numerical modeling of asteroid survivability and possible scenarios for the morokweng crater forming impact the fate of the impactor is an important aspect of the impact cratering process defining impactor material as surviving if it remains solid i e does not melt or vaporize during crater formation previous numerical modeling and experiments have shown that survivability decreases with increasing impact velocity impact angle with respect to the horizontal and target density here we show that in addition to these impactor survivability depends on the porosity and shape of the impactor increasing impactor porosity decreases impactor survivability while prolate shaped polar axis equatorial axis impactors survive impact more so than spherical and oblate shaped polar axis equatorial axis impactors these results are used to produce a relatively simple equation which can be used to estimate the impactor fraction shocked to a given pressure as a function of these parameters by applying our findings to the morokweng crater forming impact we suggest impact scenarios that explain the high meteoritic content and presence of unmolten fossil meteorites within the morokweng crater in addition to previous suggestions of a low velocity and or high angled impact this work suggests that an elongated and or low porosity impactor may also help explain the anomalously high survivability of the morokweng impactor

selective dissolution of magnetic iron oxides with the acid ammonium oxalate ferrous iron extraction technique ii natural loess and palaeosol samples summary chemical extraction techniques are being introduced into environmental magnetism studies to aid in the interpretation of magnetic climate proxies previous studies have shown that the acid ammonium oxalate ferrous iron aao fe 2 extraction technique can be used to selectively dissolve very fine grained magnetite and maghemite from synthetic samples here we present the results of a study of this extraction technique to serve as a tool for selective dissolution of pedogenic magnetic minerals from a loess palaeosol transect before and after extraction the samples were subjected to classic mineral magnetic methods measurement of low field susceptibility and hysteresis parameters as well as first order reversal curve analysis in addition acquisition curves of the isothermal remnant magnetization irm were fitted with logarithmic distributions these analyses showed the magnetic dominance of lowcoercivity magnetic minerals by subtracting the irm remaining after extraction from that before extraction the magnetic fraction that was dissolved could be characterized as well supplying extra information concerning the performance of the extraction technique the aao fe 2 method successfully dissolved the superparamagnetic and part of the singledomain material from the palaeosol samples in one extraction step repeating the extraction resulted in hardly any further changes to the magnetic content of the samples the magnetic characteristics of the loess samples remained stable throughout the extraction experiment the combination of the aao fe 2 extraction with mineral magnetic analysis has successfully identified the pedogenic contribution in our samples therefore variations in the lithogenic fraction potentially present in pedogenically enhanced intervals can be assessed improving the merit of mineral magnetic climate proxy parameters

high noble metal concentrations in a late pliocene sediment a 2 3 myr old layer in a sediment from the antarctic ocean contains ir and au at levels comparable with those at the cretaceous tertiary boundary a sizable fraction of the noble metals is contained in vesicular millimetre sized poly mineralic grains that closely resemble ablation debris from chondritic meteorites and there is little doubt that the noble metals resulted from the accretion of a large extraterrestrial object no massive extinctions or other evidence of environmental stress seem to be associated with this accretionary event

rate effect experiments on round tipped penetrometer insertion into uniform snow snow penetrometers are being developed to detect stratigraphy indicative of slab avalanches results are presented here from experiments performed to assess the relationship between the velocity of a round tipped penetrometer through uniform snow and the resulting force response the range of velocities used is commensurate with that used to drive a manually driven penetrometer through the snow a characteristic spike is noted in profiles during the initial stage of deformation which appears to be more pronounced for the harder snow layers tested an investigation of snow deformation using video analysis of a split axis rod deforming snow against a clear plastic window indicates that the spike in the force signal corresponds to the development of a compaction zone below the penetrometer tip once shear forces that develop in the compacted snow are overcome deformation proceeds in a steady state and there is little or no relationship between the force response and velocity over the velocity range of our experiments

sedimentary signatures and processes during marine bolide impacts a review abstract studies of submarine impact craters resulting from impacts of comets or asteroids demonstrate that the presence of water and the physical properties of target rocks have a major influence on sedimentary processes associated with meteorite impacts this results in difference in sedimentary signature of bolide impacts in marine environments compared to subaerial impact craters in subaerial impacts the targets are commonly hard rocks frequently of igneous and or metamorphic origin whereas in submarine impacts the targets are mostly unconsolidated or poorly lithified sediments or sedimentary rocks with high volumes of pore water such differences result in variability in crater morphology and in sedimentary processes inside and outside the impact area impacts in shallow water marine neritic environments produced craters with low or absent rims and wide and shallow brims as characterize by both the montagnais on the scotian shelf the mjolnir in the barents sea 45 and 40 km in diameter respectively and the chesapeake bay 90 km in diameter lack of elevated rims is thought to be the result of current reworking and resurge of the water back into the excavated cavity as the water in the crater is vaporized during this process resurge gullies can be cut across the rim while mass and debris flows turbidites and other gravity deposits are produced as results of tsunami and crater wall and central high collapse during and after the crater excavation stage such deposits are found both within and outside the crater structure the only difference between gravity deposits triggered by an impact or other rare events such as earthquakes is the admixture of various melt particles and possible enrichments in iridium in the former impacts near the shelf edge may cause partial collapse of the continental margin as shown by the montagnais and chicxulub impacts some of the gravity and debris flows generated by margin collapse may be channelized with final deposits up to several hundred meters thick extending for hundreds of kilometers from the impact site other impact features such as shatter cones tektites spherules and ni spinels shocked quartz isotropication and partial melts are common to both submarine and subaerial impacts theoretical calculations of the destructive forces of mega tsunami waves triggered by meteorite impact in the ocean greatly exceed those based on geologic evidence a dearth of gigantic tsunami evidence for the chicxulub impact outside of the gulf of mexico where from theoretical modelling the maximum near bottom orbital velocity of water flow crossing the deep north atlantic basin should have been 1 m s could be the result of the mitigating effect of the bathymetry of surrounding area causing wave diffraction and interference calculated maximum horizontal orbital velocity near the seafloor at the shelf for the montagnais impact is 22 m s for a 200 m high wave 5 5 m s for a 50 m high wave at 500 km decreasing to 0 5 m s at 1000 km strong enough to scour the deep ocean bottom and produce distinct erosion surfaces and disconformities in marine sedimentary record however lack of cores across impact horizon prevents confirmation of occurrence of such bottom water flows

cone penetration testing cpt in antarctic firn an introduction to interpretation commercial cone penetration testing cpt equipment was adapted to allow penetrative testing in hard polar firn to depths of 10 m the apparatus is hydraulically driven rate controllable and able to penetrate firn with a resistance of 10 mpa it can be mounted on many types of typical polar vehicles requiring connection to only hydraulics and 12 v electricity data recorded include both cone tip resistance and sleeve friction a parameter not previously examined through such testing this paper describes the development and calibration of the equipment and examines factors including snow density penetration rate and cone size and shape that are shown to affect cpt interpretation cpt can be used efficiently in polar environments to potentially provide estimates of physical parameters in hard firn to substantial depth

a brief introduction to cone penetration testing cpt in frozen geomaterials the cone penetration test has been successfully used to classify soil for 100 years however it has received only limited contemporary use in frozen geomaterials the historical and contemporary use of the cone penetration test in various frozen geomaterials is considered here and contemporary data from recent work in polar snow are examined it is probable that many material physical properties e g density strength and microstructure can be obtained directly from cone penetration testing it appears under utilized as a contemporary scientific and engineering investigative tool in frozen geomaterials

laboratory investigations of marine impact events factors influencing crater formation and projectile survivability given that the earths surface is covered in around two thirds water the majority of impact events should have occurred in marine environments however with the presence of a water layer crater formation may be prohibited indeed formation is greatly controlled by the water depth to projectile diameter ratio as discussed in this paper previous work has shown that the underlying target material also influences crater formation e g gault and sonett 1982 baldwin et al 2007 in addition to the above parameters we also show the influence of impact angle impact velocity and projectile density for a variety of water depths on crater formation and projectile survivability the limiting ratio of water depth to projectile diameter on cratering represents the point at which the projectile is significantly slowed by transit through the water layer to reduce the impact energy to that which prohibits cratering we therefore study the velocity decay produced by a water layer using laboratory analytical and numerical modelling techniques and determine the peak pressures endured by the projectile for an impact into a water depth five times the projectile diameter the velocity of the projectile is found to be reduced to 26 32 its original value for deep water impacts we find that up to 60 of the original mass of the projectile survives in an oblique impact where survivability is defined as the solid or melted mass fraction of the projectile that could be collected after impact

numerical modeling for target water depth estimation of marine target impact craters 1 marine impacts can develop a crater in the seafloor if the target water depth is shallow in relation to the size of the impactor the geology of this marine target crater is influenced by the layer of water in the upper part of the target the influence increases with increased water depth the target water depth is essential when calculating the magnitude of the impact event as the seafloor crater merely expresses some of the expended energy the target water depth for a marine target crater is often estimated by facies analysis of sediments related to the impact crater unfortunately often with ambiguous results we propose to combine the conventional methods with numerical modeling of the target water depth based on the special target water related features of the crater we used geological data from the lockne crater as constraints in a simulation with the sova hydrocode the simulations were done for three different target water depths 200 m 500 m and 1000 m within the likely depth range for the middle ordovician sea in which the impact occurred in order to obtain the minimum estimated size of the lockne crater by an asteroid impact at 20 km s the water depth must have been slightly less than 1 km and the impactor radius must have been about 400 m it was not possible to generate a crater with the geological features of lockne for target water depths of less than about 500 m however the ratio may be further constrained by factors such as impactor density impact angle and impact velocity

numerical modeling of impact induced modifications of the deep sea floor abstract the mechanics of oceanic impact events differ in several respects from the process that accompanies the strike of an asteroid on land in order to explore the cratering process on a water covered target a series of 2d hydrocode simulations for impact velocities of 10 15 20 and 30 km s and water depth diameter ratios between 5 and 7 have been carried out in particular these simulations were aimed to examine the effects of the asteroid on the deep sea floor the interaction of the impacting body and the water column causes loss of the body s kinetic energy both through oceanic drag and through mass loss due to hydrodynamic heating prior to hitting the ocean bottom regardless of whether the impactor actually hits the ocean floor the shock wave generated in the water column by the impact of the body on the water surface will leave behind unique traces in the marine sediments for example an asteroid of 1 km in diameter arriving at the ocean surface with a velocity of 20 km s induces a shock pressure of 6 gpa in the oceanic crust at a water depth of 5 km the passage of the shock wave along the water ocean bottom interface causes significant disturbance in the sediment layer moreover the collapse of the transient cavity that results from the passage of the projectile through the water column causes a strong surge of water that generates a displacement and redeposition of sediments on the ocean floor in order to examine sediment transport processes we introduce computationally a large amount of massless particles within the projectile and the target material and follow the movement of each individual particle tracer particles represent only forced material movement and do not account for any frictional forces thus comparisions with real sediment disturbances may be qualitative only for an impact velocity of 20 km s and a water depth diameter ratio of 5 this procedure reveals significant particle movements within a distance of 15 km from the center of the impact the only known deep sea impact structure so far the eltanin impact in the bellingshausen sea antarctica is characterized by a zone of chaotically mixed sediments that most probably originated from impact induced turbulent water currents based on the present observations which do not allow the identification of an impact structure at the ocean bottom our model yields estimates of a projectile diameter of 1 km and an impact velocity of 20 km s

quantification of the hand hardness test snow hardness is the resistance to penetration it can be measured by the swiss rammsonde or estimated by the hand hardness test according to the international classification of seasonal snow on the ground icssg snow hardness is divided into five levels without ice however the hand test is subjective and provides only an index value of snow hardness the main objective of this study was to determine the hardness using an alternative method which can be applied in the same way as the hand test and which can deliver accurate data in this study the conventional hand hardness test was used additionally a digital force gauge push pull gauge was applied where the hardness was measured horizontally for comparison with the hand hardness test the push pull gauge could be provided with five different attachments the size and design of each attachment corresponded to the equivalent application of the hand hardness test fist four fingers one finger pencil knife this paper indicates how snow hardness measured by hand is related to snow hardness measured with the push pull gauge moreover the variability of the hardness both vertical and horizontal is demonstrated the results show agreement with the icssg for hand hardness indices 3 4 and 5 for hand hardness indices 1 and 2 the range indicated by the icssg is below the lower quartile of the measurements

a new instrument for determining strength profiles in snow cover thermo resistographe realise a l aide d une jauge de contrainte et un systeme d acquisition de donnees microprocesseur z80

laboratory impacts into dry and wet sandstone with and without an overlying water layer implications for scaling laws and projectile survivability scaling laws describing crater dimensions are defined in terms of projectile velocity and mass densities of the materials involved strength of the target and the local gravity here the additional importance of target porosity and saturation and an overlying water layer are considered through 15 laboratory impacts of 1 mm diameter stainless steel projectiles at 5 km s 1 into a an initially uncharacterized sandstone porosity 17 and b coconino sandstone porosity 23 the higher porosity dry sandstone allows a crater to form with a larger diameter but smaller depth than in the lower porosity dry sandstone furthermore for both porosities a greater volume of material is excavated from a wet target than a dry target by 27 30 comparison of our results with pi scaling dimensionless ratios of key parameters characterizing cratering data over a range of scales suggests that porosity is important for scaling laws given that the new data lie significantly beneath the current fit for ice and rock targets on a v versus 3 plot v gives cratering efficiency and 3 the influence of target strength an overlying water layer results in a reduction of crater dimensions with larger craters produced in the saturated targets compared to unsaturated targets a water depth of approximately 12 times the projectile diameter is required before craters are no longer observed in the targets previous experimental studies have shown that this ratio varies between 10 and 20 gault and sonett 1982 in our experiments 25 of the original projectile mass survives the impact

oceanic impacts a growing field of fundamental geoscience the importance of oceanic impacts of collisional events and resulting energy release are briefly described data collection methods from the eltanin a mesosiderite projectile deep water impact are presented

impact induced phyllosilicate formation from olivine and water abstract shock recovery experiments on mixtures of olivine and water with gas air were performed in a previous study to demonstrate water mineral interactions during impact events furukawa et al 2007 the products of these former experiments were investigated in the present study using transmission electron microscopy scanning electron microscopy and x ray powder diffraction with the aim of finding evidence of aqueous alteration serpentine formed on the surface of shocked olivine with well developed mosaicism the yield of serpentine depended on the water olivine ratio in the starting material indicating progressive serpentinization under water rich conditions comminution and mosaicism were developed in shocked olivine grains the temperature and pressure changes of the samples during the experiments were estimated by constructing hugoniots for mixtures of olivine and water combined with the results of an additional fracturing experiment on a shocked container pressures and temperatures reached 4 6 7 2 gpa and at least 230 390 c respectively for 0 7 s during in shock compression post shock temperatures reached a maximum of 1300 c when the shock wave reached the gas in the sample cavity the serpentine formed after the post shock temperature maximum most likely when temperatures dropped to between 200 and 400 c this is the first experiment to demonstrate the formation of phyllosilicates using heat supplied by an impact the present results and estimations suggest that phyllosilicates could form as a result of impacts into oceans as well as by impacts on terrestrial and martian crustal rocks and on some asteroidal surfaces where liquid or solid h 2 o is available a significant amount of phyllosilicates would have formed during the late heavy bombardment of meteorites on the hadean earth and such phyllosilicates might have affected the prebiotic carbon cycle

shock metamorphism on the ocean floor numerical simulations abstract impact craters are unknown in deep ocean basins important reasons for this are that the ocean crust is younger than continents and the impacts are weakened by the water column laboratory experiments can show specific features of water impacts however impact velocities are too small

experimental and numerical investigation of the sintering rate of snow sintering rates in snow were investigated by measuring changes in penetration resistance with time and by using a numerical snow metamorphism model periodic snow micro penetrometer smp measurements were performed on uniform snow samples covering a wide range of densities the mean penetration resistance of snow increased with time according to a power law with an average exponent of 0 18 simulated changes in the bond to grain ratio for simplified spherical ice grains followed a power law with an average exponent of 0 18 showing that the mean penetration resistance as measured with the smp closely relates to bond to grain ratio in snow for lower density snow samples consisting mostly of dendritic snow morphologies the measured increase in penetration resistance was lower this is likely the result of two competing processes 1 strengthening of the snow sample due to the creation and growth of bonds and 2 weakening of the snow sample due to the formation of unbonded small rounded particles at the expense of larger dendritic forms on the other hand the rate of increase in penetration resistance for snow samples consisting of closely packed depth hoar was similar to that of rounded grains

cone penetration testing in snow the application of the electric cone penetrometer test in snow has been investigated and compared with results from the ram penetrometer test which is normally used for snow profiling and slope stability analysis a special cone penetrometer system was built consisting of a sensitive 1 cm2 electric cone depth transducer and battery operated chart recorder the instruments were tested in april 1985 at three different locations in the swiss alps and the test results were compared with those of the ram penetrometer tests the tests yielded repeatable results up to a depth of 4 m with a high resolution of different snow layers the electric cone tests show more layers than found in the ram profile and snow pit analyses in soft snow the ram resistances appear to be on average about 30 lower than cone resistance values recommendations are given for the future use of electric cone penetration testing in snow key words snow snowpack analysis cone penetration test ram penetrometer cone resistance ram

unmelted meteoritic debris collected from eltanin ejecta in polarstern cores from expedition ant xii 4 abstract a total of 1 7 g of unmelted meteorite particles have been recovered from fs polarstern piston cores collected on expedition ant xii 4 that contain ejecta from the eltanin impact event most of the mass 1 2 g is a large single specimen that is a polymict breccia similar in mineralogy and chemistry to howardites or the silicate fraction of mesosiderites most of the remaining mass is in several large individual pieces 20 75 mg each that are polymict breccias fragments dominated by pyroxene and an igneous rock fragment the latter has highly fractionated ree similar to those reported in mafic clasts from mesosiderites other types of specimens identified include fragments dominated by maskelynite or olivine these pieces of the projectile probably survived impact by being blown off the back surface of the eltanin asteroid during its impact into the bellingshausen sea

smart 1 end of life shallow regolith impact simulations the smart 1 end of life impact with the lunar surface was simulated with impacts in a two stage light gas gun onto inclined basalt targets with a shallow surface layer of sand this simulated the probable impact site where a loose regolith will have overlaid a well consolidated basaltic layer of rock the impact angles used were at 5 and 10 from the horizontal the impact speed was 2 km s 1 and the projectiles were 2 03 mm diameter aluminum spheres the sand depth was between approximately 0 8 and 1 8 times the projectile diameter implying a loose lunar surface regolith of similar dimensions to the smart 1 spacecraft a crater in the basement rock itself was only observed in the impact at 10 incidence and where the depth of loose surface material was less than the projectile diameter in which case the basement rock also contained a small pit like crater in all cases the projectile ricocheted away from the impact site at a shallow angle this implies that at the smart 1 impact site the crater will have a complicated structure with exposed basement rock and some excavated rock displaced nearby and the main spacecraft body itself will not be present at the main crater

geological record and reconstruction of the late pliocene impact of the eltanin asteroid in the southern ocean in 1995 an expedition on board the research vessel fs polarstern explored the impact site of the eltanin asteroid in the southern ocean the only known asteroidimpact into a deep ocean basin analyses of the geological record of the impact region place the event in the late pliocene 2 15 myr and constrain thesize of the asteroid to be 1 km the explosive force inferred for this event places it at the threshold of impacts believed to have global consequences and its studyshould therefore provide a baseline for the reconstruction and modelling of similar events which are common on geological timescales

discovery of a 25 cm asteroid clast in the giant morokweng impact crater south africa meteorites provide a sample of solar system bodies and so constrain the types of objects that have collided with earth over time meteorites analysed to date however are unlikely to be representative of the entire population and it is also possible that changes in their nature have occurred with time large objects are widely believed to be completely melted or vaporized during high angle impact with the earth consequently identification of large impactors relies on indirect chemical tracers notably the platinum group elements here we report the discovery of a large 25 cm unaltered fossil meteorite and several smaller fragments within the impact melt of the giant 70 km diameter 145 myr old morokweng crater south africa the large fragment clast resembles an ll6 chondrite breccia but contains anomalously iron rich silicates fe ni sulphides and no troilite or metal it has chondritic chromium isotope ratios and identical platinum group element ratios to the bulk impact melt these features allow the unambiguous characterization of an impactor at a large crater furthermore the unusual composition of the meteorite suggests that the morokweng asteroid incorporated part of the ll chondrite parent body not represented by objects at present reaching the earth

velocity scaling of impact craters in water ice over the range 1 to 7 3 km s 1 the impact cratering behavior of polycrystalline ice at a temperature of 259 3 k has been investigated by 16 impacts with 1 mm aluminum 2017 alloy spheres density 2790 kg m 3 over the velocity range 1 to 7 3 km s 1 using a two stage light gas gun crater cross sectional profiles and diameter depth and volume data are presented it is found that there is no significant difference in power law energy exponents for scaling of crater diameter and volume between these data and previous low velocity 1 km s 1 ice impact data dimensionless pi group scaling was also found to scale the data in a way which can be readily combined with earlier lower velocity data and data at a lower ice temperature

the clay mineralogy of sediments related to the marine mjolnir impact crater the 40 km diameter mjolnir crater is located on the central barents sea shelf north of norway it was formed about 142 2 6 myr ago by the impact of a 12 km asteroid into the shallow shelf clays of the hekkingen formation and the underlying triassic to jurassic sedimentary strata a core recovered from the central high within the crater contains slump and avalanche deposits from the collapse of the transient crater and central high these beds are overlain by gravity flow conglomerates with laminated shales and marls on top here impact and post impact deposits in this core are studied with focus on clay mineralogy obtained from xrd decomposition and simulation analysis methods the clay sized fractions are dominated by kaolinite illite mixed layered clay minerals and quartz detailed analyses showed rather similar composition throughout the core but some noticeable differences were detected including varying crystal size of kaolinite and different types of illites and illite smectite these minerals may have been formed by diagenetic changes in the more porous fractured beds in the crater compared to time equivalent beds outside the crater rim long term post impact changes in clay mineralogy are assumed to have been minor due to the shallow burial depth and minor thermal influence from impact heated target rocks instead the clay mineral assemblages especially the abundance of chlorite reflect the impact and post impact reworking of older material previously an ejecta layer the sindre bed was recognized in a nearby well outside the crater represented by an increase in smectite rich clay minerals genetically equivalent to the smectite occurring in proximal ejecta deposits of the chicxulub crater such alteration products from impact glasses were not detected in this study indicating that little if any impact glass was deposited within the upper part of the crater fill crater fill deposits inherited their mineral composition from triassic and jurassic sediments underlying the impact site

catastrophic disruption of icy bodies with sub surface oceans abstract several icy bodies in the outer solar system have extensive internal oceans in several bodies the oceans are believed to be so extensive they decouple the interior core from the icy surface a major evolutionary driver in the solar system is high speed impacts which lead to cratering or even disruption of the target body here we consider how the presence of an internal ocean modifies the energy density needed to disrupt an icy body with an internal ocean we find that in laboratory experiments on decimetre scale bodies the energy density to cause disruption is 16 25 1 35 j kg 1 compared to 18 0 0 7 j kg 1 for solid ice bodies this suggests that for the purposes of impacts the bodies behave as if a solid with the same density predictions of the lifetimes of such icy bodies against impact disruption thus need not take the interior ocean into account

a synthetic study to assess the applicability of full waveform inversion to infer snow stratigraphy from upward looking ground penetrating radar data snow stratigraphy and liquid water content are key contributing factors to avalanche formation upward looking groundpenetrating radar upgpr systems allow nondestructive monitoring of the snowpack but deriving density and liquid water content profiles is not yet possible based on the direct analysis of the reflection response we have investigated the feasibility of deducing these quantities using full waveform inversion fwi techniques applied to upgpr data for that purpose we have developed a frequency domain fwi algorithm in which we additionally took advantage of time domain features such as the arrival times of reflected waves our results indicated that fwi applied to upgpr data is generally feasible more specifically we could show that in the case of a dry snowpack it is possible to derive snow densities and layer thicknesses if sufficient a priori information is available in case of a wet snowpack in which it also needs to be inverted for the liquid water content the algorithm might fail even if sufficient a priori information is available particularly in the presence of realistic noise finally we have investigated the capability of fwi to resolve thin layers that play a key role in snow stability evaluation our simulations indicate that layers with thicknesses well below the gpr wavelengths can be identified but in the presence of significant liquid water the thin layer properties may be prone to inaccuracies these results are encouraging and motivate applications to field data but significant issues remain to be resolved such as the determination of the generally unknown upgpr source function and identifying the optimal number of layers in the inversion models furthermore a relatively high level of prior knowledge is required to let the algorithm converge however we feel these are not insurmountable and the new technology has significant potential to improve field data analysis