers and moderate to large values of the gradient richardson and buoyancy reynolds numbers

geodar data and the flow regimes of snow avalanches geodar a custom radar system images avalanches over the entire slope with high spatial and temporal resolution at the experimental test site vallee de la sionne in switzerland between winter seasons 2009 10 and 2014 15 data has been acquired from 77 avalanches these data sets describe a wide variety of avalanches which we classify in terms of seven flow regimes and combinations thereof these flow regimes expand on previous classifications with four identifiable dense flow regimes where interaction between granules and with the flow bed dominates dynamics and two different dilute flow regimes where interaction between snow particles and the air becomes dominant there is a further regime identified where snow balls simply roll down the mountain a cold dense regime and a warm shear regime behave like non cohesive granular flows with velocity shear throughout the flow a sliding slab regime and a warm plug regime occur when cohesion dominates and causes the flow units to act as solid like objects sliding on a thin shear zone an intermittent regime connects the cold dense regime with the suspension regime and is characterised by highly fluctuating density and surging activity geodar enables localization of these flow regimes and transitions between them in time and space we discuss flow regime transitions in terms of snow properties topography speed and size of the avalanches this paper also serves as a reference for the data set which is made publicly available and should prove to be an invaluable resource for the development of physically based avalanche models

exhumation of the ultrahigh pressure tso morari unit in eastern ladakh nw himalaya a case study exhumation processes of the ultra high pressure uhp tso morari dome nw himalaya are investigated using structural petrological and geochronological data the uhp tso morari unit is bounded by the low grade metamorphic indus suture zone to the ne and mata unit to the sw three deformation phases d1 d2 and d3 are observed only d3 is common to the uhp unit and the surrounding units in the uhp unit the first deformation phase d1 produced upright folds under eclogitic conditions 20 kbar 580 60 c d1 is overprinted by d2 structures related to a nw se trending open anticline this phase is characterized by blueschist mineral associations and corresponds to the quasi isothermal decompression from a depth of 90 km eclogitic conditions up to 30 40 km the final exhumation phase of the tso morari unit is dominated by tectonic denudation and erosion d3 associated with a slight temperature increase radiochronological analyses indicate that the uhp exhumation process began during the eocene exhumation was fast during d1 d2 and slowed down through d3 in oligocene time the change in the deformation style from d1 d2 to d3 in the tso morari unit coincides with changes in the exhumation rates and in the metamorphic conditions these changes may reflect the transition from an exhumation along the subduction plane in a serpentinized wedge to the vertical uplift of the tso morari unit across the upper crust

powder snow avalanches approximation as non boussinesq clouds with a richardson number dependent entrainment function 1 this paper presents an investigation into non boussinesq particle driven gravity currents such as powder snow avalanches and pyroclastic flows for a finite volume current to maintain its non boussinesq character i e a substantial density difference with its surroundings and therefore high velocities it must counterbalance the entrainment of surrounding fluid by entraining particles from the bed a number of theoretical models have assumed that the volume growth rate of such currents is controlled by the local slope and the density ratio between the current and the ambient fluid an alternative assumption according to which the volume growth rate is controlled solely by the overall richardson number is examined here both assumptions were used successively in the same theoretical model primarily developed by a g kulikovskiy and e i sveshnikova then by p beghin the model predictions were compared to laboratory experiments release of a finite volume down an inclined channel with particle entrainment from the bed and field data a well documented large powder snow avalanche in switzerland in both cases the assumption of a slope dependent volume growth rate received little support whereas assuming that the entrainment coefficient is controlled by the richardson number makes it possible to describe the velocity and volume variations fairly well except for highly concentrated particle driven currents in the laboratory

petrogenetic and tectonic significance of young leucogranites from the northwestern himalaya pakistan in the himalaya of northwestern pakistan small discordant bodies of leucogranite intrude metamorphosed basement of the indian crust as the first step in assessing the tectonic significance of these granites we have used the shrimp ion microprobe to obtain u pb dates on zircon zircons of igneous appearance are scarce in the leucogranites and with one exception are associated with xenocrystic components which occur as discrete grains and as cores rimmed by young zircon zircons of igneous appearance are high in u 5000 to 40 000 ppm low in th u 0 01 to 0 05 and frequently colored a distinct blue xenocrystic components give a range of proterozoic ages consistent with ages previously reported for indian crust in sharp contrast zircons of igneous appearance yield clusters of concordant tertiary ages two leucogranite dikes from southern localities yield rather old emplacement ages of about 35 ma swat and about 50 ma naran together with previously determined 40ar 39ar and fission track cooling ages these ages document immediate and rapid metamorphism and denudation following eocene collision three leucogranite dikes from northern localities within the nanga parbat haramosh massif are very young having emplacement ages of about 2 3 ma 5 ma and 7 ma the formation and emplacement of these leucogranites during the rapid late tertiary denudation of the nanga parbat region suggests to us that decompression melting may be a viable mechanism for leucogranite genesis

air pressure data from the vallee de la sionne avalanches of 2004 1 despite their clear danger to humans snow avalanches are hard to document they occur in inaccessible and dangerous locations often at times of bad weather observation instruments frequently malfunction in the harsh conditions or are destroyed measurements of powder snow avalanches are particularly difficult as these occur less frequently and are usually very large to understand the air flow in front of and inside powder snow avalanches we have designed an air pressure sensor to survive the harsh conditions it consists of a differential pressure transducer with a high frequency response built into a specially designed housing unit we mounted this 10 m from the ground on a measurement mast in the vallee de la sionne avalanche test site in switzerland data from five powder snow avalanches over the winter of 2004 were recorded three of these were natural releases and two were artificially triggered with explosives we present an analysis of the sensor response and an interpretation of the signals in terms of simple flow fields we show how these data can be used to deduce information about the speed size and location of the avalanches using a dipole approximation our sensor has two major limitations the length of the internal tubing produces low frequency resonances and there is only one transducer so a complete flow model is needed to deduce the three velocity components and pressure we discuss these limitations and give a design for a new sensor to overcome them

stratigraphy and structure of the indus suture in the lower swat pakistan nw himalaya abstract we present a geological map detailed structural description and new subdivisions of the indus suture zone lithologies in northeast pakistan lower swat region the indus suture zone is a dominantly fore arc related assemblage obducted onto the indian plate initial southward thrusting was followed by the reactivation of the indus suture as a ductile brittle normal fault significant strike slip faulting may have taken place at this stage later brittle reverse faults demonstrate that shortening outlasted normal faulting the comparison of the structural evolution of the indus suture zone and the indian plate shows that both terrains were sharing the deformational history possibly since the earliest stage of collision the lower swat area records a full orogenic cycle from early rifting through continent arc collision to orogenic collapse we present a geodynamic model that integrates all these elements

thrust tectonics and the deep structure of the pakistan himalaya the systematic restoration of thrust systems provides a powerful constraint on the deep structure of orogenic belts a balanced cross section through the imbricated upper crust of the indian plate in the footwall to the main mantle thrust of the western himalaya restores to a minimum width of 730 km the implicit shortening being in excess of 470 km this requires the himalaya and southern tibetan region to be underlain by a wedge of indian crust however a full appraisal of gross crustal structure awaits deep seismic control

field experiments and numerical modeling of mass entrainment in snow avalanches 1 snow entrainment alters the speed and hence the run out distance of avalanches yet little is known about this significant process we studied entrainment in snow avalanches using observations from 1 the swiss vallee de la sionne test site 2 the italian pizzac site 3 catastrophic avalanches that occurred during the winter 1998 1999 in switzerland and 4 a medium sized spontaneous avalanche that occurred in 2000 in davos switzerland we determined mass and energy balances for 18 avalanche events on average the mass increased by a factor of 4 the primary mode of entrainment appeared to be frontal ploughing although entrainment behind the avalanche front was also observed step entrainment where a snow cover layer fractures and is entirely consumed by the avalanche also occurred basal erosion was negligible mass availability and snow cover structure were the limiting factors governing entrainment other factors such as track topography and avalanche dimension played a secondary role using the experimental results we introduced an entrainment model into a saint venant type flow model where the internal shear deformation of the avalanche is governed by a bagnold law and the shear stress at the basal layer is treated as a voellmy fluid the model with entrainment not only improves the prediction of the velocities and flow heights in comparison to measurements but also reproduces the variations in run out distances which characterize avalanches with similar terminal velocities but different masses

geo tectonic framework of the himalaya of n pakistan in the karakorum range there is a structurally complicated cretaceous are comprising the kohistan sequence on its northern side the northern suture consists of a mega melange and is bounded to the s by tightly folded pillow bearing volcanics and sediments to the s the kohistan plutonic belt consists of southwards a early foliated and late post tectonic tonalites and diorites b aplites and pegmatites up to 30 of rock volume c basic dykes up to 10 m thick d the chilas complex a stratiform cumulate body over 300 km long and 8 km thick chromite layered dunites gabbros and norites with a low pressure granulite facies mineral fabric of tectonic origin e an amphibolite belt with a complex mixture of other rocks and f the jijal complex a 200 km 2 tectonic wedge of high pressure granulites and chromite layered dunites cumulate graded units in the chilas complex show that it is folded by an isoclinal anticline f 1 the mid upper crust of the are is folded by a 50 km half wavelength f 2 syncline the whole kohistan sequence with its two phases of isoclinal folds was tilted during himalayan collision so that the structures are now subvertical the southern suture main mantle thrust has a wedge of glaucophane schists the indian plate contains a basement of psammites and schists intruded by cambrian granites and overlain by isoclinally folded and metamorphosed carbonates and shales

the intermittency regions of powder snow avalanches powder snow avalanches are typically composed of several regions characterized by different flow regimes these include a turbulent suspension cloud of fine particles a dense basal flow and an intermittency frontal region which is characterized by large fluctuations in impact pressure air pressure velocity and density but whose origin remains unknown in order to describe the physical processes governing the intermittency region we present data from four large powder snow avalanches measured at the vallee de la sionne test site in switzerland which show that the intermittency is caused by mesoscale coherent structures these structures have a length of 3 14 meters and a height of 10 m or more the structures can have velocities as much as 60 larger than the avalanche front speed and are characterized by an air particle mixture whose average density can be as high as 20 kg m 3 this average density increases the drag on large granules by a factor of up to 20 compared to pure air so that each structure can maintain denser snow clusters and single snow granules in suspension for several seconds the intermittency region has importance for the dynamics of an avalanche as it provides an efficient mechanism for moving snow from the dense layer to the powder cloud but also for risk assessment as it can cause large forces at large heights above the basal dense layer

frontal dynamics of powder snow avalanches 1 we analyze frontal dynamics of dilute powder snow avalanches sustained by rapid blow out behind the front such material injection arises as a weakly cohesive snow cover is fluidized by the very pore pressure gradient that the particle cloud induces within the snowpack we model cloud fluid mechanics as a potential flow consisting of a traveling source of denser fluid thrust into a uniform airflow stability analysis of a mass balance involving snow cover and powder cloud yields relations among scouring depth frontal height speed mixed mean density and impact pressure when the frontal region achieves a stable growth rate we compare predictions with field measurements show that powder clouds cannot reach steady frontal speed on a uniform snowpack with constant cloud width and derive a criterion for cloud ignition because static pressure is continuous across the mean air cloud interface and deviatoric stresses are negligible frontal acceleration is insensitive to local slope but instead arises from a deficit of flow induced suction in the wake we calculate how far a powder cloud travels until its frontal mixed mean density becomes stable and show how topographic spread can hasten its collapse

sequential porphyroblast growth and crenulation cleavage development during progressive deformation abstract six stages of crenulation cleavage development during a single deformation event d2 can be recognised in both matrix and porphyroblast inclusion trails in the robertson river formation n e australia these stages progress from undeformed to crenulation and differentiated crenulation of s1 through development of differentiated crenulation cleavage s2 and differentiated schistosity s2 to homogeneous foliation s2 these rocks underwent prograde metamorphism during d2 and chloritoid garnet staurolite andalusite and sillimanite isograds have been mapped most rocks are rich in porphyroblasts which commonly contain well defined inclusion trails the geometry of these trails varies from one mineral type to the next depending on the timing of porphyroblast growth relative to the stage of crenulation cleavage development in the schistose matrix the deformation history involved progressive bulk inhomogeneous shortening and the strain is very heterogeneous on all scales partly as a consequence of this hence each of the six stages of crenulation cleavage development formed locally at various times during d2 therefore if a porphyroblast grew late in the deformation it could overgrow all stages of crenulation cleavage development including the very early ones the temperature increased during metamorphism in any one locality and consequently some porphyroblasts overgrew others that were unstable in the new conditions preserving them from destruction hence the precise timing of mineralogical reactions deduced from isograds and mineral chemistry relative to the stages in schistosity development can also be determined in the andalusite zone the sequence of porphyroblasts in decreasing order of age is biotite garnet biotite staurolite andalusite dissolution of garnet occurred during growth of staurolite and especially andalusite and dissolution of staurolite accompanied andalusite growth

comments on avalanche flow models based on the concept of random kinetic energy in a series of papers bartelt and co workers developed novel snow avalanche models in which random kinetic energy rke rk a k a granular temperature is a key concept the earliest models were for a single constant density layer using a voellmy model but with r k dependent friction parameters this was then extended to variable density and finally a suspension layer powder snow cloud was added the physical basis and mathematical formulation of these models are critically reviewed here with the following main findings i key assumptions in the original rke model differ substantially from established results on dense granular flows in particular the effective friction coefficient decreases to zero with velocity in the rke model ii in the variable density model non canonical interpretation of the energy balance leads to a third order evolution equation for the flow depth or density whereas the stated assumptions imply a first order equation iii the model for the suspension layer neglects gravity and disregards well established theoretical and experimental results on particulate gravity currents some options for improving these aspects are discussed

tectonostratigraphic subdivisions of the himalaya a view from the west 1 indian plate rocks in the central himalaya have traditionally been divided into orogen parallel fault bound tectonostratigraphic zones a straightforward westward extrapolation of these zones has proved problematic in part because of a lack of consensus on the existence or significance of major faults within the metamorphic zone of the indian plate in pakistan where more than 10 locations for the main central thrust mct have been proposed we address this ambiguity by systematically tracing established central himalayan tectonostratigraphy around the western himalayan syntaxis and across pakistan this exercise reveals the following stratigraphic and structural relationships 1 there is a westward decrease in neogene shortening across the himalayan fold and thrust belt such that there is no age equivalent thrust in pakistan with displacement and metamorphic juxtaposition equivalent to the central himalayan mct 2 shortening across the fold and thrust belt in western pakistan is concentrated in the unmetamorphosed foreland as opposed to the metamorphic zone in the central himalaya 3 lesser himalayan higher himalayan and tethyan rocks are in stratigraphic order within the metamorphic zone of pakistan which appears to be the metamorphic equivalent of kashmir tethyan stratigraphy 4 the combination of early paleozoic and late paleozoic tectonism in pakistan has locally eliminated upper proterozoic higher himalayan rock and lower to middle paleozoic tethyan rock from the metamorphic zone of pakistan 5 late cretaceous and or early paleocene proto himalayan deformation in the pakistan foreland telescoped and eroded stratigraphy prior to the main phase of himalayan orogeny 6 tectonostratigraphic zones are offset in eastern pakistan by the transverse jhelum balakot fault 7 there is no evidence within the indian plate of pakistan for a large scale normal fault system comparable to the south tibetan detachment system 8 stratigraphy as well as the age and tectonic setting of deformation and metamorphism must be taken into account when drawing tectonostratigraphic zones

impact pressures and flow regimes in dense snow avalanches observed at the vallee de la sionne test site 1 a fundamental problem in avalanche engineering is to determine the impact pressures exerted on structures this task is complicated because snow avalanches flow in a variety of regimes primarily depending on snow temperature and moisture content in this paper we address this problem by analyzing measured impact pressures flow velocities and flow depths of five vallee de la sionne avalanches the measurements are made on a 20 m high tubular pylon instrumented with high frequency pressure transducers and optoelectronic velocity sensors in the observed avalanches we find both subcritical and supercritical flow regimes typical froude numbers were smaller than 6 the subcritical regime fr 1 is characterized by a flow plug riding above a highly sheared basal layer the measured pressures are large and velocity independent in contradiction to calculation procedures pressure fluctuations increase with flow depth indicating a kinematic stick slip phenomena which is largest at the basal layer supercritical flow regimes 1 fr 6 are characterized by a sheared flow all over the avalanche depth in this regime the impact pressure is velocity dependent we derive relationships governing impact pressure as a function of the froude number and therefore flow regime encompassing all the observed avalanches