the role of magma injection in localizing black smoker activity the mechanisms for localization of black smoker systems at mid ocean ridges remain to be fully understood seismic data for a segment of the juan de fuca ridge with long lived black smoker vents reveal ongoing magma recharge into the crustal magma chamber thereby providing an explanation for the localization

age dates of valley network drainage basins and subbasins within sabae and arabia terrae mars the precise timing of valley network drainage basin formation is critical to understanding the history of water and climate on mars to determine whether there are any variations in ages within separate drainage basins and subbasins that may reflect local or regional variations in climate or resetting from resurfacing e g impact ejecta or lava flows we dated 27 basins and subbasins in sabaea and arabia terrae the age dating basin technique we employed allowed sufficient precision to give accurate ages and shows that fluvial activity within the basins and subbasins ceased at approximately the same time around the early hesperian late hesperian transition our results support the hypothesis that valley networks formed during a unique fluvial optimum that may have shut off gradually because of a global climate change that affected all areas simultaneously on mars

the effect of subauroral polarization streams on ionosphere and thermosphere during the 2015 st patrick s day storm global ionosphere thermosphere model simulations

rheological evolution of the ocean crust a microstructural view rheological studies of the oceanic lithosphere have used direct observations of rocks and inferences based on thermal mechanical and experimental models modeling studies help to constrain an average crust and mantle rheology and the deep seated processes that control regional scale strength and stress field variations the smoothing of fine scale variations in such models can obscure many of the geological processes that influence strain localization and deformation partitioning in the ocean crust examination of deformation mechanisms and histories in ocean crust rocks provides a complementary approach to modeling examples of structures and deformation histories in diabases from deep sea drilling project ocean drilling program site 504b the hayes and atlantis fracture zones mid atlantic ridge and the troodos ophiolite cyprus are presented in conjunction with a synthesis of microstructural studies of the ocean crust over the last 25 years a survey of brittle quasi plastic and synmagmatic viscous deformation is used to demonstrate the influence of primary compositional and textural characteristics and variable magmatic and hydrothermal histories on deformation mechanisms and strain localization in the ocean crust geological evidence indicates that hydrothermal fluids strongly influence the nature of deformation and that effective stresses may be low due to fluid overpressures melt distribution will strongly influence strain localization at the base of the crust and synkinematic hydration during crystal plastic deformation plays a key role in the relative strengths of polyphase oceanic lithologies a schematic distribution of failure mechanisms in the ocean crust is used to discuss the controls on variations in lateral and vertical strength profiles and their possible relation to spreading rates although microstructural studies of ocean crust are still in their infancy they provide valuable constraints for rheological models and further insights to explain the distribution of seismicity at spreading centers and acoustic signatures

a proposed production model of rapid subauroral ion drifts and their relationship to substorm evolution multisatellite data are used to examine the temporal relationship between subauroral ion drifts said and the phases of an auroral substorm utilizing images of auroral luminosities taken by the dynamics explorer 1 de 1 spacecraft and observations of particle injection at geosynchronous orbit we identify the time of expansive phase onset and estimate the time at which recovery begins noting the times at which said are observed simultaneously by the de 2 spacecraft we find that said typically occur well after substorm onset more than 30 min during the substorm recovery phase substantial westward ion drifts and field aligned currents are observed well equatorward of the auroral oval during the expansion phase of a substorm but the drifts lack the narrow spike signature associated with said prior to substorm onset and after substorm recovery field aligned currents are absent equatorward of the auroral oval and the ionosphere is very nearly corotating a phenomenological model of said production is proposed that qualitatively agrees with the observed ionospheric signatures and substorm temporal relationship in this model substorm generated subauroral field aligned currents close via pedersen currents with the outward flowing region 1 currents at higher latitudes these pedersen currents flow in the region of low conductivity equatorward of the auroral oval and are associated with relatively large poleward directed electric fields the frictional heating of the ions caused by collisions with the corotating neutral atmosphere substantially increases the rate of ion atom interchange between o and n2 subsequent fast recombination of no with electrons further reduces the subauroral f region conductivities with a corresponding increase in the electric field and the frictional heating this heating leads to thermal expansion substantial field aligned plasma flow and very large depletions in the f peak concentration thus additionally reducing the height integrated pedersen conductivity

ionospheric disturbances observed by dmsp at middle to low latitudes during the magnetic storm of june 4 6 1991 this paper extends a recent study of electric field penetration into the inner magnetosphere observed by the combined release and radiation effects crres satellite and the defense meteorological satellite program dmsp satellite f8 during the magnetic storm of june 4 6 1991 to consider its ionospheric consequences effects include the development of 1 km s subauroral ion drift said structures the formation of midlatitude density troughs and the vertical transport of equatorial plasma bubbles nearly simultaneous auroral electron and plasma drift measurements were acquired by three dmsp satellites with f8 and f9 in one hemisphere and flo in the other moderate to strong said structures were consistently detected for 10 hours during the early main phase of the storm weak saids were encountered during 8 hours of the early recovery phase dmsp data show that saids with similar characteristics developed at magnetically conjugate locations and extended for at least 3 hours in local time simultaneous measurements show that the saids spanned temporally grooving but latitudinally narrow plasma density troughs these observations suggest that the magnetospheric sources of saids act more like voltage than current generators energetic electron fluxes electric fields and plasma waves measured by crres indicate that during this storm the ring current shielding charges and said sources were located in regions of high plasma density characteristic of the plasmasphere the sequence in which dmsp detected equatorial plasma density irregularities is consistent with model predictions that stormtime electrodynamics at low latitudes operate on distinctive fast and slow timescales fejer and schcrliess 1997

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 mapping of land components from digital elevation data an algorithm for automating the mapping of land components from digital elevation data is described land components are areas of relatively uniform slope and aspect and often correspond with ridge crests shoulders head slopes back slopes or foot slopes aspect regions which generally span from stream to ridge are first identified by generalizing an aspect map derived from digital elevation data the aspect regions are then split successively into land components by grouping pixels above or below an automatically determined contour of elevation or distance from stream the contour approximates a slope break the land components mapped in this way give a complete polygonization of a hilly landscape and are a reasonable approximation of manually mapped land components

westward plasma drift in the midlatitude ionospheric f region in the midnight dawn sector in this paper we report the observations of a sharp ionospheric plasma velocity reversal boundary at subauroral latitudes during magnetic storms in the midnight dawn sector the zonal plasma drift was eastward poleward of the velocity boundary and became westward equatorward of the boundary the latitudinal extent of the westward drifts was 20 a local maximum of the drift occurred only 2 5 below the boundary the magnitude of the maximum velocity was 200 400 m s 1 between 2100 and 0300 local time lt and as high as 780 m s 1 near midnight the large westward plasma drift immediately equatorward of the velocity boundary first occurred at 2100 lt and continuously extended across midnight to the dawn sector the location of the maximum velocity coincided with the minimum density within the midlatitude ionospheric trough the latitude of the velocity boundary decreased from geographic latitude 53 to 43 corresponding to geomagnetic latitude 65 to 55 between 2100 and 0800 lt we propose that the large westward drift at subauroral latitudes is driven by the polarization jet electric fields in the ring current and that the lower latitude westward drift with moderate magnitude is caused by the disturbance wind dynamo

development of a brine dominated hydrothermal system at temperatures of 400 500 c in the upper level plutonic sequence troodos ophiolite cyprus abstract microthermometric analyses of quartz hosted fluid inclusions in fresh and epidotized plagiogranites from the troodos ophiolite cyprus indicate that brine rich fluids 46 56 wt nacl equivalent at temperatures 400 500 c were pervasive throughout many of the plagiogranite bodies high salinity fe bearing inclusions along healed microfractures homogenize by halite dissolution at temperatures of 400 500 c liquid dominated low salinity 2 7 wt nacl secondary fluid inclusions are ubiquitous in all plagiogranite and gabbro samples studied homogenization of the low salinity inclusions occurs at uncorrected temperatures of 200 400 c the quartz hosted high salinity fluids represent either phase separation of hydrothermal seawater or an exsolved magmatic aqueous phase at uncorrected temperatures of 400 500 c migration and segregation of brine and vapor phases into fractures near the margins of the crystallizing plagiogranite bodies resulted in preferential entrapment of the fe rich brines in the deep seated high temperature portions of the hydrothermal system subsequent fracturing of the upper plutonic rocks at temperatures of 200 400 c allowed penetration by seawater which pervasively altered the plagiogranites hydration reactions involving formation of secondary minerals and or mixing with phase separated fluids resulted in fluid salinities two times that of seawater

tectonic forcing of longitudinal valleys in the himalaya morphological analysis of the ladakh batholith north india abstract longitudinal valleys form first order topographic features in many mountain belts they are commonly located along faults that separate tectonic zones with varying uplift histories the indus valley of ladakh northern india runs northwestwards following the boundary between the relatively undeformed ladakh batholith to the north east and the folded and thrusted zanskar mountains to the south west in this region the shyok valley on the northern side of the batholith approximately parallels the course of the indus this study investigates geomorphic variations in transverse catchments that drain the ladakh batholith into the indus and shyok rivers the batholith has been divided into three zones based on varying structural characteristics of its northeastern and southwestern boundaries morphometric analysis of 62 catchments that drain into the indus and shyok valleys was carried out using three digital datasets and supported by field observations morphometric asymmetry is evident in the central zone where the shyok valley is considered tectonically inactive but the indus valley is bound by the northeastwardly thrusting indus molasse and the batholith in this zone the catchments that drain into the indus valley are more numerous shorter thinner and have lower hypsometric integrals than those that drain into the shyok by linking these observations with the regional geology and thermochronological data it is proposed that high sediment discharge from the deformed indus molasse indus valley has progressively raised base levels in the indus valley and resulted in sediment blanketing of the opposing tectonically quiescent catchments that drain southwestwards off the batholith the indus molasse thrust front has propagated at least 36 km towards the ladakh batholith over the last 20 ma hence it is proposed that this long term asymmetric structural deformation and exhumation has forced the indus longitudinal valley laterally into the ladakh batholith resulting in the morphometric asymmetry of its transverse catchments

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

reducing elevation roundoff errors in digital elevation models abstract a smoothing algorithm is presented for the removal of roundoff error inherent in almost all digital elevation data elevation adjustments are kept within the tolerance of roundoff error so that the resulting terrain model is not over smoothed after smoothing the digital elevation model is more suitable for use with algorithms that seek to automatically delineate stream networks and basins of a watershed the algorithm is specifically intended for use with gridded data and is particularly effective when used with elevations originating from the 7 5 min quadrangles provided by the united states geological survey

superdarn observations during geomagnetic storms geomagnetically active times and enhanced solar wind driving the super dual auroral radar network superdarn was built to study ionospheric convection at earth and has in recent years been expanded to lower latitudes to observe ionospheric flows over a larger latitude range this enables us to study extreme space weather events such as geomagnetic storms which are a global phenomenon on a large scale from the pole to magnetic latitudes of 40 we study the backscatter observations from the superdarn radars during all geomagnetic storm phases from the most recent solar cycle and compare them to other active times to understand radar backscatter and ionospheric convection characteristics during extreme conditions and to discern differences specific to geomagnetic storms and other geomagnetically active times we show that there are clear differences in the number of measurements the radars make the maximum flow speeds observed and the locations where they are observed during the initial main and recovery phase we show that these differences are linked to different levels of solar wind driving we also show that when studying ionospheric convection during geomagnetically active times it is crucial to consider data at midlatitudes as we find that during 19 of storm time the equatorward boundary of the convection is located below 50 of magnetic latitude

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

why does near ridge extensional seismicity occur primarily in the indian ocean abstract the possibility that thermoelastic stresses due to plate cooling contribute significantly to the stress field and seismicity in young oceanic lithosphere has been a subject of considerable recent interest this effect is suggested by three key observations a decrease in seismicity with lithospheric age the fact that focal mechanisms show extension perpendicular to the spreading direction and a depth stratification of mechanism types a difficulty with this idea is that although thermoelastic stresses should be comparable in different regions the intraplate seismicity seems to occur in local concentrations in particular the ridge parallel extensional seismicity occurs preferentially in the central indian ocean region we explore the possibility that much of the data favoring thermoelastic stresses can be interpreted in terms of stresses resulting from individual plate geometry and local boundary effects in particular the dramatic concentration of extensional seismicity in the central indian ocean region is consistent with finite element results for the intraplate stress incorporating the effects of the himalayan collision and the various subduction zones the ridge parallel extensional stresses show a decrease with age similar to that of the seismicity as earthquakes in this area provide a major portion of the data for both ridge parallel extension and depth stratification these effects may be due more to the regional stress we thus propose that thermoelastic stresses provide a low level background in all plates but that the dominant effect is that of individual plate geometry and local boundary effects

a phenomenon based approach to upslope contributing area and depressions in dems description of the terrain surface through digital elevation models dems strongly depends on data collection methods and dem data structures for efficiency and availability reasons regular point distributions are most common which yield artefacts such as depressions and preferential flow directions these facts need to be considered when natural phenomena are modelled as is shown for handling depressions and for estimation of flow paths and upslope contributing areas analysis of the main reasons for the occurrence of depressions shows that they usually better reflect the terrain than their surroundings thus the most common remedial method of raising depressions is rejected algorithms that cut a flow path from the depression through its bounding barrier are favoured instead several flow routing algorithms are evaluated for their behaviour in regular grids it is shown that the multiple flow direction mfd algorithm that distributes water from a grid cell to the lower of its eight neighbours proportionally to their elevation differences slope exhibits correct flow directions and the best rotation invariance it is suggested that the estimation of upslope contributing areas tcas is undertaken in two steps first a high quality flow direction data set is derived by a well behaved mfd algorithm or by subgrid modelling of flow paths secondly the upslope contributing areas are obtained by counting the upslope elements

characterization of fluvial activity in parana valles using different age dating techniques martian valley networks provide the best evidence that the climate on mars was different in the past although these features are located primarily in heavily cratered terrain of noachian age 3 7 ga the ages of the features and the time when they were active is not well understood from superposed craters several recent global studies determined that most valley networks formed during the late noachian to early hesperian however there were some disparities between the techniques in this study our principal objective was to test the reliability of the different age dating techniques to better understand their accuracy and limitations we applied these techniques to parana valles using a variety of high resolution images taken from different instruments that allow us to identify smaller craters d 125 m while providing sufficient coverage to support a statistically reliable sampling of crater populations which is necessary to reduce the uncertainties in age determination our results indicate that parana valles formed during the early hesperian period but that the crater density d 353 m is heterogeneous inside the parana valles basin the crater population decreases from the headwaters downstream recording a resurfacing event that is most likely related to the erosion of downstream sub basins the terrain near the source area is late noachian to early hesperian in age while terrains closer to the outlet are early to late hesperian in age crater densities d 125 m inside the valley are also heterogeneous and record several resurfacing events on the valley floor where the width of the valley network narrows to 2 km we found evidence of an amazonian age eolian deposit that is a relatively thin layer of only few meters that was probably deposited as a result of topographic influences our results validate the reliability of several proposed age dating techniques but we also determined the accuracy and applicability of these techniques our results also demonstrate that crater populations can be used to not only determine the relative ages of valley networks but also to map the distribution of sedimentary materials and the extent of resurfacing events that occurred after valley network formation

a statistical study of the subauroral polarization stream over north american sector using the millstone hill incoherent scatter radar 1979 2019 measurements this work conducts a statistical study of the subauroral polarization stream saps feature in the north american sector using millstone hill incoherent scatter radar measurements from 1979 to 2019

fluid temperature and salinity characteristics of the matagami volcanogenic massive sulfide district quebec fluid inclusions hosted within various lithologic units of the 40 million metric ton mt matagami district abitibi greenstone belt preserve samples of archean volcanogenic massive sulfide vms and postvolcanogenic massive sulfide hydrothermal fluid microthermometric measurements on ore hosted primary two phase liquid vapor inclusions from matagami s south limb deposits indicate that the vms hydrothermal fluid was highly saline 16 2 4 7 wt nacl cacl2 equiv 1 n 230 and of moderate temperature trapping temperature tt 208 32 c 1 n 230 a fluid with these characteristics is capable of transporting 5 10 4 m 30 ppm zn as zncl3 and zncl4 2 chloride complexes however the low temperature of this fluid precluded efficient cu transport 3 ppm which may in part explain the relatively cu poor nature of the matagami deposits calculated densities of this ore fluid as high as 1 10 g cm3 are consistent with a bottom hugging brine model however a subset of the data indicate a fluid less dense than ambient seawater suggesting that buoyant hydrothermal plumes were also present a microthermometrically determined high cacl2 content xnacl 0 55 molar na ca 2 3 1 for the vms ore hosted primary fluid is consistent with an archean hydrothermal fluid more ca rich than modern day seawater quartz epidote veins located in the hydrothermal cracking zone of the bell river complex host primary liquid vapor halite inclusions these inclusions are interpreted to be samples of the deep seated equivalent to the vms ore hosted hydrothermal fluid described above microthermometry indicates that these inclusions trapped a high temperature brine tt 373 44 c 1 n 92 38 2 1 9 wt nacl equiv 1 n 92 we interpret this brine to be a phase separated product of modified model seawater 3 2 wt nacl an exsolved magmatic fluid or a combination thereof deep within the hydrothermal system at 650 to 670 c and a near lithostatic pressure of 90 mpa phase separation and subsequent convection lowered the temperature of the brine prior to its entrapment within the hydrothermal cracking zone the occurrence of high temperature brine overlain by lower temperature salinity fluid suggests a two cell convection model consistent with metal mass balance calculations for the south limb the high salinity of the ore hosted fluid inclusions indicates two possibilities 1 a significant amount of brine was incorporated into the upper cell and mixed with heated seawater during convection 2 archean seawater itself was very saline and of variable salinity with the cooling of the bell river complex lower temperature fluids dominantly of seawater origin circulated deep within the hydrothermal system modified by water rock interaction yet not phase separated these fluids sealed off the remnant permeability of the fracture network of the hydrothermal cracking zone and were locally trapped as secondary liquid vapor fluid inclusions homogenization temperature th 242 17 c 9 1 1 6 wt nacl equiv 1 n 14 hosted within the bell river complex quartz epidote vein material post and or waning stage vms hydrothermal activity is evident from the presence of quartz epidote veins crosscutting wabassee group hanging wall rocks microthermometry on quartz hosted primary liquid vapor fluid inclusions suggests that this activity occurred at relatively low temperatures th 76 177 c n 212 over a wide range of salinity 6 0 32 4 wt nacl cacl2 equiv n 212 and with a high apparent cacl2 content xnacl 0 06 these fluid inclusion data illustrate the importance of subsea floor chemical and physical processes directly related to metal transport and deposition in vms systems in particular phase separation deep within the hydrothermal system is interpreted as a key process for generating saline brines capable of forming significant ore deposits

fracture analysis of a volcanogenic massive sulfide related hydrothermal cracking zone upper bell river complex matagami quebec application of permeability tensor theory located in the matagami mining district of the abitibi greenstone belt quebec the bell river complex is a 5 km thick tholeiitic layered gabbro and or anorthosite body 2724 6 2 5 1 9 mau pb which likely acted as the heat source that drove hydrothermal convection and volcanogenic massive sulfide vms hydrothermal mineralization in the area abundant fractures and veins crosscutting the western lobe of the bell river complex formed over a range of temperatures from 250 to 700 c the 250 to 400 c assemblage quartz epidote sericite chlorite plagioclase is the most widespread and occurs as orthogonal anastomosing and random vein sets vein densities average between 15 and 25 veins per m2 locally reaching as high as 40 to 60 veins per m2 these veins typically 1 to 3 mm wide are interpreted to represent thermal cracking associated with hydrothermal fluid mineralization in the district furthermore they crosscut earlier higher temperature pyroxene plagioclase 600 c and magnetite rich 300 600 c veins 1 10 mm wide densities commonly 0 5 veins per m2 detailed field measurements of quartz epidote vein geometries coupled with permeability tensor theory have produced a first order approximation of the maximum model permeability structure veins unfilled of the hydrothermal cracking zone representative district wide values indicate maximum model bulk permeabilities of 10 10 to 10 8 m2 for the hydrothermal cracking zone similar to permeabilities calculated for the fractured sheeted dike complexes of the semail and troodos ophiolites however a high flow zone located within the central parts of the hydrothermal cracking zone is characterized by a maximum model permeability of 10 7 m2 locally 1 m2 the high flow zone reaches maximum model permeability values as high as 10 6 to 10 5 m2 where two or more veins occur with apertures in excess of 2 cm mapping has shown that the hydrothermal cracking zone is confined to an 350 m thick interval located within a strongly layered gabbro and or anorthosite horizon of the layered zone upper bell river complex the base of this interval is 1 000 m below the top of the bell river complex furthermore in and around the town of matagami the dominant orientation of quartz epidote veins parallels the orientation of the layering 110 15 this parallelism is further reflected in the orientation of the calculated quartz epidote vein permeability tensors 94 30 1 n 71 the parallelism suggests that heterogeneities associated with the layer contacts provided planes of low tensile strength along which the hydrothermal cracks preferentially developed such an interpretation further explains why the hydrothermal cracking zone appears to be restricted to the strongly layered zone there are many more low tensile strength planes zones of quartz epidote veining approximately orthogonal to layering are also present the orthogonal veins are usually less continuous and commonly truncated but not crosscut by layer parallel veins the orthogonal subset of veins is interpreted to represent short pathways that allowed fluids to travel between adjacent layer parallel veins however locally longer layering orthogonal quartz epidote veins showing offsets of 10 to 30 cm normal to the layering of the bell river complex may represent initial conduits that allowed fluids to travel into overlying stratigraphy and through to the paleosea floor although volumetrically small in comparison with the permeability structure of the bulk sea floor the significantly higher permeability of the hydrothermal cracking zone indicates its importance in controlling the flow paths and fluxes of fluids deep within the hydrothermal system

subauroral electric fields and magnetospheric convection during the april 2002 geomagnetic storms 1 we analyze the ionospheric electric fields during the geomagnetic storms of april 2002 using data from the dmsp satellites the subauroral potential drop sa in the evening sector exceeded 60 kv at times and was often a substantial fraction of total cross polar cap potential drop pc at storm commencement the subauroral electric field penetration moved rapidly equatorward reaching the lowest magnetic latitude well before the end of the storms main phases pc and sa were correlated well with ae with no time delay however the correlations of pc and sa with dst occurred with significant time delays about an hour for pc and longer for sa the largest values of pc were seen near the end of the storm main phases while the largest values of sa were seen well into the recovery phases the results of this study have important implications on models attempting to describe the dynamics of the plasmasphere the inner magnetosphere and the ring current

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

eruption styles of basalt in oceanic spreading ridges and seamounts effect of magma temperature and viscosity basalts erupted along oceanic zones of spreading and on intraplate seamounts at depths where hydroexplosions are not likely follow various styles of eruption quiet eruptions produce a variety of forms including lava lakes and sheet pillow and pavingstone lavas reactive eruptions occur instead when the lava is thermally shattered as in the formation of hyaloclastites the stresses induced in a rapidly cooling lava flow are important in determining the different lava forms with lava lakes and sheet flows resulting from low stresses pillows from higher stresses and hyaloclastites from even higher stresses which cause rupture calculations show that if we consider basaltic lavas of the same composition the intensity of the stresses induced in the cooling lava increases proportionally to the initial viscosity and inversely to the temperature and rate of discharge of the lava at eruption the viscosity is strongly dependent on the crystal liquid ratio of the magma at eruption the temperature and viscosity of the lava at eruption are related ultimately to the thermal regime of the lithosphere below viscosity tends to increase going from fast to slow spreading ridges and to intraplate seamounts within a given ridge segment temperature tends to decrease and viscosity to increase approaching a transform or overlapping boundary thus the model predicts that going from fast to slow spreading ridges i e from east pacific rise to mid atlantic ridge the probability of forming lava lakes and sheet flows decreases and the probability of forming pillow flows increases moreover within a given ridge segment the areal sheet to pillow ratio should decrease as a transform or overlapping boundary is approached sheet flows should be significant only in the earliest stages of the growth of large intraplate seamounts pillows and hyaloclastites in later stages the probability of forming hyaloclastites should be low in spreading ridges higher in intraplate seamounts recent high resolution observations on the east pacific rise the galapagos rift the mid atlantic ridge and the red sea are consistent with the model because they show that 1 the areal ratio of lava lakes and sheet flows over pillows decreases going from fast to slow spreading ridges 2 within a given ridge segment it decreases approaching a transform and 3 hyaloclastites are important on seamounts only

improving hydrological information acquisition from dem processing in floodplains extraction of hydrological information from digital elevation models dems is a required step when conducting any spatially distributed hydrological modelling in particular automated methods are proposed to extract the drainage structure from the dem however a realistic river network is not always derived from conventional dem processing methods indeed inaccuracy occurs in flat areas corresponding to floodplains in these areas additional sources of information are required to extract the correct drainage direction from the dem in this study it is demonstrated that traditional approaches of dem preprocessing such as the commonly known stream burning fail to provide correct maps of drainage directions and catchment areas when the extension of flat areas is large a new method is proposed to take advantage of available imagery data this method is based on a double dem burning process dem is first burned in the main rivers using the channel network and then in the floodplain using the spatial distribution of floodplains provided by classified satellite images in this sense the method has been referred to as the floodplain burning approach or simply fb approach spatial distribution of floodplains is derived from a multitemporal sar image classification a system of equations is used to vary the elevation offset required to be burnt in each cell representing the floodplain according to the minimal distance from the channel network which is calculated by a distance transformation the fb approach was applied to a sub basin located within the larger amazon river basin the region is characterized by large floodplain extensions basin delineation maps derived from the new method were compared with those obtained from the traditional stream burning method and highlighted more realistic results copyright 2008 john wiley sons ltd

fractal analyses of tree like channel networks from digital elevation model data abstract digital elevation models dems are generally used to automatically map the channel network and to delineate subbasins the most common approach to extract a channel network from dems consists of specifying a threshold area s which is the minimum area required to drain to a point for a channel to form this threshold area is usually specified arbitrarily although it is recognized that different threshold areas will result in substantially different channel networks for the same basin in this paper we study the effect of s that is also the scale of observation on the morphometric properties external and internal links length of drainage paths mainstream length and scaling properties such as horton s and strahler s laws and fractal dimension three basins located in southern france were extensively studied the results indicate that morphometric properties vary considerably with s and thus values reported without their associated s should be used in hydrologic analysis with caution then the fractal geometry is used to take into account the dependence of measured values on observation scales which is not possible with classical hydrological indexes the use of fractals allows first to point out self similarity in the structure of channel networks and then to quantify the tree like organization new catchment shape indexes independent of the observation scale s are defined these indexes are useful for comparing catchments and for measuring the irregularity level of the channel network

thermal contraction and the state of stress in the oceanic lithosphere nonuniform contraction of the oceanic lithosphere as it cools and thickens following its formation at the axis of a spreading center results in a complex three dimensional state of deviatoric stress which can be separated into two parts a thermal bending stress due to changes in the vertical temperature distribution and a thermal contraction stress due to lateral variations in the vertically averaged temperature we examine thermal contraction stresses due to temperature changes in a thin semi infinite rectangular plate bounded by the spreading center axis two stress free boundaries representing transforms or fracture zones define the plate width or ridge segment length l with the bottom of the elastic plate defined by a prescribed temperature the plate thickens as the square root of age as expected for a thermal boundary layer due to vertical conductive cooling above this prescribed temperature elastic stresses are assumed to relax quickly stresses are obtained by properly accounting for the rate of accumulation of the vertically averaged stress as initially stress free material is added to bottom of the cooling thickening plate the state of thermal contraction stress calculated from this model is characterized by large tensile stresses at the boundaries of the plate and relatively low stresses in the plate interior at the ridge axis ridge parallel tensile stresses are about 300 mpa the same as if the plate were not allowed to contract in this direction along the transform boundary the maximum transform parallel tensile stress occurs at a distance l 2 from the ridge transform intersection where its magnitude is comparable to the stress at the ridge axis the tangential stresses at the plate boundary decrease rapidly with distance from the boundary at a distance of l 4 from the ridge axis the ridge axis parallel stresses are one tenth of their ridge axis magnitude the stress magnitudes are independent of both spreading rate and ridge segment length a large transform parallel tensile stress may control the length of transform offsets thermal bending moments are influenced by the large thermal contraction stresses near the ridge axis however a short distance from the ridge these moments attain their free horizontal contraction values which previous studies have shown to cause observable bending of the plate and a geoid anomaly at fracture zones flexure due to thermal bending moments will concentrate bending stresses at a distance from the fracture zone determined by the flexural length of the plate thus providing a natural length scale controlling the spacing of transforms

hemispheric asymmetry of subauroral ion drifts statistical results a large database of more than 18 000 subauroral ion drift said events from dmsp observations from 1987 to 2012 is used to systematically investigate the features of said said occurs mostly at 62 60 magnetic latitude mlat and 22 15 22 45 magnetic local time mlt for geomagnetically quiet conditions and at 58 56 mlat and 22 15 22 45 mlt for geomagnetically disturbed conditions in the north hemisphere nh south hemisphere sh respectively significant north south asymmetries in said occurrence shape and geomagnetic activity variations are found in this statistical study the latitudinal width of a said is larger in the nh than in the sh an interesting finding of this work is that the said occurrence probability peaks have an 180 difference in longitude between the two hemispheres in the geographic coordinates for both geomagnetically quiet and disturbed conditions the said width peaks in almost the same geomagnetic meridian zone with a geomagnetic longitude of 80 120 in both hemispheres significant hemispheric asymmetries and spike signatures with sharp dips are found in all the latitudinal profiles of the horizontal velocities of saids the said is highly correlated to geomagnetic activity indicating that the location and evolution of the said might be influenced by global geomagnetic activity auroral dynamics and the dynamics of ring currents

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

westward plasma drifts in the nighttime equatorial ionosphere during severe magnetic storms a new type of penetration electric fields caused by subauroral polarization stream

on the intermittency and crystallization mechanisms of sub seafloor magma chambers summary the conventional view of a magma chamber being an essentially permanent feature of a fast spreading ridge is not compatible with the physics of either oceanic crustal structure or internal magma convection cumulates form a large volumetric fraction of many ophiolites and are deposited at the bottom of magma chambers so they are not available as an insulating layer between magma and seawater extrusives and dykes are cracked and highly permeable to hydrothermal convection so they also do not offer much thermal resistance to the cooling of magma only the layer of plated or isotropic gabbro often observed between cumulates and dykes is limited to conductive heat transport a 0 5 km thickness implies a chamber lifetime of no more than l0kyr km of magma the intermittency of the chamber on such a short time scale requires that the plates move apart to make room much more rapidly than they could at the steady spreading rate fluctuating magma pressure can achieve such intermittent movement by stress change diffusion through an elastic lithosphere overlying a viscous asthenophere however the space needed implies stress diffusion almost all around the earth and this in turn requires that the intermittent spreading be substantially synchronized all along a major segment of ridge the pressure dependent slopes of equilibrium temperatures between crystal phases and liquid silicate magmas exceed the adiabatic gradients of the magmas themselves by about 1 c kb if this temperature difference is considered the convective drive a 3 km high chamber reaches a rayleigh number of 3 x and a nusselt number of about 8000 the plated layer should grow until the heat loss rate decreases to that supplied by cumulatedepositing convection implying a plated layer about 0 5 km thick in agreement with observations the boundary layer turbulent core structure of convection at high rayleigh and reynolds numbers is consistent with the formation of banded cumulates when a new type of fluid circulation is taken into account if a suspended crystal phase is present in the bulk fluid a slow convection mode is possible where flow velocities are restricted by the equilibration rate between crystals and fluid and the temperature profile is determined by the thermodynamics of crystal fluid equilibria

average characteristics and activity dependence of the subauroral polarization stream 1 data from the millstone hill incoherent scatter radar taken over two solar cycles 1979 2000 are examined to determine the average characteristics of the disturbance convection electric field in the midlatitude ionosphere radar azimuth scans provide a regular database of ionospheric plasma convection observations spanning auroral and subauroral latitudes and these scans have been examined for all local times and activity conditions we examine the occurrence and characteristics of a persistent secondary westward convection peak which lies equatorward of the auroral two cell convection individual scans and average patterns of plasma flow identify and characterize this latitudinally broad and persistent subauroral polarization stream saps which spans the nightside from dusk to the early morning sector for all kp greater than 4 premidnight the saps westward convection lies equatorward of l 4 60 invariant latitude spans 3 5 of latitude and has an average peak amplitude of 900 m s in the predawn sector saps is seen as a region of antisunward convection equatorward of l 3 55 spanning 3 of latitude with an average peak amplitude of 400 m s

mid ocean ridge sulfide deposits evidence for heat extraction from magma chambers or cracking fronts numerous seafloor observations show that the sizes of high temperature hydrothermal sulfide edifices vary dramatically with spreading rate on fast spreading ridges venting occurs from spindly chimneys which reach heights of about 10 m while on slow spreading ridges vents are frequently located near the tops of large sulfide mounds whose volumes may reach 105 106 m3 we argue that such variations are the result of a profound difference in the nature of hydrothermal heat extraction between fast spreading ridges where spreading occurs predominantly by magmatism and slow spreading ridges where there is a significant component of tectonic extension along fast spreading ridges a steady state axial magma chamber can be insulated by a relatively thick conductive boundary layer because heat extraction is limited by low permeability in such systems episodes of vigorous venting are linked to diking events not only because these introduce a significant heat source into the upper crust but also because the intrusion of a dike is the primary source of increased permeability near the ridge axis over a time scale of the order of a decade mineral deposition tends to clog the reaction and upflow zones and there is a high probability that young sulfide structures will be buried by subsequent eruptions on slow spreading ridges tectonic extension maintains the fluid pathways necessary to support vigorous convection in the waning stages of magmatism hydrothermal circulation driven by a downward migrating cracking front can cool the entire crust leading to the formation of very large sulfide deposits as the depth of circulation increases overburden pressures reduce the permeability and the hydrothermal heat fluxes decrease progressively once hydrothermal fluids penetrate the moho serpentinization clogs the fluid pathways and high temperature venting ceases until it is reactivated by a fresh magmatic intrusion

seismic structure of 15 ma oceanic crust formed at an ultrafast spreading east pacific rise evidence for kilometer scale fracturing from dipping reflectors 1 a grid of seismic reflection data from 15 ma cocos plate offers an unprecedented view of the structure of mature oceanic crust formed at an ultrafast spreading 200 mm yr full rate east pacific rise epr the data contain an unexpected quantity of bright reflectors throughout the crust generally 5 km in length significant reflection dip angles 10 30 are seen only on the isochron profiles and several reflectors have a confirmed isochron dip orientation certain upper crustal reflectors ucrs appear to form a single network with isochron dip the most prominent example apparent reflection coefficient 0 2 projects toward a 70 m disruption in the igneous seafloor and waveform analysis demonstrates that the reflector is likely the product of a low velocity zone on the order of tens of meters thick our observations suggest that the isochron dipping ucrs represent small slip kilometer scale faults fractures and none are primarily related to the seismic 2 3 boundary or to the sheeted dike gabbro transition lower crustal reflectors lcrs have no preferred orientation or regular pattern on the 30 km scale of this survey certain lcrs may be similar to the ucrs in origin while others may originate from near axis ductile flow lithologic banding off axis magmatism or some combination thereof overall reflectors in this area are abundant and complex consistent with previous off axis studies but at odds with observations of young crust 5 ma near the epr this dichotomy may be resolved by a delay in reflector formation through some combination of postaccretionary tectonics magmatism and hydrothermal alteration

heat flow maintained in ocean basins of great age investigations in the north equatorial west pacific summary multipenetration heat flow measurements have been made at four sites in deep basins of the west central pacific ocean the west mariana basin central mariana basin nauru basin and central pacific basin the final heat flows are respectively 46 6 f 0 5 49 4 f 0 2 44 2 f 0 9 and 49 5 f 1 1 mw m each site was surveyed by single channel seismic reflection profiling and provided a gravity core the instrument measured thermal conductivity in situ over the entire depth intervals used for determination of the gradients and the reduction scheme iterated conductivity and heat capacity changes into the fitting procedure both of entry frictional decays and of conductivity heat pulse decays the absolute accuracy of the instrument should approach 2 per cent and the first site would make a good intercalibration standard for heat flow measurement the heat flow variation between the sites is real and there is also a significant variation in the isostatically reduced depths of the sites there is no age progression of either depth or heat flow and when five other good multidata points are included the relationship between depth and heat flow conforms to that expected from simple cooling models only in an average sense for the whole group the most plausible explanation for the variations is that heat flow and thermal elevation are dependent on different levels of deep lithosphere reheating at different times between 70 and 120myr ago it is suggested that additional topographic variation is caused by the different accumulations of sediment and lava flows at each site and to errors in the isostatically reduced depths due to incomplete knowledge of the stratigraphy down to the crust mantle interface these explanations of the topographic variation could be tested by seismic refraction measurements

marine tectonics processes at mid ocean ridges the use of multibeam echo sounders and various side looking sonar systems has greatly increased our knowledge and understanding of mid ocean ridge mor processes since the last iugg review on mid ocean ridge research macdonald 1983 the extensive use of swath mapping tools such as sea beam deep tow seamarc i and ii the application of multichannel seismic reflection techniques to the detection of axial magma chambers and the use of satellite data in the study of oceanic lithosphere have rejuvenated marine tectonics and have generated and stimulated a large number of important contributions this review will focus on what we feel were the major developments in marine tectonics with an emphasis on mid ocean ridges in the last four years certain topics such as marine seismicity and satellite studies are only briefly mentionned for reference and will be covered in greater detail in other reviews because of the exponential growth in the number of publications related to mors during 1982 1986 only a few references pertinent to each of the major research topics will be quoted in the text as examples but the reader will find an extensive bibliography at the end of the text references published prior to 1982 were added only where appropriate

correlation of the subauroral polarization streams saps with the dst index during severe magnetic storms 1 the subauroral polarization stream saps is the enhanced poleward electric field westward plasma flow in the region equatorward of the auroral electron precipitation boundary in the dusk midnight sector an important characteristic of saps is its great intensification during magnetic storms however the relationship of saps characteristics to the strength of magnetic storms is not well known using defense meteorological satellite program dmsp satellite measurements we have examined the location magnetic latitude of the saps channel during four severe magnetic storms with minimum dst values between 271 and 422 nt we find that the latitude of the saps channel varies directly with the magnitude of dst for example in one storm case saps moved from 60 magnetic latitude at the storm sudden commencement with dst of near zero to 38 at the end of the storm main phase with dst of 422 nt we have identified more than 300 locations of saps and corresponding dst values during the four storms the most important finding is that the saps latitude is linearly correlated with dst and an empirical formula is derived if the saps channel is mapped along the magnetic field lines to the magnetospheric equatorial plane the mapped saps location corresponds to the inner edge of the ion plasma sheet and is close to the peak of the ring current the result of this paper suggests a promising method of using ionospheric satellite and radar measurements of saps to monitor the evolution of the plasma sheet inner boundary and ring current during magnetic storms

effects of faulting on crustal stresses during mountain formation on io abstract the vast majority of mountains observed on io are tectonic upthrusted blocks a product of compressional forces the mechanism behind their formation is generally understood to be related to io s heat pipe volcanism and crustal subsidence compressional thermoelastic stresses from sustained local or regional shut down of io s heat pipe volcanism could be potentially important orogenic drivers as well kirchoff and mckinnon 2009 formation of mountains on io variable volcanism and thermal stresses icarus 201 598 614 at the same time extensional tectonic features rifts pull apart basins simple graben are found on io furthermore results from a two dimensional finite element model of thrust fault formation in the ionian environment show that natural kinematics of fault motion creates localized regions of near surface extension while compressional stresses at depth are greatly reduced bland and mckinnon 2016 mountain building on io driven by deep faulting nat geosci 9 429 432 in light of these observations and model results we refine our previous one dimensional advective heat pipe model of io s crustal stresses exploring another horizontal boundary strain end member which is the laterally unconfined or integral stress condition first suggested by turcotte 1974 are transform faults thermal contraction cracks j geophys res 79 2573 2577 we also explore the effects of directly incorporating brittle failure limits and liquid sulfur through pore pressure on these failure limits horizontally unconfined vertical boundaries serve as an end member representation for stress release on preexisting faults and in the context of io predict extensional failure in the upper crust in response to deeper compression of either subsidence and or thermal origin including these modifications greatly decreases the size of the region in compressional failure in the lower crust unless the effects of pore sulfur are included as in our previous work the most favorable condition for mountain formation on io is suggested to be a combination of subsidence stress thermal stress from a decrease in volcanic heat piping and crustal thinning due to basal melting

magmatism in the evolution of the south china sea geophysical characterization abstract timing distribution and intensity of magmatism are critical to understanding deep lithospheric processes in the opening of the south china sea scs based primarily on multichannel seismic reflection data and aided with gravity and magnetic anomalies we identify various igneous features such as sills stocks volcanic edifices and volcanoes which are often characterized by high positive seismic amplitudes and or by chaotic or blank reflections beneath them because of their seismic shielding effect we estimate the timing of igneous activities and analyze their areal distribution in the scs region based on seismic stratigraphy we confirm that most igneous emplacements in the scs margins occurred after the cessation of seafloor spreading and are sparse and volumetrically small during the rifting and seafloor spreading phases supporting magma poor margins prior to the breakup of the continental lithosphere by contrast post spreading magmatic activities are widespread in the continental slope areas and in the central scs basin and are most likely triggered by extension in relation to cooling and subsidence of the oceanic and attenuated continental lithosphere which could accumulate a total thermal contractional displacement up to 24 km

midlatitude ionospheric disturbances during magnetic storms and substorms 1 we present periodic 2 hour magnetospheric and ionospheric oscillations observed with multiple space based and ground based instruments during the severe magnetic storm of 25 september 1998 periodic particle injections were observed at geosynchronous orbit ground magnetometers registered very large as high as 3000 nt magnetic deviations in the nightside auroral zone the millstone hill incoherent scatter radar at magnetic latitude 55 measured periodic enhancements of ionospheric eastward ion velocity from midnight to 1000 mlt the periodic variations in the magnetometers and millstone hill radar were well correlated with the magnetospheric particle injections the observations are consistent with the occurrence of periodic magnetospheric substorms during a magnetic storm during each substorm cycle the ionospheric auroral zone expanded to the latitude of the millstone hill radar so the radar was periodically within the auroral zone and detected the auroral plasma return flows after substorm activity stopped the millstone hill radar measured near noon in phase periodic oscillations of the ionospheric f region electron density and temperature which may be due to particle precipitation from the ring current and or plasmasphere into the midlatitude ionosphere we suggest that magnetospheric substorms during magnetic storms have a cycle time of 2 hours the magnetosphere can sustain similar oscillations for several cycles even though the substorm activity has stopped all the observed periodic variations in the geosynchronous particle injections in the auroral magnetic deviations and in the ionospheric ion velocity are related to the periodic magnetospheric substorms and oscillations

spatial resolution sensitivity of catchment geomorphologic properties and the effect on hydrological simulation the geomorphologic area function and width function that characterize the forms of hillslope and river networks are two key parameters employed in the gbhm geomorphology based hydrological model for representing the hydrological processes together with other spatial information one fundamental issue on the use of the geomorphologic properties is the spatial resolution sensitivity in both the threshold area for river network generation and digital elevation model dem resolution the threshold area is the minimum drainage area required to initiate the river the dem resolution depends on the available elevation data in the present study multifractal analysis was used to investigate the sensitivity of width functions extracted by different threshold areas and the sensitivity of area functions extracted from various resolutions of dems fifteen japanese catchments were selected for the sensitivity analysis based on 250 m mesh dem data it was found that the river networks generated with larger threshold areas tend to lose the detailed scaling information when the dem mesh size increases the river networks extracted with the same threshold area become sparser and the topography tends to be flat and scaling structures of the area functions become simpler the runoff generations of the gbhm were influenced by the dem resolution the effect of the dem resolution on the hydrological response is related to the temporal resolution with more influence on the hourly response compared with the daily response from the relation between the scaling structure expressed by the multifractal spectrum and the hydrological response of a catchment it was found that the detailed scaling information had more effect on the hydrological response of higher temporal resolution copyright 2001 john wiley sons ltd

dynamic subauroral ionospheric electric fields observed by the falkland islands radar during the course of a geomagnetic storm ion drift said located between 53 and 58 magnetic south and lasting 6 5 hours was observed by the falkland islands radar in the pre midnight sector coincident flow data from the dmsp satellites and the magnetically near conjugate northern hemisphere blackstone hf radar reveal that the said was embedded within the broader subauroral polarization streams saps dmsp particle data indicate that the said location closely followed the equatorward edge of the auroral electron precipitation boundary while remaining generally poleward of the equatorward boundary of the ion precipitation the latitude of the said varied throughout the interval on similar timescales to variations in the interplanetary magnetic field and auroral activity while variations in its velocity were more closely related to ring current dynamics these results are consistent with said electric fields being generated by localized charge separation in the partial ring current but suggest that their location is more strongly governed by solar wind driving and associated large scale magnetospheric dynamics

thermal stresses due to cooling of a viscoelastic oceanic lithosphere theories based upon thermal contraction of cooling oceanic lithosphere provide a successful basis for correlating seafloor bathymetry and heat flow the horizontal components of the contraction of the lithosphere as it cools potentially give rise to large thermal stresses current methods to calculate these stresses assume that on the time scales of cooling the lithosphere initially behaves as an inviscid fluid and instantly freezes into an elastic solid at some critical temperature these instant freezing methods inaccurately predict transient thermal stresses in rapidly cooling silicate glass plates because of the temperature dependent rheology of the material the temperature dependent rheology of the lithosphere may affect the transient thermal stress distribution in a similar way and for this reason the authors use a thermoviscoelastic model to estimate thermal stresses in young oceanic lithosphere this theory is formulated here for linear creep processes that have an arrhenius rate dependence on temperature results show that the stress differences between instant freezing and linear thermoviscoelastic theory are most pronounced at early times 0 20 m y when the instant freezing stresses may be twice as large the solutions for the two methods asymptotically approach the same solution with time a comparison with intraplate seismicity shows that bothmore methods underestimate the depth of compressional stresses inferred from the seismicity in a systematic way less

shift a distributed runoff model using irregular triangular facets abstract shift sistema hidrologico de facetas triangulares is a computational system that allows for the 1 creation editing and visualization of a watershed digital elevation model dem based on the triangular irregular network tin concepts 2 input and interpolation of soil river bed and rainfall data and 3 calculation and routing of runoff in all the facets and reaches the tin dem model is constructed from a set of points where the slope changes abruptly afterwards the drainage network is automatically identified and an interactive editor allows the addition or deletion of points to eliminate network discontinuities rainfall data are interpolated by means of a procedure based on the minimization of the bending energy of a thin plate in order to calculate and route the runoff the system determines the routing sequence of river segments and for each one identifies the facets forming the contributing area and determines a cascade of overland flow planes then for each element and time interval the system calculates the infiltration and routes the resultant runoff by a numerical solution of the kinematic wave equations this information is saved and the user can see the hydrograph for any facet or reach

is the drainage network a fractal sierpinski space the most common approach to extract the channel network from digital elevation models is to specify a threshold area s which is the minimum area required to drain to a point within which a channel forms this threshold area is usually specified arbitrarily although it is recognized that different threshold areas will result in substantially different channel networks for the same basin this paper studies the effects of s which is also the scale of observation on scaling and morphometric properties such as the number of sources and the areas of source basins and lateral basins the gardon basin located in southern france was extensively studied the results indicate that morphometric properties vary considerably with s and that the spatial distribution of source basins can be considered as a fractal sierpinski space a simple model based on the procedure similar to the sierpinski carpet construction is proposed to explain empirical relations between the number of source areas and the threshold s the model presents a new approach to estimate basin fractal properties and defines new indices to characterize the spatial distribution of first order basins this methodology is useful for hydrologists and geomorphologists dealing with river networks and spatial patterns of various basin properties such as vegetation soil soil moisture and human activities

time and temperature dependent convection models of cooling reservoirs application to volcanic sills a comparison between parameterized and two dimensional finite element reservoir cooling models is described the models feature strongly temperature dependent newtonian rheology and thermal boundary conditions simulating sills cooled from above cooling histories predicted by the parameterized scheme are found to be in excellent agreement with the more exact finite element calculations for viscosity variations of up to 105 occurring at a given time in the reservoir

a physically based catchment partitioning method for hydrological analysis we propose a partitioning method for the topographic surface which is particularly suitable for hydrological distributed modelling and shallow landslide distributed modelling the model provides variable mesh size and appears to be a natural evolution of contour based digital terrain models the proposed method allows the drainage network to be derived from the contour lines the single channels are calculated via a search for the steepest downslope lines then for each network node the contributing area is determined by means of a search for both steepest upslope and downslope lines this leads to the basin being partitioned into physically based finite elements delimited by irregular polygons in particular the distributed computation of local geomorphological parameters i e aspect average slope and elevation main stream length concentration time etc can be performed easily for each single element the contributing area system together with the information on the distribution of geomorphological parameters provide a useful tool for distributed hydrological modelling and simulation of environmental processes such as erosion sediment transport and shallow landslides copyright 2000 john wiley sons ltd

algorithm for precise drainage basin delineation computer based terrain models have become increasingly popular as a tool for automating much of the geometrical data acquisition necessary for hydrologic analyses an algorithm is presented that uses triangulated irregular networks tins to accurately delineate drainage basin boundaries boundary delineation can be performed for areas that drain to individual points or stream networks defined on the tin a special feature of the algorithm is that the segments of the stream network need not correspond to channel edges this allows greater flexibility in defining stream networks on the tin and makes it possible to apply the boundary delineation algorithm to urban areas where the stream networks may be dominated by manmade structures such as streets and canals or to rural areas where the terrain exhibits little relief once the basin boundaries are established geometric parameters such as basin areas slopes and maximum flow distances are easily computed these tools can be combined with hydrologic modeling software such as hec 1 to create a comprehensive hydrologic modeling environment

reheating of old oceanic lithosphere deductions from observations deep wide oceanic basins are the only regions of old seafloor where depth is truly representative of thermal isostasy when the depths of these basins are corrected for the effect of sediment accumulation and variation in crustal thickness the principal non thermal factors have been eliminated we collect the most precise and reliable values of heat flow for the same basins from multi penetration measurements with in situ thermal conductivity or deep sea drilling thermal gradients backed up by surface surveys the 9 data points that result from this selection process have been plotted on a depth versus heat flow graph and compared to published thermal models of lithosphere when considered without regard to age all the points fall at greater depths than predicted by the plate models with constant temperature lower boundaries and remarkably close to boundary layer cooling with parameters determined from the pre 80 ma depth and heat flow history of the ocean floor they are differentiated by their heat flows not much by their depths and the order they plot in along the heat flow axis is random with respect to crustal age modeling of discrete reheating events shows that near boundary layer conditions are re established after about 40 myr but corresponding to a younger than real age the data therefore favor discrete reheating events rather than a continuously hot basal boundary as implicitly assumed by the plate model lithospheric reheating appears to start only on ocean floor 100 ma the data alone cannot discriminate between a few discrete reheating events due to convective peel off at the base of the lithosphere or one or more catastrophic events however the distribution of points from the blake bahama basin is more consistent with distal reheating associated with the bermuda hotspot than local convective peel off

tectonics controls on fluvial landscapes and drainage development in the westernmost part of switzerland insights from dem derived geomorphic indices abstract this work focuses particularly on the geomorphological evidence for the tectonic controls on the development of the present day fluvial landscapes in the westernmost part of switzerland the tectonic deformation was evaluated on the basis of a combined analysis of several classical geomorphic indices hypsometric curves and integrals transverse topographic symmetry index and channel s bottom gradients through high precision dem processing a new optimization strategy was applied for defining geomorphic anomalies related to tectonic activity along the channels of three rivers based on a combined investigation of topographic swath longitudinal profiles geological and geophysical observations the results show that the abnormally high values of hypsometric integral are spatially occurred on the hanging walls of thrust faults while abnormally low ones are spatially observed in the same locations of paleo ice stream pathways observations obtained from transverse topographic symmetry index display asymmetries in the most of the studied drainage basins with a predominant se direction of lateral migration this direction is in agreement with the dominant dip direction of the bedding planes within the study area abnormal changes in the channel s bottom gradients which almost coincide in space with pronounced change in the depth of the subsurface geologic layers and in the geophysical properties are marked by distinct topographic relief in areas where rivers flow above blind and emergent faults our analysis not only confirms that there is a significant tectonic control on the evolution of drainage systems but also revealed a possible evidence for the reactivation of some inherited faults

differential thermal stresses in the earth summary rocks have a significant thermal expansion coefficient and a high modulus of elasticity small thermal changes can therefore generate very substantial stresses a convenient idealized example is the mechanically free cooling thermal boundary layer in a material that suddenly turns from plastic to rigid in cooling through a rigidus temperature this simplified case can be solved analytically for both a linear and an error function temperature profile a compressed layer develops near the surface with a logarithmic singularity of stress at the boundary at a depth of 0 2 of the elastic thickness the stress changes to tensile and peaks at 15 per cent of the confined shrinkage stress in the middle of the rigid layer the situation is similar to the stresses in one half of a piece of tempered glass like the tempered glass both the cooling lithosphere and a plated boundary to a magma chamber are subject to breakage when cracks are induced in the tensile layer positive pore magma pressure is required to overcome confining pressure at depth in the lithosphere but cracking could become catastrophic in the plated boundary to a near surface magma chamber