isolation of the global mlt thermal response to recurrent geomagnetic activity received 25 may 2009 revised 7 july 2009 accepted 13 july 2009 published 7 august 2009 1 recurrent geomagnetic activity at multi day periodicities near 5 5 7 and 9 day subharmonics of solar rotation have been associated with high speed solar wind stream variations and have recently been shown to induce congruent multi day periodic responses in the global upper atmosphere the ability to relate these periodicities in geomagnetic activity to global temperature observations from the timed saber instrument enables isolation of the global thermal response in the lower thermosphere and mesosphere due to geomagnetic activity observations from the timed saber instrument at altitudes below 120 km clearly show a zonally symmetric s 0 modulation in the global temperature field at a 9 day period known to result from recurrent geomagnetic activity forced by corotating interaction regions cirs the temporal variation of this zonally symmetric 9 day perturbation in temperature is strongly correlated to the 9 day variations in the kp geomagnetic activity index in 2005 with the most significant correlation occurring above 110 km and polewards of 40 latitude in both hemispheres the temperature amplitude at the 9 day period is in excess of 10 k above 110 km and increasing in amplitude poleward of 40 the phase of the temperature maximum associated with such disturbances is coherent with altitude and hemisphere with the disturbance occurring first near 110 km and then peaking at altitudes above and below this region hours later citation chang l c j p thayer j lei and s e palo 2009 isolation of the global mlt thermal response to recurrent geomagnetic activity geophys res lett 36 l15813 doi 10 1029 2009gl039305

quantitative assessment of the piping erosion susceptibility of loess derived soil horizons using the pinhole test abstract the pinhole test is an empirical test based on the qualitative evaluation of the dispersivity colloidal erodibility of compacted fined grained soils this paper evaluates the pinhole test device for the quantitative assessment of the susceptibility of soil horizons to piping assesses the effects of hydraulic head water quality antecedent soil moisture content and soil disturbance on the hydrological and erosion response during pipeflow and formulates recommendations for the application of the pinhole test to study piping erosion processes in total 255 pinhole test experiments were conducted the results obtained from disturbed soil samples ap horizon indicate i a significant positive linear increase in pipeflow discharge qw and sediment discharge qs with increasing hydraulic head ii no relationship between qw and antecedent soil moisture content asm but significant and negative relationship between qs and asm and iii significantly higher qs for distilled water than for tap water the use of disturbed soil samples resulted in significantly more rapid flow responses and lower sediment discharges than for undisturbed soil samples the pinhole test experiments performed on different loess derived soil horizons show that the plowed topsoil ap and the underlying clay enriched horizon bt are at least two times less susceptible to piping than the decalcified c1 and the calcareous horizons c2 this confirms field observations indicating that loess derived soil horizons are very susceptible for piping erosion especially when the c horizon crops out this study demonstrates that the pinhole test is suitable for assessing the susceptibility of soil horizons to piping in a quantitative way i e qw qs the time to outflow and the cross section of the pipe after the test we recommend the use of i two different hydraulic heads i e 180 and 1020 mm ii distilled water iii contrasting antecedent soil moisture contents of the soil samples to be tested and iv different soil sampling methods to investigate the effect of soil disturbance and particularly to obtain a better understanding of the sediment response during pipeflow

changes to the dispersive characteristics of soils along an evolutionary slope sequence in the vera badlands southeast spain implications for site stabilisation abstract in dispersive marls near vera badland gullies are eroding into a previously stable matorral covered landscape this relatively recent activity was probably triggered by minor climatic or land use change in this landscape calvo cases and harvey earth surface processes and landforms 21 1996 725 argued that new gully head slopes with differing aspect represent a sequence of progressive erosion using this interpretation as a basis slope surface materials were explored for evidence of material chemical stabilisation by sampling along profiles positioned centrally on those slopes the extent to which the inferred geomorphic sequence is paralleled by progressive changes in site geochemistry is considered crusts and subsoils differ significantly in terms of ph and sodium adsorption ratio sar but not calcium content the crust is thus distinctive but not calcic rather the ph differences suggest a process involving an organic agent probably algae slope position was an important discriminant taking sar alone differences between crusts and subsoils were not significant at the slope base but increased in significance with distance up the profile considering differences between the three profiles the middle profile had significantly higher sar values both in the crust and at depth than the other profiles whereas late slope subsoils and crusts taken alone are not dispersive sar the potential stabilisation of this type of badland soil and surface is finally considered whereas harvey harvey a m 1982 the role of piping in the development of badlands and gully systems in southeast spain in bryan r yair a eds badland geomorphology and piping geobooks norwich pp 317 335 argues that site morphology suggests that geomorphological instability increases through time the soil sequence suggests decreases in material dispersivity and consequently surface autostabilisation it is concluded that the concept of badland stabilisation needs further clarification

the causes of piping in a set of abandoned agricultural terraces in southeast spain this study aims to identify some of the factors contributing to the piping process in abandoned terraces in seven sites located in the murcia region southeast spain the local landscape has the appearance of badland geomorphology possessing deep valleys which until the 1970s were terraced and cultivated the terraces have now been abandoned to the piping process the research focuses on the relationship between the size and position of pipes and the physical and geochemistry properties of the local highly dispersive marl lithology and the extent to which the reworking of the materials for terrace cultivation has exacerbated piping erosion morphologically the terracing in the stream beds has resulted in a series of gentle benches separated by steeper risers with variable drop riser height a series of flat infiltration surfaces result and because the resculpting produces a reduced bulk density infill with enhanced throughflow infiltrating water is forced along steep hydraulic gradients to a low outfall at the base of the riser paralleling studies of land levelling and terrace abandonment in similar materials elsewhere piping in the study area is shown to be closely related to the physical and chemical characteristics of the materials its sodicity and dispersive character considerable differences in structure texture mineralogical composition and material s surface crust and subsoil geochemical properties emerged from site signature plots and these results suggest that agricultural processes affect the dispersive character of the crust materials presumably because agricultural activity increases the buffering effect of organic acids on the dispersed clay this is supported by the observation that on the one site that was levelled but not used for agriculture a stable organically distinct crust like the abandoned agricultural sites has not formed the changes to the material s aggregate stability and bulk density properties when terracing occurs is examined but insufficient evidence is available from the data collected to unpick the causes of aggregate stability changes in the study plots the way in which differences between crust and subsoil enhance infiltration is discussed and the role of the terrace drop in influencing hydraulic gradients and pipe development is illustrated a possible index to describe the relationship between evacuated material volumes and the controlling parameters discussed above is tested it is concluded that terracing which is intended as a conservation practice has in dispersive materials actually enhanced piping leading to the abandonment of farming

burial history and kinetic modeling for hydrocarbon generation part i the galo model this paper discusses the principles and applications of the galo computer program which generates numerical simulations of the evolution of a sedimentary basin the program calculates variations in the sedimentary bed thickness predicts the thermal regime in the sedimentary cover or in the basement and estimates the potential hydrocarbon yield of the source rocks alternative methods for determining the magnitude of tectonic subsidence of the basement surface within the framework of a local isostasy model are applied to provide a detailed model of the sequential tectonic thermal events involved in the development of the basin the program determines reaction parameters controlling the maturation of the organic matter in source rocks these parameters are based largely on the hydrocarbon pyrolysis yield data and the stage of maturation of the organic matter entered into the program neglecting this stage drastically displaces the reaction spectrum toward higher energies leading to considerable underestimation of hydrocarbon output

combining geomorphological mapping and near surface geophysics gpr and ert to study piping systems abstract this paper aims to provide a more comprehensive characterization of piping systems in mountainous areas under a temperate climate using geomorphological mapping and geophysical methods electrical resistivity tomography ert and ground penetrating radar gpr the significance of piping in gully formation and hillslope hydrology has been discussed for many years and most of the studies are based on surface investigations however it seems that most surface investigations underestimate this subsurface process therefore our purpose was to estimate the scale of piping activity based on both surface and subsurface investigations we used geophysical methods to detect the boundary of lateral water movement fostering pipe development and recognize the internal structure of the underlying materials the survey was carried out in the bere nica wyzna catchment in the bieszczady mountains eastern carpathians poland where pipes develop in cambisols at a mean depth of about 0 7 0 8 m the geophysical techniques that were used are shown to be successful in identifying pipes gpr data suggest that the density of piping systems is much larger than that detectible from surface observations alone pipe length can be 6 5 9 2 maximum 49 higher than what surface mapping suggests thus the significance of piping in hillslope hydrology and gully formation can be greater than previously assumed these results also draw attention to the scale of piping activity in the carpathians where this process has been neglected for many years the ert profiles reveal areas affected by piping as places of higher resistivity values which are an effect of a higher content of air filled pores due to higher soil porosity intense biological activity and well developed soil structure in addition the ert profiles show that the pipes in the study area develop at the soil bedrock interface probably above the layers of shales or mudstones which create a water restrictive layer our results illustrate the suitability and limitations of gpr and ert to study soil piping in general geophysical surveying is useful for gathering more information on pipe density potential pipe detection and recognition of the internal structure of materials underlying the pipes however the interpretation of radargrams and ert profiles should be always accompanied by detailed terrain mapping due to potential disturbances affecting geophysical profiles

improvements to the dispersion status of piped gully soils following reworking and stabilisation by vegetation the physical and chemical properties of sodic gully bank soil material deposited as in channel sedimentary structures below a pipe system in alkaline marls colorado usa were re analysed for their dispersive status using a new methodology the original samples were taken from in gully sedimentary structures with differing densities of established vegetation cover taking the more fully established vegetation densities to suggest increasing time since the soil samples were reworked by hydraulic processes the samples were assigned to a three point scale fresh no vegetation stabilised some vegetation and stabilised revegetated using detailed site descriptions these groups were found to be significantly different from each other in terms of the sar1 and ec2 the material s ph was also significantly different following revegetation the site signatures for each class suggest that a model of stabilisation for the soils following revegetation can be usefully described by this approach

longitudinal variations of positive dayside ionospheric storms related to recurrent geomagnetic storms 1 we have performed an analysis of case events and statistics of positive ionospheric storms in the dayside region of the equatorial ionization anomaly during recurrent geomagnetic storms rgss which dominate in geomagnetic and ionospheric conditions on the declining phase of solar activity in 2004 to 2008 it is shown that total electron content tec has a tendency to minimize before the beginning of rgss and to peak 3 to 4 days after i e on the rgs recovery phase produced by high intensity long duration continuous auroral activity the maximum of tec coincides with the maximum of solar wind velocity within high speed solar wind streams an analysis of electron content vertical profiles derived from two independent methods using ionosondes and constellation observing system for meteorology ionosphere and climate formosa satellite mission 3 radio occultation showed that in the maximum of an ionospheric storm on 28 march 2008 the f2 layer thickens nmf2 increases by 50 and hmf2 elevates by a few tens of kilometers the response of positive ionospheric storms to solar heliospheric and geomagnetic drivers reveals a prominent longitudinal asymmetry in the longitudinal range from 90 to 90 the solar illumination plays a major role and in the range from 90 to 120 the influence of heliospheric and geomagnetic drivers becomes significant the highest correlations of the tec enhancements with the heliospheric and geomagnetic drivers were found during december february r increased from 0 3 to 0 5 we speculate that the dynamics controlling this might result from an effect of solar zenith angle storm time effects of thermospheric o n2 enhancement and penetrating electric fields of interplanetary and magnetospheric origin

space time variability of denudation rates at the catchment and hillslope scales on the tyrrhenian side of central italy studies on denudation rates can provide insight into the influence of climate change tectonics and human activities on landscape evolution research performed in central italy has shown considerable spatial variability of denudation rates in the major river basins these studies have focused mainly on the tyrrhenian side of the italian peninsula where plio pleistocene marine deposits filling nw se elongated sedimentary basins have been uplifted during the quaternary up to several hundreds of meters above present sea level small sub catchments developed on clays are affected by sharp and or rounded edged badlands i e calanchi and biancane representing denudation hot spots in the present day morphoclimatic framework in this paper we analyze the relationships between indirectly estimated denudation rates at the catchment scale and field monitoring data at the hillslope scale we attempt to better understand and quantify all hillslope processes that contribute to seasonal variability of denudation to help with predicting the net input from hot spots to the overall estimated sediment yield at the basin outlets at the hillslope scale we discuss in particular the variability of denudation rates at calanchi and biancane badlands as a function of their different morphoevolution

hydro geomorphological consequences of the abandonment of agricultural terraces in the mediterranean region key controlling factors and landscape stability patterns abstract traditional cultivation terraces are one of the most ancient and conspicuous agricultural landscapes in mountain and hilly regions of the mediterranean basin spreading out from asia the first terraces in the mediterranean region date from the bronze age and the classical hellenic and roman periods reaching their greatest spatial extent during the eighteenth and nineteenth centuries under optimum management these systems contribute to the conservation of soil and water resources by increasing infiltration and decreasing sediment yield however traditional management and cultivation ceased on many terraced landscapes of the northern shore mediterranean countries during the twentieth century with variable results an extensive bibliographic review and meta analysis was carried out to explore the main effects of land abandonment of mediterranean agricultural terraces on local hydrological and geomorphological processes our results point to the development of vegetation cover and degradation of terraced structures e g walls terrace risers channels as the main critical factors controlling the hydrological behaviour i e runoff production and hydrological connectivity of abandoned terrace systems severe geomorphological problems in the form of intense surface erosion aggressive piping and gullying occurred under special climatic semi arid climate lithologic dispersive marls and structural high vertical hydraulic gradient conditions dense colonization by vegetation proved to be of major importance for controlling surface erosion vegetation however showed a limited capacity to control the activity of mass movements in most cases mass movements in the form of small soil slips primarily affected long abandoned terraces in hillslope concavities and valley bottom positions that concentrate surface and subsurface water fluxes and show recurrent soil saturation in humid terraced landscapes characterized by high hillslope gradients and terrace risers the most devastating effects of mass movements took place in the form of debris slips and terrace cascading landslides triggered by extreme rainfall a variety of management options non intervention stewardship of natural rewilding processes and active rehabilitation can be applied depending on vegetation development potential site hydro geomorphic vulnerability and local socio economic interests effective conservation approaches will be required to preserve the environmental socio cultural and historical values of these ancient anthropogenic landscapes

time and temperature in petroleum formation application of lopatin s method to petroleum exploration n v lopatin in the soviet union has developed a method for taking both time and temperature into account as factors in thermal maturation of kerogen lopatin s time temperature index of maturity tti values correlate with the thermal regimes corresponding to generation and preservation of hydrocarbons because such information is potentially of great interest for oil exploration a calibration and evaluation have been made of lopatin s method within the limitations of the data presently available the following statements can be made 1 the rate of the chemical reactions involved in thermal maturation of organic material appears to double with every 10 c 18 f rise in temperature 2 threshold values of lopatin s time temperature index of maturity tti are 15 onset of oil generation 75 peak oil generation 160 end oil generation 500 40 oil preservation deadline 1 000 50 oil preservation deadline 1 500 wet gas preservation deadline 65 000 dry gas preservation deadline 3 tti values calculated from lopatin reconstructions consistently agree with other maturation parameters commonly used by petroleum geochemists potential applications of lopatin s method for oil exploration include timing of oil generation calculation of volume of hydrocarbons generated within a basin and determination of economic deadlines

erosion in mediterranean landscapes changes and future challenges abstract intense erosion processes are widespread in the mediterranean region and include sheet wash erosion rilling gullying shallow landsliding and the development of large and active badlands in both subhumid and semi arid areas this review analyses the main environmental and human features related to soil erosion processes and the main factors that explain the extreme variability of factors influencing soil erosion particularly recent land use changes the importance of erosion in the mediterranean is related to the long history of human activity in a region characterized by low levels of annual precipitation the occurrence of intense rainstorms and long lasting droughts high evapotranspiration the presence of steep slopes and the occurrence of recent tectonic activity together with the recurrent use of fire overgrazing and farming these factors have resulted in a complex landscape in which intensification and abandonment wealth and poverty can co exist the changing conditions of national and international markets and the evolution of population pressure are now the main drivers explaining land use changes including farmland abandonment in mountain areas the expansion of some subsidized crops to marginal lands and the development of new terraces affected by landslides and intense soil erosion during extreme rainstorm events the occurrence of human related forest fires affecting thousands of hectares each year is a significant problem in both the northern and southern areas of the mediterranean basin here we highlight the rise of new scientific challenges in controlling the negative consequences of soil erosion in the mediterranean region 1 to reduce the effects and extent of forest fires and restructure the spatial organization of abandoned landscapes 2 to provide guidance for making the eu agricultural policy more adapted to the complexity and fragility of mediterranean environments 3 to develop field methods and models to improve the identification of runoff and sediment contributing areas 4 to contribute to the conservation of landscapes i e bench terraced fields having high cultural and productivity values 5 to improve knowledge of the hydrological and geomorphological functioning of badlands with the aim of reducing sediment yield and accessibility 6 to better understand the effect of climate change on soil erosion in the mediterranean region and 7 to improve quantitative information on long term soil erosion

agricultural land degradation by piping erosion in chaco plain northwestern argentina abstract soil piping has been pointed out as an important water erosion agent in a wide range of climatic regions it is responsible for high soil losses in loess derived soils the goal of this study is to evaluate the factors that are acting in the generation of piping processes and explain the mechanism of pipe collapse initiation the study was carried out in loess derived soils located in a rural area of the chaco plain between tucuman and santiago del estero provinces in northwestern argentina pipe collapse types were described and soil loss estimation was performed factors influencing the process were studied under six different categories i e physico chemical and soil mechanical soil mineralogical microstructural biological and land use properties in the study area pipes took place in agricultural fields principally in pastures with slope gradients between 1 and 3 soil pipe collapse occurred in the area as a consequence of sudden wetting of the collapsible soils during summer storms pipe collapse forms vertical pipes or macropores that provide pathways for runoff directly into the soil pipe network in addition tension cracks adjacent to pipe collapses can provide pathways for preferential flow from the surface to the soil pipe network with successive water infiltration the size of the pipes tends to increase and evolves to advanced stages of the process by internal erosion and eventually more pipe collapse blind gully formation is the final step of the piping process after the pipes roof collapse

morphometric and hydraulic geometry assessment of a gully in sw spain abstract gully erosion represents one of the most significant types of land degradation in the mediterranean areas giving place to important on and off site effects in this paper a second order gully located in sw spain is analyzed along the gully 28 cross sections were established and measured with a leica tcrm1102 laser total station approximately every 6 months from 2001 to 2007 the sections were located at variable distance placing them in areas where active erosion was evident in total 13 field measurements were carried out and the geometric characteristics of 28 cross sections were obtained morphometric analyses were carried out in both the main gully and a tributary reach by applying an empirical relationship between channel length and eroded volume morphometric variables of the gully sections were combined into two dimensionless groups and a morphological similarity between different linear erosion landforms rills ephemeral and permanent gullies was obtained then the coefficient of variation of the calculated volumes was used to compare the instability between the main gully and the tributary reach finally the hydraulic geometry of the gully was assessed by calibrating three empirical power equations which relate bankfull discharge with mean flow velocity cross sectional depth and width the hydraulic characterization of the main gully and the tributary reach was investigated for each field survey and a different behavior was detected the hydraulic analysis also demonstrated that higher values of discharge provide better predictions of flow velocity the size of the main and tributary gullies affects the discharge width relationship and that gully depth is the variable which can be predicted with the highest accuracy

processes that control mineral and element abundances in shales abstract a shale s composition can be used to infer physical chemical and biological processes that have acted on it over its life history and this knowledge is used to surmise conditions at the time when each process was active this review lists the most important processes that control shale mineral and element abundances during each of the five stages of its life history 1 during weathering transport and deposition the most important processes are chemical weathering hydraulic sorting and mixing adsorption reverse weathering and incorporation of organic matter and biominerals 2 during early diagenesis the most important processes are exchange across the water sediment interface compaction microbial respiration mineral transformations and concretion formation 3 during burial diagenesis the most important processes are compaction catagenesis and metagenesis and mineral transformations 4 during exhumation the most important processes are decompaction brine invasion groundwater penetration and microbial respiration 5 during weathering the most important processes are organic matter oxidation mineral oxidation and hydrolysis groundwater transport and disaggregation this classification of processes provides a way to envision how concurrent and consecutive processes that occurred over a shale s life history have affected its mineralogy and chemical composition

burial history and thermal evolution of the southern and western saharan basins synthesis and comparison with the eastern and northern saharan basins a quasi two dimensional analysis of burial history and thermal evolution was carried out along eight profiles for sedimentary sections in 24 wells in the southern and western saharan basins with the aid of one dimensional nonsteady numerical reconstructions the modeling shows that thermal activation during the permian triassic jurassic was most intense in the timimoun basin and the northern part of the ahnet and mouydir basins with a heat flow of about 70 80 mw m2 and a lithosphere thickness of 40 50 km activation was more moderate in the sbaa subbasin and reggane basin with a heat flow of approximately 63 67 mw m2 and a crustal thickness of 55 60 km these values are comparable to those for the eastern saharan basins where the intensity of the triassic activation decreased considerably from north to south the present day thermal regime of the ahnet and reggane basins and the central part of the timimoun basin is comparable to that of the illizi basin where the present day lithosphere is as thin as 25 km and recent volcanism has occurred moderate extension of the lithosphere with a maximum total amplitude of about 1 16 during the cenozoic is assumed in our modeling in the reggane basin and the southern half of the timimoun basin as well as in the central and eastern part of the illizi basin thermal analysis of the saharan basins has shown that the hercynian erosion can account for only a minor part of the jumps observed in the vitrinite profiles ro intrusive activity and the associated hydrothermal heat transfer during the triassic and early jurassic accurately explain the steplike character of maturation profiles in the saharan basins in particular the lower level of catagenesis and conservation of oil deposits in the relatively hot sbaa subbasin are the result of less intensive hydrothermal intrusive heating of the basin during the jurassic as compared to that in neighboring basins this could also be ascribed to a deeper location of the lithosphere and probably deeper intrusions in the sbaa subbasin this relatively moderate thermal regime of the sbaa subbasin might be connected to its structural position of as it was a shoulder to neighboring deeper depressions

quantitative study of piping processes in badland areas of the ebro basin ne spain abstract in the ebro basin piping is an ubiquitous erosion process in badland areas occurring in two main situations on slopes of exposed tertiary clays and in recently incised silty clay holocene valley fill sediments the quantitative importance of the main factors controlling piping processes in those conditions was obtained by statistical analysis based on multiple and stepwise regressions piping erosion is strongly related to a high sodium absorption ratio sar which favours clay dispersion however the statistical analysis indicates that the chemical characteristics and the physical chemical behaviour are a necessary condition but are not sufficient on their own to develop piping processes on the slopes piping is controlled by the physical and chemical properties of the material such as the dispersion index the granulometric fraction smaller than 4 m ph and crack density in the valley fill sediments piping is mainly controlled by the sulphate concentration in the water extract from saturated paste which is also associated with high sar values and the dispersion index in both geomorphic situations piping is always related to high crack density and high topographic gradient

origin and evolution of sarinena lake central ebro basin a piping based model abstract the origin and nature of the numerous lakes in the central ebro basin have been interpreted according to the prevailing arid or semiarid conditions the easily eroded materials and the solubility of the gypsum and or carbonate rich tertiary cenozoic substratum involving important dissolution karstic and or aeolian deflation however the origin of sarinena lake the largest in the central ebro basin remains unknown since the typical lake generating processes in the region are not applicable this work provides significant clues to the genesis and evolution of sarinena lake in a regional context the combination of geomorphological mapping and high resolution lidar data together with sedimentological observations the characterisation of soils and sediments around the lake and the application of high resolution geophysical techniques suggest that piping is the major genetic process driving the evolution of the sarinena depression and lake field evidence demonstrates that piping is at present the most important erosive process in the region generating significant collapse and surface lowering sarinena lake is located within a deep endorheic depression excavated from na rich tertiary materials this work hypothesises that once an early fluvially originated palustrine area had developed the progressive lowering of the regional water table linked to regional fluvial incision favoured the establishment of a hydrological gradient high enough to trigger piping processes within the claystones and siltstones underlying the original palustrine area the quaternary evolution of the sarinena lacustrine basin was then controlled by successive water table fluctuations linked to different phases of incision and alluvial deposition in the surrounding fluvial systems all the evidence supporting a piping related origin for this lake together with examples of lakes generated by similar processes in different contexts is used to propose a new genetic type of lacustrine depression generated by piping processes under favourable conditions

burial history and kinetic modeling for hydrocarbon generation part ii applying the galo model to saharan basins the galo basin evolution model described in makhous et al 1997 is applied to evaluate hydrocarbon generation and migration histories in several saharan basins three basins the oued el mya ghadames and illizi are located in the central and eastern parts of the saharan platform and are investigated in detail the ahnet mouydir timimoun reggane and other basins located in the southern and western parts of the platform are also studied the modeling results combined with geochemical data are used in a synthesis of the regional framework the thermal gradients in the ghadames and illizi basins are greater than those in the oued el mya basin this difference is attributed to differences in sedimentation and subsidence rates to less hercynian erosion and to fewer occurrences of evaporates in the akfadou region of the ghadames basin and in the mereksen region of the illizi basin in the southern and western parts of the illizi province the major subsidence occurred before hercynian uplift very moderate hercynian uplift in the ghadames and illizi basins did not involve a significant decrease of temperatures and organic matter maturation continued but at slower rates as a result the realization of hydrocarbon potential appears to be higher than would be expected favorable traps are located near subsided areas where the source shales particularly the devonian were not subjected to uplift and erosion in this respect the eastern sahara including the ghadames and illizi basins is a favored province analysis of the distribution of present day temperatures and paleotemperatures in the paleozoic sediments of the triassic province oued el mya ghadames trias and north illizi basins combined with effective source rock occurrences shows that favorable conditions for hydrocarbon generation during the paleozoic occurred essentially in the southern and southwestern parts of the province hydrocarbon generation during the mesozoic took place mainly in the central and northern parts of this province however some of the hydrocarbon accumulations in the northern and northeastern parts of oued el mya basin and in the northern and western ghadames basin were subsequently destroyed by the hercynian orogeny in the illizi basin ordovician and devonian structures are the most likely traps for hydrocarbons generated during the paleozoic whereas in the ghadames and oued el mya basins structures formed prior to the late cretaceous are preferentially favorable for oil accumulation gas accumulations are found in traps formed in the late cretaceous or later when source shales were buried to 3 3 3 5 km and more

variations in soil dispersivity across a gully head displaying shallow sub surface pipes and the role of shallow pipes in rill initiation a small bifurcating gully head displaying shallow pipe development was surveyed to explore how far three dimensional patterns of geochemistry and sediment size can be related to hydraulic gradients in the local marl bedrock almeria se spain the crust sub crust and parent materials were sampled every 20 cm across a 2 m by 3 m grid and then analysed for dispersive and granulometric characteristics spatial patterns of sodium adsoption ratio sar for each layer were plotted separately in situ material at depths of 5 10 cm was only weakly dispersive and the thin 0 2 cm depth crust is also found to be mostly non dispersive paralleling ndings from other eld sites in almeria however the signature relating sar to electrical conductivity for each layer shows that in places the immediate sub crust layer 2 5 cm is highly dispersive the pattern is not random rather the sar of this sub crust layer follows inferred hydraulic gradients the dispersive hot spots being located in the most incised part of the small gully exacerbating the erodibility of that position patterns of sediment particle size and sorting do not correlate with inferred hydraulic gradients but surface material is slightly siltier than the sub crust clay fraction increased with depth and sar is shown to have a weak inverse relationship to particle size this association between sar and the increased clay fractions in the lower layers supports the inference that massive pipe enlargement in the messinian rich unit is suppressed by sub surface swelling since a reduction in in ltration capacity fc with depth can be inferred from these results in ltrating water must be de ected into the already vulnerable sub crust layer during rainfall events explaining the development of shallow pipe forms at preferential depths it is concluded that calcium replaces sodium in the crust during leaching leaving a calcic crust and a sub crust that is sodic and prone to subsequent pipe enlargement rill morphology in these materials also suggests that rills develop from these pipes when pipe roofs collapse i e rill discontinuity bridges steep headwalls and rills with excessively high depth to width ratios copyright 2004 john wiley sons ltd

characteristics and controlling factors of bank gullies in two semi arid mediterranean environments abstract bank gullies are gullies that are formed due to a height drop caused by a terrace or a river bank which develop by headward retreat in erodible hillslopes this study aims i to investigate the morphology of actively eroding bank gullies i e geometrical characteristics resulting from past erosion and active erosion processes shaping the gully and ii to find relationships with environmental site characteristics such as topographical parameters material properties and climate the ultimate goal is to identify the most important controlling factors of past and present bank gully erosion fifty five active bank gullies formed in different lithologies by various erosion processes have been selected in the guadalentin basin and the surroundings of guadix southeast spain for each bank gully site geometrical and topographical parameters of both the channel and the drainage basin were measured erosion features indicating activity at the gully head such as tension cracks plunge pools undercutting fluting piping and rill or sheet erosion on sloping side walls were mapped and samples were taken from distinct lithological layers that were considered to influence the type and intensity of erosion processes a relationship could be shown between the presence of piping and fluting and a number of material characteristics including particle size distribution dispersion behaviour and electrical conductivity on the other hand lithology appeared not to be a differentiating factor on gully development in the long run as expressed by the total eroded volume v this parameter was most strongly related to the drainage basin area in which the entire bank gully had been formed a o explaining 66 of the variance the relationship is v 1 75 a o 0 59 no significant difference was found between regression lines through sub datasets of different soil textural classes finally multiple regression was used to include both topographical parameters and material characteristics in an explanatory and or predictive equation for the total eroded bank gully volume the results of the analyses using the entire dataset including the sites in the guadalentin as well as in the guadix area have been compared with the results for the separate study areas differences are not only related to topographical and lithological characteristics but may also be the consequence of a different climate in the two areas

lower silurian hot shales in north africa and arabia regional distribution and depositional model abstract lowermost silurian organic rich hot shales are the origin of 80 90 of palaeozoic sourced hydrocarbons in north africa and also played a major role in petroleum generation on the arabian peninsula in most cases the shales were deposited directly above upper ordovician peri glacial sandstones during the initial early silurian transgression that was a result of the melting of the late ordovician icecap deposition of the main organic rich shale unit in the north african arabian region was restricted to the earliest silurian rhuddanian stage acuminatus atavus and probably early cyphus graptolite biozones during this short period 1 2 m y a favourable combination of factors existed which led to the development of exceptionally strong oxygen deficiency in the area in most countries of the study area the post rhuddanian silurian shales are organically lean and have not contributed to petroleum generation the distribution and thickness of the basal silurian hot shales have been mapped in detail for the whole north african region using logs from some 300 exploration wells in libya tunisia algeria and morocco in addition all relevant accessible published and unpublished surface and subsurface data of the lower silurian shales in north africa and arabia have been reviewed including sedimentological biostratigraphic and organic geochemical data the lowermost silurian hot shales of northern gondwana are laterally discontinuous and their distribution and thickness were controlled by the early silurian palaeorelief which was shaped mainly by glacial processes of the late ordovician ice age and by pan african and infracambrian compressional and extensional tectonism the thickest and areally most extensive basal silurian organic rich shales in north africa occur in algeria tunisia and western libya while on the arabian peninsula they are most prolific in saudi arabia oman jordan and iraq the hot shales were not deposited in egypt which was a large palaeohigh at that time the depositional model presented may help in better understanding the source potential of the basal silurian shales in less explored regions of north africa and arabia including morocco northern niger and the kufra basin in southeast libya

morphology and development of selected badlands in southeast spain implications of climatic change four areas were selected to represent a range of processes characteristic of badland surfaces in southeast spain petrer and monnegre in alicante vera and tabernas in almeria at petrer rilling and swelling processes produce a deeply cracked surface drained by a finely textured network of shallow rills at monnegre piping and rilling are differentially developed on slopes ultimately controlled by basal incision at vera aspect controlled lichen and vegetation cover produce a sequence of badland development within which the relative importance of piping mass movement and rilling varies through the sequence at tabernas simple overland flow is the dominant process but aspect influences rill network density and badland evolution the factors controlling badland development can be grouped into those related to gross morphology to surface cover and runoff generation and to material properties these factors are effective over varying timescales implying that morphological response times differ among the selected badlands

the role of some site geochemical processes in the development and stabilisation of three badland sites in almeria southern spain samples of both surface and subsurface soils were collected on various surfaces in three badland areas of differing ages tabernas vera and mocatan in almeria province southern spain data were explored with the aim of identifying any diagnostic geochemical relationships between site ec ph sediment size and sar which might constitute typical signatures for site materials with some success data for the three sites are further used to explore the hypothesis that changes in site geochemistry through time are involved in badland stabilisation it was found that 1 the physico chemical properties of the three sites can be differentiated by the functional relationship between ec and sar and this may represent a useful tool in characterising sites where piping predominates 2 there is some equivocal evidence that sediment size distribution may play an additional role in site diagnosis and evolution and 3 surfaces appear to lose sodium over time the suggestion being that sodium is either progressively buffered by calcium during leaching or exchanges with hydrogen on the cation exchange sites under a vegetation cover since other research suggests that smectite can also relocate down the profile on some marl sites reducing hydraulic conductivity and suppressing pipes we argue that the surface at tabernas may be capable of long term autostabilisation in which piping intensity progressively reduces however this possibility really applies only to fine grained densely structured materials and evidence from the silty triassic rich unit in the mocatan basin suggests that without a high clay content piping may be expected to increase through time from this standpoint contemporary badland morphology at mocatan does not represent an early stage of the forms seen in vera and tabernas

identification characterisation and analysis of the oltrepo pavese calanchi in the northern apennines italy abstract badlands are characteristic erosional forms distributed along the entire apennines in the italian context badland areas are called calanchi the plural of the word calanco in this paper we present the first calanchi inventory map of the oltrepo pavese area northern apennines italy in total 263 calanchi were mapped using remote sensing techniques like orthophotos google earth images as well as field recognition moreover calanchi were characterised from a geomorphologic geologic and a morphometric point of view the calanchi of the oltrepo pavese have been categorised in two geomorphological classes based on process related morphologies in the study area calanchi mainly occur in soft sedimentary bedrock materials such as melanges marls claystones and interstratified rocks the results show that calanchi formations are often related to faults and tectonic lineaments present in the study area moreover we analyse a 5 m cell size digital terrain model to detect correlations between calanchi and morphometric indices the calanchi defined and categorised for the first time in the study area show typical morphometric characteristics of apennine calanchi forms and features in particular they occur on concave south facing slopes on soft bedrock formations finally a multitemporal air photo interpretation over a 40 years period indicated a general decrease in calanchi areas the area reduction is mainly correlated to intensive land use changes combined with variations of precipitation pattern the revegetation trend was also confirmed by ndvi analysis based on landsat satellites images the calanchi were digitized and stored in a gis database providing the information for future quantitative modelling assessments

testing gis morphometric analysis of some sicilian badlands abstract calanchi badlands are erosion landforms characterized by areas with scarce or absent vegetation steep slopes knife edge divides and high erosion rates they are originated by a combination of morphogenetic processes partly similar to those shaping bigger fluvial landforms and therefore can be considered as field laboratories this paper presents the results of an investigation carried out in two badland sites located in sicily where the geometry of 25 calanchi has been characterized using digital elevation models having a mesh size equal to 2 m for each landform a power length volume relationship is established this relationship demonstrates that length of calanchi channels can be used as a reliable predictor of eroded volume as already verified for smaller linear erosion landforms such as rills ephemeral and permanent gullies moreover length volume width and depth of calanchi are combined into two dimensionless groups allowing to establish a morphological similarity between rills ephemeral permanent gullies and the studied badlands furthermore the hack s law which relates channel length to drainage basin area is applied to the 25 calanchi basins obtaining an exponent of this power law smaller than 0 5 this result indicates that basins do not become necessarily more elongate with increasing size finally the relationships between maximum length and width of the landforms are analyzed demonstrating that calanchi basins become wider and not longer and narrower when evolving and increasing their size

long and short term evolution of several mediterranean denudation hot spots the role of rainfall variations and human impact abstract severe slope denudation is one of the most important environmental problems in the mediterranean region in particular badlands are widespread in central italy as a result of extensive clayey outcrops current climatic conditions and rapid quaternary uplift human activity may significantly affect the development and evolution of these denudation hot spots especially through changes in land use this work is focused on a badland site that has developed over the last 30 years on a gently sloping area of cropland in central italy the site named bargiano underwent cropland abandonment in 1980 and was selected to evaluate the effects of external forcing such as human impact and rainfall variations on the development of water erosion processes the remnants of the 1980 cropland surface and the present eroded surface were sampled using differential global positioning system techniques to perform a volumetric estimation of the eroded material and to calculate the average erosion rate for fairly large time spans the dgps survey was coupled with a 2 year monitoring with erosion pins in the region which permitted comparisons between long and short term average erosion rates in addition the analysis of the rainfall series recorded at the orvieto pluviometric station allowed us to assess and evaluate the role of critical rainfall events on denudation intensity finally a further comparison of the measured and estimated erosion rates from the bargiano site with the data recorded at other long lasting monitoring stations that are set up in certain key areas of central italy the tevere river and ombrone river basins revealed that the bargiano experimental hillslope experienced considerably higher erosion rates than were noted at the other sites our investigations demonstrated that cropland abandonment caused an increase in the erosion rate relative to what happened in natural areas characterized by similar physiographic conditions this finding is consistent with previously reported results for other badlands found in the mediterranean area moreover the results obtained suggest that after the abandonment of its cropland the bargiano site evolved in a cyclical manner that was driven by intrinsic thresholds to a greater extent than it was affected by external climatic changes

the iapetus model a plate tectonic concept for the variscan belt of europe abstract a plate tectonic model is presented explaining the evolution of the variscan belt of europe it regards the iapetus ocean and its branch the tornquist sea as the only ocean involved in the caledonian variscan and alleghenian mega orogen the iapetus and its marginal basins disappeared through oblique subduction and collision in the following sequence 1 1 northeastern iapetus including the tornquist sea caledonian orogeny 2 2 central iapetus acadian orogeny 3 3 adjacent marginal basins variscan orogeny and 4 4 southwestern iapetus alleghenian orogeny the area of the variscides was part of the continental margin of gondwana made up of ridges and ensialic basins no ocean lay within the variscan area during the palaeozoic although patches of oceanic crust probably existed in rift basins e g the lizard ophiolite after the silurian early devonian closure of northwestern and central iapetus the variscan area was surrounded by cratons on three sides in a manner similar to that around the modern mediterranean sea the subsequent variscan orogeny was essentially an ensialic thrusting and folding induced by a further approach of gondwana toward laurentia after the variscan collision gondwana rotated clockwise to the west by moving along a strike slip zone this rotation during the carboniferous opened the palaeo tethys in the east and caused the alleghenian collision in the west the middle ordovician to permian palaeogeography is presented on a series of maps modelling tectonic displacement and plate motions avalonia is interpreted as the ordovician volcanic island arc of gondwana separated from mainland gondwana by an oceanic gulf or a back arc basin the iberian arc may have originated by a continental escape of iberia from the center of collision into the oceanic gulf the variscan austro alpine and southern alpine units are today located near their earliest early carboniferous position

features and evolution of slip structures in badlands areas se spain abstract slips are little known mud coated structures several centimeters thick produced by gravity driven flows on free vertical surfaces we have differentiated a sequence formed by three main morphologies mud drips slips and pseudo stalactites this study located in the badlands of the guadix and baza basins se spain suggests that formation of muddy morphologies on subvertical walls is determined by the physico chemical characteristics of colloidal suspensions slurries related to rainy periods and does not indicate any substrate decay multiple braided microchannels internally structured like irregular book pages are commonly found each formed by mudflows during rainy episodes these morphologies constitute a temporary sink of fine erosive materials they consist of scarcely sorted mixtures of heterogeneous matter of a detrital cohesive nature with low clay contents which inherit the features of the parent materials the current semiarid environmental conditions appear to favor conservation rather than development the differences observed in the slips of the guadix and baza basins can be determined by the different geomorphological evolution of the two basins and to a lesser extent by the properties of the slurries that fed the slips

physical chemical and mineralogical properties of parent materials and their relationship with the morphology of badlands abstract badlands are present throughout the world but not everywhere do they have the same morphology the main objective of this study is to try to understand why these different morphologies occur by analysing the physical chemical and mineralogical characteristics of the parental material in which badlands have developed the study was carried out in three areas of the region of murcia south east spain abanilla mula and gebas several analyses were carried out i field analysis orientation slope length and shape of the slope presence and characteristics of the rills vegetation vegetation pedestals exposed roots stoniness physical and biological crusts saline efflorescence cracks popcorn piping processes sedimentation areas and mass movements ii physical chemical analysis of the soils colour texture aggregate stability bulk density organic matter ph electrical conductivity cations and cation exchange capacity total or equivalent calcium carbonate sodium absorption ratio and exchangeable sodium percentage and iii mineralogical analysis the results of the analyses reveal how the rounded shapes in the badlands that appear in abanilla have significant differences with respect to the angled shapes of mula and gebas which could explain the different morphologies in general abanilla has very small amount of sand higher bulk density small amount of organic matter lower cation exchange capacity and very high salinity as shown in the values of electrical conductivity sodio sar and esp on the other hand similarities were found between the badlands of the region of murcia with the calanchi angled shapes and biancane rounded shapes of italy

controls on the spatial distribution of natural pipe outlets in heavily degraded blanket peat abstract natural soil pipes are recognised as a common geomorphological feature in many peatlands and they can discharge large quantities of water and sediment however little is known about their morphological characteristics in heavily degraded peat systems this paper presents a survey of pipe outlets in which the frequency and extent of natural soil pipes are measured across a heavily gullied blanket peat catchment in the peak district of northern england over a stream length of 7 71 km we determined the occurrence and size of 346 pipe outlets and found a mean frequency of 22 8 km 1 gully bank topographic position was an important control on the size and depth of pipe outlets aspect had a large influence on pipe outlet frequency with southwest and west facing gully banks hosting more than 43 of identified pipe outlets pipe outlets on streambanks with signs of headward retreat were significantly larger and closer to the peat surface compared to pipe outlets that issued onto uniform streambank edges we suggest that larger pipe frequencies are observed on gully banks that are more susceptible to desiccation cracking and propose that future peatland restoration works could prioritise mitigating against pipe formation by revegetating and reprofiling south and west facing gully banks

assessment of grass root effects on soil piping in sandy soils using the pinhole test abstract soil piping is an important land degradation process that occurs in a wide range of environments despite an increasing number of studies on this type of subsurface erosion the impact of vegetation on piping erosion is still unclear it can be hypothesized that vegetation and in particular plant roots may reduce piping susceptibility of soils because roots of vegetation also control concentrated flow erosion rates or shallow mass movements therefore this paper aims to assess the impact of grass roots on piping erosion susceptibility of a sandy soil the pinhole test was used as it provides quantitative data on pipeflow discharge sediment concentration and sediment discharge tests were conducted at different hydraulic heads i e 50 mm 180 mm 380 mm and 1020 mm results showed that the hydraulic head was positively correlated with pipeflow discharge sediment concentration and sediment discharge while the presence of grass roots expressed as root density was negatively correlated with these pipeflow characteristics smaller sediment concentrations and sediment discharges were observed in root permeated samples compared to root free samples when root density exceeds 0 5 kg m 3 piping erosion rates decreased by 50 compared to root free soil samples moreover if grass roots are present the positive correlation between hydraulic head and both sediment discharge and sediment concentration is less pronounced demonstrating that grass roots become more effective in reducing piping erosion rates at larger hydraulic heads overall this study demonstrates that grass roots are quite efficient in reducing piping erosion rates in sandy soils even at high hydraulic head 1 m as such grass roots may therefore be used to efficiently control piping erosion rates in topsoils

geomorphic threshold conditions for gully erosion in southwestern iran boushehr samal watershed globally a large amount of research has been dedicated to furthering our understanding of the factors and mechanisms affecting gully erosion however despite the importance of gully erosion in arid and semi arid regions of iran there has been no comprehensive study of the geomorphic threshold conditions and factors influencing gully initiation the aim of this article is to investigate the gullying processes and threshold conditions of permanent gullies in an arid region of iran based upon examination of the slope area s a relationship the data were collected through field and laboratory studies as well as digital elevation model dem analyses in total 97 active headcuts were identified across the three study sites and classified based on dominant initiation process including piping landsliding and overland flow soil properties including ec sar and soil texture as well as landuse practices were found to be the major factors initiating piping and bank gullies all gullies initiated by landsliding and seepage processes were found to be located in steep areas 28 40 slope with their distribution further influenced by the lithology and presence of a cohesionless sand layer within the soil profile an inverse relationship between upslope area a and local slope s in which the and coefficients varied was further investigated based on the dominant gullying process and land use gullies occurring in the rangelands that were dominated by overland flow had the strongest relationship while landsliding dominated gullies did not have a statistically significant s a relationship in comparison to theoretical and literature based relationships for gully initiation relatively low values for were obtained 0 182 to 0 266 possibly influenced by the presence of seepage and subsurface processes in many gullies however this is consistent with other studies in arid regions and may reflect greater potential for gullying in arid zones due to low vegetation cover and high variation in rainfall in addition the soil attributes together with land use practices influenced gully initiation thresholds application of the solved s a relation for predicting vulnerable areas to gullying indicates that it is possible to predict the location of gullies with an acceptable level of accuracy however other environmental factors should be integrated with the s a relationship to more accurately identify the location of permanent gullies in arid regions

plate tectonics and cratonal geology in northeast africa egypt sudan the stratigraphical interpretation of the strata of nubia allows for the first time in connection with structural petrological and sedimentological investigations to reconstruct the geological development of this cratonal area after cratonization during the panafrican event extensional trends in wsw ene direction caused a structural relief striking nnw sse the collision between gondwana and the northern continents during the carboniferous resulted in the uplifting of large parts of the northeast african plate and was accompanied by more or less east west striking faults and magmatic intrusions erosion of paleozoic sediments in middle and southern egypt and reversal of the main drainage direction was the consequence this caused deposition of karroo type strata in northern sudan including glacial deposits at the base along the sudanes egyptian border

burial history and thermal evolution of the northern and eastern saharan basins the numerical one dimensional reconstruction of the burial history and thermal evolution of the sedimentary section and basement was conducted for 32 wells in the east algerian basins with the help of the galo basin modeling system these reconstructions allowed the performance of a quasi two dimensional analysis of the burial history of the basins changes in rock temperatures the lithosphere thickness and maturation conditions of organic matter during basin development along the four profiles crossing the study region the modeling assumed that the highest thermal activation in the history of the saharan basins with the heat flow more than 100 mw m2 and the thinnest lithosphere on the order of 25 35 km took place during the late carboniferous to permian in the dahar and oued el mya basins the uplift responsible for this activation caused erosion of 2000 3000 m of ordovician to lower carboniferous strata the ghadames and illizi basins were subjected at the same time to more moderate erosion and thermal activation with heat flow less than 75 mw m2 in the triassic cretaceous interval maximum subsidence occurred in the northern areas which were characterized by maximal thermal activation and the thinnest lithosphere in the permian at present the situation is opposite to that in the permian the highest thermal regime occurs in the southern areas of the study region and especially in the illizi basin where heat flow reaches and even exceeds 100 mw m2 and the thickness of the lithosphere decreases as much as 30 km the modeling also assumes stretching of the lithosphere in the northeastern and central parts of the illizi basin with maximal amplitude of about 1 16 during the cenozoic the analysis shows that the hercynian erosion could account for only a few of the abrupt changes in vitrinite profiles in the saharan basins and that triassic and later intrusive activity and associated hydrothermal heat transfer accurately explain the steplike character of maturation profiles

impact of lithology and soil properties on abandoned dryland terraces during the early stages of soil erosion by water in south east spain soil erosion by water in abandoned dry terraces is one of the most important environmental problems in semiarid areas enhancing biological degradation and reducing possible resources that can be obtained however little is known about the effects of the types of lithology and soil properties on the early stages of soil erosion therefore the main aim of this research was to assess the effect of different lithologies marls limestones and metamorphic phyllites schists and greywackes materials and soil properties on the early stages of soil erosion by water in abandoned dry terraces compared with similar terraces still in agricultural use soil analyses texture aggregate stability and bulk density and 22 rainfall simulations were carried out under dry conditions during the experiments local inclination vegetation and stone cover total organic matter and antecedent soil moisture were also quantified the results showed that the highest soil loss 41 41 g m2 in cultivated plots and 17 05 g m2 in the abandoned plots and runoff 3 79 l m2 in the abandoned plot occurred on marl substrata marls also showed the shallowest infiltration front 9 cm and lowest infiltration rate 4 3 cm min limestones and especially metamorphic areas showed a lower degree of soil erosion higher infiltration rates and deeper infiltration fronts

the effect of some watershed soil characteristics and morphometric factors on the relationship between the gully volume and length in fars province iran abstract a survey consisting of 146 first order gullies selected from five sites with different land use soil and watershed properties was carried out to estimate the parameters of the empirical power function in order to describe the relationship between the gully volume and length in fars province iran subsequently the gullies were clustered into seven groups a to g based on nine morphometric factors the linearized functions were fitted to the natural logarithms of the volume and length in each group and the parameters a and b were determined the obtained a and b parameters are in the ranges of 1 0 10 8 and 0 8 1 4 respectively comparison of a and b parameters in each group with the mean of nine factors and the mean soil watershed and land use characteristics in each group showed that the gully volume and average cross section are correlated with the gully depths in different sections and the gully head slopes also it was shown that the parameters of fitted functions to the plots of gully volumes versus gully lengths are proportional to width at the gully heads the gully widths at the top and bottom of the five meter sections are correlated with the average upstream watershed area of the gullies

badlands denudation hot spots the role of parent material properties on geomorphic processes in 20 years monitored sites of southern tuscany italy abstract some monitoring stations have been recording for 20 years the geomorphic processes acting on calanchi and biancane badlands located in the tyrrhenian side of central italy field monitoring was aimed at studying the dynamics of surface processes such as sheet rill and gully erosion shallow landsliding piping and tunneling considering their space time variability as a consequence of both natural factors and human pressure this paper shows the results of grain size geochemical and mineralogical composition of parent materials from upper orcia valley sites southern tuscany to further elucidate the role of their properties on processes acting on both bare and vegetated surfaces parent materials properties are discussed with respect to the initiation and development of different badlands processes in particular clay dispersivity at different depths in the sample sites is examined as a well known controlling factor of accelerated erosion thus providing some interesting clues for understanding the spatial variability of denudation rates in the considered badlands sites

a new empirical model for estimating calanchi erosion in sicily italy abstract calanchi plural of calanco are typical badland landforms of the italian landscape they consist of dense networks of v shaped valleys with a sparse or absent vegetation cover which frequently develop on unconsolidated or poorly consolidated clayey deposits in this paper the dimensional analysis and the incomplete self similarity theory were used to deduce a model relating the volume of sediments eroded from the calanchi area to a set of geometric attributes of their tributary areas the morphometric characteristics of 209 calanchi basins were used to calibrate and validate the model the predictive skill of the model was assessed by calculating the mean square error and the nash sutcliffe model efficiency coefficient the model was found to provide a reliable prediction of eroded volume from basins entirely covered by calanchi landforms as well as from basins only partially affected by badland erosion processes furthermore as the residuals between the calculated and the measured volume of the eroded material are normally distributed the deterministic model may be considered complete meaning that no other variables are necessary to explain the studied physical process in other words the model is able to predict erosion volume in calanchi landforms from a deterministic point of view

late archaic wells on the gila river indian community arizona eight prehistoric wells dug to a depth of 2 m below the modern ground surface were found in the alluvial sediments of mcclellan wash on gila river indian community in southern arizona charcoal from the sediments filling the wells yielded radiocarbon ages of 1000 b c the time in which wells were dug coincides with a period of general regional aridity and high enso activity in the american southwest digging to access water may have occurred in response to period s of resource uncertainty or as a logistical activity that engaged increasingly resource tethered late archaic early agricultural populations these activities laid the foundation for agricultural practices that eventually became the dominant mode of subsistence in the low lying areas of the sonoran desert