textures of peritectic crystals as guides to reactive minerals in magmatic systems new insights from melting experiments peritectic crystals in igneous rocks may be derived from either the source or country rocks or may have formed by reactive assimilation of source inherited solids primary magmatic minerals during self or magma mixing or country rock xenoliths or xenocrysts identifying such peritectic crystals is important for constraining the components and textures of igneous rocks and the underlying processes of magmatic evolution in this study we demonstrate that peritectic olivine formed in melting experiments crystallizes as clusters of euhedral to subhedral crystals olivine replacing orthopyroxene amphibole and phlogopite forms crystal clusters with distinct crystal to melt ratios 2d surface area grain boundary segmentation and inclusion relations in our experiments the textures of peritectic crystals are primarily controlled by the stability temperature and decomposition rate of reactive minerals high temperature minerals such as orthopyroxene slowly decompose to form high density clusters of large crystals with long grain boundary segments the sio2 rich peritectic melt produced favours formation of melt inclusions low temperature minerals such as amphibole and phlogopite rapidly decompose to form low density clusters of small crystals with short grain boundary segments the relatively sio2 poor peritectic melt produced results in the formation of fewer melt inclusions host melt composition has a minor effect on the textures of peritectic olivine formed in the melting experiments of this study and previous contamination experiments but affects the assemblages of the peritectic crystal clusters cluster density and 2d surface area of peritectic olivine tend to decrease whereas grain boundary segment length increases with increasing experimental temperature and h2o content using textural criteria that distinguish olivine formed after different minerals in our melting experiments we hypothesize that two olivine populations from a basaltic andesitic lava flow of the tatara san pedro volcanic complex chile may be peritectic crystals formed after amphibole and orthopyroxene both amphibole and orthopyroxene are common in xenoliths preserved in some tatara san pedro lava flows one notable difference between the experimental and natural olivine crystals is that the natural olivine crystals have 2d surface areas and 2d grain boundary segments up to 1000 and 100 times larger respectively than those produced in our experiments we propose that this size difference is primarily controlled by comparatively slow heating and decomposition of reactive crystals and textural coarsening of peritectic crystals during prolonged magma residence in the natural system

cirques in the sierra de guadarrama and7 somosierra mountains iberian central system shape size and controlling factors the guadarrama and somosierra mountain ranges form the eastern sector of the iberian central system and hosted numerous glaciers during the late pleistocene mis2 glaciation was of low intensity with glaciers of small sizes strongly controlled by the climatic context and the topography this study analyses the shape size distribution and location of 96 cirques existing in these mountain ranges in addition to the standard morphometric parameters and controlling factors altitude aspect and lithology used in most studies additional factors were considered here in relation to the pre glacial relief and fracture network the data were obtained and processed using arcgis 10 4 and relations between the parameters and controlling factors were evaluated using statistical methods the results indicate that most are simple cirques tending to isometry with low vertical incision capacity considerable variation in size and predominantly east facing in the context of the iberian peninsula and other european mountains these cirques are among the most isometric the lowest in height and present the least overdeepening the development of these cirques has generally been the result of random combination of various factors thus i the largest cirques are located at intermediate altitudes with the headwall located on the main divides at former torrential valley heads or at the headwalls of fracture corridor valleys and are north facing ii the longest cirques are located at former torrential valley heads on metamorphic bedrock i e schists slates and on uniform slopes finally the prevailing eastern aspects are explained by topoclimatic factors and are in agreement with previous studies which have proposed a circulation weather type cwt model throughout the iberian peninsula during the last glacial period similar to its current configuration

a transient heating event in the history of a highlands troctolite from apollo 12 soil 12033 a 1 5 mm clast of a highlands troctolite attached to a glassy alkali rich soil breccia was identified in a thin section of 1 2 mm particles from apollo 12 soil sample 12033 the troctolite consists of euhedral olivines fo89 in a groundmass of granulitic plagioclase an95 each olivine grain is rimmed by a thin selvage of olivine plagioclase glass containing vesicles and minute crystallites of spinel olivine and plagioclase this unique texture records a complex history beginning with the formation of the troctolite as a plutonic cumulate followed by subsolidus metamorphism partial remelting vesculation crystallite growth and quenching experimental runs on plagioclase olivine melting rates show that at temperatures above incipient melting the grain boundary selvages in the lunar troctolite would have formed very rapidly in less than about 10 min preservation of selvage glass required rapid cooling the troctolite was subject to a heat pulse most likely accompanying an impact event the same event or more probably a later one welded the troctolite to the soil breccia inasmuch as this particle was found on oceanus procellarum at a site crossed by a ray from copernicus and because olivine has been identified by remote sensing experiments as the dominant mafic mineral in the central peak of copernicus we suggest that the troctolite is a fragment of copernicus ejecta

an assessment procedure for glacial hazards in the swiss alps glacial hazards such as ice avalanches glacial lake outburst floods and debris flows have caused severe damage in populated mountain regions such as the swiss alps assessment of such hazards mus

developments in the characterization of complex rock slope deformation and failure using numerical modelling techniques recent advances in the characterization of complex rock slope deformation and failure using numerical techniques have demonstrated significant potential for furthering our understanding of both the mechanisms processes involved and the associated risk this paper illustrates how rock slope analyses may be undertaken using three levels of sophistication level i analyses include the conventional application of kinematic and limit equilibrium techniques with modifications to include probabilistic techniques coupling of groundwater simulations and simplistic treatment of intact fracture and plastic yield such analyses are primarily suited to simple translational failures involving release on smooth basal rear and lateral surfaces where the principle active damage mechanisms are progressive failure and or asperity breakdown level ii analyses involve the use of continuum and discontinuum numerical methods in addition to simple translation level ii techniques can be applied to complex translational rock slope deformations where step path failure necessitates degradation and failure of intact rock bridges along basal rear and lateral release surfaces active damage processes in this case comprise not only strength degradation along the release surface e g asperity breakdown but also a significant component of brittle intact rock fracture level iii analyses involve the use of hybrid continuum discontinuum codes with fracture simulation capabilities these codes are applicable to a wide spectrum of rock slope failure modes but are particularly well suited to complex translation rotational instabilities where failure requires internal yielding brittle fracturing and shearing in addition to strength degradation along release surfaces through a series of rock slope analyses the application of varied numerical methods are discussed particular emphasis is given to state of the art developments and potential use of level iii hybrid techniques d 2005 elsevier b v all rights reserved

formation conditions of plagioclase bearing type i chondrules in co chondrites a study of natural samples and experimental analogs abstract about ten percent of type i feo poor chondrules in unequilibrated co chondrites contain plagioclase that appears to be igneous in origin crystallizing at a late stage of solidification of host chondrule melts we have studied plagioclase bearing chondrules in detail and compared them with plagioclase free chondrules in order to determine the formation conditions of plagioclase and the constraints that the presence of plagioclase places on the conditions of chondrule formation plagioclase bearing chondrules have similar textures mineral compositions and bulk compositions to plagioclase free chondrules the only possible chemical difference that might control the presence or absence of plagioclase in a given chondrule is that most plagioclase bearing chondrules have a slightly higher bulk al ca ratio than plagioclase free chondrules we carried out dynamic cooling experiments on a type iab chondrule analog in order to investigate chondrule formation conditions our experiments at slow cooling rates

dissolution kinetics of plagioclase in the melt of the system diopside albite anorthite and origin of dusty plagioclase in andesites the textures and kinetics of reaction between plagioclase and melts have been investigated experimentally and origin of dusty plagioclase in andesites has been discussed in the experiments plagioclase of different compositions an96 an61 an54 an23 and an22 surrounded by glasses of six different compositions in the system diopside albite anorthite was heated at temperatures ranging from 1 200 to 1 410 c for 30 min to 88 h textures were closely related to temperature and chemical compositions a crystal became smaller and rounded above the plagioclase liquidus temperature of the starting melt glass and remained its original euhedral shape below the liquidus whatever the temperature the crystal melt interface became rough and often more complicated sieve like texture composed of plagioclase melt mixture in the scale of a few m was developed from the surface of the crystal inward formation of mantled plagioclase if the crystal is less calcic than the plagioclase in equilibrium with the surrounding melt and the interface remained smooth if the crystal is more calcic than the equilibrium plagioclase from these results the following two types of dissolution have been recognized 1 a crystal simply dissolves in the melt which is undersaturated with respect to the phase simple dissolution and a crystal is partially dissolved to form mantled plagioclase by reaction between sodic plagioclase and calcic melt partial dissolution the amount of a crystal dissolved and reacted increased proportional to the square root of time this suggests that these processes are controlled by diffusion probably in the crystal mantled plagioclase produced in the experiments were very similar both texturally and chemically to some of the so called resorbed plagioclase in igneous rocks chemical compositions and textures of plagioclase phenocrysts in island arc andesites of magma mixing origin have been examined cores of clear and dusty plagioclase were clacic about an90 and sodic about an50 respectively this result indicates that dusty plagioclases were formed by the partial melting due to reaction between sodic plagioclase already precipitated in a dacitic magma and a melt of intermediate composition in a mixed magma during the magma mixing

stability analysis of cut slopes using empirical kinematical numerical and limit equilibrium methods case of old jeddah mecca road saudi arabia the stability of natural and man made rock slopes has always been of great concern for engineering geology studies to ensure a safe and functional design of excavated slopes the first and most crucial step is to use reliable input parameters while searching for possible failure modes at the preliminary design stage it is highly important for practicing engineers to determine the best material property for a chosen failure criterion this study aims to analyze the stability condition of a case road cut from different aspects for this purpose two well known failure criteria proposed for rock masses and rock joints were applied in the study depending on the scale of the problem in the slope face the hoek brown failure criterion was used to obtain input data required for modeling intact rock and rock mass behavior and the barton bandis shear strength criterion to determine the input data necessary for the modeling of rock joint behavior smrtool and dips 7 0 programs were utilized to analyze the structurally controlled instabilities due to discontinuities in the cut slope slide 2018 and rs2 9 0 programs were executed to examine the stability condition of cut slope subjected to circular and non circular failures respectively according to the results of numerical and limit equilibrium methods no stability problem occurred in the case of slope due to non sliding circular or non circular slip failures however according to the results of empirical and kinematical analyses some structurally controlled sliding failure modes of planar wedge and toppling were expected on the slope face the result of this study clearly shows that to reach a final decision different analysis methods should be used to evaluate the stability of cut slopes by considering various conditions of jointed rock masses

little ice age glaciers in britain glacier climate modelling in the cairngorm mountains it is widely believed that the last glaciers in the british isles disappeared at the end of the younger dryas stadial 12 9 11 7 cal kyr bp here we use a glacier climate model driven by data from local weather stations to show for the first time that glaciers developed during the little ice age lia in the cairngorm mountains our model is forced from contemporary conditions by a realistic difference in mean annual air temperature of 1 5 c and an increase in annual precipitation of 10 and confirmed by sensitivity analyses these results are supported by the presence of small boulder moraines well within younger dryas ice limits and by a dating programme on a moraine in one cirque as a result we argue that the last glaciers in the cairngorm mountains and perhaps elsewhere in upland britain existed in the lia within the last few hundred years rather than during the younger dryas

an empirical failure criterion for rocks and jointed rock masses abstract a new triaxial strength equation is proposed as fitting the available laboratory triaxial test data it is shown how the five triaxial parameters unconfined compressive tensile and shear strengths coefficient of friction and exponent in the triaxial equation can be inter related by three equations a relation between intact rock strength rock mass strength ratio and barton s rock quality 1974 is next developed based on geomechanical data for four longwall panels and in situ coal strength data this relation and the coefficient of internal friction from barton s classification are used in the three inter relations to evaluate the rest of the triaxial parameters for rock masses performance of the failure criterion is studied using practical cases of rock structures in coal and coal measure strata viz five longwall caving panels and four coal pillars

numerical analysis of initiation and progressive failure in natural rock slopes the 1991 randa rockslide the 1991 randa rockslide in the swiss alps involved several complex mechanisms relating to geological mechanical and hydrological processes for which no clear trigger can be asserted this paper investigates the concept of progressive failure and the numerical modelling of rock mass strength degradation in natural rock slopes using the randa rockslide as a working example results from continuum i e finite element modelling are presented to illustrate a hypothesis suggesting that initiation of a progressive rock mass degradation process ultimately leading to failure began following deglaciation of the valley below discontinuum distinct element modelling is then applied to investigate the underlying mechanisms contributing to the episodic nature of the rockslide finally the use of a hybrid method that combines both continuum and discontinuum techniques to model fracture propagation are discussed in the context of modelling progressive slide surface development linking initiation and degradation to eventual catastrophic failure

the deglaciation of eastern scotland cosmogenic 10be evidence for a lateglacial stillstand cosmogenic nuclide analysis using 10be has been used to date a lateglacial stillstand in the eastern highlands of scotland at 16 6 13 6 kyr bp the dates constrain the extent of the local cairngorm ice cap and the larger scottish ice sheet at a particular stage during deglaciation the geomorphological and sedimentological evidence suggests that the glacial stillstand persisted for around 1 kyr independent 14c dating from loch etteridge within strathspey shows that deglaciation proceeded rapidly after ca 15 kyr bp critically this study demonstrates that glaciers last occupied the valleys of the cairngorms immediately prior to the lateglacial interstadial bolling allerod contrary to previous assumptions that the last large scale glaciation of the massif took place in the loch lomond stadial younger dryas this later event in the cairngorms was therefore confined to the high corries

rate and mechanism in prograde metamorphism for a given rate of heat input into a prograde metamorphic sequence the extent of overstep of reaction temperature disequilibrium depends on the slowest of three sequential steps a surface detachment of reactant minerals b transport of material to the site of mineral growth and c nucleation and growth of the product mineral we have developed analytical expressions which enable determination of the rates of mineral dissolution and growth and of advective and diffusive mass transport during metamorphism the dissolution and growth steps are linear functions of the driving force g of the overall reaction while diffusion may take place either through a grain boundary fluid film or through the disorganized grain boundary itself

a review and analysis of silicate mineral dissolution experiments in natural silicate melts abstract we present a database and a graphical analysis of published experimental results for dissolution rates of olivine quartz plagioclase clinopyroxene orthopyroxene spinel and garnet in basaltic and andesitic melts covering a range of experimental temperatures 1100 1500 c and pressures 10 5 pa 3 0 gpa the published datasets of donaldson 1985 1990 and brearly and scarfe 1986 are the most complete experimental dissolution rates from all datasets are recalculated and normalized to a constant oxygen basis to allow for direct comparison of dissolution rates between different minerals dissolution rates range from 5 10 10 oxygen equivalent moles o e m cm 2 s 1 for olivine in a basaltic melt to 1 3 10 5 o e m cm 2 s 1 for garnet in a basaltic melt values of ln are arthenian for the experiments examined and activation energies range from 118 to 1800 kj o e m for quartz and clinopyroxene respectively the relationship between calculated a rt for the dissolution reactions where a is the thermodynamic potential affinity and values of is linear for olivine plagioclase and quartz we interpret this as strong evidence in support of using calculated a as a predictor of for at least superliquidus melt conditions

reconstructing high magnitude low frequency landslide events based on soil redistribution modelling and a late holocene sediment record from new zealand a sediment record is used in combination with shallow landslide soil redistribution and sediment yield modelling to reconstruct the incidence of high magnitude low frequency landslide events in the upper part of a catchment and the history of a wetland in the lower part eleven sediment cores were obtained from a dune impounded wetland at te henga west auckland northern new zealand sediment stratigraphy and chronology were interpreted by radiocarbon dating foraminiferal analysis and provisional tephrochronology gradual impoundment of the wetland began c 6000 cal yr bp coinciding with the start of a gentle sea level fall but complete damming and initial sedimentation did not begin until c 1000 cal yr bp after damming four well defined sediment pulses occurred and these are preserved in the form of distinct clay layers in most of the sediment cores for interpreting the sediment pulses a physically based landslide model was used to determine spatially distributed relative landslide hazard applicable at the catchment scale an empirical landslide soil redistribution component was added and proved able to determine the volumes and spatial pattern of eroded and deposited soil material sediment delivery ratio and the impact on total catchment sediment yield sediment volumes were calculated from the wetland cores and corresponding landslide scenarios are defined through back analysis of modelled sediment yield output in general at least four major high magnitude landslide events both natural and intensified by forest clearance activities occurred in the catchment upstream of te henga wetland during the last c 1000 years the spatial distribution of modelled critical rainfall values for the catchment can be interpreted as an expression of shallow landslide hazard the magnitude of the sediment pulses represented in the wetland can be back calculated to critical rainfall thresholds representing a shallow landslide model scenario

simulation of snow shielding corrections for cosmogenic nuclide surface exposure studies abstract snow cover reduces cosmogenic nuclide production rates in bedrock corrections for snow cover can be more than 10 in mountainous mid latitude regions where many glacial chronologies have been constructed using cosmogenic nuclide surface dating of landforms most published snow corrections use historic climate data of limited duration that are not likely to reflect adequately the full range of snow conditions over the time of exposure we present a model for describing the impact of snow burial on long term exposure histories of landforms the model applies an energy balance approach to snowpack evolution and incorporates both historic and long term climate proxy data attenuation of cosmogenic fast neutrons is modeled alternatively as a simple exponential decrease with increased shielding or as a thin surface layer with constant production followed by an exponential decrease with increasing depth the choice of attenuation model has little effect on the modeled results for the cairngorms but will have a more significant effect in regions characterized by thinner less dense snowpacks spatial variability in snow cover is modeled as a function of elevation only ignoring local variability in snow accumulation as a result of slope aspect wind redistribution and local topography thus model results reveal general spatial and temporal trends in snow shielding effects rather than site specific corrections applications to data from the cairngorm mountains of scotland show that the constant plus exponential cpe production rate depth profile reduces but does not eliminate snow shielding effects under present day conditions snow at 900 m in the cairngorm mountains reduces average production rates by 6 using the cpe profile and 9 with the exponential profile ep long term climate simulations from 15 5 ka through today produce larger snow shielding effects mainly because they predict an increased proportion of precipitation as snowfall during the younger dryas at 900 m this long term simulation reduces average cosmogenic isotope production rates by 12 cpe and 14 ep these results indicate that snow shielding corrections based on historic climate records may be a potential source of systematic error in midlatitude mountainous regions

estimating bulk rheological properties of flowing snow avalanches from field data reference lhe article 2004 002view record in web of science record created on 2007 09 04 modified on 2016 08 08

modification of slope mass rating smr by continuous functions this study was partially funded by the spanish ministry of science and technology and feder project tec 2005 06863 by the valencia regional government project gv06 179 and grupos03 085 and by the university of alicante project vigrob 157

assessment of rock slope stability for a segment of the ankara pozanti motorway turkey abstract the ciftehan pozanti segment of the ankara pozanti motorway is problematic due to the existence of lithological units with variable characters ten cut slopes are planned along km 352 350 km 358 000 of the proposed motorway the purpose of this study is to determine engineering geological properties of the rocks exposed along the motorway and to assess excavatability and stability of the cut slopes both field and laboratory studies were carried out during this research field studies involved detailed discontinuity surveys laboratory tests were carried out to determine unit weight point load strength index and shear strength parameters of the discontinuities in the study area recrystallized limestone dolomite limestone microgabbro reefal limestone conglomerate and quaternary deposits are exposed however the cut slopes are located within microgabbro reefal limestone dolomite limestone and recrystallized limestone hard to extremely hard ripping with local blasting for the fresh inner part of the rocks is recommended for the excavatability in eight cut slopes wedge failure is expected based on the field observations and stability analyses of the cut slopes slope flattening with various angles wire mesh and drainage ditches are suggested

evaluating the contribution of avalanching to the mass balance of himalayan glaciers avalanching is a prominent source of accumulation on glaciers that have high and steep valley walls surrounding their accumulation zones these glaciers are typically characterised by an extensive supraglacial debris cover and a low accumulation area ratio despite an abundance of such glaciers in the rugged landscapes of the high himalaya attempts to quantify the net avalanche contribution to mass balance and its long term variation are almost missing we first discuss diagnostic criteria to identify strongly avalanche fed glaciers second we develop an approximate method to quantify the magnitude of the avalanche accumulation exploiting its expected control on the dynamics of these glaciers the procedure is based on a simplified flowline model description of the glacier concerned and utilises the known glaciological mass balance velocity and surface elevation profiles of the glacier we apply the method to three himalayan glaciers and show that the data on the recent dynamics of these glaciers are consistent with a dominant contribution of avalanches to the total accumulation as a control experiment we also simulate another himalayan glacier where no significant avalanche contribution is expected and reproduce the recent changes in that glacier without any additional avalanche contribution

structurally controlled instability damage and slope failure in a porphyry rock mass abstract rock slopes fail through structurally controlled mechanisms global circular failures or complex mechanisms depending on structural patterns and rock mass damage here structural geology rock mass characterisation terrestrial laser scanning tls ground based radar interferometry gb insar and finite element modelling are integrated to explore relationships between structure damage and global slope failure at mt gorsa trentino italy there a porphyry quarry has been excavated in complex strongly anisotropic rhyolitic ignimbrite rock masses the slope was affected by a major rockslide in 2003 and undergoes continuing instability site investigations and gb insar monitoring revealed that the 2003 failure was a roto translational rockslide involving about 400 000 m3 of disrupted rock structural analysis of tls and field data shows that the slope is affected by widespread structurally controlled mechanisms sliding toppling strain localization in kink bands the non obvious relationships between structurally controlled and global roto translational slope failure mechanisms are investigated by characterising rock mass damage in different slope sectors a new approach to quantify rock mass damage by mapping the geological strength index and interpreting its topographic signatures in tls point clouds is presented a persistent geological marker is systematically mapped in tls point clouds and correlations between attitude variability statistics and rock mass damage are established providing an efficient assessment tool rock mass damage increases in kinematic domains affected by structurally controlled instability gsi 35 40 and is maximum in areas of ongoing global instability gsi 15 20 the 2003 rockslide occurred inside a damaged rock mass zone with gsi

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

past and future mass balance of ka roimata o hine hukatere franz josef glacier new zealand despite their relatively small total ice volume mid latitude valley glaciers are expected to make a significant contribution to global sea level rise over the next century due to the sensitivity of their mass balance systems to small changes in climate here we use a degree day model to reconstruct the past century of mass balance variation at ka roimata o hine hukatere franz josef glacier new zealand and to predict how mass balance may change over the next century analysis of the relationship between temperature precipitation and mass balance indicates that temperature is a stronger control than precipitation on the mass balance of franz josef glacier the glacier s mass balance relative to its 1986 geometry has decreased at a mean annual rate of 0 02 m a 1 w e between 1894 and 2005 we compare this reduction to observations of terminus advance and retreat of which franz josef glacier has the best record in the southern hemisphere for the years 2000 05 the relative mass balance ranged from 0 75 to 1 50 m a 1 w e with 2000 01 the only year showing a negative mass balance in a regionally downscaled intergovernmental panel on climate change mean warming scenario the annual relative mass balance will continue to decrease at 0 02 m a 1 w e through the next century

gis based cell model for simulating debris flow runout on a fan summary a gis based cell model based on a kinematic approach is proposed to simulate debris flow routing on a fan the sediment water mixture is modeled as a monophasic continuum and the flow pattern is discretized by square cells 1 m in size that coincide with the dem cells flow occurs from cells with a higher mixture free surface to those with a lower mixture free surface a uniform flow law is used if the elevation of the former cell is higher than that of the latter otherwise the flow is simulated using the broad crested weir law erosion and deposition are simulated using an empirical law that is adjusted for a monophasic continuum the sediment concentration in the routing volume is computed at each time step and controls both erosion and deposition the cell model is used to simulate a debris flow that occurred on the rio lazer dolomites north eastern italian alps on november 4th 1966 furthermore the hydrologic and the hydraulic conditions for the initiation of debris flow are simulated providing the solid liquid hydrograph of the resulting debris flow a number of simulations has been carried out with physically reasonable parameters the results are compared with the extension of the debris flow deposition area and the map of observed depths of deposited sediments this comparison shows that the proposed model provides good performance the analysis of sensitivity carried out by systematically varying the model parameters shows that lower performances are associated with parameter values that are not physically reasonable the same event is also simulated using a cellular automata model and a finite volume two dimensional model the results show that the two models provide a sediment deposition pattern less accurate than that provided by the present cell model

power laws and snow avalanches 1 this paper presents evidence of frequency size power laws in several groups of snow avalanche paths other natural hazards such as earthquakes and forest fires exhibit similar power law relationships in addition an analysis of the response of one group of snow avalanche paths to storms through time demonstrates a power law between the response of the system and the binned frequency of those responses our results as well as our experience with these complex non linear systems are consistent with self organized criticality the practical implication of this work is that the frequency size relationship for small and medium sized avalanches may be useful for quantifying the risk of large snow avalanches within a group of avalanche paths

effects of melt viscosity and silica activity on the rate and mechanism of quartz dissolution in melts of the cmas and cas systems the dissolution rate of quartz in melts of the cmas and cas systems at 1 600 c and 1 5 gpa is a function of both the silica activity of the melt and its viscosity in melts with low silica activity quartz dissolves more quickly than in higher asio2 melts regardless of viscosity for melts with equal asio2 dissolution is faster in the low viscosity melt quartz dissolution is controlled by interface kinetics in three of the four melts used in this study for times much greater than predicted by the model of zhang et al in contrib mineral petrol 102 492 513 1989 one melt which was previously shown to adhere to the predicted behaviour at lower temperature shows a significant activation time at higher temperature all the dissolution data indicate that there are likely to be three distinct domains of dissolution behaviour although the details of why a particular melt falls in any one domain require further study although the current database is small the relationship between quartz solubility and the dissolution constant indicate that solubility may be a useful parameter for predicting dissolution rates particularly if silica activity and melt viscosity are also known

a 2 d numerical model of snow ice energy balance and ice flow for paleoclimatic interpretation of glacial geomorphic features abstract standard methods of interpreting the paleoclimates recorded in alpine glacial geomorphic features rely on estimates of paleoglacier shape commonly assume that relationships between mass balance gradient and equilibrium line altitude of modern glaciers apply equally well to glaciers of in many cases dramatically different climates and do not account for the varying influence of topography on glacial extent while those methods may be adequate for many studies there are an increasing number of areas in which that level of analysis does not match the level of detail of the glacial chronologies being developed as an alternative we present a physically based 2 d glacier model that can be used to determine steady state glacier shapes and distributions for a wide range of climatic conditions the model requires only a modest amount of data beyond that which would be required for simpler methods and includes a relatively accurate representation of the effects of topography on the largest component of the surface energy balance shortwave radiation it calculates 2 d in the horizontal plane distribution of snow accumulation using a surface mass and energy balance approach and calculates the resultant glacier shapes with a 2 d flow model in addition to offering a potentially more accurate reconstruction of paleoclimatic conditions the model provides a means of performing detailed sensitivity analysis establishing relationships between similar deposits in basins of different shape and aspect and of predicting glacier shape terminus position in areas not yet explored

snow avalanche mass balance calculation and simulation model verification two or three dimensional avalanche simulation models offer a wide range of applications however a challenging model verification process is demanded accompanied by a reliable determination of model input parameters we show that a verification process can be arranged with remote monitoring data from an artificially triggered avalanche leading to the calculation of avalanche mass balance two numerical methods are applied to increase the quality of the parameter fit and to reduce the number of simulations the quality of the parameter fit is verified by comparing measured and simulated run out lengths in addition a cross check is performed using velocities derived from doppler radar measurements

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

significance of snowblow in the generation of loch lomond stadial younger dryas glaciers in the western pennines northern england geomorphological mapping has identified the former existence of five cirque glaciers that formed during the loch lomond stadial in the western pennines northern england landforms in mallerstang which previously have been interpreted as moraine ridges are shown to be better explained as large complex landslides reconstruction of these former glaciers has allowed the calculation of the former equilibrium line altitudes ela by a number of different methods values for the ela show a range across the area from 311 m to 608 m od but with low values 311 m and 428 m for the two western glaciers these are explained by the existence of large plateau areas adjacent to the former glaciers which contributed additional mass to the glaciers by snowblow on to the glacier surfaces delimitation of the potential snowblow area for each glacier shows that it has a distinct orientation with the western sector 225 315 being statistically significant with the ela indicating the importance of winds from this direction in determining the existence of these palaeoglaciers the significance of snowblow for the generation of small glaciers in marginal areas means that such local factors must be investigated before regional firn line trends are determined in former glaciated areas

an ice cap landsystem for palaeoglaciological reconstructions characterizing the younger dryas in western scotland abstract this paper reviews the contrasting behaviours of ice caps and icefields defines a generic landsystem model that can effectively discriminate between them and applies the model to landform sediment assemblages in an area of western scotland such a model is necessary since many palaeoenvironmental inferences from formerly glaciated terrains are based on the geometry extent and dynamics of reconstructed ice masses the validity of these glacier reconstructions is dependent on the accurate initial interpretation of relict landforms and sediments and their inter relationships a new landsystems model is presented here in which individual geological and geomorphological elements are checked against a set of eight theoretical diagnostic criteria that characterize the style of former glaciation when applied to a 1200 km 2 area of the western scottish highlands the landsystem tool predicts 1 an extensive younger dryas ice cap with a maximum surface elevation of 900 m above sea level implying colder or wetter conditions than previously thought and 2 the survival of an independent mountain icefield in part of the area during deglaciation glaciological theory proxy palaeoenvironmental data and established glacier climate topography relationships support these predictions thereby giving credibility to the landsystem methodology as a generic tool for palaeoglaciological reconstructions

distributed mass balance modelling on two neighbouring glaciers in ortles cevedale italy from 2004 to 2009 a 6 year application of an enhanced temperature index mass balance model to careser and la mare glaciers eastern italian alps is presented the two glaciers exhibit very different characteristics and a comprehensive dataset of distributed mass balance measurements was used to test the model performance the model was run using meteorological data acquired outside the glaciers the work was focused on two main aspects 1 the development of a morphological redistribution procedure for snow and 2 the comparison of three different melt algorithms proposed in the literature the results show that the simple method proposed for snow redistribution can greatly improve simulation of winter balance and further improvements would be achievable by collecting data on inaccessible and high altitude areas all three melt formulations displayed a good skill level and very similar results in modelling the mass balance distribution over glacier areas with slightly better results from a multiplicative algorithm in capturing the vertical balance gradient the simulation errors are related to aspect and elevation and tend to be spatially aggregated some assumptions concerning the spatial and temporal distribution of air temperature and incoming solar radiation although reasonable and widely used in the literature may be responsible for this aggregation hence there is a need to further investigate the processes that regulate the distribution of melt energy and that appear to control the current deglaciation phase in this area

formation of hybrid cumulates melatroctolites in intrusion 4 of the honningsvag intrusive suite northern norway new mapping shows that the 1160 m thick layered series of the mafic to ultramafic intrusion 4 of the honningsvag intrusive suite north norwegian caledonides comprises approximately 25 feldspathic peridotite 55 melatroctolite olivine rich troctolite 5 troctolite 2 olivine melagabbro olivine rich olivine gabbro and 13 15 olivine gabbro the cumulate sequence can be divided into eight macrocyclic units the base of each unit resulting from magma replenishment compositions of olivine and plagioclase obtained from ca 1700 electron microprobe point analyses display complex and limited variations fo87 74 and an80 67 relative to stratigraphic height the origin of olivine rich cumulates such as melatroctolites 52 72 olivine and olivine melagabbros 29 37 olivine in large quantities is difficult to explain by either simple fractional crystallisation or conventional layer forming processes a new genetic model is proposed involving suspension of pre existing cumulus crystals during magma recharge in a periodically replenished magma chamber their partial resorption and simultaneous crystallisation of liquidus olivine cumulates formed in this way represent mixtures of crystals that crystallised from compositionally different magmas and are therefore termed hybrid cumulates apart from their distinctly non cotectic bulk modal proportions the hybrid nature of the olivine rich cumulates is evidenced by partially resorbed plagioclases enclosed within cumulus olivines the occurrence of resorbed plagioclase inclusions in olivine gabbros and large variations in modal plagioclase content suggest that these may also be hybrid cumulates d 2002 elsevier science b v all rights reserved

possible erosion mechanisms in snow avalanches snow erosion and entrainment processes in avalanches are classified according to their mechanisms the flow regimes in which they occur and their spatial position within the avalanche simple but process specific models are proposed for erosion by impacts abrasion plowing and blasting on the basis of order of magnitude estimates the first three mechanisms are clearly expected to be important the fourth mechanism stipulates that the compaction of the snowcover ahead of the avalanche leads to the flow of escaping air just in front of the avalanche that may disrupt the snowcover and support formation of a saltation layer the effects of this hypothetical mechanism resemble those of the plowing mechanism all mechanisms depend strongly on the snow properties but with plausible parameter values erosion rates at or above the experimentally found rates are obtained the entrainment rate of an avalanche is most often limited by the shear stress needed to accelerate the eroded snow to avalanche speed

mass balance estimates for haut glacier d arolla switzerland from 2000 to 2006 using dems and distributed mass balance modeling a distributed mass balance modeling approach is required to assess the impact of future climate scenarios on water availability in glaciated basins accurate estimation of water stored within the snow firn and ice of such basins requires knowledge of the distributed snow and ice mass balance throughout the year in this study we estimate the annual mass balance and runoff for haut glacier darolla switzerland from 2000 to 2006 our estimations are based on observed elevation changes from three digital elevation models dems derived from aerial photographs in september 1999 and 2005 and october 2006 in addition to these estimations we implement a combined field observation and a distributed mass balance modeling approach an energy balance model driven by meteorologi cal variables from automatic weather stations inside the catchment area including gravitational snow transport is run for the period 2005 06 the model results are validated with direct snow water equiv alent measurements as well as with runoff measurements combining the mass balance measurements energy balance calculations and measured runoff we estimate the contribution from ice melt to the runoff for this period to be 25 30 the contribution from snowmelt 50 60 and the contribution from rain 15 25 our model results also show that the snow distribution affects both snow and ice melt it is therefore important for water resources management to understand the distribution of snow in alpine catchments as it seems to be the controlling factor for the timing of streamflow throughout the year as well as for the total availability of water

a spectrum of disequilibrium melting preserved in lava hosted partially melted crustal xenoliths from the wudalianchi volcanic field ne china abstract disequilibrium melting has been established as a common process occurring during crustal anatexis and thus demonstrates that crustal assimilation is not a closed system observations of extreme compositional heterogeneity within partial melts derived from crustal xenoliths have been documented in several recent examples however the retention or transfer of elements to and from residues and glasses and their relative contributions to potential crustal contaminants warrants further investigation recent eruptive products of the huoshaoshan volcano in the holocene wudalianchi volcanic field of northeast china contain crustal xenoliths which preserve a spectrum of partial melting both petrographically and geochemically thus providing an excellent natural example of crustal anatexis correlations exist between the volume of silicic glass preserved within the xenoliths and bulk rock sio2 70 83 wt al2o3 8 16 wt glass 87sr 86sr 0 715 0 908 abundances of elements common in feldspars and micas sr ba rb and elements common in accessory minerals y zr nb these correlations are likely associated with the consumption of feldspars and micas and the varying retention of accessory phases during partial melting the xenoliths which contain greater volumes of silicic glass and residual quartz interpreted as being the most melted were found within pahoehoe lava whilst the least melted xenoliths were found within scoria of the summit cone of huoshaoshan thus it is interpreted that the extent of melting is linked to the immersion time in the lava which we estimate to be on the order of days however the least partially melted samples display geochemical evidence in support of melt loss evidenced by the relatively depleted nature of their whole rock compositions and the larger difference between whole rock and glass yet the more melted samples appear to have experienced less melt loss thus the extent of melting cannot be linked linearly to the volume of melt loss which occurs small scale mm mingling and transfer of material from the enclosing lava to the xenolith are observed however modelling of potential contaminant compositions is inconsistent with crustal contamination during lava petrogenesis it is thus more likely that any crustal contamination in these eruptives is extremely localized within this open magmatic system and most likely occurs at the contact zone between the xenolith and host lava

a mass conserving fast algorithm to parameterize gravitational transport and deposition using digital elevation models 1 many natural phenomena such as snow avalanches debris flows or lahars involve gravitational transport and deposition that is largely governed by topography this paper describes a fast and mass conserving algorithm to parameterize mass transport and deposition mtd over a digital elevation model the algorithm is an extension to existing flow routing and terrain parameterization techniques its fast execution allows application over large areas or its incorporation into other models e g distributed glacier mass balance in mountain topography the proposed method does not include effects of kinetic energy and thus neglects potential uphill flow of fast moving mass the application of mtd is described at the example of small and frequent snow avalanches in steep terrain for which the required parameters are approximated from published data the algorithm mtd has been developed and is described for the gravitational redistribution of snow but it is also applicable to other types of mass movements

comparison of mass balances for vernagtferner oetzal alps as obtained from direct measurements and distributed modeling the direct comparison of modeled glacier mass balance distribution with field measure ments could be problematic as the methodology of determination and the processes considered at the point or catchment scale could differ strongly moreover direct measurements cover only small parts of a glacier and model performance is thus difficult to assess outside these regions remaining opportunities for model validation include comparison of snowlines as derived from remote sensing data and maps of the mass balance distribution as interpreted by observers with local knowledge this study compares such hand drawn maps of the vernagtferner oetzal alps mass balance with the modeled pattern as obtained from a distributed energy mass balance model of intermediate complexity the model is driven by measured daily values of temperature global radiation and precipitation from a nearby climate station and grids of mean daily potential global radiation and climatologic annual precipitation sums compared with the direct measurements the calculated mean mass balance and equilibrium line altitude agreed very well in both balance years although the spatial pattern of the mass balance distribution displayed larger deviations in regions influenced by snowdrift or local topographic undulations however compared with the remaining snow as visible on a satellite image from 1999 the modeled snowline pattern for a larger sample of glaciers is in very good agreement

mineral textures and zoning as evidence for open system processes investigations of mineral textures and zoning as evidence for open system processes during magmatic evolution have always been a centerpiece of petrological studies and have provided some of the best evidence for magma mixing and crustal contamination for many decades e g milch 1905 kuno 1936 eichelberger 1975 sato 1975 anderson 1976 in fact evidence from mineral studies was instrumental in the acceptance of magma mixing as important petrological process ever since it was initially proposed by bunsen 1851 in recent years mineral studies are invigorated by the development of high precision high resolution analytical instruments and techniques through which textural information and compositional data are combined e g jerram and davidson 2007 as minerals respond texturally and compositionally to changing magmatic environments they preserve in their crystal growth stratigraphy a wealth of information regarding their past history of magmatic processes and compositions cf ginibre et al 2007 on the other hand magmatic liquids melts are snapshots of current magmatic states and provide less direct evidence of the processes responsible for their evolution in addition liquids may crystallize thereby destroying the direct evidence they provide with an appropriate set of observations and measurements we can correlate textures with mineral compositions and thus produce a richer composite picture of magmatic evolution than compositional data of minerals alone this contribution reviews the zoning and textures of minerals frequently encountered in volcanic rocks many of which apply equally to plutonic rocks and the interpretations ascribed to these features in terms of open system magmatic processes first i will address the analytical tools that are used to acquire textural and compositional data followed by a brief review of open system processes and a summary of the relevant textures from that point on i will address some mineral specific aspects followed by a discussion

an approach to modelling the impact of snow drift on glaciation in the cairngorm mountains scotland this paper uses a geographical information system gis to develop a rule based model of the effect of snow drifting on glacier growth in the cairngorm mountains scotland during the younger dryas interval we develop a qualitative model of snow drift that uses a number of simple heuristics to generate a map of relative accumulation at a 50 m resolution over the massif relative susceptibility to snow drifting is then compared for a number of different zones under varying wind directions we conclude that under the conditions tested in our model glaciation of the cairngorms during the younger dryas was confined to the high corries and that the pattern of snow drifting suggested by our model points to dominant southerly winds copyright 1999 john wiley sons ltd

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

thermochronological evolution of an intra plate magmatic event inferred from an integrated modeling approach a case study in the westerwald germany abstract a lava sample from the tertiary westerwald volcanic field was selected for a detailed study using various analytical techniques in combination with petrological thermodynamic and diffusion modeling to extract information related to the thermochronological evolution of a magmatic event before eruption the lava sample contains large olivine phenocrysts which are compositionally zoned and two coexisting but chemically distinct melts a host melt with basaltic composition and small spherical pockets of a less abundant trachytic melt globules the sample was analyzed by electron microprobe x ray fluorescence xrf x ray diffraction xrd and electron backscatter diffraction ebsd the primary melt of the host lava was determined using the program primelt2 xls partial fractional crystallization of olivine was modeled using the program alphamelts timescale and cooling rate were retrieved by fitting the measured fe mg zoning along two directions in four olivine grains from the host lava using a 3 d numerical diffusion model the measured variation of ca is also consistent with a chemical diffusion process while a numerical growth model applied to the same olivines does not appear to explain the fe mg zoning chemical zoning of major elements in the melt globules were reproduced with a multicomponent diffusion model the results of this study show that the host magma fractionated about 9 of olivine in a first stage then the crystallization proceeded without further separation of mineral phases modeling of diffusion in the olivine crystals suggests that this second stage lasted at least 5 yrs and the temperature of the melt decreased from 1120 1150 c to 1090 c during this time according to the results of the multicomponent diffusion model applied to the melt globules the coexistence of the two melts was extremely short less than few hours possibly recording the assimilation of the globules during eruption or cooling of the whole system on the surface

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

superelevation of flowing avalanches around curved channel bends flowing avalanches are those with a dense core of flowing granular material at the base which dominates the dynamics causing friction sometimes when avalanches descend they encounter curved channel bends which cause the flowing material to superelevate or climb up on the wall of the channel bend so that the level of the flowing snow is higher on the outside of the bend than at the center of the channel this can provide important information about avalanche speeds the conventional approach for estimating speeds is mathematically equivalent to one developed from equations based on fluid mechanics with a balance between fluid pressure force and centrifugal force to yield a simple expression which relates channel radius avalanche speed and superelevation geometry in this paper the conventional theory is replaced by one which relates avalanche speed to basal friction as appropriate for flowing snow passive snow pressure accounting for friction between snow particles channel radius and superelevation geometry it is shown that the conventional theory is physically unrealistic for flowing snow modeled as a frictional material also the conventional theory will result in lower speed estimates than the new formulation for the same amount of superelevation

lateglacial surface exposure dating in the monadhliath mountains central highlands scotland we constrain the deglaciation history of the monadhliath mountains since the last glacial maximum using glacial geomorphology and surface exposure dating collectively these data clarify the glacial history of the monadhliath mountains at the close of the devensian cold period 10be exposure ages indicate deglaciation of the last devensian ice sheet at 15 1 1 4 ka at ca 640 m od the exposure ages are consistent with basal radiocarbon ages from nearby loch etteridge 5 km to the south east 15 3 0 2 kcal bp1 boulders from moraines in three monadhliath corries yielded exposure ages between 11 8 ka and 9 8 ka 470 600 m od suggesting that a lateglacial advance occurred during the younger dryas stadial the limited extent of these younger dryas glaciers in the monadhliath mountains results from the combined effect of a drier climate experienced in the eastern part of the central highlands ice cap and topographical factors our reconstruction largely supports the deglaciation model of golledge et al 2008 and confirms that a sw to ne precipitation gradient dominated scotland during the younger dryas

snow depth structure fractal behavior and interannual consistency over haut glacier d arolla switzerland snow depth patterns over glaciers are controlled by precipitation snow redistribution due to wind and avalanches and the exchange of energy with the atmosphere that determines snow ablation while many studies have advanced the understanding of ablation processes less is known about winter snow patterns and their variability over glaciers we analyze snow depth on haut glacier d arolla switzerland in the two winter seasons 2006 2007 and 2010 2011 to 1 understand whether snow depth over an alpine glacier at the end of the accumulation season exhibits a behavior similar to the one observed on single slopes and vegetated areas and 2 investigate the snow pattern consistency over the two accumulation seasons we perform this analysis on a data set of high resolution lidar derived snow depth using variograms and fractal parameters our first main result is that snow depth patterns on the glacier exhibit a multiscale behavior with a scale break around 20 m after which the fractal dimension increases indicating more autocorrelated structure before the scale break than after second this behavior is consistent over the two years with fractal parameters and their spatial variability almost constant in the two seasons we also show that snow depth patterns exhibit a distinct behavior in the glacier tongue and the upper catchment with longer correlation distances on the tongue in the direction of the main winds suggesting spatial distinctions that are likely induced by different processes and that should be taken into account when extrapolating snow depth from limited samples

distributed glacier mass balance modelling as an important component of modern multi level glacier monitoring modern concepts of worldwide glacier monitoring include numerical models for 1 interconnecting the different levels of observations local mass balance representative length change glacier inventories for global coverage and 2 extrapolations in space coupling with climate models and time backward and forward in this context one important new tool is distributed mass balance modelling in complex mountain topography this approach builds on simplified energy balance models and can be applied for investigating the spatio temporal representativity of the few mass balance measurements for estimating balance values at the tongue of unmeasured glaciers in order to derive long term average balance values from a great number of glaciers with known length change and for assessing special effects such as the influence of sahara dust falls on the albedo and mass balance or autocorrelation effects due to surface darkening of glaciers with strongly negative balances experience from first model runs in the swiss alps and from applications to the extreme conditions in summer 2003 provides evidence about the usefulness of this approach for glacier monitoring and analysis of glacier changes in high mountain regions the main difficulties concern the spatial variability of the input parameters e g precipitation snow cover and surface albedo and the uncertainties in the parameterizations of the components of the energy balance field measurements remain essential to tie the models to real ground conditions

an exercise in glacier length modeling interannual climatic variability alone cannot explain holocene glacier fluctuations in new zealand abstract recent model studies suggest that interannual climatic variability could be confounding the interpretation of glacier fluctuations as climate signals paleoclimate interpretations of moraine positions and associated cosmogenic exposure ages may have large uncertainties if the glacier in question was sensitive to interannual variability here we address the potential for interannual temperature and precipitation variability to cause large shifts in glacier length during the holocene using a coupled ice flow and mass balance model we simulate the response of cameron glacier a small mountain glacier in new zealand s southern alps to two types of climate forcing equilibrium climate and variable climate our equilibrium results suggest a net warming trend from the early holocene 10 69 0 41 ka 2 7 c cooler than present to the late holocene ce 1864 1 3 c cooler than present interannual climatic variability cannot account for the holocene glacier fluctuations in this valley future studies should consider local environmental characteristics such as a glacier s climatic setting and topography to determine the magnitude of glacier length changes caused by interannual variability

modeling of gas driven magmatic overturn tracking of phenocryst dispersal and gathering during magma mixing 1 we present a combined multiphase numerical and crystal tracking approach that provides a framework to investigate the transport and zoning of crystals associated with a gas driven mixing event mixing in compositionally intermediate to silicic magmatic systems is often initiated by gas exsolution in the recharging magma causing a density inversion and subsequent overturn the overturn is simulated for a range of bubble volume fractions bubbles and therefore indirectly for a range of reynolds numbers re all simulations show chaotic flow dynamics with fast overturn timescales of minutes to hours the large scale mixing is inefficient during a single overturn resulting in a continuously stratified system with respect to bubble volume fraction the crystal tracking algorithm provides us with information on the small scales i e 10 cm on this length scale we observe gathering of different crystals during the overturn that typically ranges on the order of tens of meters thus a complex crystal population may arise within a single overturn this gathering and dispersal of crystals is strongest and most uniform for high re for low re crystal populations are characterized by less gathering of crystals that originated from distal portions of the magma body during the overturn the crystals pass through environments of changing chemical potential we apply the damkohler number da which compares the crystallization or dissolution to the advection timescale results show an asymmetry between crystallization and dissolution crystallization times are too slow during gas driven overturn to record transient changes in chemical potential crystals most likely only record their initial as well as their final chemical environment in contrast dissolution and advection rates are of similar order suggesting potential dissolution during the overturn on the basis of the results for gas driven overturn we expect that slower physical mixing processes may be continuously recorded in the zonation pattern of the crystal phases as long as the changes in chemical potential produce crystal growth

the assignment of drainage direction over flat surfaces in raster digital elevation models abstract drainage direction assignment over flat surfaces in raster digital elevation models dem has been a stubborn problem for dem processing methods a new approach that improves upon current methods of flat surface treatment is presented the approach is based on the recognition that in natural landscapes drainage is generally away from higher and towards lower terrain to produce such a drainage dem elevations of a flat surface are modified to impose two gradients one away from higher terrain and one towards lower terrain subsequent processing of the dem produces a drainage pattern over the flat surface that is topographically consistent and exhibits flow convergence properties the proposed approach is not restricted by the shape of the flat surface the number of outlets on its edge or the complexity of the surrounding topography a comparison with the drainage pattern of an established method that displays the parallel flow problem shows significant improvements in producing realistic drainage patterns the proposed approach extends automated dem processing to digital landscapes for which existing methods cannot provide adequate flow directions over flat surfaces to conduct a drainage analysis the necessary algorithmic details for implementation of the approach are provided 1997 elsevier science b v

stability assessment of himalayan road cut slopes along national highway 58 india himalaya is one of the most tectonically and seismically active mountain chains in the world having complex geological and geotechnical conditions the himalayan region experiences frequent slope failure posed due to various natural and anthropogenic causes slope instability issues have consequent effects on the socio economic development of the people and the region in a large scale in the present study stability analysis of vulnerable road cut slopes along nh 58 from rishikesh to devprayag in the lesser himalayas has been conducted critical slopes were identified by considering the geological and the geotechnical complexities within the region rock mass characterisation techniques have been employed for slope stability assessment rock mass rating rmr slope mass rating smr and continuous slope mass rating csmr methods have been applied to evaluate different stability levels of rock mass along the highway spatial variation of stability classes using rmr smr and csmr techniques has been analysed on geographic information system gis tool kinematic analysis technique was also employed to identify the different modes of structurally controlled failures in jointed rock mass accordingly remedial measures have been suggested to improve slope stability

cosmogenic 10be and 26al exposure ages of tors and erratics cairngorm mountains scotland timescales for the development of a classic landscape of selective linear glacial erosion abstract the occurrence of tors within glaciated regions has been widely cited as evidence for the preservation of relic pre quaternary landscapes beneath protective covers of non erosive dry based ice here we test for the preservation of pre quaternary landscapes with cosmogenic surface exposure dating of tors numerous granite tors are present on summit plateaus in the cairngorm mountains of scotland where they were covered by local ice caps many times during the pleistocene cosmogenic 10be and 26al data together with geomorphic relationships reveal that these landforms are more dynamic and younger than previously suspected many cairngorm tors have been bulldozed and toppled along horizontal joints by ice motion leaving event surfaces on tor remnants and erratics that can be dated with cosmogenic nuclides as the surfaces have been subject to episodic burial by ice an exposure model based upon ice and marine sediment core proxies for local glacial cover is necessary to interpret the cosmogenic nuclide data exposure ages and weathering characteristics of tors are closely correlated glacially modified tors and boulder erratics with slightly weathered surfaces have 10be exposure ages of about 15 to 43 ka nuclide inheritance is present in many of these surfaces correction for inheritance indicates that the eastern cairngorms were deglaciated at 15 6 0 9 ka glacially modified tors with moderate to advanced weathering features have 10be exposure ages of 19 to 92 ka these surfaces were only slightly modified during the last glacial cycle and gained much of their exposure during the interstadial of marine oxygen isotope stage 5 or earlier tors lacking evidence of glacial modification and exhibiting advanced weathering have 10be exposure ages between 52 and 297 ka nuclide concentrations in these surfaces are probably controlled by bedrock erosion rates instead of discrete glacial events maximum erosion rates estimated from 10be range from 2 8 to 12 0 mm ka with an error weighted mean of 4 1 0 2 mm ka three of these surfaces yield model exposure plus burial ages of 295 71 84 520 141 178 and 626 85 102 ka a vertical cosmogenic nuclide profile across the oldest sampled tor indicates a long term emergence rate of 31 2 mm ka these findings show that dry based ice caps are capable of substantially eroding tors by entraining blocks previously detached by weathering processes bedrock surfaces and erratic boulders in such settings are likely to have nuclide inheritance and may yield erroneous too old exposure ages while many cairngorm tors have survived multiple glacial cycles rates of regolith stripping and bedrock erosion are too high to permit the widespread preservation of pre quaternary rock surfaces

the prediction of hillslope flow paths for distributed hydrological modelling using digital terrain models the accuracy of the predictions of distributed hydrological models must depend in part on the proper specification of flow pathways this paper examines some of the problems of deriving flow pathways from raster digital terrain data in the context of hydrological predictions using topmodel distributed moisture status is predicted in topmodel on the basis of spatial indices that depend on flow path definition the sensitivity of this index to flow path algorithm and grid size is examined for the case where the surface topography is a good indicator of local hydraulic gradients a strategy for the case where downslope subsurface flow pathways may deviate from those indicated by the surface topography is described with an example application

magma ascent rates volcanoes can erupt explosively generating high columns of ash and occasional pyroclastic flows or they can erupt slowly forming lava flows and domes this variation reflects significant differences in mass eruption rate e g wilson et al 1980 mass eruption rates in turn are controlled by the rates of magma ascent through the volcanic conduit and the conduit size the magma ascent rate itself is a function of the pressure in the magma storage region the physical properties of the magma such as its density viscosity and crystallinity and the resistance to flow in the conduit that connects the magma storage zone to the surface papale and dobran 1994 mastin and ghiorso 2001 pinkerton et al 2002 sparks et al 2006 a number of important characteristics of volcanic eruptions are affected or controlled by the rate at which magma ascends from depth for example the bubble content i e vesicularity and the degree of crystallization that develop in the melt phase can be significantly different in rapidly vs slowly ascended magma in fact the inability of rapidly ascending magma to effectively lose exsolved gas may be one factor causing an eruption to change from effusive to explosive behavior as recently documented for the soufriere hills eruption on montserrat in the west indies sparks et al 1998 therefore in order to better understand the processes involved and the changes that occur in volcanic eruptions it is important to quantify the rates at which different magmas rise to the surface the fact that the rate of magma ascent controls a number of reactions that occur in volatile rich magmas suggests several ways to study magma ascent rates using reaction data and theoretical flow models one reaction that is a direct result of magma ascent is the exsolution of volatiles from the melt

testing and application of a model for snow redistribution snow_blow in the ellsworth mountains antarctica wind driven snow redistribution can increase the spatial heterogeneity of snow accumulation on ice caps and ice sheets and may prove crucial for the initiation and survival of glaciers in areas of marginal glaciation we present a snowdrift model snow blow which extends and improves the model of purves mackaness and sugden 1999 journal of quaternary science 14 313 321 the model calculates spatial variations in relative snow accumulation that result from variations in topography using a digital elevation model dem and wind direction as inputs improvements include snow redistribution using a flux routing algorithm dem resolution independence and the addition of a slope curvature component this paper tests snow blow in antarctica a modern environment and reveals its potential for application in palaeoenvironmental settings where input meteorological data are unavailable and difficult to estimate specifically snow blow is applied to the ellsworth mountains in west antarctica where ablation is considered to be predominantly related to wind erosion processes we find that snow blow is able to replicate well the existing distribution of accumulating snow and snow erosion as recorded in and around blue ice areas lastly a variety of model parameters are tested including depositional distance and erosion vs wind speed to provide the most likely input parameters for palaeoenvironmental reconstructions