tsunami generation and propagation from the mjolnir asteroid impact in the late jurassic period about 142 million years ago an asteroid hit the shallow paleo barents sea north of present day norway the geological structure resulting from the impact is today known as the mjlnir crater the present work attempts to model the generation and the propagation of the tsunami from the mjolnir impact a multi material hydrocode sova is used to model the impact and the early stages of tsunami generation while models based on shallow water theories are used to study the subsequent wave propagation in the paleo barents sea we apply several wave models of varying computational complexity this includes both three dimensional and radially symmetric weakly dispersive and nonlinear boussinesq equations as well as equations based on nonlinear ray theory these tsunami models require a reconstruction of the bathymetry of the paleo barents sea the mjolnir tsunami is characteristic of large bolides impacting in shallow sea in this case the asteroid was about 1 6 km in diameter and the water depth was around 400 m contrary to earthquake and slide generated tsunamis this tsunami featured crucial dispersive and nonlinear effects a few minutes after the impact the ocean surface was formed into an undular bore which developed further into a train of solitary waves our simulations indicate wave amplitudes above 200 m and during shoaling the waves break far from the coastlines in rather deep water the tsunami induced strong bottom currents in the range of 30 90 km h which presumably caused a strong reworking of bottom sediments with dramatic consequences for the marine environment

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

characteristics of thermokarst lakes and their influence on permafrost in qinghai tibet plateau abstract about 250 thermokarst lakes with an average size of 5580 m2 and a total size of 139 104 m2 are spread between the kunlun mountain pass and the fenghuo mountain pass along the qinghai tibet railway where ice rich and warm permafrost exists approximately 56 of the lakes are elliptical and 23 are elongated the water depth varies between 0 4 and 3 m most of the lakes in the chumarhe high plain and other mountain regions are shallower than the thickness of winter ice 60 to 80 cm and are frozen to the bottom during the cold seasons however in the hoh xil hill region and beiluhe basin the water depth is greater than the thickness of winter ice and the relatively warm lake bottoms can cause considerable disturbance to the surrounding continuous permafrost the lakes in the chumarhe high plain are saltwater or brine lakes and in other regions the lakes contain freshwater or brackish water ages of formation enlargement rates water and lake bottom temperatures the configuration of permafrost and active layer thickness were measured at a typical thermokarst lake in the beiluhe basin between 2007 and 2009 the lake formed about 890 years ago and is 150 m long 100 m wide with a water depth of 2 5 m now the size of the lake is growing at a rate of about 1 m a at some shores the lakeshores are underlain by permafrost which terminates almost vertically at their edge the mean annual temperature measured at lake bottom in the centre was 5 45 c while the temperature of permafrost at 15 m depth in the lakeshore varied from 0 84 c near the edge of the lake to 1 26 c at 80 m from the edge the corresponding active layer depths varied from 2 45 to 1 80 m the configuration of the talik indicates that no permafrost is found beneath the centre of the lake

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

offshore breaking of impact tsunami the van dorn effect revisited 1 we report on calculations of the shoaling and off shore breaking of typical wavetrains from sub km impactors into the deep ocean we use the coulwave code to compute the propagation of waves through simple bathymetry profiles typical of the north american pacific coast and the gulf of mexico numerical results are consistent with those predicted by nonlinear shoaling theory our primary result is that large long period waves of the type considered should indeed break far offshore as suggested by w g van dorn for similar waves generated by underwater explosions typical breaking distances range from 3 17 km for the pacific coast and up to 200 km for the gulf coast the inclusion of bottom friction affects the results for very gentle slopes like the gulf coast a modest amount of bottom friction supplies enough dissipation to suppress wave breaking

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

quantifying evaporation and its decadal change for lake nam co central tibetan plateau most lakes in the interior tibetan plateau have expanded rapidly since the late 1990s because of a lack of observations lake water balances and their changes are far from well understood evaporation is a component of the lake water balance and this study quantifies its magnitude decadal change and its contribution to the water balance changes in lake nam co one of the largest lakes on the tibetan plateau with an area of approximately 2000 km2 and a mean depth of approximately 40 m the lake temperature and the evaporation are simulated by the flake model the simulation results are validated against observed lake temperature profile from 2013 and moderate resolution imaging spectroradiometer lake surface temperature data from 2000 to 2014 the simulated latent heat flux and sensible heat flux are validated against bowen ratio derived estimates for 2013 based on the validated simulation results the long term mean annual evaporation is approximately 832 69 mm and this value is much less than the potential evaporation estimated using the penman monteith equation the annual evaporation from 1980 to 2014 displays a complex decadal oscillation mainly due to the changes in energy related terms air temperature and radiation the mean lake evaporation since the late 1990s is greater than previous periods thus this change in evaporation has suppressed the recent expansion of nam co

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

run up from impact tsunami summary we report on calculations of the on shore run up of waves that might be generated by the impact of subkilometre asteroids into the deep ocean the calculations were done with the coulwave code which models the propagation and shore interaction of non linear moderate to long wavelength waves kh using the extended boussinesq approximation we carried out run up calculations for several different situations 1 laboratory scale monochromatic wave trains onto simple slopes 2 10 100 m monochromatic wave trains onto simple slopes 3 10 100 m monochromatic wave trains onto a compound slope representing a typical bathymetric profile of the pacific coast of north america 4 time variable scaled trains generated by the collapse of an impact cavity in deep water onto simple slopes and 5 full amplitude trains onto the pacific coast profile for the last case we also investigated the effects of bottom friction on the run up for all cases we compare our results with the so called irribaren scaling the relative run up r h0 s h0 l0 1 2 where the run up is r h0 is the deep water waveheight l0 is the deep water wavelength s is the slope and is a dimensionless quantity known as the irribaren number our results suggest that irribaren scaling breaks down for shallow slopes s 0 01 when 0 1 0 2 below which r h0 is approximately constant this regime corresponds to steep waves and very shallow slopes which are the most relevant for impact tsunami but also the most difficult to access experimentally

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

a numerical study of the run up generated by three dimensional landslides 1 a large set of numerical experiments are designed to examine the maximum run up generated by three dimensional 3 d submerged and subaerial solid body landslides a depth integrated numerical model is utilized allowing for the efficient simulation of landslides in shallow and intermediate water six dimensionless parameters are introduced the slide thickness the slide wave number a slide shape parameter the horizontal aspect ratio of the slide the specific gravity of the slide mass and the slope of the beach six sets of simulations are first presented wherein one of the six dimensionless parameters are singularly varied this allows for the identification of parameter dependence on maximum run up after combining the dependencies a number of relationships appear most notably a very clear division between the near and far field is observed where here the far field is defined as the region displaced from the projection of the landslide on the nearby beach where edge waves may dominate the wave pattern for submerged slides a nondimensional estimation of the maximum run up just landward of the slide is found as well as the location and magnitude of the secondary run up peak this secondary peak is due to the propagation of edge waves and is in some cases larger than the peak immediately landward of the slide the results presented in this paper may be useful for preliminary hazard assessment where a simple and quick estimation of the maximum run up height and locations are required additionally the formulas developed will be particularly beneficial to those developing 3 d landslide experiments

scaling and reproducibility of craters produced at the experimental projectile impact chamber epic centro de astrobiologia spain the experimental projectile impact chamber epic is a specially designed facility for the study of processes related to wet target e g marine impacts it consists of a 7 m wide funnel shaped test bed and a 20 5 mm caliber compressed n2 gas gun the target can be unconsolidated or liquid the gas gun can launch 20 mm projectiles of various solid materials under ambient atmospheric pressure and at various angles from the horizontal to test the functionality and quality of obtained results by epic impacts were performed into dry beach sand targets with two different projectile materials ceramic al2o3 max velocity 290 m s 1 and delrin max velocity 410 m s 1 23 shots used a quarter space setting 19 normal 4 at 53 from horizontal and 14 were in a half space setting 13 normal 1 at 53 the experiments were compared with numerical simulations using the isale code differences were seen between the nondisruptive al2o3 ceramic and the disruptive delrin polymer projectiles in transient crater development all final crater dimensions when plotted in scaled form agree reasonably well with the results of other studies of impacts into granular materials we also successfully validated numerical models of vertical and oblique impacts in sand against the experimental results as well as demonstrated that the epic quarter space experiments are a reasonable approximation for half space experiments altogether the combined evaluation of experiments and numerical simulations support the usefulness of the epic in impact cratering studies

complex craters relationship of stratigraphy and rings to impact conditions one of the key issues associated with the understanding of large scale impacts is how the observable complex crater structural features e g central peaks and pits flat floors ring shaped ridges and depressions stratigraphic modifications and faults relate to the impactor s parameters e g radius velocity and density and the nonobservable transient crater measures e g depth of penetration and diameter at maximum penetration we have numerically modeled large scale impacts on planets for a range of impactor parameters gravity and planetary material strengths from these we found that the collapse of the transient cavity results in the development of a tall transient central peak that oscillates and drives surface waves that are arrested by the balance between gravitational forces and planetary strength to produce a wide range of the observed surface features in addition we found that the underlying stratigraphy is inverted outside of the transient cavity diameter overturned flap region but not inside this change in stratigraphy is observable by remote sensing drilling seismic imaging and gravity mapping techniques we used the above results to develop scaling laws and to make estimates of the impact parameters for the chicxulub impact and also compared the calculated stratigraphic profile with the internal structure model developed by hildebrand et al 1998 using gravity seismic and other field data for a stratigraphy rotation diameter of 90 km the maximum depth of penetration is 43 km the impactor diameter was also calculated from the scaling relationships we get for a 2 7 g cm 3 asteroid impacting at 20 km s or a 1 0 g cm 3 comet impacting at 40 km s an impactor diameter of 13 km and for a comet impacting at 60 km s an impactor diameter of 10 km

field survey and numerical simulations a review of the 1998 papua new guinea tsunami the papua new guinea png tsunami of 1998 is re examined through a detailed review of the field survey as well as numerous numerical computations the discussion of the field survey explores a number of possible misinterpretations of the recorded data the survey data are then employed by a numerical model as a validation tool a boussinesq model and a nonlinear shallow water wave nlsw model are compared in order to quantify the effect of frequency dispersion on the landslide generated tsunami the numerical comparisons indicate that the nlsw model is a poor estimator of offshore wave heights however due to what appears to be depth limited breaking seaward of sissano spit both numerical models are in agreement in the prediction of maximum water elevations at the overtopped spit by comparing three different hot start initial profiles of the tsunami wave it is shown that the initial shape and orientation of the tsunami wave is secondary to the initial displaced water mass in regard to prediction of water elevations on the spit these numerical results indicate that agreement between numerical prediction of runup values with field recorded values at png cannot be used to validate either a nlsw tsunami propagation model or a specific landslide tsunami hot start initial condition finally with the use of traditional tsunami codes a new interpretation of the png runup measurements is presented

characteristics of oceanic impact induced large water waves re evaluation of the tsunami hazard the potential hazard of a meteorite impact in the ocean is controversial with respect to the destructive power of generated large ocean waves tsunamis we used numerical modeling of hypervelocity impact to investigate the generation mechanism and the characteristics of the resulting waves up to a distance of 100150 projectile radii the wave signal is primarily controlled by the ratio between projectile diameter and water depth and can be roughly classified into deep water and shallow water impacts in the latter the collapse of the crater rim results in a wave signal similar to solitary waves which propagate and decay in agreement with shallow water wave theory the much more likely scenario for an asteroid impact on earth is a relatively small body much smaller than the water depth striking the deep sea in this case the collapse of the transient crater results in a significantly different and much more complex wave signal that is characterized by strong nonlinear behavior we found that such waves decay much more rapidly than previously assumed and cannot be treated as long waves for this reason the shallow water theory is not applicable for the computation of wave propagation and more complex models full solution of the boussinesq equations are required

impact of a cosmic body into earth s ocean and the generation of large tsunami waves insight from numerical modeling 1 the strike of a cosmic body into a marine environment differs in several respects from impact on land oceans cover approximately 70 of the earth s surface implying not only that oceanic impact is a very likely scenario for future impacts but also that most impacts in earth s history must have happened in marine environments therefore the study of oceanic impact is imperative in two respects 1 to quantify the hazard posed by future oceanic impacts including the potential threat of large impact generated tsunami like waves and 2 to reconstruct earth s impact record by accounting for the large number of potentially undiscovered crater structures in the ocean crust reconstruction of the impact record is of crucial importance both for assessing the frequency of collision events in the past and for better predicting the probability of future impact we summarize the advances in the study of oceanic impact over the last decades and focus in particular on how numerical models have improved our understanding of cratering in the oceanic environment and the generation of waves by impact we focus on insight gleaned from numerical modeling studies into the deceleration of the projectile by the water cratering of the ocean floor the late stage modification of the crater due to gravitational collapse and water resurge furthermore we discuss the generation and propagation of large tsunami like waves as a result of a strike of a cosmic body in marine environments

when a cosmic impact strikes the sea bed most bolides that collide with the earth hit the sea limited knowledge about marine target impacts hampers predictions about their perilousness this study presents geological features that are particular to craters formed at sea the features are most likely a result of the influence of the target on the cratering process marine target craters form only if the target sea is shallow enough to admit sufficient kinetic energy into the sea bed when the crater diameter is large compared to the water depth the crater resembles its counterparts that are formed on land craters formed in deeper water are concentric and often lack melt sheets and rim walls but have deposits and radial gullies formed by the resurge of the sea impacts on the deep shelf are probably much more energetic than is suggested by the dimensions of the preserved crater

radiatively driven convection in ice covered lakes observations scaling and a mixed layer model penetrative convection is discussed where the instability is driven by radiative heating of water below the temperature of maximum density convection of this type occurs in ice covered freshwater lakes in late spring when the snow cover vanishes and solar radiation is absorbed beneath the ice cover the vertical temperature structure bulk mixed layer scaling and mixed layer deepening are examined for a number of temperate and polar lakes a bulk mixed layer scaling for this type of convection is based on energy arguments underlying the classical deardorff convective scaling the depth of the convective layer serves as an appropriate length scale however a modified scale that takes account of the energetics of a distributed radiation source term replaces the surface buoyancy flux velocity scale used by deardorff the scaling compares favorably with large eddy simulations of turbulence kinetic energy tke and with both observations and large eddy simulations of the tke dissipation rate mixed layer deepening is simulated with a model of convection beneath lake ice the model describes the structure of the stably stratified layer just beneath the ice with a stationary solution to the heat transfer equation the structure of the entrainment layer is parameterized with a zero order jump approach the entrainment equation is derived from the mixed layer tke budget and bulk mixed layer scaling entrainment regimes characteristic of convection beneath ice are analyzed it is shown that if the deardorff convective velocity scale is replaced with a scale incorporating the distributed buoyancy flux the entrainment equation describing atmospheric and oceanic convective boundary layers also applies beneath the ice model predictions compare well with data from observations in a number of lakes we propose and compare with observations an extension of the mixed layer model that allows for the inclusion of salinity although the salt concentration is low in most temperate and polar lakes its dynamical effect can be significant close to the temperature of maximum density less

formation of resurge gullies at impacts at sea the lockne crater sweden the lockne crater in sweden is a marine target crater formed in a shelf sea approximately 460 ma ago the crater structure consists of an inner crater surrounded by an outer inclined surface that extends to almost 12 km from the center marine craters differ in several respects from craters formed on land one special feature is the formation of resurge gullies excavated by the erosional force of the resurging sea water after the impact the formation of these gullies strongly depends on the ratio crater rim height to water depth as well as on the size of the impact structure such gullies are known from very few marine target craters at the lockne impact site four gullies are identified each of which cuts radially through the rim of the outer crater the rapid collapse of that part of the crater cavity which formed in the seawater resulted in forceful flooding of the crater the resurging seawater not only contained fallback ejecta on its way towards the cavity on the sea bottom it incorporated fractured lithologies from the sea bottom as well this entrained material disintegrated during transport and constitutes today the dominantly monomict lower part of the resurge sequence the resurge flood was highly turbulent highly erosive and developed to a probable hyperconcentrated flow or a possible water flood the erosion in the gullies proceeded as headward erosion down to the transition zone between the brecciated and the less disintegrated crystalline basement

constraining the characteristics of tsunami waves from deformable submarine slides as a marine hazard submarine slope failures have the potential to directly destroy offshore infrastructure and if a tsunami is generated it also endangers the life of those who live and work at the coastline the hazard and risk from tsunamis generated by submarine mass failure is difficult to quantify and evaluate due to the problems to constrain the characteristics of the triggered submarine landslide which introduces unquantifiable uncertainty to hazard assessments based on numerical modelling to lower the uncertainty we present a method that determines material parameters for the slide body to constrain the generated tsunami waves our method employs the distribution of landslide run out masses and their comparison with simulations it assumes that the slide material can be approximated by bulk values during the slide motion to demonstrate our method we make use of valdes slide run out masses off the chilean coast

thermal structure and water ice heat transfer in a shallow ice covered thermokarst lake in central qinghai tibet plateau abstract a large number of lakes and ponds are unevenly distributed over the qinghai tibet plateau qtp little is known about their ice processes and thermal regimes seasonal ice mass balance thermal regime and stratification of under ice water were investigated in a shallow thermokarst lake in central qtp using in situ observations and global reanalysis data congelation ice grew to 60 70 cm depth while continuous surface sublimation caused a total ice loss of over 30 cm the bulk lake temperature below ice remained above 3 0 c through the ice freezing period and rose gradually up to 7 9 c during the melting period the vertical thermal structure of under ice water consisted of a stable strongly stratified interfacial layer il and an underlying convective layer reaching the lake bottom a warm layer existed just beneath the il since the middle equilibrium period and increased in thickness and temperature there was seasonal variation of il depth and temperature gradient in response to the ice thermodynamics and atmospheric conditions the calculated daily water ice heat flux fw was of 10 w m 2 magnitude seasonal variation of fw manifested both diffusive and convective heat transport to the ice water interface this study suggests that strong penetration of solar radiative flux is the dominant contributor to high fw which results in a relatively thin ice compared with other equivalent high latitude climate

multiyear sea ice thermal regimes and oceanic heat flux derived from an ice mass balance buoy in the arctic ocean the conductive and oceanic heat fluxes and the mass balance of sea ice were investigated utilizing an ice mass balance buoy imb deployed in the arctic ocean after imb deployment the ice thinned from 1 95 m in late august to 1 46 m by mid october 2008 from then on ice growth until mid june 2009 increased the ice thickness to 3 12 m the ice temperature and consequently the conductive heat flux at the ice surface exhibited persistent high frequency variations due to diurnal and synoptic scale atmospheric forcing these signals propagated downward with damped magnitude and temporal lag the competition of oceanic and conductive heat flux dominated the low frequency variations of ice growth however high frequency variations in ice growth were controlled largely by the oceanic heat flux from mid november 2008 to mid june 2009 the average oceanic heat flux along a track from 86 2 n 115 2 w to 84 6 n 33 9 w was 7 1 w m2 this was in agreement with that derived from an imb deployed in 2005 about 1 5 to the north of our buoy we attributed the relatively high oceanic heat flux 10 15 w m2 observed during autumn and early winter to summer warming of the surface ocean upward mixing of warm deep water as observed when our buoy drifted over the shallow region of the lomonosov ridge 85 4 85 9 n 52 2 66 4 w demonstrated the impact of bathymetry on the oceanic heat flux under ice cover and consequently on the basal ice mass balance 2013 american geophysical union all rights reserved

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

10be content in clasts from fallout suevitic breccia in drill cores from the bosumtwi impact crater ghana clues to preimpact target distribution rocks from drill cores lb 07a crater fill and lb 08a central uplift into the bosumtwi impact crater ghana were analyzed for the presence of the cosmogenic radionuclide 10be the aim of the study was to determine the extent to which target rocks of various depths were mixed during the formation of the crater filling breccia and also to detect meteoric water infiltration within the impactite layer 10be abundances above background were found in two out of 24 samples from the lb 07a core and in none of five samples from the lb 08a core after excluding other possible explanations for an elevated 10be signal we conclude that it is most probably due to a preimpact origin of those clasts from target rocks close to the surface our results suggest that in crater breccias were well mixed during the impact cratering process in addition the lack of a 10be signal within the rocks located very close to the lake sediment impactite boundary suggests that infiltration of meteoric water below the postimpact crater floor was limited this may suggest that the infiltration of the meteoric water within the crater takes place not through the aerial pore space but rather through a localized system of fractures

how big was the chesapeake bay impact insight from numerical modeling the chesapeake bay impact structure virginia is the largest impact crater in the united states the important question of how large the impactor was that formed the crater remains unanswered this is primarily due to peculiarities of the crater structure revealed by seismic exploration that complicate comparisons with other terrestrial and extraterrestrial craters one potential explanation for the unusual structure of the chesapeake bay crater is that the cratering process was affected by rheologic variations in the target at the time of impact using numerical modeling we find that for a sufficient contrast in material strength between the sedimentary and crystalline units at the chesapeake bay impact site we can produce a model of the final crater that is consistent with observational constraints and hence we can infer the energy released during the impact 1 75 3 10 6 mt in the absence of target strength variations the final crater diameter is likely to have been 40 km rather than the observed 80 90 km

current aligned dewatering sheets and enhanced primary current lineation in turbidite sandstones of the marnoso arenacea formation turbidite sandstones of the miocene marnoso arenacea formation northern apennines italy display centimetre to decimetre long straight to gently curved 0 5 to 2 0 cm regularly spaced lineations on depositional stratification planes sometimes these lineations are the planform expression of sheet structures seen as millimetre to centimetre long vertical pillars in profile both occur in the middle and upper parts of medium grained and fine grained sandstone beds composed of crude to well defined stratified facies including corrugated hummocky like convolute dish structured and dune stratification and are aligned sub parallel to palaeoflow direction as determined from sole marks often in the same beds outcrops lack a tectonic related fabric and therefore these structures may be confidently interpreted to be sedimentary in origin lineations resemble primary current lineation formed by the action of turbulence during bedload transport under upper stage plane bed conditions however they typically display a larger spacing and micro topography compared to classic primary current lineation and are not associated with planar parallel finely laminated sandstones this type of enhanced lineation is interpreted to develop by the same process as primary current lineation but under relatively high near bed sediment concentrations and suspended load fallout rates as supported by laboratory experiments and host facies characteristics sheets are interpreted to be dewatering structures and their alignment to palaeoflow only noted in several other outcrops previously inferred to be a function of vertical water escape following the primary depositional grain fabric for the marnoso arenacea beds sheet orientation may be genetically linked to the enhanced primary current lineation structures current aligned lineation and sheet structures can be used as palaeoflow indicators although the directional significance of sheets needs to be independently confirmed these indicators also aid the interpretation of dewatered sandstones suggesting sedimentation under a traction dominated depositional flow with a discrete interface between the aggrading deposit and the flow as opposed to under higher concentration grain or hindered settling dominated regimes

observation and simulation of lake air heat and water transfer processes in a high altitude shallow lake on the tibetan plateau lakes are an important part of the landscape on the tibetan plateau most of the plateau lakes area has been expanding in recent years but lake atmosphere energy and water interaction is poorly understood because of a lack of observational data and adequate modeling systems based on the eddy covariance observation over a high altitude shallow and small lake the small nam co lake during an ice free period from 10 april to 30 august 2012 this study analyzes the lake air heat and water vapor turbulent transfer processes and evaluates two popular lake air exchange models a bulk aerodynamic transfer model b model and a multilayer model m model our main results are as follows 1 observations show that the bulk transfer coefficient ce and roughness length zoq for water are higher than those for heat ch and z0h especially under low wind speed 2 both models underestimate turbulent fluxes due to inaccurate values of the charnock coefficient and the roughness reynolds number rr which are both important parameters for calculating the roughness length for momentum z0m over water 3 within a reasonable range of 0 013 0 035 for rough flow and rr for smooth flow rr 0 11 are 0 031 and 0 54 respectively by our observation the wave pattern of shorter wavelength gives a larger z0m in the small and shallow lake and 4 the b model and the m model gave consistent results and both models are more suitable for simulation of turbulent flux exchange after z0m optimization

the verification of millennial scale monsoon water vapor transport channel in northwest china summary long term changes of the asian summer monsoon water vapor transport play a pivotal role in the variability of monsoon precipitation paleo climate simulations have shown that there is an important monsoon vapor transport channel in western china previous studies mostly focused on the correlation between monsoon precipitation and intensity little research has been done on the verification of the water vapor channel compared with speleothem and lacustrine systems the hydrological cycle of land surface sediments is more directly related to the monsoon water vapor in this study we used carbonate 18 o and organic matter 13 c of the surface eolian sediments from the piedmont of the northern qilian mountains to verify the monsoon water vapor on the holocene millennial scale two surface sedimentary sections were selected to study paleo monsoon water vapor transport proxy data including carbonate 18 o and organic matter 13 c of surface eolian sediments as well as total organic matter and carbonate content were obtained from the two eolian sections we also synthesized transient simulations of the ccsm3 and the kiel climate models the pmip 3 0 project and trace isotopic simulations were also compared with the reconstructed monsoon water vapor transport our findings indicate that the strength of the holocene asian summer monsoon is consistent with the water vapor transport in western china that has significant impacts to long term monsoon precipitation in northern china this study verifies a significant millennial scale correlation between the monsoon strength and monsoon water vapor transport intensity along the eastern qinghai tibet plateau

ice processes and surface ablation in a shallow thermokarst lake in the central qinghai tibetan plateau the qinghai tibetan plateau qtp is characterized by a cold climate and a large number of lakes the long ice season necessitates study of the widespread ice covers in the region an unprecedented multidisciplinary field campaign was conducted on lake ice processes in the central qtp during the period 2019 13 the study lake generally froze up in late october or early november and broke up in mid or late april with a maximum ice thickness of 50 70 cm the mass balances at both ice surface and bottom were measured continuously significant ice surface sublimation ablation was detected and accounted for up to 40 of the whole ice thickness over the ice season a simple heat transfer model was developed for the surface ice loss the calculated values were in good agreement with the observations they also indicated that atmospheric conditions including low air humidity and prevailing strong winds are the primary drivers of the ice surface sublimation

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

numerical modelling of generation propagation and run up of tsunamis caused by oceanic impacts model strategy and technical solutions summary hypervelocity impacts of asteroids in marine environments produce tsunami waves independent of the water depth and the diameter of the projectile however the characteristics of the induced waves are affected by these parameters we present a model consisting of the wellknown sale impact model and a non linear wave propagation model to study the generation and subsequent spread out of the initial wave pattern caused by the strike of an asteroid or comet in the ocean the numerical simulation of oceanic impacts requires some changes and extensions to the original sale code especially the handling of different materials water and solid rocks is crucial as they are involved in the cratering process for the simulation of the propagation of tsunami waves that are generated by the impact process we use a newly developed wave propagation model which is based on the non linear shallow water theory with boundary conditions derived from the impact model the run up of the tsunami wave on the coastline is implemented as a special case of reflection and is realized by the wellestablished most code besides the model description we exemplify the capability of our modelling scheme by the simulation of the strike of an asteroid 800 m in diameter on a 5000 m deep ocean at 10 2 km s 1 the subsequent propagation of the induced tsunami waves over an artificial bathymetry and the run up of the wave on the coast

tsunami backwash deposits with chicxulub impact ejecta and dinosaur remains from the cretaceous palaeogene boundary in the la popa basin mexico the la popa basin in north eastern mexico features outstanding continuous three dimensional exposures of the cretaceous palaeogene boundary event deposit in shallow shelf environments pierced by salt stocks in the area to the south east of the el papalote diapir the cretaceous palaeogene deposit consists of two superimposed sedimentary units and erosively overlies upper maastrichtian sand siltstones with soft sediment deformation and liquefaction structures the basal unit 1 is an up to 8 m thick chaotic carbonate rich bed that discontinuously fills incised gutters and channels besides abundant silicic and carbonate ejecta spherules from the chicxulub impact unit 1 includes large sandstone boulders and abundant shallow water debris for example mud clasts algae bivalve shells gastropod shells and vertebrate remains unit 1 is conformably overlain by unit 2 distal to the diapir unit 2 consists of a centimetre to decimetre thick conglomeratic coarse bioclast and spherule bearing sandstone bed closer to the diapir unit 2 becomes a metre thick series of four to eight conglomeratic to fine grained graded sandstone beds rich in shell debris and ejecta spherules unit 2 is conformably overlain by structureless to parallel laminated sandstone beds that may mark the return to the pre event depositional regime the sedimentary characteristics of the cretaceous palaeogene deposit including its erosive base its sheet like geometry the presence of multiple graded beds evidence for upper flow regime conditions and the absence of bioturbation support an origin by a short term multiphase depositional event the occurrence of soft sediment deformation structures for example liquefaction below the cretaceous palaeogene deposit suggests that earthquakes were the first to occur at la popa then shelf collapse and strong backflow from the first tsunami waves may have triggered erosion and deposition by violent ejecta rich hyperconcentrated density flows unit 1 subsequently a series of concentrated density flows resulting from tsunami backwash surges may have deposited the multiple graded bedding structures of unit 2 the specific depositional sequence and the fe mg rich as well as si k rich composition of the ejecta spherules both provide a critical link to the well known deep marine cretaceous palaeogene boundary sites in the adjacent burgos basin in north eastern mexico moreover the pulse like input of chicxulub ejecta material at the base of the event deposit allows for correlation with other cretaceous palaeogene boundary sites in the gulf of mexico and the atlantic as well as in central and northern america the presence of diverse dinosaur and mosasur bones and teeth in the event deposit is the first observation of such remains together with chicxulub ejecta material these findings indicate that dinosaurs lived in the area during the latest maastrichtian and suggest that the tsunami waves not only eroded deltas and estuaries but the coastal plain as well

what is a mega tsunami abstract no unambiguous and widely accepted definition currently exists for the term mega tsunami this is in spite of the rapidly growing popularity of the expression in the scientific literature especially in recent years following the devastation wrought by the 2004 indian ocean and 2011 tohoku oki tsunamis a comprehensive literature search is revealing we find that although there have been several previous attempts at a definition the term mega tsunami has generally been applied in a rather arbitrary fashion to a number of tsunami characteristics such as wave height or amplitude at both source and distant locations run up height geographical extent and impact this haphazard situation is undesirable in response we propose a stricter definition for mega tsunami that is based solely on initial wave height amplitude at source exceeding 100 m 50 m respectively a source related definition conveniently avoids any difficulties associated with the potential influence of coastal physical attributes e g configuration bathymetry geomorphology on tsunami parameters at affected locations using this definition it becomes apparent that mega tsunamis can only include those rare events on geological timescales generated by large bolide impacts violent volcanic activity or oceanic island flank collapse and possibly extreme tsunamigenic submarine earthquakes most seismically triggered events instead fall into the group of souteigai tsunamis i e unexpected tsunamis which are considered exceptional according to historical experience and local perspectives

a crater and its ejecta an interpretation of deep impact we apply recently updated scaling laws for impact cratering and ejecta to interpret observations of the deep impact event an important question is whether the cratering event was gravity or strength dominated the answer gives important clues about the properties of the surface material of tempel 1 gravity scaling was assumed in pre event calculations and has been asserted in initial studies of the mission results because the gravity field of tempel 1 is extremely weak a gravity dominated event necessarily implies a surface with essentially zero strength the conclusion of gravity scaling was based mainly on the interpretation that the impact ejecta plume remained attached to the comet during its evolution we address that feature here and conclude that even strength dominated craters would result in a plume that appeared to remain attached to the surface we then calculate the plume characteristics from scaling laws for a variety of material types and for gravity and strength dominated cases we find that no model of cratering alone can match the reported observation of plume mass and brightness history instead comet like acceleration mechanisms such as expanding vapor clouds are required to move the ejected mass to the far field in a few hour time frame with such mechanisms and to within the large uncertainties either gravity or strength craters can provide the levels of estimated observed mass thus the observations are unlikely to answer the questions about the mechanical nature of the tempel 1 surface

basin scale circulation and heat fluxes in ice covered lakes a field and theoretical study of the mean circulation patterns gravity currents and heat fluxes in a mid latitude ice covered lake is presented thermistor chains captured the lake wide pressure gradients and thermal regime acoustic instruments measured bottom and interior velocities and a sediment temperature probe measured sediment temperatures and heat fluxes typical rossby numbers showed that the mean circulation was geostrophic in the form of either an anti cyclonic or a cyclonic basin scale gyre each gyre reached a steady state after 10 15 d circulating at a maximum velocity of 1 mm s 1 the gyres persisted throughout most of the winter and generally decayed with time the cyclonic gyre was generated by the lateral temperature gradients created by sediment heat release it was not possible to determine the driver of the anti cyclonic gyre because most ice covered lakes are controlled by the earth s rotation anti cyclonic and cyclonic circulation is postulated as being the most common mean interior flow pattern the horizontal heat fluxes were of the same order as the vertical heat fluxes which is consistent with the findings of previous research the sediment heat flux decayed with time stabilizing after 60 d a scaling analysis of down sloping advection with dynamic seasonal scale temperatures showed that a warmer lake and an increase in the length to depth geometric aspect ratio both within a given lake and an increase in lake size all increased advection time scales and therefore circulation time scales near the boundaries

interannual variations in the hydrothermal regime around a thermokarst lake in beiluhe qinghai tibet plateau abstract thermokarst is a term associated with the thaw of ice rich permafrost and the resulting formation of irregular depressions in the landscape from thaw settlement thermokarst lakes may subsequently develop from ponds formed in depressions these lakes commonly have collapsing shorelines and the development of thermokarst terrain and associated thermal erosion may significantly influence the stability of infrastructure and the hydrothermal conditions of the surrounding permafrost in this study we examined interannual variations in the hydrothermal regime of a thermokarst lake in beiluhe basin based on field data measured in 2006 2013 the timing and nature of lake ice growth and melt were recorded we observed considerable seasonal differences in lake water level 0 5 m and differences in water level between the lake and the water table in the surrounding ground over 1 0 m the nearly saturated ground at the lakeshore 35 in maximum volumetric water content highlights the seepage effect from the lake to the surrounding ground the vertical temperature profile from 2 m air to 2 m lake bottom and to 60 m depth in the ground was measured the annual mean air temperature lake surface temperature and annual mean lake bottom temperature in 2010 2011 were approximately 3 6 0 4 and 5 c respectively the thermal offsets between the air and the lake surface and between the lake surface and lake bottom were 3 and 7 c respectively the annual mean lake bottom temperatures ranged from 2 3 to 6 9 c at water depths from 1 2 to 2 1 m the asymmetry of the bathymetry has resulted in distinct thermal regimes beneath the lake bottom in different locations a through talik was present at the deepest side of the lake but some permafrost extended laterally beneath the lake bottom at the shallower side forming an hourglass shape in cross section at one end lateral thermal erosion along the lakeshore was linked to the lake bottom temperature and lake depth variation in permafrost table depth from the lake center to the lakeshore was greater on the east side near deeper water 2 m than at the west side where water was shallower 70 cm the results from this study have highlighted the hydrothermal relations between thermokarst lake development and permafrost conditions

field investigation of winter thermo and hydrodynamics in a small karelian lake during late winter 18 march 7 april 1994 temperature and current measurements were made in lake vendyurskoe russia including three surveys at six cross sections of the lake also the temperature profile evolution was registered with two thermistor chains at two stations bottom depths of 7 6 and 11 5 m until the time of ice breakup temperature gradients were measured just below the ice cover and in the upper 1 ocm layer of the bottom sediments the isotherms were found to be almost horizontal and evenly spaced vl rtically so no conditions for largescale density induced currents existed the heat flux from sediments to water ranged from 0 6 to 2 0 w m 2 these values were inversely related to the depth the heat flux from water to ice ranged from 0 7 to 1 2 w rn2 when water heating from solar radiation penetration became apparent this flux increased by a factor of two when solar radiation increased convection occurred in the upper layers of the water column when solar radiation heating became significant at the beginning of spring the average net heat flux at the ice water interface during daytime was 7 7 w m 2 weak currents few mm s l with a seiche like character were observed which most likely resulted from ice cover oscillations winter thermo and hydrodynamics in dimictic lakes have only been sparsely studied and are far from being well understood because dimictic lakes can be ice covered for several months the influences of water temperature currents and mixing during this period play an important role for the water quality and ecological state of the lake the dynamic processes are different when the lake is ice covered than when it is not thermal regime the thermal regime is rather stable during winter having small horizontal temperature differences the vertical temperature structure has a continuous increase from 0 c at the ice water interface to 4 c and higher in the bottom layers hutchinson 1957

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

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

efficient disruption of small asteroids by earth s atmosphere accurate modelling of the interaction between the atmosphere and an incoming bolide is a complex task but crucial to determining the fraction of small asteroids that actually hit the earth s surface most semi analytical approaches have simplified the problem by considering the impactor as a strengthless liquid like object pancake models1 2 but recently a more realistic model has been developed that calculates motion aerodynamic loading and ablation for each separate particle or fragment in a disrupted impactor3 4 here we report the results of a large number of simulations in which we use both models to develop a statistical picture of atmosphere bolide interaction for iron and stony objects with initial diameters up to 1 km we show that the separated fragments model predicts the total atmospheric disruption of much larger stony bodies than previously thought in addition our data set of 1 000 simulated impacts combined with the known pre atmospheric flux of asteroids with diameters less than 1 km5 6 7 8 9 10 11 12 elucidates the flux of small bolides at the earth s surface we estimate that bodies 220 m in diameter will impact every 170 000 years

the global reach of the 26 december 2004 sumatra tsunami numerical model simulations combined with tide gauge and satellite altimetry data reveal that wave amplitudes directionality and global propagation patterns of the 26 december 2004 sumatra tsunami were primarily determined by the orientation and intensity of the offshore seismic line source and subsequently by the trapping effect of mid ocean ridge topographic waveguides

physics of crustal fracturing and chert dike formation triggered by asteroid impact 3 26 ga barberton greenstone belt south africa archean asteroid impacts reflected in the presence of spherule beds in the 3 2 3 5 ga barberton greenstone belt bgb south africa generated extreme seismic waves spherule bed s2 provides a field example it locally lies at the contact between the onverwacht and fig tree groups in the bgb which formed as a result of the impact of asteroid possibly 50 km diameter scaling calculations indicate that very strong seismic waves traveled several crater diameters from the impact site where they widely damaged onverwacht rocks over much of the bgb lithified sediments near the top of the onverwacht group failed with opening mode fractures the underlying volcanic sequence then failed with normal faults and opening mode fractures surficial unlithified sediments liquefied and behaved as a fluid these liquefied sediments and some impact produced spherules filled near surface fractures today represented by swarms of chert dikes strong impact related tsunamis then swept the seafloor p waves and rayleigh waves from the impact greatly exceeded the amplitudes of typical earthquake waves the duration of extreme shaking was also far longer probably hundreds of seconds than that from strong earthquakes dynamic strains of 10 3 occurred from the surface and downward throughout the lithosphere shaking weakened the onverwacht volcanic edifice and the surface layers locally moved downhill from gravity accommodated by faults and open mode fractures coast parallel opening mode fractures on the fore arc coast of chile formed as a result of megathrust events are the closest modern analogs it is even conceivable that dynamic stresses throughout the lithosphere initiated subduction beneath the onverwacht rocks

motion of a fragmented meteoroid through the planetary atmosphere meteor observations and crater field investigations support the view that some meteoroids undergo fragmentation into a finite number of splinters which move a long distance without further disruption the motion of these fragments cannot be described in the frame of liquid like models the primary purpose of this study is to achieve some success in improving the alternative model of separate fragments which is based on studying the motion of a finite number of fragments interacting with each other through the air pressure the three dimensional 3 d numerical technique is elaborated for the direct modeling of the flow around several arbitrarily arranged fragments the model allows us to calculate the ablation mass rate and aerodynamic loading for each fragment the new approach hybrid model based on the simultaneous solution of the 3 d hydrodynamic equations for the airflow and the differential equations for the motion of discrete particles is proposed to study the debris cloud evolution taking into account successive fragmentation the simplified version of this model was applied to the sikhote alin meteorite shower benesov bolide and small meteoroids impacts against the martian surface

the role of shortwave radiation in the summer decay of a sea ice cover heat balance models of ice leads and the underlying water column were used to investigate the role of shortwave radiation in the summer decay of a sea ice cover because of the potential importance of positive feedback between decreasing ice concentration and increasing solar input to the ocean particular emphasis was given to the treatment of heat transfer and lateral melting in leads the rate of heat loss to floe edges was calculated from lead temperatures using an empirical boundary layer parameterization coefficients for this parameterization were obtained from field measurements in the dynamically active ice cover of the greenland sea during the 1984 marginal ice zone experiment and in the static ice of mould bay northwest territories field coefficients were found to be considerably larger than those previously obtained in the laboratory suggesting that heat transfer rates near floe edges were controlled more by winds and currents than by local density differences model studies of individual leads indicate that heat losses to the atmosphere cause lateral melt rates to asymptotically approach a constant value as lead size increases thus although very wide leads transmit considerable energy to the underlying ocean they have relatively little effect on lateral melting other results provide information on the relative importance of horizontal heat transfer rates ice thickness floe perimeter atmospheric forcing and oceanic heat flux in general the calculations indicate that much of the shortwave radiation entering the ocean is absorbed below the ice where it contributes to bottom ablation rather than lateral melting this suggests that previous work has seriously overestimated the magnitude of the feedback between ice concentration and incident shortwave radiation

rapid degradation of permafrost underneath waterbodies in tundra landscapes toward a representation of thermokarst in land surface models waterbodies such as lakes and ponds are abundant in vast arctic landscapes and strongly affect the thermal state of the surrounding permafrost in order to gain a better understanding of the impact of small and medium sized waterbodies on permafrost and the formation of thermokarst a land surface model was developed that can represent the vertical and lateral thermal interactions between waterbodies and permafrost the model was validated using temperature measurements from two typical waterbodies located within the lena river delta in northern siberia impact simulations were performed under current climate conditions as well as under a moderate and a strong climate warming scenario the performed simulations demonstrate that small waterbodies can rise the sediment surface temperature by more than 10 c and accelerate permafrost thaw by a factor of between 4 and 5 up to 70 of this additional heat flux into the ground was found to be dissipated into the surrounding permafrost by lateral ground heat flux in the case of small shallow and isolated waterbodies under moderate climate warming the lateral heat flux was found to reduce permafrost degradation underneath waterbodies by a factor of 2 under stronger climatic warming however the lateral heat flux was too small to prevent rapid permafrost degradation the lateral heat flux was also found to strongly impede the formation of thermokarst despite this stabilizing effect our simulations have demonstrated that underneath shallow waterbodies 1 m thermokarst initiation happens 30 to 40 years earlier than in simulations without preexisting waterbody

computer modelling of the water resurge at a marine impact the lockne crater sweden abstract when a cosmic impact occurs at sea the resulting crater can form completely in the water mass or extend into the seafloor at intermediate to great water depths the collapse of the water cavity generates a forceful resurge of water along the seafloor towards the central part of the crater the erosive effects as well as certain conspicuous deposits from resurge flows are known from several craters this study uses numerical modelling to estimate the magnitude of the resurge in the case of the 455 myr old marine target lockne impact crater sweden the water depth at the lockne target site was at least 200 m possibly even as great as 1 km field evidence show that the resurge was strong enough to erode gullies hundreds of metres wide tens of metres deep and kilometres long with computer modelling we studied the behaviour of the flow to get a notion of its magnitude the calculations required simplification of the reality we used a fixed seafloor topography and pure water a rim in the water mass is expected but was neglected in the calculations the simplification likely led to underestimation of the magnitude of the resurge the effect of different target water depths was studied at 200 m target water depth about 1 2 10 11 m 3 of water were needed to fill the lockne crater including the water cavity this took about 2200 s it has been suggested that the main gully formation occurs when the resurge passes the inner rim of the crater that phase lasts for about 700 s with a 500 m target water depth these processes are 3 4 times faster the erosive force of the flow i e unit stream power is 1 9 10 5 wm 2 in the 200 m water depth model this is of the same magnitude as the lake missoula flood the greatest catastrophic flooding known on earth at 500 m target water the unit stream power is a magnitude greater

numerical simulations of the mjolnir marine impact crater 1 the 40 km diameter mjolnir crater in the barents sea was created by a meteoroid impact into a 400 m shallow sea about 142 ma we have used a multimaterial hydrocode with depth depending target strength to model numerically the cratering and early modification stages of the mjolnir impact our models are constrained by the observed crater morphology and structure the best results were obtained for a composite target strength structure very low strength for the upper 3 km of sedimentary rocks and gradual increase from 3 to 6 5 km depth before using strength values typical for granitic rocks at greater depths the low strength of the target sediments at shallow depths led to exceptionally intensive slumping and gravitational collapse of the order of 2 0 2 5 considerably larger than the average expected values for typical terrestrial craters as a result we obtain a crater collapse in between simple and complex where slumping and gravitational collapse counteract the crater floor uplift and lead to suppression and burial of the central high the mjolnir impact in a shallow sea was responsible for a major disturbance of the water column following the impact induced outward water surge large amplitude tsunamis were formed and the rapid resurge of seawater into the excavated crater transported large amounts of ejecta and crater wall material back into the crater accounting for the redestribution of ejecta material and extensive infilling

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

low energy deposition in the chicxulub crater during the impact to post impact transition article i nfo the crater fill units that were deposited during the terminal stages of the formation of the shallow marine chicxulub crater in northern yucatan were interpreted by some authors as products of a catastrophic resurge of water this interpretation contrasts markedly with the dominant sand grain size b300 m and the abundant small scale current cross bedding structures indicative of low energy deposition to solve this discrepancy we applied first principles of physical sedimentology in an analysis of grain size and sedimentary structures to determine current velocities and minimum water depths required to generate the observed sedimentary bedforms we combine this approach with numerical modeling of crater formation in order to explore the dimensions of the ejecta ring wall being formed by a chicxulub impactor in water depths of 1000 m we find that the ejecta wall reaches heights in the order of 1200 m above sea floor and 200 m above sea level it thus prevented the resurge of water into the crater cavity and consequently also the subsequent formation of a collapse wave the ring wall significantly retarded the refilling of the crater cavity with seawater and refilling took place by permeation through and localized erosion of the ring wall this resulted in low energy currents with velocities between 1 5 and 0 18 m s 1 slowly reentering the crater and depositing the cm scale low energy laminated and crossbedded sandy terminal impact deposits

the effect of the oceans on the terrestrial crater size frequency distribution insight from numerical modeling on earth oceanic impacts are twice as likely to occur as continental impacts yet the effect of the oceans has not been previously considered when estimating the terrestrial crater size frequency distribution despite recent progress in understanding the qualitative and quantitative effect of a water layer on the impact process through novel laboratory experiments detailed numerical modeling and interpretation of geological and geophysical data no definitive relationship between impactor properties water depth and final crater diameter exists in this paper we determine the relationship between final and transient crater diameter and the ratio of water depth to impactor diameter using the results of numerical impact models this relationship applies for normal incidence impacts of stoney asteroids into water covered crystalline oceanic crust at a velocity of 15 km s 1 we use these relationships to construct the first estimates of terrestrial crater size frequency distributions over the last 100 million years that take into account the depth area distribution of oceans on earth we find that the oceans reduce the number of craters smaller than 1 km in diameter by about two thirds the number of craters 30 km in diameter by about one third and that for craters larger than 100 km in diameter the oceans have little effect above a diameter of 12 km more craters occur on the ocean floor than on land below this diameter more craters form on land than in the oceans we also estimate that there have been in the region of 150 impact events in the last 100 million years that formed an impact related resurge feature or disturbance on the seafloor instead of a crater

pliocene mass failure deposits mistaken as submarine tsunami backwash sediments an example from hornitos northern chile abstract in this study we question the former interpretation of a shallow marine backwash tsunami origin of a conspicuous pliocene coarse clastic unit at hornitos northern chile and instead argue for a debris flow origin for this unit we exclude a relation to a tsunami in general and to the eltanin impact in particular the observed deposit at hornitos was not generated either directly impact triggered tsunami or indirectly submarine mass flow caused by seismic shaking by an impact re calculation of the alleged impact tsunami including consideration of the van dorn effect shows that an impact in the southern ocean did not cause a significant tsunami at hornitos impact related seismic shaking was not able to trigger slides several thousands of kilometers away because the eltanin event was a deep sea impact that did not create a crater additionally the biostratigraphic age of 5 1 2 8 ma of the associated la portada formation is not concurrent with the newly established age of 2 511 0 07 ma for the eltanin impact instead we argue for an origin of the conspicuous unit at hornitos as a debris flow deposit caused by an earthquake in the andean subduction zone in northern chile our re interpretation considers the local synsedimentary tectonic background a comparison to recent submarine tsunami sediments and recent examples of mass wasting deposits along the chilean margin the increased uplift during the pliocene caused oversteepening of the coastal scarp and entailed a contemporaneous higher frequency of seismic events that triggered slope failures and cliff collapses the coarse clastic unit at hornitos represents an extraordinary potentially tsunami generating mass wasting event that is intercalated with mass wasting deposits on a smaller scale

axisymmetric circulation driven by marginal heating in ice covered lakes below the temperature of maximum density tmd in freshwater lakes heating at the lateral margins produces gravity currents along the bottom slope akin to katabatic winds in the atmosphere and currents on continental shelves we describe axisymmetric basin scale circulation driven by heat flux at the shorelines in polar lake kilpisjarvi a dense underflow originating near the shore converges toward the lake center where it produces warm upwelling and return flow across the bulk of lake water column the return flow being subject to coriolis force creates a lake wide anticyclonic gyre with velocities of 2 4 cm s 1 while warm underflows are common on ice covered lakes the key finding is the basin scale anticyclonic gyre with warm upwelling in the core this circulation mechanism provides a key to understanding transport processes in semi enclosed basins subject to negative buoyancy flux due to heating or cooling at temperatures above tmd at their lateral boundaries

asteroid impact tsunami of 2880 march 16 summary nasa scientists have given a 1 1 km diameter asteroid 1950 da a 0 0 to 0 3 per cent probability of colliding with the earth in the year 2880 this article examines a scenario where 1950 da strikes the sea 600 km east of the united states coast travelling at 17 8 km s 1 the asteroid would blow a cavity 19 km in diameter and as deep as the ocean 5 km at the impact site tsunami waves hundreds of metres high would follow as the transient impact cavity collapses the tsunami disperses quickly but because the waves are so large initially destructive energy carries basin wide within two hours of the scenario impact 100 m waves make landfall from cape cod to cape hatteras within 12 hours 20 m waves arrive in europe and africa water velocity at the deep ocean floor exceeds 1 m s 1 to 800 km distance strong enough to leave a widespread tsunami signature in the sedimentary record

constraints on interpretation of the eltanin impact from numerical simulations the results of numerical simulations of the eltanin impact are combined with the available geological data in order to reconstruct the impact dynamics and to get some constraints on the impact parameters numerical simulations show that the eltanin projectile size should be less than 2 km for a 45 oblique impact and less than 1 5 km for a vertical impact on the other hand we demonstrate that the projectile diameter cannot be considerably smaller than 1 km otherwise the impact induced water flow cannot transport eroded sediments across large distances the maximum displacement approximately equals the water crater radius and rapidly decreases with increasing distances numerical simulations also show that ejecta deposits strongly depend on impact angle and projectile size and therefore cannot be used for reliable estimates of the initial projectile mass the initial amplitudes of tsunami like waves are estimated the presence of clay rich sediments typical for the abyssal basins in cores ps2709 and ps2708 on the freeden seamounts bellingshausen sea southern ocean combined with numerical data allow us to suggest a probable point of impact to the east of the seamounts the results do not exclude the possibility that a crater in the ocean bottom may exist but such a structure has not been found yet

source discriminants for near field tsunamis summary we present numerical simulations of tsunami run up in the near field for a data set of 72 models of sources involving both seismic dislocations and landslides by varying one by one the parameters describing the source and the receiving beach we are able to separate their individual influence on the amplitude and distribution of run up which we characterize by forming several dimensionless parameters principally the ratio i 2 of its maximum amplitude to its lateral extent along the beach we find that i 2 remains less than 10 4 for seismic dislocation sources but is greater than this threshold for all physically realistic models of underwater landslides thus it can be used as a discriminant for the nature of the source of a near field tsunami for seismic dislocations we also consider the ratio i 1 of maximum run up to seismic slip on the fault plane and validate numerically the previously suggested rule of thumb that this ratio cannot be much greater than 1 in the case of underwater landslides we show that the distribution of near field run up is primarily controlled by the 2 d wall of water displaced on the ocean surface as an initial condition to the simulation and is practically independent of its extension in the third dimension perpendicular to the beach we apply this approach to nine profiles of tsunami run up obtained experimentally during recent field surveys and show that our method successfully identifies the 1998 papua new guinea tsunami as having been generated by an underwater landslide thus confirming the results of shipboard and hydroacoustic investigations it also strongly suggests a similar mechanism for the generation of the near field aleutian tsunami of 1946 april 1