an aerodynamic roughness length map derived from extended martian rock abundance data many boundary layer processes simulated within a mars general circulation model mgcm including the description of the processes controlling dust rising from the martian surface are highly sensitive to the aerodynamic roughness length z0 on the basis of rock size frequency distributions inferred from different martian landing sites and earth analog sites we have first established that lognormal modeled rock size frequency distributions are able to reproduce correctly the observed martian rock populations we have validated the hypothesis that the rock abundance of a given area could be estimated at a first order from its thermophysical properties namely its thermal inertia i and its albedo we have demonstrated the possibility of using rock abundance to estimate the roughness density on mars and to retrieve subsequently the aerodynamic roughness length by using semi empirical relationships based on terrestrial wind tunnel and field measurements by combining our methodology with remote sensing measurements of the thermal emission spectrometer aboard mars global surveyor we have derived a global map of the aeolian aerodynamic roughness length with a 1 8 1 8 resolution over the entire martian surface contrary to what is often assumed the martian aeolian aerodynamic roughness length is spatially highly heterogeneous at the fullest resolution the martian aerodynamic roughness length varies from 10 3 cm to 2 33 cm about 84 of the martian surface seems to be characterized by an aeolian aerodynamic roughness length value lower than 1 cm the spatially uniform value that most of the mgcms simulations have assumed recently since the aerodynamic roughness length z0 is a key parameter in deriving the erosion threshold wind velocities we anticipate a significant impact of our findings on the efficiencies for lifting dust in future mgcms

late jurassic bimodal magmatism in the northern sea floor remnant of the rocas verdes basin southern patagonian andes magmatic and detrital zircon ages from the rocas verdes basin a tectonically juxtaposed remnant of sea floor in the magallanes fold and thrust belt southern patagonia south america indicates that a rifting phase of the rocas verdes basin occurred between 152 and 142 ma and was accompanied by bimodal magmatism a dacite dyke cross cutting pillow basalt successions and a plagiogranite dyke in mixed mafic felsic terranes of the basal sarmiento ophiolite complex contain 150 ma zircon crystals indicating that mafic submarine volcanism had started prior to or during the late jurassic 10 15 ma earlier than previously thought the silicic pyroclastic rocks of the tobifera formation with two samples dated at 148 and 142 ma were heralded by synrift sedimentation along fault bounded grabens within palaeozoic metasediments no evidence for an active volcanic arc during the early formation of the rocas verdes basin was detected in detrital zircon grains of the lower sedimentary member of the tobifera formation a minimum of 25 ma of continuous sedimentation in the rocas verdes basin is suggested by detrital zircon grains in the upper member of the zapata formation the rocas verdes basin was rimmed on the western side by an incipient and subaerial magmatic arc only in its later evolution

eocene stratigraphy of southeastern tierra del fuego island argentina recognizing folded and thrusted eocene foreland strata of the oil producing austral basin provides new insights on the paleogene evolution of tierra del fuego island and the adjacent atlantic shelf field mapping and petrographic and micropaleontologic studies at the punta torcida anticline depict an eocene composite section about 1600 m thick assigned to the la despedida group this group is divided into three formations punta torcida 215 m leticia 520 m and cerro colorado 855 m these formations are subdivided into informal members in the punta torcida formation the lower member is composed of dark gray mudstones with thin sandstone beds the middle member of the punta torcida contains mudstones with small sandstone lenses both the lower and middle members have a high radiolarian content the upper member contains mudstones lithologic succession presence of pyrite and a well preserved benthic assemblage having little diversification suggest a regressive sequence formed in shelf settings with a dysaerobic to anoxic bottom planktonic foraminifera indicate a ypresian age equivalent to upper zone p6 to basal zone p9 tropical planktonic zones in the leticia formation the lower and upper members are glauconite rich highly bioturbated sandstones in the middle member rich in pyrite and carbonized plant material the glauconite is rare or absent large channels filled with cross stratified sandstone lenses and having a general absence of planktonic foraminifera suggest estuarine restricted marine settings planktonic foraminifera indicate a late middle eocene age basal zone p12 to middle of zone p14 indicating a hiatus with the underlying punta torcida formation the cerro colorado formation a coarsening and thickening upward succession of mudstones and sandstones is a major shelfal transgressive regressive sequence punctuated by minor deepening and shallowing its four members record different benthic assemblages that reflect cooling waters the uppermost member bears abundant radiolarians and planktonic foraminifera typical of an oxygen minimum habitat and indicating a late eocene age upper zone p15 to upper zone p16 the microfauna and stratigraphic position of the lower three members are consistent with a latest middle eocene age middle of zone p14 to lower zone p15 in preliminary observations on the outcrop area of late cretaceous paleogene strata between cabo san pablo and bahia thetis two important angular unconformities were recorded one at the contact between the estratos de policarpo and the rio bueno la despedida group and the other at the contact between the la despedida group and the cabo pena rio leona formations

relationships of aeolian erosion and deposition with lidar derived landscape surface roughness following wildfire the reduction of vegetation by wildfire can subject stable soil surfaces to increased aeolian transport vegetation and associated microtopography function as surface roughness elements that influence the entrainment transport and deposition of sediment by wind in burned and unburned semiarid shrublands we examined whether surface roughness derived from lidar can explain variability in aeolian surface change following wildfire in loess soils of a cold desert shrub steppe in se idaho usa erosion bridges were installed in fall 2007 following a late summer wildfire to monitor soil surface change at sites in burned and downwind unburned areas surface elevation measurements were made when the erosion bridges were installed and again in fall 2008 surface change was determined from the difference in relative elevation between the two dates airborne lidar data were acquired in fall 2007 following erosion bridge installation surface roughness was calculated at 2 m raster resolution using the standard deviation of all lidar elevations within the 2 m cells after elevations were detrended to remove the effects of topographic slope surface change varied as a function of surface roughness among burned and unburned surfaces with net erosion occurring on the relatively smooth burned surfaces and net deposition occurring on the rough unburned surfaces site mean surface change decreased linearly as a function of the inverse of site mean surface roughness r2 0 77 p 0 00 quantile regression analysis indicated that changes in surface roughness were related to proportionally greater changes in erosion compared to deposition analysis of surface change at finer spatial scales suggested that aeolian processes occurred with strong spatial patterns on burned but not unburned surfaces future research to examine relationships between aeolian transport and fine spatial resolution topographic variability for example from ground based lidar systems is recommended

tectonics of the umbria marche romagna arc central northern apennines italy new paleomagnetic constraints we present the results of a paleomagnetic study carried out on 32 sites from mainly messinian clayey sediments distributed throughout the external umbria marche romagna arc umra these data together with published results from coeval sediments demonstrate that this arc is an orocline in its central northern sector bending not well constrained in time was due to about 15 clockwise rotations of the central part of this arc and to counterclockwise rotations farther north in this latter area post messinian counterclockwise rotations are of the same amplitude as those calculated for some classic mesozoic paleomagnetic sections in northern umbria suggesting a plio pleistocene age for the rotations reported from the older sequences

simple spatially distributed models for predicting flood inundation a review abstract in this paper we review recent progress in the use of reduced complexity models for predicting floodplain inundation we review the theoretical basis for modelling floodplain flow with simplified hydraulic treatments based on a dimensional analysis of the one dimensional shallow water equations we then review how such schemes can be applied in practice and consider issues of space discretization time discretization and model parameterisation before going on to consider model assessment procedures we show that a key advantage of reduced complexity codes is that they force modellers to think about the minimum process representation necessary to predict particular quantities and act as a check on any tendency to reductionism at the same time however the use compared to standard hydraulic codes of strong simplifying assumptions requires us to also address the question how simple can a model be and still be physically realistic we show that by making explicit this debate about acceptable levels of abstraction reduced complexity codes allow progress to be made in addressing a number of long standing debates in hydraulics

quantifying relationships of burning roughness and potential dust emission with laser altimetry of soil surfaces at submeter scales abstract decrease in surface roughness by the reduction of vegetation is one mechanism by which fire can promote aeolian transport in a variety of landscapes the extent to which fire might alter the roughness of the soil surface at fine spatial scales and the effect of this alteration on post fire aeolian response is not well known we examined relationships in the field between dust emissions and subcentimeter level soil surface roughness at submeter spatial scales with a terrestrial laser scanner and portable wind tunnel analog based on aeolian theory we hypothesized that observed relationships would differ from those determined in previous studies with laser altimetry at landscape scales meter kilometer length scales we examined four semiarid shrublands in southern idaho usa containing a distinct pattern of undershrub and interspace microsites including recently burned and unburned conditions mixed models were used to determine effects of burning on surface roughness and the response of dust emissions to changes in surface roughness results indicated that burned soil surfaces were rougher than unburned soil surfaces dust emissions were enhanced by increases in roughness on burned soil surfaces and in the absence of nonerodible roughness elements i e plants this finding is expectedly in contrast to previous work that demonstrated an inverse relationship between soil erosion and surface roughness determined with lidar light detection and ranging at landscape scales vegetated and unvegetated surfaces relationships of lidar derived roughness and aeolian emissions are scale dependent and vary with environmental factors of fire and vegetation these findings are integral for future research that attempts to parameterize model based predictions of aeolian emissions with lidar derived roughness

magnetic fabric of clay sediments from the external northern apennines italy abstract we report on the anisotropy of magnetic susceptibility ams analyses of fine grained sediments deposited during the messinian in foredeep basins at the front of the northern apenninic chain the data refer to 32 sampling sites mostly distributed in the fine grained intervals of the laga and colombacci formations extending along the belt for a total length of about 300 km rock magnetism analyses indicate that the magnetic susceptibility and its anisotropy are in most cases dominated by the paramagnetic minerals of the clay matrix in order to delineate the contribution of the ferrimagnetic fraction to the overall susceptibility fabric the anisotropy of the anhysteretic remanent magnetisation was investigated at some representative sites the magnetic fabric of the studied sediments mostly reflects the effects of compaction showing a predominant magnetic foliation parallel to the bedding plane at all the sites a well distinct magnetic lineation was also found which is parallel to the fold axes and thrust fronts both at local and regional scales this feature is maintained in sequences that differ for sedimentological character and age implying that the magnetic lineation was produced by a mild tectonic overprint of the primary sedimentary compactional fabric the relationship between the magnetic lineation trends and the vertical axis rotations detected by speranza et al speranza f sagnotti l mattei m 1997 j geophys res 102 3153 3166 indicates that the magnetic lineation formed during the compressive phases of the messinian early pliocene when the apenninic front was almost rectilinear and oriented n320

underthrusting and exhumation a comparison between the external hellenides and the hot cycladic and cold south aegean core complexes greece 1 after their emplacement in the course of the late mesozoic and the cenozoic the hellenic nappes became fragmented during late orogenic extension since the late eocene here we focus on the transition of underthrusting during nappe emplacement to exhumation during late orogenic extension to this end we compared previously published data on the structural geological and metamorphic history of the underthrusted parts of the tripolitza and ionian nappes which were exhumed in the cycladic and south aegean windows with newly obtained data on the sedimentary stratigraphic and structural development of the part of these nappes in the foreland in front of the subduction thrust the results allow the identification of two major events event 1 took place around the eocene oligocene transition and marks the onset of underthrusting of the tripolitza nappe below the pindos nappe and the ionian nappe below the tripolitza nappe respectively this led to the uplift and erosion of the pindos unit and the onset of deposition of the tripolitza and ionian flysch in front of the pindos thrust together with the formation of mylonites at the base of the metamorphosed portions of the pindos unit related to the underthrusting of the tripolitza unit event 2 occurred in the latest oligocene to earliest miocene and marks the decoupling of the ionian unit from the underthrusting plate the accretion of the tripolitza and ionian units to the overriding plate and the onset of late orogenic extension and exhumation in the overriding plate this led to the formation of the south aegean and cycladic core complexes and the subsidence of the klematia paramythia half graben throughout the early miocene

the curved magallanes fold and thrust belt tectonic insights from a paleomagnetic and anisotropy of magnetic susceptibility study the magallanes fold and thrust belt ftb presents a large scale curvature from n s oriented structures north of 52 s to nearly e w in tierra del fuego island we present a paleomagnetic and anisotropy of magnetic susceptibility ams study from 85 sites sampled in cretaceous to miocene marine sediments magnetic susceptibility is lower than 0 0005 si for 76 sites and mainly controlled by paramagnetic minerals ams results indicate that the sedimentary fabric is preserved in the undeformed areas of tierra del fuego and the more external thrust sheets units where an incipient lineation due to layer parallel shortening is recorded prolate ams ellipsoids indicating a significant tectonic imprint in the ams fabric are observed in the internal units of the belt ams results show a good correlation between the orientation of the magnetic lineation and the fold axes however in peninsula brunswick the ams lineations are at 20 counterclockwise to the strike of the fold axes pretectonic stable characteristic remanent magnetizations chrm were determined in seven sites a counterclockwise rotation 21 2 9 2 is documented by chrm data from four sites near the hinge of the belt in peninsula brunswick and near canal whiteside while there is no evidence of rotation near the nearly e w oriented vicuna thrust within tierra del fuego the curved shape of the cenozoic magallanes ftb is not related to vertical axis rotation and thus the magallanes ftb can be considered as a primary arc

airborne laser altimeter measurements of landscape topography abstract measurements of topography can provide a wealth of information on landscape properties for managing hydrologic and geologic systems and conserving natural and agricultural resources this article discusses the application of an airborne laser altimeter to measure topography and other landscape surface properties the airborne laser altimeter makes 4000 measurements per second with a vertical recording resolution of 5 cm data are collected digitally with a personal computer a video camera borehole sighted with the laser records an image for locating flight lines gps data are used to locate flight line positions on the landscape laser data were used to measure vegetation canopy topography height cover and distribution and to measure microtopography of the land surface and gullies with depths of 15 20 cm macrotopography of landscape profiles for segments up to 4 km were in agreement with available topographic maps but provided more detail larger gullies with and without vegetation and stream channel cross sections and their associated floodplains have also been measured and reported in other publications landscape segments for any length could be measured for either micro or macrotopography airborne laser altimeter measurements of landscape profiles can provide detailed information on landscape properties or specific needs that will allow better decisions on the design and location of structures i e roads pipe and power lines and for improving the management and conservation of natural and agricultural landscapes

relative paleointensity of the geomagnetic field during the brunhes chron abstract we conducted a paleomagnetic study of four sediment cores taken from different regions in the low latitudes of the pacific ocean in order to recover relative paleointensity variations during the brunhes chron three cores have good age control from oxygen isotope stratigraphy we extensively examined rock magnetic uniformity by the iso thermal remanent magnetization irm acquisition and the alternating field demagnetization of the anhysteretic remanent magnetization arm and the irm only rock magnetically homogeneous sediments were used biogenic magnetites were found in all but one core and their dissolution in early diagenesis was not significant the four cores showed coherent variations of the remanent intensity normalized by the arm implying that these variations represent the behavior of the geomagnetic field long term paleointensity variations during the brunhes chron are characterized by an asymmetric pattern rapid increases in the intensity occurred just after the brunhes matuyama transition in the mid brunhes from about 500 to 400 ka and during the last 100 ka and gradual decreases between them the first one supports the idea of rapid regeneration of the geomagnetic field after polarity reversals 1 the other two may have been triggered by very short polarity reversals

the origin of tectonic lineation in extensional basins combined neutron texture and magnetic analyses on undeformed clays abstract in extensional sedimentary basins fine grained sediments that appear undeformed at the outcrop scale can carry a magnetic fabric consistent with the regional deformation pattern the origin of the magnetic lineation which is often found in extensional basins is not yet well understood in clays from extensional basins in southern italy the magnetic lineation is tectonically controlled and oriented perpendicular to the main normal faults a combined analysis of magnetic and mineral fabrics was made to gain insight into the processes that lead to a lineation in extensional settings low field high field and low temperature susceptibility measurements were used to distinguish the ferrimagnetic and paramagnetic contributions to the magnetic susceptibility and its anisotropy the magnetic anisotropy of the sediments is predominantly carried by paramagnetic phyllosilicates neutron texture analysis was used to evaluate the spatial distribution of chlorite basal planes results demonstrate that the orientation of the magnetic lineation is related to the spatial distribution of chlorite lying parallel to the common axis of differently oriented basal planes a quantitative correlation between the magnetic and rock fabric was made comparing the low and high field magnetic anisotropy ams hfa to the theoretical anisotropy calculated from the chlorite preferred orientation a good linear correlation is found between the degree of theoretical anisotropy and the ams and hfa results show that the integrated approach of magnetic and mineral fabric investigations represents a valid alternative tool for detecting grain scale and regional deformation patterns in weakly deformed extensional basins where macroscopic evidence of deformation is often not visible

bending of the bolivian orocline and growth of the central andean plateau paleomagnetic and structural constraints from the eastern cordillera 22 24 s nw argentina 1 we report new paleomagnetic and structural data from late cretaceous to mio pliocene continental sandy silty sedimentary rocks from the eastern cordillera central andes here n s to nne ssw ridges hosting paleozoic basement and upper cretaceous continental red beds overthrust thick adjacent cenozoic basins pretilting and likely primary reliable directions gathered at 15 sites document 45 9 9 4 30 1 23 9 and 15 4 19 3 clockwise cw rotations with respect to south america occurring after the late cretaceous 80 ma oligo miocene 20 30 ma and late miocene pliocene 5 10 ma respectively conversely four upper cretaceous sites from the walls of a n s left lateral strike slip fault yavi abra pampa fault yield a null rotation about 20 km to the west flower structures and subvertical syntectonic strata dated at 14 26 0 19 ma are exposed along the subparallel abra moreta left lateral strike slip fault relying on data from the literature on the period when deformation began we suggest that since eo oligocene times 30 40 ma the eastern cordillera has undergone a regional cw rotation of 40 50 synchronous with crustal shortening and large scale bending of the andean salient the cw rotation is possibly still active today as documented by regional gps data from the andes since 15 ma ago the activity of n s left lateral strike slip faults induced counterclockwise rotations along the fault zone locally annulling the regional cw rotation in agreement with a previous model we speculate that mid miocene strike slip activity accommodated the progressive southward spreading of the altiplano puna high altitude plateau laterally migrating from the overthickened crustal region of the salient apex

new constraints on the chronology magnitude and distribution of deformation within the central andean orocline 1 constructing an accurate kinematic model for crustal thickening in the central andes is hampered by the inability of 2 d balanced cross sections to resolve the 3 d displacement field within the poorly studied orocline core this study presents new structural and thermochronometer data from the orocline axis in the central andes that constrains the magnitude and timing of deformation through 1 a balanced cross section quantifying shortening perpendicular to strike 2 field observations that constrain translational displacements parallel to strike and 3 thermochronology that brackets the age of exhumation and deformation mapping results show that north directed right lateral motion has been accommodated on at least one major strike slip fault in the eastern cordillera ec shortening perpendicular to fault strike is 179km 41 for the ec and inter andean zone ia and 86km 39 for the sub andes sa apatite fission track cooling ages indicate rapid ec ia exhumation from 46 to 18ma and 15 to 0ma in the sa zircon and apatite u th he ages show that rapid exhumation began 10 5ma in the sa these results are integrated with existing paleomagnetic and gps rotation data in map view reconstructions to quantify the magnitude of translational faulting related to oroclinal bending the reconstructions suggest that at least 85km of north directed translational displacement has been accommodated within the orocline core orogen parallel displacement and vertical axis rotations have focused crustal thickening at the orocline core and facilitated development of a high elevation plateau suggesting a genetic link between large scale oroclines and plateaus

effects of lidar derived spatially distributed vegetation roughness on two dimensional hydraulics in a gravel cobble river at flows of 0 2 to 20 times bankfull abstract the spatially distributed effects of riparian vegetation on fluvial hydrodynamics during low flows to large floods are poorly documented drawing on a lidar derived meter scale resolution raster of vegetation canopy height as well as an existing algorithm to spatially distribute stage dependent channel roughness this study developed a meter scale two dimensional hydrodynamic model of 28 3 km of a gravel cobble bed river corridor for flows ranging from 0 2 to 20 times bankfull discharge with and without spatially distributed vegetation roughness results were analyzed to gain insight into stage dependent and scale dependent effects of vegetation on velocities depths and flow patterns at the floodplain filling flow of 597 49 m 3 s adding spatially distributed vegetation roughness parameters caused 8 0 and 7 4 increases in wetted area and mean depth respectively while mean velocity decreased 17 5 vegetation has a strong channelization effect on the flow increasing the difference between mid channel and bank velocities it also diverted flow away from densely vegetated areas on the floodplain vegetation stands caused high velocity preferential flow paths that were otherwise unaccounted for in the unvegetated model runs for the river as a whole as discharge increases overall roughness increases as well contrary to popular conception

the opening of the magellan strait and its geodynamic implications terra nova 25 13 20 2013 abstract the existence of a neogene quaternary rift system responsible for the opening of the eastern magellan strait has been one of the more peculiar tectonic features of the southernmost andes since its discovery more than a decade ago however until now there has been no explanation pinpointing the specific tectonic factors that led to the development of the rift this work focuses on the interaction between the fault systems and the tectonic regimes that have affected tierra del fuego north of the south america scotia left lateral strike slip plate boundary due to a good match between a jurassic extensional fault array orientation and the principal stress directions related to the strike slip plate boundary we conclude that jurassic transfer faults reactivated extensionally generating the magellan rift system this process was enhanced by northward continental drift and has implications for the geodynamic behind the separation of south america from antarctica

crustal growth during back arc closure cretaceous exhumation history of cordillera darwin southern patagonia the cordillera darwin metamorphic complex is unique in the andes in exposing kyanite staurolite schist north of the beagle channel in southern patagonia garnet in amphibolite facies pelitic schists from bahia pia has patchy textures whereby some grains consist of clear grossular rich garnet with fine grained s1 inclusion trails truncated by regions of turbid spessartine pyrope rich garnet with biotite muscovite plagioclase and quartz inclusions micron scale aqueous inclusions in turbid garnet are consistent with recrystallization facilitated by fluid ingress s2 inclusion trails indicate this was broadly contemporary with the growth of kyanite and staurolite in the matrix pseudosection modelling in na2o cao k2o feo mgo al2o3 sio2 h2o tio2 fe2o3 nckfmashto is used to infer a p t path dominated by decompression from 12 to 9 kbar at t 620 c coupled with garnet mode decreasing from 5 to 1 u th pb in situ dating of s2 monazite indicates that staurolite and kyanite growth and thus exhumation was underway before 72 6 1 1 ma contact aureoles developed adjacent to late granite intrusions include sillimanite bearing migmatites formed at p 6 kbar after 72 ma metamorphism of southern cordillera darwin induced by continental underthrusting beneath the arc related to closure of the rocas verdes back arc basin was terminated by thrusting controlled exhumation with the rocks at p 9 kbar by c 73 ma and 6 kbar by c 70 ma

roughness dependent geographical interpolation of surface wind speed averages modele bicouche de couche limite pour le calcul regional du climat en moyenne sur une saison du vent de surface a partir des donnees de station dans la couche de surface les mesures du vent sont corrigees objectivement pour une exposition imparfaite de la station a l aide de la rugosite deduite du facteur de rafale pour chaque secteur azimutal ceci fournit a 60 m une v du vent de messechelle u m representation de blocs d etendue 5 5 km 2 le moyennage regional de u m dans la couche d eleman est effectuee par des methodes geistrophiques de similitude analyse de toutes les donnees de vent relatives aux pays bas plats a l aide d une serie de 30 ans de l indice annuel de ventosite en vue de l ajustement temporel des series non simultanees ceci conduit a une cartographie objectivement interpolee pour les vents de surface augmentee des valeurs de distribution et de v extreme extension possible de la methode a un terrain complexe

observation and simulation of lake air heat and water transfer processes in a high altitude shallow lake on the tibetan plateau lakes are an important part of the landscape on the tibetan plateau most of the plateau lakes area has been expanding in recent years but lake atmosphere energy and water interaction is poorly understood because of a lack of observational data and adequate modeling systems based on the eddy covariance observation over a high altitude shallow and small lake the small nam co lake during an ice free period from 10 april to 30 august 2012 this study analyzes the lake air heat and water vapor turbulent transfer processes and evaluates two popular lake air exchange models a bulk aerodynamic transfer model b model and a multilayer model m model our main results are as follows 1 observations show that the bulk transfer coefficient ce and roughness length zoq for water are higher than those for heat ch and z0h especially under low wind speed 2 both models underestimate turbulent fluxes due to inaccurate values of the charnock coefficient and the roughness reynolds number rr which are both important parameters for calculating the roughness length for momentum z0m over water 3 within a reasonable range of 0 013 0 035 for rough flow and rr for smooth flow rr 0 11 are 0 031 and 0 54 respectively by our observation the wave pattern of shorter wavelength gives a larger z0m in the small and shallow lake and 4 the b model and the m model gave consistent results and both models are more suitable for simulation of turbulent flux exchange after z0m optimization

estimates of effective aerodynamic roughness length over mountainous areas of the tibetan plateau wind profile data were measured by a wind profiler at qoms the qomolangma station for atmospheric environmental observation and research chinese academy of sciences and in separate experiments gps radiosondes were used at shiquanhe station and litang station on the tibetan plateau tp all three stations are located in the most rugged areas of the tp qoms is surrounded by the himalaya shiquanhe station by the transhimalaya and litang station is near the hengduan mountains using observational wind profile data effective aerodynamic roughness length z0meff and zero plane displacement height d0 are determined using the neutral logarithmic wind profile law the results show that the values of z0meff derived from the wind profiles can be considerably larger than the small scale aerodynamic roughness lengths of the land surface around the three stations subsequently several parametrization schemes which use land surface characteristics to estimate z0meff and d0 such as roughness obstacle height and density were assessed the result indicates that of all the methods available that proposed by grant and mason where the drag coefficient d 0 5 gives the best estimate of z0meff the interim european centre for medium range weather forecasts ecmwf re analysis era interim dataset underestimates effective aerodynamic roughness length in mountainous areas of the tp due to its use of a smaller drag coefficient of d 0 4 for estimating d0 the method of kutzbach performs well when the density of roughness obstacles is low whereas the method of raupach et al gives a more reliable estimate when is high although this analysis has some limitations it can feasibly account for form drag being exerted by an unresolved topography in the mountainous areas of the tp

the late jurassic to present evolution of the andean margin drivers and the geological record 1 uncommonly long lived subduction and variable plate geometry along the south american andean plate margin resulted in diverse relationships between magmatic flux and extensional and contractional deformation as recorded by the overriding continental plate convergence velocities absolute overriding plate velocities and subducting slab ages were resolved along the trench from 170 ma to the present using a recently developed kinematic global plate model to identify any relationship between subduction conditions deformation style and magmatic features in the overriding plate key correlations reflect the dependence of macroscopic crustal strain style on subduction mechanism and relative plate vectors extensional back arc basins involving mafic oceanic crust developed only when the overriding plate velocity of south america was directed away from the trench and the modeled age of the subducting slab was older than 50 myr the development of fold and thrust belts and uplift of major plateaus was accompanied by trench normal convergence velocities in excess of 4 cm yr parameters investigated in this study revealed no correlation with the timing of major magmatic events nor was any correlation observed with the structural style of fold and thrust belts

estimation of effective aerodynamic roughness of walnut gulch watershed with laser altimeter measurements a new method to estimate the effective aerodynamic roughness of a complex landscape is presented high resolution elevation profiles measured with an airborne laser altimeter have been used to compute geometrical parameters of three landscape elements of the walnut gulch experimental watershed arizona mean crop height its standard deviation and the frequency distribution as a function of penetration depth of plant elements hit by the laser beam have been calculated for short segments 1 m measured over intervening grass between shrubs longer segments have been applied to obtain the mean height and spacing of taller shrubs and trees finally laser profiles covering the entire watershed gave the mean amplitude and wavelength of hillocks and ridges the aerodynamic roughness length of the intervening grass is estimated using the ratio of standard deviation to vegetation height corrected for instrument noise times mean height an effective roughness length which parameterizes the total stress due to grass and taller shrubs and trees is calculated first finally a watershed scale effective roughness length is calculated combining the amplitude and wavelength of hillocks and ridges with the roughness length obtained in the previous step

predicting floodplain inundation raster based modelling versus the finite element approach we compare two approaches to modelling floodplain inundation a raster based approach which uses a relatively simple process representation with channel flows being resolved separately from the floodplain using either a kinematic or diffusive wave approximation and a finite element hydraulic model aiming to solve the full two dimensional shallow water equations a flood event on a short c 4 km reach of the upper river thames in the uk is simulated the models being validated against inundation extent as determined from satellite synthetic aperture radar sar imagery the unconstrained friction parameters are found through a calibration procedure where a measure of fit between predicted and observed shorelines is maximized the raster and finite element models offer similar levels of performance both classifying approximately 84 of the model domain correctly compared with 65 for a simple planar prediction of water surface elevation further discrimination between models is not possible given the errors in the validation data the simple raster based model is shown to have considerable advantages in terms of producing a straightforward calibration process and being robust with respect to channel specification copyright 2001 john wiley sons ltd

continental underthrusting and obduction during the cretaceous closure of the rocas verdes rift basin cordillera darwin patagonian andes 1 the patagonian andes record a period of cretaceous neogene orogenesis that began with the compressional inversion of a late jurassic rift called the rocas verdes basin detrital zircon ages from sediment that filled the southern part of the basin provide a maximum depositional age of 148 ma suggesting that the basin opened approximately simultaneously along its length during the late jurassic structural data and u pb isotopic ages on zircon from granite plutons near the beagle channel 55 s show that basin inversion involved two stages of shortening separated by tens of millions of years an initial stage created a small 60 km wide thrust wedge that placed the basaltic floor of the rocas verdes basin on top of adjacent continental crust prior to 86 ma structures and metamorphic mineral assemblages preserved in an exhumed middle to lower crustal shear zone in cordillera darwin suggest that this obduction was accompanied by south directed subduction of the basaltic crust and underthrusting of continental crust to depths of 35 km beneath a coeval volcanic arc a subsequent stage of out of sequence thrusting culminating in the paleogene shortened basement and upper jurassic igneous rock in the internal part of the belt by at least 50 km forming a bivergent thrust wedge this latter period coincided with the exhumation of rocks in cordillera darwin and expansion of the fold thrust belt into the magallanes foreland basin this orogen provides an important example of how orogenesis initiated and led to continental underthrusting and obduction of basaltic crust during closure of a quasi oceanic rift basin

obliquely convergent tectonics and granite emplacement in the trans saharan belt of eastern nigeria a synthesis abstract the eastern nigeria terrane belongs to the 3000 km long trans saharan belt which was formed in the neoproterozoic between 750 and 500 ma by continental collision between the converging west african craton congo craton and east saharan block the study area consists mostly of gneisses and migmatites that underwent granulite facies metamorphism 800 c 800 mpa in contrast with western nigeria and cameroon no basement cover relationship has been identified which is in agreement with a monocyclic metamorphic history around 640 ma the area underwent a nappe tectonics with eastward displacement emplacement of bt ms granites and granulite facies peak later on around 615 ma nappes were towards the north numerous hbl bt granite plutons were emplaced around 585 ma during north south strike slip regional deformation the anisotropy of magnetic susceptibility fabric helps in defining strain localization along narrow north south to nne ssw vertical shear zones during the exhumation history exhumation of the terrane assessed using u pb ar ar and rb sr methods was presumably slow with uplift rates around 0 2 0 5 mm year preliminary estimates of contemporaneous horizontal movements suggest that they were one order of magnitude larger

fractal modeling of airborne laser altimetry data abstract airborne laser altimetry is a remote sensing technique that can provide high resolution data on the roughness of the landscape both for estimating water balance components and for distinguishing between landscapes models of the scale dependent roughness are needed to find scales most appropriate for these purposes our objectives were to apply fractal scaling to high resolution profiling laser altimetry data and to determine fractal parameters for differentiating land cover data were collected at the usda ars jornada experimental range in new mexico over grass dominated and shrub dominated sites along four transects at each site scale dependent root meansquare rms roughness and data power spectrums were computed from 100 000 data points 2 km from each transect a linearity measure and piecewise linear approximation were applied to find intervals of the fractal scaling the rms roughness data had two intervals of self affine fractal scaling on grass transects and four such intervals on shrub transects reduction in the number of data points did not lead to a decrease in roughness but caused a smoothing dependency of fractal dimension on scale ten and hundred meter scales were appropriate for distinguishing between grass and shrub transects on the basis of fractal dimensions

floodplain friction parameterization in two dimensional river flood models using vegetation heights derived from airborne scanning laser altimetry two dimensional 2 d hydraulic models are currently at the forefront of research into river flood inundation prediction airborne scanning laser altimetry is an important new data source that can provide such models with spatially distributed floodplain topography together with vegetation heights for parameterization of model friction the paper investigates how vegetation height data can be used to realize the currently unexploited potential of 2 d flood models to specify a friction factor at each node of the finite element model mesh the only vegetation attribute required in the estimation of floodplain node friction factors is vegetation height different sets of flow resistance equations are used to model channel sediment short vegetation and tall and intermediate vegetation the scheme was tested in a modelling study of a flood event that occurred on the river severn uk in october 1998 a synthetic aperture radar image acquired during the flood provided an observed flood extent against which to validate the predicted extent the modelled flood extent using variable friction was found to agree with the observed extent almost everywhere within the model domain the variable friction model has the considerable advantage that it makes unnecessary the unphysical fitting of floodplain and channel friction factors required in the traditional approach to model calibration copyright 2003 john wiley sons ltd

magallanes fagnano continental transform fault tierra del fuego southernmost south america 1 multichannel seismic reflection profiles gravity measurements and bathymetric soundings in conjunction with field geological reconnaissance and remote sensing images reveal with unprecedented detail the morphostructure of a major segment of the south america scotia plate boundary in the tierra del fuego region this segment known as the magallanes fagnano fault system is a continental transform margin arranged in an en echelon geometry along which prominent asymmetric basins were developed data acquired off the atlantic coast of isla grande the main island of tierra del fuego in its central and eastern part and in the central and western magallanes strait image the surface and subsurface structure of the transform fault and its associated basins the magallanes fagnano fault system is composed of distinct tectonic lineaments that are segments of the transform system and are represented by mostly near vertical faults in the atlantic sector the fault system trends broadly n70 e and seems to be composed by a single master fault along which a highly asymmetric basin has formed at around 63 w the fault terminates by splaying into secondary normal faults that dissipate the horizontal displacement along the system in the central eastern part of isla grande the fault segments have been principally identified from analyses of remote sensing images on the basis of their morphological expression these segments are located within river valleys and are generally associated with localized gravity minima lago fagnano a 105 km long e w trending depression is a large mostly asymmetric pull apart basin developed within the principal displacement zone of the magallanes fagnano fault system restraining bends and overlapping step over geometry characterize the central part of the magallanes strait along the western part of the fault system in the vicinity of the pacific entrance of the magallanes strait asymmetric sedimentary basins have also developed the sedimentary architecture of the basins formed within the principal displacement zone of the fault in which the thick end of the depositional wedge abuts the transform segment suggest simultaneous strike slip motion and transform normal extension a common feature found in other continental transtensional environments strike slip faulting in the tierra del fuego region is also documented along other prominent lineaments which parallel the magallanes fagnano fault system along at least two of these lineaments characterized by a remarkable morphological expression widespread quaternary activity occurs the present day motion between the south america and scotia plates is slow 5 mm yr also the modern seismicity monitored in the tierra del fuego region is low individual events 3 5 in magnitude the low seismicity may be explained by the slow relative motion between plates and may be further affected by slip partitioning along the different segments which make up the magallanes fagnano fault array and along the subsidiary wrench lineaments that traverse the region

influence of attenuated lithosphere and sediment loading on flexure of the deep water magallanes retroarc foreland basin southern andes flexural subsidence in foreland basins is controlled by applied loads such as topography water sediment and subcrustal forces and the mechanical properties of the lithosphere we investigate the controls on subsidence observed within the upper cretaceous magallanes retroarc foreland basin of southern south america to evaluate the impact of lateral variations in flexural rigidity due to late jurassic extension conventional elastic models cannot explain the observed basin deflection and thick accumulation of deep water cenomanian turonian basin strata however models in which the lithosphere has been previously thinned and deflects under topographic and sedimentary loads successfully reproduce regional subsidence patterns results satisfy paleobathymetric observations in the magallanes basin and suggest that lithospheric thinning is necessary to produce both long wavelength and deep subsidence during late cretaceous basin evolution results indicate that elastic thickness decreases westward from 45 25 km in the distal foreland to 37 15 km beneath the foredeep these findings are consistent with a westward reduction in crustal thickness associated with the jurassic extensional history of the patagonian lithosphere our results also show that sediment loading exerts an important control on regional deflection patterns and promotes a wider region of subsidence and reduced forebulge uplift we propose that lateral variations in mechanical properties and large sediment loads restrict depocenter migration and may cause the foredeep to remain fixed for prolonged periods of time these findings confirm that loading of thinned lithosphere imposes different mechanical controls on the flexural profile and have potential implications for other retroarc foreland basins characterized by earlier extensional histories

cenozoic crustal thickening wrenching and rifting in the foothills of the southernmost andes abstract the southernmost andes form an orocline between the patagonian cordillera trending n s and the fueguian cordilleras trending e w on the foreland side is the magellan basin the area has a history of paleozoic compression triassic to early cretaceous rifting and late cretaceous to quaternary compression in response to changing plate tectonics major structures of late cretaceous and cenozoic age vary along the strike in the patagonian cordillera and foothills folds and thrusts trend nnw slightly oblique to the orogen whereas strike slip faults are parallel to the orogen and right lateral in the fueguian cordilleras and foothills folds and thrusts trend ese slightly oblique to the orogen whereas strike slip faults are parallel to the orogen and left lateral in the axial zone of the magellan basin folds and thrusts are parallel to the orogen and rifts are sub perpendicular to it to a first approximation the pattern of structures has mirror symmetry about the axis of the magellan basin in detail however wrenching appears to be more prevalent in the fueguian cordillera and foothills than it is in the patagonian cordillera and foothills minor faults of cenozoic age are common in the foothills from a kinematic analysis of fault slip data 1 shortening and stretching directions are mostly sub horizontal 2 shortening directions vary in trend from ene in the patagonian foothills to ne in the fueguian foothills and 3 stretching directions are sub parallel to traces of major thrusts in the fueguian cordillera and foothills strike slip faulting is prevalent in the patagonian foothills crustal thickening is prevalent over strike slip faulting the kinematics reflect a combination of thrusting and wrenching and they are consistent with the major structures to investigate the origin of the cenozoic structures we used analogue models on a fully lithospheric scale where an oceanic plate subducted beneath a continental corner the corner was an area of transition from frontal subduction to transcurrent motion the boundary conditions may not have been fully realistic but the experiments did account for the major elements of the structural pattern in southernmost south america including rifts that are perpendicular to the orogen and counterclockwise block rotations

constraints on deformation of the southern andes since the cretaceous from anisotropy of magnetic susceptibility the southernmost segment of the andean cordillera underwent a complex deformation history characterized by alternation of contractional extensional and strike slip tectonics key elements of southern andean deformation that remain poorly constrained include the origin of the orogenic bend known as the patagonian orocline here renamed as patagonian arc and the exhumation mechanism of an upper amphibolite facies metamorphic complex currently exposed in cordillera darwin here we present results of anisotropy of magnetic susceptibility ams from 22 sites in upper cretaceous to upper eocene sedimentary rocks within the internal structural domain of the magallanes fold and thrust belt in tierra del fuego argentina ams parameters from most sites reveal a weak tectonic overprint of the original magnetic fabric which was likely acquired upon layer parallel shortening soon after sedimentation magnetic lineation from 17 sites is interpreted to have formed during compressive tectonic phases associated to a continuous n s contraction our data combined with the existing ams database from adjacent areas show that the early cretaceous late oligocene tectonic phases in the southern andes yielded continuous contraction variable from e w in the patagonian andes to n s in the fuegian andes which defined a radial strain field a direct implication is that the exhumation of the cordillera darwin metamorphic complex occurred under compressive rather than extensional or strike slip tectonics as alternatively proposed if we agree with recent works considering the curved magallanes fold and thrust belt as a primary arc i e no relative vertical axis rotation of the limbs occurs during its formation then other mechanisms different from oroclinal bending should be invoked to explain the documented radial strain field we tentatively propose a kinematic model in which reactivation of variably oriented jurassic faults at the south american continental margin controlled the late cretaceous to cenozoic evolution of the magallanes fold and thrust belt yielding the observed deformation pattern

the origin of tectonic fabrics in undeformed clays the early stages of deformation in extensional sedimentary basins 1 an integrated approach was used to detect tectonic effects in apparently undeformed fine grained clay sediments filling extensional basins in southern italy results from low and high field anisotropy of magnetic susceptibility and mineral fabric deduced by neutron texture analysis show penetrative deformation on a grain scale the well defined tectonic magnetic lineation is parallel to the stretching direction and located at the intersection of the basal planes of phyllosilicates forming grain scale folds and crenulations this spatial configuration reflects basin scale deformation processes and suggests the existence of a nearly uniaxial stress field during the incipient extensional phases the integrated approach of magnetic and mineral fabric investigations is a valid tool to detect grain scale and regional deformation pattern in weakly deformed extensional basins where macroscopic evidence of deformation is not visible