a spectral approach for analyzing the rill structure over hillslopes part 1 development of stochastic theory abstract the rill structure over the soil surface plays an important role in determining the runoff and sediment loss from hillslopes the microtopography is often complicated and representation of the hillslope surface on a rill by rill basis is uneconomical and impractical a spectral approach combined with a stochastic theory is proposed for the rill profile the theory develops appropriate probability distribution laws for rill amplitudes and rill periods interrill areas under the assumption that the spectrum of the rill profile is narrow banded this study establishes a foundation for future studies dealing with parameter estimation and determining the global roughness and erodibility for runoff and sediment discharge predictions over hillslopes

an experimental study of rill erosion and morphology abstract rill erosion is recognized as an important process of water erosion on agricultural land the objectives of this study are to examine the effects of rainfall intensity on rill network development and to present some indicators for a quantitative description of rill morphology a soil pan 10 m long 3 m wide and 0 5 m deep and with an adjustable slope gradient from 0 to 30 was subjected to three successive rains under rainfall intensities of 50 and 100 mm h 1 the results showed that rainfall intensity significantly affected rill erosion especially in the active period of rill network development the magnitude of rill erosion was 28 5 and 33 1 kg m 2 and contributed 78 6 and 76 2 to the soil loss under rainfall intensities of 50 and 100 mm h 1 respectively the formation of rill network under the 50 mm h 1 intensity was more complex than that under the 100 mm h 1 intensity for the latter rill networks developed fast and then varied slightly the mean rill inclination angle mean rill density degree of rill dissection and mean rill tortuosity complexity cmean increased with the increase of rains under the same rainfall intensity the value was the optimal derivative morphological indicator to estimate rill erosion and morphology which was followed in descending order by mean cmean and

geology and geochemistry of archaean granites in the kalgoorlie region of the eastern goldfields western australia a syn collisional tectonic setting abstract granites in the kalgoorlie region of the archaean yilgarn craton are predominantly biotite granodiorite and monzogranite with some hornblende bearing varieties granites are divided on the basis of field relationships petrography and chemical composition into five supersuites an older supersuite containing four suites pre dates regional folding and four supersuites post date regional folding the potassic composition of the mainly silica rich granites 68 sio2 suggest that the most appropriate source for the majority of supersuites is continental crust with a composition in the range tonalite to granodiorite most supersuites evolved by fractional crystallization mainly of biotite and plagioclase some suites contain synplutonic dykes and microgranite xenoliths that crystallized from enriched mantle derived magmas there was only limited and local chemical interaction between granite and mantle derived magmas geometric and temporal relationships between regional structures and granites indicate that the granites were emplaced during a major orogenic event however s type granites which are widespread in some modern syn collision settings are absent in the kalgoorlie region the predominance of high fo2 i type granites in the study area probably reflects the absence of large graphite bearing metasedimentary accumulations in the lower crustal source regions the distribution of suites and supersuites implies a common source region beneath the kalgoorlie and gindalbie granite greenstone terranes suggesting that they shared a common geological history dating back to late greenstone deposition

mars orbiter camera observations of the martian south polar cap in 1999 2000 the spring summer recession of the south polar cap of mars in 1999 2000 has been investigated using the wide angle cameras of the mars orbiter camera experiment on mars global surveyor the 1999 2000 regression closely resembles the recession observed by viking orbiters in 1977 although the rates of recession are quite similar the current recession was slightly ahead of that in 1977 throughout spring the rapid development of dark terrain dubbed cryptic terrain by hugh kieffer in one sector of the south cap between ls 198 and 223 is documented the emergence and separation of the mountains of mitchel has also been recorded in detail culminating with its complete disappearance at solstice the 2000 residual cap is almost identical to that in 1977 this observation does not resolve the mystery of the very different appearance of the residual cap in 1972 the albedos in the residual cap region and in bright seasonal frost increase rapidly to high values at around solstice and then level out until the seasonal frost disappears observations of more martian years will be needed to constrain the amount of interannual variability and its relation to other phenomena such as dust storms

the timing of gold mineralization across the eastern yilgarn craton using u pb geochronology of hydrothermal phosphate minerals the highly mineralized eastern goldfields of the eastern yilgarn craton is an amalgamation of dominantly neoarchaean granitoid greenstone terranes and domains that record a history of early rifting followed by westward directed collision with initial arc formation collision and clastic basin formation and final accretion to the western yilgarn proto craton between 2 66 and 2 60 billion years ago the gold deposits that define this region as a world class gold province are the product of orogenic processes that operated during accretion late in the tectonic history after initial compressional deformation d1 d2 and the majority of granitoid magmatism minor gold was also deposited throughout the entire tectonic history in magmatic hydrothermal related systems however such mineralization mostly 0 3 g t gold is nowhere economic unless it overprints or is overprinted by much higher grade orogenic gold lodes robust shrimp u pb geochronology of gold related hydrothermal xenotime and monazite supports structural studies that gold mineralization occurred during late transpressional events d3 d4 shortly before cratonization however westward migration of collision and accretion produced a complementary diachroneity in the timing of gold mineralization of 5 to 20 m y between c 2 65 ma in the east including laverton district kurnalpi terrane to c 2 63 ma in the west including kalgoorlie terrane across the eastern part of the craton the robust geochronology refutes previous suggestions that significant gold mineralization events extended from de to d4 in the evolution of the orogen and that the kalgoorlie gold deposits formed over a period of 45 m y the crustal continuum model is applicable within terranes where orogenic gold depositional events were penecontemporaneous but must be modified to account for diachroneity of orogenic events and gold mineralization across the eastern goldfields

geochemistry and tectonic setting of two contrasting archaean felsic volcanic associations in the eastern goldfields western australia abstract archaean felsic volcanic rocks from two areas in the eastern yilgarn craton of western australia comprise dacite and rhyolite with subordinate basalt and andesite one suite from one of the areas black flag group is dominated by subaqueous dacite lava lobes and their reworked products the other suite from the other area melita and jeedamya volcanics consists of abundant rhyolitic and rhyodacitic pyroclastic deposits with less abundant dacitic lava flows both suites are intercalated with volumetrically subordinate basic and intermediate volcanic rocks black flag group dacites and rhyolites have steep ree patterns la yb cn about 40 and no eu anomaly high sr and al2o3 low nb and y hence high sr y melita and jeedamya dacites and rhyolites have flatter ree patterns la yb cn between 2 and 9 negative eu anomalies eu eu 0 4 0 6 and higher zr nb y and lower sr hence lower sr y on chemical grounds mafic rocks in both areas are genetically unrelated to felsic volcanic rocks black flag group andesites dacites and rhyolites are probably unrelated by fractional crystallization but resulted from 22 28 partial melting of amphibolite leaving a residual mineralogy of amphibole plagioclase garnet ilmenite clinopyroxene alternatively andesites may have been derived by partial melting of a metasomatised mantle source jeedamya rhyodacite could have been produced by 35 vapour absent melting of tonalite leaving a residual mineralogy of plagioclase orthopyroxene amphibole ilmenite the source would have had a slightly lree enriched pattern with a positive eu anomaly residual garnet in the source of black flag group rocks requires melting at depths greater than 35 km which is below the base of the present tectonically thinned crust the most likely source is subducted oceanic crust with black flag group rocks erupted in a back arc basin melita and jeedamya felsic volcanic rocks resulted from melting of thicker continental crust adjacent to the back arc

experimental investigation of morphological characteristics of rill evolution on loess slope abstract the development of rill is the result of a complex interaction of soil properties with high spatial and temporal variability the rill morphology may act as a determinant as well as a stochastically driven process the description of their complex morphology requires geostatistics and nonlinear theories a study of the morphological characteristics of rill evolution was performed via indoor soil pan rainfall simulations experiments were run with loessial soil bulk density of 1 25 g cm 3 under a rainfall intensity of 90 mm h with a 20 slope gradient a detailed scan of the slope topographic analysis and statistical analyses were the main methods utilized in the study statistical analyses showed that characteristic parameters exhibited differences in the expression of the dynamic change of soil loss according to the comparison of quantitative methods we found that the fractal dimension can reflect the complexity of rill network but it is not able to reflect the dynamic changes of the erosion process perfectly in contrast geomorphologic comentropy is sensitive to the dynamic changes of soil erosion intensity and its variation can reflect the dynamic changes of erosion perfectly the topological parameters can reflect the degree of stability in the rill network structure but it is not suitable for reflecting the dynamic changes of erosion intensity the geomorphologic comentropy was evaluated as the most appropriate characterization parameter for the rill morphology description

araneiform terrain formation in angustus labyrinthus mars abstract the south polar area of mars exhibits an abundance of distinctive and exotic landforms most of which occur within the region covered by the seasonal co2 cap araneiform terrain also referred to as terrain covered by spiders is one of these unusual geomorphic features resulting from co2 sublimation driven seasonal erosion the high resolution imaging science experiment hirise on board nasa s mars reconnaissance orbiter mro spacecraft has repeatedly imaged angustus labyrinthus informally known as the inca city region 81 s 296 e over a period of four martian years showing a variety of classic polar features associated with sublimation and deposition including spiders we mapped the spiders spatial distribution in the inca city region and classified them in view of their morphological and topographic characteristics into four types fat thin half and elongated spiders the latter two are reported for the first time in this work we find that the formation mechanisms of half and elongated spiders were substantially influenced by ridge boundaries topography and pre existing linear depressions respectively based on our observations we extend the conceptual model of spider erosion explaining new elements of the spider formation process we interpret the causes of deviating araneiform species from thin spiders i e half elongated and fat spiders in the context of the extended model we consider the migration of pressurized co2 through the porous substrate towards breaches in the ice cover and the influence of the substrate s cohesive strength on the development of spider legs analysis of the spatial distribution of a fat spider population revealed that the initiation locations of spiders are not random but more evenly spaced indicating the existence of an inhibited zone around a newly formed spider consistent with our interpretations of the formation mechanism our case study in the inca city region provides new understanding in the formation process of basal sublimation driven features and thus offers new insight into polar surface processes

morphology and influencing factors of rills in the steep slope in yuanmou dry hot valley sw china abstract it is very important to understand rill morphology in order to understand its dynamics to reveal the morphology and influencing factors of rills in the steep slope rss in the yuanmou dry hot valley the total station photogrammetric technique and microtopographic profiler were used to obtain the parameters of the cross sections and longitudinal profiles of the rss and 12 parameters were used to characterize the rill morphology the results show that the morphology of rills clearly varied between each layer the topography soil properties and ferruginous cemented layer all exerted important influences on the rill morphology the average depth decreased with increasing slope length and the depths dominated by silt and sand were larger than that dominated by clay the average width and average width depth ratio increased with increasing slope length and the width and the width depth ratio that was dominated by clay was larger than that dominated by silt and sand the shape ratio of the rill cross section ranged from 0 50 to 0 58 and the shape of the cross section gradually changed from narrow and deep to wide and shallow with increasing slope length concave convex degree tended to be larger in the segment with ferruginous cement in the longitudinal profile the gradient gradually decreased with decreasing slope gradient and increasing slope length the presence of the ferruginous cemented layer and topsoil crust resulted in abnormal changes in the shape of the rill it is helpful to further understand the mechanisms of rill erosion under different conditions

observations of the south seasonal cap of mars during recession in 2004 2006 by the omega visible near infrared imaging spectrometer on board mars express 1 the omega visible near infrared imaging spectrometer on board mars express has observed the southern seasonal cap in late 2004 and 2005 and then in the summer of 2006 these observations extended from the period of maximum extension close to the southern winter solstice to the end of the recession at ls 325 the spectral range and spectral resolution of omega make it possible to monitor the extent and effective grain size of co2 ice and h2o ice on the ground the level of contamination of co2 ice and h2o ice by dust and the column density of m sized ice grains in the atmosphere the co2 seasonal cap is very clean and clear in early southern winter contamination by h2o ice spreads eastward from the hellas basin until the southern spring equinox during southern spring and summer there is a very complex evolution in terms of effective grain size of co2 ice and contamination by dust or h2o ice h2o ice does not play a significant role close to the southern summer solstice contamination of co2 ice by h2o ice is only observed close to the end of the recession as well as the few h2o ice patches already reported by bibring et al 2004a these observations have been compared to the results of a general circulation model with good qualitative agreement on the distribution of h2o ice on the surface and in the atmosphere resolving the remaining discrepancies will improve our understanding of the water cycle on mars

mars south polar spring and summer behavior observed by tes seasonal cap evolution controlled by frost grain size thermal emission spectrometer tes observations of the recession phase of mars south polar cap are used to quantitatively map this recession in both thermal and visual appearance geographically nonuniform behavior interior to the cap is characterized by defining several small regions which exemplify the range of behavior for most of the cap while temperatures remain near the co2 frost point albedos slowly increase with the seasonal rise of the sun then drop rapidly as frost patches disappear over a period of 20 days a cryptic region remains dark and mottled throughout its cold period tes observations are compared with first order theoretical spectra of solid co2 frost with admixtures of dust and h2o the tes spectra indicate that the cryptic region has much larger grained solid co2 than the rest of the cap and that the solid co2 here may be in the form of a slab the mountains of mitchel remain cold and bright well after other areas at comparable latitude apparently as a result of unusually small size of the co2 frost grains we found little evidence for a significant presence of h2o although co2 grain size may be the major difference between these regions incorporated dust is also required to match the observations a self cleaning process carries away the smaller dust grains comparisons with viking observations indicate little difference in the seasonal cycle 12 martian years later the observed radiation balance indicates co2 sublimation budgets of up to 1250 kg m 2 regional atmospheric dust is common localized dust clouds are seen near the edge of the cap prior to the onset of a regional dust storm and interior to the cap during the storm

albedo of the south pole on mars determined by topographic forcing of atmosphere dynamics the nature of the martian south polar cap has remained enigmatic since the first spacecraft observations in particular the presence of a perennial carbon dioxide ice cap the formation of a vast area of black slab ice known as the cryptic region and the asymmetric springtime retreat of the cap have eluded explanation here we present observations and climate modelling that indicate the south pole of mars is characterized by two distinct regional climates that are the result of dynamical forcing by the largest southern impact basins argyre and hellas the style of surface frost deposition is controlled by these regional climates in the cold and stormy conditions that exist poleward of 60 degrees s and extend 180 degrees in longitude west from the mountains of mitchel approximately 30 degrees w surface frost accumulation is dominated by precipitation in the opposite hemisphere the polar atmosphere is relatively warm and clear and frost accumulation is dominated by direct vapour deposition it is the differences in these deposition styles that determine the cap albedo

density of mars south polar layered deposits both poles of mars are hidden beneath caps of layered ice we calculated the density of the south polar layered deposits by combining the gravity field obtained from initial results of radio tracking of the mars reconnaissance orbiter with existing surface topography from the mars orbiter laser altimeter on the mars global surveyor spacecraft and basal topography from the mars advanced radar for subsurface and ionospheric sounding on the mars express spacecraft the results indicate a best fit density of 1220 kilograms per cubic meter which is consistent with water ice that has 15 admixed dust the results demonstrate that the deposits are probably composed of relatively clean water ice and also refine the martian surface water inventory

characterization of the rill geometry over straight hillslopes through spatial scales abstract experimental evidence is presented which shows that there exists a spatial scale over which ergodic assumptions are applicable for rilled hillslope surfaces the property of expected spatial rill density esrd is defined and this property is shown to stabilize after the averaging interval is more than 20 ft over the hillslope the rilled hillslope geometry may be readily quantified in terms of this easily measurable quantity the rill geometry has a significant influence on the surface distribution of overland flow and sediment transport an analysis of the spatial scales suggests that a continuum representation may be utilized in modeling these hydrodynamic flow phenomena for a complete characterization of the rilled hillslope geometry the distributions of the rill widths and rill depths at various locations along the hillslope have been presented these preliminary results show that the mean rill widths the mean rill depths and the esrd increase with increasing slope lengths the distributions of the rill widths and rill depths suggest that these quantities may be modeled by truncated gaussian or gamma distributions at different spatial locations the rill geometry properties may be related to hydrologic and geomorphologic properties of the hillslope it is suggested that the esrd is a better descriptor of the rill geometry on the hillslope than the rill density because of the wide variations exhibited by the distributions of the rill widths

compact reconnaissance imaging spectrometer for mars crism south polar mapping first mars year of observations 1 we report on mapping of the south polar region of mars using data from the compact reconnaissance imaging spectrometer for mars crism instrument our observations have led to the following discoveries 1 water ice is present in the form of pole circling clouds originating from the circum hellas region beginning prior to ls 162 and diminishing markedly at ls 200 204 2 it has previously been inferred by thermal infrared observations by titus et al 2003 and co2 h2o mixture spectral models by langevin et al 2007 that surface water ice was present in the cryptic region in the final stages of sublimation the high resolution of crism has revealed regions where only water ice is present not a co2 h2o ice mixture this water ice disappears completely by ls 252 and may be the source of water vapor observed by crism in southern latitudes between ls 240 260 by m smith et al 2009 3 we have estimated surface co2 ice grain size distributions for the south pole residual cap sprc and the seasonal co2 ice cap that covers it throughout summer spring and summer our analysis suggests that grain sizes peak at ls 191 199 with an apparent grain size of 7 1 cm by the end of the summer period our analysis demonstrates minimum apparent grain sizes of 5 1 mm predominate in the sprc 4 fine grained co2 ice condenses from ls 0 40 and extends symmetrically away from the geographic pole extending beyond 80 s by ls 4 10 no evidence for unusual co2 depositional processes in the cryptic region is observed up to ls 16

composite synvolcanic intrusions associated with precambrian vms related hydrothermal systems large subvolcanic intrusions are recognized within most precambrian vms camps of these 80 are quartz diorite tonalite trondhjemite composite intrusions the vms camps spatially associated with composite intrusions account for 90 of the aggregate sulfide tonnage of all the precambrian intrusion related vms camps these low alumina low k and high na composite intrusions contain early phases of quartz diorite and tonalite followed by more voluminous trondhjemite they have a high proportion of high silica 74 sio2 trondhjemite which is compositionally similar to the vms hosting rhyolites within the volcanic host rock successions the quartz diorite and possibly tonalite phases follow tholeiitic fractionation trends whereas the trondhjemites fall within the composition field for primitive crustal melts these transitional m i type primitive intrusive suites are associated with extensional regimes within oceanic arc environments subvolcanic composite intrusions related to the archean sturgeon lake and noranda and paleoproterozoic snow lake vms camps range in volume from 300 to 1 000 km3 three have a sill morphology with strike lengths between 15 and 22 km and an average thickness between 1 500 and 2 000 m the fourth has a gross stock like shape the vms deposits are principally restricted to the volcanic strata above the strike length of the intrusions as are areally extensive thin exhalite units the composite intrusions contain numerous internal phases which are commonly clustered within certain parts of the composite intrusion these clusters underlie eruptive centers surrounded by areas of hydrothermal alteration and which contain most of the vms deposits early quartz diorite and tonalite phases appear to have intruded in rapid succession evidence includes gradational contacts magma mixing and disequilibrium textures they appear to have been emplaced as sill dike swarms these early phases are present as pendants and xenoliths within later trondhjemite phases the trondhjemite phases contain numerous internal contacts indicating emplacement as composite sills common structural features of the composite intrusions include early xenolith phases abundant small comagmatic dikes fractures and veins and in places columnar jointing internal phases may differ greatly in texture from fine to coarse grained aphyric and granophyric through seriate to porphyritic mineralogical and isotopic evidence indicates that early phases of each composite intrusion are affected by pervasive to fracture controlled high temperature 350 450 c alteration reflecting seawater rock interaction trondhjemite phases contain hydrothermal magmatic alteration assemblages within miarolitic cavities hydrothermal breccias and veins this hydrothermal magmatic alteration may in part be inherited from previously altered wall rocks two of the four intrusions are host to cu mo rich intrusive breccias and porphyry type mineralization which formed as much as 14 ma after the main subvolcanic magmatic activity the recognition of these precambrian subvolcanic composite intrusions is important for greenfields vms exploration as they define the location of thermal corridors within extensional oceanic arc regimes which have the greatest potential for significant vms mineralization the vms mineralization may occur for 2 000 m above the intrusions in some cases vms mineralization has been truncated or enveloped by late trondhjemite phases of the composite intrusions evidence that much of the trondhjemitic magmatism postdates the principal vms activity is a critical factor when developing heat and fluid flow models for these subseafloor magmatic hydrothermal systems

determining the mean depth of overland flow in field studies of flow hydraulics in field studies of interrill overland flow conducted on runoff plots the mean depth of flow is usually obtained by averaging measurements of flow depth at regularly spaced points across the plot including points where there is no flow although this procedure may be appropriate in studies aimed at runoff prediction it is not in studies concerned with flow hydraulics in the latter studies more realistic results can be obtained by excluding those points where the depth is zero and reducing the width of flow in proportion to the number of points excluded failure to do this results in the underestimation of the actual mean flow depth reynolds number and friction factor where discharges are small or microtopography is large this underestimation is likely to be significant

yearly comparisons of the martian polar caps 1999 2003 mars orbiter camera observations abstract the mars global surveyor mars orbiter camera wide angle cameras were used to obtain images of the north and south seasonal and residual polar caps between 1999 and 2003 wide angle red camera images were used in assembling mosaics of the north and south polar recessions and regression rates were measured and compared there are small variations in the north polar recession between 2000 and 2002 especially between l s 7 and l s 50 however there is no evidence for the plateau in the recession curves that has been observed in some prior years the south polar recession changes very little from year to year and the 2001 dust storm had little if any effect on the average cap recession that year albedo values of the geographic north pole were measured using wide angle red and blue camera images and the residual south polar cap configuration was compared between the three years observed by moc the albedo of the geographic north pole generally varies between 0 5 and 0 6 as measured from moc wide angle red camera images there were only minor variations near the edges of the residual south polar cap between the three years examined

neoarchaean metamorphic evolution of the yilgarn craton a record of subduction accretion extension and lithospheric delamination abstract the greater part of the metamorphic record of the yilgarn craton formed during a protracted middle neoarchaean orogenic cycle spanning from about 2750 to 2620 ma at least six distinct metamorphic events are defined by parageneses in different tectono stratigraphic settings this review characterizes the middle neoarchaean metamorphic response of the entire craton using large databases rock descriptions from 60 000 sites in government databases and 1040 pt determinations from all sources are used to construct metamorphic map patterns for each of these metamorphic events p t paths and timing of each metamorphic event are characterized using petrology and the well constrained pt determinations from this study n 287 combined with metamorphic age determinations from all sources n 114 the spatial patterns and metamorphic conditions of each event provides critical constraints on tectonic settings and changes in tectonics over 130 million years the record of metamorphism in conjunction with stratigraphic kinematic and magmatic constraints shows that the neoarchaean craton evolved from an accretionary crustal growth phase ma and m1 to thermal reworking of the crust during massive influx of granitic intrusions m2 and lithospheric extension after the termination of subduction m3 these events were followed by lithospheric delamination resulting in a craton wide diffusion delayed thermal pulse that coincided with renewed contraction m4 m1 metamorphism at 2748 19 2727 8 and 2706 10 ma experienced high p moderate t hairpin clockwise p t paths during burial of magmatic arc margins during terrane accretion events m2 regional contact type metamorphism at 2671 6 ma tracked low p moderate t clockwise p t paths in back arc settings during voluminous felsic magmatism related to shallow subduction m3 metamorphism at 2656 5 ma experienced low p moderate t anticlockwise p t paths in post volcanic rift basins formed during lithospheric extension m4 metamorphic peaks at 2644 4 and 2629 7 ma experienced low p high t clockwise p t paths during regional scale thermal pulses resulting from lower crust and mantle lithosphere delamination at 2665 2668 ma

perennial water ice identified in the south polar cap of mars the inventory of water and carbon dioxide reservoirs on mars are important clues for understanding the geological climatic and potentially exobiological evolution of the planet1 from the early mapping observation of the permanent ice caps on the martian poles2 3 the northern cap was believed to be mainly composed of water ice whereas the southern cap was thought to be constituted of carbon dioxide ice however recent missions nasa missions mars global surveyor and odyssey have revealed surface structures4 altimetry profiles5 underlying buried hydrogen6 and temperatures of the south polar regions that are thermodynamically consistent with a mixture of surface water ice and carbon dioxide7 here we present the first direct identification and mapping of both carbon dioxide and water ice in the martian high southern latitudes at a resolution of 2 km during the local summer when the extent of the polar ice is at its minimum we observe that this south polar cap contains perennial water ice in extended areas as a small admixture to carbon dioxide in the bright regions associated with dust without carbon dioxide at the edges of this bright cap and unexpectedly in large areas tens of kilometres away from the bright cap

oxygen isotope alteration in the noranda mining district abitibi greenstone belt quebec a regional whole rock oxygen isotope survey carried out in the noranda district shows how oxygen isotope alteration can be used to guide exploration for massive sulfide deposits the survey is based on 588 outcrop whole rock oxygen isotope determinations from 478 sites in a approximately 35 by 50 km area between the destor porcupine and cadillac larder lake breaks from east of the horne mine to west of the magusi river mine the mean isotopic composition of all samples is 7 4 or 2 per mil smow nested analysis of variance of 478 isotopic determinations from 371 of these sites shows that 74 percent of the total variance in whole rock delta 18 o r r whole rock is associated with outcrop location 21 percent with outcrop sampling and 5 percent with sample analysis an analysis of 259 determinations indicates that rock type is statistically no more important than outcrop sampling the statistical analysis indicates that isotopic variations greater than or 1 per mil can be used to map the hydrothermal circulation responsible for massive sulfide mineralization specific traverses visually confirm the lack of 18 o dependence on rock type and the utility of a 2 per mil interpretive band the large scale pattern of isotopic alteration in the noranda district is dominated by a nearly continuous 2 to 3 km wide annulus at the margins of the flavrian pluton of delta 18 o r 18 o r 18 o r depletion is surrounded up section by a approximately 10 km wide band of patchy but intense 18 o enrichment 8 5 14ppm the combined pattern of concentric light and heavy alteration has a diameter of approximately 30 km the clericy intrusion shows a similar pattern of isotope alteration on a smaller 10 km diam scale the lake dufault pluton seems to have been isotopically altered by continuing convection driven by the flavrian hydrothermal system modeling suggests that the 18 o depletion is produced by water circulating toward and along the edges of an intrusion and that the surrounding heavy alteration is produced either by seawater recharge or limited hydrothermal discharge the large scale and coherency of the alteration pattern centered on the flavrian pluton is remarkable and indicates that this pluton drove a major long lived approximately 10 m y hydrothermal system in which convection penetrated to an 8 kin depth the intensity and coherency of the 18 o depletion correlates with the tonnage of associated massive sulfide mineralization oxygen isotope depletion may in general mark the margins of plutons that have driven sufficient hydrothermal circulation to produce economic massive sulfide deposits up section it may be possible to screen plutons for up section massive sulfide exploration potential by collecting and isotopically analyzing approximately 50 samples from five traverses across a pluton9s margins additional samples may provide details light fingers that guide exploration to particular deposits

do deterministic sediment detachment and transport equations adequately represent the process interactions in eroding rills an experimental field study abstract this paper tackles two main questions by linking observations determination of hydraulic parameters and measurement of sediment transport with the formulae used in soil erosion models first do constant shear stress values in different rills with constant soil parameters result in the same soil detachment values secondly deterministic soil erosion models make the assumption that there is a relationship often further assumed to be linear between shear stress and soil detachment is this suitable for representing real erosion process combinations in natural rills following most process based deterministic soil erosion models derived hydraulic and erosion parameters should be similar however the results from the different experiments showed clear differences in sediment concentration transport rates and other measured as well as calculated values in contrast to our experimental results a model simulation would produce erosion parameters with low variations represented by the relative measurement error and the empirical variation coefficient this reveals the general problems of using process based deterministic models for erosion in shallow rills while soil erosion models simulate the processes resulting from the shear forces of flowing water on the soil surface other processes like side wall failure headcut retreat and plunge pool dynamics are not taken into account our results suggested that these other processes may contribute substantially to rill erosion processes the results of this study strongly suggested that the model concept of most physical based soil erosion models is inadequate for modeling rill erosion processes measured total rill erosion rates were the sum of erosion rates caused by a combination of different soil erosion processes with different spatial and temporal distribution this combination cannot be described by a single equation

apportioning contributions of individual rill erosion processes and their interactions on loessial hillslopes abstract channels rill ephemeral gully gully and river channel exhibit a continuum of sizes and flow magnitudes rill erosion as the initial stage of channel erosion accounts for 80 of total eroded sediments on sloping farming lands in many parts of the world previous researches often regard rill erosion as an entirety or focus on individual rill erosion process separately few attentions have been paid to the contributions of individual processes including rill headcut advance bed incision sidewall expansion and their interactions to the over all rill erosion thus simulated upslope inflow experiments were designed to investigate the impacts of individual processes involved and their interactions in rill erosion under four inflow rates 1 0 2 0 3 0 and 4 0 l min 1 and two slope gradients 15 and 20 photogrammetry and manual sampling were used to measure hillslope morphology variation and sediment delivery repectively the results show that headcut advance bed incision and sidewall expansion interact with each other and exhibit both independent and dependent features across spatial and temporal scales headcut advance interacts with bed incision and sidewall expansion before rill head advancing to a critical slope length initial rill depth and width are determined by initial headcut morphology bed incision and sidewall expansion dominate rill erosion before and after the non erodible layer is exposed to concentrated flow respectively headcut advance contributed the largest amount of rill erosion 44 68 followed by bed incision 27 44 and sidewall expansion 3 8 12 headcut advance contributed more 63 83 to total rill width increment while bed incision contributed larger percentage 51 65 to total rill depth increment prediction equations for length width and depth of a single rill on a loessial hillslope and empirical equations of rill erosion for the individual erosion processes were fitted and validated quantification and understanding of the contributions of individual rill erosion processes provides the necessary scientific basis for the development of process based rill erosion models and then for preventions of soil losses and land degradation

accumulation and erosion of mars south polar layered deposits mars polar regions are covered with ice rich layered deposits that potentially contain a record of climate variations the sounding radar sharad on the mars reconnaissance orbiter mapped detailed subsurface stratigraphy in the promethei lingula region of the south polar plateau planum australe radar reflections interpreted as layers are correlated across adjacent orbits and are continuous for up to 150 kilometers along spacecraft orbital tracks the reflectors are often separated into discrete reflector sequences and strong echoes are seen as deep as 1 kilometer in some cases the sequences are dipping with respect to each other suggesting an interdepositional period of erosion in australe sulci layers are exhumed indicating recent erosion

massive co2 ice deposits sequestered in the south polar layered deposits of mars shallow radar soundings from the mars reconnaissance orbiter reveal a buried deposit of carbon dioxide co2 ice within the south polar layered deposits of mars with a volume of 9500 to 12 500 cubic kilometers about 30 times that previously estimated for the south pole residual cap the deposit occurs within a stratigraphic unit that is uniquely marked by collapse features and other evidence of interior co2 volatile release if released into the atmosphere at times of high obliquity the co2 reservoir would increase the atmospheric mass by up to 80 leading to more frequent and intense dust storms and to more regions where liquid water could persist without boiling

the polar deposits of mars the tantalizing prospect of a readable record of martian climatic variations has driven decades of work toward deciphering the stratigraphy of the martian polar layered deposits and understanding the role of the residual ice caps that cover them spacecraft over the past decade have provided a massive infusion of new data into mars science polar science has benefited immensely due to the near polar orbits of most of the orbiting missions and the successful landing of the phoenix spacecraft in the northern high latitudes topographic thermal radar hyperspectral and high resolution imaging data are among the datasets that have allowed characterization of the stratigraphy of the polar layered deposits in unprecedented detail additionally change within the residual ice caps has been monitored with spacecraft instruments for several years these new data have provided a golden opportunity to understand the interplay between the martian orbit climate and polar ice

cold jets in the martian polar caps 1 mars seasonal polar caps display dark ice local darker spots aligned elongate patches and radially dendritic forms that reverse albedo contrast the unexpected variety and sequence of these features are explained on the basis of processes involving co2 dust sand and h2o these processes are largely related to the atmosphere being near its saturation temperature and they have few terrestrial analogies in the simplest case the 1 m thick seasonal cap initially dusty cleans itself and becomes translucent after sunrise and is impermeable over extensive regions except for local vents the slab ice sublimates at the base and is levitated on high pressure gas causing humidity exchange with deeper layers subslab gas converging toward the vents erodes channels in the soil and ejects this material in high velocity jets recent spectral observations indicate great variety in the details

sublimation of mars s southern seasonal co2 ice cap and the formation of spiders 1 in this paper we define and describe morphological features that have colloquially been termed spiders and map their distribution in the south polar region of mars we show that these features go through a distinct seasonal evolution exhibiting dark plumes and associated fan shaped deposits during the local defrosting of the seasonal cap we have documented the seasonal evolution of the cryptic region and have found that spiders only occur within this terrain these observations are consistent with a geyser like model for spider formation association with the transparent cryptic portion of the seasonal cap is consistent with basal sublimation and the resulting venting of co2 gas also consistent with such venting is the observation of dark fan shaped deposits apparently emanating from spider centers spiders are additionally confined to the polar layered deposits presumably due to the poorly consolidated and easily eroded nature of their upper surface

marci and moc observations of the atmosphere and surface cap in the north polar region of mars abstract we used mgs moc and mro marci daily mapping images of the north polar region of mars from 16 august 2005 ls 270 to 21 may 2009 ls 270 covering portions of three consecutive martian years my 27 my 29 to observe the seasonal behavior of the polar ice cap and atmospheric phenomena the rate of cap regression was similar in my 28 and my 29 but was advanced by 3 5 of ls 7 8 sols in my 29 the spatial and temporal behaviors of dust and condensate clouds were similar in the two years and generally in accord with prior years dust storms 100 km2 were observed in all seasons with peak activity occurring at ls 10 20 from 50 n to 70 n and at ls 135 140 from 70 n to 90 n the most active quadrant was 0 90 w in my 28 shifting to 180 270 w in my 29 the majority of regional storms in both years developed in longitudes from 10 w to 60 w during late summer the larger storms obscure the north polar region in a cloud of dust that transitions to north polar hood condensate clouds around autumnal equinox changes in the distribution of perennial ice deposits especially in olympia planum were observed between the 2 years with the my 29 ice distribution being the most extensive observed to date modeling suggests that the small bright ice patches on the residual cap are not the result of slope or elevation effects rather we suggest that they are the result of local meteorological effects on ice deposition the annual darkening and brightening of peripheral areas of the residual cap around summer solstice can be explained by the sublimation of a brighter frost layer revealing an underlying darker ice rich layer that itself either sublimes to reveal brighter material below or acts as a cold trap attracting condensation of water vapor that brightens the surface an alternative explanation invokes transport and deposition of dust on the surface from the cap interior and later removal of that dust the decrease in cap albedo and accompanying increase in near surface atmospheric stability may be related to the annual minimum of polar storm activity near northern summer solstice

hirise observations of gas sublimation driven activity in mars southern polar regions i erosion of the surface the high resolution imaging science experiment hirise on the mars reconnaissance orbiter mro has imaged the sublimation of mars seasonal co2 polar cap with unprecedented detail for one complete martian southern spring in some areas of the surface beneath the conformal coating of seasonal ice radiallyorganized channels are connected in spidery patterns the process of formation of this terrain erosion by gas from subliming seasonal ice has no earthly analog the new capabilities high resolution color and stereo images of hirise enable detailed study of this enigmatic terrain two sites are analyzed in detail one within an area expected to have translucent seasonal co2 ice and the other site outside that region stereo anaglyphs show that some channels grow larger as they go uphill implicating gas rather than liquid as the erosive agent dark fans of material from the substrate are observed draped over the seasonal ice and this material collects in thin to thick layers in the channels possibly choking off gas flow in subsequent years resulting in inactive crisscrossing shallow channels in some areas there are very dense networks of channels with similar width and depth and fewer fans emerging later in the season are observed subtle variations in topography affect the channel morphology a new terminology is proposed for the wide variety of erosional features observed

distinct basement terranes identified from granite geochemistry in late archaean granite greenstones yilgarn craton western australia abstract hidden basement terranes have been identified by a geochemical study of granites that intrude deformed greenstones in the eastern goldfields of the yilgarn craton the granites are calc alkaline rocks with a high average silica content 72 5 wt lie mainly in the compositional range of granodiorite to monzogranite and are derived from melting of pre existing sialic crust the greenstones comprise several tectono stratigraphic terranes that were essentially assembled before intrusion of the granites the distribution of granite types generally shows no spatial relationship to these terranes or to terrane boundary faults the emu fault which separates the kurnalpi terrane to the east from the kalgoorlie and gindalbie terranes to the west provides an exception granites to the east of this fault have lower tio 2 feo 2 and mgo and generally higher na 2 o compared to granites to the west these contrasting compositions result from differences within the source regions and are interpreted to reflect two distinct basement terranes the basement terrane beneath the kurnalpi region had a higher proportion of tonalite than was present beneath the kalgoorlie and gindalbie terranes we suggest that a regional tonalite trondhjemite granodiorite basement was accreted prior to complete accumulation of the greenstones and was later recycled to form the granites the emu fault is inferred to reflect a suture in the underlying basement of the greenstones

subaqueous intermediate to silicic composition explosive volcanism a review abstract mass flow deposits of pyroclastic debris commonly consist of two parts a lower coarse grained basal section and an upper finer grained bedded section subaqueous pyroclastic flow deposits particularly those derived from a vertically directed eruption appear better sorted than their subaerial counterparts because of the efficient sorting characteristics of water compared to air subaqueous deposits frequently are depleted in bubble wall pumice that floats off and vitric ash that remains in suspension hence the deposits show a relative enrichment of crystals especially at the bases from 1 flotation and suspension of the vitric material and 2 ingestion of water at the head of the flow a subaqueous volcaniclastic flow deposit may contain evidence indicative of both turbulent and non turbulent movement the flow may have had a turbulent head and non turbulent body or flow transformations may have occurred from 1 collapse of the eruption column 2 changes in slope and in the velocity of the flow and or 3 the amount of water mixed into the flow retention of heat in the subaqueous environment may be enhanced by lateral eruptions high eruption rates large eruptive volumes and little or no mixing of pyroclastic debris with water the lack of welded subaqueous deposits in the geologic record may be a result of 1 effusive rather than explosive eruptions in a deep water environment 2 explosive phreatic disintegration of pyroclastic flows in a shallow subaqueous environment and or 3 the inability of subaerial pumiceous pyroclastic flows to penetrate the land water interface characteristics of explosive intermediate to silicic composition subaqueous volcanic eruptions also have been summarized in terms of 1 environment of the eruption 2 orientation of the eruption and 3 composition of the juvenile debris these three aspects of explosive subaqueous volcanism are ideal end members and gradations no doubt occur

interannual and seasonal changes in the south seasonal polar cap of mars observations from my 28 31 using marci the mars color imager marci camera on the mars reconnaissance orbiter provides daily synoptic coverage that allows monitoring of seasonal cap retreat and interannual changes that occur between mars years my and over the southern summer we present the first analysis of this data for the southern seasonal cap evolution observed in my 28 29 30 and 31 2 2007 to 07 2013 observation over multiple mars years allows us to compare changes between years as well as longer term evolution of the high albedo deposits at the poles seasonal cap retreat is similar in all years and to retreats observed in other years by both optical and thermal instruments the cryptic terrain has a fairly consistent boundary in each year but numerous small scale variations occur in each my observed additionally numerous small dark deposits are identified outside the classically identified cyptic region including inca city and other locations not previously noted the large water ice outlier is observed to retain seasonal frost the longest outside the polar dome and is also highly variable in each my the development of the cryptic anti cryptic hemispheres is inferred to occur due to albedo variations that develop after dust venting starts and may be caused by recondensation of co2 ice on the brightest and coldest regions controlled by topographic winds ground ice may play a role in which regions develop cryptic terrain as there is no elevation control on either cryptic terrain or the late season brightest deposits

no signature of clear co2 ice from the cryptic regions in mars south seasonal polar cap the seasonal polar ice caps of mars are composed mainly of co2 ice a region of low 30 albedo has been observed within the south seasonal cap during early to mid spring the low temperature of this cryptic region has been attributed to a clear slab of nearly pure co2 ice with the low albedo resulting from absorption by the underlying surface here we report near infrared imaging spectroscopy of the south seasonal cap the deep and broad co2 absorption bands that are expected in the near infrared with a thick transparent slab of co2 ice are not observed models of the observed spectra indicate that the low albedo results from extensive dust contamination close to the surface of a co2 ice layer which could be linked to atmospheric circulation patterns the strength of the co2 absorption increases after mid spring so part of the dust is either carried away or buried more deeply in the ice layer during the co2 ice sublimation process

depth distribution of interrill overland flow and the formation of rills a gumbel distribution for maxima is proposed as a model for the depths of interrill overland flow the model is tested against three sets of field measurements of interrill overland flow depths obtained on shrubland and grassland hillslopes at walnut gulch experimental watershed southern arizona the model is found to be a satisfactory fit to 81 of the 90 measured distributions the shape and location parameters of all fitted distributions are strongly correlated with discharge however whereas a common relationship exists between discharge and for all depth distributions the relationships with vary systematically downslope using the gumbel distribution as a model for the distribution of overland flow depths a probabilistic model for the initiation of rills is developed drawing upon the previous work of nearing as an illustration of this approach we apply this model to the shrubland and grassland hillslopes at walnut gulch it is concluded that the presence of rills on the shrubland but not on the grassland is due to the greater runoff coefficient for the shrubland and or the greater propensity of the shrubland for soil disturbance compared with the grassland finally a generalized conceptual model for rill initiation is proposed this model takes account of the depth distribution of overland flow the probability of flow shear stress in excess of local soil shear strength the spatial variability in soil shear strength and the diffusive effect of soil detachment by raindrops copyright 2005 john wiley sons ltd

long term observations of southern winters on mars estimations of column thickness mass and volume density of the seasonal co2 deposit from hend odyssey data 1 in this paper we have analyzed neutron spectroscopy data gathered by the high energy neutron detector hend instrument on board mars odyssey for two martian years of orbital mapping we focused on the observations of the martian southern seasonal cap for this period of time nuclear methods based on numerical modeling allow us to derive an estimation of the distribution of co2 frost column density and mass from the temporal variations of neutron flux between summer and winter seasons we have estimated the seasonal behavior of both the column density and mass of co2 frost comparison between two martian years revealed minor 10 interannual variations of co2 thickness at the south pole during the middle of southern winter it was found that maximal mass of the southern seasonal cap is achieved at ls 160 and is equal to 6 6 0 6 1015 kg we found that this result corresponds well with previous hend results nasa ames gcm predictions gamma ray spectrometer estimates and estimations from gravity models based on mgs and mars odyssey tracking data in our analysis we also compared to processed mola data linear thicknesses of snow depths to measure the value of the volume density of the southern seasonal cap and we found that it may vary in the range 400 1250 kg m3

exposed water ice discovered near the south pole of mars the mars odyssey thermal emission imaging system themis has discovered water ice exposed near the edge of mars southern perennial polar cap the surface h2o ice was first observed by themis as a region that was cooler than expected for dry soil at that latitude during the summer season diurnal and seasonal temperature trends derived from mars global surveyor thermal emission spectrometer observations indicate that there is h2o ice at the surface viking observations and the few other relevant themis observations indicate that surface h2o ice may be widespread around and under the perennial co2 cap

north and south subice gas flow and venting of the seasonal caps of mars a major geomorphological agent 1 dark polygons associated with fans and spots appear during the spring on the southern seasonal cap the basal sublimation of the translucent cap and the venting of the co2 gas are responsible for their formation as previously proposed for the spots and fans dark polygons appear when dark material emerges from elongated vents whereas spots and fans form from point sources a class of erosive features etched polygons is associated with depressions a few meters to tens of meters in diameters connected to a network of radiating troughs spiders spiders are shaped by the scouring action of the confined gas converging toward point sources whereas the etched polygons result from the forced migration of the co2 gas over longer distances the minimum age of the spiders is 104 years they result from one of the most efficient erosive processes on mars displacing 2 orders of magnitude more dust per year than a typical dust storm or than all the dust devils during the same time period in the north parts of the seasonal cap are translucent between ls 355 and ls 60 and are associated with spots fans dark polygons and possibly spiders suggesting that the basal sublimation and venting of the cap triggers a subice gas and dust flow that is modifying the morphology of the surface layer however perennial features are extremely uncommon on the north regolith indicating that the conditions for their formation or conservation are not met the reduced basal energy budget of the north cap compared to the south and the shorter seasonal life time of the north translucent ice may explain the relative scarcity of features in the north the polar layered deposits contain the stratigraphic record of climatic changes and catastrophic events both polar deposits may have been locally disrupted by the seasonal subice gas flow and the stratigraphic record may have been partially lost

a spectral approach for analyzing the rill structure over hillslopes part 2 application abstract this paper deals with examining the bandwidth of the spectral density functions of rill profiles from transect measurements at three cross slope locations over decomposed granite hillslopes in northern california parameter estimation for the probabilistic description of rill heights under the narrow banded spectrum assumption was then considered the theoretical predictions of the rill structure agree fairly well with the corresponding observed results estimation of extreme valued rills and significant rill heights is addressed to quantify the severity of the rilled hillslope surface it is concluded that the spectral approach is a valid method for quantifying the rill structure for use in physical models of water flow and sediment transport over rilled hillslope surfaces

seasonal recession of martian south polar cap 1992 hst observations the seasonal recession of the south polar cap of mars has been studied using the wide field planetary camera images from hubble space telescope obtained during the summer of 1992 when the angular size of mars was between 5 and 6 arc sec the observations cover the interesting period betweenls 259 and 284 when the recession is rapid and the asymmetry in the cap is large these will be the only hst observations of this season during the 1990s because of the solar elongation constraint on telescope pointing the well known mountains of mitchel outlier which has been observed by viking and by many ground based observers nearls 260 is clearly present in the first set of hubble images the latitude of the cap edge the displacement of the center of the cap from the geographical pole and the albedo of the polar deposits determined from these images are consistent with observations of these quantities by viking in 1977 the data are not compatible with a recession as advanced as that deduced from the 1956 telescopic observations

precambrian tectonic history of the west australian craton and adjacent orogens this review is a synthesis of the precambrian geology of the west aus tralian craton and its fringing orogens it describes the evidence that has recently been reinvestigated and reinterpreted to reveal a long dynamic history of repeated aggregation and dispersal of crustal fragments cratons are large composite geological units of continental crust that have survived intact for significant periods of geological time they are generally tabular bodies with great areal extent millions of square kilo meters and lithospheric thickness 200 400 km orogens are narrow steep zones of tectonic and metamorphic activity associated with the deposition of sediments and the intrusion of plutonic rocks they occur within or along the margins of continents and are generally a few hundred kilometers wide thousands of kilometers long and extend to the base of the litho sphere most orogens are initially associated with compressive tectonics crustal thickening and the transient formation of mountain belts cratons and orogens may survive for very long periods of time but as part of a thin crust on a dynamic mantle they are inherently mobile and travel as rafts for great distances around the surface of the earth they may be torn apart dispersed and reassembled with other continental fragments the boundaries of these crustal fragments once established remain zones of crustal weakness that may be reactivated as intra continental mobile belts or lines along which cratons are assembled and dismembered cf hoffman 1 988

age and origin of granitic rocks in the kalgoorlie norseman region of western australia implications for the origin of archaean crust three granites from the norseman area at stennet rocks buldania rocks and east of lake johnston have u pb zircon ages of 2691 8 95 c l 2689 22 and 2661 8 ma respectively one stennet rocks contains 3100 3200 ma cores providing support for oversby s 1975 argument that all three plutons were derived by anatexis of much older basement common leads within the zircons show evidence of having been derived from within the rock and represent mixtures of initial rock leads and radiogenic leads the unusually 208pb rich compositions of the common leads suggest the breakdown of a th rich phase perhaps uranothorite as a major contributor to the radiogenic component available zircon geochemical and isotopic data are used to develop a two stage model for archaean crustal development in this region with formation of primitive crust of broadly andesitic composition from depleted mantle or basalt beginning at 3400 ma followed by extensive thermal reworking and possibly continued growth over the period 3000 3300 ma in the second stage at 2700 ma anatexis resulted in large scale intra crustal differentiation giving a thick upper granitic layer and a lower crust residual from anatexis it is this second major thermal event that is recorded by most geochronometers implicit in the andesitic crustal growth model is that because the sm nd and rb sr ratios of newly formed archaean crust are close to mantle values this process is transparent to the sm nd and rb sr isotope systems until recycling of incompatible element rich sediment becomes important following the late archaean production of a wide spread differentiated upper crust

hirise observations of gas sublimation driven activity in mars southern polar regions ii surficial deposits and their origins abstract the high resolution imaging science experiment hirise onboard mars reconnaissance orbiter mro has been used to monitor the seasonal evolution of several regions at high southern latitudes and in particular the jet like activity which may result from the process described by kieffer jgr 112 e08005 doi 10 1029 2006je002816 2007 involving translucent co 2 ice in this work we mostly concentrate on observations of the inca city 81 s 296 e and manhattan 86 s 99 e regions in the southern spring of 2007 two companion papers hansen et al this issue and portyankina et al this issue discuss the surface features in these regions and specific models of the behaviour of co 2 slab ice respectively the observations indicate rapid on set of activity in late winter initiating before hirise can obtain adequately illuminated images ls 2 titus et al 2007 agu abstract p41a 0188 these deposits originate from araneiform structures spiders boulders on ridges cracks on slopes and along linear cracks in the slab ice on flatter surfaces the type of activity observed can often be explained qualitatively by considering the local topography some dark fans are observed to shorten enormously in length on a timescale of 18 days we consider this to be strong evidence that outgassing was in progress at the time of hirise image acquisition and estimate a total particulate emission rate of 30 g s 1 from a single typical jet feature brighter deposits at inca city become increasingly hard to detect after ls 210 in the inca city region the orientations of surficial deposits are topographically controlled the deposition of dark material also appears to be influenced by local topography suggesting that the ejection from the vents is at low velocity 1 and that a ground hugging flow process a sort of cryo fumarole may be occurring the failure up to this point to obtain a clear detection of outgassing though stereo imaging is consistent with low level transport the downslope orientation of the deposits may result from the geometry of the vent or from catabatic winds at many sites more than one ejection event appears to have occurred suggesting re charging of the sources around ls 230 the brightness of the surface begins to drop rapidly on north facing slopes and the contrast between the dark deposits and the surrounding surface reduces this indicates that the co 2 ice slab is being lost completely in some areas at around this time by ls 280 at inca city the ice slab has effectively gone crism band ratios and themis brightness temperature measurements are consistent with this interpretation

observations of the northern seasonal polar cap on mars i spring sublimation activity and processes abstract spring sublimation of the seasonal co2 northern polar cap is a dynamic process in the current mars climate phenomena include dark fans of dune material propelled out onto the seasonal ice layer polygonal cracks in the seasonal ice sand flow down slipfaces and outbreaks of gas and sand around the dune margins these phenomena are concentrated on the north polar erg that encircles the northern residual polar cap the mars reconnaissance orbiter has been in orbit for three mars years allowing us to observe three northern spring seasons activity is consistent with and well described by the kieffer model of basal sublimation of the seasonal layer of ice applied originally in the southern hemisphere three typical weak spots have been identified on the dunes for escape of gas sublimed from the bottom of the seasonal ice layer the crest of the dune the interface of the dune with the interdune substrate and through polygonal cracks in the ice pressurized gas flows through these vents and carries out material entrained from the dune furrows in the dunes channel gas to outbreak points and may be the northern equivalent of southern radially organized channels araneiform terrain albeit not permanent properties of the seasonal co2 ice layer are derived from timing of seasonal events such as when final sublimation occurs modification of dune morphology shows that landscape evolution is occurring on mars today driven by seasonal activity associated with sublimation of the seasonal co2 polar cap

distribution of the ices exposed near the south pole of mars using thermal emission imaging system themis temperature measurements 1 understanding the present and past water cycle on mars requires an accurate knowledge of the distribution and amount of h2o available near the surface in this article we present a map of the distribution of the surface material exposed between 87 s and 70 s in the summer e g co2 and h2o ices dust based on temperature measurements made by thermal emission imaging system themis our compositional map 100 m per pixel is in good agreement with spectral mapping returned by observatoire pour la mineralogie l eau la glace et l activite omega and compact reconnaissance imaging spectrometer for mars crism exposed water ice covers a total surface area of approximately 40 000 km2 a large fraction of the water ice is exposed at the periphery of the co2 cap an approximately 25 000 km2 large patch centered at 83 5 s and 345 e is discovered and represents the largest exposure of water ice in the southern hemisphere it is not located on the south polar layered deposits but on the surrounding mantled terrains themis vis moc and hirise images indicate that the surface roughness of exposed water ice terrains is typically lower than that of the surrounding dust polygonal patterns are observed on the water ice but not exclusively there is a strong correlation between the surface albedo the composition of the exposed material and the timing of the initial seasonal co2 frost deposition and final removal these exposed water ice outcrops are not stable in the present environment and lose a vertical layer of tens to hundreds of micrometer a year to the atmosphere the spike of water vapor above the south pole during the southern summer occurs while the water ice is still covered by a layer of seasonal co2 frost indicating that the sublimation of the exposed water ice is not the main contributor of vapor for the southern atmosphere as water ice is not stable it may indicate the past location of part of the co2 perennial cap that has been eroded

observations of the northern seasonal polar cap on mars iii crism hirise observations of spring sublimation we analyze a series of targeted crism and hirise observations of seven regions of interest at high latitudes in the northern polar regions of mars these data allow us to investigate the temporal evolution of the composition of the seasonal ice cap during spring with a special emphasis on peculiar phenomena occurring in the dune fields and in the vicinity of the scarps of the north polar layered deposits nplds the strength of the spectral signature of co2 ice continuously decreases during spring whereas the one of h2o ice first shows a strong increase until ls 50 this evolution is consistent with a scenario previously established from analysis of omega data in which a thin layer of pure h2o ice progressively develops at the surface of the volatile layer during early spring ls 10 widespread jet activity is observed by hirise while strong spectral signatures of co2 ice are detected by crism later around ls 20 40 activity concentrates at the dune fields where crism also detects a spectral enrichment in co2 ice consistent with kieffer s model kieffer h h 2007 j geophys res 112 e08005 doi 10 1029 2006je002816 for jet activity effects of wind are prominent across the dune fields and seem to strongly influence the sublimation of the volatile layer strong winds blowing down the scarps could also be responsible for the significant spatial and temporal variability of the surface ice composition observed close to the npld

variability of the south polar cap of mars in mars years 28 and 29 abstract we have used mars reconnaissance orbiter data from 2007 and 2009 to compare summer behaviors of the seasonal and residual south polar caps of mars in those two years we find that the planet encircling dust storm that occurred in the first of the two mars years enhanced the loss of seasonal co 2 deposits relative to the second year but did not have a large effect on the continuing erosion of the pits and mesas within the residual cap materials this suggests that the increase of bright frost in some regions of the residual cap observed between mariner 9 and viking can be accommodated within observed martian weather variability and does not require unknown processes or climate change

the 1997 spring regression of the martian south polar cap mars orbiter camera observations the mars orbiter cameras moc on mars global surveyor observed the south polar cap of mars during its spring recession in 1997 the images acquired by the wide angle cameras reveal a pattern of recession that is qualitatively similar to that observed by viking in 1977 but that does differ in at least two respects the 1977 recession in the 0 to 120 longitude sector was accelerated relative to the 1997 observations after l s 240 the mountains of mitchel also detached from the main cap earlier in 1997 comparison of the moc images with mars orbiter laser altimeter data shows that the mountains of mitchel feature is controlled by local topography relatively dark low albedo regions well within the boundaries of the seasonal cap were observed to have red to violet ratios that characterize them as frost units rather than unfrosted or partially frosted ground this suggests the possibility of regions covered by co 2 frost having different grain sizes

diversity within a unified model for archaean gold mineralization in the yilgarn craton of western australia an overview of the late orogenic structurally controlled gold deposits abstract the archaean yilgarn craton has produced 3000 tonnes of gold mainly from structurally controlled deposits that formed during the latest stages of an orogenic event that affected the entire craton and culminated in the period 2 66 2 63 ga as a group these late orogenic deposits encompass a wide range of host rocks structural settings and structural styles and alteration types however several consistent features justify grouping the deposits into a single class of mineralization these features include timing relative to orogenesis high gold to base metal ratios an association with potassium metasomatism and carbonation of host rocks low sulfide contents and a low salinity h 2 o co 2 ch 4 ore fluid most deposits formed in domains of low mean stress during east west regional compression and preserve evidence in the form of quartz vein arrays and hydraulic breccias for high fluid pressures and rock dilation the range of ore depositional conditions implied by alteration assemblages at various deposits makes the term mesothermal an inappropriate description for this class of mineralization the term late orogenic structurally controlled gold deposits is proposed as one which more completely encompasses the class of mineralization described in this overview late orogenic structurally controlled gold deposits formed in thermal equilibrium with high grade metamorphic rocks at the margins of the greenstone belts but were retrograde with respect to lower grade host rocks in the cores of greenstone belts these relationships probably reflect diachronous metamorphism and a single gold mineralization event which was contemporaneous with the later high grade metamorphism geochronological data indicate gold deposition at ca 2 63 ga in the western part of the yilgarn craton isotopic data suggest similar depositional ages in the eastern part of the craton eastern goldfields superterrane but this timing is difficult to reconcile with field relationships that suggest broad contemporaneity between regional metamorphism and gold mineralization at ca 2 66 ga the main competing genetic models for late orogenic structurally controlled gold mineralization in the yilgarn craton propose an orthomagmatic deeply sourced or metamorphogenic ore fluid none of these models can account satisfactorily for all the features of the late orogenic structurally controlled gold deposits

evolution of south seasonal cap during martian spring insights from high resolution observations by hirise and crism on mars reconnaissance orbiter 1 we use data from the high resolution imaging science experiment hirise camera and the compact reconnaissance imaging spectrometer for mars crism imaging spectrometer onboard the mars reconnaissance orbiter to follow the evolution of the appearance and composition of 12 regions of the south polar layered deposits from spring to summer time we distinguish three steps in the evolution of the volatile layer a decrease of both co2 band strength and albedo until ls 190 210 a significant increase in both until ls 240 260 and finally a rapid decrease until the complete defrosting of the ground in contrast the water ice band displays a more monotonic decrease analysis of hirise color images acquired simultaneously with crism data allows a plausible interpretation of this evolution in early springtime ls 200 intense jet activity results in deposition of fans of large mineral grains and a wide spatial distribution of fine grains the small scale topography controls the presence and location of the jets by allowing more solar energy to be collected on slopes grains from the dust fans warm and sink through the co2 layer resulting in a bluish color at the locations of the fans around ls 190 210 as the atmosphere warms up the surface of the ice layer sublimes and releases dust and water resulting in its brightening the last phase of the process consists in a progressive defrosting resulting in a patchwork of frozen and unfrozen areas

laboratory investigations of rill dynamics on soils of the loess plateau of china abstract we conducted a laboratory study on rill network evolution with detailed measurements under controlled experimental conditions the concepts of fractal geometry entropy and topology were used to quantify rill erosion intensity and morphology the objectives of this study are to reveal rill erosion processes and rill network development under different rainfall intensities and to present some indicators to provide a quantitative description of rill morphology a soil pan 5 m long 1 m wide and 0 6 m deep with slope gradient of 20 was subjected to three successive rainfall events under rainfall intensities of 66 94 and 127 mm h 1 the results showed that rainfall intensity played a major role in rill erosion the development of a rill network is most rapid under medium intensity rainfall rainfall intensity that is too weak or too strong is not conducive to rill development as rainfall duration increased under the same rainfall intensity the values of soil loss rill density geomorphologic comentropy and nodes increased rill network development was slow at the early stage but became more rapid at a later stage the results also indicated that the geomorphologic comentropy was the best basic morphological indicator of rill erosion and the number of rill nodes was the best derived morphological indicator of rill morphology which was followed in descending order by the fractal dimension rill density and bifurcation ratio

the archaean ravensthorpe terrane western australia synvolcanic cu au mineralization in a deformed island arc complex abstract the archaean 2 95 3 00 ga ravensthorpe greenstone belt in the southern yilgarn craton western australia can be subdivided into three tectonostratigraphic units the ravensthorpe terrane the carlingup terrane and the cocanarup greenstones the ravensthorpe terrane comprising the manyutup tonalite and the annabelle volcanics is a low k calc alkaline intrusive extrusive complex that is similar to modern island arc associations geochemical data and a close timing and spatial relationship suggest a co magmatic relationship between manyutup tonalite and annabelle volcanics these rocks have lower k 2 o and less fractionated rare earth element patterns than typical granitoids and acid to intermediate volcanic rocks of the yilgarn craton widespread propylitic alteration of the manyutup tonalite does not obscure magmatic trends the ravensthorpe terrane was thrust eastwards over the adjoining carlingup terrane during an accretionary event that was accompanied by regional metamorphism volcanic and volcaniclastic metasedimentary rocks that comprise the annabelle volcanics contain cu zn cu au and au mineralization in various states of deformation and metamorphism from upper greenschist to upper amphibolite facies conditions strata bound cu zn sulphide mineralization in upper amphibolite facies volcanic rocks at west river are associated with a broad area of cordierite orthoamphibole rock cu au mineralized sulphide rich shears in a greenschist facies environment at kundip are associated with intense chloritization of volcanic wallrocks alteration of volcanic rocks at both localities involved enrichment of fe and mg and depletion of ca and na and is interpreted as the product of sea floor alteration followed by metamorphism these and other base metal rich deposits in the ravensthorpe terrane are interpreted as deformed and metamorphosed stringer zones that formed within an archaean synvolcanic submarine hydrothermal system of the type that is commonly linked to massive sulphide deposits sulphide and base metal poor gold quartz vein deposits are also present in the ravensthorpe terrane these probably formed at a later stage during regional deformation low k calc alkaline rocks such as those that comprise the ravensthorpe terrane are uncommon in the yilgarn craton as is synvolcanic cu au mineralization

depth distribution and density of co2 deposition on mars observations by the mars orbiter laser altimeter have been used to detect subtle changes of the polar surface height during the course of seasonal cycles that correlate with the expected pattern of co2 deposition and sublimation using altimetric crossover residuals from the mars orbiter laser altimeter we show that while zonally averaged data capture the global behavior of co2 exchange there is a dependence of the pattern on longitude at the highest latitudes the surface height change is as high as 1 5 2 m peak to peak and it decreases equatorward decomposition of the signal into harmonics in time allows inspection of the spatial pattern and shows that the annual component is strongly correlated with the residual south polar cap deposits and to a lesser extent with the north polar cap in the north the second harmonic semiannual component correlates with the location of the ice deposits the phases of the annual cycles are in agreement with observations by the thermal emission spectrometer of the timing of the annual disappearance of co2 frost from the surface at the high latitudes at lower latitudes frost sublimation crocus date predates the mean depositional minima as expected these global scale volumetric measurements of the distribution of condensed co2 can be combined with measurements of the deposited column mass density derived from the neutron spectrometer on board mars odyssey to yield an estimate of the density of the seasonally exchanging material of 0 5 0 1 g cm 3 these constraints should be considered in models of the martian climate system and volatile cycles

experimental study on soil erosion prediction model of loess slope based on rill morphology abstract rill erosion frequently occurs in agriculturally disturbed dry areas despite many research efforts over recent decades the characteristics of rill erosion and its intrinsic mechanisms remain unclear the objectives of this study were to investigate the impacts of rill morphology evolution on rill erosion processes a soil pan 5 m long 1 m wide and 0 6 m deep and with an adjustable slope gradient of 0 30 was subjected to rainfall simulation experiments under three intensities of representative erosive rainfall 66 94 and 127 mm h 1 the rill morphology evolution exhibited significant nonlinear change regulation and the stronger the rainfall intensity the clearer the nonlinear feature the equation between rill morphological characteristics with geomorphological comentropy and bifurcation ratio was generated which indicated that the contribution rate of geomorphological comentropy to sediment yield was 80 and the contribution rate of bifurcation ratio was 20 for the experimental treatments a soil erosion model was constructed with and without rill development and the coefficient to describe the influence of rill development on slope erosion was obtained the rill erosion coefficient was embedded into an existing soil erosion model for steep slopes as a result when rill erosion occurred on the slope the contribution of the rill morphology to the rill erosion was fully realized by the model verification indicated that the accuracy of the model was significantly improved in previous studies the accuracy of slope water erosion prediction model was low because the evolution process of slope topography was not considered our results solve the spatial variability problem in the slope erosion prediction model and improve the simulation accuracy of the soil erosion prediction model on a loess slope

dark spots and cold jets in the polar regions of mars new clues from a thermal model of surface co2 ice observations of the martian co2 ice cap in late winter and spring have revealed exotic phenomena unusual dark spots fans and blotches form as the south polar seasonal co2 ice cap retreats the formation mechanisms of these features are not clearly understood theoretical models suggest that photons could penetrate deep into the co2 ice down to the regolith leading to basal sublimation and gas and dust ejection we have developed a detailed thermal model able to simulate the temporal evolution of the regolith co2 ice layer atmosphere column it takes into account heat conduction radiative transfer within the ice and the atmosphere and latent heat exchange when there is a phase transition we found that a specific algorithm fully coupling these three components was needed to properly predict ice sublimation below the surface our model allows us to determine under what conditions basal sublimation is possible and thus when and where it can occur on mars our results show that basal sublimation is possible if we consider large pathlengths and very little dust content within the ice moreover the model can explain how dark spots can appear very early after the end of the polar night at high latitudes we also evaluate the importance of the different parameters in our simulations contrary to what was suggested by theoretical models the role of seasonal thermal waves is found to be limited solar radiation alone can initiate basal sublimation which therefore only depends on the co2 ice properties three main modes were identified one where condensation sublimation only occurs at the surface in the case of small grains and or high dust content one where basal sublimation is possible large pathlengths and very little dust content and an intermediate mode where sublimation within the ice may occur we suggest that these different modes could be keys to understanding many processes that occur at the surface of mars like the anticryptic area behavior or the recent reported activity in gullies

a mid archaean island arc complex in the eastern akia terrane godthabsfjord southern west greenland a relict oceanic island arc complex in the eastern akia terrane godthabsfjord southern west greenland constitutes a magmatic and geotectonic link between c 3 05 3 0 ga tonalitic orthogneiss and enclaves of older supracrustal amphibolite the relict arc forms isoclinally folded panels of volcaniclastic meta andesite with major and trace element island arc signatures intercalated with volcano sedimentary schist tholeiitic amphibolite and opx rich cumulate rocks a zircon u pb age of 3071 1 ma obtained from a volcano sedimentary schist is marginally older than the main orthogneisses and is the first depositional age reported from a supracrustal rock within akia terrane granite sheets were emplaced at c 3005 2980 ma synkinematically with the isoclinal folding and were followed by peak metamorphism at 2990 2970 ma with substantial recrystallization of volcanic zircon and mobility of large ion lithophile elements the identification of the arc complex provides new insight into mid archaean continental crustal accretion in west greenland and substantiates previous ideas that the orthogneisses are products of slab melting in convergent plate tectonic settings the presence of the arc complex also implies that archaean high grade orthogneiss amphibolite associations may not represent plate tectonic environments distinct from granite greenstone associations but expose deeper sections of the same convergent systems

the genesis of the archaean welcome well volcanic complex western australia the welcome well volcanic complex east of leonora western australia is interpreted to be the eroded remnant of an archaean stratovolcano andesitic flows and intercalated mudflow deposits comprising the volcanic centre give way to coarse poorly sorted lithic wackes that were deposited in alluvial fans skirting the lower slopes or base of the subaerial volcanic edifice these deposits are succeeded both laterally and vertically by fine grained subaqueous turbiditic sediments that are intercalated with pillowed tholeiitic basalts

distribution morphology and influencing factors of rills under extreme rainfall conditions in main land uses on the loess plateau of china abstract rill erosion is one of the main forms of soil erosion of the hillslopes on the loess plateau of china few studies have evaluated the effects of land use on the distribution and morphology of rills under extreme rainstorms a total of 50 rill survey sites were selected in a typical watershed of the loess plateau of china to investigate the rill distribution and morphology of three land uses fallow land fl slope farmland sf and annual grassland ag under extreme rainstorm conditions called 7 26 rainstorm seven parameters rill width rill depth width depth ratio cross section area rill density degree of rill dissection and rill erosion modulus were used to characterize rill morphology and the basic soil and vegetation properties bulk density particle size distribution and vegetation coverage and topographic factors slope length gradient direction were measured it was found that rills developed on three land uses and those with widths ranging from 5 to 20 cm accounted for 80 rills developed on fl were deeper than those on sf and ag almost all rills on fl had a depth of 5 20 cm 90 3 while the depth of rills on sf and ag were mainly smaller than 15 cm 91 5 and 91 9 respectively in addition to width rill depth and cross section area of sf and ag were also significantly less than those of fl sf and fl had a relatively high width depth ratio and dissection degree however land use had no significant effect on rill density crop plantations sf and grass restoration ag significantly reduced rill erosion modulus 28 70 and 45 07 reduction respectively land use topography soil and vegetation factors significantly affected rill morphology p 0 001 based on redundancy analysis rda and can explain 48 0 of the total variability of rill morphology with slope length vegetation coverage and slope gradient having the greatest influences most of the rill morphological parameters significantly decreased as the vegetation coverage increased but they significantly increased with increasing slope length and slope gradient this study clearly illustrates the severe rill erosion caused by this rainstorm and indirectly indicates that crop harvesting fl aggravates rill erosion and that revegetation ag can effectively contain rill erosion therefore rehabilitation efforts should be focused on revegetation grassland and or woodland on steep slopes to control soil erosion

geochemistry of volcanic rocks associated with cu zn and ni cu deposits in the abitibi subprovince volcanogenic massive sulfide vhms deposits in the abitibi subprovince are preferentially associated with volcanic successions containing 150 m thicknesses of felsic volcanic rocks approximately 50 by area of volcanic terranes and are found within volcanic sequences of at least three distinct affinities group i which is host to greater than half of the volcanogenic massive sulfide deposits by tonnage and which comprises only approximately 10 percent by area of volcanic terranes is composed of bimodal tholeiitic basalt basaltic andesite and high silica rhyolite the basaltic andesites and high silica rhyolites are characterized by high high field strength element and heavy rare earth element ree contents low light to heavy ree ratios most with la n yb n 0 8 3 and strong negative eu anomalies the kamiskotia matagami and chibougamau lower cycle volcanogenic massive sulfide areas all of which are also underlain by large synvolcanic gabbroic complexes are associated with group i volcanic sequences the kidd creek potter normetal and horne deposits are also included in this category group ii which is host to one third of the volcanogenic massive sulfide deposits by tonnage and which is also approximately 10 percent by area of volcanic terranes is composed of bimodal transitional tholeiitic to calc alkalic andesitc and rhyolite characterized by intermediate high field strength element contents and slightly higher ree ratios la n yb n 1 4 noranda camp excluding the horne deposit and val d or camp group iii is host to only one known deposit the selbaie mine which is unusual in that much of its mineralization cuts stratigraphy the selbaie mine sequence contains calc alkalic andesite rhyolite with relatively low high field strength element and ree contents and higher ree ratios la n yb n 3 9 the vast majority of volcanogenic massive sulfide bearing mafic and felsic volcanic rocks in the abitibi subprovince have la n yb n 5 barren volcanic sequences are group iv calc alkalic basaltic andesite to rhyodacite with low high field strength element and relatively high ree ratios la n yb n 8 20 represented by the upper skead group the quebec hunter mine group and the upper cycle chibougamau rocks and group v mafic to felsic alkalic volcanic rocks with high ree ratios la n yb n 12 62 represented by the timiskaming opemisca and ridout series rocks group i is most similar to thickened oceanic rift suites e g galapagos spreading center iceland east rift group ii is similar to suites in rifled island arcs e g hokuroku district japan and group iii is comparable to continental arc suites e g southern volcanic zone central chile groups iv and v are comparable to arc related suites derived from metasomatized mantle with variable amounts of crustal contamination e g setouchi area japan roman province italy known ni cu deposits in volcanic sequences are hosted exclusively in komatiitic flows and hypabyssal sills represented by chill compositions with high mgo contents 20 35 wt anhydrous very low incompatible element contents and depleted signatures la n sm n 0 5 0 8 zr y 2 5 alexo marbridge and shaw dome deposits in comparison to most barren komatiites in the abitibi subprovince their depleted trace element signatures indicate minimal crustal assimilation which would appear contrary to the widely held view that crustal contamination e g addition of silica sulfur oxygen of a mantle derived melt is necessary for sulfur saturation and magmatic sulfide segregation this problem may be reconciled by considering the dynamics of komatiite flows lesher and arndt 1990 where contaminated present address 23 euclid avenue ottawa ontario canada kis 2w2 komatiite liquid segregated and deposited sulfide and was subsequently swept downstream and replenished by uncontaminated magma over the deposit as the flow ebbed and cooled when considered together with geologic features such as evidence for thermal erosion in the footwall langmuir deposits and the presence of sulfidic footwall rocks shaw dome deposits the distinctive depleted geochemical signature of mineralized komatiites is useful in exploration for ni cu deposits

petrogenesis of archaean trondhjemites tonalites and granodiorites from eastern finland major and trace element geochemistry

aeolian processes as drivers of landform evolution at the south pole of mars abstract we combine observations of surface morphology topography subsurface stratigraphy and near surface clouds with mesoscale simulations of south polar winds and temperature to investigate processes governing the evolution of spiral troughs on the south pole of mars in general we find that the south polar troughs are cyclic steps that all formed during an erosional period contrary to the troughs at the north pole which are constructional features the shallow radar instrument sharad onboard mars reconnaissance orbiter detects subsurface stratigraphy indicating relatively recent accumulation that occurred post trough formation in many locations using optical instruments especially the thermal emission imaging system themis we find low altitude trough clouds in over 500 images spanning 6 mars years the locations of detected clouds correspond to where recent accumulation is detected by sharad and offers clues about surface evolution the clouds migrate by season moving poleward from 71 s at l s 200 until l s 318 when the last cloud is detected our atmospheric simulations find that the fastest winds on the pole are found roughly near the external boundary of the seasonal co 2 ice cap thus we find that the migration of clouds and katabatic jumps corresponds spatially to the retreat of the co 2 seasonal ice as detected by titus 2005 and that trough morphology through recent accumulation is integrally related to this seasonal retreat

distribution of depth of overland flow on desert hillslopes and its implications for modeling soil erosion abstract data collected during field experiments on hillslopes in southern arizona reveal that the depth of overland flow in interrill areas can be approximated by a negative exponential distribution soil erosion over the greater part of most hillslopes is equal to detachment capacity flow detachment in interrill areas is generally modeled using a du boys type equation in which shear stress is calculated using the mean depth of flow it is shown that using the mean depth rather than the distribution of depth can result in the severe underestimation of flow detachment insofar as the exponential density is characterized by a single parameter that is the reciprocal of the mean a knowledge of the mean depth is all that is needed to specify the distribution thus utilization of the depth distribution rather than the mean depth does not require any additional information yet it yields much more accurate estimates of flow detachment and hence soil erosion in interrill areas