transient sediment supply in a high altitude alpine environment evidenced through a 10be budget of the etages catchment french western alps although beryllium 10 10be concentrations in stream sediments provide useful synoptic views of catchment wide erosion rates little is known on the relative contributions of different sediment supply mechanisms to the acquisition of their initial signature in the headwaters here we address this issue by conducting a 10be budget of detrital materials that characterize the morphogenetic domains representative of high altitude environments of the european alps we focus on the etages catchment located in the ecrins pelvoux massif southeast france and illustrate how in situ 10be concentrations can be used for tracing the origin of the sand fraction from the bedload in the trunk stream the landscape of the etages catchment is characterized by a geomorphic transient state high topographic gradients and a large variety of modern geomorphic domains ranging from glacial environments to scarcely vegetated alluvial plains beryllium 10 concentrations measured in the etages catchment vary from similar to 1 x 104 to 4 5 x 105 atoms per gram quartz while displaying consistent 10be signatures within each representative morphogenetic unit we show that the basic requirements for inferring catchment wide denudation from 10be concentration measurements are not satisfied in this small dynamic catchment however the distinct 10be signature observed for the geomorphic domains can be used as a tracer we suggest that a terrestrial cosmogenic nuclide tcn budget approach provides a valuable tool for the tracing of material origin in basins where the let nature do the averaging principles may be violated

sediment yield exceeds sediment production in arid region drainage basins we use 10 be and 26 al to determine long term sediment generation rates identify significant sediment sources and test for landscape steady state in nahal yael an extensively studied hyperarid drainage basin in southern israel comparing a 33 yr sediment budget with 33 paired 10 be and 26 al analyses indicates that short term sediment yield 113 138 t km 2 yr 1 exceeds long term sediment production 74 16 t km 2 yr 1 by 53 86 the difference suggests that the basin is not in steady state but is currently evacuating sediment accumulated during periods of more rapid sediment generation and lower sediment yield nuclide data indicate that 1 sediment leaving the basin is derived primarily from hillslope colluvium 2 bedrock weathers more rapidly beneath a cover of colluvium than when exposed and 3 long term erosion rates of granite schist and amphibolite are similar

temporally and spatially uniform rates of erosion in the southern appalachian great smoky mountains we measured 1 0 be in fluvial sediment samples n 27 from eight great smoky mountain drainages 1 330 km 2 results suggest spatially homogeneous sediment generation on the 10 4 10 5 yr time scale and 100 km 2 spatial scale at 73 11 t km 2 yr 1 equivalent to 27 4 m m y of bedrock erosion this rate is consistent with rates derived from fission track long term sediment budget and sediment yield data all of which indicate that the great smoky mountains and the southern appalachians eroded during the mesozoic and cenozoic at 30 m m y in contrast unroofing rates during the paleozoic orogenic events that formed the appalachian mountains were higher 10 2 m m y erosion rates decreased after termination of tectonically driven uplift enabling the survival of this ancient mountain belt with its deep crustal root as an isostatically maintained feature in the contemporary landscape

cosmic ray labeling of erosion surfaces in situ nuclide production rates and erosion models a number of in situ cosmogenic radionuclides and stable nuclides have been measured in natural exposed rock surfaces with a view to study their in situ production and rock erosion rates 1 the in situ radionuclides can be used for a high resolution tomography of the erosional history of an exposed surface two stable nuclides 3he 21ne and five radionuclides 10be 26al 36cl 14c 39ar having half lives in the range of 300 1 5 106 yr half life are measurable in many rock types a prerequisite for the application of the in situ nuclides for the study of erosional histories of surfaces is a knowledge of their production rates under different irradiation conditions altitude latitude irradiation geometry and shielding relative nuclide production rates can be determined fairly accurately using the extensive available data on cosmic ray neutrons 2 absolute nuclide production rates cannot generally be predicted with any accuracy because of lack of data on excitation functions of nuclides unless some normalization is possible as was done in the case of several cosmic ray produced isotopes in the atmosphere 3 based on a recent natural calibration experiment in which erosion free surfaces exposed to cosmic radiation for 11 000 yrs were sampled the absolute production rates of 10be and 26al in quartz have been accurately estimated for mountain altitudes in sierra nevada 4 the absolute production rates of 10be and 26al in quartz can therefore be estimated fairly accurately for any given latitude and altitude some measurements of 14c in rocks of low erosion rate 5 similarly allow an estimate of its production rate attempts made to measure the in situ production rates of 3he in rocks have not yet led to a convergent production rate in view of the importance of knowing the production rates of isotopes of he ne and ar i present here theoretical estimates of their production rates based on available cross section data i discuss the information that can be extracted from the study of the in situ nuclides in rocks useful parameters characterizing the exposure history of a rock surface are 1 the effective surface exposure age and 2 the time averaged erosion rate the implications of these parameters for single and multiple nuclide studies are discussed in terms of the erosion models considered

rheology of porous volcanic materials high temperature experimentation under controlled water pressure abstract we present a suite of 21 high temperature uniaxial deformation experiments performed on 25 by 50 mm unjacketed cores of porous 0 8 sintered rhyolitic ash the experiments were performed at both atmospheric dry and elevated water pressure conditions wet experiments used a constant displacement rate of 2 5 10 6 m s 1 corresponding to a strain rate o of 5 10 5 s 1 a single experiment was run at 2 5 10 5 m s 1 o 5 10 4 s 1 dry experiments were conducted mainly at 900 c but also included a suite of lower temperature experiments at 850 800 and 750 c wet experiments were performed at 650 c under water pressures of 1 2 5 and 5 mpa and at a fixed p h 2 o of 2 5 mpa for temperatures of 385 450 and 550 c during deformation strain is manifest by shortening of the cores reduction of porosity flattening of ash particles and radial increase of the cores the continuous reduction of porosity leads to a dynamic transient strain dependent rheology and requires strain to be partitioned between a volume porosity loss and a shear radial increase component these data demonstrate the effect of porosity on the rheology of dry and hydrous melts the effect of increasing porosity is to expand the window for ductile deformation for dry melts by delaying the onset of brittle deformation by 50 c 875 c to 825 c the effect is more pronounced in hydrous melts 0 67 0 78 wt h 2 o where the ductile to brittle transition is depressed by 140 to 150 c increasing water pressure also delays the onset of strain hardening due to compaction driven porosity reduction these rheological data are pertinent to any volcanic processes involving high temperature porous magmas e g magma flow in conduits welding of pyroclastic materials

lithologically influenced geomorphic responses to holocene climatic changes in the southern colorado plateau arizona a soil geomorphic and ecologic perspective abstract the semiarid landscape occupied by the navajo and hopi peoples on the colorado plateau in northeastern arizona in the southwestern united states is characterized by an extensive network of deeply incised arroyos since the early 20th century many researchers have proposed that the recent formation of arroyos in this region and also many attributes of modern vegetation communities were caused directly by overgrazing of vegetation by domestic livestock of the navajo other researchers however have proposed other causes for such features such as climatic change we believe that the landforms soils and vegetation of a small area located on antelope mesa in this region underlain by the highly erodible materials of the miocene bidahochi formation may have been more sensitive to minor climatic changes of the holocene than landscapes of massive mesozoic sandstones that dominate the colorado plateau in the antelope mesa area the presence of actively filling channels rather than arroyos in the upper parts of many drainage basins and associated soils and ecologic patterns indicate that the aggradation 1 was initiated in downstream reaches and within the past two centuries 2 may be linked to recently accelerated slope erosion and 3 is unrelated to past or ongoing grazing this suggests the ongoing aggradation may be related to recent minor climatic changes geochronologic and soil geomorphic evidence indicate that the most recent cycle of arroyo incision and filling may be a small scale analogue for larger magnitude older cycles that produced regionally recognizable paired terraces that are attributable to previous holocene climate changes we propose that climatic change and more specifically increases in precipitation caused an acceleration in the erosion of the steep typically minimally vegetated slopes of the bidahochi formation the beginning of the neoglacial period ca 2 3 ka effects of which are documented by other proxy records in this region may be the climatic change that triggered widespread deposition of a large mid holocene alluvial unit in this region alternating episodes of eolian activity and soil formation in the study area and in this general region provide independent evidence of holocene climatic changes our interpretations of the origin of the cut and fill cycles that emphasize the role of drainage basin lithology and differ significantly from previous interpretations emphasize the linkage of climatic changes groundwater levels and arroyo incision this study reveals the importance of integrating soil and ecologic studies with geomorphologic research such an approach may be critical in helping understand how anthropogenically induced climatic changes of the next century could impact geomorphic processes and the ecology of arid and semiarid regions

quantitative application of poststack acoustic impedance inversion to subsalt reservoir development the cost and complexity of deep water subsalt development wells is so great that a very limited spatial sampling of the target reservoir is achievable with well data thus the quantitative use of seismic data becomes of paramount importance poststack seismic amplitude inversion and poststack seismic attribute analysis and modeling are frequently employed to perform quantitative prediction of reservoir properties from surface seismic data several authors have shown that both absolute and relative acoustic impedance aai and rai respectively derived from poststack seismic amplitude inversion can be useful for quantitative estimates of summary reservoir properties such as average porosity net to gross and others this includes suprasalt and minibasin clastic reservoirs typically encountered in the middle and lower tertiary plays in the deep water gulf of mexico several of which are also encountered subsalt where depth to target can exceed 9000 m and highest frequencies at target are often rather l

large scale erosion rates from in situ produced cosmogenic nuclides in european river sediments abstract we have calculated long term erosion rates of 20 100 mm kyr from quartz contained 10be in the bedload of middle european rivers for catchments ranging from 102 to 105 km2 these rates average over 10 40 kyr and agree broadly with rock uplift incision and exhumation rates historic soil erosion rates and erosion rates calculated from the measured sediment loads of the same rivers moreover our new erosion rate estimates correlate well with lithology and relief however in the regen neckar loire and meuse catchments cosmogenic nuclide derived erosion rates are consistently 1 5 4 times greater than the equivalent rates derived from measured river loads this may be due to the systematic under representation of high magnitude low frequency transport events in the gauging records which cover less than a century alternatively the discrepancy may derive from spatially non uniform erosion and preferential tapping of deeper sections of the irradiation profile a third explanation relates the high cosmogenic nuclide derived erosion rates to inheritance of an elevated pleistocene erosion signal uncertainties associated with the cosmogenic nuclide derived erosion rate estimates are not greater than the potential errors in conventional estimates therefore the cosmogenic nuclide approach is an effective tool for rapid catchment wide assessment of time integrated rates of bedrock weathering and erosion and we anticipate its fruitful application to the quaternary sedimentary record

ultralong offset data acquisition can complement full waveform inversion and lead to improved subsalt imaging full waveform inversion fwi has proved itself as a valuable tool for updating and improving the accuracy of subsurface velocity models for optimum performance particularly in complex geological environments such as subsalt targets in the gulf of mexico gom fwi requires 3d seismic data containing low frequencies and long offsets for onshore seismic surveys it is relatively straightforward and cost effective to record long offset data however for offshore surveys it can incur the additional cost of ocean bottom cable obc acquisition or multivessel towed streamer techniques the recent introduction of dual coil shooting multivessel full azimuth acquisition has provided a highly efficient method of delivering marine 3d seismic data sets with long offsets tests using synthetic data and a real gom dual coil acquisition data set with full azimuth distribution and long up to 14 3 km offsets demonstrate significant potential for improving the accuracy of velocity models and the reliability of the r

water solubility and speciation in shoshonitic and latitic melt composition from campi flegrei caldera italy abstract we report new data on water solubility in two melt compositions representative of volcanic units of the campi flegrei caldera italy the first composition is a primitive shoshonite and the second one is a more evolved latitic composition that have been chosen because of their less evolved nature compared to the other erupted products of campi flegrei water solubility was investigated at pressures from 25 to 200 mpa and 1200 c following synthesis in an internal heated pressure vessel ihpv the glasses obtained from water saturated experiments were analysed using both fourier transform infra red spectroscopy ftir and karl fischer titration kft kft was used as an independent method to obtain water concentration for the calibration of molar absorptivities of infrared bands at 3550 cm 1 total water 4500 cm 1 hydroxyl groups and 5200 cm 1 molecular water water solubility in the shoshonitic melts is similar to that of a basalt while a slightly higher water solubility is observed for the latitic composition as regards the speciation we have investigated the water speciation for the shoshonitic composition only and we have made a comparison between the data resulting using different molar absorptivities obtained for basaltic compositions similar to our shoshonite

the viscosity of latitic melts from lipari aeolian islands italy inference on mixing mingling processes in magmas abstract the viscosity of latitic melts occurring as enclaves in the rhyolitic lava flow of rocche rosse rr lipari aeolian islands italy has been measured in the high t range 1323 1473 k for a dissolved water content varying from 1 23 to 4 39 wt measurements were performed by the falling sphere method in an internally heated gas pressure vessel as expected the viscosity of latite decreases with increasing water content and temperature no pressure effect was detected between 200 and 500 mpa combining the new viscosity data for hydrous melts with data for dry latite of similar base composition giordano d mangiacapra a potuzak m russell j k romano c dingwell d b di muro a 2006 an expanded non arrhenian model for silicate melt viscosity a treatment for metaluminous peraluminous and peralkaline liquids chemical geology 229 42 56 we propose an empirical equation to estimate the viscosity of latitic melts as a function of temperature and water content over the range 101 to 1012 pa s the obtained relationship reproduces the experimental data with a 1 standard deviation of 0 22 log units however the empirical model is not constrained by data for hydrous melts at high viscosity and therefore it can only be used at low temperatures for water poor melts the viscosity data were used to model mixing mingling processes between latitic and rhyolitic magmas at conditions relevant for the rocche rosse rr lipari aeolian islands and la fossa cone 1888 1890 lfc vulcano aeolian islands eruptions the results demonstrate that the ratio between mafic and silicic end members is the main parameter governing mixing mingling interactions between magmas this study suggests a faster ascent of magma underneath vulcano compared to lipari which may be taken into account in hazard forecasting

10be constrains the sediment sources and sediment yields to the great barrier reef from the tropical barron river catchment queensland australia abstract estimates of long term background sediment generation rates place current and future sediment fluxes to the great barrier reef in context without reliable estimates of sediment generation rates and without identification of the sources of sediment delivered to the reef prior to european settlement c 1850 determining the necessity and effectiveness of contemporary landscape management efforts is difficult here using the 2100 km 2 barron river catchment in queensland australia as a test case we use in situ produced 10 be to derive sediment generation rate estimates and use in situ and meteoric 10 be to identify the source of that sediment which enters the coral sea near cairns previous model based calculations suggested that background sediment yields were up to an order of magnitude lower than contemporary sediment yields in contrast in situ 10 be data indicate that background 43 t km 2 y 1 and contemporary sediment yields 45 t km 2 y 1 for the barron river are similar these data suggest that the reef became established in a sediment flux similar to what it receives today since western agricultural practices increased erosion rates large amounts of sediment mobilized from hillslopes during the last century are probably stored in queensland catchments and will eventually be transported to the coast most likely in flows triggered by rare but powerful tropical cyclones that were more common before european settlement and may increase in strength as climate change warms the south pacific ocean in situ and meteoric 10 be concentrations of coral sea beach sand near cairns are similar to those in rivers on the atherton tablelands suggesting that most sediment is derived from the extensive low gradient uplands rather than the steep more rapidly eroding but beach proximal escarpment

the effect of water on the viscosity of a haplogranitic melt under p t x conditions relevant to silicic volcanism the viscosities of hydrous haplogranitic melts synthesized by hydrothermal fusion at 2 kbar pressure and 800 to 1040 c have been measured at temperatures just above the glass transition and at a pressure of 1 bar using micropenetration techniques the micropenetration viscometry has been performed in the viscosity range of 109 pa s to 1012 pa s the samples ranged in water content from 0 4 to 3 5 wt for samples with up to 2 5 wt h2o the water contents have been determined using infrared spectroscopy obtained before and after each viscometry experiment to be constant over the duration of the measurements above this water content a measurable loss of water occurs during the viscometry the viscosity data illustrate an extremely nonlinear decrease in viscosity with added water the viscosity drops drastically with the addition of 0 5 wt of water and then shallows out at water contents of 2 wt an additional viscosity datum point obtained from the analysis of fluid inclusions in a water saturated hpg8 confirms a near invariance of the viscosity with the addition of water between 2 and 6 wt these measurements may be compared directly with the data of hess et al 1995 in press for the effects of excess alkali and alkaline earth oxides on the viscosity of hpg8 also obtained at 1 bar the viscosity of the melts compared on an equivalent molar basis increases in the order h2o li2o na2o k2o rb2o cs2o bao sro cao mgo beo the extraordinary decrease in melt viscosity with added water is poorly reproduced by the calculation scheme of shaw 1972 for the range of water contents investigated here the speciation of water in the quenched glasses can be used to quantify the dependence of the viscosity on hydroxyl content considering only the hydroxyl groups as active fluidizers in the hydrous melts the nonlinearity of the viscosity decrease and the difference with the effects of the alkali oxides becomes larger consequences for degassing calcalkaline rhyolite are discussed

breakthrough acquisition and technologies for subsalt imaging the recently introduced method of wide azimuth data acquisition offers better illumination noise attenuation and lower frequencies to more accurately determine a velocity field for imaging for the field data experiment to demonstrate the technologies we used a gulf of mexico gom wide azimuth data set that allows us to take advantage of possible low frequencies relatively large crossline offsets and increased illumination the input data was processed through true 3d azimuthal surface related multiple elimination srme with zero phasing and debubble eliminating the surface related multiples aids the velocity determination and helps uncover the subsalt sediments at the final imaging stage after the initial velocity derivation which was constrained to wells and geology full waveform inversion fwi was used to further update the velocity field to achieve an enhanced image the methodology used follows the top down approach where suprasalt sediment model is developed followed by the top of salt

climate and surface properties hydrological response of small arid and semi arid watersheds abstract a positive relationship between annual rainfall and geomorphic processes runoff and erosion rates and environmental factors water regime soil and vegetation cover is often assumed for arid and semi arid areas with an annual rainfall in the range of 100 300 mm this assumption disregards the fact that changes along a climatic gradient at desert margins are not limited to purely climatic factors they are often accompanied by a parallel change in surface properties especially the relative extent of rocky or soil covered surfaces that differ greatly in their response to rainfall this raises the issue whether the change in surface properties along a climatic gradient enhances the assumed positive effects of rainfall increase or limits it the hypothesis advanced in this paper is that runoff generation and rate in arid and semi arid areas are primarily controlled by surface properties rather than by the absolute amounts of storm and annual rain amounts hydrological data collected at two instrumented watersheds located one in an arid rocky area and the second in a semi arid soil covered area support this hypothesis the implications of data obtained for runoff generation and flow continuity under changing climatic conditions are analyzed they point to the fact that the same regional climatic change may have different and even opposite effects on the hydrological response of different adjoining surface units this response is expected to be strongly controlled by the specific local surface conditions that prevailed in the area prior to the climatic change

elastic full waveform inversion application using multicomponent measurements of seismic data collection abstractrecent computational improvements allowed us to simulate elastic wavefields in a 3d manner and undertake the challenge of executing elastic full waveform inversion efwi the 3d seg eage overthrust synthetic data were used to run the initial tests which included using all three components for the simulation the inversion targeted two regions the channel system and the overthrusted zone which proved the effectiveness of efwi to delineate geology in terms of vp and vs velocity fields for the field data experiment to demonstrate the technologies we elected to use a gulf of mexico ocean bottom cable data set which allowed us to take advantage of relatively large offsets along with the 4c acquisition the input data were minimally processed mostly through noise removal and the initial model was a gaussian smoothed version of grid tomography output which is done by a prestack migrated gather flattening process during ewfi a multiscale approach was followed to ensure convergence and the earl

origin and deformation of intra salt sulphate layers an example from the dutch zechstein late permian from salt mine galleries and well data it is known that thick rock salt layers can contain anhydrite and carbonate layers with thicknesses on the millimetre to tens of metre scale the relatively thick zechstein 3 anhydrite carbonate layer in the northern netherlands has been studied previously using 3 d seismic data observations from geophysical well logs in this study reveal the presence of thin sulphate layers on the sub seismic scale imbedded in the zechstein 2 z2 salt core samples thin sections seismic data and geochemical measurements were used to determine the mineralogy and origin of one of these z2 sulphate layers bromine analyses show that they mark a freshening event in the z2 salt which can be correlated over large distances in the northern netherlands their core calibrated log signature indicates that the z2 sulphate layers consist either of pure anhydrite or of anhydrite and polyhalite the mineralogy and thickness of the sulphate layers are interpreted to vary between synsedimentary morphologic lows thin anhydrite polyhalite couplets and highs thicker anhydrite layers such a combination of core observations and well log analysis is a powerful tool to detect lateral trends in evaporite mineralogy and to reconstruct the environmental setting of their formation salt internal geometries can further be used to distinguish between different deformation mechanisms in our study area the distribution of sulphate layers within the z2 salt indicates that subjacent salt dissolution was not the dominant process leading to salt related deformation

discontinuous ephemeral streams abstract many ephemeral streams in western north america flowed over smooth valley floors before transformation from shallow discontinuous channels into deep arroyos these inherently unstable streams of semiarid regions are sensitive to short term climatic changes and to human impacts because hillslopes supply abundant sediment to infrequent large streamflow events discontinuous ephemeral streams appear to be constantly changing as they alternate between two primary modes of operation either aggradation or degradation may become dominant attainment of equilibrium conditions is brief disequilibrium is promoted by channel entrenchment that causes the fall of local base level and by deposition of channel fans that causes the rise of local base level these opposing base level processes in adjacent reaches are maintained by self enhancing feedback mechanisms the threshold between erosion and deposition is crossed when aggradational or degradational reaches shift upstream or downstream extension of entrenched reaches into channel fans tends to create continuous arroyos upvalley migration of fan apexes tends to create depositional valley floors with few stream channels less than 100 years is required for arroyo cutting but more than 500 years is required for complete aggradation of entrenched stream channels and valley floors discontinuous ephemeral streams have a repetitive sequence of streamflow characteristics that is as distinctive as sequences of meander bends or braided gravel bars in perennial rivers the sequence changes from degradation to aggradation headcuts concentrate sheetflow a single trunk channel conveys flow to the apex of a channel fan braided distributary channels end in an area of diverging sheetflow and converging sheetflow drains to headcuts the sequence is repeated at intervals ranging from 15 m for small streams to more than 10 km for large streams lithologic controls on the response of discontinuous ephemeral streams include 1 amount and size of sediment yielded from hillslopes 2 infiltration capacity of valley floor alluvium that influences both the unit stream power available for upstream headcut migration and the attenuation of flashy streamflow events by riparian vegetation in sheetflow reaches and 3 cohesiveness of alluvium which affects headcut and streambank morphology and rates of arroyo extension downcutting and widening initiation of arroyo cutting may be too complex to be attributed to a single cause such as change in mean annual precipitation or grazing by livestock but is most likely associated with a decrease in density of protective plant cover on hillsides and along valley floors relatively larger unit stream power makes downstream reaches more susceptible to initial entrenchment during floods than headwaters reaches and favors persistent arroyos entrenchment continues until an equilibrium longitudinal profile is briefly attained then channel widening occurs streambanks are undercut and aggradation begins

the deep magmatic system of the campi flegrei caldera italy 1 melt inclusions in phenocrysts of the minopoli2 shoshonite and fondo riccio latite eruptive products campi flegrei caldera 10 2 to 9 5 ka bp constrain the nature of deep phlegraean magmatic fluids their role in volcanism and give new insights into the magmatic plumbing system the analyzed melt inclusions show that co2 is an abundant gaseous species confirming the results of geochemical studies on the magmatic gas fraction involved in present day fumarolic emissions volatile concentrations within the melt inclusions require gas melt equilibria between 8 and 9 km depth and closed system degassing in presence of ascending co2 rich fluids of deep provenance magmas later re equilibrate at depths up to 3 2 km i e above the top of the carbonate basement these observations correlate well with independent geophysical and geochemical evidence and are useful constraints for volcanic hazards assessment at campi flegrei

timing of surficial process changes down a mojave desert piedmont abstract we measured 10 be and 26 al in 29 sediment samples to infer the history and millennial scale rates of change down a low gradient piedmont a common but enigmatic landform that dominates the mojave desert nuclide data suggest that a large volume of sediment was deposited on the proximal east range road piedmont in fort irwin california 75 500 yr ago since then this material has been stable or eroding slowly in contrast on the distal piedmont 3 5 km from the upland source basins soil stratigraphy suggests that there have been alternating periods of surface stability erosion and deposition over the last 70 000 yr nuclide data from samples amalgamated along cross piedmont transects suggest that long term average down gradient sediment speeds range from 9 cm yr 1 near the uplands to 22 cm yr 1 6 km down piedmont these speeds are similar to 10 be estimated sediment speeds down three other piedmonts in the mojave desert suggesting that piedmont surface morphologies dominated by shallow migrating channels have similar sediment transport rates the timing of surface process change down the east range road piedmont is determined by a combination of sediment available in the source basins sediment transport rates and the size of the piedmont

the effect of water and fo2 on the ferric ferrous ratio of silicic melts new experiments on the effect of dissolved water on the ferric ferrous ratio of silicic melts have been performed at 200 mpa between 800 c and 1000 c and for fo2 between nno 1 35 and nno 6 6 water saturated conditions were investigated compositions studied include six metaluminous synthetic melts with feotot progressively increasing from 0 47 to 4 25 wt two natural obsidian glasses one peraluminous and the other peralkaline and a synthetic rhyolitic glass having the composition of the matrix glass of the june 15 1991 pinatubo dacite ferrous iron was analyzed by titration and feotot by electron microprobe variation of quench rate was found to have no detectable effect on the ferric ferrous ratio of the hydrous silicic melts investigated at nno no dependence of the ferric ferrous ratio with temperature is observed at fo2 nno 1 the experimental ferric ferrous ratios are equal or lower than calculated the peralkaline samples show the same type of behaviour a non linear relationship between xfe2o3 xfeo and fo2 implies that a term for dissolved water must be added to the kc equation if it is to be applied to the calculation of ferric ferrous ratios of hydrous silicic melts above nno 1 the ferric ferrous ratio is essentially controlled by the anhydrous melt composition and fo2 however differences exist between measured and calculated ferric ferrous ratios of silicic melts that are not all attributable to the effect of dissolved water additional work is needed to describe more precisely the dependence of the ferric ferrous ratio on anhydrous melt composition the oxidizing effect of water is restricted to relatively reduced magmatic liquids in oxidized calk alkaline magma series the presence of dissolved water will not largely influence melt ferric ferrous ratios

reverse time migration of offset vertical seismic profiling data using the excitation time imaging condition to apply reverse time migration to prestack finite offset data from variable velocity media the standard time zero imaging condition must be generalized because each point in the image space has a different image time or times this generalization is the excitation time imaging condition in which each point is imaged at the one way traveltime from the source to that point reverse time migration with the excitation time imaging condition consists of three elements 1 computation of the imaging condition 2 extrapolation of the recorder wave field and 3 application of the imaging condition computation of the imaging condition for each point in the image is done by ray tracing from the source point this is equivalent to extrapolation of the source wave field through the medium extrapolation of the recorded wave field is done by an acoustic finite difference algorithm imaging is performed at each step of the finite difference extrapolation by extracting from the propagating wave field the

reverse time migration migration of stacked or zero offset sections is based on deriving the wave amplitude in space from wave field observations at the surface conventionally this calculation has been carried out through a depth extrapolation we examine the alternative of carrying out the migration through a reverse time extrapolation this approach may offer improvements over existing migration methods especially in cases of steeply dipping structures with strong velocity contrasts this migration method is tested using appropriate synthetic data sets

late quaternary history of the chemehuevi mountain piedmont mojave desert deciphered using 10be and 26al we used the cosmogenic nuclides 10 be and 26 al as cosmic ray dosim eters to track sediment movement across the incised chemehuevi mountain piedmont surface the piedmont extends 12 km from highland source basins to an ephemeral wash at the toe of the piedmont nuclide activity in sediment from steep source basins and from the bedrock pediment allows us to estimate rates of sediment generation and thus the rate at which sediment is supplied to the piedmont from weathering rock analysis of amalgamated sediment samples collected along 4 km long transects spaced at 1 km intervals from the mountain front provide context for understanding nuclide activity in sediment samples collected from two soil pits and demonstrate that sediment steadily moves down the channel network samples from the two soil pits allow for estimates of sediment deposition rates and thus further illuminate piedmont history model results suggest that the chemehuevi mountains are eroding about 40 mm ky 1 whereas the mountain proximal bedrock pediment and the interpiedmont saw tooth range are eroding more slowly 10 to 21 mm ky 1 and 9 5 mm ky 1 respectively cosmogenic nuclide profiles in two soil pits suggest a complex history of deposition at rates between 19 to 39 mm ky 1 and stability over the past 60 ky a change in process from sediment deposition to sediment transport occurred distally on the piedmont approximately 8 ky ago while the mid piedmont piedmont surface has been stable since the mid holocene the incised chemehuevi mountain piedmont is changing at rates similar to planar and uniformly active piedmonts such as those adjacent to the iron and granite mountains all three piedmonts have average sediment grain velocities of decimeters per year long term source basin erosion rates between 35 to 40 mm ky depositional hiatuses around the pleistocene holocene climatic transition from moister to drier conditions and pleistocene deposition rates of 18 to 39 mm ky such similarity in piedmont behavior despite clear differences in morphology and appearance might suggest large scale geologic and climatic controls on the generation transport and deposition of sediment in the mojave desert

a general viscosity model of campi flegrei italy melts abstract viscosities of shoshonitic and latitic melts relevant to the campi flegrei caldera magmas have been experimentally determined at atmospheric pressure and 0 5 gpa temperatures between 840 k and 1870 k and h2o contents from 0 02 to 3 30 wt the concentric cylinder technique was employed at atmospheric pressure to determine viscosity of nominally anhydrous melts in the viscosity range of 101 5 103 pa s the micropenetration technique was used to determine the viscosity of hydrous and anhydrous melts at atmospheric pressure in the high viscosity range 1010 pa s falling sphere experiments were performed at 0 5 gpa in the low viscosity range from 100 35 to 102 79 pa s in order to obtain viscosity data of anhydrous and hydrous melts the combination of data obtained from the three different techniques adopted permits a general description of viscosity as a function of temperature and water content using the following modified vft equation l o g a b t c d t e e x p g w t where is the viscosity in pa s t the temperature in k w the h2o content in wt and a b c d e and g are the vft parameters this model reproduces the experimental data 95 measurements with a 1 standard deviation of 0 19 and 0 22 log units for shoshonite and latite respectively the proposed model has been applied also to a more evolved composition trachyte from the same area in order to create a general model applicable to the whole compositional range of campi flegrei products moreover speed data have been used to constrain the ascent velocity of latitic shoshonitic and trachytic melts within dikes using petrological data and volcanological information geometrical parameters of the eruptive fissure and depth of magma storage we estimate a time scale for the ascent of melt from 9 km to 4 km depth where deep and shallow reservoirs respectively are located in the order of few minutes such a rapid ascent should be taken into account for the hazard assessment in the campi flegrei area

cosmogenically enabled sediment budgeting we used 10 be and 26 al to constrain the millennial scale sedi ment and nuclide budget for a common long studied but poorly understood landform in arid regions the desert piedmont we sampled the chemehuevi mountain piedmont a complex multi surfaced landform in the mojave desert western united states the nuclide data indicate that sediment is produced more rapidly 1 1 3 10 5 kg yr 21 km 22 in steep mountain source basins than on the low gradient pediment 4 0 3 10 4 kg yr 21 km 22 or the intra piedmont mountain range 2 5 3 10 4 kg yr 21 km 22 however the bulk of the sediment in transport is derived from erosion of the large abandoned alluvial surface 3 9 3 10 4 kg yr 21 km 22 the combination of mass and nuclide budgeting suggests that sediment transport speeds decrease downslope from tens of meters per year in confined channels on the proximal pediment to decimeters per year in unconfined distributaries on distal wash surfaces the sed iment and nuclide budgeting approach we use is particularly valu able in arid regions where geomorphically significant events are infrequent and dating control is poor thus confounding traditional sediment budgeting techniques

using 10be and 26al to determine sediment generation rates and identify sediment source areas in an arid region drainage basin we measured 10 be and 26 al in 64 sediment and bedrock samples collected throughout the arid 187 km 2 yuma wash drainage basin southwestern arizona from the measurements we determine long term time integrated rates of upland sediment generation 81f 5gm 2 year 1 and bedrock equivalent lowering 30f 2mm a 1 consistent with other estimates for regions of similar climate lithology and topography in a small f 8k m 2 upland sub basin differences in nuclide concentrations between bedrock outcrops and hillslope colluvium suggest weathering of bedrock beneath a colluvial cover is a more significant source of sediment 4010 4 kg year 1 than weathering of exposed bedrock surfaces 1010 4 kg year 1 mixing models constructed from nuclide concentrations of sediment reservoirs identify important sediment source areas hillslope colluvium is the dominant sediment source to the upper reaches of the sub basin channel channel cutting of alluvial terraces is the dominant source in the lower reaches similarities in nuclide concentrations of various sediment reservoirs indicate short sediment storage times 10 3 years nuclide concentrations measured in channel sediment from tributaries of yuma wash and in samples collected along the length of the wash were used to construct mixing models and determine sediment sources to the main stem channel we find an exponential decrease in the channel nuclide concentrations with distance downstream suggesting that as much as 40 of sediment discharged from yuma wash has been recycled from storage within basin fill alluvium sediment generation and denudation rates determined from the main stem are greater 25 than rates determined from upland sub basins suggesting that currently sediment may be exported from the basin more quickly than it is being generated in the uplands independence of nuclide concentration and sediment grain size indicates that channels transport sediment in discrete pulses before rapidly depositing poorly sorted material suggesting that differences in transport times for different size materials are minimal d 2002 elsevier science b v all rights reserved

3d prestack plane wave full waveform inversion prestack depth migration has been used for decades to derive velocity distributions in depth numerous tools and methodologies have been developed to reach this goal exploration in geologically more complex areas exceeds the abilities of existing methods new data acquisition and data processing methods are required to answer these new challenges effectively the recently introduced wide azimuth data acquisition method offers better illumination and noise attenuation as well as an opportunity to more accurately determine velocities for imaging one of the most advanced tools for depth imaging is full waveform inversion prestack seismic full waveform inversion is very challenging because of the nonlinearity and nonuniqueness of the solution combined with multiple iterations of forward modeling and residual wavefield back propagation the method is computer intensive especially for 3d projects we studied a time domain plane wave implementation of 3d waveform inversion we found that plane wave gathers

slow rates of rock surface erosion and sediment production across the namib desert and escarpment southern africa slow erosion has characterized the namib desert the namibian escarpment and the adjacent namibian highlands over the pleistocene paired analyses n 66 of in situ produced 10be and 26al in quartz bearing samples of bedrock primarily from inselbergs of sediment from dry river and stream channels and of clasts from desert surfaces reveal large inventories of these cosmogenic nuclides indicating significant landscape stability over at least the past million years bedrock samples n 47 collected in three transects from the coast across the escarpment and into the highlands show no spatial pattern in elevation normalized nuclide abundance despite a difference in mean annual precipitation map between sample sites at the coast map 400 mm yr 1 average model erosion rates inland of the escarpment 3 2 1 5 n 9 are indistinguishable from average rates seaward of the escarpment 3 6 1 9 n 38 indicating that rock on the pedimented coastal plain is eroding at the same rate as rock in the highlands sediment samples n 3 from small streams suggest that the landscape as a whole is eroding more rapidly than the bedrock outcrops and that a basin in the steep escarpment zone is eroding several times faster 16 m my 1 than either a basin in the highlands 5 m my 1 or a basin in the coastal plain 8 m my 1 data from large rivers n 4 constrain erosion rates averaged over 105 yrs and 104 to 105 km2 between 3 and 9 m my 1 small quartz clasts n 12 collected from four desert surfaces record extraordinarily long variable and in some cases complex exposure histories simple 10be model ages are as high as 1 8 my some minimum total histories considering both 10be and 26al and including both burial and exposure exceed 2 7 my as a group the namibian cosmogenic data do not support the model of significant and on going escarpment retreat the similarity of erosion rates calculated from 10be analysis of fluvial sediments and longer term 107 yr average mass removal rates estimated by others using fission track analysis of rock suggests that namibian erosion rates have reached a steady state and are changing little over time at outcrop scales the concordance of 10be and 26al in most bedrock samples suggests that the model of steady uniform bedrock erosion is valid there is no indication of intermittent burial shedding of thick rock slabs or stripping of previous cover at an intermediate scale a transect of bedrock samples north of gobabeb demonstrates that the northern boundary of the massive namib sand sea has been steady and unshifting similarly low cosmogenically estimated erosion rates across west and central namibia suggest that the landscape is in geomorphic steady state its overall appearance changing only slowly through time

reversed time migration in spatial frequency domain during the past decade finite difference methods have become important tools for direct modeling of seismic data as well as for certain interpretation processes one of the earliest applications of these methods to seismics is the pioneering contribution of alterman who in a series of papers alterman and karal 1968 alterman and aboudi 1968 alterman and rotenberg 1969 alterman and loewenthal 1972 demonstrated the usefulness of such numerical computations for the propagation of seismic waves in elastic media a clear exposition of these techniques as well as a comparison of results obtained from them with the corresponding analytical solutions can be found in alterman and karal 1968 this subject was further developed and extended to more complicated models by boore 1970 ottaviani 1971 and kelly et al 1976 claerbout introduced a somewhat different finite difference approach claerbout 1970 claerbout and johnson 1971 for modeling the acoustic waves which often dominate the reflection seismogram in his approach the original wave equation which governs the propagation of the acoustic waves is modified in such a way so as to allow the propagation of either only upcoming or only downgoing waves by moving the coordinate frame with the downgoing waves claerbout showed that one could greatly reduce computation time using the same concepts he showed claerbout and doherty 1972 how to use a similar scheme for migrating a seismic section by downward continuation of the upcoming waves this migration method is an interesting extension of the ideas of hagedoorn 1954 and was found to be extremely useful with real data larner and hatton 1976 loewenthal et al 1976

sensitivity analysis of pediment development through numerical simulation and selected geospatial query abstract dozens of references recognizing pediment landforms in widely varying lithologic climatic and tectonic settings suggest a ubiquity in pediment forming processes on mountain piedmonts worldwide previous modeling work illustrates the development of a unique range in arid semiarid piedmont slope 3 m y 1 restrict pediment development by fostering piedmont incision and or wholesale removal stripping of regolith mantles prior to footslope pediment development simulations illustrate an insensitivity to alternating layers of sandstone and shale 3 15 m thick oriented in various geometric configurations vertical horizontal and dip slope and generating different regolith hydrologic properties and exhibiting weathering rate variations up to 3 fold higher fluxes and residence times of subsurface groundwater in more humid environments as well as dissolution type weathering lead to a thickening of regolith mantles on erosional piedmonts on the order of 10 1 m and an elimination of pediment morphology an initial test of the model sensitivity analysis in arid semiarid environments for which field reconnaissance and detailed geomorphic mapping indicate the presence of pediments controlled by climatic conditions soil hydrologic properties vegetation characteristics and bedrock weathering style that are known and constant supports our modeling results that pediments are more prevalent in hydrologically open basins

h 2 o solubility in basalt at upper mantle conditions this study presents a new experimental approach for determining h2o solubility in basaltic melt at upper mantle conditions traditional solubility experiments are limited to pressures of 600 mpa or less because it is difficult to reliably quench silicate melts containing greater than 10 wt dissolved h2o to overcome this limitation our approach relies on the use of secondary ion mass spectrometry to measure the concentration of h dissolved in olivine and on using the measured h in olivine as a proxy for the concentration of h2o in the co existing basaltic melt the solubility of h2o in the melt is determined by performing a series of experiments at a single pressure and temperature with increasing amounts of liquid h2o added to each charge the point at which the concentration of h in the olivine first becomes independent of the amount of initial h2o content of the charge added adsorbed h2o indicates its solubility in the melt experiments were conducted by packing basalt powder into a capsule fabricated from san carlos olivine which was then pressure sealed inside a ni outer capsule our experimental results indicate that at 1000 mpa and 1200 c the solubility of h2o in basaltic melt is 20 6 0 9 wt 2 standard deviation this concentration is considerably higher than predicted by most solubility models but defines a linear relationship between h2o fugacity and the square of molar h2o solubility when combined with solubility data from lower pressure experiments further our solubility determination agrees with melting point depression determined experimentally by grove et al 2006 for the h2o saturated peridotite solidus at 1000 mpa melting point depression calculations were used to estimate h2o solubility in basalt along the experimentally determined h2o saturated peridotite solidus the results suggest that a linear relationship between h2o fugacity and the square of molar solubility exists up to 1300 mpa where there is an inflection point and solubility begins to increase less strongly with increasing h2o fugacity

reconciliation of experimental results on h2o speciation in rhyolitic glass using in situ and quenching techniques in order to resolve the controversy over how to interpret experimental h2o speciation results using in situ and quenching techniques we have carried out an infrared spectroscopic study to determine whether the molecular h2o 5230 cm 1 and oh 4520 cm 1 band intensity variation with measurement temperature below glass transition is owing to species interconversion or to the temperature dependence of molar absorptivities by comparing rhyolitic glasses with different total h2o content from 0 18 to 0 76 wt we show that the peak height of the 4520 cm 1 band increases by a similar relative amount about 2 if the baseline is fit with a flexicurve and 10 if the baseline is fit by a straight line from 25 to 400oc independent of the total h2o content the results show that 1 the molar absorptivities do indeed change with temperature and 2 in our experiments below the glass transition temperature species concentrations do not change noticeably with temperature and the band intensity variations are caused mainly by changes in the shape of the absorbance bands with temperature the absence of unquenchable species reaction in the glass state on our experimental time scale confirms that speciation data can be obtained using the quench technique from 400 to 600oc on the other hand the temperature dependence of the molar absorptivities must be quantified for the full potential of the in situ technique to be realised 1999 elsevier science b v all rights reserved

solubility of water in magmas to 2 kbar high water concentrations 4 6 wt are found in the quenched glass inclusions of phenocrysts of explosive silicic and intermediate eruptions accordingly we have measured the solubility of water in a wide range of natural liquids up to 2 kbar with data from the literature we have developed a simple thermodynamically based empirical model for the solubility of water as a function of temperature 700 1200 c pressure 1 2000 bar and composition the model works well for both pure h 2 o and mixed fluid compositions fits the data to 0 5 wt 2 and may be used to successfully model the degassing and eruption behavior in most volcanic systems as well as the magmatic exsolution processes that lead to ore deposition due to the nature of the regression however it should not be extrapolated to conditions beyond the range of the data

stochastic model for the long term transport of stored sediment in a river channel we develop a stochastic model for the transport of stored sediment down a river channel the model is based on probabilities of transition of particles among four different sediment storage reservoirs called active often mobilized semiactive inactive and stable hardly ever mobilized the probabilities are derived from computed sediment residence times two aspects of sediment storage are investigated flushing times of sediment out of a storage reservoir and changes in the quantity of sediment stored in different reservoirs due to seasonal sediment transport into and out of a reach we apply the model to redwood creek a gravel bed river in northern california although the redwood creek data set is incomplete the application serves as an example of the sorts of analyses that can be done with the method the application also provides insights into the sediment storage process sediment flushing times are highly dependent on the degree of interaction of the stable reservoir with the more mobile sediment reservoirs the most infrequent and highest intensity storm events which mobilize the stable reservoir are responsible for the long term shifts in sediment storage turnover times of channel sediment in all but the stable reservoir are on the order of 750 years suggesting this is all the time needed for thorough interchange between these sediment compartments and cycling of most sediment particles from the initial reservoir to the ocean finally the markov model has adequately characterized sediment storage changes in redwood creek for 1947 1982 especially for the active reservoir the model replicates field observation of the passage of a slug of sediment through the active reservoir of the middle reach of redwood creek in the 18 years following a major storm in 1964 that introduced large quantities of landslide debris to the channel

h2o in rhyolitic glasses and melts measurement speciation solubility and diffusion dissolved h2o in silicate melts and glasses plays a crucial role in volcanic eruptions on terrestrial planets and affects glass properties and magma evolution in this paper major progress on several aspects of the h2o melt or glass system is reviewed consistency among a variety of data is investigated discrepancies are evaluated and confusion is clarified on the infrared measurement of total h2o and species concentrations calibration for a variety of glasses has been carried out at room temperature the measurements for h2o in rhyolitic glasses have undergone the most scrutiny resulting in the realization that absorptivities for the near infrared bands depend on total h2o content although the variation of the absorptivities does not seem to significantly affect the determination of total h2o it does affect the determination of molecular h2o and oh species concentrations calibration of the infrared technique for h2o in rhyolitic glasses still needs much improvement especially at high total h2o furthermore it is now almost certain that the molar absorptivities also depend on the measurement temperature in in situ studies hence it will be necessary to carry out calibrations in situ at high temperatures on h2o speciation results from two experimental approaches the quench technique and the in situ technique are very different leading to controversy in our understanding of true speciation a solution is presented to reconcile this controversy it is almost certain that the quench technique does not suffer from a quench problem but interpretation of in situ results suffered from ignoring the dependence of the molar absorptivities on measurement temperature accurate calibration at high temperatures is necessary for the quantitative application of the in situ technique to h2o speciation in silicate melts and glasses on h2o solubility in silicate melts recent experimental work has significantly expanded the t p range of solubility measurements and recent solubility models fill a gap for predicting solubility for a wide range of melt compositions i present a solubility model for rhyolitic and quasi rhyolitic melts over a wide range of t and p 500 1350 c 0 8 kbar by incorporating the role of speciation the solubility model is able to recover the experimental solubility data and has extrapolative value although the partial molar volume of h2o derived from the solubility model differs from that derived from density measurements on h2o diffusion recent studies on h2o diffusion in a quasi rhyolitic melt at 800 1200 c 0 5 5 kbar and up to 7 total h2o not only provide important new diffusion data but are also challenging earlier understanding of h2o diffusion based on data in rhyolitic glasses at 400 550 c 1 bar and 0 2 1 8 total h2o a comparison between the earlier model and recent data is made the recent high temperature diffusivities at total h2o 2 can be predicted by the earlier model however at higher total h2o the earlier model fails new work is under way to understand the diffusion mechanisms at high h2o contents

use of cosmogenic radionuclides as a sediment tracer in the santa cruz littoral cell california united states we demonstrate that cosmogenic radionuclides can be employed to trace sediment when the sources have sufficiently distinct concentrations and develop a theoretical mixing model for a rocky coastline littoral system we combine the resulting mixing model with existing cosmogenic radionuclide methods that quantify river inputs and terrace ages to determine the major components of the long term littoral sediment budget of the santa cruz california coastline sediment derived from coastal basins eroding at 0 2 mm yr has a much lower concentration than sediment derived from 60 84 ka terrace sands atop backwearing seacliffs the complex pattern of cosmogenic radionuclide concentrations in littoral sands along 100 km of coastline can be explained by mixing sediment derived from seacliffs backwearing at 10 cm yr with that delivered by rivers having widely different amounts of sediment discharge

denudation rates determined from the accumulation of in situ produced 10be in the luquillo experimental forest puerto rico we present a simple method for estimation of long term mean denudation rates using in situ produced cosmogenic 10be in fluvial sediments procedures are discussed to account for the effects of soil bioturbation mass wasting and attenuation of cosmic rays by biomass and by local topography our analyses of 10be in quartz from bedrock outcrops soils mass wasting sites and riverine sediment from the icacos river basin in the luquillo experimental forest puerto rico are used to characterize denudation for major landform elements in that basin the 10be concentration of a discharge weighted average of size classes of river sediment corresponds to a long term average denudation of 43 m ma 1 consistent with mass balance results

seismic waveform inversion in the frequency domain part 2 fault delineation in sediments using crosshole data a crosshole experiment was carried out in a layered sedimentary environment in which a normal fault is known to cut through the section initial traveltime inversions produced stable but low resolution images from which the fault could be only vaguely inferred to image the fault wavefield inversion was used to produce a velocity model consistent with the detailed phase and amplitude of the data at a number of frequencies our wavefield inversion scheme uses a classical descent type algorithm for decreasing the data misfit by iteratively computing the gradient of this misfit by repeated forward and backward propagations our propagator is a full wave equation frequency domain acoustic finite difference method the use of the frequency space domain yields computational advantages for multisource data and allows an easy incorporation of viscous effects by running wavefield inversion on the field data a quantitative velocity image was produced that yielded a significantly improved image of the fault when compared with the original traveltime inversions because the original field data were noisy and contained a high degree of multiple scattering from the layering of the sediments the transmitted arrivals were selectively windowed to enhance the image the sediments at the site were strongly attenuating we therefore used a viscoacoustic model during the modeling and the inversion that correctly simulated the observed decrease in amplitude with increasing frequency and source receiver offset furthermore since the traveltime inversion indicated a high degree of anisotropy at the site a fixed homogeneous level of anisotropy was used during the inversion tests at varying levels of anisotropy confirmed the improvement in image quality and in data fit when anisotropy was incorporated the final image was verified by examining the distribution of the residuals in the frequency domain by comparing time domain modeled wavefields with the observed data and by direct comparison with borehole logs

predrill prediction of subsalt pore pressure from seismic impedance abstract a target oriented predrill pore pressure prediction method using seismically estimated acoustic impedance is applied to recently acquired and processed dual coil data in the green canyon and walker ridge areas of the gulf of mexico three deepwater subsalt wells are used in the study one was used as a calibration well and the other two were used as blind wells for comparing prediction results with the measured pore pressure and mud weight data all three wells are in the green canyon area penetrating thick salt bodies a new seismic inversion method is used for inversion of seismic impedance the pore pressure method uses a direct transform of the inverse of acoustic impedance with two adjustable parameters the optimization of the parameters is done through an iterative process to match the pore pressure gradient obtained from the well acoustic impedance with those of pore pressure measurements and mud weights within a tolerable range of those data for the calibration well the optimized p

water and the viscosity of andesite melts the viscosity of a synthetic andesite like melt has been measured between 1010 and 1014 p for water contents in the range 0 3 5 wt the very slow kinetics of water exsolution over this viscosity range allowed the measurements to be made at 1 bar with a high precision after a steep viscosity decrease of 5 orders of magnitude for 1 wt h2o an additional 2 5 wt h2o causes a further viscosity decrease of only 2 orders of magnitude these viscosity decreases are qualitatively similar to those observed previously for more silica rich compositions the new data join smoothly with available high temperature measurements made at high pressures on water bearing andesite melts because the intrinsic effects of pressure are as small for water bearing as for water free samples the depressing effect of water on the viscosity of natural andesite melts can be estimated changes in water speciation as a function of either temperature or pressure do not seem to have marked effects on the viscosity although quantitative applications are not yet possible the configurational entropy theory accounts qualitatively for these features

spatially averaged long term erosion rates measured from in situ produced cosmogenic nuclides in alluvial sediment spatially averaged erosion rates of small catchments can be accurately inferred from the concentrations of cosmogenic nuclides in stream sediment here we test this technique at two catchments by comparing erosion rates inferred from cosmogenic nuclides with rates of alluvial fan deposition over the past 16 000 years these two independent estimates agree within one standard error demonstrating that cosmogenic nuclide signatures of stream sediment can be used to measure spatially averaged long term erosion rates using this technique we show that long term erosion rates are an exponential function of average hillslope gradient at these sites

migration by extrapolation of time dependent boundary values migration of an observed zero offset wavefield can be performed as the solution of a boundary value problem in which the data are extrapolated backward in time this concept is implemented through a finite difference solution of the two dimensional acoustic wave equation all depths are imaged simultaneously at time 0 the imaging condition and all dips right up to vertical are correctly migrated numerical examples illustrate this technique in both constant and variable velocity media

tectonic and climatic controls on the spatial distribution of denudation rates in northern chile 18 s to 23 s determined from cosmogenic nuclides in the arid region of northern chile the environmental conditions are favorable for measuring tectonic and climatic influences on catchment denudation rates in the absence of vegetation previous studies of denudation rates from cosmogenic 10be and 26al concentrations are limited to single drainages in this study we examine catchment to orogen scale spatial variation in denudation rates between 18 23 s in the coastal and western cordilleras of northern chile 10be and 26al data were obtained from 33 catchments to examine the relative roles of tectonics and climate on catchment averaged denudation rates at broader scales we examine whether denudation rates and orogen topography reflect the 3d plate geometry of the region cosmogenic nuclide derived denudation rates range from 0 4 0 5 to 20 6 1 5 m myr in the coastal cordillera and from 1 4 0 7 to 168 0 19 8 m myr in the western cordillera the controls on the denudation rates are evaluated using a statistical factor analysis of ten selected catchment parameters denudation rates indicate a strong linear relationship with channel steepness indices but insignificant correlations and covariation with mean annual precipitation rates drainage area stream order mean elevation mean local relief mean basin slope and analyzed grain size of the sampled sediments moreover denudation rates are better correlated with tectonic controls at catchment scale than orogen scale plate tectonics in the western and coastal cordillera

multiparameter full waveform inversion of multicomponent ocean bottom cable data from the valhall field part 1 imaging compressional wave speed density and attenuation multiparameter full waveform inversion fwi is a challenging quantitative seismic imaging method for lithological characterization and reservoir monitoring the difficulties in multiparameter fwi arise from the variable influence of the different parameter classes on the phase and amplitude of the data and the trade off between these in this framework choosing a suitable parametrization of the subsurface and designing the suitable fwi workflow are two key methodological issues in non linear waveform inversion we assess frequency domain visco acoustic fwi to reconstruct the compressive velocity vp the density or the impedance ip and the quality factor qp from the hydrophone component using a synthetic data set that is representative of the valhall oil field in the north sea we first assess which of the vp and vp ip parametrizations provides the most reliable fwi results when dealing with wide aperture data contrary to widely accepted ideas we show that the vp parametrization allows a better reconstruction of both the vp and ip parameters first because it favours the broad band reconstruction of the dominant vp parameter and secondly because the trade off effects between velocity and density at short to intermediate scattering angles can be removed by multiplication to build an impedance model this allows for the matching of the reflection amplitudes while the broad band velocity model accurately describes the kinematic attributes of both the diving waves and reflections then we assess different inversion strategies to recover the quality factor qp in addition to parameters vp and a difficulty related to attenuation estimation arises because on the one hand the values of qp are on average one order of magnitude smaller than those of vp and and on the other hands model perturbations relative to the starting models can be much higher for qp than for vp and during fwi in this framework we show that an empirical tuning of the fwi regularization which is adapted to each parameter class is a key issue to correctly account for the attenuation in the inversion we promote a hierarchical approach where the dominant parameter vp is reconstructed first from the full data set i e without any data preconditioning to build a velocity model as kinematically accurate as possible before performing the joint update of the three parameter classes during a second step this hierarchical imaging of compressive wave speed density and attenuation is applied to a real wide aperture ocean bottom cable data set from the valhall oil field several geological features such as accumulation of gas below barriers of claystone and soft quaternary sediment are interpreted in the fwi models of density and attenuation the models of vp and qp that have been developed by visco acoustic fwi of the hydrophone data can be used as initial models to perform visco elastic fwi of the geophone data for the joint update of the compressive and shear wave speeds

regolith thickness instability and the formation of tors in arid environments 1 we present model results suggesting that a physical erosion bedrock weathering feedback is responsible for the development of isolated bedrock knobs tors inselbergs that often punctuate otherwise smooth pediments of homogeneous basement lithology tors and larger more heavily jointed and morphologically complex exposures inselbergs may arise as a consequence of fluctuations in rainfall and sediment transport conditions combined with a bedrock weathering mechanism that depends on regolith thickness hydrogeochemical considerations and field observations in arid granitic environments suggest that the relationship between weathering rate and regolith thickness exhibits a maximum for a finite thickness of cover we have encapsulated this simple erosion weathering feedback in a numerical model simulating arid semiarid landscape evolution that produces low sloping pediments punctuated by tors tors form during periods of higher effective moisture resulting in local base level incision and regolith thinning on pediments invoking a transition in which mantled surfaces lower at rates exceeding the bare bedrock weathering rate this condition favors the emergence and growth of tors in areas covered by regolith thickness less than a threshold value subsequent shifts in climate or local base level that restore sediment surface lowering rates less than the bare bedrock weathering rate will lead to a progressive decrease in tor height and ultimately their disappearance thus according to this model tors in arid environments represent possibly transient features related to fluctuations in climate or local transport conditions rather than palimpsests of an ancient landscape derived from differential subsurface weathering followed by regolith stripping

the solubility of h_ 2 o in melts in the system sio_ 2 al_ 2 o_ 3 na_ 2 o k_ 2 o at 1 to 2 kbars the solubilities of water in six melts in the system k 2 o na 2 o al 2 o 3 sio 2 were determined at 970 1630 bars and 800 c melts were synthesized hydrothermally in pt capsules in cold seal vessels and then quenched isobarically the solubilities were determined by micromanometric measurement of h 2 o evolved during vacuum fusion of vesicle free glass wafers and are reproducible to 2 8 2 s d of the concentration the solubilities at 970 bars for the granitic and phonolitic minimum melts are 2 88 pm 0 10 wt and 5 01 pm 0 14 wt respectively both peralkaline and peraluminous granitic melts have higher h 2 o solubilities than the 1 kbar p h 2 o minimum melt and indicate the existence of minima in solubilities at molar na k al 1 along joins of constant sio 2 two melts at constant sio 2 and na k al ratio but varying in na na k 0 57 0 69 molar have the same solubility 2 88 pm 0 10 2 74 pm 0 10 wt the compositional depend

sinkhole detection using 2d full seismic waveform tomography we have developed an application of 2d time domain waveform tomography for detection of embedded sinkholes and anomalies the measured seismic surface wavefields were inverted using a full waveform inversion fwi technique based on a finite difference solution of 2d elastic wave equations and the gauss newton inversion method the key advantage of this approach is the ability to generate all possible wave propagation modes of seismic wavefields body waves and rayleigh waves that are then compared with measured data to infer complex subsurface properties the pressure wave p wave and shear wave s wave velocities are inverted independently and simultaneously the fwi was applied to one synthetic and two real experimental data sets the inversion results of synthetic data showed the useful capability of the waveform analysis in identifying an embedded void the inversion results of real data sets showed that the waveform analysis was able to delineate 1 an embedded concrete culvert and 2 a complex profile with an embedded void and highly variable bedrock laterally and vertically an independent invasive test standard penetration test was also conducted to verify the seismic test results

explicit treatment of inheritance in dating depositional surfaces using in situ 10be and 26al we describe a new strategy for dating depositional landscape surfaces using in situ produced cosmogenic radionuclides crns that removes the complication of nuclide inheritance by clasts prior to depositon two amalgamated samples each consisting of 30 clasts one from the surface and one from a fixed depth in the subsurface constrain this crn inheritance and date the surface the inheritance may be used to estimate minimum exhumation rates and maximum transport times within the geomorphic system we test the technique using sup 10 be and sup 26 al to date the third fr3 of five terraces along the fremont river utah and the third wr3 of 15 along the wind river wyoming whereas effective ages based solely upon the surface samples yield 118 138 ka fr3 and 93 ka wr3 the subsurface samples reveal that inheritance accounts for 22 wr3 to 43 fr3 of the total crn concentration taking this into account yeilds terrace ages of nearly 61 81 ka for fr3 and nearly 67 76 ka for wr3 we explore the dependence of age estimates on the accumulation history of the terrace silt caps 22 refs 3 figs 1 tab

estimating rates of denudation using cosmogenic isotope abundances in sediment we propose as a testable hypothesis a basin scale approach for interpreting the abundance of in situ produced cosmogenic isotopes an approach which considers explicitly both the isotope and sediment flux through a drainage basin unlike most existing models which are appropriate for evaluating in situ produced cosmogenic isotope abundance at discrete points on earth s surface our model is designed for interpreting isotope abundance in sediment because sediment is a mixture of materials in favourable cases derived from throughout a drainage basin we suggest that measured isotope abundances may reflect spatially averaged rates of erosion we investigate the assumptions and behaviour of our model and conclude that it could provide geomorphologists with a relatively simple means by which to constrain the rate of landscape evolution if a basin is in isotopic steady state and if sampled sediments are well mixed

quantifying sediment transport on desert piedmonts using 10be and 26al in situ produced 10 be and 26 al measured in 40 sediment samples collected from the iron and granite mountain piedmonts eastern mojave desert provide a unique view of piedmont modification processes and process rates over the 10 3 to 10 5 year time scale cosmogenic nuclide based models suggest that the iron and granite mountains generate 0 11 0 13 and 0 082 0 097 m 3 of sediment per year per meter of rangefront respectively the sediment moves down the piedmont in an active transport layer atl which is 20 to 30 cm thick based on visual observations measurements of depth to a buried b horizon cosmogenic nuclide data and maximum ephemeral channel depths sediment in this layer is well mixed vertically and horizontally on the 10 2 year time scale indicating that the small ephemeral channels which dominate the piedmont surface migrate quickly interpretive models of increasing nuclide activities at depth in two pits suggest steady sediment deposition on the piedmont at rates between 17 21 and 38 45 m ma 1 until the late pleistocene epoch when a discontinuity to markedly lower nuclide activities in the isotopically well mixed active transport layer suggests that deposition stopped a significant change in piedmont behavior nuclide activities in 10 amalgamated surface samples each collected along a different 4 km long transect increase steadily away from the mountain front thus we infer that sediment is uniformly dosed by cosmic rays as it is transported down the iron and granite mountain piedmonts interpretive models suggest that long term average sediment speeds down the iron and granite mountain piedmonts are a few decimeters to a meter per year d 2002 published by elsevier science b v

kinetics of the reaction h2o o 2oh in rhyolitic and albitic glasses preliminary results the kinetics of homogeneous reactions are important in understanding the cooling history of rocks and in understanding experimental speciation data we have experimentally studied the kinetics of the interconversion reaction between h 2o molecules and oh groups in natural rhyolitic glasses 0 5 2 3 total water and a synthetic albitic glass l total water at 400 600 c the reaction rate increases with temperature and total water content equilibrium is not always approached monotonically the speciation may first depart from equilibrium and then come back to equilibrium experimental reaction rates agree with those inferred from previous speciation data of rhyolitic glasses quenched from 850 c the experimental data are modeled successfully by considering both the reaction and the diffusion of oh that brings oh groups together to react this study shows that species concentrations in glasses quenched from 600 c reflect those at experimental temperatures unless the water content is higher than that used in the present study species concentrations in glasses with total water contents 0 8 wt and which were rapidly quenched in water from 850 c do not represent their equilibrium concentrations in the melt at 850 c but record a lower apparent equilibrium temperature that depends on water content and quench rate natural rhyolitic glasses and glass inclusions do not record preeruptive melt speciation though total water content may be conserved the experimental data are used to infer cooling rates for natural obsidian glasses pyroclastic glass fragments from the bb site of mono craters have cooling rates similar to air cooled experimental charges 3 c s different types of glasses from the mono craters have different cooling rates which cover four orders of magnitude some natural obsidians appear to have had complex cooling histories the wide range of cooling rates and thermal histories is consistent with previous inferences that some obsidian clasts at the mono craters formed as glass selvages lining volcanic conduits or dikes that were subsequently caught up in the explosive eruption which led to variable degrees of transient heating followed by rapid cooling and deposition these experimental data reveal surprisingly rich detail in water speciation in volcanic glasses and show how at least in principle quantitative constraints on thermal histories can be extracted by experimentation and application of kinetic models

the present state of the magmatic system of the campi flegrei caldera based on a reconstruction of its behavior in the past 12 ka abstract new geochemical and sr isotope data have been acquired on samples representative of volcanic units erupted inside the resurgent campi flegrei caldera cfc over the past 12 ka these data integrated with previous published petrological and with newly acquired geochronological volcanological and geothermal data shed light on the nature and timing of the processes that controlled the evolution of the phlegraean magmatic system in the past 12 ka three isotopically and geochemically distinct magmatic components were erupted at the cfc as either homogeneous or mixed magma batches one component campanian ignimbrite component cic 87 sr 86 sr 0 70735 0 70740 is similar to the trachytic magma extruded during the first phase of the campanian ignimbrite ci eruption 37 ka a second component neapolitan yellow tuff component nytc 87 sr 86 sr 0 70750 0 70757 is similar to the latitic alkali trachytic magma batches extruded during the course of the neapolitan yellow tuff nyt eruption 12 ka a third component minopoli component mic 87 sr 86 sr 0 7086 is similar to the trachybasaltic magma of the minopoli 2 mi eruption 9 7 ka these components were erupted as either single batches of magma or mixed ci nyt or mi nyt batches of magma through vents located either along the structural boundary of the nyt caldera or inside the nyt caldera mainly on portions of the resurgent block under extensional stress the ci and nyt components represent residual portions of older large volume magma reservoirs which have fed eruptions since about 60 and 15 ka respectively the least evolved mi component was erupted only during the 12 9 5 ka and 8 6 8 2 ka epochs of activity through vents located on a ne sw regional fault system this component could represent a deeper reservoir tapped by the ne sw regional fault system reactivated after the nyt caldera collapse deeper mi and shallower ci and nyt magmatic systems interacted by mixing among batches of magma during their rise to surface overall the data suggest that the cfc magmatic system today is characterized by the presence of two larger independent reservoirs filled by residual portions of the ci and nyt magmas these generated many smaller shallower pockets of evolved magma that fed most of the eruptions that occurred in the cfc over the past 12 ka moreover a deeper reservoir mi tapped by the ne sw regional fault system provided batches of less evolved magma that mixed with magma present in the shallower pockets

cosmogenic exposure and erosion history of australian bedrock landforms exceptionally high activities of in situ produced 1 0 be and 2 6 al indicate that australian bedrock surfaces are some of the most stable in the world these cosmogenic nuclides demonstrate that australian granite exposed and sampled at 10 sites along a transect from the eyre peninsula 33 s to the kakadu area in the northern territory 14 s has in some places eroded only decimeters over the past million years however nuclide activities are not saturated in any of the 61 exposed samples we analyzed mandating that the surfaces we sampled are losing mass albeit slowly over time such mass loss indicates that inselbergs are dynamic landforms confounding the assignment of discreet ages to inselberg surfaces nevertheless the differential between slow rates of erosion measured on the very stable uppermost parts of these landforms and the more rapid rates measured below their flanks and below the adjacent grus covered planes suggests that the forms of many large inselbergs which stand meters to tens of meters high must be at least tertiary in age and possibly much older activities of 1 0 be and 2 6 al in 61 exposed australian samples range from 5 1 0 1 10 6 to 5 3 0 6 x 10 5 atoms g 1 and 2 1 0 1 x 10 7 to 3 4 0 5 x 10 6 atoms g 1 respectively normalized to sea level at latitudes of 60 using only neutron scaling activities of 1 0 be and 2 6 al in seven shielded samples 3 5 13 m below the surface are much lower ranging from 3 4 0 2 x 10 4 to 7 0 0 1 x 10 4 atoms g 1 and 1 6 0 1 x 10 5 to 2 8 0 2 x 10 5 atoms g 1 respectively 2 6 al 1 0 be ratios of exposed samples range from 3 89 0 19 to 6 29 0 82 if 2 uncertainty ranges and a nominal sea level high latitude 1 0 be production rate of 5 17 atoms g 1 yr 1 are considered ratio data for all but one surface sample are consistent with continuous surface or near surface exposure and or erosion rock surfaces farther north in australia where the climate is more humid have lower nuclide activities thus we infer that surface stability is inversely related to mean annual precipitation from 61 exposed samples we calculated maximum limiting single nuclide model erosion rates of 0 3 0 1 to 5 7 1 0 m m y and minimum limiting single nuclide model exposure ages of 105 16 to 1310 190 ka by assuming a sea level high latitude 1 0 be production rate of 5 17 atoms g 1 yr 1 seven shielded samples in which the nuclide inventory is muon generated also have nuclide activities consistent with similarly low rates of erosion but over even longer time scales it appears that the eyre peninsula inselbergs have been and are eroding so slowly that they may well be direct descendents of cenozoic and perhaps even mesozoic forms

rates of sediment supply to arroyos from upland erosion determined using in situ produced cosmogenic 10be and 26al using 10be and 26al measured in sediment and bedrock we quantify rates of upland erosion and sediment supply to a small basin in northwestern new mexico this and many other similar basins in the southwestern united states have been affected by cycles of arroyo incision and backfilling several times in the past few millennia the sediment generation 275 65 g m 2 yr 1 and bedrock equivalent lowering rates 102 24 m myr 1 we determine are sufficient to support at least three arroyo cycles in the past 3 000 years consistent with rates calculated from a physical sediment budget within the basin and regional rates determined using other techniques nuclide concentrations measured in different sediment sources and reservoirs suggest that the arroyo is a good spatial and temporal integrator of sediment and associated nuclide concentrations from throughout the basin that the basin is in steady state and that nuclide concentration is independent of sediment grain size differences between nuclide concentrations measured in sediment sources and reservoirs reflect sediment residence times and indicate that subcolluvial bedrock weathering on hillslopes supplies more sediment to the basin than erosion of exposed bedrock

tracking painted pebbles short term rates of sediment movement on four mojave desert piedmont surfaces 1 to quantify short term sediment movement rates across mojave desert piedmonts 1600 painted and numbered pebbles were laid out in paired orthogonal 20 m lines at 4 sites and resurveyed five times over 2 years and revisited 2 years later pebble lines cross shallow 5 15 cm ephemeral channels and adjacent unconsolidated interfluves the latter being the dominant landform at all sites two sites are located on surfaces that have been or are impacted by military training activities including the use of tracked vehicles the two other sites have not been disturbed by human impact three different processes transport pebbles episodic streamflow in ephemeral channels transports a few pebbles long distances decimeters to meters down gradient bioturbation moves many pebbles small distances centimeters in any direction and vehicular disturbance transports pebbles varying distances centimeters to meters in any direction significant down gradient sediment movement occurred dominantly in channels where flowing water was concentrated interfluves were stable surfaces where little transport occurred off road vehicle use is coincident with accelerated pebble movement pebbles moved further and faster down gradient at the disturbed iron mountain and east range road sites mean speeds of 0 18 and 0 34 m yr 1 respectively than at the undisturbed chemehuevi and goldstone sites mean speeds of 0 17 and 0 02 m yr 1 respectively mean pebble movement is highly and negatively correlated with vegetation density short term pebble movement rates are several times lower than long term 103 to 104 year rates suggesting the importance of rare extreme precipitation events for sediment transport such as those of fall and winter 2004