the measurement and modelling of rill erosion at angle of repose slopes in mine spoil the process of rill erosion causes significant amounts of sediment to be moved in both undisturbed and disturbed environments and can be a significant issue for agriculture as well as mining lands rills also often develop very quickly from a single rainfall event to a season and can develop into gullies if sufficient runoff is available to continue their development this study examines the ability of a terrestrial laser scanner to quantify rills that have developed on fresh and homogeneous mine spoil on an angle of repose slope it also examines the ability of the siberia erosion model to simulate the rill s spatial and temporal behaviour while there has been considerable work done examining rill erosion on rehabilitated mine sites and agricultural fields little work has been done to examine rill development at angle of repose sites results show that while the overall hillslope morphology was captured by the laser scanner with the morphology of the rills being broadly captured the characteristics of the rills were not well defined the digital elevation model created by the laser scanner failed to capture the rill thalwegs and tops of the banks therefore delineating a series of ill defined longitudinal downslope depressions these results demonstrate that an even greater density of points is needed to capture sufficient rill morphology nevertheless siberia simulations of the hillslope demonstrated that the model was able to capture rill behaviour in both space and time when correct model parameters were used this result provides confidence in the siberia model and its parameterization the results demonstrate the sensitivity of the model to changes in parameters and the importance of the calibration process copyright 2007 john wiley sons ltd

iron magnesium order disorder in an orthopyroxene crystal from the johnstown meteorite abstract equilibrium reversals of fe 2 mg distribution between the m1 and m2 sites of an orthopyroxene from the johnstown meteorite were achieved at several temperatures between 700 and 1000 c one single crystal was used for the whole thermal treatment and for collecting all the x ray data after quenching the intracrystalline ion exchange for the bulk chemical composition mg 1 453 fe 0 441 cr 0 024 ca 0 054 mn 0 015 fe 0 005 ti 0 003 al 0 005 si 1 960 al 0 040 o 6 is given by ln k d 3027 39 t k 0 872 0 013 where k d is the distribution coefficient for the reaction fe m2 2 mg m1 mg m2 fe m1 2 a transmission electron microscopy tem study of part of the crystal showed the presence of very thin augite lamellae and guinier preston zones indicating a relatively rapid cooling of the host rock at temperatures close to 1000 c the new temperature scale yields a relatively high quenching temperature of 379 8 c for the pyroxene which appears consistent with a rapid cooling estimated few degrees per hundred years of a magmatic cumulate excavated by an impact on its parental body

nitrate fluctuations at the water table implications for recharge processes and solute transport in the chalk aquifer this study investigates fluctuations in nitrate concentration at the water table to improve understanding of unsaturated zone processes in the chalk aquifer sampling was conducted using a novel multi level sampler during periods of water table rise over 5 years at a vertical resolution of 0 05 m nitrate concentration increased as the water table seasonally recovered with similar inter annual trends with depth the rising water table activated horizontal fractures facilitating the delivery of water elevated by up to 10 mg l of nitrate with respect to the adjacent groundwater below these fractures are considered to activate via piston displacement of water from the adjoining matrix hydrograph analysis identified 16 events which significantly perturbed the water table within 24 48 h of rainfall consistent nitrate concentrations indicate recharge through persistent fracture flow from the surface was not generally the primary driver of the rapid water table response during these events instead the response was attributed to the piston displacement of porewater immediately above the water table however a single event in november 2012 delivered relatively dilute recharge indicating rapid persistent fracture flow following rainfall was possible to a depth of 14 15 m decreases in porewater nitrate concentration around fracture horizons and the dilution of many groundwater samples with respect to porewaters indicate a fresher source of water at depth this was considered most likely to be a result of near surface water bypassing the matrix because of widespread mineralization on fracture surfaces which retard water and solute exchange therefore persistent fracture flow maybe considered a frequent process operating independently of the matrix and is not necessarily event driven

two dimensional kinematic wave model of overland flow a two dimensional kinematic wave model was developed for simulating runoff generation and flow concentration on an experimental infiltrating hillslope receiving artificial rainfall experimental observations on runoff generation and flow concentration on irregular hillslopes showed that the topography of the slope surface controlled the direction and flow lines of overland flow the model simulated results satisfactorily compared with experimental observations the erosive ability of the concentrated flow was found to mainly depend on the ratio of the width and depth of confluent grooves

importance of the accretion process in asteroid thermal evolution 6 hebe as an example widespread evidence exists for heating that caused melting thermal metamorphism and aqueous alteration in meteorite parent bodies previous simulations of asteroid heat transfer have assumed that accretion was instantaneous for the first time we present a thermal model that assumes a realistic incremental accretion scenario and takes into account the heat budget produced by decay of 26al during the accretion process by modeling 6 hebe assumed to be the h chondrite parent body we show that in contrast to results from instantaneous accretion models an asteroid may reach its peak temperature during accretion the time at which different depth zones within the asteroid attain peak metamorphic temperatures may increase from the center to the surface and the volume of high grade material in the interior may be significantly less than that of unmetamorphosed material surrounding the metamorphic core we show that different times of initiation and duration of accretion produce a spectrum of evolutionary possibilities and thereby highlight the importance of the accretion process in shaping an asteroid s thermal history incremental accretion models provide a means of linking theoretical models of accretion to measurable quantities peak temperatures cooling rates radioisotope closure times in meteorites that were determined by their thermal histories

a model for flow in the chalk unsaturated zone incorporating progressive weathering summary groundwater from unconfined chalk aquifers constitutes a major water resource in the uk the unsaturated zone in such systems plays a crucial role in the hydrological cycle determining the timing and magnitude of recharge and the transport and fate of nutrients however despite more than three decades of study our physical understanding of this system is incomplete in this research state of the art instrumentation provided high temporal resolution readings of soil moisture status rainfall and actual evaporation from two sites in the pang and lambourn catchments berkshire uk for a continuous two year period 2004 5 a parsimonious physically based model for the flow of water through the chalk unsaturated zone including a novel representation of the soil and weathered chalk layers was developed the parameters were identified by inverse modelling using field measurements of water content and matric potential the model was driven by rainfall and evaporation data and simulated fluxes throughout the profile including the discrete matrix and fracture components down to the water table but not the water table response results showed that the model was able to reproduce closely the observed changes in soil moisture status recharge was predominantly through the matrix and the recharge response was strongly attenuated with depth however the activation of fast recharge pathways through fractures in the chalk unsaturated zone was highly sensitive to rainfall intensity relatively modest increases in rainfall led to dramatically different recharge patterns with potentially important implications for groundwater flooding the development and migration of zero flux planes with time and depth were simulated the simulations also provided strong evidence that for water table depths greater than 5 m recharge fluxes persist throughout the entire year even during drought conditions with important implications for the calculation of specific yield from baseflow estimates and the representation of recharge in groundwater models

cooling history of lunar mg suite gabbronorite 76255 troctolite 76535 and stillwater pyroxenite sc 936 the record in exsolution and ordering in pyroxenes we have determined cooling rates of orthopyroxene crystals from two mg suite lunar samples gabbronorite 76255 and troctolite 76535 and one terrestrial sample orthopyroxenite sc 936 from the stillwater complex on the basis of their fe mg ordering states in addition a cooling rate of 76255 was determined by modeling the formation of exsolution lamellae in pyroxenes the m1 m2 site occupancies of the orthopyroxene crystals were determined by single crystal x ray diffraction and the rate constant for the ordering reaction was used along with calibrations of the equilibrium intracrystalline fractionation of fe and mg as a function of temperature to calculate cooling rates the closure temperatures tc of cation ordering are 525 c for 76255 500 c for 76535 and 350 c for sc 936 corresponding to cooling rates of 4 10 2 c year at the closure temperature for the lunar samples and 10 6 c year for the stillwater sample a cooling rate for 76255 determined by simulating the exsolution process is 1 7 10 2 c year at a closure temperature for exsolution of 700 c the fe mg ordering cooling rate determined for 76535 reflects a complex thermal history superimposed on the initial plutonic provenance established for this sample mccallum i s schwartz j m 2001 lunar mg suite thermobarometry and petrogenesis of parental magmas j geophys res 106 27969 27983 the preservation of a crystallization age of 4 51 ga and a metamorphic age of 4 25 ga for 76535 is consistent with a model in which excavation of this sample from the lower lunar crust took place while the sample was at a temperature above the closure temperatures for the sm nd u pb and ar ar isotopic systems temperatures in excess of the isotopic closure temperatures i e 600 c in the lower lunar crust were maintained by heat diffusing from concentrations of u and th rich kreep material at the base of the crust on the other hand 76255 formed at a much shallower depth in the lunar crust 2 km and was well below its isotopic closure temperatures at the time of excavation most likely during the serenitatis basin forming impact event both lunar samples were reheated during transport to the surface and deposition in hot ejecta blankets the reheating was short lived but apparently sufficient to redistribute fe and mg in m sites in orthopyroxenes for the lunar samples the cooling rates based on fe mg ordering represent final stage cooling within an ejecta blanket

peak metamorphic temperatures in type 6 ordinary chondrites an evaluation of pyroxene and plagioclase geothermometry quantifying the peak temperatures achieved during metamorphism is critical for understanding the thermal histories of ordinary chondrite parent bodies various geothermometers have been used to estimate equilibration temperatures for chondrites of the highest metamorphic grade type 6 but results are inconsistent and span hundreds of degrees because different geothermometers and calibration models were used with different meteorites it is unclear whether variations in peak temperatures represent actual ranges of metamorphic conditions within type 6 chondrites or differences in model calibrations we addressed this problem by performing twopyroxene geothermometry using quilf95 on the same type 6 chondrites for which peak temperatures were estimated using the plagioclase geothermometer nakamuta and motomura 1999 we also calculated temperatures for published pyroxene analyses from other type 6 h l and ll chondrites to determine the most representative peak metamorphic temperatures for ordinary chondrites pyroxenes record a narrow overlapping range of temperatures in h6 865 926 c l6 812 934 c and ll6 874 945 c chondrites plagioclase temperature estimates are 96 179 c lower than pyroxenes in the same type 6 meteorites plagioclase estimates may not reflect peak metamorphic temperatures because chondrule glass probably recrystallized to plagioclase prior to reaching the metamorphic peak the average temperature for h l and ll chondrites 900 c which agrees with previously published oxygen isotope geothermometry is at least 50 c lower than the peak temperatures used in current asteroid thermal evolution models this difference may require minor adjustments to thermal model calculations

cation ordering of orthopyroxenes from the skaergaard intrusion implications for the subsolidus cooling rates and permeabilities we have determined the quenched cation ordering states of five orthopyroxene crystals collected from the marginal border group and the lower zone a and b of the skaergaard intrusion and modeled these data to retrieve their closure temperatures tc of fe mg ordering and cooling rates according to existing thermal models for the skaergaard pluton conductive cooling dominated the high and low temperature regimes which were separated by an intermediate temperature regime in which the cooling was controlled primarily by convective fluid circulation the cooling rates retrieved from the quenched cation ordering states of the orthopyroxene crystals strictly apply to temperatures around the closure temperatures of the ordering states 340 400 c which fall at the transition from convective to the lower temperature conductive cooling the cooling rates obtained from the cation ordering states of orthopyroxene vary from 1 to 270 k ka these results agree well with a thermal model calculated using an assumed average permeability of 10 12 cm2 for the pluton but not completely with a model calculated on the basis of an average permeability of 10 13 cm2 although both values produced shifts of 18o that are comparable to those observed in the pluton

a new calibration to determine the closure temperatures of fe mg ordering in augite from nakhlites recently it has been shown that the relatively low closure temperature tc of 500 100 c calculated for augite from miller range nakhlite mil 03346 13 using the available geothermometers would correspond to a slow cooling rate inconsistent with the petrologic evidence for an origin from a fast cooled lava flow moreover previous annealing experiments combined with hr sc xrd on an augite crystal from mil 03346 clearly showed that at 600 c the fe2 mg degree of order remained unchanged thus suggesting that the actual tc is close to this temperature in order to clarify this discrepancy we undertook an ex situ annealing experimental study at 700 800 and 900 c until the equilibrium in the intracrystalline fe2 mg exchange is reached using an augite crystal from miller range nakhlite mil 03346 13 with a composition of about en36fs24wo40 these data allowed us to calculate the following new geothermometer calibration for martian nakhlites where the application of this new equation to other martian nakhlites nwa 988 and nakhla suggests that for augite with composition close to that of mil 03346 the tc is up to 170 c higher with respect to the one calculated using the previous available geothermometer equation thus suggesting a significantly faster cooling in agreement with petrologic evidence

recharge of the upper chalk aquifer at a site in hampshire england 2 solute movement abstract this paper describes a field experiment to study the movement of solutes through the unsaturated zone of the chalk using soil physical techniques to calculate water fluxes and sequential soil coring to measure solute concentrations with depth and time deuterium oxide was used as a tracer to follow water movement nitrate leaching beneath spring barley was calculated below the root zone approximately 40 kg ha 1 yr 1 of nitrate nitrogen were leached beyond root depth 1 m in the two study years at concentrations of between 20 and 75 mg l 1 and at a downward velocity of 0 85 m yr 1

soils slopes and source rocks application of a soil chemistry model to nutrient delivery to rift lakes abstract the topographic evolution of rift basins may be critical to the deposition of lacustrine source rocks such as the organic rich lower cretaceous shales of the south atlantic margin soils have been proposed as a key link between topography and source rock deposition by providing nutrients for the algae growth in rift lakes decreasing topographic relief from active rift to late rift has several effects on soils soils become thicker and finer erosion of dead surface and soil organic matter decreases and the fractionation of precipitation between runoff and infiltration may favor increased infiltration this hypothesis is tested by application of century a complex box model that simulates transfer of nutrients within soil pools the model is first applied to a rainforest soil with several parameters individually varied infiltration experiments show that the concentrations of c n and p in groundwater decrease rapidly as infiltration decreases whether due to increased slope or to decreased precipitation increased erosion of surface plant litter and topsoil results in substantially decreased nutrient concentrations in groundwater increased sand content in soil causes an increase in nutrient concentration we integrate these variables in analyzing topographic swathes from the rio grande rift comparing the southern part of the rift where topography is relatively old and reduced to the northern rift c and p concentrations in groundwater increase as slope gradient decreases resulting in substantially larger c and p concentrations in groundwater in the southern rift than the northern rift nitrogen concentrations in groundwater depends on whether infiltration varies as a function of slope gradient in experiments where the fraction of infiltrated precipitation decreased with increasing slope n concentrations was also substantially higher in the southern rift but in experiments where that fraction was held constant n concentrations was lower in the southern rift these simulations demonstrate that evolving topography during rift development can significantly influence nutrient concentrations in groundwater and if these nutrients flow into rift lakes and stimulate organic productivity account for the deposition of rich oil prone source rocks in late rift stages

penecontemporaneous metamorphism fragmentation and reassembly of ordinary chondrite parent bodies the occurrence and proportions of petrologic types among ordinary chondrites have been explained by internal heating of three h l ll parent asteroids of 100 km radius e g miyamoto et al 1982 this conventional onion shell model predicts an inverse relation between petrologic type and metallographic cooling rate but none has been observed scott and rajan 1981 devised a metamorphosed planetesimal model to explain this discrepancy whereby metamorphism occurs in planetesimals a few kilometers in radius which then accrete to form r 100 km parent bodies metallographic cooling rates are then controlled by burial depth thermal and collisional constraints on the metamorphosed planetesimal model are examined here and the model is found to be applicable only to highly insulating 26al rich planetesimals that can accrete intact without being shattered by impact or to shattered planetesimals whose fragments are not widely dispersed over the target surface an alternative model is presented here in which onion shell parent bodies are collisionally fragmented during metamorphism and then gravitationally reassembled if reassembly times are short days then metallographic cooling rates would be determined by burial depth in the reaccreted parent body this model unlike previous ones can explain both coherent and incoherent cooling rates of breccia clasts by collisions during or after metamorphism respectively

a simple model of variable residence time flow and nutrient transport in the chalk summary a basic problem of modelling flow and transport in chalk catchments arises from the existence of a deep unsaturated zone with complex interactions between flow in fractures and water held in the fine pores of the rock matrix the response of the water table to major infiltration episodes is rapid of the order of days however chemical signals are strongly damped suggesting that this water is of varying age with a corresponding mixed history of nutrient loading clearly this effect should be represented in any model of nutrients in chalk systems the applicability of simplified physically based model formulations to represent the dual response in an integrated way has been investigated by a variety of researchers but it has been shown that these approximations break down in application to the chalk mathias et al mathias s butler a p jackson b m wheater h s this issue characterising flow in the chalk unsaturated zone in wheater h s peach d neal c editors hydrology on locar in the pang lambourn special issue of j hydrol doi 10 1016 j jhydrol 2006 04 010 present a dual permeability model that explains the observed response but such complex formulations are not readily incorporated in catchment scale nutrient models this paper reviews previous approaches to modelling the chalk and then presents a pragmatic approach with transport of solute and water through the unsaturated zone treated separately and combined at the water table varying residence times are included through considering the distance between the water table and the soil surface and the history of nutrient application at the surface if an average rate of downwards migration of the nutrients is assumed it is possible to derive a travel time distribution of nitrate transport to the water table using a dtm digital terrain model map of elevation and information on groundwater levels this distribution can then be implemented through difference equations the rationale behind the model and the resulting algorithm is described and the algorithm then applied to a hypothetical case study of nutrient loading located in the lambourn a groundwater dominated chalk catchment in southern england simulated groundwater concentrations are very similar in magnitude and variability to observed chalk groundwater series suggesting that this simple conceptual model may well be able to capture the dominant responses of nutrient transport through the chalk

multiple parent bodies of ordinary chondrites abstract thermal histories of chondrite parent bodies are calculated from an initial state with material in a powder like form taking into account the effect of consolidation state on thermal conductivity the very low thermal conductivity of the starting materials makes it possible for a small body with a radius of less than 100 km to be heated by several hundred degrees even if long lived radioactive elements in chondritic abundances are the only source of heat the maximum temperature is determined primarily by the temperature at which sintering of the constituent materials occurs the thermal state of the interior of a chondrite parent body after sintering has begun is nearly isothermal near the surface however where the material is unconsolidated and the thermal conductivity is much lower the thermal gradient is quite large this result contradicts the conventional onion shell model of chondrite parent bodies but because the internal temperature is almost constant through the whole body it supports a multiple parent bodies model according to which each petrologic type of chondrite comes from a different parent body

controls on preferential recharge to chalk aquifers summary there is evidence that under certain conditions rapid preferential recharge via the fracture network can occur in chalk aquifers this has potentially important implications for contaminant migration through the chalk unsaturated zone cuz and for groundwater flooding in chalk catchments in the case of groundwater flooding deficiencies in modelling aquifer response have been attributed to inadequate representation of flow processes in the cuz in this paper we consider two complementary approaches for assessing controls on preferential recharge to chalk aquifers an empirical approach and a physically based modelling approach we show that the main controls on preferential recharge to chalk aquifers are the characteristics of rainfall events in terms of duration and intensity the physical properties of the near surface and the antecedent soil moisture in the near surface we demonstrate a number of deficiencies when past models of the cuz are applied to the problem of simulating preferential recharge notably that the assumption of instantaneous equilibrium between fractures and matrix is not valid particularly during extreme recharge events in order to simulate preferential recharge fractures and matrix must be modelled as separate but interacting domains this was achieved using a dual continua model the model was computationally demanding but was able to reproduce observed behaviour including apparently hysteretic soil moisture characteristic relationships in the near surface and rapid preferential recharge fluxes in response to high intensity rainfall events

effect of sediment density on bed load transport experiments on transport by water of synthetic lightweight sediments of specific gravities 1 0 s 2 5 and uniform grain size d 3 5mm are described the results confirm the dimensional reasoning

an active fracture model for unsaturated flow and transport in fractured rocks the unsaturated zone at yucca mountain a potential repository site of high level nuclear waste is a complex hydrologic system in which a variety of important flow and transport processes is involved to quantify these processes as accurately as possible is a theoretically challenging and practically important issue in this study we propose a new formulation for modeling flow and transport in unsaturated fractured rocks the formulation is mainly based on a hypothesis that only a portion of connected fractures are active in conducting water analysis of the relevant data with the new formulation suggests that about 18 27 of the connected fractures in the topopah spring welded tsw unit the potential repository unit of yucca mountain are active under ambient conditions the relatively high percentage of active fractures is consistent with field observations from a variety of sources sensitivity analyses are performed to investigate effects of the activity of connected fractures on flow and transport behavior in unsaturated rocks

four year comparison of water contents beneath a grass ley and a deciduous oak wood overlying triassic sandstone in lowland england summary differences in the seasonal water dynamics of a sand soil overlying triassic sandstone have been investigated to a depth of 9 m beneath both a grass ley and a pendunculate oak woodland within clipstone forest nottinghamshire england fortnightly measurements with a neutron probe over a four year period allowed a comparison of the soil rock water content to depths rarely reported in spring the rate of decrease of water content of the uppermost 2 m of soil was much greater under grass than oak woodland in contrast the rate of decrease under oak was greater after leafing out in may while the rate of rewetting in early autumn was lower for this land use until senescence and leaf fall in late autumn in the uppermost 2 m of soil a depth that includes all plant roots the soil moisture minima were between 47 and 58 mm lower under oak than grass in each year of monitoring as a result of both these drier conditions and the comparatively late leaf fall of this species penetration of the winter season wetting front to 2 m was delayed by between one and three months at the oak site relative to grass in years of near average rainfall rewetting at 9 m lags by 10 12 months compared to the surface giving an average penetration rate for the wetting front to this depth of 25 30 mm day 1 with little observable differences between the land uses preferential flow is evident under both sites affecting the profile to 3 m in all years and to at least 6 m following winters experiencing exceptional rainfall

characterising the vertical variations in hydraulic conductivity within the chalk aquifer summary various field methods have been used to examine and quantify the vertical variations in aquifer properties within the chalk aquifer at a locar site in berkshire uk the site contains three 100 m open boreholes and three sets of two nested piezometers within an area of about 100 m 2 there is also an 86 m deep abstraction borehole about 40 m from the site the techniques that have been used at the site include geophysical logging borehole imaging packer testing dilution testing and pumping tests the packer test results show that the permeability of the aquifer varies by three orders of magnitude over the 70 m of tested material with a strongly non linear decrease with depth below ground level comparison with the borehole images show that some of the highly permeable zones appear to be associated with obvious fractures however large fractures can be seen in zones which have much lower permeability while some highly permeable zones appear to be associated with poorly developed fractures single borehole dilution tests have shown that there are differences in flow velocity depth profiles over a few tens of meters across the site these are inferred to be because the different boreholes although of similar drilled depth and very close proximity intersect slightly different parts of the fracture network and hence the groundwater flow system in particular a flowing feature at the base of one borehole is not intersected by the second which is drilled from a slightly higher elevation a dilution test carried out whilst the aquifer was being pumped shows that different fractures become active when the aquifer is stressed this has implications for the interpretation of flow logs performed under pumping

shock metamorphism of ordinary chondrites a revised petrographic classification of progressive stages of shock metamorphism of ordinary chondrites is proposed six stages of shock s1 to s6 are defined based on shock effects in olivine and plagioclase as recognized by thin section microscopy the characteristic shock effects of each shock stage are s1 unshocked sharp optical extinction of olivine s2 very weakly shocked undulatory extinction of olivine s3 weakly shocked planar fractures in olivine s4 moderately shocked mosaicism in olivine s5 strongly shocked isotropization of plagioclase maskelynite and planar deformation features in olivine and s6 very strongly shocked recrystallization of olivine sometimes combined with phase transformations ringwoodite and or phases produced by dissociation reactions s6 effects are always restricted to regions adjacent to melted portions of a sample which is otherwise only strongly shocked in stages s3 to s6 localized melting results from stress and temperature peaks which locally deviate from the equilibration shock pressure due to differences in shock impedance these melting effects are a opaque melt veins shock veins b melt pockets with interconnecting melt veins c melt dikes and d troilite metal deposits in fractures based on a critical evaluation of data from shock recovery experiments a shock pressure calibration for the six shock stages is proposed which defines the s1 s2 s2 s3 s3 s4 s4 s5 and s5 s6 transitions at 5 5 10 15 20 30 35 and 45 55 gpa respectively whole rock melting and formation of impact melt rocks or melt breccias occurs at about 75 90 gpa the symbol for the shock stage may be used in combination with the symbol for the petrologic type to abbreviate the complete classification of a chondrite e g h5 s3 we propose this new shock classification and pressure calibration system to replace previous systems which are out of date with respect to the pressure calibration nominally restricted to l chondrites and based on incomplete and in part illdefined sets of shock effects we have classified seventy six ordinary chondrites using the new classification system and conclude the following 1 1 shock effects and the sequence of progressively increasing degrees of shock metamorphism are very similar in h l and ll groups differences in the frequency distribution of shock stages are relatively minor e g l chondrites appear to have the largest fraction with stages s5 and s6 this suggests that the collisional histories of the h l and ll parent bodies were similar 2 2 petrologic type 3 chondrites are deficient in stages s4 to s6 and with increasing petrologic type the frequency of stages s4 to s6 increases we suggest that the more porous and volatile rich type 3 chondrites are subject to melting at a lower shock pressure than the nonporous chondrites of higher petrologic type volatiles trapped in pores cause shock induced dispersal of the shocked and melted material into small particles which are not expected to survive as meteorites 3 3 stage s3 is the most abundant in nearly all petrologic types 4 4 at shock pressures in excess of about 35 gpa s5 and s6 4he and 40ar are almost completely lost pressures below 10 gpa s1 and s2 do not cause noble gas losses

reclassification and thermal history of trenzano chondrite we present a new single crystal x ray diffraction xrd study performed on a suite of six orthopyroxene grains from the low shocked h6 trenzano meteorite the quenched intracrystalline fe 2 mg ordering state in orthopyroxene preserves the memory of the cooling rate near closure temperature tc thus yielding useful constraints on the last thermal event undergone by the host rock the orthopyroxene tc of 522 13 c calculated using a new calibration equation obtained by stimpfl 2005b is higher than in previously published h chondrite data the orthopyroxene cooling rate at this tc is about 100 c kyr this fast rate is inconsistent with the much slower cooling rate expected for h6 in the onion shell structural and thermal model of chondrite parent bodies a petrographic study carried out at the same time indicated that the trenzano meteorite is an h5 chondrite and not an h6 chondrite as it is officially classified furthermore the two pyroxene equilibrium temperature of trenzano 824 24 c calculated with quilf95 is similar to the two pyroxene temperature of 750 840 c obtained for the carcote h5 chondrite kleinschrot and okrusch 1999

a tracer investigation into the importance of fissure flow in the unsaturated zone of the british upper chalk abstract the displacement and recovery of surface applied 15 no 3 2 h and cl in the unsaturated zone of the british upper chalk was followed over a 4 year period recovery of cl in the chalk matrix under the treated plot was equivalent to 110 of that applied that of 2 h was 57 in the treated plot lateral flow of 2 h was evident from cores taken outside the plot and if this is included together with 2 h estimated to have been lost by evapotranspiration the recovery approached 100 recovery of 15 no 3 was 100 1 year after tracer application falling to 9 4 after 4 years no evidence of denitrification was obtained from background no 3 cores and it was concluded that the shortfall in no 3 recovery was due to uptake by grass from depths of 50 70 cm the tracer profiles and recoveries were not consistent with significant vertical macrofissure flow but the lack of seasonal periodicity in background 2 h profiles suggested that some microfissure flow could be occurring the displacement of the tracer peaks when considered with the estimates of recharge indicated that only 50 of the water filled matrix was conducting flow

heterogeneous behaviour of unconfined chalk aquifers infer from combination of groundwater residence time hydrochemistry and hydrodynamic tools chalk groundwater is an important aquifer resource in france and also in much of northwestern europe large areas between the paris basin the london basin denmark and the northwest of germany as it is intensively exploited for human use with a large proportion reserved for drinking water the improvement of the knowledge on chalk aquifer hydrodynamical functioning and groundwater geochemistry is essential for the management of this resource to achieve this aim we developed a methodology based on a combination of hydrodynamic hydrochemistry and groundwater dating tools a study site of about 500 km2 was selected in ne france where chalk outcrops at 15 sampling points including boreholes and rivers mainly from chalk aquifer drainage groundwater geochemistry were monitored monthly for 2 years from june 2017 to june 2019 groundwater level in boreholes were monitored hourly with in situ water loggers in addition two sampling campaigns for the analysis of cfcs and sf6 have been conducted in boreholes in high and low water level periods to define the groundwater residence time the aquifer at the majority of sampling sites has an inertial behavior with respect to recharge as no impact of individual rainfall event was observed rapid piezometric response following rainfalls was observed at one site suggesting the presence of locally highly developed fracture network contrariwise high spatial and temporal heterogeneities of geochemistry was observed on the study area according to the mixing process piston flow exponential or binary mixing defined at each sampling site groundwater dating indicated rather heterogeneous ages ranging from less than 20 years to more than 50 years a combination of hydrogeological setting residence time and land use information was used to explain the hydrochemical heterogeneities highlighting the main factors governing the chalk groundwater geochemistry including water level fluctuation thickness of the unsaturated zone superficial formations distribution of fracture network aquifer river relations and human activities a conceptual model was proposed to clarify the hydrogeosystem functioning of unconfined chalk aquifers the proposed methodology can be used for the study of other worldwide aquifers chalk or not with the aim to provide appropriate recommendations in terms of water management

estimation of natural groundwater recharge in the karoo aquifers of south africa abstract a 3 year project to study the natural groundwater recharge of aquifers in the semi arid karoo formations of south africa was undertaken two typical karoo aquifers at dewetsdorp and de aar were selected for study purposes data were collected from both the saturated and unsaturated zone neutron probe measurements showed that there was no increase in the water content beneath a depth of 1m below the surface even with the exceptionally high rainfall in february 1988 neutron measurements indicated that very little soil matrix flow occurred which implied that most of the recharge occurred along preferred pathways a triangular finite element network was used to determine the relative saturated volume fluctuations svf of the aquifers from the observed water level changes over a period of time which allowed determination of the storativity s and the recharge the main advantage of the method lies in determining recharge and storativity which are both unknowns in the water balance equation and which both contribute to the water level response the svf method showed that the recharge in the karoo formations of south africa varies between 2 and 5 of the annual rainfall in areas which are overlain by a thick soil cover the recharge is less than 3 while recharge in hilly areas with a thin soil cover may be of the order of 5

advances in modelling groundwater behaviour in chalk catchments groundwater in chalk catchments is a major resource that also helps support internationally important habitats and ecosystems its dual porosity and dual permeability properties coupled with large scale structural features such as hard rock layers and marls produce a highly complex hydrogeological system recent impacts from groundwater flooding as well as vulnerability to drought have raised questions over the ability of traditional approaches to model these aquifers current work on near surface hydrological processes has highlighted the importance of the soil and weathered zone for controlling recharge rates in addition karst like features sedimentary deposits and valley bottom processes govern stream aquifer interaction and present a challenge in their representation in any modelling system methods that have and are being developed to incorporate these features and their use in modelling chalk catchments are described these are required in order to address major challenges such as groundwater flooding and drought impacts both of which could become more frequent and intense as a result of climate change

spatial heterogeneity of high resolution chalk groundwater geochemistry underground quarry at saint martin le noeud france chalk groundwater is an important aquifer resource in france because it accounts for a production of 12 million m3 y 1 with a large proportion reserved for drinking water processes occurring in the unsaturated zone uz and the overlying superficial formations have a high impact on chalk groundwater geochemistry and require better understanding the study site is a former underground chalk quarry located near beauvais france that extends over 1200 m in length at a depth ranging from 20 to 30 m the water table intersects the cavity creating 15 underground lake that give access to the chalk groundwater lakes geochemistry has been studied water samples were collected in july 2013 and major ion concentrations were analyzed uz and clay with flints thickness above each lake were estimated qualitatively using an electromagnetic sensor em31 and underground gps the results unexpectedly showed that groundwater quality varied widely in spatial terms for both allochthonous and autochthonous ions e g hco3 ranged from 2 03 to 4 43 meq l 1 no3 ranged from 0 21 to 1 33 meq l 1 principal component analysis indicated the impact of agricultural land use on water quality with the intake of no3 as well as so42 cl and ca2 chalk groundwater geochemistry is compared with the nature and structure of the uz we highlight correlations 1 between thick clay with flints layers and the ions mg2 and k and 2 between uz thickness and na in conclusion this paper identifies various ion sources agriculture clay with flints and chalk and demonstrates different processes in the uz dissolution ionic exchange and solute storage

experimental investigation of solute transport in unsaturated fractured rock an experiment is designed to perform tracer tests in an unsaturated fractured rock with a horizontal fracture data from an intact and an artificial sandstone sample was collected and used to discuss the effect of the fracture on tracer migration the delay time of the tracer in the fracture was further determined in terms of the fracture aperture involved an alternative electrical conductivity or electrical resistance method was developed to measure the change in the tracer concentration with time and space the method causes no disturbance to the flow and concentration fields and is convenient to use the test results show the fluctuations in the tracer concentrations and there were 2 3 peak values of concentration in the monitored sections related to the heterogeneity of the water content and pore distribution also the fracture was found to delay migration of the tracer before it is filled with the tracer solution and quicken the velocity of migration afterwards this results in accumulation of the tracer near the fracture furthermore the delay time of the tracer increases with fracture aperture in a nonlinear manner

initiation of motion in overland flow this article reports the results of an experimental study concerning the initial movement of sediment in overland flow experiments were carried out in a small flume using water and quartz materials of various grain sizes the comparison of our experimental results with classic criteria showed that the shields curve and the criterion of yang can also be used for turbulent overland flow generally higher shear stresses are necessary to provoke bed instability under laminar flow conditions especially at higher shear velocity particle reynolds numbers a relative roughness effect also exists in laminar flow contrary to the observations by savat on fixed beds laminar flow does not show an uncommon selectivity when loose homogeneous beds are considered

estimation of groundwater recharge to chalk and sandstone aquifers using simple soil models abstract on the assumption that the water draining below the root zone is potentially available for groundwater recharge two current uk methods for estimating annual groundwater recharge have been compared with a new soil model using data from four sites under permanent grass in the uk two sites representative of the chalk aquifer at bridgest farm hampshire and fleam dyke cambridgeshire and two sites on the triassic sandstone at bicton college devon and bacon hall shropshire a four root layers model frlm the penman grindley model and the uk meteorological office rainfall and evaporation calculation system morecs were used the new soil model was run with potential evaporation as input both from the morecs and from the penman monteith equation the models were run for the chalk sites both with and without a bypass flow of 15 of rainfall bypass was not considered for the sandstone sites the performance of the models was tested against neutron probes measurements of soil moisture deficits in addition the annual groundwater recharge estimated from the models was compared with the published values obtained from the zero flux plane method generally the penman grindley model was more successful in predicting the time for soil to return to its field capacity than in predicting the magnitude of the soil moisture deficit the annual groundwater recharge was predicted with reasonable accuracy the morecs relatively tended to overestimate the soil moisture deficits and to delay the time at which the soil returns to its field capacity the consequences were underestimates of annual groundwater recharge owing either to the higher values of potential evaporation calculated from the morecs or tothe high available water capacity values associated with the soils under consideration the new soil model frlm predicts the soil moisture deficits successfully and hence is reliable in estimating the annual groundwater recharge the model is capable of doing this with potential evaporation input calculated either from the morecs or from the penman monteith equation the model also demonstrated that the inclusion of 15 of rainfall as bypass flow is viable for chalk sites

postshock annealing and postannealing shock in equilibrated ordinary chondrites implications for the thermal and shock histories of chondritic asteroids abstract in addition to shock effects in olivine plagioclase orthopyroxene and ca pyroxene petrographic shock indicators in equilibrated ordinary chondrites oc include chromite veinlets chromite plagioclase assemblages polycrystalline troilite metallic cu irregularly shaped troilite grains within metallic fe ni rapidly solidified metal sulfide intergrowths martensite and various types of plessite metal sulfide veins large metal and or sulfide nodules silicate melt veins silicate darkening low ca clinopyroxene silicate melt pockets and large regions of silicate melt the presence of some of these indicators in every petrologic type 4 to 6 ordinary chondrite demonstrates that collisional events caused all equilibrated oc to reach shock stages s3 s6 those type 4 to 6 oc that are classified as shock stage s1 on the basis of sharp optical extinction in olivine underwent postshock annealing due to burial beneath materials heated by the impact event those type 4 to 6 oc that are classified s2 on the basis of undulose extinction and lack of planar fractures in olivine were shocked to stage s3 s6 annealed to stage s1 and then shocked again to stage s2 some oc were probably shocked to stage s3 after annealing it seems likely that many oc experienced multiple episodes of shock and annealing because 40ar 39ar chronological data indicate that mil 99301 ll6 s1 was annealed 4 26 ga ago presumably as a consequence of a major impact it seems reasonable to suggest that other equilibrated s1 and s2 oc which contain relict shock features were also annealed by impacts because some type 6 s1 oc e g guarena kernouve portales valley all of which contain relict shock features were annealed 4 44 4 45 ga ago during a period when impacts were prevalent and most oc were thermally metamorphosed it follows that impact induced annealing could have contributed significantly to oc thermal metamorphism

mechanisms of groundwater recharge and pesticide penetration to a chalk aquifer in southern england abstract in order to assess the potential for enhanced agrochemical contamination of shallow groundwaters a field study was established on the upper chalk in hampshire uk two instrumented sites 380 m apart were established on a hillslope one on the interfluve with a deep water table 18 m depth the other on the dry valley bottom where the groundwater was close to the surface 4 m depth hourly measurements of water potentials in the unsaturated zone to 3 0 m depth identified very different groundwater recharge processes between the two sites in response to the same storm event on the interfluve site with the deep water table only matrix flow through the chalk unsaturated zone at 3 m depth was identified in contrast at the dry valley bottom with a shallow water table both rapid preferential flow and matrix flow processes were observed at a 3 m depth the correlation between groundwater depth measurements and unsaturated profile moisture content measurements demonstrated the importance of the capillary fringe in sustaining a higher moisture content in the unsaturated zone at the shallow groundwater site the resulting reduced water storage capacity for vertical drainage fluxes meant that little water was required to wet the shallow profile before rapid preferential flow events demonstrated by rapid water potential responses occurred however where the groundwater was deeper intermediate storage sites located on chalk surfaces and at chalk ped block contact points remained empty and unsaturated water potential profiles showed that rainfall pulses were attenuated as these sites absorbed the downward water fluxes consequently preferential events at these deep groundwater sites are rare the importance of these intermediate storage sites in controlling recharge processes is highlighted the potential mass load of pesticide transported to the shallow groundwater in preferential events during 1996 7 was determined using bromide tracer studies water balance calculations and measured groundwater pesticide concentrations an estimated 0 1 of the applied pesticide reached the shallow groundwater along preferential pathways in 1996 7 calculations under a worst case scenario showed that this value did not increase beyond 0 2 of pesticide applied

thermal history of mesosiderites quantitative constraints from compositional zoning and fe mg ordering in orthopyroxenes abstract we have derived mathematical relations to calculate cooling rates from the extent of compositional zoning developed during cooling across the interface of a natural diffusion couple these relations were used to calculate the high temperature cooling rates of the mesosiderites lowicz and clover springs from the available data on compositional zoning across core overgrowth interface of orthopyroxene grains we have also determined the cation ordering in four selected orthopyroxene crystals from bondoc and estherville mesosiderites with very high precision and used these data to calculate their low temperature cooling rates the compositional zoning of orthopyroxene crystals reflects extremely rapid cooling rates at least 1 c 100 years in the temperature range 850 1150 c however simultaneous consideration of both metallographic and cation ordering data for estherville within the framework of either an asymptotic or an exponential cooling model requires a cooling rate of l c ma near 250 c the cation ordering data for bondoc for which no metallographic data are yet available are suggestive of even slower cooling rate which implies excavation from a somewhat greater depth in the parent body however within the limits of their uncertainties the measured site occupancies of the orthopyroxene crystals from bondoc can be reconciled with a cooling rate similar to that of estherville the calculated cooling rates at both high and low temperatures have been used to develop a thermal evolution model of mesosiderites the suggested model is not incompatible with an asteroidal parent body for these meteorites further it is shown that the closure temperature of ar ar age must be tied to the slow cooling rate below 500 c

solution to the kinematic wave approach to overland flow routing with rainfall excess given by philip s equation a solution to the kinematic wave equations for overland flow routing where the lateral inflow term is determined from a constant rainfall rate and the infiltration model of philip is presented the solution utilizes the method of characteristics and while it is not completely analytical it is reduced to a simple numerical procedure which does not require the use of finite differences the analysis presented deals with both the rising and falling stages example calculations water surface profiles and hydrographs are shown

a simulation model for unified interrill erosion and rill erosion on hillslopes a mathematical model was developed for simulating runoff generation and soil erosion on hillslopes the model is comprised of three modules one for overland flow one for soil infiltration and one for soil erosion including rill erosion and interrill erosion rainfall and slope characteristics affecting soil erosion on hillslopes were analysed the model results show that the slope length and gradient time distribution rainfall and distribution of rills have varying influence on soil erosion erosion rate increases nonlinearly with increase in the slope length a long slope length leads to more serious erosion the effect of the slope gradient on soil erosion can be both positive and negative thus there exists a critical slope gradient for soil erosion which is about 45 for the rate of erosion at the end of the slope and about 25 for the accumulated erosion copyright 2005 john wiley sons ltd

modelling flow and heat transfer through unsaturated chalk validation with experimental data from the ground surface to the aquifer abstract during the winter and spring of 2000 2001 large floods occurred in northern france somme river basin and southern england patcham area of brighton in valleys that are developed on chalk outcrops the floods durations were particularly long more than 3 months in the somme basin and caused significant damage in both countries to improve the understanding of groundwater flooding in chalk catchments an experimental site was set up in the hallue basin which is located in the somme river basin france unsaturated fractured chalk formation overlying the chalk aquifer was monitored to understand its reaction to long and heavy rainfall events when it reaches a near saturation state the water content and soil temperature were monitored to a depth of 8 m and the matrix pressure was monitored down to the water table 26 5 m below ground level the monitoring extended over a 2 5 year period 2006 2008 under natural conditions and during two periods when heavy artificial infiltration was induced the objective of the paper is to describe a vertical numerical flow model based on richards equation using these data that was developed to simulate infiltrating rainwater flow from the ground surface to the saturated aquifer the marthe computer code which models the unsaturated saturated continuum was adapted to reproduce the monitored high saturation periods composite constitutive functions hydraulic conductivity saturation and pressure saturation that integrate the increase in hydraulic conductivity near saturation and extra available porosity resulting from fractures were introduced into the code using these composite constitutive functions the model was able to accurately simulate the water contents and pressures at all depths over the entire monitored period including the infiltration tests the soil temperature was also accurately simulated at all depths except during the infiltrations tests which contributes to the model validation the model was used to calculate the aquifer recharge over a long period that included droughts and floods the calculated recharge is realistic as it makes it possible to simulate the corresponding monitored groundwater level data which increases confidence in the modelling approach

analysis of water level response to rainfall and implications for recharge pathways in the chalk aquifer se england summary water table response to rainfall was investigated at six sites in the upper middle and lower chalk of southern england daily time series of rainfall and borehole water level were cross correlated to investigate seasonal variations in groundwater level response times based on periods of 3 month duration the time lags in days yielding significant correlations were compared with the average unsaturated zone thickness during each 3 month period in general for cases when the unsaturated zone was greater than 18 m thick the time lag for a significant water level response increased rapidly once the depth to the water table exceeded a critical value which varied from site to site for shallower water tables a linear relationship between the depth to the water table and the water level response time was evident the observed variations in response time can only be partially accounted for using a diffusive model for propagation through the unsaturated matrix suggesting that some fissure flow was occurring the majority of rapid responses were observed during the winter spring recharge period when the unsaturated zone is thinnest and the unsaturated zone moisture content is highest and were more likely to occur when the rainfall intensity exceeded 5 mm day at some sites a very rapid response within 24 h of rainfall was observed in addition to the longer term responses even when the unsaturated zone was up to 64 m thick this response was generally associated with the autumn period the results of the cross correlation analysis provide statistical support for the presence of fissure flow and for the contribution of multiple pathways through the unsaturated zone to groundwater recharge

metallic minerals thermal histories and parent bodies of some xenolithic ordinary chondrite meteorites we have studied metal grains in the hosts and lithic fragments of widely differing petrologic types in four xenolithic chondrftes using reflected light microscopy and electron probe analysis in weston and fayetteville which both contain solar flare tracks and solar wind gases kamacite taenite and tetrataenite ordered feni and troilite show a variety of textures on a wood plot of central ni content vs dimension taenite analyses scatter as if metal grains cooled at rates of 10 1000 and 1 100 k myr respectively through 700 k although metal in an h6 clast in fayetteville plots coherently with a cooling rate of 50 k myr we propose that metal grains cooled at these rates in chondritic clasts at different locations before host and clasts were compacted and were not subsequently heated above 650 k we predict a similar history for all gas rich ordinary chondrites by contrast metallic minerals throughout bhola and mezo madaras show more uniform textures and plot coherently giving cooling rates in the range 750 to 600 k of 0 1 and 1 k myr respectively we conclude that host and xenoliths in both chondrites were slowly cooled after compaction thus clasts in these chondrites experienced peak metamorphic temperatures and slow cooling through 700 k in different environments according to the conventional onion shell model for h l or ll chondrite parent bodies material of petrologic types 3 5 was arranged in successive shells around a type 6 core prior to catastrophic collisions which mixed all types intimately but if peak metamorphic temperatures were reached during not after accretion as seems plausible maximum metamorphism may have occurred in planetesimals 10 km in radius cooling through 700 k may then have occurred in larger bodies that accreted from these planetesimals iron meteorites mesosiderites and some achondrites may also have experienced melting in planetesimals and slow cooling in larger bodies

thermal history of alh 84001 meteorite by fe2 mg ordering in orthopyroxene a single orthopyroxene crystal from the martian meteorite allan hills alh 84001 was studied by x ray diffraction xrd and electron microprobe analysis empa to retrieve information about its thermal history both sets of data were used to measure the fe 2 mg order degree between the m1 and m2 sites expressed by the distribution coefficient kd the 529 30 c closure temperature tc of the fe 2 mg ordering process of alh 84001 orthopyroxene fs28 was calculated using stimpfl 2005a 2005b lnkd versus 1 t equation obtained for intermediate iron sample at this tc the orthopyroxene cooling rate calculated by ganguly s 1982 numerical method was 0 1 c day this study puts new constraints on the last high temperature thermal episode recorded by orthopyroxene with reference to the geological history treiman 1998 we ascribe this episode to the i3 event and we interpret the tc of 529 c as a lower limit for this impact heating our data confirm that experimentally defined physical conditions for the formation of magnetite from decomposition of carbonates took place on the martian surface during event i3

recharge of the upper chalk aquifer at a site in hampshire england 1 water balance and unsaturated flow abstract measurements of the annual cycle of changes in water content and potential in the 40 m thick unsaturated zone of upper chalk at a site in southern england are described measured evaporation continued at the penman potential rate until the soil moisture deficit reached 175 mm this suggested that a root constant of 200 mm would be more appropriate than the much lower values generally used the field capacity concept could not be reconciled with the timing of renewed water recharge and the reasons for this are discussed the mechanisms of water flow through the unsaturated zone of the chalk are examined and it is shown that at this upper chalk site matrix flow is the dominant recharge mechanism

the significance of flow in the matrix of the chalk unsaturated zone the significance of flow in the matrix of the chalk unsaturated zone in comparison with flow in fractures has been the subject of much debate in this article important elements of the literature are discussed in detail and several simple modelling analyses based on steady state flow are presented a study of the sensitivity of solute spreading to fracture spacing in models that ignore matrix flow shows that this latter assumption is generally incompatible with observed solute profiles unless unrealistically small fracture spacings are assumed the effect of air phase continuities e g bedding planes on matrix flow has also been examined these discontinuities are frequently interrupted by points of connectivity between matrix blocks an issue therefore is the relationship between connectivity and its effect on inter block conductance a simple analysis of the laplace equation shows that just 1 connectivity represents an effective pathway equivalent to 18 of the local rock hydraulic conductivity obviously when there is no fracture flow solute spreading is significantly reduced however dual permeability model simulations show that matrix flow reduces solute spreading in the presence of persistent fracture flow all of the above studies suggest that flow in the matrix of the chalk unsaturated zone is significant and that ignoring it may result in a serious misunderstanding of the system

hydrologic mechanisms governing fluid flow in a partially saturated fractured porous medium in contrast to the saturated zone within which fluid moves rapidly along fractures the fractures with apertures large relative to the size of matrix pores will desaturate first during the drainage process and the bulk of fluid flow would be through interconnected pores in the matrix within a partially drained fracture the presence of a relatively continuous air phase will produce practically an infinite resistance to liquid flow in the direction parallel to the fracture the residual liquid will be held by capillary force in regions around fracture contact areas where the apertures are small normal to the fracture surfaces the drained portion of the fractures will reduce the effective area for liquid flow from one matrix block to another matrix block a general statistical theory is constructed for flow along the fracture and for flow between the matrix blocks to the fractures under partially saturated conditions results are obtained from an aperture distribution model for fracture saturation hydraulic conductivity and effective matrix fracture flow areas as functions of pressure the effects of distortion of flow paths by the air pockets are taken into account by a phase separation constriction factor in a generalized cubic law for fracture flow under a partially saturated condition the reduction of matrix fracture flow area is taken into account by summing the aperture distribution function to a saturation cutoff aperture which is inversely proportional to the suction head drainage from a column of fractured tuff is simulated using available parameters for the densely welded tuff of the topopah spring member at yucca mountain southern nevada the column is bounded by discrete vertical fractures and dissected by horizontal fractures with the fracture spacings determined by the frequencies and orientations of fractured cores the fraction of fracture surfaces with coatings is assumed to correspond to the fraction of in situ fracture contact area the characteristic curves for the matrix are based on laboratory measurements of tuff samples from the cases simulated for the fractured porous columns with discrete vertical and horizontal fractures and porous matrix blocks explicitly taken into account it is observed that the highly transient changes from fully saturated conditions to partially saturated conditions are extremely sensitive to the fracture properties however the quasi steady changes of the fluid flow of a partially saturated fractured porous system could be approximately simulated without taking the fractures into account

orthopyroxene as a geospeedometer thermal history of kapoeta old homestead 001 and hughes 004 howardites 1dipartimento di scienze della terra universitti di pavia via ferrata 1 27100 pavia italy 2dipartimento di mineralogia e petrologia universitti di padova c so garibaldi 37 35122 padova italy 3dipartimento di scienze della terra universitil di messina salita sperone 31 98166 messina s agata italy 4centro grandi strumenti universitti di pavia via bassi 21 27100 pavia italy correspondence author s e mail address domeneghetti crystal unipv it

estimating infiltration recharge using a response function model abstract rainfall infiltration influences both the quantity and quality of groundwater systems the knowledge of the process of infiltration recharge is of great importance to the management of groundwater systems and the hydraulically connected streams in this study a response function model is developed to estimate soil water flux at the water table or the process of infiltration recharge from rainfall and evaporation data the gamma probability density function is modified to represent the travel time distribution of infiltrating water by rainfall events the travel time distribution is used to determine the recharge process according to the effective infiltration of a rainfall event the effective infiltration is the amount of soil water pushed down into groundwater by infiltrating water of a rainfall event and is evaluated based on the vadose zone soil water balance superposition is employed to compute the recharge rate produced by a sequence of rainfall events estimations of soil water flux at different groundwater depths are compared with lysimetric observations in the field good agreements between the estimated and observed results confirm the reliability of the response function model for predicting infiltration recharge processes

mechanisms of water storage and flow in the unsaturated zone of the chalk aquifer abstract it is known that the volumes of water draining from some chalk catchments in recessions are significantly greater than can be explained by gravity drainage from fissure porosity the most likely source of this water is slow drainage from the matric porosity above the water table this paper suggests that the location of this storage is in the irregularities on the fissure surfaces studies of resin impregnated blocks of chalk failed to reveal the presence of hydrologically significant microfissures or macropores that could be the source of additional drainage ultrasonic measurements at varying values of effective stress show no indication of changes in the acoustic transmission properties that could be attributed to closure of microfissures drainage and mercury intrusion measurements indicate that there is significant storage on block surfaces the drainage measurements confirm that the storage is of the order of magnitude about 0 3 needed to explain the slow drainage this additional storage explains why the water table is slow to respond after recharge events and why the chalk is resilient to drought the presence of storage in the unsaturated zone implies that the position of the water table may not be an accurate indicator of groundwater resources the concept of filling and draining of irregularities on fissure surfaces also leads to a new model for the generation of fissure flow in the unsaturated zone of the chalk this suggests that fissure flow can be generated at any depth in the profile and in a sequence of uniform vertical permeability is likely to originate near the water table rather than high in the unsaturated zone

cooling rates of diogenites a study of fe2 mg ordering in orthopyroxene by single crystal x ray diffraction the iron magnesium exchange between m1 and m2 sites in orthopyroxene is a reversible reaction that records the latest event in the thermal evolution of the host rock a kinetic analysis of this process has been applied to 16 orthopyroxene single crystals from 7 different diogenites to constrain the cooling history of their parent body the fe2 mg ordering degrees have been determined by single crystal x ray diffraction the fe2 mg ordering closure temperatures were very homogeneous within each sample and ranged for all diogenites studied between 311 29 c and 408 10 c cooling rates at these closure temperatures were calculated using a numerical method developed by ganguly 1982 these ranged between 5 c 104 year in johnstown and 0 8 c year in roda a comparison with other achondrites studied with the same method showed that increasing closure temperatures correspond to increasing cooling rates and that meteorites from a same parent body exhibit similar closure temperature and cooling rate values the cooling rates obtained for these diogenites at their low closure temperatures should probably be ascribed to a complex thermal history of their parent body thus confirming miyamoto and takeda s theory 1994a of excavation of deep crustal material due to impact events the differences on cooling rate values for different diogenites could be due to different burial depths in the fragment ejected from the parent body

numerical investigation of steady liquid water flow in a variably saturated fracture network numerical simulation was used to study steady liquid water movement in a 5 m by 5 m vertical section containing a hypothetical fracture network under conditions of variable saturation the fracture network was assumed to be embedded within an impermeable rock matrix three variations of a network were considered the mixed network consisted of two fracture sets a subvertical set containing five 125 m average aperture fractures and a subhorizontal set containing four 25 m average aperture fractures the other two networks had identical fracture orientation and contained either all 125 m or all 25 m average aperture fractures the tough simulator was used to calculate the total steady liquid water flux through the network the flux through individual fracture segments and the pressure head at each fracture segment a unit hydraulic gradient was imposed on the network by applying fixed pressure head boundaries ranging from 0 25 to 0 0 m of water of equal value to the top and bottom saturation and permeability versus pressure head relations for the two sets of fractures were determined with the vsfrac model which assumed that aperture was variable within an individual fracture results showed that the spatial distributions of pressure head and flux within the network as well as the location of the dominant pathways depended strongly on the prescribed boundary pressure head for the mixed network both pressure head and flux tended to become more spatially uniform when the boundary pressure head approached the pressure head at which the permeability thickness products of the large and small aperture fractures are equal the crossover pressure head these results imply that for systems similar to the one considered here interpretation of actual measurements of pressure head and flux may be quite complex and that representation of variably saturated fracture networks as an equivalent continuum may be more valid for some ranges in pressure head than for others equivalent permeability as a function of pressure head was calculated for the fracture network illustrating how information collected on individual fractures may be used to estimate the flow properties of rock at larger scales

equilibrated ordinary chondrites constraints for thermal history from iron magnesium ordering in orthopyroxene iron magnesium ordering was determined in orthopyroxenes from two suites of unshocked shock stage s1 s2 equilibrated l and ll chondrites 10 grains from 5 meteorites and 7 grains from 4 meteorites respectively by means of single crystal x ray diffraction scxrd this study together with a previous investigation of h chondrites 13 grains from 8 meteorites produces an internally consistent data set about the thermal record in equilibrated ordinary chondrites eocs the major feature outlined by cation ordering in eoc orthopyroxenes is that h l and ll chondrites share a common low temperature record that is a common range of similar cooling rates in the 340 480 c interval for the petrographic types 4 to 6 as a consequence the thermal evolution of eocs consists of at least two subsolidus stages the first stage occurred at temperatures 480 c where petrographic types were established in distinct environments the second stage occurred when eocs irrespective of chemical class and type cooled through 340 480 c in environments characterized by close temperature time conditions quantitative estimates of minimal cooling rates for eocs range from a few c ka to 102 c ka in the 340 480 c interval possibly final ordering was attained in environments where moderate radiative heat loss was possible and thus indicating shallow burial depths in the parent body

original structures and fragmentation and reassembly histories of asteroids evidence from meteorites abstract if chondritic meteorites were internally heated after accretion had ended then the hottest material would have been buried the deepest and should have cooled the slowest if this is correct there ought to be a correlation between cooling rate and petrographic type a measure of the extent to which chondrites were metamorphosed i e heated published and new cooling rates derived from the compositions of metallic iron nickel grains do not display this correlation implying either that chondrite parent asteroids never had onion shell structures or that bodies with onion shell structures were broken up and reassembled prior to cooling to below 500 c the temperature at which cooling rate information is recorded in metallic iron nickel chondritic regolith breccias formed from materials that resided on the surfaces of their parent asteroids metallic iron nickel grains in h and l chondrite regolith breccias indicate that the breccia constituents cooled at rates ranging from 1 to 1000 k myr based on thermal calculations these cooling rates suggest that the materials spread out on the surfaces of h and l chondrite parent asteroids originated at depths ranging from about one kilometer to several tens of kilometers craters deep enough to excavate tens of kilometers cannot form on typical asteroidal bodies only 100 to 300 km in diameter without disrupting them therefore it appears that at least some asteroids namely the parent bodies of h and l chondrites were disrupted after cooling to below 300 c and then reassembled to create surfaces containing rocks that originated at a wide range of depths these results support theoretical calculations suggesting that many asteroids were broken up and subsequently reassembled into gravitationally bound rubble piles

sediment transport capacity of sheet and rill flow application of unit stream power theory theoretical equations for calculating the unit stream power of both sheet and rill flow were developed and used to predict the sediment transport capacity of such flows independent data sets from three sources representing both finely aggregated clay soils and coarse textured nonaggregated soils sheet rill and composite sheet rill flow systems and a range of slopes were used to test the utility of the method the results were very good and demonstrated the simplicity and robustness of the method for shallow overland flow the best results were obtained when the critical unit stream power at incipient sediment motion was treated as a constant value that was independent of slope the results also suggest that a unique value of critical unit stream power for rill initiation exists that is independent of soil type for noncohesive loams or fine sands and finely aggregated clay soils the sediment transport capacity can be accurately predicted from a knowledge of the physical characteristics of the soil or bed material alone for aggregated clay soils this requires information on the aggregate size distribution and the effects of soil particle size differentiation as flow rates and unit stream powers increase with the transition from sheet to rill flow

analysis of rainfall recharge relationships abstract understanding the recharge process and its relationship with rainfall is of critical importance to the management of groundwater systems and enormous effort has been made to estimate the amount and process of recharge by infiltration using precipitation data in the present research in situ lysimeter experiments and numerical simulations were used to study the relationships between rainfall and recharge by infiltration at different groundwater depths four lysimeters 1 5 3 4 5 and 5 m deep were installed in the field to measure the infiltration recharge rates under conditions of fixed water tables at the bottoms of the soil columns annual infiltration recharges at different groundwater depths were obtained through the lysimeter measurements the effect of rainfall pattern and annual rainfall distribution on infiltration recharge was simulated at various groundwater depths using a numerical model based on soil water dynamics and comparisons of the simulated and observed recharges showed very good agreement relationships between rainfall and infiltration recharge at different groundwater depths were investigated using the lysimeter measurements and computer simulations groundwater systems were classified into three categories i e shallow water table intermediate water table and deep water table based on the relationship between rainfall and infiltration recharge at different groundwater depths

evidence for a shallow highly permeable zone in the chalk of hampshire u k abstract studies of the chalk in the u k in the last 10 15 years have shown that it is generally the top 20 50 m below the water table which provides most of the aquifer yield an investigation in hampshire in connection with a river augmentation scheme using seasonal groundwater abstraction shows the chalk in the area to have a particularly thin and well developed 6 m thick zone possessing both high transmissivity and storativity evidence is put forward to support its existence

megaregolith insulation and the duration of cooling to isotopic closure within differentiated asteroids and the moon ages determined for extraterrestrial samples by the sm nd and rb sr techniques are commonly assumed to record igneous crystallization events because in solid silicates nd and sr diffuse at exceedingly slow rates however we find that for coarse grained igneous cumulate rocks from the moon or from a large thoroughly brecciated asteroid this assumption may not be reliable the moon and at least one asteroid the parent body of the eucrite diogenite and howardite meteorites appear to have been largely molten at or about the time they formed we have modeled global cooling of the moon and large r 40 250 km asteroids starting at or near the solidus a crucial factor in determining the prevailing interval ic of cooling between igenous crystallization and isotopic closure for any given depth in the crust is the extent to which the body is insulated by a regolith megaregolith layer of porous fragmental impact debris given plausible assumptions regarding the thicknesses of such layers on the moon and the eucrite parent asteroid and regarding the radius of the eucrite asteroid our results indicate that deep crustal regions tend to remain above the nd and sr isotopic closure temperature for intervals that are long in comparison to the precision of modern nd and sr based age measurements and in comparison to suggested chronologic scenarios of global differentiation ic intervals of as long as 100 m y may be common among available samples of primordial deep crustal cumulates from both bodies chronologies for the gross solidification of the moon and the eucrite asteroid should allow for the possibility that any single age for a coarse grained plutonic or cumulate textured rock might be many tens of millions of years younger than the igneous crystallization age

sodic plagioclase thermometry of type 6 ordinary chondrites implications for the thermal histories of parent bodies the structural states of sodic plagioclase crystals of 50 m in size from three h6 two l6 and one ll6 chondritic meteorites have been determined by measuring the 131 parameter with a gandolfi camera after analyzing chemical compositions the temperature for each sodic plagioclase crystal has been determined by plotting the 131 parameter corrected for the influence of k on the relation diagram between the 131 parameter and the temperature of synthesis of sodic plagioclase by smith 1972 the temperature obtained is assigned to the crystallization temperature of sodic plagioclase and the maximum plagioclase temperature for each meteorite can be assumed to correspond to the maximum temperature attained by each meteorite during metamorphism the maximum metamorphic temperatures estimated are 725 742 c for the h6 chondrites 808 820 c for the l6 chondrites and 800 c for the ll6 chondrite these temperatures are lower than those based on ca contents of clinopyroxenes dodd 1981 mcsween et al 1988 but are consistent with those based on ca contents of orthopyroxenes mcsween and patchen 1989 langenhorst et al 1995 jones 1997 the k content of sodic plagioclase correlates with the temperature obtained from the structural state this positive correlation suggests that sodic plagioclase has formed in the course of equilibration processes of alkali elements in prograde metamorphism i e during heating processes the results of this study i e the maximum metamorphic temperature of the h6 chondrites is lower than that of the l6 chondrites by 80 c and meteorites of the same chemical group show very similar maximum metamorphic temperatures are in accordance with the predictions of calculations based on the 26al heat source and the onion shell structure model of the parent bodies

processes of water movement through a chalk coombe deposit in southeast england the processes of water movement through the coombe deposit in a chalk dry valley near eastbourne in southeast england were investigated using simple methods based on regular weekly measurements of rainfall soil water content and soil water potential the drainage flux recharge through the soil was determined using the water balance method during the winter and the zero flux plane zfp method after the appearance of the zfp in the spring the unsaturated hydraulic conductivity was derived applying darcy s law in a novel way using the measured potential gradients and weekly drainage fluxes the derived conductivity characteristics were adequate to identify the flow mechanisms to illustrate the difference in behaviour between the horizons of the soil profile and to give some indication of pore water velocities the mean daily drainage flux at 2 85 m depth during the recharge period from 10 october 1980 to 29 may 1981 was 1 6 mm d 1 weekly mean rates of up to 3 7 mm d 1 were observed but peak short term rates must have considerably exceeded this figure it was shown that in the lower part of the coombe deposit when drainage fluxes are large much of the flux passes through a very small proportion of the wetted cross sectional area of the soil this gives rise to pore water velocities of at least 3 m d 1 at a depth of 2 85 m and 0 5 m d 1 between 0 5 m and 2 5 m depth these results show that pollutants may be moved very rapidly through the profile in this and similar material the core sampling techniques normally used to monitor pollutant movement in the chalk are unlikely to succeed in detecting this movement not only because it is transient but also because it occupies only a very small proportion of the water filled pores

self potential as a predictor of seawater intrusion in coastal groundwater boreholes abstract monitoring of self potentials sps in the chalk of england has shown that a consistent electrical potential gradient exists within a coastal groundwater borehole previously affected by seawater intrusion si and that this gradient is absent in boreholes further inland furthermore a small but characteristic reduction in this gradient was observed several days prior to si occurring we present results from a combined hydrodynamic and electrodynamic model which matches the observed phenomena for the first time and sheds light on the source mechanisms for the spatial and temporal distribution of sp the model predictions are highly sensitive to the relative contribution of electrochemical exclusion and diffusion potentials the exclusion efficiency in different rock strata geoelectric heterogeneity largely due to marls and hardgrounds with a relatively high exclusion efficiency was the key factor in controlling the magnitude of the modeled sp gradient ahead of the saline front and its evolution prior to breakthrough the model results suggest that where sufficient geoelectric heterogeneity exists borehole sp may be used as an early warning mechanism for si

unsaturated flow and solute transport through the chalk tracer test and dual permeability modelling a tracer test was carried out in the unsaturated chalk at the fleam dyke research site in cambridgeshire uk to investigate the role of the chalk fractures and matrix in unsaturated flow and solute transport the experiment under natural rainfall conditions involved distributing deuterated water on a grass covered lysimeter a cube of volume 125 m3 and on an adjacent 4 m 4 m field plot tracer migration was monitored through regular core sampling and collection of lysimeter drainage water the presence of occasional secondary peaks in sampling of the vertical tracer profile suggested the occurrence of fracture flow allowing some tracer to bypass the chalk matrix however in the 15 months following application none of the tracer was detected in the lysimeter drainage at 5 m depth modelling of the tracer results was undertaken with the 1 d numerical transient dual permeability model macro 5 0 initially developed for macroporous soils modelling results showed that macro 5 0 could reliably simulate transient recharge through the chalk the simulations suggested that fracture flow is important at the site but that it is only initiated at 1 m depth or deeper the extent of fracture flow appeared to be highly variable in different layers of the profile varying between 40 and 85 of the cumulative flux mainly depending on the saturated hydraulic conductivity of the matrix diffusion between the fractures and the matrix tended to equalize solute concentrations in both flow domains although solute bypass through the fractures occurred in some chalk strata besides diffusive exchange the modelling stressed the importance of advective exchange of solutes the results suggest that the chalk aquifer at the fleam dyke site is only moderately vulnerable to pollution even though for moderate rainfall conditions some bypass flow was possible

field observation of flow in a fracture intersecting unsaturated chalk flow through a natural fracture crossing unsaturated chalk in an arid region was investigated in a field experiment using a specially designed experimental setup the setup allowed complete control of the flow domain inlet and outlet water flux into and out of the fracture was measured in small segments of the fracture openings and flow trajectories were identified using seven fluorobenzoic acid tracers a 5 day percolation experiment on a 5 3 m long fracture showed significant spatial and temporal variability of the flow regime flow through fracture openings did not reach a steady state either in individual segments or across the entire flow domain although the boundary conditions were kept relatively steady for the entire duration of the experiment flow trajectories within the fracture plane varied over time however most of the flow was confined to small sections of the fracture over 70 of the flux was transmitted through 20 of the studied fracture openings observations from the tracer tests suggest that flow paths can coexist near each other without water mixing probably because the fracture fill generates unconnected flow paths across the main fracture void

transient simulations of flow and transport in the chalk unsaturated zone chalk is a fractured porous medium composed of matrix blocks bounded by interconnected fractures furthermore there are a number of commonly observed and apparently contradictory phenomena these include a fast water table response slow solute migration and very little solute dispersion to the authors knowledge no unified physically based numerical model has been able to reconcile all of these points in this paper these issues were addressed through the development of a transient dual permeability model of flow and transport the behaviour of the model was explored through a hypothetical scenario the one dimensional model featured a fixed water table at 10 m depth a recharge time series derived using the penman grindley model in conjunction with daily precipitation and monthly potential evaporation data from the kennet valley berkshire was applied at the top of the model a conservative solute that could be tritium chloride or nitrate was applied to the recharge for 1 year subsequent years involved the input of clean water the simulations suggested that although transient effects have been previously neglected overlying soil and gravelly chalk layers are likely to cause significant attenuating effects on flow such that most flow occurs through the matrix fracture flow was found to be episodic and infrequent and represented between 17 and 30 of the annual recharge

unshocked equilibrated h chondrites a common low temperature record from orthopyroxene iron magnesium ordering a suite of eight unshocked equilibrated h chondrites ranging from petrographic type 4 to 6 la villa raguli fro 90076 miami fro 90049 estacado fro 90156 and acfer 314 was selected for a systematic study of orthopyroxene cation ordering temperatures the closure temperatures of the fe mg exchange lie within the 384 48 c to 480 28 c range regardless of the petrographic type data suggests that metamorphosed h chondrites share a similar thermal evolution close to 380 480 c indeed this indicates that h4 h5 and h6 chondrites were located in petrogenetic environments characterized by similar temperature time conditions when cooling through the above temperature interval

stochastic sediment transport in soil erosion a stochastic model governing the downslope transport of a sediment particle during an erosion event is described particles alternate between resting on the soil bed and being transported by the overland flow probability densities and moments are constructed for the distribution of a particle s position at a given time and also for time of passage to a given location we show that a suitable averaging of the stochastic particle motions in our model gives rise to the deterministic erosion differential of hairsine and rose hairsine p rose c 1991 soil sci soc am j 55 2 320 324 the model generalized h einstein s stochastic model der geschiebebetrieb als wahrscheinlichkeitsproblem verlag rascher zurich 1937 for bedload transport in streams

hydrological processes in the chalk unsaturated zone insights from an intensive field monitoring programme as part of the nerc lowland catchment research programme locar the pang lambourn catchments berkshire uk have been extensively instrumented to provide an improved understanding of the hydrological processes in the unsaturated zone of the chalk a subject of much debate over the past 30 years to quantify the movement of water through the unsaturated zone it is necessary to measure matric potential and water content as well as input and output fluxes from precipitation evapotranspiration and groundwater recharge previous studies have indicated the need for fine temporal resolution data to monitor this system effectively due to the challenges faced in meeting this objective a monitoring scheme was designed that combines a variety of instrumentation to provide the required range accuracy and spatial and temporal resolution of data this paper firstly presents an overview of the monitoring programme and a critical discussion of the instrumentation used subsequently the field data are used to characterise the hydrological properties of the unsaturated zone and to gain insight into recharge processes the interpretation of the data presented in this paper indicate that in the chalk unsaturated zone at west ilsley matrix flow is the dominant recharge mechanism

gravity driven infiltration instability in initially dry nonhorizontal fractures experimental evidence demonstrating gravity driven wetting front instability in an initially dry natural fracture is presented an experimental approach is developed using a transparent analog rough walled fracture to explore gravity driven instability three different boundary conditions were observed to produce unstable fronts in the analog fracture application of fluid at less than the imbibition capacity inversion of a density stratified system and redistribution of flow at the cessation of stable infiltration the redistribution boundary condition analogous to the cessation of ponded infiltration is considered in a series of systematic experiments gravitational gradient and magnitude of the fluid input were varied during experimentation qualitative observations imply that finger development is strongly correlated to the structure of the imbibition front at the onset of flow redistribution measurements of fingertip velocity are used to develop a first order relationship with fingertip length measured finger width is compared to theoretical predictions based on linear stability theory

the dynamic process of slope rill erosion analyzed with a digital close range photogrammetry observation system under laboratory conditions abstract as the main process of soil erosion in the loess plateau of china rill erosion accounts for a large proportion of the total erosion on the slope quantifying the rill shape is crucial for studying the mechanisms and evolution of rill erosion the objective of this study is to monitor the dynamic process of slope rill erosion using on a digital close range photogrammetry observation system during continuous rainfall artificial simulated rainfall experiments were conducted and images were obtained at different time intervals we used hydrological analysis and profile analysis tools in geographic information system gis technology to extract rill networks and their main parameters to quantitatively describe the erosion processes of rill morphology the results showed that 1 compared with the error from the traditional runoff sediment measurement method the average error of the system for estimating soil loss was 7 06 and 1 05 respectively and the highest precision for a single observation was 99 46 2 the rill erosion process could be divided into several stages raindrop splashing eclipse drop pit erosion cave rill cutting head rill erosion rill network and 3 after rainfall lasted for 80 min the density and the degree of splitting increased continuously and the maximum rill width and depth both showed fluctuating trends the area of 7 5 m to 9 5 m away from the top of the surface was the most active area of rill erosion the digital close range photogrammetric observation system can accurately obtain evolution information about rill erosion morphology during continuous rainfall which provides a reference for future studies of soil erosion processes