diameters and albedos of satellites of uranus the five known satellites of uranus are too small and distant to permit direct measurement of their diameters consequently products of the masses of the satellites and estimates of their bulk densities and surface albedos have been used in discussions of their probable dimensions in the absence of measurements the presence of water ice on the surfaces of ariel umbriel titania and oberon has been established spectrophotometrically1 4 and the brightnesses of the satellites have been measured photoelectrically5 determination of the masses of the uranian satellites depends on observations of perturbations of the satellite orbits and results chiefly in upper limits to the products of the masses of various pairs of satellites6 7 the new diameter measurements reported here were made using the photometric radiometric technique of diameter determination this widely used technique has enabled the measurement of the diameters and albedos of approximately 250 asteroids and many planetary satellites a recent recalibration of the technique using independent measurements of the diameters of three solar system objects results in absolute accuracies of better than 5 our new albedo measurements show that umbriel titania and oberon are similar in albedo to j4 callisto while ariel is very similar in albedo to s7 hyperion the diameters of all four satellites are similar to those of the large icy saturnian satellites s5 rhea and s8 iapetus

paraglacial rock slope stability glaciation and deglaciation along with their associated climatic and non climatic processes modify slope stresses and influence slope stability paraglacial slope failures are those that are a part of or influenced by the transition from glacial conditions to non glacial conditions gravitational failure of rock slopes is a primary and dominant process of slope evolution in mountainous terrain and is the subject of this paper which 1 reviews the approaches taken for researching paraglacial rock slope failure patterns and processes 2 summarises the spatial and temporal patterns of post glacial failures 3 assesses the factors influencing slope stability during glaciation and deglaciation 4 explores some of the applications of paraglacial research and 5 highlights some of the outstanding issues to be resolved and provides recommendations for terminology relating to paraglacial slope processes

the tertiary structural and thermal evolution of the central alps compressional and extensional structures in an orogenic belt the western alpine arc has been created during the cretaceous and the tertiary orogenies the interference patterns of the tertiary structures suggest their formation during continental collision of the european and the adriatic plates with an accompanying anticlockwise rotation of the adriatic indenter extensional structures are mainly related to ductile deformation by simple shear these structures developed at a deep tectonic level in granitic crustal rocks at depths in excess of 10 km in the early palaeogene period of the tertiary orogeny the main tertiary nappe emplacement resulted from a nw thrusting of the austroalpine penninic and helvetic nappes heating of the deep zone of the upper cretaceous and tertiary nappe stack by geothermal heat flow is responsible for the tertiary regional metamorphism reaching amphibolite facies conditions in the lepontine gneiss dome geothermal gradient 25 c km the tertiary thrusting occurred mainly during prograde metamorphic conditions with creation of a penetrative nw se oriented stretching lineation xi finite extension parallel to the direction of simple shear earliest cooling after the culmination of the tertiary metamorphism some 38 ma ago is recorded by the cooling curves of the monte rosa and mischabel nappes to the west and the suretta nappe to the east of the lepontine gneiss dome the onset of dextral transpression with a strong extension parallel to the mountain belt and the oldest s vergent backfolding took place some 35 to 30 ma ago during retrograde amphibolite facies conditions and before the intrusion of the oligocene dikes north of the periadriatic line the main updoming of the lepontine gneiss dome started some 32 30 ma ago with the intrusion of the bergell tonalites and granodiorites concomitant with s vergent backfolding and backthrusting and dextral strike slip movements along the tonale and canavese lines argand s insubric phase subsequently the center of main updoming migrated slowly to the west reaching the simplon region some 20 ma ago this was contemporaneous with the westward migration of the adriatic indenter between 20 ma and the present the western aar massif toce culmination was the center of strong uplift the youngest s vergent backfolds the glishorn anticline and the berisal syncline fold the 12 ma rb sr biotite isochron and are cut by the 11 ma old rhone simplon line the discrete rhone simplon line represents a late retrograde manifestation in the preexisting ductile simplon shear zone this fault zone is still active today the oligocene neogene dextral transpression and extension in the simplon area were concurrent with thrusting to the northwest of the helvetic nappes the prealpes 35 15 ma and with the jura thin skinned thrust 11 3 ma it was also contemporaneous with thrusting to the south of the bergamasc 35 5 ma and milan thrusts 16 5 ma the oligocene neogene dextral transpression in the central alps is of the same age as the thrusting to the west and southwest in the external french part and to the east in the internal italian part of the alpine arc of the western alps

thermal history of the h chondrite parent body implications for metamorphic grade and accretionary time scales abstract multiple temperature age constraints for eight h chondrite samples have been used to provide insight into the thermal history of their parent body through combination with numerical models of thermal evolution assuming internal heating by 26al and conductive cooling the effect of spreading accretion out over time is the principal focus of this work a wide range of body size and date of accretion is systematically tested for different values of accretion rate in order to quantify and illustrate the parameter space that is consistent with the available thermo chronological data we conclude that the h chondrite samples considered have a thermal history consistent with a parent body that at some stage had a concentric onion shell internal structure that body had a radius no larger than 130 km and accretion most probably took place over a time interval on the order of 0 0 0 2 myr approximately 2 myr after cai condensation in any case the time interval of accretion is unlikely to have been more than 0 5 myr supporting evidence in favour of rapid accretion possibly through reassembly of the fragments of an earlier generation of bodies furthermore the h chondrites studied here are inferred to have come from a wide depth range within the body where they experienced metamorphism indicating that preservation of the onion shell structure is unlikely the presence of an insulating regolith does not modify this conclusion as appropriate thermal histories for the three h6 samples considered cannot be reproduced at depths near the surface asteroid 6 hebe may be the parent body of the h chondrites but the high bulk density of the latter is difficult to reconcile with a rubble pile structure of pure h chondrite material finally optimized thermal histories are used to constrain the temperatures characterizing boundaries between petrological types 800 1000 and 1140 k for the h3 4 h4 5 and h5 6 boundaries respectively in detail the type 6 samples studied here are inferred to have experienced a similar peak temperature on the order of 1180 k but spent different times at that temperature while samples of lower metamorphic grade experienced different peak temperature but spent more or less the same time within 10 k of peak temperature on the order of 1 ma these results constitute a quantitative framework within which variations in petrographic and textural properties may be interpreted

metamorphism and partial melting of ordinary chondrites calculated phase equilibria abstract constraining the metamorphic pressures p and temperatures t recorded by meteorites is key to understanding the size and thermal history of their asteroid parent bodies new thermodynamic models calibrated to very low p for minerals and melt in terrestrial mantle peridotite permit quantitative investigation of high t metamorphism in ordinary chondrites using phase equilibria modelling isochemical p t phase diagrams based on the average composition of h l and ll chondrite falls and contoured for the composition and abundance of olivine ortho and clinopyroxene plagioclase and chromite provide a good match with values measured in so called equilibrated petrologic type 4 6 samples some compositional variables in particular al in orthopyroxene and na in clinopyroxene exhibit a strong pressure dependence when considered over a range of several kilobars providing a means of recognising meteorites derived from the cores of asteroids with radii of several hundred kilometres if such bodies existed at that time at the low pressures p permitting constraints on the minimum size of parent asteroid bodies the phase diagrams predict the onset of partial melting at 1050 1100 c by incongruent reactions consuming plagioclase clinopyroxene and orthopyroxene whose compositions change abruptly as melting proceeds these predictions match natural observations well and support the view that type 7 chondrites represent a suprasolidus continuation of the established petrologic types at the extremes of thermal metamorphism the results suggest phase equilibria modelling has potential as a powerful quantitative tool in investigating for example progressive oxidation during metamorphism the degree of melting and melt loss or accumulation required to produce the spectrum of differentiated meteorites and whether the onion shell or rubble pile model best explains the metamorphic evolution of asteroid parent bodies in the early solar system

surface materials on unusual planetary object chiron abstract we present the first jhk near infrared colorimetry giving some indication of the surface materials on the peculiar object 2060 chiron the colors appear to exclude relatively clean bright ice surfaces such as those of europa ganymede rhea dione and theoretically studied micronscale clean ice particles the colors are consistent with those of numerous outer solar system asteroids which in all measured cases have albedos of only a few percent c rd or dm type spectra and no known h 2 o ice absorption features the colors are also consistent with theoretical colors for certain size distributions of dirty ice grains these and additional vjhk colorimetric data suggest that the spectrally dominant surface is c type material probably dark carbonaceous like silicate dust with a possible admixture of ice grains on a microscale if chiron has the low albedo common to such material on known interplanetary bodies its diameter would be about 310 to 400 km placing chiron among the eight largest asteroids relationships to comet observations are discussed

large scale slope remodelling by landslides geomorphic diversity and geological controls kamienne mts central europe abstract the kamienne mts in the sudetes central europe bear widespread evidence of landsliding which mainly occurred at the boundary between carboniferous and permian clastic sedimentary rocks and overlying permian volcanic and sub volcanic rocks 47 individual landslides have been delimited using a combination of lidar derived dem analysis and field mapping they have been characterized through a range of geomorphometric parameters and cluster analysis reveals four major groups in terms of surface expression and consequently likely origin and history spatial analysis confirms distinct association of landslides with the steepest terrain and north to east aspect of slopes but distance from lithological contact emerges as the critical parameter 80 of the total landslide area is located within 200 m of a contact on either side of it joint measurements within head scarps at selected landslides indicate that displacements took place along steeply dipping joints in the volcanic cap but the existence of low angle detachment surfaces in the underlying sedimentary formations is inferred the spatial distribution of slope deformations coupled with apparently different although yet unspecified ages of individual landslides suggests that remodelling of the mountain range by landslides is an ongoing process geomorphic history of the area excludes glacial or fluvial erosion and resultant slope de buttressing as the cause of instability rather landslides are considered as mechanisms by which slopes which have become too high and steep due to long term differential erosion restore their strength equilibrium

a model for planetesimal meltdown by 26al and its implications for meteorite parent bodies the melting of planetesimals heated by 26 al has been modelled using a new finite difference method that incorporates convection as an example we consider a planetesimal with a radius of 64 km which accretes instantaneously at t 0 75 myr after the formation of calcium aluminum rich inclusions from cold 250 k nebular dust with 50 porosity at t 0 9 myr t 700 k the planetesimal shrinks to a radius of 50 km due to sintering at t 1 2 myr t 1425 k the fully insulated interior deeper than a few kilometers starts to melt and at t 1 5 myr t 1725 k with 50 melting convection starts by t 2 myr the planetesimal is a globe of molten convecting slurry inside a thin residual crust from about t 2 5 myr the crust thickens rapidly as the power of 26 al fades planetesimals probably melt in this manner when they accrete before t 1 3 myr and are large enough to insulate themselves r 20 km for accretion at t 0 rising to 80 km at t 1 3 myr melting behavior will also be affected by the level of 60 fe in nebular dust by the extent of devolatilization reactions and basalt segregation during heating and by gradual accretion the model suggests that a the parent bodies of differentiated meteorites had accreted before about t 1 5 to 2 myr and before most chondritic parent bodies had formed and b that molten planetesimals may be a source for chondrule melt droplets

oxygen isotope studies of achondrites abstract oxygen isotope abundances provide a powerful tool for recognizing genetic relationships among meteorites among the differentiated achondrites three isotopic groups are recognized l snc mars 2 earth and moon and 3 hed howardites eucrites diogenites the hed group also contains the mesosiderites main group pallasites and silicates from iiiab irons the angrites may be marginally resolvable from the hed group within each of these groups internal geologic processes give rise to isotopic variations along a slope 1 2 fractionation line as is well known for terrestrial materials variations of 17o from one planet to another are inherited from the inhomogeneities in the solar nebula as illustrated by the isotopic compositions of chondrites and their constituents among the undifferentiated achondrites five isotopic groups are found 1 aubrites 2 winonaites and iab iiicd irons 3 brachinites 4 acapulcoites and lodranites and 5 ureilites the isotopic compositions of aubrites coincide with the earth and moon and also with the enstatite chondrites these bodies apparently were derived from a common reservoir the isotopic composition of which was established at the chondrule scale by nebular processes isotopic similarities between chondrites and achondrites are seen only for the following instances 1 enstatite chondrites and aubrites 2 h chondrites and he irons and 3 l or ll chondrites and iva irons the isotopic data also support the following genetic associations 1 winonaites and iab iiicd irons 2 acapulcoites and lodranites and 3 ureilites and dark inclusions of c3 chondrites an attempt to reconcile the whole planet isotopic compositions of earth mars and the eucrite parent body with mixing models of their chemical compositions failed it is not possible to satisfy both the chemical and isotopic compositions of the terrestrial planets using known primitive solar system components

metal veins in the kernouve h6 s1 chondrite evidence for pre or syn metamorphic shear deformation abstract kernouve is an h6 chondrite that experienced a very small degree of late stage shock loading s1 however kernouve contains fe ni metal vein like structures whose formation have been attributed to an early impact event to establish the formation conditions of metal veins in kernouve we examined the three dimensional 3d arrangement of metal vein like structures and typical metal grains in two samples of kernouve with x ray microtomography ct at resolutions of 11 m voxel we additionally investigated the 3d structure of the porosity present in kernouve using ct at two different resolutions 3 and 11 m voxel these data and optical microscopy support the hypothesis that kernouve has experienced little post metamorphic shock however the moderate 5 8 vol porosity of kernouve is in the form of intergranular voids rather than cracks which indicates any cracking that may have existed in the relatively brittle silicate grains was annealed we estimate that 70 80 of the primordial porosity in kernouve was removed by impact related compaction moreover we found no collective orientation of metal grains so high metamorphic temperatures following compaction erased any common orientation of metal grains due to compaction we propose that the metal vein structures can be explained as a pre or syn metamorphic shock induced process which we infer was primarily shear deformation with some uniaxial compaction also occurring the coarse metal veins probably formed by accumulation of ductile metal grains along shear zones a process that would have been facilitated by having an already warm h chondrite parent body when shock occurred i e syn metamorphic shock the complexity of shape including numerous tendrils expanding from the primary structure of the veins in kernouve is likely due to the coalescence of metal by metamorphic growth after the shear event the metal veins in kernouve thus appear to record evidence for early shock induced metal mobilization and the maximum shock pressure experienced by kernouve may have been 21 gpa our study suggests that collision induced segregation of metal occurred at an early stage in low gravity planetesimals consistent with the idea that this process could have been important for the differentiation of such objects

future retreat of great aletsch glacier we model the future evolution of the largest glacier of the european alps great aletsch glacier switzerland during the 21st century for that purpose we use a detailed three dimensional model which combines full stokes ice dynamics and surface mass balance forced with the most recent climate projections ch2018 as well as with climate data of the last decades as a result all ch2018 climate scenarios yield a major glacier retreat results range from a loss of 60 of today s ice volume by 2100 for a moderate co 2 emission scenario rcp2 6 being in line with the paris agreement to an almost complete wastage of the ice for the most extreme emission scenario rcp8 5 our model results also provide evidence that half of the mass loss is already committed under the climate conditions of the last decade

contact metamorphism and anatexis of torridonian arkose by minor intrusions of the rum igneous complex inner hebrides scotland

the early impact histories of meteorite parent bodies we have developed a statistical framework that uses collisional evolution models shock physics modeling and scaling laws to determine the range of plausible collisional histories for individual meteorite parent bodies it is likely that those parent bodies that were not catastrophically disrupted sustained hundreds of impacts on their surfaces compacting heating and mixing the outer layers it is highly unlikely that many parent bodies escaped without any impacts processing the outer few kilometers the first 10 20 myr were the most important time for impacts both in terms of the number of impacts and the increase of specific internal energy due to impacts the model has been applied to evaluate the proposed impact histories of several meteorite parent bodies up to 10 parent bodies that were not disrupted in the first 100 myr experienced a vaporizing collision of the type necessary to produce the metal inclusions and chondrules on the cb chondrite parent around 1 5 of bodies that were catastrophically disrupted after 12 myr sustained impacts at times that match the heating events recorded on the iab winonaite parent body more than 75 of 100 km radius parent bodies which survived past 100 myr without being disrupted sustained an impact that excavates to the depth required for mixing in the outer layers of the h chondrite parent body and to protect the magnetic field on the cv chondrite parent body the crust would have had to have been thick approximately 20 km to prevent it being punctured by impacts

thermal evolution model for the h chondrite asteroid instantaneous formation versus protracted accretion abstract we present a model of the thermal evolution of asteroids assuming an onion shell model for the h chondrite parent body we obtain constraints for the h chondrite asteroid parameters by fitting empirical h chondrite cooling ages of estacado guarena kernouve mt browne richardton allegan nadiabondi ste marguerite and forest vale by using a genetic algorithm for parameter optimisation the model improves previous calculations on the thermal history calculated in the instantaneous accretion approximation considering sintering and porosity dependent heat conduction the model is extended to include a finite growth time of the parent body to study whether the meteoritic record constrains the duration of the growth phase of the parent body where it assembles most of its mass it is found that only short accretion times of up to 0 1 ma are compatible with the empirical data on h chondrite cooling histories best fit models yield excellent agreement with the cooling age data particularly they indicate that i 26 al was the major heat source driving metamorphism while 60 fe contributed rather marginally ii maximum temperatures remained below partial melting temperatures throughout the body indicating that no partial differentiation occurred on the h chondrite parent asteroid iii the h chondrite asteroid formed 2 ma after cais briefly after most ordinary chondrite chondrules formed if 26 al abundance defines a chronological sequence

thermal constraints on the early history of the h chondrite parent body reconsidered abstract reconstructions of the early thermal history of the h chondrite parent body have focused on two competing hypotheses the first posits an undisturbed thermal evolution in which the degree of metamorphism increases with depth yielding an onion shell structure the second posits an early fragmentation reassembly event that interrupted this orderly cooling process here we test these hypotheses by collecting a large number of previously published closure age and cooling rate data and comparing them to a suite of numerical models of thermal evolution in an idealized parent body we find that the onion shell hypothesis when applied to a parent body of radius 75 130 km with a thermally insulating regolith is able to explain 20 of the 21 closure age data and 62 of the 71 cooling rates furthermore six of the eight meteorites for which multiple data at different temperatures are available can be accounted for by onion shell thermal histories we therefore conclude that no catastrophic disruption of the h chondrite parent body occurred during its early thermal history the relatively small number of data not explained by the onion shell hypothesis may indicate the formation of impact craters on the parent body which while large enough to excavate all petrologic types were small enough to leave the parent body largely intact impact events fulfilling these requirements would likely have produced transient crater diameters at least 30 of the parent body diameter

contribution of early impact events to metal silicate separation thermal annealing and volatile redistribution evidence in the pultusk h chondrite three dimensional x ray tomographic reconstructions and petrologic studies reveal voluminous accumulations of metal in pultusk h chondrite at the contact of these accumulations the chondritic rock is enriched in troilite the rock contains plagioclase rich bands with textures suggesting crystallization from melt unusually large phosphates are associated with the plagioclase and consist of assemblages of merrillite and fluorapatite and chlorapatite the metal accumulations were formed by impact melting rapid segregation of metal sulfide melt and the incorporation of this melt into the fractured crater basement the impact most likely occurred in the early evolution of the h chondrite parent body when post impact heat overlapped with radiogenic heat this enabled slow cooling and separation of the metallic melt into metal rich and sulfide rich fractions this led to recrystallization of chondritic rock in contact with the metal accumulations and the crystallization of shock melts phosphorus was liberated from the metal and subsumed by the silicate shock melt owing to oxidative conditions upon slow cooling the melt was also a host for volatiles upon further cooling phosphorus reacted with silicates leading to the formation of merrillite while volatiles partitioned into the residual halogen rich dry fluid in the late stages the fluid altered merrillite to patchy cl f apatite the above sequence of alterations demonstrates that impact during the early evolution of chondritic parent bodies might have contributed to local metal segregation and silicate melting in addition postshock conditions supported secondary processes compositional textural equilibration redistribution of volatiles and fluid alterations

high resolution x ray computed tomography and its application to ore deposits from data acquisition to quantitative three dimensional measurements with case studies from ni cu pge deposits high resolution x ray computed tomography hrxct is a nondestructive technique that allows exploration of the three dimensional distribution of minerals and pore space in natural and synthetic rock samples recent technological developments allow the characterization of samples up to few centimeters in diameter at a resolution down to 0 7 m this combined with the development of dedicated workflows algorithms and softwares is opening new doors for the quantitative three dimensional characterization of ores at the sample scale when combined with three dimensional image analysis hrxct provides quantitative three dimensional mineralogical and textural measurements volume shape three dimensional relationship that are impossible to assess accurately by any other method this manuscript describes the principles of hrxct and presents dedicated methodologies from data acquisition throught to quantitative three dimensional measurements these methodologies are applied to ni cu pge ore samples but are suitable for a range of geologic materials the combination of hrxct with quantitative three dimensional image analysis applied to geologic materials hosting ore deposits provides a better understanding of ore mineralogy ore forming processes and parameters required for mineral or metallurgical processing with benefit for both academic studies and mineral industry applications

experimental partial melting of the st severin ll and lost city h chondrites we have performed melting experiments between 1170 1325 c and at an oxygen fugacity of iw 1 on the ordinary chondrites lost city h and st severin ll in order to investigate the origin of diogenites and their possible relationship to eucrites low ca pyroxene disappears from the lost city residuum just above 1220 c at a mg near 66 accordingly lost city does not have a sufficiently large stability field for orthopyroxene to be a likely parent composition for melts which could crystallize diogenites in contrast orthopyroxene in st severin persists up to about 1325 c at which point it has a mg similar to that of typical diogenites 75 this is only marginally compatible with diogenite origins as the most magnesian pyroxenes from diogenites mg 82 and howardites mg 85 are more mgo rich than any pyroxene formed from a st severin melt accordingly if diogenites formed from a source having the bulk composition of an ordinary chondrite than either the fo2 had to be lower than that inferred for eucrite formation or more likely the parent body had a lower fesi ratio than that of an ll chondrite also low temperature melts of st severin are depleted in elements compatible with pyroxene and so while broadly eucritic do not closely match the compositions of eucrites that are thought to be primary partial melts hence it doesn t appear possible to produce both diogenites and eucrites from the same source region composition if eucrites are primary partial melts reconnaiss mce experiments at higher oxygen fugacity iw 2 produce broadly angritic melts for lost city as was observed for murchison and allende in contrast our na2o poor st severin charge produced a broadly eucritic melt at this higher fo2 this difference in melting behavior is probably because ll chondrites have a much lower bulk fesi ratio than the h cm or cv chondrites

petrologic evidence for collisional heating of chondritic asteroids abstract the identification of the mechanism s responsible for heating asteroids is among the major problems in planetary science because of difficulties with models of electromagnetic induction and the decay of short lived radionuclides it is worthwhile to evaluate the evidence for collisional heating localized impact heating is responsible for forming shock veins melt pockets metal sulfide mixtures vugs agglutinates and a wide variety of melt rock clasts new evidence for localized impact heating comes from the high proportion of relict type 6 material among impact melt bearing ordinary chondrites oc this relict material was probably metamorphosed by residual heat within large craters olivine aggregates composed of faceted crystals with 120 triple junctions occur within the melted regions of the chico and rose city oc melt rocks the olivine aggregates formed from shocked mosaicized olivine grains that underwent contact metamorphism large scale collisional heating is supported by the correlation in oc between petrologic type and shock stage no other heating mechanism can readily account for this correlation the occurrence of impact melt rock clasts in oc that have been metamorphosed along with their whole rocks indicates that some impact events preceded or accompanied thermal metamorphism such impact events occurring during or shortly after accretion are probably responsible for substantially melting 0 5 of oc these events most have heated a larger percentage of oc to subsolidus temperatures sufficient to have caused significant metamorphism if collisional heating is viable then oc parent asteroids must have been large large oc asteroids in the main belt may include those of the s iv spectral subtype collisional heating is inconsistent with layered onion shell structures in oc asteroids wherein the degree of metamorphism increases with depth but the evidence for such structures is weak it seems likely that collisional heating played an important role in metamorphosing chondritic asteroids

paraglacial history and structure of the moosfluh landslide 1850 2016 switzerland abstract rock slopes next to the tongue of the great aletsch glacier switzerland are characterized by rapid environmental adjustment to non glacial conditions this study investigates and describes in detail the historic development of the largest rock slope instability in this area called moosfluh landslide we study in detail the structure evolution and stability since the end of the little ice age lia until september 2016 and discuss their relationships with the evolution of the great aletsch glacier since the lateglacial period in 2016 around 50 m of glacial ice thickness were left at the moosfluh landslide toe where in 1850 glacial ice was 400 m thick the changing stability conditions at the interface with the melting valley glacier are studied based on novel balanced cross sections and kinematic model of the moosfluh landslide dominated by toppling phenomena in metamorphic rock the morphology and evolution of this landslide since the lia are investigated with multi temporal landslide maps based on aerial digital photogrammetry adp applied to historic images since 1961 internal deformation at moosfluh is accommodated by shear slip along uphill facing foliation and fault planes and by extensional faulting forming tension cracks and graben structures at the landslide head together with digital image correlation dic and total station monitoring tps the moosfluh landslide displacement history was reconstructed evidencing post egesen landslide displacements and an acceleration of movements since the lia and especially since 2007 the displacement rates increase from few mm per year until the nineties to several meter per day in september 2016 different kinematic models have been tested and changes in the moosfluh rock slope stability in response to retreating glacial ice and changing groundwater conditions was explored with limit equilibrium analysis of the stepped planar block toppling model of goodman and bray 1976 for the observed conditions and a toppling joint friction angle of 19 the simulated factor of safety drops non linearly from the lia maximum 1 12 to the year 2007 1 02 when the height of ice above the valley bottom melted down to 100 m this study illustrates with unprecedented detail the time scales displacement magnitudes and structural evolutions of a large toppling mode slope instability in a paraglacial setting the long term cumulative slope displacements between the egesen stadial and the lia are of the same magnitude as the cumulative displacements between the lia and the year 2016 as large portions of the studied slope underwent multiple retreats and advances of the great aletsch glacier during the lateglacial and postglacial period the observed onset of large slope displacements should be related to incremental damage slip weakening and weathering occurring along steeply dipping toppling fractures during the lia

helicopter borne ground penetrating radar investigations on temperate alpine glaciers a comparison of different systems and their abilities for bedrock mapping abstracton the basis of a large data set comprising approximately 1200 km of profile lines acquired with different helicopter borne ground penetrating radar gpr systems over temperate glaciers in the western swiss alps we have analyzed the possibilities and limitations of using helicopter borne gpr surveying to map the ice bedrock interface we have considered data from three different acquisition systems including 1 a low frequency pulsed system hanging below the helicopter bgr 2 a stepped frequency system hanging below the helicopter radar systemtechnik gmbh rst and 3 a commercial system mounted directly on the helicopter skids geophysical survey systems incorporated gssi the systems showed considerable differences in their performance the best results were achieved with the bgr system on average the rst and gssi systems yielded comparable results but we observed significant site specific differences a comparison with ground based gpr data found that the quality of helicopter

interfacial tension between magmatic sulfide and silicate liquids constraints on kinetics of sulfide liquation and sulfide migration through silicate rocks we have measured the interfacial tension sf between sulfide and silicate melts over the temperature range from 1250 to 1325 c by in situ measurement of the shapes of sessile drops of sulfide immersed in silicate melt sitting upon level alumina substrates the silicate melt was an alkali free synthetic basaltic liquid the sulfide melts were synthetic mixtures of fe cu ni s or fe s o the interfacial tension ranges from about 500 mj m 2 for sulfide of fes composition to approximately 600 mj m 2 for sulfide containing 16 wt cu or 6 5 wt ni and up to 650 mj m 2 for fe s o liquid containing 4 wt o contact angles vary from 150 to 180 showing that sulfide liquid does not wet oxide minerals in silicate magmas the density of sulfide melt does not depend strongly on cu or ni content remaining between 4 0 and 4 5 g cm 3 over the range of cu and ni contents expected in sulfide magmas but increases substantially to about 5 5 g cm 3 in fe s o melts containing 4 wt o our results can be combined with conventional concepts of nucleation theory to indicate that when silicate magmas exist at small degrees of supersaturation sulfide drops may nucleate rarely and at widely spaced intervals leading to kinetic control of the compositions of the resulting droplets in light of our results we use simple scaling arguments to argue that sulfide magmas are not capable of migrating through partially molten silicate rocks by capillary forces alone but may be forced through narrow grain boundaries or grain edges only by the flow of the enclosing silicate melt during melt extraction by compaction of partially molten mantle peridotite it is highly unlikely that silicate flow rates could be sufficiently rapid to permit the entrainment of droplets of sulfide liquid at temperatures below the solidus of enclosing silicate rocks sulfide melt will be free to travel along fractures or grain boundaries the mobility of sulfide melts through completely solidified silicate rocks may account for the widespread observation that late stage highly fractionated sulfide liquids have escaped from cooling bodies of massive sulfide to form veins and disseminations of cu rich sulfide minerals in their silicate host rocks

shock metamorphism of ordinary chondrites a revised petrographic classification of progressive stages of shock metamorphism of ordinary chondrites is proposed six stages of shock s1 to s6 are defined based on shock effects in olivine and plagioclase as recognized by thin section microscopy the characteristic shock effects of each shock stage are s1 unshocked sharp optical extinction of olivine s2 very weakly shocked undulatory extinction of olivine s3 weakly shocked planar fractures in olivine s4 moderately shocked mosaicism in olivine s5 strongly shocked isotropization of plagioclase maskelynite and planar deformation features in olivine and s6 very strongly shocked recrystallization of olivine sometimes combined with phase transformations ringwoodite and or phases produced by dissociation reactions s6 effects are always restricted to regions adjacent to melted portions of a sample which is otherwise only strongly shocked in stages s3 to s6 localized melting results from stress and temperature peaks which locally deviate from the equilibration shock pressure due to differences in shock impedance these melting effects are a opaque melt veins shock veins b melt pockets with interconnecting melt veins c melt dikes and d troilite metal deposits in fractures based on a critical evaluation of data from shock recovery experiments a shock pressure calibration for the six shock stages is proposed which defines the s1 s2 s2 s3 s3 s4 s4 s5 and s5 s6 transitions at 5 5 10 15 20 30 35 and 45 55 gpa respectively whole rock melting and formation of impact melt rocks or melt breccias occurs at about 75 90 gpa the symbol for the shock stage may be used in combination with the symbol for the petrologic type to abbreviate the complete classification of a chondrite e g h5 s3 we propose this new shock classification and pressure calibration system to replace previous systems which are out of date with respect to the pressure calibration nominally restricted to l chondrites and based on incomplete and in part illdefined sets of shock effects we have classified seventy six ordinary chondrites using the new classification system and conclude the following 1 1 shock effects and the sequence of progressively increasing degrees of shock metamorphism are very similar in h l and ll groups differences in the frequency distribution of shock stages are relatively minor e g l chondrites appear to have the largest fraction with stages s5 and s6 this suggests that the collisional histories of the h l and ll parent bodies were similar 2 2 petrologic type 3 chondrites are deficient in stages s4 to s6 and with increasing petrologic type the frequency of stages s4 to s6 increases we suggest that the more porous and volatile rich type 3 chondrites are subject to melting at a lower shock pressure than the nonporous chondrites of higher petrologic type volatiles trapped in pores cause shock induced dispersal of the shocked and melted material into small particles which are not expected to survive as meteorites 3 3 stage s3 is the most abundant in nearly all petrologic types 4 4 at shock pressures in excess of about 35 gpa s5 and s6 4he and 40ar are almost completely lost pressures below 10 gpa s1 and s2 do not cause noble gas losses

first surface velocity maps for glaciers of monte tronador north patagonian andes derived from sequential pleiades satellite images we apply cross correlation to pleiades satellite images to generate accurate high resolution monthly surface velocity maps of monte tronador glaciers between march and june 2012 measured surface displacements cover periods as short as 19 days with a precision of 0 58 m 11 m a 1 these glaciers follow a radial flow pattern with maximum surface speeds of 390 m a 1 associated with steep icefalls the lower reaches of the debris covered tongues of verde and casa pangue glaciers are almost stagnant whereas ventisquero negro another debris covered glacier shows acceleration at the front due to calving into a proglacial lake low elevation debris covered glacier tongues show increasing velocities at the beginning of the accumulation season whereas higher elevation clean ice tongues reduce their speed during this period this contrasting behavior is probably in response to an increase in water input to the subglacial system from winter rainfall events at low elevations and a decrease in meltwater production at higher elevations these sequential velocity maps can help to identify the controls on glacier surface velocity aid in the delimitation of ice divides and could also contribute to more realistic calibration of ice flux mass balance models in this glacierized area

shock experiments with the h6 chondrite kernouve pressure calibration of microscopic shock effects shock recovery experiments were carried out on samples of the h6 chondrite kernouve at shock pressures of 10 15 20 25 30 35 45 and 60 gpa and preheating temperatures of 293 k low temperature experiments and 920 k high temperature experiments using a calculated equation of state of kernouve pressure pulse durations of 0 3 to 1 2 s were estimated the shocked samples were investigated by optical microscopy to calibrate the various shock effects in olivine orthopyroxene oligoclase and troilite the following pressure calibration is proposed for silicates 1 undulatory extinction of olivine gpa 2 weak mosaicism of olivine from 10 15 gpa to 20 25 gpa 3 onset of strong mosaicism of olivine at 20 25 gpa 4 transformation of oligoclase to diaplectic glass completed at 25 30 gpa low temperature experiments and at 20 25 gpa high temperature experiments 5 onset of weak mosaicism in orthopyroxene at 30 35 gpa low temperature experiments and at 25 30 gpa high temperature experiments and 6 recrystallization or melting of olivine starting at 45 60 gpa low temperature experiments and at 35 45 gpa high temperature experiments and completed above 45 60 gpa in the high temperature experiments troilite displays distinct differences between the samples shocked at low and high temperatures in the low temperature experiments the following effects can be observed in troilite 1 undulatory extinction up to 25 gpa 2 twinning up to 45 gpa 3 partial recrystallization from 30 to 60 gpa and 4 complete recrystallization 35 gpa whereas in the high temperature experiments troilite shows 1 complete recrystallization from 10 up to 45 gpa and 2 melting and crystallization above 45 gpa localized shock induced melting is observed in samples shocked to pressures 15 gpa in the high temperature experiments and 30 gpa for the low temperature experiments in the form of feni metal and troilite melt injections and intergrowths and as pockets and veins of whole rock melt obviously the onset and abundance of shock induced localized melting strongly depends on the initial temperature of the sample

investigation of the h7 ordinary chondrite watson 012 implications for recognition and classification of type 7 meteorites abstract despite the fact that the number of officially classified meteorites is now over 45 000 we lack a clearly defined sequence of samples from a single parent body that records the entire range in metamorphic temperatures from pristine primitive meteorites up to the temperatures required for extensive silicate partial melting here we conduct a detailed analysis of watson 012 an h7 ordinary chondrite to generate some clarity on the textural and chemical changes associated with equilibrium based silicate partial melting in chondritic meteorites to do this we compare the textures in the meteorite with those preserved in metamorphic contact aureoles on earth the most distinctive texture generated by the partial melting that affected watson 012 is an extensively interconnected plagioclase network which is clearly observable with a petrographic microscope enlarged metal troilite grains are encapsulated at widenings in this plagioclase network and this is clearly visible in reflected light together with these features we define a series of other characteristics that can be used to more clearly classify chondritic meteorites as being of petrologic type 7 to provide comprehensive evidence of silicate partial melting and strengthen the case for using simple petrographic observations to classify similar meteorites we use high resolution x ray computed tomography to demonstrate that the plagioclase network has a high degree of interconnectedness and crystallised as large cm scale skeletal crystals within an olivine orthopyroxene clinopyroxene framework essentially pseudomorphing a melt network back scattered electron imaging and element mapping are used to show that some of the clino and orthopyroxene in watson 012 also crystallised from silicate melt and the order of crystallisation was orthopyroxene clinopyroxene plagioclase x ray diffraction data supported by bulk geochemistry are used to show that plagioclase and ortho and clinopyroxene were added to the watson 012 sample by through flowing basaltic melt along with the absence of glass and granophyre this interconnected network of coarse grained skeletal plagioclase indicates that the sample cooled slowly at depth within the parent body the evidence of melt flux indicates that watson 012 formed in the presence of a gravitational gradient and thus at significant distance from the centre of the h chondrite parent body the gravitational gradient at the centre would be zero our interpretation is that incipient silicate partial melting in watson 012 occurred when a region of radiogenically heated h6 material located at considerable depth possibly at 15 20 km from surface was heated by an additional ca 200 300 c in association with a large shock event due to insulation at depth within an already hot parent body the post shock temperature equilibrated and remained above the solidus long enough for widespread equilibrium based silicate partial melting and for melt to migrate although the observed melting may have been facilitated by additional heating from an impact event this is not an example of instantaneous shock melting which produces thermal disequilibrium at short length scales and distinctly different textures a small number of h l and ll chondrites have been previously classified as being of petrologic type 7 with our new criteria to support that classification these represent our best opportunity to explore the transition from high temperature sub solidus metamorphism through the onset of silicate partial melting in three different parent bodies

on the pseudomorphing of melt filled pores during the crystallization of migmatites pseudomorphs of melt filled pores recognized by their generally cuspate shape are used as diagnostic for the former presence of partial melt they are commonly observed in migmatites from the mid to deep crust although they occur in the smaller pores in migmatites from shallower levels 1 2 kbar the pseudomorphing of meltfilled pores is controlled by the kinetics of nucleation and is a consequence of the greater supersaturation required for nucleation in a small pore compared with a larger one we examine three migmatites in detail a contact metamorphosed cherty band from an iron formation an archaean regional granulite from an accretionary prism and an amphibolite facies sample from the roots of an archaean mountain chain the greater undercooling required for nucleation in progressively smaller pores is recorded by the composition of plagioclase pseudomorphs a study of dihedral angles at the corners of pseudomorphed pores demonstrates that melt solid textural equilibrium was probably attained only in the contact aureole the regional granulite preserves an almost unmodified reaction controlled melt distribution with little evidence for either melt solid textural equilibration or solid solid re equilibration whereas the reactioncontrolled melt distribution in the regional amphibolite facies example has been modified by a partial approach to solid solid textural equilibrium it is not clear whether the differences in dihedral angle population are due to differences in uplift and exhumation rates or due to the presence of h2o on grain boundaries

beyond debuttressing mechanics of paraglacial rock slope damage during repeat glacial cycles cycles of glaciation impose mechanical stresses on underlying bedrock as glaciers advance erode and retreat fracture initiation and propagation constitute rock mass damage and act as preparatory factors for slope failures however the mechanics of paraglacial rock slope damage remain poorly characterized using conceptual numerical models closely based on the aletsch glacier region of switzerland we explore how in situ stress changes associated with fluctuating ice thickness can drive progressive rock mass failure preparing future slope instabilities our simulations reveal that glacial cycles as purely mechanical loading and unloading phenomena produce relatively limited new damage however ice fluctuations can increase the criticality of fractures in adjacent slopes which may in turn increase the efficacy of fatigue processes bedrock erosion during glaciation promotes significant new damage during first deglaciation an already weakened rock slope is more susceptible to damage from glacier loading and unloading and may fail completely we find that damage kinematics are controlled by discontinuity geometry and the relative position of the glacier ice advance and retreat both generate damage we correlate model results with mapped landslides around the great aletsch glacier our result that most damage occurs during first deglaciation agrees with the relative age of the majority of identified landslides the kinematics and dimensions of a slope failure produced in our models are also in good agreement with characteristics of instabilities observed in the field our results extend simplified assumptions of glacial debuttressing demonstrating in detail how cycles of ice loading erosion and unloading drive paraglacial rock slope damage

oxygen isotope studies of ordinary chondrites several stages in the evolution of ordinary chondritic meteorites are recorded in the oxygen isotopic composition of the meteorites and their separable components chondrules fragments clasts and matrix the whole rock isotopic compositions reflect the iron group of the meteorite h l or ll isotopic uniformity of h3 to h6 and l3 to l6 are consistent with closed system metamorphism within each parent body ll3 chondrites differ slightly from ll4 to ll6 implying a small degree of opensystem aqueous alteration and carbon reduction on the scale of individual chondrules the meteorites are isotopically heterogeneous allowing recognition of the solar nebular processes of chondrule formation chondrules for all classes of ordinary chondrites are derived from a common population which was separate from the population of chondrules in carbonaceous or enstatite chondrites chondrules define an isotopic mixing line dominated by exchange between 16o rich and 16o poor reservoirs the oxygen isotopic compositions of chondrites serve as fingerprints for identification of genetic association with other meteorite types achondrites and iron and for recognition of source materials in meteoritic breccias

reconstructing the evolution of a deep seated rockslide marzell and its response to glacial retreat based on historic and remote sensing data abstract in this study a combination of different topographic data from historic topographic maps and remote sensing is used to reconstruct and monitor the behaviour of the high alpine ice contact rockslide system marzell and its response to glacial debuttressing in the eastern alps topographic data from archives historical topographic maps national glacier inventories aerial images orthoimages and als data and data from monitoring campaigns geodetic measurements terrestrial laser scanning and uav imaging campaigns are processed to georeferenced images and or elevation data respectively the data from different data sources is compiled and analysed with the aim to i reconstruct the extent thickness and volume changes of the glacier since 1893 and ii to analyse the rockslide deformation evolution by extracting information about the displacement direction dip angle velocity and partial failure of rockslide slabs since 1951 the rockslide is compound of different rockslide slabs which move downwards as rigid blocks along basal shear zones the analyses and interpretation of the data suggest a rotational type of rockslide failure mechanisms the rockslide activity correlates with the ice volume loss at the adjacent part of the glacier in the period between 1971 and 1997 the annual average rockslide activity was about 0 05 m a and the annual average ice thickness loss was 0 1 m a since the end of the last century the annual average ice thickness loss increased dramatically to 5 m a in that period the rockslide activity accelerated the highest rockslide activity up to 1 5 m a was observed in the 2000s when half of the slope toe was exposed because of glacier retreat since 2010 a deceleration of the rockslide can be observed in the vicinity of the rockslide the glacier almost disappeared and lost 99 88 of its ice volume between 1893 and 2014 the geomorphological and geological information gathered about the rockslide evolution and the glacier retreat form the base for further rockslide analyses and allow to study and model the influence from glacial debuttressing

glacier and lake level variations in west central europe over the last 3500 years on the basis of glacier and lake level records this paper attempts for the first time a comparison between high resolution palaeohydrological and palaeoglaciological data in west central europe over the past 3500 years a data set of tree ring width radiocarbon and archaeological data in addition to historical sources were used to reconstruct fluctuations of the great aletsch the gorner and the lower grindelwald glaciers in the swiss alps the three ice streams experienced nearly synchronous advances at c 1000 600 bc and ad 500 600 800 900 1100 1200 and 1300 1860 these glacier fluctuations show strong correspondence with lake level variations reconstructed in eastern france jura mountains and pre alps and on the swiss plateau this supports the hypothesis of climatically driven fluctuations historical data available for the period since ad 1550 reveal in detail various meteorological conditions behind the successive glacier advances however in agreement with the general trend shown by th

postshock annealing and postannealing shock in equilibrated ordinary chondrites implications for the thermal and shock histories of chondritic asteroids abstract in addition to shock effects in olivine plagioclase orthopyroxene and ca pyroxene petrographic shock indicators in equilibrated ordinary chondrites oc include chromite veinlets chromite plagioclase assemblages polycrystalline troilite metallic cu irregularly shaped troilite grains within metallic fe ni rapidly solidified metal sulfide intergrowths martensite and various types of plessite metal sulfide veins large metal and or sulfide nodules silicate melt veins silicate darkening low ca clinopyroxene silicate melt pockets and large regions of silicate melt the presence of some of these indicators in every petrologic type 4 to 6 ordinary chondrite demonstrates that collisional events caused all equilibrated oc to reach shock stages s3 s6 those type 4 to 6 oc that are classified as shock stage s1 on the basis of sharp optical extinction in olivine underwent postshock annealing due to burial beneath materials heated by the impact event those type 4 to 6 oc that are classified s2 on the basis of undulose extinction and lack of planar fractures in olivine were shocked to stage s3 s6 annealed to stage s1 and then shocked again to stage s2 some oc were probably shocked to stage s3 after annealing it seems likely that many oc experienced multiple episodes of shock and annealing because 40ar 39ar chronological data indicate that mil 99301 ll6 s1 was annealed 4 26 ga ago presumably as a consequence of a major impact it seems reasonable to suggest that other equilibrated s1 and s2 oc which contain relict shock features were also annealed by impacts because some type 6 s1 oc e g guarena kernouve portales valley all of which contain relict shock features were annealed 4 44 4 45 ga ago during a period when impacts were prevalent and most oc were thermally metamorphosed it follows that impact induced annealing could have contributed significantly to oc thermal metamorphism

analysis of ordinary chondrites using powder x ray diffraction 1 modal mineral abundances abstract powder x ray diffraction xrd is used to quantify the modal abundances in wt of 18 h 17 l and 13 ll unbrecciated ordinary chondrite falls which represents the complete petrologic range of equilibrated ordinary chondrites types 4 6 the xrd technique presents an effective alternative to traditional methods for determining modal abundances such as optical point counting and electron microprobe phase emp mapping the majority of chondrite powders in this study were previously prepared for chemical characterization from 8 to 20 g of material which is consistent with the suggested mass 10 g necessary to provide representative sampling of ordinary chondrites olivine and low ca pyroxene are the most abundant phases present comprising one half to three fourths of total abundances while plagioclase high ca pyroxene troilite and metal comprise the remaining xrd measured mineralogy pigeonite may also be present in some samples but it is fitted using a high ca pyroxene standard so exact abundances cannot be measured directly using xrd comparison of xrd measured abundances with calculated cross iddings pirsson washington cipw normative abundances indicates that systematic discrepancies exist between these two data sets particularly in olivine and high ca pyroxene this discrepancy is attributed to the absence of pigeonite as a possible phase in the cipw normative mineralogy oxides associated with pigeonite are improperly allocated resulting in overestimated normative olivine abundances and underestimated normative high ca pyroxene abundances this suggests that the cipw norm is poorly suited for determining mineralogical modal abundances of ordinary chondrites

voyager 2 in the uranian system imaging science results voyager 2 images of the southern hemisphere of uranus indicate that submicrometersize haze particles and particles of a methane condensation cloud produce faint patterns in the atmosphere the alignment of the cloud bands is similar to that of bands on jupiter and saturn but the zonal winds are nearly opposite at mid latitudes 70 degrees to 27 degrees where winds were measured the atmosphere rotates faster than the magnetic field however the rotation rate of the atmosphere decreases toward the equator so that the two probably corotate at about 20 degrees voyager images confirm the extremely low albedo of the ring particles high phase angle images reveal on the order of 10 2 new ringlike features of very low optical depth and relatively high dust abundance interspersed within the main rings as well as a broad diffuse low optical depth ring just inside the main rings system nine of the newly discovered small satellites 40 to 165 kilometers in diameter orbit between the rings and miranda the tenth is within the ring system two of these small objects may gravitationally confine the e ring oberon and umbriel have heavily cratered surfaces resembling the ancient cratered highlands of earth s moon although umbriel is almost completely covered with uniform dark material which perhaps indicates some ongoing process titania and ariel show crater populations different from those on oberon and umbriel these were probably generated by collisions with debris confined to their orbits titania and ariel also show many extensional fault systems ariel shows strong evidence for the presence of extrusive material about halfof miranda s surface is relatively bland old cratered terrain the remainder comprises three large regions of younger terrain each rectangular to ovoid in plan that display complex sets of parallel and intersecting scarps and ridges as well as numerous outcrops of bright and dark materials perhaps suggesting some exotic composition

deformation and thermal histories of ordinary chondrites evidence for post deformation annealing and syn metamorphic shock abstract we show that olivine microstructures in seven metamorphosed ordinary chondrites of different groups studied with optical and transmission electron microscopy can be used to evaluate the post deformation cooling setting of the meteorites and to discriminate between collisions affecting cold and warm parent bodies the l6 chondrites park shock stage s1 bruderheim s4 leedey s4 and morrow county s5 were affected by variable shock deformation followed by relatively rapid cooling and probably cooled as fragments liberated by impact in near surface settings in contrast kernouve h6 s1 portales valley h6 7 s1 and mil 99301 ll6 s1 appear to have cooled slowly after shock probably by deep burial in warm materials in these chondrites post deformation annealing lowered apparent optical strain levels in olivine additionally kernouve morrow county park mil 99301 and possibly portales valley show evidence for having been deformed at an elevated temperature 800 1000 c the high temperatures for morrow county can be explained by dynamic heating during intense shock but kernouve park and mil 99301 were probably shocked while the h l and ll parent bodies were warm during early endogenically driven thermal metamorphism thus whereas the s4 and s5 chondrites experienced purely shock induced heating and cooling all the s1 chondrites examined show evidence for static heating consistent with either syn metamorphic shock kernouve mil 99301 park post deformation burial in warm materials kernouve mil 99301 portales valley or both the results show the pitfalls in relying on optical shock classification alone to infer an absence of shock and to construct cooling stratigraphy models for parent bodies moreover they provide support for the idea that secondary metamorphic and tertiary shock processes overlapped in time shortly after the accretion of chondritic planetesimals and that impacts into warm asteroidal bodies were common

glacial valley cross profile development the influence of in situ rock stress and rock mass strength with examples from the southern alps new zealand abstract the evolution of the glacial valley cross profile form is commonly attributed primarily to the glaciological variables that control the erosion of the channel however studies in the new zealand southern alps suggest that the rock mass strength rms of the eroded rock mass is a major control on slope stability and hence on the final form of the trough rms of the slope rock will alter with time and erosional excavation and oversteepening of the valley slopes the in situ rock stress field induced by 1 the extreme topography in the axial ranges of the new zealand southern alps and 2 tectonically by collision of the australian and pacific crustal plates may play a role in valley slope development by controlling the location of rock failure and reducing rms this provides weakened rock that may provide sites for selective glacial erosion of the rock mass hence valley form evolution models should also take into account the rms and the in situ stress field acting in the eroded rock mass this study has implications for the development and modification of alpine glacial troughs in similar tectonic settings elsewhere

hydraulic and acoustic properties as a function of porosity in fontainebleau sandstone laboratory measurements have been made of the permeability k free porosity l compressional velocities vp or ve and compressional attenuations qp or qe in fontainebleau sandstone over a continuous range of porosities from 3 to 28 this large variation was achieved without any composition change fontainebleau sandstone is made of fine quartz grains with regular grain size 250 m permeability was measured with a falling head permeameter velocities and attenuations were obtained either through an ultrasonic experiment for frequencies around 500 khz or through a resonant bar technique experiment for frequencies around 5 khz and in both cases with varying water saturation the results show an excellent correlation between permeability k and total porosity for all our samples for low porosities 3 to 9 permeability in millidarcies is 2 75 10 5 7 33 while for high porosities 9 to 28 permeability k in millidarcies is given by 0 303 3 05 the correlation is also excellent between free porosity and total porosity on the other hand the correlation between acoustic properties and total porosity is not as clear as for hydraulic properties whatever the frequency 500 khz or 5 khz or the water saturation on the average velocity decreases and attenuation roughly increases with increasing total porosity velocity and attenuation values are related to the variation of grain contact structure and two samples with the same porosity and permeability may exhibit different velocities and attenuations the clear correlation between hydraulic properties and porosity is related to constant grain size while the lack of correlation for acoustic properties emphasizes the importance of the microstructure

portales valley petrology of a metallic melt meteorite breccia portales valley pv is an unusual metal veined meteorite that has been classified as an h6 chondrite it has been regarded either as an annealed impact melt breccia as a primitive achondrite or as a meteorite with affinities to silicated iron meteorites we studied the petrology of pv using a variety of geochemical mineralogical techniques our results suggest that pv is the first well documented metallic melt meteorite breccia mineral chemical and other data suggest that the protolith to pv was an h chondrite the composition of feni metal in pv is somewhat fractionated compared to h chondrites and varies between coarse vein and silicate rich portions it is best modeled as having formed by partial melting at temperatures of 940 1150 c with incomplete separation of solid from liquid metal solid metal concentrated in the coarse vein areas and s bearing liquid metal concentrated in the silicate rich areas possibly as a result of a surface energy effect both carbon and phosphorus must have been scavenged from large volumes and concentrated in metallic liquid graphite nodules formed by crystallization from this liquid whereas phosphate formed by reaction between p bearing metal and clinopyroxene components depleting clinopyroxene throughout much of the meteorite and growing coarse phosphate at metal silicate interfaces some phosphate probably crystallized from p bearing liquids but most probably formed by solid state reaction at 975 725 c phosphate forming and feo reduction reactions were widespread in pv and entailed a change in the mineralogy of the stony portion on a large scale portales valley experienced protracted annealing from supersolidus to subsolidus temperatures probably by cooling at depth within its parent body but the main differences between pv and h chondrites arose because maximum temperatures were higher in pv a combination of a relatively weak shock event and elevated pre shock temperatures probably produced the vein and breccia texture with endogenic heating being the main heat source for melting and with stress waves from an impact event being an essential trigger for mobilizing metal portales valley is best classified as an h7 metallic melt breccia of shock stage s1 the meteorite is transitional between more primitive chondritic and evolved achondrite iron meteorite types and offers clues as to how differentiation could have occurred in some asteroidal bodies

evaluation of meteorites as habitats for terrestrial microorganisms results from the nullarbor plain australia a mars analogue site unambiguous identification of biosignatures on mars requires access to well characterized long lasting geochemical standards at the planet s surface that can be modified by theoretical martian life ordinary chondrites which are ancient meteorites that commonly fall to the surface of mars and earth have well characterized narrow ranges in trace element and isotope geochemistry compared to martian rocks given that their mineralogy is more attractive to known chemolithotrophic life than the basaltic rocks that dominate the martian surface exogenic rocks e g chondritic meteorites may be good places to look for signs of prior life endemic to mars in this study we show that ordinary chondrites collected from the arid australian nullarbor plain are commonly colonized and inhabited by terrestrial microorganisms that are endemic to this mars analogue site these terrestrial endolithic and chasmolithic microbial contaminants are commonly found in close association with hygroscopic veins of gypsum and mg calcite which have formed within cracks penetrating deep into the meteorites terrestrial bacteria are observed within corrosion cavities where troilite fes oxidation has produced jarosite kfe so oh where terrestrial microorganisms have colonized primary silicate minerals and secondary calcite these mineral surfaces are heavily etched our results show that inhabitation of meteorites by terrestrial microorganisms in arid environments relies upon humidity and ph regulation by minerals furthermore microbial colonization affects the weathering of meteorites and production of sulfate carbonate fe oxide and smectite minerals that can preserve chemical and isotopic biosignatures for thousands to millions of years on earth meteorites are thus habitable by terrestrial microorganisms even under highly desiccating environmental conditions of relevance to mars they may therefore be useful as chemical and isotopic standards that preserve evidence of life thereby providing the possibility of universal context for recognition of microbial biosignatures on earth mars and throughout the solar system

chronology of the last glacial cycle in the european alps chronological data for glacier advances in the european alps between the last interglacial eemian and the holocene are summarised 115 to 11 ka during this time glaciers were most extensive extending tens of kilometres out onto the forelands between 30 and 18 ka that is synchronous with the global ice volume maximum of marine isotope stage mis 2 evidence for ice expanding to just past the mountain front for an earlier major glacier advance comes from swiss sites where advances have been luminescence dated to mis 5d 100 ka and mis 4 70 ka up to now no such evidence has been found in the eastern alps by 18 ka more than 80 of the late wurmian ice volume had gone subsequently glaciers readvanced reaching into the upper reaches of the main valleys during the lateglacial gschnitz stadial which likely occurred around 17 ka with final moraine stabilisation no later than 15 4 ka the link of the egesen stadial with the younger dryas climate deterioration is supported by exposure ages from four sites as well as minimum limiting radiocarbon dates from bogs within former glacier tongue areas key questions on the spatial and temporal variability of ice extents throughout the last glacial cycle have yet to be answered copyright 2008 john wiley sons ltd

red material on the large moons of uranus dust from the irregular satellites abstract the large and tidally locked classical moons of uranus display longitudinal and planetocentric trends in their surface compositions spectrally red material has been detected primarily on the leading hemispheres of the outer moons titania and oberon furthermore detected h2o ice bands are stronger on the leading hemispheres of the classical satellites and the leading trailing asymmetry in h2o ice band strengths decreases with distance from uranus we hypothesize that the observed distribution of red material and trends in h2o ice band strengths results from infalling dust from uranus irregular satellites these dust particles migrate inward on slowly decaying orbits eventually reaching the classical satellite zone where they collide primarily with the outer moons the latitudinal distribution of dust swept up by these moons should be fairly even across their southern and northern hemispheres however red material has only been detected over the southern hemispheres of these moons during the voyager 2 flyby of the uranian system subsolar latitude 81 s consequently to test whether irregular satellite dust impacts drive the observed enhancement in reddening we have gathered new ground based data of the now observable northern hemispheres of these satellites sub observer latitudes 17 35 n our results and analyses indicate that longitudinal and planetocentric trends in reddening and h2o ice band strengths are broadly consistent across both southern and northern latitudes of these moons thereby supporting our hypothesis utilizing a suite of numerical best fit models we investigate the composition of the reddening agent finding that both complex organics and amorphous pyroxene match the spectral slopes of our data we also present spectra that span l l bands 2 9 4 1 m a previously unexplored wavelength range in terms of spectroscopy for the uranian satellites and we compare the shape and albedo of the spectral continua in these l l band data to other icy moons in the jovian and saturnian systems additionally we discuss possible localized enhancement of reddening on titania subtle differences in h2o ice band strengths between the southern and northern hemispheres of the classical satellites the distribution of constituents on miranda and the possible presence of nh3 hydrates on these moons in closing we explore potential directions for future observational and numerical modeling work in the uranian system

partial melting and melt migration in the acapulcoite lodranite parent body we review petrologic evidence that the acapulcoites and lodranites formed by 1 vol to probably 20 vol whole rock partial melting of a chondritic precursor material at low degrees of partial melting only fe ni fes cotectic melting occurred migration distances for partial melts were short resulting in the formation of acapulcoites with essentially chondritic troilite and plagioclase contents but achondritic textures at high degrees of partial melting both fe ni fes and basaltic plagioclase pyroxene partial melts formed and the melts may have migrated out of the source rock the partial melt residues which are more or less depleted in fe ni fes and plagioclase are the lodranites melt migration was complex most acapulcoites which experienced relatively low degrees of partial melting lost little if any of the partial melt one acapulcoite lew 86220 represents a unique case in which fe ni fes and basaltic partial melts appear to have migrated from a lodranite source region into a cooler acapulcoite region where they were trapped in cases of the relatively high degrees of partial melting experienced by lodranites melts may have been partly selectively or totally removed from the rocks and fe ni fes and or basaltic partial melts may have been removed to different degrees and may in fact have been trapped on occasion in greater than chondritic proportions we model vein and dike formation and melt migration by calculating the excess pressures and vein and dike sizes for varying degrees of partial melting our calculations are broadly consistent with observations indicating that melt migration is inefficient at low degrees of partial melting and extremely efficient at high degrees of partial melting although the size of the acapulcoite lodranite parent body and the volatile contents of the chondritic precursor rocks are poorly constrained the lack of basaltic rocks in the world s meteorite collections complementary to the lodranites suggests that basaltic partial melts may have been accelerated off the body by explosive volcanism of the type envisioned by wilson and keil 1991 and ejected into space the diversity of rocks from the acapulcoite lodranite parent body may provide a basis for better understanding the diverse range of spectral subtypes recognized among the s type asteroids

magma crystallization and viscosity a study of molten basalts from the piton de la fournaise volcano la reunion island abstract the viscosity of three molten basalts produced by fusion of lavas issued from different eruptions of the piton de la fournaise la reunion island has been investigated above the liquidus and at high degrees of supercooling for all basalts crystallization took place rapidly above the glass transition range which made static measurements problematic because of time dependent non newtonian rheology by contrast reproducible results were obtained in dynamic measurements made at a constant heating rate of 5 k mn partial crystallization resulted in strong viscosity increases which were primarily due to the presence of solid inclusions comparisons with phase equilibria experiments performed for the same samples at higher temperatures show that crystallization takes place differently below the liquidus and at strong degrees of supercooling as recently described for simpler systems these differences in nucleation and growth are controlled by the relative mobilities of the cations diffusing within the melt to attach themselves to crystal melt interfaces a consequence is that the composition evolution of the residual melt differs in equilibrium and irreversible crystallization in turn this contrast induces opposite viscosity variations for the residual melt

shock and thermal history of northwest africa 4859 an annealed impact melt breccia of ll chondrite parentage containing unusual igneous features and pentlandite abstract northwest africa 4859 nwa 4859 is a meteorite of ll chondrite parentage that shows unusual igneous features and contains widely distributed pentlandite the most obvious unusual feature is a high proportion of large 3 cm diameter igneous textured enclaves lites interpreted as shock melts that were intruded into an ll chondrite host one such lite appears to have been produced by whole rock melting of ll chondrite initial rapid partial crystallization and subsequent slow cooling of the residual melt in the host to produce a differentiated object other unusual features include mm sized overgrowth objects fine grained plagioclase rich bands and coarse troilite 7 mm across grains all these features are interpreted as having crystallized from melts produced by a single transient shock event followed by slow cooling a subsequent shock event of moderate s3 intensity produced veining and transformed some of the pyroxene into the clinoenstatite polytype pentlandite together with associated troilite in nwa 4859 probably formed by the breakdown of a monosulfide precursor phase at low temperature 230 c following the second shock event nwa 4859 is interpreted to be an unusual impact melt breccia that contains shock melt which crystallized in different forms at depth within the parent body

are icelandic rock slope failures paraglacial age evaluation of seventeen rock slope failures in the skagafjorður area based on geomorphological stacking radiocarbon dating and tephrochronology in iceland there are numerous rock slope failures especially in the tertiary basaltic formations of the northern eastern and northwestern regions the temporal pattern of rock slope failures is fundamental for understanding post glacial events in the skagafjor ur district central northern iceland 17 rock slope failures were investigated to determine the age of their occurrence a geomorphic survey was carried out to identify and characterize landform units both on the rock slope failures and in their immediate vicinity in this coastal area we used geomorphological stacking which included the relationship between rock slope failures and raised beaches caused by glacial isostatic rebounds the chronology of which was established in previous studies we searched for depressions on the rock slope failures to then excavate a series of pits and map the stratigraphy the resulting stratigraphic framework was then validated using i radiocarbon dating of wood remains and ii tephrochronology both of which were complemented by age depth model calibration the results confirm that all the rock slope failures potentially occurred before the boreal 8 ka while 94 occurred before the preboreal 10 ka they all potentially occurred after the glacial retreat following the maximal ice extent and the preboreal more precisely 11 of them potentially occurred between the preboreal and the first half of the holocene this study demonstrates the relationship between the deglaciation and destabilization of slopes during the paraglacial phase debuttressing decompression glacial isostatic rebound seismic activity etc which are also controlling factors favouring landsliding but are difficult to identify for each individual rock slope failure

chemical alteration and ree mobilization in meteorites from hot and cold deserts the effects of terrestrial weathering on ree mobilization are evaluated for a variety of uncommon meteorites found in antarctica and in hot deserts the meteorites analyzed include 7 non cumulate eucrites 10 shergottites 3 nakhlites 2 lunar meteorites 4 angrites 10 acapulcoites 1 winonaite and 1 brachinite in situ concentration measurements of lanthanides and selected other minor and trace elements were made on individual grains by secondary ion mass spectrometry sims in antarctic meteorites oxidation converts ce 3 to ce 4 which is less soluble than the trivalent ree resulting in ce anomalies the mineral most affected is low ca pyroxene however not all grains of a given mineral are and distinct analyses of a single grain can even yield ree patterns with and without ce anomalies the effect is most pronounced for antarctic eucrites in which ce anomalies are observed not only in individual minerals but also in whole rock samples although ce anomalies are observed in meteorites from hot deserts as well the most characteristic signs of chemical alteration in this environment are a lree enrichment with a typical crustal signature as well as sr ba and u contaminations these can modify the whole rock ree patterns and disturb the isotope systematics used to date these objects the lree contamination is highly heterogeneous affecting some grains and not others of a given mineral mainly olivine and low ca pyroxene the two minerals with the lowest ree concentrations the major conduit for ree movement is through shock induced cracks and defects and the highest levels of contamination are found in altered material filling such veins and cracks meteorites that experienced low shock levels and those that are highly recrystallized are the least altered copyright 2003 elsevier ltd

the ungrouped chondrite el medano 301 and its comparison with other reduced ordinary chondrites abstract el medano 301 em 301 is an ungrouped chondrite with overall texture and trace element distribution similar to those of ordinary chondrites ocs but with silicate olivine and low ca pyroxene compositions that are more reduced than those in ocs with average olivine and low ca pyroxene of fa3 9 0 3 and fs12 8 4 9 respectively these values are far lower than the values for ocs and even for chondrites designed as reduced chondrites low ca pyroxene is the dominant mineral phase and shows zoning with higher mgo contents along the crystal rims and cracks reverse zoning the co content of kamacite is also much lower than the concentrations observed in ocs below detection limit of 0 18 wt versus 0 44 37 wt oxygen isotopic composition is 17o 0 79 0 78 and slightly different from that of ocs the lower modal olivine pyroxene ratio different infrared ir spectra lower co content of kamacite lower mean feo contents of olivine and pyroxene different kamacite texture and different oxygen isotopic composition show that em 301 does not belong to a known oc group em 301 shows similarities with chondritic clasts in cumberland falls aubrite and with northwest africa 7135 nwa 7135 and acfer 370 ungrouped chondrites however dissimilar to nwa 7135 and the clasts it does not contain highly reduced mineral phases like daubreelite our observations suggest the formation of em 301 in a nebular region compositionally similar to ocs but with a different redox state with oxygen fugacity o2 in this region lower than that of ocs and higher than that of enstatite chondrites condensation region a second possibly nebular phase of reduction by the production of reducing gas phases e g c rich could be responsible for the subsequent reduction of the primary material and the occurrence of reverse zoning in the low ca pyroxene and lower average fa fs ratio based on the ir spectra of em 301 we suggest the possibility that the parent body of this chondrite was a v type asteroid

temperatures of granulite facies metamorphism constraints from experimental phase equilibria and thermobarometry corrected for retrograde exchange this study assesses temperatures of formation of common granulites by combining experimental constraints on the p t stability of granulite facies mineral associations with a garnet orthopyroxene grt opx thermobarometry scheme based on al solubility in opx corrected for late fe mg exchange we applied this scheme to 414 granulites of mafic intermediate and aluminous bulk compositions our findings suggest that granulites are much hotter than traditionally assumed and that the p t conditions of the amphibolite granulite transition portrayed in current petrology textbooks are significant underestimates by over 100 c for aluminous and intermediate granulites mean corrected temperatures based on our method are 890 17 and 841 11 c respectively uncertainties reported as 95 confidence limits on the mean consistent with minimum temperatures for orthopyroxene production by fluid absent partial melting in these bulk compositions in contrast mean temperatures based on grt opx fe mg exchange equilibria using the same thermodynamic data are 732 22 and 723 11 c respectively well below the minimum temperatures for opx stability for mafic granulites the mean corrected temperature using our method is 816 12 c similar to the mean temperature of 793 13 c from fe mg exchange reasons for the differences between the mafic granulites and aluminous intermediate granulites are unclear but may be due to the lower al concentrations in opx in the mafic rocks and possible deficiencies in the thermodynamic modelling of these low concentrations we discuss a number of well known granulite terrains in the context of our findings including the adirondacks the acadian granulites of new england the incipient charnockites of southern india and sri lanka and the kerala khondalite belt our findings carry implications for thermotectonic models of granulite formation a computer program to perform our thermobarometry calculations rclc is available from the journal of petrology website at http www petrology oupjournals org or from the authors at http www geo ucalgary ca pattison drm pattison rclc htm

influence of daily surface temperature fluctuations on rock slope stability case study of the rochers de valabres slope france the present paper describes a rockfall that has affected the rochers de valabres slope france s southern alps region and discusses one possible mechanism for the occurrence of this rockfall along with the potential for future ones in the absence of an obvious explanatory trigger factor we set out to examine whether natural daily surface temperature changes could have played a role in this event in particular it is suspected that these slight yet repeated perturbations may be a preparatory factor for rockfalls with a day to day cumulative effect a numerical model strengthens this hypothesis by showing that thermally induced deformations can be sufficient to cause the gradual downward creep of a rock block located in an awkward position to investigate this notion more thoroughly a currently vulnerable part of the rochers de valabres slope has been instrumented with a high precision geodetic monitoring system total station it is believed that this device is able to capture thermally induced movements if specific precautions are taken the instrumented rock volume is used as a test site in the aim of better understanding the consequences of surface temperature changes on slope stability measured data with a precision level never before achieved on rock slopes are compared herein with numerical modelling results the initial conclusions of the long term study we are conducting indicate that surface temperature changes play an important while not easily quantifiable role in preparing rockfalls

slope instability in relation to glacial debuttressing in alpine areas upper durance catchment southeastern france evidence from field data and 10be cosmic ray exposure ages the upper durance catchment is an area prone to rock slope failures such failures reflect the combination of high relief litho structural controls and paraglacial stress release the aim of this study is to determine the role of deglacial unloading and resulting paraglacial stress release in conditioning or triggering slope failure former dimensions of the durance glacier are reconstructed then combined with digital elevation model data in a raster geographic information system to quantify the spatial pattern of stresses associated with glacial loading at the last glacial maximum preliminary calculations suggest that major rock falls and rock avalanches are associated with areas subject to the highest decompression stresses focus on two case studies allows the consequences of paraglacial stress release on slope instability to be evaluated description of slope failure runout deposits allows reconstruction of the nature of slope failure surface exposure dates based on concentration of cosmogenic 10be allows the timing of both deglaciation and that of post glacial rock slope failures to be established it is shown that rock slope failures are concentrated on lower valley side slopes within the area occupied by ice at the last glacial maximum and that their locations coincide with zones of inferred high glacial loading stress consistent with interpretation of both bedrock disruption and large scale rock slope failures as paraglacial phenomena induced by stress release following deglaciation timing of initial rock avalanche runout deposition at one site is consistent with this conclusion though later instability episodes at the same site may have occurred independent of the influence of paraglacial stress release

quantifying carbon fixation in trace minerals from processed kimberlite a comparative study of quantitative methods using x ray powder diffraction data with applications to the diavik diamond mine northwest territories canada abstract the capacity of mine waste to trap co2 is in some cases much larger than the greenhouse gas production of a mining operation in mine tailings the presence of secondary carbonate minerals that trap co2 can therefore represent substantial fixation of this greenhouse gas the abilities of three methods of quantitative phase analysis to measure trace nesquehonite mgco3 3h2o in samples of processed kimberlite have been assessed the method of reference intensity ratios rir the internal standard method and the rietveld method with x ray powder diffraction data tests on synthetic mixtures made to resemble processed kimberlite indicate that both the rir and rietveld methods can be used accurately to quantify nesquehonite to a lower limit of approximately 0 5 wt for conditions used in the laboratory below this value estimates can be made to a limit of approximately 0 1 wt using a calibration curve according to the internal standard method the rir method becomes increasingly unreliable with decreasing abundance of nesquehonite primarily as a result of an unpredictable decline in preferred orientation of crystallites for rietveld refinements structureless pattern fitting was used to account for planar disorder in lizardite by considering it as an amorphous phase rietveld refinement of data collected from specimens that were serrated to minimize preferred orientation of crystallites gives rise to systematic overestimates of refined abundances for lizardite and underestimates for other phases the resulting pattern of misestimates may be mistaken for the effect of amorphous and or nanocrystalline material in samples this effect is mitigated by collecting data from non serrated specimens which typically give relative errors on refined abundances for major and minor phases in the range of 5 20 however relative error can increase rapidly for abundances less than 5 wt nonetheless absolute errors are sufficiently small that estimates can be made for the amount of co2 stored in secondary nesquehonite using the rir method or the rietveld method for abundances 0 5 wt and a calibration curve for abundances

wetting behavior of partial melts during crustal anatexis the distribution of hydrous silicic melts in polycrystalline aggregates of quartz the equilibrium distribution of hydrous silicic melts in polycrystalline aggregates of quartz was characterized in a series of partial melting and melt distribution experiments in the systems quartz albite orthoclase h2o and quartz anorthite h2o at 650 to 1000 mpa and 800 to 900 c near equilibrium textures in these experiments are characterized by very low quartz quartz melt wetting angles and by a substantial number of thin melt films along grain boundaries wetting angles in the h2o saturated experiments are as follows 18 at 800 c 1000 mpa and 12 at 900 c 1000 mpa in the granitic system 18 at 850 c 650 mpa 15 at 900 c 650 mpa and 15 at 900 c 1000 mpa in the quartzanorthite system in the granitic system at 900 c 1000 mpa a decrease of h2o content in melt from 17 wt at saturation to 6 wt results in a slight increase of wetting angle from 12 to 16 these low wetting angles and the observation that many grain boundaries are wetted by melt films indicate that the ratio of quartz quartz to quartz melt interfacial energies ss s1 is high 2 secondary electron imaging of fracture surfaces of melt poor samples provided a three dimensional insight into the geometry of melt at low melt fraction melt forms an interconnected network of channels along grain edges as predicted for isotropic systems with wetting angles below 60 this high permeability geometry suggests that the segregation of granitic melts is not as sluggish as previously anticipated simple compaction calculations for a permeability range of 10 12 to 10 9 m2 indicate that segregation may operate at low to moderate melt fractions below 30 vol within relatively short time scales i e 105 to 106 years quartzmelt textures show significant deviations from the equilibrium geometries predicted for isotropic partially molten systems the most consistent deviation is the pervasive development of crystallographically controlled planar faces of quartz these faces provide definitive evidence for non isotropic quartz melt surface energy for most silicates other than quartz the grain scale distribution of partial melts deviates even more significantly from equilibrium distributions in isotropic systems accordingly in order to describe adequately melt distributions in most natural source regions the equilibrium model should be modified to account for anisotropy of solid liquid interfacial energy

probing the regoliths of the classical uranian satellites are their surfaces mantled by a layer of tiny h2o ice grains abstract we investigate whether the surfaces of the classical moons of uranus are compositionally stratified with a thin veneer of mostly tiny h2o ice grains 2 m diameters mantling a lower layer composed of larger grains of h2o ice dark material and co2 ice 10 50 m diameters near infrared observations 1 2 5 m have determined that the h2o ice rich surfaces of these moons are overprinted by concentrated deposits of co2 ice found almost exclusively on their trailing hemispheres however best fit spectral models of longer wavelength datasets 3 5 m indicate that the spectral signature of co2 ice is largely absent and instead the exposed surfaces of these moons are composed primarily of tiny h2o ice grains to investigate possible compositional layering of these moons we have collected new data using the infrared array camera irac onboard the spitzer space telescope 3 5 m spectral modeling of these new data is consistent with prior analyses suggesting that the exposed surfaces of the uranian moons are primarily composed of tiny h2o ice grains furthermore analysis of these new data reveal that the trailing hemispheres of these moons are brighter than their leading hemispheres over the 3 to 5 m wavelength range except for miranda which displays no hemispherical asymmetries in its irac albedos our analyses also reveal that the surface of ariel displays five distinct regional scale albedo zones possibly consistent with the spatial distribution of co2 ice on this moon we discuss possible processes that could be enhancing the observed leading trailing albedo asymmetries exhibited by these moons as well as processes that could be driving the apparent compositional stratification of their near surfaces

holocene glacier culminations in the western alps and their hemispheric relevance the natural variability of holocene climate defi nes the baseline to assess ongoing climate change greenland ice core records indicate warming superimposed by abrupt climate oscillations in the early holocene followed by a general cooling trend throughout the middle and late holocene that culminated during the little ice age lia tropical precipitation changes correlate with these patterns throughout the holocene here we use mountain glaciers in the european alps to reconstruct the regional holocene climate evolution and to test for a link between mid latitude north atlantic and tropical climate our precise 10 be chronology from tsidjiore nouve glacier western swiss alps indicates a glacier culmination during the earliest holocene 11 4 k y ago likely related to the preboreal oscillation based on our data no holocene glacier advance of similar amplitude occurred until 3 8 k y ago when the glacier reached lia limits the 10 be ages between 500 and 170 yr correspond to the lia while the youngest 10 be ages overlap with the historically recorded post lia glacier positions integrating our data with existing records we propose a hemispheric climate link between the alps north atlantic temperature and tropical precipitation patterns for the holocene supporting the concept of a pervasive climate driver these fi ndings from northern mid latitudes are consistent with the hypothesis formulated for the tropics that the earth s thermal equator responding to north atlantic temperature changes might have migrated southward throughout the holocene reaching the southern turning point toward the end of the lia

monitoring and analysis of active rockslide glacier interactions moosfluh switzerland abstract valley glaciers have traditionally been expected to significantly influence the stability and movement rates of adjacent paraglacial landslides however detailed studies related to the mechanical and displacement interactions between glacier ice and unstable rock slopes are very rare here we present a detailed in situ investigation of the spatial variations of the displacement field of the great aletsch glacier in the surroundings of a large active instability i e the moosfluh landslide a deep seated gravitational slope deformation with superimposed large 1 5 million m3 secondary rockslides formed during fall 2016 we performed repeat uav based photogrammetric surveys during 3 days 74 h and applied digital image correlation techniques to record high resolution surface displacement vector fields of the landslide stable slopes and adjacent glacier our results show that the secondary rockslide adjacent to the glacier is composed of two parts of 1 5 and 2 8 million m3 volume respectively showing significant differences in mean displacement velocities 0 4 and 0 9 m in 74 h respectively excluding rapid movements from detached blocks both rockslide compartments induce clear deflections of the glacier flow field moving with a maximum velocity of about 0 3 to 0 4 m in 74 h this influence is highest near the ice contact boundary and decreases within a distance of about 100 200 m from the rock slope instability we investigate the viscous forces at the landslide glacier contact using a straightforward analytical model for an incompressible rockslide block sliding along a planar cohesionless surface into ice these forces are then applied to a slope stability model based on the limit equilibrium concept representing the real geometry at the interface boundary to quantitatively explore the true buttressing effects of valley glaciers on an already moving slope instability we show that the viscous ice deformation plays an important role in mediating the displacement velocities of landslides in unstable conditions while on the other hand the slope support from the valley glacier has very little influence on the stability of the investigated rockslides as most valley glaciers are currently strongly retreating due to global warming uncovering significant numbers of pre lia slope instabilities this detailed investigation provides important hints on their potential displacement behavior understanding the factors controlling landslide velocity is of great importance for hazard analyses and early warning hence this study has implications beyond academic interest e g for the planning and operation of alpine infrastructure such as cable cars or hydropower systems

implications of using broadband photometry for compositional remote sensing of icy objects water ice has such a low absorption coefficient at visual wavelengths 0 01 cm 1 that a very small amount of particulate material can significantly darken an icy surface a variety of ice plus particle mixtures were studied to show that particulate contaminations of 1 by weight even 0 1 or less in some cases in ice or frosts result in reflectance levels close to that of the contaminants in a very clear ice no bubbles it is plausible to have a reflectance 0 05 for particulate contaminations 10 7 by weight for submicron dark particles such as carbon lampblack scattering conditions compete for domination with contaminants for control of visual reflectance implying that the apparent reflectivity level and color of a surface is a poor indicator of ice content a dark surface e g albedo 0 05 does not necessarily imply that there us very little water ice present infrared jhk colors of water ice and other minerals including ice mineral mixtures show that some orthopyroxenes can have jhk colors very similar to fine grained water frosts in general it is possible that the jhk colors of an ice plus particulate mixture can fall anywhere in the classical j h versus h k diagram thus the diagram cannot be used to distinguish a predominately rock surface from one which is predominantely ice for one specific case an important exception is the case where both the j h and h k colors are 0 2 it appears that such colors indicate a relatively pure icy surface in some cases the diagram might be used as a statistical tool to distinguish between the compositions of surfaces within a class of objects but the validity of such comparisons decreases for different classes such as the main belt asteroids when compared to outer solar system satellites where water ice is more stable

structure from motion photogrammetry a low cost effective tool for geoscience applications abstract high resolution topographic surveying is traditionally associated with high capital and logistical costs so that data acquisition is often passed on to specialist third party organisations the high costs of data collection are for many applications in the earth sciences exacerbated by the remoteness and inaccessibility of many field sites rendering cheaper more portable surveying platforms i e terrestrial laser scanning or gps impractical this paper outlines a revolutionary low cost user friendly photogrammetric technique for obtaining high resolution datasets at a range of scales termed structure from motion sfm traditional softcopy photogrammetric methods require the 3 d location and pose of the camera s or the 3 d location of ground control points to be known to facilitate scene triangulation and reconstruction in contrast the sfm method solves the camera pose and scene geometry simultaneously and automatically using a highly redundant bundle adjustment based on matching features in multiple overlapping offset images a comprehensive introduction to the technique is presented followed by an outline of the methods used to create high resolution digital elevation models dems from extensive photosets obtained using a consumer grade digital camera as an initial appraisal of the technique an sfm derived dem is compared directly with a similar model obtained using terrestrial laser scanning this intercomparison reveals that decimetre scale vertical accuracy can be achieved using sfm even for sites with complex topography and a range of land covers example applications of sfm are presented for three contrasting landforms across a range of scales including an exposed rocky coastal cliff a breached moraine dam complex and a glacially sculpted bedrock ridge the sfm technique represents a major advancement in the field of photogrammetry for geoscience applications our results and experiences indicate sfm is an inexpensive effective and flexible approach to capturing complex topography

large ice contact slope movements glacial buttressing deformation and erosion glaciers and slope movements may act simultaneously to erode and modify glaciated slopes undercutting by glaciers can destabilize slopes but the extent to which slope failure may progress prior to subsequent glacier withdrawal has not hitherto been considered the traditional view has been that the buttressing effect of ice prevents slope movement the problem with this view is that ice is one third the density of rock and flows under low applied stress consequently failed slopes may move into the glacier if they exert a stress in excess of the resistance provided by the glacier slope movement rate depends on ice rheology and other factors influencing driving and resisting stresses simple viscous equations are used to investigate these variables the equations predict that small 108 m3 rockslides to test these estimates field evidence is presented of slope movements in glaciated valleys of new zealand narrowing or squeezing of glaciers adjacent to unstable rock slopes is demonstrated and considered to be the result of slope movement for one site geomorphic mapping and slope movement monitoring data show that movement rates are of similar order of magnitude to those predicted by the viscous equations closer agreement could be achieved with the application of modelling techniques that can more realistically model the complex slope geometries and stability factors encountered or by obtaining additional empirical data to calibrate the models this research implies that while the concept of glacial debuttressing the reduction of slope support from withdrawal of glaciers is valid complete debuttressing is not a prerequisite for the movement of ice contact rock slopes these slope movements may contribute to the erosional processes of glaciers and the evolution of glaciated slopes in a previously unrecognized way copyright 2012 john wiley sons ltd

surface exposure dating of the great aletsch glacier egesen moraine system western swiss alps using the cosmogenic nuclide 10be egesen moraines throughout the alps mark a glacial advance that has been correlated with the younger dryas cold period using the surface exposure dating method in particular the measurement of the cosmogenic nuclide 10 be in rock surfaces we attained four ages for boulders on a prominent egesen moraine of great aletsch glacier in the western swiss alps the 10 be dates range from 10 460 1100 to 9040 1020 yr ago three 10 be dates between 9630 810 and 9040 1020 yr ago are based upon samples from the surfaces of granite boulders two 10 be dates 10 460 1100 and 9910 970 yr ago are based upon a sample from a quartz vein at the surface of a schist boulder in consideration of the numerous factors that can influence apparently young 10 be dates and the scatter within the data we interpret the weighted mean of four boulder ages 9640 430 yr including the weighted mean of two 10 be dates of the quartz vein as a minimum age of deposition of the moraine all 10 be dates from the great aletsch glacier egesen moraine are consistent with radiocarbon dates of nearby bog bottom organic sediments which provide minimum ages of deglaciation from the moraine the 10 be dates from boulders on the great aletsch glacier egesen moraine also are similar to 10 be dates from egesen moraines of vadret lagrev glacier on julier pass in the eastern swiss alps both the morphology of the great aletsch glacier egesen moraine and the comparison with 10 be dates from the inner vadret lagrev egesen moraine support the hypothesis that the climatic cooling that occurred during the younger dryas cold episode influenced the glacial advance that deposited the great aletsch glacier egesen moraine because of the large size and slow response time of great aletsch glacier we suggest that the great aletsch glacier egesen moraine was formed during the last glacial advance of the multiphased egesen cold period the kromer stage during the preboreal chron copyright 2004 john wiley sons ltd

verifying and quantifying carbon fixation in minerals from serpentine rich mine tailings using the rietveld method with x ray powder diffraction data most carbon on earth is bound within minerals and increasing the uptake of atmospheric carbon dioxide into minerals may reduce the greenhouse gas content of the atmosphere we document carbon disposal through the mineralization of mine tailings at clinton creek yukon territory and cassiar british columbia we confirm crystallographic binding of carbon in these tailings and quantify carbon dioxide uptake using quantitative phase analysis with the rietveld method for x ray powder diffraction data planar disorder in the structures of the kaolinite serpentine group minerals makes rietveld refinements of x ray powder diffraction data for serpentinites problematic using structureless pattern fitting and with the addition of a known quantity of a well crystallized material the problem of structural disorder is overcome by considering the serpentine minerals as amorphous phases we test the accuracy and precision of this refinement method using synthetic serpentine rich mine tailings of known composition estimates of the abundance of hydrated magnesium carbonates in these tailings have a precision of approximately 5 relative for mineral species present in amounts greater than 10 wt precise estimates of carbonate mineral content and crystallographically bound atmospheric co 2 are made for samples of serpentine rich tailings from clinton creek and cassiar results for mine tailings are also compared to mineralogically similar samples from a carbonate playa at atlin british columbia the potential for decomposition of metastable hydrated magnesium carbonate phases to geologically stable magnesite may represent long term stability of the products of mineral sequestration in mine tailings

the uranian satellites water ice on ariel and umbriel abstract new near infrared reflectance spectra are presented for ariel and umbriel water ice on the surface of ariel and umbriel is verified from spectral signatures in the 2 m region however the weaker bands in umbriel s spectrum indicate that its surface is significantly different from ariel either in degree of contamination with dark material or in microstate umbriel may have a lower albedo than ariel titania and oberon and therefore may have a diameter comparable to that of titania

lateglacial and early holocene dynamics of adjacent valley glaciers in the western swiss alps the alps play a pivotal role for glacier and climate reconstructions within europe detailed glacial chronologies provide important insights into mechanisms of glaciation and climate change we present 26 10be exposure dates of glacially transported boulders situated on moraines and ice moulded bedrock samples at the belalp cirque and the great aletsch valley switzerland weighted mean ages of 10 9 11 1 11 0 and 9 6 ka for the belalp on up to six individual moraine ridges constrain these moraines to the egesen kartell and schams stadials during lateglacial to early holocene times the weighted mean age of 12 5 ka for the right lateral moraine of the great aletsch correlates with the egesen stadial related to the younger dryas cooling these data indicate that during the early holocene between 11 7 and 9 2 ka glaciers in the swiss alps seem to have been significantly affected by cold climatic conditions initiated during the younger dryas and the preboreal oscillation these conditions resulted in glacier margin oscillations relating to climatic fluctuations during the second phase of the younger dryas and continuing into boreal times as supported by correlation of the innermost moraine of the belalp cirque to the schams early holocene stage copyright 2011 john wiley sons ltd

thermal evolution and interaction between impact melt sheet and footwall a genetic model for the contact sublayer of the sudbury igneous complex canada 1 the sudbury igneous complex sic and associated ni cu pge mineralization has been interpreted in terms of a large meteorite impact event in this study the thermal relationship between the large cooling melt sheet and the surrounding country rock is examined in terms of its role in an evolving thermal gradient rather than as a passive receptacle for the melt sheet above thermal modeling of this environment is undertaken using physical and thermal constraints appropriate to the sic and assuming heat dissipation from the 2 5 km thick superheated melt sheet 1800 c by either diffusion with zero convection or by rapid convection within the melt sheet with zero convection basal cooling produces a solid base which lowers conductivity such that the immediate footwall rocks reach 1000 c producing partial melting that extends 200 m into the footwall in a rapidly convecting melt sheet the initial footwall chill is remelted and high temperatures maintained within the sheet close to the contact this results in higher temperatures being attained in the immediate footwall 1100 1200 c inducing complete melting of proximal footwall and partial melting to depths of 500 m below the melt sheet proximal footwall consists of paleoproterozoic huronian basalts granitoids and sediments exposed in the south range overlying archaean gneisses and granitoids total and partial melting of this material early in the cooling history of the melt sheet and the subsequent gravitational accommodation of these melts according to density would produce a basalt dominated basal liquid corresponding to the so called contact sublayer the thermal aureole predicted by our models is consistent with that preserved around the north range of the sic assuming 800 m of thermally induced erosion at the contact

gravitational spreading of mountain ridges coeval with late weichselian deglaciation impact on glacial landscapes in trollaskagi northern iceland abstract during the late weichselian deglaciation the coastal mountains of northern central iceland have experienced significant paraglacial readjustment processes in the form of conspicuous rock slope failures and deep seated gravitational slope deformation dsgsd local topographic slopes and ridges were deeply reshaped by these large scale paraglacial processes located on the eastern side of skagafjor ur one of the largest fjords of northern iceland the oslandshli arfjoll and hnjukar ridges 65 49n 19 14w exhibit geomorphic evidence of spectacular dsgds several series of dsgsd induced landforms such as crestal graben and troughs initiated by ridge top splitting were investigated over a 30 km 2 area on the basis of geomorphological mapping we recognized i a ridge top splitting event mainly controlled by glacial debuttressing induced by a minimal 300 m lowering of the glacier surface in the deildardalur valley ii a rapid late weichselian deglaciation of the deildardalur valley spanning a few thousands of years ice free stage probably reached around 14 000 years cal bp iii ridge top splitting having an influence on large scale glacial patterns by guiding and facilitating glacial erosion along ridge top grabens resulting in accelerated trough widening based on these interpretations we propose an evolutionary sequence of both the kinematic stages of the dsgsd and the late weichselian deglaciation at the valley scale this work provides new insights into i the patterns of the late weichselian deglaciation in the skagafjor ur area especially in tributary valleys of the fjord ii the timing of large scale paraglacial ridge top deformations in relation to the post lgm deglaciation and iii the influence of paraglacial dsgsd features on large scale glacial erosional patterns

constraints on the role of impact heating and melting in asteroids received 1996 august 30 accepted in revised form 1997 january 30 abstract imaging of asteroids gaspra and ida and laboratory studies of asteroidal meteorites show that im pacts undoubtedly played an important role in the histories of asteroids and resulted in shock metamorphism and the formation of breccias and melt rocks however in recent years impact has also been called upon by numerous authors as the heat source for some of the major geological processes that took place on asteroids such as global thermal metamorphism of chondrite parent bodies and a variety of melting and igneous events the latter were proposed to explain the origin of ureilites aubrites mesosiderites the eagle station pallasites acapulcoites lodranites and the iab iiicd and iie irons we considered fundamental observations from terrestrial impact craters combined with results from laboratory shock experiments and theoretical consider ations to evaluate the efficiency of impact heating and melting of asteroids studies of terrestrial impact craters and relevant shock experiments suggest that impact heating of aster oids will produce two types of impact melts 1 large scale whole rock melts total melts not partial melts at high shock pressure and 2 localized melts formed at the scale of the mineral constituents mineral specific or grain boundary melting at intermediate shock pressures the localized melts form minuscule amounts of melt that quench and solidify in sifu thus preventing them from pooling into larger melt bodies partial melting as defined in petrology has not been observed in natural and experimental shock metamor phism and is thermodynamically impossible in a shock wave induced transient compression of rocks the total impact melts produced represent a minuscule portion of the displaced rock volume of the parent crater internal differentiation by fractional crystallization is absent in impact melt sheets of craters of sizes that can be tolerated by asteroids and impact melt rocks are usually clast laden thermal metamorphism of country rocks by impact is extremely minor experimental and theoretical considerations suggest that 1 single dis ruptive impacts cannot raise the average global temperature of strength or gravity dominated asteroids by more than a few degrees 2 cumulative global heating of asteroids by multiple impacts is ineffective for asteroids less than a few hundred kilometers in diameter 3 small crater size low gravity and low impact velocity suggest that impact melt volume in single asteroidal impacts is a very small 0 014 1 fraction of the total displaced crater volume 4 total impact melt volume formed during the typical lifetime of an asteroid is a small fraction 0 001 of the volume of impact generated debris and 5 much of the impact melt generated on asteroidal targets is ejected from craters with velocities greater than escape velocity and thus not retained on the asteroid the inescapable conclusion from these observations and calculations is that impacts cannot have been the heat source for the origin of the meteorite types listed above and we must turn to processes other than impact such as decay of short lived radionuclides or electromagnetic induction during an early t tauri phase of the sun to explain heating and melting of the parent bodies of these meteorites

contemporary glacier retreat triggers a rapid landslide response great aletsch glacier switzerland the destabilization and catastrophic failure of landslides triggered by retreating glaciers is an expected outcome of global climate change and poses a significant threat to inhabitants of glaciated mountain valleys around the globe of particular importance are the formation of landslide dammed lakes outburst floods and related sediment entrainment based on field observations and remote sensing of a deep seated landslide located at the present day terminus of the great aletsch glacier we show that the spatiotemporal response of the landslide to glacier retreat is rapid occurring within a decade our observations uniquely capture the critical period of increase in slope deformations onset of failure and show that measured displacements at the crown and toe regions of the landslide demonstrate a feedback mechanism between glacier ice reduction and response of the entire landslide body these observations shed new light on the geomorphological processes of landslide response in paraglacial environments which were previously understood to occur over significantly longer time periods

shock post shock annealing and post annealing shock in ureilites the thermal and shock histories of ureilites can be divided into four periods 1 formation 2 initial shock 3 post shock annealing and 4 post annealing shock period 1 occurred 4 55 ga ago when ureilites formed by melting chondritic material impact events during period 2 caused silicate darkening undulose to mosaic extinction in olivines and the formation of diamond lonsdaleite and chaoite from indigenous carbonaceous material alkali rich fine grained silicates may have been introduced by impact injection into ureilites during this period about 57 of the ureilites were unchanged after period 2 during period 3 events impact induced annealing caused previously mosaicized olivine grains to become aggregates of small unstrained crystals some ureilites experienced reduction as feo at the edges of olivine grains reacted with c from the matrix annealing may also be responsible for coarsening of graphite in a few ureilites forming euhedral appearing idioblastic crystals orthopyroxene in meteorite hills met 78008 may have formed from pigeonite by annealing during this period the rb sr internal isochron age of 4 0 ga for met 78008 probably dates the annealing event at this late date impacts are the only viable heat source about 36 of ureilites experienced period 3 events but remained unchanged afterwards during period 4 7 of the ureilites were shocked again as is evident in the polymict breccia elephant moraine eet 83309 this rock contains annealed mosaicized olivine aggregates composed of small individual olivine crystals that exhibit undulose extinction ureilites may have formed by impact melting chondritic material on a primitive body with heterogeneous o isotopes plagioclase was preferentially lost from the system due to its low impedance to shock compression brief melting and rapid burial minimized the escape of planetary type noble gases from the ureilitic melts incomplete separation of metal from silicates during impact melting left ureilites with relatively high concentrations of trace siderophile elements

petrology and geochemistry of patuxent range 91501 a clast poor impact melt from the l chondrite parent body and lewis cliff 88663 an l7 chondrite we have performed petrologic and geochemical studies of patuxent range pat 91501 and lewis cliff lew 88663 pat 91501 originally classified as an l7 chondrite is rather a unique near total impact melt from the l chondrite parent body lewis cliff 88663 was originally classified as an achondrite but we find that it is a very weakly shocked l7 chondrite pat 91501 is an unshocked homogeneous igneous textured ultramafic rock composed of euhedral to subhedral olivine low ca pyroxene augite and chrome rich spinels with interstitial albitic plagioclase and minor silica alumina alkali rich glass only 10 relic chondritic material is present olivine grains are homogeneous fa25 2 26 8 low ca pyroxene wo1 9 7 2en71 9 78 2fs19 9 20 9 and augite wo29 8 39 0en49 2 55 3fs11 8 14 9 display a strong linear tio2 al2o3 correlation resulting from igneous fractionation plagioclase is variable in composition or3 0 7 7ab79 8 84 1an8 2 17 2 chrome rich spinels are variable in composition and zoned from cr rich cores to ti al rich rims some have evolved compositions with up to 7 9 wt tio2 pat 91501 bulk silicate has an l chondrite lithophile element composition except for depletions in zn and br siderophile and chalcophile elements are highly depleted due to sequestration in centimeter size metal troilite nodules the minerals in lew 88663 are more uniform in composition than those in pat 91501 olivine grains have low cao and cr2o3 contents similar to those in l5 6 chondrites pyroxenes have high tio2 contents with only a diffuse tio2 al2o3 correlation low ca pyroxenes are less calcic wo1 6 3 1en76 5 77 0fs20 4 21 4 while augites wo39 5 45 6en46 8 51 1fs7 6 9 4 and plagioclases or2 6 5 7ab74 1 83 1an11 2 23 3 are more calcic spinels are homogeneous and compositionally similar to those in l6 chondrites lew 88663 has an l chondrite bulk composition for lithophile elements and only slight depletions in siderophile and chalcophile elements that are plausibly due to weathering and or sample heterogeneity