morphology and dynamics of explosive vents through cohesive rock formations shallow explosive volcanic processes such as kimberlite volcanism and phreatomagmatic and phreatic activity produce volcanic vents exhibiting a wide variety of morphologies including vertical pipes and v shaped vents in this study we report on experimental and numerical models designed to capture a range of vent morphologies in an eruptive system using dimensional analysis we identified key governing dimensionless parameters in particular the gravitational stress to fluid pressure ratio 2 p gh and the fluid pressure to host rock strength ratio 3 p c we used combined experimental and numerical models to test the effects of these parameters the experiments were used to test the effect of 2 on vent morphology and dynamics a phase diagram demonstrates a separation between two distinct morphologies with vertical structures occurring at high values of 2 and diagonal ones at low values of 2 the numerical simulations were used to test the effect of 3 on vent morphology and dynamics in the numerical models we see three distinct morphologies vertical pipes are produced at high values of 3 diagonal pipes at low values of 3 and horizontal sills at intermediate values of 3 our results show that vertical pipes form by plasticity dominated yielding in high energy systems high 2 and 3 whereas diagonal and horizontal vents dominantly form by fracturing in lower energy systems low 2 and 3 although our models are two dimensional they suggest that circular pipes result from plastic yielding of the host rock in a high energy regime whereas v shaped volcanic vents result from fracturing of the host rock in lower energy systems

traces of the marine mjolnir impact event abstract the sediments of the barents sea region carry geological information reflecting the influence of the mjolnir impact event at the volgian ryazanian boundary even in remote locations without any direct macroscopic geological and paleontological evidence the ejecta distribution in the area was probably highly asymmetrical but geological and related geochemical and paleontological signals in the sediments show the environmental consequences of the impact e g impact generated waves tsunami currents changing redox conditions to be more symmetrically distributed the influences of the asteroid impact are seen in the distributional anomalies ir th u ni cr and prasinophycean algae of the genus leiosphaeridia of studied cores from 30 to 500 km away from the crater a core from about 800 km southwest of the crater carries no obvious direct evidence of the impact this study shows that additional geological parameters other than e g shocked quartz spherules ir anomalies may carry information indicating possible environmental impact influence even more than 10 crater diameters away from the impact site

airburst generated tsunamis this paper examines the questions of whether smaller asteroids that burst in the air over water can generate tsunamis that could pose a threat to distant locations such airburst generated tsunamis are qualitatively different than the more frequently studied earthquake generated tsunamis and differ as well from tsunamis generated by asteroids that strike the ocean numerical simulations are presented using the shallow water equations in several settings demonstrating very little tsunami threat from this scenario a model problem with an explicit solution that demonstrates and explains the same phenomena found in the computations is analyzed we discuss the question of whether compressibility and dispersion are important effects that should be included and show results from a more sophisticated model problem using the linearized euler equations that begins to addresses this

cocorp profiling across the southern oklahoma aulacogen overthrusting of the wichita mountains and compression within the anadarko basin cocorp consortium for continental reflection profiling deep reflection profiles recorded across the wichita mountains and anadarko basin suggest that significant crustal shortening occurred in the final stages of the evolution of the southern oklahoma aulacogen the crystalline rocks of the wichita mountains were thrust in pennsylvanian time northeastward over sedimentary rocks of the anadarko basin along a series of faults with moderate average 30 to 40 and southwesterly dips these faults can be traced possibly as deep as 20 to 24 km listric thrust faults and hanging wall anticlines developed in the sedimentary rocks of the basin these features contrast with conventional interpretations of pennsylvanian structures as the result of predominantly vertical movements along high angle faults and they suggest that pennsylvanian downwarping of the anadarko basin was at least partially due to thrust loading truncations of reflections from cambrian ordovician rocks in the deepest part of the basin suggest normal faulting which would support ideas of an early extensional stage in the aulacogen cycle the distinctive precambrian layering seen on earlier cocorp data recorded south of the wichita mountains cannot be recognized under the anadarko basin and the proterozoic basin containing that layering may have been bounded on its north side by a precambrian fault this inferred fault was probably twice reactivated during formation of the southern oklahoma aulacogen once during late precambrian early cambrian extension and again during pennsylvanian compression the popular view that aulacogens originated from radial rifting of updomed homogeneous continental crust is probably too simplified and a more important constraint on their location and development may be the nature of pre existing lines of weakness

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

impact tsunami eltanin employing classical tsunami theory and elementary assumptions about the initial shape of impact cavities we compute tsunami from the eltanin asteroid collision at 2 15 ma an eltanin impactor 4 km in diameter would have blown an initial cavity as deep as the ocean and 60 km wide into the south pacific and delivered a 200 300 m high tsunami to the antarctic peninsula and the southern tip of south america 1200 1500 km away new zealand 6000 km distant would have met 60 m waves generalizing these results to other size impactors we fit simplified tsunami attenuation laws to maximum tsunami heights extracted from the full wave calculations if eltanin was 1 km in diameter instead of 4 km its waves would have been at least five times smaller an asteroid the size of chicxulub 10 km diameter had it fallen into water deeper than 1000 m would have sent a 100 m tsunami out to 4000 km distance even if shoaling amplifications are neglected r 2002 elsevier science ltd all rights reserved

how did the meers fault scarp form paleoearthquake or aseismic creep a soil mechanical perspective abstract studies confirm that the meers fault in southwestern oklahoma has been active in recent times the most recent movement occurred about 1100 y ago in late holocene there is as much as 5 m vertical and possibly appreciably more left lateral strike slip displacements on the fault during faulting the quaternary soils 1 along the fault were folded as well as ruptured in some places almost all of the deformation is accommodated by ductile folding of the soils having this kind of deformation with no record of an earthquake associated with the meers fault during historical times raises the question whether the present scarp was formed seismically by earthquake event s or aseismically by slow deformation aseismic fault creep to determine how the scarp was formed i have developed a multidisciplinary study which involved geological soil mechanical and soil micromorphological techniques geological mapping delineated the deformation stratigraphy and any features that might be associated with the faulting the mapping was also needed to reconstruct the sequence of events that formed the scarp at the study site consolidation tests using the casagrande 1936 method for finding maximum effective stresses were used to determine the states of stresses imposed on the soil deposits when they were first faulted these states of stresses were then compared to the states of stresses needed to slowly deform or shear the soils in triaxial and direct drained shear tests the direction of maximum principal stress was determined by mohr s circle and soil micromorphological analyses the results of soil mechanical analysis show that the faulting of the quaternary soils along the fault had to be sudden or fast which indicates that the scarp was probably created seismically during faulting the soils were anisotropically consolidated or compacted thereby recording in their structure the states of stresses that caused faulting to occur the direction of the maximum principal horizontal stress is between n62 e and n72 e indicating rotation of principal stress axes the technique developed for this study can be used in similar areas where active faults offset quaternary soils with relatively unchanging moisture contents below some depth also for shallow depths this technique might give more reliable young tectonic stress measurements both magnitude and orientation than other techniques such as overcoring hydraulic fracturing and wellbore breakouts because it is used on geologically recent units which unlike lithified rocks have not yet existed through millions of years of deformation

the mjolnir marine impact crater porosity anomaly abstract we have developed a quantitative model for the porosity change induced by the mjolnir impact using density and seismic traveltime distributions and postimpact sediment deformation compared with the surrounding undisturbed platform sediments the porosity increased immediately after impact up to 6 3 in the collapsed and brecciated crater periphery whereas porosity decreased by 1 in the dense central uplift following impact the crater was progressively buried by a 2 2 5 km thick overburden which caused radially varying differential compaction among the disrupted sedimentary rocks this compaction has significantly affected the postimpact crater evolution and decreased the porosity anomaly to values of 2 5 in the periphery and 2 2 in the center high resolution seismic profiles reveal possible gas related seismic amplitude anomalies spatially related to the 13 33 km3 excess pore space in impact deformed strata along the crater periphery potential plays may include lower to middle jurassic sands structurally trapped by impact generated tilted fault blocks and the synimpact extensively fractured allochthonous breccia however the crater is a very high risk hydrocarbon prospect because reservoir properties may have been destroyed by the deep mesozoic burial followed by large scale cenozoic uplift and erosion nonetheless the mjolnir porosity anomaly provides new data about the postimpact crater deformation similar data are almost entirely absent from the terrestrial impact record

cometary impacts into ocean their recognition and the threshold constraint for biological extinctions the montagnais impact crater is presently the only site in the ocean where the effect of a meteorite fall on marine organisms has been studied the impact crater is 45 km in diameter and was formed at 50 8 ma by a fall of probably an old cometary nucleus 3 4 km in diameter into shallow 600 m ocean comparison of the impact structure and related deposits with those on land shows several major differences of which the most significant is the absence of an elevated crater rim instead the crater perimeter is bevelled and eroded as a consequence of impact induced bottom currents and turbulent return water flow into the excavating cavity by this process most of the fall out breccia is reworked back into the crater cavity where it accumulates in much larger thickness than in impact craters on land at a microscopic scale the shock metamorphism features are about the same as those for land impacts geochemically impacts of comet nucleii may not leave a recognizable signature at the impact horizon except for a minor increase in iridium thus stratigraphic horizons associated with extinctions and or major changes in biota have to be closely examined for other impact indicators like the presence of tectites glass spherules and quartz grains with shock features occurrence of megatsunami wave deposits extensive erosion on continental margins margin failures and faunal mixing above erosional unconformities are other potential impact indicators there is no single indicator that can provide sufficient proof of an impact event such interpretations have to be based on multiparameter studies of global extent since many of the impact indicators are only of regional extent the lack of extinction of any marine plankton genera or of bottom dwellers at the montagnais impact site allows us to place a lower limit for biological extinctions caused by cometary impacts on those with nucleus 4 km in diameter the calculated frequency for a cometary impact which could result in a 10 extinction of marine genera is about 6 10 7 yr 1 and for the k t boundary type of extinctions about 2 10 8 yr 1 even allowing for a large degree of uncertainty in these estimates it is unlikely that the biological extinction events for the last 250 ma identified by sepkoski 1990 could have been all caused by meteorite impacts

calculations of asteroid impacts into deep and shallow water contrary to received opinion ocean impacts of small 500 m asteroids do not produce tsunamis that lead to world wide devastation in fact the most dangerous features of ocean impacts just as for land impacts are the atmospheric effects we present illustrative hydrodynamic calculations of impacts into both deep and shallow seas and draw conclusions from a parameter study in which the size of the impactor and the depth of the sea are varied independently for vertical impacts at 20 km s craters in the seafloor are produced when the water depth is less than about 5 7 times the asteroid diameter both the depth and the diameter of the transient crater scale with the asteroid diameter so the volume of water excavated scales with the asteroid volume about a third of the crater volume is vaporised because the kinetic energy per unit mass of the asteroid is much larger than the latent heat of vaporisation of water the vaporised water carries away a considerable fraction of the impact energy in an explosively expanding blast wave which is responsible for devastating local effects and may affect worldwide climate of the remaining energy a substantial portion is used in the crown splash and the rebound jet that forms as the transient crater collapses the collapse and rebound cycle leads to a propagating wave with a wavelength considerably shorter than classical tsunamis being only about twice the diameter of the transient crater propagation of this wave is hindered somewhat because its amplitude is so large that it breaks in deep water and is strongly affected by the blast wave s perturbation of the atmosphere even if propagation were perfect however the volume of water delivered per metre of shoreline is less than was delivered by the boxing day 2004 tsunami for any impactor smaller than 500 m diameter in an ocean of 5 km depth or less near field effects are dangerous for impactors of diameter 200 m or greater hurricane force winds can extend tens of kilometers from the impact point and fallout from the initial splash can be extremely violent there is some indication that near field effects are more severe if the impact occurs in shallow water

advances in the study of mega tsunamis in the geological record abstract extreme geophysical events such as asteroid impacts and giant landslides can generate mega tsunamis with wave heights considerably higher than those observed for other forms of tsunamis in this paper we review recent advances in the study of mega tsunamis in the geological record focusing on well documented examples that have captured particular attention over the past decade we provide up to date background on the source mechanisms of tsunami generation during asteroid impacts and ocean island landslides which are the largest landslides on earth we also discuss the main sources of uncertainty for modelling such mega tsunamis and for addressing associated hazards

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

two dimensional synthetic seismogram modeling of wide angle seismic data from the wichita uplift oklahoma abstract in conjunction with the 1979 cocorp wichita uplift survey wide angle reflection refraction data were recorded on a fixed array the object of the present study is to model and interpret these wide angle data to add independent constraints on the deep structure of the wichita uplift three common receiver profiles were extracted from the data recording apertures were 3 2 to 23 4 km to the north of the array 4 2 to 14 9 km to the east and 4 2 to 12 6 km to the west these profiles are modeled by iterative fitting of high frequency synthetic seismograms computed by asymptotic ray theory the model derived contains low velocity 2 0 to 2 16 km sec surficial sediments that vary in thickness these account for strong local travel time variations of 0 05 sec and for a small but persistent ghost arrival that follows all the main branches with a delay of 0 2 sec the basement granites rhyolites and gabbros are very near the surface throughout the study area both granite and gabbro outcrops are seen basement p wave velocities are therefore relatively high representative velocities are 4 7 km sec at 0 8 km depth 6 2 at 1 8 6 4 at 2 8 and 6 5 at 4 0 local velocities as high as 7 4 km sec may be present the basement is fairly transparent beneath the wichita uplift with only a few local reflectors present this is consistent with the cocorp results

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

importance of pre impact crustal structure for the asymmetry of the chicxulub impact crater the final geometry of an impact crater can be significantly influenced by the geological and geomorphological structure of the impact site therefore it may not on its own provide accurate information regarding the direction and angle of impact

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

deep drilling into the chesapeake bay impact structure samples from a 1 76 kilometer deep corehole drilled near the center of the late eocene chesapeake bay impact structure virginia usa reveal its geologic hydrologic and biologic history we conducted stratigraphic and petrologic analyses of the cores to elucidate the timing and results of impact melt creation and distribution transient cavity collapse and ocean water resurge comparison of post impact sedimentary sequences inside and outside the structure indicates that compaction of the crater fill influenced long term sedimentation patterns in the mid atlantic region salty connate water of the target remains in the crater fill today where it poses a potential threat to the regional groundwater resource observed depth variations in microbial abundance indicate a complex history of impact related thermal sterilization and habitat modification and subsequent post impact repopulation

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

montagnais a submarine impact structure on the scotian shelf eastern canada the first impact crater in the ocean has been identified on the outer continental shelf off nova scotia canada the crater is well preserved and buried by 510 m of tertiary and quaternary marine sediments the crater is a circular structure at least 45 km wide and 2 7 km deep with a central structural uplift the uplift is at least 1 250 m and possibly 2 900 m in height its upper surface is 11 5 km across and it has a central pit 3 5 km wide in the center an exploratory oil well located near the center of the structure encountered cambro ordovician metamorphic rocks of the basement which are fractured with planar deformation features in quartz representative of pressures in the 8 to 12 gpa range the uplifted basement is covered by 552 m of breccia shock induced features are common they include planar lamellae in quartz and feldspars partial to total isotropization of silicates and the occurrence of mixed tectosilicate glasses some of which exhibit flow textures with total dissociation of the mafic components to ill defined aggregates these features are diagnostic of a 35 to 50 gpa shock level for parts of the breccia the top of the breccia is covered by a 40 5 m thick suevite zone two crystalline melt rock horizons 72 and 34 m thick are enclosed in the breccia even though the feldspars in the melt are labradorite to bytownite in composition the chemical composition of the rock is rhyolitic with 70 77 of sio 2 similar to the composition of the basement there is no obvious enrichment in siderophile elements except an increase in iridium 0 1 0 3 ppb the occurrence of a thick section of impact melt rocks and breccia capping the central uplift is a feature not recognized in other complex impact craters and may be a function of impact into a marine environment dating by 39 ar 40 ar indicates that the impact occurred at about 51 ma late early eocene and this is confirmed by biostratigraphic data from immediately overlying sediments the compositional and structural imprint left on the montagnais structure by the colliding body points to the impactor being most probably the nucleus of a comet

birps deep seismic reflection studies of the british caledonides the western isles north channel winch traverse fig 1 an extension of the successful moist profile1 was recorded in 1982 at sea along the west coast of britain for birps british institutions reflection profiling syndicate by the geophysical company of norway geco the purpose of the winch traverse was to study crustal structure of the caledonian foreland to cross the caledonian orogen and to establish the three dimensional geometry of mantle reflectors originally seen on moist we describe here the data first emphasizing british caledonian structures and then discussing features of the deep crust of wider significance the data are of very good quality and contain clear moho and upper mantle reflections the lower crust is surprisingly reflective deeply penetrative thrusts are observed and there is firm evidence that several of the mesozoic basins round the shores of the united kingdom were formed by reactivation of older features

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

catastrophic collapse of the volcanic island of hierro 15 ka ago and the history of landslides in the canary islands landslides play an important role in the evolution of many volcanic islands producing huge fields of blocky volcanic debris on their submarine slopes sidescan sonar images presented in this paper provide evidence for a large debris avalanche el golfo on the northern flank of hierro island in the canary islands angular blocks as much as 1 2 km across and 200 m high cover the debris avalanche surface el golfo avalanche is related to both the canary debris flow and a volcaniclastic turbidite found in the madeira abyssal plain 600 km west of the canaries dating of the turbidite and the failure scarp onshore indicates that the failure probably occurred between 13 and 17 ka there appears to be a general correlation between volcaniclastic turbidites in the abyssal plain sequence and landslides in the canaries during the past 750 ka tentatively this correlation suggests that seven major landslides have affected the canaries in that time

the eltanin asteroid impact possible south pacific palaeomegatsunami footprint and potential implications for the pliocene pleistocene transition large asteroid impacts are rare and those into the deep ocean are rarer still the eltanin asteroid impact around 2 51 0 07 ma occurred at a time of great climatic and geological change associated with the pliocene pleistocene boundary numerical models of the event indicate that a megatsunami was generated although there is debate concerning its magnitude and the region wide extent of its influence we summarise the existing evidence for possible eltanin megatsunami deposits in antarctica chile and new zealand while also examining other potential sites from several locations mainly around the south pacific region in reviewing these data we note that these events were unfolding at the same time as those associated with the pliocene pleistocene boundary and as such most of the geological evidence from that time has a climatic interpretation the potential climatic and geological ramifications of the eltanin asteroid impact however have failed to be considered by most researchers studying this time period although we are not advocating that all geological activity at that time is connected with the eltanin asteroid impact it raises interesting questions about the role potentially played by such catastrophic events in contributing to or even triggering epochal transitions copyright 2012 john wiley sons ltd

structure of the southern keweenawan rift from cocorp surveys across the midcontinent geophysical anomaly in northeastern kansas this is the published version copyright 1984 american geophysical union all rights reserved

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

inversion of airborne gravity gradient data southwestern oklahoma the diagonal elements of the gravity gradient tensor as recorded by the bell airborne gravity gradient survey system ggss are used to determine the basement topography in southwestern oklahoma this determination is accomplished through a nonlinear inverse procedure based on the conjugate gradient algorithm the resulting model contains a ridge of shallow basement material or 3 0 km deep trending east southeast this ridge is bounded on the north and the south by basement troughs the northern trough extends as deep as 10 0 km the gradient field which results from this model fits most of the ggss observations within their estimated errors of 12 0 e 1 eotvos 10 super 6 mgal cm the model is in general agreement with a set of available oil well depths to the basement and with inferred faults in these igneous rocks to assess the derived solution the problem was linearized about the final model and the linear parameter resolution and parameter covariances were computed generally the basement depths are well resolved and the resolution matrix is diagonally dominant furthermore the parameter standard errors are small 72 parameters out of 98 have errors less than 1 0 km

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