normal faulting and the topographic roughness of mid ocean ridge flanks the ocean floor on the flanks of mid ocean ridges is covered by abyssal hills topographic features elongated perpendicularly to the direction of relative plate motion these topographic features are interpreted as normal fault blocks and or volcanic constructions that originated near the ridge axis and were later rafted onto the ridge flanks by seafloor spreading the purpose of this paper is to quantify the topographic roughness of a profile perpendicular to the strike of a number of normal faults given a fault population and a mechanical model for the response of the lithosphere to faulting we obtain expressions for the variation in root mean square roughness with profile length and for the power spectral density of a profile given three parameters a fault density number of faults per unit length crossed by the profile an average squared fault scarp height and a characteristic length of flexure to keep matters simple we make a number of assumptions and approximations namely that the lithosphere behaves as an elastic plate that faults have an infinite length and a vertical dip that the response of topography to a number of faults is simply the sum of the responses to each fault and that faults have random locations and scarp heights independently chosen from some statistical distribution the theory predicts that the roughness length relationship power spectral density should follow power laws for scales wavelengths less than a characteristic scale proportional to the length scale of flexure we compare the predictions of the theory with actual measurements of mid ocean ridge flank roughness and find good first order agreement in particular we use independent estimates of fault densities average squared fault scarp heights and flexural length scales to predict the topographic roughness of the east pacific rise and we find that normal faulting can explain all the observed topographic roughness nevertheless there are some differences between predictions and observations these differences are likely to be due to processes other than faulting that create topographic relief e g volcanism and to spatial correlations of fault scarp heights despite these shortcomings the approach presented here provides a first step in understanding the topographic roughness signal by quantifying the contribution of the geological processes that generate surface relief

violent breaking wave impacts part 1 results from large scale regular wave tests on vertical and sloping walls abstract as part of an investigation into the detailed characteristics of wave impacts experimental data are presented for the impact pressures and forces generated by waves up to 1 7 m high breaking onto a vertical wall and a wall inclined at 27 to the vertical particular attention is given to the influence of entrained and entrapped air and by selecting regular wave conditions that produce impacts trends are identified for highly variable phenomena that could easily be missed when masked by the even greater variability associated with irregular waves the characteristics of the impacts are found to depend on the breaker conditions and four different types of impact are identified and discussed the distinctive features of low aeration and high aeration impacts are considered in some detail and it is shown that a high level of aeration does not always reduce the peak pressure although it tends to increase both the rise time and duration consequently high levels of aeration can increase both the force and impulse on the structure alternate compression and expansion of the air can also generate potentially detrimental sub atmospheric pressures the largest impact pressures tend to occur around still water level and distributions in terms of both the incident wave height and the peak pressure are presented in dimensionless terms for each type of impact although the highest pressures are associated with low and high aeration impacts the results suggest that slightly breaking and broken wave impacts should not be neglected and percentage exceedance curves are included to give an indication of the frequency of extreme values whilst nominally identical waves often produce very different spatial and temporal pressure distributions the impulse on the structure during an impact is far less variable and is shown to be broadly proportional to the peak momentum flux of the incident waves the pressures forces and impulses associated with an impact on the sloping wall tend to be lower than those on the vertical wall in the same circumstances however the total impulse caused by a whole wave event impact plus quasi hydrostatic phases is found to be independent of wall slope in accordance with basic principles the paper concludes by demonstrating that for the conditions investigated the impact can account for up to 30 of the total impulse

cosmic ray labeling of erosion surfaces in situ nuclide production rates and erosion models a number of in situ cosmogenic radionuclides and stable nuclides have been measured in natural exposed rock surfaces with a view to study their in situ production and rock erosion rates 1 the in situ radionuclides can be used for a high resolution tomography of the erosional history of an exposed surface two stable nuclides 3he 21ne and five radionuclides 10be 26al 36cl 14c 39ar having half lives in the range of 300 1 5 106 yr half life are measurable in many rock types a prerequisite for the application of the in situ nuclides for the study of erosional histories of surfaces is a knowledge of their production rates under different irradiation conditions altitude latitude irradiation geometry and shielding relative nuclide production rates can be determined fairly accurately using the extensive available data on cosmic ray neutrons 2 absolute nuclide production rates cannot generally be predicted with any accuracy because of lack of data on excitation functions of nuclides unless some normalization is possible as was done in the case of several cosmic ray produced isotopes in the atmosphere 3 based on a recent natural calibration experiment in which erosion free surfaces exposed to cosmic radiation for 11 000 yrs were sampled the absolute production rates of 10be and 26al in quartz have been accurately estimated for mountain altitudes in sierra nevada 4 the absolute production rates of 10be and 26al in quartz can therefore be estimated fairly accurately for any given latitude and altitude some measurements of 14c in rocks of low erosion rate 5 similarly allow an estimate of its production rate attempts made to measure the in situ production rates of 3he in rocks have not yet led to a convergent production rate in view of the importance of knowing the production rates of isotopes of he ne and ar i present here theoretical estimates of their production rates based on available cross section data i discuss the information that can be extracted from the study of the in situ nuclides in rocks useful parameters characterizing the exposure history of a rock surface are 1 the effective surface exposure age and 2 the time averaged erosion rate the implications of these parameters for single and multiple nuclide studies are discussed in terms of the erosion models considered

late cenozoic deposits at reedy glacier transantarctic mountains implications for former thickness of the west antarctic ice sheet abstract deposits corresponding to multiple periods of glaciation are preserved in ice free areas adjacent to reedy glacier southern transantarctic mountains glacial geologic mapping supported by 10be surface exposure dating shows that reedy glacier was significantly thicker than today multiple times during the mid to late cenozoic longitudinal surface profiles reconstructed from the upper limits of deposits indicate greater thickening at the glacier mouth than at the head during these episodes indicating that reedy glacier responded primarily to changes in the thickness of the west antarctic ice sheet surface exposure ages suggest this relationship has been in place since at least 5 ma the last period of thickening of reedy glacier occurred during marine isotope stage 2 at which time the glacier surface near its confluence with the west antarctic ice sheet was at least 500 m higher than today

experimental investigation and numerical modelling of steep forced water waves steep forced water waves generated by moving a rectangular tank are investigated both experimentally and numerically our main focus is on energetic events generated by two different types of external forcing horizontal motions are arranged to give wave impact on the sidewall steep standing waves forced by vertical acceleration can result in spectacular breaking modes similar to and more energetic than those reported by jiang perlin schultz 1998 hereinafter j98 among them we find thin sheets derived from sharp crested waves mode a of j98 and the flat topped crest or table top breaker mode b of j98 we report here on experimental observations of table top breakers showing remarkably long periods of free fall motion previously such breakers have only been observed in numerical computations both types of breakers often thin as they fall to give thin vertical sheets of water whose downward motion ends in either a small depression and a continuing smooth surface or air entrainment to appreciable depths experimental results are compared graphically with numerical results of two theoretical models one is an extended set of boussinesq equations following wei et al 1995 which are successful up to wave slopes of o 1 the other numerical comparison is with a fully nonlinear irrotational flow solver dold 1992 which can follow the waves to breaking

ross sea paleo ice sheet drainage and deglacial history during and since the lgm onshore and offshore studies show that an expanded grounded ice sheet occupied the ross sea embayment during the last glacial maximum lgm results from studies of till provenance and the orienta

the radiocarbon reservoir effect in proglacial lakes examples from antarctica abstract we studied the apparently old radiocarbon ages from lakes in the dry valleys of antarctica the radiocarbon reservoir effect in these lakes results from two components the inherited age and the residence age the inherited age is derived from input of old carbon primarily from subsurface melt of adjacent glaciers the residence age comes from in situ aging of lake water in an environment sealed from the atmosphere our results indicate that surface melt of glaciers introduces little ancient carbon to the lake system because of rapid gas equilibration with the atmosphere subsurface melt in lakes with large glacier cross sectional areas at the grounding line however can contribute a significant amount of ancient carbon leading to lake bottom reservoir effects in excess of 2700 yr this value can increase to 20 000 yr immediately at the grounding line in most lakes however surface melt far exceeds that from the subsurface and dilutes the effect of ancient carbon making the inherited age relatively low residence ages generally are on the order of a few thousand years but can be as much as 10 000 yr because a residence age is reset when the lake loses its ice cover and is exposed to wind driven mixing its magnitude can provide important information about lake history

the effect of entrained air in violent water wave impacts the effects of entrained air in cushioning water impact on a wall are estimated by using a flow which has many similarities to the severe flip through impacts that have been identified for water waves hitting a vertical wall this is a filling flow which rapidly fills a confined region such as a crack between blocks or the space beneath a deck projecting from the coast peregrine kalliadasis 1996 the main properties of the filling flow are easily calculated including the high pressure peak which corresponds to the pressure peak of a flip through this work extends the study of filling flows to the case where the filling liquid is an air water mixture thus giving explicit results for the reduction of peak pressure due to the compressibility of entrained air the behaviour of a bubbly liquid subject to substantial pressure changes is considered expressions are derived for an air water mixture treated as a compressible fluid the reduction in pressure from the incompressible case is found to be large even for relatively small air content and depends more on the reduction in fluid volume than any other feature of the pressure density relation results are presented in such a way that they may be used to estimate compressibility corrections to both the maximum and background pressures in a flip through wave impact if corresponding incompressible pressure values are available

multiscale spectral analysis of bathymetry on the flank of the mid atlantic ridge modification of the seafloor by mass wasting and sedimentation the results of a multiscale spectral analysis of bathymetric data on the flank of the mid atlantic ridge are described data were collected during two cruises using hydrosweep multibeam tens of kilometers to 0 2 km scale range and mesotech scanning pencil beam sonar attached to remotely operated vehicle jason 1 km to 0 5 m scale range these data are augmented by visual data which enabled us to identify bathymetric profiles which are over unsedimented or thinly sedimented crust our analysis therefore is focused primarily on statistical characterization of basement morphology work is concentrated at two sites site b on 24 ma crust in an outside corner setting and site d on 3 ma crust in an inside corner setting at site b we find that an anisotropic band limited fractal model i e the von karman model proposed for abyssal hill morphology by goff and jordan 1988 is not sufficient to describe the full range of scales observed in this study our observations differ from this model in two ways 1 strike and cross strike dip spectral properties converge for wavelengths smaller than 300 m and 2 in both strike and dip directions the fractal dimension changes at 10 m wavelength from 1 27 at larger scales to 1 0 at smaller scales the convergence of strike and dip spectral properties appears to be associated with destruction of ridge parallel fault scarps by mass wasting which develops canyon like incisions that cross scarps at high angles the change in fractal dimension at 10 m scale appears to be related to a minimum spacing of significant slope breaks associated with scarps which are created by faulting and mass wasting at site d although there is no significant abyssal hill anisotropy the spectral properties at all scales are consistent with the von karman model the fractal dimension at this site 1 15 is less than at site b this difference may be reflect different morphology related to crustal formation at inside corner versus outside corner position or more likely differences in the degree of mass wasting the smoothing of seafloor morphology by sediments is evident in hydrosweep periodograms where relative to basement roughness spectral power decreases progressively with decreasing wavelength

horst and graben structures on the flanks of the mid atlantic ridge in the mark area 23 22 n submersible observations abstract south of the kane fracture zone 23 40 n the mid atlantic ridge is segmented into 20 100 km long spreading cells in which morphology seismic and gravity signatures change along and across the ridge axis the rift valley considered as a typical structure along slow spreading ridges can be symmetric or asymmetric and segment centers experience strong magmatic activity whereas low magma supply results in thinning of the crust at segment tips along the segment centered on the snake pit neovolcanic ridge 23 22 n the rift valley is clearly asymmetric and mantle and lower crustal rocks are commonly exposed on the steepest and highest ridge flanking wall in this area we analyzed submersible observations gravinaute cruise collected up to 50 km on both sides of the axis to discuss the proceses responsible for the axial valley shape its possible relationship with deep rock exposures and to determine the origin of off axis structures our data reveal that the structure and the geology vary on both walls of the axial valley and is different from the volcanic and tectonic organization observed on the neovolcanic ridge itself furthermore the structure of the off axis domain in different from the axial valley and rift mountains are organized in a set of regularly spaced relief about 10 km on both flanks of the ridge scarps which built these topographic highs face either toward the axis or away thus the off axis morphology appears as a set of horsts and grabens which could partly result from off axis tectonic processes and or from a shifting of the volcano tectonic activity out of the axial valley during the last 3 ma off axis data show that serpentinized peridotites more commonly observed on the western rift valley wall crop out on the western flank up to 30 away from the axis models proposed to account for such rock exposure are usually related to the formation of the deep axial valley along slow spreading ridges here we propose that mantle rocks are exposed only in a very particular structural context which is directly controled by the ridge segmentation and is independent of the shape of the axial valley symmetric or not serpentinites crop out within a v shaped structure corresponding with the boundary between two adjacent segments where seismic and gravity data reveal that the crust is thin and the lithosphere is thick here the crust is fed by a lower magma supply than at the segment center snake pit area thus we interpret this segment end to be a region of extremely thin crust where modest normal fault can bring mantle rocks to the surface

prediction of occurrence of breaking waves in deep water abstract a method to evaluate the frequency of occurrence of breaking waves in deep water is developed based on the joint probability distribution of wave excursion and associated time interval for a non narrow band random process wave breaking that takes place along an excursion crossing the zero line as well as that which occurs along an excursion above the zero line is considered the breaking criterion is obtained from measurements of irregular waves generated in the tank it is found that the functional relationship between wave height and period at the time of breaking of the irregular waves is by and large different from that known for regular waves comparisons between computed and observed frequencies of occurrence of wave breaking made for four different sea conditions generated in the tank show reasonably good agreement the effect of sea severity on the frequency of occurrence of breaking waves is obtained by carrying out numerical computations using a family of wave spectra the probability

volcanic growth faults and the origin of pacific abyssal hills the topographic features known as abyssal hills characterize 30 of the ocean floor and yet their origin has been the subject of vigorous debate for over 40 years submersible based investigations show that pacific abyssal hills are created on the flanks of the east pacific rise as horsts and grabens which lengthen with time hills are bounded on one side by ridge facing scarps produced by normal faulting and on the other by more gentle slopes produced by volcanic growth faulting

ocean basin evolution and global scale plate reorganization events since pangea breakup we present a revised global plate motion model with continuously closing plate boundaries ranging from the triassic at 230 ma to the present day assess differences among alternative absolute plate motion models and review global tectonic events relatively high mean absolute plate motion rates of approximately 9 10 cm yr 1 between 140 and 120 ma may be related to transient plate motion accelerations driven by the successive emplacement of a sequence of large igneous provinces during that time an event at 100 ma is most clearly expressed in the indian ocean and may reflect the initiation of andean style subduction along southern continental eurasia whereas an acceleration at 80 ma of mean rates from 6 to 8 cm yr 1 reflects the initial northward acceleration of india and simultaneous speedups of plates in the pacific an event at 50 ma expressed in relative and some absolute plate motion changes around the globe and in a reduction of global mean plate speeds from about 6 to 4 5 cm yr 1 indicates that an increase in collisional forces such as the india eurasia collision and ridge subduction events in the pacific such as the izanagi pacific ridge play a significant role in modulating plate velocities

a 2 million year glacial chronology of the hatherton glacier antarctica and implications for the size of the east antarctic ice sheet at the last glacial maximum abstract a series of distinct glacial deposits flanking the margins of the upper hatherton glacier an outlet glacier in the central transantarctic mountains are used to constrain the behaviour of the antarctic ice sheets cosmogenic exposure ages of 18 erratics from four glacial drifts covering the ice free dubris and bibra valleys range in age from 5 to 1997 ka our results document four glacial advance and retreat events superimposed on an overall long term ice thickness reduction of about 500 m since the mid pleistocene the lack of field evidence and absence of lgm exposure ages in the glacial deposits of the hatherton glacier supports our conclusion that at the lgm the east antarctic ice sheet was of similar size or may have been slightly smaller than present minimum exposure ages from the oldest two glacial events represented by the isca and danum drifts are 1 2 ma and 0 5 ma respectively the britannia ii drift previously assumed to mark the maximum extent of the last glacial maximum advance has a mean 10 be age of 126 3 2 ka n 5 ages from the younger britannia i drift suggest that since the mid holocene 6 5 1 2 ka n 5 approximately 200 m of additional ice has been lost

faulting patterns near 19 30 s on the east pacific rise fault formation and growth at a superfast spreading center 1 structural mapping from high resolution sonar and bathymetric data collected near 19 30 s on the southern east pacific rise epr reveals multiple packets of small closely spaced outward dipping faults that form antithetic to larger inward dipping faults the mean spacing and height of inward dipping scarps are 1 6 and 1 9 times greater than those of outward dipping faults and the median spacing and height of inward dipping scarps are 2 0 and 1 7 times greater respectively accordingly inward dipping faults are less abundant 35 45 but accommodate more 50 55 of the roughly 4 0 strain although previous studies have shown that epr fault populations exhibit exponential size frequency distributions one dimensional throw and spacing data from the 19 30 s region are not described well by this model the first major 40 m scarp height fault is observed within 1 4 km of the ridge crest and invariably dips inward further off axis a transition from greater inward dipping to greater outward dipping fault abundance constrains the minimum half width of the active plate boundary zone to be 5 15 km inspection of additional data sets from 16 and 18 30 s indicates a pattern of large inward dipping faults with associated hanging wall deformation similar to that observed in the 19 30 s region this pattern is distinct from the horst and graben morphology observed along the fast spreading northern epr the pervasive hanging wall deformation observed on the flanks of the southern epr suggests master fault geometries that are more sharply curved or kinked at depth relative to their abyssal hill equivalents on the northern epr boundary element modeling indicates the pattern and geometry of faulting observed along the southern epr is consistent with fault nucleation above a shallow sill like magma chamber with internal overpressure since the influence of the sill on fault growth is strongly dependent on the depth of the sill the different patterns of faulting observed along the northern and southern epr may reflect the small difference in axial magma chamber depth between these two regions with a slightly shallower chamber beneath the southern epr

design and construction of caisson breakwaters the japanese experience abstract the history of breakwater construction in japan is reviewed and present design methods of vertical breakwaters are discussed in terms of wave forces and breakwater stability current design techniques of vertical breakwaters in japan are the culmination of many years of experiences and practical research in this field the goda formula which accurately predicts the design wave forces under most conditions of vertical breakwaters is an excellent aid in the design of the breakwaters under certain conditions excessive impulsive forces due to the action of breaking waves are exerted on the upright section such conditions must be minimized in the design of vertical breakwaters and the adoption of vertical breakwaters covered with wave dissipating concrete blocks or the wave dissipating caisson breakwaters offer potential solutions of this problem the bearing capacity of rubble mound foundation and the stability of armor units are also discussed

glacial cycles drive variations in the production of oceanic crust glacial cycles redistribute water between oceans and continents causing pressure changes in the upper mantle with consequences for the melting of earth s interior using plio pleistocene sea level variations as a forcing function theoretical models of mid ocean ridge dynamics that include melt transport predict temporal variations in crustal thickness of hundreds of meters new bathymetry from the australian antarctic ridge shows statistically significant spectral energy near the milankovitch periods of 23 41 and 100 thousand years which is consistent with model predictions these results suggest that abyssal hills one of the most common bathymetric features on earth record the magmatic response to changes in sea level the models and data support a link between glacial cycles at the surface and mantle melting at depth recorded in the bathymetric fabric of the sea floor

do sea level variations influence mid ocean ridge magma supply a test using crustal thickness and bathymetry data from the east pacific rise abstract recent studies suggest that eustatic sea level fluctuations induced by glacial cycles in the pleistocene influence mantle melting and volcanic eruptions at mid ocean ridges with models predicting variations in oceanic crustal thickness and seafloor bathymetry linked to sea level change analyses of seafloor bathymetry have found evidence of significant spectral energy at frequencies consistent with milankovic cycles of 1 23 1 41 and 1 80 1 120 ka 1 however other studies emphasize the need for crustal thickness observations to test the sea level hypothesis here we investigate the hypothesis of climate driven periodicity in mid ocean ridge magmatism through analysis of a unique bathymetry and crustal thickness dataset derived from a 3d multi channel seismic investigation of the east pacific rise from 9 42 to 57 n crustal thickness data spans the last 235 ka in age and reveals three axis parallel zones of 200 800 m thicker crust the amplitude and spacing of these thick crust ridges which are most prominent on the east flank of the ridge are consistent with predictions of sea level modulated mantle melting similarly spaced ridges are apparent in the longer duration 470 ka seafloor bathymetry data spectral analysis of these datasets shows peaks centered near 1 80 ka 1 and locally near 1 41 ka 1 on the east flank in both bathymetry and crustal thickness west flank spectral results show intermittent peaks near 1 100 ka 1 and 1 41 ka 1 in crustal thickness and no coherent peak frequencies in bathymetry data we attribute differences between the east and west flank to the impacts of spatially variable asymmetric spreading and small changes in the locus of accretion observed half spreading rates are dominantly faster to the east with small ridge jumps transferring crust from the west flank lagged cross correlations between sea level and crustal thickness indicate a maximum when the latter is lagged by 45 ka which align thick crust zones with the 100 ka periods of lower sea level crustal thickness is also directly compared with seafloor bathymetry indicating a component of compensated topography with rms relief at the seafloor of 10 to 29 of crustal thickness variations however complexity inherited from variable asymmetric spreading and seafloor faulting is also apparent and results provide new insights into how the crustal accretion filter modulates the recording of magma supply variations in the crust and in seafloor relief while the significance of the statistical analysis of these ridge records is limited by the short duration of the available crustal thickness dataset and effects of asymmetric spreading the novel observations of crustal thickness varying at timescales of 80 100 ka require a mechanism and the sea level hypothesis provides a plausible explanation

a global and regional stochastic analysis of near ridge abyssal hill morphology this paper presents the results of a global and regional stochastic analysis of near ridge abyssal hill morphology the analysis includes the use of sea beam data for the estimation of stochastic parameters up to order 4 these parameters provide important quantitative physical information regarding abyssal hills including their rms height azimuthal orientation characteristic width aspect ratio hausdorff dimension skewness tilt and peakiness the global data set consists of 64 sea beam swaths near the rivera cocos and nazca spreading sections of the east pacific rise the mid atlantic ridge and the central indian ridge in one form of analysis the parameters are averaged among spreading rate bins each of the spreading rate subsets can be identified as unique from the others in at least one aspect the slowest spreading rate subset mid atlantic data exhibit the largest scales rms height and characteristic width and length of abyssal hills these parameters generally decrease as spreading rate increases up to the fast spreading rate data pacific cocos but increase going from fast to very fast pacific nazca spreading rate data this indicates some complexity in the relationship between spreading rate and abyssal hill morphology the plan view aspect ratio is nearly twice as large for the fast spreading rate data than for any of the other subsets and is smallest for the very fast spreading rate data the fractal dimension is nearly identical for all spreading rate subsets the vertical skewness is positive for the slow and medium spreading rate data indicating larger peaks than troughs and negative for the fast spreading rate data indicating larger troughs than peaks the kurtosis or peakiness is everywhere larger than the gaussian value of 3 and tends to be larger in the atlantic than the pacific the tilting parameter provides substantial evidence indicating steeper inward facing slopes in the medium and fast spreading rate data but only marginal evidence for it in the slow spreading rate data from an analysis of correlations among parameters it is found that subsets sometimes behave differently from the entire data set in particular while over the global data set the characteristic width exhibits a well resolved positive trend when plotted versus rms height these parameters exhibit a more gradual positive trend in the mid atlantic data and a negative trend in the pacific cocos data in addition the plan view aspect ratio while generally uncorrelated with rms height for the global data set is positively correlated with rms height for the pacific cocos data set these results emphasize a strong uniqueness of the pacific cocos data relative to the rest of the data global set the pacific cocos data consist of 27 swaths concentrated between the siquieros and orozco fracture zones these data provide very good abyssal hill coverage of this well mapped and well studied region and form the basis of a regional analysis of the correlation between ridge morphology and stochastic abyssal hill parameters in this analysis it is found that abyssal hill parameters are correlated with the depth of the adjacent ridge axis indicating that the relative abundance in magma supply which likely controls the ridge axis depth may also be an important influence on the formation of abyssal hills

late quaternary evolution of reedy glacier antarctica abstract fresh deposits above the margins of reedy glacier show that maximum ice levels during the last glaciation were several hundred meters above present near the glacier mouth and converged to less than 60 m above the present day surface at the head of the glacier exposure ages of samples from five sites along its margin show that reedy glacier and its tributaries thickened asynchronously between 17 and 7 kyr bp at the quartz hills located midway along the glacier maximum ice levels were reached during the period 17 14 kyr bp farther up glacier the ice surface reached its maximum elevation more recently 14 7 10 2 kyr bp at the caloplaca hills 9 1 7 7 kyr bp at mims spur and around 7 kyr bp at hatcher bluffs we attribute this time transgressive behavior to two different processes at the glacier mouth growth of grounded ice and subsequent deglaciation in the ross sea embayment caused a wave of thickening and then thinning to propagate up glacier during the lateglacial and holocene increased snow accumulation on the east antarctic ice sheet caused transient thickening at the head of the glacier an important result of this work is that moraines deposited along reedy glacier during the last ice age cannot be correlated to reconstruct a single glacial maximum longitudinal profile the profile steepened during deglaciation of the ross sea thinning at the quartz hills after 13 kyr bp while thickening upstream near its confluence with mercer ice stream rapid thinning beginning prior to 7 8 kyr bp reduced the level of reedy glacier to close to its present level thinning over the past 1000 years has lowered the glacier by less than 20 m

violent breaking wave impacts part 2 modelling the effect of air when an ocean wave breaks against a steep fronted breakwater sea wall or a similar marine structure its impact on the structure can be very violent this paper describes the theoretical studies that together with field and laboratory investigations have been carried out in order to gain a better understanding of the processes involved the wave s approach towards a structure is modelled with classical irrotational flow to obtain the different types of impact profiles that may or may not lead to air entrapment the subsequent impact is modelled with a novel compressible flow model for a homogeneous mixture of incompressible liquid and ideal gas this enables a numerical description of both trapped air pockets and the propagation of pressure shock waves through the aerated water an exact riemann solver is developed to permit a finite volume solution to the flow model with smallest possible local error the high pressures measured during wave impacts on a breakwater are reproduced and it is shown that trapped air can be compressed to a pressure of several atmospheres pressure shock waves reflected off nearby surfaces such as the seabed can lead to pressures comparable with those of the impact typical examples of pressure time histories force and impulse are presented and discussed in terms of their practical implications the numerical model proposed is relevant for a variety of flows where air effects are important further applications including extended studies of wave impacts are discussed 2009 cambridge university press

accumulation and marine forcing of ice dynamics in the western ross sea during the last deglaciation ice shelf grounding lines off the coast of antarctica have retreated over the past 20 000 years precise dating of moraines suggests the timing of retreat in the ross sea was controlled by the interplay between accumulation and ocean forcing

late pleistocene evolution of scott glacier southern transantarctic mountains implications for the antarctic contribution to deglacial sea level abstract glacial deposits preserved adjacent to scott glacier southern transantarctic mountains provide a record of past fluctuations in the thickness of the west antarctic ice sheet geologic mapping of these deposits in conjunction with emerging 10 be surface exposure data indicate that the most recent expansion of scott glacier occurred during the last glacial maximum in response to grounding of ice in the ross sea embayment at that time the ice surface at the confluence of scott glacier and the west antarctic ice sheet lay at 1100 m elevation while this ice surface reconstruction is in accord with other geologic estimates from throughout the ross sea embayment it contrasts with most computer based simulations which tend to overestimate former ice thickness in the southern ross sea together with recently modelled estimates of antarctica s contribution to sea level this finding calls into question an antarctic source for meltwater pulse 1a

probability of wave slamming and the magnitude of slamming loads on offshore wind turbine foundations abstract physical model tests were analyzed with the objective to establish a formulae for the probability of wave slamming on offshore wind turbine foundations and the associated slamming force furthermore the effect of wave slamming is analyzed for a monopile wind turbine foundation using a state of the art aeroelastic model the laboratory measurements were carried out in deltares atlantic basin as part of the joint industry project wave impacts on fixed turbines in short jip wifi long crested and irregular waves typical for the north sea were applied and more than 130 design storms and 500 slamming impacts were analyzed a simple closed form expression for the probability of wave slamming is presented and a reasonable agreement with the laboratory measurements shown a criterion for when wave slamming should be included in design computations is formulated based on the sea state steepness it is observed that wave slamming occurs during tests with a flat seabed and that seabed features such as sand waves significantly increase the probability of wave slamming furthermore a simplified slamming load formulation is proposed based on observations from a subset of the laboratory tests the magnitude of the slamming load is validated against the remaining part of the laboratory measurements and compared with existing slamming load formulations the new formulation is in better agreement with the underlying measurements than existing formulations and is of a simpler form which makes it easier to apply the new slamming load formulation is applied in design computations for a realistic wind turbine with the offshore wind farm gemini as base case the computations show that wave slamming at this specific location is not governing the structural design however wave slamming may introduce high accelerations in the transition piece located in the free surface zone where waves are impacting the structure

frequency effects in the dynamic lateral stiffness of monopiles in sand insight from field tests and 3d fe modelling with the offshore wind industry rapidly expanding worldwide geotechnical research is being devoted to foundation optimisation most intensively for large diameter monopiles the analysis and desi

shipping of water on a two dimensional structure part 2 the water shipping problem is modelled in a two dimensional framework and studied experimentally and numerically for the case of a fixed barge shaped structure the analysis represents the second step of the research discussed in greco et al j fluid mech vol 525 2005 p 309 the numerical investigation is performed by using both a boundary element method and a domain decomposition strategy the model tests highlight the occurrence of dam breaking type water on deck a with and b without an initial plunging phase and c an unusual type of water shipping connected with blunt water deck impacts here called a hammer fist type event never documented before cases a a nd c are connected with the most severe events and the related features and green water loads are discussed in detail a parametric analysis of water on deck phenomena has also been carried out in terms of the local incoming waves and bow flow features we classify such phenomena in a systematic way to provide a basis for further investigations of water on deck events the severity of a type water on deck events is analysed in terms of initial cavity area and water front velocity along the deck the former increases as the square power of the modified incoming wave front crest steepness while the latter scales with its square root the two dimensional investigation gives useful quantitative information in terms of waterfront velocity for comparison with three dimensional water on deck experiments on fixed bow models interacting with wave packets

rapid early holocene deglaciation in the ross sea antarctica deglaciation of the ross sea following the last ice age provides an important opportunity to examine the stability of marine ice sheets and their susceptibility to changing environmental conditions insufficient chronology for ross sea deglaciation has helped sustain i the theory that this region contributed significantly to meltwater pulse 1a mwp 1a and ii the idea that ross sea grounding line retreat occurred in a swinging gate pattern hinged north of roosevelt island we present deglaciation records from southern transantarctic mountain glaciers which delivered ice to the central ross sea abrupt thinning of these glaciers 9 8 kyr bp coincided with deglaciation of the scott coast 800 km to the north and ended with the ross sea grounding line near shackleton glacier this deglaciation removed grounded ice from most of the central and western ross sea in less than 2 kyr the ross sea sector neither contributed nor responded significantly to mwp 1a

late quaternary ice surface fluctuations of hatherton glacier transantarctic mountains abstract former longitudinal profiles of hatherton glacier an outlet through the transantarctic mountains constrain nearby polar plateau elevations and ice shelf grounding in the southwestern ross embayment four gravel drift sheets of late quaternary age beside hatherton glacier are from youngest to oldest hatherton britannia i britannia ii and danum the hatherton drift limit is uniformly 20 to 70 m above the present ice surface the britannia ii drift limit is within 100 m of the present surface of uppermost hatherton glacier but is 450 m above middle hatherton glacier extrapolation of this profile downglacier indicates a surface elevation 1100 m above the present ross ice shelf the britannia i drift limit is parallel to but 50 100 m below britannia ii drift the danum drift limit is parallel to but 50 100 m above the britannia ii profile from correlation with drifts near mcmurdo sound and from local 14 c dates we assign an early holocene age to hatherton drift a late wisconsin age to britannia drifts and an age of marine isotope stage 6 to danum drift by our age model the upper reaches of hatherton glacier and presumably the adjacent polar plateau have not exceeded their current elevations by more than 100 150 m during the last two complete global glacial interglacial cycles whereas the middle and lower reaches of hatherton glacier have thickened considerably during the last two global glaciations late wisconsin and marine isotope stage 6 the effect of ice shelf grounding probably was the major control of these changes of hatherton glacier holocene ice surface lowering probably represents the last pulse of grounding line recession in the southwestern ross embayment

quantitative analysis of sea ice draft 1 methods for stochastic modeling this paper seeks to develop a robust set of tools for estimating the stochastic properties of sea ice drafts five parameters are estimated along with their formal uncertainties mean draft rms topographic variation characteristic length fractal dimension and normalized skewness these provide an objective basis for terrain classification a recent 10 km by 10 km upward looking submarine sonar survey serves as a test case data profiles are compared with synthetic profiles generated from the statistical parameters estimated from the data these provide a means of qualitatively assessing the success of the stochastic model at characterizing the principal morphological properties in general the comparisons are good providing confidence in the applicability and versatility of the stochastic model a few exceptions are notable but these also provide valuable insight into our understanding of the morphology of sea ice draft

holocene ice recession at polygon spur reedy glacier antarctica the holocene history of outlet glaciers affords information on the behavior and mechanisms controlling the extent of the east antarctic ice sheet here we present both new radiocarbon and recalcul

stochastic modeling of seafloor morphology inversion of sea beam data for second order statistics at scale lengths less than 100 km or so statistical descriptions of seafloor morphology can be usefully employed to characterize ridge crest processes off ridge tectonics and vulcanism sedimentation and postdepositional transport we seek to develop methods for the estimation of seafloor statistics that take into account the finite precision resolution and sampling obtained by actual echo sounding systems in this initial paper we restrict our attention to the problem of recovering second order statistics from data sets collected by multibeam devices such as sea beam the seafloor is modeled as a stationary zero mean gaussian random field completely specified by its two point covariance function we introduce an anisotropic two point covariance function that has five free parameters describing the amplitude orientation characteristic wave numbers and hausdorff fractal dimension of seafloor topography we formulate the general forward problem relating this model to the statistics of an ideal multibeam echo sounder in particular the along track autocovariance functions of individual beams and the cross covariance functions between beams of arbitrary separation using these second moments as data functionals we then pose the inverse problem of estimating the seafloor parameters from realistic noisy data sets with finite sampling and beamwidth and we solve this inverse problem by an iterative linearized least squares method the inversion method is applied to sea beam transit data from both the pacific and atlantic oceans sea beam system noise stands out as a sharp spike on the along track autocovariance function and can be modeled as a white noise process whose amplitude generally increases with beam angle the five parameters in our second order model can be estimated from the inversion of data sets comprising 100 200 km of track length in general the cross track wave number is the most poorly determined although uncertainties in the assumed sea beam response may bias the values of the fractal dimension using the assumed beamwidth the measured noise values and the seafloor parameters recovered from the inversion we generate sea beam synthetics whose statistical character can be directly compared with raw sea beam data for most of the track segments we have processed thus far the synthetics are similar to the data in the case of one atlantic profile however the comparison clearly indicates the necessity of incorporating higher order statistics the space domain procedures described in this paper can be extended for this purpose

dating quaternary lacustrine sediments in the mcmurdo dry valleys antarctica abstract reports of erroneously old 14c dates for modern antarctic materials have thrown doubt into 14c chronologies the carbon reservoir effect purported to exist in quaternary lacustrine sediments of the mcmurdo dry valleys was investigated by studying 14c distribution and testing alternate dating techniques our results show that the carbon reservoir effect is not pervasive stream and near shore microbial mats and dissolved inorganic carbon dic in the surface waters of lake fryxell are in equilibrium with modern 14co2 the surface waters of lake hoare and lake bonney however have dic 14c ages of 1650 and 2080 yr b p respectively these older age estimates are suggested to be due to the direct input of large amounts of glacial melt with relict dic on the other hand lake fryxell receives only a minor component of its inflow directly from a glacier while a large component must travel long distances in numerous shallow ephemeral streams after leaving local valley glaciers this mode of melt water input allows the water to equilibrate with modern co2 before entering the lake bottom water 14c ages for lake hoare closely match surface sediment ages supporting the widely published period 1200 yr b p after a 1650 yr reservoir correction when most dry valley lakes apparently evaporated to small brine ponds and or disappeared completely lake bonney bottom water is 8000 yr b p carbon dating is shown to be a viable technique for lake edge deposits and possibly lake bottom deposits where a correction to the sediment surface age can be obtained however we conclude that deep water paleolake deposits can not be reliably dated using 14c alone because of an inability to determine the age of the reservoir correction i e accounting for the initial carbon reservoir plus the age of the bottom water a suite of alternative and complimentary dating techniques were tested on modern and late holocene lacustrine deposits these include thermoluminescence tl 210pb 137cs and paleomagnetism of these techniques tl or the more sensitive optically stimulated luminescence holds the most promise for correcting lake sediment 14c ages tl dating of the modern lake hoare sediments showed an 1000 yr relict signal this signal is unaffected by the age of the lake water both 210pb and 137cs occurred in very low levels in the sediments and do not appear to be viable dating techniques for the perennially ice covered lakes of the mcmurdo dry valleys paleomagnetism was not suited to the coarse grained nature of lake hoare bottom sediments but could be a useful alternative given a finer sediment type

wind effects on shoaling wave shape near the shore cross shore winds strongly affect the location of the break point and the breaking wave height from casual observation from the beach wind direction onshore or offshore and speed also appear to affect wave shape i e skewness and asymmetry although as of yet this effect has not been quantified near the shore the effect of wind on shoaling wave shape is investigated with laboratory experiments using monochromatic waves and onshore directed wind wind increases the shoaling wave energy at discrete multiples of the primary frequency and has a significant effect on the wave shape at both a deeper and shallower shoaling locations at the shallower location the ratio of wave energy at 2 times the primary frequency to the primary frequency is also a function of wind speed indicating interaction between the wind and the nonlinear wave shoaling process nearshore wave models do not account for these wind effects incorrect predictions of third order velocity moments wave shape believed to control wave driven sediment transport would result in incorrect beach morphological evolution predictions

late quaternary ice surface fluctuations of beardmore glacier transantarctic mountains abstract former longitudinal profiles of beardmore glacier an outlet through the transantarctic mountains constrain polar plateau elevations near the center of antarctica and ice shelf grouding in the southern ross embayment three gravel drift sheets of late quaternary age occur alongside beardmore glacier plunket drift the youngest is parallel to and 7 30 m above the present ice surface the upper limit of beardmore drift intermediate in age is within 35 40 m of the present ice surface near the polar plateau but about 1100 m above the present ice surface near the glacier mouth the upper limit of meyer drift the oldest is parallel to and 30 50 m above beardmore drift from correlation with numerically dated drifts farther north we assign an early holocene age to plunket drift a late wisconsin age to beardmore drift and an age of marine isotope stage 6 to meyer drift by our age model beardmore glacier was close to current elevations in its upper reaches and thickened considerably in its middle and lower reaches during the last two global glaciations represented by beardmore and meyer drifts most likely grounded ice in the southern ross embayment caused such thickening of beardmore glacier almost to the polar plateau a concomitant decline in precipitation is implied by ice cap retreat on the nearby dominion range and is consistent with little change of upper beardmore glacier ice shelf grounding most likely resulted from lowered sea level and or basal melting lower than present precipitation was probably caused by colder air temperatures and more distant open water the plunket profile records holocene ice surface lowering from increased surface ablation decreased ice flow or grounding line recession

wave impact pressure and its effect upon bodies lying on the sea bed abstract this paper is concerned with the very large sudden pressures produced by water wave impact on a vertical wall numerical and theoretical models are briefly described and we show that there are significant pressure gradients along an impermeable sea bed away from the wall this aspect of wave impact pressure has not previously been noted the effects of such transient pressure gradients on bodies lying on the bed are examined in the light of pressure impulse theory our theoretical results indicate that bodies may be displaced by these pressure gradients when ordinary fluid drag is insufficient to move them we discuss the impulse and the speed imparted to a rigid body lying within a region of pressure impulse which has constant horizontal gradient and we show that the impulse is related to the body s volume and shape analytic results are given for a hemi ellipsoidal boulder which is free to translate in a direction perpendicular to the wall the analysis for the hemi ellipsoid encompasses the special cases of a semi circular cylinder and a semi circular disc the case of a circular cylinder which touches the bed is also discussed and it is shown that there is a significant vertical impulse on the body in addition to the horizontal component of the impulse

seismic structure across the rift valley of the mid atlantic ridge at 23 20 mark area implications for crustal accretion processes at slow spreading ridges the results from a 53 km long wide angle seismic profile across the rift valley of the mid atlantic ridge south of the kane transform near 23 20 n mark area provide new constraints on models of tectonic extension and magmatic accretion along slow spreading mid ocean ridges anomalously low middle and lower crustal p wave velocities beneath the neovolcanic snake pit ridge are consistent with elevated axial temperatures and with the presence of 4 1 partial melt evenly distributed within the lower crust in preferentially oriented elongated thin films if the melt inclusions have larger aspect ratios melt fractions can be up to 17 3 this and other geological observations suggest that the study area is presently in a magmatically active period the igneous crust is anomalously thin beneath both flanks of the median valley 2 3 2 5 km thus the mantle rocks observed along the western rift valley wall at pink hill were probably emplaced at shallow levels within the valley floor during a period of very low magma supply and were later exposed on the valley walls by normal faulting the crust within the eastern rift valley and flanking rift mountains is seismically heterogeneous with igneous crustal thickness variations of 2 2 km over horizontal distances of 5 km this heterogeneity indicates that the magma supply in the area has fluctuated during the last 2 m y thus magmatic and amagmatic periods at slow spreading ridges may alternate over much shorter temporal scales that previously inferred from sea surface gravity data