high resolution study of layering within the percolation and soaked facies of the greenland ice sheet within the percolation and soaked facies of the greenland ice sheet the relationship between radar derived internal reflection horizons and the layered structure of the firn column is unclear we conducted two small scale ground penetrating radar gpr surveys in conjunction with 10 m firn cores that we collected within the percolation and soaked facies of the greenland ice sheet the two surveys were separated by a distance of 50 km and 340 m of elevation leading to 40 days of difference in the duration of average annual melt at the higher site 1997 m a s l which receives less melt we found that internal reflection horizons identified in gpr data were largely laterally continuous over the grid however stratigraphic layers identified in cores could not be traced between cores over any distance from 1 5 to 14 0 m thus we found no correlation between firn core stratigraphy observed directly and radar derived internal reflection horizons at the lower site 1660 m a s l which receives more melt we found massive ice layers 0 5 m thick and stratigraphic boundaries that span 15 m horizontally some ice layers and stratigraphic boundaries correlate well with internal reflection horizons that are laterally continuous over the area of the radar grid internal reflection horizons identified at 1997 m a s l are likely annual isochrones but the reflection horizons identified at 1660 m a s l are likely multi annual features we find that mapping accumulation rates over long distances by tying core stratigraphy to radar horizons may lead to ambiguous results because 1 there is no stratigraphic correlation between firn cores at the 1997 m location and 2 the reflection horizons at the 1660 m location are multi annual features

an experimental and computer simulation study of erosion on a mine tailings dam wall mine tailings dams pose a signi cant risk to the environment if not correctly designed built and maintained the effect of erosion on a back lled and capped earthen dam wall was examined by construction of an analogue in an experimental model landscape simulator the ability of a computer based erosion model to simulate erosion processes on the experimental structure was examined the experimental landscape simulator uses a rainfall simulator to create overland ow and erode an arti cial soil at the commencement of rainfall erosion occurred rapidly with deep gullies developing on the dam wall batter the gullies developed by downcutting with consequent bank collapse and slumping and followed ow lines towards their source a physically based erosion model siberia was used to simulate erosion on the experimental dam wall erosion and consequent development of the experimental structure were modelled by siberia the ability of siberia to model incision and landscape development in the experimental setting was further examined by use of a simple one dimensional experimental catchment the laboratory experiment and computer simulations demonstrated that erosion on the tailings dam is driven by concentrated runoff and that runoff control is crucial to the long term stability of such structures the study demonstrates that computer based erosion models can be used to predict how erosion occurs on the experimental landscapes examined thus providing con dence in their use and application copyright 2004 john wiley sons ltd

extensive liquid meltwater storage in firn within the greenland ice sheet surface melt water from the greenland ice sheet can become trapped in firn delaying its journey to the sea radar and ice core observations provide direct evidence of a perennial aquifer in the firn layer in southern greenland that represents a potentially significant contribution to the greenland mass budget

stratigraphy of the 1902 and 1929 nuee ardente deposits mt pelee martinique mild nuee ardentes in 1902 1903 and 1929 1930 at mt pelee formed high aspect ratio h a r deposits i e deposits with a high thickness extent ratio in the riviere blanche channel several violent nuees ardentes from may to august 1902 yielded low aspect ratio l a r deposits unevenly blanketing an area of 58 km2 on the southwestern flank of the volcano three closely spaced nuees ardentes on august 30 additionally affected 56 km2 on the southeastern flank the l a r deposits are divided into eight stratigraphic units u1 u8 either compound or consisting of a single flow unit the deposits of the largest nuees ardentes on may 8 20 and august 30 1902 are identified as u1 u3 and u8 respectively and can be traced over most of the area individual l a r flow units are lenticular and show large erratic lateral variations of thickness and grain size most flow units consist of three distinct beds bed 1 is a few centimeters thick lenticular fines depleted layer bed 2 is the thickest layer and contains more silt sized ash than bed 1 it is normally graded as a whole though reverse grading may occur in the lower part bed 2 generally consists of two parts bed 2a nonbedded and bed 2b finer grained and laminated with cross bedding and duned structures bed 3 is a thin silty capping layer which contains accretionary lapilli the distribution of the l a r flow units especially of the coarse grained facies suggests that they were formed from overpressured blast flows expanding radially from the vent at a high rate in the same manner as the laterally directed blast of mount st helens on may 18 1980 the transport system of the major 1902 nuees ardentes was an inflated relatively low concentration turbulent cloud as suggested by several lines of evidence 1 the transported material was able to cross ridges up to 300 m high 2 many scour and fill and other erosional features can be observed in the deposits at any distance from the vent 3 survivors within the devastated area on may 8 did not experience a dense low profile cloud but instead a choking hot ash laden cloud 4 many human corpses in st pierre remained where they fell instead of having floated away if the current flow surge terminology were to be used the 1902 blast flows would be better considered as pyroclastic surges the normally graded multi layered structure of the flow units is also consistent with deposits primarily formed from relatively low concentration flows

unconformable stratigraphy in east antarctica part i large firn cosets recrystallized growth and model evidence for intensified accumulation unconformable firn stratigraphy exists throughout a 650 km long radar profile that we recorded down flow of megadune fields in the byrd glacier east antarctica catchment profile segments reveal cosets of prograding bedding sequences up to 90 m thick and with lateral along crest dimensions up to tens of kilometers we profiled them in oblique section and nearly parallel to the prevailing wind the prograding snow accumulates on broad low windward slopes located above ice bed depressions which implies long term slope stability the apparent subglacial control implies that the accumulation progrades in balance with ice velocity which we measured at 30 ma 1 the sequences prograde over intensely modified and recrystallized wind glaze firn visible in the profiles as unstratified layers and zones up to several tens of meters thick the intense recrystallization eliminates density stratification and the altered layers appear to thicken into a connected network modeling of coset formation using wind and ice flow reproduces their dimensions and morphology however accumulation rates well above current regional estimates and existing data for megadunes are required because of the measured ice speed and required slope stability the consistent unconformable strata along our traverse show that coset and recrystallized morphology extend far beyond the megadune fields

southeast greenland high accumulation rates derived from firn cores and ground penetrating radar despite containing only 14 of the greenland ice sheet by area the southeastern sector has the highest accumulation rates and hence receives 30 of the total snow accumulation we present accumulation rates obtained during our 2010 arctic circle traverse derived from three 50 m firn cores dated using geochemical analysis we tracked continuous internal reflection horizons between the firn cores using a 400 mhz ground penetrating radar gpr gpr data combined with depth age scales from the firn cores provide accumulation rates along a 70 km transect we followed an elevation gradient from 2350 to 1830m to understand how progressive surface melt may affect the ability to chemically date the firn cores and trace the internal layers with gpr from the firn cores we find a 52 0 43 m w e a 1 increase in average snow accumulation and greater interannual variability at the lower site than the upper site the gpr profiling reveals that accumulation rates are influenced by topographic undulations on the surface with up to 23 variability over 7 km these measurements confirm the presence of high accumulation rates in the southeast as predicted by the calibrated regional climate model polar mm5

stratigraphic variation within polar firn caused by differential accumulation and ice flow interpretation of a 400 mhz short pulse radar profile from west antarctica we investigate causes of the stratigraphic variation revealed in a 177 km 400 mhz short pulse radar profile of firn from west antarctica the profile covers 56 m depth and its direction was close to those of the ice flow and mean wind the average near surface accumulation rates calculated from the time delays of one radar horizon consistently show minima on leeward slopes and maxima on windward slopes confirming an earlier study based on stake observations the stratigraphic variation includes up to 30 m depth variation in individual horizons over tens of km fold limbs that become progressively steeper with depth and fold hinge loci that change direction or propagate down ice with depth over distances far less than predicted by the ice speeds we use an accumulation rate model to show how local rate anomalies and the effect of ice speed upon a periodic variation in accumulation rate cause these phenomena and we reproduce two key features seen in the stratigraphic variations we conclude that the model provides an explanation of changes in spatial stratigraphy and local measures of accumulation history given the constraints of surface topography ice and wind velocities and a general accumulation rate for an area

variability in accumulation rates from gpr profiling on the west antarctic plateau isochronal layers in firn detected with ground penetrating radar gpr and dated using results from ice core analyses are used to calculate accumulation rates along a 100 km across flow profile in west antarctica accumulation rates are shown to be highly variable over short distances elevation measurements from global positioning system surveys show that accumulation rates derived from shallow horizons correlate well with surface undulations which implies that wind redistribution of snow is the leading cause of this variability temporal changes in accumulation rate over 25 185 year intervals are smoothed to along track length scales comparable to surface undulations in order to identify trends in accumulation that are likely related to changes in climate results show that accumulation rates along this profile have decreased in recent decades which is consistent with core derived time series of annual accumulation rates measured at the two ends of the radar profile these results suggest that temporal variability observed in accumulation rate records from ice cores and gpr profiles can be obscured by spatial influences although it is possible to resolve temporal signals if the effects of local topography and ice flow are quantified and removed

spatial and temporal variability of surface mass balance near talos dome east antarctica 1 predictions concerning antarctica s contribution to sea level change have been hampered by poor knowledge of surface mass balance snow accumulation is the most direct climate indicator and has important implications for paleoclimatic reconstruction from ice cores snow accumulation measurements stake core snow radar taken along a 500 km transect crossing talos dome east antarctica have been used to assess accumulation signals and the representativeness of ice core records stake readings show that accumulation hiatuses can occur at sites with accumulation rates below 120 kg m 2 yr 1 differences between cores and stakes can lead to statistical misidentification of annual layers determined from seasonal signals at sites with accumulation rates below 200 kg m 2 yr 1 because of nondetection of higher and lower values achieving 10 accuracy in the reconstruction of snow accumulation from single cores requires high accumulation 750 kg m 2 yr 1 low accumulation sites are representative if cumulative rates computed over several years are used to reach the 750 kg m 2 yr 1 threshold temporal variability of accumulation over the last two centuries shows no significant increase in accumulation wind driven processes are a fundamental component of surface mass balance spatial variations in accumulation are well correlated with surface slope changes along the wind direction and may exceed 200 kg m 2 yr 1 within 1 km wind driven sublimation rates are less than 50 kg m 2 yr 1 in plateau areas and up to 260 kg m 2 yr 1 in slope areas and account for 20 75 of precipitation whereas depositional features are negligible in surface mass balance

phase center of l band radar in polar snow and ice backscatter from an aggregate of inhomogeneities combine to form an apparent surface reflection particularly in relation to interferometric synthetic aperture radar the depth z of this reflection can reside well below the true surface when the transmissivity at the interface between air and the aggregate is high snow and ice provide good examples for which we calculate z with different accumulation history and physical properties using a 0 5 3 0 ghz ground penetrating radar we acquired our data along transects in antarctica and svalbard we find values of z 40 in low absorbing antarctic firn and 10 meters in glaciers and ice shelves where melt freeze cycles and lateral mass movement lead to an electrically more heterogeneous snow and ice column the heterogeneity reduces dielectric contrast more rapidly with depth thus z is found at shallower depth but still resides several meters beneath the snow surface

scaling and elevation in river networks the analysis of large river networks obtained from digital elevation models has given insight into the variation of channel slope with scale investigators have recently suggested that channel slopes are self similar with magnitude or area as a scaling parameter our data indicates otherwise in particular the variance of channel slope is larger than that predicted by simple self similarity this suggests multiscaling the scaling exponent for the standard deviation is approximately half the corresponding exponent in the relationship of the slope mean to magnitude or area a model for channel slopes based on a point process of elevation drops along the channel is presented the model reproduces observed multiscaling properties when the density of elevation increments is related to area or magnitude as a

groundmass crystallization of mount st helens dacite 1980 1986 a tool for interpreting shallow magmatic processes the 1980 1986 eruption of mount st helens volcano provides an unprecedented opportunity to observe the evolution of a silicic magma system over a short time scale groundmass plagioclase size measurements are coupled with measured changes in matrix glass plagioclase and fe ti oxide chemistry to document increasing groundmass crystallinity and thus to better constrain proposed physical models of the post may 18 1980 magmatic reservoir measurements of plagioclase microlite and microphenocryst sizes demonstrate that relatively rapid growth approximately 10 9 cm s of groundmass plagioclase occurred immediately subsequent to may 18 relatively rapid plagioclase growth continued through the end of 1980 at an average rate of 3x10 11 cm s plagioclase growth rates then decreased to 1x10 11 cm s through 1986 changes in groundmass crystallinity are reflected in changes in both matrix glass and plagioclase microphenocryst rim chemistry although the matrix glass composition appears to have remained approximately constant from 1981 1986 after a rapid compositional change from may 18 until the end of 1980 plagioclase microphenocrysts show increasingly more complex zoning patterns with time microphenocryst core compositions are commonly positively correlated with crystal size both of these observations indicate continuous groundmass plagioclase growth through 1986 magmatic temperatures estimated from fe ti oxide pairs are approximately constant through 1981 at eruption temperatures of 930 c and at log fo2 of 10 8 by 1985 1986 oxide temperatures decreased to 870 c chemical and textural changes can be explained by 1 rapid degassing and crystallization in response to the intrusion of magma into a shallow 4 5 km reservoir toward the end of the may 18 1980 eruption 2 continued crystallization at a much reduced rate through 1986 due to slow cooling of the shallow magma reservoir growth rates and consequent chemical changes appear to decrease at the end of 1980 this is coincident with the change in eruption style from explosive eruptions sometimes followed by dome growth to solely extrusive dome building events and can be explained by the expected viscosity increase of both degassing and increasing crystallinity the model of twostage crystallization of magma in a shallow reservoir is consistent with conclusions from gas studies casadevall et al 1983 gerlach and casadevall 1986 a b patterns of crater deformation chadwkck et al 1988 and post 1980 seismicity endo et al 1990 although it does not explain the experimental data of hill and rutherford 1989 on the growth rate of amphibole reaction rims textural measurements on mount st helens dacite can also be used to evaluate crystallization kinetics in silicic magmas systems for which experimental data is almost non existent plagioclase growth rates are 5 10 times slower than estimated plagioclase growth rates in basaltic systems a result consistent with the higher viscosity of a more silicic melt furthermore patterns of textural change both average crystal size and number density are similar to those observed during the 1984 mauna loa eruption by lipman and banks 1987 suggesting that the only modification to the crystallization behavior of plagioclase required in extrapolation from basaltic systems is a moderate decrease in rates such that the rate of crystallization scales with the melt viscosity

airborne radar and ice core observations of annual snow accumulation over thwaites glacier west antarctica confirm the spatiotemporal variability of global and regional atmospheric models 1 we use an airborne radar method verified with ice core accumulation records to determine the spatiotemporal variations of snow accumulation over thwaites glacier west antarctica between 1980 and 2009 we also present a regional evaluation of modeled accumulation in antarctica comparisons between radar derived measurements and model outputs show that three global models capture the interannual variability well r 0 9 but a high resolution regional model racmo2 has better absolute accuracy and captures the observed spatial variability r 0 86 neither the measured nor modeled accumulation records over thwaites glacier show any trend since 1980 although an increase in accumulation may potentially accompany the observed warming in the region the projected trend is too small to detect over the 30 year record

slope aspect affects geomorphic dynamics of coal mining spoil heaps in belgium abstract after the abandonment of coal mining in belgium in the 1960s 1980s many coal tips have been left to themselves increasingly these coal tips are regarded as socio cultural heritage and protected for their environmental value this research analyses the spatial distribution of the main geomorphic processes sheet and rill erosion landsliding rock fragment movement and root throw occurring on coal tips in belgium through mapping of the processes and their causal factors five spoil heaps spread over the major coal basins were studied in detail the spoil heaps were subdivided in homogeneous land units especially with regard to slope gradient vegetation cover and slope aspect qualitative and quantitative observations were done on processes and potential causal factors regressions showed that generally the expression of slope processes on the studied coal tips is 1 strongly dependent on westerly aspect of the slopes 2 independent of slope gradient which presents a narrow range 3 impeded by grass cover and 4 not fully predictable due to variability in type and age of dumped mine spoil

u series disequilibrium in arc magmas induced by water magma interaction abstract volcanic rocks from subduction zones are widely believed to originate by partial melting of mantle lherzolite modified by the addition of a fluid or melt extracted from the down going slab u series disequilibrium in such magmas is commonly attributed to this particular melting process a detailed study of u series isotopes in the 650 y b p eruptive sequence of mt pelee martinique shows that plinian products are in radioactive equilibrium whereas dome forming products of the same eruption are characterized by 238u 230th disequilibrium the same features apply to other plinian and dome forming products of this volcano and systematically correspond to different eruptive styles we attribute these characteristics to variable superficial interaction of magmas with the hydrothermal system during the final stages of eruption rather than to deep magma genesis processes this conclusion might be generally applicable to arc magmas

testing of the siberia landscape evolution model using the tin camp creek northern territory australia field catchment the siberia landscape evolution model was used to simulate the geomorphic development of the tin camp creek natural catchment over geological time measured hydrology erosion and geomorphic data were used to calibrate the siberia model which was then used to make independent predictions of the landform geomorphology of the study site the catchment located in the northern territory australia is relatively untouched by europeans so the hydrological and erosion processes that shaped the area can be assumed to be the same today as they have been in the past subject to the caveats regarding long term climate fluctuation a qualitative or visual comparison between the natural and simulated catchments indicates that siberia can match hillslope length and hillslope profile of the natural catchments a comparison of geomorphic and hydrological statistics such as the hypsometric curve width function cumulative area distribution and area slope relationship indicates that siberia can model the geomorphology of the selected tin camp creek catchments copyright 2002 environmental research institute of the supervising scientist commonwealth of australia

stratigraphic continuity in 400 mhz short pulse radar profiles of firn in west antarctica we track dated firn horizons within 400mhz short pulse radar profiles to find the continuous extent over which they can be used as historical benchmarks to study past accumulation rates in west antarctica the 30 40cm pulse resolution compares with the accumulation rates of most areas we tracked a particular set that varied from 30 to 90m in depth over a distance of 600 km the main limitations to continuity are fading at depth pinching associated with accumulation rate differences within hills and valleys and artificial fading caused by stacking along dips the latter two may be overcome through multi kilometer distances by matching the relative amplitude and spacing of several close horizons along with their pulse forms and phases modeling of reflections from thin layers suggests that the 37 to 50db range of reflectivity and the pulse waveforms we observed are caused by the numerous thin ice layers observed in core stratigraphy constructive interference between reflections from these close high density layers can explain the maintenance of reflective strength throughout the depth of the firn despite the effects of compaction the continuity suggests that these layers formed throughout west antarctica and possibly into east antarctica as well

spatial distribution of snow in western dronning maud land east antarctica mapped by a ground based snow radar spatial distribution of snow in western dronning maud land east antarctica mapped by a ground based snow radar

pioneer vegetation as an indicator of the geochemical parameters in abandoned mine sites using hyperspectral airborne data a general problem that is associated with open pit mining is the total displacement of the former landscape s geocomponents overburden conveyor bridges have an irreversible impact on the environment the consequence of this is a completely new system the so called post mining landscapes these are characterized by extreme geochemical milieus especially acidity which is caused by weathering processes acid mine drainage these extreme environments are often left to natural succession because of the enormous costs and poor prospects of a successful reclamation this study investigated the relationship between pioneer vegetation e g calamagrostis epigejos and the geochemical properties of heap material using hyperspectral airborne hymap data in the west bohemian lignite district near sokolov czech republic thus a fully constrained linear spectral unmixing algorithm was applied to link the geochemical parameters with fractional abundances due to the limitation of pure surfaces in the data set of such fragmented and mixed areas a three stage semiautomated endmember extraction was developed the first stage included the selection of pure surface types using a decision tree with a self developed narrow band and normalized difference indices the second stage extracted the potential endmembers using the sequential maximum angle convex cone algorithm the third stage identified the final endmembers and eliminated the spectral outliers by comparing the extractions to field laboratory spectral libraries the abundance fraction image of the pioneer vegetation which was generated by the linear spectral unmixing showed the spatial distribution and density of the vegetation a linear regression model was used to calibrate the abundance image against the ph value the regression model successfully predicted the ph values of the soil r 2 0 67 rpd 1 42 this method demonstrated that hyperspectral remote sensing data could be used for ecological medium and long term monitoring as well as for spatial assessments in post mining areas in addition this approach works with a small amount of geochemical measurements and the sparse availability of endmembers

revealing the nature of radar reflections in ice dep based fdtd forward modeling 1 successful simulation of ground penetrating radar gpr traces in polar ice is achieved by numerical finite difference time domain fdtd forward modeling properties of the modeled medium are taken from high resolution dielectric profiling dep of the upper 100 m of an ice core from dronning maud land antarctica the gpr reference trace is calculated from stacking of a normal moveout corrected common midpoint survey carried out near the borehole location the excellent agreement of synthetic and gpr based results demonstrates the capability of fdtd models to reproduce radargrams from ice core properties for interpretation of radio echo sounding data and emphasizes the exploitation of radar data for improved interpretations of glaciological climate proxys in addition to presenting modeling results we perform sensitivity experiments to investigate the nature and origin of radar reflection in ice discuss reasons for the failure of modeling studies in the past and indicate new approaches

the humped soil production function eroding arnhem land australia we report erosion rates and processes determined from in situ produced beryllium 10 10be and aluminum 26 26al across a soil mantled landscape of arnhem land northern australia soil production rates peak under a soil thickness of about 35 cm and we observe no soil thicknesses between exposed bedrock and this thickness these results thus quantify a well defined humped soil production function in contrast to functions reported for other landscapes we compare this function to a previously reported exponential decline of soil production rates with increasing soil thickness across the passive margin exposed in the bega valley south eastern australia and found remarkable similarities in rates the critical difference in this work was that the arnhem land landscapes were either bedrock or mantled with soils greater than about 35 cm deep with peak soil production rates of about 20 m ma under 35 40 cm of soil thus supporting previous theory and modeling results for a humped soil production function we also show how coupling point specific with catchment averaged erosion rate measurements lead to a better understanding of landscape denudation specifically we report a nested sampling scheme where we quantify average erosion rates from the first order upland catchments to the main sixth order channel of tin camp creek the low 5 m ma rates from the main channel sediments reflect contributions from the slowly eroding stony highlands while the channels draining our study area reflect local soil production rates 10 m ma off the rocky ridge 20 m ma from the soil mantled regions quantifying such rates and processes help determine spatial variations of soil thickness as well as helping to predict the sustainability of the earth s soil resource under different erosional regimes copyright 2009 john wiley sons ltd

ground penetrating radar response to fracture fluid salinity why lower frequencies are favorable for resolving salinity changes time lapse ground penetrating radar gpr surveys exploit signal amplitude changes to monitor saline tracers in fractures and to identify groundwater flow paths however the relationships between gpr signal amplitude phase and frequency with fracture aperture and fluid electrical conductivity are not well understood we used analytical modeling numerical simulations and field experiments of multifrequency gpr to investigate these relationships for a millimeter scale aperturefracturesaturatedwithwaterofvaryingsalinity we found that the response of lower frequency radar signals detects changes in fluid salinity better than the response of higher frequency signals increasing fluid electrical conductivity decreases low frequency gpr signal wavelength which improves its thin layer resolution capability we concluded that lower signal frequencies such as 50 mhz and saline tracers of up to 1 s m conductivity are preferablewhenusinggprtomonitorflowinfracturedrock furthermore we found that gpr amplitude and phase responsesaredetectableinthefieldandpredictablebyemtheory and modeling therefore they can be related to fracture aperture and fluid salinity for hydrologic investigations of fractured rockflowandtransportproperties

a descriptive and quantitative approach regarding erosion and development of landforms on abandoned mine tailings new insights and environmental implications from se spain abstract the san cristobal perules mining site in mazarron in southeast spain was subjected to about a hundred years of intense mining activity for lead silver and zinc metallurgical operations smelting calcination gravity concentration carried out during the late nineteenth century early twentieth century induced significant land transformation and the most conspicuous wastes of this period consist of a chaotic piling of old tailing deposits later on during the mid twentieth century modern tailings resulting from froth flotation were accumulated filling small valleys these latter valley fill tailings rose sequentially according to the upstream construction method progressively raising the level of the dam during the process once abandoned both types of tailing deposits underwent severe erosion resulting in a mosaic of erosional and sedimentary landforms developed upon e g gully formation and within them e g piping we made an inventory and classification of these landforms our study shows the geomorphic work to reestablish a new steady state between the tailings deposits and the local erosive conditions this scenario implies several hazards related to the extremely high heavy metal contents of these tailings and the geomorphic instability of the deposits we also quantified the tailings tonnage and erosion that occurred at one of the tailings dams el roble as shown by an oblique aerial photograph taken in 1968 this dam had a terraced topography whereas in 2013 this morphology had evolved into a badland type relief with deep parallel gullies by recognizing and surveying specific remnant points along the benches and outslopes of the older terraced topography we were able to build up a first digital elevation model dem 1 reflecting the initial topography a second dem this time showing the present topography allowed quantification of erosion via material loss dem 1 dem 2 this yields an erosion rate 1968 2009 of 151 8 mg mt ha 1 y 1 which matches well typical values for erosion of mined areas commonly above 100 mg mt ha 1 y 1 abandoned mine tailing deposits are extremely common in the semiarid scenarios of the sw usa australia chile and peru given the similarities of these scenarios with se spain the example from mazarron may provide useful new insights regarding the erosion and geomorphic evolution of such tailing deposits these matters should be addressed in key environmental actions such as mine closure plans and land reclamation projects a solution may come via restoration of these deposits through landform design involving the building up of stable mature landscapes which in turn can withstand erosion much more easily

h2o and halogen f cl br behaviour during shallow magma degassing processes abstract degassing paths of silicic h2o rich magmas during explosive plinian and dome forming eruptions may be represented in simple evolution diagrams relating the residual volatile content of the melt to the volume ratio of gas over melt vg vl these parameters are measurable in erupted magma fragments they are used for interpreting the h2o and halogen contents determined in a series of variously degassed volcanic clasts from the 650 y b p eruption at mt pelee martinique fwi which is characterized by the succession of a dome extrusion and a plinian activity h2o degassing of plinian pumice clasts are modeled by an equilibrium closed system evolution which allows to calculate the partition coefficients of halogen between the aqueous fluid and the rhyolitic melt d v l i 1 for f 10 1 5 for cl and 3 7 1 for br at around 900 c the strong increase of the dv li values of cl and br during dome extrusion is explained by an open system degassing model with a simultaneous crystallization of the melt some significant br enrichments relative to cl in dome fragments are attributed to interactions with an hydrothermal fluid close to seawater in composition the models allow calculation of cl and br contents of aqueous fluids generated by the different degassing paths cl contents are 0 5 mol l for closed system evolution and vary between 0 2 and 1 mol l during open system evolutions these fluids are able to extract significant amounts of chloride complexed metals and silica from the magma during dome forming eruptions they also may generate mineralization of the wall rocks or the rising dome itself e g silica precipitation which may seal the volcanic system and be responsible for the dome explosivity and the transition from dome forming to plinian eruptive style the cl br ratio of initial melts of p1 eruption 250 is much lower than the basaltic and exospheric ratios 400 suggesting that strong cl br fractionation may occur during the production or the differentiation of subduction related magmas

volcanic degassing of bromine and iodine experimental fluid melt partitioning data and applications to stratospheric chemistry abstract in order to understand the degassing behavior of heavy halogens in volcanic processes we experimentally studied the distribution of cl br and i between albite melt and hydrous fluids containing 0 01 2 wt of nacl nabr or nai respectively all experiments were carried out at 2 kbar and 900 c in rapid quench cold seal autoclaves with a run duration of 7 days the major element compositions and cl contents of the glassy run products were measured by electron microprobe bromine and iodine were measured by proton induced x ray emission fluid compositions were obtained by mass balance all halogens investigated were found to partition strongly into the fluid phase over the range of concentrations studied the halogen contents in the melt are proportional to the concentrations in the fluid the fluid melt partition coefficients df m are 8 1 0 2 for cl 17 5 0 6 for br and 104 7 for i the logarithm of df m is linearly correlated with the ionic radius of the halogenide ion on the basis of our experimental data we estimate the amount of bromine injected into the stratosphere by major volcanic explosions for the 1991 mount pinatubo eruption we obtain br yields of 11 25 kt as minimum estimates these numbers are comparable to the total annual influx of bromine into the stratosphere from all other natural and anthropogenic sources about 100 kt year since bromine is much more efficient in destroying stratospheric ozone than chlorine it could at least be partially responsible for the massive ozone depletion observed after the 1991 mount pinatubo eruption

transition from dome forming to plinian eruptive styles controlled by h2o and cl degassing the transition from a plinian pumice to an effusive dome forming eruptive style is frequently observed in volcanic systems and is generally attributed to the progressive loss of volatiles from magma stored in a superficial reservoir this explosive effusive transition has been explained by the evolution from a closed to an open system of degassing1 2 3 4 but in this context an eruption at mt pelee martinique french west indies dated at 650 years ago which exhibited a rarely observed5 6 succession from dome forming to plinian activity in a short interval of time7 is at odds with such an explanation in this eruption near surface explosions of the dome produced two peleean turbulent pyroclastic flows whose deposits are similar to those of the effusive 1902 eruption and then plinian activity produced pumice fallouts and flows the reconstruction of the degassing paths of both eruptive regimes using the densities and the h2o and cl contents of the clasts shows that the interaction of rising magma with hydrothermal fluids at shallow depth may play a critical role in determining eruptive style

fragmentation of magma during plinian volcanic eruptions the ratio of the volume of vesicles gas to that of glass liquid in pumice clasts v g v l reflects the degassing and dynamic history experienced by a magma during an explosive eruption v g v l in pumices from a large number of plinian eruption deposits is shown here to vary by two orders of magnitude even between pumices at a given level in a deposit these variations in v g v l do not correlate with crystallinity or initial water content of the magmas or their eruptive intensities despite large ranges in these variables gas volume ratios of pumices do however vary systematically with magma viscosity estimated at the point of fragmentation and we infer that pumices do not quench at the level of fragmentation but undergo some post fragmentary evolution on the timescale of plinian eruptions pumices with viscosities 109 pa s can expand after fragmentation as long as their bubbles retain gas at a rate inversely proportional to their viscosity once the bubbles connect to form a permeable network and lose their gas expansion halts and pumices with viscosities 105 pa s can collapse under the action of surface tension textural evidence from bubble sizes and shapes in pumices indicates that both expansion and collapse have taken place the magnitudes of expansion and collapse therefore depend critically on the timing of bubble connectivity relative to the final moment of quenching we propose that bubbles in different pumices become connected at different times throughout the time span between fragmentation and quenching after accounting for these effects we derive new information on the fragmentation process from two characteristics of pumices the most important is a relatively constant minimum value of v g v l of 1 78 64 vol vesicularity in all samples with viscosities 105 pa s this value is independent of magma composition and thus reflects a property of the eruptive mechanism the other characteristic is that highly expanded pumices 85 vol vesicularities are common which argues against overpressure in bubbles as a mechanism for fragmenting magma we suggest that magma fragments when it reaches a vesicularity of 64 vol but only if sheared sufficiently strongly the intensity of shear varies as a function of velocity in the conduit which is related to overpressure in the chamber so that changes in overpressure with time are important in controlling the common progression from explosive to effusive activity at volcanoes

experimental constraints on the origin of chlorine emissions at the soufriere hills volcano montserrat experimental study of cl solubility in a rhyolitic melt composition corresponding to the phenocryst free matrix of the recently erupted soufriere hills andesite provides insights into the origin of cl emitted to the atmosphere during the eruption the experiments were done at 25 250 mpa 860 890 c and they involved equilibration of the estimated matrix composition 71 wt sio2 molar na2o k2o al2o3 0 6 with a cl rich aqueous fluid or aqueous fluid hydrosaline brine the cl concentrations in glasses from the experimental run products 0 48 0 68 wt cl are significantly higher than those observed in natural matrix glasses 0 20 wt cl and melt inclusions 0 30 0 07 wt cl these results indicate that if the pre eruptive montserrat magma was vapour saturated the vapour phase would have been cl poor and there was not a co existing hydrosaline brine this interpretation based on cl solubility data is supported by the observed coincidence between remote sensing measurements of cl emissions as hcl and petrological estimates of cl emissions based on the volume of magma extruded and cl contents of melt inclusions and matrix glasses with correction for groundmass crystallization during ascent the cl emissions during the soufriere hills eruption are thus proposed to simply reflect syn eruptive degassing of magma during ascent

the international trans antarctic scientific expedition itase an overview from its original formulation in 1990 the international trans antarctic scientific expedition itase has had as its primary aim the collection and interpretation of a continent wide array of environmental parameters assembled through the coordinated efforts of scientists from several nations itase offers the ground based opportunities of traditional style traverse travel coupled with the modern technology of gps crevasse detecting radar satellite communications and multidisciplinary research by operating predominantly in the mode of an oversnow traverse itase offers scientists the opportunity to experience the dynamic range of the antarctic environment itase also offers an important interactive venue for research similar to that afforded by oceanographic research vessels and large polar field camps without the cost of the former or the lack of mobility of the latter more importantly the combination of disciplines represented by itase provides a unique multidimensional space and time view of the ice sheet and its history itase has now collected 20 000 km of snow radar recovered more than 240 firn ice cores total length 7000 m remotely penetrated to 4000 m into the ice sheet and sampled the atmosphere to heights of 20 km

the explosive eruption of soufriere hills volcano montserrat west indies 17 september 1996 on 17 september 1996 the soufriere hills volcano started a 9 hour period of dome collapse involving 11 7 106 m dre of lava after 2 5 hours of quiescence a sustained explosive eruption began estimated eruption parameters are plume height at least 11 3 km and a maximum of 15 km 180 m s for launch velocities of ballistic clasts peak explosion pressure of 27 5 mpa magma water contents of 2 5 5 magma discharge rates from 2300 to 4300 m s ejecta volume of 3 2 0 9 106 m dre ejecta consists of pumice 1160 kg m higher density vesiculated ejecta 1300 to 2000 kg m dense glassy clasts 2600 kg m breccias cut by tuffisite veins and hydrothermally altered lithics the ejecta are interpreted as a conduit assemblage with evacuation of the conduit down to depths of about 3 to 5 km the eruption was triggered by unloading of a gas pressurised conduit due to dome collapse

accumulation at south pole comparison of two 900 year records two 900 year records of annual accumulation at south pole are compared to evalu ate the origin and significance of observed variations despite difficulties establishing absolute timescales due to problems identifying annual layer markers the two records can be correlated with confidence after moderate smoothing this correlation shows that over the time period considered 1050 1956 a d no climatically significant changes in accumulation occurred in stead fluctuations preserved in the two cores reflect spatial variations in snow accumulation as sociated with nonuniform deposition induced by surface relief on the scale of several kilometers

post mining landform evolution modelling 2 effects of vegetation and surface ripping computer simulations of the topographic evolution of the proposed post mining rehabilitated landform for the era ranger mine showed that for the unvegetated and unripped case the landform at 1000 years would be dissected by localized erosion valleys maximum depth 7 6 m with fans maximum depth 14 8 m at the outlet of the valleys valley form simulated by siberia has been recognized in nature this indicates that siberia models natural processes efficiently for the vegetated and ripped case reduced valley development maximum 1000 year depth 2 4m and deposition maximum 1000 year depth 4 8m occurred in similar locations as for the unvegetated and unripped case i e on steep batter slopes and in the central depression areas of the landform for the vegetated and ripped condition simulated maximum valley depth in the capping over the tailings containment structure was c 2 2 m by modelling valley incision decisions can be made on the depth of tailings cover required to prevent tailings from being exposed to the environment within a certain time frame a reduction in thickness of 1 m of capping material over tailings equates to c 1 000 000 mm3 over a 1 km2 tailings dam area this represents a saving of c 1 500 000 in earthworks alone incorporation of siberia simulations in the design process may result in cost reduction while improving confidence in environmental protection mechanisms copyright 2000 environmental research institute of the supervising scientist commonwealth of australia

holocene accumulation and ice sheet dynamics in central west antarctica 1 we derive depth age relationships across the ice divide between the ross and amundsen seas by tracking radar detected layers from the byrd ice core and a dated 105 m core near the divide the depth age relationships and an ice flow model are used to establish histories of accumulation and ice sheet dynamics over the past 8000 years results show that accumulation was approximately 30 higher than today from 5000 to 3000 years ago antarctic climate variability today is dominated by periodic fluctuations in strength of the circumpolar vortex which raises the possibility that the vortex was systematically weaker during the period of high accumulation accumulation today decreases almost linearly across the divide it is unlikely that this pattern has changed through the holocene the radar detected stratigraphy shows no evidence of the arched layers that are expected beneath a stable divide that is frozen to its bed implying that the divide has also been migrating and or the basal ice has been sliding through the holocene we cannot rule out the possibility of sliding because the basal ice is near its pressure melting point other evidence indicates that divide migration is likely the ross sea sector is now near steady state but it had a strong negative imbalance 200 years ago when kamb ice stream was active in contrast recent speedups of pine island and thwaites glaciers have likely caused the mass balance of the amundsen sea sector to become negative the divide is likely migrating toward the ross sea today

water solubility and chlorine partitioning in cl rich granitic systems effects of melt composition at 2 kbar and 800 c abstract experiments have been conducted in the system na2o k2o al2o3 sio2 h2o cl2o 1 at 2 kbar and 800 c to determine the effects of melt composition on the solubility of water in haplogranite melt and on the distribution of cl between aqueous fluid and haplogranite melt the melts studied include peraluminous subaluminous and peralkaline haplogranites and quartz albite and quartz orthoclase compositions the solubility of water at 2 kbar and 800 c in water saturated haplogranite melts varies strongly as a function of melt composition water solubility in melt decreases in the order strongly peralkaline haplogranite quartz albite composition moderately peralkaline haplogranite peraluminous haplogranite subaluminous haplogranite quartz orthoclase composition d cl wt cl in fluid wt cl in melt is a strong function of system composition d cl increases as the concentration of cl in the system increases a comparison of the distribution of cl between haplogranite melts of subaluminous peraluminous and peralkaline compositions and aqueous fluids shows that with similar concentrations of cl in the system d cl is largest for subaluminous melts a nk 1 having relatively high k2o concentrations as the a nk of melt increases or decreases from 1 or as the n nk of the melt increases both d cl and the concentration of cl in the fluid decrease the experimental data imply that complexes involving cl and na in hydrous subaluminous granite melts are dominant furthermore the data imply that in hydrous peraluminous granite melts cl complexes with network modifying a13 and in hydrous peralkaline granite melts cl complexes with network modifying na k on a molar basis cl apparently complexes with network modifying a13 in peraluminous melts as strongly as it does with na and k in peralkaline melts experimental studies of cl partitioning in granitic systems suggest that the strongest enrichment of magmatic hydrothermal fluids in cl and ore metals complexed with cl will most likely occur in fluids exsolved from subaluminous granite magmas that are relatively enriched in k2o sio2 and cl and relatively depleted in f co2 and na2o

use of a landscape simulator in the validation of the siberia catchment evolution model declining equilibrium landforms this paper presents a study to test the ability of the current generation of landscape evolution models to correctly predict landscape form from measured erosion processes landscapes generated by the siberia landscape evolution model were compared to experimental model landscapes in declining equilibrium the model simulations were compared using geomorphologically and hydrologically significant parameters comparisons of the simulated landscapes with the experimental landscapes were carried out using the hypsometric curve width function cumulative area distribution and area slope relationship these comparisons demonstrate that siberia can correctly simulate the experimental model landscape at declining equilibrium the simulation showed sensitivity to the spatial distribution of the rainfall particularly with respect to hypsometry using the correct measured distribution of rainfall was necessary rather than using a spatially uniform rainfall distribution the results also highlighted the importance of digital terrain map dtm error in deriving geomorphic statistics the observed landform had a consistently larger width function than the simulation only when the simulations were corrupted with elevation errors with statistical properties of the errors in the experimental landscape dtm as measured by photogrammetry did the observed and simulated width functions match

monitoring the 1980 1982 eruptions of mount st helens compositions and abundances of glass the mount st helens eruptive sequence of 1980 through 1982 reflects the tapping of successively less water rich more highly crystallized and more viscous highly phyric dacitic magmas these changes reflect both syn and preeruption processes the decreasing water content points to a continued decline in the volume and intensity of explosive pyroclastic activity this decreasing water content appears to be composed of a long term trend established during a long period of repose about 130 years imposed on short term trends established during short periods about 7 to 100 days of repose between eruptions in the present eruptive cycle the last two eruptive cycles of this volcano the t a d 1800 and w cycles about a d 1500 exhibited similar trends these changes are inferred from a combination of petrographic bulk chemical and electron and ion microprobe analyses of matrix and melt inclusion glasses

nature of radio echo layering in the antarctic ice sheet detected by a two frequency experiment a two frequency radio echo sounding experiment was carried out at dome fuji the second highest dome in east antarctica and along a 1150 km long traverse line from the dome to the coast the goal was to determine the dominant causes of the radio echo internal reflections and to investigate their possible changes with depth ranges and regions from the two frequency 60 mhz and 179 mhz radio echo responses at various sites we distinguished four zones each of the zones is characterized by a dominant cause of radio echo internal reflection as follows in the pd zone changes in dielectric permittivity are mainly due to density fluctuations in the pcof zone changes in dielectric permittivity are mainly due to changes in crystal orientation fabrics and in the ca zone changes in electrical conductivity are mainly due to changes in acidity induced by past volcanic eruptions in each of these three zones the changes occur commonly along isochrones in addition a basal echo free zone the fourth zone was found to appear always below the pcof zone these four zones and their distribution suggested variations of the physical conditions within the ice sheet

state of the antarctic and southern ocean climate system this paper reviews developments in our understanding of the state of the antarctic and southern ocean climate and its relation to the global climate system over the last few millennia climate over this and earlier periods has not been stable as evidenced by the occurrence of abrupt changes in atmospheric circulation and temperature recorded in antarctic ice core proxies for past climate two of the most prominent abrupt climate change events are characterized by intensification of the circumpolar westerlies also known as the southern annular mode between 6000 and 5000 years ago and since 1200 1000 years ago following the last of these is a period of major trans antarctic reorganization of atmospheric circulation and temperature between ad1700 and 1850 the two earlier antarctic abrupt climate change events appear linked to but predate by several centuries even more abrupt climate change in the north atlantic and the end of the more recent event is coincident with reorganization of atmospheric circulation in the north pacific improved understanding of such events and of the associations between abrupt climate change events recorded in both hemispheres is critical to predicting the impact and timing of future abrupt climate change events potentially forced by anthropogenic changes in greenhouse gases and aerosols special attention is given to the climate of the past 200 years which was recorded by a network of recently available shallow firn cores and to that of the past 50 years which was monitored by the continuous instrumental record significant regional climate changes have taken place in the antarctic during the past 50 years atmospheric temperatures have increased markedly over the antarctic peninsula linked to nearby ocean warming and intensification of the circumpolar westerlies glaciers are retreating on the peninsula in patagonia on the sub antarctic islands and in west antarctica adjacent to the peninsula the penetration of marine air masses has become more pronounced over parts of west antarctica above the surface the antarctic troposphere has warmed during winter while the stratosphere has cooled year round the upper kilometer of the circumpolar southern ocean has warmed antarctic bottom water across a wide sector off east antarctica has freshened and the densest bottom water in the weddell sea has warmed in contrast to these regional climate changes over most of antarctica near surface temperature and snowfall have not increased significantly during at least the past 50 years and proxy data suggest that the atmospheric circulation over the interior has remained in a similar state for at least the past 200 years furthermore the total sea ice cover around antarctica has exhibited no significant overall change since reliable satellite monitoring began in the late 1970s despite large but compensating regional changes the inhomogeneity of antarctic climate in space and time implies that recent antarctic climate changes are due on the one hand to a combination of strong multi decadal variability and anthropogenic effects and as demonstrated by the paleoclimate record on the other hand to multi decadal to millennial scale and longer natural variability forced through changes in orbital insolation greenhouse gases solar variability ice dynamics and aerosols model projections suggest that over the 21st century the antarctic interior will warm by 3 4 1oc and sea ice extent will decrease by 30 ice sheet models are not yet adequate enough to answer pressing questions about the effect of projected warming on mass balance and sea level considering the potentially major impacts of a warming climate on antarctica vigorous efforts are needed to better understand all aspects of the highly coupled antarctic climate system as well as its influence on the earth s climate and oceans

a model of vulcanian eruptions at galeras volcano colombia abstract a series of six vulcanian eruptions at galeras volcano colombia occurred during 1992 1993 these eruptions followed the emplacement of a lava dome in late 1991 which was accompanied by cooling crystallizing and partial solidification of the column of magma plugging the conduit five of the eruptions were preceded by episodes of monochromatic long period seismicity suggesting cyclic pressurization of the magma the quiescent intervals between eruptions generally decreased with each successive eruption we propose a model of gas release from magma into confined stationary pore spaces by 5 10 crystallization of anhydrous minerals causing repeated overpressurization of the magmatic system using initial lithostatic pressures of 20 100 mpa 800 3900 m depth gas buildup by crystallization indicates overpressures of 3 17 mpa which is the approximate fracture criterion for a magma chamber our galeras data suggest two models of pressurization 1 gas exsolution may have occurred at similar depths but with progressively smaller overpressures being developed before each successive eruption according to this model the comparatively long quiescent periods between the first eruptions resulted in relatively large amounts of gas exsolution from the magma and accumulation in pore spaces whereas the shorter quiescent periods for the later eruptions exsolved less gas the decrease in overpressure with time may have resulted from progressive fracturing of partly solidified magma during the eruptions which progressively decreased the tensile strength and increased the permeability of the magma 2 since overpressures are smaller at shallower depths for a given amount of crystallization the first eruptions of 1992 1993 were caused by gas exsolution at shallow depths while the last eruptions having shorter quiescent intervals resulted from a greater amount of gas exsolution at greater depths in this case the rate of gas exsolution varied as a function of depth the two scenarios for pressurization may be combined into a more general model involving edifice weakening and the development of a shallow hydrothermal system from continued degassing of the magma plug as weakening of the edifice formed an extensive system of fractures the shallow hydrothermal system deepened due to meteoric water input and magmatic degassing with time a greater number of fractures were filled and partly sealed by hydrothermal minerals at progressively deeper levels as a result the source of the overpressure also deepened with time

experimental study of chlorine behavior in hydrous silicic melts chlorine solubility in silicate melts has been investigated at 830 850 plus minus 5c and at pressures ranging from 50 to 200 mpa using both natural pantellerite rhyolite phonolite and synthetic sio sub 2 al sub 2 o sub 3 k sub 2 o na sub 2 o compositions and a stated h sub 2 o nacl kcl fluid phase near 4 molal at 100 mpa cl contents in pantelleritic melts reach a solubility plateau at initial aqueous phase molality near 2 this plateau coincides with a large immiscibility gap between aqueous and chloride rich fluids with the coexisting cl saturated aqueous phase cl ranges from 2 720 plus minus 120 ppm in rhyolite to 8 960 plus minus 85 ppm in pantellerite and reaches 6 270 plus minus 170 ppm in phonolite at 100 mpa between 50 and 200 mpa the cl content in pantelleritic melt decreases from 9 640 plus minus 200 ppm to 5 040 plus minus 150 ppm although cl solubility increases with increasing feo sup in high sio sub 2 melts it is mainly controlled by the al si and na k al molar ratios of the melt with a minimum at na k al 1 in a series of synthetic rhyolitic to pantelleritic melts the experimental results suggest that chlorine occurs as alkali chloride complexes in high sio sub 2 more melts they also indicate that cl is concentrated in the aqueous fluids in equilibrium with sio sub 2 rich melts the exact value of d depending on melt composition and melt chlorine concentration volcanic degassing will create chlorine rich hydrothermal fluids and decrease chlorine melt content less

the long term stability of engineered landforms of the ranger uranium mine northern territory australia application of a catchment evolution model there is a need to assess the long term stability of engineered landforms associated with the rehabilitation of ranger uranium mine northern territory australia as it is a requirement that mill tailings must be contained for periods in excess of 1000 years the geomorphic model siberia is calibrated on hydrologic and erosion data collected by a combination of monitoring and rainfall simulation experiments on the waste rock dumps of ranger preliminary analysis of ranger s preferred above grade option suggests that erosion of the order of 7 to 8 m will occur on the structure in a period of 1000 years this depth of erosion may be sufficient to compromise the integrity of containment it is shown that siberia has significant advantages over steady state erosion models suggestions are made for the design that will enhance the stability of the structure and extend the structural life of the containment 1998 john wiley sons ltd

high resolution radar mapping of internal layers at the north greenland ice core project existing accumulation maps with reported errors of about 20 are determined from sparsely distributed ice cores and pits a more accurate accumulation rate might be obtained by generating continuous profiles of dated layers from high resolution radar mapping of near surface internal layers in the ice sheet isochrones to generate such profiles we designed and developed an ultrawideband radar for high resolution mapping of internal layers in the top 200 m of ice and tested it at the north greenland ice core project drill site reflection profiles of 2 and 10 km length reveal horizons that we correlate with electrical conductivity measurement ecm recordings our results show that the radar determined depth of internal layers is within 2 m of that in an ice core collected at a nearby location preliminary frequency analyses of layer reflections reveal that the reflections are strongest at the 500 1000 mhz frequency range long term accumulation rate computed from radar data is within 5 of that obtained from snow pits

inversion for the density depth profile of polar firn using a stepped frequency radar 1 translating satellite measurements of ice sheet volume change into sea level contribution requires knowledge of the profile of density as a function of depth within the ice sheet and how this profile changes over time this paper describes an interferometric method of inverting ground penetrating radar returns for the profile of firn density as a function of depth the method is an interferometric implementation of the common midpoint approach performed using a stepped frequency phase sensitive ground penetrating radar by recording the phase difference of returns with a range of antenna separations the different path lengths through the firn allow recovery of a smoothed representation of the density profile this density model is characterized by three parameters surface density and two decay lengths for porosity each operating over a different density range our results suggest that the stepped frequency radar used here can accurately recover differences in two way traveltime and produce useful estimates of the density profile in a test of the method performed at summit station in greenland the recovered density depth profile agreed with independent density measurements from an ice core and a neutron probe to within 6 root mean square error

petrologic evidence for pre eruptive pressure temperature conditions and recent reheating of andesitic magma erupting at the soufriere hills volcano montserrat w i the recent eruption of the soufriere hills volcano in montserrat july 1995 to present september 1997 has produced an andesitic dome sio 2 59 61 wt the eruption has been caused by invasion of mafic magma into a preexisting andesitic magma storage region p 130 mpa 5 km depth the composition of the andesite has remained essentially constant throughout the eruption but heating by the mafic magma increased the andesite temperature from 830 c to 880 c prior to being heated the stable mineral assemblage in the andesite was plagioclase amphibole orthopyroxene titanomagnetite ilmenite quartz the rise in temperature from 830 c to 880 c fo 2 1 log unit above nno has caused quartz to become unstable and has also caused changes in silicate and fe ti oxide mineral compositions the andesitic magma is likely saturated with an h 2 o rich vapor phase in the upper part of the magma storage region melt h 2 o content is 4 7 wt

antarctic firn compaction rates from repeat track airborne radar data i methods while measurements of ice sheet surface elevation change are increasingly used to assess mass change the processes that control the elevation fluctuations not related to ice flow dynamics e g firn compaction and accumulation remain difficult to measure here we use radar data from the thwaites glacier west antarctica catchment to measure the rate of thickness change between horizons of constant age over different time intervals 2009 10 2010 11 and 2009 11 the average compaction rate to approximately 25m depth is 0 33ma exp 1 with largest compaction rates near the surface our measurements indicate that the accumulation rate controls much of the spatio temporal variations in the compaction rate while the role of temperature is unclear due to a lack of measurements based on a semi empirical steady state densification model we find that surveying older firn horizons minimizes the potential bias resulting from the variable depth of the constant age horizon our results suggest that the spatiotemporal variations in the firn compaction rate are an important consideration when converting surface elevation change to ice mass change compaction rates varied by up to 0 12ma exp 1 over distances less than 6km and were on average greater than 20 larger during the 2010 11 interval than during 2009 10

the design of post mining landscapes using geomorphic principles nature can provide analogues for post mining landscapes in terms of landscape stability and also in terms of the rehabilitated structure blending in with the surrounding undisturbed landscape in soil mantled landscapes hillslopes typically have a characteristic pro le that has a convex upper hillslope pro le with a concave pro le lower down the slope in this paper hillslope characteristic form is derived using the area slope relationship from pre mining topography at two sites in western australia using this relationship concave hillslope pro les are constructed and compared to linear hillslopes in terms of sediment loss using the siberia erosion model it is found that concave hillslopes can reduce sediment loss by up to ve times that of linear slopes concave slopes can therefore provide an alternative method for the construction of post mining landscapes an understanding of landscape geomorphological properties and the use of erosion models can greatly assist in the design of post mining landscapes copyright 2003 john wiley sons ltd

unconformable stratigraphy in east antarctica part ii englacial cosets and recrystallized layers complex unconformable englacial stratigraphy including a segment of distinctive cosets of bed sequences occurs throughout the thickness of a 3 2 mhz ice sheet radar profile we acquired across the upper byrd glacier east antarctica catchment some cosets span 10 km are 100 m thick and are delineated by distinct horizons at 40 90 m depth in firn comparisons between 200 mhz and specially processed 3 2 mhz profiles reveal that the delineating horizons result from density modified layers produced by decades to millennia of subaerial exposure as detailed in our related paper part i these comparisons together with reflected waveforms at depth also reveal that the modified layers retain their chemical stratification and therefore the original unconformable surface two profile segments show high amplitude transverse folds spanning much of the ice sheet thickness the parallel nature of most of them suggests basal sliding beneath long term up ice flow accumulation zones which we identify in satellite images as the likely sources for the cosets the unconformable stratigraphy at depths greater than 2000 m shows that antidunal deposition and intense firn recrystallization zones have persisted for tens of thousands of years in this region of east antarctica

detection and monitoring of stratigraphic markers and temperature trends at the greenland ice sheet project 2 using passive microwave remote sensing data satellite passive microwave sensors provide a sensitive means of studying ice sheet surface processes that assists ice core interpretation and can extend local observations across regional scales analysis of special sensor microwave imager ssm i brightness temperature tb data supports ice core research in two specific ways first the summer hoar complex layers used to date the holocene portion of the greenland ice sheet project 2 ice core can be defined temporally and spatially by ssm i 37 ghz vertically v and horizontally h polarized b ratio v h trends second comparison of automatic weather station temperatures to ssm i 37 ghz v tb data shows that they are an effective proxy temperature record in this region also the tb data can be correlated with proxy temperature trends from stable isotope ratio 18o and d profiles from snow pits and this allows the assignment of dates to specific snow depths

a physical explanation for an observed area slope elevation relationship for catchments with declining relief a general relationship between the contributing area slope and mean elevation of catchments with relief declining after a tectonic uplift event is presented this relationship is based on the continuity equation for runoff and erosion processes in the catchment the key hypothesis underlying this relationship is that as a catchment declines the nondimensionalized catchment approaches a constant form this hypothesis is verified for computer simulated catchments the area slope elevation relationship covers several cases catchments declining toward a peneplain catchments declining from a high slope dynamic equilibrium resulting from a high rate of tectonic uplift to a low slope one resulting from a lower rate of tectonic uplift and catchments declining from an elevated initial condition as for example in the decline of a mine spoil heap a previously published relationship between slope and area for catchments in dynamic equilibrium and based on runoff and erosion physics is shown to be a special case of this general relationship the new area slope elevation relationship is compared with data from simulated catchments and a field catchment it is thus shown that for declining catchments the area slope elevation relationship is a good predictor of catchment form for catchments with declining relief it is argued that the slope area elevation relationship is sufficient with the planiform drainage pattern to completely define the elevation properties of the catchment such as for instance the hypsometric curve

radar response of firn exposed to seasonal percolation validation using cores and fdtd modeling we use ground penetrating radars gprs firn cores and electromagnetic finite difference time domain fdtd numerical modeling to characterize the gpr response to a frozen high arctic firn pack as a result of extensive summertime percolation the firn pack comprises a high fraction of ice layers lenses and vertical glands we show that the gpr response on the firn pack mainly depends on the following 1 the thickness of the ice layers 2 the distance between layers 3 the layer roughness and 4 the presence or absence of elliptical ice lenses using 3 d fdtd modeling we show that the gpr is not sensitive to typical ice glands which implies that the gpr underestimates firn heterogeneity such that firn stratigraphy in percolation and wet snow zones could be incorrectly interpreted as being better preserved than it actually is we find that thin ice layers 0 05 m or multiple thin ice layers give a strong response thicker ice layers typically give a weaker backscatter per unit area mainly due to the lack of interference of the reflections from the upper and lower interfaces but are due to their continuity easily trackable ice layers with a thickness comparable to the gpr wavelength give 180deg phase shifted upper and lower reflections and are in general separated by a band of low gpr response due to the lack of permittivity contrast within the ice layers despite the ice lenses relatively short horizontal correlation length as inferred from cores bands of high amplitude clutter caused by these features can be traced over several kilometers in gpr profiles

results from a new model of river basin evolution this paper briefly describes a model of the erosional development of catchments and their channel networks the model differentiates between the dominant transport processes in hillslope and channels the development of channels and hillslopes occurs in an integrated manner as a function of physically observable mechanisms the growth of a river basin is qualitatively described the model concepts are used to study the basin during periods of growth transient periods as well as during dynamic equilibrium this leads to hypotheses about the relationship between slopes relief tectonic uplift erodability runoff and catchment area it is shown that the model leads to very reasonable and desirable behaviour of hillslopes during retreat and degradation

hcl emissions at soufriere hills volcano montserrat west indies during a second phase of dome building november 1999 to october 2000 hcl so2 mass ratios measured by open path fourier transform spectroscopy op ftir in the volcanic plume at soufriere hills volcano montserrat are presented for the second phase of dome building between november 1999 and november 2000 hcl so2 mass ratios of greater than 1 and hcl emission rates of greater than 400 t day 1 characterise periods of dome building for this volcano the data suggest that chlorine partitions into a fluid phase as the magma decompresses and exsolves water during ascent this is substantiated by a correlation between chlorine and water content in the melt derived from the geochemical analysis of plagioclase melt inclusion and matrix glasses from phase i and ii of dome growth the matrix glass from the november 1999 and march 2000 domes indicate an open system degassing regime with a fluid melt partition coefficient for chlorine of the order of 250 300 september 1997 glasses have higher chlorine contents and may indicate a switch to closed system degassing prior to explosive activity in september and october 1997 the op ftir hcl time series suggests that hcl emission rate is strongly related to changes in eruption rate and we infer an emission rate of over 13 5 kt day 1 hcl during a period of high extrusion rate in september 2000 a calculation of the hcl emission rate expected for varying extrusion rates from the open system degassing model suggests a hcl emission rate of the order of 1 4 kt day 1 is indicative of an extrusion rate of between 2 and 8 m3 s 1 monitoring of hcl at soufriere hills volcano provide a proxy for extrusion rate with changes in ratio between hcl and so2 occurring rapidly in the plume order of magnitude changes occur in hcl emission rates over the time scale of hours to days making these changes easy to detect during the day to day monitoring of the volcano mean water emission rates are calculated to range from 9 24 kt day 1 during dome building activity calculated from the predicted mass ratio of h2o hcl in the fluid at the surface and ftir derived hcl emission rates

a physical explanation of an observed link area slope relationship an observed log log linear relationship between channel slope and contributing area is explained by the erosional physics that lead to catchment form it is postulated that tectonic uplift is in balance with the fluvial erosion down wasting that dominates catchment erosion and it is shown that this relationship results in the observed log log linear relationship at dynamic equilibrium in addition it has been observed that there are deviations from this log log linear relationship near the catchment divide with observed slopes being lower than those predicted from the relationship this is explained by noting that for small areas fluvial erosion effects are dominated by soil creep and rain splash modeled by diffusive physics the area at which this deviation from log log linearity occurs is that point on the hillslope at which diffusive physics like soil creep and rain splash begin to dominate fluvial erosion these predictions are confirmed by numerical simulations using a catchment evolution model

an evaluation of an enhanced soil erosion and landscape evolution model a case study assessment of the former nabarlek uranium mine northern territory australia the assessment of post mining landscapes as case studies is an important part of the evaluation of current rehabilitation practices a necessary part of this assessment is to predict the surface stability of the landform using erosion and landform evolution modelling techniques in the short term erosion on a rehabilitated mine site can lead to increased sediment loads and transport of other mine related contaminants in downstream waterways it is well recognized that in many mine areas the erodibility of surface materials can and does vary this is a particularly significant issue on mine sites where the surface conditions may range from areas of undisturbed natural surface materials waste rock dumps constructed with materials exhumed from the sub surface and other areas that have a mix of waste rock and soil to enhance the growth of vegetation a further significant issue is that when the subsurface materials are exposed to surface conditions they can weather rapidly changing their erodibility this paper uses a new version of the siberia landscape evolution and soil erosion model to evaluate the former nabarlek uranium mine site in the northern territory australia this new version of siberia uses spatially variable erosion and hydrology parameters across the study domain to represent different erodibilities of surface materials thus allowing better representation of catchment heterogeneity the results demonstrate that the model predicts erosion rates similar to that of other modelled results and independent field data providing confidence in the model and its parameterization the tailings deposited in the mined out pit and capped with waste rock appear to be safely encapsulated for the modelled period copyright 2008 john wiley sons ltd and commonwealth of australia department of the environment and water resources supervising scientist

post mining landform evolution modelling 1 derivation of sediment transport model and rainfall runoff model parameters data were collected from three sites on the waste rock dump at era ranger mine 1 the cap site which was unvegetated and unripped with a surface slope of 2 8 per cent 2 the batter site surface slope 20 7 per cent also unvegetated and unripped but with a covering of coarse rock material and 3 the soil site surface slope 1 2 per cent which had c 90 per cent vegetation cover of low shrubs and grasses and had been topsoiled and surface ripped natural rainfall events were monitored on the sites to collect rainfall runoff and soil loss data to parameterize a sediment transport model of the form t s q dt and the distfw rainfall runoff model low frequency high intensity events resulted in the greatest soil loss to accurately predict sediment loss during high intensity events storms with a range of intensities were selected to derive the sediment transport model distfw hydrology model parameters were derived by fitting four monitored events simultaneously the selected parameters for the vegetated and ripped case may overpredict discharge for some rainfall events resulting in conservative design of erosion control features on rehabilitated landforms copyright 2000 environmental research institute of the supervising scientist commonwealth of australia

techniques for measuring high resolution firn density profiles case study from kongsvegen svalbard on an 11 m firn ice core from kongsvegen svalbard we have used dielectric profiling dep to measure electrical properties and digital photography to measure a core optical stratigraphy cos profile we also used a neutron scattering probe np to measure a density profile in the borehole from which the core was extracted the np and dep derived density profiles were similar showing large scale 30 cm variation in the gravimetric densities of each core section fine scale features 10 cm are well characterized by the cos record and are seen at a slightly lower resolution in both the dep and np records which show increasing smoothing a combination of the density accuracy of np and the spatial resolution of cos provides a useful method of evaluating the shallow density profile of a glacier improving paleoclimate interpretation mass balance measurement and interpretation of radar returns

restoring earth surface processes through landform design a 13 year monitoring of a geomorphic reclamation model for quarries on slopes the application of geomorphic principles to land reclamation after surface mining has been reported in the literature since the mid 1990s mostly from australia canada and the usa this paper discusses the reclamation problems of contour mining and quarries on slopes where steep gradients are prone to both mass movement and water erosion to address these problems simultaneously a geomorphic model for reclaiming surface mined slopes is described called the highwall trench concave slope model it was first applied in the 1995 reclamation of a quarry on a slope la revilla in central spain the geomorphic model does not reproduce the original topography but has two very different sectors and objectives i the highwall trench sector allows the former quarry face to evolve naturally by erosion accommodating fallen debris by means of a trench constructed at the toe of the highwall ii the concave slope base sector mimicking the landforms of the surrounding undisturbed landscape promotes soil formation and the establishment of self sustaining functional ecosystems in the area protected from sedimentation by the trench the model improves upon simple topographic reconstruction because it rebuilds the surficial geology architecture and facilitates re establishment of equilibrium slopes through the management and control of geomorphic processes thirteen years of monitoring of the geomorphic and edaphic evolution of la revilla reclaimed quarry confirms that the area is functioning as intended the highwall is backwasting and material is accumulating at the trench permitting the recovery of soils and vegetation on the concave slope however the trench is filling faster than planned which may lead to run off and sedimentation on the concave slope once the trench is full the lesson learned for other scenarios is that the model works well in a two dimensional scheme but requires a three dimensional drainage management breaking the reclaimed area into several watersheds with stream channels copyright 2010 john wiley sons ltd

gpr reflection profiles of clark and commonwealth glaciers dry valleys antarctica englacial horizons deeper than 100 m are absent within 100 mhz ground penetrating radar gpr surface profiles we recorded on clark and commonwealth glaciers in the antarctic dry valleys region both glaciers show continuous bottom horizons to 280 m with bottom signal to noise ratios near 30 db density horizons should fade below 50 m depth because impermeable ice occurred by 36 m folding within commonwealth glacier could preclude radar strata beneath about 80 m depth but there is no significant folding within clark glacier strong sulfate concentrations and contrasts exist in our shallow ice core however it appears that high background concentration levels and possible decreased concentration contrasts with depth placed their corresponding reflection coefficients at the limit of or below our system sensitivity by about 77 m depth further verification of this conclusion awaits processing of our deep core chemistry profiles

phase structure of radar stratigraphic horizons within antarctic firn we have recorded reflection profiles of firn through large areas of west antarctica and part of the east antarctic plateau using 400 mhz short pulse radar the locations show accumulation rates that vary from well above to well below the vertical radar resolution most reflection horizons have extensive lateral continuity and are composed of distinctive wavelets with a consistent phase polarity sequence within their successive half cycles we modeled these waveforms and conclude that they arise from thin double layers of ice over hoar which is consistent with the standard model of firn stratification in addition we conclude that ice hoar layers are extensive throughout west antarctica and also present although more sparsely beneath the antarctic plateau

impact of slope aspect on hydrological rainfall and on the magnitude of rill erosion in belgium and northern france abstract the impact of slope aspect on hydrological rainfall and on the magnitude of rill erosion has rarely been studied the dominant wind direction in belgium and northern france is the southwest which brings large amounts of rain with it we investigated whether this leads to greater rates of rill erosion on the southwestern slopes due to the greater amount of hydrological precipitation on these slopes the study was executed on six barren conical spoil heaps which are excellent study objects to bring the slope aspect in relation with rill erosion three indicators for rill erosion volume of rills drainage density and mean distance of the head cut of the five uppermost rills till the top of the spoil heap were associated with four explanatory factors slope gradient vegetation density rock fragment cover and slope aspect the amount of hydrological rainfall is the greatest on the western and southwestern slopes as a result the largest volume of rills was measured on the slopes facing the southwest 96 which indicates that there is a connection between the slope aspect and the magnitude of rill erosion on the northeastern 32 and eastern 36 slopes the volume of rills is lower due to the effect of rain shadow the other explanatory factors showed little influence on the magnitude of rill erosion as the spoil heaps were selected to be similar in as many parameters as possible

runoff erosion process on different underlying surfaces from disturbed soils in the three gorges reservoir area china abstract disturbed soil accumulation caused by all man made activities during the producing and constructing process of large scale projects is the main landform occurred artificial water and soil loss because of its different producing sources and soil rock ratios the underlying surfaces from disturbed soil accumulation often characterize a unique soil erosion process under same runoff scouring condition taking the ubiquitous purple soil deposits and yellow sand deposits associated with different soil rock ratio as examples the study aimed to explore the difference in both hydraulic properties and sediment yield characteristics on disturbed soils some field scouring experiments were conducted in chongqing china these results indicate that i runoff regime on all underlying surfaces from disturbed soils often manifest as turbulent and subcritical flow during runoff scouring process ii for rocky disturbed soils from purple soil sediment production rate shows continuously waving variations and the average sediment production rates are 0 28 11 65 33 69 73 00 and 177 37 g m 2 min respectively when flow discharge increase from 5 to 25 l min gradually the collapse on gully wall caused by its gravity from underlying surfaces is the important cause for the fluctuating variations of the sediment production rate iii the influencing degree of hydrodynamic parameters on sediment yield is in such order as q p v these study results could be used to control artificial erosion caused by production and construction projects and to provide some important parameters for soil and water loss predicting in the three gorges reservoir area of chongqing

gpr characterization of a lacustrine uxo site we used 135 mhz ground penetrating radar gpr reflection profiles to determine if high explosive he depth bombs were possibly detonated within a small new england lake formerly used as a bombing range as well as the depths and distribution of inert and possibly unexploded ordnance uxo within the subbottom sediments maximum water depth was 8 6 m the primary munitions were unarmed practice bombs but terrestrial fragments from he depth bombs led us to seek stratigraphic obliteration and distortion as evidence of their use the low water conductivity and quartz rich sediments provided more than 8 m of subbottom penetration beneath slope and shelf sediments the high permittivities of the water and subbottom sediments provided good antenna directivity excellent 2d migrations multicentimeter vertical resolution and a unique pulse waveform signature for metal objects our line profiles revealed hundreds of subbottom diffractions which implied an areal distribution of thou sands of suspicious object

the october 1902 plinian eruption of santa maria volcano guatemala abstract the october 1902 eruption of santa maria volcano guatemala was one of the largest this century it was preceded by a great earthquake on april 19 centered at the volcano as well as numerous other major earthquakes the 18 20 hour long plinian eruption on october 25 produced a column at least 28 km high reaching well into the stratosphere the airfall pumice deposit covered more than 1 2 million km2 with a trace of ash and was only two meters thick at the vent white dacitic pumice dark gray scoriaceous basalt with physically and chemically mixed intermediate pumice and loose crystals of plagioclase hornblende hypersthene biotite and magnetite make up the juvenile components of the deposit lithic fragments are of volcanic plutonic and metamorphic origin the plinian deposit is a fine grained crystal rich single pumice fall unit and shows inverse grading mapping of the deposit gives a volume of 8 3 km3 within the one mm isopach crystal concentration studies show that the true volume erupted was at least 20 km3 equivalent to 8 5 km3 of dense dacite and that 90 of the ejecta was less than 2 mm in diameter the plinian volume eruption rate averaged 1 2 105 m3s 1 and the average gas muzzle velocity of the column exceeded 270 ms 1 a total of 8 3 1018 j of energy were released by the eruption a knowledge of both theoretically derived eruption parameters and contemporary information allows a detailed analysis of eruption mechanisms this eruption was the major stratospheric aerosol injection in the 1902 1903 period however mid to low latitude northern hemisphere temperature deviation data for the years following the eruption show no significant temperature decrease this may be explained by the sulfur poor nature of dacite magmas suggesting that volatile composition rather than mass of volatiles is the controlling parameter in climatic response to explosive eruptions