crustal spreading on venus evidence from topography morphology symmetry and map patterns abstract evidence for numerous features similar to terrestrial divergent plate boundaries and spreading centers are present in the topography and morphology of western aphrodite terra venus head and crumpler 1987 linear discontinuities cutting across the strike of western aphrodite terra cross strike discontinuities or csds were examined in further detail it was found that 1 1 they represent the most prominent regional structural trend in western aphrodite and are readily distinguishable from linear patterns caused by ground tracks in the pioneer venus orbiter data 2 2 individual csds are either deep troughs or steep regional scarps and steps 3 3 the spacing between the more prominent csds ranges from about 500 to 1500 km average spacing is 850 km and 4 4 there is a distinctive structural trend orthogonal to the strike of the csds additional smaller scarps and slopes with characteristics of known csds occur in the arecibo altimetric profiles at spacings of as little as 50 km in agreement with previous suggestions of sotin et al 1989 that other smaller csds with less offset may occur in domains between the more prominent ones previously mapped the detailed characteristics of the csds detailed trough and scarp like form association with ridge offsets linear terminations linear slope traces parallelism great length are all very similar to the characteristics of transform faults and fracture zones on the earth s seafloor and this additional analysis supports the earlier interpretation that csds represent analogs to terrestrial oceanic fracture zones assessment of bilateral symmetry of topography and other elements across western aphrodite terra indicate that 1 1 an accurate prediction of the large and small scale symmetrical elements in both the altimetry data and radar images within each domain on one flank of the highlands may be made by substitution of a mirror image of the opposite flank and 2 2 smaller wavelength symmetrical elements are revealed in the altimetric profiles by subtracting the background regional symmetry and examining the residuals residual altimetry profiles obtained in this manner show that individual altimetry features several hundred kilometers wide and several hundred meters high are frequently located at the same distance from the axis of regional symmetry on the north and the south flanks of the highlands topography and geometric features such as ridge crests and transforms have specific predictable relationships in a crustal spreading environment tests were made in western aphrodite for such organized relationships predicted to occur in association with ridge crest offsets at transform faults and fracture zones it was found that 1 a topographic stepdowns occur across csds in accordance with the general consequences of juxtaposing lithospheres of different relative ages 2 b the correct direction of stepdown down toward older crust and lithosphere occurs relative to that predicted from ridge crest offsets and 3 c the observed amount of stepdown is similar in many cases to that predicted from the observed ridge crest offsets these analyses of cross strike discontinuities topographic and image symmetry across aphrodite and predictions of topography based on ridge crest and fracture zone geometric relationships further support the earlier interpretation that the 7500 km extent of western aphrodite terra represents the site of crustal spreading and displays many of the characteristics of terrestrial divergent plate boundaries

high temporal resolution so2 flux measurements at erebus volcano antarctica abstract the measurement of so2 flux from volcanoes is of major importance for monitoring and hazard assessment purposes and for evaluation of the environmental impact of volcanic emissions we propose here a novel technique for accurate and high time resolution estimations of the gas flux we use two wide field of view uv spectrometers capable of collecting instantaneously light from thin parallel cross sections of the whole gas plume obviating the need for either traversing scanning or imaging it enables tracking of inhomogeneities in the gas cloud from which accurate evaluation of the plume velocity can be made by correlation analysis the method has been successfully applied on mt erebus volcano antarctica it yields estimations of the plume velocity and gas flux at unprecedented time resolution 1 hz and high accuracy uncertainty of 33 during a 2 h experiment on 26 december 2006 so2 flux varied between 0 17 and 0 89 0 2 kg s 1 with a vertical plume velocity varying between 1 and 2 5 0 1 m s 1 these measurements provide insight into the short term variations of the passive degassing of this volcano renowned for its active lava lake a cyclicity in flux ranging from about 11 24 min is evident we propose two physical mechanisms to explain this degassing pattern associated to periodic supply of either gas rich magma or gas alone into the lake the dual wide field of view doas technique promises better integration of geochemical and geophysical observations and new insights into gas and magma dynamics as well as processes of magma storage and gas segregation at active volcanoes

scaling gridded river networks for macroscale hydrology development analysis and control of error a simple and robust river network scaling algorithm nsa is presented to rescale fine resolution networks to any coarser resolution the algorithm was tested over the danube river basin and the european continent coarse resolution networks at 2 5 5 10 and 30 min resolutions were derived from higher resolution gridded networks using nsa and geomorphometric attributes such as river order shape index and width function these parameters were calculated and compared at each resolution simple scaling relationships were found to predict decreasing river lengths with coarser resolution data this relationship can be used to correct river length as a function of grid resolution the length corrected width functions of the major river basins in europe were compared at different resolutions to assess river network performance the discretization error in representing basin area and river lengths at coarser resolutions were analyzed and simple relationships were found to calculate the minimum number of grid cells needed to maintain the catchment area and length within a desired level of accuracy this relationship among geomorphological characteristics such as shape index and width function derived from gridded networks at different resolutions suggests that a minimum of 200 300 grid cells is necessary to maintain the geomorphological characteristics of the river networks with sufficient accuracy

venus trough and ridge tessera analog to earth oceanic crust formed at spreading centers one type of tessera terrain on venus the trough and ridge tessera exhibits a distinctive morphology composed of throughgoing generally parallel linear valleys and shorter orthogonal valleys and ridges the similarity of this pattern to oceanic crustal topography and morphology is examined oceanic crust on earth is characterized by a distinctive orthogonal pattern with transforms and fracture zones in one direction and linear abyssal hills developed parallel to the rise crest in the other similarities between the components of the tessera terrain and terrestrial seafloor fabric and structure are found in terms of linearity parallelism length width spacing orthogonality and general morphology a difference is that trough and ridge tessera tend to occur as plateau like regions at intermediate elevations average 2 km above the surrounding plains while terrestrial seafloor ranges in elevation from that observed at rise crests and oceanic plateaus such as iceland down to depths of several kilometers on the abyssal floors where the orthogonal pattern is often masked by sedimentation on the basis of the similarities it is proposed that trough and ridge tessera may have originated through processes analogous to those responsible for the ocean floor fabric on earth forming at a rise crest similar to divergent boundaries on the earth s seafloor and evolving to its present morphology and configuration through processes of crustal spreading the plateau like nature of the trough and ridge tessera distribution could be the result of localized crustal thickening in the spreading process producing elevated iceland like plateaus whose texture is preserved from subsequent lowland volcanic flooding some regions of more complex tessera patterns may result from deformation of the basic trough and ridge pattern of tessera this hypothesis can be tested with global high resolution imaging and altimetry data and gravity data from the magellan mission

an assessment of a ka band radar interferometer mission accuracy over eurasian rivers the water elevation recovery satellite mission is dedicated to the determination of land surface water extent elevation and slope using a ka band radar interferometer karin as its primary instrument determining these parameters to the accuracy desired for hydrologic applications is challenging the scientific objectives of the mission have been set up to 10 cm for the height budget and 10 murad 1 cm 1 km for the slope budget in this paper we implement a virtual mission simulation and use it to examine the measurement performances for three case studies in europe a relatively small river such as the meuse in northern western europe the lena river in russia one of the major siberian rivers and lake leman in western europe we simulate karin data with the associated instrument and geophysical error sources and implement ground processing techniques to go from the original raw data to science data we examine the impact of external errors in detail and implement calibration techniques that rely on the use of ancillary topographic data such as the shuttle radar topography mission digital elevation model dem we find that the impact of external errors can be reduced to a few centimeters the random error budget can also be reduced below 10 cm by means of appropriate processing the scientific requirements of the mission are shown to be met for all cases

lithospheric flexure at fracture zones bathymetric profiles across six major fracture zones fz s in the north pacific are used to demonstrate the absence of vertical slip on the fossil fault planes the scarp heights on these fz s are constant with age and equal to the initial vertical offsets at the ridge transform fault fz intersections because of the frozen in scarp and the differential subsidence of lithosphere far from the fz the lithosphere bends in the vicinity of the fz this flexure results in a characteristic ridge trough topographic fz signature the flexural amplitude which is the difference between the scarp height and the overall change in depth across the fz increases with age good fits to the bathymetric profiles across the mendocino and pioneer fz s are obtained by modelling the topography as the flexure of a thin elastic plate with an age dependent effective elastic thickness results of the modelling indicate that the base of the elastic lithosphere is approximately defined by the 450 c isotherm maximum bending stresses at fz s are on the order of 100 mpa substantially less than the stresses encountered at subduction zones because the mendocino and pioneer fz s are separated by less than a flexural wavelength they are elastically coupled

lithologic and tectonic controls on bedrock channel form at the northwest himalayan front 1 recognition that channel form reflects a river s ability to erode rock and transport material has spawned stream power models that estimate incision patterns by approximating energy dissipation within a channel these models frequently assume that channel width scales as a power law with drainage area partly because drainage area is easily extracted from digital elevation models dems however this assumption is often confounded by local variations in rock strength and rock uplift rate that can cause channel constriction downstream here we investigate the morphological response to spatial changes in rock strength and rock uplift rate of 10 bedrock channels traversing the mohand range along the northwest himalayan front we present a new method to continuously measure and compare channel width slope and other hydraulic parameters that integrate satellite imagery and dem analysis our method corrects for an 13 overestimation of average channel gradient from a 90 m resolution dem that arises from short circuits of fine scale meanders we find that channels 1 narrow 1 km upstream from knickpoints formed by an increase in rock strength 2 adjust laterally more than vertically in response to downstream decreases rock erodibility and uplift rate and 3 meander where shear stresses are high and channel widths are low we attribute these results to a high ratio of sediment supply to transport capacity which enhances lateral erosion relative to vertical incision our results suggest that substrate strength and sediment supply substantially influence channel form and that channel width should be explicitly measured when interpreting tectonic signals from bedrock channel morphology

venus tectonics an overview of magellan observations the nearly global radar imaging and altimetry measurements of the surface of venus obtained by the magellan spacecraft have revealed that deformational features of a wide variety of styles and spatial scales are nearly ubiquitous on the planet many areas of venus record a superposition of different episodes of deformation and volcanism this deformation is manifested both in areally distributed strain of modest magnitude such as families of graben and wrinkle ridges at a few to a few tens of kilometers spacing in many plains regions as well as in zones of concentrated lithospheric extension and shortening the common coherence of strain patterns over hundreds of kilometers implies that even many local features reflect a crustal response to mantle dynamic processes ridge belts and mountain belts which have characteristic widths and spacings of hundreds of kilometers represent successive degrees of lithospheric shortening and crustal thickening the mountain belts of venus as on earth show widespread evidence for lateral extension both during and following active crustal compression venus displays two principal geometrical variations on lithospheric extension the quasi circular coronae 75 2600 km diameter and broad rises with linear rift zones having dimensions of hundreds to thousands of kilometers both are sites of significant volcanic flux but horizontal displacements may be limited to only a few tens of kilometers few large offset strike slip faults have been observed but limited local horizontal shear is accommodated across many zones of crustal stretching or shortening several large scale tectonic features have extremely steep topographic slopes in excess of 20 30 over a 10 km horizontal scale because of the tendency for such slopes to relax by ductile flow in the middle to lower crust such regions are likely to be tectonically active in general the preserved record of global tectonics of venus does not resemble oceanic plate tectonics on earth wherein large rigid plates are separated by narrow zones of deformation along plate boundaries rather tectonic strain on venus typically involves deformation distributed across broad zones tens to a few hundred kilometers wide separated by comparatively undeformed blocks having dimensions of hundreds of kilometers these characteristics are shared with actively deforming continental regions on earth the styles and scales of tectonic deformation on venus may be consequences of three differences from the earth 1 the absence of a hydrological cycle and significant erosion dictates that multiple episodes of deformation are typically well preserved 2 a high surface temperature and thus a significantly shallower onset of ductile behavior in the middle to lower crust gives rise to a rich spectrum of smaller scale deformational features 3 a strong coupling of mantle convection to the upper mantle portion of the lithosphere probably because venus lacks a mantle low viscosity zone leads to crustal stress fields that are coherent over large distances the lack of a global system of tectonic plates on venus is likely a combined consequence of a generally lesser strength and more limited horizontal mobility of the lithosphere than on earth

variable so2 emission rates for anatahan volcano the commonwealth of the northern mariana islands implications for deriving arc wide volatile fluxes from erupting volcanoes 1 we report new spectroscopic derived so2 emission rates for anatahan volcano mariana islands measurements of so2 fluxes reveal large fluctuations over the 2003 2005 period from 78 kg s 1 which occurred on the same day as resurgent volcanic activity march 2005 to 50 kg s 1 and 25 kg s 1 made days weeks after the start of eruptive sequences in 2003 and 2004 respectively even the lowest values make anatahan a major global source of so2 over the past decade these so2 emission rates are used to estimate the co2 flux from the arc as a whole 3 6 40 107 mol km 1 yr 1 such values are significantly higher than estimates derived using other approaches they are also high compared to other convergent margins e g central america where the input flux of co2 is substantially greater our results caution against including volatile fluxes from actively degassing volcanoes to produce volatile outputs considered representative of entire arc fronts

volcanic episodicity and a non steady state rift valley along northeast pacific spreading centers evidence from sea marc i sea marc i side looking sonar images and sea beam bathymetry along a 400 km stretch of the juan de fuca ridge crest provide evidence that excessive extrusive volcanism periodically builds a crestal ridge along the axis of seafloor spreading an elongate summit depression esd or rift valley is commonly observed in the spine of this crestal ridge the crestal ridge volcanic landform has a distinctive shape that is recognized in bathymetric contours both along the spreading axis and at least up to 30 km away from the axis the landform has a plan form shape that resembles a side view of an archer s bow with the long dimension of the bow form parallel to the strike of the ridge in cross section the bow form is flat on top and has steep flanks these bow form shapes can be explained by magma that rises into the crust at a discrete center and flows laterally into belts of ridge parallel dikes similar to icelandic fissure eruptions both the variable dimensions of the esd along axis of the juan de fuca ridge and the relationship among volcanic flow morphologies within and beyond the esd suggest the four different segments of the juan de fuca ridge presented in detail here display different stages in a cycle of oceanic crust accretion this cycle includes episodes in which there is 1 extrusive volcanic construction which widen the crestal ridge prior to the collapse of the summit depression 2 collapse within the summit region of the crestal ridge to form an esd during a phase of volcanic inactivity and 3 renewed magmatism in the esd as its floor widens by extension and brittle fracture of the upper crust this episodic model implies that the width of the young seafloor affected by volcanic extrusion or dominated by tectonic stretching varies through time

are oceanic fracture zones locked and strong or weak new evidence for volcanic activity and weakness traditionally oceanic fracture zones and other lithospheric and crustal faults have been viewed as zones of weakness that are vulnerable to seismic and volcanic activity this notion has recently been questioned on the basis of evidence showing that initial depth offsets scarp height across some pacific fracture zones are preserved even after 100 m y of differential subsidence this evidence suggests that some parts of oceanic fracture zones are locked shortly after they drift away from ridge transform intersections because the fracture zones seem to be strong welds differential cooling stresses cause flexure in the lithosphere on both sides of the fracture in this paper we briefly review the seemingly contradictory evidence for the thermomechanical characteristics of oceanic fracture zones locked and strong vs slipped and weak and present new evidence indicating that parts of some fracture zones are volcanically active volcanism is an indication of relative weakness because strain and failure are required to open volcanic conduits this and other evidence for the inherent weakness of fracture zones can be reconciled with evidence for strength if different segments of fracture zones exhibit contrasting thermomechanical behavior more data are needed to determine whether this is so and whether there are systematic patterns of distribution for weak and strong parts of individual fracture zones

venus gravity anomalies and their correlations with topography this report provides a summary of the high resolution gravity data obtained from the pioneer venus orbiter radio tracking data gravity maps covering a 70 latitude band through 360 of longitude are displayed as line of sight and vertical gravity topography converted to gravity and bouguer gravity maps are also shown in both systems topography to gravity ratios are made over several regions of the planet there are markedly different ratios for the aphrodite area as compared to the beta and atla areas

applications of quantitative thermal infrared hyperspectral imaging 8 14 μm measuring volcanic so 2 mass flux and determining plume transport velocity using a single sensor remote measurements of sulfur dioxide so2 path concentration and emission rate mass flux released by passive volcanic degassing are a key diagnostic of volcanic behavior so2 gas concentrations are also important for public health despite the significance of measuring so2 mass flux at active volcanoes an accurate method is still very difficult to obtain due largely to uncertainties of plume transport velocities and radiative transfer calculations here we present a new infrared imaging method for deriving so2 flux at active volcanoes with less than 20 plume transport velocity and radiative transfer uncertainties the thermal hyperspectral imager thi was used for this study thi is an uncooled remote sensing long wave thermal infrared tir imaging hyperspectral sensor that can obtain 50 wavelength samples between 8 and 14 m measurements of so2 at the summit of k lauea volcano collected using thi are presented where we obtained for the periods of july 24 26 2017 and february 5 6 2018 a so2 flux raging between 0 and 20 kg s with occasional peaks higher than 40 kg s the spatial distribution of so2 path concentrations was obtained from the thi images by processing them using a newly developed so2 retrieval algorithm the so2 amenable lookup table algorithm so2 alta the sampling rate 30 hz of the microbolometer camera within thi means raw frames can be used for wind velocity derivation volcanic plume motion can be thus inferred by tracking plume features in sequential frames using spatial correlation techniques and knowing the camera angular orientation volcanic so2 flux was estimated from the spatial distribution of so2 and wind velocity we evaluated temporal trends of the so2 flux during the day and the night at the summit of k lauea volcano under both clear sky weather with northeasterly trade winds and cloudy sky conditions with low variable wind these tests showed that the camera and techniques described in this paper provide an effective tool for monitoring so2 fluxes remotely with less than 20 plume transport velocity and radiative transfer uncertainties and under a variety of background conditions clear and cloudy sky cold and hot backgrounds

formation of curved seafloor fabric by changes in rift propagation velocity and spreading rate application to the 95 5 w galapagos propagator the geometry of oceanic spreading centers can change by rift propagation in which a new ridge segment propagates and preempts a preexisting one as the locus of relative motion between the two plates shifts the dying and growing ridge segments are joined by a boundary usually a transform which migrates with time causing seafloor to be transferred from one plate to the other as a result originally ridge parallel isochrons in a zone between the growing and failed rifts can be reoriented to trends oblique to both the ridge and spreading direction an attractive feature of this model is that the reorientation occurs by strictly rigid plate tectonics since relative motion occurs only between points on different plates recent surveys of the galapagos propagating rift system at 95 w show seafloor fabric curving away from the growing rift and toward the failed rift these observations have been interpreted as requiring a zone of distributed simple shear between the two rifts such behavior would represent a local deviation from rigid plate tectonics since relative motion would be distributed over a finite region not part of either of the two plates here we explore possible rigid plate models for the formation of curved seafloor lineaments by rift propagation we find that such fabric can be generated by changes either in the velocity rate or direction of rift propagation or in the spreading rate during rift propagation the curvature of various tectonic elements is diagnostic of the different possibilities the geometry observed at the galapagos can result from either rift propagation acceleration or a spreading rate decrease during the last few hundred thousand years the reverse curvature could result from either deceleration of rift propagation or an increase in spreading rate propagator acceleration and spreading rate slowing which produce similar structural trends could in principle be distinguished using spreading rate data at galapagos however since either would have occurred within the present period of normal polarity both are consistent with the magnetic anomaly data we thus conclude that the data interpreted as requiring a shear zone are equally consistent with two distinct models based on rigid plate tectonics it may however be possible to discriminate between rigid and shear models using fabric observations at other propagators the shear model requires that the sense of curvature at galapagos be a ubiquitous feature of active propagators in contrast the rigid plate tectonic model allows for fabric with a variety of orientations including reverse curvature formed by either propagation deceleration or increasing spreading rate and linear fabric formed by constant propagation and spreading velocities

evidence for divergent plate boundary characteristics and crustal spreading on venus detailed examination of the topography and morphology of western aphrodite terra reveals numerous features that are similar to terrestrial divergent plate boundary characteristics individual domains between fracturezone like discontinuities contain a variety of bilaterally symmetrical topographic elements that suggest that topographic features have been created at rise crests rifted and separated and moved laterally to their present symmetrical positions the topographic and morphologic similarities together with strikingly similar mirror image map patterns on both sides of the rise axis suggest that western aphrodite terra shares the characteristics of oceanic divergent plate boundaries and is the site of crustal spreading on venus topographic profiles are consistent with spreading rates of the order of several centimeters per year

the july august 2001 eruption of mt etna sicily the july august 2001 eruption of mt etna stimulated widespread public and media interest caused significant damage to tourist facilities and for several days threatened the town of nicolosi on the s flank of the volcano seven eruptive fissures were active five on the s flank between 3 050 and 2 100 m altitude and two on the ne flank between 3 080 and 2 600 m elevation all produced lava flows over various periods during the eruption the most voluminous of which reached a length of 6 9 km mineralogically the 2001 lavas fall into two distinct groups indicating that magma was supplied through two different and largely independent pathways one extending laterally from the central conduit system through radial fissures the other being a vertically ascending eccentric dike furthermore one of the eccentric vents at 2 570 m elevation was the site of vigorous phreatomagmatic activity as the dike cut through a shallow aquifer during both the initial and closing stages of the eruption for 6 days the magma column feeding this vent was more or less effectively sealed from the aquifer permitting powerful explosive and effusive magmatic activity while the eruption was characterized by a highly dynamic evolution complex interactions between some of the eruptive fissures and changing eruptive styles its total volume 25 106 m3 of lava and 5 10 106 m3 of pyroclastics was relatively small in comparison with other recent eruptions of etna effusion rates were calculated on a daily basis and reached peaks of 14 16 m3 s 1 while the average effusion rate at all fissures was about 11 m3 s 1 which is not exceptionally high the eruption showed a number of peculiar features but none of these except the contemporaneous lateral and eccentric activity represented a significant deviation from etna s eruptive behavior in the long term however the 2001 eruption could be but the first in a series of flank eruptions some of which might be more voluminous and hazardous placed in a long term context the eruption confirms a distinct trend initiated during the past 50 years toward higher production rates and more frequent eruptions which might bring etna back to similar levels of activity as during the early to mid seventeenth century

review of the evolution of geochemical monitoring networks and methodologies applied to the volcanoes of the aeolian arc italy abstract fluids discharged from volcanic systems are the direct surface manifestation of magma degassing at depth and provide primary insights for evaluating the state of volcanic activity we review the geochemical best practice in volcanic surveillance based to a huge amount of monitoring data collected at different active volcanoes using both continuous and discontinuous approaches the targeted volcanoes belong to the aeolian arc located in the tyrrhenian sea italy and they have exhibited different activity states during the monitoring activities reported here la fossa cone on vulcano island has been in an uninterrupted quiescent stage characterized by variable solfataric activity in contrast stromboli island has shown a persistent mild explosive activity episodically interrupted by effusive eruptions in 1985 2002 2007 and 2014 panarea island which is the summit of a seamount rising from the seafloor of the southern tyrrhenian sea showed only undersea fluid release the only observable clues of active volcanism at panarea island have been impulsive changes in the undersea fluid release with the last submarine gas burst event being observed in november 2002 the geochemical monitoring and observations at each of these volcanoes has directly involved the volcanic plume and or the fumarole vents thermal waters and diffuse soil degassing depending on the type of manifestations and the level of activity encountered through direct access to the magmatic samples when possible and the collection of as much observable data related to the fluid release as possible the aim has been i to verify the thermodynamic equilibrium condition ii to discern among the possible hydrothermal magmatic marine and meteoric sources in the fluid mixtures iii to develop models of the fluid circulation supported by data iv to follow the evolution of these natural systems by long term monitoring and v to support surveillance actions related to defining the volcanic risk and the evaluation and possible mitigation of related hazards the examples provided in this review article show the close relationships among data analysis interpretation and modeling we particularly focus on describing the fieldwork procedures since any theoretical approach must always be verified and supported by field data rather than just by experiments controlled in laboratory indeed the natural systems involve many variables producing effects that cannot be neglected the monitored volcanic systems have been regarded as natural laboratories and all of the activities have focused on both volcanological research and surveillance purposes in order to ensure that these two goals have overlapped an appendix is also included that explains the scientific approach to the systematic activities regarding geochemical monitoring of volcanic activity

accurately measuring volcanic plume velocity with multiple uv spectrometers a fundamental problem with all ground based remotely sensed measurements of volcanic gas flux is the difficulty in accurately measuring the velocity of the gas plume since a representative wind speed and direction are used as proxies for the actual plume velocity there can be considerable uncertainty in reported gas flux values here we present a method that uses at least two time synchronized simultaneously recording uv spectrometers flyspecs placed a known distance apart by analyzing the time varying structure of so2 concentration signals at each instrument the plume velocity can accurately be determined experiments were conducted on k lauea usa and masaya nicaragua volcanoes in march and august 2003 at plume velocities between 1 and 10 m s 1 concurrent ground based anemometer measurements differed from flyspec measured plume speeds by up to 320 this multi spectrometer method allows for the accurate remote measurement of plume velocity and can therefore greatly improve the precision of volcanic or industrial gas flux measurements

plate kinematics of the south atlantic chron c34 to present a high resolution seafloor spreading history of the south atlantic since chron c34 is constrained by a combination of seasat altimeter data and underway marine geophysical data a set of 45 finite rotation poles defines the relative position of africa and south america at roughly 2 m y intervals a set of 12 stage poles constrain the relative motion of these two plates at 5 to 10 m y intervals the position of the stage poles continuously migrates reflecting the continuously changing azimuths of the fracture zones major changes in spreading direction are observed in the late cretaceous and early cenozoic as the fracture zones sweep out broad s shaped curves similar to the pattern seen on the kane fracture zone in the central atlantic small offset fracture zones were found to be the most accurate recorders of changes in plate motion large offset fracture zones such as the agulhas falkland fracture zone were the least reliable recorders at 30 s spreading rates decrease throughout the late cretaceous from a high of 75 mm yr at the end of chron c34 to a low of 30 mm yr around chron c27 a period of slow spreading between chron c30 and chron c20 corresponds to a zone of fracture zone proliferation an increase in the amplitude of geoid anomalies over fracture zones greater relief on topographic profiles and locally evidence of intraplate crustal deformation spreading rates increase at chron c20 to about 50 mm yr and then gradually decrease during the late paleogene and neogene a comparison of synthetic fracture zones based on the south atlantic stage poles to the observed trends of fracture zones in the equatorial atlantic indicates that the vema and marathon fracture zones were generated by south atlantic spreading as opposed to central atlantic spreading at least as far back as 35 m y ago and possibly 50 m y ago

real time measurement of volcanic so 2 emissions validation of a new uv correlation spectrometer flyspec a miniaturized lightweight and low cost uv correlation spectrometer the flyspec has been devel oped as an alternative for the cospec which has long been the mainstay for monitoring volcanic sulfur dioxide fluxes field experiments have been conducted with the flyspec at diverse volcanic systems including masaya nicaragua po as costa rica stromboli etna and vulcano italy villarica chile and kilauea usa we present here those validation measurements that were made simultaneously with cospec at kilauea between march 2002 and february 2003 these experiments with source emission rates that ranged from 95 to 1 560 t d 1 showed statistically identical results from both instruments so2 path concentrations ranged from 0 to 1 000 ppm m with average correlation coefficients greater than r 2 0 946 the small size and low cost create the opportunity for flyspec to be used in novel deployment modes that have the potential to revolutionize the manner in which volcanic and industrial monitoring is performed

the dual beam mini doas technique measurements of volcanic gas emission plume height and plume speed with a single instrument the largest error in determining volcanic gas fluxes using ground based optical remote sensing instruments is typically the determination of the plume speed and in the case of fixed scanning instruments also the plume height we here present a newly developed technique capable of measuring plume height plume speed and gas flux using one single instrument by simultaneously collecting scattered sunlight in two directions the angle between the two measurement directions is fixed removing the need for time consuming in field calibrations the plume height and gas flux is measured by traversing the plume and the plume speed is measured by performing a stationary measurement underneath the plume the instrument was tested in a field campaign in may 2005 at mt etna italy where the measured results are compared to wind fields derived from a meso scale meteorological model mm5 the test and comparison show that the instrument is functioning and capable of estimating wind speed at the plume height

a mechanism for tectonic deformation on venus in the absence of identifiable physiographic features directly associated with plate tectonics alternate mechanisms are sought for the intense tectonic deformation observed in radar images of venus one possible mechanism is direct coupling into an elastic lithosphere of the stresses associated with convective flow in the interior spectral green s function solutions have been obtained for stresses in an elastic lithosphere overlying a newtonian interior with an exponential depth dependence of viscosity and a specified surface density distribution driving the flow at long wavelengths and for a rigid elastic fluid boundary condition horizontal normal stresses in the elastic lid are controlled by the vertical shear stress gradient and are directly proportional to the depth of the density disturbance in the underlying fluid the depth and strength of density anomalies in the venusian interior inferred by analyses of long wavelength gravity data suggest that stresses in excess of 100 mpa would be generated in a 10 km thick elastic lid unless a low viscosity channel occurring beneath the lid or a positive viscosity gradient uncouples the flow stresses the great apparent depth of compensation of topographic features argues against this however thus supporting the importance of the coupling mechanism if there is no elastic lid stresses will also be very high near the surface providing also that the viscosity gradient is negative

role of local wind circulation in plume monitoring at mt etna volcano sicily insights from a mesoscale numerical model 1 mesoscale simulations at mt etna volcano sicily italy validated by measurements highlight the fundamental role played by the local wind field in the dispersion of a gaseous volcanic plume during the night downslope surface winds over hill flow and katabatic breezes force the plume to follow the steep morphology whereas during the day very frequent nnw synoptic winds crash into the cone and are contrasted by se strong sea breezes and anabatic winds with the consequent formation of convective ascendant currents the local mesoscale wind reconstruction can provide useful improvements in gaseous flux estimation far away synoptic wind velocities often used in these flux evaluations might be inadequate we propose a 3d numerical mesoscale wind reconstruction to evaluate plume dynamics and from it plume flux and potential hazard throughout all the hours of the day

a high accuracy map of global terrain elevations spaceborne digital elevation models dems are a fundamental input for many geoscience studies but they still include nonnegligible height errors here we introduce a high accuracy global dem at 3 resolution 90 m at the equator by eliminating major error components from existing dems we separated absolute bias stripe noise speckle noise and tree height bias using multiple satellite data sets and filtering techniques after the error removal land areas mapped with 2 m or better vertical accuracy were increased from 39 to 58 significant improvements were found in flat regions where height errors larger than topography variability and landscapes such as river networks and hill valley structures became clearly represented we found the topography slope of previous dems was largely distorted in most of world major floodplains e g ganges nile niger and mekong and swamp forests e g amazon congo and vasyugan the newly developed dem will enhance many geoscience applications which are terrain dependent

venus geology and tectonics hotspot and crustal spreading models and questions for the magellan mission spacecraft and ground based observations of venus have revealed a geologically young and active surface with volcanoes rift zones orogenic belts and evidence for hotspots and crustal spreading yet the processes responsible for these features cannot be identified from the available data the magellan spacecraft will acquire an unprecedented global data set which will provide a comprehensive and well resolved view of the planet this will permit global geological mapping an assessment of the style and relative importance of geological processes and will help in the understanding of links between the surface geology and mantle dynamics of this earth like planet

geologic evidence of hotspot activity on venus predictions for magellan a number of distinctive types of geologic features have been identified on venus that are interpreted to be related to thermal plumes including domal rises coronae and major composite shield volcanoes we document the basic characteristics of these features as well as their distribution the three types of features have related morphologies and we interpret them to represent a continuum of features formed by mantle plumes at scales from 100 s to over 1000 km the artemis structure located in aphrodite terra is proposed to be a large corona if crustal spreading processes are operating on venus hotspot features should form chains on the surface as seen in terrestrial ocean basins on the basis of current data on hotspot related feature distribution on venus no clear evidence exists for hotspot chains the complete distribution of hotspot features in magellan data will be used to understand better the relationship between interior processes and surface features as well as to provide a test for the crustal spreading hypothesis

atmospheric dispersion of natural gases at vulcano island abstract various computational scenarios are analyzed for the evaluation of volcanic co 2 and so 2 concentrations in the air over the island of vulcano aeolian archipelago north of sicily simulations were done using a 3d mesoscale meteorological model for complex terrain local wind depends on differences in land heating and cooling and on island topography row model outputs were used by a lagrangian particle model to simulate dispersion of gases emitted from crater fumaroles both models were able to reproduce observations simulation of the fumarolic gas dispersion at vulcano were performed for selected summertime conditions when more than 10 000 tourists reside in the area of vulcano porto in the inhabited area nw of the cone the highest concentrations of gases occur near sunrise due to nocturnal stratification and downslope breezes from the volcano present gas emission rates from crater fumaroles do not pose any hazard for humans an so 2 output rate two orders of magnitude higher with respect to a considered case of 30 tons per day may pose an hazard

a tectonic model for ridge transform ridge plate boundaries implications for the structure of oceanic lithosphere abstract the first order geologic and morphologic relationships at along and proximal to ridge transform ridge plate boundaries are used to construct an empirical and speculative tectonic model the distinctive but variable morphotectonic fabric and crustal structure of the transform domain are the product of a tectonic continuum that ranges from very slow rates of strain associated with very thick edges of lithosphere slowly slipping ridge transfrom ridge plate boundaries to extremely high rates of strain associated with very thin edges of lithosphere fast slipping ridge transform ridge plate boundaries the geometry of a ridge transform intersection necessitates the juxtaposition of a relatively cold thick edge of lithosphere against the truncated end of an accreting plate boundary the cold face of lithosphere cools the adjacent wedge of asthenosphere rising beneath the axis of accretion and restricts the amount of partial melting thus attenuating the volume of basaltic melt segregated from the asthenosphere per unit time the shallow level manifestation of this cold edge effect is a thinner oceanic crust at depth the evolving lithosphere thickens rapidly as the cold edge is approached creating changes in the properties of the young lithosphere and forming a weld of upper mantle material against the cold edge of truncating lithosphere the ridge transform weld of upper mantle material creates a shear couple in the lithosphere underlying the intersection resulting in the progressive reorientation of the maximum tensile stress from normal to the ridge axis at some distance from the ridge transform intersection to an oblique angle near the boundary the brittle carapace of oceanic crust that overlies the mantle weld will deform accordingly with the development of oblique dip slip faults the model predicts that the geologic expressions of this cold boundary effect will become more dramatic with increasing thickness of the truncating edge at very slow rates of accretion 100 km juxtapose thick 30 50 km edges of lithosphere against the accreting plate boundary all but nullifying the processes that lead to the emplacement of normal oceanic lithosphere in this environment a relatively strong mantle weld will form at the ridge transform intersection and the thick edges of opposing lithosphere along the length of the transform will tend to confine the strike slip tectonism to a relatively narrow and temporally stable principal transform displacement zone in contrast at very fast rates of accretion large offset transforms 100 km place relatively thin edges of lithosphere

tessera terrain venus characterization and models for origin and evolution tessera terrain is the dominant tectonic landform in the northern high latitudes of venus mapped by the venera 15 and 16 orbiters and is concentrated in the region between the mountain ranges of western ishtar terra and aphrodite terra tesserae are characterized by regionally high topography a high degree of small scale surface roughness and sets of intersecting tectonic features available pioneer venus line of sight gravity data suggest that tessera terrain is compensated at shallow depths relative to many topographic highs on venus and may be supported by crustal thickness variations three types of tessera terrain can be defined on the basis of structural patterns subparallel ridged terrains t sub sr trough and ridge terrain t sub tr and disrupted terrain t sub ds observed characteristics of tessera terrain are compared to predictions of models in order to begin to address the question of its origin and evolution formational models in which high topography is created along with surface deformation include 1 horizontal convergence 2 mantle upwelling 3 crustal underplating and 4 a seafloor spreading analogy modification models in which deformation occurs as a response to the presence of elevated regions consist of 1 gravity sliding and 2 gravitational relaxation the authorsmore find that horizontal convergence and late stage gravitational relaxation are the most consistent with basic observations for subparallel ridged terrain and disrupted terrain understanding of the basic structural characteristics of trough and ridge terrain is more tentative and models involving a spreading process or convergence and relaxation merit further study less

a simple global river bankfull width and depth database 1 hydraulic and hydrologic modeling has been moving to larger spatial scales with increased spatial resolution and such models require a global database of river widths and depths to facilitate accurate river flow routing hydraulic geometry relationships have a long history in estimating river channel characteristics as a function of discharge a simple near global database of bankfull widths and depths along with confidence intervals was developed based on hydraulic geometry equations and the hydrosheds hydrography data set the bankfull width estimates were evaluated with widths derived from landsat imagery for reaches of nine major rivers showing errors ranging from 8 to 62 correlation of 0 88 although it was difficult to verify whether the satellite observations corresponded to bankfull conditions bankfull depth estimates were compared with in situ measurements at sites in the ohio and willamette rivers producing a mean error of 24 the uncertainties in the derivation approach and a number of caveats are identified and ways to improve the database in the future are discussed despite these limitations this is the first global database that can be used directly in hydraulic models or as a set of constraints in model calibration

diffuse emission of hydrogen from poas volcano costa rica america central we report the results of four soil h2 surveys carried out in 2000 2003 at poas volcano costa rica to investigate the soil h2 distribution and evaluate the diffuse h2 emission as a potential surveillance tool for poas volcano soil gas h2 contents showed a wide range of concentration from 0 2 to 7 059 ppmv during the four surveys maps of soil gas h2 based on sequential gaussian simulation showed low h2 concentration values in the soil atmosphere 0 7 ppmv for most of the study area whereas high soil gas h2 values were observed inside the active crater of poas a significant increase in soil gas h2 concentration was observed inside the active crater during 2001 and 2002 with respect to year 2000 followed by a decrease in 2003 the observed spatial and temporal variations of soil h2 concentration have been well correlated with seismicity microgravimetry and fumarolic chemistry changes which occurred during this study these observations evidence changes in the shallow magmatic hydrothermal system of poas and it might be related to a potential magmatic intrusion during the period 1998 2004 therefore monitoring diffuse h2 emission of poas has become an important geochemical tool for the monitoring of its volcanic activity

quantitative tests for plate tectonics on venus if plate tectonics exists on venus the rate of topographic dropoff from spreading centers should be about half that on earth due to greater rock fluid density contrast and lower temperature differential between the surface and interior using 1 1 mean elevations 21 000 km of ridge were identified on venus and 33 000 km on earth heights h at distances up to 1000 km to either side of the ridges were analyzed to make least squares determinations of the parameters ho h and n in where s is off crest distance the venus ridges have a much less well defined mode in crest heights ho than the earth ridges and a somewhat smaller exponent n on the average indicating greater concavity fixing n to the theoretical value of 0 5 plate velocities were inferred from the h s using h t from north atlantic and north pacific data on earth these velocity solutions were compared to those from plate rotations which indicate the h t is probably about 40 too high for a global mean the resulting plate creation rates on venus assuming comparable total heat generation and taking into account the density and temperature differences are 0 7 km yr or less and indicate that not more than 15 of venus s energy is delivered to the surface by plate tectonics in contrast to 2 9 km yr and 70 energy delivery on earth

the geology of venus mental questions about the origin and evolution of the terrestrial planets and is of cri tical significance to comparative planetology the last 25 years of solar system exploration have provided unprecedented views of the earth moon mars and mercury these views have shown that the smaller terrestrial planetary bodies those one half the radius of the earth or less the moon mercury and mars are characterized by globally continuous unsegmented litho spheres that stabilized very early in the history of the solar system and by ancient surfaces that preserve the several billion year 0 1d record of early heavy bombardment and early heating and volcanism head solomon 1981 in contrast the earth is characterized by a globally segmented laterally moving lithosphere which is created at divergent plate boundaries and destroyed at convergent plate boundaries movement is measured in centimeters per year and the average age of the surface of the planet is less than 2 b y plate tectonics and plate recycling are fundamental mechanisms of heat loss for the earth in contrast to conduction which is the dominant mechanism for the smaller one plate planetary bodies solomon head 1982 what are the reasons for these differences is size or perhaps position in the solar system and initial conditions the key venus which is approximately the same size and density as earth and is the closest planet to earth offers an opportunity to test these ideas

a kinematic model for the evolution of the gorda plate the magnetic lineation pattern produced by the gorda rise reflects a complex tectonic history marked by propagating ridges and nonrigid deformation of the gorda plate the pacific side lineation pattern is matched using a kinematic model which incorporates northward and southward propagating ridge segments and ridge rotation by superimposing flexural slip style deformation on the resulting gorda side lineations and allowing convergent motion at the mendocino fracture zone the gorda magnetic pattern is also successfully predicted a similar model but one which does not allow convergence at the mendocino fracture zone fails to produce the observed lineation pattern model predictions of the amount of material that would be obducted at the mendocino due to convergence between the gorda and pacific agree with bathymetric and density estimates of the amount of material located along the mendocino ridge

use of motion estimation algorithms for improved flux measurements using so 2 cameras abstract article history received 3 april 2014accepted 18 august 2014available online xxxxkeywords so 2 uxso 2 cameraplume speedplume modellingoptical owmotion estimation so 2 cameras are rapidly gaining popularity as a tool for monitoring so 2 emissions from volcanoes severaldifferent so 2 camera systems have been developed with varying patterns of image acquisition in space timeand wavelength despite this diversity there are two steps common to the work owsofmostofthesesystems aligning images of different wavelengths to calculate apparent absorbance and estimating plume transportspeeds both of which can be achieved using motion estimation algorithms here we present two suchalgorithms adualtreecomplexwavelettransform basedalgorithmandthefarnebackopticalflowalgorithm weassesstheiraccuracyusingasyntheticdatasetcreatedusingthenumericcloud resolvingmodelatham andthen apply them to real world data from villarrica volcano both algorithms are found to perform well and theatham simulations offer useful datasets for benchmarking and validating future algorithms 2014 the authors published by elsevier b v this is an open access article under the cc by license http creativecommons org licenses by 3 0

atmospheric dispersion of volcanic co 2 at vulcano island abstract intensive carbon dioxide emanations occur throughout the island of vulcano aeolian archipelago north of sicily italy the main sources of co 2 on the island are the hot fumaroles 500 c of the northern ridge of the la fossa crater the fumaroles of the baia di levante and the emission areas spread out both on the slopes of the cone and in the nearby plain the carbon dioxide from the soil can be considered as being emitted at air temperature in this work co 2 concentrations in the air over the island are estimated by means of two numerical codes this paper takes advantage of the parallel knowledge gained from a previously written paper for so 2 emissions from the la fossa volcanic cone j volcanol geotherm res 75 1997 283 here the attention is focused on co 2 and on the roles the different co 2 sources play in the inhabited area of vulcano porto village in the model chain the wind flow is simulated using a 3d mesoscale meteorological model for complex terrain the simulations are performed for the most significant large scale wind conditions derived from a meteorological analysis of the region flow model outputs are then used by way of a lagrangian particle model to simulate the dispersion of the gas and to calculate the concentrations the space and time evolution of gas concentration is discussed for various sources and output rates simulations show that the contributions to the concentrations at the inhabited area of vulcano porto village of 1 the cone slopes and the la forgia vecchia emitting areas and 2 of the crater fumaroles are both negligible the main contribution comes from the soil emission at the volcano feet results agree well with field measurements indicating a sharp decrease in co 2 concentration downwind and nocturnal peaks of few hundred ppm in the areas emitting 10 3 cm 3 co 2 stp cm 2 s the approach shows the absence of any risk to population at the present emission rates

the geology and geomorphology of the venus surface as revealed by the radar images obtained by veneras 15 and 16 a region by region condensed description of almost all of the area that was radar photographed by veneras 15 and 16 is presented using some generalizations the diversity of terrain was reduced to a discrete set from which a geological morphological map was constructed the predominant type of terrain of the studied area is a plain that was tentatively subdivided into five morphological types ridge and band patchy rolling plain dome and butte plain smooth plain and high smooth plain stratigraphically the ridge and band plains are the oldest and the smooth plains are the youngest the stratigraphic position of the other types is yet to be determined large sections of the plains show similarities to the mare type basaltic plains of the moon mercury and mars other types of terrain are combinations of ridges and grooves in various patterns linear parallel orthogonal diagonal or chevron like and chaotic in some places the ridge and groove terrain is stratigraphically below the plain material but in other places it appears to be plain material that has been subsequently deformed near the eastern and western boundaries of ishtar terra large several hundred kilometers in diameter ring like features can be seen that are named coronae or ovoids evidence of tectonic deformation and the presence of flow like patterns support their designation as volcano tectonic features beta regio seems to be an uplifted plain showing evidence of rifting and volcanism all types of terrain are sparesely peppered with craters of obvious impact morphology their average density gives the plain an age range of 0 5 to 1 109 years the fact that many impact craters are still in the pristine state indicates a very low rate of surface reworking at least for the last 0 5 to 1 109 years no evidence for water erosion sedimentation processes has been found the tectonic activity of venus has no equivalent on the moon mercury or even mars and can be compared only with that of the earth intensive horizontal deformation previously known only on earth occurs on venus but in a characteristic venusian style

styles of tectonic deformations on venus analysis of venera 15 and 16 data analysis of the radar images obtained by veneras 15 and 16 leads to the conclusion that the ridge and groove structures on the surface of venus are the result of tectonic deformation although the mechanism of such deformation cannot yet be unequivocally deduced several styles of deformation can be described areal deformation occurs where horizontal stresses have operated over large areas shear deformation appears in bands showing differential longitudinal deformation transversal stresses operating over long and relatively narrow areas have produced belt deformation circular deformation is related to a specific locus of the stresses the absence of densely cratered areas indicates that the terrains were deformed after the period of heavy bombardment the origin of the stresses could be drag of the lithosphere by asthenospheric currents or gravity induced spreading of surface material over upwellings a general conclusion is that in the surveyed area of venus neither terrestrial plate tectonics nor lunar highland type terrain exists

global scale flow routing using a source to sink algorithm in this paper the development and global application of a new approach to large scale river routing is described it differs from previous methods by the extent to which the information content of high resolution global digital elevation models is exploited in a computationally efficient framework the model transports runoff directly from its source of generation in a land model cell to its sink on a continental margin or in an internally draining basin and hence is referred to as source to sink routing rather than from land cell to land cell which we call cell to cell routing it advances the development of earlier source to sink models by allowing for spatially distributed flow velocities attenuation coefficients and loss parameters the method presented here has been developed for use in climate system models with a specific goal of generating hydrographs at continental margins for input into an ocean model however the source to sink approach is flexible and can be applied at any space time scale and in a number of other types of large scale hydrological and earth system models hydrographs for some of the world s major river basins resulting from a global application as well as hydrographs for the nile river from a more detailed application are discussed

uv camera measurements of fumarole field degassing la fossa crater vulcano island abstract the uv camera is becoming an important new tool in the armory of volcano geochemists to derive high time resolution so2 flux measurements furthermore the high camera spatial resolution is particularly useful for exploring multiple source so2 gas emissions for instance the composite fumarolic systems topping most quiescent volcanoes here we report on the first so2 flux measurements from individual fumaroles of the fumarolic field of la fossa crater vulcano island aeolian island which we performed using a uv camera in two field campaigns in november 12 2009 and february 4 2010 we derived 0 5 hz so2 flux time series finding fluxes from individual fumaroles ranging from 2 to 8 7 t d 1 with a total emission from the entire system of 20 t d 1 and 13 t d 1 in november 2009 and february 2010 respectively these data were augmented with molar h2s so2 co2 so2 and h2o so2 ratios measured using a portable multigas analyzer for the individual fumaroles using the so2 flux data in tandem with the molar ratios we calculated the flux of volcanic species from individual fumaroles and the crater as a whole co2 684 t d 1 and 293 t d 1 h2s 8 t d 1 and 7 5 t d 1 and h2o 580 t d 1 and 225 t d 1

venus limited extension and volcanism along zones of lithospheric weakness three global scale zones of possible tectonic origin are described as occurring along broad low rises within the equatorial highlands on venus lat 50 n to 50 s long 60 to 310 the two longest of these tectonic zones the aphrodite beta and themis atla zones extend for 21 000 and 14 000 km respectively several lines of evidence indicate that beta and atla regiones located at the only two intersections of the three major tectonic zones are dynamically supported volcanic terranes associated with currently active volcanism rift valleys south of aphrodite terra and between beta and phoebe regiones are characterized by 75 to 100 km widths raised rims and extensions of only a few tens of kilometers about the same magnitudes as in continental rifts on the earth horizontal extension on venus was probably restricted by an early choking off of plate motion by high crustal and upper mantle temperatures and the subsequent loss of water and an asthenosphere

bilateral topographic symmetry patterns across aphrodite terra venus western aphrodite terra venus is characterized by a series of parallel linear structural discontinuities 2000 4000 km in length and 100 200 km wide which strike at high angles to the general topographic trend of the aphrodite terra highlands the broad characteristics of the cross strike discontinuities csds are similar to both strike slip fault zones and terrestrial oceanic fracture zones in an effort to distinguish between these two hypotheses topographic profiles were taken across aphrodite terra to test for bilateral symmetry of the type associated with thermal boundary layer topography at divergent plate boundaries on earth in addition to a broad bilateral symmetry at a range of angles across aphrodite terra detailed bilateral symmetry is observed within domains between linear discontinuities in directions generally parallel to the strike of the discontinuities in addition within a domain the centers of symmetry of several profiles define a linear rise crest that is oriented normal to the bounding csds and terminates against them furthermore linear rise crests are offset in a right lateral sense along the csds between domains by 200 1200 km if the discontinuities represent strike slip movement then retrodeformation of the axes of symmetry along the csds to form a straight line should form a broadly symmetrical topographic high instead when the topography is retrodeformed the edges of the highlands are characterized by distinctive misfits of topography at the edge of the rise where it intersects the csds the nature and configuration of the csds the characteristics of the topography and topographic patterns including bilateral topographic symmetry generally parallel to csds within domains the existence of linear rise crests defined by the axes of bilateral symmetry within domains and the offsets of these linear rise crests between domains all suggest that western aphrodite terra on venus is similar to terrestrial oceanic divergent plate boundary environments and that the cross strike discontinuities are analogous to oceanic fracture zones rather than strike slip faults

a statistical correlation between ridge crest offsets and spreading rate ridge crest offsets follow the statistical distribution n a exp b ln l lo where n is the cumulative number of ridge crest offsets with lengths greater than l lo is the cutoff length and a and b are constants we measured a and b for the slow spreading mid atlantic ridge the intermediate spreading juan de fuca ridge and the fast spreading east pacific rise the predicted mean distances between offsets greater than 4 km long are 30 32 and 74 km on the slow intermediate and fast spreading ridge crests these distances are in agreement with observations of other workers and calculations of modal ridge lengths

so2 flux measurements at mount etna sicily since 1987 over 220 measurements of the so2 flux at mount etna have been carried out using a correlation spectrometer cospec with different measuring techniques mainly with cospec mounted on a ground based vehicle this paper reports and analyzes the data obtained between october 1987 and december 1991 during this period three distinct time intervals characterized by particular so2 emission patterns were identified the first interval a showed a mean so2 flux of 5500 t d associated with relatively quiet summit crater eruptive activity the second interval b included two eruptive periods september october 1989 and january february 1990 associated with high fluxes reaching 10 000 25 000 t d the third interval c started in concert with a regional earthquake december 13 1990 and showed first a decrease and then an increase of so2 emissions before the onset of the major 1991 1993 flank eruption analysis of the data reveals a cyclic pattern to the so2 emissions over prolonged periods a nearly constant supply of so2 from the volcano s main feeder system especially evident in the long term a two to fivefold increase above mean flux values from 10 000 to 25 000 t d when occurring with paroxysmal eruptive activity and minimal flux values 1000 t d about 1 month prior to important eruptive events

characterization of venera 15 16 geologic units from pioneer venus reflectivity and roughness data abstract geologic units have been defined for the surface of venus from venera 15 16 image data a characterization of these geologic units is carried out using information on surface properties derived from pioneer venus pv reflectivity and rms slope data the geologic context provided by venera 15 16 units allows additional more specific interpretations of surface radar properties to be made characterization of venera units results in the definition of four groups of venera units i smooth rocky units ii rough rocky units iii rough high dielectric units and iv diffusely scattering units on the basis of correlations of surface morphology to spatial and statistical distributions in rms slope and reflectivity data we test models for the origin of the surface properties of some units we conclude that plains and tectonic units can be contrasted in terms of the average roughness of the surface and that tectonic deformation appears to roughen the surface at 0 5 to 10 m and 5 to 50 cm scales this tectonic weathering process appears to dominate the erosional regime of venus unlike earth or mars production and transport of soils dominates only a small portion 5 of the surface some of the venera units display distinctive spatial and statistical distributions of pv radar data in particular apparent low reflectivity in the tesserae appears to be caused by small 5 50 cm rock fragments on the surface which cause diffuse scattering at pioneer venus wavelenghts analysis of models for the formation of these fragments suggests that they are due to the pervasive deformation undergone by the tesserae finally aspects of this study have been used to extend results of venera image data analysis southward of 30 n lat resulting in a prediction of the distribution of tessera such results can aid in magellan investigations

radiative transfer corrections for accurate spectroscopic measurements of volcanic gas emissions there is widespread use of passive remote sensing techniques to quantify trace gas column densities in volcanic plumes utilizing scattered sunlight as a light source examples include passive doas cospec and the so2 camera in order to calculate trace gas concentrations or volcanic emission fluxes knowledge about the optical path through the plume is necessary in the past a straight photon path through the plume has always been assumed although it was known that this is not always true here we present the results of model studies conducted specifically to quantify the effects of realistic radiative transfer in and around volcanic plumes on ground based remote sensing measurements of so2 the results show that measurements conducted without additional information on average photon paths can be inaccurate under certain conditions with possible errors spanning more than an order of magnitude both over and underestimation of the true column density can occur actual errors depend on parameters such as distance between instrument and plume plume so2 concentration plume aerosol load as well as aerosol conditions in the ambient atmosphere as an example a measurement conducted with an so2 camera is discussed the results of which can only be correctly interpreted if realistic radiative transfer is considered finally a method is presented which for the first time allows the retrieval of actual average photon paths in spectroscopic i e doas measurements of adequate resolution by allowing for a wavelength dependent column density during the evaluation of doas measurements we show how radiative transfer effects can be corrected using information inherently available in the measured spectra thus greatly enhancing the accuracy of doas measurements of volcanic emissions

accurate measurement of volcanic so2 flux determination of plume transport speed and integrated so2 concentration with a single device 1 ground based measurements of volcanic sulfur dioxide fluxes are important indicators of volcanic activity with application in hazard assessment and understanding the impacts of volcanic emissions upon the environment and climate these data are obtained by making traverses underneath the volcanic plume a few kilometers from source with an ultraviolet spectrometer measuring integrated so2 concentrations across the plume s cross section and multiplying by the plume s transport speed however plume velocities are usually derived from ground based anemometers located many kilometers from the traverse route and hundreds of meters below plume altitude complicating the experimental design and introducing large flux can be 100 errors here we present the first report of a single instrument capable of accurate volcanic so2 flux measurements this device records integrated so2 concentrations and plume heights during traverses between traverses two in plume so2 time series are measured from underneath the plume with the instrument corresponding to zenith and inclined user specified angle from vertical in the direction of the volcano fields of view respectively the distance between the points of intersection of the two views with the plume is found on the basis of the determined plume height and the two signals are cross correlated to determine the lag between them enabling accurate derivation of the wind speed we present flux data with errors 12 obtained in this way at mt etna during july 2004

mapping large scale river flow hydraulics in the amazon basin 1 research on actual requirements for a numerically consistent representation of flow dynamics in large scale river flood models are needed to improve both modeling performance and computational efficiency still regional and global scale characterizations of river hydrodynamics are absent a first attempt to map river hydrodynamics in the amazon basin is presented flood wave type maps at 0 25 spatial resolution are derived from a classification method based on the analysis of saint venant equation terms global river geometry data sets derived from both digital elevation models and empirical equations supported by stream gauge observations are used as input variables errors of input variables are estimated and a sensitivity analysis is performed results show that 64 5 of rivers headwaters and high slope rivers can be represented by the kinematic wave ki 34 5 main amazon tributaries low slope and wetland regions by the diffusive wave df and 1 lower amazon by the full saint venant equations sv in a rigorous scenario i e a case where the most restricted classification of each grid cell is considered 33 is classified as ki 62 as df and 5 as sv most of the basin presents subcritical flow with very low froude number fr while the andean region is dominated by larger fr values and supercritical flow can be found according to our evaluation mostly based on in situ data the map has a percentage of detection of 83 4

evolution of ridges by asymmetrical spreading in late cretaceous time the relatively straight crest of the east pacific rise developed a remarkably orderly crenelate pattern contrary to previous statements such a pattern can evolve by orthogonal asymmetrical spreading without ridges jumping or otherwise affecting plate rigidity such evolution has been observed in wax experiments serrate ridges may also evolve if spreading is not orthogonal to transforms

a compendium of causes and effects of processes at transform faults and fracture zones a flowchart has been constructed which consolidates into a single conceptual framework a large number of the phenomena and processes which have been observed or postulated at transform faults tfs and fracture zones fzs oceanic ridge ridge transform faults and their aseismic extensions are emphasized the upstream end of the flowchart contains large scale boundary conditions imposed by the position of a particular transform fault in space and time for example slip rate the downstream end of the flowchart contains small scale features characteristic of individual tfs or fzs for example the existence of a fz parallel ridge features of both the upstream and the downstream ends of the flowchart can be mapped measured or otherwise derived by direct observation the middle of the flow chart includes processes and phenomena which are inferred to result from the upstream boundary conditions and to cause the downstream small scale features for example thermal conduction across the plate boundary phenomena in this black box in the center of the flowchart cannot be directly observed with present technology but must be inferred the advantages of ordering knowledge into such a flowchart are that inconsistancies gaps in understanding self limiting phenomena feedback loops and previously unrecognized relationships stand out and that the boundary between inference and observation is clearly drawn

gravity driven deformation of the crust on venus intense horizontal deformation features are observed on the surface of venus despite the apparent absence of terrestrial style plate tectonics high surface temperature low erosion rate and regions of elevated terrain suggest that gravity spreading may be responsible for some of these features gravity spreading on the earth is known to cause extensive deformation in certain thin skinned tectonic regions where the uppermost layers become detached along a decollement while the high pore pressures and soft sedimentary rocks frequently observed along decollements on the earth are not plausible for venus temperature induced regions of ductile deformation may exist simple viscous models of gravity spreading above a ductile region of the crust are developed to examine the effects of rheology thermal gradient surface slope and crustal thickness on deformation for a reasonable range of parameters the models show that surface slope driven ductile deformation at relatively shallow depths in the crust is possible and may be capable of detaching the uppermost rigid portion of the crust resulting in horizontal translation

along axis variations within the plate boundary zone of the southern segment of the endeavour ridge abstract the width of and along axis variations within the plate boundary zone of the southern segment of the endeavour ridge of the juan de fuca ridge system have been quantified using sea marc i sidelooking sonar imagery the sonar imagery was calibrated with video and photographic surveying to provide visual corroboration of the activity spacing and offset of faults and fissures this ridge segment contains an axial high bisected along its length by a summit depression whose width relief of its rims depth of its floor and spacing of faults and fissures vary systematically away from the midpoint of the ridge segment toward its tips the axial high and its summit depression are likened to an elongated shield volcano that is being disrupted by collapse of its crest into a widening linear caldera the observed distribution of faults and fissures could be produced by mechanisms which stretch young ocean crust which is characterized by rheological properties which vary with distance from the center of the elongated volcano reprints jhd

patterns of river width and surface area revealed by the satellite derived north american river width data set as hydraulic hydrologic and biogeochemical models evolve toward greater spatial resolution and larger extent robust morphometric data sets are essential to constrain their results here we present the landsat derived north american river width narwidth data set the first fine resolution continental scale river centerline and width database narwidth contains measurements of 2 4 105 km of rivers wider than 30 m at mean annual discharge we find that conventional digital elevation model derived width data sets underestimate the abundance of wide rivers to calculate the total surface area of north american rivers we extrapolate the strong observed relationship between river width and total surface area at different river widths r2 0 99 for 100 2000 m widths to narrower rivers and streams we conservatively estimate the total surface area of north american rivers as 1 24 0 15 0 39 105 km2 1 confidence intervals values 20 15 38 greater than previous estimates used to evaluate greenhouse gas efflux from rivers to the atmosphere

mercury gas emissions from la soufriere volcano guadeloupe island lesser antilles abstract quantifying mercury hg emissions from active volcanoes is of particular interest for better constraining the global cycle and environmental impact of this highly toxic element here we report on the abundance of total gaseous tgm hg 0 g hg ii g and particulate hg p mercury in the summit gas emissions of la soufriere andesitic volcano guadeloupe island lesser antilles where enhanced degassing of mixed hydrothermal magmatic volatiles has been occurring since 1992 from the southern summit crater we demonstrate that hg in volcanic plume occurs predominantly as gaseous mercury with a mean tgm hg p mass ratio of 63 combining the mean tgm h 2 s mass ratio of the volcanic plume 3 2 10 6 measured close to the source vent with the h 2 s plume flux 0 7 t d 1 determined simultaneously allows us to estimate a gaseous mercury emission rate of 0 8 kg yr 1 from la soufriere summit dome somewhat lower tgm s tot mass ratio in fumarolic gases from the source vent 4 4 10 7 suggests that plume chemical composition is not well represented by the emission source fumaroles due to chemical processes prior to or upon discharge current mercury emission from la soufriere volcano represents a very small contribution to the estimated global volcanic budget for this element

karin on swot characteristics of near nadir ka band interferometric sar imagery the principal instrument of the nasa cnes wide swath altimetry mission surface water and ocean topography swot is the ka band radar interferometer karin a bistatic synthetic aperture radar sar system operating on near nadir swaths on both sides of the satellite track there are limited reports on backscattering from natural surfaces at this short wavelength and particular observation geometry near field backscattering measurements on water as well as the first interferometric airborne sar acquisitions at ka band covering the 0 6 3 9 incidence range of karin were therefore conducted the experimental results confirm expected characteristics of near nadir ka band interferometric sar imagery such as strong water land radiometric contrast typically in the order of 10 db and very high interferometric coherence on water

apparent downwind depletion of volcanic so2 flux lessons from masaya volcano nicaragua a series of 707 measurements at masaya in 2005 2006 and 2007 reveals that so2 emissions 15km downwind of the active vent appear to be 33 to 50 less than those measured only 5km from the vent measurements from this and previous studies indicate that dry deposition of sulfur from the plume and conversion of so2 to sulfate aerosols within the plume each may amount to a maximum of 10 loss and are not sufficient to account for the larger apparent loss measured however the so2 measurement site 15km downwind is located on a ridge over which local trade winds and the entrained plume accelerate greater wind speeds cause localized dilution of the plume along the axis of propagation the lower concentrations of so2 measured on the ridge therefore lead to calculations of lower fluxes when calculated at the same plume speed as measurements from only 5km downwind and is responsible for the apparent loss of so2 due to the importance of so2 emission rates with respect to hazard mitigation petrologic studies and sulfur budget calculations measured fluxes of so2 must be as accurate as possible future campaigns to measure so2 flux at masaya and similar volcanoes will require individual plume speed measurements to be taken at each flux measurement site to compensate for dilution and subsequent calculation of lower fluxes this study highlights the importance of a comprehensive understanding of a volcano s interaction with its surroundings especially for low boundary layer volcanoes

sulphur dioxide fluxes from mount etna vulcano and stromboli measured with an automated scanning ultraviolet spectrometer gruppo nazionale per vulcanolgia gnv the ec 5th framework project multimo and nerc grant gr9 04655

thermal stress and the spacings of transform faults bathymetric charts are used with satellite altimeter profiles to locate major ridge transform intersections along five spreading ridges the ridges are the mid atlantic ridge the east pacific rise the chile rise the pacific antarctic rise and the southeast indian ridge analysis of these data show spacings between transform faults w increase linearly with spreading rate w 6 28 m y this linear correlation is explained by a thermoelastic model of a cooling strip of lithosphere spreading at a rate the traction free boundaries of the thin elastic strip simulate cracks in the lithosphere at transform faults a two dimensional thermoelastic solution for the in plane stress shows the largest stress component is tensional and parallel to the ridge stresses are zero at the ridge and increase as age to a maximum value at an age of w 4 all stress components are small for ages greater than w when the transform spacing is large compared with the spreading rate w 100 m y thermal stresses exceed the strength of the lithosphere for ages between 0 and 30 ma the observed maximum ratio of transform spacing to spreading rate w 10 m y results in low thermal stresses that only exceed the strength of the lithosphere for ages less than 1 ma thus transform faults relieve most of the thermal stress model predictions also agree with earthquake studies showing that normal faults in young lithosphere have tensional axes aligned with the ridge moreover oceanic intraplate earthquakes rarely occur in lithosphere older than 30 ma as predicted by the model these and other geophysical observations confirm turcotte s hypothesis that transform faults are thermal contraction cracks

estimation of river discharge propagation speed and hydraulic geometry from space lena river siberia 1 moderate resolution imaging spectroradiometer modis derived measurements of lena river effective width we display a high predictive capacity r2 0 81 mean absolute error 60 90 km 2 3 time valley width satellite derived we q rating curves and hydraulic geometry b exponents converge upon stable values b 0 48 indicating transferability of the discharge retrieval method between different locations put another way at length scales exceeding 60 90 km all subreaches display similar behavior everywhere at finer reach length scales e g 0 25 1 km longitudinal extraction of b exponents represents the first continuous mapping of a classical hydraulic geometry parameter from space while at least one gauging station is required for calibration results suggest that multitemporal satellite data can powerfully enhance our understanding of water discharge and flow conveyance in remote river systems

surface characteristics of venus derived from pioneer venus altimetry roughness and reflectivity measurements the three primary data sets for the pioneer venus orbiter radar experiment topography roughness and reflectivity contain important information about the geological and textural characteristics of the surface of venus we have subdivided the range of roughness and reflectivity values into three categories as follows roughness in degrees rms slope relatively smooth 1 2 5 transitional from smooth to rough 2 5 5 and relatively rough 5 and fresnel reflectivity surfaces dominated by soil or porous material 0 2 we have analyzed each of these data sets and their relationships to each other in order to define areas of the surface that are characterized by distinctive properties e g rough rocky surfaces smooth soil surfaces we then describe the abundance and areal distribution of such areas and locally calibrate the geological significance of some of the surface types by examining high resolution images from spacecraft and earth based observatories we find that the majority of venus is covered by regionally contiguous rock and bedrock surfaces many of the smooth surfaces we interpret to be of volcanic origin most likely lava flows while rougher surfaces are locally characterized by tectonic deformation of several types soil surfaces cover less than about 27 of the planet and are generally patchy in their distribution on the basis of the distribution of these surfaces we see no evidence for the extensive preservation of an ancient global regolith or for widespread topographically controlled erosion lateral transport and sedimentation the small percentage of the surface of venus characterized by high dielectric material appears to originate from several processes including primary lava flows probably containing enrichments of high dielectric materials such as metal or metal oxides e g theia mons in beta regio and exposure of high dielectric materials by tectonic deformation e g maxwell montes in ishtar terra these global data set correlations provide a fundamental frame work for understanding the nature of the surface of venus and will permit extrapolation of local and regional findings from future geochemical and imaging experiments to a global context

estimation of bathymetric depth and slope from data assimilation of swath altimetry into a hydrodynamic model 1 the proposed surface water and ocean topography swot mission would provide measurements of water surface elevation wse for characterization of storage change and discharge river channel bathymetry is a significant source of uncertainty in estimating discharge from wse measurements however in this paper we demonstrate an ensemble based data assimilation da methodology for estimating bathymetric depth and slope from wse measurements and the lisflood fp hydrodynamic model we performed two proof of concept experiments using synthetically generated swot measurements the experiments demonstrated that bathymetric depth and slope can be estimated to within 3 0 microradians or 50 cm respectively using swot wse measurements within the context of our da and modeling framework we found that channel bathymetry estimation accuracy is relatively insensitive to swot measurement error because uncertainty in lisflood fp inputs such as channel roughness and upstream boundary conditions is likely to be of greater magnitude than measurement error

regional linear cross strike discontinuities in western aphrodite terra venus western aphrodite terra venus is characterized by a series of parallel linear structural discontinuities 2000 4000 km in length and 100 200 km wide which strike at high angles to the general topographic trend of the highlands the detailed characteristics of these features are similar to terrestrial oceanic fracture zones and strike slip fault zones either interpretation implies the presence of large scale horizontal tectonic movement on venus

three dimensional transport speed of wind drifted ash plumes using ground based radar 1 the main utilization of mobile ground based doppler radars is to quantify the dynamics of eruptive activity by aiming directly at the emission source we show that they can also provide information on the initial lateral transport speed of weak ash plumes bent over by crosswind the method is illustrated by measurements made with a transportable volcano doppler radar voldorad at arenal volcano costa rica the near source displacements of the plume are tracked through echo onsets induced by ash entering successive probed volumes in the radar beam a constant transport velocity is commonly reached within a few seconds of the initial ash emission as wind advection and buoyancy take over momentum the plume azimuth and upraise angles are constrained by comparing the amplitude decrease of the radar echoes as a function of distance from the source with results from a simple geometric plume model the three dimensional vector of the ash cloud transport speed is then reconstructed with an accuracy of a few percent this method may have applications for volcano monitoring for determining pyroclast fluxes for the modeling of tephra dispersal and for remote measurements of volcanic gas fluxes

orogenic belts on venus recent radar observations of venus show evidence for three types of deformational features in the linear mountain belts of ishtar terra linear ridges and troughs oriented parallel to the strike of the mountains and interpreted to be anticlines and synclines broad low arches similar to mare ridge type features seen on the moon and interpreted to represent low angle thrusting and buckling and linear discontinuities that cut across the strike of the ridges and troughs and are interpreted to represent strike slip movement on the basis of the localized concentration of these features their orientations and patterns of distribution and their association with linear mountainous topography we conclude that they mark the location of concentrated horizontal compressional deformation and that akna and freyja montes represent erogenic belts on venus

large scale hydrologic and hydrodynamic modeling using limited data and a gis based approach summary in this paper we present a large scale hydrologic model with a full one dimensional hydrodynamic module to calculate flow propagation on a complex river network the model uses the full saint venant equations and a simple floodplain storage model and therefore is capable of simulating a wide range of fluvial processes such as flood wave delay and attenuation backwater effects flood inundation and its effects on flood waves we present the model basic equations and gis algorithms to extract model parameters from relatively limited data which is globally available such as the srtm dem gis based algorithms include the estimation of river width and depth using geomorphological relations river cross section bottom level and floodplain geometry extracted from dem etc we also show a case study on one of the major tributaries of the amazon the purus river basin a model validation using discharge and water level data shows that the model is capable of reproducing the main hydrological features of the purus river basin also realistic floodplain inundation maps were derived from the results of the model our main conclusion is that it is possible to employ full hydrodynamic models within large scale hydrological models even using limited data for river geometry and floodplain characterization

gloria survey of the east pacific rise near 3 5 s tectonic and volcanic characteristics of a fast spreading mid ocean rise abstract a long range sidescan sonar gloria survey of an approximately 100 km square area of the east pacific rise crest between 3 s and 4 s extends results obtained in the same area by lonsdale 1977 using deep tow the axial linear volcano was found to be continuous over a distance of 75 km the presence of major inward and outward facing fault scarps was confirmed but the gloria data show several distinct differences between the two fault sets the inward dipping faults are more numerous more closely spaced and longer than the outward dipping ones and their dip slopes backscatter sound more extensively than those of the outward dipping faults moreover most of them appear to be formed within 2 km of the axis whereas the majority of the outward dipping faults begin to develop between 5 and 8 km from the axis these differences suggest that the two sets of faults have different origins the horizontal pattern of inward dipping faults is similar to those observed on other mid ocean rises at all spreading rates though the lengths and separations of the scarps are slightly and their throws considerably less than on slower spreading rises this common horizontal pattern suggests that inward dipping faults on all rises have a common mode of formation regardless of spreading rate horizontal tension is probably the dominant factor but an additional mechanism is needed to explain the polarization of fault dips that occurs in the region 2 8 km from the axis the similarity of major fault spacings on the east pacific rise to those on slower spreading rises suggests that faulting is invariant in space rather than time and that the lithosphere where these faults are formed about 2 km from the spreading axis has a similar small thickness for all spreading rates this is attributed to the regulating effect of hydrothermal circulation and plate cooling

automated high time resolution measurements of so2 flux at soufriere hills volcano montserrat we report here the first results from an automated telemetered uv scanning spectrometer system for monitoring so2 emission rates at soufriere hills volcano montserrat two spectrometers receive light by way of a motor driven stepping prism and telescope in order to make vertical scans of the volcanic plume spectral data from these spectrometers situated 2 800 m apart and 4 500 m from the volcano are relayed back to the observatory every 4 5 s via radio modems a full scan of the plume is accomplished every 1 6 min by the time synchronised spectrometers and a so2 emission rate is calculated using the so2 slant concentrations scan angles and plume speeds estimated from the wind speed from a telemetered weather station near to the volcano the plume s position and dimensions are calculated using the angular data from the two spectrometers the plume height varies significantly diurnally and seasonally and is important in order to minimise the error on so2 emission rates the new scanning system scanspec provides so2 emission rates from 08 00 to 16 00 h local time every day preliminary results highlight a number of features of the so2 time series and plume dynamics and give our first indications of the errors and limits of detection of this system so2 emission rates vary widely on all time scales minutes days months this new system has already provided the first real and consistent indication that so2 emission rates vary on a minutes to hours basis which can be correlated with volcanic activity for example rockfall and pyroclastic flow activity it is anticipated that this system at soufriere hills will yield information on shallow processes occurring on short time scales periods of minutes to hours as well as deep processes relating to magma supply rates which will be associated with longer wavelength so2 signals of weeks to months

tessera terrain on venus a survey of the global distribution characteristics and relation to surrounding units from magellan data the tessera terrain on venus comprised of areas of high radar backscatter complex deformation patterns relative to other units and topography standing higher than surrounding plains covers 35 33 106 km2 about 8 of the surface of venus and is nonrandomly distributed being preferentially located at equatorial and higher northern latitudes with a distinct paucity below about 30 s individual tessera occurrences range in area from the lower limits of our measurements about 200 km2 up to the largest tessera ovda with an area of about 8 6 106 km2 or about 2 of the surface area of venus the size frequency distribution of tessera patches is strongly unimodal and skewed toward smaller sizes reflecting the great abundance of small tessera fragments modes of occurrence include 1 large clusters e g aphrodite terra and ishtar terra 2 arc like segments which may extend for thousands of kilometers and are either concave inward toward the major tessera cluster development or away from it 3 areas where tesserae are rare or absent which occur both as low lying plains e g guinevere planitia and as elevated regions e g atla regio tessera terrain has a bimodal elevation frequency distribution with the main peak at about 0 1 km and an additional peak at about 3 km above mean planetary radius in terms of number of occurrences however tesserae do not display a correlation with elevation at the global scale since small tessera patches commonly occupy low lying regions although tessera exhibit a range of gravity signatures many occurrences are interpreted to represent relatively shallow crustal levels of compensation tessera boundaries include type i sinuous embayed dominated by adjacent lava plains embaying tessera massifs 73 of total tesserae boundaries and type ii linear tectonic only a small percentage of the length of all boundary types show no lava embayment and could be interpreted as tectonically active for long periods subsequent to initial tessera formation occurrence of broad slopes of post tessera embayed plains away from tessera boundaries suggests that regional tilting occurred subsequent to final tessera deformation in some places several lines of evidence suggest the possibility that a widespread tessera like basement comprising at least 55 of the surface of venus is buried under a cover of lava plains a few hundred meters to as much as 2 4 km thick a wide variety of deformational structures and patterns is observed within the tessera including those representing extension compression shear and transpression in some cases the apparently complex patterns can be resolved into single event kinematic interpretations involving noncoaxial deformation e g itzpapalotl while in other cases polyphase deformation is more likely e g central ovda and thetis where relations can be determined stratigraphically earliest deformation within the tessera is primarily related to crustal shortening and compression phase i followed by pervasive extensional deformation commonly oriented normal to the strike of phase i features generally along the same principal stress direction phase ii evidence also exists for the contemporaneous formation of these distinctive deformation patterns lava plains within and adjacent to the tessera embay both of these fabrics but sometimes overlap in time with phase ii extensional deformation and with regional tilting tessera terrain as a geologic unit occupies the lowest portion of the stratigraphic column in all areas that we have observed an observation consistent with many other mapping studies we see no evidence for transitional stages between tessera and volcanic rises and or lowlands that might represent a long term sequence of upwelling or downwelling followed by crustal deformation and tessera formation no impact craters deformed by phase i deformation have yet been observed on tessera suggesting that phase i tessera deformation sufficiently intense to eradicate earlier impact craters ceased relatively abruptly somewhat before 300 500 m y ago however the starting time and thus duration of tessera formation is unknown on the basis of the very small number of on tessera craters deformed by phase ii extensional deformation this period probably did not last more than several tens of millions of years after the cessation of phase i little observable deformation of the tessera terrain appears to have taken place in the last several hundred million years during which time the vast volcanic plains were emplaced although tilting of early plains along some tessera margins is observed building on the global synthesis presented here future analyses of individual tessera occurrences will provide the detailed descriptions kinematic interpretations and strain histories necessary to assess and distinguish between the several catastrophic and uniformitarian models for tessera formation

measurement of volcanic so2 fluxes with differential optical absorption spectroscopy abstract measurements of volcanic sulphur dioxide fluxes are important indicators of volcanic activity and are crucial to understanding the impacts of volcanic emissions upon the environment and climate for more than thirty years correlation spectrometers cospecs have provided valuable service in this respect however given the vintage and operational costs of these devices research groups and volcano observatories have recently begun using state of the art lightweight compact and inexpensive usb2000 ultraviolet spectrometers as a replacement technology with differential absorption spectroscopy so2 concentration retrievals in order to widen the dissemination of the latter approach an overview of this methodology is given here covering hardware protocols and the use of freely available software written for this purpose

stress analysis of tellus regio venus based on gravity and topography comparison with venera 15 16 radar images the tectonics of the tellus regio highland of venus have been examined using pioneer venus altimetry and gravity data and venera 15 16 radar images a thin elastic shell model has incorporated the pioneer venus data to calculate both global long wavelength and regional shorter wavelength stresses for various assumed values of crust lithosphere and mantle thickness and modes of compensation the effects of these parameters on the calculated stress magnitudes have been examined the model also allows calculation of crustal thickness and mantle density anomalies the resulting calculated stress fields have been compared to the surface morphology observed in the venera 15 16 radar images and interpreted in terms of the stress history the best fitting parameters are consistent with minor amounts of lithospheric flexure being necessary to produce the observed surface features the highland region is underlain by a thick 15 20 km crust which is responsible for most of the topographic support a positive density anomaly exists below this crust the denser mantle may represent the down welling portion of a flow field in which the horizontal flow feeding the downwelling has entrained mobile crustal material dynamically maintaining a thickened crustal root near the stagnation point of the flow below tellus regio this hot crustal material may have intruded the overlying cooler crust causing lithospheric inflation and surface volcanism this scenario is in agreement with the available gravity and radar data and can explain the general surface morphology of tellus regio

the first decade of gloria in 10 years of operation gloria has been used on 26 cruises and has inonified more than 1 of the ocean floor the paper reviews the scientific achievements of this new tool and assesses the contributions which it has made to understanding the geological features and the processes creating them a complete bibliography of gloria papers is included in the references and the best examples of sonographs obtained over different terrain are illustrated

fortuna tessera venus evidence of horizontal convergence and crustal thickening structural and tectonic patterns mapped in fortuna tessera are interpreted to reflect a change in the style and intensity of deformation from east to west beginning with simple tessera terrain at relatively low topographic elevations in the east and progressing through increasingly complex deformation patterns and higher topography to maxwell montes in the west these morphologic and topographic patterns are consistent with east to west convergence and compression and the increasing elevations are interpreted to be due to crustal thickening processes associated with the convergent deformational environment using an airy isostatic model crustal thicknesses of approximately 35 km for the initial tessera terrain and crustal thicknesses of over 100 km for the maxwell montes region are predicted detailed mapping with magellan data will permit the deconvolution of individual components and structures in this terrain

tectonic rotations in extensional regimes and their paleomagnetic consequences for oceanic basalts paleomagnetic samples of many deep sea drilling project dsdp basalts have shallower inclinations than would be inferred from the paleolatitude at which the basalts were extruded at mid ocean ridges rather than arising from peculiarities of the geomagnetic field the anomalous magnetic directions may result from tectonic rotations along the listric normal faults which often characterize extensional tectonic regimes several lines of evidence support this conclusion observations of the basin and range province an extensional tectonic regime occurring in continental crust observations of the troodos complex cyprus an oceanic extensional tectonic regime now exposed on land and analysis of possible fault patterns associated with the magma chambers postulated to occur at some mid oceanic ridges the tectonic rotations resulting from movement along the listric normal faults occur about a horizontal axis generally perpendicular to the extension direction and typically amount to 30 to 50 although rotations as large as 70 to 90 are not uncommon the paleomagnetic consequences of these rotations can be calculated for dsdp basalts if the original strike and latitude of a ridge are known at four dsdp sites for which adequate data are available namely sites 319 332 410 and 417 rotations ranging from 50 to 70 are required to explain the paleomagnetic results if the original strike and location of the ridge are not known as is the case for most of the older parts of the pacific ocean the paleomagnetic data and the inferred rotation determine a relationship between possible ridge strikes and locations this information combined with a similar but independent relationship derived from the marine magnetic anomalies puts severe constraints on the original strike and location of the ridge

flood routing in mild sloped rivers wave characteristics and downstream backwater effect abstract unsteady flow routing in a mild sloped river with gradually varying flow depth induced by the downstream backwater effect is theoretically investigated the saint venant equations and other routing models are linearized at the base flow state a steady and spatially varying subcritical flow represented by the m1 or m2 water surface profile the linear stability analysis is adopted to study the physical mechanisms responsible for wave attenuation or amplification and wave retardation or acceleration in open channels when the flow is spatially varying analytical descriptions of the propagation characteristics such as wave celerity and wave attenuation factor for all range of wave numbers are derived and expressed in terms of channel property steady uniform flow froude number dimensionless wave number base flow depth and base flow pressure gradient the downstream backwater effect on wave characteristics of various widely used flood routing models is discussed

spatially resolved so2 flux emissions from mt etna we report on a systematic record of so2 flux emissions from individual vents of etna volcano sicily which we obtained using a permanent uv camera network observations were carried out in summer 2014 a period encompassing two eruptive episodes of the new south east crater nsec and a fissure fed eruption in the upper valle del bove we demonstrate that our vent resolved so2 flux time series allow capturing shifts in activity from one vent to another and contribute to our understanding of etna s shallow plumbing system structure we find that the fissure eruption contributed 50 000 t of so2 or 30 of the so2 emitted by the volcano during the 5 july to 10 august eruptive interval activity from this eruptive vent gradually vanished on 10 august marking a switch of degassing toward the nsec onset of degassing at the nsec was a precursory to explosive paroxysmal activity on 11 15 august

terrestrial spreading centers under venus conditions evaluation of a crustal spreading model for western aphrodite terra abstract assessment of terrestrial spreading centers under venus environmental conditions indicates that the major difference between earth and venus would be the influence of the enhanced surface temperature on upper mantle temperatures on venus and the resulting increase in crustal thickness and elevation of isostatically compensated topography crust on venus produced at average spreading centers would be about 15 km thick in contrast to the average crustal thickness on earth of about 5 km we have used this model and the pioneer venus altimetry and gravity data to test the hypothesis of head and crumpler 1987 6 that western aphrodite terra represents the location of crustal spreading on venus the topographic data are processed such that all points within equally spaced 100 km wide bins parallel to the proposed axis are stacked together and the average value of topography in each bin is calculated providing average profiles out to a distance of 2000 km on either side of the axis the topography is shown to be very symmetric about the axis with data points less than 1000 km from the axis providing a fit to thermal boundary layer topography comparable to that seen in spreading centers on earth at 1000 km on either side of the axis steep topographic slopes exist this change in topography could be explained by variations of about 15 km in crustal thickness with the crust being thicker in the central domain by a ridge jump or by mechanisms unrelated to crustal spreading for processing line of sight los acceleration data we first show that static and dynamic calculations give the same results for track numbers 427 449 this allows us to determine a synthetic orbit track parallel to the cross strike dis continuities csd s and to compare it with observed los accelerations gravity data for this domain were then processed in a manner similar to that for topography models give a reasonable fit to the data for half spreading rates between 0 3 and 0 5 cm yr we conclude that a spreading center model for ovda regio could account for the observed topography and los gravity anomalies if it had the following characteristics a central domain with a 30 km thick crust that has been spreading at about 0 5 cm yr for the last 200 myr over a mantle whose temperature is about 1600 c at about 200 myr ago a change in upper mantle temperature of about 100 c is required prior to this time the decreased upper mantle temperature would have produced a thinner crust averaging about 15 km at the spreading center this thinner crust would now lie on the flanks of ovda regio at distances greater than 1000 km from the spreading center and would be in excess of 200 myr old on the basis of our analysis we conclude that the hypothesis that ovda regio in western aphrodite terra is the site of crustal spreading on venus is consistent with the topography and gravity data