impact cratering in sandstone the memin pilot study on the effect of pore water abstract planetary surfaces are subjected to meteorite bombardment and crater formation rocks forming these surfaces are often porous and contain fluids to understand the role of both parameters on impact cratering we conducted laboratory experiments with dry and wet sandstone blocks impacted by centimeter sized steel spheres we utilized a 40 m two stage light gas gun to achieve impact velocities of up to 5 4 km s 1 cratering efficiency ejection velocities and spall volume are enhanced if the pore space of the sandstone is filled with water in addition the crater morphologies differ substantially from wet to dry targets i e craters in wet targets are larger but shallower we report on the effects of pore water on the excavation flow field and the degree of target damage we suggest that vaporization of water upon pressure release significantly contributes to the impact process

seasonal contrasts in snow cover characteristics on ross sea ice floes snow cover characteristics on ice floes in the ross sea antarctica were examined during cruises in autumn 1998 and summer 1999 the autumn snow cover was shallower colder and had higher and more variable salinity and smaller single and composite grain sizes than the summer snow cover the autumn snow cover was dominated by rounded particles in chains of grains and clusters while the summer snow cover was composed primarily of melt clusters there was extensive flooding of the summer snow cover at the snow ice interface the summer snow cover was nearly isothermal and close to the melting point it exhibited obvious signs of melting and refreezing in the form of ice lenses pipes and superimposed ice although no melt ponds were evident many of the ice lenses were located directly above the saline standing water found on most of the summer ice floes

internal structure of the moon inferred from apollo seismic data and selenodetic data from grail and llr the internal structure of the moon is important for discussions on its origin and evolution however the deep structure of the moon is still debated due to the absence of comprehensive seismic data this study explores lunar interior models by complementing apollo seismic travel time data with selenodetic data which have recently been improved by gravity recovery and interior laboratory grail and lunar laser ranging llr the observed data can be explained by models including a deep seated zone with a low velocity s wave velocity 2 9 0 5 km s and a low viscosity 3 1016 pa s the thickness of this zone above the core mantle boundary is larger than 170 km showing a negative correlation with the radius of the fluid outer core the inferred density of the lowermost mantle suggests a high tio2 content 11 wt which prefers a mantle overturn scenario

a strain based porosity model for use in hydrocode simulations of impacts and implications for transient crater growth in porous targets numerical modelling of impact cratering has reached a high degree of sophistication however the treatment of porous materials still poses a large problem in hydrocode calculations we present a novel approach for dealing with porous compaction in numerical modelling of impact crater formation in contrast to previous attempts e g p alpha model snowplow model our model accounts for the collapse of pore space by assuming that the compaction function depends upon volumetric strain rather than pressure our new e alpha model requires only four input parameters and each has a physical meaning the model is simple and intuitive and shows good agreement with a wide variety of experimental data ranging from static compaction tests to highly dynamic impact experiments our major objective in developing the model is to investigate the effect of porosity and internal friction on transient crater formation we present preliminary numerical model results that suggest that both porosity and internal friction play an important role in limiting crater growth over a large range in gravity scaled source size

polynomial and power functions for glacial valley cross section morphology an empirical evaluation of glacial trough cross section shape is performed on seven vertical cross sections in three sierra nevada valleys glaciated during the late quaternary power and second order polynomial functions are fitted by statistical regression power functions are very sensitive to subtle valley bottom topographic features and require precise specification of the valley bottom centre location this dependency is problematic given under representation of valley bottoms by conventional contour sampling methods and the common alteration of valley bottom morphology by non glacial processes power function exponents vary greatly in response to these and other non genetic factors and are not found to be reliable indicators of overall valley morphology second order polynomials express overall valley shape in a single robust function they are applied to both bedrock and sediment floored glacial valleys with negligible statistical bias except where side slopes are stepped or convex upward or where valley form is asymmetrical they can describe alluviated or severely eroded valleys and can objectively identify indi vidual components of polymorphic valleys because valley bottom and centre locations need not be specified mathematical expressions of parameters useful for geomorphic measurements and glaciological modelling are analytically derived from the polynomials as functions of the three polynomial coefficients these parameter equations provide estimates of valley side slopes mean and maximum depth midpoint location width area boundary length form ratio and symmetry

numerical modelling of impact melt production in porous rocks abstract melting of rocks by impact is a fundamental geologic process that results from shock wave compression and subsequent release from high pressure shock melted material is found in many terrestrial craters however most impact craters in sedimentary targets which are typically porous have been reported as containing significantly less melt than craters in nonporous crystalline targets to investigate the effect of porosity on shock melting we present a numerical modelling approach that combines a porosity compaction model with an equation of state for the solid component to demonstrate that our model accurately calculates shock pressures in porous materials we compare these results with hugoniot data for porous quartzite coconino sandstone and calcite our results show that the presence of porosity significantly reduces the critical pressure required for melting which enhances melt production we show that this effect is reduced but not totally diminished by faster shock wave decay in porous materials so that all other things being equal impact melt production is greater when target porosity is higher we conducted a series of simulations of impacts into targets of different material composition quartzite calcite dunite and porosity of up to 50 and varied the impact velocity between 6 and 50 km s we found a significant increase in the production of impact melt with increasing velocity in agreement with several previous studies and quantify the net increase in impact melt due to target porosity for the nonporous case our results agree well with estimated melt volumes at terrestrial impact craters over a range in size 7 90 km in diameter in porous targets our results contradict the widely cited observation of a melt deficiency in sedimentary target craters however our model results agree well with recently revised estimates of melt volumes at terrestrial craters formed in sedimentary or mixed sedimentary and crystalline targets this further strengthens the view that substantial volumes of impact melt should be produced during impacts into porous sedimentary targets and that the apparent paucity of impact melt in some sedimentary target craters may be due to difficulties in recognizing impact melts derived from sedimentary rocks

structural tectonic and glaciological controls on the evolution of fjord landscapes abstract the fjord landscape of south america stretching 1500 km between golfo corcovado 43 s and tierra del fuego 56 s is the largest continuous fjord landscape on earth this paper presents the results of new structural geological and geomorphological mapping of this landscape using optical satellite images and digital elevation models first order geological structures are represented by strike slip faults forming lineaments up to hundreds of kilometres long the strike slip faulting has been active since late cretaceous times and is responsible for the presence of a conspicuous structural cleavage visible as lineaments up to 10 km long a detailed analysis of these second order lineaments from digital image data was carried out in three sectors in sector 1 located northwest of the north patagonian icefield there are three distinct mean orientations characterized by a main nearly orogen parallel orientation az 145 and two orogen oblique secondary orientations az 20 and az 65 in sector 2 located west of the south patagonian icefield there are also three separate mean orientations with most of the lineaments concentrated between azimuths 0 and 80 mean at 36 and two other orogen oblique means at azimuth 122 and 163 in sector 3 around the cordillera darwin there is a single main orogen parallel mean at 100 115 in all three sectors mapped fjord orientations bear a striking similarity to the structural data with fjords orientated preferentially in the same direction as structural lineaments we infer that successive glaciations followed the same ice discharge routes widening and deepening pre existing geological structures at the expense of the surrounding terrain to create the fjord landscape this study has broader implications for ice sheet reconstructions and landscape evolution beneath ice sheets because we demonstrate that the primary control on fjord development in glaciated areas is geological and not glaciological

using parabolas to describe the cross sections of glaciated valleys it is widely accepted that the simple power curve y axb can be used to describe the cross section of glaciated valleys there are however good reasons to suppose that this particular form of equation is inappropriate for this purpose

tomography based characterization of ice air interface dynamics of temperature gradient snow metamorphism under advective conditions snow at or close to the surface commonly undergoes temperature gradient metamorphism under advective flow which alters its microstructure and physical properties a functional understanding of this process is essential for many disciplines from modeling the effects of snow on regional and global climate to assessing avalanche formation time lapse x ray microtomography was applied to investigate the structural dynamics of temperature gradient snow metamorphism exposed to an advective airflow in controlled laboratory conditions experiments specifically analyzed sublimation and deposition of water vapor on the ice structure in addition an analysis of the ice air interface dynamics was carried out using a macroscopic equivalent model of heat and water vapor transport through a snow layer the results indicate that sublimation of the ice matrix dominated for flow rates 10 6 m3 s 1 while during increased mass flow rates the water vapor deposition supplied by the advective flow counteracted sublimation a flow rate dependence of water vapor deposition at the ice interface was observed asymptotically approaching an average estimated maximum deposition rate on the whole sample of 1 05 10 4 kg m 3 s 1 the growth of microsized whisker like crystals on larger ice crystals was detected on microscope photographs leading to an increase of the specific surface area and thus suggest a change of the physical and optical properties of the snow the estimated values of the curvature effect of the ice crystals and the interface kinetic coefficient are in good agreement with previously published values

ice sheet erosion patterns in valley systems in northern sweden investigated using cosmogenic nuclides erosion patterns associated with glaciation of trunk and hanging valley systems in northern sweden were investigated using cosmogenic nuclide 10be apparent exposure ages and inferred nuclide inheritance sequences of samples taken across valleys known to have been covered repeatedly by the fennoscandian ice sheet revealed two primary patterns of erosion in vavlavagge the exposure age pattern is consistent with 2 m of glacial erosion during the last glacial cycle along the entire profile at ravtasvaggi dievssavaggi and alisvaggi exposure ages in the valley bottom contrast with apparent exposure ages two to four times older on the valley sides the older ages on the valley sides reflect cosmogenic nuclide inheritance due to limited 2 m bedrock erosion of the valley sides during the last glacial cycle the pattern and scale of erosion in these valleys indicates that glacial valley formation is a result of multiple glacial cycles rather than the result of topographic modification during a single glacial cycle initial data comparing hanging valley and trunk valley sites do not show distinct differences in apparent exposure ages slightly older ages for samples from hanging valley bottoms may suggest nuclide inheritance indicating lower erosion than in trunk valley bottoms as would be expected given the marked topographic step between hanging and trunk valleys although quantifying the amount of erosion depends on the assumed cosmogenic nuclide inheritance prior to the onset of erosion the pattern of erosion is independent of this hence the observed pattern of cosmogenic nuclide concentrations provides constraints on spatial patterns of erosion and helps to refine understanding of the timing and extent of landform modification by glaciation copyright 2005 john wiley sons ltd

hydrocode modeling of the sierra madera impact structure we present the first hydrocode simulations of the formation of the sierra madera structure west texas usa which was caused by an impact into a thick sedimentary target sequence we modeled sierra madera using the isale hydrocode and here we present two best fit models 1 a crater with a rim final crater diameter of 12 km in agreement with previous authors interpretations of the original structure and 2 a crater 16 km in diameter with increased postimpact erosion both models fit some of the geologic observational data but discrepancies with estimates of peak shock pressure extent of deformation and stratigraphic displacement remain this study suggests that sierra madera may be a larger crater than previously reported and illustrates some of the challenges in simulating impact deformation of sedimentary lithologies as many terrestrial craters possess some amount of sedimentary rocks in the target sequence numerical models of impacts into sedimentary targets are essential to our understanding of target rock deformation and the mechanics of crater formation

formation and strengthening of layers of dry faceted crystals above artificial melt freeze crusts from overburden stress in a controlled environment layers of faceted crystals were grown from naturally fallen snow above wet snow layers in a temperature controlled laboratory static loads were then applied to the weak layers to represent overburden snow eleven experiments with constant loads were analyzed equivalent to 260 to 1500 pa of overburden stress the density of the slab above the weak layer increased with time following a power law relationship with an average exponent of 0 10 shear strength of the weak layer increased with time for all experiments also following a power law relationship early time rates of strength gain averaged 250 pa day 1 for the constant load experiments over the first 3 5 days decreasing to an average of 1 pa day 1 after approximately 30 days exponents for the power law relationships ranged between 0 09 and 0 35 with an average of 0 26 0 08 sintering was likely the dominant process for strength gain although densification probably contributed as well three experiments were conducted in which the overburden

positive feedbacks associated with erosion of glacial cirques and overdeepenings the principal points of water input to a glacier are the bergschrund in cirques and crevasse fields lower on the glacier crevasse fields commonly occur over convexities at the heads of overdeepenings in glacier beds the amplitude of subglacial water pressure fluctuations is large just down glacier from these points of water input erosion by quarrying is likely in such areas erosion is thus inferred to be localized on the headwalls of cirques and overdeepenings in the case of overdeepenings this leads to a positive feedback process in which a perturbation in the bed causes crevassing at the surface resulting in erosional forces that accentuate the perturbation when subglacial water flows up an adverse bed slope leading out of a cirque or overdeepening much of the viscous energy dissipated is used to warm the water to keep it at the pressure melting temperature as the ice thins and the pressure decreases in such situations subglacial conduits are maintained by high water pressures rather than by melting of conduit walls in the limit water pressures apparently become so high that water is forced out along the ice bed interface and the conduits collapse the products of erosion are then no longer flushed out and a protective till layer accumulates by limiting erosion on such adverse bed slopes this till layer controls the geometry of these overdeepened basins

faceted crystal formation in the northeast greenland low accumulation region snow pit analysis in the low accumulation region in northeast greenland indicated a mean annual accumulation of 12 1 6 cm it also revealed numerous faceted layers that were not related to the summer horizon of previous years in general the faceted crystals were found under a wind crust these crusts appear to originate during the winter snow and air temperature data from automatic weather stations suggest that the katabatic storms are responsible for the formation of the wind crusts and the faceted layers frequent abrupt temperature changes up to 30 c were observed within two days due to turbulent mixing of cold air inversions the near surface air temperature variations are correlated with wind speed the latter leading the former by 6 9 hours for increasing wind and 1 4 hours for decreasing wind because of low accumulation katabatic storms affect the same snow surface for several months causing repeated air temperature fluctuations this leads to strong vapor pressure gradients and faceted crystal growth in the top snow layer on average we found two faceted layers in addition to the summer layer per year for a 4 year record in addition to its climatological significance in the snow record the formation of these layers is especially important to understand for the interpretation of microwave satellite observations of the firn

temporal constraints on glacial valley cross profile evolution two thumb range central southern alps new zealand abstract a key problem in understanding valley evolution in alpine landscapes has been the lack of an independent timescale against which to measure morphological change here we outline that by using space as a proxy for time the role of glaciation in producing classic u shaped valleys can be quantified the two thumb range in new zealand s central southern alps is undergoing rapid tectonic transport and uplift as it is advected towards the alpine fault repeated cycles of glacial erosion during the quaternary have fashioned an alpine landscape in the north of the range close to the main divide and alpine fault while valleys in the less glaciated south of the range have rounded divides and convex fluvial cross profiles using known rates of tectonic transport and uplift of the southern alps coupled with an offshore oxygen isotope 18o record from the chatham rise and glacio geological reconstructions time constraints can be applied to the erosional development of valleys it is possible to estimate the duration of glacial occupancy of valleys in the two thumb range and the pattern is one of very limited glaciation of the southern valleys with glacial occupancy increasing northwards the key trend identifiable is that valley cross profiles become u shaped with c 400 600 kyr of glacial occupancy other models have shown a flattening of valley long profiles with increased glaciation implying glaciers erode larger volumes of rock from mountains than rivers from a cross profile perspective the simple change in geometry from v to u shape concurs with these models indeed the transition from v to u shape with increasing relief and glaciation indicates glaciers may erode greater volumes of rock from mountain belts than rivers

impact excitation of a seismic pulse and vibrational normal modes on asteroid bennu and associated slumping of regolith we consider an impact on an asteroid that is energetic enough to cause resurfacing by seismic reverberation and just below the catastrophic disruption threshold assuming that seismic waves are not rapidly attenuated in asteroids with diameter less than 1 km we identify a regime where rare energetic impactors can excite seismic waves with frequencies near those of the asteroid s slowest normal modes in this regime the distribution of seismic reverberation is not evenly distributed across the body surface with mass spring model elastic simulations we model impact excitation of seismic waves with a force pulse exerted on the surface and using three different asteroid shape models the simulations exhibit antipodal focusing and normal mode excitation if the impulse excited vibrational energy is long lasting vibrations are highest at impact point its antipode and at high surface elevations such as an equatorial ridge a near equatorial impact launches a seismic impulse on a non spherical body that can be focused on two additional points on an the equatorial ridge we explore simple flow models for the morphology of vibration induced surface slumping we find that the initial seismic pulse is unlikely to cause large shape changes long lasting seismic reverberation on bennu caused by a near equatorial impact could have raised the height of its equatorial ridge by a few meters and raised two peaks on it one near impact site and the other near its antipode

controls on spatial variations of glacial erosion in the qilian shan northeastern tibetan plateau abstract understanding interactions between topography and glacial erosion is a key to advancing knowledge of mountain landscape evolution and is often hampered by the lack of quantitative data for glacial erosion here we examine spatial variations in glacial erosion in the qilian shan using a power law model y axb fit to cross profiles of glacial valleys we further analyze the impacts of glacial dynamics topography and lithology on the degree of glacial erosion using qualitative and quantitative methods although the distribution of glacial erosion is controlled by the combined effects of glacial dynamics topography and lithology average glacier size or ice flux and mean slope above the equilibrium line altitude are dominant controls in addition the topographic data analyzed through a b fr diagram suggests two opposite types of glacial valley cross profile development temperate maritime glacier valleys are mainly dominated by overdeepening while continental glacier valleys are mainly dominated by a widening process although this varies with lithology

boulder stranding in ejecta launched by an impact generated seismic pulse abstract we consider how an impact generated seismic pulse affects the surface of an asteroid distant from the impact site with laboratory experiments on dry polydisperse gravel mixtures we track the trajectories of particles ejected from the surface by a single strong upward propagating pressure pulse high speed video images show that ejecta trajectories are independent of particle size and collisions primarily take place upon landing when they land particles are ballistically sorted as proposed by shinbrot et al 2017 leaving larger particles on the surface and smaller particles more widely dispersed a single strong pulse can leave previously buried boulders stranded on the surface boulder stranding due to an impact excited seismic pulse is an additional mechanism that could leave large boulders present on the surface of rubble asteroids such as 162173 ryugu 101955 bennu and 25143 itokawa

evolution of the specific surface area of snow during high temperature gradient metamorphism the structural evolution of low density snow under a high temperature gradient over a short period usually takes place in the surface layers on clear cold nights in this paper x ray computed microtomography microct was combined with numerical simulations to investigate the temperature gradient metamorphism tgm on different types of snow precipitation particles pp small rounded particles rgsr and large rounded particles rglr were each observed in high temperature gradients 100 500 k m 1 at a mean temperature of 4 c the specific surface area ssa was used to characterize the tgm which were influenced by both the magnitude of the temperature gradient and the initial snow structures pp samples experienced a logarithmic decrease of ssa with time and the depth hoar structures created under high tgm 500 k m 1 have higher ssa compared to those under lower tgm unlike previous observations for initial rounded and connected structures like rglr samples the ssa increased during tgm simulated normal vapor flux distributions for different snow types were used to help understand the structural evolution under tgm understanding the ssa increase is important in order to predict the enhanced uptake of chemical species by snow or increase in snow albedo

seismic wave attenuation in the uppermost glacier ice of storglaciaren sweden we conducted seismic refraction surveys in the upper ablation area of storglaciaren a small valley glacier located in swedish lapland we estimated seismic wave attenuation using the spectral ratio method on the energy travelling in the uppermost ice with an average temperature of approximately 1 c attenuation values were derived between 100 and 300 hz using the p wave quality factor q p the inverse of the internal friction by assuming constant attenuation along the seismic line we obtained mean q p 6 1 we also observed that q p varies from 8 1 to 5 1 from the near offset to the far offset region of the line respectively since the wave propagates deeper at far offsets this variation is interpreted by considering the temperature profile of the study area far offset arrivals sampled warmer and thus more attenuative ice our estimates are considerably lower than those reported for field studies in polar ice 500 1700 at 28 c and 50 160 at 10 c and hence are supportive of laboratory experiments that show attenuation increases with rising ice temperature our results provide new in situ estimates of q p for glacier ice and demonstrate a valuable method for future investigations in both alpine and polar ice

a discussion of hirano and aniya s 1988 1989 explanation of glacial valley cross profile development in a rational explanation of cross profile morphology for glacial valleys and of glacial valley development hirano and aniya 1988 present an explanation for the apparent catenary form of glaciated valley cross profiles based on the assumption that glacial erosion works towards minimizing friction between a glacier and its channel however as there is as yet no convincing justification for the application of such extremum principles to this problem it is not clear how useful this type of analysis might be in more detail hirano and aniya s analysis includes assumptions about patterns of basal water pressures and the controls on friction inconsistent with other work in this area furthermore as hirano and aniya 1989 point out the catenary solution they derive is the maximum rather than the minimum friction solution the underlying reason for this surprising result is that the variational principle hirano and aniya use is inappropriately structured for the problem being addressed as it does not involve a cross section area i e ice discharge constraint hirano and aniya also discuss the progressive development of glacial valley cross profiles but their analysis is hindered by the fact that most of the data they present are purely morphological and thus cannot be used to assess form development as a function of either time or extent of glacial erosion the only possible exceptions are graf s 1970 data which give morphological parameters as a function of valley order but these do not unequivocally support hirano and aniya s conclusions and are used with implicit assumptions about the relationship between valley order and time of glacial occupation or magnitude of glacial erosion that are incorrect or uncorroborated respectively however if we accept the common assumption that glacial erosion results in a progression from initial v shaped to broadly u shaped parabolic or catenary forms hirano and aniya s argument that there are two distinct types of form development incision in alpine situations versus valley widening under ice sheets is justified and is an important observation that needs to be addressed in future models of glacial valley development

longitudinal variations in cross section morphology along a glacial valley a case study from the tien shan china a new model the variable width depth ratio vwdr model is used to analyze longitudinal variations in cross section morphology along glacial valleys in the vwdr the cross sectional shape of a valley is expressed as a function of the width depth ratio at various heights above the valley floor two parameters m a measure of the breadth of the valley floor and n a measure of the steepness of the valley sides appear in the model we have used the vwdr model to study morphological variations of cross sections along glacial valleys in the middletien shan mountains china and find that 1 in valleys without tributaries m increases the valley floor becomes wider and n becomes more negative valley sides become steeper from the head of the valley to the equilibrium line and then m decreases and n becomes less negative to the end of the valley 2 in valleys with tributaries a similar pattern is observed with an oscillating maximum in m and minimum in n in those sections where a tributary enters the main valley these characteristics are believed to reflect a maximization of glacial erosion potential in the vicinity of the equilibrium line and in locations of confluence

the memin research unit scaling impact cratering experiments in porous sandstones the memin research unit multidisciplinary experimental and modeling impact research network is focused on analyzing experimental impact craters and experimental cratering processes in geological materials memin is interested in understanding how porosity and pore space saturation influence the cratering process here we present results of a series of impact experiments into porous wet and dry sandstone targets steel iron meteorite and aluminum projectiles ranging in size from 2 5 to 12 mm were accelerated to velocities of 2 5 7 8 km s 1 yielding craters with diameters between 3 9 and 40 cm results show that the target s porosity reduces crater volumes and cratering efficiency relative to nonporous rocks saturation of pore space with water to 50 and 90 increasingly counteracts the effects of porosity leading to larger but flatter craters spallation becomes more dominant in larger scale experiments and leads to an increase in cratering efficiency with increasing projectile size for constant impact velocities the volume of spalled material is estimated using parabolic fits to the crater morphology yielding approximations of the transient crater volume for impacts at the same velocity these transient craters show a constant cratering efficiency that is not affected by projectile size

the relative efficiency and influence of glacial and fluvial erosion on tibetan plateau landscapes abstract driven by climate change periods of dominating glacial and fluvial erosion have both sculpted mountain ranges during the quaternary to understand the evolution of mountain landforms there is considerable interest in knowing which erosion agent leads to more incision how glacial thermal regime impacts erosion and landscape development and whether glacial erosion can result in increased relief to investigate the relative efficiency of glacial and fluvial erosion and the influence of glacial thermal regime on topography we compare two different mountain ranges the qionglai shan monsoonal temperate glaciation and lenglongling subcontinental glaciation in western china we use a 1 d model to construct presumptive fluvial longitudinal profiles if glaciation had not occurred and compare these with the actual glacial profiles to obtain relative incision rates of fluvial and glacial erosion results demonstrate that glacial incision is smaller than fluvial incision in lenglongling and larger than fluvial incision in the qionglai shan which may be influenced by different tectonics and glacier types topographic analysis of glacial and fluvial valleys with similar drainage areas show that glacial erosion results in valley widening local valley relief increase induced by isostatic uplift and slope gradient increase in lenglongling however there is no local valley relief and slope increase observed in the qionglai shan which may reflect slope process responses to threshold hillslope limiting the height above valley bottoms

snow crystal growth with varying surface temperatures and radiation penetration the temperature field is derived for a sinusoidally varying surface temperature with varying solar radiation penetration the growth rates of snow crystals are calculated to explain the rapidly growing layers of faceted crystals i e depth hoar that form just below the surface at high altitudes and in polar snow the solutions also show that a layer of wet snow can exist just below the surface even on days when the surface temperature remains sub freezing

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

development of glacial valley cross sections under conditions of spatially variable resistance to erosion abstract a simulation model that examines the development of valley cross profiles as a result of glacial erosion has been constructed by placing a finite element model for ice flow within an iterative program that modifies channel cross section form on the basis of an erosion equation the simulation model has previously been used to examine how different flow laws erosion laws and ice discharge histories affect medium scale landform development this allows us to better understand the development of glacial landforms and also provides a critical test for erosion and flow laws within the erosion component of the simulation program it is possible to specify spatial variations in bedrock erodibility in order to examine the effect of spatially variable lithologies on form development as an initial test of form development under these conditions a central area of enhanced erodibility is placed in the valley center in this case active glacial channels develop that are narrower and deeper than those which occur with homogenous bedrock this change in form occurs as long as the weaker zone is small enough that the active channel does not eventually narrow to a stage such that it is entirely contained within the weaker material and as long as it is large enough that it continues to have a significant impact on overall discharge through the section form variation occurs because the weaker central zone enhances the lateral gradient of the erosion rate which is critical for form development a central area of more erodible bedrock changes not only the form of the active glacial channel but also the convexity of side slopes that are left above the glacier as it erodes downwards into the landscape the absence of a classic u shaped cross section should not be taken a priori to suggest either absence of glacial erosion or ineffective glacial erosion rather the combination of active glacial and hillslope processes in a landscape with spatially and temporally variable ice discharge and rock characteristics can create a diverse set of cross section forms

a microstructural dry snow metamorphism model for kinetic crystal growth historically dry snow metamorphism has been classified by the thermal environment and thermodynamic processes in a snowpack snow experiencing predominantly macroscopic isothermal conditions develops different microstructure than snow subjected to large temperature gradients as such much previous research has been categorized by and limited to specific thermal conditions the current research expands a generalized approach for the movement of heat and mass to include a snow crystal kinetic growth model an existing spiral defect propagation theory for kinetic growth on simple faceted geometry is utilized primary crystal habit as a function of temperature is incorporated a model of heat and mass transfer through an ice and pore structure is coupled with phase change thermodynamics during kinetic growth a kinetic growth microstructure model is developed and integrated into heat and mass transfer representations which are solved using finite difference techniques the kinetic morphology model approximates frequently observed hopper type crystals the snow microstructure is allowed to change at every step resulting in a transient description of kinetic growth metamorphism variable kinetic growth rates are demonstrated based on temperature and on crystallographic orientation relative to a temperature gradient crystals preferentially aligned with the temperature gradient have significantly higher growth rates supporting previous observations of predominant crystal habits developing under temperature gradient conditions grain size dispersion increase with time is demonstrated and supported experimentally in the literature a dominant grain growth theory based on crystallographic orientation that has been previously postulated is supported a broad range of metamorphic geometric parameters and thermal conditions may now be simulated with a single model

field investigation of near surface metamorphism of snow buried surface hoar and near surface faceted crystals are known to lead to deadly avalanches over the course of three winter seasons a field investigation detailing the environmental conditions leading to the formation of these crystals was performed weather stations on north and south facing aspects were established the weather data were accompanied by detailed daily observations and grain scale photographs of the snow surface during the three seasons 35 surface hoar and 47 near surface facets events were recorded the mean weather conditions for the entire dataset all three seasons and both stations were compared to the nights when surface hoar formed the comparison yielded five parameters that were statistically linked to the formation of surface hoar incoming longwave radiation snow surface temperature wind velocity relative humidity and the air snow temperature difference a similar comparison between the daytime mean values for all days with near surface facet events revealed three parameters with statistically significant differences thus these parameters short and longwave radiation and relative humidity could be statistically linked to facet formation this research also suggests that environmental conditions in the daytime hours before and after surface hoar formation are statistically similar to the conditions causing near surface facet formation

winter snow cover on the sea ice of the arctic ocean at the surface heat budget of the arctic ocean sheba temporal evolution and spatial variability 1 the evolution and spatial distribution of the snow cover on the sea ice of the arctic ocean was observed during the surface heat budget of the arctic ocean sheba project the snow cover built up in october and november reached near maximum depth by mid december then remained relatively unchanged until snowmelt ten layers were deposited the result of a similar number of weather events two basic types of snow were present depth hoar and wind slab the depth hoar 37 of the pack was produced by the extreme temperature gradients imposed on the snow the wind slabs 42 of the snowpack were the result of two storms in which there was simultaneous snow and high winds 10 m s 1 the slabs impacted virtually all bulk snow properties emphasizing the importance of episodic events in snowpack development the mean snow depth n 21 169 was 33 7 cm with a bulk density of 0 34 g cm 3 n 357 r2 of 0 987 giving an average snow water equivalent of 11 6 cm 25 higher than the amount record by precipitation gauge both depth and stratigraphy varied significantly with ice type the greatest depth and the greatest variability in depth occurring on deformed ice ridges and rubble fields across all ice types a persistent structural length in depth variations of 20 m was found this appears to be the result of drift features at the snow surface interacting with small scale ice surface structures a number of simple ways of representing the complex temporal and spatial variations of the snow cover in ice ocean atmosphere models are suggested

quantitative analysis of impact induced seismic signals by numerical modeling we quantify the seismicity of impact events using a combined numerical and experimental approach the objectives of this work are 1 the calibration of the numerical model by utilizing real time measurements of the elastic wave velocity and pressure amplitudes in laboratory impact experiments 2 the determination of seismic parameters such as quality factor q and seismic efficiency k for materials of different porosity and water saturation by a systematic parameter study employing the calibrated numerical model by means of numerical experiments we found that the seismic efficiency k decreases slightly with porosity from k 3 4 10 3 for nonporous quartzite to k 2 6 10 3 for 25 porous sandstone if pores are completely or partly filled with water we determined a seismic efficiency of k 8 2 10 5 which is approximately two orders of magnitude lower than in the nonporous case by measuring the attenuation of the seismic wave with distance in our numerical experiments we determined the seismic quality factor q to range between 35 for the solid quartzite and 80 for the porous dry targets for water saturated target materials q is much lower 10 the obtained values are in the range of literature values translating the seismic efficiency into seismic magnitudes we show that the seismic magnitude of an impact event is about one order of magnitude smaller considering a water saturated target in comparison to a solid or porous target obtained seismic magnitudes decrease linearly with distance to the point of impact and are consistent with empirical data for distances closer to the point of impact the seismic magnitude decreases more rapidly with distance for a water saturated material compared to a dry material

a rational explanation of cross profile morphology for glacial valleys and of glacial valley development the fact that the cross profile of the glacial valley could be well approximated by parabolas y axb b 2 0 is explained by the variation principle assuming that the glacier erosion works towards minimizing thefriction between ice and bedrock the variation principle proves that the ideal or fully developed morphology of the glacial valley should be a catenary the curve which a chain hanging from two fixed points forms maclaurin s series expansion of the catenary equation shows that a parabola is a very good approximation of the catenary hence the good approximation of the cross profile by parabolas different catenaries are generated by changing the form ratio depth rim width and are then approximated by y axb by the method of last squares the b values obtained become only fractionally larger than 2 0 with invreasing form ratios of up to 1 0 indicating that b values would range in practice between 1 0 and about 2 0 two types of trend in the relationship between b values and the form ratio were obtained from several glaciers for one type the b value becomes larger with increasing form ratios and for the other the opposite the first type is called the rocky mountain model after its source of data and represents overdeepening of the glacial valley development the second type is caalled the patagonia antarctica model representing a widening instead of a deepening process of development these differences are attributed to the nature of the glaciers which produced these valleys i e alpine glaciers and continental ice sheets

ice cap erosion patterns from bedrock 10be and 26al southeastern tibetan plateau quantifying glacial erosion contributes to our understanding of landscape evolution and topographic relief production in high altitude and high latitude areas combining in situ be 10 and al 26 ana

lagrangian based simulations of hypervelocity impact experiments on mars regolith proxy most of the surface of mars is covered with unconsolidated rocky material known as regolith high fidelity models of the dynamics of impacts in such material are needed to help with the interpretation of seismic signals that are now recorded by seis the seismometer of insight we developed a numerical model for impacts on regolith using the novel hybrid optimization software suite hoss which is a lagrangian code mixing finite and discrete element formulations we use data from hypervelocity impact experiments performed on pumice sand at the nasa ames vertical gun range to identify and calibrate key model parameters the model provides insight into the plastic elastic transition observed in the data and it also demonstrates that gravity plays a key role in the material response waveforms for receivers situated vertically below the impact point are correctly modeled while more research is needed to explain the shallow receivers signals

snow avalanche formation 1 snow avalanches are a major natural hazard endangering human life and infrastructure in mountainous areas throughout the world in many countries with seasonally snow covered mountains avalanche forecasting services reliably warn the public by issuing occurrence probabilities for a certain region however at present a single avalanche event cannot be predicted in time and space much about the release process remains unknown mainly because of the highly variable layered character of the snowpack a highly porous material that exists close to its melting point the complex interaction between terrain snowpack and meteorological conditions leading to avalanche release is commonly described as avalanche formation it is relevant to hazard mapping and essential to short term forecasting which involves weighting many contributory factors alternatively the release process can be studied and modeled this approach relies heavily on snow mechanics and snow properties including texture while the effect of meteorological conditions or changes on the deformational behavior of snow is known in qualitative or semiquantitative manner the knowledge of the quantitative relation between snow texture and mechanical properties is limited but promising developments are under way fracture mechanical models have been applied to explain the fracture propagation and micromechanical models including the two competing processes damage and sintering have been applied to explain snow failure there are knowledge gaps between the sequence of processes that lead to the release of the snow slab snow deformation and failure damage accumulation fracture initiation and fracture propagation simultaneously the spatial variability that affects damage fracture initiation and fracture propagation has to be considered this review focuses on dry snow slab avalanches and shows that dealing with a highly porous media close to its melting point and processes covering several orders of scale from the size of a bond between snow grains to the size of a mountain slope will continue to be very challenging

seismoacoustic coupling induced by the breakup of the 15 february 2013 chelyabinsk meteor on 15 february 2013 around 03 20 00 utc the largest meteor reported since the 1908 tunguska event was observed as a fireball traveling through the earth s atmosphere exploding in an air burst near the city of chelyabinsk russia the rarity of such an event provides a unique window on the physics of meteoroid collision we report the fine seismic detection of rayleigh waves produced by the coupling of ground motion with the incident shock wave at distances up to 4000 km from the event combining information from seismic beam forming analysis recon structed trajectory from casual video records and remote sensing we identify the rayleigh waves as being initiated by the shock wave produced by the main blast that occasioned damages and injuries in chelyabinsk from the rayleigh wave observations we report a magnitude ms 3 7 seismic source

the global effects of impact induced seismic activity on fractured asteroid surface morphology abstract impact induced seismic vibrations have long been suspected of being an important surface modification process on small satellites and asteroids in this study we use a series of linked seismic and geomorphic models to investigate the process in detail we begin by developing a basic theory for the propagation of seismic energy in a highly fractured asteroid and we use this theory to model the global vibrations experienced on the surface of an asteroid following an impact these synthetic seismograms are then applied to a model of regolith resting on a slope and the resulting downslope motion is computed for a full range of impactor sizes next this computed downslope regolith flow is used in a morphological model of impact crater degradation and erasure showing how topographic erosion accumulates as a function of time and the number of impacts finally these results are applied in a stochastic cratering model for the surface of an eros like body same volume and surface area as the asteroid with craters formed by impacts and then erased by the effects of superposing craters ejecta coverage and seismic shakedown this simulation shows good agreement with the observed 433 eros cratering record at a main belt exposure age of 400 200 myr including the observed paucity of small craters the lowered equilibrium numbers loss rate production rate for craters less than 100 m in diameter is a direct result of seismic erasure which requires less than a meter of mobilized regolith to reproduce the near observations this study also points to an upper limit on asteroid size for experiencing global surface modifying seismic effects from individual impacts of about 70 100 km depending upon asteroid seismic properties larger asteroids will experience only localized regional seismic effects from individual impacts

apollo lunar seismic experiment final summary processing and initial analysis of the entire set of apollo lunar seismic data collected continuously from 1969 through 1977 have now been completed recent results include 1 better defined deep moonquake locations which appear to be bounded rather sharply between about 800 km and 1000 km depths with concentrations near both boundaries and 2 middle mantle 500 to 1000 km depth seismic velocities of vp 8 3 0 4 km sec and vs 4 6 0 2 km sec which are significantly higher than previous estimates and represent an increase of velocities from the upper mantle as opposed to a decrease in previous estimates

the influence of rock mass strength on glacial valley cross profile morphometry a case study from the southern alps new zealand the erosional morphology in the vicinity of the main divide of the southern alps and fiordland new zealand appears to be a product of the interaction between alpine fault induced tectonic processes rock mass strength of the uplifted and eroded bedrock and the processes acting to denude the developing mountain landscape the magnitude of the effects of glacial erosion on the landscape is directly controlled by the size and physical properties of the glaciers whilst the form of the trough is a direct consequence of the rock mass strength rms properties of the slope rock realistic models of development of the cross profile shape of glacial valleys must take into consideration the rms properties of the eroded substrate

a reply to a discussion of hirano and aniya s 1988 1989 explanation of glacial valley cross profile development by jonathan m harbor the extremum principle is again justified as a valid and relevant approach to cross sectional form of the glacial valley it is accepted that the extremum previously obtained was a maximum and not a minimum for friction but this still appears to be a valid application of the principle harbor s more detailed discussion is recognized as valid assuming the presence of appreciable water pressures and that hallet s theory is to be preferred over boulton s but these assumptions do not always seem appropriate while the importance of time for valley evolution is fully accepted the extremum approach is still thought to be useful for example in maximizing cross section for a given resistance

earth impact effects program a web based computer program for calculating the regional environmental consequences of a meteoroid impact on earth we have developed a web based program for quickly estimating the regional environmental consequences of a comet or asteroid impact on earth www lpl arizona edu impacteffects this paper details the observations assumptions and equations upon which the program is based it describes our approach to quantifying the principal impact processes that might affect the people buildings and landscape in the vicinity of an impact event and discusses the uncertainty in our predictions the program requires six inputs impactor diameter impactor density impact velocity before atmospheric entry impact angle the distance from the impact at which the environmental effects are to be calculated and the target type sedimentary rock crystalline rock or a water layer above rock the program includes novel algorithms for estimating the fate of the impactor during atmospheric traverse the thermal radiation emitted by the impact generated vapor plume fireball and the intensity of seismic shaking the program also approximates various dimensions of the impact crater and ejecta deposit as well as estimating the severity of the air blast in both crater forming and airburst impacts we illustrate the utility of our program by examining the predicted environmental consequences across the united states of hypothetical impact scenarios occurring in los angeles we find that the most wide reaching environmental consequence is seismic shaking both ejecta deposit thickness and air blast pressure decay much more rapidly with distance than with seismic ground motion close to the impact site the most devastating effect is from thermal radiation however the curvature of the earth implies that distant localities are shielded from direct thermal radiation because the fireball is below the horizon

experimental study on impact induced seismic wave propagation through granular materials abstract impact induced seismic waves are supposed to cause movements of regolith particles resulting in modifications of asteroidal surfaces the imparted seismic energy is thus a key parameter to determining the scale and magnitude of this seismic shaking process it is important to study the propagation velocity attenuation rate and vibration period of the impact induced seismic wave to estimate the seismic energy hence we conducted impact cratering experiments at kobe university using a 200 m glass beads target to simulate a regolith layer and measured the impact induced seismic wave using three accelerometers set on the target surface at differences ranging from 3 2 to 12 7 cm the target was impacted with three kinds of projectiles at 100 m s 1 using a one stage gas gun the propagation velocity of the seismic wave in the beads target was 108 9 m s 1 and the maximum acceleration gmax in the unit of m s 2 measured by each accelerometer showed good correlation with the distance from the impact point normalized by the crater radius x r irrespective of projectile type they also were fitted by one power law equation gmax 102 19 x r 2 21 the half period of the first peak of the measured seismic waves was 0 72 ms and this duration was almost consistent with the penetration time of each projectile into the target according to these measurements we estimated the impact seismic efficiency factor that is the ratio of seismic energy to kinetic energy of the projectile to be almost constant 5 7 10 4 inside the crater rim while it exponentially decreased with distance from the impact point outside the crater rim at a distance quadruple of the crater radius the efficiency factors were 4 4 10 5 for polycarbonate projectile and 9 5 10 5 for alumina and stainless steel projectiles

intense pp reflection beneath the aseismic forearc slope of the japan trench subduction zone and its implication of aseismic slip subduction 1 strong anticorrelation between intensity of plate boundary pp reflection and seismicity had been revealed by a seismic reflection refraction survey conducted in 1996 in a seismic aseismic boundary region on the forearc slope of the japan trench amplitude of the strong reflection was explained by the presence of a thin layer 200 m of low p wave velocity 3 4 km s at the top of the plate boundary we conducted another seismic survey in 2001 in the same region as that of 1996 and verified the strong anticorrelation with planer extension along the plate boundary therefore existence of the thin layer of low p wave velocity along the plate boundary is expected within the aseismic regions extremely low p wave velocities along the plate interface at depths of around 10 20 km suggest that the layer may include fluid clay minerals and or serpentine chlorite because these materials have low mechanical strength or cause low friction between the overriding and subducting plates large strain may not be accumulated and aseismic slip may be dominant as a result of the above speculation the intense reflection observed within the aseismic regions may imply aseismic slip between the plates amplitude of the plate boundary pp reflection phase was found maximum about reflections from deeper plate interface although the reflected waves propagate for longer distances one possible explanation to this phenomenon is the presence of serpentinized wedge mantle material that is buoyancy driven to move along the top of the slab

formation of refrozen snowpack layers and their role in slab avalanche release 1 in a variety of snow climates numerous slab avalanches release over crusts consisting of refrozen snow slab avalanches sometimes release in weak layers of faceted crystals that developed while underlying wet layers froze into crusts often within a day weak layers of faceted crystals can also develop when less permeable and more conductive crusts alter the temperature and vapor pressure gradients these processes create interfaces where differences in grain radii can contribute to weak bonding in western canada layers of faceted crystals facet layers on crusts are most common in early and late winter when thaws and rain are more frequent also thin facet layers occur in spring when surface melting by solar radiation is common shear strength tests on facet layers show an initial strength loss during faceting followed by a slow strength increase the spatial distribution of poorly bonded crusts can be interpreted from the interaction of terrain and meteorology that caused the antecedent wet layer

timing and extent of quaternary glaciations in the tianger range eastern tian shan china investigated using 10be surface exposure dating abstract reconstructing glacial chronologies with consistent methods is critical for efforts to examine the timing and pattern of past climate change cosmogenic 10be surface exposure dating has been widely used to constrain the timing of glacial events on the tibetan plateau and in central asia however few such studies have been conducted in the chinese tian shan and available 10be ages from this region have only provided evidence for glacial events during the global last glacial maximum glgm and lateglacial here we present 45 10be surface exposure ages from glacial landforms in the ala and daxi valleys two formerly glaciated valleys draining the tianger range eastern tian shan combined with previously published 10be surface exposure ages from the daxi valley in the source area of the urumqi river the new ages record five major glacial events during marine oxygen isotope stages mis 6 or older 4 3 2 and 1 during the little ice age lia landforms from glacial events since mis 2 are found on the northern slope of the tianger range daxi valley whereas evidence for the older glacial events is only preserved on its southern slope ala valley this disparity may be caused by different preservation and micro climatic conditions on the northern and southern slopes of this mountain range due to differences in gradient and aspect the lia glacial advances are apparently the only holocene glacial event recorded in this area earlier holocene glacial events were probably so restricted in extent that they were destroyed by subsequent lia advances

on the mathematical description of glaciated valley cross sections morphometric analyses of glaciated valleys typically involve attempts to fit empirical data from valley cross profiles to quadratic parabolic or power law equations with the choice of equation depending on the goal of the analysis in assessing the relative merits of these two types of equations some confusion has arisen because of apparent variations in coordinate system datums between studies which have made use of the power law equation however we show that this confusion relates to a simple mathematical error rather than any true difference in methodology of more significance however is the fact that in fitting a power law equation to observed profiles significant bias is introduced by the use of a logarithmic data transformation because of this implicit bias power law equation parameters are influenced most strongly by data points close in elevation to the centre of the valley and so failure to account for the depositional elements which frequently occur in these areas can lead to significant errors if the aim of the analysis is to characterize the form of the erosional profile

the determination of the seismic quality factor q from vsp data a comparison of different computational methods1 ten methods for the computation of attenuation have been investigated namely amplitude decay analytical signal wavelet modelling phase modelling frequency modelling rise time pulse amplitude matching technique spectral modelling and spectral ratio in particular we have studied the reliability of each of these methods in estimating correct values of q using three synthetic vsp seismograms for plane p waves with different noise contents the investigations proved that no single method is generally superior rather some methods are more suitable than others in specific situations depending on recording noise or geology the analytical signal method has been demonstrated to be superior if true amplitude recordings are available otherwise spectral modelling or in the noise free case the spectral ratio method is optimal finally two field vsps in sediments are investigated only in the case of the highest quality vsp can significant information be deduced from the computed attenuation

modeling damage and deformation in impact simulations numerical modeling is a powerful tool for investigating the formation of large impact craters but is one that must be validated with observational evidence quantitative analysis of damage and deformation in the target surrounding an impact event provides a promising means of validation for numerical models of terrestrial impact craters particularly in cases where the final pristine crater morphology is ambiguous or unknown in this paper we discuss the aspects of the behavior of brittle materials important for the accurate simulation of damage and deformation surrounding an impact event and the care required to interpret the results we demonstrate this with an example simulation of an impact into a terrestrial granite target that produces a 10 km diameter transient crater the results of the simulation are shown in terms of damage a scalar quantity that reflects the totality of fragmentation and plastic strain both total plastic strain the accumulated amount of permanent shear deformation regardless of the sense of shear and net plastic strain the amount of permanent shear deformation where the sense of shear is accounted for damage and plastic strain are both greatest close to the impact site and decline with radial distance however the reversal in flow patterns from the downward and outward excavation flow to the inward and upward collapse flow implies that net plastic strains may be significantly lower than total plastic strains plastic strain in brittle rocks is very heterogeneous however continuum modeling requires that the deformation of the target during an impact event be described in terms of an average strain that applies over a large volume of rock large compared to the spacing between individual zones of sliding this paper demonstrates that model predictions of smooth average strain are entirely consistent with an actual strain concentrated along very narrow zones furthermore we suggest that model predictions of total accumulated strain should correlate with observable variations in bulk density and seismic velocity

in situ measurements of impact induced pressure waves in sandstone targets in the present study we introduce an innovative method for the measurement of impact induced pressure waves within geological materials impact experiments on dry and water saturated sandstone targets were conducted at a velocity of 4600 m s using 12 mm steel projectiles to investigate amplitudes decay behavior and speed of the waves propagating through the target material for this purpose a special kind of piezoresistive sensor capable of recording transient stress pulses within solid brittle materials was developed and calibrated using a split hopkinson pressure bar experimental impact parameters projectile size and speed were kept constant and yielded reproducible signal curves in terms of rise time and peak amplitudes pressure amplitudes decreased by 3 orders of magnitude within the first 250 mm i e 42 projectile radii the attenuation for water saturated sandstone is higher compared to dry sandstone which is attributed to dissipation effects caused by relative motion between bulk material and interstitial water the proportion of the impact energy radiated as seismic energy seismic efficiency is in the order of 10 3 the present study shows the feasibility of real time measurements of waves caused by hypervelocity impacts on geological materials experiments of this kind lead to a better understanding of the processes in the crater subsurface during a hypervelocity impact

the seismic signatures of recently formed impact craters on mars we investigated the seismic signatures of recent impact crater clusters on mars that would be recorded by the interior exploration using seismic investigations geodesy and heat transport insight seismometers we used a database of 77 measured and dated impact sites with craters with diameters between 2 1 and 33 8 m along with inferred impact angle bolide trajectory and varying target material properties to empirically scale for the momentum expected seismic source function and radiation pattern of impacts the impact source is simulated in a local 3 d finite difference wave propagation code and coupled to teleseismic distances by scaling the spectra of 1 d global synthetic seismograms we use the insight seismometer noise floors to estimate detectability of impact s across azimuth and distance our experiments reveal that impact clusters have a higher peak corner frequency resulting from energy contributed by smaller craters to the power spectrum we also find that the time separation between individual impacts in a cluster is small 100 hz to resolve individual impacts within the cluster two of the clusters in our database 20 m effective diameter would have been detectable by insight with the assumptions that the martian background noise and seismic attenuation are both low joint detection of surface changes from newly formed crater s in images and by insight will provide precise source locations that are crucial for constraining the internal structure of mars

seismic detection of meteorite impacts on mars abstract meteorite impacts provide a potentially important seismic source for probing mars interior it has recently been shown that new craters can be detected from orbit using high resolution imaging which means the location of any impact related seismic event could be accurately determined thus improving the constraints that could be placed on internal structure using a single seismic station this is not true of other seismic sources on mars such as sub surface faulting which require location using multiple seismic stations this study aims to determine the seismic detectability of meteorite impacts and assess whether they are a viable means of probing deep internal structure first we derive a relation between crater diameter and equivalent seismic moment based on observational data compiled from impact tests controlled explosions and earthquake seismology second this relation was combined with updated cratering rates based on newly observed craters to derive the impact induced seismicity on mars which we estimate to total 10 13 10 14 n m per year finally seismic waveform modelling was used to determine the detectability of these impacts based on reasonable assumptions about likely seismometer performance and background noise levels for our nominal noise instrument case we find that detectable impacts at teleseismic distances source receiver offsets greater than 60 are very rare and occur approximately once every 10 years for our most optimistic noise instrument case approximately one such event occurs each year this suggests that using solely meteorite impacts is not a reliable way of probing the martian interior although local impacts are more frequently detectable and could provide important constraints on near surface seismic properties

a rational explanation of cross profile morphology for glacial valleys and of glacial valley development a further note the authors discovered a misinterpretation in their original paper which is corrected here

impact cutoff frequency momentum scaling law inverted from apollo seismic data abstract we perform the analysis of both long and short period data for 40 large meteoroid impacts event gathered by the apollo lunar seismic network we extract the linear momentum released by the impact and the cutoff frequency of the recorded seismic spectrum related to the radiation process of the shock wave generated by the impact by using a proxy to the local porosity based on the density of surface craters and well correlated to the most recent grail observations we demonstrate that the seismic cutoff frequencies for 40 selected impacts correlate with this proxy and therefore likely with the porosity at the impacted areas our finding shows that lunar seismic records of meteoroid impacts represent unique geophysical data documenting medium to high energy 0 1 1 kt tnt yield impact processes including the interaction of shock waves with porous media this work can be applied to the analysis of the seismic data to be obtained by the insight mission in 2016 and the investigation of the lateral variations in the martian regolith

numerical modeling of the development of u shaped valleys by glacial erosion the steep sided valleys and overdeepened basins of alpine landscapes are well known products of glaciation yet relatively little is known about how the dynamics of ice flow and glacial erosion interact to give rise to such landforms by linking a finite element model for ice flow through a glacier cross section with an erosion model it is possible to investigate the development of one of the most striking glacial landforms the u shaped valley in addition to providing a detailed understanding of landform development such modeling provides a way to test current understanding of the controls on glacial sliding and erosion to simulate valley development i first model flow through an initial glacier cross section and calculate the glaciological parameters that govern erosion i then numerically simulate erosion to produce a modified transverse profile for which a new flow field and erosion pattern are computed a number of iterations permits examination of the progressive transformation of cross section form which can be compared with field data model predictions of the cross section flow field are in close accord with data from the athabasca glacier and include marked lateral variations in sliding velocity with an erosion law dependent on basal velocity the model predicts the rapid transformation of a v shaped cross section into a recognizably glacial form over a time period on the order of 10 4 yr and the eventual development of a steady state quasi parabolic glacier cross section better agreement with empirical data from glaciated valleys is obtained by including temporal variations in ice discharge in order to mimic the characteristics of 100 000 yr glacial cycles the high discharge phase dominates form development and at low discharges cross section form is essentially inherited from the central part of the form that developed during the preceding high discharge phase

measurements of seismic waves induced by high velocity impacts implications for seismic shaking surrounding impact craters on asteroids abstract on asteroids impact induced seismic shaking is an important geological process related to the modifications of the surface features that are due to the movement of regolith grains on the asteroid surface mass movements caused by seismic shaking e g landslides and crater erasures were recently observed by several spacecrafts to elucidate the seismic shaking areas induced by impacts on asteroids it is necessary to determine the excitation and the decay processes of impact induced seismic waves here we conducted impact cratering experiments using 500 m quartz sand to simulate an asteroid surface at the institute of space and astronautical science isas japan aerospace exploration agency jaxa we used 4 75 mm and 2 mm diameter projectiles with density from 14 9 to 1 2 g cm 3 the impact velocity ranged from 7 to 0 2 km s 1 we measured the acceleration waveform by using three to five accelerometers setting on the target surface and we examined three parameters characterizing the impact induced seismic wave with varying distances from the impact point the propagation velocity vprop the maximum acceleration gmax and the half period of the first upward peak thalf the vprop was obtained to be 52 4 7 2 m s 1 regardless of the impact velocity and the projectile properties and the thalf slightly depended on the impact velocity as v i 0 14 but was independent of the projectile properties the gmax had a close relationship with the distance from the impact point normalized by the crater rim radius x rrim regardless of the impact velocity and the projectile properties the obtained empirical equation was shown as gmax 102 21 x rrim 3 18 by using the empirical equations we obtained herein we observed that the seismic energy normalized by the kinetic energy of a projectile es ek decreased with the increase of the normalized distance x rrim we also estimated the area of impact induced seismic shaking on an idealized small 500 m in diameter body at the impact velocity of 5 km s 1