river bed aggradation due to overloading this paper presents the analytical solution of the aggradation problem for a more appropriate boundary condition the analytical results are compared with the laboratory experimental data

imaging a crustal low velocity layer using reflected seismic waves from the 2014 earthquake swarm at long valley caldera california the magmatic system roof

aggradation degradation process in alluvial channels the effects of sediment size gradation i and sediment loading ratio m on the aggradation degradation process and related flow characteristics in an alluvial channel were investigated experimentally three different size gradations of sediment were used for each gradation experiments were carried out for four different sediment loading conditions namely initial equilibrium overloading underloading and clear water hydraulic characteristics sediment transport rates and gradations were measured during experiments a linear model of sediment transport under overloading and underloading conditions was developed experimental results show that with nonuniform sediment the aggradation degradation cycle is found to be irreversible under a given loading ratio speeds of the aggradation wave and degradation wave increase with increasing i and with decreasing m the recovery ratios of bed elevation and bed slope decrease as i increases regression relations have also been derived from the experimental

nitrate production beneath a high arctic glacier svalbard natural environmental isotopes of nitrate and ammonium are used in conjunction with major ion chemistry and hydrological data to establish controls upon the biogeochemical cycling of nitrogen beneath a high arctic polythermal glacier midtre lovenbreen here high nitrate concentrations in subglacial meltwaters suggest that the subglacial environment may be furnishing nitrate in excess of that released from the snowpack and glacier ice isotopic values of 18ono3 suggest the provenance of such excess nitrate to be microbial in origin and 15nno3 indicates the source nitrogen compounds to have high 15n values relative to supraglacial runoff we address the nitrification of supraglacial ammonium the mineralization of organic nitrogen and the oxidation of geologic ammonium as potential sources of this additional nitrate mass fluxes of n compounds in a subglacial river and their 15n ratios indicate that the nitrification of supraglacial ammonium delivered to the glacier bed can account for much but not all of the excess nitrate the additional source most likely involves the mineralization of organic nitrogen although 15n values in rock samples suggest that the dissolution of rock derived ammonium cannot be discounted if large fractionation effects occur during dissolution our results therefore agree with previous catchment scale mass balance studies at the site which report a major internal loss of nh4 from the snowpack following melt however at the catchment scale the nh4 loss is greater than the excess of no3 observed in runoff indicating that microbial assimilation of ammonia into organic matter in a range of other habitats is also likely the identification of nh4 assimilation and nitrification further highlights the non conservative behaviour of nitrogen in glacial environments and testifies to the importance of microbially mediated reactions in the biogeochemical cycling of nitrogen in an environment that has until recently been regarded as biologically inert

nitrogen in rock occurrences and biogeochemical implications 1 there is a growing interest in the role of bedrock in global nitrogen cycling and potential for increased ecosystem sensitivity to human impacts in terrains with elevated background nitrogen concentrations nitrogen bearing rocks are globally distributed and comprise a potentially large pool of nitrogen in nutrient cycling that is frequently neglected because of a lack of routine analytical methods for quantification nitrogen in rock originates as organically bound nitrogen associated with sediment or in thermal waters representing a mixture of sedimentary mantle and meteoric sources of nitrogen rock nitrogen concentrations range from trace levels 200 mg n kg 1 in granites to ecologically significant concentrations exceeding 1000 mg n kg 1 in some sedimentary and metasedimentary rocks nitrate deposits accumulated in arid and semi arid regions are also a large potential pool nitrogen in rock has a potentially significant impact on localized nitrogen cycles elevated nitrogen concentrations in water and soil have been attributed to weathering of bedrock nitrogen in some environments nitrogen released from bedrock may contribute to nitrogen saturation of terrestrial ecosystems more nitrogen available than required by biota nitrogen saturation results in leaching of nitrate to surface and groundwaters and where soils are formed from ammonium rich bedrock the oxidation of ammonium to nitrate may result in soil acidification inhibiting revegetation in certain ecosystems collectively studies presented in this article reveal that geologic nitrogen may be a large and reactive pool with potential for amplification of human impacts on nitrogen cycling in terrestrial and aquatic ecosystems

overview and classification of wavefield seismic imaging methods the literature and seismic processing practice overflow with a diversity of wave equation migration methods so what makes wave equation migration a wave equation migration what is the commonality of these methods and how do they differ this article provides a framework for understanding different wave equation migration methods

nitrogen in future biosphere studies this article suggests a theme for future nitrogen studies involving the functioning and evolution of the biosphere together with certain aspects of human biology it is hoped that this theme could be developed into a multi authored book at some point in the future although numerous new case studies may be required the biosphere can be considered to be a single interactive system comprised of numerous component parts including the atmosphere rain rivers lakes oceans continental ecosystems marine ecosystems soils and sediments in order to study the internal complexity of each of the components and the relationships that exist between them one can choose a common theme the author believes that nitrogen is a good prospect because of its ubiquitous nature and complex chemistry the burial of sedimentary volatiles in the continental crust has contributed to the long term chemical evolution of the exterior environments of the earth the most marked effects notably the accumulation of atmospheric oxygen have been due to the burial of reduced carbon an understanding of the passage of sedimentary volatiles through the crust will provide important constraints on the evolution of the biosphere and may lead to a more meaningful comparative planetology carbon is difficult to trace through crustal processes because its high temperature form graphite is incompatible with the crystal structures of silicate minerals however the high temperature form of sedimentary nitrogen ammonium readily enters into potassic minerals and it can be easily traced through crustal processes herein the fate of sedimentary nitrogen is traced from wet sediments through metamorphic rocks into granites and other crustal melts without the trapping of nitrogen in the crust and the liberation of oxygen that is a consequence of biological nitrogen fixation the n2 o2 of the atmosphere may have been about 82 9 to 16 3 and the total atmospheric pressure about 1 2 atm most of the changes in the oxygen content is due to dilution by nitrogen with only about 5 of the present atmospheric oxygen being a consequence of nitrogen fixation the ancient continental surfaces would have been volcanic deserts containing little 1 ppm or no nitrogen today nitrogen rich soils support continental ecosystems one can use nitrogen as a window to speculate on the colonisation of the continents by land plants herein nitrogen fixation by legumes is considered in detail and by drawing analogies with the present day the author speculates on the colonisation of the continents by land plants having speculated on the co evolution of the atmosphere soils and continental ecosystems one can place a human being in the centre of a tropical forest and begin to examine how they relate to the modern biosphere the chosen example is the metabolism of plant protein and the roles of glutamate dehydrogenase gdh vitamin b2 and flavin mononucleotide fmn the realisation of this theme would imply numerous new case studies notably those concerning the continental crust where nitrogen studies were linked to mineralogy petrology and other geochemical tracers including sr o al and k and where the short range order of 15n were taken into consideration

geologic nitrogen in terrestrial biogeochemical cycling recent research implicates geologic nitrogen as a large and reactive pool of nitrogen that can have significant ecological effects this study was conducted to determine the landscape distribution of geologic nitrogen and the fate of this nitrogen during rock to soil transformation in the lower mokelumne river watershed located in the western sierra nevada of california mineralogy and chemistry were determined for six major lithologies in the study area to examine the spatial distribution of nitrogen in bedrock in addition soil samples were collected from two watersheds having high stream water nitrate concentrations to determine the fate of nitrogen during weathering and soil formation with the exception of diorite all bedrock contained detectable concentrations of nitrogen 153 1801 and 98 739 mg n kg 1 for metasedimentary and metavolcanic lithologies respectively a significant amount of nitrogen was released during soil formation 2350 and 2570 kg n ha 1 for soils formed on greenstone and slate respectively this amount of nitrogen represents from 30 to 50 of the current soil nitrogen pool in these ecosystems nitrogen released from bedrock contributes to an excess of available nitrogen relative to biotic demands leading to nitrate leaching and elevated concentrations of nitrate in stream water given the widespread occurrence of geologic nitrogen and the large global inventory of nitrogen contained within bedrock the role of geologic nitrogen as a source of nitrogen for terrestrial biogeochemical cycling must be considered

seismic imaging using microseismic events results from the san andreas fault system at safod 1 we have developed a new passive seismic imaging approach that consists of two steps first the hypocenter of the microseismic event is precisely located second this event is treated as a pseudo active seismic source and the reflections within the recorded wavefield are processed by using a directional migration algorithm in order to construct a high resolution image of the illuminated subsurface region in this paper we demonstrate the application of our approach to a number of microseismic events recorded by a borehole array in the san andreas fault observatory at depth main hole results obtained were high resolution 3 d images of different se nw oriented reflectors related to the san andreas fault saf system in the close vicinity of the borehole to support our approach we compared our findings with other active and passive seismic images and analyzed the correlation with borehole lithology we revealed a predominantly satisfactory agreement for both juxtapositions furthermore the stacked image of several microearthquakes provides a spatial characterization of the complex internal structure of the saf with much higher resolution than can be obtained from surface seismic reflection data

nonlinear teleseismic tomography at long valley caldera using three dimensional minimum travel time ray tracing the authors explore the impact of three dimensional minimum travel time ray tracing on nonlinear teleseismic inversion this problem has particular significance when trying to image strongly contrasting low velocity bodies such as magma chambers because strongly refracted and or diffracted rays may precede the direct p wave arrival traditionally used in straight ray seismic tomography they use a simplex based ray tracer to compute the three dimensional minimum travel time ray paths and employ an interative technique to cope with nonlinearity results from synthetic data show that their algorithm results in better model reconstructions compared with traditional straight ray inversions the authors reexamine the teleseismic data collected at long valley caldera by the u s geological survey the most prominent feature of their result is a 25 30 low velocity zone centered at 11 5 km depth beneath the northwestern quandrant of the caldera beneath this at a depth of 24 5 km is a more diffuse 15 low velocity zone in general the low velocities tend to deepen to the south and east the authors interpret the shallow feature to be the residual long valley caldera magma chamber while the deeper feature may represent basaltic magmas ponded in the midcrust the deeper position of the prominent low velocity region in comparison to earliermore tomographic images is a result of using three dimensional rays rather than straight rays in the ray tracing the magnitude of the low velocity anomaly is a factor of approximately 3 times larger than earlier models from linear arrival time inversions and is consistent with models based on observations of ray bending at sites within the caldera these results imply the presence of anywhere from 7 to 100 partial melt beneath the caldera 40 refs 1 fig 1 tab less

a magma mass beneath casa diablo further evidence from reflected seismic waves a forty station seismographic network operating in long valley caldera in california during the summer of 1997 recorded a number of earthquakes with unusual secondary phases the phases can be seen on several stations throughout the network allowing the use of particle motions and differential travel times to examine their nature and points of origin based on amplitude frequency and travel time considerations it appears that some of the phases are mode converted s to p reflec tions from a zone below the casa diablo area near mammoth lakes ca the locus of reflection points was imaged using time domain signal migration and stacking under the assumptions of first order scattering theory the results indicate that the reflecting zone is a curved 1 5 km by 2 km surface 7 6 km below and 1 4 km west of the casa diablo geothermal plant previous studies show low p wave velocities and high s wave attenuations in the same location as the reflecting zone an amplitude analysis of the suspected reflec tions suggests they are produced by large contrasts in material properties with the possible range of transitions including solid to partially molten or dry to fluid satu rated rock given these observations plus the volcanic history of the caldera and its recent tectonic activity the most straightforward interpretation of the reflections is that they come from either the top of a sill or intrusion or the overlying hydrothermal system of such structures

nitrogen release from rock and soil under simulated field conditions abstract a laboratory study was performed to simulate field weathering and nitrogen release from bedrock in a setting where geologic nitrogen has been suspected to be a large local source of nitrate two rock types containing nitrogen slate 1370 mg n kg 1 and greenstone 480 mg n kg 1 were used along with saprolite and bc horizon sand from soils derived from these rock types the fresh rock and weathered material were used in batch reactors that were leached every 30 days over 6 months to simulate a single wet season nitrogen was released from rock and soil materials at rates between 10 20 and 10 19 mol n cm 2 s 1 results from the laboratory dissolution experiments were compared to in situ soil solutions and available mineral nitrogen pools from the bc horizon of both soils concentrations of mineral nitrogen no 3 nh 4 in soil solutions reached the highest levels at the beginning of the rainy season and progressively decreased with increased leaching this seasonal pattern was repeated for the available mineral nitrogen pool that was extracted using a kcl solution estimates based on these laboratory release rates bracket stream water no 3 n fluxes and changes in the available mineral nitrogen pool over the active leaching period these results confirm that geologic nitrogen when present may be a large and reactive pool that may contribute as a non point source of nitrate contamination to surface and ground waters

experimental determination of the ammonium partitioning among muscovite k feldspar and aqueous chloride solutions abstract the cation exchange equilibria muscovite nh 4 cl tobelite kcl kal 2 alsi 3 o 10 oh 2 nh 4 cl aq nh 4 al 2 alsi 3 o 10 oh 2 kcl aq k feldspar nh 4 cl buddingtonite kcl kalsi 3 o 8 nh 4 cl aq nh 4 alsi 3 o 8 kcl aq are determined by hydrothermal experiments at 400 500 600 c at 400 mpa and piston cylinder experiments at 500 600 c at 1500 mpa along the entire k nh4 compositional range the composition of solid phases are determined by xrd emp and ftir methods nh4 k ratios in coexisting 2 3 molal chloride solutions by ion chromatography muscovite tobelite and k feldspar buddingtonite form complete solid solutions series at all conditions consistent phase relations and mass balances indicate equilibrium between solid solutions and fluids in both the k nh4 muscovite and k nh4 feldspar fluid systems nh4 strongly fractionates into the fluid in the range from 400 to 600 c 400 to 1500 mpa fractionations are slightly temperature and pressure dependent the distribution coefficient k d solid fluid x nh 4 solid x k solid x k fluid x nh 4 fluid varies within the experimental range from 0 10 at xkbulk 0 81 to 0 46 at xkbulk 0 20 for muscovite fluid and from 0 05 at xkbulk 0 91 to 0 70 at xkbulk 0 15 for feldspar fluid nh4 is preferentially incorporated into feldspar relative to mica with kdfsp ms ranging between 1 36 and 2 0 at 400 mpa and between 1 13 and 1 5 at 1500 mpa as xkbulk varies from 0 15 to 0 89 results are evaluated thermodynamically assuming equal mixing of nh4cl and kcl in the fluid mixing energies of solids were estimated using multidimensional regression and a regular solution model for the muscovite tobelite equilibrium values of s 11 7 j k 1 mol 1 v 2 1 j mpa 1 mol 1 and w 4 6 kj mol 1 and for the k feldspar buddingtonite equilibrium s 8 8 j k 1 mol 1 v 1 1 j mpa 1 mol 1 and w 5 4 kj mol 1 were derived results are used to calculate partition coefficients d among phases at very low nh4 bulk concentrations between 400 and 600 c dnh4fluid ms ranges from 7 to 8 at 400 mpa and is 5 at 1500 mpa dnh4fluid ms is 6 to 7 at 400 mpa and about 5 at 1500 mpa dnh4fsp ms is between 1 and 1 2 at all conditions partition coefficients are valid for nh4 contents of up to several hundred ppm in mica and feldspar well within the concentration range observed in many rocks combining the data with that of k nh4 partitioning between phlogopite and fluid results in dnh4phl ms 3 5 and dnh4phl ms 3 at 550 c 200 to 400 mpa nh4 concentrations in coexisting muscovite biotite and k feldspar from a variety of rocks show near equilibrium distributions nh4 k partitioning between major k bearing minerals and saline fluids allows for assessment of the dehydration history of metamorphic rocks during prograde metamorphism water is progressively produced by dehydration reactions and expelled along rock s p t path nitrogen is subsequently removed due to preferred fractionation of nh4 into fluids the remaining nh4 is continuously redistributed among muscovite and biotite and at higher grades k feldspar with biotite as the main solid phase carrier of ammonium the large fractionation effect of nh4 among most phases highlights its potential as tracer of devolatilization processes and fluid rock interactions

geologic nitrogen and climate change in the geochemical budget of karkevagge swedish lapland abstract while nitrogen is an essential nutrient for plant growth in the terrestrial environment and generally fixed by biological processes in soils in arctic and alpine environments n is a severely limited nutrient because of both climatic and soil constraints it is widely believed that geologic nitrogen is such a small component of the nitrogen cycle that this source is generally not viewed as being a significant component however it has been estimated that in fact as much as 20 of the total nitrogen budget may be stored in geological materials and where n is severely limited such as in arctic and alpine environments geologic n may in fact be a dominant source of n for biological processes nitrogen saturation may therefore have substantial impacts on geochemical cycles involving both soil and water chemistry in order to determine the potential for the rocks and soils of karkevagge to be significant sources of n samples of the principal rock units of the valley along with soil developed on a variety of rock types were sampled ammonia ammonium contents were determined using ion chromatography ammonia ammonium contents of the sampled rock materials display a wide range of abundances with marble containing a mean nh4 abundance of 4300 mg n kg quartz schist 1600 mg n kg biotite schist 4300 mg n kg and garnet mica schist 4500 mg n kg soil ammonia ammonium abundances were found to be 1600 mg n kg n pool abundances range from 2 5 kg m3 for marble to 8 7 for garnet mica schist soil n pools were found to be 3 0 kg m3 the inorganic n present as ammonia ammonium measured in bedrock represents substantial n input into the geochemical budget the n in bedrock originates from organically bound nitrogen associated with sediment or geothermal waters representing a mixture of sedimentary mantle and meteoric sources nitrogen in the soil originates from the weathering of n rich rocks the presence of unweathered nitrate minerals or fluid inclusions released to the soil and ultimately to plants by assimilation by biota or nitrification geologic nitrogen in karkevagge rocks and soils may represent a large and reactive pool with the potential for considerable impact on the geochemical system to investigate the potential responses of nitrogen release as well as other nutrients to increasing co2 concentration scenarios flow through leaching experiments were conducted on crushed rock samples and soils from the study area leaching experiments revealed two to three fold increases in both n and k release with a tripling of carbon dioxide concentrations ammonium shows more rapid release than potassium which suggests substantial changes in nitrogen cycling with increasing co2 enrichment of the atmosphere

imaging salt with turning seismic waves turning seismic waves which first travel downward and then upward before and after reflection have been recorded in a 3 d seismic survey conducted over an overhanging salt dome careful processing of these turning waves enables the imaging of the underside of the salt dome and of intrusions of salt into vertical faults radiating from the dome when seismic wave velocity increases with depth waves that initially travel downward are reflected and may turn so as to travel upward before reflection a simple geometrical argument suggests that these turning waves are likely to exhibit abnormal moveout in com mon midpoint cmp gathers in that reflection time decreases with increasing source receiver offset this abnormal moveout and the attenuation of turning waves by most migration methods suggest that conventional seismic processing does not properly image turning waves the most important step in imaging turning waves assuming that they have been recorded is the migration process simple and inexpensive modifications to the conventional phase shift migration method enable turning waves to be imaged for little additional computational cost the examples provided in this paper suggest that these and other such modifications to conventional processing should be used routinely when imaging salt domes

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

constraints on the upper crustal structure of the long valley mono craters volcanic complex eastern california from seismic refraction measurements during the summers of 1982 and 1983 field work was completed on 10 new seismic refraction profiles in the long valley mono craters region located within the technically active zone between the eastern sierra nevada and the basin and range province the four profiles presented here sample the upper 7 10 km of the crust within the western half of long valley cladera the mono craters ring fracture system and the normal crust north and northeast of long valley the entire area shares a common crystalline basement consisting primarily of mesozoic granitic rocks at a depth of 2 km beneath the topographic surface the p wave velocity is uniformly 5 6 km s beneath which the velocity increases with a gradient of about 0 1 s 1 clear secondary arrivals observed on a profile crossing the west part of the caldera support evidence from 1972 seismic refraction profiles for a reflecting boundary at a depth of 7 8 km beneath the west margin of the resurgent dome which may represent the top of a magma chamber structural details resolved in the upper 2 km of the crust lead to the following conclusions 1 p wave velocities in the crystalline basement at depths shallower than 2 km vary from 3 6 to 5 0 km s this variation reflects differences in the degree of fracturing of the upper portion of the basement 2 an apparently homogeneous basement in the upper 7 10 km beneath the mono craters ring fracture system indicates that any extensive magma chamber must be at least 10 km deep there 3 the downdropped crystalline basement beneath the western half of long valley caldera dips genty 5 10 to the northeast apparent offsets along steeply dipping caldera bounding faults are 1 0 1 7 km along the northern western and southern sides of the caldera with largest offsets in the north 4 rocks forming the caldera fill fall into essentially three p wave velocity groups from the surface downward these velocity groups are 100 400 of 1 2 1 8 km s material corresponding to unconsolidated fluvial or lacustrine deposits or highly fractured rhyolite flows 200 400 m of 2 8 3 1 km s material corresponding to sparsely jointed postcaldera rhyolite rhyodacite and basalt flows and approximately 1000 m of 3 9 4 4 km s material corresponding to deposits of bishop tuff

hypersaline fluids generated by high grade metamorphism of evaporites fluid inclusion study of uranium occurrences in the western zambian copperbelt in the pan african lufilian belt western zambian copperbelt uranium mineralizations preferentially scattered in kyanite talc micaschists metamorphosed evaporitic sediments or concentrated along transposed quartz veins provide an opportunity to 1 understand the time space relationship between the ore minerals and the deformation of the host rocks 2 identify the different fluid events associated with specific stages of quartz deformation and 3 characterize the ore fluid geochemistry in terms of fluid origin and fluid rock interactions in the u occurrences studied in lolwa and mitukuluku domes region western zambian copperbelt two mineralizing stages are described the first generation of ore fluids 53 59 wt cacl2 13 15 wt nacl n2 h2 in the gas phase of fluid inclusions circulated during the high temperature quartz recrystallization at 500 700 c this temperature is in agreement with the p t conditions recorded during the crustal thickening related to continental collision at ca 530 ma la icpms analyses show the presence of uranium within this fluid with a concentration mode around 20 ppm the second generation of ore fluid 21 32 wt nacl 19 21 wt cacl2 co2 co in the gas phase of fluid inclusions percolated at lower temperature conditions at the brittle ductile transition between 200 and 300 c this temperature could be related to the exhumation of the high grade metamorphic rocks at ca 500 ma the formation of h2 and co is interpreted as the result of radiolysis in the presence of dissolved uranium in the aqueous phase of these fluid inclusions finally a late fluid 14 16 wt naclequiv circulated in the brittle domain but seems unrelated to u re mobilization event

seasonal and event scale variations in solute chemistry for four sierra nevada catchments abstract hydrobiogeochemical processes controlling stream water chemistry were examined in four small 2 catchments having contrasting bedrock lithologies in the western sierra nevada foothills of california the mediterranean climate with its cool wet and hot dry cycle produces strong seasonal patterns in hydrological biological and geochemical processes stream water solutes fall into three general groups according to seasonal fluctuation in concentration strong rainy season minimum dry season maximum cl so 4 2 base cations weak rainy season minimum dry season maximum si and rainy season maximum dry season minimum no 3 and k solute dynamics in soil solutions and stream water suggest that mixing of drainage waters from bedrock and soil sources regulate stream water solute concentrations patterns are further altered by the leaching of solutes accumulated in the soil over the summer period of desiccation and the temporal discoupling of nutrient cycles that occurs due to differences in the timing between vegetation growth late spring and leaching early winter solute concentrations are remarkably similar between watersheds with varying bedrock types with the exception of nitrate sulfate and bicarbonate three watersheds have nitrogen bearing metasedimentary bedrock that contributes to elevated nitrate concentrations in stream waters watersheds whose bedrock includes mineralized veins of sulfide and carbonate minerals similarly have greater sulfate and bicarbonate concentrations in stream water hydrobiogeochemical processes are highly dynamic at the seasonal and storm event temporal scales and spatially complex at the watershed scale making management of stream water chemical composition such as nitrate concentrations very challenging

bed load transport of mixed size sediment fractional transport rates bed forms and the development of a coarse bed surface layer fractional transport rates bed surface texture and bed configuration were measured after a mixed size sediment had reached an equilibrium transport state for seven different flow strengths in a recirculating laboratory flume fractional transport rates were also measured at the beginning of each run when the bed was well mixed and planar the start up observations allow us to describe the variation of fractional transport rates with bed shear stress for a constant bed surface texture and bed configuration the start up and equilibrium observations together allow for the first time an unambiguous description of the mutual adjustment among the transport the bed configuration and the bed surface as the transport system moves toward equilibrium we find that a substantial interaction exists among the transport bed surface and bed configuration bed forms and a coarse surface layer coexist over a range of bed shear stress under some flow conditions the size and shape of the bed forms are controlled by the presence of the coarse surface layer at higher flows the coarse surface layer is eliminated by scour in the lee of the bed forms if the bed surface is defined as that over which the bed forms move a coherent relation between the bed surface texture and the transport grain size distribution may be defined at equilibrium the transport rates of all fractions were not equally mobile defined as identical transport and bed grain size distributions although equal mobility was approached for runs in which the bed shear stress was more than twice that for initial motion of the mixture under some flow conditions the transport was observed to adjust away from equal mobility as the bed adjusted from a well mixed start up condition to an equilibrium state development of a partial static armor wherein some individual grains become essentially immobile even though other grains in the same fraction remain in transport is suggested to explain these adjustments between the transport and bed surface grain size distributions constraints on equilibrium mixed size sediment transport are defined the special conditions for which equal mobility must hold and the relevance to natural conditions of flume results and the equal mobility concept are discussed

crustal refraction profile of the long valley caldera california from the january 1983 mammoth lakes earthquake swarm seismic refraction profiles recorded north of mammoth lakes california using earthquake sources from the january 1983 swarm complement earlier explosion refraction profiles and provide velocity information from deeper in the crust in the area of the long valley caldera eight earthquakes from a depth range of 4 9 to 8 0 km confirm the observation of basement rocks with seismic velocities ranging from 5 8 to 6 4 km sec extending at least to depths of 20 km the data provide further evidence for the existence of a partial melt zone beneath long valley caldera and constrain its geometry this evidence is in the form of pronounced secondary arrivals which we interpret as waves that have propagated through a volume with low q the magma chamber and reflected from the lower boundary of the southern edge of this volume at depths of 18 to 20 km

nitrogen and carbon flow from rock to water regulation through soil biogeochemical processes mokelumne river watershed california and grand valley colorado 1 soil denitrification is an ecologically important nitrogen removal mechanism that releases to the atmosphere the greenhouse gas n2o an intermediate product from the reduction of no3 to n2 in this study we evaluate the relationship between soil carbon and denitrification potential in watersheds with bedrock acting as a nonpoint source of nitrogen testing the hypothesis that nitrate leaching to stream water is in part regulated by denitrification two sites one in a mediterranean climate and the other in an arid climate were investigated to understand the interplay between carbon and denitrification potential both sites included carbonaceous bedrock with relatively high nitrogen concentrations 1 000 mg n kg 1 and had low background nitrogen concentrations in surface and groundwater there was a net accumulation of carbon and nitrogen in soil relative to the corresponding bedrock with the exception of carbonaceous shale from the arid site there the concentration of carbon in the soil 15 620 mg c kg 1 was less than the shale parent 22 460 mg c kg 1 consistent with the bedrock being a source of soil carbon rates of denitrification potential 0 5 83 g n kg 1 hr 1 derived from laboratory incubations appeared to be related to the ratio of dissolved organic carbon and nitrate extracted from soils these data indicate that microbial processes such as denitrification can help maintain background nitrogen concentrations to tens of m n in relatively undisturbed ecosystems when nitrogen inputs from weathering bedrock are accompanied by sufficient organic carbon concentrations to promote microbial nitrogen transformations

s wave attenuation structure in long valley caldera california from three component s to p amplitude ratio data using s to p amplitude ratios measured from three component seismograms we tomographically imaged spatial variations in s wave attenuation in parts of long valley caldera data from seismograms of local earthquakes in the long valley caldera region that occurred during 1984 were employed with the s to p amplitude ratio technique with corrections for source radiation pattern to determine q s resolution is limited throughout most of the model however significant resolution and acceptable error in parts of the model allow meaningful interpretation of the results the primary result is the image of a low q s anomaly at 7 8 km depth beneath the resurgent dome this is independent evidence for high temperatures and possible magma accumulation at this location other regions of anomalously low q s are marginally significant or poorly resolved of these low q s at 4 5 km depth beneath the inyo domes has the most potential significance the similarity of the results from the three component data and from the vertical component data implies that vertical component data which are generally more abundant can be used with confidence

three dimensional seismic model of the sierra nevada arc california and its implications for crustal and upper mantle composition a three dimensional p wave velocity model of south central california from the coast ranges to the sierra nevada shows that the crust under most of the southern sierra nevada batholith has seismic velocities 5 9 6 3 km s below the continental average the crust is not much thicker on average about 35 km than in the adjacent great valley and basin and range province apart from a small northward thickening crustal root under the western sierra nevada that reaches a depth of 42 km crustal velocities above the continental average are observed beneath much of the great valley due to a high velocity body underlying the sedimentary basin and the foothills metamorphic belt 6 4 7 0 km s upper mantle velocities are generally low 7 8 km s but span a wide range 7 4 8 2 km s we display the velocity model in several cross sections and maps of moho depth and average crustal velocity the measured velocities in the upper and mid crust of the sierra nevada batholith are in good agreement with laboratory measurements on sierra nevada tonalites after corrections for density and temperature peridotite xenoliths from the eastern sierra nevada suggest strong upper mantle anisotropy which could explain some of the velocity heterogeneity in the sierra nevada mantle by the time cretaceous subduction related magmatism ceased the sierra nevada arc must have had a thick mafic lower crust yet a principal result of our work is that today the batholith has a crust of mainly felsic composition throughout a subcrustal layer with velocities below normal pn velocities 7 6 km s may indicate the presence of lower crustal material in eclogite facies

seismic reflection studies in long valley caldera california seismic reflection studies in long valley caldera california indicate that seismic methods may be successfully employed to image certain types of features in young silicic caldera environments however nearsurface geological conditions within these environments severely test the seismic reflection method data quality are degraded by static reve t eration and band limiting problems due to these near surface conditions in long valley seismic reflection and refraction methods were used to image both the shallow and deep geothermal aquifers within the area the deep geothermal aquifer the welded bishop tuff was imaged as a fairly continuous reflector across the western moat of the caldera near surface refraction information indicates that there may be a buffed paleochannel system or horst and graben system that could control the shallow geothermal flow pattem high amplitude events observed in a wide angle survey were offginally interpreted as reflections from a contemporary magma body however a migration of the events utilizing the new generalized cellular migration algorithm indicates that these events are probably reflections from the faults of the caldera ring fracture system the reflections may be caused by the high acoustic impedance contrast associated with the juxtaposition of relatively low velocity low density caldera fill against the granite plutons and metasediments of the sierran basement along this fault system

bedload sheets in heterogeneous sediment field observations in streams with beds of coarse sand and fine gravel have revealed that bedload moves primarily as thin migrating accumulations of sediment and coarse grains cluster at their leading edge these accumulations are one or two coarse grains high and are much longer 0 2 0 6 m long in sand 0 5 2 0 m in fine gravel than their height the authors propose the term bedload sheet for these features and the authors argue that they result from an instability inherent to bedload movement of moderately and poorly sorted sediment in essence coarse particles in the bedload slow or stop each other trap finer particles in their interstices and thus cause the coarse particles to become mobile again bedload sheets develop on the stoss side of dunes causing the dune to advance incrementally with the arrival of each sheet successive deposition of coarse sediment from the leading edge followed by fine sediment may generate the grain size sorting that distinguishes cross bedding available flume experiments and field observations indicate that bedload sheets are a common but generally unrecognized feature of heterogeneous sediment transport

seismic velocity structure and earthquake relocation for the magmatic system beneath long valley caldera eastern california abstract a new three dimensional 3 d seismic velocity model and high precision location catalog for earthquakes between 1984 and 2014 are presented for long valley caldera and its adjacent fault zones in eastern california the simul2000 tomography algorithm is applied to derive the 3 d vp and vp vs models using first arrivals of 1004 composite earthquakes obtained from the original seismic data at the northern california earthquake data center the resulting vp model reflects geological structures and agrees with previous local tomographic studies the simultaneously resolved vp vs model is a major contribution of this study providing an important complement to the vp model for the interpretation of structural heterogeneities and physical properties in the study area the caldera is dominated by low vp anomalies at shallow depths due to postcaldera fill high vp and low vp vs values are resolved from the surface to 3 4 km depth beneath the center of the caldera corresponding to the structural uplift of the resurgent dome an aseismic body with low vp and high vp vs anomalies at 4 2 6 2 km depth below the surface is consistent with the location of partial melt suggested by previous studies based on vp models only and the inflation source locations based on geodetic modeling the sierran crystalline rocks outside the caldera are generally characterized with high vp and low vp vs values the newly resolved velocity model improves absolute location accuracy for the seismicity in the study area and ultimately provides the basis for a high precision earthquake catalog based on similar event cluster analysis and waveform cross correlation data the fine scale velocity structure and precise earthquake relocations are useful for investigating magma sources seismicity and stress interaction and other seismological studies in long valley

rhyolite intrusions in the intracaldera bishop tuff long valley caldera california abstract drilling of the long valley exploratory well on the resurgent dome in the long valley caldera revealed 300 m cumulative thickness of granophyric intrusions within the 1180 m thick 760 ka intracaldera bishop tuff the intrusions are aphyric to sparsely plagioclase phyric high silica high barium and low strontium rhyolites they resemble the lavas of the early rhyolite the first phase of post caldera volcanism a mean 40 ar 39 ar age of 590 17 ka from a part of a shallow intrusion is coeval with early rhyolite volcanism a second mean age of 454 17 ka from the same intrusion may reflect either younger early rhyolite activity with no external equivalent or hydrothermal resetting of the argon system hydrothermal alteration of the intrusions is characterized by introduction of quartz calcite and pyrite and formation of illite smectite high co 2 content of fluids apparently inhibited zeolite formation alteration varies locally within intrusions and intrusive groups and does not vary systematically with depth oxygen shows consistent depletion of the 18 o isotope from an initial magmatic composition of 6 0 to 8 5 to values ranging from 1 4 to 0 4 the constant oxygen isotope depletion most likely reflects alteration of intrusions due to local emplacement induced hydrothermal circulation rather than a caldera scale hydrothermal system in contrast 18 o depletion of the host bishop tuff increases regularly with depth except at an intrusive contact a pre early rhyolite geothermal gradient of approximately 70 c km was inferred this is substantially higher than the current gradient but substantially lower than expected for the case of a conductive regime over a shallow residual magma chamber either the intrusions were fed from a deep chamber or a cool hydrologic recharge regime was established early in caldera history the age thickness and suspected lateral extent of these shallow intrusions are such that emplacement of the intrusions rather than inflation of a shallow chamber is responsible for resurgence of the central long valley caldera similar intrusions occur in another well on the resurgent dome lv13 21 but not in wells located off the dome

attenuation of p and s waves in a magma chamber in long valley caldera california shallow earthquakes around the southwest boundary of long valley caldera west of the hilton creek fault are characterized by lack of s waves at regional seismic network stations to the northwest north and northeast and p waves for these same station event combinations are deficient in frequencies higher than about 2 3 hz earthquakes east of the hilton creek fault and southeast of the caldera have normal p and s wave signatures at the same stations these effects are explained by propagation through a magma chamber in the south central part of long valley caldera at depth greater than 7 8 km

evidence for the contemporary magmatic system beneath long valley caldera from local earthquake tomography and receiver function analysis 1 we present a new p wave and s wave velocity model for the upper crust beneath long valley caldera obtained using local earthquake tomography and receiver function analysis we computed the tomographic model using both a graded inversion scheme and a traditional approach we complement the tomographic vp model with a teleseismic receiver function model based on data from broadband seismic stations mlac and mkv located on the se and sw margins of the resurgent dome inside the caldera the inversions resolve 1 a shallow high velocity p wave anomaly associated with the structural uplift of a resurgent dome 2 an elongated wnw striking low velocity anomaly 8 10 reduction in vp at a depth of 6 km 4 km below mean sea level beneath the southern section of the resurgent dome and 3 a broad low velocity volume 5 reduction in vp and as much as 40 reduction in vs in the depth interval 8 14 km 6 12 km below mean sea level beneath the central section of the caldera the two low velocity volumes partially overlap the geodetically inferred inflation sources that drove uplift of the resurgent dome associated with caldera unrest between 1980 and 2000 and they likely reflect the ascent path for magma or magmatic fluids into the upper crust beneath the caldera

a global marine fixed nitrogen isotopic budget implications for holocene nitrogen cycling 1 a nitrogen stable isotopic model was constructed in order to constrain the holocene marine fixed nitrogen budget the primary sources and sinks considered were riverine and atmospheric sources nitrogen fixation sedimentary and water column denitrification and sediment burial the source budget was found to be insensitive to changes in nitrogen fixation rates and thus could not be used to constrain this term however the isotopic value of fixed nitrogen losses was very sensitive to the amount of sedimentary denitrification if the isotopic value of marine fixed nitrogen has not changed during the holocene as supported by sedimentary records then in order to balance the isotopic value of sinks and sources approximately 280 tg n yr 1 of sedimentary denitrification is required if such a high rate of denitrification has been sustained throughout the holocene it implies that present day estimates of marine nitrogen fixation are grossly underestimated it also implies that the marine nitrogen budget has a residence time of less than 2000 years