model experiments on large tabular iceberg evolution ablation and strain thinning antarctic tabular icebergs are important active components of the ice ocean system to investigate the relevance of inherent ice dynamics to iceberg evolution we developed a numerical model based on the fundamental equations of ice shelf flow and heat transfer forced by environmental parameters of the ice ocean atmosphere system model experiments with idealized icebergs of constant density show that the strain thinning rate for a typical iceberg with a thickness of 250 m and a temperature of 158c is about 1 m a 1 sensitivity studies for different scenarios of environmental conditions confirmed the reliability of our model a 5 year simulation of the evolution of iceberg a 38b yielded a mean decrease in thickness from 220 m to 106 3 m 95 of which was caused by basal melting 1 by surface melting and 4 by strain thinning we found iceberg spreading decelerating by about 75 and ice temperatures being strongly affected by progressive erosion of the relatively warm basal layers and warming in the uppermost part according to the model results basal melting is the primary cause of change of iceberg geometry during drift whereas strain thinning is only relevant in cold areas where basal melting is low

change in climate ocean and ice sheet conditions in the ross embayment antarctica at 6 ka evidence from the ross embayment antarctica suggests an abrupt cooling and a concomitant increase in sea ice cover at about 6000 sp 6 ka stable isotope delta d concentrations in the taylor dome ice core at the western edge of the ross embayment decline rapidly after 6 ka and continue to decline through the late holocene methanesulfonic acid concentrations at taylor dome show opposite trends to delta d sediment cores from the western ross sea show a percentage minimum for the sea ice diatom fragilariopsis curta between 9 and 6 ka when taylor dome delta d values are highest followed by an increase through the late holocene radiocarbon dates from raised beach deposits indicate that the retreat of ice shelves in the ross embayment ceased atabout 6 ka coincident with the environmental changes inferred from the sediment and ice core records the similarity in timing suggests an important role for climate in controlling the evolution of ice shelf margins following the end of the last 9 glaciation

relating the occurrence of crevasses to surface strain rates the presence of crevasses on the surface of ice masses indicates that a fracture criterion has been met understanding how crevasses form will provide information about the stress and strain rate fields in the ice this study derives a relationship between measurements of strain rate and observations of crevassing on the surface of ice masses a literature search yielded 17 polar and alpine locations where strain rates had been measured and crevassing recorded by plotting strain rates converted to stresses using a creep law using axes representing the surface parallel principal stresses failure envelopes were derived by enclosing measurements where surface crevassing was absent the derived failure envelopes were found to conform well to theoretical ones predicted by the coulomb and the maximum octahedral shear stress von mises theories of failure the derived failure envelopes were scaled by the tensile strength which was found to vary from 90 to 320 kpa there was no systematic variation of tensile strength with either temperature at 10 m depth or the method used to locate the crevasses the observed variation in tensile strength could result from variations in ice properties e g crystal size impurity content or density or could be related to uncertainty in the constitutive relation creep flow and fracture share a very similar temperature dependence suggesting similar crystal scale processes are responsible for both the observed relationship will provide a supplementary tool with which to verify and test models of ice dynamics against remotely sensed imagery the study also indicates that a temperature rise of a few degrees throughout the ice column will not result directly in any increase in calving rates from the large antarctic ice shelves such as the filchner ronne or ross ice shelves

tidal flexure at ice shelf margins hinge zones accommodate the differential tidal movement between floating ice shelves which move with the sea tide and grounded ice sheets which do not observations on rutford ice stream and ronne ice shelf antarctica using the kinematic method of global positioning system have yielded the first continuous tidal displacement profiles from an ice sheet hinge zone the form of these tidal displacement profiles indicates that the flexure can be fit to an elastic beam model using a parameter space optimization technique the model matches the observed tidal deflection profile to within 5 cm which is similar to the observational uncertainty the same model and parameter fitting technique is then successfully applied to various other published and unpublished tidal displacement data from doake ice rumples bach ice shelf and ekstrom ice shelf antarctica and jakobshavns glacier greenland i conclude that the elastic beam model with a single value of the elastic modulus 0 88 0 35 gpa adequately describes almost all the data and so can usefully be applied elsewhere earlier studies of tidal dissipation in ice shelf hinge zones based on a viscous or transient creep rheology showed that perhaps 30 of global tidal energy dissipation could be occurring in ice shelf hinge zones this study suggests however that an elastic rheology may be equally appropriate in which case this estimation of the tidal energy dissipation is excessively high

three dimensional modeling of tsunami forces on coastal communities abstract recent research on tsunami inundation of coastal communities has largely focused on numerical modeling of tsunami runup on two dimensional 2d slopes or three dimensional 3d topographies with more complex shorelines the coastal bathymetry that are generally applied are based on bare earth topography few studies have simulated overland flow around existing macro roughness features such as nearshore buildings and bridges this is often due to both lack of available data and the fact that it can be computationally demanding to incorporate these additional features a consequence of omitting the built infrastructure from models is that to predict tsunami forces and corresponding structural demand extrapolations from overland flow data is necessary and for densely populated communities these flow predictions may not be appropriate in this work a high resolution 3d computational fluid dynamics approach is used to model tsunami inundation of a 1 50 model scale idealized community representative of the town of seaside or usa for which existing experimental data is available several buildings were selected and flow characteristics water level velocity and momentum flux in the vicinity of these buildings were validated against experimental data several computational domains were analyzed and it is shown that local flow characteristics can be captured using subdomains of the community reducing computational demand force predictions using direct integration of predicted pressure were compared with bare earth momentum flux calculations and the importance of incorporating the constructed environment in force prediction models is discussed finally comparisons with seismic load predictions for a selected building are presented for comparison

the 11 march 2011 east japan earthquake and tsunami tsunami effects on coastal infrastructure and buildings the 11 march 2011 east japan earthquake and tsunami caused unprecedented damage to well engineered buildings and coastal structures this report presents some notable field observations of structural damage based on our surveys conducted along the sanriku coast in april and june 2011 engineered reinforced concrete buildings failed by rotation due to the high velocity and deep tsunami inundation entrapped air in the buildings and soil liquefaction by ground shaking could have contributed to the failure the spatial distribution pattern of destroyed and survived buildings indicates that the strength of tsunami was affected significantly by the locations of well engineered sturdy buildings weaker buildings in the shadow zone tended to survive while jet and wake formations behind the sturdy buildings enhanced the tsunami forces we also found that buildings with breakaway walls or breakaway windows doors remained standing even if the surrounding buildings were washed away or destroyed several failure patterns of coastal structures seawalls were observed flow induced suction pressure near the seawall crown could have caused the failure of concrete panels that covered the infill remarkable destruction of upright solid concrete type seawalls was closely related with the tsunami induced scour and soil instability the rapid decrease in inundation depth during the return flow phase caused soil fluidization down to a substantial depth this mechanism explains severely undermined roads and foundations observed in the area of low flow velocities

an ice shelf mechanism for heinrich layer production the effect of an ice shelf in the labrador sea on ice rafted sediment delivery to the glacial north atlantic is investigated using a finite element numerical model of ice shelf flow discharge into the shelf from hudson strait creates a thick central core extending downstream into the shelf that is flanked by relatively thin ice melting at the base of the deep keel would produce cool fresh water which would rise to refreeze along the keel s flanks debris deposited by melting deep central ice could create the heinrich layers observed in the labrador sea while the debris rich ice protected by basal freezing on the flanks of the thick ice plume could transport sediment over large distances heinrich layers would be produced solely by external climate forcing without changes in ice sheet flow the mechanism is plausible if the lifetime of the ice shelf is about 1000 years

marine ice formation in a suture zone on the larsen c ice shelf and its influence on ice shelf dynamics 1 antarctic ice shelves are fed primarily by the glaciers flowing into them downstream of promontories separating these glaciers supercooled water can rise and freeze into suture zones leading to the accretion of marine ice marine ice bodies have been found in several antarctic ice shelves but little is known about their detailed geometry rate of accretion or influence on ice dynamics in this study we investigate marine ice in a suture zone downstream of the joerg peninsula in the southern part of the larsen c ice shelf antarctic peninsula we present ground penetrating radar data from which we infer the base of the meteoric ice and in combination with gps data and assuming hydrostatic equilibrium estimate marine ice thickness within a suture zone we show that the joerg peninsula suture zone contains marine ice layer which is increasing in thickness along flow from 140 m to 180 m over 20 km implying an average basal accretion rate of 0 5 m a 1 in our study area we examined the impact of this inferred marine ice on ice shelf dynamics by modeling the suture zone within an ice flow model the results which replicate observed surface velocities and strain rates show that the warmer and thus softer ice of the suture zone serves to channel shear deformation this enables decoupling of neighboring flow units with different flow velocities while maintaining the structural integrity of the ice shelf

three dimensional simulation of tsunami run up around conical island abstract at the circular babi island in the flores tsunami 1992 and pear shaped island in the okushiri event 1993 unexpectedly large tsunami run up heights in the lee of conic islands were observed the flume and basin physical model studies were conducted in the coastal hydraulic laboratory engineering research and development center u s army corps of engineers to provide a better understanding of the physical phenomena and verify numerical models used in predicting tsunami wave run up on beaches islands and vertical walls reasonably accurate comparison of run up height of solitary waves on a circular island has been obtained between laboratory experimental results and two dimensional computation model results in this study we apply three dimensional rans model to simulate wave run up on conical island in the run up computation we obtain that 3d calculations are in very good comparison with laboratory and 2d numerical results a close examination of the three dimensional velocity distribution around conical island to compare with depth integrated model is performed it is shown that the velocity distribution along the vertical coordinate is not uniform and velocity field is weaker in the bottom layer and higher on the sea surface the maximum difference about 40 appears at the time when solitary wave reached the circular island

large scale ice flow over a viscous basal sediment theory and application to ice stream b antarctica recent seismic studies of ice stream b antarctica and field analysis of mid latitude glacial deposits suggest that deformable basal sediments e g water saturated till are important in determining ice sheet flow if the ratio of till viscosity to effective ice viscosity is small vertical shear associated with horizontal flow is confined to the deforming bed alone ice flow over a deformable bed is thus akin to that of floating ice shelves because ice shelves flow over inviscid seawater for some antarctic ice streams and possibly for portions of the late wisconsin ice sheets in north america and eurasia basal drag associated with deforming basal sediment does not induce significant vertical gradients of horizontal velocity instead basal drag affects the flow as if it were a horizontal body force balanced by longitudinal and transverse deviatoric stress gradients comparison of the observed flow of ice stream b to finite element simulations incorporating a viscous basal till suggest that a simple till theology is sufficient to explain the current velocity profile these simulations also highlight the importance of horizontal deviatoric stress in regions where driving stress and basal stress do not locally balance while bed deformation is critical to ice stream existence sensitivity tests suggest that ice shelf back pressure is still a crucial control affecting ice stream response to atmospheric and oceanic climate

thermohaline circulation below the ross ice shelf a consequence of tidally induced vertical mixing and basal melting the warmest water below parts of the ross ice shelf resides in the lowest portion of the water column because of its high salinity vertical mixing caused by tidal stirring can thus induce ablation by lifting the warm but dense water into contact with the ice shelf a numerical tidal simulation indicates that vertically well mixed conditions predominate in the southeastern part of the sub ice shelf cavity where the water column thickness is small basal melting in this region is expected to be between 0 05 and 0 5 m yr and will drive a thermohaline circulation having the following characteristics high salinity shelf water at 1 8oc formed by winter sea ice production in the open ross sea flows along the seabed toward the tidal mixing fronts below the ice shelf and meltwater at 2 2oc produced in the wellmixed region flows out of the sub ice shelf cavity along the ice shelf bottom sensitivity of this ablation process to climatic change is expected to be small because high salinity shelf water is constrained to have the sea surface freezing temperature

a modified theory of bottom crevasses used as a means for measuring the buttressing effect of ice shelves on inland ice sheets bottom crevasses are fractures that extend upward into floating ice shelves they form when seawater penetrates the base of the ice shelf and ruptures the ice up to the level at which englacial stresses equal the stress of the seawater for a freely floating ice shelf the penetrating level of closely spaced crevasses is estimated at about half the ice thickness h for an isolated crevasse the level is about h 4 however an analysis of the heights and locations of bottom crevasses in the ross ice shelf shows that none of the crevasses approach the predicted limits perhaps because the existing theory does not include the back stress b which is present in bounded ice shelves by reformulating the theory to include a back stress term b can be evaluated experimentally from radar measurements of crevasse height and ice thickness the magnitude of b 2 bars in the grid northwest corner of the ice shelf suggests the ice shelf is playing an important role in buttressing the inland ice sheet

petrogenesis and tectonic setting of early paleozoic granites and high mg diorites in the northern qilian orogen china abstract the northern qilian orogenic belt n qob was formed by oceanic subduction and collision between the alashan and central qilian belt in the early paleozoic new zircon u pb ages hf isotopic and whole rock elemental data of the intrusive rocks in the central n qob have been conducted to constrain the tectonic evolution of n qob zircon dating results revealed that the ladonggou suyougou granitic plutons and xichagou dioritic pluton were emplaced at 505 3 ma 471 3 m and 425 3 ma respectively the ladonggou monzogranite displays depletion of nb ta ti p and negative ehf t values 6 5 to 0 3 and old hf crustal model ages 1 5 1 9 ga suggesting generation from melting of ancient crust above subducted north qilian oceanic slab the suyougou granite possesses geochemistry of i type granite the relative enrichment of liles depletion of hfses and negative eu anomalies as well as prominent hf isotope heterogeneities and old hf crustal model ages 2 1 2 5 ga suggest a magma source of ancient crust mixed with minor mantle derived melts in a subduction related setting diorites from the xichagou plutonare characterized by high mg values enrichments in cr ni y yb and high sr y ratios and convincing subduction related features suggesting generation from partial melting of subducted sediments mixed with mantle components taking all these geochemistry and geochronology together with the regional geology we interpreted the ladonggou monzogranite suyougou granite and xichagou diorite were related to the long term northward subduction of north qilian oceanic lithosphere during ca 505 and 425 ma

an investigation of low stress ice rheology on the ward hunt ice shelf deformation of the ward hunt ice shelf northwest territories canada can be used to study the rheology of ice in the low stress low strain rate regime 10 12s 1 finite element simulations are separately displayed to demonstrate what the effects of ice salinity ice temperature and sea ice back pressure have on the spreading rates of this ice shelf we conclude that in general these effects tend to obscure any differences between the commonly used non newtonian flow law and the newtonian flow law recently reinterpreted from field measurements the numerical simulations indicate that there are specific locations where useful field measurements could be carried out on the ice shelf

a comparative modeling study of the brunt ice shelf stancomb wills ice tongue system east antarctica two diagnostic dynamic thermodynamic ice shelf models are applied to the brunt ice shelf stancomb wills ice tongue system located off caird coast coats land antarctica the brunt ice shelf stancomb wilis ice tongue system is characterized as a thin unbounded ice shelf with an atypical and highly heterogeneous structure in contrast to other ice shelves a composite mass of icebergs that calved at the grounding line and were then locked within fast sea ice exists between the fast moving stancomb wills ice stream and the slow moving brunt ice shelf we simulate the present flow regime of the ice shelf that results from the ice thickness distribution and the inflow at the grounding line with two different models and compare the model results with feature tracking and insar flow velocities we then incorporate two observed features a rift and a shear margin into the models with two different approaches and demonstrate the effects of variations in numerical values for the shear strength and viscosity in these zones on the simulated velocity field a major result is that both kinds of implementation of the rifts lead to similar effects on the entire velocity field while there are discrepancies in the vicinity of the rifts

a thin viscous sheet model for continental deformation summary for the purposes of describing its large scale and long term deformation the continental lithosphere is regarded as a continuum obeying a newtonian or a power law rheology the flow of a thin sheet of power law material overlying an inviscid substrate is studied under the assumption that vertical gradients of the horizontal velocity are negligible a numerical model is used to investigate the deformation of such a sheet under conditions approximating those of continent continent collision the material flows in response to forces applied to its boundaries for example the indenting of one continent by another and to forces in its interior arising from gradients in crustal thickness the horizontal divergence of the flow produces changes in the crustal thickness and hence a time dependent form to the flow itself for a given set of boundary conditions the flow depends on the stress exponent in the power law rheology n and on the argand number which is a measure of the ratio between the stress arising from crustal thickness contrasts and the stress required to deform the material at the ambient strain rates when the effective viscosity of the medium is very high ar o crustal thickness variations do not influence the flow if the material is newtonian n l the deformation associated with an influx of material approximating an indenter is of much greater lateral dimension than the width of the indenter whereas when material has a power law rheology n 3 5 are used the deformation is confined to a region of lateral extent comparable to that of the indenter as ar increases the forces arising from crustal thickness contrasts exert more influence on the flow and the maximum crustal thickness that can be sustained by a given influx of material is related by a simple expression to the effective viscosity of the medium at the ambient strain rates in the limit of a very weak medium ar 10 the lithosphere is unable to sustain appreciable crustal elevation contrasts the results of these numerical experiments show that systems in which the effective viscosities are such that the maximum deviatoric stresses are between 1 kbar

correction to a thin viscous sheet model for continental deformation summary the governing equation derived by england mckenzie for the deformation of a thin viscous shell contains an error we give the correct derivation here and correct those figures where the change makes a visible difference the correct results differ quantitatively from those of england mckenzie but their conclusions are not affected

present stability of the larsen c ice shelf antarctic peninsula we modelled the flow of the larsen c and northernmost larsen d ice shelves antarctic peninsula using a model of continuum mechanics of ice flow and applied a fracture criterion to the simulated velocities to investigate the ice shelf s present day stability constraints come from satellite data and geophysical measurements from the 2008 09 austral summer ice shelf thickness was derived from bedmap and icesat data and the density depth relationship was inferred from our in situ seismic reflection data we obtained excellent agreements between modelled and measured ice flow velocities and inferred and observed distributions of rifts and crevasses residual discrepancies between regions of predicted fracture and observed crevasses are concentrated in zones where we assume a significant amount of marine ice and therefore altered mechanical properties in the ice column this emphasizes the importance of these zones and shows that more data are needed to understand their influence on ice shelf stability modelled flow velocities and the corresponding stress distribution indicate that the larsen c ice shelf is stable at the moment however weakening of the elongated marine ice zones could lead to acceleration of the ice shelf due to decoupling from the slower parts in the northern inlets and south of kenyon peninsula leading to a velocity distribution similar to that in the larsen b ice shelf prior to its disintegration

rheology of glacier ice a new method for calculating the stress field in bounded ice shelves is used to compare strain rate and deviatoric stress on the ross ice shelf antarctica the analysis shows that strain rate per second increases as the third power of deviatoric stress in newtons per square meter with a constant of proportionality equal to 2 3 x 10 25

rheology of the lithosphere selected topics we review recent results concerning the rheology of the lithosphere with special attention to the following topics 1 the flexure of the oceanic lithosphere 2 deformation of the continental lithosphere resulting from vertical surface loads and forces applied at plate margins 3 the rheological stratification of the continents 4 strain localization and shear zone development and 5 strain induced crystallographic preferred orientations and anisotropies in body wave velocities we conclude with a section citing the 1983 1986 rock mechanics literature by category

dynamics and mass balance of the ice sheet ice shelf regime at nivlisen antarctica as derived from a coupled three dimensional numerical flow model

numerical model studies of antarctic ice sheet ice shelf ocean systems and ice caps the cryosphere is an essential component of the global climate system equally affecting climate processes significantly and being subject and particularly sensitive to changes in climate conditions numerical models are an important tool for assessing climate change impacts on the antarctic ice sheet ice shelf ocean system they not only complement field and satellite remote sensing investigations but are often the only feasible alternative for addressing some of the important parameters and processes over the last few years our group has made significant progress in developing and applying innovative numerical methods in this paper we provide a brief overview of some of the methods employed and the major results obtained for a number of case studies in the atlantic sector of antarctica

investigating tidal flexure on an ice shelf using kinematic gps the positions of ice stream grounding zones are uniquely sensitive to changes in the mass balance of the ice sheet present methods for locating groundingzone features are either imprecise or require considerable effort in interpretation and so are of little value for change studies we present a new method which uses the kinematic gps technique to locate the position of the limit of tidal flexure the method involves the collection of at least two surface elevation profiles along the same track through the grounding zone at different times during the tidal cycle the elevation profiles obtained coincide upstream of the limit of flexure but diverge downstream of the limit of flexure subtracting the profiles produces a tidal def1ection profile which shows directly the response of the ice shelf to the tidal forcing we present two examples of the use of this method both on rutford ice stream antarctica the first is across the grounding zone and shows that the method is capable of measuring grounding positions to around 200 m precision the second taken across an active shear margin shows a tidal deflection profile with an absence of steps that would indicate the presence of fracture planes penetrating from the ice base to sea level

ductile deformation and the origin of layered gabbro in ophiolites layered gabbros in ophiolites have been commonly interpreted in terms of crystallization beneath oceanic spreading centers in magma chambers up to 30 km wide and 3 6 km deep although large steady state magma chambers provide a possible explanation for the limited diversity of mid ocean ridge basalts their existence is not supported by geophysical observations sinton and detrick 1992 recently reviewed seismic data from oceanic spreading centers and concluded that there is little evidence for steady state magma chambers beneath slow spreading ridges and that fast spreading ridges appear to be underlain by small 1 4 km wide magma chambers perched on large 8 km wide zones of low velocity material which are interpreted to consist of partially molten crystal cumulates in this paper we compare the geology of the gabbroic rocks of the samail ophiolite which is thought to have formed by fast spreading with results of a finite element analysis of the sinton detrick model for fast spreading centers our results demonstrate that flow similar to that postulated by sleep 1975 within a thick zone of cumulates during crustal extension could produce orientations of foliation and layering approximating those observed in the samail gabbros as a consequence of this deformation 1 layers deposited on the floor of the magma chamber will be deformed and rotated into upwardly concave shapes that dip toward the spreading center 2 the gross fabric defined by these orientations may greatly exceed the dimensions of the deforming regime let alone the magma chamber 3 feeder dikes that penetrate the cumulate pile near the spreading axis will be rotated into parallel with the layering but those that invade farther from the ridge will be less deformed and retain crosscutting relationships and 4 total deviatoric strain should increase down section toward the moho so that primary magmatic structures and textures will be modified or obliterated in the lowermost gabbros upward migration of melts through the subsiding and deforming crystal mush may damp out cryptic varition in the gabbros and help maintain the magma chamber in a compositional steady state

the effects of basal melting on the present flow of the ross ice shelf antarctica on utilise un modele mixte aux elements finis et differences finies de l ecoulement et du transfert de chaleur avec deux hypotheses fusion nulle partout et fusion equilibrant tout epaississement a grande echelle

laboratory experiments of tsunami runup on a circular island laboratory experiments of a 7 2 m diameter conical island were conducted to study three dimensional tsunami runup the 62 5 cm tall island had 1 on 4 side slopes and was positioned in the center of a 30 m wide by 25 m long flat bottom basin solitary waves with height to depth ratios ranging from 0 05 to 0 20 and source lengths ranging from 0 30 to 7 14 island diameters were tested in water depths of 32 and 42 cm twenty seven capacitance wave gages were used to measure surface wave elevations at incident and four radial transects on the island slope maximum vertical runup measurements were made at 20 locations around the perimeter of the island using rod and transit a new runup gage was located on the back or lee side of the island to record runup time series

force mass and energy budgets of the crary ice rise complex antarctica the stress mass and energy dissipation budgets of crary ice rise are analyzed using field data collected during the 1983 1985 austral summers and in previous field programs in addition the net back pressure and ice discharge rate along the grounding lines of ice streams are calculated to assess the effect of the ice rise on the surrounding flow comparison of the ice rise budgets with the analysis of grounding line data confirms the influence of the ice rise on ice sheet stability and suggests that crary ice rise may have formed recently in response to an acceleration of one of the ice streams it is concluded that feedback between ice stream acceleration and ice rise formation may control the future evolution of the above ice stream and promote long term grounding line stability in the face of strong natural fluctuations

tidal flexure of jakobshavns glacier west greenland jakobshavns glacier a floating outlet glacier on the west greenland coast was surveyed during july 1976 the vertical displacements of targets along two profiles perpendicular to the fjord wall bounding the north margin of the glacier were analyzed to determine the effect of flexure caused by tidal oscillations within the fjord an analysis based on the assumption that vertical displacements of the glacier reflected pure elastic bending yielded the conclusion that the effective thickness of the ice i e the thickness which remained unaffected by surface and basal cracking and which behaved as a continuum was 160 m 2 6 km upglacier from the calving front and 110 m 0 6 km from the calving front an analysis based on the more realistic assumption that observed bending reflected elastic and viscoplastic deformation yielded the conclusion that the average effective thickness of the ice was 316 74 m 40 of the estimated 800 m total thickness 2 6 km from the calving front and 160 48 m 21 of the estimated 750 m total 0 6 km from the calving front a constitutive relationship appropriate for hard glide during flexure was used

a numerical model of interactions between a polar ice stream and the ocean application to ice stream e west antarctica a time dependent numerical model has been developed to study the dynamics of a polar ice stream grounded below sea level the model was applied to ice stream e one of the two most active ice streams draining the ross sea sector of the west antarctic ice sheet the retarding force or back stress from the floating ross ice shelf needed to hold the model grounding line in dynamic equilibrium was found to compare closely with retarding force mapped from field data by earlier investigators this implies that the grounding line of ice stream e is in fact close to dynamic equilibrium neither advancing nor retreating rapidly if the ice stream and its catchment area are approximately in mass balance sensitivity tests showed that the model ice stream is more sensitive to changes in back stress from the ice shelf than to changes in the accumulation rate changes in back stress can be caused by changes in the average thickness of the ice shelf the model was used to simulate retreat of the ice stream from the edge of the continental shelf in the ross sea during the holocene period of rising sea level the sea floor was assumed to be isostatically depressed but to remain rigid during retreat the effect of the assumed retreat history of the ross ice shelf on the computed timing of grounding line retreat was investigated by considering several alternative ice shelf histories the results support the conclusion of earlier investigators that the ross ice shelf caused the grounding line to stop retreating near its present position after extensive retreat during the holocene in addition the timing of retreat of the calving front of the ross ice shelf exerted major influence on the timing of retreat of the ice stream grounding line

survey of 2011 tohoku earthquake tsunami inundation and run up 1 at 14 46 local time on march 11 2011 a magnitude 9 0 earthquake occurred off the coast of northeast japan this earthquake generated a tsunami that struck japan as well as various locations around the pacific ocean with the participation of researchers from throughout japan joint research groups conducted a tsunami survey along a 2000 km stretch of the japanese coast more than 5300 locations have been surveyed to date generating the largest tsunami survey dataset in the world on the sendai plain the maximum inundation height was 19 5 m and the tsunami bore propagated more than 5 km inland along the ria coast from about 50 to 200 km north of sendai the narrow bays focused the tsunami waves generating the largest inundation heights and run ups the survey data clearly show a regional dependence of tsunami characteristics

optical measurements of tsunami inundation through an urban waterfront modeled in a large scale laboratory basin abstract this paper presents optical measurements of tsunami inundation through an urban waterfront in a laboratory wave basin the physical model was constructed at 1 50 scale and was an idealization of the town of seaside oregon the fixed bed model was designed to study the initial inundation zone along an urban waterfront such that the flow around several large buildings could be observed this paper presents an analysis of the optical measurements made with two overhead video cameras focusing on tracking the leading edge of the tsunami inundation through the urban waterfront and quantifies the accuracy of the algorithm used to track the edge the results show that the methodology provides high resolution information in both time and space of the leading edge position and that these data can be used to quantify the influence of large macro roughness features on the tsunami inundation processes in laboratory settings the overall effect of the macro roughness was to decrease the bore propagation speed relative to the control section with no macro roughness the bore speed could be reduced by as much as 40 due to the presence of the macro roughness relative to the control section

on the disintegration of ice shelves the role of fracture dans une plateforme glaciaire contrairement au cas des glaciers les crevasses de surface peuvent atteindre le niveau de mer et les crevasses de fond remonter jusqu a ce niveau les crevasses jouent alors un role important dans la desintegration de la plateforme la fracturation est examinee en fonction des contraintes generales et locales on applique l etude a la stabilite de plateformes de l antarctique ouest

formulation of ice shelf dynamic boundary conditions in terms of a coulomb rheology coastal boundaries where fast flowing ice shelves shear past stagnant grounded ice are typically riven with surface crevasses seawater filled basal crevasses and tidal strand cracks here we formulate a boundary condition describing stress transmission through these fractured boundaries in terms of the coulomb law as a result of this formulation agreement between finite element simulations of the ross ice shelf flow and field observations is improved over agreement obtained with formulations which do not account for ice failure our results additionally suggest that shear stress transmitted through ice shelf boundaries is lower than previously thought

paleoclimatic constraints on the maintenance of possible ice shelf cover in the norwegian and greenland seas we examine the controversial issue of whether or not an integrated ice shelf existed in the norwegian and greenland seas during glacial events of the pleistocene our method consists of testing for equilibrium ice shelf configurations with the use of a finite element model that predicts ice shelf evolution under a variety of atmospheric and oceanic forcing conditions ice flow at the margins of the simulated hypothetical ice shelf is determined from one of denton and hughes 1981 reconstructions of continental glaciation applicable to the last glacial maximum our results suggest that the existence of the ice shelf and possibly surrounding marine based ice sheets depends most sensitively on oceanic heat flux a heat flux of approximately 4 80 j m 2 s 1 corresponding to an area average basal melting rate of 0 50 m a 1 ice equivalent is near the upper limit allowing ice shelf equilibrium greater heat flux is found to cause an initial 450 m thick ice shelf to rapidly collapse the equilibrium ice shelf configurations examined provide effective buttressing support for the marine ice sheet grounded in the barents sea 18 kyr b p tests confirming the existence of ice shelf cover in the norwegian and greenland seas are possible through a comparison of the sedimentary record of ice rafted debris with ice shelf flow patterns deduced from our simulations

field studies of bottom crevasses in the ross ice shelf antarctica analyse des crevasses observees par sondages radar aeriens et terrestres localisation de leurs points de formation

a numerical study of swash flows generated by bores abstract article history received 10 october 2007received in revised form 15 march 2008accepted 4 april 2008available online 4 june 2008keywords swash zonetsunami runupdam breakborenon linear shallow water equationsreynolds averaged navier stokes equationnon linear k model the dynamic processes of bore propagation over a uniform slope are studied numerically using a 2 dreynolds averaged navier stokes rans solver coupled to a non linear k turbulence closure and avolume of uid vof method the dam break mechanism is used to generate bores in a constant depthregion present numerical results for the ensemble averaged ow eld are compared with existingexperimental data as well as theoretical and numerical results based on non linear shallow water nsw equations reasonable agreement between the present numerical solutions and experimental data isobserved using the numerical results small scale bore behaviors and ow features such as the bore collapseprocess near the still water shoreline the mini collapse during the runup phase and the back wash bore inthe down rush phase are described in the case of a strong bore the evolution of the averaged turbulencekinetic energy tke over the swash zone consists of two phases in the region near the still water shoreline the production and the dissipation of tke are roughly in balance in the region farther landwards of the still water shoreline the tke decay rate is very close to that of homogeneous grid turbulence on the other hand in the case of a weak bore the bore collapse generated turbulence is con ned near the bottom boundarylayer and the tke decays at a much slower rate 2008 elsevier b v all rights reserved

fault friction regional stress and crust mantle coupling in southern california from finite element models ongoing deformation of southern california is simulated in a set of 63 models in an attempt to empirically determine fault friction to a previous code for simulation of anelastic crustal strain we introduce a new finite element to represent a curved fault of arbitrary rheology we also add several selfconsistent patterns of horizontal drag on the base of the crust caused by independent upper mantle flow a grid of isoparametric finite elements represents the regional fault geometry and the known variations in elevation and heat flow plate tectonic velocity boundary conditions are applied solutions include the time averaged flow velocities and fault slip rates and vertically averaged stresses each model is scored by comparing its slip rate predictions with 56 rates from dated offset geologic features in membrane stress models the optimal fault friction is 0 4 0 6 frictional self heating of faults is not a major factor determining strength addition of crust mantle coupling improves results if convergence of north american and pacific lithospheres is assumed to occur under the transverse ranges among such models those with fault friction of about 0 3 score best by most norms of the prediction error these have over 80 of regional strain in faults and only a small amount of block deformation however one model with friction of 0 85 scores better by the percent of correct predictions norm this model has only half the regional strain as fault slip and matches slow rates well but underpredicts slip rates over 1 cm yr furthermore its predictions are degraded considerably if hydraulic lubrication of thrust faults is assumed the low friction models are unaffected we conclude that some source of variation in fault friction remains unmodeled but that at least the fastslipping faults in california have low friction similar to that of hydrated clay gouges appendix is available with entire article on microfiche order from american geophysical union 2000 florida avenue n w washington dc 20009 document b84 001 2 50 payment must accompany order