time domain reflectometry models as a tool to understand the dielectric response of volcanic soils the transmission of an electromagnetic wave through the soil using time domain reflectometry tdr permits the determination of its water content h given the composite dielectric constant of the soil ec via topp s equation this is possible since the dielectric constant of water is much larger than that of the soil s solid phase 80 vs 5 and therefore changes in soil moisture content lead to variations in ec however organic soils and those of volcanic origin do not obey the universal relationship ec h originally obtained by topp hence several authors have proposed alternative empirical ec h relationships volcanic soils are particular with respect to their low bulk density large porosity and specific surface mainly due to the strong aggregation of particles and high concentration of fe oxihydroxides and also due to the presence of allophanic clays with large surface area and water affinity thus it is likely that the water retention characteristics of volcanic soils will exhibit an atypical dielectric behaviour this work shows that physical models which incorporate parameters such as bulk density porosity and surface area can interpret the anomalous dielectric behaviour of volcanic soils among these models we shall distinguish those which consider three phases water air soil and those which separate the water content in two phases i e free and bound water four phase models four phase models help identify two distinct linear dielectric regimes dominated by free and bound water respectively for at least some soils soil porosity is shown to play an important role in the dielectric behaviour of volcanic soils we also found that soil andic parameters provide an a priori diagnosis criterion to evaluate the departure of volcanic soils from topp s curve additionally we propose an alternative general ec h calibration relationship for these kinds of soils which may be incorporated in commercial tdr devices for laboratory and field water content determination d 2003 elsevier science b v all rights reserved

an efficient and comprehensive method for drainage network extraction from dem with billions of pixels using a size balanced binary search tree abstract with the increasing resolution of digital elevation models dems computational efficiency problems have been encountered when extracting the drainage network of a large river basin at billion pixel scales the efficiency of the most time consuming depression filling pretreatment has been improved by using the o n log n complexity least cost path search method but the complete extraction steps following this method have not been proposed and tested in this paper an improved o n log n algorithm was proposed by introducing a size balanced binary search tree bst to improve the efficiency of the depression filling pretreatment further the following extraction steps including the flow direction determination and the upslope area accumulation were also redesigned to benefit from this improvement therefore an efficient and comprehensive method was developed the method was tested to extract drainage networks of 31 river basins with areas greater than 500 000 km 2 from the 30 m resolution aster gdem and two sub basins with areas of approximately 1000 km 2 from the 1 m resolution airborne lidar dem complete drainage networks with both vector features and topographic parameters were obtained with time consumptions in o n log n complexity the results indicate that the developed method can be used to extract entire drainage networks from dems with billions of pixels with high efficiency

geomorphology and evolution of the late pleistocene to holocene fluvial system in the south eastern llanos de moxos bolivian amazon in the bolivian amazon several paleochannel generations are preserved their wide spectrum of morphologies clearly provides crucial information on the type and magnitude of geomorphic and hydrological changes within the drainage network of the andean foreland therefore in this study we mapped geomorphological characteristics of paleochannels and applied radiocarbon and optically stimulated luminescence dating seven paleochannel generations are identified significant changes in sinuosity channel widths and river pattern are observed for the successive paleochannel generations our results clearly reflect at least three different geomorphic and hydrological periods in the evolution of the fluvial system since the late pleistocene changes in discharge and sediment load may be controlled by combinations of two interrelated mechanisms i spatial changes and re organizations of the drainage network in the upper catchment and or ii climate changes with their associated local to catchment scale modifications in vegetation cover and changes in discharge inundation frequencies and magnitudes which have likely affected the evolution of the fluvial system in the llanos de moxos in summary our study has revealed the enormous potential which geomorphic mapping and analysis combined with luminescence based chronologies hold for the reconstruction of the late pleistocene to recent fluvial system in a large portion of amazonia

gravity anomalies and flexure of the brazilian shield beneath the bolivian andes abstract seismological and geological data suggest that the brazilian shield is now underthrusting beneath the sub andes in order to constrain the minimum amount of shortening that results from this underthrusting we analyzed bouguer gravity anomalies over the shield and the bolivian andes assuming that they are due primarily to variations in crustal thickness that in turn are due to the flexure of an effectively elastic plate brazilian shield loaded by the weight of the andean mountain range gravity anomalies show that airy type isostatic equilibrium does not exist the sub andes are overcompensated and the chaco plain to the east is undercompensated the flexure of the plate can help explain both the overcompensation and the undercompensation if the brazilian shield behaves as an essentially elastic plate that extends at least 150 km and probably 200 km beneath the sub andes and the cordillera oriental and if the flexural rigidity of the plate is between 0 1 and 2 10 24 n m the fit of observed and calculated anomalies however is far from perfect and additional sources of short wavelength anomalies appear to be present assuming that the sediments and sedimentary rocks in the sub andes and cordillera oriental were deposited on the brazilian shield and that later they were overthrust eastward onto one another causing the present topography and the deflection of the plate we computed a family of estimates for the minimum amount of crustal shortening these estimates depend strongly on the amount of sedimentary rock deposited before deformation which does not seem to be well constrained by published geologic mapping nevertheless the calculations suggest that at least 100 km of crustal shortening have occurred and probably more implying that the andes may have been built mostly by crustal shortening

automated recognition of valley heads from digital elevation models applications of landform recognition in map making geographical information systems and in improving the storage and representation of earth surface information are described reasons are given for the use of digital elevation models for landform recognition increasing availability of data easier data integration and automation of landform recognition an automated technique for recognizing valley heads from digital elevation models is presented the technique has been developed for valley head recognition because valley heads are known locations of geomorphological activity and because areal features have been largely ignored in the automated landform recognition literature the problem of valley head recognition is divided into valley head location and valley head delineation and the technique is developed using a dem representing a simple artificial landscape two methods are given for valley head location in the first valley heads are located at valley ends in the second valley heads are located at cells which would have water flowing into them from many directions if water was flowing over the terrain the latter method locates all the valley heads on the artificial landscape the cells locating valley heads are iteratively grown to adjacent cells that are concave in plan and not flat to delineate the valley head at best 82 per cent valley head cells on the artificial landscape are correctly recognized with a 43 per cent commission error the method is tested on real data where it is less successful because of the variability of real landscapes and the inadequacy of the methods chosen for valley network delineation machine learning of thresholds and a method involving inspection of profiles across a dem cell are suggested as methods to improve the automated valley head recognition technique

influence of the drainage network identification method on geomorphological properties and hydrological response the influence of the method of identification of the drainage network on its geomorphological characteristics and on its hydrological response is analysed blue lines photo interpreted networks and networks generated from digital elevation models dems by an automatic algorithm are compared with field observations for two small alpine catchments the comparisons are carried out in quantitative terms by using several geomorphological indices and functions and by calculating the hydrological response of the networks as represented by their geomorphologic instantaneous unit hydrograph giuh the results show that the effect of the identification method on the geomorphological indices and on the hydrological response is significant and that the threshold area for channel initiation is not constant moreover the available data show a poor correlation between local slope and threshold area finally the influence of the threshold area on the shape of the giuh is larger when the residence time on the hillslopes is of the same order as the residence time in the network in the opposite case the variability of the flow velocity along the network seems to play an important role 1997 john wiley sons ltd

automated recognition of valley lines and drainage networks from grid digital elevation models a review and a new method abstract the literature on valley and drainage line recognition from grid digital elevation models dems is reviewed two problems preventing the successful delineation of fully connected drainage networks of single line width are identified a the positioning of the ends of drainage networks and b the assignment of drainage directions to a dem in particular the assignment of drainage directions across flat areas and at closed depressions in the dem pits a new method for drainage network delineation is suggested which incorporates an alternative method for drainage direction assignment over a dem this method is found to produce realistic directions and performs well on two complex dems

rotation of the peruvian block from palaeomagnetic studies of the central andes palaeomagnetic studies were performed on the rocks of the central andes to test the hypothesis of oroclinal bending of the andes around the peru chile border natural remanent magnetization of mesozoic volcanic and sedimentary rocks of peru shows a counterclockwise shift of declination by several tens of degrees relative to the field directions of the same ages in the stable south american craton two mesozoic dyke swarms from arica region northernmost chile also indicate about 20 of declination shift in a counterclockwise sense these results suggest a considerable amount of counterclockwise rotation of large area north of arica that is oroclinal bending of the andes around some hinge near the peru chile border one neogene dyke swarm sampled in central peru also gave declination which deviates counterclockwisely by 15 if this declination shift is a result of the wide area tectonic rotation as suggested by the mesozoic rocks oroclinal bending appears to have continued until relatively recent times

quantitative analysis of morphometric parameters of kali river basin southern india using bearing azimuth and drainage bad calculator and gis this study deals with the application of visual basic program bearing azimuth and drainage bad calculator which employs a new and easy methodology for extraction of watershed morphometric parameters using bad calculator morphometric analysis was carried out for the kali river basin of southwest coast of india the basin forms a part of the western ghats which is an important mountain range of the indian sub continent and runs nearly parallel to the coast spatial maps of six morphometric parameters have been prepared from the results obtained various linear areal shape and relief morphometric parameters of fifth and sixth order basins have been calculated and interpreted majority of the sub basins show less uniform values 3 to 4 of rbm which indicate the uniform and systematic branching pattern of streams high dd zones are found in the western ghats region whereas low dd zones are observed in the eastern part of the basin and near the estuary the eastern part of the basin shows low fs values whereas nw and sw parts of the basin show high fs values compared to manual measurement bad calculator requires minimal time to quantify the morphometric parameters experimental results show that the software is effective in calculating drainage parameters such as drainage density frequency bifurcation ratio etc using the text file of esri shapefile

spatial time domain reflectometry and its application for the measurement of water content distributions along flat ribbon cables in a full scale levee model spatial time domain reflectometry spatial tdr is a new measurement method for determining water content profiles along elongated probes transmission lines the method is based on the inverse modeling of tdr reflectograms using an optimization algorithm by means of using flat ribbon cables it is possible to take two independent tdr measurements from both ends of the probe which are used to improve the spatial information content of the optimization results and to consider effects caused by electrical conductivity the method has been used for monitoring water content distributions on a full scale levee model made of well graded clean sand flood simulation tests irrigation tests and long term observations were carried out on the model the results show that spatial tdr is able to determine water content distributions with an accuracy of the spatial resolution of about 3 cm compared to pore pressure measurements and an average deviation of 2 vol compared to measurements made using another independent tdr measurement system

paleogeography and andean structural geometry northwest argentina neogene tectonic segmentation of the andean cordillera in northwestern argentina is a function of both the dip of the subducted plate and of major paleogeographic structures and sedimentary basins vergence fault dip and lateral continuity of neogene structures can be related to the character and pre existing geometries and structures of the materials in which they form south of 27 s the thick skinned sierras pampeanas which occur mostly over a flat segment of the subducted nazca plate formed where little sedimentary cover overlay crystalline basement north of 24 s the thin skinned subandean belt overlying an inclined slab segment formed within a thick elongate eastward tapering trough of paleozoic and mesozoic sediments that may represent a complex of pre andean foreland basin deposits the transitional region between 24 27 s the santa barbara system and cordillera oriental is characterized paleogeographically by complex cross trending structures and irregular basin geometries and the neogene structures are equally complex and variable the paleogeographic features of nw argentina are a product of compressional tectonism during much of the paleozoic that resulted in an orogenic belt oriented obliquely to the modern andes this earlier orogen was disrupted by several zones of transverse structures and by cretaceous extensional or pull apart basins these features clearly influence the geometry of the superposed andean structures more intriguing however is the possibility that preexisting structures of the continental lithosphere may in some way help to modify the geometry of the subducted plate

clustered rectangular lakes of the canadian old crow basin abstract this paper investigates the origin and development of the tightly clustered lakes within the old crow and bluefish basins utilizing landsat imagery seasat synthetic aperture radar sar and the available scientific literature the old crow basin and the smaller neighboring bluefish basin are located in the northwest yukon territory of canada 150 km south of the beaufort sea and just east of the canadian alaskan border both basins situated in pleistocene lake deposits of sand gravel silt and peat are characterized by numerous densely clustered rectangular or arrowhead shaped shallow lakes with linear shore lines the straight edges of these lakes exhibit strong nearly orthogonal preferred alignments directed northwest and northeast these lakes evidently originated as relatively small thaw or thermokarst lakes that subsequently coalesced into larger lakes with edges and orientations controlled by a fracture pattern in the consolidated underlying rocks possibly the old crow granite the fracture pattern may be the result of horizontal tertiary or later compressional forces along the kaltag porcupine fault or it may have originated in the relatively undeformed consolidated basinal sediments as a result of downwarping and subsequent uplifting the lake forming process is ongoing with new lakes being formed to replace older lakes in all stages of being obliterated

application of the promethee technique to determine depression outlet location and flow direction in dem with the fast growing progress of computer technologies spatial information on watersheds such as flow direction watershed boundaries and the drainage network can be automatically calculated or extracted from a digital elevation model dem the stubborn problem that depressions exist in dems has been frequently encountered while extracting the spatial information of terrain several filling up methods have been proposed for solving depressions however their suitability for large scale flat areas is inadequate this study proposes a depression watershed method coupled with the preference ranking organization method for enrichment evaluations promethees theory to determine the optimal outlet and calculate the flow direction in depressions three processing procedures are used to derive the depressionless flow direction 1 calculating the incipient flow direction 2 establishing the depression watershed by tracing the upstream drainage area and determining the depression outlet using promethee theory 3 calculating the depressionless flow direction the developed method was used to delineate the shihmen reservoir watershed located in northern taiwan the results show that the depression watershed method can effectively solve the shortcomings such as depression outlet differentiating and looped flow direction between depressions the suitability of the proposed approach was verified

lake patterns as related to neotectonics in subsiding basins the example of the ucamara depression peru abstract two northeast trending elongated lakes from the andean foredeep ucamara depression south maranon basin are analyzed in relation to basement structures neotectonic and scismotectonic data from the surrounding areas lake puinahua 25 60 km lies over pre cretaceous basement faults and lake punga 9 35 km which subsided in a historical times lies over a paleozoic basement uplift p axes from earthquake focal mechanisms located east and west of the ucamara depression are parallel to the lakes the trend of lineaments together will neotectonic data from the craton border suggest that lakes develop along extensional faults the western limit of the lakes are lie over folds from the front of the sub andean zone comparison of elongated lakes from the ucamara depression with other lakes from the andean foredeep suggests close relationships between lake pattern and geodynamics ria lakes are located along the front of the upper foothills and are possibly related to subsidence due to tectonic overloading of the sub andean border elongated lakes from the ucamara depression are situated in front of the wide low foothills of the sub andean thrust and fault belt subsidence is related to block faulting and tectonic overloading is weak these results are compared with previous studies of rectangular lakes from the beni basin which appear to be related to the bending of the craton border analysis of lake pattern is suggested as a complementary approach for the neotectonic study of active subsiding areas

calibration of time domain reflectometry technique using undisturbed soil samples from humid tropical soils of volcanic origin time domain reflectrometry tdr is used to measure the apparent dielectric number ka in soils we studied two soil types humitropept and hapludand of low bulk density about 0 7 mg m 3 at 0 05 m to 0 8 mg m 3 at 0 3 m depth and high organic matter content about 7 at 0 05 m to 4 at 0 3 m depth soils are located in a humid tropical environment average annual soil water content is 0 51 to 0 58 m3 m 3 for calibration undisturbed soil blocks with a tdr probe installed in the center were saturated and then allowed to dry by evaporation volumetric water content was calculated from measured ka values and from gravimetric measurements because we used undisturbed soil samples our calibration accounts for the natural heterogeneity in soils we tested the suitability of various calibration functions relating ka to soil water content for our soils tdr technique underestimated the actual soil water content by 0 05 0 15 m3m 3 when using the widely applied topp calibration function a three phase mixing model with a geometry parameter 0 47 fit our data best we consider mixing models to be a robust approach for calibration of tdr technique on various soils

neotectonics of the subandes brazilian craton boundary using geomorphological data the maranon and beni basins abstract active and abandoned fluvial traces are used together with neotectonic seismotectonic and subsurface structural data to study the neotectonic evolution of the peruvian and bolivian foreland basins the maranon basin to the north and the beni basin to the south are located near the ends of the peru bolivia andean segment this segment lies above the flat slab subduction of the nazca plate beneath the andes the surface of these basins shows a complex network of present day rivers and fossil river traces a relative chronology of the river traces deduced from morphological criteria allows the identification of successive shifting of fluvial belts up to the present position of the main rivers as it enters the ucamara depression the ucayali river is deflected to the northeast successive shifts of the deflection point are directed upstream along the upper reaches of the river along the foothills simultaneously the maranon river is deflected to the north lining up with the straight ne trending lower reaches of the huallaga river in the central part of the depression the rivers trend northeast southwest parallel to the main strike of the basement faults this regional trend is also parallel to 1 the greatest principal stress observed both to the east and the west of the depression and to 2 the neotectonic faults on the margin of the brazilian craton the beni basin is characterized by a counterclockwise shift of the beni river successive shifts of the river involve the northward migration of the deflection point of the beni river as it enters the basin a fault connected to the foothill margin controls this downstream movement recent erosion of the flood plain surface to the east suggests a tendency of the craton margin to ascend no coaxial stress resulting from either plate motion or from collapse of the andean topography seems to control the directional shift of rivers in the basins

automated river course ridge and basin delineation from digital elevation data starting from a digital elevation model dem formed by a triangular irregular network tin of facets an algorithm that allows for the tracking of the path of steepest slope downstream or upstream from any point on the topographic surface has been developed the analysis shows that when starting such a path in a downstream upstream direction from point p down up to a point m and then from point m in an upstream downstream direction and if the path returns to point p then the segment pm corresponds to a pure streamline otherwise it corresponds to a river course ridge this property allows an easy way to delineate the network of river courses and ridges likewise the repetitive use of this algorithm allows for the definition of basin and sub basins also called contributing areas to any point on a river course finally it is shown how a regular grid dem can be treated as a particular case of the tin dem which gives generality to the presented procedures

river reach length and slope estimates for large scale hydrological models based on a relatively high resolution digital elevation model application of regular grid based distributed hydrological models requires information related to river drainage networks such as flow directions flow accumulated areas basin delineation and length and slope of river reaches for every grid cell most of those data may be extracted automatically from digital elevation models dem however when dealing with large basins available dems are usually in higher spatial resolution than the model grid upscaling procedures have therefore been developed to extract low resolution flow directions and flow accumulated areas from relatively high resolution dems this paper presents a new methodology which extends the upscaling method to automatically extract length and slope of river reaches for large scale grid based hydrological models the proposed method is new and is believed to be the first attempt to produce such information automatically from dems the methodology was applied to parts of the uruguay river basin in south america using the globally wide available dem produced by the shuttle radar topography mission srtm 90m quality of results was assessed by comparing calculated river lengths with distances measured over vectorized river networks which were assumed to be correct it was shown that the proposed methodology adequately assigns river lengths to every model cell while ensuring that the whole length of the streams is considered the effect of dem resolution on calculated river length errors was analyzed by resampling the srtm dem to three different cell sizes with best results obtained for the higher resolution dem the modification of the original high resolution dem through the process known as stream burning was also tested largely improving the quality of the results finally optimal distance transforms were used for the calculation of distance increments instead of euclidean local distances giving results that were generally better the quality of results for calculated slope values could not be assessed because no reliable data were available for comparison

a geometrical model of bound water permittivity based on weighted averages the allophane analogue abstract the soil permittivity is affected by the volume fractions of bound and free water but also by the geometries of the soil components and the shape of water inclusions allophanic clays have a hollow spherical geometry with high water holding capacity and thus representing an ideal system to investigate geometrical effects on the permittivity of water in porous media a new weighted averaging procedure is developed which provides estimates of the permittivity of rotationally hindered water bonded to allophane spherules and takes into account both the spherical shape of allophane and the number of water layers stored this averaging procedure renders two distinct estimates for the inner and outer allophane water permittivity in agreement with previous experimental results these distinctive dielectric constants for allophane water are shown to be relevant to most water content reading applications near and below the gigahertz range is shown that presented averaging procedure may more generally serve as a simple mechanism to include geometrical effects on water absorbed to other non planar structures such as micropores and soil particles of cylindrical or ellipsoidal geometry

problems in automated recognition of valley features from digital elevation models and a new method toward their resolution valley recognition methods given in the literature fail to produce valley networks suitable for locating valley heads for one of two main reasons a they are based on the concept of higher than or b they are based on contributing area thresholds in this paper a new method for recognizing valley bottoms is presented this is based on two improvements of carroll s 1983 method and produces a network that reflects the topography well the network is used to locate valley heads once located the valley heads are delineated using criteria suggested by geomorphologists and hydrologists the resultant valley heads are generally well recognized although two problems are evident a there are a number of commission errors and b the valley heads recognized by the method are too small

a new procedure for gridding elevation and stream line data with automatic removal of spurious pits abstract a morphological approach to the interpolation of regular grid digital elevation models dems from surface specific elevation data points and selected stream lines is described the approach has given rise to a computationally efficient interpolation procedure which couples the minimization of a terrain specific roughness penalty with an automatic drainage enforcement algorithm the drainage enforcement algorithm removes spurious sinks or pits yielding dems which may be used to advantage in hydrological process studies the drainage enforcement algorithm has also been found to significantly increase the accuracy of dems interpolated from sparse but well chosen surface specific elevation data moreover it facilitates the detection of errors in elevation data that would not be detected by more conventional statistical means and forms a sound physical basis for cartographic generalization

the origin of tensile fracture lineaments abstract fracture controlled lineaments commonly seen where brittle basement is exposed at the earth s surface are generally restricted to a small number of sets with angles of 45 90 between sets the length frequency distribution of lineaments in each set follows a truncated poisson function such lineaments usually show almost no shearing offset suggesting a tensile origin a simple mechanical model of tensile fracturing is used to explain the spacing directions and length of lineaments as well as their depth frequency distribution results suggest that the penetration depth of tensile fractures which produce lineaments at the earth s surface is directly related to their length and that the fracture density is inversely proportional to fracture depth finally the angles between lineament sets may be controlled by the ratio of strength of unfractured rock to that of pre existing fractures which might heal with time the most likely source of tension is tectonic uplift fractures due to typical uplifts of 0 5 1 km over distances of 10 100 km may penetrate as brittle fractures to several kilometres into the crust perhaps to the depth at which seismic activity ceases

paleomagnetic study of cretaceous rocks of peru south america evidence for rotation of the andes abstract paleomagnetic data for the cretaceous volcanic and sedimentary rocks in the andean region of peru are given reliable paleomagnetic field directions were obtained for three cretaceous albian to cenomanian formations from calcareous sediments in northern peru stable remanent magnetization directions were also derived from twelve cretaceous lava flows and dikes in coastal peru paleomagnetic data of the same age from the stable areas of south america such as brazil demonstrate that the paleomagnetic poles are nearly coincident with the present pole but peruvian paleomagnetic directions studied here showed several tens of degrees of counterclockwise declination shifts this suggests counterclockwise tectonic rotation of an extensive block which includes the whole of andean peru

fresh shallow valleys in the martian midlatitudes as features formed by meltwater flow beneath ice significant numbers of valleys have been identified in the martian midlatitudes 30 60 n s spatially associated with extant or recent ice accumulations many of these valleys date to the amazonian but their formation during these cold dry epochs is problematic in this study we look in detail at the form distribution and quantitative geomorphology of two suites of these valleys and their associated landforms in order to better constrain the processes of their formation since the valleys themselves are so young and thus well preserved uniquely we can constrain valley widths and courses and link these to the topography from the mars orbiter laser altimeter and high resolution stereo camera data we show that the valleys are both qualitatively and quantitatively very similar despite their being 5000 km apart in different hemispheres and around 7 km apart in elevation buffered crater counting indicates that the ages of these networks are statistically identical probably forming during the late amazonian 100 ma in both localities at least tens of valleys cross local drainage divides apparently flowing uphill we interpret these uphill reaches to be characteristic of flow occurring beneath a now absent relatively thin order 101 102 m regionally extensive ice cover ridges and mounds occasionally found at the foot of these valley systems are analogous to eskers and aufeis like refreezing features on the basis of their interaction with these aufeis like mounds we suggest that this suite of landforms may have formed in a single short episode perhaps order of days probably forced by global climate change

geodynamic environment of quaternary morphostructures of the subandean foreland basins of peru and bolivia characteristics and study methods abstract the quaternary evolution of western amazon basins is considered using morphostructural analysis of fluvial belts and lakes meandering rivers from the basin surface are analyzed using three scales of elements the ridge and swale pattern the mosaic pattern and the fluvial belt lake patterns are differentiated according to their shape the hydrological environment and the structural context influences of basement structures and neotectonic deformations when known are considered the morphostructural patterns are discussed in the context of a balance of internal tectonic and external hydraulic and sedimentologic processes special attention is focussed on the effect of neotectonics which is generally neglected on the formation and the location of quaternary morphostructures the adaptation of study methods and sampling to the characteristics of the different morphostructures is considered

the nature distribution and formation of pans in arid zones abstract pans closed depressions are a widespread feature of many of the world s drylands by using literature survey air photographs topographic maps orbital photographs and imagery combined with field work it is possible to describe the major areas where these features occur their distribution is controlled to a great extent by the availability of susceptible surfaces they also develop in certain particular environmental settings palaeolacustrine basins palaeodrainages interdunes and on coastal plains many of the pans have a distinctive morphology while on their lee sides they may have lunette dunes many processes combine to create and maintain pans and these can be considered in a general model which has certain key elements the first of these is that the area should not be one where fluvial processes are fully integrated it should also not be one where aeolian accumulation is such as to infill any irregularities in the land s surface if these two predisposing conditions are fulfilled then under dryland conditions if susceptible surfaces are present there are various circumstances that may lead to hollow development and enlargement although in some cases such processes as solution suffosion and animal activities may play a role we believe that the predominant reason why pans have the characteristics that they do including their shapes lunettes alignments etc is that they result from the operation of the twin processes of salt weathering and aeolian deflation

the proterozoic history of eastern bolivia abstract about 100 000 km2 of the previously unmapped bolivian sector of the central brazil shield has been studied by proyecto precambrico an anglo bolivian technical cooperation programme the lower proterozoic is represented by the lomas maneches granulite group and the bulk of the chiquitania paragneiss complex which were formed during the trans amazonic orogenic cycle 2000 ma the middle proterozoic spans the orogenic cycles of san ignacio 2000 1300 ma and sunsas unmetamorphosed upper proterozoic and possibly cambrian sediments on the southern and eastern flanks of the shield represent marine transgressions related to the intra continental braziliano orogenic cycle east trending dolerite dykes were probably intruded during this period within the shield

automatically derived catchment boundaries and channel networks and their hydrological applications abstract a method of generating drainage networks and catchment boundaries from gridded ground elevation data a digital terrain model is presented the method includes an algorithm for coping with localised low points in the data the paper suggests two objective ways of comparing the conventionally mapped with the automatically generated drainage network emphasis is placed on the way that this approach is capable of benefiting a variety of hydrological applications in particular the automatic estimation of flow statistics from catchment characteristics

tectonic and magmatic evolution of the andes of northern argentina and chile abstract two orogenic cycles both with different evolution are developed in the western margin of the south american continent in northern argentina and chile the paleozoic hercynic cycle and the meso cenozoic andean cycle the hercynic cycle a wide marine basin extending westward of the cordillera oriental which developed in cambrian ordovician times marks the beginning of this cycle in contrast to peru and bolivia where this basin developed between two precambrian blocks the western margin of this basin in northern argentina and chile is still unknown the ordovician sedimentation and accompanied volcanism ends with the ocloyic deformation phase and its synkinematic granitic plutonism two basins were developed in the silurian devonian separated by the puna arc uplifted during this ocloyic phase the shallow water marine terrigeneous sediments which were deposited in them were deformed by a new tectono magmatic associated phase chanic phase carboniferous to lower permian marine carbonates were deposited west of the puna arc and red beds east of it later on during the permian to triassic a magmatic belt was developed along the cordillera occidental the rhyolites ignimbrites and the granitic to granodioritic related intrusives are well represented in chile although the overall geologic history of this period is known many problems concerning its origin and relations to plate tectonics are still unsolved the andean cycle during this cycle a series of magmatic arc systems related to the subduction of the pacific crust was built up along the western margin of south america huge volumes of calc alkaline lavas and related plutons were emplaced since the jurassic along belts parallel to the present coastline showing a general eastward migration trend up to the lower cretaceous an ensialic back arc basin was formed east of this magmatic arc thousands of meters of marine and continental sediments were deposited in it this basin disappeared during the middle cretaceous probably as a result of the final opening of the atlantic and the active westward movement of the south american plate since middle cretaceous times the magmatic arc has been the fundamental paleogeographic element the arc progressively migrated stepwise eastward each step marked by a tectonic phase subduction related crustal erosion could explain the lack of fore arc petrotectonic assemblages the eastward magmatic polarity which characterizes this section of the andes could also be explained by such a mechanism

a new concept in modeling the dielectric response of sandstones defining a wetted rock and bulk water system experimental data for the real part of the dielectric constant k of three sandstone samples are considered as a function of the level of water saturation sw in the frequency range 60 khz to 4 mhz existing theoretical models have previously shown poor agreement with k versus sw data for rock samples undoubtedly due to the complexity involved in adequately accounting for geometrical and electrochemical effects in analyzing the data presented here we find a pronounced increase in k in the low saturation region which in all cases can be attributed to the establishment of geometrical and surface effects associated with the rock water interface when this increase in k is accounted for by defining wetted matrix parameters the data show excellent agreement with existing theoretical models

normal faulting block tilting and decollement in a stretched crust extensional tectonics cover a wide range of crustal structures from narrow continental rifts to large continental areas if we except continental and oceanic rifts stretched portions of the crust exhibit complex faulting patterns at upper levels with high angle and low angle normal faults very little is known concerning the geometry of structures and physical processes at depth it is therefore difficult to extrapolate surface observations to the crustal scale five general models are proposed that combine continuous and discontinuous deformation and geometrical and geological tests are proposed two natural examples the west armorican atlantic margin and eldorado mountains basin and range province are presented they are characterized by an association of high angle normal faults tilted blocks and low angle normal faults field and geometrical arguments are given to demonstrate that low angle faults are controlled by decollement surfaces along preexisting interfaces geometrical implications of the tilted block pattern are presented and the gravity gliding hypothesis is proposed as a possible explanation of block tilting when associated with low angle normal faults in such cases the amount of stretching cannot be related to bulk thinning of the crust

insights into fold growth using fold related joint patterns and mechanical stratigraphy despite how common folds are as structural features along strike fold propagation has proven elusive to document however if a fold grows laterally along its axis early formed fold related joints may differ significantly in orientation from joints that form later in this paper we integrate mechanical stratigraphy with joint pattern analysis to determine relative timing of jointing additionally we demonstrate that joint patterns can be related to stresses on both the top and bottom of the bed during flexure we present joint data from eight sedimentary beds on the fold terminus at sheep mountain anticline wyoming usa the joint patterns around the terminus show two distinct patterns joints in six of the beds show a radial pattern around the terminus whereas joint patterns in the two remaining beds differ from proximal units despite being in the same structural position fracture resistance calculations confirm that the beds with mis oriented fractures are less resistant to fracturing than other units in the study and therefore would have fractured earlier in fold growth history we present a plate bending model that illustrates potential joint patterns around a plunging fold nose from stresses along both the top and bottom of the bed the joint strike predictions for the area in front of the inflection line on the fold nose match the orientations in our less resistant beds which are now positioned behind the inflection line suggesting that the fold grew laterally the combined analysis of fracture pattern and mechanical stratigraphy provides a new way to investigate fold evolution

origin of rectangular and aligned lakes in the beni basin of bolivia abstract the origin of aligned rectangular shaped lakes in the beni basin of bolivia has been investigated utilizing landsat imagery shuttle imaging radar and the available scientific literature the lakes tend to line up in two preferred orientations northwest and northeast they occur in cenozoic sediments of the beni basin situated between the brazilian shield and the andean foredeep available evidence suggests that the shapes and orientations of the lakes are primarily controlled by a nearly orthogonal fracture pattern propagated upward from the underlying granitic brazilian shield basement these orientations and shapes may reflect a reactivated ancient global fracture pattern or may be the result of an e w greatest principal compressive stress 1 and subsequent downwarping and uplifting of the beni basin during the cenozoic andean orogeny the lakes themselves may occupy down dropped basement blocks induced in the gently upwarped basement while unusual these lakes are not unique this suggests that transmission of basement structure through overlying sediments may occur in other regions but that special conditions such as little or no lateral compression of the sediments the absence of high trees and vegetation stability of surface material from drifting and a high water table are necessary to preserve and enhance such surface features

the origin of oriented lakes evidence from the bolivian amazon the presence of hundreds of rectangular and oriented lakes is one of the most striking characteristics of the llanos de moxos lm landscape in the bolivian amazon oriented lakes also occur in the arctic coastal plains of russia alaska and canada and along the atlantic coastal plain from northeast florida to southeast new jersey and along the coast of northeast brazil many different mechanisms have been proposed for their formation in the lm plafker s 1964 tectonic model in which subsidence results from the propagation of bedrock faults through the foreland sediments is the most accepted however this model has not been verified here we present new results from stratigraphic transects across the borders of three rectangular and oriented lakes in the lm a paleosol buried under mid holocene sediments is used as a stratigraphic marker to assess the vertical displacement of sediments on both sides of the alleged faults our results show that there is no vertical displacement and therefore that plafker s model can be ruled out we suggest that among all the proposed mechanisms behind lake formation the combined action of wind and waves is the most likely the evidence from the lm provides new hints for the formation of oriented lakes worldwide

interaction between meander dynamics and floodplain heterogeneity in a large tropical sand bed river the rio beni bolivian amazon the evolution of meandering river floodplains is predominantly controlled by the interplay between overbank sedimentation and channel migration the resulting spatial heterogeneity in floodplain deposits leads to variability in bank erodibility which in turn influences channel migration and planform development despite the potential significance of these feedbacks few studies have quantified their impact upon channel evolution and floodplain construction in dynamic settings e g locations characterized by rapid channel migration and high rates of overbank sedimentation this study employs a combination of field observations geographic information system gis analysis of satellite imagery and numerical modelling to investigate these issues along a 375 km reach of the rio beni in the bolivian amazon results demonstrate that the occurrence of clay rich floodplain deposits promotes a significant reduction in channel migration rates and distinctive styles of channel evolution including channel straightening and immobilization of bend apices leading to channel narrowing clay bodies act as stable locations limiting the propagation of planform disturbances in both upstream and downstream directions and operate as hinge points around which the channel migrates spatial variations in the erodibility of clay rich floodplain material also promote large scale 10 50 km differences in channel sinuosity and migration although these variables are also likely to be influenced by channel gradient and tectonic effects that are difficult to quantify numerical model results suggest that spatial heterogeneity in bank erodibility driven by variable bank composition may force a substantial c 30 reduction in average channel sinuosity compared to situations in which bank strength is spatially homogeneous copyright 2015 john wiley sons ltd

the geology and tectonic setting of the velasco alkaline province eastern bolivia the velasco alkaline province of mesozoic age is situated near to the bolivian brazilian border and is enclosed in precambrian gneisses of the brazilian shield it consists of an early volcanic suite and a series of 14 interfering circular ring and elliptical plutons and is associated with a silicified carbonatite complex the combined length of the province is nearly 80 km and it outcrops over an area of 440 km 2 the plutonic rock types range from foyaite to aegirine granite but each individual pluton may be classified as either over or under saturated the province was built up by a series of plutonic events which for the most part were aligned along a ne trending lineament normal faulting was active during the development of the province although the velasco alkaline province lies over 1500 km from the eastern continental margin it is deduced that it defines a plume generated triple point initiated at the same time as the break up of the south american africa plate

tracking geomorphic signatures of watershed suburbanization with multitemporal lidar abstract urban development practices redistribute surface materials through filling grading and terracing causing drastic changes to the geomorphic organization of the landscape many studies document the hydrologic biologic or geomorphic consequences of urbanization using space for time comparisons of disparate urban and rural landscapes however no previous studies have documented geomorphic changes from development using multiple dates of high resolution topographic data at the watershed scale this study utilized a time series of five sequential light detection and ranging lidar derived digital elevation models dems to track watershed geomorphic changes within two watersheds throughout development 2002 2008 and across multiple spatial scales 0 01 1 km 2 development induced changes were compared against an undeveloped forested watershed during the same time period changes in elevations slopes hypsometry and surface flow pathways were tracked throughout the development process to assess watershed geomorphic alterations results suggest that development produced an increase in sharp topographic breaks between relatively flat surfaces and steep slopes replacing smoothly varying hillslopes and leading to greater variation in slopes examinations of flowpath distributions highlight systematic modifications that favor rapid convergence in unchanneled upland areas evidence of channel additions in the form of engineered surface conduits is apparent in comparisons of pre and post development stream maps these results suggest that topographic modification in addition to impervious surfaces contributes to altered hydrologic dynamics observed in urban systems this work highlights important considerations for the use of repeat lidar flights in analyzing watershed change through time novel methods introduced here may allow improved understanding and targeted mitigation of the processes driving geomorphic changes during development and help guide future research directions for development based watershed studies