magnetic evidence for slow seafloor spreading during the formation of the newfoundland and iberian margins there is considerable debate concerning the nature and origin of the thin crust within the ocean continent transition oct zones of many passive non volcanic continental margins located between thinned continental and true oceanic crust this crust is usually found to be underlain by upper mantle material of 7 2 7 4 km s velocity at shallow depths 1 2 km it has been proposed that such crustal material could have originated either by exhumation of upper mantle material during rifting of continents or by slow seafloor spreading one of the examples of occurrence of such a crust are the conjugate margins of newfoundland and iberia here we present an interpretation of magnetic data from these regions to show that their oct zones are underlain by crustal material formed by slow seafloor spreading 6 7 mm yr soon after iberia separated from the grand banks of newfoundland in the late jurassic similarities in the magnetic anomalies and velocity distributions from these regions with those from the sohm abyssal plain a region lying immediately south of the newfoundland basin and formed by seafloor spreading at a similar rate of spreading give further support to such an interpretation the idea that these regions were formed by unroofing of upper mantle during rifting of iberia from newfoundland may be likely but the presence of weak magnetic anomalies in these regions which bear all the characteristics of seafloor spreading anomalies makes it difficult to ignore the possibility that these regions could be underlain by oceanic crust formed during slow seafloor spreading the similarities in velocity structure and the presence of small amplitude magnetic anomalies both across this pair of conjugate margins of the north atlantic and that of the labrador sea suggest that this oct velocity structure may be the norm rather than the exception across those passive non volcanic margins where the initial seafloor spreading was slow furthermore the existence of similar velocity distributions along a few active spreading centers raises the possibility of formation of similar crust across slow spreading ridges fl 2000 elsevier science b v all rights reserved

shoreline features of titan s ontario lacus from cassini vims observations we analyze observations of titan s south polar lake ontario lacus obtained by cassini s visual and infrared mapping spectrometer during the 38th flyby of titan t38 2007 december 5 these near closest approach observations have the highest signal to noise the finest spatial resolution and the least atmospheric influence of any near infrared lake observation to date we use the large spatially flat and low albedo interior of ontario lacus as a calibration target allowing us to derive an analytical atmospheric correction for emission angle the dark lake interior is surrounded by two separate annuli that follow the lake interior s contours the inner annulus is uniformly dark but not so much as the interior lake and is generally 5 10 kilometers wide at the lake s southeastern margin we propose that it represents wet lakebed sediments exposed by either tidal sloshing of the lake or seasonal methane loss leading to lower lake volume the exterior annulus is bright and shows a spectrum consistent with a relatively low water ice content relative to the rest of titan it may represent fine grained condensate deposits from a past era of higher lake level together the annuli seem to indicate that the lake level for ontario lacus has changed over time this hypothesis can be tested with observations scheduled for future titan flybys

tsunami observations in rivers from a perspective of tsunami interaction with tide and riverine flow the observations of the 2011 tohoku tsunami and the 2010 chilean tsunami in several rivers in japan and in the columbia river in the usa are analyzed for patterns of tsunami behavior in river environments tsunamis in rivers exhibit actions very different from those observed on an open coast but very similar among different rivers though the action scale in different rivers varies greatly we describe two tsunami effects in rivers as observed in field data first the river tide modulates the tsunami wave in a very specific way common to all rivers second a strong near field tsunami can cause significant prolonged water accumulation in lower river reaches both effects are inherent in tidal river environments and have been reproduced numerically in a simplified 1 d river using a non linear shallow water model with bottom friction the numerical experiments highlight the indispensable role of a tsunami s interaction with tide and riverine flow

the bathymetry of a titan sea construct the depth profile the bathymetry of titan s large sea ligeia mare from cassini radar data collected during the 23 may 2013 t91 nadir looking altimetry flyby we find the greatest depth to be about 160 m and a seabed slope that is gentler toward the northern shore consistent with previously imaged shoreline morphologies low radio signal attenuation through the sea demonstrates that the liquid for which we determine a loss tangent of 3 1 10 5 is remarkably transparent requiring a nearly pure methane ethane composition and further that microwave absorbing hydrocarbons nitriles and suspended particles be limited to less than the order of 0 1 of the liquid volume presence of nitrogen in the ethane methane sea expected based on its solubility and dominance in the atmosphere is consistent with the low attenuation but that of substantial dissolved polar species or suspended scatterers is not

analytical evolution of tsunamis induced by near shore earthquakes on a constant slope ocean strong near shore earthquakes are the most frequent sources of tsunamis in many oceans of the world in the framework of the nonlinear shallow water theory the initial sea surface tsunami elevation is assumed to equal the sea floor co seismic displacement produced by the seismic event this is quantified by means of the analytical formulas due to okada 1985 1992 dealing with seismic faults buried in an elastic medium in this work the propagation of tsunamis is studied along two dimensional profiles on an idealized constant slope sea bed an approximation that allows one to reduce the governing nonlinear equations to a linear problem by means of the classical carrier greenspan 1958 approach we introduce an analytical solution that is sufficiently general to account for initial conditions associated with paradigmatic cases of sea bottom deformations produced by near shore earthquakes such as subsidence or uplift of the coastal area and can be also used to treat more complex deformations the main result is that the amplification of the tsunami height at the coast is found to range between approximately 1 and 2 the amplification is around 1 for tsunamis induced by earthquakes with their epicentre inland and tends to grow as the fault moves seaward we restrict our analysis to earthquakes that dislocate the shore region within the class of sources that we consider the tsunamis that are most amplified are the ones having initial profiles with a crest trough crest system or conversely with a trough crest trough system the bottom slope is found to have no effect on tsunami run ups and run downs but to influence tsunami periods and tsunami speed remarkably breaking analysis shows that wave breaking does not occur if the initial wave height is less than 8 9 m and that the simplest sea level profiles which are associated with earthquakes with their epicentre on land are not expected to break even if their initial height exceeds 19 m

understanding caldera structure and development an overview of analogue models compared to natural calderas abstract understanding the structure and development of calderas is crucial for predicting their behaviour during periods of unrest and to plan geothermal and ore exploitation geological data including that from analysis of deeply eroded examples allow the overall surface setting of calderas to be defined whereas deep drillings and geophysical investigations provide insights on their subsurface structure collation of this information from calderas worldwide has resulted in the recent literature in five main caldera types downsag piston funnel piecemeal trapdoor being viewed as end members despite its importance such a classification does not adequately examine a the structure of calderas particularly the nature of the caldera s bounding faults and b how this is achieved including the genetic relationships among the five caldera types various sets of analogue models specifically devoted to study caldera architecture and development have been recently performed under different conditions apparatus materials scaling parameters stress conditions the first part of this study reviews these experiments which induce collapse as a result of underpressure or overpressure within the chamber analogue the experiments simulating overpressure display consistent results but the experimental depressions require an exceptional amount of doming seldom observed in nature to form therefore these experiments are not appropriate to understand the structure and formation of most natural calderas the experiments simulating underpressure reveal a consistent scenario for caldera structure and development regardless of their different boundary conditions these show that complete collapse proceeds through four main stages proportional to the amount of subsidence progressively characterized by 1 downsag 2 reverse ring fault 3 peripheral downsag 4 peripheral normal ring fault the second part of this study verifies the possibility that these latter calderas constitute a suitable analogue to nature and consists of a comprehensive comparison of the underpressure experiments to natural calderas this shows that all the experimental structures as well as their progressive development are commonly observed at natural calderas highlighting a consistency between models and nature as the shallow structure of experimental calderas corresponds to a precise architecture at depth it provides a unique key to infer the deeper structure of natural calderas recognizing diagnostic surface features within a caldera will thus allow it to be categorized within a precise structural and evolutionary context the general relationship between the evolutionary stage of a caldera and its d s diameter subsidence ratio allows such a quantification with stage 1 calderas characterized by d s 40 stage 2 by 18 the four stages adequately explain the architecture and development of the established caldera end members along a continuum where one or more end members downsag piston funnel piecemeal trapdoor may correspond to a specific stage while such a continuum is controlled by progressive subsidence specific collapse geometries will result from secondary contributory factors roof aspect ratio collapse symmetry pre existing faults these considerations allow proposing an original classification of calderas incorporating their structural and genetic features

geochemistry and regional significance of the early cretaceous bimodal basalt felsic associations on grand banks eastern canada cretaceous mafic rocks are present in several wells on the grand banks of newfoundland near the southwest grand banks jurassic transform margin and along the trend of the collector magnetic anomaly in the brant and mallard wells felsic volcanic subvolcanic and pyroclastic rocks are several hundreds of meters thick seismic reflection profiles show that the volcanic rocks are locally bounded by rejuvenated faulted margins of early rift basins beneath the mid cretaceous postrift unconformity the early cretaceous age of the volcanic rocks is confirmed by k ar geochronology trace element and isotopic composition of both mafic and felsic rocks are quite different from those of plume related cretaceous rocks elsewhere on the eastern north american margin mafic rocks have a pb isotopic composition unusually enriched in 207 pb 204 pb which is similar to late triassic early jurassic mafic rocks along the eastern appalachians nd isotopic compositions are closer to typical ocean island basalt oib sources observed isotopic compositions suggest mafic magma was partially melted from continental margin lithospheric mantle enriched with small amounts of hydrous or silica rich phases of oib affinity whole rock geochemistry isotopic composition and mineral chemistry show that the felsic rocks resemble alkaline a type granite those from mallard have some crustal contamination those from brant which is located closer to the continental margin edge have almost pristine mantle isotopic characteristics indicating an oib source magma the spatial distribution of cretaceous volcanic products suggests that magma was generated along the reactivated transform margin and that major faults in continental crust acted as magma conduits partial melting of continental margin lithospheric mantle resulted from extensional decompression probably aided by a weak plume related thermal anomaly as on other transform margins magmatic products reflect a complex mantle history

characterization of titan s ontario lacus region from cassini vims observations abstract liquid hydrocarbons were long predicted on titan s surface before the radar instrument onboard cassini detected lakes poleward of 70 n in july 2006 before that the cassini imaging science subsystem iss observed a lake like feature in the south pole named ontario lacus in july 2004 here we analyze one observation of ontario lacus taken by the visual and infrared mapping spectrometer vims on 2007 december 5 during the t 38 flyby this is the best spatially resolved image of a titan lake to date by an imaging spectrometer and has been previously reported in brown et al brown r h soderblom l a soderblom j m clark r n jaumann r barnes j w sotin c buratti b baines k h nicholson p d 2008 nature 454 607 610 and in barnes et al barnes j w et al 2009 icarus 201 217 225 the observing geometry and our data processing will be explained followed by a discussion of the main characteristics of the image the analyzed image covers a small portion of ontario lacus and shows what appears from radar data to be a region of modest slope ramp adjacent to the dark lake itself our analysis of 5 0 m spectral data suggests that the previously reported absorption feature of ethane seen at shorter wavelengths may be produced by damp sediments adjacent to the main liquid basin the latter appears to be absorbing all of the photons incident upon it in the 5 m spectral region and shows no discernible absorption features a characterization of the basin composition and morphology is developed with the help of iss and radar observations the simplest model consistent with the data is an optically deep lake surrounded by a region in which ethane propane possibly methane and other less volatile hydrocarbons and nitriles are present mixed into spectroscopically neutral sediments the dominance of relatively low vapor pressure organics outside the lake itself suggests a retreat of ontario lacus associated with evaporation on seasonal or longer timescales consistent with analysis of radar and iss images

titan s cloud seasonal activity from winter to spring with cassini vims abstract since saturn orbital insertion in july 2004 the cassini orbiter has been observing titan throughout most of the northern winter season october 2002 august 2009 and the beginning of spring allowing a detailed monitoring of titan s cloud coverage at high spatial resolution with close flybys on a monthly basis this study reports on the analysis of all the near infrared images of titan s clouds acquired by the visual and infrared mapping spectrometer vims during 67 targeted flybys of titan between july 2004 and april 2010 the vims observations show numerous sporadic clouds at southern high and mid latitudes rare clouds in the equatorial region and reveal a long lived cloud cap above the north pole ubiquitous poleward of 60 n these observations allow us to follow the evolution of the cloud coverage during almost a 6 year period including the equinox and greatly help to further constrain global circulation models gcms after 4 years of regular outbursts observed by cassini between 2004 and 2008 southern polar cloud activity started declining and completely ceased 1 year before spring equinox the extensive cloud system over the north pole stable between 2004 and 2008 progressively fractionated and vanished as titan entered into northern spring at southern mid latitudes clouds were continuously observed throughout the vims observing period even after equinox in a latitude band between 30 s and 60 s during the whole period of observation only a dozen clouds were observed closer to the equator though they were slightly more frequent as equinox approached we also investigated the distribution of clouds with longitude we found that southern polar clouds before disappearing in mid 2008 were systematically concentrated in the leading hemisphere of titan in particular above and to the east of ontario lacus the largest reservoir of hydrocarbons in the area clouds are also non homogeneously distributed with longitude at southern mid latitudes the n 2 mode wave pattern of the distribution observed since 2003 by earth based telescopes and confirmed by our cassini observations may be attributed to saturn s tides although the latitudinal distribution of clouds is now relatively well reproduced and understood by the gcms the non homogeneous longitudinal distributions and the evolution of the cloud coverage with seasons still need investigation if the observation of a few single clouds at the tropics and at northern mid latitudes late in winter and at the start of spring cannot be further interpreted for the moment the obvious shutdown of the cloud activity at titan s poles provides clear signs of the onset of the general circulation turnover that is expected to accompany the beginning of titan s northern spring according to our gcm the persistence of clouds at certain latitudes rather suggests a sudden shift in near future of the meteorology into the more illuminated hemisphere finally the observed seasonal change in cloud activity occurred with a significant time lag that is not predicted by our model this may be due to an overall methane humidity at titan s surface higher than previously expected

tsunami run up on a plane beach in a tidal environment we analytically solve the nonlinear shallow water theory for the tsunami run up on a plane beach in the presence of tide and show that over a plane beach the tide in the nearshore zone can be considered static uniform in space and frozen in time with this assumption we find an exact analytical solution for the tsunami run up height as a function of the amplitude of the incident wave and analyse the influence of the tide on the tsunami run up characteristics we confirm these results by calculation of the total tsunami and tidal run up field using analytical solutions of the initial nonlinear shallow water equations

tsunami modelling with static and dynamic tides in drowned river valleys with morphological constrictions tsunami modelling is widely used to estimate the potential impacts of tsunamis models require a tide input which can be either static representing a specific tide level such as highest astronomic tide or dynamic which represents a moving tide level although commonly used static tide inputs do not account for tsunami tide interactions which are known to be non linear and more significant in estuaries when compared to the open coast to demonstrate the differences between tsunami models using static or dynamic tide inputs a series of models were carried out for two new south wales estuaries sydney harbour and port hacking model boundary conditions phased a mw 9 0 puysegur source tsunami with multiple tide scenarios fourteen distinct scenarios with dynamic tides were created by phasing the largest tsunami wave peak at regular intervals across the tidal range for comparison static tide models were run using equivalent tide levels the situations where static tide models provide results comparable or more conservative than dynamic tide models are for the first 1 2 h after tsunami arrival at high tides and when compared to dynamic falling tides at the same tide level differences are most apparent upriver of geomorphological constrictions the effects of geomorphological constrictions were further examined using idealised model setups with a constriction variable results show that constrictions affect downriver maximum water levels tsunami wave heights upriver water accumulation and inundation maxima and distributions these results have implications for estuaries vulnerable to erosion at constriction sites during a tsunami event

titan an exogenic world abstract all landforms on titan that are unambiguously identifiable can be explained by exogenic processes aeolian fluvial impact cratering and mass wasting previous suggestions of endogenically produced cryovolcanic constructs and flows have without exception lacked conclusive diagnostic evidence the modification of sparse recognizable impact craters themselves exogenic can be explained by aeolian and fluvial erosion tectonic activity could be driven by global thermal evolution or external forcing rather than by active interior processes a lack of cryovolcanism would be consistent with geophysical inferences of a relatively quiescent interior incomplete differentiation only minor tidal heating and possibly a lack of internal convection today titan might be most akin to callisto with weather an endogenically relatively inactive world with a cool interior we do not aim to disprove the existence of any and all endogenic activity at titan nor to provide definitive alternative hypotheses for all landforms but instead to inject a necessary level of caution into the discussion the hypothesis of titan as a predominantly exogenic world can be tested through additional cassini observations and analyses of putative cryovolcanic features geophysical and thermal modeling of titan s interior evolution modeling of icy satellite landscape evolution that is shaped by exogenic processes alone and consideration of possible means for supplying titan s atmospheric constituents that do not rely on cryovolcanism

global scale surface spectral variations on titan seen from cassini vims we present global scale maps of titan from the visual and infrared mapping spectrometer vims instrument on cassini we map at 64 near infrared wavelengths simultaneously covering the atmospheric windows at 0 94 1 08 1 28 1 6 2 0 2 8 and 5 m with a typical resolution of 50 km pixel or a typical total integration time of 1 s our maps have five to ten times the resolution of ground based maps better spectral resolution across most windows coverage in multiple atmospheric windows and represent the first spatially resolved maps of titan at 5 m the vims maps provide context and surface spectral information in support of other cassini instruments we note a strong latitudinal dependence in the spectral character of titan s surface and partition the surface into 9 spectral units that we describe in terms of spectral and spatial characteristics

dissolution on titan and on earth toward the age of titan s karstic landscapes titan s polar surface is dotted with hundreds of lacustrine depressions based on the hypothesis that they are karstic in origin we aim at determining the efficiency of surface dissolution as a landshaping process on titan in a comparative planetology perspective with the earth as reference our approach is based on the calculation of solutional denudation rates and allow inference of formation timescales for topographic depressions developed by chemical erosion on both planetary bodies the model depends on the solubility of solids in liquids the density of solids and liquids and the average annual net rainfall rates we compute and compare the denudation rates of pure solid organics in liquid hydrocarbons and of minerals in liquid water over titan and earth timescales we then investigate the denudation rates of a superficial organic layer in liquid methane over one titan year at this timescale such a layer on titan would behave like salts or carbonates on earth depending on its composition which means that dissolution processes would likely occur but would be 30 times slower on titan compared to the earth due to the seasonality of precipitation assuming an average depth of 100 m for titan s lacustrine depressions these could have developed in a few tens of millions of years at polar latitudes higher than 70 n and s and a few hundreds of million years at lower polar latitudes the ages determined are consistent with the youth of the surface 1 gyr and the repartition of dissolution related landforms on titan

138 121 ma asthenospheric magmatism prior to continental break up in the north atlantic and geodynamic implications along the galicia and gorringe banks and in the iberia abyssal plain of the north atlantic unroofed sub continental mantle fills the gap between true oceanic crust and the continental crust margin these lithospheric peridotites are intruded by gabbros and dolerites and locally covered by basalts primary magmatic zircons extracted from gabbros and meta gabbros of the two banks were dated by the u pb chronometer and initial hafnium isotope signatures hfi were determined on the same grains for mt gettysburg at gorringe gabbro emplacement ages of 137 5 0 5 2 ma and 135 7 0 8 ma are obtained and corresponding hfi lie at 20 5 0 3 2 and 19 5 0 4 substantiating magma formation from severely lile depleted mantle domains gabbro zircons from mt ormonde at gorringe yield a much younger age of 77 1 0 4 ma and the hf isotopes document an intermediately lile depleted mantle source having a hfi of 7 6 0 4 given its age and hf signature emplacement of this rock can be ascribed to the alkaline magmatic event that also affected the iberian continent in upper cretaceous time concerning the galicia section zircons from a meta gabbro yield an emplacement age of 121 7 0 4 ma and a hfi of 14 0 0 2 and a hfi of 14 6 0 2 is obtained for zircons from a previously dated meta gabbro of identical age these results indicate magma extraction from mantle reservoirs that are slightly less lile depleted than those sampled by the about 20 myr older gorringe gabbros the data demonstrate that magmatism occurring prior to complete separation of europe from america was essentially of asthenospheric origin both the 138 135 ma ages for the gorringe gabbros and 122 ma ages for the galicia gabbros are at least 5 myr older than the oldest sediments on gorringe and the break up unconformity at the galicia bank respectively magma source signatures of the syn rift gabbros are in agreement with values expected for differently depleted cretaceous morb type mantle reservoirs and the age difference for magmatism between the gorringe and galicia banks suggests a rate of 4 4 0 3 cm yr for northward progression of continental rifting based on the new results a structural model for iberia america rifting is discussed putting forward the idea that magma emplacement produces a level of weakness and decollement between the rifting crust and its underlying lithospheric mantle

gabbroic pegmatite intrusions iberia abyssal plain odp leg 173 site 1070 magmatism during a transition from non volcanic rifting to sea floor spreading the unroofed mantle grows younger outboard just as is the case for on the iberia abyssal plain ocean drilling program site 1070 normal volcanic sea floor gabbroic pegmatites and related rocks 127 4 ma u pb zircon intrude upper mantle that was subsequently exposed and serpentinized during early cretaceous non volcanic rifting the pegmatites include a 3 4 m dike or sill the main pegmatite numerous dikelets of

run up of tsunamis and long waves in terms of surf similarity abstract in this paper we review and re examine the classical analytical solutions for run up of periodic long waves on an infinitely long slope as well as on a finite slope attached to a flat bottom both cases provide simple expressions for the maximum run up and the associated flow velocity in terms of the surf similarity parameter and the amplitude to depth ratio determined at some offshore location we use the analytical expressions to analyze the impact of tsunamis on beaches and relate the discussion to the recent indian ocean tsunami from december 26 2004 an important conclusion is that extreme run up combined with extreme flow velocities occurs for surf similarity parameters of the order 3 6 and for typical tsunami wave periods this requires relatively mild beach slopes next we compare the theoretical solutions to measured run up of breaking and non breaking irregular waves on steep impermeable slopes for the non breaking waves the theoretical curves turn out to be superior to state of the art empirical estimates finally we compare the theoretical solutions with numerical results obtained with a high order boussinesq type method and generally obtain an excellent agreement

the rift to drift transition in the southern north atlantic a stuttering start of the morb machine comment and reply comment jagoutz et al 2007 1 argue for a long history of alkaline to mid oceanic ridge basalt morb type magmatism occurring during the transition from amagmatic to magmatic rifting at the iberia newfoundland conjugate margin u pb zircon ages suggest that magmatism spanned the range of 110 127

tsunami run up and draw down on a plane beach tsunami run up and draw down motions on a uniformly sloping beach are evaluated based on fully nonlinear shallow water wave theory the nonlinear equations of mass conservation and linear momentum are first transformed to a single linear hyperbolic equation to solve the problem with arbitrary initial conditions we apply the fourier bessel transform and inversion of the transform leads to the green function representation the solutions in the physical time and space domains are then obtained by numerical integration with this semi analytic solution technique several examples of tsunami run up and draw down motions are presented in particular detailed shoreline motion velocity field and inundation depth on the shore are closely examined it was found that the maximum flow velocity occurs at the moving shoreline and the maximum momentum flux occurs in the vicinity of the extreme draw down location the direction of both the maximum flow velocity and the maximum momentum flux depend on the initial waveform it is in the inshore direction when the initial waveform is predominantly depression and in the offshore direction when the initial waves have a dominant elevation characteristic

comparison of titan s north polar lakes with terrestrial analogs 1 the discovery of hydrocarbon lakes in the polar regions of titan offers a unique opportunity to compare terrestrial lakes with those in an extraterrestrial setting we selected 114 terrestrial lakes formed by different processes as analogs for comparison with the 190 titanian lakes that we had mapped in our previous study using the shuttle radar topography mission srtm c band backscatter data and the srtm water body data swbd we carried out an assessment of manual mapping versus existing automated mapping techniques and found the automated techniques to produce as good representations of the lake shorelines as the manual mapping in the terrestrial dataset we then calculated and compared terrestrial and titanian shoreline statistical parameters including fractal dimension shoreline development index and an elongation index we found different lake generation mechanisms on earth produce statistically different shorelines however we cannot identify any one mechanism or set of mechanisms to be responsible for forming the depressions enclosing the lakes on titan on the basis of our statistical analyses

geomorphological significance of ontario lacus on titan integrated interpretation of cassini vims iss and radar data and comparison with the etosha pan namibia abstract ontario lacus is the largest lake of the whole southern hemisphere of titan saturn s major moon it has been imaged twice by each of the cassini imaging systems imaging science subsystem iss in 2004 and 2005 visual and infrared mapping spectrometer vims in 2007 and 2009 and radar in 2009 and 2010 we compile a geomorphological map and derive a hydrogeological interpretation of ontario lacus based on a joint analysis of iss vims and radar sar datasets along with the t49 altimetric profile acquired in december 2008 the morphologies observed on ontario lacus are compared to landforms of a semi arid terrestrial analog which resembles titan s lakes the etosha pan located in the owambo basin namibia the etosha pan is a flat floored depression formed by dissolution under semi arid conditions of a surface evaporitic layer calcretes controlled by groundwater vertical motions we infer that ontario lacus is an extremely flat and shallow depression lying in an alluvial plain surrounded by small mountain ranges under climatic conditions similar to those of terrestrial semi arid regions channels are seen in the southern part of ontario lacus in vims and radar data acquired at a 2 years time interval their constancy in location with time implies that the southern portion of the depression is probably not fully covered by a liquid layer at the time of the observations and that they most probably run on the floor of the depression a shallow layer of surface liquids corresponding to the darkest portions of the radar images would thus cover about 53 of the surface area of the depression of which almost 70 is located in its northern part these liquid covered parts of the depression where liquid ethane was previously identified are interpreted as topographic lows where the alkanofer raises above the depression floor the rest of the depression and mostly its southern part is interpreted as a flat and smooth exposed floor likely composed of a thick and liquid saturated coating of photon absorbing materials in the infrared this hypothesis could explain its dark appearance both in the infrared and radar data and the persistence of channels seen on the depression floor over the time shorelines are observed on the border of ontario lacus suggesting past high stand levels of the alkanofer table the analogy with the etosha pan suggests that ontario lacus depression developed at the expense of a soluble layer covering the region dissolution of this layer would be controlled by vertical motions of the alkanofer table over the time during flooding events liquid hydrocarbons covering the depression floor would dissolve the surface layer increasing progressively the diameter of the depression on geological timescales during drought episodes liquid hydrocarbons of the underground alkanofer would evaporate leading to crystallization of evaporites in the pores and at the surface of the substratum and to the formation of the regional soluble layer the presence of specific landforms lunette dunes or evaporites is compatible with such evaporitic regional settings alternatively but not exclusively the surface soluble layer might have formed by accumulation on the ground of soluble compounds formed in the atmosphere

organic sedimentary deposits in titan s dry lakebeds probable evaporite we report the discovery of organic sedimentary deposits at the bottom of dry lakebeds near titan s north pole in observations from the cassini visual and infrared mapping spectrometer vims we show evidence that the deposits are evaporitic making titan just the third known planetary body with evaporitic processes after earth and mars and is the first that uses a solvent other than water

the rift to drift transition in the southern north atlantic a stuttering start of the morb machine comment and reply reply beard s 2008 1 welcome comment offers us the opportunity to discuss and clarify certain aspects of our paper jagoutz et al 2007 2 beard raises points about our reinterpretation of his originally postulated genetic link between albitite clasts recovered from a breccia and a coarse

magmatism at the west iberia non volcanic rifted continental margin evidence from analyses of magnetic anomalies we discuss the magmatic development of the west iberia non volcanic rifted continental margin in the north atlantic ocean so called non volcanic rifted continental margins are characterized by a lack of syn rift magmatism and are considered to be largely amagmatic however this is clearly an oversimplification since seafloor spreading itself is a magmatic process and it is implausible that seafloor spreading begins instantaneously we concentrate our attention on the recently described zone of exhumed continental mantle zecm to investigate what magmatic processes accompanied the breakup of the continental lithosphere and the subsequent formation of the zecm leading to the onset of seafloor spreading we use magnetic anomalies supplemented by the interpretations of multichannel seismic reflection profiles and wide angle seismic experiments presented elsewhere forward and inverse modelling of a sea surface magnetic anomaly chart and of surface and deep towed magnetometer profiles shows that anomalies within the zecm differ in trend amplitude and source type from those in the adjacent oceanic crust and thinned continental crust the zecm anomalies appear to be caused by elongated source bodies within 8 km of the top of the acoustic basement aligned parallel to the margin we interpret such bodies as syn extensional intrusions that increase in volume oceanward they eventually merge in the vicinity of a margin parallel basement peridotite ridge to give rise to a continuous crust that records reversals in the earth s magnetic field from the time of anomaly m4 n m5 r i e to mark the onset of seafloor spreading we find no evidence for anomalies formed by seafloor spreading at either slow or ultraslow rates before m5 r 128 ma

are the basins of titan s hotei regio and tui regio sites of former low latitude seas 1 features observed in the low latitude basins of hotei regio and tui regio on titan have attracted the attention of the cassini era investigators at both locations visual infrared mapping spectrometer vims observed isolated 5 m bright 500 km wide features described as lobate in shape several studies have proposed that these materials are cryo volcanic flows we propose an alternative explanation recently published topographic profiles across hotei regio and tui regio indicate these features appear to occur in large regional basins at least along the direction of the profiles cassini synthetic aperture radar sar images show that the terrains surrounding both topographically low lying 5 m bright features exhibit fluvial networks that appear to converge into the probable basins the 5 m bright features themselves correspond to fields of discrete radar bright depressions whose bounding edges are commonly rounded and cumulate in planform in sar images these fields of discrete radar bright depressions strongly resemble fields of features seen at titan s high latitudes identified as dry lakes thus the combination of 1 the resemblance to high latitude dry lakes 2 location in the centers of regional depressions and 3 convergence of fluvial networks are inferred by us to best explain the features of hotei regio and tui regio as sites of paleolake clusters and perhaps former now dry seas these low latitude paleolake clusters or former seas if real may be evidence of substantially larger inventories of liquid alkanes in titan s past

titan s inventory of organic surface materials 1 cassini radar observations now permit an initial assessment of the inventory of two classes presumed to be organic of titan surface materials polar lake liquids and equatorial dune sands several hundred lakes or seas have been observed of which dozens are each estimated to contain more hydrocarbon liquid than the entire known oil and gas reserves on earth dark dunes cover some 20 of titan s surface and comprise a volume of material several hundred times larger than earth s coal reserves overall however the identified surface inventories 3 104 km3 of liquid and 2 105 km3 of dune sands are small compared with estimated photochemical production on titan over the age of the solar system the sand volume is too large to be accounted for simply by erosion in observed river channels or ejecta from observed impact craters the lakes are adequate in extent to buffer atmospheric methane against photolysis in the short term but do not contain enough methane to sustain the atmosphere over geologic time unless frequent resupply from the interior buffers this greenhouse gas at exactly the right rate dramatic climate change on titan is likely in its past present and future

effects of wave forcing on a subterranean estuary wave and tide are important forcing factors that typically co exist in coastal environments a numerical study was conducted to investigate individual and combined effects of these forces on flow and mixing processes in a near shore subterranean estuary a hydrodynamic model based on the shallow water equations was used to simulate dynamic sea level oscillations driven by wave and tide the oscillating sea levels determined the seaward boundary condition of the coastal aquifer where variably saturated variable density flow was modeled the simulation results showed that waves induced an onshore upward tilt in the phase averaged sea level wave set up the resulting hydraulic gradient generated pore water circulations in the near shore zone of the coastal aquifer which led to formation of an upper saline plume usp similar to that due to tides however mixing of recirculating seawater in the usp with underlying fresh groundwater was less intensive under the high frequency wave oscillations in the case of combined forcing wave induced circulations coupled with the intra tidal flows strengthened the averaged circulating pore water flows in the near shore zone over the tidal period the circulating flows increased exchange between the subterranean estuary and ocean contributing 61 of the total submarine groundwater discharge for the simulated condition in comparison with the 40 and 49 proportions caused by the same but separate tidal and wave forcing respectively the combined forces also created a more extensive usp with the freshwater discharge zone shifted further seaward the freshwater flow paths in the intertidal subterranean estuary were altered with a significant increase of associated transit times the interplay of wave and tide led to increased mixing between discharging fresh groundwater and recirculating seawater these results demonstrated the complexity of near shore groundwater systems and have implications for future investigations on the fate of land sourced chemicals in the subterranean estuary prior to discharge to the ocean

the runup of solitary waves this is a study of the runup of solitary waves on plane beaches an approximate theory is presented for non breaking waves and an asymptotic result is derived for the maximum runup of solitary waves a series of laboratory experiments is described to support the theory it is shown that the linear theory predicts the maximum runup satisfactorily and that the nonlinear theory describes the climb of solitary waves equally well different runup regimes are found to exist for the runup of breaking and non breaking waves a breaking criterion is derived for determining whether a solitary wave will break as it climbs up a sloping beach and a different criterion is shown to apply for determining whether a wave will break during rundown these results are used to explain some of the existing empirical runup relationships

rapid and extensive surface changes near titan s equator evidence of april showers although there is evidence that liquids have flowed on the surface at titan s equator in the past to date liquids have only been confirmed on the surface at polar latitudes and the vast expanses of dunes that dominate titan s equatorial regions require a predominantly arid climate we report the detection by cassini s imaging science subsystem of a large low latitude cloud system early in titan s northern spring and extensive surface changes spanning more than 500 000 square kilometers in the wake of this storm the changes are most consistent with widespread methane rainfall reaching the surface which suggests that the dry channels observed at titan s low latitudes are carved by seasonal precipitation

age progressive volcanism in the new england seamounts and the opening of the central atlantic ocean radiometric ages k ar and oar 39ar methods have been determined on dredged volcanic rocks from seven of the new england seamounts a prominent northwest southeast trend ing volcanic lineament in the northwestern atlantic ocean the oar 39ar total fusion and increnental heating ages show an increase in seamount construction age from southeast to northwest that is consistent with northwestward motion of the north american plate over a new england hot spot between 103 and 82 ma a linear volcano migration rate of 4 7 cm yr fits the seamount age distribution these ages fall within a longer age progression from the corner seamounts 70 to 75 ma at the eastern end of the new england seamounts to the youngest phase of volcanism in the white mountain igneous province new england 100 to 124 ma the new england hot spot estimated from the new radio metric ages and motion of north america in the hot spot reference frame to be near 28on 33ow probably generated a short line of mid to late tertiary age seamounts on the african plate but appears to be presently inactive the hot spot reference frame is used to calculate the motion of the north american plate away from the african plate from early cretaceous time to the present rominent magnetic anomalies recorded in the central atlantic seafloor give the positions of the spreading ridge for a bange of known ages hot spots that now underlie the african plate in the eastern central atlantic new england canary madeira cape verde azores could have produced cretaceous seamount and island chains on the north american plate during the early opening of the central atlantic each of these hot spots has been overridden by spreading ridges at pre dictable times some of these hot spot crossings are expressed as geochemical anomalies in the oceanic crust now far removed from spreading ridges

tsunami wave run up on a vertical wall in tidal environment we solve analytically a nonlinear problem of shallow water theory for the tsunami wave run up on a vertical wall in tidal environment shown that the tide can be considered static in the process of tsunami wave run up in this approximation it is possible to obtain the exact solution for the run up height as a function of the incident wave height this allows us to investigate the tide influence on the run up characteristics

tide tsunami interaction in columbia river as implied by historical data and numerical simulations the east japan tsunami of 11 march 2011 propagated more than 100 km upstream in the columbia river visual analysis of its records along the river suggests that the tsunami propagation was strongly affected by tidal conditions a numerical model of the lower columbia river populated with tides and a downstream current was developed simulations of the east japan tsunami propagating up the tidal river reproduced the observed features of tsunami waveform transformation which did not emerge in simulations of the same wave propagating in a quiescent state river this allows us to clearly attribute those features to nonlinear interaction with the tidal river environment the simulation also points to possible amplification of a tsunami wave crest propagating right after the high tide previously deduced from the recordings of the 1964 alaska tsunami in the river

estimating erosional exhumation on titan from drainage network morphology 1 drainage networks on titan earth and mars provide the only known examples of non volcanic fluvial activity in our solar system the drainage networks on titan are apparently the result of a methane ethane cycle similar to earth s water cycle the scarcity of impact craters and the uneven distribution of fluvial dissection on titan suggest that the surface may be relatively young the purpose of this study is to assess the importance of erosion relative to other plausible mechanisms of resurfacing such as tectonic deformation cryovolcanism or deposition of aerosols we present a new method based on a measure of drainage network shape known as the width function to estimate cumulative erosion into an initially rough surface we calibrate this method with a numerical landscape evolution model and successfully test the method by applying it to river networks on earth with different exhumation histories to estimate erosional exhumation on titan we mapped fluvial networks in all synthetic aperture radar swaths obtained by the cassini spacecraft through t71 application of our method to the most completely imaged drainage networks indicates that for two of four regions analyzed titan s fluvial networks have produced only minor erosional modification of the surface for the best constrained region in the northern high latitudes we find that fluvial networks reflect spatially averaged erosion of more than 0 4 but less than 9 of the initial topographic relief this result implies either a recent non fluvial resurfacing event or long term fluvial incision rates that are slow relative to the rate of resurfacing

exhumed mantle forming transitional crust in the newfoundland iberia rift and associated magnetic anomalies transitional zones located between iberia and north america formed during continental rifting and mostly consist of exhumed mantle in this study we show that ages of exhumed mantle at ocean drilling program odp sites 1068 and 1070 in the iberia abyssal plain and site 1277 in the newfoundland basin are similar to ages determined from magnetic lineations created by serpentinization during mantle exhumation on the basis of paleomagnetic and geological data and a comparison with a fossil ocean continent transition in the alps we envisage a first episode of mantle serpentinization during which a strong component of magnetization was acquired followed by a second episode occurring at the contact with cold seawater and which only affects the upper tens of meters of the exhumed mantle the inversion of magnetic data euler deconvolution shows that magnetic sources are n s trending horizontal cylindrical bodies located within the highly serpentinized upper crust therefore the serpentinization process is able to produce magnetic lineations formed in a similar way to those formed by seafloor spreading within transition zones sequences of magnetic anomalies can provide information concerning the timing of the emplacement of crust but not on its nature oceanic versus exhumed mantle this discovery enables us to date the exhumation of mantle rocks in transition zones and allows kinematic reconstructions of the final stages of continental rifting during rifting the deep distal continental margins and the adjacent transitional zones in the newfoundland iberia rift system were formed by ultraslow extension from early berriasian to late valanginian early hauterivian and by slow extension from early hauterivian to the late aptian early albian boundary therefore transitional zones share many similarities with slow and ultraslow spreading midoceanic ridges

titan s diverse landscapes as evidenced by cassini radar s third and fourth looks at titan abstract cassini s third and fourth radar flybys t7 and t8 covered diverse terrains in the high southern and equatorial latitudes respectively the t7 synthetic aperture radar sar swath is somewhat more straightforward to understand in terms of a progressive poleward descent from a high dissected and partly hilly terrain down to a low flat plain with embayments and deposits suggestive of the past or even current presence of hydrocarbon liquids the t8 swath is dominated by dunes likely made of organic solids but also contain somewhat enigmatic probably tectonic features that may be partly buried or degraded by erosion or relaxation in a thin crust the dark areas in t7 show no dune morphology unlike the dark areas in t8 but are radiometrically warm like the dunes the huygens landing site lies on the edge of the t8 swath correlation of the radar and huygens disr images allows accurate determination of its coordinates and indicates that to the north of the landing site sit two large longitudinal dunes indeed had the huygens probe trajectory been just 10 km north of where it actually was images of large sand dunes would have been returned in place of the fluvially dissected terrain actually seen illustrating the strong diversity of titan s landscapes even at local scales

a global topographic map of titan abstract cassini radar sartopo and altimetry data are used to construct a global gridded 1 1 elevation map for use in global circulation models hydrological models and correlative studies the data are sparse and so most of the map domain 90 is populated with interpolated values using a spline algorithm the highest 520 m gridded point observed is at 48 s 12 w the lowest point observed 1700 m below a 2575 km sphere is at 59 s 317 w this may be a basin where liquids presently in the north could have resided in the past if the deepest point were once a sea with the areal extent of present day ligeia mare it would be 1000 m deep we find four prominent topographic rises each 200 km wide radar bright and heavily dissected distributed over a 3000 km arc in the southeastern quadrant of titan 40 60 s 15 150 w

is titan s shape caused by its meteorology and carbon cycle 1 titan s shape is characterized by a difference between the long equatorial radius and the polar radius that is several hundred meters larger than that predicted by the flattening due to its spin rate the north polar region is covered by large mare filled with hydrocarbons including ethane moreover global circulation models predict ethane precipitation on the polar areas this study shows that the shape of titan can be explained by the subsidence associated with the substitution of methane with ethane rich liquids percolating into the crust which as suggested by evolution models may be composed of methane clathrate hydrates such substitutions have been observed in laboratory experiments this process would provide an additional methane source as required for sustaining the presence of this constituent in titan s atmosphere through its history a 270 m subsidence of the polar caps is explained by the circulation of 1 5 to 6 1018kg of ethane in the top three kilometers of an initially methane clathrate crust this process would have operated during the last 300 1200 myr at the present ethane production rate

determining titan surface topography from cassini sar data a technique referred to as sartopo has been developed for obtaining surface height estimates with 10 km horizontal resolution and 75 m vertical resolution of the surface of titan along each cassini synthetic aperture radar sar swath we describe the technique and present maps of the co located data sets a global map and regional maps of xanadu and the northern hemisphere hydrocarbon lakes district are included in the results a strength of the technique is that it provides topographic information co located with sar imagery having a topographic context vastly improves the interpretability of the sar imagery and is essential for understanding titan sartopo is capable of estimating surface heights for most of the sar imaged surface of titan currently nearly 30 of the surface is within 100 km of a sartopo height profile other competing techniques provide orders of magnitude less coverage we validate the sartopo technique through comparison with known geomorphological features such as mountain ranges and craters and by comparison with co located nadir altimetry including a 3000 km strip that had been observed by sar a month earlier in this area the sartopo and nadir altimetry data sets are co located tightly within 5 10 km for one 500 km section have similar resolution and as expected agree closely in surface height furthermore the region contains prominent high spatial resolution topography so it provides an excellent test of the resolution and precision of both techniques