aeolian dune migration along the ceara coast north eastern brazil aeolian dune dimensions and migration rates are analysed along the ceara coast north east brazil dunes that are currently mobile along the ceara coast are composed of barchans and sand sheets the results show that barchans maintain an equilibrium form which can be characterized by values of dimensionless shape parameters h w and w l where h is the dune height w is the wing to wing width and l is the dune length dunes are highly mobile with average migration rates of 17 5 m year 1 for barchans and 10 m year 1 for sand sheets the calculated migration rates were found to depend strongly on dune dimensions for both barchans and sand sheets i e the larger the dune is the lower the migration rate will be this size dependence was associated with the existence of a representative common transport rate along the dune fields which induces a different dune migration rate dependent on dune size finally from the observed dune evolution an aggregated scale aeolian sediment transport was inferred this bulk transport rate of the order of 90 100 m3 m 1 year 1 is only valid for a timescale of years to decades which is the timescale used in dune evolution analysis

combined discrete and continuous gravity observations at mount etna systematic investigation of discrete gravity measurements has continued at mount etna since 1986 the network now covers an area of 400 km2 with about 70 stations 0 5 3 km apart mass redistributions occurring at depths ranging between about 8 km below sea level and a few hundred metres below the surface magma level changes within the shallower parts of the feeding conduits have been identified from these data conventional discrete microgravity monitoring on a network of stations furnishes only instantaneous states of the mass distribution at continuously active systems in order to obtain information on the rate at which the volcanic processes and thus mass transfers occur three stations for continuously recording gravity where installed on mount etna in 1998 a 16 month long sequence from one of the continuously running stations pdn located 2 km from the active northeast crater at the summit of etna volcano is presented after removing the effects of earth tide and tilt the correlation of the residual gravity sequence with simultaneous recordings of meteorological parameters acquired at the same station was analysed once the meteorological effects have also been removed continuous gravity changes are within 10 gal of gravity changes measured using conventional microgravity observations at sites very close to the continuous station this example shows how discrete and continuous gravity observations can be used together at active volcanoes to get a fuller and more accurate picture of the spatial and temporal characteristics of volcanic processes

very shallow earthquakes and brittle deformation in active volcanic areas the eatnean region as an example abstract some aspects of the stress field acting in active volcanic areas were investigated by studying the relationship between surficial seismicity h 1 2 km and the brittle deformation pattern of the etna volcano the magmatic composition and structural character of mt etna are described together with its geodynamic regional context after a discussion of the problem of the state of stress in active volcanoes and a definition of very shallow seismicity the high level of surficial seismicity the morphology of the sedimentary basement and the kinematic behaviour of the faults suggest that the eastern flank of mt etna is a shallow seismotectonic domain structurally decoupled from the rest of the volcanic body this flank shows a tendency to slide in an eastern direction and is bound to the north by a left lateral oblique slip normal fault trending e w and in the south by an arcuate fault system with right lateral features right lateral oblique slip normal faults

volcanism and mantle crust evolution the etna case abstract mount etna is located in a particular region of convergence of african and eurasian plates where intense post collisional tectonics caused considerable uplift however we present arguments supporting the hypothesis that volcanism and associated seismic activity would result from a local mantle uprise leading to a horst probably linked to a deep rooted hot spot it ensued deformation and fracturing of the overlying crust with emission of aphyric tholeiitic basalts directly from their mantle source and subsequent development of a deep reservoir or complex of intrusions at the top of a mantle diapir near 30 km depth this is advocated by the appearance of porphyritic alkaline lavas whose mineral equilibria and differentiation processes are consistent with an 8 10 kbar pressure and by the development of central volcanoes the horst itself appears to have begun in the sw sector of the present volcanic area its uplift was greater westward as seen from the trend of the terraces along the simeto river and became later obvious toward the se these differential movements produced fractures and faults which are to day evident in the southern area of mt etna the growth of the horst then proceeded in a ne direction following the regional tectonic lines and with a greater intensity along the side facing se crossed by the regional nnw sse line aeolian maltese escarpment the seismicity and ground deformation registered over the last twenty years support the proposed model earthquakes are unfrequent in the lower southern and western areas of the volcano whereas they are numerous and stronger to the north east in the summit area above 1600 m a s l and in the eastern sector along the nw se faults and fractures finally a digital elevation model recently published reveals the existence of two tectonic domains the first one is associated with the horst and contains prevalently ne sw oriented faults whereas the second is mainly linked to regional tectonics with nnw sse and nw se faults and fractures

modelling vegetated dune landscapes this letter presents a self organising cellular automaton model capable of simulating the evolution of vegetated dunes with multiple types of plant response in the environment it can successfully replicate hairpin or long walled parabolic dunes with trailing ridges as well as nebkha dunes with distinctive deposition tails quantification of simulated landscapes with eco geomorphic state variables and subsequent cluster analysis and pca yields a phase diagram of different types of coastal dunes developing from blow outs as a function of vegetation vitality this diagram indicates the potential sensitivity of dormant dune fields to reactivation under declining vegetation vitality e g due to climatic changes nebkha simulations with different grid resolutions demonstrate that the interaction between the abiotic geomorphic processes and the biological vegetation component life introduces a characteristic length scale on the resultant landforms that breaks the typical self similar scaling of un vegetated bare sand dunes

new evidence for the form and extent of the pernicana fault system mt etna from structural and soil gas surveying a multidisciplinary study based on structural and soil gas surveys was carried out in order to investigate the relationship between soil co2 degassing and the tectonic setting of the lower northeastern flank of mt etna volcano the results show that anomalous soil co2 emissions occur mainly along faults trending wnw ese and also where these faults intersect the other main fault set trending ne sw that displaces the study area in particular anomalies in co2 degassing were revealed both along the pernicana fault and along another fault fiumefreddo fault which may represent the prolongation of the former towards the ionian sea coast in the areas where these structures show evident surface faulting they are all characterised by left lateral displacements and aseismic creep behaviour furthermore the geochemical survey revealed that these faults join in an area devoid of geological evidence of surface faulting and continue underneath an apparently unfaulted alluvial cover near the coastline in the light of these findings we suggest that the pernicana and fiumefreddo faults are discrete segments of a near continuous left lateral shear zone affecting the whole north eastern flank of mt etna as far as the ionian coast

early stage aeolian protodunes bedform development and sand transport dynamics early stage aeolian bedforms or protodunes are elemental in the continuum of dune development and act as essential precursors to mature dunes despite this we know very little about the processes and feedback mechanisms that shape these nascent bedforms whilst theory and conceptual models have offered some explanation for protodune existence and development until now we have lacked the technical capability to measure such small bedforms in aeolian settings here we employ terrestrial laser scanning to measure morphological change at the high frequency and spatial resolution required to gain new insights into protodune behaviour on a 0 06 m high protodune we observe vertical growth of the crest by 0 005 m in two hours our direct measurements of sand transport on the protodune account for such growth with a reduction in time averaged sediment flux of 18 observed over the crestal region detailed measurements of form also establish key points of morphological change on the protodune the position on the stoss slope where erosion switches to deposition is found at a point 0 07 m upwind of the crest this finding supports recent models that explain vertical dune growth through an upwind shift of this switching point observations also show characteristic changes in the asymmetric cross section of the protodune flow form feedbacks result in a steepening of the lee slope and a decline in lower stoss slope steepness by 3 constituting a reshaping of protodune form towards more mature dune morphology the approaches and findings applied here a demonstrate an ability to quantify processes at requisite spatial and temporal scales for monitoring early stage dune evolution b highlight the crucial role of form flow feedbacks in enabling early stage bedform growth alluding to a fluctuation in feedbacks that require better representation in dune models and c provide a new stimulus for advancing understanding of aeolian bedforms

aeolian sand strip mobility and protodune development on a drying beach examining surface moisture and surface roughness patterns measured by terrestrial laser scanning ephemeral aeolian sand strips are commonplace on beaches their formation during high energy sand transport events often precedes the development of protodunes and their dynamics present interesting feedback mechanisms with surface moisture patterns however due to their temporary nature little is known of their formation mobility or the specifics of their interaction with beach surface characteristics similarly surface moisture has an important influence on sediment availability and transport in aeolian beach systems yet it is difficult to quantify accurately due to its inherent variability over both short spatial and temporal scales whilst soil moisture probes and remote sensing imagery techniques can quantify large changes well their resolution over mainly dry sand close to the aeolian transport threshold is not ideal particularly where moisture gradients close to the surface are large in this study we employed a terrestrial laser scanner to monitor beach surface moisture variability during a three and a half hour period after a rain event and investigated relationships between bedform development surface roughness and surface moisture our results demonstrate that as the beach surface dries sand transport increases with sediment erosion occurring at the wet dry surface boundary and deposition further downwind this dynamic structure dependent upon changing surface moisture characteristics results in the formation of a rippled sand strip and ultimately a protodune our findings highlight dynamic mobility relationships and confirm the need to consider transient bedforms and surface moisture across a variety of scales when measuring aeolian transport in beach settings the terrestrial laser scanner provides a suitable apparatus with which to accomplish this

effects of time dependent moisture content of surface sediments on aeolian transport rates across a beach wildwood new jersey u s a a one day field investigation on an unvegetated backbeach documents the importance of surface sediment drying to aeolian transport surface sediments were well sorted fine sand moisture content of samples taken in the moist areas on the backbeach varied from 2 9 to 9 2 per cent lack of dry sediment inhibited transport prior to 08 50 by 09 10 conspicuous streamers of dry sand moved across the moist surface barchan shaped bedforms 30 to 40 mm high and composed of dry sand moisture content 0 10 per cent formed where sand streamers converged the surface composed of dry sand increased from 5 per cent of the area of the backbeach at 09 50 to 90 per cent by 12 50 mean wind speeds were beetween 5 6 and 8 6 m s 1 at 6 m above the backbeach corresponding shear velocities were always above the entrainment threshold for dry sand and below the threshold for the moist sand on the backbeach measured rates of sand trapped by vertical cylindrical traps increased during the day relative to calculated rates the measured rate of sand trapped on the moist foreshore was higher than the rate trapped on the backbeach during the same interval indicating that the moist foreshore moisture content 18 per cent was an efficient transport surface for sediment delivered from the dry portion of the beach upwind measured rates of sand trapped show no clear relationship to shear velocities unless time dependent surface moisture content is considered results document conditions that describe transport across moist surfaces in terms of four stages including 1 entrainment of moist sediment from a moist surface 2 in situ drying of surface grains from a moist surface followed by transport across the surface 3 entrainment and transport of dry sediment from bedforms that have accumulated on the moist surface and 4 entrainment of sand from a dry upwind source and transport across a moist downwind surface 1997 john wiley sons ltd

the dynamic effects of moisture on the entrainment and transport of sand by wind abstract there is an increasing awareness of the influence of surface moisture on aeolian entrainment and transport of sediment existing wind tunnel studies have shown the impact of a limited range of moisture contents on entrainment thresholds but similar investigations are lacking in the field the research reported here investigated the influence of changes in surface moisture content on sand entrainment and transport on a meso tidal beach in anglesey north wales high frequency 1 hz wind velocities measured with hot wire anemometers were combined with grain impact data from a sensit monitor and mass flux measurements from a standard sand trap surface and near surface moisture contents were assessed gravimetrically from surface sand scrapes and also directly by using a thetaprobe critical threshold values for entrainment were specified using a modified form of the time fraction equivalence method stout j e zobeck t m 1996a establishing the threshold condition for soil movement in wind eroding fields proceedings of the international conference on air pollution from agricultural operations mwps c 3 kansas city 7 9 february 1996 pp 65 71 results indicate a time dependent change in dominant control of the sand transport system from moisture to wind speed dependent upon the moisture content of the surface sediment this interchange between controlling parameters on both entrainment and transport was very sensitive to prevailing moisture conditions and took place over a period of minutes to hours under conditions experienced in the experiments presented here the critical moisture threshold for sediment entrainment was determined to be between 4 and 6 higher than the 1 4 specified in previous wind tunnel experiments furthermore a moisture content of nearly 2 where moisture was adhered to transported sediment appeared to have little or no impact on the rate of sand flux

aeolian dune field geomorphology modulates the stabilization rate imposed by climate 1 the activity of inland aeolian dune fields is typically related to the external forcing imposed by climate active bare dunes are associated with windy and or arid settings and inactive vegetated dunes are associated with humid and or calm environments when a climate shifts the dune field reacts however the behavior rate and potential impact of diverse dune geomorphologies on these transitions are poorly understood here we use a numerical model to systematically investigate the influence of dune field geomorphology dune height organization and collisions on the time a dune field takes to stabilize to generate diverse initial un vegetated dune field geomorphologies under unidirectional winds we varied pre stabilization growth time and initial sediment thickness termed equivalent sediment thickness est following dune field development from a flat bed we introduced vegetation simulating a climate shift and transport vegetation feedbacks slowly stabilized the dune fields qualitatively very young and immature dune fields stabilized quickly whereas older dune fields took longer dune fields with greater est stabilized quicker than those with less est larger dunes stabilized quicker because of low celerity which facilitated higher vegetation growth rates extended stabilization times were associated with the extension of parabolic dunes dune dune collisions resulted in premature stabilization the frequency of collisions was related to dune spacing quantitatively comparing the distribution of deposition rates in a dune field to the deposition tolerance of vegetation provides a promising predictor of relative stabilization time dune fields with deposition rates dominantly above the deposition tolerance of vegetation advanced unimpeded and prolonged stabilization as parabolic dunes paleoenvironmental reconstructions or predictions of dune field activity should not assume that dune activity directly translates to climate considerable lags to stabilizing climate shifts may exist in unidirectional dune forms

fluvial aeolian interactions part i modern systems two modern fluvial aeolian depositional systems great sand dunes national monument colorado and the mojave river wash california are remarkably similar in spite of different climates sizes fluvial sediment textures and relative directions of aeolian and fluvial transport dune growth and migration and deflation of blowouts create 8 10 m of local relief in unflooded aeolian landscapes there are six prominent fluvial aeolian interactions 1 fluvial flow extends into the aeolian system until it is dammed by aeolian landforms 2 interdune areas overbank interdunes upstream of aeolian dams and alongside channels are flooded 3 water erodes dunes alongside channels and interdunes 4 flood waters deposit sediment in interdune areas 5 fluvially derived groundwater floods interdunes interdune playas 6 wind erodes fluvial sediment and redeposits it in the aeolian system unique and characteristic sediments are deposited in overbank interdunes and in interdune playas reflecting alternate fluvial and aeolian processes and rapidly changing flow and salinity conditions these fluvial aeolian interdune deposits are characterized by irregular concave up bases and flat upper surfaces containing mudcracks or evaporite cement characteristic low relief surfaces form in aeolian systems as an effect of flooding fluvial deposits are resistant to aeolian deflation aeolian sand is preserved when flood sediments are deposited around the bases of the dunes thus repetitive fluvial and aeolian aggradation tends to be stepwise as interdune floors are suddenly raised during floods the effects of flooding should be easy to recognize in ancient aeolianites even beyond the area covered with overbank muds

analysis of simultaneous gravity and tremor anomalies observed during the 2002 2003 etna eruption abstract in this paper we discuss the data collected by a large aperture array of broadband seismometers and a continuously recording gravity station during the 2002 2003 eruption of etna volcano italy seismic signals recorded during the eruption are dominated by volcanic tremor whose energy spans the 0 5 5 hz frequency band on three different occasions 12 november 19 20 november and 8 9 december 2002 we observed marked increases of the tremor amplitude up to a factor of 4 which occurred simultaneously with gravity decreases up to 30 gal the three concurrent gravity tremor anomalies last 6 to 12 hours and terminate with rapid up to 2 hours changes after which the signals return back to their original levels based on volcanological observations encompassing the simultaneous anomalies we infer that the accumulation of a gas cloud at some level in the conduit plexus feeding a new eruptive vent could have acted as a joint source this study highlights the potential of joint gravity seismological analyses to both investigate the internal dynamic of a volcano and to improve the confidence of volcanic hazard assessment

dune and dune field development on padre island texas with implications for interdune deposition and water table controlled accumulation abstract portions of the back island dune fields on padre island texas undergo seasonal destructive and constructive phases in which they are reduced to a nearly planar surface during the winter and then reform during the spring and summer initial depositional sites for dry sand that we observed were associated with roughness elements that caused a lowering of the transport capacity of the flow bedforms develop through a series of morphologic and dynamic stages 1 irregular patches of dry sand 2 wind ripple protodunes with leeward flow expansion 3 grainfall protodunes with a range from leeward flow expansion to flow separation 4 barchan dunes with grainflow and 5 crescentic ridges that characterize the mature field the survival and further development of protodunes and dunes is f vored by increased size a more advanced stage of development unidirectional and moderate wind and a plentiful sand supply these factors can be viewed as the result of the interrelationship of aspects of eolian transport the nature of leeward secondary airflow patterns and sand supply dune field ordering occurs by repeated merging splitting cannibalization and lateral linking of dunes on padre island and other areas of dunes that we studied flow conditions across portions of interdune flats favor the transport of dry loose sand from interdune flats onto the dunes so that dunes grow at the expense of interdune flats dry surface deposits are therefore unlikely to accumulate on interdune flats but rather to characterize interdune depressions that may represent the minimum d stance to which an interdune flat can be closed otherwise accumulations on interdune flats most commonly should be formed on wet or damp surfaces or occur associated with some mechanism that protects the deposits from deflation padre island dune fields represent a type of eolian system where accumulations of dunes and interdune flats occur during periods of a water table rise with bypassing and deflation occurring as the water table becomes static or falls respectively

modelling the formation of residual dune ridges behind barchan dunes in north east brazil residual dune ridges are often formed by vegetation growing along a line some distance upwind of the lower stoss slope of migrating dunes this process is common in areas where vegetation germinates along the edge of the water during the rainy period when the water level is higher and interdune areas are flooded the phenomenon occurs on a large scale in north east brazil because of the rise and fall in groundwater level at the end of the rainy season each residual dune ridge corresponds to the position of the dune during the wet period in each year therefore variations in the distance between these residual dune ridges could be used potentially to monitor climatic fluctuations in rainfall and wind to examine the potential use of these residual dune ridges for the reconstruction of past climatic fluctuations a model that simulates them under varying conditions of wind rainfall and evaporation rates was formulated the model was tested for sensitivity to climatic variability in north east brazil and validated against residual dune ridge displacements as measured in the field and from high spatial resolution satellite images based on the results it is concluded that residual dune ridges may not form in north east brazil in years which are exceptionally

importance of gravitational spreading in the tectonic and volcanic evolution of mount etna the interaction between gravity and thermal effects largely determines the structural and magmatic evolution of volcanic constructs at scales spanning several orders of magnitude from small cones to the oceanic crust1 3 although gravitational spreading is a direct consequence of this interaction and a fundamental process in volcano growth it is rarely recognized as such here we describe a striking example of this process at etna volcano in italy the volcano and its clay rich substratum are slowly spreading towards the east and south driven by gravity spreading produces extensional structures in the summit region and contpressional structures at the base of the volcano eastward movement of the volcanic edifice over a stationary magma supply may be the cause of an apparent westward migration of volcanic activity as gravitational spreading seems to control the location and magnitude of shallow seismicity and flank eruptions an appreciation of its effects could become an essential element of future volcanic hazard evaluation our model proposed here for etna may also be relevant to a reinterpretation of the geological history of a number of other volcanoes

temporal variations in gravity at mt etna italy associated with the 1989 and 1991 eruptions results are presented from 11 microgravity surveys on mt etna between 1987 and 1993 a period including the major 1989 and 1991 1993 flank eruptions and subordinate 1990 activity measurements were made with lacoste and romberg d 62 and d 157 gravity meters along a network around the volcano between 1000 and 1900 m a s l and since 1992 a n s summit profile gravity changes of as much as 200 gal were observed at scales from the size of the summit region to that of the volcano none was associated with significant changes in ground elevation the data show an increase in gravity for 2 years before the 1989 eruption the increase is attributed to the accumulation of magma 0 25 1 7 109 m3 in an elongate zone oriented nnw sse between 2 5 and 6 km below sea level part of this magma was injected into the volcanic pile to supply the 1989 and 1990 eruptions it also probably fed the start of the 1991 1993 eruption since this event was not preceded by significant gravity changes a large gravity increase up to 140 gal detected across the volcano between june and september 1992 is consistent with the arrival in the accumulation zone of 0 32 2 2 109 m3 of new magma thus favoring continued flank effusion until 1993 a large gravity decrease 200 gal in the summit region marked the closing stages of the 1991 1993 event and is associated with magma drainage from the upper levels of etna s central feeding system

fluvial aeolian interactions part ii ancient systems an understanding of fluvial aeolian deposition derived from modern case examples in a previous study is applied to the permian cutler formation and cedar mesa sandstone on the colorado plateau these formations supply an excellent three dimensional exposure of intertonguing fluvial and aeolian strata four distinct facies associations form the bulk of the cutler formation and cedar mesa sandstone 1 aeolian dune deposits 2 wet interdune deposits 3 fluvial channel deposits and 4 overbank interdune deposits in addition two distinctive types of erosion surfaces are found within the cutler formation and cedar mesa sandstone pebble to granule rich erosion surfaces aeolian deflation surfaces and flood surfaces fluvial and aeolian intertonguing result in extensive tabular sheets of aeolian sandstone separated by flood surfaces and overbank interdune deposits fluvial channels are associated with the deposits overlying flood surfaces and are incised into the underlying aeolian sandstones overbank interdune deposits and wet interdune deposits cover flood surfaces and intertongue with overlying aeolian sandstones the primary characteristics of ancient fluvial aeolian deposition are overbank interdune deposits and pronounced extensive erosion surfaces flood surfaces which are parallel to underlying fluvial sandstones and thus trend parallel to the palaeoslope and palaeohydrological gradient

post eruptive gravity changes from 1990 to 1996 at krafla volcano iceland the 1975 1984 krafla rifting episode was a major lava and dyke producing event associated with the release of extensional strain accumulated over more than 200 years at the divergent plate boundary in north iceland the present work provides a unique example of gravity decreases and increases sustained over a long period following a major eruptive episode at a rift volcano after height correction persistent net gravity decreases over the source of observed mogi type deflation occur with gravity increases occurring further away from this centre of deformation gravity decreases are interpreted in terms of drainage from a shallow magma chamber the net gravity decreases require that at least 4 1010 kg of magma must have been drained during the 6 year observation period assuming a density of 2700 kg m 3 this magma would occupy 1 5 107 m3 and by analogy with results obtained for kilauea this implies a magma chamber volume change of 4 1 106 m3 this is consistent with the chamber volume change deduced from ground deformation data assuming a poisson s ratio of 0 25 and a mogi source net gravity increases are more spatially extensive and are most likely caused by migration of the steam water interface and or closure of micro fractures in lavas above the magma chamber during post eruptive cooling and contraction we present a model for the krafla magma chamber in which a cooling contracting and draining magma body causes subsidence at the surface these results contrast with observations from the askja caldera iceland where post eruptive deflation has been shown to be accompanied by negligible net gravity changes above the mogi type source in the caldera long term post eruptive deflation and magma drainage have not been observed at subduction related volcanoes this may be a function of a difference in magma viscosity

barchan dunes stabilized under recent climate warming on the northern great plains we use light detection and ranging lidar imagery and optical stimulation luminescence dating to show that stable parabolic dunes on the canadian prairies originated from active barchan dunes 200 years ago residual dune ridges marking former lower stoss slope positions of migrating dunes record the transformation of barchan dunes to parabolic dunes between a d 1810 and 1880 parabolic dunes stabilized by ca a d 1910 with a few larger dunes and blowouts still active today a dry cool climate permitted sand transport to out compete vegetation stabilization and with lowered water tables maintain desert like barchan dunes with bare interdune sand sheets these findings explain why dune fields of the southern canadian prairies are currently more active than those of the united states great plains and the observation that dunes have stabilized under twentieth century warming our results emphasize the importance of viewing dune field responses to short term disturbances in the context of longer term system response particularly when relatively modest climatic changes can cause major shifts in dune activity

complex systems in aeolian geomorphology aeolian geomorphology provides a rich ground for investigating earth surface processes and landforms as complex systems sand transport by wind is a classic dissipative process withnon linear dynamics while dunefield evolution is a prototypical self organisation phenomenon bothofthesebroadareasofaeoliangeomorphologyarediscussedandanalysedinthecontextofcomplexityandasystems approach afeedbackloopanalysisoftheaeolianboundary layer flow sediment transport bedforminteractions basedoncontemporary physicalmodels revealsthatthesystemisfundamentallyunstable oratmostmeta stable andlikelytoexhibitchaoticbehaviour recent field experimental research on aeolian streamers and spatio temporal transport patterns however indicates that sand transport by wind may be wholly controlled by a self similar turbulence cascade in the boundary layer flow and that key aspects of transport event timeseriescanbefullyreproducedfromacombinationof self organised 1 fforcing motionthreshold andsaltationinertia theevolutionof various types of bare sand dunes and dune field patterns have been simulated successfully with self organising cellular automata that incorporateonlysimplifiedphysically basedinteractions rules becauseoftheirundefinedphysicalscale however itnotclearwhether they in fact simulate ripples bedforms or dunes landforms raising fundamental cross cutting questions regarding the difference between aeolian dunes impact ripples and subaqueous current ripples and dunes an extended cellular automaton ca model currently under development incorporates the effects of vegetation in the aeolian environment and is capable of simulating the development of nebkhas blow outs and parabolic coastal dunes preliminary results indicate the potential for establishing phase diagrams and attractor trajectories for vegetated aeolian dunescapes progress is limited however by a serious lack of appropriate concepts for quantifying meaningful state variables at the landscape scale state variables currently used in the bare sand models are far from capturing the rich 3d topography and patterns and are not sufficiently discriminative to distinguish different attractors the vegetationcomponentintheextendedmodel andindeedecogeomorphicsystemsingeneral poseevengraverchallengestoestablishing

intrusive mechanism of the 2002 ne rift eruption at mt etna italy inferred through continuous microgravity data and volcanological evidences 1 in october 2002 a new eruption began at etna lava flows were issued from two different fissure systems on the ne and s flanks of the volcano a continuous microgravity sequence acquired at a station on the n slope 2800 m a s l shows a marked decrease about 400 gal in less than one hour about 4 hours before lava was first emitted from the eruptive fissures along the ne rift this anomaly reversed soon afterward at a high rate the strong gravity decrease is interpreted as the opening by external forces of a shallow fracture system 1 km w of the gravity station magma from the central conduit entered the new fracture system passively and propagated through it towards lower portions of the ne rift both the arrangement of the new fracture system and the eruptive dynamics are in keeping with the inferred intrusive mechanism

surface moisture induced feedback in aeolian environments aeolian dune development is influenced by feedback between surface properties and sediment transport yet little is known about the larger scale temporal and spatial natures of this relationship surface moisture is particularly influential and is generally recognized in aeolian environments for its ability to increase the critical shear velocity required to entrain sediment in beach settings or alternatively to sustain vegetation and stabilize surfaces at a dune field scale however conceptual models and field work have alluded to its importance in protodune initiation while field observations infer that seasonal moisture input may contribute to residual dune ridge formation at the dune field scale this has the potential to reveal geomorphic adaptation to variations in climate and identify a recognizable signature in the rock record this article presents a simulation model that produces geomorphological features similar to field observations and is capable of examining the implications of surface and transport feedback at both scales results 1 reveal the control of surface moisture at different temporal scales 2 display complexity in the development of multiple spatial scales within a cellular automaton framework 3 highlight the importance of transient sand strips and sediment supply frequency in aeolian transport dynamics and protodune development and 4 explore the relationship and significance of feedback duration development time and bedform spatial scale in the development of incipient dunes this study illustrates the importance of considering geomorphic feedback when assessing the influence of surface moisture in aeolian process dominated systems

geochemical consequences of increased late cenozoic weathering rates and the global co2 balance since 100 ma large imbalances in the relative net co2 flux over the last 100 m y are obtained from independently derived estimates of co2 uptake by weathering and organic carbon burial and of co2 outgassing assumed proportional to the mean mid ocean ridge mor spreading and mantle plume production mpp rates increasing the river flux of ca mg p and c by 50 since 30 ma to parallel the proposed increase in the sr river flux needed to explain the sr isotopic evolution of seawater richter et al 1992 has a large impact on the global carbon cycle by reducing the excess net co2 imbalance in the late cenozoic co2 uptake is calculated by assuming that 19 of the ca river flux and 60 of the mg river flux are derived from weathering silicates and that mg is removed in the oceans by 1 1 molar exchange reactions with calcsilicates an increase in the mg river flux combined with an overall decrease in the mor spreading rate predicts as much as a factor of 2 increase in the seawater mg concentration since 100 ma the net organic carbon burial flux burial minus weathering largely reflects changes in the bulk carbonate 13c record and to a lesser extent variations in the net carbonate burial flux and mean 13c value of the carbonate weathering flux organic carbon burial efficiency is markedly less than that of p from the middle middle miocene to the present because of early diagenetic transfer of organic p to francolite and oxidation of organic carbon during reworking of margin sediments by sea level fluctuations the large co2 imbalance of the late cretaceous requires significantly less carbonate subduction or greater weathering rates a co2 balance can be achieved in the miocene by decreasing the proposed increase in river fluxes by up to half or by variably increasing the amount of carbonate subducted variations in shallow water carbonate burial and hence the global carbonate record are currently too poorly known to differentiate between the above possibilities the decrease in the excess co2 flux generally parallels the trend to cooler climate inferred from the 18o record but periods of large co2 imbalance generally precede 18o shifts by several million years

winter variability of aeolian sediment transport threshold on a cold climate dune abstract changes in surface conditions on cold climate aeolian dunes are pronounced during winter dunes are wet snow covered and or frozen for extended periods of time it is unknown how the critical wind speed for sediment transport threshold varies and how threshold may influence sediment transport predictions although the impact of surface conditions on threshold has been examined in synthetic experiments wind tunnels complicated feedbacks between threshold sand transport and surface conditions that occur in natural environments suggest that a ground based empirical approach may provide enhanced insight in this study we investigate threshold variability for 73 days during fall winter spring surface conditions from 18 november 2008 to 30 may 2009 in the bigstick sand hills of saskatchewan canada simultaneous measurements of threshold and atmospheric variables air temperature relative humidity solar radiation wind speed and direction were used to examine the extent to which surface erodibility was regulated by meteorology time lapse images of the surface from a co located camera were used for quality control and interpreting changes in the surface affecting threshold results reveal that threshold varied throughout the deployment 25 75 quartiles 6 92 8 28 m s 1 mean 7 79 m s 1 threshold variability was especially evident at two scales i event timescale and ii seasonal timescale event scale variability peaked during mid winter in one event the threshold varied by 6 m s 1 in 2 h with freezing and re freezing of the surface and relatively constant atmospheric conditions the causes of event scale variability are complex though qualitatively related to changes of wind direction antecedent meteorological conditions and vertical variations of grain scale bonding agents such as pore ice and moisture seasonal scale changes manifested as an increase in threshold during fall peaking in mid winter and decreasing in spring increased threshold in mid winter was linked to lower insolation and air temperature suggesting low erodibility due to the presence of pore ice correlation coefficients of threshold versus atmospheric variables yielded relatively weak correlations air temperature r 0 322 relative humidity r 0 388 solar radiation r 0 309 that also varied according to wind direction suggesting that the link between atmospheric conditions and surface erodibility on cold climate dunes is complex this contrasts with results from field based studies in warmer climates and controlled wind tunnel experiments which show a more direct link between atmospheric variables temperature and humidity and surface erodibility nevertheless our results do show a seasonal pattern of threshold that could be important for modeling cold climate aeolian sediment transport

stoss side mud drapes deposits of interdune pond margins arcuate mud drapes have been observed in an interdune area in southern tunisia they are believed to have been formed by deposition from ponded water around aeolian dunes during flood events they are preferentially preserved on the stoss side of the dunes as a result of subsequent dune migration and exhibit extensive evidence of animal tracks they are useful in illustrating dune interdune dynamics and recording the type of animals present

eolian dunes computer simulations and attractor interpretation a simple computer simulation algorithm for the transport of sand by wind produces forms resembling barchan crescentic ridge linear and star natural dune classes sand is moved as slabs composed of many grains that are picked up at random transported in a specified direction and deposited 1 with a probability that depends on the local presence or absence of sand or 2 in shadow zones in the lee of dunes the simulated dune fields are interpreted as complex systems with sand dune classes being dynamical attractors of these systems the evolution of dunes once formed becomes decoupled from the details of eolian sand transport