tectonics of the antarctic scotia plate boundary near elephant and clarence islands west antarctica over 5000 km of new bathymetric data collected from near the northern antarctic peninsula 60 s 63 5 s latitude 53 5 w 63 w longitude show the morphology of an irregular segment of the antarctic scotia plate boundary and nearby shetland microplate the irregular plate boundary is formed by an oblique intersection 70 of the sinistral transpressional shackleton fracture zone sfz and the sinistral transtensional south scotia ridge transform ssr near elephant ei and clarence ci islands mapped boundaries of the shetland microplate include the south shetland trench and the volcanic rift axis of bransfield strait marginal basin bathymetric data single channel seismic reflection profiles and geosat ers 1 free air gravity data show a southeast trending fault zone on the northeast side of a prominent ridge in the sfz the fault zone is defined by scarps that affect ocean floor sediments fault bounded subbasins rotated sedimentary layers angular unconformities linear gravity trends and transtensional followed by contractional deformation southeast of a termination of the sfz ridge at the south shetland trench the fault zone subdivides into segments displaying steep scarps up to 23 and canyons on the northeast margin of the ei platform these features become east west trending nearer to the western ssr south of the islands southwest trending extensional or transtensional fault zones disrupt the bransfield strait volcanic rift axis these data suggest that 1 recent 4 ma changes in the configuration of the antarctic plate near the antarctic peninsula caused a segment of the sfz transform to adjust to a more stable rectilinear geometry with the ssr transform and 2 diffuse transtension resulting from current antarctic scotia relative motion is dissecting the shetland microplate near ei and ci and transferring slivers of the scotia plate onto the antarctic plate

rift propagation detachment faulting and associated magmatism in bransfield strait antarctic peninsula multichannel seismic data from bransfield strait a young 4 ma marginal basin located at the nw tip of the antarctic peninsula reveal a complex array of rifting styles short of clearly defined seafloor spreading the strait is undergoing basinwide extension while enriched mid ocean ridge basalts have been dredged from topographic highs in the ne part of the basin seismic evidence does not support the formation of oceanic crust there acoustic signatures of volcanic crust at known axial deep highs extend laterally subseafloor their distribution and style support propagation of volcanism and associated extension from ne to sw active extensional structures along both margins control a strong physiographic asymmetry the south shetland islands margin is composed of a few closely spaced large offset normal faults the gentler antarctic peninsula margin exhibits broader distributed extension to the ne normal fault polarity reversal structures nfprs dominate listric faults sole into nw dipping low angle reflectors interpreted as detachments to the sw larger nfprs and convex up geometries up to 20 km across suggest broad uplift rather than detachment based extension such uplift may precedes seafloor volcanism and rapid associated deflation along detachments nw se trending accommodation zones also segment the basin along strike bransfield strait extension may result both from plate boundary tectonics at the south shetland trench and at the evolving antarctic scotia plate boundary extension was probably initiated by onset of subduction rollback at the trench as a slab window opened from the sw augmented extension in the ne part of the basin may be a response to left lateral transtension associated with reorganization of the triple junction at the shackleton fracture zone south scotia ridge intersection

landward fining from multiple sources in a sand sheet deposited by the 1929 grand banks tsunami newfoundland abstract a sandy deposit from the 1929 grand banks tsunami in newfoundland contains sediment from two distinct sources one from an inferred gravel shoreline close to the deposit and one from a sandy dune some 200 m seaward of the deposit the deposit ranges from 0 to 15 cm thick and is composed of a bimodal mix of fine and coarse sand we took approximately 100 core samples of this deposit in an attempt to characterize lateral grain size trends within the sand although the coarse fraction does fine with distance inland the fine fraction does not change size over the study area and the aggregate grain size changes in no systematic way we interpret this deposit to represent the mixture of material picked up at the bar with material picked up at the gravel shoreline the bar material does not fine in part because it is already fairly well sorted but also because it is far from its source the shoreline material on the other hand is poorly sorted so that the tsunami took only those grains it was capable of moving and deposited them near their source we estimated the size of the tsunami by determining the flow depth flow velocity combinations required to advect sand from the bar to the back of the deposit and by estimating the shear velocity required for motion of the largest grain we found during our survey this modeling indicates an average flow depth of about 2 5 2 8 m over the area at a flow velocity of 1 9 2 2 m s this estimate compares well with eyewitness accounts of a maximum flow depth of 7 m at the shoreline if our estimate represents an average over the whole study area

orbital forcing of the martian polar layered deposits since the first images of polar regions on mars revealed alternating bright and dark layers there has been speculation that their formation might be tied to the planet s orbital climate forcing1 2 3 4 but uncertainties in the deposition timescale exceed two orders of magnitude estimates based on assumptions of dust deposition ice formation and sublimation and their variations with orbital forcing suggest a deposition rate of 10 3 to 10 2 cm yr 1 refs 5 6 whereas estimates based on cratering rate result in values as high as 0 1 to 0 2 cm yr 1 ref 7 here we use a combination of high resolution images of the polar layered terrains8 high resolution topography9 and revised calculations of the orbital and rotational parameters of mars to show that a correlation exists between ice layer radiance as a function of depth obtained from photometric data of the images of the layered terrains and the insolation variations in summer at the martian north pole similar to what has been shown for palaeoclimate studies of the earth10 11 12 for the best fit between the radiance profile and the simulated insolation parameters we obtain an average deposition rate of 0 05 cm yr 1 for the top 250 m of deposits on the ice cap of the north pole of mars

post subduction margin structures along boyd strait antarctic peninsula abstract the pacific margin of the antarctic peninsula to the southwest of the hero fracture zone hfz is a former subducting margin which became inactive following the arrival of ridge crest segments of the antarctic phoenix ridge at the margin during the tertiary in contrast the part of the margin to the northeast of the hfz remains active tertiary convergence was approximately perpendicular to the margin and ongoing motion is thought to have the same orientation a new seismic reflection profile running along boyd strait just northeast of the landward projection of the hfz shows major structural components similar to those typically observed along the margin to the southwest of the hfz in order of increasing proximity to the margin these components are the inner shelf the shelf basin the mid shelf basement high msbh and the outer shelf the continuation of the post subduction margin structures to the active margin suggests that the boundary between crust with passive and active margins characteristics is not sharply defined our postulated scenario for tectonic evolution along boyd strait is that 1 before the arrival of the last ridge crest segment to the southwest of the hfz the inner shelf and the shelf basin were part of a cretaceous tertiary arc and forearc area 2 after the arrival thermal effects resulting from interaction of the ridge crest with the margin just southwest of the hfz lead to the formation of the msbh to the northeast but msbh uplift in boyd strait did not prevent concurrent cross shelf sediment transport contributing to development of an extensive outer shelf on the seaward flank of the msbh 3 recent extension in bransfield strait a marginal basin to the northeast of the landward projection of the hfz has caused about 10 km of seaward deflection in the strike of the part of the msbh to the northeast of the projection of the hfz

mars water isotope d h history in the strata of the north polar cap inferences about the water cycle abstract a time varying stable isotope model for the d h history of mars water cycle is developed with variable atmosphere space loss rate ground and ice cap flux rates it considers coupled ground reservoirs and traces d h in the air and reservoirs secularly and over obliquity cycles the various flux rates are prescribed time variables that simulate surface flux and solar driven space loss rates predicted bulk averages for the ice cap ground ice reservoirs and atmosphere span the observed ranges reported by mumma et al mumma m j novak r e disanti m a bonev b dello russo n magee sauer k 2003 the martian atmosphere conference reports of sixth international conference on mars atmosphere no 3186 when the dominant obliquity cycle variations are scaled so that the model delivers present seasonal variations the present long term bulk d h average for the ice cap is 2 7 equivalent to 1700 in d wrt smow the obliquity driven d h cycle in the ice cap s layers varies between 3 and 6 the smaller more accessible reservoirs have larger bulk averages with the smallest being able to reach d h values over 9 within 10 5 years small hypothetical solar activity driven variations in the escape rate to space and in the fractionation constant krasnopolsky v a feldman p d 2001 science 294 1914 1917 for the escape process can produce a solar wiggle whose d h amplitude can reach 0 1 d amplitude of 100 because of the temporal variability a single modern measured atmospheric d h ratio at a particular ls cannot tell very much about the total water inventory of mars a bulk average for the northern ice cap and better still a dated vertical profile of d h from the ice cap would however go a long way towards illuminating the modern water history of mars the age and stability of the northern ice cap and the d h history locked in the layering is discussed an ice cap that is very young and exchanges its mass through the atmosphere often will necessarily have a large d h

lithospheric loading by the northern polar cap on mars abstract new topography data for the northern polar region on mars returned by the the mars orbiter laser altimeter mola during the aerobraking hiatus and science phasing orbits allow characterization of the topography of the present northern polar cap and its environs models for loading of an elastic shell by an axisymmetric load approximating the present polar cap geometry indicate that the maximum deflection of the subice basement is in the range 1200 to 400 m for an elastic lithosphere of thickness 40 to 200 km overlain by a cap of pure h 2 o ice corresponding model cap volumes increase from 1 5 to 1 8 10 6 km 3 as elastic lithosphere thickness decreases from 200 to 40 km the presence of sediments in the polar cap increases the depth to basement and resulting cap volume for a given value of elastic lithosphere thickness one dimensional heat flow calculations indicate that the temperature at the base of the cap may approach the melting point of cap material if the lithosphere underlying the cap is thin the basal temperature is 170 k for a 200 km thick lithosphere overlain by pure ice but is as great as 234 k for a 40 km thick lithosphere overlain by a cap with a high sediment ice ratio constraints on elastic lithosphere thickness are weak but geologic mapping and mola data suggest that a flexurally derived circumpolar depression filled with sediments is consistent with elastic lithosphere thickness values in the range 60 120 km gravity and topography over the whole cap are poorly correlated possibly due to viscous relaxation of long wavelength topography but gravity and topography over the western portion of the main cap are consistent with an elastic lithosphere thickness of 120 km for a crustal thickness of 50 km both mola data and geological information suggest a formerly larger northern polar cap the relationship of time scales for changes in the polar cap volume and extent to time scales for viscous relaxation of topography has important implications for investigations of even present polar cap topography viscoelastic calculations show that the maxwell time for an earth like mantle viscosity for mars 10 21 pa s is 10 5 yr the maxwell time scales directly with the martian mantle viscosity so that values as high as 10 7 yr are possible time scales for changes in polar cap volume are poorly constrained but major changes in cap volume over periods of 10 6 10 8 yr are consistent with current understanding of polar cap processes

evidence for ice flow prior to trough formation in the martian north polar layered deposits the relative importance of surface mass fluxes and ice flow in shaping the north polar layered deposits npld now or in the past remains a fundamental and open question motivated by observation of an apparent ice divide on gemina lingula also known as titania lobe we propose a two stage evolution leading to the present day topography on that lobe of the npld ice flow approximately balances surface mass fluxes in the first stage but in the second stage ice flow has minimal influence and topography is modified predominantly by the formation of troughs we focus here on evidence for the first stage by testing the fit of topography between troughs to an ice flow model we find that independent model fits on distinct flow paths closely match inter trough topography uniformly over a broad region on gemina lingula with mutually consistent and physically reasonable fitting parameters however our model requires ice to occupy and flow in spaces where troughs currently incise the ice we therefore infer that the troughs and the distribution of mass balance that caused them post date deposition of the inter trough material and its modification by flow because trough formation has apparently altered inter trough topography very little we infer that trough formation must have been rapid in comparison to the still unknown time scale of flow since troughs began to form we view the evidence for past flow as strong but we do not think that topographic evidence alone can be conclusive observations of englacial stratigraphy using orbital sounding radars will yield conclusive tests of our inferred mechanism for the formation of inter trough topography

spatial thickness variability of the 2011 tohoku oki tsunami deposits along the coastline of sendai bay abstract soon after the 2011 tohoku oki event approximately 1300 tsunami deposit thickness data were collected spatially by the governors to cover the entire tsunami affected area sendai plain along the sendai bay coastline this dataset along with high resolution and high precision data of flow depth and pre tsunami and post tsunami elevation enables us first to conduct a direct comparison of the sedimentation and erosion volumes as well as the tsunami hydrodynamic features e g flow depth and sediment thickness the total balance of sedimentation and erosion volumes revealed that the volume of tsunami deposited sediments can be explained roughly using the erosion volumes at the beach and sand dunes for sandy deposits and at rice paddy fields for muddy deposits both the flow depth and sediment thickness showed positive correlations with the distance from the shoreline while sediment thickness is no correlation to the elevation except in the zone closest to the shoreline where erosion is present in addition a statistical relation was found between the flow depth and sediment thickness in fact the frequency distribution of sediment concentration defined here as the sediment thickness divided by the maximum flow depth at each survey site fits well with the logarithmic normal distribution with geometric average of about 2 this fit indicates that the tsunami deposits on the sendai plain can be explained generally if we simply assume that the saturated level of the sediment concentration in the flow is limited to about 2 on average irrespective of the grain size such a simple explanation might be applicable only for the tsunami deposits on the sendai plain because the topography is remarkably flat and low therefore the tsunami inundation process is relatively simple nevertheless a possible relation between tsunami flow depth and sediment thickness suggested here would be very useful to consider the ideal sedimentary process of the tsunami deposits and to improve forward and inverse modelings

joint geophysical and petrological models for the lithosphere structure of the antarctic peninsula continental margin summary the antarctic peninsula ap is a composite magmatic arc terrane formed at the pacific margin of gondwana through the late mesozoic and cenozoic subduction has stopped progressively from southwest to northeast as a result of a series of ridge trench collisions subduction may be active today in the northern part of the ap adjacent to the south shetland islands the subduction system is confined by the shackleton and hero fracture zones the magmatic arc of the ap continental margin is marked by high amplitude gravity and magnetic anomaly belts reaching highest amplitudes in the region of the south shetland islands and trench the sources for these anomalies are highly magnetic and dense batholiths of mafic bulk composition which were intruded in the cretaceous due to partial melting of upper mantle and lower crustal rocks 2 d gravity and magnetic models provide new insights into crustal and upper mantle structure of the active and passive margin segments of the northern ap our models incorporate seismic refraction constraints and physical property data this enables us to better constrain both moho geometry and petrological interpretations in the crust and upper mantle model along the dss 12 profile crosses the ap margin near the anvers island and shows typical features of a passive continental margin the second model along the dss 17 profile extends from the drake passage through the south shetland trench islands system and bransfield strait to the ap and indicates an active continental margin linked to slow subduction and on going continental rifting in the backarc region continental rifting beneath the bransfield strait is associated with an upward of hot upper mantle rocks and with extensive magmatic underplating

reconstructing relative flooding intensities responsible for hurricane induced deposits from laguna playa grande vieques puerto rico extreme coastal flooding primarily during hurricane strikes has deposited sand rich layers in laguna playa grande a back barrier lagoon located on the island of vieques puerto rico silici clastic grain size distributions within these overwash deposits fine landward away from the barrier and toward the mainland a simple advective settling model can explain this pattern of lateral sorting and is used to constrain the relative magnitude of past flooding events a deposit associated with the a d 1928 san felipe hurricane is used as a modern analogue to test the technique which produces reasonable estimates for wave heights that exceed the barrier during the event a 5000 yr reconstruction of local flooding intensity is developed that provides a measure of the competence for each overwash event to transport coarser grained sediment a fixed distance into the lagoon this reconstruction indicates that although the laguna playa grande record exhibits large scale changes in hurricane frequency on centennial to millennial time scales the magnitude of these events has stayed relatively constant over the last 5000 yr no evidence exists for an anomalously large hurricane or tsunami event with a competence for sediment transport greater than historical hurricane events

a method to infer past surface mass balance and topography from internal layers in martian polar layered deposits internal layers in ice masses can be detected with ice penetrating radar in a flowing ice mass each horizon represents a past surface that has been subsequently buried by accumulation and strained by ice flow these layers retain information about relative spatial patterns of accumulation and ablation mass balance internal layers are necessary to accurately infer mass balance patterns because the ice surface shape only weakly reflects spatial variations in mass balance additional rate controlling information such as the layer age the ice temperature or the ice grain sizes and ice crystal fabric can be used to infer the absolute rate of mass balance to infer mass balance from the shapes of internal layers we solve an inverse problem the solution to the inverse problem is the best set or sets of unknown boundary conditions or initial conditions that when used in our calculation of ice surface elevation and internal layer shape generate appropriate predictions of observations that are available we also show that internal layers can be used to infer martian paleo surface topography from a past era of ice flow even though the topography may have been largely altered by subsequent erosion we have successfully inferred accumulation rates and surface topography from internal layers in antarctica using synthetic data we demonstrate the ability of this method to solve the corresponding inverse problem to infer accumulation and ablation rates as well as the surface topography for martian ice if past ice flow has affected the shapes of martian internal layers this method is necessary to infer the spatial pattern and rate of mass balance

tsuflind enkf inversion of tsunami flow depth and flow speed from deposits with quantified uncertainties abstract deciphering quantitative information from tsunami deposits is especially important for analyzing paleotsunami events in which deposits comprise one of the leftover physical evidences the physical meaning of the deciphered quantities depends on the physical assumptions that are applied the aim of our study is to estimate the characteristics of tsunamis and quantify the associated errors and uncertainties to achieve this goal we apply the tsuflind enkf inversion model to study the deposition of an idealized deposit created by a single tsunami wave and one real case from the 2004 indian ocean tsunami tsuflind enkf combines tsuflind for the deposition module with the ensemble kalman filtering enkf method in our modeling we assume that grain size distribution and thickness from the idealized deposits at different depths can be used as an observational variable our results indicate that sampling methods and sampling frequencies of tsunami deposits influence not only the magnitude of the inverted variables but also their errors and uncertainties an interesting result of our technique is that a larger number of samples from a given tsunami deposit does not automatically mean that the inversion results are more robust with smaller errors and decreased uncertainties tsuflind enkf presents the final inversion results as a probability density distribution function instead of only one value or range of values

radiocarbon constraints on antarctic peninsula ice sheet retreat following the last glacial maximum lgm abstract we present marine sedimentologic and radiocarbon data for the timing of retreat of the largely marine based antarctic peninsula ice sheet since the last glacial maximum lgm our findings indicate minimum estimates of deglaciation between 18 000 and 9000 calibrated years before present cal yr bp roughly in phase with the northern hemisphere deglaciation and eustatic sea level rise our findings show this retreat occurred progressively from the outer middle and inner continental shelf regions as well as progressively from the north to the south retreat initiated on the outer shelf of the northern peninsula by 18 000 cal yr bp and continued southward by 14 000 cal yr bp on the outer shelf of marguerite bay several thousand years earlier than estimated by numeric models while individual cores yield estimates of glacial retreat that may vary up to 1100 years we note steps in the data occur at 14 000 and possibly 11 000 cal yr bp coincidental to rapidly rising eustatic sea level including the well documented melt water pulses mwp 1a and 1b these data support the hypothesis that rapidly rising sea level is associated with marine ice sheet destabilization although additional dates are necessary to substantiate this finding this study highlights problems with radiocarbon dating acid insoluble organic aio matter in proximal lateglacial sediments as well as the need for more accurate dating techniques

effects of ridge crest trench interaction on antarctic phoenix spreading forces on a young subducting plate precise measurements of spreading rates on marine magnetic profiles collected to the west of the antarctic peninsula have enabled some consideration of the forces governing plate motion since antarctic phoenix motion has been controlled by the local rather than global force balance over the last 35 m y the total effective driving force per unit length of trench is calculated to have ranged between 2 6 and 3 6 1012 n m which is much less than is commonly thought necessary to support subduction conventional calculations may overestimate slab pull for old slabs because they neglect the effect of extensional disruption in limiting the contribution to the balance of forces at the trench the low estimate of driving forces obtained here implies that resistive forces are also smaller than is generally assumed driving forces show a strong correlation with observed spreading rates which indicates that resistive forces were largely velocity dependent fluid migration up the subduction zone may elevate temperatures in and around the shear zone reducing resistive forces below the levels required by purely conductive models changes in convergence rate may affect the depths of both the brittle ductile deformation boundary and the basalt eclogite phase change causing a negative feedback which would appear as a velocity dependent resistive force the different driving forces acting on the ne and sw parts of the phoenix plate as a consequence of older oceanic lithosphere at the trench in the ne caused antarctic phoenix spreading to take place about a near pole to the sw since 21 m y ago and ultimately resulted in disruption of the phoenix plate about 9 m y ago spreading rates decreased abruptly about 6 m y ago probably because of e w compression across the long transform faults bounding the phoenix plate however spreading on the last three segments of the antarctic phoenix ridge continued at least until 4 m y ago either spreading stopped progressively from sw to ne or the final stage took place about a very near pole to the sw a magnetic quiet zone extends up to 95 km from the margin between the tula fracture zone and the north anvers fracture zone and is thought to indicate that the ridge crest became buried by terrigenous sediment prior to collision the absence of a magnetic quiet zone associated with the most recent ridge crest trench collisions suggests a change in sedimentary regime during the late miocene anomalously fast apparent spreading rates between 23 and 21 m y ago are thought to indicate an error in this part of the magnetic reversal time scale

testing for flow in the north polar layered deposits of mars using radar stratigraphy and a simple 3d ice flow model 1 the water ice rich north polar layered deposits npld of mars play a key role in the martian climate through an active exchange of water vapor with the atmosphere conditions are not currently amenable for flow of the npld however gross morphological evidence for past flow suggests the possibility of a warmer climate in the past here we present the first comparison of internal stratigraphy predicted by a flow model with that observed by an orbital radar sounder we have analyzed radar data from gemina lingula the southernmost tongue of the npld acquired by the shallow radar on board nasa s mars reconnaissance orbiter the data shows extensive internal reflections and several radar reflectors were mapped to create gridded surfaces of this part of the npld all the mapped radar reflectors were smooth with no sudden dips towards the surface or the bedrock the internal radar reflectors were then compared with modeled isochrones in two different areas of gemina lingula under the assumption of flow occurring results indicate that flow of ice is unlikely to have occurred between the main dome and gemina lingula furthermore we found no evidence for the existence of a prior ablation zone in gemina lingula as predicted in another study

seismicity and tectonics of the south shetland islands and bransfield strait from a regional broadband seismograph deployment 1 we investigate the tectonics of the south shetland trench and bransfield strait by performing a detailed study of local seismicity during 1997 1999 we deployed seven land seismometers and 14 ocean bottom seismometers in the south shetland island region the data we obtained indicate a high level of local seismicity mb 2 5 and we accurately located 150 earthquakes many of the earthquakes occur at locations and depths indicative of ongoing subduction in the south shetland trench a focal mechanism for the largest event in the forearc indicates shallow angle thrusting the maximum depth of seismicity is 65 km but the majority of the events are shallower than 30 km these seismic results are consistent with recent magnetic gps and multichannel seismic reflection data that suggest continued subduction at a very slow rate the south shetland trench thus represents an extreme end member of hot subduction resulting from slow convergence of young lithosphere and the absence of intermediate depth earthquakes is consistent with thermal assimilation of the slab at shallow depths we have located many earthquakes associated with volcanism and rifting in bransfield strait a swarm of events near a submarine volcano suggests current magmatic activity a normal faulting focal mechanism in the northeastern part of the strait gives evidence of extension earthquakes associated with rifting in the northeastern portion of the strait are clustered along well established rifts but the seismicity is much more diffuse to the southwest this observation is consistent with other evidence that extension has propagated from northeast to southwest

seismic stratigraphy of the antarctic peninsula pacific margin a record of pliocene pleistocene ice volume and paleoclimate multichannel seismic profiles across the pacific margin of the antarctic peninsula show a series of oblique progradational sequences these sequences exhibit a variety of unusual characteristics that suggest they were produced by the action of ice sheets grounded out to the shelf edge at times of glacial maximum reflection events from deeper stratigraphic levels followed down the continental slope and onto the rise overlie ocean crust of known age showing that at least eight such glacial sequences have been deposited within the past 6 m y similar groundings have probably occurred on most antarctic margins but the depositional record is particularly well preserved at this margin because of pliocene pleistocene thermal subsidence neogene global sea level fluctuations have been attributed to changes in volume of continental ice sheets the depositional sequences on the pacific margin of the antarctic peninsula are thought to record west antarctic ice sheet fluctuations directly further investigation of these sequences would assess the relation between fluctuations in ice volume and the low latitude record of global sea level change

relationship between the maximum extent of tsunami sand and the inundation limit of the 2011 tohoku oki tsunami on the sendai plain japan abstract this paper focuses on the relationship between the maximum extent of sandy tsunami deposits and inundation distance of the 2011 tohoku oki tsunami inundation limits of the tohoku oki tsunami were assessed over seven shore normal transects along the sendai coastal plain inundation distances were found to range from 0 6 to 4 0 km at the maximum extent of the tsunami deposit the sand unit ranged in thicknesses from 0 1 to 4 0 cm the maximum limit of the 0 5 cm thick sand layer extended to over 90 of the inundation distance where the inundation distance was less than 2 5 km this observation is consistent with previous studies that examined characteristics of recent tsunami events that had inundation distances of at least 2 km the maximum limit of the 0 5 cm thick sand layer extended to 3 km 57 76 of the inundation distance where the inundation distance was more than 2 5 km our results are important for estimating paleo tsunami inundation distances based on the landward extent of sand deposits and valuable for the assessment of future tsunami risks in other coastal areas in the world which have been devastated by huge tsunamis in the past

horizontal and vertical variation of 2004 indian tsunami deposits an example of two transects along the western coast of thailand abstract we investigated horizontal and vertical variations in modern tsunami deposits along two transects at nam khem and khao lak western coast of thailand deposited by the large tsunami associated with the earthquake magnitude 9 0 of 26 december 2004 off sumatra indonesia tsunami waves 6 10 m high struck the area approximately 2 h after the earthquake tsunami deposits cover the low lying coastal plains and extend more than 1 km inland from the shoreline no landward decrease in sediment thicknesses was found clearly at either transect terrace scarps and a steep slope behind the coastal plain probably stopped tsunami deposition further inland causing substantial sediments to be deposited in front of these features very clear vertical variations in grain size and multiple layers are found in the deposits to about 600 m inland at nam khem fine grained sediments overlie the coarse grained sediments of the basal layer of the tsunami deposits at some sites the fine grained sediments are overlain by another layer of coarse grained sediments suggesting deposits laid down in succession by multiple waves the basal coarse grained sediments at nam khem fine landward the up flow waned inland based on the assumption that the grain size of the basal deposits relates to the strength of the up flow these results are potentially useful in disaster prevention and coastal environmental change management as well as for interpreting paleotsunami deposits in geological records

the mars water cycle at other epochs recent history of the polar caps and layered terrain abstract the martian polar caps and layered terrain presumably evolve by the deposition and removal of small amounts of water and dust each year the current attributes of the cap therefore represent the incremental transport during a single year as integrated over long periods of time we have investigated the role of condensation and sublimation of water ice in this process by examining the seasonal water cycle during the past 10 7 years in our model axial obliquity eccentricity and l s of perihelion vary according to dynamic models at each epoch we calculate the seasonal variations in temperature at the two poles keeping track of the seasonal co 2 cap and the summertime sublimation of water ice into the atmosphere net exchange of water between the two caps is calculated based on the difference in the summertime sublimation between the two caps or on the sublimation from the other cap if one is covered with co 2 frost all year despite the simple nature of our model and the tremendous complexity of the martian climate system our results suggest two significant conclusions 1 only a relatively small amount of the available water in the polar deposits actually cycles between the poles on orbital evolution time scales such that it is to some extent the same water molecules moving back and forth between the two caps 2 the difference in elevation between the two caps results in different seasonal behavior such that there is a net transport of water from south to north averaged over long time scales this transport would cause the north cap to grow at the expense of the south cap until the product of water sublimation rate and cap area was equal for the caps minimizing any subsequent net transport these results can help explain 1 the apparent inconsistency between the timescales inferred for layer formation and the much older crater retention age of the cap and 2 the difference in sizes of the two residual caps with the south cap being smaller than the north

sediment lithofacies processes and sedimentary models in the central bransfield basin antarctic peninsula since the last glacial maximum abstract this work provides a regional perspective on the links between glacial glacimarine and marine sedimentary processes occurring since the last glacial maximum along the central bransfield basin antarctic peninsula from shallow to deep areas by combining information provided by gravity cores from shelf to deep basin settings swath bathymetry and high resolution reflection seismic and sub bottom topas profiles seven lithofacies have been identified their textural compositional and x radiographic characteristics as well as their spatial distribution allow the differentiation of two stages of deposition involving distinct sedimentary processes the last glacial maximum was characterised by subglacial deformation by the antarctic peninsula ice sheet as it reached its most extended position on the distal mid slope platforms of the central bransfield basin proglacial debris flows occurred on the external edges of the mid slope platforms and lower slope since the last deglaciation glacimarine proglacial debris flows glacimarine proglacial processes and turbid glacial meltwater and open marine sedimentary processes turbidity currents sliding and contour current activity have predominated in the central bransfield basin glacial cyclicity is the main factor controlling the sedimentary processes in the basin but several secondary factors including physiography sediment entry points and oceanography have been identified as local controls on the sediment distribution the unusual physiography of the central bransfield basin where slope platforms form wide flat surfaces seaward from glacial troughs is a key factor in the widespread occurrence of glacial and glacimarine processes on the entire continental margin

observations of the north polar region of mars from the mars orbiter laser altimeter elevations from the mars orbiter laser altimeter mola have been used to construct a precise topographic map of the martian north polar region the northern ice cap has a maximum elevation of 3 kilometers above its surroundings but lies within a 5 kilometer deep hemispheric depression that is contiguous with the area into which most outflow channels emptied polar cap topography displays evidence of modification by ablation flow and wind and is consistent with a primarily h2o composition correlation of topography with images suggests that the cap was more spatially extensive in the past the cap volume of 1 2 3 10 6 to 1 7 3 10 6 cubic kilometers is about half that of the greenland ice cap clouds observed over the polar cap are likely composed of co 2 that condensed out of the atmosphere during northern hemisphere winter many clouds exhibit dynamical structure likely caused by the interaction of propagating wave fronts with surface topography

tsunami geomorphology erosion and deposition from the 15 november 2006 kuril island tsunami the 15 november 2006 kuril earthquake mw 8 1 8 4 and tsunami enabled us to collect a compelling data set of coastal geomorphic change in the kuril islands from 3 months before to 9 and 21 months after the tsunami our pre tsunami and post tsunami surveys of the islands including four topographic profi les measured in 2006 and reoccupied in 2007 allow us the confi dence to attribute many changes to the tsunami in spite of an absence of eyewitness accounts in the central islands areas with low runup 15 m underwent massive erosion that dramatically altered the coastline tsunami deposits roughly corresponded with the extent of tsunami runup and inundation the amount of sediment eroded by the tsunami far outweighed the amount deposited on land in all cases studied the tsunami was dominantly erosive in the kuril islands because the high relief topography of the coastline accelerated tsunami outfl ow

the state and future of mars polar science and exploration as the planet s principal cold traps the martian polar regions have accumulated extensive mantles of ice and dust that cover individual areas of 10 6 km 2 and total as much as 3 4 km thick from the scarcity of superposed craters on their surface these layered deposits are thought to be comparatively young preserving a record of the seasonal and climatic cycling of atmospheric co 2 h 2o and dust over the past 10 5 10 8 years for this reason the martian polar deposits may serve as a rosetta stone for understanding the geologic and climatic history of the planet documenting variations in insolation due to quasiperiodic oscillations in the planet s obliquity and orbital elements volatile mass balance atmospheric composition dust storm activity volcanic eruptions large impacts catastrophic floods solar luminosity supernovae and perhaps even a record of microbial life beyond their scientific value the polar regions may soon prove important for another reason providing a valuable and accessible reservoir of water to support the long term human exploration of mars in this paper we assess the current state of mars polar research identify the key questions that motivate the exploration of the polar regions discuss the extent to which current missions will address these questions and speculate about what additional capabilities and investigations may be required to address the issues that remain outstanding

the cenozoic subduction history of the pacific margin of the antarctic peninsula ridge crest trench interactions new magnetic anomaly identifications w of the shackleton fracture zone show 5 spreading sections separated by fracture zones in the 2 most southerly the ridge crest collided with a trench at the margin of the antarctic peninsula only 6 5 and 4 ma ago the latest of a series of collisions starting at the base of the peninsula so ma ago following each collision spreading and subduction both stopped opposite the south shetland trench and actively extending bransfield strait spreading also stopped 4 ma ago but before the spreading centre reached the trench the tendency of the subducting plate to continue sinking probably initiated the opening of the bransfield strait the parallelism between fracture zone orientation on the descending plate and convergence direction previously thought responsible for the tectonic segmentation of the peninsula was effective for only 10 30 ma before collision before that either the fracture zones did not extend to the trench or the subducting ocean floor formed at the farallon phoenix nazca aluk boundary with fracture zones oblique to the subduction direction the aleutian arc kula ridge model in which arc magmatism virtually ceases when ocean floor younger than 25 30 ma occurs beneath the arc fits the distribution of antarctic peninsula radiometric dates explaining a 50 60 ma gap between collisions and youngest ages in the s and possibly the migration of the youngest activity towards the trench thus gaps in the geologic record of arc magmatism need not imply cessation of subduction the progressive steepening of the peninsular margin towards the 4 ma collision site suggests tectonic erosion of the fore arc as the ridge crest approached

north polar stratigraphy and the paleo erg of mars an accurate self consistent way of coregistering the imaging and topographic data sets of the mars global surveyor mission was developed and used to begin a stratigraphic analysis of the northern polar region a distinct change in the layering style exists at a definite stratigraphic horizon near the base of the north polar layered deposits occurrences of the contact between two distinct layered units can be mapped hundreds of kilometers apart at nearly the same mars orbiter laser altimeter mola elevation the lower layered unit has a consistent association with sand dunes leading to the conclusion that it is an eroding sand rich deposit that predates most of the overlying north polar layered deposits which exhibits the expected features of a dust ice mixture these results suggest that an areally extensive erg was in existence before the present ice cap and that the present circumpolar erg is likely composed of material reworked from this older deposit the volume of this lower unit is estimated to be on the order of 10 5 km 3 the presence of this deposit implies that there existed a period in mars history when there was no icy polar cap a dramatic climatic change leading to the deposition of the upper layered icy unit in the present day polar layered deposits represents a major event in mars history however owing to uncertainties in the mechanics of layered deposits formation such an event cannot be dated at this time

if martian ice caps flow ablation mechanisms and appearance abstract assuming that the northern ice cap of mars is thick enough to flow like terrestrial ice sheets a model is presented that explains i the origins movement and spiral nature of the scarp trough complexes ii the reentrant valleys like chasma boreale and iii the layered terrain accumulation and ablation are discussed in relation to the scarps and a model is developed relating them to ice flow and scarp velocities and to the particle paths within the ice cap a brief summary of terrestrial ice sheet flow and mass balance is given in order to illustrate and clarify the concepts used to model the martian ice caps

waxing and waning of the perennial north polar h2o ice cap of mars over obliquity cycles abstract the perennial north polar h2o ice cap of mars is investigated with the dynamic thermodynamic ice sheet model sicopolis computational results for flow velocities ice temperatures and surface accumulation ablation rates are presented for the steady state with present conditions as well as for transient scenarios over idealized obliquity cycles with periods of 1 3 myr and 125 kyr the transient simulations lead to a stop and go type dynamics with a cold and almost stagnant modern ice cap and a warmer flowing ice cap for past large obliquity periods the most likely scenario for the present ice cap comprises an ice volume of 1 2 million km3 a maximum thickness of 3 km the absence of pronounced local isostasy h2o ice accumulation rates of the order of tenth mm water equivalent w e per earth year yr flow velocities of the order of mm yr and an ice base far below pressure melting

a flow model for the polar caps of mars a mechanical model with circular symmetry is examined to test the hypothesis that the martian ice caps are composed of flowing water ice together with some rock debris in contrast with most or all previous models no assumption of a steady state is made instead the accumulation and ablation is assumed to be insignificant and it is suggested that after a sufficient time the profile would have settled down to a particular collapsing form calculated by halfar 1983 higher modes of flow would have decayed relatively quickly to calculate the time constant it is necessary to consider carefully the distribution of temperature with depth the time constant is sensitive to the grain size which is assumed to be 1 10 mm and is a significant unknown as is also the effect of preferred crystal orientation apart from this the main uncertainty is the value of the upward heat flux with a heat flux of 30 mw m 2 the water ice hypothesis is consistent with an age of about 10 7 years for both the north and the south polar caps the north cap being the younger by a factor of about 7

forearc tectonic evolution of the south shetland margin antarctic peninsula the main provinces of the south shetland margin antarctic peninsula characterized on the basis of multichannel seismic long range side scan sonar and swath bathymetry data include from northwest to southeast 1 the oceanic crust of the former phoenix plate flexed down toward the margin and affected by normal faulting in the upper crust 2 a narrow trench with a horizontally layered sediment fill which onlaps the thin sedimentary cover on the oceanic crust and shows incipient deformation near its landward edge 3 an accretionary prism with a complex internal structure the toe of which is overthrust above the youngest trench deposits 4 a midslope forearc basin with an asymmetric synformal structure and 5 the continental shelf which includes two distinct tectonic provinces calculations of the late cenozoic convergence history at the trench indicate a rapid decrease in convergence rate after 6 7 ma from about 60 mm yr resulting from the slowing and eventual cessation of spreading on the antarctic phoenix ridge once spreading had completely ceased 3 5 2 4 ma the convergence rate at the trench equalled the rate of extension in bransfield strait which was probably less than 10 mm yr at first but may have increased since 1 3 ma and this in turn would imply a corresponding increase in convergence rate above the basal detachment the toe of the accretionary prism is composed of a stack of thrust fault bounded wedges laterally and vertically segmented by normal faults most of the trench fill sediments are overthrust by the toe of the accretionary prism and subducted beneath it for as far as they can be traced on the seismic profiles this suggests that there may be tectonic erosion of the forearc since a large part of the trench sediment appears to be derived from erosion on the forearc slope the forearc basin records a long history of subsidence during which the depocenter migrated landward paralleling retrogradational erosion of the distal margin of the basin subduction of the hero fracture zone at approximately the same location since 10 ma may have enhanced tectonic erosion of the accretionary prism in the forearc basin a synform is coincident with a bathymetric reentrant but its axis is oblique to the trends of both the basin and the fracture zone the origin of this synform and the final phase of uplift of the blueschist facies terrane on which smith island stands are probably related to their position above the subducting fracture zone ridge the present elevation of smith island is thought to result from uplift which followed a ridge crest trench collision directly southwest of the hero fracture zone at 5 5 ma the northwestern edge of the mesozoic to early cenozoic arc batholith trending northeast southwest on the shelf is proposed to have acted as a backstop to the accretionary prism during cenozoic subduction

a model for tsunami flow inversion from deposits tsuflind abstract modern tsunami deposits are employed to estimate the overland flow characteristics of tsunamis with the help of the overland flow characteristics the characteristics of the causative tsunami wave can be estimated the understanding of tsunami deposits has tremendously improved over the last decades there are three prominent inversion models a moore s advection model moore et al 2007 b soulsby s model soulsby et al 2007 and c tsusedmod jaffe gelfenbuam 2007 tsuflind incorporates all three models and adds new modules to better simulate tsunami deposit formation and calculate flow condition tsuflind takes grain size distribution thickness water depth and topography information as inputs tsuflind computes sediment concentration grain size distribution of sediment source and initial flow condition to match the sediment thickness and grain size distribution from field observation furthermore tsuflind estimates the flow speed froude number and representative wave amplitude the model is tested by using field data collected at ranganathapuram india after the 2004 india ocean tsunami tsuflind reproduces the field measurement grain size distribution with less than 5 error tsunami speed in this test case is about 4 7 ms 1 at 150 m inland and decreases to 3 3 ms 1 350 m inland from the shoreline the estimated wave amplitude of the largest wave for this test case is about 5 to 7 m

modeling the 1100 bp paleotsunami in puget sound washington 1 recent paleoseismic and geologic studies indicate that a tsunami occurred 1100 years ago in puget sound this study aims to reproduce and validate the model tsunami using a finite difference model based on nonlinear shallow water theory and abathymetry topography computational grid that takes into account the 1 meter rise in sea level that has occurred in the region during the past 1100 years estimates of tsunami height the extent of inundation and the current velocity pattern are provided at the northern head of cultus bay whidbey island where paleotsunami sand deposits have been found the model demonstrates that a tsunami generated when the background water level was at mean high water or above could have surged across the then existing coastal marsh penetrated the full length of the shallow bay and deposited the observed sand layers

sedimentary features observed in the tsunami deposits at rikuzentakata city abstract the march 11 2011 tohoku oki tsunami triggered by an earthquake off the east coast of northeastern honshu island tohoku region japan deposited large amounts of sediment on land including the sendai plain and sanriku coast this study reports on the characteristics of the tsunami deposits in rikuzentakata city southeastern iwate prefecture northeastern japan a field survey identified the inundation pattern of the tsunami in this region and the facies model of the tsunami deposits at the bay head deltas of estuarine systems the tsunami deposits in rikuzentakata city generally consist of one to four units that represent a discrete runup or backwash flow each unit is characterized by initial inverse grading and successive normal grading that correspond to the accelerating and decelerating stages of the flow respectively an internal erosional surface often developed between the inverse graded and normal graded units it corresponds to the maximum shear velocity of the flow and truncates the underlying inverse graded unit in the case of the runup unit silty fine grained drapes overlay the graded sandy interval a correlation of the sedimentary structures and grain fabric analysis revealed that the tohoku oki tsunami inundated rikuzentakata city at least twice and that the flow velocity exceeded 2 4 m s paleontological analysis of the sediment and kriging estimation of the total volume of the tsunami deposit implied that the sediments were sourced not only from eroded beach sands but also from the seafloor of hirota bay or more offshore regions

cenozoic prograding sequences of the antarctic continental margin a record of glacio eustatic and tectonic events abstract sedimentary sections up to 6 14 km thick lie beneath many areas of the antarctic continental margin the upper parts of the sections contain up to 6 km of cenozoic glacial and possibly non glacial sequences that have prograded the continental shelf up to 85 km we describe the cenozoic sequences using two general categories based on their acoustic geometries type ia sequences which account for most prograding of the antarctic continental shelf have complex sigmoidal geometries and some acoustic characteristics atypical of low latitude margins such as troughs and mounds lying parallel and normal to the shelf edge and high velocities 2 0 2 6 km s for flat layers within 150 m of the seafloor type iia sequences which principally aggrade the paleoshelf lie beneath type ia sequences and have mostly simple geometries and gently dipping reflections the prograding sequences are commonly located near the seaward edges of major mesozoic and older margin structures relatively rapid cenozoic subsidence has occured due to the probable rifting in the ross sea thermal subsidence in the antarctic peninsula and isostatic crustal flexure in wilkes land in prydz bay and the weddell sea prograding sequences cover mesozoic basins that have undergone little apparent cenozoic tectonism grounded ice sheets are viewed by us and others as the principal mechanism for depositing the antarctic prograding sequences during the initial advance of grounded ice the continental shelf is flexurally overdeepened the inner shelf is heavily eroded and gently dipping glacial strata are deposited on the shelf i e type iia sequences the overdeepened shelf profile is preserved a during glacial times by grounded ice sheets episodically crossing the shelf eroding sediments from onshore and inner shelf areas and depositing sediments at the front of the ice sheet as outer shelf topset banks and continental slope foreset aprons i e type ia sequences and b during interglacial times like today by little or no clastic sedimentation on the continental shelf other than beneath retreated ice shelves lying far from the continental sheld edge ice streams carve broad depressions across the shelf and carry abundant basal sediments directly to the continental shelf edge thereby creating troughmouth fans and sheet like prograding sequences i e type ia sequences numerous acoustic unconformities and multiple overcompacted layers within the prograding sequences suggest major fluctuations of the antarctic ice sheet the available drilling and seismic interpretations provide the following history 1 cenozoic ice sheets have existed in places near the continental shelf since middle to late eocene time 2 a grounded antarctic ice sheet first expanded to the continental shelf edge with probable overdeepening of the outer shelf in late eucene to early oligocene time in prydz bay possibly in early miocene time in the ross sea and at least by middle miocene time in the weddell sea 3 the relative amounts of shelf prograding and inferred ice volume variations and related sea level changes have increased since middle to late miocene time in the eastern ross sea prydz bay and possibly weddell sea our analysis is preliminary further acoustic surveys and scientific drilling are needed to resolve the proximal antarctic record of glacio eustatic climatic and tectonic events recorded by the prograding sequences

martian north polar layered deposits stratigraphy implications for accumulation rates and flow 1 we have used mars orbiter camera moc images and mars observer laser altimeter mola data to correlate specific layers within the upper 500 m of the martian north polar layered deposits in many troughs using these correlation results we derive relative accumulation rates across the polar layered deposits and through time we identify two major layer sequences one lying stratigraphically above the other each consistent with an overall curving downward layer structure with shallow slopes but with significant localized variations in layer height major disruptions of stratigraphy such as angular unconformities do not appear within the correlated layer sequences on local and broad scales each layer sequence exhibits a different relative accumulation rate pattern indicating that this rate has not remained constant through time and has been affected by localized processes the overall pattern of the lower layer sequence is similar to that of a classic terrestrial ice sheet with a decreasing relative accumulation rate away from the center of the polar layered deposits southward the upper layer sequence exhibits no obvious overall trends we also compare our correlation results to predictions of the effects of simple ice flow on layer structure finding that mass balance patterns have overprinted any effects of large scale ice flow flow has not been significant compared to mass balance in forming the overall structure of the correlated layers

local variation of inundation sedimentary characteristics and mineral assemblages of the 2011 tohoku oki tsunami on the misawa coast aomori japan abstract the 2011 tohoku oki tsunami caused severe damage to the coastal regions of eastern japan and left a sediment veneer over affected areas we discuss differences in depositional characteristics of the 2011 tohoku oki tsunami from the viewpoint of the sediment source coastal topography and flow height the study area on the misawa coast northern tohoku includes a 20 km long coastline with sandy beaches coastal dunes and a gently sloping lowland this landscape assemblage provides an opportunity to examine the effects of topography on the characteristics of the tsunami deposit during field surveys conducted from april 10 to may 2 2011 we described the thickness facies and structure of the tsunami deposit we also collected sand samples at approximately 20 m intervals along 13 shore perpendicular transects extending up to 550 m inland for grain size and mineral assemblage analysis the tsunami flow height was estimated by measuring the elevation of debris found in trees broken tree limbs or water marks on buildings the nature of the coastal lowland affected the flow height and inundation distance in the southern part of the study area where there is a narrow 100 m wide low lying coastal strip the run up height reached 10 m on the landward terrace slopes to the north the maximum inundation reached 550 m with a run up height of 3 2 m on the wider low lying coastal topography the average flow height was 4 5 m the tsunami eroded coastal dunes and formed small scarps along the coast immediately landward of the coastal dunes the tsunami deposit was more than 20 cm thick but thinned markedly inland from this point close to the dunes the deposit was composed largely of medium sand 1 2 with planar and parallel bedding but with no apparent upward fining or coarsening the grain size was similar to that of the coastal dune and we infer that the dunes were the local source material for the tsunami deposit at this point the mineral assemblage of the tsunami deposit was dominated by orthopyroxene and clinopyroxene and was also similar to the dune and beach sand at sites more than half the inundation distance inland the thinner tsunami deposit consisted mainly of fine sand 2 375 with some upward fining the difference in grain size and sedimentary characteristics was probably caused by differences in sediment transportation and depositional processes we infer that the well sorted finer sediments were deposited out of suspension whereas the relatively coarse sands were laid down from traction flows the depositional characteristics of the 2011 tohoku oki tsunami deposit appeared to have been affected mainly by the coastal topography and the extent of erosion at any one point as opposed to flow height

the ascraeus mons fan shaped deposit volcano ice interactions and the climatic implications of cold based tropical mountain glaciation abstract amazonian aged fan shaped deposits extending to the northwest of each of the tharsis montes in the tharsis region on mars have been interpreted to have originated from mass wasting volcanic tectonic and or glacial processes we use new data from mro mgs and odyssey to characterize these deposits building on recent evidence for cold based glacial activity at pavonis mons and arsia mons we interpret the smaller ascraeus fan shaped deposit to be of glacial origin our geomorphological assessment reveals a number of characteristics indicative of glacial growth and retreat including 1 a ridged facies interpreted to be composed of drop moraines emplaced during episodic glacial advance and retreat 2 a knobby facies interpreted to represent vertical downwasting of the ice sheet and 3 complex ridges showing a cusp like structure we also see evidence of volcano ice interactions in the form of 1 an arcuate inward facing scarp interpreted to have formed by the chilling of lava flows against the glacial margin 2 a plateau feature interpreted to represent a subglacial eruption and 3 knobby facies superimposed on flat topped flows with leveed channels interpreted to be subglacial inflated lava flows that subsequently drained and are covered by glacial till we discuss the formation mechanisms of these morphologies during cold based glacial activity and concurrent volcanism on the basis of a mid to late amazonian age 250 380 ma established from crater size frequency distribution data we explore the climatic implications of recent glaciation at low latitudes on mars gcm results show that increased insolation to the poles at high obliquities 45 forces sublimation of polar ice which is transported to lower latitudes and deposited on the flanks of the tharsis montes we assess how local orographic effects the mass balance of the glacier and the position of equilibrium line altitudes all played a role in producing the observed geomorphologies in doing so we outline a glacial history for the evolution of the ascraeus mons fan shaped deposit and compare its initiation growth and demise with those of arsia mons and pavonis mons

gas hydrate versus geological features the south shetland case study abstract a gas hydrate reservoir is hosted in marine sediments of an accretionary prism located offshore the south shetland islands antarctic peninsula and affected by widespread deformations to analyse gas hydrate distribution and fluid circulation inside sediments available velocity models were used seismic velocities are translated in terms of hydrate porosity which is the difference between the reference porosity i e the porosity without gas hydrate and the effective porosity i e the porosity reduced by the gas hydrate presence the pre stack depth migration sections underlined the presence of several geological features such as gentle and open folds fractures and faults in this paper we observed a relationship between syncline anticline structures and hydrate presence in particular a relationship is underlined between the hydrate porosity values and the distance from the hinge of the anticline the hydrate porosity increases toward the limbs of anticline the micro fracturing model supports the idea that the syncline favours the hydrate formation while the anticline favours the free gas accumulation below the bottom simulating reflector

a numerical model for tsunami induced morphology change we describe the development of a time resolved model for tsunami induced morphology change based on an existing boussinesq model for weakly dispersive free surface waves coupled to a depth integrated model for sediment concentration and an equation for bed level change the model allows for spatial variability in bottom friction coefficients and accounts for the presence of non erodible beds or finite depths of available sediment the model is verified using one laboratory data set and against field observations of morphology change in the crescent city ca harbor during the 2011 tohoku tsunami event the model is then applied to a hypothetical example illustrating the impact of tsunami inundation on an undeveloped barrier island

2004 indian ocean tsunami inflow and outflow at phuket thailand at bangtao beach phuket the 2004 indian ocean tsunami produced a repeated sequence in which rapid inflow of turbulent water was followed by ponding and then by gradual outflow photographs and eyewitness accounts show an initial withdrawal followed by series of inflows the tsunami left behind a sand sheet as much as 25 cm thick that contains parallel inclined landward and seaward lamina in addition to the normal grading commonly reported from tsunami deposits the sheet contains evidence for two times of vigorous inflow each of these is marked by mud rip ups medium to coarse sand that grades upward to fine landward inclined laminae and a sharp basal contact the top of the sand sheet when observed in the first days after the tsunami abounded in current dune and ripple bedforms of mostly landward orientation the tsunami s first positive wave left noonshore sedimentary record in this pitting area the second wave deposited sand that is much less extensive and slightly finer than that of the third wave the deposit of both these waves contains multiple fining upward sequences possibly due to multiple surges in one wave train the depth averaged flow velocity estimated from thickness and grain size are in the range 7 21 m s whereas a near bottom threshold velocity calculated from bedforms reveals the order of magnitude difference from 1 74 to 1 03 m s 2007 elsevier b v all rights reserved

the polar deposits of mars the tantalizing prospect of a readable record of martian climatic variations has driven decades of work toward deciphering the stratigraphy of the martian polar layered deposits and understanding the role of the residual ice caps that cover them spacecraft over the past decade have provided a massive infusion of new data into mars science polar science has benefited immensely due to the near polar orbits of most of the orbiting missions and the successful landing of the phoenix spacecraft in the northern high latitudes topographic thermal radar hyperspectral and high resolution imaging data are among the datasets that have allowed characterization of the stratigraphy of the polar layered deposits in unprecedented detail additionally change within the residual ice caps has been monitored with spacecraft instruments for several years these new data have provided a golden opportunity to understand the interplay between the martian orbit climate and polar ice

forward modeling of ice topography on mars to infer basal shear stress conditions 1 understanding the history of ice caps on mars could reveal important information about martian geologic and climatic history to do this an ice reconstruction model is needed that operates over complex topography and can be constrained with a limited number of free parameters in this study we developed a threshold sliding model for ice cap morphology based on the classic model of nye later incorporated into the models of reeh and colleagues we have updated the nye reeh model with a new numerical algorithm although the model was originally developed to model perfectly plastic deformation it is applicable to any ice body that deforms when a threshold basal shear stress is exceeded the model requires three inputs a digital elevation model of bed topography a mask grid that defines the position of the ice terminus and a function defining the threshold basal shear stress to test the robustness of the model the morphology of the greenland ice sheet is reconstructed using an empirical equation between threshold basal shear stress and ice surface slope the model is then used to reconstruct the morphology of ice draping impact craters on the margins of the south polar layered deposits using an inferred constant basal shear stress of 0 6 bar for the majority of the examples this inferred basal shear stress value is almost 1 3 of the average basal shear stress calculated for the greenland ice sheet what causes this lower basal shear stress value on mars is unclear but could involve the strain weakening behavior of ice

rb sr geochronology of graham land antarctica thirty five new rb sr whole rock and mineral isochrons are reported for igneous rocks from graham land magmatism was essentially continuous but peaks of activity occurred in early jurassic early cretaceous late cretaceous and eocene times the oldest dated granite is triassic 209 3 ma volcanic rocks were erupted throughout this history and some previously supposed upper jurassic volcanic rocks must be mid cretaceous or younger a change in magma type from uniformly acid to predominantly basic or intermediate combined with westward migration of the arc may be partly responsible for previously reported transverse geochemical variations there is a marked trend of decreasing initial 87 sr 86 sr ratio of the plutonic rocks with time from c 0 707 to 0 704 although volcanic rocks tend to have higher values this trend is ascribed to the waning influence of an as yet unidentified pre magmatic crustal basement due to increasing depth of magma generation close parallels to the observed age pattern imply continuity of the andean belt through southern south america into graham land back to early mesozoic times and are not compatible with reconstructions of gondwana in which the antarctic peninsula is located w of south america

modeling concentric crater fill in utopia planitia mars with an ice flow line model abstract impact craters in the mid latitudes of mars are commonly filled to variable degrees with some combination of ice dust and rocky debris concentric surface features visible in these craters have been linked to debris transportation and glacial and periglacial processes concentric crater fill ccf observed today are interpreted to be the remains of repeated periods of accumulation and sublimation during the last tens to hundreds of million years previous work suggests that during phases of high obliquity ice accumulates in crater interiors and begins to flow down steep crater slopes slowly filling the crater during times of low obliquity ice is protected from sublimation through a surface debris layer consisting of dust and rocky material here we use an ice flow line model to understand the development of concentric crater fill in a regional study of utopia planitia craters we address questions about the influence of crater size on the ccf formation process the time scales needed to fill an impact crater with ice and explore commonly described flow features of ccf we show that observed surface debris deposits as well as asymmetric flow features can be reproduced with the model using surface mass balance data from global climate models and a credible obliquity scenario we find that craters less than 80 km in diameter can be entirely filled in less than 8 my beginning as recently as 40 ma ago uncertainties in input variables related to ice viscosity do not change the overall behavior of ice flow and the filling process we model ccf for the utopia planitia region and find subtle trends for crater size versus fill level crater size versus sublimation reduction by the surface debris layer and crater floor elevation versus fill level

sediment sources and sedimentation processes of 2011 tohoku oki tsunami deposits on the sendai plain japan insights from diatoms nannoliths and grain size distribution abstract the 11th march 2011 tohoku oki tsunami inundated the low lying sendai plain japan more than 5 km inland leaving sand and mud deposits over most of the area in order to establish the sources of the tsunami deposits and interpret processes of their sedimentation samples were collected from the deposits underlying soils and the beach along a shore perpendicular transect and analysed for grain size diatom assemblages and nannoliths the fining inland tsunami deposits consisted of poorly to moderately sorted medium to coarse sand within 2 km of the coastline and very poorly to poorly sorted mud farther inland more specifically there was a slight fining of the coarse to medium sand mode within the sandy deposits and an increased contribution of the coarse and very coarse silt fraction in the mud deposits the tsunami deposits also exhibited vertical changes including fining upward and coupled coarsening fining upward trends few diatoms were present in beach sediments soils and tsunami deposits within 1 km of the coastline while diatoms were more abundant farther inland diatom assemblages in the soil and tsunami deposits were similar and dominated by species typical of freshwater brackish habitats while no typically marine species were encountered nannoliths were generally absent in the studied sediments except for few specimens our data indicate that there was probably no or only a very minor component of marine sediments transported onland by the tsunami the sandy tsunami deposits within 1 km of the coastline were mostly derived from beach and dune erosion from 1 to 2 km landward the contribution of these sources decreased while sources comprising local soil erosion and the entrainment of sediments from the teizan bori canal increased farther inland local soil erosion was the major sediment source for the mud deposits the tsunami deposits were most likely deposited during at least two inundations mostly out from suspension resulting in an upward grain size fining trend however bed load deposition was also important in the sandy deposits as suggested by a common grain size upward coarsening position on c m diagrams and frequent horizontal lamination the present study reveals that even very large tsunamis may not transport marine sediments onland and thus many commonly applied indicators of tsunami deposits based on the assumption of their offshore origin marine diatoms foraminifera nannoliths marine sediments may be of limited use

insights from geochemistry and diatoms to characterise a tsunami s deposit and maximum inundation limit abstract geochemical proxies and diatom assemblages were used in combination with grain size characteristics not only to describe the deposit left behind by the 27 february 2010 maule tsunami at las canas maule region chile but also to trace the maximum inundation limit of the event the sandy deposit was laid down between 160 and 260 m inland behind an eroded sand dune and a lagoon but reached only 60 of the total tsunami inundation distance of 380 m which was marked by organic debris pumice clasts and wooden logs it consisted of coarse to medium sand that thinned and fined inland at the most seaward point the 22 cm thick deposit exhibited a fining upward unit overlain by a couplet of coarsening fining upward units suggesting deposition by at least two waves while farther inland the fining upward deposit was probably left behind by only one wave chemical proxies ca ti vs sr ba allow us to distinguish the deposit from the surrounding soil and indicate that it was sourced from the beach and or dune area with diatom assemblages confirming the marine origin of the deposit saltwater indicators e g cl s provide evidence for the maximum inundation limit beyond the extent of the sandy deposit despite dilution and dissolution by 500 mm of rainfall in the six months since the tsunami marine and marine brackish diatom assemblages decreased landward but were found up to the inundation limit and immediately beyond suggesting the effect of diatom bearing sea spray at the wave front or redistribution of the detrital assemblage associated with tsunami inundation due to wind while the latter might result in a slight over estimation of the inundation distance they can be used in combination with chemical proxies to trace the maximum inundation distance of recent and past tsunamis thus allowing for a better estimation of the magnitude of past events post depositional processes were found to have affected the thinner sandy deposits

styles of early diagenesis and the preservation potential of onshore tsunami deposits a re survey of isla mocha central chile 2 years after the february 27 2010 maule tsunami abstract the style of early diagenesis and preservation of onshore tsunami deposits are poorly constrained only tsunami surveys and subsequent re surveys can fill this information gap here we present the results of a first re survey in 2012 on isla mocha following the original survey in 2010 in the wake of the february 27 2010 maule earthquake and tsunami in central chile as a result of this tsunami a large number of boulders consisting of clay rich fine sandstones representing the miocene age bedrock of the island had been transferred from the tidal to shallow subtidal zone onto the coastal plain coarse clastic sediment mixtures of pebbles granules and sand entrained at coastal plain terraces and transported up to the maximum runup position c 600 m from the coast by the inflow had been left behind as extensive backflow blankets on the lower coastal plain in 2012 vegetation had covered the 2010 tsunami deposits sediment beyond 200 m from the coast had been removed by a combination of surface processes and grazing cattle grain size distributions of the preserved sediment show an increase of the sand fraction at the expense of the coarser grain sizes boulders show patterns resembling mud cracks on the surface and evidence of disintegration into smaller fragments and sand veneers of dried algae documenting the derivation of the boulders from the tidal zones had flaked off partly or completely from most rock surfaces at the northern wind facing coast of the island a c 130 m long and 1 2 m high beach ridge had accumulated most likely from reworked tsunami sediment boulders deposited by tsunamis are commonly assigned a high preservation potential we demonstrate for the first time that such boulders may in fact disintegrate rapidly and disappear from the record over short geological time scales given a lithology susceptible to weathering the degree of modification to the lsla mocha tsunami boulders and deposits strongly questions the applicability of inverse models using paleotsunami deposit thickness and grain size distributions to infer parameters and magnitudes of the causative tsunamis inverse models would consequently underestimate tsunami flow parameters and may result in the inference of erroneous transport modes and event magnitudes our study gives strong evidence in support of re survey studies following the deposition of tsunami sediments by tracing and quantifying the changes affecting them

ice sheet extent of the antarctic peninsula region during the last glacial maximum lgm insights from glacial geomorphology we present marine geological and geophysical data for the antarctic peninsula that call for a larger ice sheet reconstruction during the last glacial maximum lgm than suggested by previous studies such glacial reconstructions are important for quantifying post lgm sea level rise and providing boundary conditions for general circulation models megascale glacial lineations on the continental shelf surrounding antarctica provide documentation for grounded ice that was streaming swath bathymetry data nbp02 01 reveal lineations in each of the major glacial troughs except for smith trough which features grooves and bedrock drumlins 0 5 3 km spacing 1 20 elongation ratios on crystalline bedrock we place the maximum extent of ice at the seaward limit of the lineations at or near megascale glacial lineations imaged in this study and other areas surrounding antarctica including the ross sea pine island bay have a consistent morphology with elongation ratios of 80 1 and spacings of 200 600 m mode of 300 m in contrast lineations bundles canals et al 2000 in the gerlache boyd trough exhibit larger spacing 1 5 km and the upstream portions 7 km are carved directly into bedrock rather than till as suggested by previously unpublished air gun 120 hz seismic data these features have yet to be dated however they are believed to have been active during the lgm radiocarbon dates in glaciomarine sediments foraminifera and organic matter from seven glacial troughs indicate that megascale glacial lineations were formed during the lgm other geomorphic features such as the grounding zone wedge in the northwestern weddell sea formed when the ice sheet was retreating the initial retreat of the grounded ice from the outer shelf occurred by 18 500 cal yr b p the inner shelf was mostly ice free by 13 000 cal yr b p this is significantly earlier than numerical models which suggest antarctic deglaciation began at 12 000 cal yr b p this also suggests the peninsula area contributed to global sea level rise associated with meltwater pulse mwp 1a

creep of water ices at planetary conditions a compilation many constitutive laws for the flow of ice have been published since the advent of the voyager explorations of the outer solar system conflicting data have occasionally come from different laboratories and refinement of experimental techniques has led to the publication of laws that supersede earlier ones in addition there are unpublished data from ongoing research that also amend the constitutive laws here we compile the most current laboratory derived flow laws for water ice phases i ii iii v and vi and ice i mixtures with hard particulates the rheology of interest is mainly that of steady state and the conditions reviewed are the pressures and temperatures applicable to the surfaces and interiors of icy moons of the outer solar system advances in grain size dependent creep in ices i and ii as well as in phase transformations and metastability under differential stress are also included in this compilation at laboratory strain rates the several ice polymorphs are rheologically distinct in terms of their stress temperature and pressure dependencies but with the exception of ice iii have fairly similar strengths hard particulates strengthen ice i significantly only at high particulate volume fractions ice iii has the potential for significantly affecting mantle dynamics because it is much weaker than the other polymorphs and its region of stability which may extend metastably well into what is nominally the ice ii field is located near likely geotherms of large icy moons

scenarios for the formation of chasma boreale mars abstract the martian polar caps feature large chasmata and smaller trough systems which have no counterpart in terrestrial ice sheets chasma boreale cuts about 500 km into the western part of the north polar cap is up to 100 km wide and up to 2 km deep one possible formation mechanism is by a temporary heat source under the ice due to tectono thermal or volcanic activity which melts the ice from below it is demonstrated by model simulations that this process is feasible a moderately increased heat flux of 0 5 1 w m 2 sustained over at least tens of thousands of years producing a topographic depression which resembles the real chasma associated meltwater discharge rates are small 1 km 3 a 1 but can exceed 10 km3 a 1 if a stronger heat flux of 10 w m 2 is assumed local ice flow velocities during the process of chasma formation can exceed 1 m a 1 at the head and scarps of the chasma however if the thermal anomaly shuts down glacial flow quickly decreases so that the chasma can stay open for an indefinite amount of time without an ongoing sustaining process under the climate conditions of the most recent millions of years

p wave velocity structure beneath the northern antarctic peninsula evidence of a steeply subducting slab and a deep rooted low velocity anomaly beneath the central bransfield basin summary upper mantle structure between 100 and 300 km depth below the northern antarctic peninsula is imaged by modelling p wave traveltime residuals from teleseismic events recorded on the king sejong station ksj the argentinean italian stations juba and espz an iris gsn station pmsa and the seismic experiment in patagonia and antarctica sepa broad band stations for measuring traveltime residuals we applied a multichannel cross correlation method and inverted for upper mantle structure using vandecar s method the new 3 d velocity model reveals a subducted slab with a 70 dip angle at 100 300 km depth and a strong low velocity anomaly confined below the se flank of the central bransfield basin the low velocity is attributed to a thermal anomaly in the mantle that could be as large as 350 560 k and which is associated with high heat flow and volcanism in the central bransfield basin the low velocity zone imaged below the se flank of the central bransfield basin does not extend under the northern bransfield basin suggesting that the rifting process in that area likely involves different geodynamic processes

combining constraints from tsunami modeling and sedimentology to untangle the 1969 ozernoi and 1971 kamchatskii tsunamis 1 large tsunamigenic earthquakes occurred in 1969 mw 7 7 and 1971 mw 7 8 along the bering sea and northernmost pacific coast of kamchatka both resultant tsunamis were recorded on tide gauges but only the 1969 tsunami has cataloged observations of runup and these observations are limited and questionable we used a combination of field mapping of tsunami deposits and tsunami modeling to augment this historical record we mapped tsunami deposits above a d 1956 and 1964 volcanic ash layers along more than 200 km of shoreline however the 1969 and 1971 tsunami deposits are not distinguishable in the field the distribution of tsunami deposit elevation has two latitudinal peaks from 58 to 57 sediment runup typically ranges from 2 to 4 m decreasing to the south from 57 to 56 sediment runup typically ranges from 3 to 6 m maximum more than 10 m increasing to the south models of local runup for the 1969 and 1971 tsunamis explain most of the sediment distribution differentiate the two tsunamis in some localities and elucidate the earthquakes focal mechanisms and rupture areas

crustal structure of the antarctic peninsula sector of the gondwana margin around anvers island from geophysical data abstract we investigated the crustal structure of the northern antarctic peninsula ap a composite magmatic arc terrane at the pacific margin of gondwana it was formed in mesozoic cenozoic by collision accretion of allochthonous terranes to the gondwana margin during subduction and progressive ridge collision of former phoenix plate under the ap the ap is distinguished by belts of high amplitude gravity and magnetic anomalies inferred to indicate the presence of plutons of mafic composition comprising the huge ap batholith for a better understanding of the lithosphere structure and tectonic processes of the ap continental margin we performed 2d gravity and magnetic modeling along line iii iii which crosses the margin south of anvers island our model incorporates data on seismic refraction dss 13 and reflection line 8545 03 profiles and physical property data our modeling shows that the crust of the ap margin near anvers island is of continental type and comprises two crustal domains which were welded together during mid cretaceous collision on the east there is a thick 40 km high velocity density continental crust of the gondwana margin which occupies the ap inner shelf and mainland and larsen ice shelf the space between the gondwanian block and oceanic crust of the bellingshausen sea is occupied by thinner 26 km crust of lower densities of supposed accreted terrane characterized by gravity anomalies caused probably by accretional tectonics as a result of cretaceous subduction two belts of magnetic anomalies forming the pma pacific margin anomaly probably belong to different crustal domains the western belt of the pma relates to accretional block while the eastern belt of the pma corresponds to the gondwana margin block this may represent an evidence that the pma relates to a tectono magmatic event occurred after collision of gondwana margin and accreted terrane in mid cretaceous and had been imprinted on already formed continental margin

k ar geochronology of the south shetland islands lesser antarctica apparent lateral migration of jurassic to quaternary island arc volcanism abstract approximately 70 k ar whole rock ages for low k tholeiitic and andesitic volcanic and intrusive rocks from the south shetland islands antarctica including about 50 not previously published are reviewed activity mainly spanned the range 130 to 30 ma jurassic cretaceous to oligocene miocene with a very recent 2 ma more alkaline renewal throughout the main period of activity magmatism or perhaps its cessation migrated continuously northeastwards along the length of the island chain

a simple model for calculating tsunami flow speed from tsunami deposits abstract this paper presents a simple model for tsunami sedimentation that can be applied to calculate tsunami flow speed from the thickness and grain size of a tsunami deposit the inverse problem for sandy tsunami deposits where grain size and thickness vary gradually in the direction of transport tsunami sediment transport is modeled as a steady spatially uniform process the amount of sediment in suspension is assumed to be in equilibrium with the steady portion of the long period slowing varying uprush portion of the tsunami spatial flow deceleration is assumed to be small and not to contribute significantly to the tsunami deposit tsunami deposits are formed from sediment settling from the water column when flow speeds on land go to zero everywhere at the time of maximum tsunami inundation there is little erosion of the deposit by return flow because it is a slow flow and is concentrated in topographic lows variations in grain size of the deposit are found to have more effect on calculated tsunami flow speed than deposit thickness the model is tested using field data collected at arop papua new guinea soon after the 1998 tsunami speed estimates of 14 m s at 200 m inland from the shoreline compare favorably with those from a 1 d inundation model and from application of bernoulli s principle to water levels on buildings left standing after the tsunami as evidence that the model is applicable to some sandy tsunami deposits the model reproduces the observed normal grading and vertical variation in sorting and skewness of a deposit formed by the 1998 tsunami

estimation of tsunami characteristics from deposits inverse modeling using a deep learning neural network tsunami deposits provide information for estimating the magnitude and flow conditions of paleotsunamis and inverse models have potential for reconstructing hydraulic conditions of tsunamis from th

high resolution imaging science experiment hirise observations of glacial and periglacial morphologies in the circum argyre planitia highlands mars 1 the landscape of the argyre planitia and adjoining charitum and nereidum montes in the southern hemisphere of mars has been heavily modified since formation of the argyre impact basin this study examines morphologies in the argyre region revealed in images acquired by the high resolution imaging science experiment hirise camera and discusses the implications for glacial and periglacial processes distinctive features such as large grooves semicircular embayments in high topography and streamlined hills are interpreted as glacially eroded grooves cirques and whalebacks or roche moutonnee respectively large boulders scattered across the floor of a valley may be ground moraine deposited by ice ablation glacial interpretations are supported by the association of these features with other landforms typical of glaciated landscapes such as broad valleys with parabolic cross sections and stepped longitudinal profiles lobate debris aprons interpreted as remnant debris covered glaciers or rock glaciers and possible hanging valleys aligned boulders observed on slopes may also indicate glacial processes such as fluting alternatively boulders aligned on slopes and organized in clumps and polygonal patterns on flatter surfaces may indicate periglacial processes perhaps postglaciation that form patterned ground at least portions of the argyre region appear to have been modified by processes of ice accumulation glacial flow erosion sediment deposition ice stagnation and ablation and perhaps subsequent periglacial processes the type of bedrock erosion apparent in images suggests that glaciers were at times wet based the number of superposed craters is consistent with geologically recent glacial activity but may be due to subsequent modification

flow speed estimated by inverse modeling of sandy tsunami deposits results from the 11 march 2011 tsunami on the coastal plain near the sendai airport honshu japan abstract tsunami deposits contain information about the flow that created them which can be interpreted to estimate tsunami magnitude sandy deposits near sendai airport are modeled using an inverse sediment transport model to explore the spatial and temporal variation of tsunami flow speed in the 11 march 2011 tohoku oki tsunami the 2011 deposits contain grain size signatures of both sediment transport convergences and sediment settling out of suspension sediment transport convergences form massive or inversely graded intervals sediment falling out of suspension forms a specific type of normal grading termed suspension grading the jaffe and gelfenbaum 2007 inverse sediment transport model which relates the thickness and bulk grain size of suspension graded intervals to tsunami flow speed was applied to 24 suspension graded intervals ranging in thickness from 2 to 4 cm at 7 trenches located from about 250 to 1350 m inland from the shoreline modeled tsunami flow speeds range from 2 2 to 9 0 m s and were strongly dependent on the choice of manning s n roughness parameterization flow speeds were highest from about 75 300 m landward of the forested sand dunes where the tsunami encountered lower roughness in a low lying area as it traveled downslope and decreased by 16 as the tsunami moved inland over the subsequent 596 m as many as 5 suspension graded intervals interpreted as forming during the onshore flow of up to 5 waves were identified at each location with a tendency for an inland decrease in the number of suspension graded intervals suggesting fewer waves inland tsunami flows tended to be fastest in the lower two intervals earlier waves and slowest in the uppermost interval last wave of the deposits modeled reconstructions of the suspension graded intervals at a vertical resolution of 1 cm reproduced observed upward fining of the distributions reasonably well supporting the use of the inverse model estimates of the time required to form 99 of the thickness of the suspension graded intervals ranged 2 to 5 min allowing that sediment falling from suspension could have formed these portions of the deposits in the time between waves application of the inverse model to determine paleotsunami flow speeds from deposits although now possible is complicated by uncertainty in roughness as inverse approaches to estimating roughness and tsunami flow speed improve the magnitude of paleotsunamis will be better understood and the ability to assess tsunami hazard from paleotsunami deposits will improve

experimental tsunami deposits linking hydrodynamics to sediment entrainment advection lengths and downstream fining abstract a goal of paleotsunami research is to quantitatively reconstruct wave hydraulics from sediment deposits in order to better understand coastal hazards simple models have been proposed to predict wave heights and velocities based largely on deposit grain size distributions gsds although seemingly consistent with some recent tsunamis little independent data exist to test these equations we conducted laboratory experiments to evaluate inversion assumptions and uncertainties a computer controlled lift gate instantaneously released 6 5 m 3 of water into a 32 m flume with shallow ponded water creating a hydraulic bore that transported sand from an upstream source dune differences in initial gsds and ponded water depths influenced entrainment transport and deposition while the source dune sand was fully suspendable based on size alone experimental tsunamis produced deposits dominated by bed load sand transport in the upstream 1 3 of the flume and suspension dominated transport downstream the suspension deposits exhibited downstream fining and thinning at 95 confidence a published advection settling model predicts time averaged flow depths to approximately a factor of two and time averaged downstream flow velocities to within a factor of 1 5 finally reasonable scaling is found between flume and field cases by comparing flow depths inundation distances froude numbers rouse numbers and grain size trends in suspension dominated tsunami deposits justifying laboratory study of sediment transport and deposition by tsunamis

reduction effect of tsunami sediment transport by a coastal forest numerical simulation of the 2011 tohoku tsunami on the sendai plain japan abstract we examined the effect of the coastal forest on tsunami sediment movement on the sendai plain japan during the 2011 tohoku tsunami using a numerical simulation of sediment transport to account for the variable roughness coefficient in the coastal forest a composite equivalent roughness coefficient was adopted the simulated mean concentration of suspended sediment wave height flow velocity and inundation limit were significantly reduced by the coastal forest for fine to medium sand the volumes of maximum deposition and erosion were reduced to 57 83 of those in the simulation without the coastal forest these reductions were particularly notable for fine sand the maximum extent and thickness of the sand layer were also reduced the simulated sediment thickness and extent with the coastal forest for finer grain sizes roughly agreed with the observations while the simulated results for coarser sand underestimated the observations the reduction of sediment transport due to the coastal forest suggests that land use conditions and the vegetation environment at the time of a tsunami should be considered when studying historical and paleo tsunamis using the geological evidence

the instability of a south polar cap on mars composed of carbon dioxide abstract if the martian south polar cap were composed of solid carbon dioxide would it be sufficiently stable against collapse under its own weight this question is examined in the light of new experiments on the creep of solid carbon dioxide and new high resolution topographic mapping of the south polar cap the conclusion from a simple model is that with the strongest of three flow laws compatible with the measurements co 2 is strong enough to support a cap of this material with thickness about 1800 m for 10 7 years or more which is the age suggested by the cratering record however none of the three possible flow laws will allow a 3000 m cap the thickness suggested by stereogrammetry to survive for 10 7 years indicating that the south polar ice cap is probably not composed of pure co 2 ice

the global topography of mars and implications for surface evolution elevations measured by the mars orbiter laser altimeter have yielded a high accuracy global map of the topography of mars dominant features include the low northern hemisphere the tharsis province and the hellas impact basin the northern hemisphere depression is primarily a long wavelength effect that has been shaped by an internal mechanism the topography of tharsis consists of two broad rises material excavated from hellas contributes to the high elevation of the southern hemisphere and to the scarp along the hemispheric boundary the present topography has three major drainage centers with the northern lowlands being the largest the two polar cap volumes yield an upper limit of the present surface water inventory of 3 2 to 4 7 million cubic kilometers

tsunami inundation sediment transport and deposition process of tsunami deposits on coastal lowland inferred from the tsunami sand transport laboratory experiment tstle abstract the processes of tsunami inundation sediment transport and deposition on coastal lowlands are investigated experimentally we conducted large scale experiments with land slopes of 0 00 and 0 01 and compared them with experiments conducted previously with a slope of 0 02 the ratio of marine originated sediment in the inland deposits decreased as the land slope decreased reflecting the strong inundation flow and weak return flow the sediment concentration near the bed increased remarkably and supplied a greater quantity of coarse sand inland when the land slope decreased indicating the strong influence of land slope on bed load the extent of sandy deposits and the inundation limit nearly corresponded with the sloping topographies however the inundation flow reached much farther inland than the sandy deposits on the flat i e level topography this was because the extent of sandy deposits was determined by the flow speed which depended in turn on the wave speed whereas the inundation limit was determined by the inland water mass which depended in turn on the waveform the floating load reached the inundation limit and formed very thin and sparse muddy deposits considering the uncertainty of the waveform and the difficulty of detecting muddy deposits it is more feasible to estimate the wave speed from the extent of sandy deposits the spatial distributions of sandy deposits for various waves land slopes and topographies were characterized by the nondimensional area density and inundation distance this result suggested the possibility of quantitative comparison among field investigations of tsunami deposits under various conditions the formation of an inverse grading layer experimentally observed in a wide range of inland deposits was attributed to kinetic sieving the bed load under slow deposition was speculated to thicken the inverse grading layer by reworking the coarse sand additionally the sediment behind dunes became liquefied and showed shear deformation during the erosion the shear deformation of liquefied sediment below the erosional surface might leave sedimentary characteristics specific to earthquake tsunamis

inverse tsunami flow modeling including nonequilibrium sediment transport with application to deposits from the 2011 tohoku oki tsunami tsunami deposits provide important clues to understand ancient tsunami events several inverse models have been proposed to estimate the magnitude of paleotsunamis from their deposits however existing models consider neither non uniform transport of suspended sediment nor turbulent mixing which are essential factors governing sedimentation from suspension in tsunami flows here we propose a new inverse model of tsunami deposit emplacement considering both transport of non uniform suspended load and entrainment of basal sediments this inversion model requires the spatial distribution of deposit thickness and the pattern of grain size distributions of the tsunami deposit along a 1d shoreline normal transect as input data it produces as output run up flow velocity inundation depth and concentration of suspended sediment to solve for advection of non uniform suspended load a transformed coordinate system is adopted which increases computational efficiency tests of model inversions using artificial data successfully allow reconstruction of the original input values suggesting the effectiveness of our optimization method we apply our new inversion model to the 2011 tohoku oki tsunami deposit on sendai plain japan the thickness and grain size distribution of the tsunami deposit was measured along a 4 km long transect normal to the coastline the result of our inversion fits well with the observations from aerial videos and field surveys we conclude that this method is suitable for the analysis of ancient tsunami deposits and that it has the advantage of requiring relatively little information about the condition of the emplacing paleotsunami for reconstruction

influence of ice rheology and dust content on the dynamics of the north polar cap of mars abstract the evolution and dynamics of the north polar cap residual ice cap layered deposits complex of mars is simulated with a thermomechanical ice sheet model we consider a scenario with ice free initial conditions at 5 ma before present due to the large obliquities which prevailed prior to this time the north polar cap is then built up to its present shape driven by a parameterized climate forcing surface temperature surface mass balance based on the obliquity and eccentricity history the effects of different ice rheologies and different dust contents are investigated it is found that the build up scenarios require an accumulation rate of approximately 0 15 0 2 mm a 1 at present the topography evolution is essentially independent of the ice dynamics due to the slow ice flow owing to the uncertainties associated with the ice rheology and the dust content flow velocities can only be predicted within a range of two orders of magnitude likely present values are of the order of 0 1 1 mm a 1 and a strong variation over the climatic cycles is found for all cases computed basal temperatures are far below pressure melting

sedimentology of rocky shorelines 3 hydrodynamics of megaclast emplacement and transport on a shore platform oahu hawaii abstract megaclasts of well cemented coralgal limestone have been emplaced onto a shore platform by large waves on the north shore of oahu hi emplacement and movements of the largest ca 96 ton megaclast have been dated using aerial photographs hydrodynamic forces at the low submerged shoreline cliff are computed using design wave characteristics based on linear wave theory and experimental results considering the local wave climate and near shore bottom topography force exerted by a tsunami has been estimated based on the 1946 aleutian tsunami the computed forces are evaluated in terms of the initial fracturing along a given failure plane that is required in order for the detachment to occur the analysis shows that tsunami as well as large swell waves are capable of quarrying the megaclast provided that sufficient initial fracturing is present dislodgement and emplacement most likely occurred in a sequence during impact of a single wave on the shoreline cliff swell waves however are seldom capable of emplacing large blocks onto the platform due to their rapid disintegration after breaking so that most blocks quarried from the cliff edge fall back onto the submarine terrace emplacement of large boulders seems to require extreme sea waves with periods longer than storms or north pacific swells usually produce transport mechanisms on the shore platform vary depending on megaclast shape sliding is a common mechanism of transport for larger and irregular megaclasts whereas somewhat smaller and platy megaclasts are occasionally found in overturned positions

lineations on the white accumulation areas of the residual northern ice cap of mars their relation to the accublation and ice flow hypothesis abstract mars orbiter camera moc images of the whiter areas of the residual north polar cap p c thomas et al 2000 nature404 161 164 show a gentle hummocky pitted surface that has been popularly called cottage cheese terrain the pits are 1 or 2 m deep and tens of meters across they are typically joined in roughly linear strings or long depressions and these features are referred to here as lineations the lineations tend to have one or occasionally two preferred directions we have examined the moc imagery for the north cap and using high resolution images that have good wide angle context images were able to determine the lineation angles for 31 sites scattered over most of the ice cap we propose a process that will produce linear features in the white areas then relate the orientation of the lineations over much of the north cap to these processes and the inferred ice flow direction there is first order agreement between the measured sign of the lineation angles and those predicted assuming ice flow higher accumulations and velocities are predicted in the catchment for ice that flows into chasma boreale this comes from the indications that katabatic winds are concentrated in this catchment

nature of serpentinization of ultramafic rocks from hero fracture zone antarctic constraints from stable isotopes abstract serpentinites from the hero fracture zone drake passage antarctica contain serpentine amphibole talc chlorite and magnetite as well as relict olivine pyroxene and spinel from a spinel peridotite precursor two episodes of serpentinization are recognized the first event produced lizardite and antigorite whereas the second produced only lizardite the initial and subsequent serpentinization events occurred at about 178 283 c and 170 298 c respectively calculated water rock ratios of the serpentinization events are less than 5 for the initial event and greater than 5 for the subsequent event a model involving deep seawater infiltration in the fracture zone followed by serpentinization of mantle peridotite and buoyancy driven uplift controlled by relatively small scale faults and not by a large scale detachment fault is invoked to explain the emplacement of serpentinite on the surface